Appendix I

Glossary of terms

 

A Ampere.

Abbott A manufacturer of single-conductor connectors used on feeder cable.

Absorption filter A filter which transmits selected wavelengths. The absorbed energy is converted to heat which raises the temperature of the filter.

AC (1) Alternating current. (2) Camera assistant.

Ace A 1 kW Fresnel light.

Acting area That portion of a stage used by the actors during a performance.

Adapter A device used to convert from one type of connector to another.

Additive colour mixing The superimposition of light beams, usually consisting of the primary colours, whereby the resultant light is the addition of the various wavelengths concerned (see Subtractive Colour Mixing).

Alligator clip, Crocodile (croc) clip, Bulldog clip Metallic spring loaded clamp, similar to a clothes peg, with pointed teeth on the jaws of the clamp. Used for making temporary electrical connections. Also used to hold gels to barndoors.

Alternating current (a.c.) Electric current whose flow alternates in direction. The time of flow in one direction is a half period and the length of all half periods is the same. The normal waveform of a.c. is sinusoidal.

Ambient light General background light.

American National Standards Institute (ANSI) An independent association that establishes standards to promote consistency and interchangeability among manufacturers. This organisation was formerly known as the United States of America Standards Institute (USASI or ASI) and previously as the American Standards Association (ASA). Three-letter ANSI codes are used to identify light bulbs (e.g. EGT is a 1 kW bulb).

Ammeter A meter for measuring amperage.

Ampacity Current capacity of cable, connectors, etc. (USA).

Ampere A unit of current. One ampere will flow through a resistance of 1 Q under a pressure of 1V.

Ampere-hour A measure of a battery capacity equal to the number of amperes times the number of hours of charge that a battery can deliver.

Anode A positive electrode.

Apple box A reinforced plywood box used on the set for many purposes, including to raise an actor who is too short or to raise furniture. Apple boxes come in four sizes: full (20 × 12 × 8), half (20 × 12 × 4), quarter (20 × 12 × 2) and pancake (20 × 12 × 1) –measured in inches.

Arc The discharge created between two electrodes usually with a fairly low voltage and high current. Has to be controlled by a ballast arrangement (see also Carbon Arc).

Arc light Old term for a luminaire using a carbon arc discharge as the source of illumination. Also describes modern discharge sources such as MSR, HMI, CSI, etc.

Articulated arm An adjustable device consisting of short pieces of tubular metal joined together by ball and socket joints. Used to hold gobos or flags, normally attached to a stand or rigged on other grip equipment or scenery.

Artificial light Light coming from any source other than the sun, sky or moon.

ASA (1) American Standards Association (now the ANSI). (2) The exposure index (EI) rating of a film emulsion, also referred to as ISO.

Aspect ratio The ratio of the width to the height of any imaging system. The standard aspect ratios are 4:3 (standard TV), 16:9 (high-definition TV), 1.66:1 (European film standard), 1.85:1 (American wide screen standard) and 2.36:1 (Anamorphic 35 mm).

Atmosphere The mood of a scene created by the lighting, set design, costumes and make-up. Additionally, influenced by sound effects, music, etc.

AWG (American Wire Gauge) These sizes are based on the diameter of the wire expressed in mils (1/1000 in) or its cross sectional area (CSA), expressed as circular mils (Cmils) (see Cmils).

Baby 1kW Fresnel luminaire.

Baby stand A stand with a 5/8 inch stud.

Baby stud A 5/8 inch mounting stud that mates with a 5/8 inch receptacle.

Backdrop (Backing) A scenic painting or enlarged photograph transparency used to limit the view of the audience or a camera through openings such as doorways or windows.

Backing lighting The illumination provided for scenery and backdrops.

Backlight A luminaire used to light the subject from the rear to help separation from backings and to increase the three-dimensional effect.

Bail U-shaped part of a lighting fixture that attaches the fixture to the stand (see Yoke).

Bailing wire (USA) A thin flexible wire used as safety wire for barndoors, snoots and other luminaire attachments.

Balance (a) The relationship of light and shade in a scene to establish the mood and atmosphere e.g. high key or low key. (b) The maintenance of lighting levels between scenes to prevent exposure differences (see High key, Low key).

Ballast The electrical device, required for all discharge lamps, that limits current through the lamp. Additional functions may be incorporated in the basic unit such as starting circuits and dimming control.

Banded cable Several single-conductor cables banded together at intervals, formed into a bundle.

Bank Used to describe groups of lights, such as several scoops or softlights. Also luminaires containing several PAR lamps.

Barndoor Movable flaps attached to a Fresnel or PC luminaire to shape the light beam.

Barrel (Colloq. Bar) A metal tube, generally 48-mm diameter, for suspending luminaires or scenery. Usually manufactured from steel or aluminium.

Base (1) The basket on the underside of a fixture. (2) The base of a lamp is the porcelain part. (3) The lamp socket is also sometimes called the base.

Base light The basic intensity of ‘soft’ lighting required to satisfy the minimum viewing or technical requirements.

Basher A small luminaire of around 500 W used as a kicker.

Bates A common name for three-pin connectors (20 A, 30 A, 60 A, 100 A).

Batten (a) Horizontal pipe on which luminaires or scenery can be hung. (b) Compartmented multi-colour floodlight unit for theatrical lighting. (c) Refers to 3 × 1 inch timber.

Battery belt A battery pack mounted on a belt that can be worn around the waist during location shooting.

Battery pack Used on location where an electrical supply from the mains is not available. The most popular batteries for size to weight ratio are nickel-cadmium. Typical luminaires used with battery packs have open-faced reflectors, containing a tungsten halogen or discharge lamp.

Bazooka An adjustable extension tube with a 1/8 inch spigot for mounting luminaires on catwalks. It is similar to a small stand minus its legs.

Bead board Styrofoam used to make soft bounce light.

Beam The unidirectional flow of total light output from a source, usually a luminaire.

Beam angle Those points on the light output curve which are 50% of maximum output. The included angle between these two points is the beam angle.

Beam light Lens less luminaire with a parabolic reflector to give a parallel light beam.

Beaver board A nail-on plate mounted to an apple box.

Best boy The assistant chief lighting technician or second electrician. The best boy is the gaffer's chief assistant.

Big eye A 10 kW incandescent fixture with an extra large lens (Mole Richardson).

Black wrap Thick aluminium foil painted with matt black to control spill light from luminaires.

Blackbody A body which completely absorbs any heat or light radiation falling upon it.

Blackbody radiation Radiation that comes from an ideal blackbody. The distribution of energy is dependent only on the temperature of the blackbody and is governed by Planck's radiation law.

Blacklight Radiation in the near ultraviolet (320–400 nm) used to make paints, dyes and materials fluoresce. As UV radiation is invisible to the eye, it is possible to use it for special effects where apparently, in darkness, materials glow as though they were normally illuminated. As with any other UV radiation, it is important that it does not cause any hazard to human beings.

Blackout To switch all channels to ‘off’ on a lighting console. Also refers to switching off all illumination, except the exit lights.

Blackout switch A master on/off switch used for controlling the overall production lighting for either stage or studios.

Blind Refers to changes made on a lighting console which do not affect the ‘live’ console output (usually called Blind Plotting).

Blonde A 2 kW open faced luminaire.

Board A name for a control desk (derived from switchboard).

Boom An extendible arm fixed to a stand to mount small lighting fixtures which may be moved to adjust the lighting on the subject.

Boomerang A device attached to the front of the luminaire holding sets of filters. They are generally provided at the front of follow spots for colour changing.

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

Bracket The small supports on the front of a luminaire which hold the barndoors, colour frame, scrims and other accessories.

Brail To pull a lighting suspension or piece of scenery out of its normal hanging position by means of attached rope lines.

Branch circuit As defined by the American NEC, circuits that are downstream of the last overcurrent protection.

Branchaloris A branch of a tree or bush held in front of a light to create a moving or stationary foliage pattern.

Bridge A narrow platform suspended over the acting area. Luminaires and projection devices mounted on the bridge are accessible during performance.

Brightness See Luminance.

Brightness ratio The ratio of maximum-to-minimum luminances occurring within a scene.

British Standards Institute (BSI) Produced technical specifications and other documents which are made generally available. The main aim of the Institute is to maintain standards, quality and safety in goods and products.

Broad A wide angle floodlight.

Brute A 225 ampere d.c. high intensity carbon spotlight with a 24 inch diameter Fresnel lens.

Bubble Slang term used in the TV and film industries to describe lamps of any type.

Build A gradual increase in light level or in the number of light sources used.

Bulb An old term describing the bulbous glass envelope of an electric lamp.

Bull switch A main switch used on the main feeder or on sub-feeder lines.

Bump To briefly flash lighting channels ‘up’ or ‘down’.

Busbar Copper bars (1/4 inch thick) to which lug connectors are attached.

