Stage Lighting Glossary

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Act Curtain: See "Grand Drape"
AEA: Actors' Equity Association – The union representing actors and stage managers in the United States.
Alternating Current: Electricity quickly alternating directions through a circuit. The frequency with which this alternation occurs was once called "Cycles per Second" (CPS), but now is referred to as Hertz, abbreviated "Hz". In America, the standard is 60 Hz. In Europe, the standard is 50HZ.
Amperes (or Amps): The measurement of current. One ampere is 6.2411018 electrons (or one coulomb) per second.
Apron: The stage area which is downstage of the proscenium arch.
Arena Stage: A stage with the audience surrounding it on all four sides.
Autofollow: A cue which is automatically run as soon as the preceding cue is complete.
Batten: A horizontal pipe or strip of wood, usually as wide as, or wider than, the width of the stage, hung overhead. Battens which run upstage/downstage, as opposed to side to side, are referred to as "tabs".
Beam Angle: The central portion of the cone of light, in which the intensity does not fall below 50% of maximum. See Photometrics.
Beamlight (or Beam Projector): A lighting fixture with a large parabolic reflector and no lens. Often used with low voltage lamps (e.g.: 24V, 1000W) Casts very intense nearly parallel beam. Historically, these were used frequently in opera and musicals as a soft edged follow spot.
Bench Focus: The process of adjusting the lamp socket, in an ellipsoidal reflector spotlight, so that the field of light is even, with no "hot" spots.
Black Wrap TM: A flexible matte black aluminum used to mask light leaks and shape beams of light. Although often used as a generic term, "Black Wrap" is a trade mark of GAMPRODUCTS, Inc. Rosco makes a similar product called "Cinefoil".
Blacklight: Ultra-violet light discharge lamp. Most common are actually fluorescent tubes, but unlike the fluorescent lights in your office or classroom, the phosphor on the envelope emits light in the near ultraviolet range rather than white light. Other types include high intensity discharge lamps.

Blacklights cause specially-treated surfaces to fluoresce while in the absence of visible light, absorptive surfaces tend to disappear.

Boom: A vertically-mounted lighting position, usually mounted to a wall or threaded into a base or flange on the floor. When booms are mounted downstage of the proscenium, they are known as box booms.
Borderlight: See "X-Ray"
C-Clamp: See "pipe clamp"
Candela: Photometric unit describing the amount of light emitted from a light source.
Centerline: An imaginary DS/US line that bisects the stage, usually labeled with symbol like this:

Channel: A control path that allows the console to vary the output level of one or more dimmers or other devices. The channel can be physical (controlled by a button, switch or slider) or virtual, (controlled by a numeric keypad).
Channel Hookup (or Switchboard Hookup): A spreadsheet listing each fixture in the show with all its relevant information, including, color, template, accessories, dimmer, circuit, channel, wattage, and purpose. The channel hookup is arranged in order of channel number.
Chromatic Aberration: A type of distortion in which a lens fails to focus all colors to the same point, resulting in a field of light which looks like this (exaggerated for effect):

