techref.info: Basics

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

A to D
Analogue to digital convertor

AC
Short for Alternating Current
Abbreviation for Air Conditioning

ACL (Aircraft Landing Light)
A PAR-64 with a very narrow beam that operates at 28 volts

Adapter
Electrical connector that allows two or more devices to be connected to a single power outlet. Normally this is wired in parallel, ie both devices receive the same voltage but the current is divided between them. Occasionally they may be wired in series, to split the voltage between devices.

Additive Colour Mixing
The sum of various wavelengths of light.

Advance Bar
Lighting bar positioned just downstage of the proscenium arch.

AJ
Slang for an Adjustable Spanner

Alternating Current (AC)
Electric current whose flow alternates in direction. The time of flow in each direction is a half period. The normal waveform of ac is sinusoidal.

American National Standards Institute (ANSI)
Independent industry-wide association which creates standards and promotes interchangeability among manufacturers.

Amp (Ampere)
The standard unit of measurement of electrical current passing through a circuit. Cables, fuses and switches are designated by current carrying capacity.

Arc Lamp
A discharge lamp in which the light is emitted by an arc discharge or by its electrodes.

Aspect Ratio
The ratio of the width to the height of any imaging system.

back to top Asynchronous
Signals that start at any time and are not locked or synchronised to the receiving device by a separate clock line.

Backlight
Light coming from upstage, behind scenery or actors. It is used to create depth or 3D form to the lighting.

Baffle
A sheet of material used to prevent light spill from a luminaire.

Balanced Line
A data communications cable where two wires are present, one of which carries the signal, the other an inverted copy of the signal (its complement). Balanced lines have excellent noise and interference rejection properties.

Ballast
A power supply used with Arc or discharge type lamps to control current through the bulb.

Bar
A horizontal metal tube (or pipe) which can be rigidly fixed or hung from flying lines and from which lighting equipment or scenery is flown. The normal diameter is 48mm, but can be up to 60mm. When mounted vertically, it is known as a boom.

Barndoor
A rotatable accessory that fits onto the front of a wash luminarie, consisting of four hinged flaps which can be adjusted to prevent light spill in a particular direction. Profile spot lanterns use shutters to achieve a greater degree of control and accuracy.

Barrel
See Bar.

Base Address
When working with DMX512, the address to which the lowest numbered channel in a device will respond. Subsequent channels in the same device will respond to subsequent channels on the DMX512 link.

Batten
Compartmentalised floodlights normally hung above stage, usually set up with a number of seperate circuits to facilitate colour mixing. See also Groundrow. Low-voltage battens are commonly used as light curtains and for single colour washes.

Baud Rate
The number of bits per second. For DMX512, this is 250,000 (250k baud).

Beam
The size, shape, and sharpness of the image of the light as projected onto a surface are described as the beam.

Beam Angle
The included angle between those points on opposite sides of the beam axis where the intensity drops to a fixed percentage of maximum. Some measurements use a value of 50%, others 10%.

Beam Light
Lantern which uses a parabolic reflector and a low-voltage high-intensity lamp to produce an intense near-parallel beam.Commonly used as soft-edged followspots.

Birdie
A compact low-voltage display luminaire containing a Par16 or MR16 lamp. So called because it is similar to in design, but much smaller than, the Parcan, and is hence "one under Par" (it's a golfing reference). Normally requires a 12 Volt external transformer, but is ideal for concealing in pieces of set or as downstage uplights.

Bit
The smallest piece of information used by computers; a bit is on or off, low or high, true or false, zero or one.

Blacklight
Another term for Ultra-violet (UV) light.

Blackout (BO)
Complete absence of stage lighting. Blue working lights backstage normallyremain on and are not usually under the control of the lighting board, except during a Dead Blackout (DBO), when there is no onstage light at all. Exit signs and other emergency lighting must remain on at all times.

Bleed
In electrical terms, bleed refers to a small amount of voltage output (or bleeding through) a dimmer circuit, even when the control signal is at zero.

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 (Preview)
Refers to changes made on a lighting console, which do not effect the "live" console output.

BNC
The BNC is a type of bayonet connector. Short for Bayonet Neill Concelman connector (sometimes erroneously called a British Naval Connector or Bayonet Nut Connector), the BNC is used for terminating coaxial cable. Thus the BNC connector is used for professional video connections. A threaded version of the BNC connector, known as the TNC (for Threaded Neill-Concelman) is also available. It has superior performance to the BNC connector at microwave frequencies.

Board
Any control desk, but usually that for stage lighting control. Originally known as the switchboard or dimmer board, it is now usually remote from the dimmers. The lighting operator is said to be 'on the board' and is sometimes known as the 'board op'.

Boom
A vertical metal tube (or pipe) onto which lighting fixtures or scenery can be fixed. For lighting purposes horizontal boom-arms are usually mounted, carrying the lanterns. Booms are often used behind wings for side-lighting. Lighting booms have a base plate or 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 procenium arch (Pros. Boom) or hanging from the ends of lighting bars.
An arm mounted on a microphone stand.

Boomerang
Mechanical Colour changer normally found in followspots.

Border
A narrow horizontal masking piece, used to mask the lighting rig and flown scenery from the audience.

Bounce Lighting
Directing light onto a large diffuse surface to produce a soft reflected light.

Box Truss
Structure built of aluminium or steel and designed as a portable support for lighting equipment and scenic elements.

Brail
To pull a piece of scenery or lighting bar out of its normal hanging position by attaching rope lines.

