Glossary of Terms - S

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.


A video transmission standard that uses a 4 pin mini-DIN connector to send video information on two signal wires called luminance(brightness, Y) and chrominance(colour, C). S-Video is also referred to as Y/C. A composite signal, typically found coming out of an RCA jack on the back of most VCRs has the Y and C information combined into one signal. The advantage of having luminance and chrominance separated is that a comb filter is not needed inside the video projector to separate the composite signal into the luminance and chrominance signals. A comb-filter can reduce the sharpness of your video image.

Chain or wire fixed around lantern and lighting bar or boom to prevent danger in the event of failure of the primary support (eg Hook Clamp). A requirement of most licensing authorities. In the UK, current legislation

An arrangement of lanterns in which to maximum number of spotlights is placed in every possible position.

General name for a moving mirror lantern, especially those used in discos, rather than the more flexible units used in theatre.


    A pre-programmed lighting state which can be faded in and out during a one night show when there's no time for plotting.
    A subdivision of a play.

Many types of projection screen are available. Some are multi-purpose, some only for front projection, some only for back projection. If a screen is not self-supporting, it often has eyelets around the outside edge which are used to "lace" the screen onto a larger frame. See also PROJECTION.


    A coarse gauze
    A fine metal mesh used to reduce the intensity of light from TV lanterns without affecting colour temperature.


A French and international broadcast standard for video and broadcasting. Higher resolution than NTSC.

Separately powered lighting system for use throughout the building in the event of failure of the primary system. Usually battery powered. Maintained lighting is on all the time, regardless of changes in the stage lighting, and is battery backed-up.
Non-maintained systems only light in the event of power failure or an alarm condition.
Secondary lighting systems should be regularly checked by an electrician to ensure they operate correctly.

The study of signs - many conventions in lighting design rely on signs (blue must be night-time, red is evil etc.)

An output used to patch a signal from a channel or bus of a mixer to an external signal processor such as an echo or digital delay.

The minimum input signal required to produce a specified level of output. In an amplifier, the input sensitivity is the amount of voltage at the input necessary to drive the amplifier to its rated power output. Loudspeaker sensitivity is the power level necessary to produce a stated SPL at a given distance from the loudspeaker, usually rated at 1 watt 1 meter.

An arrangement of circuit components, end-to-end, to form a single path for current.

A circuit in which some of the components or elements are connected in parallel, and one or more of these parallel combinations are in series with other components of the circuit.

An adaptor consisting of a plug and two sockets wired in series. Enables two identical 110 Volt loads to be safely run from a 240 Volt supply (UK).

A type of equalization circuit that has a shelf-like characteristic at the upper or lower ends of the spectrum. A shelving EQ at 15 kHz, in the boost position, would increase the high frequencies up to 15 kHz where it would shelf.

The common Australian term for AJ's, c-wrenches, spanners etc.

The lowest lantern on a lighting boom. Named because of the proximity of sharp parts of the lantern to the flesh of the lower leg.

Normally refers to a Short-Nose Parcan - a lighting instrument that uses a normal size PAR lamp, but has been shortened to either make it less obtrusive, or to get a wider beam angle.

A lens designed to project the largest possible image from short distance. Most front room projectors use a short throw lens. They are often required for rear projection, where the depth behind the screen is limited. A typical short throw lens might produce a diagonal image size of 10 ft, from a distance of 7 to 10 ft.

Part of a profile lantern. Metal blade which can be used to shape the edge of the beam. Shutters (normally four) are located in the gate at the centre of the lantern. Similar in effect to barndoors on a Fresnel or PC lantern, but a lot more flexible.

A pair of metal rings attached to the side or top of a followspot which enables the operator to accurately line up the beam (by looking down the length of the followspot through the rings) before turning it on. See GHOSTING.

The ratio of the amplitude or level of a desired signal at any point to the amplitude or level of noise at the same point.

