Glossary of Technical Theatre Terms – Lighting (beginners)

13A PLUG
Standard domestic power connector in the UK. Three rectangular metal contacts (live, neutral and earth) with a fuse built-in (2A, 3A, 5A, 7A, 10A or 13A fuses are interchangable).

15A PLUG
Standard power connector in UK theatres. Three round metal contacts (live, neutral and earth); the principal difference from the domestic 13A connector is that the 15A version has no fuse.

A.J. / AJ
n. Jargon for an Adjustable Spanner. (UK) Known in the US as a C Wrench (short for Crescent Wrench).

A1
Lighting Industry Forum code which identifies the (original) recommended usage of different lamp types. A1 coded lamps are for use in projection. See also CP, T, P2, K.
Lamps List

ABTT
(UK) The Association of British Theatre Technicians, which was formed in 1961 as a charity, to provide a forum for discussion among theatre technicians, architects and managers of all disciplines, and disseminate information of a technical nature, to all its members.
ABTT Website

AC
Short for ALTERNATING CURRENT. An AC cord or cable is used to connect between a mains power socket and a piece of equipment.
A range of different connectors are used to connect to the equipment. The 3-contact IEC cable is common in Europe, and is sometimes known as a Kettle Lead. A figure 8 cable is used on smaller equipment which is double-insulated and has just two connections. Powercon is used on heavier duty equipment and locks into place to prevent accidental disconnection.

ACCENT LIGHTING
Lighting on a particular item or area on stage, to make it stand out or for aesthetic reasons, rather than to light an actor or functional area. Examples include lighting on specific architectural features on the set or in the theatre to make them 'pop' or because they're particularly significant. 

ACCESSORIES
Additional equipment that adds functionality to a larger piece of equipment but which are not necessarily stored with (or sold with) the equipment. 
Accessories for a Fresnel stage lantern are a colour frame and a barn door. The Fresnel cannot function without a lamp or a power cable, so these aren't usually seen as accessories. 

ADAPTOR
1) Connector which allows two or more electrical devices to be connected to a single power outlet. The connection is normally parallel, that is, each device is fed the same voltage, but the current is divided between them. Sometimes known as a 'Twofer'. A three-way splitter is known as a 'Threefer'. A Series splitter is also available where a voltage is shared equally between two loads.
2) Also an ADAPTOR can be the same as a JUMPER.
See SERIES SPLITTER, JUMPER and GRELCO.

ADDITIVE COLOUR MIXING
See COLOUR MIXING.

ADJUSTABLE SPANNER
See A.J.

ADVANCE BAR
(UK) Lighting bar positioned just downstage of the proscenium arch. Also known as ANTE PROSCENIUM (from Latin 'Before' or "In Front').

AERIAL GOBO
A gobo projected from a moving light or profile which is focussed into the air above the stage or audience, in order to add atmosphere and dimensional texture through smoke or haze in the venue.

ALPD
Formerly the ALD (Association of Lighting Designers), the association was renamed in mid 2021 to the Association of Lighting Production and Design (UK)
ALPD Website

ALTERNATING CURRENT*
An electric current that reverses direction in a circuit at regular intervals. Abbreviated to AC. UK mains electricity is AC and changes direction 50 times per second (that is, the frequency is 50Hz).
See also DIRECT CURRENT.

AMBER DRIFT
A phenomenon seen when tungsten halogen lamps are dimmed which results in the light output becoming warmer (lower in colour temperature) as it becomes dimmer. LED lights maintain the same colour when dimmed, unless they have been designed to emulate the amber drift of tungsten light sources. 

AMBIENT LIGHT
The light in a venue with no stage-lighting sources switched on. Background light.

AMPERE
The standard unit for measurement of electrical current passing through a circuit (usually abbreviated to AMP). Written as 'I' in equations. Cables, fuses and switches are designated by their current carrying capacity.
(Following phrase refers to UK standards). Square pin plugs are rated at 13 Amps maximum and Round pin plugs at either 5 Amps or 15 Amps maximum, depending on the size of the pins. If a cable rated at 5 Amps is used with a load of 15 Amps (for example), the cable will overheat and possibly catch fire.

ANIMATION DISC
See EFFECTS.

ATTRIBUTES
The controllable parameters of a colour-changing or moving light are known as the ATTRIBUTES.
All moving lights will have PAN and TILT, with many having COLOUR wheels, GOBO selection, gobo rotation etc. as additional attributes.
LEDs can operate in a number of modes, based on the number of colour sources they have, as well as whether certain parts of the beam can be separately controlled. A basic LED fixture might operate in 3 channel mode, with the 3 controllable parameters being RED, GREEN and BLUE. More complex fixtures might add AMBER and/or WHITE, and the latest LED fixtures may have LIME as well.

AUTOFOLLOW
A cue which automatically runs after the completion of the previous one. 
Originally known as a Follow-On cue. 
See also WAIT TIME. 

AUTOMATED FIXTURE
See MOVING LIGHT.

BACK PROJECTION
See PROJECTION.

BACK-UP
A section of a lighting control board (sometimes a separate unit) which provides an alternative method of control should the main board fail.

BACKLIGHT
Light coming from upstage, behind scenery or actors, to sculpt and separate them from the background.
Any kind of lantern can be used for backlighting, but commonly Fresnels or PCs are used, and sometimes Parcans. 
Moving LED washlights are extremely popular for backlighting, as they can be easily refocussed and coloured to match the scene. 
See also TOPLIGHT.

BALCONY RAIL
See CIRCLE FRONTS.

BAR
The horizontal metal (steel or alloy) tube (usually 48mm in external diameter, but can be up to 60mm) hung from flying lines (or forming part of a grid) from which lighting equipment and scenery etc. may be suspended. Also known as a BARREL. When vertical, known as a BOOM. Sometimes known as a PIPE in the US, although many curse that usage, and demand the use of Batten ; 'A pipe is what you smoke; a batten is what you hang your instruments from.'
Language, especially in theatre, is rarely universal! In German, ZUGSTANGE.
Many lighting bars are internally wired (and are known as IWBs or Internally-Wired Bars), featuring cabling inside the bar and sockets mounted at regular intervals along the bar, and a connection box at one end to enable the bar to be plugged into dimmers. Lighting bars nowadays need 'hot power' sockets and DMX outlets, as well as the more usual dimmer output sockets into which traditional theatre lighting equipment is connected. 

BARNDOORS
A rotatable attachment consisting of two or four metal flaps (hinged) which is fixed to the front of a Fresnel or PC type lantern to cut off the beam in a particular direction(s).
Profile lanterns use SHUTTERS to achieve a greater degree of control and accuracy.
Barndoors are also available for parcans and birdies. BLACKWRAP can be used to reduce additional light spill where barndoors aren't doing the job.

BARREL
See BAR.

BATTENS
1) Timber at the top and bottom of a cloth. A Sandwich batten is used to carry a hanging cloth. It comprises two flat pieces of timber screwed together with the edge of the cloth between them.
2) Timber used for joining flats together for flying.
3) Compartmentalised floodlights set up to allow colour mixing. See also GROUNDROW. Low voltage battens are commonly used as light curtains & for colour washes. Known in the US as a STRIPLIGHT, BORDER LIGHT or X-LIGHTS. 
4) US term interchangable with PIPE for a flying bar.

BC HOLDER
Type of UK domestic lampholder that has largely been replaced by the ES (Edison Screw) and the GES (Goliath Edison Screw) for general lighting applications in the theatre. Stage lighting equipment uses prefocus lamp bases. (Most types of Festoon still use BC holders.)

BEAM ANGLE
The angle of the cone of light produced by a lantern.
The Field Angle is a measurement of the width of the cone of light produced by the lantern until the light falls off to 10% intensity. This is a wider angle then the Beam Angle, which is a measurement of the cone of light until the light falls off to 50% of full intensity. 
For a sharply focussed profile, the Field angle and the Beam angle will be very similar (or identical). For a Fresnel or Parcan, there will be a difference between the two. It's best to use Beam Angle when calculating lantern coverage.

BEAMLIGHT
Lensless lantern which uses a parabolic reflector and a low voltage high intensity lamp to produce an intense near-parallel beam. Also known as a Beam Projector.
A PARCAN is a special type of beamlight.
Beamlite in the Backstage Heritage Collection

BEGINNERS
A call given by Stage Management to bring those actors who appear in the first part of a play to the stage. e.g. "Act One Beginners to the stage, please". The actors are then called by name.
A similar call is given after the interval (e.g. "Act Two Beginners to the stage please").
The call is usually given 5 minutes before the advertised performance start time, but this may vary depending on how long the actors take to get into position.
See also HALF, QUARTER.
See Calls and Cans

BELTPACK
Part of the communication ('cans') system in a theatre, the Beltpack contains the controls and circuitry to drive the HEADSET worn by crew members. Each beltpack connects into the headset ring and back to a PSU (Power Supply Unit) which is powered from the mains.
See also CANS.

BIRDIE
A compact low voltage display luminaire containing a Par 16 or MR16 lamp. So called because it is similar to, but much smaller than, the Parcan, and is hence "one under Par". (In golf terminology, a birdie is a score one below the par for that particular hole).
Low voltage birdies require a 12 Volt external transformer. Mains voltage birdies are also available.
Due to its compactness, the birdie is ideal for concealing in pieces of set or as downstage uplights. The beam angle can be narrow - a range of different lamps are available with differing beam widths.
See also MR16.
Types of Lantern

BLACK HOLE
An accidentally unlit portion of the stage.

BLACK LIGHT
See ULTRA-VIOLET.

BLACKOUT
1) Complete absence of stage lighting. Blue working lights backstage should remain on and are not usually under the control of the board, except during a Dead Blackout (DBO), when there is no onstage light. Exit signs and other emergency lighting must remain on at all times.
2) The act of turning off (or fading out) stage lighting (e.g. "This is where we go to blackout")
3) Blackout Check (or Dark Check) takes place in some multi-purpose venues to ensure that window curtains or blinds are closed and that there is no stray light either from adjacent rooms or the outside world, before the audience is admitted. 

BLACKWRAP
(Trade Name) Thin black aluminium product which is used to temporarily mask light coming out of a luminaire's body, or to control spill. A self-adhesive tape version is also available.

BLEED THROUGH
Transformation from a scene downstage of a gauze to another scene upstage, by slowly crossfading lighting from downstage to upstage. If a gauze is lit steeply, or from the sides, it will appear solid. If this light is turned off and light added to the set upstage of it, it will disappear.

BLIND PLOTTING
The facility on some lighting control desks for the operator to make changes to the stored lighting cues without affecting the state on stage. 
Pressing the BLIND button leaves the current state on stage, and can instantly update other cues as required. Once you are finished, pressing LIVE will return to normal operation. 

BLINDERS
1) Lamps arranged around the stage directed into the auditorium, originally to prevent spectators seeing the stage during scene changes when the house tabs were not lowered. Now used for effect in rock concerts etc.
2) A strip of dense black material fastened behind a crack between two flats or scenic pieces to prevent light leak.
3) Cloth hung behind a gauze to prevent transparency before the effect is required (sometimes known as a Gauze Blinder or Scrim Blinder)

BLUE-OUT
(Lighting) A fade to blue backlight only. Better than a full blackout, especially if the scene change is well choreographed.

BLUES
Blue lights used backstage in a performance situation. See also working lights.

BOARD
The main control for the stage lighting. Originally known as the switchboard or dimmerboard, it is now usually remote from the dimmers. The lighting operator for a show is said to be "on the board", and is sometimes known as the "board op". In the US, the board operator is said to be "running the lights".
Known in the US as the Light Board. Also known as the Lighting Desk, LX desk, control desk, lighting console.
The links below take you through 3 generations of lighting control - initially directly controlling the dimmers using large levers, then remote operation using manual faders, then the current generation of computerised controls where lighting states are recalled at the touch of a button or the click of a mouse. 
Direct Lighting Controls on Backstage Heritage Collection
Manual Lighting Controls on Backstage Heritage Collection
Memory Lighting Controls on Backstage Heritage Collection

BOOM
1) Vertical scaffolding pole (usually 48mm diameter) on which horizontal boom arms (also known as sidearms or de-rig arms) can be mounted, carrying lanterns. Often used behind wings for side-lighting etc. Booms have a base plate (known as a TANK TRAP) or boom stand at the bottom and are tied off to the grid or fly floor at the top (not always necessary for short booms). Booms can also be fixed to the rear of the proscenium arch (Pros. Boom) or hanging from the ends of lighting bars. Sometimes known in the US as a LIGHT TREE. A light tree mounted upstage of a Tormentor is known as a Torm Tree. A boom used in the wings for dance lighting is sometimes known as a BALLET BOOM (which consists of 3 lanterns on each boom, at shin height, waist height, and head height, known as SHINS, MIDS and HEADS). 
2) An arm mounted on a microphone stand.
3) A long lightweight support for a directional microphone used to capture dialogue in TV/Film production. 
Boom Arms - Doughty Engineering (UK)

BOOM ARM
See BOOM.

BOOM BASE
A wooden board or heavy-duty metal panel with vertical scaffold tube adaptor used as a base for lighting booms. Although the base provides a degree of support (especially with added brace weights) booms often require additional support from above.
See also Tank Trap, which is a purpose-made all-metal boom base. 

BOOTH
(US) Control Room.

BORDER
A narrow horizontal masking piece (flattage or cloth), normally of neutral colour (black) to mask the lighting rig and flown scenery from the audience, and to provide an upper limit to the scene. Often used in conjunction with LEGS.
In part of the 20th century, borders were made from asbestos materials, but are now made from fire-retardant cloth (e.g. Wool Serge). 
Spanish: Bambolina

BOUNCE
1) Diffuse light that has been reflected from the stage, walls, cyclorama etc.
2) 'Bounce' is sometimes used for a flat (non-curved) cyclorama. Strictly, a bounce is a white or light blue cloth onto which light is bounced to backlight another cloth. A bounce doesn't need to be seamless, whereas a cyclorama should be.
3) Film/TV: A large piece of white material / board which is used to bounce and diffuse light towards actors on a film/tv set. 
4) Describes the fast in/out movement of 'bouncing' flown house tabs, traditionally used during curtain calls. This can also apply to the fast blackout/lights up cues that happen at curtain calls. When taking curtain calls, the Stage Manager would instruct the head flyman 'On the Bounce Please' for all calls prior to the final call, which was always 'Hand over Hand', i.e. slowly.
5) This facility was available on many multitrack tape machines. Describes the mixing down of multiple sounds from different tracks onto one track, hence freeing up the other tracks to be re-used. It allowed many sounds to be recorded onto one tape. The term now refers to the digital equivalent - taking multiple audio tracks and mixing them together at their set levels onto a single (pair of) tracks. 

BRAIL
A horizontal rope, wire or chain attached at either end of a piece of scenery or lighting bar pulling it upstage or downstage of its naturally hanging position to allow another flying item to pass, or to improve its position. See also BREAST LINE.
In a hemp house, to 'Brail' a static piece a single dead line was put round the 'short' and 'long' line to move the piece to a new position. A running brail was a breast which allowed the flown piece still to fly in or out, in its new position.

BREAKOUT
A connection at the end of a multicore cable which allows the connection of many items to it. (e.g. there is a breakout box at the end of a sound multicore cable which allows you to plug microphone cables into it).

BREAKUP
A commonly used abstract GOBO which gives a textured effect to the light, without throwing a specific pattern onto the stage. Used to add interest to light beams. A leafy breakup is used for outdoor scenes / forests / spooky wood etc. to break up the light on the actors faces.

BRIDGE
1) A walkway, giving access to technical and service areas above the stage or auditorium, or linking fly-floors.
See also CATWALK.
2) A lighting position above the auditorium, commonly with a catwalk above it to access lighting equipment and electrical systems is known in Dutch as a Zaalbrug.
3) A section within a song which provides a break from the previous verse / chorus, to prepare for the final chorus or climax, and can also provide a contrast with the previous lyrical tone or style.

BUILD
1) During lighting plotting, to construct a state from blackout, or to add to an existing state.
2) An increase in light or sound level. See CHECK.
3) A period of set construction ('The Build').

BULB
See LAMP.

BUMP
A flash or sudden jump in light level (a snap cue) (see also FLASH BUTTON).

BUMP CUE
A lighting cue that instantly bumps the lighting up to a brighter level (a time of 0 seconds). Usually at the end of a musical number to draw the applause. The bump cue is sometimes called a 'button'. 

BURNT OUT
A coloured gel that has lost its colour or melted through due to excessive heat in front of a lantern. Dark blues and greens etc. are most susceptible, and may need replacing during a long run.