Busbar lug (USA) A small electrical ‘G-clamp’ made from brass used to attach large cables to busbars. Has good electrical conductivity and high current rating.

Butterfly set A frame used to support a net or silk over the top of the action. The silk reduces and softens direct sunlight.

‘C’ Clamp See Hook clamp.

CCD (Charge coupled device) A charge coupled device is a solid state chip covered in several hundred thousand photosensitive cells. Each photosensitive cell represents one piece of picture information (pixel). All CCDs have the same colour sensitivity, therefore filters for the red, green and blue component have to be used.

CCT (Correlated colour temperature) Many sources of light energy do not have the same characteristics as black body radiators, but sources which have a mainly white light output can be given a correlated colour temperature. This is defined as that temperature of the blackbody radiator which most closely matches that of the light source in question. It therefore gives a rough guide to the blueness or redness of the source.

C-stand A multi-purpose stand used for setting flags and nets. Short for Century stand.

CID Metal halide discharge lamp with a correlated colour temperature of 5600 K.

CIE Commission International de l'Eclairage. The international body which regulates standards applied to lighting, with various committees comprising representatives from all over the world.

CIE Diagram Shows the mixture of colours within the spectrum (see Tri-stimulus).

CSI A discharge lamp which approximates to sunlight for colour balance (CCT 4000 K).

Cable crossover A special rubber ramp used to protect cable from being damaged by being run over and to protect pedestrians from tripping over cable.

Cam-lok A type of single pole connector used for feeder cables.

Camera light A luminaire mounted on a camera for lighting along or near the optical axis, usually to provide catch lights for the subjects’ eyes.

Can Permanently installed switch gear containing busbars on a sound stage.

Candela Unit of luminous intensity.

Candlepower A term that was used for intensity but has been replaced by the candela.

Carbon arc A d.c. arc source in which the arc is produced in air between a pair of carbon electrodes. These electrodes burn away and must be advanced during operation.

Cathode A negative electrode.

Catwalk A metal or wooden walkway usually used in the film industry to provide access and additional suspension points for luminaires.

Celo cuke A wire mesh painted with a random pattern and placed in front of a light to throw a subtle pattern.

Chain vice grip A mounting device that uses a bicycle chain and vice grip to create a tight clamp around pipes, poles, or tree limbs.

Channel The circuit from the lighting control console to its associated dimmer.

Channel number Reference number entered by a key pad; or used by dedicated faders.

Chase A series of programmed sequential steps activating channels from a lighting console.

Chaser lights A linear string of lamps wired and controlled so that the lights appear to be following in sequence.

Chiaroscuro A strongly contrasting treatment of light and shade in drawing and painting. Translated from the Italian, the word means ‘half-revealed’.

Chicken coop An overhead suspended light box that provides general downward ambient or fill light. Also called a coop.

Chimera A specially designed, lightweight, collapsible soft box manufactured by Chimera Photographic Lighting.

Chroma In TV, the information which gives the colour of the image as distinct from its luminance (brightness).

Chroma key A TV special effect which uses a monochromatic coloured background to allow electronic switching to another picture. Deep blue is commonly used for the background when the foreground involves people.

Chromaticity The colour of light, as defined by its chromaticity co-ordinates, generally using the CIE diagram.

Cinevator stand A heavy-duty stand used for the largest types of lights. The mechanism that raises and lowers the light is driven by an electric motor.

Circuit The electrical path from a dimmer to the luminaire.

Circuit breaker An electrical switch positioned in the circuit that will automatically operate to break the flow of current under abnormal conditions.

Cmils (USA) A Cmil is the cross-sectional area of copper wire 1/1000 of an inch in diameter.

One square inch will consist of 1 000 000 square mil or 1 273 240 cmil.

Cold mirror A dichroic coated glass surface which reflects visible light but allows infrared energy to pass through the reflector so that the reflected light contains less heat.

Colour A sensation of light induced in the eye by electromagnetic waves of a certain frequency –the colour being determined by that frequency.

Colour balance Usually describes the effectiveness of film when exposed under various coloured light e.g. daylight film is balanced for 5600 K light, whereas tungsten film is balanced for 3200 K. Can also describe a slight bias introduced by filters to create a warmer or cooler picture.

Colour chart A chart of standard colours filmed at the head of a roll of film as a colour reference for the lab.

Colour compensation (CC) A reading obtained from a colour meter indicating the amount of green or magenta gel needed to neutralise off-colour hues, usually present in fluorescent lights.

Colour correction

1. The use of special filter materials to correct for: (a) daylight to tungsten, (b) tungsten to daylight, and (c) spectral aberrations in light sources.
2. Colour correction is also used for film processing to ensure that the various scenes blend together for continuity of picture quality.

Colour filter A translucent material used to change the colour and quantity of light passing through it. The original filters were made from gelatine –hence all filters tend to be known as ‘gels’. Modern filters are manufactured from high grade plastics and glass. With tungsten luminaires of 2 kW and above it is usually necessary to have stand off colour frames to prevent the filter from bleaching and burning.

Colour frame A frame used to support colour media at the front of the luminaire.

Colour media Any coloured transparent material that can be placed in front of a luminaire. These are often referred to as ‘gels’ (for gelatine). Glass and other plastic materials are also used.

Colour meter A tri-stimulus colour meter contains three photo cells which are filtered to detect the primary values of blue, green and red light. The incident light level can be derived from the output of the green photo cell as this relates to the photopic curve. To obtain the colour temperature of a source, meters of this type will compute a point on the spectrum locus from an analysis of the red, blue and green receptors.

Colour rendering index (Ra) The evaluation of the effect of a light source on a set of coloured test pieces representing portions of the visible spectrum. The higher the Index towards its maximum of ‘100’ the better the colour reproduction. Sources in general require an Index greater than 90 to prevent noticeable colour distortion.

Colour scroller A device fitted as an add-on extra to a luminaire to provide a colour changing system. Usually consists of around 16 colours glued together and activated by a motor in linear motion and controlled by a digital input signal.

Colour temperature A method of specifying the colour of a source which emits light in a continuous spectrum. Expressed in Kelvin units, the range used in media lighting is from 2600 K (white lights with a high red content) to 6000 K (white light with a high blue content). Note: Cannot be used with discharge sources, although sometimes used as a guide to approximation of colour (see Correlated Colour Temperature).

Colour wheel A circular mechanism holding several different colours mounted in front of a luminaire which can be rotated by hand or by a motor drive.

Combo stand A junior stand with a 1/8 inch receptacle used to hold reflector boards and larger lights.

Complementary colours A pair of colours in the additive colour mixing system which combine to make white light.

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.

Condor A vehicle with a telescoping boom arm used as a platform to position lights 30–120 ft in the air.

Console Name for a control desk (derived from organ console).

Contactor An electrical switch used within an electrical system to control the on/off state of the supply. Usually operated by an electromagnetic coil.

Continuity (Electrical) The unbroken flow of electricity through various conductors.

Continuity tester A device that runs a small amount of voltage through a conductor and lights a small bulb or makes a sound if the conductor is continuous.

Contrast range This is the ratio of the brightness between the lightest and darkest areas in a subject. In a video system, it is the range between the maximum signal which can be satisfactorily handled without distortion and the acceptable electronic noise level of the system.

Contrast ratio The ratio of the intensity of the key light plus the fill light to the intensity of the fill light alone.

Cookie See Cucaloris.

Cosine law The equation which allows the calculation of illumination on a surface which is at an angle to the incident light.

Counterweight system Mechanical system for flying scenery in which the weight of the pieces of scenery is balanced by adjustable weights in a cradle running up and down in guides in a frame normally at the side of the stage. The system is also used for lighting bars.

Cove (Coving) Portable scenery placed on floor with a curved section to allow a visual smooth transition between the floor and cycloramas. Main purpose in TV is to hide groundrow cyc units. The film industry usually provide deeper coving constructed on set by the plasterers and immediately adjacent to the vertical surface.

Crank-up stand A heavy duty stand provided with gears and a cranked lever to raise and lower heavy luminaires.

Cribbing (USA) Blocks of wood used to level camera tracks, lighting stands and props.

Croney cone A cone-shaped attachment fitted with diffusion that fits on the front of a light to soften and control the beam.

Cross barrel Used between barrels to allow accurate positioning of luminaires.

Crossfade A gradual change in the lighting where one lighting set-up completely replaces another. Obviously, only one crossfade can occur at a time (see Move fade).

Crosslighting Illumination from two luminaires at approximately 180° to each other on opposite sides of the subject. They are generally hard sources.

Crowder hanger A fixture mount that fastens to the top of a set wall and provides two spigot holders (studs).

CTB gel A blue gel that corrects a tungsten source to daylight.

CTO gel An orange gel that corrects a daylight source to tungsten.

Cube tap A device that allows three Edison plugs to plug into one Edison socket.

