Lighting Designer's Glossary

absorption

A process by which incident radiant flux is converted to another form of energy, usually (and ultimately) heat.

accent light

Directional lighting designed to emphasize a particular object or to draw attention to a part of the field of view.

Accent Wash

A wash of light over an area, adding colour.

accommodation

The process by which the eye changes focusfrom one distance to another.

ACL Light

A very narrow beam, low voltage Par aircraft land light.

Adaption

The process of the eye getting used to or reacting to changes in light intensity

altitude

The vertical angular distance of a point in the sky above the horizon. Altitude is measured positively from the horizon to the zenith, from 0 to 90 degrees.

ambient light

Electric and/or natural lighting throughout a space that produces uniform general illumination.

Ampacity

The maximum allowable electrical current, in amperes, that a conductor can safely carry. Temperature, humidity, and other factors can affect a conductor’s ampacity.

Amperage

A component of electricity used to measure the number of electrons moving past a given point in a circuit.

AMX

Abbreviation for Analog Multiplex.

Analog Multiplex

A system that simultaneously transmits more than one analog signal.

ANSI

American National Standards Institute.

ANSI Code

A three letter system that has been devised to describe lamps of different manufacture but the same application.

artificial sky

An enclosure that simulates the luminance distribution of a real sky for the purpose of testing physical daylighting models. See hemispherical dome artificial sky and mirror-box artificial sky.

Area Lighting

The main visibility lighting for an acting area.

azimuth

The horizontal angular distance between the vertical plane containing a point in the sky and true south.

Automated Light

A luminiare that is robotic, i.e.., certain functions such as panning, tilt, focusing, dimming, beam shaping and colour are motorized and remotely operated.

AWG

American Wire Gauge

Backdrop

A vertical surface which is used to form the background.

Ballast

An electrical apparatus that limits the electrical current through an arc source.

ballast factor

The ratio of lamp lumen output on a particular ballast as compared to that lamp’s rated lumen output on a reference ballast under ANSI test conditions (free, unmoving air at 25° C)

Barndoor

A device with 2/4 or 8 doors for masking a light beam off areas.

Batten

A pipe hung on a set of lines to which lighting or scenery can be hung.

Beam Apple

The angle at which the beam edges are 50% of the centre beam candlepower.

beam component

That component of flux received directly (or by specular reflection or transmission) from a point source (such as the sun or small lamp). It is a direct component.

Beam Spread Factor

A number with which you multiply the throw distance to determine beam spread.

Blacklight

A luminaire with a beam whose wavelengths are too short to be visible, i.e.., 320 to 380nm. The ultraviolet wavelengths excite fluorescent materials, paints, etc.

Blackout

The fast shutdown of all lighting

blinding glare

Glare that is so intense that, for an appreciable length of time after it has been removed, no object can be seen.

Blind Mode

Setting up a lighting scene or preset when another is active.

Boom

A vertical pipe mounted in a base, used to hang lighting fixtures. Border Light. See Striplight. 

Breakup

An opaque or translucent material having a cutout which will allow light to pass
through the cutout area in order to protect a dappled form, such as a cloud formation. 

Bulb

The glass part of a lamp. 

Candlepower

A term used in place of intensity .

candela (cd)

The SI unit of luminous intensity (formerly called the candle). One candela equals one lumen per steradian-the luminous intensity, in a give direction, of a source that emits monochromatic radiation at a frequency of 540E12 hertz and of which the radiant intensity in that direction is 1/683 watts per steradian.

C-Clamp

Pipe clamp

chromaticity

Refers to the dominant or complementary wavelength and purity aspects of the color taken together, or of the aspects specified by the chromaticity coordinates of the color taken together.

clerestory

That part of a building rising clear of the roofs or other parts, whose walls contain windows for lighting the interior.

coefficient of utilization (CU)

The ratio of lumens from a luminaire received on the work plane to the total quantity of lumens emitted by the lamps of that luminaire.

color rendering index

A measurement of the amount of color shift that objects undergo when lighted by a light source as compared with the color of those same objects when seen under a reference light source of comparable color temperature. CRI values generally range from 0 to 100.

color temperature

The absolute temperature of a blackbody radiator having a chromaticity equal to that of the light source (see correlated color temperature).