C CLAMP / C-CLAMP
US equivalent of the UK Hook Clamp. Requires a spanner/wrench to tighten. Known as a PARROT CLAMP in the US film business.

C-WRENCH
US for SPANNER. (Abbreviation of Crescent Wrench).
See CRESCENT WRENCH

CABLE
Wiring, temporarily rigged, to carry electrical current. Depending on the size of the cable (current carrying capacity), cables are used to supply individual lanterns, whole dimmer racks, or carry signals from a microphone etc.

CABLE TIE
Lockable (and sometimes releasable) plastic strap used to tie a bundle of cables together, amongst many other things.
Cable ties are absolutely not to be used to suspend anything (of any size, or at any height). Also known as Zip Ties.

CAD
Computer-Aided Design. Using a computer to help with 2D plans and drawings, or increasingly for 3D visualisation of how a set will look, and how lighting will affect it. See also WYSIWYG.

CALL
1) A notification of a working session (eg a Rehearsal Call, Band Call, Photo Call, Focus Call). A rehearsal call for the next day / week used to be posted on a Call Sheet on the stage door noticeboard, but is now often an online document, updated by the stage management team. A 'Company Call' means the full cast and crew are called for the rehearsal. 
2) The period of time to which the above call refers. (eg "Your call for tomorrow nights show is 6.55pm")
3) A request for an actor to come to the stage because an entrance is imminent (these are courtesy calls and should not be relied on by actors - eg "This is your call for the finale Mr Smith and Miss Jones")
4) An acknowledgement of applause (eg Curtain Call)
5) The DSM on the book is said to be "calling the cues".
6) The Colour Call is a list of lighting gel required for the lighting rig.
7) The Final Call is also known as The Half - 35 minutes before the performance starts, and the latest time when the cast and crew should be in the theatre.

CALLING THE SHOW
The process of giving verbal cues to the lighting, sound, fly operators and stage crew during the performance. Usually done from the prompt corner by the DSM on the book or Stage Manager over cans.
Being 'on the book' involves verbally giving the 'GO' cues to all technical departments (lighting, sound, flies, automation, av etc). The cues are written in the prompt script. A 'STANDBY' (UK) or 'WARN' (US) cue is given first, so that the operators are ready for the actual cue.

CANS
1) Headset earpiece, microphone and beltpack used for communication and co-ordination of technical departments during a performance. (e.g. "Electrics on cans", "Going off cans", "Quiet on cans!").
A commonly used system in the UK is produced by Canford Audio under the TecPro brand. In the USA, ClearCom is commonly used.
As many of the technical operators are tied to expensive pieces of equipment, headsets are often wired. However, stage management (and any other crew who move around) often wear wireless versions, often known as radio cans. There are interfaces between wired and wireless versions enabling both to be part of the same system.
Many headset systems have multiple channels, enabling different sub-groups to communicate separately.
[Named after the well-known usage of two tin cans connected by a piece of string being able to transmit and receive a sound mechanically].
Also called 'Comms' short for Communications - the same phrases can be used (e.g. 'LX Off Comms' when leaving the operating position).
See link below for Cans Etiquette.
2) Any headphones.
3) Short for PARCANs.
Calls and Cans

CASUALS
Part-time temporary technicians (paid by the hour).

CEEFORM
(UK / Europe) A range of standard plugs & sockets for power, which are IP rated for outdoor use.
They come in a variety of sizes and colours. Blue is 230V, Red is 415V (3 phase).
Sizes available include 16A, 32A, 63A and 125A. These refer to the current-carrying capacity of the connector.

CHANNEL
A complete control path for signals in lighting or sound equipment.
In a lighting desk, the channels are directly controllable by the lighting operator. Within the desk, the channels are 'patched' to a dimmer or dimmers which the desk then sends a signal to depending on the level of the channel.
On a sound desk, the channels typically refer to a particular input or output path, and on digital sound desks can be configured in whichever way is appropriate for the event being set up. 

CHANNEL CHECK
Lighting: Function on ETC lighting consoles which flashes a channel to 100% if it is at or below 50% or down to zero if it's above 50%. 

CHASE
A repeated sequence of changing lighting states. A chase can be produced easily by the effects functions of a computerised lighting desk. There are standalone units designed to chase lighting circuits electronically in time to music (sound to light) or mechanically as a repeated sequence (as used in early neon signs).

CHEAT SHEET
A smaller version of the lighting plan, used by the lighting designer during the lighting plot. Also known as a Dimmer Layout or Magic Sheet.
Lighting control software can produce an electronic version of the Magic Sheet, which can be laid out however works best for the lighting designer, and provides shortcuts to groups of lanterns, effects and colours.

CHECK
1) Opposite of Build; a smooth diminishment of light or sound level (e.g. Lighting: 'I think we should check this state down a touch as the song begins')
2) See Prefade Listen.

CHIEF ELECTRICIAN
The senior member of the theatre's stage lighting team, although not necessarily the lighting designer. Known in the US as MASTER ELECTRICIAN.
In common with many theatre jobs, the actual duties of the Chief Electrician vary from theatre to theatre. Some chiefs are responsible for electrical maintenance of the building, some design the lighting for nearly every in-house production, some design no lighting at all, some have a team of eight staff under them, some have two. Many theatres employ casual staff to assist on lighting rigging sessions. Some theatres have a separate sound department, smaller venues have the lighting team also running sound for shows (and doing sound design for some).
Abbreviated to CLX in some UK venues.

CHINAGRAPH PENCIL
Usually white, wax-based pencil used for marking magnetic tape prior to splicing. Also used for marking identifying numbers on lighting gels.

CINEMOID
Now obsolete term for lighting colour gel, produced by Rank Strand / Strand Electric in the UK. A much thicker (and less flexible) gel than that produced nowadays.

CIRCLE FRONTS
A permanent front of house lighting position in older proscenium theatres. A number of spotlights, sometimes fitted with colour changers, are recessed into the front of the circle balcony above the stalls. Sometimes known as the Balcony Rail position.

CIRCUIT
1) The means by which a lantern is connected to a dimmer or patch panel. Numbered for reference. In a fully patchable system, the circuit number (also known as socket number) can be connected to any of a wide range of dimmers. 
The process of allocating circuits to dimmers is sometimes known as circuiting. The process of connecting lanterns to dimmers is sometimes known as plugging up. Abbreviated to 'cct'.
2) A complete electrical 'loop' around which current can flow.

CIRCUIT BREAKER
An electro-mechanical 'fuse' that can be reset, rather than having to be replaced when too much electrical current flows through a circuit.
Available in the same ratings as fuses.
See MCB, RCD.

CLEANERS
Auditorium working lights. Used for cleaning and setting up the auditorium before the house lights (usually more atmospheric) are switched on.

CLOVE HITCH
Invaluable hitch that every technician should know.
Video

CMY
Cyan / Magenta / Yellow - the three secondary (additive) colours of light which are used in moving lights for colour mixing. Some cheaper systems use three graduated colour scrolls (one of each colour) in front of a standard fixture, but these take a massive amount of intensity out of the beam, resulting in a dim light on stage. Many moving lights use a similar system with dichroic colours which are more efficient and longer-lasting.

COLOR
See COLOUR FILTER.

COLOUR
See COLOUR FILTER.

COLOUR CALL
1) A list compiled from the lighting plan of all the colours needed for the rig, and their size. This term also applies to the act of preparing colour filters and frames from such a listing.
2) A colour scroller made by Strand Lighting
Lighting Paperwork
Strand Lighting Colour Call scroller

COLOUR CHANGER
1) Scroller, where a long string of up to 16 colours is passed horizontally in front of a lantern. Remotely controlled by the lighting desk. Some scrollers have cooling fans to prolong the life of the gel string. Stronger colours will burn out faster without cooling, or if the focus of the beam is concentrated on the gel. If colours aren't lasting very long in scrollers, try changing the focus of the lantern. HEAT SHIELD clear gel should be used between the lens and the colour scroller to absorb some of the heat.
2) Wheel : Electrically or manually operated disc which is fitted to the front of a lantern with several apertures holding different colour filters which can be selected to enable colour changes. Can also be selected to run continuously.
3) Semaphore, where framed colours are electrically lowered into place in front of the lantern. Remotely controllable. Can perform additive colour mixing by lowering two colours into position at the same time.
4) Magazine : Manual semaphore-type device used on the front of a followspot. Known in the USA as a BOOMERANG.
Colour Changers at the Backstage Heritage Collection

COLOUR FILTER
A sheet of plastic usually composed of a coloured resin sandwiched between two clear pieces. The coloured filter absorbs all the colours of light except the colour of the filter itself, which it allows through. For this reason, denser colours get very hot, and can burn out very quickly.
There are a number of manufacturers of Colour Filters - Lee (UK), Rosco (US), Gam (Great American Market - US) and Apollo (US) are some of the more popular. Each manufacturer's range has a numbering system for the different colours. It's important to specify which range you're talking about when quoting numbers.
A colour filter is sometimes known as a Gel, after the animal material Gelatine, from which filters were originally made.
A colour frame is used to hold the colour filter, which slots into the colour runners in front of the lens of the lantern, just behind the barndoors (for a Fresnel or PC).
A range of specialised gels are available for non-standard purposes, including:
Neutral Density Filters - these are tinted grey, and while they don't produce grey 'colour' light (which is impossible) they do reduce the brightness of the light, without affecting the colour. They are used in TV/film on windows to cut down on natural light. 
Frosts - These are used to soften the sharp focussed edge of the beam of a profile lantern, or to smooth over any unevenness on any other beam. 

COLOUR FRAME
(or Gel Frame) A frame which holds the colour filter in the guides at the front of a lantern / lens tube.
Many different sizes of frames are needed for different lanterns.

COLOUR MIXING
Combining the effects of two or more lighting gels:
1) Additive : Focusing two differently coloured beams of light onto the same area (eg Cyc Floods). Combining colours in this way adds the colours together, eventually arriving at white. The three primary colours additively mix to form white, as do the complementary colours.
2) Subtractive : Placing two different gels in front of the same lantern. Subtractive mixing is used to obtain a colour effect that is not available from stock or from manufacturers. Because the ranges of colour are so wide, the need for subtractive mixing is reducing. Combining colours in this way reduces the light towards blackness. The three primary colours mix subtractively to form black (or to block all the light).
More on Colour Mixing

COLOUR RUNNERS
A set of metal guides in front of the lens of a lantern into which a colour frame is slotted, containing a colour filter or gel. The colour runners are sometimes used to hold barndoors (or other accessories including colour scrollers) at the front of a lantern, and sometimes these accessories fit onto the lantern using a different method.

COLOUR SCROLLER
See COLOUR CHANGER.

COLOUR TEMPERATURE
A measure of the 'warmth' or 'coolness' of light sources and colours. Measured in degrees Kelvin. A higher colour temperature light source will appear whiter (colder). The human brain automatically compensates for different colour temperatures - a film or video camera cannot, and thus what we see as white may appear to have a blue or green tint when no colour correction is used for video. Most video cameras have a 'White Balance' control to make colour temperature adjustments, to ensure white looks white on camera.
Daylight is approximately 5600°K, Tungsten Halogen is approx. 3200°K and standard incandescent lamps are 2800°K. Many discharge light sources are in use in modern theatrical productions using discharge followspots or moving lights - colour correction filters are used to balance the colour temperatures.
See also COLOUR CORRECTION.

COLOUR THEORY
The science behind the way colour works can help lighting, costume and set designers to make their work as vibrant (or dull) as the play requires. See the link below for information. 
Choosing and Using Colour

COLOUR WHEEL
See COLOUR CHANGER.

COMING IN
Warning used when flying scenery or lighting bars (electrics). 
e.g. "First Electric Coming In", "Heads on Stage - LX3 coming in!" etc.
See GOING OUT, FLYING.

COMPLEMENTARY COLOURS
Pairs of colours which, when additively mixed, combine to produce white light. Examples are red + cyan, green + magenta, and yellow + blue.

COMPOSITE GOBO
See GOBO.

CONVENTIONAL
Standard stage lighting instruments, rather than moving lights, LEDs or other effects. (e.g. 'There are 40 instruments in the rig - 20 moving lights and 20 conventionals'). 

COOKIE
See GOBO.

COSTUME PARADE
See DRESS PARADE.

COVER
Lighting that does a particular job during the show. (e.g. GENERAL COVER is the main actor light on stage, UPSTAGE COVER lights that area etc.)

CP
Lighting Industry Forum code which identifies the (original) recommended usage of different lamp types. CP coded lamps are for Film, Television and Photographic studio use and have a colour temperature of 3200°K. It's believed the CP stood for Colour Photography.
See also A1, T, P2, K.
Lamps List

CRACKED OIL
A smoke effect which creates a haze in the air to make light beams visible. This effect is rarely used now, because it has been found to be carcinogenic. See Water Cracker.

CRESCENT WRENCH
(US) A open ended adjustable hand wrench originally produced by the Crescent Tool Co. Known as a C-WRENCH.

CRI
Abbreviation for Colour Rendering Index.
A measure of the ability of a light source to reveal the colours of objects faithfully in comparison with an ideal or natural light source. A CRI of 100 for a white light source is equivalent to tungsten light, and is seen as giving an excellent rendering of colour across the spectrum.
Wikipedia entry

CROSS FADE / CROSSFADE
Bringing a new lighting state up whilst bringing the previous one down, so that the new one completely replaces the old one. Also applies to sound effects / music. Sometimes abbreviated to Xfade or XF.
A DIPLESS CROSSFADE occurs when the lighting doesn't dip significantly between states, which results in a more subtle transition.
Some sound mixers (especially those for DJs) have a cross-fader - a single fader which can be used to fade one music source out while simultaneously fading the next one in.

CROSSLIGHT
Light coming from the sides of the stage towards the centre (i.e. across the stage). Used heavily for dance lighting as it lights the body of the performer without casting shadows upstage, and it is far more sculptural than front light. Also used for additional atmosphere in many other types of performance. 
See also BACKLIGHT, PIPE ENDS. 

CUE
1) The command given to technical departments to carry out a particular operation. E.g. Lighting Cue, Fly Cue or Sound Cue. Normally given by stage management, but may be taken directly from the action (i.e. a Visual Cue).
Departments are often abbreviated: Lighting is LX, Sound is SD (or sometimes SX, but this is too similar to LX, so SD should be used). 
2) Any signal (spoken line, action or count) that indicates another action should follow (i.e. the actors' cue to enter is when the Maid says "I hear someone coming! Quick - Hide!" - this is known as a Cue Line. 
Cues given verbally may be known as 'audible cues', although as this is the normal type of cues, they're usually just called 'Cues'. Cues that technical operators take themselves, without an audible cue, are known as Visual Cues. 
3) A journal published between 1979 and 1988. A complete collection of CUE journals is available on the Backstage Heritage Collection website to read online.
The Prompt Book

CUE LIGHT
System for giving technical staff and actors silent cues by light. Cue lights ensure greater precision when visibility or audibility of actors is limited. Sometimes used for cueing actors onto the set. For technical cues, lights are normally now used just as a backup to cues given over the headset system. In the UK, a flashing Red light means stand-by or warn, green light means go. The actor / technician can acknowledge the standby by pressing a button which makes the light go steady. In the US, a red light means warn, and when the light goes off, it means GO. The UK system seems to be more secure, but it depends what you're used to.

CUE LIST
A list of sound, lighting, automation, scene change, video, followspot (etc) cues in order of their appearance in the show. Each cue is given a unique number, and the list includes a brief description of what it does (e.g. for Lighting: Blackout, Dim Downstage Wash, Red Spot Upstage; for Sound: Preshow Music, Fade Out, Snap Music to Quiet etc. )
Cue is often abbreviated to 'Q". 
Also known as a Plot Sheet. 

CUE ONLY
A philosophy of operation on many computerised lighting desks where the entire lighting state is recorded for each cue.
Some desks which use Tracking only record changes, which means dimmers (or moving lights etc) stay where they are until they're specifically changed. 
See the video below for further information. See also TRACKING. 
Tracking Video
Cue Only Video

CUE TO CUE
(also known as 'Topping and Tailing')
Cutting out action and dialogue between cues during a technical rehearsal, to save time. (e.g. "OK, can I stop you there - we'll now jump to the end of this scene. We'll pick it up from Simon's line "And from then on it was all downhill" in a moment. OK - we're all set - when you're ready please.")

CUEING
There is a standard sequence for giving verbal cues:
Stand-by 'Sound Cue 19' (Stand-by first)
'Sound Cue 19 Go' (Go last).

CURRENT
The flow of electricity (electrical charge) through a circuit. Measured in Amperes (Amps)

CUT LIST
A list of the coloured lighting gels that are needed for a particular show, including the size of the colour required. There are many different sizes of colour frames for lighting equipment.