Cucaloris A wooden cut-out pattern placed in front of a light to create a pattern.

Cue A signal, which may be written, verbal or by action, that causes motivation of artists or technical staff. Also refers to changes in the lighting set-up.

Cue light (1) A flashing or rotating light positioned outside the studio/set to warn people when a film take is happening. In TV, during rehearsals, blue lights indicate activity and red lights indicate transmission or recording conditions. (2) To activate the performer at a specified moment.

Cue number The reference number given to control system memories which contain the lighting set-up information.

Cup blocks Wooden blocks (5/2 in. square) with concave indentations. They are usually used under the wheels of lighting stands to prevent them rolling away.

Current The rate of flow of electricity measured in amperes.

where I = current in amperes, V = applied voltage and R = resistance.

With a.c., resistance is replaced by impedance (Z) or reactance (X_L X_C).

Cutter A long, thin flag used to make cuts in the light.

Cyclorama A backing, mounted in the studio, to provide a continuous surface and an illusion of infinity.

Cyclorama (cyc) lights (cyc strip) A set of open-face luminaires used to light a cyclorama. The lights are often wired from two, three, or four separate circuits to provide individual control of different colours.

Daylight Light commonly considered to have a colour temperature of between 5500 K and 6000 K. Daylight-balanced film renders colours naturally when lit with 5600 K light.

Daylight filter (a) A blue filter used to change the colour of a light source from tungsten at 3200 K to approximately 5600 K. (b) A blue filter used on a camera to allow daylight balanced film stock to be used with tungsten lighting.

DC See Direct current (also d.c.).

Dedolight A small, special light fixture with a wide range of beam angle adjustment.

Delta-connected system A system that provides a three-phase supply where the coils are connected to form the Greek letter delta (Δ).

Depth of field The depth of the scene that will be in focus on the screen. Depth of field varies with the camera's aperture, focal length, and distance from the subject and the film format.

Deuce A 2 kW Fresnel.

Deuce board A fused AC/DC distribution box having two high-amperage contactors that can be controlled from remote switches.

Devitrification The process which causes a change from a ‘glassy’ state to a crystalline state.

Dichroic filter A filter which reflects chosen wavelengths and transmits the remainder. Usually for colour correction. Are used in moving light sources for colour mixing.

Diffuser Sheets of frosted plastic or spun glass fibre used to soften the shadows produced by the light beam.

Dimmer An electronic device used to reduce current flow to a lamp and therefore allow its light intensity to be adjusted.

Dimmer curve A graph which shows the light output or voltage output of a dimmer against the channel control setting.

Dimmer room The area which has been allocated for the equipment racks which contain the dimmers and associated equipment.

Dinkie A small Fresnel luminaire which nowadays has been largely superseded by Dedolights which give a much higher light output.

Dipless crossfade When channels with the same level in different lighting set-ups do not vary in intensity during a crossfade.

Direct current (d.c.) Current that does not alternate in polarity.

Director of photography (DP) The person in charge of the lighting and camera departments. The DP has direct creative control of the image.

Discharge sources Light produced by the passage of electricity, through a gas, across two electrodes enclosed in a quartz envelope e.g. Xenon, CSI, HMI, MSR lamps (see/Arc).

Discontinuous spectrum A light source with a discontinuous spectrum, such as a standard fluorescent bulb, that does not emit light evenly across the color spectrum, but instead has spikes at particular wavelengths and emits little or no light at others, resulting in poor colour rendering.

Distribution box An electrical box with circuit protection used to change cable and connector sizing and provide assorted outlets.

DMX Multiplex protocol for transmitting digital information from control consoles to dimmers and automated luminaires. DMX512 is the most used and when the system requires more than 512 control circuits, further DMX512s have to be used.

Dog collar A short length of aircraft cable used to secure lights hung above the set. The collar is fitted with a loop at one end and a clip or karabiner at the other.

Dolly grip The grip in charge of laying dolly track and executing dolly moves and crane moves.

Dot A very small, circular flag, net, or silk used to alter only a small portion of the beam of light.

Double broad This is a twin lamp floodlight generally used on studio floors as a local filler.

Double purchase A suspension system used on counterweight bars which gears the movement of the counterweight bucket to half that of the bar itself (see Single purchase).

Doughnut effect The aberration in the centre of a luminaires’ projected beam associated with Plano-Convex lens systems, follow spots and open faced luminaires, caused by the positioning of the lamp within the optical system.

Douser (Dowser) A small metal flag used in follow spots to cut off the light beam without having to switch off the electrical supply to the source.

Down-fade The portion of a fade that involves only channels that are decreasing in level.

Downlighter Usually refers to small ceiling mounted luminaires in control areas.

Downstage The stage or studio area which is nearest the audience.

Dress a light To neaten up the light or cable.

Drop arm (Trombone) A device used to hang a luminaire lower than the normal suspension system permits. Allows the luminaires to be positioned at differing heights on lighting bars. Drop arms can be of fixed length, e.g. 0.5 m, 1.0 m, 1.5 m or variable in length where one tube slides inside another and holes are provided at 150 mm intervals to fix steel pins, thus providing a variety of heights.

Duck bill A vice grip with a baby stud on the handle and two 6 sq inch plates welded to the jaws. Used to mount foamcore and bead board on a C-stand.

Dummy load It is sometimes necessary to provide an electrical load to be able to test equipment. For example, when testing dimmers the load could be a resistance rather than a luminaire. Dummy loads are also used to balance electrical circuits for power distribution (see also Ghost load).

Duvetyne Thick, black cloth used to block the light beam.

Ears The metal brackets on the front of a luminaire that hold the barndoors and scrims (see Bracket).

Earth (Earth continuity conductor) A conductor bonded to earth, other than the neutral, to provide a safety connection for metal components which are not in the electrical circuit. It is accepted to be the point of zero potential.

Effects (a) Lighting to provide atmosphere. (b) Sequence of lighting, usually pre-programmed to give a visual effect (chasers etc.).

Effects projector A focusing luminaire used to project slides or shapes. The effects can also be motor driven.

Efficacy This is the efficiency of a light source in converting the electrical input power to light and is expressed in ‘lumens per watt’.

Efficiency This is a measure of the useful light output in lumens against the total lumens generated by the light source.

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

Electromagnetic spectrum Electromagnetic waves consist of radio waves, infrared, the visible portion of the spectrum, ultraviolet (UV), x-rays and gamma rays.

Electronic ballast A solid-state ballast. The term electronic ballast is synonymous with flicker-free low frequency square-wave ballasts for discharge sources such as the HMI, or high frequency units for fluorescent discharge sources (see Ballast, Square Wave).

Ellipsoidal spotlight (profile projector) A luminaire which uses an ellipsoidal reflector and a reasonable quality optical system to project shapes and patterns with a hard edge.

Elvis Gold lame stretched on a frame and used to bounce light.

Equipment grounding (USA) (Europe–Equipment earth) The grounding of conductive parts of equipment, such as the outer metal casing, via a green grounding wire (Europe –Green/yellow stripes).

Ethernet Data transmission system for computer networks; also used for inter-connection of lighting consoles, dimmers and VDUs in remote locations (see DMX).

Expendables Supplies, such as tape, that are used up during the course of a production.

Extension bar This is used to extend lighting barrels for accurate positioning of luminaires.

Extension cable Used where the luminaire cable is too short to reach the nearest source of power. Generally 3-core, although for high current applications may be several single core cables.

Eye light Used to create a twinkle in the eye of the subject.

F-number A set of numbers used to express the aperture of a lens which represents its light transmission. It is worked out by dividing the focal length of the lens by the diameter of the opening in the lens diaphragm. It is also colloquially known as the stop.

Fade A gradual change in light levels from one set of intensities to another.

Fade time The time between the start and end of a lighting change. Can vary between a few seconds and anything up to 60 minutes; occasionally the time may be over a longer period in theatrical productions.

Fader A control device for indirectly setting the current output of a dimmer and thus varying the light intensity. Originally were levers, but are often ‘wheels’ in modern lighting control systems.

Fall-off The diminishing intensity of light across the beam of a luminaire. Also, the reduction in light output over distance due to the inverse square law.

FAY An incandescent PAR lamp with dichroic coating that creates daylight-coloured light.

Feeder cable Large single-conductor cable or multi-core cable used to run power from the power source to distribution boxes on the set (see Extension cable, Distribution system).

Field angle Those points on the light output curve which are 10% of maximum output. The included angle between these two points is the field angle.

Filament The tungsten coil inside a lamp that glows when voltage is applied to it creating light.

Filler Light used to control shade areas. Usually a soft light but can be controlled hard light.

Film speed (a) A measure of the film's sensitivity to light expressed in numerical terms to give an ‘exposure index’ which is used in the ISO and ASA system on light meters. (b) The velocity of film passing through movie cameras or projectors and is measured in frames per second or in metres per minute.