Colour Changer

An apparatus that attaches to a luminaire and allows one to remotely introduce one or more colour frames into the beam.

Colour Correction

Adjusting the colour temperatures of various luminaire’s so that they are all the same, or to make them match existing light sources. 

Colour Filter

Any coloured transparent material that can be placed in front of a beam to colour the light.

Colour Frame

An apparatus used to hold colour filters.

Colour Temperature

A factor given for lamps, comparing their colour to that of a blackbody at a given temperature.

cone

A retinal receptor that dominates the retinal response when the luminance level is high and provides the basis for the perception of color.

contrast

The ratio of the luminance of an object to that of its immediate background.

Control Board

A remote device used to control dimmers/moving lights etc.

Control Cable

A cable used to transmit digital or analog signals from a control console to the apparatus to be controlled.

cosine law

The law that the illuminance on any surface varies as the cosine of the angle of incidence. (The angle of incidence is the angle between the normal to the surface and the direction of the incident light.)

Crank-Up Stand

A stand that is raised and lowered with the aid of a rotatable handle and gear mechanism.

Cross Bar

A bar mounted horizontally on top of a stand.

Crossfade

To fade from one scene to another.

Cross Fader

A control for fading from one preset scene to another. Cue A change in lighting.

Cyc

Short for Cyclorama . A drop used to create the illusion of infinite space.

cut-off angle

The critical viewing angle beyond which a source can no longer be seen because of an obstruction (such as a baffle or overhang).

Daisy Chain

When electrical equipment is wired from one unit to the next.

Dark Adaptation

The process of the eye adapting to changes from light to dark.

daylight factor (DF)

The ratio of daylight illumination at a given point on a given plane due to the light received directly or indirectly from a sky of assumed or known luminance distribution, to the illumination on a horizontal plane due to an unobstructed hemisphere of this sky, expressed as a percentage. Direct sunlight is excluded for both values of illumination. The daylight factor is the sum of the sky component, the external reflected component, and the internal reflected component. The interior plane is usually horizontal. If the sky condition is the C.I.E. standard overcast condition, then the DF will remain constant, regardless of absolute exterior illuminance. If used in conjunction with other than standard overcast conditions, the sky conditions should be specified. The term is also informally applied to the ratio of horizontal interior to exterior illuminance in the fenestration plane; under clear sky conditions, the DF remains constant only if the fenestration is completely diffusing (such as an ideal opalescent glass).

Dichroic

A type of metallic coating applied to glass and some other materials that allows certain wavelengths of light, or other electro magnetic radiation, to pass while reflecting all others. 

Diffusion Material

Any reflecting or transmitting media for which the reflected or transmitted light is distributed uniformly.

diffusing (surface)

Those surfaces and glazing that redistribute some of the incident flux by scattering in all directions.

Digital Multiplex (DMX)

A system that simultaneously transmits more than one digital signal.

Dim

To lower the amount of voltage to a fixture, thereby decreasing its light output. 

Dimmer

A device used to control how much voltage is supplied to a lighting fixture.

disability glare

Glare resulting in reduced visual performance and visibility . Often accompanied by discomfort glare.

discomfort glare

Glare producing discomfort. Does not necessarily interfere with visual performance or visibility.

Dipless Cross Fade

A cross fade whose transition from one setting to another is completely smooth and even.

DMX 512

A unique digital multiplex signal with specific characteristics that is used in the stage and studio lighting industry.

Downstage

The area on stage that is closest to the audience.

Dowser

Mechanical Dimming.

Drop Box

A plug box that can be dropped where power is needed.

Effect

An event or a moment intended to create a particular emotional reaction.

Effect Lighting

Lighting intended to create a mood or an impression.

Effect Wash

Effect Lighting covering a broad area.

efficacy

A measure of the luminous efficiency of a radiant flux, expressed in lumens per watt as the quotient of the total luminous flux by the total radiant flux. For daylighting, this is the quotient of visible flux incident on a surface to radiant flux on that surface. For electric sources, this is the quotient of the total luminous flux emitted by the total lamp power input.

Ellipsoidal

A luminaire embodying a lamp, an ellipsoidal reflector, a framing device, and a single or compound lens system, together with provisions for accommodating a pattern holder and patterns.

emissivity/emittance

The ratio of radiance (for directional emissivity) or radiant exitance (for hemispherical emissivity) of an element of surface on a temperature radiator to that of a blackbody at the same temperature. By Kirchoff’s Law, for a given wavelength of the electromagnetic spectrum, emissivity of a surface equals its absorptivity (and is the reciprocal of its reflectivity).

exitance

The density of light reflecting from a surface at a point, measured in lumens per square foot (formerly"footlamberts"). It is determined by multiplying the footcandles striking a diffuse reflecting surface times the reflectance of that surface.

Fade

To gradually increase or decrease the intensity of light. Far Cyc A cyclorama light placed at a distance from the cyclorama generally 8’ or more.

Fay Light

A luminaire that uses incandescent parabolic reflector lamps with a dichroic coating to provide daylight illumination. 

Feeder Cables

A set of electric cables, usually individually insulated conductors with a high ampacity, used to remotely connect portable racks, power distribution racks etc.

fenestration

Any opening or arrangement of openings (normally filled with glazing media) for the admission of daylight, including any devices in the immediate proximity of the opening that affect distribution (such as baffles, louvers, draperies, overhangs, light-shelves, jambs, sills, and other light-diffusing materials).

Field Angle

The angle a which the beam edges are 10% of the centre beam candlepower.

Fill Light

Supplementary illumination used to reduce shadows. First Electric The electrics pipe and/or its position, which is located immediately upstage of the proscenium arch. 

Fixture

A lighting unit, or luminaire. 

Flag

To wave an object or a hand in front of an instrument to determine its coverage area.

Flood

To adjust a luminaire usually by moving the lamp closer to the lens; enlarging the diameter of the beam of light emitted.

Floodlight

A luminaire consisting of only a lamp and reflector with fixed spacing; generally, the reflector has a diffused finish and is often physically large in size. The widest field of illumination from a luminaire. 

Floor Pocket

A wiring device with receptacles recessed into to the floor with a hinged cover.

fluorescent

A discharge lamp in which a phosphor coating transforms ultraviolet energy into visible light.

Flux

A measure of the amount of light. The unit is often the Lumen.

Focus

To aim a lighting fixture, or to adjust a fixture’s beam. 

Focusing Instrument

A lighting instrument whose beam size can be varied.

Follow Spot

A lighting instrument used to follow a performer on stage.

Footcandle

A unit of illumination. 1 footcandle = 1lumen/ft2.

footlambert (fl)

A unit of luminance equal to 0.3183010 candela per square foot, or to the uniform luminance of a perfectly diffusing surface emitting or reflecting light at a rate of one lumen per square foot, or to the average luminance of a surface emitting or reflecting light at that rate. An unobstructed sky of one footlambert uniform luminance contributes one footcandle of illuminance on a horizontal plane.

fovea

A small region at the center of the retina, subtending about two degrees and forming the site of the most distinct vision and greatest color discrimination.

Fresnel

A lighting instrument using a fresnel lens. (softedge beam).

Fresnel Lens

A lens that acts similarly to a piano-convex lens but is thinner and lighter due to steps on the convex side. Often the flat side has a rough surface to smooth light beams by slightly diffusing the light.

Fresnel Spotlight

A luminaire embodying a lamp and a fresnel lens, with or without the reflector, which has a soft beam edge. The field and beam angles can be varied by changing the spacing between the lamp and lens. 

Front-Of-House

The complete area of the theatre in front of the stage.

Gel

A plastic colour media for modifying a beam of light.

glare

See direct glare, disability glare, discomfort glare, reflected glare.

glare index

A method of predicting the presence of discomfort glare due to daylighting. Factors affecting the glare index include the size and relative position of fenestration, sky luminance, and interior luminance. Most widely used in Europe, the glare index is similar to the index of sensation and the discomfort glare rating, which are used in North America for electric lighting applications.

Gobo

A silhouette pattern used to project images from an ellipsoidal spotlight.

Grid

The structure above the stage, usually used to support the battens. 

Ground Cyc

A cyclorama light used from the floor.

Ground Row

Lighting strips aimed up from the base of a cyclorama or drop. The masking piece concealing these strips.

Hard Edge

A beam pattern edge that is very clear and distinguishable.

Hard Wired

A term used to describe an electrical connection that is intended to be permanent.

Hot Patching

Putting a circuit into a dimmer or hot pocket while it is on.

Hot Restrike

A term applied to an ignitor that will hot start an arc lamp.

House Lights

General lighting provided for the audience area.

House Position

A lighting position located in Front-Of-House.

hue

The attribute of a color that allows it to be classified as red, yellow, blue, and so on.

Image

The actual design of a pattern. The reproduction of an object formed by an optical system.

Incandescent

A term used to describe a lamp, or a luminaire that utilizes such a lamp, that employs the incandescence of a filament such as a light source.

IALD

International Association of Lighting Designers

IESNA

Illuminating Engineering Society of North America

illuminance

The density of incident luminous flux on a surface; illuminance is the standard metric for lighting levels, and is measured in lux (lx) or footcandles (fc).

incandescence

The emission of visible electromagnetic radiation due to the thermal excitation of atoms or molecules.

indirect sources

Surfaces which, after being illuminated by other sources (direct sources such as the sun, sky, or electric light, or other indirect sources), have measurable luminance and, in turn, become sources themselves.

infrared radiation

Radiation with wavelengths too long to be perceived by the human eye (that is, longer than 0.77 microns) and less than 1,000 microns. Room IR is infrared radiation in the 7.7-8.0 micron region and typical of that radiated from surfaces near room temperature.

inverse-square law

The law stating that the illuminance at a point on a surface varies directly with the intensity of a point source, and inversely as the square of the distance between that source and that surface.

irradiance (E)

The density of radiant flux incident on a surface.

isolux (isofootcandle) line

A line plotted on any appropriate set of coordinates to show all the points on a surface where the daylight illuminance is the same. A series of such lines for various illuminance values is called an isolux (isofootcandle) diagram.

Inky

A small fresnel spotlight with a 1.5 to 3 lens. 

Instrument

A lighting unit.

Iris

An arrangement of thin, movable, heat-resistant metal plates (leaves) that form an adjustable circular opening. 

Jumper

An electric cable and connector assembly.

Kelvin

In the metric system, a graduated scale used to measure temperature with 0O (-2730C) being the total absence of heat (absolute zero). Each degree is the same magnitude as a degree in the centigrade scale. This is the unit of temperature used to designate

Key Light

The principal source of light which establishes the character of the actor and mood of the scene.

Kilowatt (kW)

1000 watts.

kVA

Abbreviation for Kilovolt-Ampere.

Lamp

The complete assembly of a bulb, filament, base, etc. 

Lamp Bar

A pipe, usually aluminum, that has a fixtures attached at even intervals. 

Leko

A commonly used term for an ellipsoidal spotlight. Named after its inventors Levy and Kook. The names Leko and Lekolite are trademarked by Strand Lighting Co.

Lens

A transparent material, usually glass, shaped to bend light rays as they pass through it.

lamp

An electrically energized source of light, commonly called a bulb or tube.

lamp lumen depreciation

The decrease over time of lamp lumen output, caused by bulb wall blackening, phosphor exhaustion, filament depreciation and other factors.

light

Radiant energy that is capable of exciting the retina and producing a visual sensation. The visible portion of the electromagnetic spectrum (light) extends from about 0.38 to 0.77 microns.

light loss factor (LLF)

A factor used in calculating the illuminance after a given period of time and under given conditions. It takes into account temperature and voltage variations, lamp depreciation (of electric luminaries), dirt accumulation on luminaire and room surfaces, maintenance procedures and atmosphere conditions. Formerly called maintenance factor.

light shelf

A horizontal shelf positioned (usually above eye level) to reflect daylight onto the ceiling and to shield direct flare from the sky.

Lift

A height adjustable stand or tower.

Light Adaptation

The process of the eye adapting to changes from dark to light.

Lighting Bridge

A narrow platform mounted above the performing area used for mounting luminaire’s, often incorporated into a truss rig or into the grid in a theatre. 

Light Plot

The diagrammatical layout of luminaire’s and related equipment.

Limbo

A background having no detectable detail.

Line Voltage

A term that usually means 120 AC volts.

Load

The lamp or lighting instruments placed on a circuit.

lumen

The quantity of luminous flux emitted within a unit solid angle (one steradian) by a point source with one candella intensity in all directions.

lumen method

A method of estimating the interior illuminance due to window daylighting at three locations within a room. Based on empirical studies, the use of this method is primarily limited to North America.

luminaire

A complete lighting unit, consisting of a lamp or lamps together with the components required to distribute the light, position the lamps, and connect the lamps to a power supply. Often referred to as a "fixture."

luminaire dirt depreciation

A multiplier used in lighting calculations to account for the reduction in illuminance produced by the accumulation of dirt on a luminaire.

luminance

The luminous intensity of a surface in a given direction per unit area of that surface as viewed from that direction; often incorrectly referred to as "brightness."

lux (lx)

The SI unit of illuminance equal to one lumen per square meter.

Luminaire

A complete unit for the purpose of generating usable and somewhat controllable light.

Lux

A metric unit of measurement for illumination. 1 Lumen/m2 (10 lux = 1 ftc)

Magnetic Ballast

A ballast that uses a magnetic filed to limit electrical current.

Mask

To hide from view. To cut off part of a beam of light.

Matrix

A patching apparatus that can be a patch panel or diode pin matrix.

matte surface

Surface from which the reflection is predominantly diffuse, with or without a negligible specular component.

Memory Board

A contral console that has computerized functions and an ability to electronically store data.

Mini Strip

A compact striplight that uses 1 to 4 groups of ten 12 volt lamps wired in a series circuit.

Model

To use light and shadow to entrance three-dimensionality.

monitor

A raised section of roof that includes a vertically (or near-vertically) glazed aperture for the purpose of daylighting illumination.

Multiconductor Cable

An electrical cable that generally has more than three conductors.

Near Cyc

A cyclorama light placed close to the cyclorama, generally less than 8’.

near infrared (solar infrared)

The region of the electromagnetic spectrum between 0.77 to 1.4 microns. Most of the infrared solar radiation falls into this region. This near infrared (or solar IR) region is transmitted, absorbed, and reflected in a similar manner to visible light by most glazing and nonmetallic building materials.

Neutral Conductor

A current carrying conductor that is electrically connected to neutral.

Non-Dim

A circuit supplying electrical power to a luminaire by means of a switch or a relay in order to permit an on-off function rather than a dimming function.

NSP

A lamp designation that means narrow spot . 

Open Circuit

A circuit that has a physical break or disconnection.

Outriggers

Sturdy support legs that assist in stabilizing stand and lifts.

overcast sky

A sky luminance distribution three times brighter near (C.I.E. Standard Condition) the zenith than at the horizon, as defined by a formula proposed by Moon and Spencer in 1942 and adopted by the Commission International de l’Eclairge in 1955

overhang

A horizontal building projection, usually above a window, for the purpose of shading.

Par

Parabolic Aluminized Reflector, a lamp or lighting unit. 

Patch

Tying a circuit into a dimmer or a dimmer into a control channel.

photocell

A device that measures the amount of incident light present in a space.

peripheral vision

The seeing of objects displaced from the primary line of site and outside of the central visual field.

Pin Spot

A fixture providing a narrow beam of light.

point method

A method of estimating the illuminance at various locations in a building using photometric data.

Power Distribution

A term used to describe electrical equipment that is specially designed to intake electricity and route it to output wiring device or devices.

Pre-Rigged Truss

A truss section, usually provided with wheels, that has lamp bars installed. 

Preset

To have something on a control console set up in advance of need.

Primary Colours

Colours from which all other colours may be evolved by mixtures. In light, the primary colours are red, green, and blue. 

Profile Spotlight

Any spotlight, usually an ellipsoidal spotlight, that has framing shutters. 

Punch Light

A high intensity luminaire that floods an area with light.

pupil

The opening in the iris of the eye that admits light.

Rain Light

A pinspot using a low voltage, narrow beam lamp.

radiant energy (radiation)

Energy traveling in the form of electromagnetic waves. Measured in units of energy such as joules, ergs, or kilowatt-hours.

refraction

The process by which the direction of light changes as it passes obliquely from one medium to another in which its speed is different.

reflectance

The ratio of reflected flux to incident flux.

retina

A light-sensitive membrane lining the posterior part of the inside of the eye.

Ray Light Reflector

A retrofit reflector and lamp socket assembly, creates a narrow, almost cylindrical shaped beam. 

Rig

A complete structural assembly for hanging or supporting fixtures, scenery, and/or other production equipment.

rods

Retinal receptors that respond to low levels of luminance but cannot distinguish hues. Not present in the center of the fovea region.

room cavity ratio

In lighting calculations, a measure of room proportion as determined by dimensions of length, width, and height.

Safety Cable (Chain)

A steel cable that has a clip on one end and a loop on the other. Used to secure fixtures to battens or truss.

Saturated

A colour containing a high percentage of colour is considered saturated . 

Scene

A shorthand version of Scene Preset or Look.

Scoop

A flood light using a large scoop-shaped reflector.

Scrim

A thin, gauze-like curtain. When illuminated from the front it appears opaque, and when illuminated from behind it but not on it, the scrim becomes almost transparent.

skylight

A relatively horizontal glazed roof aperture for the admission of daylight.

Shin Buster

A fixture placed as close to the stage floor as possible.

Sidearm

A pipe and C-clamp arrangement used to hang a fixture.

Sliding Tree

A coupling used to hang a lighting fixture from 1/2 pipe. 

Sling

A strong flexible, webbed belt or steel cable in the shape of a loop. 

Soft Edge

A beam pattern edge that is not very distinguishable.

Soft Patch

Plugging dimmers into control channels electronically.

Special

A fixture used for one specific object or effect.

Stage Left

The actor’s left as he faces the audience.

Stage Right

The actor’s right as he faces the audience.

specular angle

The angle of mirror reflection (angle of incidence equals angle of reflectance).

specular reflection

The process by which incident light is redirected at the specular (mirror) angle.

specular transmission

The process by which incident flux passes through a surface or medium without scattering.

Striplight

A luminaire with a number of lamps arranged in a line. Often each lamp is in an individual compartment. There may be a reflector behind the lamp and/or colour media in front of the lamp. Striplights are normally wired in three or four circuits.

task light

Light that is directed to a specific surface or area to provide illumination for visual tasks.

Throw Distance

The distance from a lighting fixture to the object being lit.

Tormentor

A wall-mounted pipe for mounting lighting fixtures.

Tormentor

Lights mounted Upstage of tormentor. (hard of soft masking) Set stage right and stage left just upstage of the proscenium.

Transient Adaptation

The process of the eye adapting from viewing an area at one level of light to an area of higher or lower level.

Transmission Factor

The ability of a medium to allow for the transmission of light.

Trim Height

The height from the stage floor at which a batten is set.

Truss Section

A sturdy, lightweight support structure. 

Turn-Around

An item comprising two connectors that are of the same type and sex, electrically connected together. 

Twofer

A special power cord that has one male connector electrically connected to two female connectors via two separate cables.

Upstage

The area on stage farthest from the audience.

ultraviolet radiation (uv)

Any radiant energy within the wavelength range of 0.001 to 0.38 microns.

veiling reflection

Specular reflection superimposed upon diffuse reflection from an object that partially or totally obscures the details to be seen by reducing the contrast. Controlled by distributing the source over a larger area, relocating the source out of the reflected field of view, changing the task surface specular reflectance or tilt, or relocating the observer.
h2>visual acuity
A measure of the ability to distinguish fine details.

visual comfort probability (VCP)

The rating of a lighting system expressed as a percentage of the people who, when viewing from a specified location and in a specified direction, will be expected to find it comfortable in terms of discomfort glare.

Wash

Even, overall light on performance space or background. 

Wattage

The power consumed by a circuit.

X-Ray

See striplight.

Zoom

An optical system where the lenses adjust.