To light the cyclorama or a piece of upstage set in such a way that the actors are cast into shadow. Can be a very dramatic effect.

A special type of diffusion frost filter which stretches the light in one direction. Especially useful for lighting large cycloramas with a limited number of lanterns, or for lighting an elongated object (eg a staircase) with one lantern.

A wave whose amplitude varies as the mathematical sine of a linear function of time, also known as the sinusoidal wave.

An internally-wired lighting bar, designed for touring, with six socket outlets terminated in a multi-way connector (e.g. Socapex or Weiland). Often pre-rigged with lanterns (eg Parcans). Stored in Meatracks. A bar pre-rigged with Parcans is sometimes known as a PAR BAR.

A echo caused from reflections off the rear wall in many auditoriums. Such echo can reduce the intelligibility of a sound reinforcement system, as well as distract speakers and performers on stage. Severe slapback echo is very distracting for a musician, as it can cause confusion that makes following that beat in time extremely difficult. A professional high quality stage monitor system can mask some of the slapback echo to a certain extent by providing more direct sound from the monitor speaker in the first 25 milliseconds which the performer perceives through auditory fusion as more direct field, thus increasing the ratio of the level of the direct field to that of the slapback echo.

The failure of the amplifier's output to move as fast, voltage-wise, as the input would have it move.

Refers to the ability of an amplifier's output to accurately reflect the input waveforms' rise time transients. An amplifier is said to have a slew rate of so many volts per microsecond. A slew rate of 20 volts per microsecond (20 V/U sec.) means that the amplifier is capable of swinging 20 volts positive or negative in the period of one microsecond.



Many theatre buildings have complex fire alarm systems installed. Some theatre spaces have smoke detectors in them, which trigger a fire alarm when the space fills with smoke. The use of SMOKE MACHINES in these spaces can (and does) result in expensive call-outs of the fire department and evacuated auditoria.
There are special heat-sensitive detectors called RATE OF RISE detectors which trigger a fire alarm when the temperature rises faster than it should normally. Properly calibrated (and regularly tested) these can be as effective than the smoke detectors (which work by "seeing" smoke particles in the air). If it's not possible to get Rate of Rise detectors installed in your theatre space instead of smoke detectors, you may be able (subject to local building regulations and local fire department advice) to isolate the smoke detectors for the duration of the performance when you use smoke effects. Properly designed alarm systems incorporate timed isolation, so that smoke detectors are only off for a specific period, and automatically come on after that period.

A Smoke Machine or Fogger is an electrically powered unit which produces clouds of white non-toxic fog (available in different flavours/smells) by the vaporisation of mineral oil. It is specially designed for theatre & film use. A Haze machine, Hazer or Diffusion Fogger is used to produce an atmospheric haze, rather than clouds of smoke, and is used by many lighting designers to reveal airborne light beams. The first smoke machines came onto the market in the late 1970's.
It's essential to know whether your venue uses SMOKE DETECTORS on the fire alarm system. See that entry for more information.

A multiconductor shielded input cable which allows a single run between the microphones and the audio mixing console. Snakes often provide "return" wire pairs to permit the mixer outputs to be sent to amplifiers located on stage.

A lighting or sound cue with no fade time - the cue happens instantly.


A multipin connector which can carry a series of lighting or sound circuits. Very robust and designed for touring. Available in 19 pin (6 circuits) and 37 pin (12 circuits) configurations. Sometimes shortened to SOCA.

Asymmetric flood light used as a fill light in TV studios to eliminate shadows and balance the key light.



    On a sound desk, the solo button on each input channel silences all other inputs so that channel alone can be heard. Dangerous to use during a show, but can be useful for fault-finding or testing equipment
    On a lighting desk, SOLO mode kills all other channels except the single dimmer you're working with. Again, can be useful for identifying a channel in a large rig, but can be dangerous during a show. Some desks allow you to assign flash buttons to SOLO mode which will turn off all channels except those loaded into that flash button or submaster.