Finger A very small rectangular flag, net or silk, used to control small portions of the light beam.

Five K A colloquial term for a 5 kW spotlight.

Fixture General term for a luminaire, light, or lantern.

Flag A sheet of metal or card mounted in front of a luminaire to give a relatively sharp cut off to the light beam. The cut off is dependent upon the distance from the luminaire and improves as the distance increases. Very effective with focused luminaires such as the Fresnel but when used with open faced luminaires often requires greater distances to achieve sharp cut off. Also black Duvetyne cloth stretched over a metal frame.

Flag box A wooden box in which flags, nets, and silks are stored.

FLB filter A filter used to remove the green hue of fluorescents.

Flex arm A small jointed arm used to hold fingers and dots.

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, thus avoiding problems with synchronisation of film shutters and TV field frequencies.

Flood By focusing a lamp close to a lens, the diameter of the light beam is enlarged and thus gives the widest field of illumination.

Floodlight A luminaire which has only a reflector to control the beam and has wide angle distribution (see Soft light and Cyclorama light).

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

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

Focal length The distance of the focal point from the lens is called the focal length of the lens.

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

Focus In optics, the adjustment to give a clearly defined image. Originally used in the lighting industry to indicate the process of ‘spotting’ or ‘flooding’ the light beam of a luminaire, but is now used to indicate the general setting of a luminaire on the stage or in a ‘pop’ rig.

Follow spot A narrow angle, focusing hard edged spotlight used to follow moving artists.

Foot candle An old unit, now superseded by ‘lux’, used to describe illumination which was measured in ‘lumens per square foot’.

Foot lambert The old unit for luminance (brightness) which has been replaced by the ‘nit’.

FPS Frames Per Second.

Frequency The number of cycles per second of a.c., measured in Hertz (Hz).

Fresnel lens A convex lens built with concentric steps to enable its thickness to be reduced.

Fresnel spotlight (colloq. Fresnel) Luminaires fitted with Fresnel lenses of varying sizes, the width of the beam can be changed by varying the spacing between the lens and the lamp/reflector assembly.

Fringing Chromatic aberration in simple lenses creating dispersed colour effects around the light beam, similar to the colours of a rainbow in appearance, blue being the most predominant of the colours.

Frost Translucent gel or plastic used to diffuse light sources.

Fuse A protective device for electrical circuits; originally a piece of special wire but nowadays nearly always a metal link contained in a ceramic cartridge.

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

Gaffer clamp/grip A clamp with two jaws fitted with rubber pads and equipped with a mounting spigot to temporarily attach fittings to scenery flats, suitable horizontal and vertical surfaces and lighting equipment e.g. lighting barrel (see Mafer clamp).

Gaffer tape Heavy, fabric-based tape that rips cleanly in the direction of the weave. It is used for securing cables and luminaires on the set.

Gamma A measure of the contrast in image reproduction. In TV overall gamma relates to the receiver screen luminance and the brightness of the original scene.

Gate The optical centre of a profile projector where the shutters are positioned and an iris or ‘gobo’ can be inserted.

Gator grip See Gaffer clamp/grip.

Gel See Colour media.

Generators A diesel powered unit used to generate power on location (also used in some film studios). They are sound baffled and provide either busbars or other feeder connectors. Also called genny.

GFI Ground Fault Interrupter.

Ghost load A load that is not used to light the set and is placed on a circuit to balance the various legs of power or to bring the load on a resistance-type dimmer up to its minimum operating wattage. Also called dummy load and phantom load.

Globe (USA) A lamp or bulb.

Gnats (Gnats whisker) Slang term used in the United Kingdom to describe a very small amount (American–Scosh).

Gobo A mask placed in the gate of a profile spot to shape the beam. It is a simple form of outline projection.

Gobo arm The arm which can be attached to a gobo head on a stand on which to mount gobos. Typical lengths of arm are 500mm and 1 m.

Gobo head The metal knuckle that attaches the gobo arm to a stand. The unit consists of two metal plates with grooves to hold various sizes of arms, e.g. 1/4 in, 3/8 in, 1/2 in and 5/8 in.

Grandmaster The device (wheel or fader) which has overall control of the output of a console.

Grey Scale Chart showing gradations from white to black.

Grid (1) (USA) A resistance unit used with a carbon arc light. (2) The structure of metal tubes suspended above the stage floor for hanging luminaires (see Lighting grid).

Grid clamp A clamp that attaches to standard lighting grid barrels (48 mm OD). Several varieties are available for either bottom fixing or side fixing to the bar together with various configurations for suspension.

Grid cloth A white nylon diffusion fabric with a grid-like weave. A similar filter material is also available.

Griffolyn Trade name for plastic material. Griffolyn sheets come in 6′ × 6′, 12′ × 12′ and 20′ × 20′ available in black/white, white/white and clear. They are used as a bounce for fill. Also called griff.

Grip A crew member responsible for the non-electrical aspects of lighting and rigging, and for the camera dolly and other camera platforms.

Grip clip A metal spring clamp resembling a large clothes peg and used to clamp various materials together, e.g. tensioning cloths across wooden battens.

Grip truck (USA) The lighting truck that houses the luminaires and grip equipment during location shooting. Will hold a considerable array of equipment, some of which is there ‘just in case’.

Ground Fault Interrupter (GFI) (USA) A special type of circuit protection. There are a number of different types of GFIs. One type compares the outgoing current of a circuit to the returning current. If it detects a difference in the two (indicating a ground fault), it trips a switch to disconnect the circuit. They are also called Ground Fault Circuit Interrupters (GFCI) (see also RCD).

Grounded wire (USA) The grounded, white, current-carrying wire (neutral) of an American a.c. circuit.

(Note: Do not confuse this term with the green grounding wire).

Grounding wire (USA) The green, equipment grounding wire of an a.c. circuit (see Earth).

Groundrow A lighting unit with multiple compartments, usually arranged in linear fashion, for lighting from the base of cyclorama. The units are provided as single, twin, three or four way. The three and four way units are used for colour mixing fitted with red, blue and green filters, the fourth compartment can be fitted with ‘clear’ to dilute the colour output. A cove normally hides them from view (see Cyc lighting, Cove).

HMI (also CID and MSR) Discharge lamps which have a daylight colour balance (5600 K).

Half scrim A semi-circular scrim used to attenuate part of the light beam (see Scrim).

Halogen cycle The cycle by which halogen in a lamp returns tungsten deposits back to the filament thereby preventing blackening of the inner lamp wall.

Hard glass halogen lamp A tungsten halogen lamp with an envelope of borosilicate glass.

Hard light A luminaire that produces well-defined shadows, normally a spotlight.

Harmonic distortion When a wave shape departs from being purely sinusoidal with a sharp rise or fall in its characteristic, such as a square wave or the chopped wave form produced from thyristor dimmers, it will contain harmonics of the original frequency.

Head A luminaire (USA–light fixture).

Head cable The power and control multi-core cable which connects the ballast to a discharge source luminaire. The plugs and sockets used vary in size and pin configuration according to the various manufacturers and the power requirements.

Heat filter A filter which removes infrared from the light beam to reduce heat from the source of illumination.

Hertz (Hz) The unit of frequency which is measured in cycles per second. Other units are kilohertz (kHz) and megahertz (MHz).

Hi boy (USA) An extra tall stand for mounting luminaires.

High key Describes a scene containing mainly light tones well illuminated without large areas of strong shadow.

High leg (USA) The 208-V leg of a delta-connected three-phase system (see Delta connected system).

High roller (USA) An extra tall rolling stand, often used to fly an overhead frame.

Highest takes precedence (HTP) On a lighting control system, where the highest setting will win, when two or more pre-set levels are simultaneously selected for that channel, e.g. if ‘7’ then ‘5’ is selected for a particular channel, ‘7’ will win (see also Latest Takes Precedence).

Hoist Old term used to describe either manual or motorised lifting equipment (see Winch).

Hook clamp A clamp used for suspending luminaires from lighting bars (see C-clamp).

Hot spot (1) Usually produced by luminaire optical systems not using Fresnel lenses. The beam centre of PCs and some effects units are prone to hot spots unless the lamp is carefully focused or the manufacturer takes steps to prevent problems in practice. (2) A shiny spot or glare reflection that is distracting to the eye.

House lights A lighting system permanently installed to either illuminate an audience area or provide worklights in studios.

Housing The metal casing that encloses the lamp, reflector and optical system of a luminaire.

Hue The quality by which one colour is distinguished from another as a result of their wavelengths. It does not take into account the brightness or intensity of the colour.

Illumination The luminous flux falling on unit area of a surface. The unit of illumination is the lux (1 lumen/m²) and it is the measure of the quantity of incident light.

Impedance (z) A measure, in ohms, of the opposition to current flow in an a.c. circuit. Includes resistance and reactance.

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

Incident light See Lux.

