Glossary of Terms - P

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 fixed passive network which reduces the electrical level of an audio signal. An attenuator.

An ordered group of data and control signals transmitted through a network as a subset of a larger message.


    Some theatre announcement systems use the term "PAGE" to mean making a call (e.g. "Can you page Simon to come to the fly floor")
    A way of increasing the functionality of a control on a lighting desk. For example, most computerised lighting desks with SUBMASTERS will allow you to store more than one lighting state in each submaster. Each group of submasters is given a page number which is used to select which set you want to use.
    Also see SUBMASTER.

Connecting more than one lantern to one power outlet via an adaptor or splitter, or more than one speaker to one amplifier channel.

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


    A control on a mixing desk which allows the operator to position the channel's output in the final stereo image (L - R).
    A horizontal (side-side) movement of a camera or a moving light. See also TILT.

Also known as a projection panel, LCD projection panel, or plate. The panel is the predecessor of today's projectors. It is slightly larger and heavier than a notebook computer and the LCD it uses to produce an image is very similar to that of the notebook computer. Because panels lack their own light source, they are designed to sit on top of a transmissive overhead projector (OHP). (See the definition of Overhead Projector for lumen performance.) Because of its small size, low cost, and versatility, panels have been a popular solution for education applications where an OHP is frequently available in the classroom for other instructional purposes. A few products have been built that integrated the panel and the OHP. These were some of the earliest projectors.

An all digital interface used to transmit computer video from a PC/Notebook to a projector. Supports resolutions from 640x480(VGA) up to 1600x1200(UXGA). This digital interface might someday replace the analog VGA interface typically used to connect projectors to computers.


    Short for Parabolic Aluminised Reflector lamp. A lamp containing a filament, reflector and lens in one sealed unit. Used in PARCANs to produce a high intensity narrow beam of light. Par lamps are available in many different sizes and powers. Par sizes available include 16, 20, 36, 38, 56 and 64. (The number refers to the diameter of the lens, in eighths of an inch). The most common for theatre use are Par 64s rated at 1000W (1kW), although other wattages are available. 110V Par lamps are often used in large UK venues or for touring due to the increased light output. Because the current is greater, the lower voltage lamps have smaller thicker filaments which give a more focussed beam than the thinner 240V filaments.
    In the film business, PAR lamps are known as "bird's eyes" after the alleged inventor Clarence Birdseye.


    A bar pre-rigged with a number of Parcans is.
    See also SIX LAMP BAR.

See PAR.


    The folding frame that forms the base of a readily portable platform.
    The opposite of SERIES when referring to wiring two loads into one outlet.
    An electric circuit in which the elements or components are connected between two points with one of the two ends of each component connected to each point. The two loads share the available current, but are both given the same voltage.

A type of equalization circuit that has three variable parameters; frequency, cut or boost bandwidth, and Q (the width of the filter).


    Type of lantern which produces an intense beam of light, ideally suited to "punching" through strong colours, or for special effect. The Parcan is literally a cylinder of metal (the "can") within which sits the PAR lamp (PAR stands for Parabolic Aluminised Reflector) which consists of the bulb, a reflector and a lens in a sealed unit. The Parcan first appeared in the early 1970's in the Rock concert industry due to the intensity of the beam, and the light weight and near indestructibility of the lantern. The lens of the lamp is either clear (which produces a narrow beam), frosted (medium) or stippled (wide).
    Also see PAR and FLOORCAN.

An electronic circuit composed of passive elements, such as resistors, inductors, or capacitors, without any active elements, such as vacuum tubes or transistors generally resulting in a signal loss.

The original LCDs, these are controlled by a single processing system, for the whole screen, unlike active and poly-si, which have descrete circuits for each "pixel." This results in a panel with terrible colour dynamics and contrast (typically 15:1). They are also incredibly slow: On passive laptop computers, the cursor (or anything else) moving on the screen, goes invisible until you stop moving it (submarining) Only one or two projectors use any type of passive matrix display.