Break (DMX)
A continuous low on the DMX512 line for 88µs or more indicating the start of a new packet of information.

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 to break up the light on the actors faces.

Bridge
A narrow platform suspended over the acting area to mount luminaires, projection devices and truss spot.

Bridle
A rigging system using more than one hanging point to distribute the load.

British Standards Institute (BSI)
Produces technical specifications and other documents with the goal of maintaining, quality and safety in products.

Broadcast
Digital data signals transmitted from the control console to all equipment on a network. The signal is received by all equipment simultaneously and interpreted by each individually.

Bubble
A lamp that contains in-built reflector and lens system, such as used in a Parcan.

Build
An increase in light or sound level. See also Check.

back to top Byte
A group of eight bits.

CAD
Computer Aided Design

CAMLOCK™
Single pole connector used on professional power distribution systems. A separate connector is used for each phase/neutral/earth of the supply.

Cans
Short for Parcans.
Slang term for communications headsets worn by technicians.

Candela
Unit of luminous intensity.

Candlepower
An older term for intensity, interchangeable with candela.

Carbon Arc
A DC arc source in which the arc is produced in open air between a pair of carbon electrodes.

Casuals
Part-time temporary technicians, paid by the hour.

Catwalk
An access walkway to equipment, not necessarily across a void (as is the case with a bridge).

Centre Line
Virtual line running down the stage through the exact centre of the proscenium opening.

Chain Hoist
Electrically operated lifting device, utilising a chain.

Channel
A complete control path for signals in lighting or sound equipment.

Characteristic Impedance
The impedance of a cable supposing it had infinite length. It is equal to the value of the terminator resistor that should be used. The characteristic impedance is not the same as the cable's DC resistance.

Chase
A repeated sequence of changing lighting states. A chase can be produced easily by the effects functions of a computerised lighting desk

Chief Electrician
The senior member of a theatre's stage lighting team, although not necessarily the lighting designer.

Circuit
The means by which a lantern is connected to a dimmer or patch panel; numbered for reference.

Circuit Breaker
An electro-mechanical 'fuse' that can be reset instead of having to be replaced. See also MCB, RCD.

Chromaticity
The colour of light as defined by its chromaticity coordinates using the CIE diagram.

CID (Compact Iodide Daylight)
A high intensity discharge lamp that produces a light similar in colour temperature to daylight (c.5500K). A 1000W CID lamp produces approximately 2.5 times more light than a 2000W tungsten source.

CIE (Commission Internationale d'Eclairage)
An international lighting forum that has produced a series of universally recognised symbols for lighting plots.

Circle Fronts
A permanent front of house position in older proscenium theatre, above the circle balcony.

Cold Mirror
Dichroic coated surface that reflects light buy transmits infraret in order to reduce heat in the reflected beam.

Colour
The subjective interpretation by the human eye and nervous system of electromagnetic radiation in the 380 to 760 nm band (visible light). Energy at the short end of the visible spectrum (c. 380 - 450 nm) produces the sensation of violet, while the longest visible waves (c. 630 - 780 nm) appear red. Between these two extremes, the eye sees blue (c. 450 - 490 nm), green (c. 490 - 560 nm), and orange (c. 590 - 630 nm). Infrared light ("below the red") is that area of the spectrum adjoining the long wavelength end of the visible band. Ultraviolet light ("beyond the violet") adjoins the short wavelength end of the visible band.

Colour is a seperate classification to Hue (subjective appreciation of the dominant wavelength) and Saturation (subjective appreciation of purity).

Colour Call
A list compiled from the lighting plot of all the colours needed for the lighting rig, and their size. This term also applies to the act of preparing the filters and frames from such a listing.

Colour Changer
A colour changer attached to a lantern can be one of several types, but is basically used to change the colour of the light beam.
Scroller: a long string of colours is passed horizontally in front of a lantern, remotely controlled by the lighting desk.
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.
Semaphore: framed colours are electrically lowered into place in front of the lantern, remotely controllable. This system can perform additive colour mixing by lowering two colours into position at the same time.
Magazine: manual semaphore-type device used on the front of a followspot.

Colour Correction
The use of colour filters or dichroics to adjust for varying colour temperatures in different sources. Filters are available that correct to a wide variety of required colour temperatures.

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) and Gam (Great American Market - US) are the most 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 material Gelatine, from which filters were originally made.

Colour Frame
A frame which holds the colour filter in guides at the front of a lantern and prevents it from falling out (especially when the filter gets hot). Different lanterns need different size colour frames.

Colour Mixing
Combining the effects of two or more lighting gels:
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 (red yellow blue) additively mix to form white, as do the complementary colours.
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.

Colour Rendering Index (CRI)
The evaluation of the effect of a light source on the colour appearance of the objects in comparison with their colour appearance under a reference light source. The higher the index moves toward the maximum of "100", the better the colour reproduction.

Colour Temperature
A measure of the 'warmth' or 'coolness' of light sources and colours. Colour temperature is measured in degrees Kelvin (K).
Colour temperature is a term used to describe the colour of a light source, by comparing it with the colour of a "blackbody." A blackbody is a theoretical "complete radiator", changing its colour as its temperature is raised. It first glows dull red, then bright red, moving through orange, yellow, white, bluish white and finally blue. The colour of a candle flame is similar to a blackbody at about 1800°K. A common household tungsten light bulb produces an average colour temperature of 2800°K, whereas sunlight is about 5500°K. Integrated colour temperature refers to the final colour temperature produced by a luminaire, after the reflector and lens coatings have modified the colour temperature of the lamp itself.