A pressure wave motion propagated in an elastic medium (air) producing an auditory sensation in the ear by the change of pressure at the ear. Sound waves are produced by a vibrating body in contact with air.

The instrument used to measure noise and sound pressure levels (SPL), calibrated in decibels.


    Direct Field - the sound that emanates directly from a sound source or loudspeaker.
    Indirect Field - that sound perceived from behind a speaker system, i.e. when no direct field is present.
    Near Direct Field - the sound field that is generated close to the source or loudspeaker. Generally considered that sound field that is within a distance from the source of less than two wavelengths.
    Far Direct Field - the sound field that is perceived at a distance from the source loudspeaker that is greater than 2 wave lengths.
    Free Field - that portion of the direct field of a sound source or loudspeaker that is reflection free or not yet affected by boundaries such as walls or ceiling (such as may be encountered with an outdoor sound system).
    Reverberant Field - that sound field beyond critical distance where most of the energy arriving at the listener is in the form of reflected energy off the room's boundaries.

A facility which can link the effects panel on a lighting board to an audio input which detects treble, mid and bass beats, and can flash lights or trigger effects in time to those beats. First used when electronics allowed it cheaply in the late 1960's.


A lantern within the lighting rig which is required for a specific moment or effect within the performance, and is not part of the general cover lighting. See GENERAL COVER.

Refers to a particular band of frequencies. The normal acoustic sound spectrum is the range of human auditory perception (20 Hz to 20,000 Hz). There is also a Subsonic spectrum (considered to be below about 40 Hz) and an Ultrasonic audio spectrum (above 20,000 Hz).

See Real Time Analyzer (RTA)

Adaptor to connect many lanterns to one multicore cable. Consists of multipin connector (typically Socapex or Lectriflex), short length of cable, then a number of sockets related to the number of circuits in the cable.

An adaptor screwed onto the hanging bolt of an instrument to enable it to be used on an upright stand.

Unwanted light onstage.

Concentric rings attached to the front of a beamlight (eg Strand Pageant) to contain spill.

The level or intensity at a point in a sound field (loudness). The deviation above and below normal atmospheric pressure. The unit of measurement of Sound Pressure... the microbar. One microbar is equal to the sound pressure of 1 dyne per square centimeter, which is a sound level of 74 dB above the threshold of hearing (0.0002 microbar.) It is also equal to approximately one-millionth of normal atmospheric pressure. Sound pressure levels are stated in decibels as follows: Where P is the RMS sound pressure in microbars, and the reference is the threshold of hearing of 0.0002 microbars (50% of young men, 1 to 4 kHz).


    A box which has one signal input and has two or more individual outputs available for that signal. Used to connect one signal source to multiple other devices.
    See also ADAPTOR.

Chair for suspending followspot operator above a stage / auditorium. Normally rigged on a truss system. The operator gets to the seat up a wire rope ladder, and is strapped into the seat. He or she will normally wear a harness when getting to the chair for extra safety. The seat itself is an adapted car "bucket" seat.

General term for any lantern with a lens system. See FRESNEL, PC, PROFILE.

A new industry standard developed to ensure standard, uniform colour reproduction regardless of the type of display used. sRGB colour profile technology uses colour coordinates common to all display technologies. As a result, it eliminates the hue variations that occur between different display systems. 16:9.

A connection box at the end of a lighting or sound multicore cable.

Member of the electrics staff whose responsibility it is to set or clear electrics equipment during scene changes. May also carry out colour changes on booms etc.

Left/ Right as seen from the Actor's point of view on stage. (ie Stage Left is the right side of the stage when looking from the auditorium.)
Stage Right = OP (Opposite Prompt) French: CotÚ Jardin, Netherlands: Toneel Links (translates to Stage Left!)
Stage Left = PS (Prompt Side) French: CotÚ Cour, Netherlands: Toneel Rechts (translates to Stage Right!).