Circuit Breaker: An electrical switch which protects an electrical circuit by automatically opening when the circuit is overloaded. Differs from a fuse in that the circuit breaker, after being tripped, can be reset, whereas the fuse must be removed and replaced.
Color Temperature: A measure of the color of white light. In fact, it is the color of a "black body" heated up to that particular temperature in the Kelvin (absolute) temperature scale. A halogen incandescent lamp usually has a color temperature of between 3000K and 3600K. Higher color temperatures are bluer than are lower color temperatures. See: Color Temperature "White" Light Isn't White
Company Switch: An electrical box used for connecting temporary lighting equipment.
Count: A Romanian title of nobility. Also, the length of time (in seconds) it takes to complete a cue.
Crossfade: A gradual transition from one set of channel levels to another. The levels can be set in physical presets, as in a preset board or in virtual cues, as in a computerized memory console.
Cue (or State): The predetermined intensities of the various lighting units at a specific given time, as well as the levels of non-intensity channels for devices such as moving lights, scrollers, and LED fixtures.
Current: The measure of the number of electrons passing a certain point in one second. Measured in amperes.
Curtain Warmers: A cue designed to light the grand drape (if used) or uninhabited stage (if no front curtain is used) in order to give the audience something at which to look before the performance begins, at intermission, and after the performance ends.
Cyclorama (or Cyc): A backcloth colored pale blue, gray, or white, used as a sky backing. This was originally a curved architectural plaster background to the stage. Many cloth cycs are still curved, but flat cycs are more common today.
Dichroic: A filter or reflector to which a layer of metal oxides is added, causing it to transmit some wavelengths and reflect others. Some lighting fixtures use dichroic reflectors, which reflect light and transmit heat; this enables use of a much brighter and therefore hotter lamp. Dichroic color filters transmit only a particular color and reflect all other wavelengths as well as heat; these are used in moving lights, as they are the only color filters which can withstand the intense temperatures within the fixtures.
Dimmer: A device which regulates light intensity. Most dimmers do this by electronically controlling the electricity transmitted to the lamp (See: "SCR"). Fixtures with discharge lamps may have mechanical dimmers (properly called "dowsers") which regulate the amount of light by hiding it, similar to Venetian blinds. Older types of dimmers include autotransformers and resistance dimmers.
Dimmer Hookup: A spreadsheet listing each fixture in the show with all its relevant information, including, color, template, accessories, dimmer, circuit, channel, wattage, and purpose. The dimmer hookup is arranged in order by dimmer number.
Dimmer Profile: An indication, usually represented by a graph, indicating how the dimmer will respond to a continuous change in channel levels from 0%-100%. See "Patching"
Direct Current: Electricity flowing through a circuit in one direction only. An example of this would be a battery-powered flashlight.
DMX: Communications protocol standard, used primarily for theatre lighting systems, for sending data from lighting consoles to dimmers, motorized lights, and lighting accessory units such as color scrollers and fog machines. See DMX512.
Dowser: See: "Dimmer"
Dry Tech: A technical rehearsal in which the cues are run without actors.
Efficiency: The ratio of emitted light to power consumed.
Field Angle: The outer portion of the cone of light, in which the intensity does not fall below 10% of maximum. See Photometrics.
Fly System: A mechanical system for bringing in (moving closer to the floor) or taking out (moving farther from the floor) battens and tabs. Common types of fly systems include hemp, counterweight, and electrical winches. See the section on fly systems.
Foot Candle: Photometric intensity unit: lumen per square foot.
Frequency: The number of waves that pass a given point in space during a specific time interval. Frequency is usually measured in hertz (symbol: Hz), on hertz being one cycle/second. Light travels at such a high speed that it is measured in terahertz (symbol: THz). One THz is 1012 Hz.
Gel: Plastic medium used to change the color of a beam of light. Originally made of animal gelatin. Major manufacturers include Apollo, GAM, Lee, and Rosco.
Gobo (or Template): Metal or glass (or, in rare, very specific, situations, plastic) pattern used in ellipsoidal reflector spotlights to project an image.
Grand Drape (or Act Curtain): The main curtain in a proscenium theatre. Usually paired with the "Grand Valence".
Ground (or Earth): A direct electrical connection to the Earth. Electricity always takes the path of least resistance. In the event that a stage lighting fixture (or other piece of equipment) has faulty electrical insulation, leading to dangerous voltage passing through the metal outer body, proper grounding will drain that voltage into the Earth. The circuit breaker will pop, but you won't.
Ground Row: A row of lighting fixtures placed (usually) downstage of a backdrop in order to light it. The low-lying row of scenery that often masks the electrics ground row is also referred to as a "ground row".
Halogen Lamp (or Tungsten Halogen): A lamp whose envelope is filled with halogen rather than inert gas. In a non-halogen lamp, as the filament heats up, pieces of it evaporate and are deposited on the inside of the bulb, changing the color temperature of the lamp. In a halogen lamp, these pieces combine with the gas and are redeposited on the filament. This could make for far greater lamp life but instead has been used to enable manufacture of brighter, hotter and smaller bulbs. Due to the heat ordinary glass may not be used for the envelope; instead, a quartz alloy is used. This collects grease and therefore should not be touched; grease from the finger remains on the bulb and causes it to weaken when hot. It is easy to tell who touched the bulb and caused a greatly-reduced lamp life; the perpetrator's fingerprint will be clearly etched on the glass. If the envelope is inadvertently touched, it can be wiped clean with alcohol.

Non-halogen lamps are often referred to as "incandescent", but this is less than accurate, as halogen lamps also use the principle of incandescence (see "Lamp").

Hazer: A device which produces a light haze which hangs in the atmosphere, causing beams of light to become visible. Depending on the individual unit, may be manually controlled or controlled, via DMX, by the console.