Complimentary Colours
A pair of colours in the additive colour mixing system, which combine to produce white light; red + cyan, green + magenta, yellow + blue.

Condenser
A lens or mirror used in an optical system to collect the light being radiated from a source, which is then directed onto the gate of the projection system.

Contactor
An electrical switch used within an electrical system to control the on/off state of a device. A contactor is generally operated by an electromagnetic coil.

Contrast Ratio
This is the ratio of the brightness between the lightest and darkest areas in a subject.

Correlated Colour Temperature
Many sources do not have the same characteristics as black body radiators. However, sources that have a mainly white light output can be given a correlated Colour temperature. This is defined as that temperature of the black body radiator that most closely matches that of the light source.

Cove
Front of house lighting positions accessible via a catwalk.

Cross Fade
Bringing another lighting state up to completely replace the current lighting state. Also applies to sound effects / music. Sometimes abbreviated to Xfade or XF.

CSI (Compact Source Iodide)
A high intensity discharge lamp, most often used in followspots, with a Colour temperature of approximately 4000K.

Cue
The command given to technical departments to carry out a particular operation. E.g. Fly Cue or Sound Cue. Normally given by stage management, but may be taken directly from the action (i.e. a Visual Cue).

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. The UK system seems to be more secure, but it depends what you're used to.

Cue to Cue
Cutting out action and dialogue between cues during a technical rehearsal, to save time. (Also known as "Topping and Tailing".)

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

Cut Off Angle
The angle between the vertical axis of a source and the first line of sight at which the bare source is not visible.

Cyclorama

back to top Cyc Light (Cyc Flood)
A floodlight, usually with an asymmetrical reflector, designed to light a cyc or backdrop evenly from top to bottom.

D to A
Digital to analogue convertor

Dance Floor
The raised area inside at the forward part of a semi truck trailer

Data Rate
The rate at which serial information is sent. If there are no idle gaps between frames the data rate is equal to the baud rate.

Daylight Filter
A blue filter used to change the Colour of a light source from tungsten at 3200K to approximate daylight (5600K)

DBO (Dead Backout)
See Blackout.

Dead Hang
To fly an item without a counterweight or motor.

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.

Demux
Interface unit between the serial digital output of a memory lighting control desk to the parallel analogue signal understood by a dimmer.

Dichroic Filter
A glass filter that reflects chosen wavelengths and transmits the remainder. It differs from gels as they absorb unwanted wavelengths, turning the light to heat. Dichroic filters run cooler as they reflect the light, and therefore create a cooler light beam. Dichroic filters are longer lasting but a lot more expensive: they are predominantly used in moving lights or architectural applications.

Dichroic Lamp
A low voltage display lamp with a reflector that lets heat pass through it, rather than reflecting it. This results in a much "cooler" light beam.

Diffusion
Any material that softens the beam of light, at the same time reducing the light level.

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
The newer generation of dimmers that can respond directly to the digital multiplexed output of the lighting desk. The technology also permits the dimmer to report faults and other data back to the control board.

Dimmer
Electrical or electronic device which provides adjustable voltage to a lighting fixture to control light output. Can also be a term to refer to a mechanical device, such as a shutter, that controls output.

Dimmer Rack
A number of individual dimmer circuits mounted in a cabinet.

Dip
1) Small covered trap at stage level containing electrical outlets. (US equivalent is FLOORPOCKET)
2) Low lighting intensity when cross fading between two higher states - "there's a dip between these two states".
3) Transparent lacquer for colouring lamp bulbs - known as "Lamp Dip"

Direct Current (DC)
Electrical current that does not alternate in polarity and flows in one direction only. See also Alternating Current (AC).

Discharge Source
Light produced by passing electricity across two electrodes through a gas inside a quartz envelope.

DMX
Acronym for "Digital Multiplex." In DMX512, the 512 represents the number of channels a single data link will support. See also Multiplex.

Donut
A metal plate with a hole in the center inserted in a luminaire to sharpen the focus or reduce spill.

Double Handling
Moving scenery and other equipment more than necessary because it wasn't properly placed to being with.

Double Purchase
A suspension system used on counterweight bars that gears the movement of a single counterweight bucket to half that of the bar itself.

Douse
To de-energize a lamp in a luminaire. Douse is unrelated to intensity states.

Douser
A unit on a follow spot that produces an immediate blackout of the beam.

Downlight
A light from directly above the acting area.

Downstage
The stage area closest to the audience, ahead of the performer as he faces the audience.

Driver
The circuit that drives the transmit signal and is directly connected to the data line.

back to top Dry Ice
Frozen solid carbon dioxide (CO²) at a temperature of -87.5° 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.

Edge
In a wash luminaire, edge defines the spot or flood range of the diffusion mechanism(s). In a spot luminaire, edge defines the hardness or softness of the beam edge.

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.

Eggcrate
A device used on a soft light, consisting of small cross baffle plates to restrict the spread of the light beam.

EIA
Electronics Industry Association

EIA485
The specification of the electrical interface used by DMX512 to connect to the line. More commonly known as RS485.

Ellipsoidal Spotlight
A luminaire that uses an ellipsoidal reflector and a one or two lens optical system to project shapes and patterns with a hard edge.

back to top End Stage
The placement of a portable stage in an open, single floor building centered on the short end to provide maximum seating capacity.