    Standing waves occur in rooms because of the boundaries. A standing wave is a soundwave that once excited, stands there, i.e., the positive air pressure peaks (antinodes) and negative air pressure troughs (nodes) remain in the same position within the room's boundaries. Also known as a stationary wave.
    See also MODES.

In lighting terms, a lighting "picture" ; each lighting cue results in a different state (or a modified state).


    Refers to a steel blue / pale blue lighting gel. (Lee 117) (e.g. "Use the Steel General Cover for the scene in the castle"). See also STRAW.
    Many set construction now uses steel frames with timber cladding. Steel is stronger and lighter weight compared to timber of the same size.
    Generic term used for a plain wire rope sling. Also used when referring to roof structural steel and individual steel beams or scaffold materials and so on.


    A control on some lighting effects boards which enables the operator to "step" through a chase effect in time to music etc.
    Each separate component of a lighting effect is called a step. A chase effect with four channels flashing on will have four steps.

In a sound reproducing system, stereo refers to the use of two separate signal processing channels driving two separate power amplifiers, which in turn power two separate speaker systems. However, most times in sound reinforcement, a stereo mixer is employed to drive a mono (single channel) system in order to allow separate mixes of the program (such as speaking mics, instrurnents, vocal mics, etc).

Refers to a pale yellow lighting gel. (e.g. Use the Straw General Cover for the garden scene). See also STEEL.


    A thin linear filament lamp similar to an Architectural, but having contacts at the ends of the lamp. Available clear or opaque.
    See also BATTEN.

Device giving a fast series of very short intense light flashes which can have the effect of making action appear intermittent. Because strobe lighting can trigger an epileptic attack in sufferers, the use of a strobe must be communicated to the audience before the performance begins. Strobes should be synchronised so that they operate outside the dangerous frequency band 4 to 50 flashes per second. (i.e. a strobe should operate at less than 4 flashes per second, or more than 50 flashes per second). If the effect is momentary, this rule may be relaxed. Strobes must never be used in public areas where there are changes of level or steps. Always seek the advice of the licensing authority if you are in any doubt about the safety of strobe effects.


    Fader on a lighting desk which can have a lighting state recorded onto it for additional control, or to use when manually mixing lighting states for music concerts or one-off events.Lighting desks normally have a series of submasters (12 or 24 are common) which can have states, cues or effects loaded onto them. Some desks can have submasters set to inhibit the main output (known as INHIBITIVE SUBMASTER. For example, the FOH lighting can be loaded onto a submaster which is then brought down as the house tabs are flown in between curtain calls to block light spill onto the tabs). Multiple cues can be recorded onto some submasters through the use of pages. A PILE-ON submaster can be used to add its contents to the existing lighting state. Any number of pile-on submasters can be used in combination to modify a state.
    A separate audio mixing bus assigned to a group of mixing channels that enables the sound mixer to regulate the level of that group with one control called the Sub-Master.

A level control preceding the main (master) level control, that regulates the level of an individual sub-mix.


SVGA is used to define a specific display resolution. Resolution is defined by the number of individual dots that a display

uses to create an image. These dots are called pixels. An SVGA display has 800 horizontal pixels and 600 vertical pixels giving a total display resolution of 480,000 individual pixels that are used to compose the image delivered by a projector.

An input or output jack that performs some switching function in addition to providing an input or output for a signal. These jacks disconnect the normal flow of signal and allow for additional patching capabilities such as inserting equalizers and feedback reducers. Most typically these are 1/4" phone jacks, but some equipment manufacturers are now using switching RCA type phono connectors.

Safe Working Load.

SXGA is used to define a specific display resolution. Resolution is defined by the number of individual dots that a display uses to create an image. These dots are called pixels. An SXGA display has 1280 horizontal pixels and 1024 vertical pixels giving a total display resolution of 1,310,720 individual pixels that are used to compose the image delivered by a projector.


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