    (verb) The act of plugging a lantern into a dimmer (e.g. "Can you patch circuit 12 into dimmer 18 please").
    (noun) The system for connecting lanterns to dimmers (The Patch).
    The term also applies to sound - a PATCH BAY is used to connect outboard equipment into the sound desk and to connect sound desk outputs to amplifiers, and amplifiers to speakers.


    A board consisting of rows of sockets into which plugs can be connected to route sound signals or power for lighting circuits. Some American systems use a Pin Plug patching system.
    See also PATCH.

1. To cross-connect lighting circuits around the stage area to a chosen dimmer. Connecting lanterns to dimmers.
2. Using a cross-connect panel which enables any stage lighting channels to the control desk to control any dimmer or group of dimmers. Some large lighting boards have the facility for soft patching - a totally electronic way of patching. Some Rock Desks have a pin patch which allows groups of dimmers to be allocated to a particular control channel. Also applies to routing of sound signals.


Private Branch Exchange.

Originally short for plano-convex - the basic lans shape of many lanterns / projectors. Now short for Prism- or Pebble-convex: a type of lens with a pebbled flat surface which gives a slightly harder edge than a Fresnel, but not as hard as a Profile. PC refers to a lantern with a PC lens.

The maximum instantaneous value of a signal amplitude.

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

A device which automatically limits the level of its output signal to approximate a preset maximum value by reducing its gain when the signal exceeds a preset value.

Amplitude of an alternating voltage measured from negative peak to positive peak.

See PC.

Trick used to make a ghost appear on stage next to an actor. A sheet of glass is hung across the front of the stage so that the image of an actor standing in the orchestra pit appears to float on stage. First shown at the Royal Polytechnic Institution in London by J.H.Pepper on Christmas Eve, 1862. Following many subsequent events, Charles Dickens used it during readings of The Haunted Man. Several plays were written specially to use the effect around 1863, but the long-term future of the effect was limited by the fact that the ghost couldn't speak. Peppers Ghost is now used to great effect in smaller scale applications like the Haunted Mansion in Disney theme parks.

Dimmer levels are expressed as a percentage of the supply voltage. (100% = 230 - 240 Volts(UK)).


    Lighting positions (often on platforms) at each side of the stage, immediately behind the proscenium.
    Some theatres use the term for vertical boom positions in front of the proscenium in the house.

Pre Fade Listen. This describes a button on a mixing console that permits a channel or sub to be monitored before that channel or sub's level control or fader. This allows an operator to listen to a channel without that channel being heard by the audience.

Phase is the time interval between two related events. Two signals are in phase when they reproduce the same sound or signal simultaneously; they are out of phase to the extent that one leads or lags behind the other in time. A signal is said to be in phase with another when the voltage and current amplitudes begin at the same time and move in the same direction.

Signals that are out of phase will cancel one another according to the difference in phase in degree. A transducer (speaker or microphone) wired out of phase with another will result in reduced output from both; instead of their combined outputs adding, they will subtract due to phase cancellation.

Electricity is generated and supplied to large installations as three separate supplies, known as phases.

The property of some materials that can store light energy and glow in the dark.

A lamp used by photographers which gives a bright white light. Because it has a thin filament, it gives a good flash effect (eg lightning), but has a relatively short life, so should not be left on for any length of time.


    Device which, when attached to an acoustic musical instrument, converts sound vibrations into an electrical signal.
    A way of describing the directional sensitivity of a microphone. An Omnidirectional microphone has equal pick-up from all around, a Cardoid microphone is more sensitive from the front, a Hypercardoid has very strong directionality from the front. A figure-of eight microphone picks up front and rear, but rejects sound from the sides.
    The action of turning a followspot on a performer. (e.g. "that was a good pick-up", "your next pick-up is downstage left"). A BLIND PICKUP is on a moving performer and requires good hand-eye co-ordination. A SET PICKUP is on a specific area, is preset, and is made on a cue from the stage manager. A SIGHT PICKUP is made visually by the operator to a preset position.

Having the ability to generate a voltage when mechanical force is applied; or to produce a mechanical force when a voltage is applied, as in a piezo-electric crystal.