F-number
A set of numbers used to express the aperture of a lens that represents its light transmission. It is calculated by dividing the focal length of the lens by the diameter of the lens diaphragm opening. Also known as a "stop" of "F stop."

Fade
A fade is an increase, diminishment or change in lighting or sound level.

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.

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

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.

Field
Refers to the spread of light intensity across a beam. Most spot luminaires have an adjustable field. A flat field has an even distribution, while a peak field has a hot spot in the centre of the beam.

Field Angle
The included angle between those points on opposite sides of the beam axis where the intensity drops to 10% of maximum.

Fill Light
Light which fills the shadows created by key light.

Filter
See Colour Filter

Fit-Up
Initial assembly on stage of a production's hardware, including hanging lights, scenery, etc.

Fixture
A generic term used for a luminaire or a "light." The terms are interchangeable.

Flag
A small piece of material (usually dichroic colour or metal shutter) inserted into the light beam of an automated luminaire.

Flash Box
A small box containing the socket into which a pyro cartridge is plugged. Also known as a flash pod.

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).

Flicker Free Ballast
A solid state ballast that provides square-waves of around 100 Hz to eliminate variations in the light output of discharge sources.

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.

Flip
A command that turns the yoke of an automated luminaire 180° whilst maintaining the same focal position.

Flood
To increase the beam angle of a focus spot by moving the lamp & reflector close to the lens. The diameter of the light beam is enlarged and thus gives the widest field of illumination.

Floodlight
A luminaire that has only a reflector (no lens) to control the beam, with a wide-angle distribution. Floods are used in battens (rows) or singularly, and can be symmetric or asymmetric. See also Cyc Flood.

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

Fluorescence
The ability of some materials to convert ultraviolet energy into visible light.

Fly
To suspend scenery or equipment above a stage or studio floor by means of a suspension system that can be manually operated or driven by motors.

Fly Gallery
The gallery that extends around the sidewalls of the stage area and is used for operating the ropes that adjust the counterweight system.

Focal Length
The distance of the focal point from the lens.

Focal Point
The point where the incident parallel rays, as bent by a lens, meet in focus.

Focus
1) The session when all the lanterns in the rig are angled in the correct direction, with the correct beam size.
2) Description of how sharply defined a light beam is (such as soft focus or sharp/hard focus)

FOH
See Front of House.

Follow-On 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. 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. See also Limes, Pick-Up.

Footcandle
A term used to describe illumination that is measured in "lumens per square foot." Interchangeable with "lux," which is the metric designation.

Footlambert
An older unit for luminance (brightness) that has been replaced by the "nit."

Frame
1) A set of 11 bits of data; 1 start bit, 8 data bits (the level or start-code byte) and 2 stop bits.
2) A colour frame.

Frequency
The number of cycles per second, measured in hertz (Hz).

Fresnel
Pronounced "Fr-nell". A type of wash luminaire using a Fresnel lens which produces an even, soft-edged beam of light. Often used with Barndoors to control light spill.

Fresnel Lens
A plano-convex lens constructed with the convex surface flattened into concentric rings that collect and direct light into parallel rays. Named after French inventor, Augustin Jean Fresnel (1788 - 1827) who developed the lens for French lighthouses, in order 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.

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 luminaires mounted on the audience side of the proscenium arch, focused towards the stage.

Frost
A diffusing filter used to soften the edges of a light beam.

Full Body Harness
A harness that has an attachment point above the shoulders, so the person falling cannot become inverted and fall out of the rig.

Full Up
A bright lighting state with general cover lanterns at "full" (100%) intensity.

back to top Fuzz Light
A lamp with a revolving mirror and a Coloured plastic dome. Gives a "police light" effect.

Gaffer
Term used in the film industry to describe the chief or master technician.

Gaffer Tape / Gaffa Tape
Ubiquitous sticky cloth tape. Most common widths are 0.5" for marking out areas and 2" for everything else. Used for temporarily securing almost anything. Gaffer Tape should not be used on coiled cables or equipment. Originally known as "Gaffer's Tape", from the Gaffer on a film set. See also PVC Tape.

Gate
The optical center of a spot luminaire, where shutters, iris or gobos are positioned.

Gel
An old fashioned term for Colour Filter, from when these were made from gelatine.

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 also Special..

Generic
Standard stage lighting instruments, rather than moving lights or other intelligent effects.

Get-Out
Moving an entire production out of the venue, and into either a large waste-disposal skip, or into transport. Usually preceded by the strike.

Ghostlight
By theatrical tradition, a light left burning overnight on stage to keep friendly spirits lit and unfriendly spirits at bay, it is also believed to keep the theatrical muse of a "dark" (non-producing) theatre.

Gobo
Traditionally a thin metal plate etched with a pattern which is placed in a spot luminaire, designed to cast the design onto a surface. The image can be used soft focus to add texture, rather than a defined patten. 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 by using a glass gobo.

Gobo Holder
A metal plate designed to hold a gobo of a particular size in a lantern of a particular type.

Grand Master (GM)
See Master.

Grelco
Brand name for a 2 way 5A or 15A electrical splitter. Another name is SNAPPER (another brand name) or in the US "TWOFER". These splitters are always wired parallel (voltage equal, current shared).

Ground
The safety electrical connection to earth or to surrounding exposed metalwork.

Ground Loop
A connection between two earth/ground points at differing potentials thus causing a current flow. The magnitude of this current may cause errors or, exceptionally, damage to the equipment.