Incident light meter A light meter that reads the light falling onto the subject.

Independent Channels in a control system which only respond to one master and are ‘independent’ of the rest of the console.

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

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

Inky A 100 W Fresnel luminaire manufactured by Mole Richardson Co.

Instrument (USA) Name used for a lighting fixture (luminaire).

Internal reflector An integral reflector formed on the inner rear surface of the envelope of a lamp and is usually parabolic or elliptic in shape.

Inverse square law The equation which is used to calculate the illumination at a given distance from a source of light.

Iris A series of adjustable metal plates arranged to give a variable circular aperture. Used in lighting projectors to alter the size of the light beam.

J-box (USA) A junction box fitted with Socapex connectors and used to connect an extension cable to the existing head cable of a discharge luminaire.

Jockey boxes (USA) Metal storage containers on the underside of a truck. Jockey boxes usually store sandbags, cable, and so on.

Junior stand (USA) A stand with a 1/8 inch spigot holder.

Junior stud (USA) A 1/8 inch spigot used for larger items of lighting equipment.

Junior (USA) A 2 kW Fresnel spotlight.

Kelvin The SI unit of thermodynamic temperature. It uses the same size of degree as the Celsius scale. (Zero K =-273°C).

Key light The principal modelling light, usually a spotlight.

Kicker Generally a hard light source used to provide obvious highlights.

Kilowatt Electrical power term for 1000 W.

KVA (Kilovolt Amperes) Whereas wattage is a measure of power consumed in a circuit, KVA gives the total of voltage applied and current flowing. With unity power factor, 1 KVA = 1kW.

LD Abbreviation for Lighting Designer or Lighting Director.

Lamp A glass or quartz envelope which contains filaments or electrodes. The term lamp is often used to describe a luminaire, which is to be avoided as it can cause confusion (colloq. terms include globe, bubble, source).

Lantern See Luminaire.

Latest takes precedence (LTP) On a lighting control system, where the last selected level for a particular channel will win, e.g. if ‘7’ then ‘5’ is selected for a particular channel, ‘5’ will win (see also Highest Takes Precedence).

Leko A slang term used in America to describe ellipsoidal spotlights.

Life Usually refers to the manufacturers’ rates life in hours of a lamp at its normal voltage and is based on the average life of a number of lamps which have been tested.

Light meter A device for measuring reflected or incident light. Many modern meters also measure the colour of the source (see Luminance meter and Colour meter).

Lighting balance See Balance.

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

Lighting batten A barrel assembly with integral power feeders for luminaires.

Lighting control console A unit which contains the controls for adjusting the channel levels and thus the dimmer outputs, ‘group channel’ control, memory control, playback system and special effects.

Lighting Designer (Director) The person who creates and implements the lighting design for a production.

Lighting grid In film and TV a structure mounted at high level above the operational area, usually made from steel or aluminium or a combination of the two, for the purposes of suspending luminaires and ancillary lighting equipment.

Lighting plot The instructions and drawings of the various lighting set-ups for a production, used by the LD and electricians. (Sometimes simply known as the Plot)

Lighting ratio The ratio of the light level on the keylight side to the light level on the filled side.

Limbo Describes a state of lighting where the background details are suppressed. In TV this is usually created by ‘blackness’ whereas the film industry tends to use a white background.

Linnebach projector A lighting unit, basically a box without a lens, which contains a small point source of illumination to project soft diffused images of cut-outs or glass slides.

Louvres Thin black metallic strips located on a luminaire to reduce spill light (see Eggcrates). When fitted in front of a luminaire may also be adjustable at various angles to provide dimming without colour change (see also Shutters).

Low boy (USA) A very short stand (see Turtle).

Low key Describes a scene containing mostly dark tones with large areas of shadow and is often used to create a dramatic mood.

Lug A very heavy-duty connector for attaching feeder cables to busbars.

Lumen The lumen is the unit of ‘luminous flux’ and is defined as the amount of light which falls on 1 m² of a surface at a constant distance of 1 m from a source of one candela.

Lumens per watt The light output in lumens produced by a source for each watt of electrical power supplied to the source.

Luminaire A general term for a complete lighting unit. It includes the housing, the reflector, lens and lamps. (Colloq: light, lantern, fixture, unit, instrument, fitting).

Luminance The measure of brightness of a surface, it is measured in ‘nits’. The old unit was the ‘foot lambert’.

Luminance meter Luminance meters are used for the measurement of a light source or surface brightness. A normal luminance meter will be calibrated in candela/m² and alternatively foot lamberts (see Spot meter).

Luminous intensity A measure of the energy from a light source emitted in a particular direction. It is measured in candelas.

Lux The unit of illuminance (illumination). It is the unit of measurement for the incident light arriving at a surface. The old measuring system used foot-candles. (One foot-candle equals 10.76 lux).

Mcb Miniature circuit breaker.

Mccb Moulded case circuit breaker.

MR-16 A small projector lamp with a self contained reflector.

MT-2 A colour-correction gel used on carbon arc lights with a Y-1 gel to correct the colour temperature of a white flame arc to 3200 K.

MacBeth A blue glass filter used on some open faced luminaires which converts tungsten sources to daylight.

Mafer clamp All purpose grip clamp which can utilise different mounting attachments.

Master/Group master Usually refers to a lighting control system fader which overrides by electrical means a group of individual faders.

Matte An opaque shape used in front of a camera lens.

Matte process A shape derived on film from subjects in front of a dense, coloured background (usually blue). This image is subsequently used as a matte in the optical printing process to allow two images to be combined. With the advent of computers, the image manipulation is carried out electronically.

Matth pole (USA) A pole that braces against two opposite walls to provide a structure from which to hang a lightweight luminaire. Poles originally manufactured by Matthews as grip equipment.

Maxibrute A large rectangular luminaire fitted with either nine 1000 W PARs or twenty-four 1000 W PARs, capable of being switched in segments to provide variable light output. Often used with Full Blue filter to provide fill light when shooting in daylight on location.

Maximum overall length (MOL) The overall physical length of a lamp including all electrical contacts.

Meat axe (USA) An arm mounted to the pipe of a catwalk or to the basket of a boom platform that provides a method of placing a flag in front of a luminaire.

Meltric (USA) A five-pin, heavy-duty connector used in some power distribution systems.

Memory The term used to denote electronically recorded information which contains the lighting set-ups.

Memory effect Usually found in Nickel-Cadmium (Ni-Cad) batteries. Caused by insufficient discharge, where the battery upon recharge will only accept a limited level. In practice, shows as poor battery life.

Mickey (USA) A 1 kW open-face luminaire manufactured by Mole Richardson.

Midget (USA) A 200 W wide-beam Fresnel luminaire manufactured by Mole Richardson.

MIDI (Musical Instrument Digital Interface) A communication protocol used to link control consoles for both lighting and automated luminaire systems.

Mini A 200 W Fresnel luminaire manufactured by Mole Richardson, or a miniature soft light manufactured by LTM.

Minibrute A rectangular luminaire fitted with either six 650W PARs or nine 650W PARs, capable of being switched in segments to provide variable light output. Often used with Full Blue filter to provide fill light when shooting in daylight on location.

Minus green gel A magenta gel used to take the green out of fluorescent light.

Mired (MIcro REciprocal Degrees) A filter causes a constant shift in the reciprocal value of the colour temperature of the source, and to acheive a more manageable number the reciprocal value is multiplied by 1 million.

Mirror ball A motor driven ball with its surface covered in small mirrors. When rotated, with spotlights shining to it, it produces moving points of light.

Modelling light The terms is used to describe any luminaire, generally a hard source, that reveals the depth, shade and texture of subjects.

MoleFay (USA) A lighting unit consisting of a number of 650 W FAY lamps manufactured by Mole Richardson.

Monopole A telescopic suspension unit used to suspend one luminaire. Their length is adjusted by internal wire ropes on winding drums at the top of the unit.

Motorised luminaires Motorised effects luminaires which provide a multiplicity of projected moving images and colours. Units tend to be of two types –the light beam is modulated by a moving mirror with the luminaire stationary, or, the luminaire moves to create motion.

Move fade A fade from one lighting set-up to another where only those channels with a new intensity change; the other channels remaining static. Several ‘Move’ fades can occur at the same time (see Crossfade).

MSR Single ended discharge lamps made by Philips (see HMI).

Multiplex Control signals passed in serial digital format down a pair of screened wires. The most normal form is DMX512 and is used to control dimmers and motorised luminaires.

Munsell values The Munsell system enables three qualities to be quantified and these are:

1. hue–describes the basic colour such as red or blue;
2. value (or brightness)–refers to how light or dark the colour appears (it is a measure of the amount of reflected light); and
3. chroma (or saturation)–refers to the intensity of colour; as a colour moves away from white it becomes more and more saturated.

ND See Neutral-density.