Hue: That property of light by which the color of an object is classified as red, blue, green, or yellow in reference to the spectrum.

Incandescent: Incandescent light is formed by heating a filament to the point at which it glows. Most theatrical light, including that generated by tungsten halogen lamps, is incandescent.

Inert Gas: A gas which does not undergo chemical reactions under a set of given conditions .

Instrument Schedule: A spreadsheet listing each fixture in the show with all its relevant information, including, color, template, accessories, dimmer, circuit, channel, wattage, and purpose. The instrument schedule is arranged in order of hanging position and fixture number.

Iris: A mechanical device used to vary the diameter of the light from an ellipsoidal reflector spotlight. In most cases, the iris can easily be inserted into or removed from the fixture.
Lamp: That which is referred to commonly as a "light bulb". The lamp consists of three parts:
  • Filament: The internal coil of wire which heats up as electricity is passed through it and thereby glows and produces light. This process is called incandescence.
  • Base: The metal part of the lamp that connects it to the fixture. There are many types of base, including prefocus, bayonet, screw, and two-pin.
  • Bulb: The glass envelope that surrounds and contains the filament.
LED: Light Emitting Diode. Increasingly used as theatrical light sources as growing levels of light efficiency are reached and control technology is improved. LEDs are manufactured in various colors, most commonly red and green. White LEDS are actually blue with a phosphor envelope which transforms blue light to white. LEDs use far less power per lumen than incandescent or halogen sources, and produce far less heat, but are more expensive and complex to build and produce a very narrow spectrum of light. Modern LED theatrical fixtures use a combination of colors (at minimum, red, green, and blue, although many fixtures also have an amber channel and some have as many as seven colors) to provide built-in additive color mixing. Because LEDs provide a narrow color spectrum, the output of these fixtures often yield unsatisfactory results when lighting human skin.
Leg: A vertical masking unit place at the side of the stage in order to mask the offstage area from the audience.
Light Plot: A drawing or drawings showing the location of each fixture, its fixture type, color, channel, dimmer, and focus.
Lightwright TM: A computer program used to generate instrument schedules, channel hookups, and other paperwork from a single database/spreadsheet with error-checking and many lighting-specific data entry shortcuts. In the American professional theatre, Lightwright is the industry standard lighting database program.
Lumen: A measure of light intensity produced by a light source. Lumens are a measurement of light generated by a source, as opposed to footcandles (or lux) which measure the light received at the target, over a given area and are affected by the optics of the fixture as well as by the throw distance.
Mask: To hide from the audience's view, often with black velour curtains or other scenic elements. These elements are collectively referred to as "masking".
Multiplexing: The combining of several different message signals or data streams into one signal over a shared medium.
Nuremberg Light: A light hitting the performer from almost straight below, an uplight. So called because Albert Speer used them in the Nazi rallies at Nuremberg.
Paper Tech: A production meeting, before the first technical rehearsal, in which the stage manager, the designers, and the director discuss the various cues and the general flow of the production, without actually running the cues.
Park: A command which causes a specific channel or dimmer to remain at a given setting regardless of the level at which it is set in submasters and cues. An example of this would be a fixture which has been knocked out of focus and is shining into the audience's eyes, and therefore might be parked at 0% until such time as it can be refocused.
Photometrics: The data used to calculate the field size and intensity of a lighting fixture.
Pilaster: A slightly-projecting column built into or applied to the face of a wall. Most commonly flattened or rectangular in form, pilasters can also take a half-round form or the shape of any type of column. (Definition courtesy of Wikipedia). Pilasters are often found on either side of a proscenium arch.
Pilaster Line (or "Plaster Line"): An imaginary line between the upstage-most points of the SL and SR pilasters. This line is typically the zero-point from which DS/US measurements are based.
Pipe Clamp (or C-Clamp): The clamp that attaches a lighting fixture to the hanging position. In the US, these are usually made of malleable iron; in other parts of the world (notably the UK) they are made of more substantial material.