An inward bowing of the video image. Some projectors experience a slight amount of pincushion distortion. There are guidelines on what the specifications are for each model. The pincushion changes according to the size of the image. Pincushion is similar to bowing or barrel distortion.




    A lantern focused very tightly on a small area (eg an actors head)
    A luminaire used widely in disco installations, consisting of a low voltage (6V) Par 36 lamp (lamp code is 4515) with a very narrow beam in a metal case with built in transformer.
    Pin Spots are ideal for lighting MIRRORBALLs.

Picture In Picture.

The smallest element of a display that has the full-colour capacity of the display.

A scale drawing showing a piece of scenery, lighting layout etc from above. Lighting plans are usually drawn onto the theatre's groundplan.

Professional Lighting and Sound Association (UK). See ESTA for the American equivalent.

The part of a computerised lighting control desk which enables the operator to recall cues from the electronic memory.


    List of preparations and actions required of technical crews during the performance (eg Sound Plot = list of sound cues and levels in running order.) In the US, the term plot refers to a plan. (eg Light Plot = scale plan showing lighting instruments). See also RUNNING PLOT, STATE PLOT.
    The basic story thread running through a performance / play which gives the reason for the character's actions.

Time during which the plot for each department is prepared (eg Lighting Plotting session)

Plug and Display.

Plug and Play.

A cue inserted during / after plotting between two existing cues. (eg 8.5 is inserted between cues 8 and 9). Most computer lighting desks have the ability to either insert an additional cue in a sequence, or to link to another cue out of the sequence, and then link back again. Inserting cues into a plotted sequence on a manual lighting desk is more awkward, because it is a running plot (where only the changes between cues are noted down). Sound cues within a sequence should have lettered cues (e.g. 8A is a fade up of Cue 8 and 8B is the fade out).

A source of acoustic sound waves having definite position but no extension into space. A point source is an ideal; an imaginary single point in space. This imaginary point source provides a good approximation for distances from the point source that are much larger compared to the actual dimensions of the source. A cluster or array of horns and loudspeakers is positioned using this imaginary point in space as a reference for the actual source of the sound. Properly configured the array will perform as a single or point source of sound.

The quality of having opposite poles. In electro-magnetic-mechanical systems, some form of potential is referenced to one of two poles with different (usually opposite) characteristics, such as one which has opposite charges or electrical potentials, or opposite magnetic poles.

A mechanical means whereby pan (horizontal rotation), tilt (up and down) and focus of a lantern may be adjusted by a pole from floor level. Commonly used in TV & Film studios where fast resetting of positions is necessary.

A popular LCD technology for the top of the line LCD projectors. Monochrome Poly-Si LCDs are typically placed in each of the three colour light paths inside a projector, one each for Red, Green, and Blue. This results in increased colour saturation, with contrast ratios above 200:1. Poly-Si technology is also a bit faster than the Active Matrix TFT, for smooth video and multimedia.

The physical interface to a computer multiplexer, for connection of terminals and modems.

(after) on a mixer; post indicates that the function is derived after the channel slider or gain control.

Electrical energy, measured in watts, such as the current from an amplifier used to drive a loudspeaker. Power in watts is expressed as W = V2/R

The final active stage of the audio chain, designed to deliver maximum power to the load or speaker impedance for a given percent of distortion.

Power connector with the same body design as the SPEAKON speaker connector. Manufactured by Neutrik. Used extensively on lighting patch panels (at least in the UK) due to its smaller physical size.

A zoom lens with the zoom in and out controlled by a motor, usually adjusted from the projector's control panel and also the remote control.

Any object which appears to do onstage the same job it would do in life, or any working apparatus (eg light switch or tap). Light fittings which have to light up on the set are called Practicals.

(before) On a mixer, pre fade listen (PFL) indicates that the function is derived before the channel slider or gain control pre monitor send, the monitor send is before and independent of the channel slider or gain control. A pre monitor send is usually pre channel EQ also.

An amplifier whose primary function is boosting or amplifying the output of a low level audio-frequency source, (such as a microphone), so that the signal may be further processed without appreciable degradation of the signal-to-noise ratio of the system. An amplifier which increases electrical signals from a microphone or other instrument to a level usable by a power amplifier. Preamp levels are approximately .1 volt.