Ground Man
A rigger stationed on the ground who sets up and attaches whatever gear the "high man" may need.

back to top Groundrow
Compartmentalized floodlights at floor level used to light the bottom of cycs, etc.

Halogen Cycle
The cycle by which halogen in a lamp returns to tungsten deposits back on the filament, preventing blackening of the inner lamp envelop wall. In a tungsten halogen lamp, the tungsten combines with the halogen gas elements present in the lamp envelope and is re-deposited back onto the filament. This process requires a very high temperature to operate, so tungsten halogen lamps are able to be smaller and run hotter than their tungsten equivalents.

Hang Time
The amount of time that fog or smoke stays in the air without dissipating.

Hanging Point
The point on a truss from which attachments are made for rigging.

Hazer
See Smoke Machine.

Heads On Stage (Heads!)
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.

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 a gap between the Heat Shield and the gel, or it will not be effective.

Hertz (Hz)
The unit of frequency, measured in cycles per second.

Highest Takes Precedence (HTP)
The control logic in a lighting system whereby the highest value provided to a parameter is the value that parameter will be set on stage.

High Man
A rigger who attaches rigging for support of flown items, such as trusses.

HMI (Hydragyrum Medium arc-length Iodide)
A mercury-halide discharge lamp with a daylight Colour balance (5600K).

Hoist
An older term used to describe either manual or motorized lifting equipment.

Hookclamp
A C-shaped clamp with a wing bolt for hanging a lantern on a horizontal lighting bar (usually 50mm diameter). Introduced in the UK in 1959 by Strand, replacing the 2-bolt and 2-nut L Clamp.

Houselights
The auditorium lighting, which is commonly faded out when the performance starts.

Hot Mirror
Dichroic coated surface that transmits light but reflects infrared in order to reduce heat in the transmitted beam.

back to top Hue
The subjective appreciation of the dominant wavelength of a light source; the attribute of Colour perception by which different parts of the spectrum are distinguished (red, orange, yellow, blue, violet, and purple). Hue does not take into account the brightness or intensity (saturation) of the Colour.

Idle
The time that the DMX512 line is idle (high) and not sending any information. Also known as the "mark" condition.

Ignitor
A device that generates voltage pulses to start discharge lamps without preheating electrodes.

Illumination
The luminous flux falling on a unit area of a surface.

Impedance
A measure, in ohms, of the opposition to current flow in an ac circuit, including resistance and reactance.

Incandescence
The emission of light by raising the material to a high temperature.

Incandescent
Light source with a metal filament (tungsten) that glows white hot when current is passing through it.

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.

Inductance
Opposition of current changing in an ac circuit, which causes the current to lag behind the applied voltage. Inductance is created by turn of wire with or without an iron core.

Infrared (IR)
Wavelengths below the visible wavelength of light, felt as heat.

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.

Insert
An extra lighting state added into the sequence later. See Point Cue

Intelligent Light
See Moving Light.

Intensity
The amount of light emitted by a source, per second, in a given direction within a cone of unit solid angle. Also, the function of a luminaire related to the brightness of the beam as projected on a surface, specified by intensity data.

Internally Wired Bar (IWB)
A bar (usually aluminium) which has a number of sockets (usually 15A) positioned along its length, the wiring for which is contained within the bar.

Inverse Square Law
The equation that is used to calculate the illumination at a specified distance from a source of light.

Iris
A series of adjustable metal plates arranged to provide a variable circular aperture, used in spot luminaires to alter the size of the beam. Originally called an iris diaphragm.

back to top Isolation Voltage
The voltage that can be safely sustained between separate, isolated parts of a system.

back to top Jumper
An adaptor from one type of connector to another. For example, a 13A - 15A jumper has a 13A plug and a 15A socket at either end of a short cable. Applicable to both electrical and sound cables.

Kelvin
The unit of thermodynamic temperature, a scale that compares the visible aspects of a light source to a heated body.

Key Light
The principal source of illumination, usually a spot luminaire.

Kill
To switch off (a light/sound effect).

Kilowatt
Electrical term for 1000 watts.

Kit
General name for equipment, especially nice shiny equipment, leading to the comment "That's a nice bit of 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.

back to top Kilowatt
Electrical term for 1000 watts.

Ladder
Non-climbable structure in the shape of a ladder from which luminaires are hung in a vertical stack.

Lamp
A glass or quartz envelope that contains filaments or electrodes. What the un-initiated call a light bulb! See also Bubble.

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 (in the UK) requires that the lamp tray cannot be opened until power has been disconnected.

Lantern
General term for unit of lighting equipment including spotlight, floodlight etc. The term is now being replaced by the internationally recognised "luminaire".

Laser (Light Amplification by Stimulated Emission of Radiation)
A very high energy beam of light that remains virtually parallel throughout its length. It is visible in the air only when a haze of smoke or dust is introduced.

Latest Takes Precedence (LTP)
The control logic in a lighting system whereby the last value provided to a parameter is the value that that parameter will be set to.

LD
The Lighting Desigenr.

Lectriflex
Multipin connector for carrying multiple lighting circuits down a multicore cable. See also Socapex.

Leko
A type of ellipsoidal profile spot, much used in the USA. "Leko" is a contraction of the original manufacturers names.

Lens
Optical glass with one or both sides curved to direct light by concentrating or dispersing the light beam.

Light Centre Length (LCL)
The distance from the centre of a lamp filament to a point at the base of the lamp.