CYC FLOOD
A floodlight, usually with an asymmetrical reflector, designed to light a cyc or backcloth from the top or bottom. The asymmetric reflector helps to throw light further down the cloth, producing a more even cover. In the US, a flood at the top of the cyc is a CYC OVER, and a flood at the bottom is a CYC UNDER.
French: Cycliode
Types of lantern

DANCE LIGHTING
Lighting design for Dance is reliant on a great deal of sidelight from BOOMS at the side of the stage. There are normally at least three lanterns on each boom, and three heights - SHINS (to light feet and lower legs), MIDS and HEADS.
These booms are sometimes known as BALLET BOOMS. 

DBO (Dead Blackout)
See BLACKOUT.

DC
Short for DIRECT CURRENT.

DE-RIG
The process of removing lanterns & cabling from flying bars or grid - returning the venue to it's normal state, or as preparation for the next production.
See also STRIKE and GET-OUT.

DEAD
1) (UK) A pre-plotted height for a piece of scenery or lighting bar - 'that bar's on its dead'. The positional indicators on the rope (either PVC tape, or more traditionally cotton tape passed through the strands of the rope) are called DEADS. Sometimes flying pieces are given a number of extra deads, that may be colour coded, in addition to the 'in dead' (lower) and 'out dead' (higher - out of view). In the US, TRIM has the same meaning. Fluorescent ribbon is often used, through the fibres of the rope. The fluorescent colour shows very clearly under UV light, which is often used to light fly floors. Known as TRIM in the USA.
2) Scenery or equipment not needed for current production - 'that table's dead'.
3) An electric circuit that has been switched off or has failed - 'the circuit's dead, you can change the lamp now'
Submitted by Chris Higgs

DELAY
1) Outboard sound equipment that can momentarily stores a signal being sent to part of a P.A. system so that delayed reinforced sound reaches the audience at the same time (or just after) the live sound from the stage. Using the 'Haas Effect' the audience cannot detect the sound as amplified.
2) The term Delay Line refers to the equipment that is used to produce the delayed sound signal.  
3) A function in lighting control software / systems  which holds the start of a cue (or part of a cue) for a specified time. The Delay Time can be used to hold (for example) the Up Time of a cue for a few seconds while the stage is cleared during a dim state. 

DEMUX BOX
Short for De-Multiplex. Interface unit between the serial digital output of a memory lighting control desk to the parallel analogue signal understood by a non-digital dimmer. See MULTIPLEX SIGNAL for more.

DIAPHRAGM
1) Lighting: See IRIS.
2) Sound: The part of a microphone which responds to sound waves.
3) Human Biology: (from WIkipedia) a dome-shaped muscular partition separating the thorax from the abdomen in mammals. It plays a major role in breathing, as its contraction increases the volume of the thorax and so inflates the lungs.
4) A rare type of trapdoor. See TRAPs. 

DICHROIC FILTER
Glass colour filters which reflect all light except that which is the colour of the filter, which passes through.
Normal plastic gels absorb the unwanted colours, turning the light into heat.
Dichroic filters run cooler, and produce a much cooler beam of light. Longer lasting, but a lot more expensive, they are predominantly used in moving lights or architectural applications.
The technology was introduced to the industry in 1988, by Balzers Thin Film Coatings.

DICHROIC LAMP
A low voltage display lamp with a reflector that lets heat pass through it, rather than reflecting it. Results in a much 'cooler' light.

DIFFUSION
1) Diffusion is used on film sets to soften the harsh light either from the sun or from high-power film set lighting. It consists of a translucent fire-retardant cloth mounted in a frame, which can be attached to a crane or onto a C Stand. 
2) See FROST.

DIGITAL
Many electronic devices use digital logic. Information is handled in separate bits (either ON or OFF) rather than continuously variable analogue signals. Most computer lighting boards give a digital multiplexed output, and more and more sound equipment is going digital.

DIGITAL DIMMER
A more recent generation of stage lighting dimmers that can respond directly to the digital multiplexed output of the lighting desk (ie that don't accept an analogue voltage to provide the channel level).
The technology can also permit the dimmer to report faults and other data back to the control board.

DIM OUT
Reduction of lighting level for a scene change, that isn't quite a BLACKOUT. Also known as a GREY OUT or BROWN OUT (brown due to the warming orange/brown tones of dimmed tungsten light sources). 

DIMMER
Electrical or electronic device which controls the amount of electricity passed to a lantern, and therefore the intensity of the lamp.
Dimmers in the Backstage Heritage Collection Archive

DIMMER LAYOUT
See CHEAT SHEET.

DIMMER PER CIRCUIT
A lighting installation where there is no patching system. Each lighting circuit / socket has a dimmer always connected to it. This has advantages in that you never run out of dimmers, but allows no flexibility and can have cost disadvantages in a large space.

DIMMER RACK
A number of individual lighting dimmer circuits built into a single case. Consists of a single power input, a lighting control (DMX512) input and sockets to connect lanterns. A dimmer rack can be set to respond to any control channel by setting its start address (known as "addressing" the rack).
Also known as a Dimmer Pack (particularly where the number of dimmers in the rack is 6 or less).

DIP
1) (UK) Also called Dip Traps. Small covered trap at stage level containing electrical outlets. (US equivalent is FLOORPOCKET)
2) Any dimmer outlets at floor level around the stage (e.g. 'What's the nearest dip circuit to downstage left so I can plug the birdie in?')
3) Lighting equipment on stands at stage level. (e.g. 'We're just focussing the dips now')
4) Low lighting intensity when cross fading between two higher states - 'there's a dip between these two states'.
5) Transparent lacquer for colouring lamp bulbs - known as 'Lamp Dip'.

DIRECT CURRENT
Electric current that flows in one direction only (e.g. from a battery). Abbreviated to DC. See also ALTERNATING CURRENT.

DMX MERGE
Lighting control accessory which accepts multiple DMX inputs (e.g. from a number of lighting controllers) and merges them together to a single DMX feed to control dimmers or moving lights etc.

DMX TERMINATOR
A DMX terminator is a 3 or 5 pin XLR connector which is used at the end of a DMX run to absorb the data signal to stop it being reflected back along the DMX cable. The terminator is very easy to make, and consists of a 120 Ohm half-watt resistor soldered between pins 2 and 3 of the XLR connector. A DMX run should always be terminated, and although the system may work without one, continued operation cannot be guaranteed. A system with poor quality DMX cable (or cable of a long run) will require termination in order to operate correctly.

DMX512
Short for Digital Multiplex. See MULTIPLEXED (MUX) SIGNAL.

DOOFER
An object or tool that you're not sure of the correct name for. For example, 'Pass me the doofer so I can sort this thingy'.

DOUGHNUT
See DONUT.

DOWNLIGHT
A light from directly above the acting area. A downlight could be a spot or a wash of light.
See also BACKLIGHT

DRAMATIC PAUSE
A brief pause (a few beats) in an actors' delivery of a line to emphasise a moment or to heighten anticipation. 
It's important that the DSM does not shout out the next line, while the lead actor is pausing dramatically. 

DRESS LIGHTING
Providing a low level of lights to an open stage while the audience enter the house up until the performance starts. Also known as PRESET.

DRESS REHEARSAL
A full rehearsal, with all technical and creative elements brought together. The performance as it will be 'on the night'.
German: hauptprobe (final rehearsal)

DRY ICE
Frozen solid carbon dioxide (CO²) at a temperature of -78.5° centigrade which produces clouds of steam-loaded CO² gas forming a low-lying mist or fog when dropped into boiling water. Although non-toxic, caution is required in the storage and handling of dry ice because of its extreme cold. Water is boiled in a large tank offstage, into which the dry ice is lowered in a basket. Fans and ducts then direct the gas onto the stage. Dry ice does not support life, so care should be taken that small animals, actors etc.are not below the level of the dry ice for more than a few seconds.
See also LOW SMOKE.
Fog / Smoke / Haze On Stage

DUTY ELECTRICIAN
The member of the lighting team on duty for a particular event. Also known as DUTY LX. 

E.R.S.
(ERS) Ellipsoidal Reflector Spotlight (US)

EDISON PLUG
Heavy duty power connector in the USA - a circular plastic body with three metal contacts.
See also GPC, NEMA. 

EDISON SCREW (ES)
Circular threaded lamp holder which is one of the standard fittings for domestic light bulbs. Other common types are BC (Bayonet Cap) and SES (Small Edison Screw). GES (Giant Edison Screw) is used for large wattage lamps.
The measurements below are the diameter of the lamp base (at the crest of the thread). 

Miniature Edison Screw (MES) is 10mm (E10)
Mini Candleabra Edison Screw (Mini-Can) is 11mm (E11)
Candleabra Edison Screw (CES) is 12mm (E12)
Small Edison Screw (SES) is 14mm (E14)
Edison Screw (ES) is 27mm (E27)
Mogul base is 39mm (E39)
Giant Edison Screw (GES) is 40mm (E40)

EFFECTS PROJECTOR
Lantern used to project the image from a rotating glass effects disc. Used with an objective lens to produce the desired size of image. Commonly used discs are clouds, flames and rain.
See also: Lighting Effects

EFFECTS, LIGHTING
Physical Effects:
Animation Disc: A slotted or perforated metal disc which rotates in front of a lantern to provide 'movement' in the light. Most effective when used in front of a profile carrying a gobo.
Effect Disc: A painted glass disc rotating in front of an effects projector with an objective lens to focus the image (eg Flames, Rain, Snow).
Flicker Flame: Irregularly slotted rotating metal disc through which light is shone onto a prism-type piece of glass which scatters the beam of light and adds the 'dancing' effect of firelight to a scene.
Gobo Rotator: Motorised device inserted into the gate of a profile lantern that can be remotely controlled to rotate a gobo, usually with variable speed and direction.
KK Wheel: Slotted metal disc which rotates in front of a lantern to break up the light and provide movement. (Flicker Wheel)
Lightning: Created through the use of strobe sources or LED floods. Photoflood lamps were used in the past, but have a very short life, and aren't as bright as the other options.
Tubular Wave Ripple: Horizontal linear lamp around which a slotted cylinder is rotated providing a rising light (as reflected from water onto the side of a ship).
Programmed Effects:
Most modern lighting desks (and some very old ones) have the ability to add 'movement' to lighting states by changing the lighting states in various ways. These effects can be set up to run at the press of a button, or can start or stop when a particular cue is run. 
Chase: A number of different 'steps' are added which are then repeated until the chase is stopped. 
Flicker: Particular channels are set to randomly move between levels, with adjustable timings and other parameters.
See also: Pyrotechnics
Lighting Effects
Fog, Smoke & Haze On Stage

ELECTRIC
In the US, LX bars are ELECTRICs bars.
LX1 in the UK (first bar upstage of the proscenium arch) is FIRST ELECTRIC in the US.
In the UK, the bars front-of-house (audience side of the proscenium arch) are usually given names (e.g. Advance Bar, Front Perch, Circle Front) and upstage of the proscenium are numbered, with LX1 as the most downstage.

ELECTRICS
See LX.

ELEVATION
A working drawing usually drawn to scale, showing the side view of a set or lighting rig. See PLAN.
In the US, the term "elevation" refers to a Front elevation. A Rear elevation shows backs of scenic elements. A side view of a set is known as a "section".
See also PAINTERS' ELEVATION.

ELLIPSOIDAL
A profile lantern with an elliptical reflector and at least one lens. Also known as an ERS (Ellipsoidal Reflector Spotlight).
A common type was the LEKO, made by Strand, but this has been eclipsed by the Source Four range, made by ETC.

ENTERTAINMENT TECHNOLOGY
Any technical or practical craft used in the creation of live events or experiences. As the definition of 'live events or experiences' includes music concerts, theatre, theme parks, visitor attractions, museums and sports events, the skills needed are very broad. It's not necessary for anyone to be highly skilled in all of the crafts, but an understanding of the whole picture is very helpful, and knowing when to call in a specialist (and where to find them) is vital.

The crafts involved in entertainment technology include, but are not limited to:
Lighting (stage lighting and architectural lighting)
Sound (live and recorded)
Video and Media (projection or display)
Scenic Construction and Automation
Show Control
Animatronics
Costume
Props and Masks
Make-Up and Prosthetics

EOS
ETC lighting control software, used on a wide range of lighting systems they've designed, including the Eos desk, the Ion, Gio. 
The software had a major upgrade with version 3.0 in 2020, when the Augment3d functionality was added, enabling visualisation and a host of other features, all within the lighting control software. 
The Eos software can run on Windows or Mac PCs as well as the lighting desks, and can control lighting rigs with the addition of a Nomad dongle (to authorise) and a Gadget device to output DMX512, or via an ethernet cable to control ArtNet or s-ACN systems. 

ER / E.R.
(US) Short for Ellipsoidal Reflector - type of fixed beam profile lantern common in the US. Also known as ERS / E.R.S. See also LEKO.

ERS / E.R.S.
(US) Short for Ellipsoidal Reflector Spot. See PROFILE for more. See ER, also ERF.

ESTA
(US) Entertainment Services and Technology Association. See PLASA for the UK equivalent.
ESTA website

EXIT SIGN
Usually illuminated sign, of standard size, which should always be visible, showing an audience member and the company the nearest exit.New legislation in Europe means that the word 'EXIT' has been removed from these signs to be replaced by 'Running Man', known more politically correctly as 'Person moving purposefully'.

FADE
A fade is an increase, diminishment or change in lighting or sound level.
A snap fade is an instant change. A slow fade could be anything from 5 seconds to a few minutes (or even more, for a naturalistic sunset lighting effect). A quick fade is a couple of seconds long.
A fade out takes the lighting state to blackout (or a particular sound to silence). A fade in does the opposite.
A crossfade smoothly transitions from one state to another, without going through darkness (or silence for sound).

FADE DOWN
A slow dimming of the lights to a lower level, but not all the way to blackout. See also FADE OUT.

FADE OUT
A slow dimming of the lights, ending in blackout. See also FADE DOWN.

FADE TIMES
On computerised memory lighting control desks, a lighting fade can have two times - an up fade and a down fade.
The Up fade time refers to the time it takes dimmer levels to rise to their new positions.
The Down fade time refers to the time for dimmer levels falling to their new positions.
In a CrossFade, the fade times are the same for both elements of the fade (up and down). In a Split Fade, the times are different. 
See also DELAY, FOLLOW. 

FADE UP
An increase in lighting or sound level, over a given time period. An increase in level from an existing state is known as a BUILD.

FADER
A vertical slider which is used to remotely set the level of a lighting or sound channel.

FADER WING
A separate accessory added to a lighting desk or to a computer running lighting software, which gives you a bank of faders, which can control either individual channels, or act as submasters (storing lighting states or effects), or act as cue stacks, effectively giving you a number of playbacks. 

FAR CYC
(US) Lighting instrument used to light cycloramas or drops (see also CYC FLOOD).

FAT FINGER
A common problem among lighting & sound operators, when two buttons are accidentally pressed at the same time by a finger that's too large for the buttons. 

FEED
1) A power supply to a piece of equipment or installation is termed a 'feed'. Sound equipment and sensitive computer equipment should have a clean feed - that is, a supply that is free from interference from other equipment.
2) A signal from one system to another is also known as a feed (for example, an audio signal from the FOH desk to a TV company videoing a concert is known as a feed. A video relay of the conductor to screens in the wings is known as a Conductor Feed, etc.)

FEMALE / MALE CONNECTORS
This terminology is beginning to change, as it's not very subtle, and sometimes isn't as clear as it could be. 
Connector manufacturers and crew members refer to plug connectors (with pins) as MALE, and sockets (which receive the pins) as FEMALE. 
Many modern companies refer to plug and socket instead of the genderised terms, but that in itself can cause confusion. The situation remains confusing. 
Sound: Microphones have pins on them, so a XLR cable socket is used to connect to them. The other end of that cable is a plug, which connects to the mixing desk. 
Power: Sockets are used to supply power so that it's not possible to touch live connectors. Plugs are used to connect equipment to the supply. 

FIBRE OPTICS
A method of directing light down a very thin glass fibre. Fibre Optics are used mostly in communication, but find theatre applications in star cloths which are black backcloths with the ends of optical fibres poked through, to create a mass of pin pricks of light. A large bundle or harness of fibres may be fed from one light source, sometimes with a motorised colour or flicker wheel.
New technology enables digital sound signals to be sent down optical fibres, replacing heavy and expensive multicore cables.

