Glossary of Terms - I

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.


Nonlinear distortion characterized by the appearance of output frequencies equal to the sums and differences of integral multiples of the input frequency components. For instance, an amplifier with high IM distortion amplifying two frequencies of 100 Hz and 2,000 Hz would also generate distortion components of 1,900 Hz and 2,100 Hz.

The total opposition to alternating current flow presented by a circuit. The resistance to the flow of alternating current in an electrical circuit, generally categorized as either "high" or "low", but always expressed in ohms. Commonly used to rate electrical input and output characteristics of components so that a proper "match" can be made when interconnecting two or more devices, such as a microphone, loudspeaker or amplifier.

The condition in which the external impedance of a connected load is equal to the internal impedance of the source, thereby giving maximum transfer of energy from source to load, minimum reflection, and minimum distortion.

A type of signal that switches on and off as opposed to remaining in a steady state like a continuous sine wave. Music is more impulsive in nature than it is steady state.

Light source consisting of a metal filament (Tungsten) which glows white hot when current is passed through. See also DISCHARGE LAMP.


    An electrical power supply that is totally separate from the stage lighting control. Used for testing lanterns prior to connection to the lighting system and also for powering non-lighting equipment on stage and working lights. See NON DIM.
    A channel within the stage lighting control which has been temporarily switched to become independent from the rest of the channels which remain under the control of the operator.

That property of an electric circuit or of two neighboring circuits whereby an electromotive force is generated (by the process of electromagnetic induction) in one circuit by a change in itself or in the other.

A coil of wire used to create an impedance whose reactive component is low, therefore offering low resistance at low frequencies and high resistance at high frequencies. An inductor passes low frequencies and attenuates or rolls off high frequencies.

A baffle that effectively prevents all of the loudspeaker's rear sound waves from interfering with its front waves.

Invisible part of the electromagnetic spectrum with a longer wavelength than visible light. Infra-red remote controls are used for lighting desks and practicals. An infra-red-sensitive CCTV camera can pick up body heat activity even in a "blackout".

The traditional remote control, it transmits infra-red, just as a television remote. Typical range is limited to 30 - 35 feet. Infra-red requires line of site or a bounce off of a hard surface. The presenter must pay attention to where the remote is pointed. Some projectors have an IR sensor in both the front and rear of the projector, which can help. When working at or near the maximum distance, pointing right at the receiver is necessary. Remember "line of sight" - a person's head, directly between your remote and the projector may be enough to render it unusable. FM (radio frequency remote mousing systems, by comparison, have two distinct advantages, no line of sight requirement, and longer range.


    A way of taking control of a rogue lantern (or lanterns) at the lighting desk during the operation of a show and removing them from any further lighting states, until the inhibit is removed. Can also be used for removing the front of house lighting from a curtain call state.
    See also SUBMASTER.



    An additional route into a sound desk.
    An extra lighting state added into the sequence later. See POINT CUE.


    An electrical system in a particular building (e.g. "the stage lighting installation was tested last year")
    A piece of art designed to transform a particular room or building into something other than a room in an art gallery. Installations often use complex audio-visual equipment and can be intensely immersive experiences. As with all art, they can also be rubbish.

Same as a LANTERN or LUMINAIRE in the UK/Europe.


Method of significantly increasing data densities at conventional horizontal scan rates. Half the image is refreshed (every other scan line) to produce a field. Two fields are refreshed at rates of 87 Hz forming one 43.5 Hz frame. Causes flicker on CRT displays.

A unit that can operate under international selection of power requirements. The specs of units vary widely, but the minimum is 105-230 volts, and 50-60 cycles AC (alternating current). If you see a specification like 110v, 220v instead of a range, those ratings are usually +/- a given percent such as 10%. Some units are "self-switching" they will automatically switch to whatever power source you plug it into. Others will have to be switched (internally or externally to accommodate a different voltage or cycle range.

A state of compatibility between videoconferencing units that may support differing levels of compatibility.

A Scaffolding bar (aluminium) which has a number of sockets (usually 15A) positioned along its length, the wiring for which is contained within the bar. See SIX LAMP BAR.

Distortion produced by too strong a signal from the output of a microphone or other signal source connected to the input of a preamplifier.

A loss in gain of a system after a component has been added or inserted in the system, usually expressed in decibels.

Invert image flips the image from top to bottom to compensate for ceiling mounting a projector upside down. Projectors typically ceiling-mount upside down, because most have "keystone" correction built in to compensate for the distortion created by "pointing up" from the table to the screen. Usual positioning has the projector about even with the bottom of the screen in a "table top position," or even with the top of the screen when ceiling mounted.

Internet Protocol. Allows for videoconferencing over LAN or commercial Internet.

Many new laptops have an Infra-Red transceiver that follow a recent standard for wireless communicating with peripherals (new laser printers complying with the standard) and networks or desktop systems. If you have a laptop like this, you know the pleasure of walking into a room with a configured laser printer, and printing out documents without having to "plug-in." Only a couple of projectors are available that follow this standard. This allows their remote controls to talk directly to your laptop for remote mousing.

Adjustable aperture which, when placed in the gate of a profile lantern, varies the size of a beam of light. Originally, iris diaphragm.

Integrated Services Digital Network is an international standard for digital services on the public switched telephone network.


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