Light Curtain
A lighting effect which produces a wall of light when the area is diffused with smoke or fog. Usually produced by a number of low voltage Par lamps or an ADB Svoboda.

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

Lighting Plot
The process of recording information about each lighting state either onto paper or into the memory of a computerised lighting board for subsequent playback.

Lighting State
The format of lighting used at a particular point in the production; a lighting "picture".

Lighting Stencil
Plastic stencil containing a range of scale symbols for current lighting equipment. Greatly facilitates the drawing of lighting plans.

Limelight
An obsolete source of intensely bright light, most recently used in followspots. It was derived from a burning jet of oxygen and hydrogen with a rotating cylinder of lime. See also Lime.

Limes
Followspots and their operators. This term is still in everyday use, although Limelight is not.

Linnebach Projector
Lensless system for projecting a shape from a slide, placed in front of a floodlight, often used for shadow effects.

Load
The electrical power rating, in watts, of the equipment connected to a specific dimmer; also describes the equipment itself.

Low Voltage
Low voltage lamps give more intense light than mains voltage lamps of the same wattage.

LSB (Least Significant Bit)
The bit in a binary value that carries the least weight, for a byte this is bit 0, weight 1.

Lumen
The amount of light energy within an area.

Lumens Per Watt
The light output in lumens produced by a source for each watt of electrical power required by the lamp.

Luminaire
A general international term used for a complete lighting unit. Interchangeable with Fixture and Lantern.

Luminous Intensity
A measure of the energy from a light source emitted in a particular direction, as measured in candelas.

Lux
The metric measurement relating to incident light that falls on a subject (10.8 lux = 1 foot-candle)

LX
Short for Electrics. The department in the theatre responsible for stage lighting and sometimes sound and maintenance of the building's electrical equipment.

back to top LX tape
See PVC Tape.

Macros
Macros are a series of command strings (button presses or display selections) that can be recorded for automated playback, either through manual selection of the associated macro number, or from automated activation through the cue sheet.

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.

Mark-After-Break
The idle time between the end of break and the start of the start-code.

Master
1) An overall control on a lighting or sound control board. The Grand Master takes precedence over all other controls. 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).

Maximum Overall Length (MOL)
The overall physical length of a lamp, including the contacts.

Memory Board
An electronic storage device which enables recording and subsequent "playback" of lighting states.

MIDI (Musical Instrument Digital Interface)
A digital signal that can carry note information, show control commands or timecode information.

Mirror Ball
A lighting effect popular in discos, ballrooms etc. A large plastic ball covered with small mirror pieces. When a spotlight (usually a Pinspot) is focused onto the ball, specks of light are thrown around the room. Mirror Balls are usually motorised to rotate.

Monochromatic
Seeing the gradations of one Colour only.

Motion Control Library (MCLib)
All automated luminaire (or scroller) parameter settings, may be programmed in a MCLib. Any changes made to a Library are automatically tracked into any cues in which they were used. Also known as a Preset Focus.

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;
2) Moving Mirror: A stationary luminaire directs light onto a motorized mirror.
The term "intelligent" is used as the instrument has a processor chip and electronics built into it, not because it's clever.

MSB (Most Significant Bit)
The bit in a binary value that carries the most weight, for a byte, this is bit 7, weight 128.

MSC (MIDI Show Control)
A control protocol that is an extended version of the original MIDI. In addition to a "go" command, cue numbers and other information can be transmitted.

MSR (Medium Source Rare Earth)
High efficiency discharge lamp with a high Colour temperature.

Multicore Cable
More than one electrical circuit housed in a single flexible jacket.

back to top Multiplexed (MUX)
All modern lighting desks use this serial form of communication with dimmers. All the information from the desk is transmitted along a single pair of cables 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). However, new protocols are continually being added to keep up with more demanding equipment.

Nanometer (nm)
A unit of metric measurement equal to one billionth of a meter. Used to measure light wavelengths.

Neon
A type of discharge lighting generated by a high voltage across two electrodes at opposite ends of a long, thin glass tube filled with neon gas. Different Colours are obtained by mixing other gases, or by using florescent coatings.

Neutral Density Filter
A filter that attenuates the light passing through it without affecting the Colour of the light.

back to top Non Dim
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.

Ohm
A unit of electrical resistance.

Opaque
Absorption of electro-magnetic radiation at specific wavelengths.

Open Faced Luminaire
A luminaire with no lens system.

Open White (O/W)
Lighting with no colour filter. Known in the US as NC (no color).

Opto-Isolator
A circuit using optical techniques to isolate the electrical connections between a transmitter and a receiver.

back to top Outrigger
An extendible leg to increase the stability of access equipment.

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

Pan
Term describing the horizontal movement of an automated luminaire.

Pantograph
A mechanical device for adjusting the height of luminaires. It is usually spring balanced but can be operated by a motor or manually driven gear system.

Parabolic
A mirror shaped like a parabola that directs a beam in parallel rays.

Par Lamp
Stands for Parabolic Aluminised Reflector.
A popular stage lamp that is shaped like an automobile headlight, with a tungsten source sealed with an enclosed lens and reflector, producing a rectangular beam. Par lamps are available with a variety of different lens textures to produce a wide array of field angles.
Par sizes available include 16, 36, 38, 56 and 64 (the number refers to the diameter of the lens, in eighths of an inch). The most common for theatre use are Par 64s rated at 1000W (1kW), although other wattages are available. 110V Par lamps are often 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
A cylinder shaped lighting fixture that incorporates a Par lamp, yoke, colour frame holder slot and clamp. The type of Par lamp determines the beam spread.
The Parcan first appeared in 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. See also Floorcan.