NEC (USA) National Electrical Code –the American version of the UK Electrical Regulations.

Nanometre (nm) A unit of metric measurement equal to one billionth of a metre, which is used to measure light wavelengths.

Net A black honeycomb netting material sewn onto a rod frame that is used to reduce the intensity of part or all of a light's beam.

Neutral density filter A filter which attenuates the light passing through it without affecting the colour of that light.

Ni-cad batteries (Nickel-Cadmium) Ni-cad have the advantage of being easy to handle, robust and accept very fast charges using specialised equipment.

Nine-light A luminaire comprising nine PAR lamps used on exterior lighting.

Nit The unit of luminance, which is one candela per square metre of surface radiation. It is therefore the measure of the brightness of a surface (see Foot lambent).

Non-dim Describes the circuit which replaces the normal dimmer function, where the circuit is switched ‘on’ or ‘off’ only, either by a switch or relay system.

Nooklight A small lightweight open-face luminaire using a double-ended lamp and a V-shaped reflector.

Objective lens See Projection lens.

Offset A piece of grip hardware used to hang a luminaire out to the side of a floor stand.

Off-stage Areas that are out of the eyeline of an audience.

Ohm (Q) The unit of electrical resistance equal to the resistance through which 1 V will force 1 A.

On-stage In view of the audience.

Opal A popular, thin diffusion.

Opaque Absorbance of electro-magnetic radiation at specific wavelengths, generally refers to the fact that light is not transmitted.

Open faced luminaire Describes luminaires with no lens system, such as the ‘Redhead’ and ‘Blonde’ (see Focusing reflector light).

Overcurrent device A circuit breaker or fuse.

Overhead set A large frame with one of several types of material stretched across it, including a solid, single net, double net, silk, or griffolyn.

Pan Term describing the horizontal movement, about a point, of luminaires or equipment.

Pancake The thinnest of the apple box range used for mounting equipment at a very low level.

Pantograph A mechanical cross-armed device for varying the height of luminaires or other fittings. It is generally spring balanced but can be operated by a motor or manually driven gear system.

PAR A lamp with an integral parabolic reflector, similar to a car headlight. PAR lamps are available in a wide variety of physical sizes with differing front lenses and power outputs.

Parabolic reflector A reflector shaped like a parabola, giving it a focal point from which the majority of the light rays will be reflected outward in a parallel beam.

Parallel circuit Connection of two or more devices or loads so that the current flowing through each one follows a separate path (see Series circuit).

Parcan A simple luminaire, basically a metal tube, with a PAR lamp mounted in it. The type of lamp determines the beam spread.

Patching A term describing the connections made between channels on lighting consoles and dimming systems. (Usually accomplished by software –known as Soft patching).

Patch panel A system rather like an old telephone operators’ interconnection system (switchboard) to connect low voltage circuits or high voltage circuits. (Known as Hard patching).

PCB Printed circuit board. Individual boards are supplied with all components mounted on them and will be produced for a specific purpose e.g. a pcb for dimmer control circuits.

Peppers (USA) A line of relatively compact tungsten luminaires manufactured by LTM in sizes of 100 W, 200 W, 300 W, 420 W, 500 W, 660 W, 1000 W, and2kW.

Phantom load See Ghost load.

Phase (1) An energised single conductor. (2) The positioning of an a.c. cycle in time, relative to the other two phases. Most electrical services are either single phase or three phase (see Alternating current, Wye connected system).

Photoflood A lamp that has a colour temperature of 3400 K. These lamps, which are similar in size to household lamps, have over driven filaments to achieve the high colour temperature. Hence they have very short operating lives (see Filament).

Photopic curve This gives the standard sensitivity for the eye for wavelengths from 380 nm to 760 nm. The peak sensitivity is at 555 nm, whereas the sensitivity at 400 nm is about 1/1000th of the highest level.

Piano board (USA) Originally, a portable dimmer switchboard or road board. This term has come to be used for many types of portable dimmer switchboards.

Pigeon plate A small metal plate attached, generally to apple boxes, for supporting small luminaires.

Pin matrix A method of coupling control channels into groups by the insertion of special pins into a ‘x’ and ‘y’ matrix, where the ‘x’ axis may represent channels and the ‘y’ represent groups.

Pipe clamp (USA) See Hook clamp.

Pixel A picture element which is the smallest element of a CCD array. The definition is governed by the number of ‘pixels per area’, the higher the amount the better the resolution.

Plano-convex lens A lens which has one flat side and one convex side.

Plano-convex spotlight (PC Spot) A luminaire that gives a reasonably even beam with a very sharp edge. The PC uses a Plano-Convex lens and circular reflector and is similar to the Fresnel in construction and performance.

Plate dimmer (USA) A resistance-type dimmer commonly used with d.c. circuits.

Playback That part of a lighting control system where the lighting memories and/or other lighting states are combined and controlled by output master faders or switches.

Plugging box (USA) A distribution box. May also refer more generally to any outlet box.

Plus green gel A filter used to add green to the light output of normal lamps to match their colour to that of fluorescent lamps.

Polariser A polarising filter removes some of the planes of polarisation and allows the subject to be seen clearly.

Polarity The orientation of the positive and negative wires of a d.c. circuit or the phase and neutral wires of a.c. circuits.

Polecat Lighting support system consisting of sprung metal tubes capable of extension onto which luminaires can be mounted. Used between two surfaces, floor and ceiling or two walls. Also called pogo stick and Matth pole.

Pole operation (Colloq. Pole Op) The control of electrical and mechanical functions on luminaires and suspension equipment by means of a long metal pole. The end of the pole is fitted with either a hook or loop.

Power assisted systems Suspension equipment under the direct control of an operator, e.g. winch control motor systems.

Power factor In a.c., the ratio of the actual or effective power in watts to the apparent power in volt-amperes, expressed as a percentage.

Power The total amount of work, measured in watts. One watt is equal to 1 J/second; one horsepower is equivalent to 746 W (see Ampere, Volt).

Practical lamp A luminaire or any fixture that is shown in a scene. e.g. table lamp, that can be effectively switched on and off by an actor.

Prefocus Denotes special lamp caps so that the filament lines up precisely to the optics of a luminaire.

Prelight or prerig To rig and set the lights in advance, as close to the intended lighting scheme as possible.

Pre-set A group of faders on a manual desk which are connected to the dimmers and controlled by a ‘master fader’.

Primary colours The primary additive colours are red, green and blue. The primary sub-tractive colours are cyan, magenta and yellow (see Additive colour mixing, Subtractive colour mixing).

Prime fixture (USA) A focusing, open faced luminaire such as a Redhead or Blonde.

Priscilla (USA) A silver lame stretched on a frame and used to bounce light.

Profile spot See Ellipsoidal spotlight.

Projection lens A lens specially designed to project slides or shapes onto a surface with considerable enlargement of the slide or original material (see Objective lens).

Pup A colloquial term for a 1 kW spotlight.

Purkinje effect The change from ‘cone’ vision during daylight to ‘rod’ vision at night.

Putty knife (USA) Decorators’ putty knife which has a 5/8 inch spigot fixed to its handle. The knife can be inserted into the slot of a door frame or windowsill and the spigot will support a small luminaire.

Quartz Crystalline silica which is glass like and used to make envelopes for lamps. It is generally transparent to ultra violet radiation.

RCD (Residual Current Device) Formerly known as an earth leakage circuit breaker.

RMS Abbreviation of Root-Mean-Square. The rms value of the current is a measure of its effectiveness in producing the same heating effect in a resistance as a direct current.

Radiant flux The amount of light energy that is given off by an object each second and is measured in ‘joules per second’ (the physical unit of measurement is known as a watt).

Rag (USA) The cloth part of an overhead set.

Rain tent A tent to cover luminaires and electrical equipment in case of precipitation.

Reactance (X) A measure, in ohms, of the opposition to a.c. due to capacitance (X_C) or inductance (X_L).

Receptacle An in line female electrical connector or a socket mounted on a distribution box.

Record The action of recording (memorising) a lighting set-up on a control system.

Rectifier An electrical unit that converts a.c. to d.c.

Redhead A 800 W open faced luminaire.

Reflectance (reflection factor) The ratio of the reflected light to the incident light falling on a surface, measured in lumens.

Reflector The component in luminaires that focuses the light rays towards the lens. In a Fresnel it will be a spherical reflector whereas PAR lamps use parabolic reflectors. Effects projectors (Leko) generally use ellipsoidal reflectors.

Reflector boards Silver-covered boards typically used to bounce light, usually sunlight. Also called shinyboards.

Remainder dim A lighting console instruction which maintains the levels of selected channels, while forcing all other active channels to zero.

Rembrandt lighting Lighting style emphasising the subject by strong modelling of light and shadow. This style is reminiscent of Rembrandt's paintings, hence its name.

Remote A method of controlling the lighting from a position away from the main control system.