FILAMENT
Metal which heats up and glows white hot when electric current runs through it. Dimmable stage lights traditionally use tungsten filaments in a halogen gas (known as Tungsten Halogen lamps). As most of the electrical energy is wasted as heat, more efficient ways of creating light (e.g. LED) are now more in favour. 
The light produced by a parcan is effectively a projection of the shape of the filament (known as the Filament Image). This is especially evident with the CP60 (narrow) PAR64 lamp, which has no frosted glass or lens to soften the image. 

FILL LIGHT
(especially TV and Film lighting) Light which fills the shadows that key light creates.

FILTER
1) See Colour. 2) Electronic device to isolate and redirect specific frequencies in a speaker system.

FIRE EXTINGUISHER
Essential tools of the pyrotechnician's trade ! In the UK, they used to be colour-coded according to content (Carbon Dioxide (Black), Water (Red), Foam (Cream), Halon Gas (Green) Powder (Blue)) but now, they're all red with a small label saying what they are. Another great leap forward !.

FIRST ELECTRIC
(US) The first LX bar upstage of the proscenium arch. (Known in the UK as LX1). The next bar is known as Second Electric, and so on. 

FIT-UP
Initial assembly on stage of a production's hardware, including hanging scenery, building trucks etc.
See also GET-IN

FIXTURE
A single moving light unit. Used instead of "instrument", "lantern" or "luminaire" due to the added complexity of the equipment and the need for additional control connections.

FLAGGING
When focussing lighting, flagging means waving your hand in and out of the beam of a lantern/instrument in order to see where the beam is hitting on stage. Flagging is particularly useful in high ambient light levels. (e.g. 'Can you flag that please ?') Term probably originates from a FRENCH FLAG.

FLASH BOX
A small box containing the socket into which a pyro cartridge is plugged. Also known as a flash pod or firing pod.
German: Startbox

FLASH BUTTON
A push switch on a lighting desk which flashes selected channels / memories / submasters to full (100%) while pressed. Some Flash buttons on submasters can be set to latch (ie they stay on when pushed, until they are pushed again).
Sometimes known as a Bump Button.

FLASH COTTON
See FLASH PAPER.

FLASH OUT / THROUGH
Method of checking whether lanterns are functioning properly by flashing them on one at a time. It is good practice to flash lanterns to 70%, rather than Full to preserve lamp life.

FLASH PAPER
Flash paper is fast-burning nitrocellulose (Cellulose Nitrate) which is used by stage magicians to produce a flash of flame safely. The paper (or cotton) made from nitrocellulose burns almost instantly leaving no ash or residue.
Flash Cotton is cotton wool / string impregnated with nitrocellulose. It should be stored wet, and allowed to dry out just before use.
Wikipedia entry

FLIES
The flying system above the stage of the theatre, consisting of the FLY TOWER, FLY FLOORS, COUNTERWEIGHT systems, PULLEYs, LINES etc. 
See FLY TOWER.

FLIGHTCASE / FLIGHT CASE
Metal framed wooden box on wheels with a removable lid used for transporting equipment between venues. Flightcases are very strong, and have reinforced corners and edges. Care should be taken when lifting flightcases as they can be very heavy.
The term comes from their original use in protecting delicate equipment when being loaded into air transport and being both very strong and relatively lightweight.
Additional information by Chris Higgs

FLOOD
1) A lensless lantern that produces a broad non-variable spread of light. Floods are used in battens, or singly to light cycloramas or large areas of the stage.
See also CYC FLOOD.
2) To increase the beam angle of a Fresnel or PC by moving the lamp and reflector towards the lens. 'Flood that a bit, please!'. The opposite movement is called Spotting.
Types of lantern

FLOOR LIGHT
Lanterns mounted on low stands at stage level so they provide uplight, casting shadows across the stage.
Rigging Positions

FLOOR STAND
A low mount for a lantern so that it can sit at stage level. 
A floor stand consisting of a sheet of metal and a central support is known as a FLOOR PLATE. 
Stage Rigging Positions

FLOORCANS
A PARCAN with an extra trunnion arm / yoke, and often a short nose, which is designed to sit on the floor.

FLY BARS
The metal bars to which scenery and lanterns are attached for flying above the stage. 

FOCAL LENGTH
The focal length (property of a lens) is the point at which parallel rays from the sun will converge on passing through the lens. It follows that if a light source is placed at the focal point, the lens will produce parallel rays. If a light source is placed between the lens and the focal point, diverging beams will result. If a light source is placed beyond the focal point away from the lens, converging beams will result.

FOCUS
1) The session when all the lanterns / instruments in the rig are angled in the correct direction, with the correct beam size.
2) Description of how sharply defined a light beam is ('give that profile a sharp focus')
3) Control on projection equipment used to change the focus.
Lighting Focussing at Theatrecrafts.com

FOCUS CHART
Documentation produced by the lighting designer which shows graphically the exact focus of a particular lantern in the rig. Essential for long-running shows where the crew can use it as a reference when replacing lanterns or checking focus after cleaning etc. The charts can also be used to do a 'rough' focus before a lighting designer arrives at the venue. Touring shows sometimes use a floorcloth marked out with focus information to aid speedy focussing in a new venue.

FOCUS POINT
Function on some computerised lighting desks which allows the operator to specify a place on the stage to which moving lights can be made to move on cue. Once defined, the focus point can easily be recalled and used in multiple cues. If the location of that item is moved (e.g. the chair is moved to the right) all moving lights will automatically focus on the new location.

FOCUS SPOT
Term for both Fresnel and PC type lanterns with adjustable beam size.
Types of lantern

FOCUSING
The process of adjusting the direction and beam size of lanterns using the focus knob(s) on the side or bottom of the lantern. Does not necessarily result in a 'sharply focused' image.

FOG MACHINE
See SMOKE MACHINE.

FOH
See FRONT OF HOUSE.

FOLLOW-ON CUE / FOLLOW CUE
A cue that happens so soon after a previous cue, that it doesn't need to be cued separately.
The follow-on can be taken by the operator once a previous cue is complete, or a lighting or sound cue can be programmed to happen a specific time after a previous cue, when it is known as an Auto Follow. .
Fly follow-on cues are often taken as soon as the operator has completed a previous cue. Often abbreviated to F/O.

FOLLOWSPOT
Usually, a powerful profile lantern usually fitted with its own dimmer, iris, colour magazine and shutters mounted in or above the auditorium, used with an operator so that the light beam can be moved around the stage to follow an actor. Sometimes a beam light or other lantern may be used in the same way.
Powerful followspots use discharge lamps which cannot be dimmed, so these followspots have mechanical dimming shutters to dim the light output.
The Followspot control position is sometimes a separate room soundproofed behind glass, and sometimes in a high position within the auditorium, depending on the theatre. 
See LIMES, PICK-UP.
Followspotting Tips and Tricks
Followspots on the Backstage Heritage Collection archive

FOOT
1) The action of bracing the bottom of a ladder while a colleague climbs it (e.g. 'Can you foot this for me please? I'll only be a couple of minutes').
2) Holding the bottom edge of a flat with your foot while a colleague raises the top of it to a vertical position (known as 'footing a flat').

FOOT MARKS
Marking on lighting bar each foot (12 inches) to make rigging more accurate. The centre line (C/L) is marked on the bar, then each foot outwards from centre to stage left and stage right is marked (and sometimes numbered for ease).

FOOTLIGHTS
A compartmentalised flood batten sometimes recessed into the front edge of the stage, used to neutralise shadows cast by overhead lighting. Before battens were used, individual light bulbs with ornate shades to shield the glare from the audience were used. Modern lighting equipment renders footlights virtually obsolete except for period/special effects. See also FLOATS. 

FRESNEL
(pronounced "Fre-nell")
A type of lantern which produces an even, soft-edged beam of light through a Fresnel lens. The lens is a series of stepped concentric circles on the front and pebbled on the back and is named after its French inventor, Augustin Jean Fresnel (1788-1827). He developed the lens for French lighthouses so that they could be seen further out to sea and could achieve a longer focal length with a lot less glass than a standard plano-convex lens.
Fresnels usually have a focus knob which is used to make the beam larger (flood) or smaller (spot), by moving the lamp and reflector closer to or further from the lens. they also have a set of barndoors on the front of the lantern whih are used to cut off unwanted parts of the beam by casting a shadow.
Sometimes shortened to just 'F' (e.g. 'Can you tighten the focus on the downstage Fs so there's less spill on the front of the stage').
Types of lantern

FRONT OF HOUSE (FOH)
1) Every part of the theatre in front of the proscenium arch. Includes foyer areas open to the general public.
2) All lanterns which are on the audience side of the proscenium and are focussed towards the stage.
The backstage areas of the theatre are known as Rear of House (ROH).

FROST
A diffusing filter used to soften the edges of a light beam. Frosts are commonly used in profiles in front of house positions to achieve the same beam edge quality in all lanterns. Different strengths of diffusion frost are available from many colour filter manufacturers.
Rosco make a range called Hamburg Frost - see link below.
See also SILK.
Rosco Hamburg Frost range

FULL UP
A bright lighting state with general cover lanterns at 'full' (100%) intensity. See also FULL UP FINISH.

FUSE
Protective device for electrical equipment (E.g. dimmers). Every piece of electrical equipment has at least one fuse in its associated circuit. The thin wire inside each fuse is designed as the 'weak link' in the circuit so that once the rated current is exceeded, the wire literally melts, breaking the circuit, and preventing further damage to the rest of the equipment. 

GAFFER TAPE / GAFFA TAPE
Ubiquitous sticky cloth tape. Most common widths are .5 inch for marking out areas and 2 inch (usually black) for everything else. Used for temporarily securing almost anything. Should not be used on coiled cables or equipment. Originally known as Gaffer's Tape, from the Gaffer (Master Electrician) on a film set. Also known as Duct Tape.
See also PVC Tape.

GATE
1) The point of focus in a profile spot where the shutters are positioned and where an iris or gobo can be inserted.
2) A single base section of a folding rostrum system.
3) See NOISE GATE.

GAUZE
Cloth with a relatively coarse weave. Used unpainted to diffuse a scene played behind it. When painted, a gauze is opaque when lit obliquely from the front and becomes transparent when the scene behind it is lit . Many different types of gauze are available;
Sharkstooth gauze is the most effective for transformations, because it is the most opaque.
Vision gauze is used for diffusing a scene and for supporting cut cloths.
HoloGauze™ is a metallised gauze optimised for front projection holographic illusions.
Also known as a Scrim, American Mesh.
Gobelin Fabric is used for tapestry making and has a less coarse weave than theatrical gauze, but will work for smaller shows. 
Voile / Net curtain material will work well and takes projection very well (as the thread is much finer than cotton gauze). 
A black curtain (known as a Blinder) is sometimes needed behind a gauze to completely block light going through. The blinder is removed invisibly just before the light is faded in upstage.
Holo-Gauze
See also Lighting With A Gauze / Scrim

GEL or GELATINE
See COLOUR FILTER.

GENERAL COVER
Those lanterns in a rig which are set aside purely to light the acting areas.
The stage is normally split into a number of areas for this purpose, which can then be isolated or blended together as required by the director. 
See Special.
Designing and Focussing a General Cover

GENERIC
Standard stage lighting instruments, rather than moving lights or other effects. (e.g. 'There are 40 instruments in the rig - 20 moving lights and 20 generics'). 

GET-OUT
Moving an entire production out of the venue, and back into storage or into transport. Usually preceded by the strike (where the set is disassembled back into component parts.
The Get Out is also known as Load Out (USA) or Bump Out (AUS.) or Pack Out (NZ).

GLOVES
Used when lifting heavier lanterns or other equipment.

GO BUTTON
1) A button on a lighting or automation control console that executes a cue. The button is usually labelled GO. 
2) (Trade Name) A remote control for a computer running QLab software. 

GOBO
A thin metal plate etched to produce a design which can then be projected by a profile spotlight. There are hundreds of gobo designs available - common examples are breakup (foliage), windows and scenic (neon signs, city scapes etc.). The image can be used soft focus to add texture, rather than a defined image. A number of composite gobos in different coloured lanterns can, with careful focusing, produce a coloured image (e.g. a stained glass window). Greater detail can be achieved using a glass gobo, which consists of a thin layer of aluminium etched onto glass.

Origin of the term 'gobo'
There are a few possible origins for the word GOBO but nothing definitive yet.
Although it's tempting to believe it's an acronym or abbreviation for 'Graphical Optical BlackOut' or 'Goes Before Objective lens' this is not true, as the term is also used in connection with sound recording (a microphone gobo blocks sound from adjacent sources) and also in the film industry, where it's a piece of equipment to block light from the lens or an area. .
It could be short for Go-Between, as the gobo goes between the lamp and the lens.
Material from 1967 uses the word 'MASK', and no mention is made of 'GOBO', so we can assume the word wasn't in widespread use then for stage lighting. In the US TV/Film industry, a Gobo is a piece of material used to mask or block light, placed in front of a lantern (also known as a SHADOW MASK) and a Cookie (short for Cucaloris(from the Greek kukaloris: the breaking up of light)) is the same as a UK Gobo. PATTERN and TEMPLATE can also refer to a gobo in some areas.
In the film industry, the word gobo can be used as a verb (e.g. 'We need to gobo off that light so the camera doesn't see it').
Gobos are available in a wide range of sizes, for use in different profile lanterns and other projectors (e.g. moving lights). 
A size - 100mm outside diameter / 75mm image diameter
B size - 86mm / 64.5mm
D size - 53mm outside diameter
M size - 66mm / 48mm
E size - 37.5mm / 28mm
Moving lights use a range of different gobo sizes, so check the manufacturers website. 
Lighting Effects

GOBO HOLDER
A metal plate designed to hold a gobo of a particular size in a lantern of a particular type. 
Different size gobos need different gobo holders, and different lanterns have specific size gates, into which the gobo holder is inserted.
Glass gobos require a special type of gobo holder, which holds the gobo securely, but also allows it to expand with heat. 
The gate is between the lamp and the lenses, at the midpoint of the lantern, and is part of a profile lantern. A gobo can't be used in a fresnel or flood.

GOBO ROTATOR
See EFFECTS.

GOING DARK
Warning to people on stage that the lights are about to be switched off. Normally said during lighting plotting sessions or technical rehearsals. Obviously should not be done if there is any risky work on stage, or if anyone is up a ladder / using power tools / working on platforms / rehearsing choreography etc.

GOING OUT
Warning that a flying bar is about to be lifted. 
e.g. "LX3 Going Out".
See also COMING IN, FLYING

GRAND MASTER
See MASTER.

GRELCO
(UK) A 2 way 5A or 15A electrical splitter, originally manufactured in the UK by Grafton Electric Company (hence the name Gr el co). Another name is SNAPPER (brand name) or in the US "TWOFER". Sometimes shortened to GRELLY. A three way splitter is known as a TRELCO, TRELLY (or THREEFER in the US). These splitters are always wired parallel (voltage equal, current shared).
See SERIES SPLITTER which enables (for example) two 115V lamps to be connected to a 230V supply.
[updated courtesy John Creed, 2017]
Museum of Old Electrical Items - Grelco

GROUNDPLAN
A scaled plan (overhead) view of the theatre stage area or of a set design, to enable all technical departments to ensure that everything will fit correctly into the space available. The groundplan shows all items standing on the stage floor and any permanent items which will affect the production, and the position of any flown pieces. The set design groundplan enables the lighting designer to be clear about exact location of all items, and will have the walls of the stage drawn on it so that the stage management team and production manager can plan furniture and set moves offstage.
Typical scales are 1:24 (.5' to 1 foot) or, metrically 1:25 (1cm to .25m). Venues have a base plan showing proscenium, walls, seating etc on which individual set and lighting plans can be drawn.

GROUNDROW
1) A long piece of scenery positioned at the base of a backcloth usually to mask the very bottom of a cloth or lanterns lighting a cloth.
2) Compartmentalised floodlight battens at floor level used to light the bottom of skycloths etc, often masked by groundrow scenery. 

HALF K
A 500W lantern (usually Fresnel or PC) - K refers to Kilowatt (1000 Watts).

HANG / HANGING SESSION
The 'hang' is the American equivalent of the lighting rigging session in the UK - the time when the lighting equipment is rigged.

HAZER
See SMOKE MACHINE.

HEADS
The top lantern on a lighting boom. See SHINS and MIDS.

HEADS ON STAGE!
A shouted warning (often just 'Heads!') for staff to be aware of activity above them. Also used when an object is being dropped from above.

HEADSET
1) General term for theatre communication equipment.
2) A headphone and microphone combination used in such communications systems with a beltpack.
See also CANS.