Patch
The act of connecting equipment together. Originally applied to luminaires & dimmers, or sound desks & other equipment, now also applicable to data distribution systems etc.
To complicate matters, the physical action of connecting circuits (a Hard Patch) has been replaced in some situations by using software (a Soft Patch).
1) (verb) The act of plugging a lantern into a dimmer (e.g. "Can you patch circuit 12 into dimmer 18 please").
2) (noun) The system for connecting lanterns to dimmers (The Patch)

Patch Panel / Patch Bay
A board consisting of rows of sockets into which plugs can be connected to route sound signals or power for lighting circuits.

Pattern
See Gobo.

PC
Originally short for plano-convex; the basic lens shape of many luminaires and projectors. It now refers to Prism- or Pebble-Convex, a type of lens with a pebbled flat surface. The optical system produces a beam with a slightly harder edge than a fresnel, but not as hard as an ellipsoidal reflector.

PCB
Printed circuit board.

Percent
Dimmer levels are usually expressed as a percentage of the maximum supply voltage. (100% = approx 230 Volts in the UK.)

Perches
Lighting positions (often on platforms) 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 auditorium.

Phase (electrical)
Electricity is generated and supplied to large installations as three separate supplies, known as phases. In the UK, the three supplies are colour-coded to ease identification. Each of the Red, Yellow and Blue phases are supplied down one multicore cable to the building, but effectively give three separate 240 volt supplies.
Because there is a potential difference (voltage) of 415 volts between any two phases, 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.

Phosphorescence
The property of some materials that can store light energy and glow in the dark.

Pickup
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.

Pickup Point
The point of attachment to a building's load-bearing structure for rigging.

Pin Spot
1) A lantern focused very tightly on a small area
2) A small luminaire used widely in disco installations, consisting of a low voltage Par 36 lamp (6V 30W lamp code is 4515) with a very narrow, almost parallel, beam. The lamp is housed in a metal case with a built-in transformer.
Pin Spots are ideal for lighting Mirrorballs.

Plano-Convex Lens
A lens that has one flat side (plano) and one spherical side (convex).

Plano-Convex Spotlight
A luminaire that provides a reasonably even beam with a moderately sharp edge.

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

Plot
List of preparations and actions required of technical crews during the performance (eg Sound Plot = list of sound cues and levels in running order).

Plotting Session
Time during which the plot for each department is prepared (eg Lighting Plotting session).

Point Cue
A cue inserted during or 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.

Polarity
The orientation of the positive and negative wires of a DC circuit or the phase and neutral wires of an AC circuit.

Pole Operation
A means of adjusting the focus of a luminaire from a pole at floor level, commonly used in TV and film.

Practical
Describes a luminaire (for instance, a table lamp) that appears to be switched on and off by an actor within a scene.

Prefocus Cap
Denotes special lamp caps allowing the filament to line up precisely with the optics of a luminaire.

Preheat
Warming the lamp filament prior to fade up, allowing a smoother transition.

Preset
1) An indepenently 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.
2) The Blind Side of a Playback in a computerised control system.

Preset Focus
See Motion Control Library.

Preview (Blind) Editing
Preview Editing means that the actions taken are recorded to the appropriate luminaires, but are not executed on stage.

Primary colours
The primary additive colours of light are red, green and blue. (The primary subtractive colours are cyan, magenta and amber).

Production Desk
A table in the auditorium at which the director/designer etc sit during rehearsals (especially technical rehearsals). Usually has its own lighting and communications facilities.

Profile
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 usually 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").

Projection
1) Slides are used to project still archive images or textures. 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.
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) Video: Video projection is now being used to bring television pictures to the large screen. Cheaper than using film, but the image quality is not as good. Video projection equipment can also be more difficult to set up. 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.

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 Cable
Short for Pyrotenax, a brand name (UK) of Mineral Insulated Cable usually used in firm alarm and evacuation systems.

back to top Pyrotechnics
(Pyros). Chemical explosive or flammable firework effects with a manual detonation. Usually electrically fired with specially designed fail-safe equipment. Types of pyro range from the Theatrical Flash (a flash and a cloud of smoke) to the Maroon (which produces a very loud bang). A Gerb is a version of the Roman Candle firework, throwing a shower of sparks into the air. All pyrotechnics should be used with close reference to local licensing laws, and the manufacturers instructions. Some territories only permit licenced pyrotechnicians to use these devices.

back to top Quartz
Crystalline silica that is glass-like and used to make lamp envelopes.

RCD
Residual Current Device. Protects the user against short circuit (earth faults) and earth leakage caused by damaged cable or faulty equipment. An RCBO is a combined MCB and RCD, protecting against earth leakage/short circuit and overload.

Re-rig
To change the lighting rig from the current setup to new positions.

Rear Projection
See Projection

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").

Reflectance
The ratio of the reflected light to the incident light falling on a surface, measured in lumens.
Reflections
Spurious signals on a DMX512 line caused by incorrect termination.

Refresh Rate
The number of packets sent per second.

Repeater
An amplifier to extend cable length or to increase the number of devices on one line.

Resistance Dimmer
A now obsolete method of dimming that decreases the current available to the load by introducing a variable resistance between supply and load, based on a rheostat. The excess current is converted into heat.

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
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. (Also known as LAMP CHECK.)