Resistance (Ω) A measure, in ohms, of the opposition to current flow in a conductor or device. In d.c., volts/amperes = ohms. For a.c., see impedance.

Rheostat A resistance dimmer to control the voltage applied to a lamp. Also used to control the speed of motors.

Rig (1) Any assembly designed to support luminaires, cabling, dimmers and effects units etc. (2) To set up scenery equipment and lighting.

Riggers control A remote portable hand held control unit for controlling either luminaires or winch systems.

Rigging (USA) Collective term for suspension equipment.

Rigging bible (USA) A set of circuit diagrams showing the power layout of a studio's sound stages.

Rigging gaffer (USA) The gaffer in charge of designing and installing the cabling and electrical distribution for a large set.

Rim light A backlight that makes a rim around the head and shoulders of the subject from the perspective of the camera, enhancing the separation from the background.

Rise time In an electronic circuit the time taken for the current to rise from 10% of its amplitude to 90% of maximum. The rate of change of current influences the amount of generated voltage in an inductive circuit. The rate of change of current in a falling waveform also affects the generated voltage.

Riser (1) An extension tube to add height to a lighting stand. (2) A wooden platform used to raise the set, luminaires or the camera.

Risers The flat surfaces on the Fresnel lens rings that form the division between segments.

Ritter fan (USA) A large effects fan used to blow snow and rain; also to give the appearance of wind or speed.

SCR A Silicon Controlled Rectifier. A solid state current switching device, used in dimmers for lighting systems. It comes from the thyristor family.

SPD Spectral Power Distribution.

SWL The safe working load of a piece of lifting equipment usually quoted in lbs or kg.

Safety (USA) A safety bond, wire, chain or rope looped around the yoke of a luminaire to prevent it from falling should it come loose from its fixing point.

Safety bond (also Safety Chain) A short length of wire rope or chain formed into a loop around a suspension point, to act as a secondary means of suspension in the event of failure of the primary system. With wire rope safety bonds, regulations require that the bond should not allow a fall of more than 300mm.

Sandbag A sand-filled bag used to stabilise stands and equipment by adding dead weight or counterweight.

Saturated rig A lighting installation where luminaires are installed in sufficient numbers to cover the total acting area without rigging and de-rigging.

Saturation A term used to describe the density of a colour between the pure colour concerned and white, i.e. a deep red or pink.

Scaffold platforms (Parallels –USA) Scaffold platforms, as used by builders, are quite frequently used as mobile lighting towers. They are quick and easy to assemble as they come in preformed sections, and if used properly can be safe.

Scene machine (USA) A lighting unit that projects an image on a screen, usually from the back. The image can be made to move by scrolling through the machine or to rotate by using adjustable-speed motors. Scene machines are often used to create moving clouds across the cyclorama in theatrical productions. Known as back projection unit in the United Kingdom.

Scissor clamp A device that provides a means of hanging luminaires from a false ceiling such as those found in many modern commercial buildings.

Scissor lift A self-propelled, battery powered hydraulic lift. With a lifting capacity of between 300 kg and 600 kg and capable of heights between 6 m and 12 m. Normally used by the building industry, they have been adapted for use as mobile lighting and camera platforms.

Scissors arc A special carbon arc device used to create a lightning effect. The carbons are touched together by a flexible drive device which is actuated in a similar manner to grass shears. This has been superseded by lightning effects generally produced by xenon tubes driven from electronic generators.

Scoop A simple elliptical shaped floodlight usually fitted with a large GLS lamp giving a soft light output. Due to the type of lamp used, is prone to ‘lamp sing’ when used with thyristor dimmers.

Scrim A scrim usually consists of wire mesh placed in front of a luminaire. The size of holes and thickness of wire determine the amount of light that will pass through the mesh.

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

Sealed beam A lamp with an integral reflector and lens (see PAR).

Senior (USA) A 5 kW incandescent Fresnel luminaire manufactured by Mole Richardson Co.

Series circuit Connection of two or more devices or loads in tandem so that the current flowing through one also flows through all the others (see Parallel circuit).

Service (Electrical service) This term refers to the types of circuits installed, for example, single-phase, three-phase.

Service entrance The main switchboard into which the power lines running to a building terminate.

Set Scenery constructed for lighting and the shooting of scenes for film and TV.

Shock The nervous sensation imparted to a body by the passage of an electric current. The severity of shock is dependent upon the current flowing, the path through the body and the time for which the current flows (see RCDs).

Short circuit Unwanted current flow caused by low impedance between conductors. Usually controlled by fuses or circuit breakers.

Show card Thick card stock, usually white on one side and black on the other, used to bounce light.

Shutter Pieces of thin black metal, of varying shapes, used within a luminaire to block light. They are used to shape the light beam projected from effects spotlights and follow spots.

Shutters Venetian blind type metal slats mounted in front of a luminaire as a blackout device or dimmer (see Louvres).

Silk Originally was voile, a type of very fine silk netting used as the veil around ladies’ hats. It is used to soften and cut the intensity of light and is available in several sizes, from very small dots and fingers to very large 20 × 20 ft overheads. Today, other materials with similar properties are used.

Silver bullet (USA) A 12 kW or 18 kW discharge luminaire manufactured by Cinemills Corp.

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 (see Double purchase).

Sister lugs (USA) See Lug.

Sky-cloth Scenery used to convey the impression of an open sky (see Cyclorama).

Skypan A very shallow scoop used in the film industry, which is rather like a metal dustbin lid with a bare lamp in the middle. Used for general fill, using either 2 kW, 5 kW, or 10 kW lamps.

Snoot A conical metal tube fitted to the front of the luminaire to enable a reduction in beam size.

Snot tape Sticky adhesive substance used to attach gel to a frame.

Socapex Multi-wire cable connector used (1) on discharge source head feeder cables and (2) on multi-core cable for dimmer circuits.

Soft box A device used to create very soft, diffuse light.

Soft patch Electronic system on a lighting control desk to allocate dimmers to control channels.

Softlight A luminaire designed to produce virtually shadowless light and is generally used to control contrast. The larger the source size the softer the shadow so the design of a softlight is always a compromise between the largest source that can be achieved and the size that can be tolerated in practice.

Solid A black ‘rag’ stretched on a frame and used to cut light.

Sound stage An enclosed area with smooth level floors and a high roof with lighting grid. It is sound proofed by having thick walls and special door arrangements.

Spacelight A large cylinder consisting of a diffuser with an array of lamps inside to give soft ambient illumination.

Sparks A nickname for set lighting technician.

Specular Describes a mirror like surface. Highly reflective.

Spider box (USA) An in line connection box fitted with short busbars enabling feeder cables with lug terminations to be joined in series.

Spigot The male member attached to a yoke used for the suspension of the luminaire and also for insertion into a floor stand. Smaller luminaires used 5/8-in spigots and larger ones use a 1 1/8 in. Colloq. ‘spud’ (see Stud).

Spill light Extraneous uncontrolled light from a luminaire. May come from the rings on a Fresnel lens or escape from the aperture between the barndoors and colour frames.

Spot To focus a luminaire by moving the lamp and/or reflector away from the lens, giving a narrow beam (see Flood).

Spot meter A type of reflected meter having a very narrow angle of acceptance (1° to 20°) used to determine the light value of a specific point of interest.

Spotlight A luminaire with a focusing system which allows concentration of the light beam, thus giving greater operational control of the light level.

Square law Light is governed by a formula called the Inverse Square Law which states that the light falls off as the distance is squared.

Square wave Alternating current with a square wave shape rapidly switched between positive and negative half cycles. In lighting, they are generated by an electronic ballast which enables discharge sources to be flicker-free.

Squeezer (USA) A dimmer.

Stage box (USA) A distribution box with sockets that accept a male connectors. Stage boxes are normally referred to by the number of sockets they have: one-hole, two-hole, four-hole, or six-hole boxes.

Stage extension (USA) A high current extension cable. It has a male connector at one end and a single or twin at the other.

Stage left/right The performers left and right as they face the audience.

Staging area The area on the sound stage or location selected as a temporary place to keep the lighting equipment and technical equipment trolleys.

Stand A telescopic floor mounted tripod device which provides a means of adjusting the height of luminaires above floor level. Can be manual lift, or by a geared wind-up system.

Stick-up (USA) An extremely small, lightweight luminaire that can be taped to the wall.

Stinger (USA) An extension cable usually fitted with Edison plugs and sockets.

Stirrup Stirrup shaped receptacle, generally fitted at the base of extension arms and pantographs, allowing the attachment of luminaires by C clamps.

Stop An f-stop or a t-stop (see F-number).

Strain relief A rope tied to a cable to take the weight and reduce strain on electrical connectors.

Streaks and Tips (Trade name) (USA) Cans of hair spray that are often handy for darkening reflective surfaces.

Strike (1) To dismantle a set or to take down and put away a piece of equipment. (2) When referring to an arc or a discharge source, to strike the light means turn it on.