HEATSHIELD
Made by Rosco, Heat Shield is a special clear gel which when placed between a lamp and a coloured gel, dissipates a large amount of heat to give the gel a longer life. There must be an air gap between the Heat Shield and the gel, or it will not be effective.
Rosco website

HOME
On some lighting desks, the default position / intensity / status for any fixture or dimmer can be set, so you can easily reset a wayward fixture to where you want it to be, or to a position where you can set it to a new location / colour easily. Also useful for fault-finding, and for getting everything to a known position either at the end of the day, or when plotting a new cue. 
Video

HOOK CLAMP
A clamp with a wing bolt for hanging a lantern on a horizontal lighting bar, so that it hangs below the bar.
Introduced in the UK in 1959 by Strand, replacing the 2-bolt and 2-nut L Clamp.
Hook Clamps should not be used to overhang items above a lighting bar. A BOOM ARM can be rigged on a lighting bar (horizontal) or a boom (vertical) to rig a lantern adjacent from the bar / boom. 
Alternative clamps are available from companies such as Doughty to rig a lantern above a bar. 
See SAFETY BOND and BOOM ARM.

HOT POWER
Refers to a 'live' power feed, which does not go via a dimmer. 
Many modern pieces of equipment used in a lighting rig must not be supplied with power from a dimmer (e.g. projectors, moving lights, LED lanterns etc). They require hot power, and have an additional control input connection (DMX512) which gives them instructions what to do. 

HOT SPOT
The brightest part of the beam from a lantern, usually showing the centre. Profile lanterns have a Field control which enables a beam to be flattened so it has no hot spot.

HOUSE LIGHTS
The auditorium lighting which is commonly faded out when the performance starts, and raised again at the end of the show, and during intervals. The House Lights need to be bright enough for the audience to find their seat, to read their programme, and find their ice-cream spoon, but should still set an atmosphere. As well as the functional house lights, if there's no house curtain, there may be a preset on stage, which helps to set the tone of the show, and to reveal part of the set that looks interesting. If there is a curtain, it will usually be cross-lit in a colour to make it look interesting. 

HOUSE TO HALF
A cue given by stage management to the lighting operator to prepare for the start of the show by turning the house lights (the auditorium lighting) to 50% to quieten the audience down, and to give those who aren't yet in their seats a few vital seconds to get into place. 

IFCB
Acronym for the four palettes used to control moving lights. Intensity (brightness of the beam), Focus (position of the beam), Colour, Beam (focus quality of the beam - hard-edged, soft-edged, or split through a prism).

INCANDESCENT
Light source consisting of a metal filament (Tungsten) which glows white hot when current is passed through. See also Discharge Lamp.
How do Incandescent Light Bulbs Work?

INDEPENDENT
1) An electrical power supply that is totally separate from the stage lighting control. Used for testing lanterns prior to connection to the lighting system and also for powering non-lighting equipment on stage and working lights. See NON DIM.
2) A channel within the stage lighting control which has been temporarily switched to become independent from the rest of the channels which remain under the control of the operator.

INFRA-RED
Invisible part of the electromagnetic spectrum with a longer wavelength than visible light. Infra-red remote controls are used for lighting desks and practicals. An infra-red-sensitive CCTV camera can pick up body heat activity even in a 'blackout'.

INHIBIT
A way of taking control of a rogue lantern (or lanterns) at the lighting desk during the operation of a show and removing them from any further lighting states, until the inhibit is removed. Can also be used for removing the front of house lighting from a curtain call state. See also SUBMASTER.

INSERT
1) An additional route into a sound desk.
2) An extra lighting state added into the sequence later. See POINT CUE.

INSTRUMENT
(US) Same as a LANTERN or LUMINAIRE in the UK/Europe.

INSTRUMENT SCHEDULE
A list of the instruments / lanterns used on a show.
Usually sorted by hanging position (e.g. Front of House, First Electric etc.).

INTELLIGENT LIGHT
See MOVING LIGHT.

INTENSITY
(Lighting) A way of describing the brightness of a stage lantern. A lantern supplied with the maximum amount of electrical power a dimmer is able to produce is described at being 'at full intensity' - this is often called '100%' or just 'Full'. 
As the electrical supply is reduced, the light gets dimmer (lower intensity). When the dimmer has been faded down (or 'faded out') the intensity is said to be '0%' or 'Zero' or 'Out' or 'Off'. 

INTERNALLY WIRED BAR (IWB)
A Scaffolding bar (aluminium) which has a number of sockets (usually 15A in the UK) positioned along its length, the wiring for which is contained within the bar.
Lighting bars nowadays need 'hot power' sockets and DMX outlets, as well as the more usual dimmer output sockets into which traditional theatre lighting equipment is connected. 
Bars in new theatre installations sometimes use 16A CEEFORM sockets which are more widely used in TV/Film studios, and are more universal than the 15A socket, which is UK-only. 
See also SIX LAMP BAR.

IRIS
Adjustable aperture which, when placed in the gate of a profile lantern, varies the size of a beam of light. Originally, iris diaphragm.
Most followspots have an iris permanently installed.
The term 'Iris In' means to slowly close the iris of a followspot so that the size of the beam is reduced, until as the beam gets as small as it can go, fading (or snapping) to blackout. The speed of the movement will depend on the pace of the show / music at that point. 
Profile moving lights have iris functionality built-in, and can be adjusted in beam size. Some wash moving lights have a zoom function which reduces the size of the beam. 

JUMPER
An adaptor from one type of electrical connector to another. For example, a 13 - 15A jumper has a 13A plug and a 15A socket at either end of a short cable. Also applicable to sound cables.

K
Lighting Industry Forum code which identifies the (original) recommended usage of different lamp types. K coded lamps are for use in general purpose flood lighting, and have a colour temperature of 2850°K. See also CP, A1, T, P2.
Lamps List

KELVIN
See COLOUR TEMPERATURE.

KEY
A section on a lighting or other technical layout plan, which denotes what the symbols on the plan refer to. 
Although many symbols are standardised, there are variations, and to avoid confusion (or errors) when rigging and laying out equipment, a key is essential to ensure the requirements of the design are correctly interpreted. 
Lighting Paperwork

KEY LIGHT
(Esp. TV & Film lighting) The dominant light source/direction in a naturalistic lighting state. In a sunny drawing room, the key light would be through the window, for a naturalistic exterior scene the direction of the key light could change as the sun progressed across the sky. See FILL LIGHT.

KILL
To switch off (a light/sound effect); to strike/remove (a prop).
(e.g. Kill channel 6 please)

KILOWATT
1 kilowatt (1kW) is equal to 1000 Watts. The WATT is a measure of electrical power. The single letter 'k' is often used to represent 'kilowatt'. "2k fixture" means a 2000 Watt (or 2kW) lantern etc.

KIT
1) General name for equipment, especially nice shiny equipment, leading to the comment 'That's a nice bit of kit'
2) Short for Drum kit.

KK WHEEL
A type of animation disk which fits into the colour runners at the front of a lantern which rotates and breaks up the light beam to make it appear to be moving. Best used on a profile lantern containing a gobo. A KK Wheel is known in the US as LOBSTERSCOPE.

LADDER
1) Climbable piece of access equipment to reach a working platform or for short light-duty work at height. See ZARGES.
2) Non-climbable structure in the shape of a ladder from which lanterns can be hung in a vertical 'stack'.

LAMP
A light bulb is used in domestic situations (i.e. in the home). In the industry, we only use LAMPS. As the saying goes, 'Bulbs is what you put in the ground'.
Example usage: 'The lamp in the DSC fresnel has blown'. In the TV/Film world, a lamp is called a BUBBLE or GLOBE.

LAMP HOUSE
Part of a stage lighting instrument which contains the light source, electrical connections and (often) the bracket to attach the lantern to the lighting rig. 
Different lens tubes can be connected to a lamp house (as long as they're by the same manufacturer) so that the lantern is suited to the application for a particular event / show. 

LAMP ROUND
Periodic inspection of all light fittings around the theatre, to replace dead lamps / bulbs. Usually takes place before opening night.

LAMP TRAY
Lower section of the body of a theatre lantern on which the lamp holder is mounted. Some lamp trays are hinged, some are removable from the rest of the body. Modern safety legislation (UK) requires that the lamp tray cannot be opened until power is disconnected.

LAMPY
(colloquial term) Theatre / Rock & Roll lighting technician. Distinct from a 'Techie' who may also be a carpenter or stage crew member. A lampy only concerns him/herself with lighting.
A more generic electrician might also be called a Sparky, or Sparks.
See also JAFIE, TECHIE and NOISE BOY.

LANTERN
1) General term for unit of lighting equipment including spotlight, flood etc. Term now being replaced by the internationally recognised "luminaire" (esp. Europe) or "instrument" in the US.
See also FIXTURE and TYPES OF LANTERN link below.
2) Glazed section of roof usually in haystack form over the fly tower that automatically opens in the case of fire. An updraught is created which inhibits fire from spreading quickly into the auditorium, and prevents build-up of smoke at stage level.
Types of Lantern at Theatrecrafts.com

LD / L.D.
Lighting Designer.

LECTRIFLEX
Multipin connector for carrying multiple lighting circuits down a multicore cable. See also SOCAPEX.

LEKO
A type of ellipsoidal profile spot (aka ellipsoidal reflector spotlight or ERS), much used in the USA. Originally designed in 1933 by Joseph Levy and Edward Kook, the founders of Century Lighting (later Strand). The word is a contraction of their names (Levy & Kook). Also known as LEKOLIGHT.
Leko in the Backstage Heritage Collection archive

LENS
Optical glass with one or both sides curved, the purpose of which is to direct light by concentrating or dispersing light beams.

LENS TUBE
Part of a stage lighting instrument which contains the lens(es) and focussing adjustment controls, and the colour frame holder at the front of the instrument. 
On some instruments, the lens tube is a fixed part of the lantern. On others, it's interchangable and different lens tubes can be connected to the same lamp house (containing the lamp, and rigging equipment to hang the lantern on the lighting bar). 

LEVEL
1) The setting of a light or sound control channel. On a lighting desk, levels range from 0% to 100% (also known as FULL). On a sound desk, the bottom of the fader is ∞ (infinity) and the top may be +20. The fader is designed to be operated at it's optimal position which is labelled 0dB. The decibel (dB) scale is a measure of sound intensity. 
2) A platform used to change the height of an actor. Interesting dynamics between different characters in the play can be explored using various levels. 

LIGHT
TO BE DEFINED
How Light Works

LIGHT BOARD
See BOARD.

LIGHT CURTAIN
A lighting effect which, when an area is diffused with smoke, produces a wall of light. Produced (usually) by a batten of closely-spaced low voltage lamps wired in series.
Automated versions are available which have colour changers built-in and are able to tilt up and down. The original Light Curtain designed by Josef Svoboda is still made by ADB. (See SVOBODA, DIGITAL LIGHT CURTAIN)
Light Curtains in the Backstage Heritage Collection

LIGHTING OPERATOR
Member of the show crew who runs the lighting board during the show for the Electrics Team. Also known as LBO (Lighting Board Operator).

LIGHTING PLAN
A scale drawing detailing the exact location of each lantern used in a production and any other pertinent information (E.g. its dimmer number, focus position and colour number). Often drawn from the theatres' groundplan.
Lighting Paperwork

LIGHTING PLOT
1) The process of recording information about each lighting state into the memory of a lighting console for subsequent playback. (in USA, this term is used for a lighting plan and a lights session is when lighting states are set up.) The lighting designer communicates with the board operator, often via a comms headset, who physically types the information into the console. 
2) See also LIGHTING PLAN. 

LIGHTING STAND
Usually three-legged telescopic stand on which lighting equipment can be mounted. The stand will have a socket on the top into which a spigot can be inserted, which is bolted onto a single lantern. Or, a spigot can be attached to a scaffold clamp or a T bar to enable multiple lanterns to be rigged. Ensure the lighting stand you are using is strong enough for the lanterns you want to rig. 

LIGHTING STATE
The format of lighting used at a particular point in the production; a lighting 'picture'. A lighting cue is given by the stage manager which initiates the change from one lighting state to the next.

LIGHTING STENCIL
Plastic stencil containing a range of scale symbols for current lighting equipment. Greatly facilitates the drawing of lighting plans.
Lighting Stencils on the Backstage Heritage Collection

LIGHTS DOWN
1) Announcement by the DSM that a section of the performance has ended (e.g. Lights Down on Act One).
2) A reduction in light level - usually a note by the lighting designer for her/his own reference.

LIMELIGHT
An obsolete source of intensely bright light, most recently used in followspots.Derived from a burning jet of oxygen and hydrogen impinging on a rotatable cylinder of lime.
See LIMES.

LIMES
Followspots and their operators. This term is still in everyday use, although limelight is not. See also PICK-UP.

LIVE MODE
This is the normal mode for operation for lighting control desks, where any changes made are instantly reflected on stage. 
Many lighting control desks have a BLIND mode, where changes can be made without affecting the current state. 

LIVE MOVE
A move by a moving light while it is visible on stage (i.e. while the intensity is up). 
This may be deliberate, but can sometimes look messy, and should be avoided unless the style of the show or the lighting design requires it. 
Modern computerised desks have a 'Move While Dark' or 'Automark' function which, when enabled, means the lights will reposition themselves for the next cue once their intensity goes off on a particular cue. 

LOAD
1) The electrical power rating, in Watts, of the equipment connected to a particular lighting dimmer. 2) The equipment connected to a dimmer.

LOAD LAMP
See GHOST LOAD.

LOW VOLTAGE
Lower voltage lamps give more intense light than mains voltage lamps of the same wattage.

LUMINAIRE
The international term for lighting equipment. Not restricted to theatre lighting.

LX
Short for Electrics ('Elecs'). The department in the theatre responsible for stage lighting and sometimes sound and maintenance of the building's electrical equipment. Lighting cues in the prompt book are referred to as LX cues (abbreviated to LXQ).
(In the USA, LX cues are known as Light Cues, and may use LQ instead of LXQ). 

LX TAPE
See PVC TAPE.

MAC
A range of professional moving lights made by Martin in Denmark.
Martin website

MAGIC SHEET
A smaller version of the lighting plan, used by the lighting designer during the lighting plot. Also known as a Dimmer Layout or Cheat Sheet.
Lighting control software can produce an electronic version of the Magic Sheet, which can be laid out however works best for the lighting designer, and provides shortcuts to groups of lanterns, effects and colours.

MANUAL DESK
A lighting desk where the interface between operator and dimmer is a fader, rather than a computer. Many modern manual desks have some memory facilities built in, but there are still a large number of venues with solely manual systems.

MASTER
1) An overall control fader or lever on a lighting or sound control board. The Grand Master takes precedence over all other controls and allows the operator to fade out the entire output of the lighting desk.
On a lighting desk the PRESET MASTER allows the control of a section of the desk independently from the rest.
See also SUBMASTER.
2) An original (e.g. Master tape, master plan) which should be used only to make a copy from which to work.
3) A Department Head (e.g. Master Carpenter, Master Electrician).

MASTER ELECTRICIAN
See CHIEF ELECTRICIAN.

MEMORY BOARD
A lighting control which enables recording and subsequent 'playback' of lighting states. 
Now commonplace, and in some cases rendered unnecessary as lighting control moves to standard laptops running software such as ETC's EOS. 

MIDS
The middle lantern on a lighting boom. See SHINS and HEADS.

MIRRORBALL
Large plastic sphere covered in a mosaic of small mirrors, which reflect light outwards, to cover the area with bright dots of light. Usually suspended by a rotator (an electric motor which turns the ball). Can be very effective when lit by pinspots, or more commonly now, intense moving light beams.

MOON BOX
Lighting effect. A large shallow circular box with calico cloth on one face and low wattage lamps arranged on the back. Can be flown behind a gauze or thin cyclorama to give the effect of the moon rising.

MOVING HEAD
See MOVING LIGHT.

MOVING LIGHT
Remotely controllable "intelligent" lighting instrument. Each instrument is capable of a massive variety of effects which are operated live via a moving light control desk, or can be pre-programmed by a standard memory lighting desk. The instruments require a power supply and a data cable (normally carrying DMX512 signal from the control desk).
There are broadly two types:
1) Moving Head: A luminaire is mounted on a moving yoke which can pan side to side and can tilt the luminaire through a range.
2) Moving Mirror: A stationary luminaire directs light onto a motorized mirror.
Both types have in common:
- A discharge (non-dimmable) light source or dimmable LED source (rare variants use a tungsten source, but most new moving lights are now LED-based)
- A dimming shutter (for discharge light sources)
- Motorized rotating colour wheels. Some offer colour mixing using graduated red, green and blue wheels or prisms.
- Profile versions have motorized gobo wheels with rotation.
- Strobing effects and adjustable iris. Some also have framing shutters.
The term "intelligent" is used as the instrument has a processor chip and electronics built into it, not because it's able to interpret the designer's artistic intent! It can be incredibly frustrating trying to get moving lights to behave exactly as required in a dramatic situation. Musicals and live music performances are more forgiving.
Moving Head lanterns are sometimes known as NODDING BUCKETS, Moving Mirrors are sometimes known as WIGGLIES or SCANNERS.
All moving lights require an undimmed 'hot power' feed, so must not be connected to dimmers. Some dimmer racks can provide switched power, but many older systems cannot, so alternative power sources must be used for moving lights. 

MOVING MIRROR
See MOVING LIGHT.

MULTIPLEXED (MUX) SIGNAL
All modern lighting desks use this serial form of communication with dimmers and other equipment. Information from the desk is transmitted along a single pair of cables in sequence to the dimmer where a de-multiplexing unit (demux box) decodes the string of data and passes the correct piece of information to the correct dimmer.
The industry standard protocol (language/standard) for multiplexing is the digital USITT DMX512 (introduced in 1986, based on RS485 data protocol, and often shortened to DMX or DMX512). However, new protocols are continually being added to keep up with more demanding equipment.
Although the standard connector for DMX512 is a 5 pin XLR, as the system only uses 3 connections, a great deal of equipment uses the more common 3 pin XLR. Care should be taken when using standard microphone cables to connect devices using DMX512, as the cable is usually less capable of accurately transmitting the digital data than a more expensive DMX512 cable. Short runs with microphone cable are acceptable.
As the basic DMX512 standard is one-directional, there should be a DMX terminator at the end of the DMX run to absorb the data signals and stop them being 'reflected' back down the cable and causing communications errors and other problems.  
SMX (Strand Multiplex) is a communications protocol which enables digital dimmers to "report back" to the desk on any faults (eg blown lamps).
RDM (Remote Device Management) is an emerging upgrade to DMX512 which will include bi-directional communication between controller and device.
DMX512-A (officially ANSI E1.11) is a new standard under development at ESTA which is backwards compatible with DMX512 but has stricter safety parameters and offers some upgrades of functionality.
Among the older protocols (before DMX512) are:
AMX192 Introduced by Strand Lighting around 1975, and later used on the CD80 dimmer range. AMX stands for Analogue Multiplexed Signal, and can control up to 192 channels, using a 4-pin XLR connector.
CMX - Colortran Multiplexing Signal, also known as D192. Developed in the late 1970s and first used on the Channel Track console. Uses 5 pin XLR, and is a digital multiplexed signal (rather than the analogue multiplex that AMX used). The signal is RS422.
D54 which uses a stream of analogue voltage levels and was the Strand standard, controlling up to 384 dimmers. First introduced on Galaxy desks.
See also UNIVERSE.

NC / N.C. / N/C
1) (US) No Color (US equivalent of UK's OPEN WHITE).
2) Not Connected (in a circuit diagram).

NON DIMS
Channels, usually controlled from the lighting desk, which are switched, rather than dimmed. This enables motors, slide projectors, smoke machines etc to be controlled from the lighting desk. 
Older dimmers can be setup so that the channels go straight to full from zero at a particular channel level (e.g. 50%). However, these may not provide a properly switched output, as they are still using the output from a dimmer at full, rather than the output from a relay circuit (or switched circuit) which takes the power feed and bypasses the dimmer circuitry completely.

OFFSTAGE
1) A movement towards the nearest side of the stage from the centre. (e.g. 'Focus that spot offstage a bit please')
2) The area out of sight of the audience (e.g. 'Get that donkey offstage !')

ONSTAGE
1) A movement towards the centre of the stage from the sides. The opposite of OFFSTAGE. There is no abbreviation for onstage (as it is too easily confused with offstage).
2) The act of being on the stage (e.g. 'he joined her onstage for the finale')

OPEN WHITE
(o/w) Lighting with no colour filter. Known in the US as NC (no color).

OUTRIGGER
An extendible leg to increase the stability of access equipment (eg Tallescope, Scaffold tower).

P2
Lighting Industry Forum code which identifies the (original) recommended usage of different lamp types. P2 coded lamps are photofloods, and have a colour temperature of 3000°K. See also PHOTOFLOOD, CP, A1, T, K.
Lamps List

PAIRING
Connecting more than one lantern to one power outlet via an adaptor or splitter, or more than one speaker to one amplifier channel.

PALETTE
On lighting control systems, a palette is a collection of references for colour, position, beam type or intensity. Every cue or preset that includes the palette will be updated if the palette is modified.

PAR
Short for Parabolic Aluminised Reflector lamp. A lamp containing a filament, reflector and lens in one sealed unit. Used in PARCANs to produce a high intensity narrow beam of light. Par lamps are available in many different sizes and powers. Par sizes available include 16, 36, 38, 56 and 64. (The number refers to the diameter of the lens, in eighths of an inch, so a PAR64 lamp is 8 inches across).
The most common for theatre use are Par 64s rated at 1000W (1kW), although other wattages are available.
When the lamp was first introduced, in the 1960s, it was only available from the USA in 110V versions. In the UK, Parcans were always used in pairs, via a series splitter. 110V Par lamps are still sometimes used in large UK venues or for touring due to the increased light output. Because the current is greater, the lower voltage lamps have smaller thicker filaments which give a more focussed beam than the thinner 240V filaments.
In the film business, PAR lamps are known as 'bird's eyes' after the alleged inventor Clarence Birdseye.

PARCAN
Type of lantern which produces an intense beam of light, ideally suited to "punching" through strong colours, or for special effect. The Parcan is literally a cylinder of metal (the "can") within which sits the PAR lamp (PAR stands for Parabolic Aluminised Reflector) which consists of the bulb, a reflector and a lens in a sealed unit.
The PAR was originally available only as a 110V lamp, imported from the USA, where they were used as beam lights. The lamps were first introduced in the UK by concert hire company ESP in 1968 [Cue issue 1, page 14].
The Parcan was being widely used by the early 1970's in the Rock concert industry due to the intensity of the beam, and the light weight and near indestructibility of the lantern. The lens of the lamp is either clear (which produces a narrow beam), frosted (medium) or stippled (wide).
Parcan lamps are available in a range of different lens types:
UK (240V): CP60 is a narrow beam (clear lens), CP61 is medium beam (frosted lens), CP62 is wide beam (ribbed lens)
See also PAR and FLOORCAN.
Types of Lantern
Parcan Evolution and History

PAT TEST
Short for Portable Appliance Test. Requirement under the UK Electricity At Work Regulations (1989) to test and inspect all portable electrical equipment. This includes stage lighting equipment (lanterns, cables, portable dimmer packs etc.).

PATCH
1) (verb) The act of plugging a lantern into a dimmer (e.g. 'Can you patch circuit 12 into dimmer 18 please') or on a lighting desk allocating control channels on the desk to dimmers or fixtures in the rig - this is known as a SOFT PATCH.
If written down, this is known as a Patch Schedule or Patch List. 
2) (noun) The system for connecting lanterns to dimmers (The Patch).
The term also applies to sound - a PATCH BAY is used to connect outboard equipment into the sound desk and to connect sound desk outputs to amplifiers, and amplifiers to speakers.

PATCH PANEL
A board consisting of rows of sockets into which plugs can be connected to route sound signals or power for lighting circuits. Some American systems use a Pin Plug patching system. See also PATCH.

PATCHING
1) To cross-connect lighting circuits around the stage area to a chosen dimmer. Connecting lanterns to dimmers. This is sometimes known as a hot-patch (because you are potentially patching live power). The connectors used in a hot-patch system must not permit the user to touch live connections. 
2) Using a cross-connect panel which enables any stage lighting channels to the control desk to control any dimmer or group of dimmers. Some large lighting boards have the facility for soft patching - a totally electronic way of patching. Some Rock Desks have a pin patch which allows groups of dimmers to be allocated to a particular control channel. Also applies to routing of sound signals.

PATTERN
1) See GOBO.
2) See PATTERN NUMBER.

PATTERN NUMBER
Many older Strand lanterns are identified by their Patt. number (eg Patt.23 is a 500W profile). The numbers bear no direct relation to their size or type (although lanterns of a similar design may have similar Pattern numbers.) See http://www.strandarchive.co.uk for a complete listing.
TABS article by Frederick Bentham about the Pattern Numbering logic
Strand Lanterns with Pattern Numbers - Backstage Heritage Collection

PC
Originally short for plano-convex - the basic lens shape of many lanterns / projectors. Now short for Prism- or Pebble-convex: a type of lens with a pebbled flat surface which gives a slightly harder edge than a Fresnel, but not as hard as a Profile. PC refers to a lantern with a PC lens.
Types of lantern

PEBBLE SPOT
See PC.
Types of lantern

PERCENT
Dimmer levels are expressed as a percentage of the supply voltage. (100% = 230 - 240 Volts(UK)).

PERCH
1) A lighting position (often on a platform) at each side of the stage, immediately behind the proscenium.
Some theatres use the term for vertical boom positions in front of the proscenium in the house.
The plural is PERCHES. They may be named by position (e.g. Front Perch, Rear Perch, SL Perch etc).
2) An ancient unit of measurement, used since the 9th century, and abolished in the UK in 1963. One perch is equal to 16.5 feet, or 5.03 metres. 

PHASES
Electricity is generated and supplied to large installations as three separate supplies, known as phases, and labelled L1, L2 and L3 (for Line).
Until recently, the three lines were colour-coded Red, Yellow and Blue in the UK. Now, across Europe, the three lines are colour-coded brown, black and grey, with the neutral coloured blue.
Each of the phases and one neutral are supplied down a single multicore cable to the building, but effectively give three separate supplies. Because there is a potential difference (voltage) of 415 volts between any two phases and earth/ground, care must be taken that pieces of equipment powered by different phases are not capable of being touched at the same time in case of a fault.
This usually means that such equipment should not be on the same physical lighting bar, or in the same part of the studio theatre.

PHOTOFLOOD
A lamp used by photographers which gives a bright white light. Because it has a thin filament, it gives a good flash effect (eg lightning), but has a relatively short life, so should not be left on for any length of time.

PICK-UP
1) Device which, when attached to an acoustic musical instrument, converts sound vibrations into an electrical signal.
2) A way of describing the directional sensitivity of a microphone. An Omnidirectional microphone has equal pick-up from all around, a Cardoid microphone is more sensitive from the front, a Super-Cardoid or Hypercardoid has very strong directionality from the front. A figure-of eight microphone picks up front and rear, but rejects sound from the sides.
3) The action of turning a followspot on a performer. (e.g. 'that was a good pick-up', 'your next pick-up is downstage left'). A BLIND PICKUP is on a moving performer and requires good hand-eye co-ordination. A SET PICKUP is on a specific area, is preset, and is made on a cue from the stage manager. A SIGHT PICKUP is made visually by the operator to a preset position.

PINSPOT
1) A lantern focused very tightly on a small area (eg an actors head) - a pin spot.
2) A luminaire used widely in disco installations, consisting of a low voltage (6V) Par 36 lamp (lamp code is 4515) with a very narrow beam in a metal case with built in transformer.
Pinspots are ideal for lighting MIRRORBALLs.

PIPE ENDS
Lanterns hung at the very ends of lighting bars - used for crosslight and very common in dance or musical theatre.

PLAN
A scale drawing showing a piece of scenery, the whole set, lighting layout etc from above.
Lighting plans are usually drawn onto the theatre's GROUNDPLAN, which shows the whole stage and (at least) the front row of audience, and has the scenic design drawn onto it. The groundplan usually includes the permanent flying bars in the venue, often drawn down the side of the plan on both sides of the stage. 
A view from the side of the set (or a piece of scenery) is known as an SECTION, usually a slice through the centre line of the stag, showing the stage floor, vertical heights of scenery, lighting bar (and flown scenery) positions, and also lighting positions in the auditorium, and is used for checking lighting angles etc. 
An ELEVATION is a similar vertical slice through the venue, or individual scenic elements, and can be drawn from the front, back or side, depending on where the important detail is.
A FLOOR PLAN shows the layout of furniture / scenery for a particular show, or for an individual scene. It shows the stage area only. 
A RENDERING shows how the audience will see the set, from the auditorium, and is often in full-colour. A different rendering may be done for each scenic layout used in the show. 

PLASA / P.L.A.S.A.
Professional Lighting and Sound Association (UK).
See ESTA for the American equivalent.
PLASA website

PLAYBACK
The part of a computerised lighting control desk which enables the operator to recall cues from the electronic memory.

PLOT
1) List of preparations and actions required of technical crews during the performance (eg Sound Plot = list of sound cues and levels in running order.) In the US, the term plot refers to a plan. (eg Light Plot = scale plan showing lighting instruments). See also RUNNING PLOT, STATE PLOT.
2) Session during which lighting states are created or checked with the director, on stage, with furniture and stand-in actors. This is also the name for the session during which sound levels are set (but this should not happen at the same time as the lighting plot!). 
3) The basic story thread running through a performance / play which gives the reason for the character's actions.

PLOTTING SESSION
Time during which the plot for each department is prepared (eg Lighting Plotting session). Also known as The Plot. 
See also PLOT. 

PLUG
A power or signal connector with a pin or pins which is used to make a connection from a power or signal source (the socket) to a device or another connector. 
Plugs are not used as a source of power, because of the risk of electrocution by touching the fully exposed pin connections. 
Sockets, where the connection is shielded, are used as the source. 

POINT CUE
A cue inserted during / after plotting between two existing cues. (eg 8.5 is inserted between cues 8 and 9). Most computer lighting desks have the ability to either insert an additional cue in a sequence, or to link to another cue out of the sequence, and then link back again. Inserting cues into a plotted sequence on a manual lighting desk is more awkward, because it is a running plot (where only the changes between cues are noted down). Stage Management may prefer to call 8A instead of 8.5, but this is down to personal preference.
Sound cues which relate to an already-running cue within a sequence should have lettered cues (e.g. 8A is a fade up of Cue 8 and 8B is the fade out).

POWERCON
Power connector rated at 20 Amps with the same body type as the SPEAKON speaker connector. Manufactured by Neutrik. Used extensively on lighting patch panels (at least in the UK) due to its smaller physical size and lower cost than the standard 15A socket.
The blue connector is for power inlet, the grey connector is power outlet. The types are not interchangable, and cannot be plugged into Speakon sockets.
NB: The powerCON connector is not designed to be connected under load conditions, so should only be connected / disconnected with the power OFF. The newer TRUE1 connector can be disconnected with the load connected, and newer equipment is using this connector type instead of the older powercon. 
Neutrik Powercon page

PRACTICAL
Any object which appears to do onstage the same job it would do in life, or any working apparatus (eg light switch or tap).
A window within the set which has to open is a practical window.
Light fittings which have to light up on the set are called Practicals, and if they're suspended from the rig, they're Hanging Practicals. 

PRESET
1) Anything in position before the beginning of a scene or act (eg Props placed on stage before the performance, lighting state on stage as the audience are entering.)
2) The process of putting any part of the production into its' starting position / setting. A Preset Checklist is used by stage management and all other technical teams, to ensure that everything is correctly set to start the show.  
3) An independently controllable section of a manual lighting board which allows the setting up of a lighting state before it is needed. Each preset has a master fader which selects the maximum level of dimmers controlled by that preset. A control desk with two presets is sometimes known as a '2 scene preset' desk. 

PREVIEW
1) A performance (or series of performances) before the 'official' opening night. Previews are used to run the show with an audience before the press are allowed in to review the show. This allows technical problems to be ironed out while ensuring the cast and creative team get audience feedback. Tickets are sold at reduced price and help to spread word of mouth interest in the show.
2) A function on some memory lighting control desks with video mimics. Preview enables the operator to see the levels of dimmers and other information in a lighting state other than that on stage.

PRIMARY COLOURS
The primary additive colours of light are red, green and blue, and the subtractive colours are cyan, magenta and yellow.
The primary colours of paint are different - they're cyan, magenta and yellow (although you may have been taught they're red, blue and yellow). 

PRODUCTION DESK
Table in the auditorium at which director/designer etc sit during rehearsals (especially technical rehearsals). Usually has its own lighting and communications facilities. 
For small venues the desk is used by the lighting designer and her/his team so that they can see the lighting from the audiences' point of view. The lighting control desk may be moved to the production desk, or the desk and programmer may remain in the control room, and have a remote interface on the production desk, which may have a display screen showing the cue list etc, which the designer can configure. 
Larger shows (including Broadway and West End) will often remove large sections of audience seating in the stalls and install a number of production desks for all technical areas including lighting, projection, sound, scenic automation etc. 

PROFILE
1) A type of lantern with at least one plano-convex lens which projects the outline of any chosen shape placed in its gate, sometimes with a variable degree of hardness/softness. Profiles include four beam-shaping metal shutters, a gate to take an iris or gobo and an adjustment to make the beam smooth and even ('flat') or hot in the centre ('peaky'). See Bifocal Spot, Zoom Profile.
2) Shaped piece of scenery added to the edge of a flat instead of a straight edge. Also known as a cutout.
3) Blocking notation for an actor that is facing directly offstage. Right Profile is facing off stage right, Left Profile is facing off stage left. 
Types of Lantern
Blocking Notation

PROJECTION
1) Slides are used to project still archive images or textures. Libraries of slides contain images for every occasion. Kodak Carousel projectors are the industry standard, and some types can be linked to a controller to perform complex dissolves and fades from one projector to another. More powerful projectors are available using very intense discharge sources and large format glass slides to produce a massive image.
2) Lighting effects : Moving cloud / rain / fire effects can be achieved using a powerful lantern known as an effects projector with a motorised glass disc painted with the required effect. An objective lens is required in front of the disc to focus the image. See Effects.
3) Gobos : See GOBO.
4) Film : 35mm film projection is common in many theatres as a device for keeping the building open to the public when productions are in preparation. 16mm film projection is used in smaller venues. Film projection can, of course, also be integrated into a performance.
5) Data: Data or Video projection is now being used to bring video and computer images to the large screen. Data projectors are considerably cheaper and more versatile than other methods, and the quality is improving all of the time. Images can be front projected or back/rear projected depending on the amount of space and the effect required. For example, if actors are required to walk in front of the screen and not have the image appearing on them, back projection is the only answer.
6) Front Projection: The projector(s) are in front of the projection surface or screen, between the screen and the audience. This results in a bright image, but means that actors standing directly in front of the screen may cast a shadow on the screen (and have projection on their faces). 
7) Rear Projection / Back Projection: The projector is behind the projection surface. This means the projection image will be reversed from the point of view of the audience (all data projectors have a setting to flip or mirror the image). A standard white cloth or sheet can be used, but the image will be dimmer than it would be from the front, and (most importantly) the projector lens will be visible as a bright hot spot in the projection. To avoid this, a custom-made back projection screen should be used. Companies such as Rosco sell back projection (BP) material (a translucent plastic) which results in a very bright and clear image, and which prevents the visibility of a projection hot spot. The BP material can be stapled to a frame to form a screen of the exact size needed for the event. 
See LCD, DLP, SCREEN.

PULL
The amount of electrical power required by a touring show in a venue.

PVC TAPE
Plastic insulating tape used for taping cables to bars and for securing coiled cables. Neater and cheaper than Gaffa tape. Also known as LX tape.

PYRO
1) See PYROTECHNICS
2) Short for Pyrotenax, a brand name (UK) of Mineral Insulated Cable.

PYROTECHNICS
(often shortened to just 'Pyro') Chemical explosive or flammable firework effects with a manual detonation. Usually electrically fired with special designed fail-safe equipment.
There are many different variations of pyrotechnic effects available. The categories are as follows:
Theatrical Flash - a flash and a cloud of smoke
Maroon: produces a very loud bang. Must only be detonated inside a bomb tank covered with a protective mesh.
Gerb: version of the Roman Candle firework, throwing a shower of sparks into the air. Possibly named from the French 'Gerbe' meaning a sheaf of wheat, due to it's shape.
All pyrotechnics should be used with close reference to local licensing laws, and the manufacturers instructions. Professional advice should be sought before the first use of effects.
Some territories only permit licenced pyrotechnicians to use these devices.
The word originates from the Greek for fire, pyr. 

RACK
1) A cabinet of standard width (19') into which various components can be bolted. Racks are ideal for touring equipment, are neat, and they allow easy access to the rear and front panels.
2) See Dimmer Rack.

RCD
Residual Current Device. Protects the user against short circuit (earth faults) and earth leakage caused by damaged cable or faulty equipment. A RCBO is a combined MCB and RCD, protecting against earth leakage/short circuit and overload. Known as a GFI (Ground Fault Interruptor) in the USA.

RE-RIG
To change the lighting rig after the last performance of one show to the positions for the next show.

REAR PROJECTION
See PROJECTION.

RECITATIVE
Musical terminology for a sung dialogue passage, in the rhythm of ordinary speech, during an opera, operetta or oratorio. Often shortened to RECIT.

REFLECTOR
Highly polished metallic mirror used to direct light beam from a lamp towards the lens at the front of a lantern.

RELIGHTING
When a show is touring, a Relighter is used to reproduce the lighting design in each venue.
The original lighting designer may be present at the second venue on the tour, to check the work of the relighter.
Paperwork is produced by the original designer to enable the relighter to reproduce the design easily in venues of differing sizes.

RESISTANCE DIMMER
A now obsolete method of dimming which decreases the current available to the load by introducing a variable resistance between supply and load. The excess current is converted into heat. Based around a rheostat.

RESTORE
A cue to resume or return to any previous state, setting or function. (e.g. 'at the end of the dance number we restore to a warm general cover').
Submitted by Bert Morris.

RIG
1) The construction or arrangement of lighting equipment for a particular production.(noun)
2) Installing lighting, sound equipment and scenery etc for a particular show.(verb)

RIG CHECK
(also known as LAMP CHECK) The process of checking all lanterns in the rig are working correctly prior to each performance. Should be done daily in sufficient time to change a lamp if necessary.
Most venues do not have the electrical capacity to run all lanterns at full for a rig check, so a level of 25% is normally used.
N.B. this is NOT the same as preheating - a rig check happens before each performance and involves the whole rig, and preheating involves individual lanterns/dimmers and happens before a cue in which that lantern appears.

ROUGH FOCUS
When rigging a lighting bar (or an individual lantern) it's helpful to have an awareness of where it will be pointing during the show. When you attach the safety wire and plug the lantern into the power supply, if it isn't focussed roughly in the right direction (e.g. is it a downlighter, or is it backlighting or sidelighting), there's a danger that the cable will restrict movement when the lantern is focussed more accurately during the focus session, wasting time while the cable or safety wire is released. 
Doing a rough focus will also ensure that accessories such as barndoors do not physically obstruct the light from nearby lanterns. 

RUNNING LIGHTS
US term for the blue working lights used backstage during a performance.

RUNNING PLOT
A plot sheet giving details of the changes between cues, as distinct from a state plot which gives the whole state of the system at any time. For example, a lighting plot on a manual board is normally a running plot. It is difficult to start a running plot half way through; often the operator has to go back to the beginning and work through until the required point is reached. However, it contains the minimum information necessary to perform the cues, and is therefore more efficient on a manual lighting desk or complex sound setup.
Also used by the stage management team to keep track of prop moves and changes during the show. A preset sheet contains the status of everything at the start of the show, then the running sheet / running plot lists everything that has to happen during the show, in order.

SAFETY BOND
Chain or wire fixed around lantern and lighting bar or boom to prevent danger in the event of failure of the primary support (eg Hook Clamp). A requirement of most licensing authorities in the UK. 
As a standard safety chain does not have a rated loading, current recommendations in the UK is to use an approved (and rated) safety wire (also known as a safety bond) as a secondary suspension. 
Although hook clamps (in the UK) that support lanterns do not fail, they are subject to a number of human failings including not doing the clamp up sufficiently or not tightening the bolt at the base of the hook clamp that connects to the lantern. However, the highest risk is due to a flown lantern being struck by a piece of scenery or another lantern as it flies past. 

SAFETY CHAIN
An old form of secondary suspension used on rigged equipment. 
Because the chain cannot be rated to carry a specific load, safety chains should no longer be used in this application, but should be replaced by rated safety bonds. 

SATURATION RIG
An arrangement of lanterns in which to maximum number of spotlights is placed in every possible position.

SAVE
(US especially) To extinguish a particular lighting instrument (e.g. 'Save 14'). The instrument's lamp (and its colour filter) are thus saved for another occasion. Used when setting up lighting states.
Submitted by Peter Neilson

SCAFFOLDING
1) System of pipes, clamps and boards which is used in the construction industry to form levels to improve access to high buildings either during construction or maintenance. Shortened to Scaff. 
2) The same system can be used for set construction, with adequate supervision by experienced / qualified persons. 
3) Scaff tubes / pipes are 48mm in diameter and are used as vertical legs on platform systems by various manufacturers including Steeldeck, Metrodeck, Prolyte Staging etc. Originally made of steel, scaff tubes are usually now made from aluminium which is a much lighter weight and therefore easier to work with and safer from a manual handling point of view.
4) Horizontal bars to rig lighting equipment from are made from scaffold tubes (48mm diameter). 

SCENE
1) A pre-programmed lighting state which can be faded in and out during a one night show when there's no time for plotting.
2) A subdivision of a play. See also ACT. Scene is often shortened to 'Sc', so Sc1 refers to Scene One. 

SCREEN (PROJECTION)
Many types of projection screen are available. Some are multi-purpose, some only for front projection, some only for back projection. If a screen is not self-supporting, it often has eyelets around the outside edge which are used to 'lace' the screen onto a larger frame.
See also PROJECTION.

SCRIM
1) A coarse gauze
2) A fine metal mesh used to reduce the intensity of light from TV lanterns without affecting colour temperature.
3) Plastic gauze-like material used to line Heras fencing at festivals and other events to act as a partial sight-screen, and also to make the fencing tone in with surroundings.
See also Lighting With A Gauze / Scrim

SCROLLER
See COLOUR CHANGER.

SEMAPHORE
See COLOUR CHANGER.
Colour Changers at the Backstage Heritage Collection

SERIES SPLITTER
An adaptor consisting of a plug and two sockets wired in series. Enables two identical 110 Volt loads to be safely run from a 240 Volt supply (UK).

SHADOW
A dark area on stage resulting from a person, piece of scenery or other object blocking the rays from a light source. 
Shadows in theatre lighting may be highly desirable, or unwanted, depending on the situation. 
In the natural world, bright sunlight produces shadows, and the length of the shadow defines the time of day. A cloudy day results in hazy or no shadows. Indoor lighting produces a shadow from each light source. It follows that naturalistic lighting requires either a single shadow (to replicate sunlight) or no shadows for outdoor scenes, and a shadow per practical light source for indoor scenes. It is very difficult to achieve this ideal, but a bright backlight and a dimmed front light can help to remove/reduce shadows from the front light and create a single one from the backlight.

SHIFTER
The common Australian term for AJ's, c-wrenches, spanners etc.

SHINS
The lowest lantern on a lighting boom. Named because of the proximity of sharp parts of the lantern to the flesh of the lower leg. This especially applies to standard dance lighting, when the lanterns are positioned at optimum height to light dancers on the stage floor. When the boom is lighting scenic items or large groups, the lanterns may be higher up the boom and the term will no longer apply.
Also known as Shin Buster. The other lanterns on the boom are known as MIDS and HEADS.

SHUTTER
Part of a profile lantern. Metal blade which can be used to shape the edge of the beam. Shutters (normally four) are located in the gate at the centre of the lantern. Similar in effect to barndoors on a Fresnel or PC lantern, but a lot more flexible.
The position of a shutter in the light beam is known as the shutter cut. 
See also FRAMING SHUTTERS.

SIDELIGHT
Most associated with dance lighting, Sidelight comes from the wings of an end-on stage, and lights the dancers' / actors' bodies, without lighting the stage floor, and without lighting the scenery.
This type of light has a sculpting effect on the bodies, and really separates them from the scenery / backdrop / cyclorama, and reduces distracting shadows on the stage floor.
See also FRONT LIGHT, BACKLIGHT, CROSSLIGHT, DOWNLIGHT.

SILK
A special type of diffusion frost filter which stretches the light in one direction. Especially useful for lighting large cycloramas with a limited number of lanterns, or for lighting an elongated object (eg a staircase) with one lantern.

SLIDE
See PROJECTION.

SMOKE DETECTORS
Many theatre buildings have complex fire alarm systems installed. Some theatre spaces have smoke detectors in them, which trigger a fire alarm when the space fills with smoke. The use of SMOKE MACHINES in these spaces can (and does) result in expensive call-outs of the fire department and evacuated auditoria.
There are special heat-sensitive detectors called RATE OF RISE detectors which trigger a fire alarm when the temperature rises faster than it should normally. Properly calibrated (and regularly tested) these can be as effective than the smoke detectors (which work by 'seeing' smoke particles in the air). If it's not possible to get Rate of Rise detectors installed in your theatre space instead of smoke detectors, you may be able (subject to local building regulations and local fire department advice) to isolate the smoke detectors for the duration of the performance when you use smoke effects. Properly designed alarm systems incorporate timed isolation, so that smoke detectors are only off for a specific period, and automatically come on after that period.

SMOKE MACHINE
A Smoke Machine or Fogger is an electrically powered unit which produces clouds of white non-toxic fog (available in different flavours/smells) by the vaporisation of mineral oil. It is specially designed for theatre & film use.
A Haze machine, Hazer or Diffusion Fogger is used to produce an atmospheric haze, rather than clouds of smoke, and is used by many lighting designers to reveal airborne light beams.
The first smoke machines came onto the market in the late 1970s.
See also CRACKED OIL, DRY ICE.
It's essential to know whether your venue uses SMOKE DETECTORS on the fire alarm system. See that entry for more information.
Fog / Smoke / Haze On Stage

SNAP
A lighting or sound cue with no fade time - the cue happens instantly.
This can be acheived on a computerised lighting desk by using a fade time of zero seconds.

SNEAK
Function on ETC lighting desks which allows you to remove a channel from a 'live' lighting state at a preset speed.
(e.g. SNEAK 1 ENTER will fade channel 1 out of the current lighting state).

SOCKET
A power or signal connection point where a plug can be inserted to make a connection from the source of power. Sockets can be used as signal outputs or inputs, and are usually used as power outputs, due to the shielded connections, making it impossible to touch the live connections with fingers. 
Sockets are often wall or panel mounted, while plugs are used to connect portable equipment. 
There are exceptions of course - powercon connections which are panel mounted can be either power inputs OR outputs, and are differently colour coded to make it clear which is which, and the connectors are designed so they cannot be used incorrectly. 

SOFT LIGHT
Asymmetric flood light used as a fill light in TV studios to eliminate shadows and balance the key light.

SPECIAL
An instrument within the lighting rig which is required for a specific moment or effect within the performance, and is not part of the general cover lighting. See GENERAL COVER.

SPEED OF LIGHT
The speed of light travelling through a vacuum is 186,282 miles per second.
A light year (the distance that light will travel in one year) is around 6 trillion miles. 

SPIDER
Adaptor to connect many lanterns to one multicore cable. Consists of multipin connector (typically Socapex or Lectriflex), short length of cable, then a number of sockets related to the number of circuits in the cable.

SPIGOT
An adaptor screwed onto the hanging bolt of an instrument to enable it to be used on an upright stand.

SPILL
Unwanted light onstage.

SPILL RINGS
Concentric rings attached to the front of a beamlight (eg Strand Pageant) to contain spill.

SPLITTER
See ADAPTOR.

SPOT
1) To reduce the beam size of a fresnel or pc lantern by moving the lamp further from the lens. (e.g. 'Could you spot that down a touch, please?'). See also FLOOD.
2) A profile spotlight (e.g. 'The third spot we need for the show is on the piano DSL')
3) A moving light that can project gobos and/or a beam with hard-focussed edges. (see also WASH)
Types of lantern

SPOTLIGHT
General term for any lantern with a lens system. See Fresnel, PC, Profile.
German: Theaterscheinwerfer

STAGE BOX
A connection box at the end of a lighting or sound multicore cable.

STAGE ELECTRICIAN
Member of the electrics staff whose responsibility it is to set or clear electrics equipment during scene changes. May also carry out colour changes on booms etc.
Sometimes abbreviated to SLX. 

STAGE LEFT / RIGHT
Left/ Right as seen from the Actor's point of view on stage, when they are facing the auditorium. (ie Stage Left is the right side of the stage when looking from the auditorium.)
Stage Right = OP (Opposite Prompt) Abbreviated to SR. French: Cote Jardin, Netherlands: Toneel Links (translates to Stage Left!)
Stage Left = PS (Prompt Side) Abbreviated to SL. French: Cote Cour, Netherlands: Toneel Rechts (translates to Stage Right!).
NB: The Netherlands, Portugal and Germany use the opposite to the rest of Europe; i.e. Stage Left UK = Stage Right. The directions are seen from the director's and audience's perspective, NOT the actors. In Portugal Isquerda (left) is the equivalent of UK Stage Right and Direita (right) is the equivalent of UK Stage Left.

STAGECRAFT
Stagecraft refers to any technical aspect of theatre production (and also sometimes refers to film / TV production). It includes working in technical areas such as lighting, sound, scenic construction, costume & prop construction, stage management and makeup. It usually does NOT refer to the creative / design aspects of those technical areas.

STAND-BY / STANDBY
1) A warning given to technical staff by stage management that a cue is imminent. The member of the stage management team calling the cues will say "Standby Sound Cue 12". Technicians acknowledge by saying "Sound Standing By".
In the US, the word "Warning" replaces "Stand-by".
2) A member of the cast of a musical or play who understudies one (sometimes more) of the principal roles but is NOT also in the chorus. A standby often will not even be required to be at the venue at each performance unless they are called in to perform in the role for which they are an understudy.
See also ALTERNATE, SWING, UNDERSTUDY.
Additional information submitted by Pierce Peter Brandt

STATE
In lighting terms, a lighting 'picture' ; each lighting cue results in a different state (or a modified state).

STEEL
1) Refers to a steel blue / pale blue lighting gel. (Lee 117) (e.g. 'Use the Steel General Cover for the scene in the castle'). See also STRAW.
2) Many set construction now uses steel frames with timber cladding. Steel is stronger and lighter weight compared to timber of the same size.
3) Generic term used for a plain wire rope sling. Also used when referring to roof structural steel and individual steel beams or scaffold materials and so on.
Additional information submitted by Chris Higgs.

STRAW
Refers to a pale yellow lighting gel. (e.g. "Use the Straw General Cover for the garden scene").
See also STEEL.

STROBE
Device giving a fast series of very short intense light flashes which can have the effect of making action appear intermittent. Because strobe lighting can trigger an epileptic seizure, the use of a strobe must be communicated to the audience before the performance begins. Strobes should be synchronised so that they operate outside the dangerous frequency band 4 to 50 flashes per second. (i.e. a strobe should operate at less than 4 flashes per second, or more than 50 flashes per second). If the effect is momentary, this rule may be relaxed. Strobes must never be used in public areas where there are changes of level or steps.
Always seek the advice of the licensing authority if you are in any doubt about the safety of strobe effects.

SUBMASTER
Often shortened to SUBS.
Fader on a lighting desk which can have a lighting state recorded onto it for additional control, or to use when manually mixing lighting states for music concerts or one-off events.
Lighting desks normally have a series of submasters (12 or 24 are common) which can have states, cues or effects loaded onto them. Some desks can have submasters set to inhibit the main output (known as INHIBITIVE SUBMASTER. For example, the FOH lighting can be loaded onto a submaster which is then brought down as the house tabs are flown in between curtain calls to block light spill onto the tabs).
Multiple cues can be recorded onto some submasters through the use of pages.
A PILE-ON submaster can be used to add it's contents to the existing lighting state. Any number of pile-on submasters can be used in combination to modify a state.

SUBTRACTIVE COLOUR MIXING
See COLOUR MIXING.

SUPER TROUPER
(Trade name) Manufactured by Strong International - a range of high intensity followspots designed for large scale permanent installations or large touring shows. The Super Troupers use Xenon lamps and vary from 1600W - 2000W.
The Super Trouper is the best known of all stage lighting instruments outside of the industry due to Abba's song 'Super Trouper'.
Strong International website
Followspotting Tips and Tricks

SWATCH
A sample of fabric to demonstrate the material to use on a costume or set design, or a sample of lighting gel. A catalogue of all the gel colours made be a particular manufacturer is called a SWATCH BOOOK.
Rosco Supergel website

T
Lighting Industry Forum code which identifies the (original) recommended usage of different lamp types. T coded lamps are for theatrical use, and have a colour temperature of 3000°K. See also CP, A1, P2, K.
Lamps List

TAB DRESSING
1) Lighting focused onto the house tabs at the front of the stage to set a theatrical atmosphere before the show starts. May also involve a gobo with the show or company logo. Also known as TAB WARMERS.
2) Dressing the Tabs (or Dressing the Curtains) is the process of going along the curtain track and evening out the folds in the curtains so they are tidy and regular. 

TAB WARMERS
Lighting focused onto the house tabs at the front of the stage to set a theatrical atmosphere before the show starts. May also involve a gobo with the show or company logo. Also known as TAB DRESSING.

TABS
1) Originally "tableaux curtains" which drew outwards and upwards, but now generally applied to any stage curtains including a vertically flying front curtain (house tabs) and especially a pair of horizontally moving curtains which overlap at the centre and move outwards from that centre.
If the tabs are flown, the instruction TABS IN is used to fly them in to cover the stage, and TABS OUT reveals the stage to the audience. If the tabs move horizontally, the tabs OPEN (to reveal the stage) and CLOSE (to cover it). 
[In French, tabs are Rideau. The main tabs or house tabs are Rideau d'avant-scène. In Spanish, the main tabs are Bambalinón.
A narrow stage curtain used for masking is Pendrillon
In Italian, tabs are Sipario.]
2) TABS was a journal published by Strand Electric between 1937 and 1986, about stage lighting and other equipment produced by the company. The Backstage Heritage Collection archive has a complete collection of TABS journals for you to read online.
TABS archive

TAILS
Also known as BARE ENDS, TAILS refers to a cable or set of cables with a connector at only one end which is used for connecting a company's equipment directly to the mains supply in a venue. The connection should only be made by a qualified electrician with the power off!

TALLESCOPE
(Trade Name) A retractable alloy vertical ladder on an adjustable wheeled base. The platform at the top is just large enough to hold one person. Used for rigging lanterns, focusing etc. Collapsible enough to fit through a standard doorway. Outriggers are used to stabilise the tower from falling sideways. Two people are used to move and steady the tallescope. Sometimes known as a 'TALLEY'.
Aluminium Access Products - Tallescope Manufacturer and Service
Access Equipment

TANK TRAP
See BOOM BASE.

TECHNICAL REHEARSAL
(also known as the TECH RUN, or just TECH). Usually the first time the show is rehearsed in the venue, with lighting, scenery and sound. Costumes are sometimes used where they may cause technical problems (eg Quick changes). Often a very lengthy process. Often abbreviated to the Tech.
A DRY TECH is without actors to rehearse the integration of lighting, scenic changes etc. It follows that a WET TECH is a full technical rehearsal with actors and all technical elements, although this term isn't used as often as DRY TECH.
A PAPER TECH is a session without the set or actors when the technical and design team talk through the show ensuring everything's going to work as planned. Stage Managers can use this session to ensure all is written correctly in the Prompt Book.

TEMPLATE
See GOBO.

THREE POINT LIGHTING
An approach to traditional stage lighting taught by Stanley McCandless which uses two front lights (separated by 60 degrees horizontally) and one backlight to cover each lit area of the stage. The two front lights may be coloured differently (one 'warm' and one 'cold') so that a wide variety of lighting states can be created by blending the front lights in different intensities. 

THROW
Distance between a light source (e.g. lantern or projector) and the actor or object being lit.

TILT
1) Up and down (vertical) movement of a lantern, camera or moving light. The lantern is held in the wanted position by using a tilt knob, often on the right hand side of the lantern.The Tilt Knob needs to be undone to enable the lantern to be tilted up or down. The lantern should always be held in position when undoing the tilt knob, to prevent it dropping. See also PAN.
2) Feature on pinball machines which detects excessive movement of the case. Only related to theatre in connection with the musical 'Tommy'.

TIME
The facility on memory lighting boards for playing back timed fades at the touch of a button.

TITLE BLOCK
Rectangular area in the corner of a lighting plan (often bottom right) containing the name of the show, director, scenic and LX designer names, date of the plan, scale, and other copyright information.

TRACKING
A philosophy of operation on some lighting desks which memorises the operations required to carry out a cue, and NOT the entire state of each cue. For example, if a spotlight is added into Cue 2, it will remain on at that level through subsequent cues until a cue where all cues fade out, or a cue where that spotlight is specifically recorded at zero. This is very handy for adding in forgotten channels, or for removing errors. However, it can complicate things if you are plotting cues out of sequence. Most desks have a way of over-riding Tracking for a particular cue (known as Cue Only), or for the whole show you are working on. 
See the video below for further information. 
Tracking Video
Cue Only Video

TRANSFORMATION
An instant scene change, often effected by exploiting the varying transparency of gauze under different lighting conditions.
See also Lighting With A Gauze / Scrim

TRIPE (bundle)
Bunch of cables tied or taped together into a single unit.
Also known as a LOOM, or HOD (USA).

TRS
1) Tough Rubber Sheath. Jargon for any Rubber-sheathed power cable. (e.g. "Go get me a 10m TRS" usually means "Please get me a 10m length of 15A power cable" (in the UK, at least)). 13A cable (or 5A cable) can also be TRS, so if in doubt, ask for clarification of the connector required, or check what it's for if you're not sure. 
2) Tip Ring Sleeve. The three contacts on a stereo jack audio connector.

TRUE1 POWERCON
A more recent version of the lockable Powercon power inlet and outlet connector, which is rated at 16A and can be disconnected and connected under load, which the original powercon cannot. 
See also POWERCON. 
Neutrik True1 website

TRUNNION ARM
U-shaped bracket between the hook clamp and the main body of a lighting instrument, enabling it to be tilted to any angle.

TRUSS
A framework of alloy bars and triangular cross-bracing (commonly around 50mm diameter) providing a rigid structure, particularly useful for hanging lights where no permanent facility is available. Very often box-shaped in cross section, so known as BOX TRUSS. This type of truss is useful for touring as lanterns / speakers etc can be hung inside the truss which protects them when loading and takes up less space in the truck.
You should only use truss from reputable manufacturers, and should check the manufacturers' website for instructions on how to use it, and what limitations it may have. 
Rigging a truss incorrectly can vastly reduce its' safe working load, and can result in damage to the truss,or a far more serious failure. Always seek advice from professionals, and do not attempt to rig equipment without proper advice or supervision. 
The cross-sectional shape of truss can either be FLAT (known as Ladder Truss), SQUARE (known as Box Truss) or TRIANGULAR (known as Tri-Truss). 

TUBULAR WAVE RIPPLE
See EFFECTS.

TUNGSTEN HALOGEN
A standard tungsten filament lamp loses its brightness in its' lifetime. Tungsten Halogen lamps use a Quartz envelope ('bulb') filled with halogen gas to give an almost constant colour temperature. See Halogen Cycle.

ULTRA-VIOLET (UV)
Short wavelength source of light at the end of the visible light electromagnetic spectrum which causes specially treated materials to fluoresce on an otherwise blackened stage. Used for special effect and for lighting onstage technical areas (eg Fly Floors). Ultraviolet sources designed for stage use are known as Black Light sources and have all harmful radiations filtered out. They produce UV-A radiation, which is also present in sunlight, and is invisible to the naked eye;  in black light sources, the amount of UVA is far lower than you'd experience outside. UV-B radiation is far more harmful, and is not present in black light sources.
However, some high-intensity black light sources can be harmful to the eye so must not be used at close range to people, or where people could face the light source for any more than a few minutes. Use them to light scenery or props, or performers at a safe distance.
Black Light is used extensively in the Czech Republic where stunning effects are achieved on stages lined with black velvet. See the Image Theatre website for more.
Image Theatre website

UPLIGHT
Light from below the actors - from a light source on the stage floor.
French: contre-plong
See also DOWNLIGHT, BACKLIGHT

UPSTAGE
1) The part of the stage furthest from the audience. It's called Upstage because on a raked stage the stage slopes down towards the audience to improve sightlines. The furthest from the audience is literally higher due to the slope of the stage, so moving from close to the audience involves walking up the raked stage, towards 'Upstage'. 
US = Upstage, USC = Upstage Centre. USL = Upstage Left. USR = Upstage Right (see diagram)
See also DOWNSTAGE, ONSTAGE. 
2) When an actor moves upstage of another and causes the victim to turn away from the audience s/he is 'upstaging'. Also, an actor drawing attention to themselves away from the main action (by moving around, or over-reacting to onstage events) is upstaging.

VISUAL CUE
A cue taken by a technician from the action on stage rather than being cued by the stage manager. Often abbreviated to "Viz" or "Vis".

VOLTAGE
The pressure at which electric current is available. The UK standard voltage is 230 Volts alternating current (AC). The American standard is 120 Volts AC.
The scientific name for Voltage is Electromotive Force. The frequency at which the current alternates (between positive and negative) is measured in Hertz (Hz) and in the UK is 50Hz, and in the USA is 60Hz. 
Named after Italian physicist Alessandro Volta (1745-1827). 

WALKER
A member of the (usually) stage management team who walks around the stage on the request of the lighting designer to enable them to see how the lighting coverage is looking. It's a common mistake to focus lighting on the stage floor rather than on the performers faces, so using a walker means they can check for lighting dips. 

WASH
1) A lighting cover over the whole stage (e.g. 'We'll use the red wash for the hell scene'), usually from multiple sources. If this is the main lighting for the show, it's called the GENERAL COVER. 
2) A lantern which produces a large spread of softly focussed light, especially with moving lights (e.g. the VL4 and Mac 600 are wash luminaires). See also SPOT.
Designing and Focussing a General Cover

WATTAGE
See WATTS.

WATTS
Unit of electrical power derived from the current (or 'quantity' of electricity) multipled by the voltage (or 'pressure' at which the current is delivered). Stage lighting equipment is rated in Watts (or Kilowatts - 1kW being equal to 1000W). This refers to the amount of power required to light the lamp. A higher wattage lamp requires more power and gives a brighter light output.

WHITE GLOVE
A role is said to be 'white glove' if the person is not required or expected to help with setting up equipment, only in the operation of it. 

WINGS
1) The out of view areas to the sides of the acting area (known as FLÜGEL in German). The wings are best identified by their position on stage (e.g. "Clive exits through the downstage left wing") but they can be identified by number if there are too many exits, with the downstage wing starting as 1, with stage left and right added to identify the side (e.g. "Sarah exits 2L").
[French: les coulisses]
2) Scenery standing where the acting area joins these technical areas.

WORKING LIGHTS
1) High-brightness efficient non-dimmable lights used in a venue when the stage / auditorium lighting is not on. Used for rehearsals, fit-up, strike and resetting. The working lights are often controllable from a number of locations around the stage, including at prompt corner. As the working lights are on during rehearsals, set sessions, and during the day, they should be efficient light sources (e.g. LED or discharge lamps) rather than older types of lamp which are high-wattage. An instruction to 'Kill the Workers' solely means to turn the working lights off, rather than something more sinister. 
German: arbeitslicht
Some venues have an additional type of light source on stage solely for rehearsals, which may be less bright / intense, and more directed towards stage level rather than up the walls - these are sometimes known as Rehearsal Lights
German: probenlicht
2) Low wattage blue lights used to illuminate offstage obstacles and props tables etc. Known as 'Wing Workers', 'Blues' or 'Running Lights'.

WRENCH
American for SPANNER.

WYSIWYG
Acronym of 'What You See Is What You Get'. Mainly used in the context of a software tool for lighting design and production administration. Capable of stunning 3D rendering of lighting states, and direct connection to a lighting control desk. Enables accurate pre-visualisation of lighting designs and greatly increases the understanding between director / producer and lighting / scenic designer in the early stages of a production.
WYSIWYG product details

XFADE
See CROSS FADE.

XLR
Multipin metallic connector. (3 pin for normal sound use, 5 pin for DMX, Colour Scrollers etc). Sometimes called Cannons after the original manufacturer.
The audio standard for wiring the 3 pin connector is as follows : Pin 1 (Screen), Pin 2 (+ve / 'hot'), Pin 3 (-ve, 'cold'). (Xternal, Live, Return).
A 5 pin connector for DMX512 use has the following connections: pin 1 = screen, pin 2 = data -ve ('cold'), pin 3 = data +ve ('hot'), pin 4 and 5 are not used by many manufacturers. A comparison is made between the signals carried by the two data cables, and any differences are cancelled out, meaning that noise/data error reduction is very effective.
The connectors are available as either plug (with pins, sometimes known as Male) or socket (sometimes known as Female) variants, and are available as cable mounted (most common) or panel-mounted. The use of gendered terms (Male and Female) is being reduced as the industry catches up with the modern world. 

YOKE
The TRUNNION ARM of a lantern.

ZARGES
(Manufacturer) German manufacturer of a range of ladders. Commonly refers to the 3-part ladder used on many stages around Europe.
Zarges website
Access Equipment

ZOOM ELLIPSOIDAL
See ZOOM PROFILE.

ZOOM PROFILE
A type of profile lantern with two lenses enabling the adjustment of both size of the beam and whether it's hard or soft focus. This adjustment of focal length allows a single instrument to find many uses in various locations around the stage. The flexibility is also essential when working with gobos. Also known (in the US) as a Zoom Ellipsoidal.