RFU (Remote Focus Unit)
A handheld remote control for a lighting desk.

back to top Risers
The flat surfaces on a Fresnel lens ring that form the division between segments.

xxx
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Safety
A short length of wire rope or chain formed into a loop around a suspension point, acting as a secondary means of suspension in the event of failure of the primary method.
Saturation
Saturation is the subjective appreciation of purity, a relation of the intensity of the dominant wavelength to all other wavelengths (defined by terms such as deep, pale, light, dark).

Saturation Rig
An arrangement of luminaires in which the maximum number of lights is placed in every possible position.

SCR (Silicon Controlled Rectifier) Dimmer
A solid-state electronic device used to control incandescent lamp intensity by cutting off part of the cycle or the AC supply.

Secondary colours
Those colours produced by mixing either additive or subtractive primary colours.

Selected
A channel or group of channels that responds to manual control is said to be selected.

Shield
The outmost conductor of a cable inside of which the conductors are enclosed. Also known as the screen.

Shin Buster
The lowest luminaire on a lighting boom, so named due to the proximity of the flesh of the lower legs to sharp edges on the luminaire.

Short Circuit
Unwanted current flow of low impedance between conductors.

Shutter
Metal flags used within a luminaire to shape the beam.

Silk
A special type of diffusion filter that stretches the light in one direction.

Single Purchase
A suspension system for counterweight bars where no gearing is used. The distance of travel of the counterweight bucket will be the same as the barrel.

Six Lamp Bar
An internally-wired lighting par, designed for touring, with six sockets terminated in a multi-way connector. It is often pre-rigged with PAR lamp (PAR Bar)

SMPTE Timecode
An analog audio level signal that carries timecode information.

Snoot (Top Hat)
A conical metal tube fitted to the front of a luminaire to enable a reduction in beam size and mask the lens.

Socapex
A multi-pin connector that carries a series of lighting circuits, available in 19 and 37 pin configurations.

Soft Light
Asymmetric flood used as fill light in TV and film, used to balance the key light and eliminate shadows.

Span Set
A circle made of nylon strands encased in nylon covering that is wrapped around areas of load-bearing structures to prevent chaffing.

Special
A luminaire in the lighting rig that is required for a specific moment or effect; it is not part of the general lighting cover.

Speed
Control of the rate of change of the variable parameters of the luminaires. As opposed to time (5 seconds), speed can be thought off a Miles Per Hour.

Spill Light
Extraneous uncontrolled light from a luminaire.

Splitter
A repeater amplifier with a number of independent outputs.

Start
To energize a lamp in a luminaire. This refers only to arc sources.

Start Bit
The extra bit attached to the beginning of a byte to indicate to the receiver that a new byte is being transmitted. The start bit is always low, i.e., value zero.

Start Code
The first byte sent after a break, indicating the type of information to follow; start code = 0 for dimmer levels.

Step Lens
A plano-convex lens similar to a Fresnel lens, but with the concentric rings on the plano side.

Stop Bit
The extra bit(s) attached to a byte to indicate the end of the byte; DMX512 has two stop bits. The stop bit is always high, i.e., value one.

Strobe
A device giving a fast series of very short intense light flashes that can have the effect of making action appear intermittent. It is also used to describe a similar effect on a moving light.

Subtractive colour Mixing
The removal of light of various wavelengths by filtering or reflection.

back to top Synchronous
Signals that are locked to a master clock pulse.

Terminator
A 100-120 ohm resistor fitted to the end of a DMX512 line on the last device on the data line (across pins 2 and 3).
Telescope
A grid mounted device made from retractable sets of tubes that is used to suspend luminaires at various heights.

Thrust
A type of stage that projects into the auditorium so that the audience is seated on at least two sides of the extended section.

Tilt
Term describing the vertical movement of an automated luminaire.

Top Hat
Metal tube that fits on the front of a lighting fixture to reduce the spill of stray lighting without reshaping the beam or creating hard edges.

Torm (Tormentors)
The side curtains that hang next to the proscenium opening.

Transverse
Forming a stage where the audience is on either side of the acting area.

Tripe
A bundle of cables tied or taped together as a single unit.

Truss
A metal structure designed to support a horizontal load over an extended span.

Tungsten Halogen Lamp
Compact incandescent lamp that uses a halogen chemical cycle to prevent blackening of the lamp envelope during life.

back to top Twisted Pair
A type of cable where the inner conductors are twisted together in order to reject interference in balanced-line systems such as EIA485.

UART (Universal Asynchronous Receiver Transmitter)
The circuit that decodes serial data into byte values, and may also handle break detection.

back to top Ultraviolet
The band of short wave radiation from 400 to 10 nm, although invisible to the eye the energy is extremely powerful and can damage the eye.

Violent Failure (Violent End of Life)
An explosion of a lamp.
back to top Voltage Drop
That loss of volts that occurs through energy wastage when a current passes through a cable or electronic device.

Water Cracker
Device that produces a thin haze in the air by "cracking" water drops.

Watts
A unit of electrical power derived from the current (or quantity of electricity) multiplied by the voltage (or pressure at which the current is flowing).

back to top Wavelength
The distance from one point on a vibrating wave to the same point on the next wave. In lighting terms, blue light is short wavelength, green is medium and red is long. Beyond visible light are short wavelength Ultra Violet light and the long wavelength Infra Red light.

back to top Zoom
Used to spot luminaires, consisting of the relative movement of lens elements in an optical system to change beam width and focus.

Glossary of Common Terms

See also: