Glossary of Terms - B

A glossary of terms covering lighting, audio, vision and staging in the event and theatrical industry.

There can be a number of meanings for some terms which can vary from country to country and manufacturer to manufacturer. Information within this guide is indicative and every situation can require a different approach and solution. All care has been taken, however, Image Group NZ accepts no responsibility for inaccuracies. If you have any suggestions, comments or queries regarding this list please contact us.


Refers to a remote control, or on projector control panel, that has buttons and controls that are illuminated. This is a major asset when using the projector in a darkened or semi-darkened room. Many projectors have backlit remote controls, while the number of projectors with backlit control panels is much smaller. As projectors have gotten brighter, room lights tend to stay on. So while a nice added feature, having backlit controls is no longer important to many users.

A projector with a "long-throw" lens designed to be used from the far back of the room, often in a projection booth, balcony, or the back of an auditorium. Many typical projectors have third party lenses available for "long-throw" applications.


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

Light coming from upstage, behind scenery or actors, to sculpt and separate them from the background.


    A sheet of material used to prevent a spill of light in a lantern or in part of a set.
    A panel in a loudspeaker cabinet designed to reduce back interference noise by isolating the front and rear of the loudspeaker diaphragm.
    The term derives from its original use in preventing or baffling the speaker's rear sound waves from interfering with its front waves.
    A panel in an auditorium positioned so as to reduce sound reflections and improve the acoustics of the space.

A cable consisting of a pair of wires surrounded by either a braided shield or foil wrap with a drain wire.


    A transmission line consisting of two conductors plus a shield, capable of being operated so that the voltages of the two conductors are equal in magnitude (voltage) and opposite in polarity with respect to ground. A balanced line offers common mode rejection, or cancellation by attenuation, of signals electromagnetically induced into the signal lines.

A unit used in conjunction with discharge lamps containing capacitors, inductors and other start-up circuitry. The inductor is initially used to develop a high potential (voltage) to strike the discharge and is then used to limit the current flow while the lamp is lit.

Swinging a followspot beam around in a figure of eight pattern.

Refers to a type of filter that passes a certain band of frequencies uniformly and attenuates or reduces the level of frequencies below and above the specified bandpass.


    The number of cycles per second (Hertz) expressing the difference between the lower and upper limiting frequencies of a frequency band; also the width of a band of frequencies.
    The effective carrying capacity of a telecommunications transmission medium. Bandwidth describes how much information can be pushed through an electronic "pipe" at any given time.

The horizontal metal (steel or alloy) tube (usually 48mm in external diameter, but can be up to 60mm) hung from flying lines (or forming part of a grid) from which lighting equipment and scenery etc. may be suspended. Also known as a BARREL. When vertical, known as a BOOM.

Term to describe an electrical cable which has no connector at one end (for example, a SPEAKON to BARE ENDS cable is used to connect the terminals of a speaker cabinet to a speakon socket, and a 63A socket to bare ends might be used to wire in a temporary supply from a power distribution board before connecting equipment. Any installation work of this sort should only be carried out by a qualified electrician, and should never be done "live").

A rotatable attachment consisting of two or four metal flaps (hinged) which is fixed to the front of a Fresnel or PC type lantern to cut off the beam in a particular direction(s). Profile lanterns use SHUTTERS to achieve a greater degree of control and accuracy.

A metal plate which prevents damage to floors when using scaffolding or trussing.

A type of speaker enclosure in which the speaker's rear sound wave emerges from a critically dimensioned auxiliary opening, or port, to reinforce the bass tones.


    Timber at the top and bottom of a cloth. A Sandwich batten is used to carry a hanging cloth. It comprises two flat pieces of timber screwed together with the edge of the cloth between them.
    Timber used for joining flats together for flying.
    Compartmentalised floodlights set up so as to allow colour mixing. See also GROUNDROW. Low voltage battens are commonly used as light curtains & for colour washes. Known in the US as a STRIPLIGHT.

An outward bowing of the picture. A condition in which colours appear to flow into unintended areas of the image.

The angle of the cone of light produced by a lantern. Defined as the angle within which the lowest intensity in a beam of light from a lantern is not less than one-tenth of the maximum.

Flood lantern which uses a parabolic reflector and a low voltage high intensity lamp to produce an intense near-parallel beam. Also known as a Beam Projector.

A call given by the DSM (Deputy Stage Manager) to bring those actors who appear in the first part of a play to the stage. e.g. "Act One Beginners to the stage, please". The actors/actresses are then called by name.