Strobe light A light that creates short, bright, regular flashes of light at an adjustable speed. Speeds around 17 Hz are highly dangerous and can induce epileptic fits.

Stud Term for piece of cylindrical metal which is attached to the yoke (bail) and used for mounting luminaires onto stands, etc (see Spigot).

Studio area The total floor area contained within the walls of a studio which may not always be used as the acting area, due to fire lanes, etc.

Sub-master A controller (usually a linear slider) on a dimmer board that allows manual control of groups, effects, cues, or channels.

Subtractive colour mixing The removal of light of various wavelengths, by filtering or reflection, e.g. a magenta filter subtracts the green from the light path, whereas the pigment of yellow paint reflects the red and green components of the incident light but absorbs (subtracts) the blue. To change the colour of a light source for effect or colour correction, some form of coloured filter will be placed in the light path.

Suicide pin (USA) An adapter with two male ends.

Sun gun The term used for any small battery powered luminaire, originally a small tungsten source, now used to describe any tungsten or discharge source.

Swing (USA) A crew member who performs the tasks of both grip and electrician, as needed.

System grounding (USA) (Neutral) The grounding (earthing) of the electrical system by the neutral wire to the star point of the main power transformer and also to earth.

T-bone (USA) A metal T-shaped base with a junior receptacle, used to place larger luminaires at ground level. In the United Kingdom known as Turtle.

T-stop The f-stop is based upon the diaphragm aperture and focal length and does not account for overall transmission, therefore t-stops indicate the effective f-stop in terms of how much light passes through the lens system (see F-number).

Taco cart (Equipment trolley) (USA) A special cart that carries grip equipment, such as C-stands, apple boxes, wedges, mounting hardware, and grip expendables.

Talent On-camera people and subjects.

Telescope A grid mounted device made from retractable sets of tubes that is used to suspend luminaires at varying heights in the studio. Older types of telescopes were driven by portable power tools, modern systems are generally equipped with integral electric motors.

Three-fer (USA) An adapter that provides three female connectors from one male connector.

Three-phase A type of alternating current that has three legs. The alternating voltage cycle of each leg is a third of a cycle apart (120°) (see Harmonic distortion, Wye connected system).

Three point lighting Traditional lighting set-up using a key light, fill and back lights.

Three-riser (USA) A stand that has three extensions.

Throw Generally describes the direction of light from a luminaire and also the effective distance between the luminaire and the area being lit. The light arriving at the subject will also be influenced by the angle of incidence (cos 9).

Tie-in The connection of temporary distribution cables to a facility's electrical service panel.

Tilt Term describing the vertical movement, about a point, of luminaires or equipment. Can also refer to camera mounting heads.

Titan (USA) A 350-A carbon arc luminaire manufactured by Mole Richardson. Known as Super Brute in United Kingdom.

Tower A temporary platform usually made from scaffolding, on which to mount luminaires (see Scaffold platforms).

Tracing paper Thin, translucent paper used to white out windows.

Transformer Consists of a set of insulated windings on a laminated steel core that is used to transfer energy of a.c. Current transformers are used to sample high currents for feedback circuits in equipment such as dimmers and electronic control ballasts.

Translucent A material that, although allowing the passage of light, does not allow a clear image to pass through.

Transmission Given in percentage, is the amount of light passing through a material, particularly colour filters, scrims and diffusers. Its practical application is to give guidance as to the incident light level and exposure in stops, as an aid to balancing the overall lighting and hence the picture.

Tree A tall stand or tower that has horizontal pipes on which luminaires can be hung. Used a great deal in theatre and concert lighting.

Tri-stimulus The CIE system is based upon using a standard observer who is seated in front of a white screen. On one half of the screen is projected some arbitrary light source, on the other half of the screen is projected a combination of the three primaries. The observer has to adjust the intensity of the three primaries until both sides of the screen match exactly in colour and brightness. The amounts of red, blue and green used to match the arbitrary light source can be used to calculate the tri-stimulus value of the colour and this can be plotted on the CIE diagram.

Tripe The groups of flexible cables from a theatre lighting bar to the permanent power outlets around the periphery of the stage area.

Trombone (USA) Term for an adjustable Drop Arm (see also Drop Arm).

Truss A framework, generally made from alloy bars together with cross bracing, to provide lightweight rigging structures. Trusses are used predominantly in TV temporary lighting rigs and concert lighting to support luminaires and other equipment at high level. The size of the truss dictates the amount of weight to be supported without dangerous deflection.

Tungsten halogen Describes a family of lamps with either hard glass or quartz envelopes, tungsten filaments and halogen (usually iodine or bromine) fillings.

Tungsten halogen lamp A lamp designed to maintain an almost constant colour temperature and a high lumen output throughout its life. The halogen cycle is a regenerative process that prevents the blackening of the inside of the bulb.

Turtle stand A very low stand to position luminaires at ground level.

Tweenie (USA) A 650 W Fresnel luminaire manufactured by Mole Richardson Co.

Twist-lock A connector for which the plug inserts into the socket and then twists, locking the plug to the socket.

Two K A colloquial term for a 2 kW spotlight.

Twelve-by (USA) 12 ft square butterfly, made from silk or net.

Ultraviolet (UV) Ultraviolet radiation covers the range 4–400 nm and it begins at the short wavelength limit of visibility (violet) and extends to x-rays. It is divided into near (400–300 nm), far (300–200 nm) and extreme (below 200 nm). The near ultraviolet energy is known generally as blacklight.

Underwriters laboratory (UL) (USA) An American independent test laboratory that ensures minimum safety standards of equipment.

Undo A memory system feature for cancelling the last instruction and returning the console to its previous set-up.

Unilux (USA) A manufacturer of strobe lighting equipment that can be synchronised to a motion picture camera shutter.

Up-fade The portion of a fade that involves only channels that are increasing in level.

Variac An auto-transformer dimmer.

VEAM connector Multi-pin discharge source head feeder connectors and single conductor feeder cable connectors.

Velum See Tracing paper.

Visible spectrum The narrow band of electromagnetic radiation which lies between ultraviolet and infrared with wavelengths from 0.0004 mm (400 nm) to 0.0007 mm (700 nm) is detectable by the human eye and is known as light.

Visqueen (USA) Plastic material used to protect equipment from rain and snow.

Volt (V) A unit of electrical force. One volt is required to force one ampere of electricity though a resistance of 1 Q.

Voltage drop That loss of volts which occurs through energy wastage when a current passes through a cable or electronic device.

Volt-ampere (VA) Voltage times current. In d.c., volts × amps = watts. In a.c. circuits, inductance and capacitance will introduce reactance, causing a discrepancy between the watts and volt-amperes (see Power factor).

Voltmeter A meter used to measure voltage difference between two points in a circuit.

Wall sled (USA) A luminaire-mounting device that hangs from the top of the set wall and rests against the wall.

Wall spreader Hardware that mounts to either end of a piece of timber, creating a span from one wall to another from which luminaires can be hung.

Wash General ambient light on the acting area.

Watt (W) A unit of electrical power, the product of voltage and current.

Wattage The power consumption measured in watts or more commonly kilowatts. Is used to rate the power of equipment such as lamps, luminaires and dimmer capacity.

Wedge A triangular wooden block used to level dolly track.

Welding cable A flexible electrical cable once widely used for power distribution. Welding cable is now prohibited, except for its use as an earth wire.

Western dolly (USA) A flat-bed camera platform with large inflated tyres, steerable at one end and useful for moving heavy luminaires and cable.

Wiggy (USA) A continuity or resistance-testing device.

Winch Term used to describe either manual or motorised lifting equipment.

Wind-up stand See Crank-up Stand.

Wire rope Ropes formed from fine wires woven in complex patterns to give great strength.

Working lights See House lights.

Wrap The process of taking down luminaires and coiling cable that begins after the last shot of the day has been completed successfully.

Wye-connected system A common type of three-phase transformer arrangement, also known as a Star system. Voltage reads 415 V (208 V) between any two of the phases and 240 V (120V) between a phase and the neutral.

Xenon lamps A discharge lamp which provides a very small source. It can be accurately aligned in an optical system to give a high output efficiency. There is a safety problem with xenon lamps, because of the high internal pressures which can be from 6 to 8 atmospheres when cold and 15–20 atmospheres when hot. The manufacturers recommend that protective gloves and goggles are worn when handling the xenon lamp and special precautions are taken when transporting it.

Xenon luminaire A discharge luminaire that has a colour temperature of 5600K. Because the arc is very small, the light output is extremely efficient.

Yoke The suspension frame of a luminaire; possibly containing the drive mechanism for pan and tilt. Colloq. fork, stirrup, trunnion.

Zoom Used in profile spots and scenic projectors, consisting of the relative movement of two lenses in an optical system to change beam width and focus.