Power (or Wattage): The amount of electrical "work" being performed. Measured in watts.
Practical: A prop electrical device (usually a lighting fixture such as a chandelier or table lamp) that actually functions.
Proscenium (or Proscenium Arch): The opening in the wall which separates the stage from the seating area. Often framed on either side by pilasters.
Reflector:
  • A mirror (usually curved) in the rear of a lighting fixture.
  • Anything used to reflect light.
Resistance: The degree to which a substance opposes the passage of electricity. Measured in ohms.
Saturation: The degree of purity of a color; the degree of freedom from admixture with other colors. Also known as chroma.
Scrim: An open weave fabric which appears opaque when lit from the front, but turns transparent when objects behind it are lit (Note that a scrim is approximately 50% air, so when frontlighting it, care must be taken so the light passing through the scrim does not illuminate people or objects behind it.) Scrims are most often found in either black or white, but they are available in many colors and can even be painted (although the painter must be careful not to allow the paint to obscure the holes in the weave). The act of fading down the frontlight on a scrim while raising the intensity of the light on the objects behind it – therefore revealing those objects to the audience – is called a "bleed-through," or a "scrim-through".
Scroller: Color changing device placed on a lighting fixture, made of two cylinders with a long strip of color filters rolled around them. Digital signals control the movement of the cylinders to determine which piece of the strip is placed before the light.
Shade: A color with a low value. It is usually created by a mixture of one or more hues with black.
Shin Busters: Lighting instruments placed at the sides of the stage at or near floor level, frequently used in dance.
Sightline: The offstage-most edge of what can be seen, onstage, from the audience.
Silicon Controlled Rectifier (or SCR): An electronic device, similar in function to a transistor, but can withstand higher voltages. It behaves as a super-swift valve, opening and shutting to control the amount of electricity delivered to the lamp. Perhaps the most common technology used for dimming traditional theatrical lighting.
Special: One or more fixtures focused on a limited area, usually not part of a wash.
Spectrum: In lighting, the band of colors produced when white light is passed through a prism, comprised of red, orange, yellow, green, blue, indigo, and violet.
Stage Circuit (or Circuit): The wiring which connects the fixture (usually via an outlet) to the patch panel or dimmer.
State: See "Cue"
Tab: See "Batten"
Tension Grid: (Also known as "Tension Wire Grid" or "TWG")

Provides walking surface over performance area allowing lighting from any position overhead. Made of interwoven 1/8" aircraft cable.

[Tension grid images courtesy of Peter Albrecht Company.]

Throw: The distance from the fixture to the performer or scenic unit being lighted.
In the example below, the fixture has a beam angle of 16 and a field angle of 40. The throw is 12'. The beam width is 3'-4.5" and the field width is 8'-9".
Thrust Stage (or "Three-Quarter" Stage): A stage with the audience around it on three sides.
Tie Line: (Also known as "trick" line). Cotton rope, usually black, approximately 1/8" in diameter. Uses include tying up cables and draperies.
Tint: A color with a high value is referred to as a tint. This is usually achieved by mixing a hue with either white pigment or white light.
Tone: A color of middle value, neither a shade nor a tint.
Transmission: The degree to which a medium passes light, measured in terms of the percentage of light which is transmitted.
Trim: As a verb, refers to the act of setting the height of an overhead masking piece or electric batten, or the distance from centerline of a leg or other masking unit.

As a noun, refers to the position set by the act of trimming.

Twist-Lock®: A registered trademark of Hubbell, Incorporated, although the term (usually spelled "twistlock") is used as a generic descriptor for a specific type of locking connector regardless of manufacturer. These connectors have curved blades, and when the male connector is inserted into the receptacle and twisted, the two connectors are locked together. Note that there are several different configurations of Twist-Locks, which are not interchangeable.
Twofer: An adaptor allowing two fixtures to be plugged into one circuit.

Universe: Refers to a network of systems tied together using one system of control information. Most commonly used in relation to DMX-512, but can refer to other networked systems such as sound or video. Each universe that a control console addresses uses a separate signal output and is directed through a separate set of cables to lighting devices. Multiple universes allow a single console to control more than 512 paths of information; many modern consoles provide anywhere from 2-8 universes (1024-4096 addresses) and can be upgraded to handle far more. (Courtesy of Mark Thomason)
Value: The relative lightness or darkness of a color. Pale blue has a high value, and dark blue has a low value.
Volt: The unit of electrical pressure or electromotive force.
Wash: Multiple fixtures which, when used together, cover the entire performing area with a single color from the same direction.
Watt: The unit of electrical power.
Wavelength: The distance between any two corresponding points on successive waves.
X-Ray (or Borderlight): A striplight, hung overhead, usually running the entire width of the batten.
Zoom: A zoom lens has the ability to vary its focal length (and thus the field and beam angles). When a zoom lens is set to its narrowest setting, the field is brighter than that of the widest setting.
Other Theatre Glossaries