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

Separating the audio spectrum into two bands, i.e., high frequencies (high pass) and low frequencies (low pass) by means of an electronic crossover and using two separate amplifiers or channels of an amplifier. One amplifier or channel passes the high pass signals (high frequencies) to drive the high frequency component or horn of the speaker system. The other amplifier or channel passes the low pass signals (low frequencies) and drives the woofer or low frequency component of the speaker system. The advantage to biamp operation of a sound system is increased headroom and dynamic range.

Profile lantern with two sets of shutters, one of which produces a hard edge, and one a soft edge. Not necessary in zoom profiles, because this requirement is fulfilled by two lenses.

BIT - Binary Digit.

A compact low voltage display luminaire containing a Par 16 or MR16 lamp. So called because it is similar to, but much smaller than, the Parcan, and is hence "one under Par" (It's a golfing reference). Requires a 12 Volt external transformer, but is ideal for concealing in pieces of set or as downstage uplights. See also MR16.

Accidentally unlit portion of the stage.


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

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

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

Dimmers which are incorrectly trimmed are said to bleed. That is, the dimmer still gives a small output, causing the lantern to glow, when the control signal is at a minimum.

The facility on some lighting control desks for the operator to make changes to the plot, without affecting the state on stage.

Lamps arranged around the stage directed into the auditorium, originally to prevent spectators seeing the stage during scene changes when the house tabs were not lowered. Now used for effect in rock concerts etc.


    Blue lights used backstage in a performance situation.
    Also see WORKING LIGHTS.

(Bayonet Neill Consulman - after original inventor) Coaxial connector used for carrying a composite video signal or radio frequency signal.


    The main control for the stage lighting. Originally known as the switchboard or dimmerboard, it is now usually remote from the dimmers. The lighting operator for a show is said to be "on the board", and is sometimes known as the "board op".
    Colloquially, any control desk (e.g. Sound Board, Light Board).


    Vertical scaffolding pole (usually 48mm diameter) on which horizontal boom arms can be mounted, carrying lanterns. Often used behind wings for side-lighting etc. Booms have a base plate or stand at the bottom and are tied off to the grid or fly floor at the top (not always necessary for short booms). Booms can also be fixed to the rear of the proscenium arch (Pros. Boom) or hanging from the ends of lighting bars. Sometimes known in the US as a light tree. A light tree mounted upstage of a Tormentor is known as a Torm Tree.
    An arm mounted on a microphone stand.

A term used to indicate an increase in gain of a frequency or band of frequencies when equalizing an audio signal. Opposite of cut.

Control Room.

A narrow horizontal masking piece (flattage or cloth), normally of neutral colour (black) to mask the lighting rig and flown scenery from the audience, and to provide an upper limit to the scene. Often used in conjunction with LEGS.


    Diffuse light that has been reflected from the stage, walls, cyclorama etc.
    "Bounce" is sometimes used for a flat (non-curved) cyclorama. Strictly, a bounce is a white or light blue cloth onto which light is bounced to backlight another cloth. A bounce doesn't need to be seamless, whereas a cyclorama should be.
    Describes the fast in/out movement of "bouncing" flown house tabs, used during curtain calls. This can also apply to the fast blackout/lights up cues that happen at curtain calls.


A horizontal rope, wire or chain attached at either end of a piece of scenery or lighting bar pulling it upstage or downstage of its naturally hanging position to allow another flying item to pass, or to improve its position.

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

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

The ISDN standard that governs how phones and other electronic devices are connected to the ISDN switch.


    A walkway, giving access to technical and service areas above the stage or auditorium, or linking fly-floors.
    A videoconference bridge is usually made up of back-to-back codecs from different manufacturers to convert signals from one proprietary system to another.

Operating a stereo amplifier in mono via the bridge mode switch, which typically makes Channel A output the positive power rail and Channel B output the negative power rail. Since the signal swings between A and B Channels, the output of the amplifier is twice that of single channel operation.

Connecting one electrical circuit in parallel with another. Typically used to describe the process of connecting the output of a single device to the inputs of multiple other devices.

The attribute of visual perception in accordance with which an area appears to emit more or less light. (Luminance is the recommended name for the photo-electric quantity which has also been called brightness.)

Digital services at rates greater than 1.536 million bits (mbps), capable of supporting voice, video, and data, possibly using multiple channels.

(Especially TV and Film) Jargon for a replacement lamp.


    During lighting plotting, to construct a state from blackout, or to add to an existing state.
    An increase in light or sound level. SEE CHECK.
    A period of set construction ("The Build").

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

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

A conductor that serves as a common connector to several signal sources, most often associated with a mixer. A separate signal routing to a specified output.

Metal bar carrying incoming electrical supply into which portable dimmer racks or other large power requirements can be wired directly. An enclosure containing busbars is a Busbar Chamber.


Production & Styling Services for
events, functions and weddings

154 Fairs Road | Palmerston North
06 354 4421