A means of obtaining an output signal from the preamplifier of a channel of a mixer or musical instrument amplifier. The preamp out is actually a line level signal or 1 volt.


    Smoother lighting builds from zero are achieved when a lamp filament has been warmed (at approx 15%) in the previous state.
    Preheating lamps MAY prolong the life of the lamp by reducing the thermal "shock" of going to 100% instantly. It's good practice to preheat lamps where possible, and some computerised lighting desks provide this function at the push of a button.
    See also RIG CHECK.


    Anything in position before the beginning of a scene or act (eg Props placed on stage before the performance, lighting state on stage as the audience are entering.)
    An indepenently controllable section of a manual lighting board which allows the setting up of a lighting state before it is needed. Each preset has a master fader which selects the maximum level of dimmers controlled by that preset.

A function on some memory lighting control desks with video mimics. Preview enables the operator to see the levels of dimmers and other information in a lighting state other than that on stage.

Primary Rate Interface is the combined signal-carrying capacity of 23 B-Channels (Bearer Channels) operating at 64 kbps and one D-Channel (Data Channel) also functioning at 64 kbps. The total capacity is equal to that of 1 DS-1 circuit.

The primary additive colours of light are red, green and blue, and the subtractive colours are cyan, magenta and yellow.

Table in the auditorium at which director/designer etc sit during rehearsals (especially technical rehearsals). Usually has its own lighting and communications facilities.


    A type of lantern with at least one plano-convex lens which projects the outline of any chosen shape placed in its gate, sometimes with a variable degree of hardness/softness. Profiles include four beam-shaping metal shutters, a gate to take an iris or gobo and an adjustment to make the beam smooth and even ("flat") or hot in the centre ("peaky"). See Bifocal Spot, Zoom Profile.
    Shaped piece of scenery added to the edge of a flat instead of a straight edge. Also known as a cutout.

This usually refers to a signal source composed of music and/or speech as opposed to sine wave or noise.

The level of program material in an audio system expressed in VU.

The distance between the projector lens and the screen measured in linear units (e.g., metres, feet, or inches).

The panel is the predecessor of today's projectors. It is slightly larger and heavier than a notebook computer and the LCD it uses to produce an image is very similar to that of the notebook computer. Because panels lack their own light source, they are designed to sit on top of a transmitting overhead projector (OHP).


    Slides are used to project still archive images or textures. Libraries of slides contain images for every occasion. Kodak Carousel projectors are the industry standard, and some types can be linked to a controller to perform complex dissolves and fades from one projector to another. More powerful projectors are available using very intense discharge sources and large format glass slides to produce a massive image.
    Lighting effects: Moving cloud / rain / fire effects can be achieved using a powerful lantern known as an effects projector with a motorised glass disc painted with the required effect. An objective lens is required in front of the disc to focus the image. See Effects.
    Gobos: See GOBO.
    Film: 35mm film projection is common in many theatres as a device for keeping the building open to the public when productions are in preparation. 16mm film projection is used in smaller venues. Film projection can, of course, also be integrated into a performance.
    Video: Video projection is now being used to bring television pictures to the large screen. Cheaper than using film, but the image quality is not as good. Video projection equipment can also be more difficult to set up. Images can be front projected or back/rear projected depending on the amount of space and the effect required. For example, if actors are required to walk in front of the screen and not have the image appearing on them, back projection is the only answer.
    See SCREEN.

A projector is a device that integrates a light source, optics system, electronics and display(s) for the purpose of projecting an image from a computer or video device onto a wall or screen for large image viewing. There are hundereds of products available in the market and they are differentiated by their resolution, performance and features. These devices attach to a computer or video device as you would connect a monitor.


    A formal set of conventions governing the formatting and relative timing of message exchange between two communicating systems.

The boost in low-frequency response when a unidirectional or proximity effect microphone is used close to a sound source.

Public Switched Telephone Network. The telecommunications network commonly accessed by ordinary telephones, key systems, PBX trunks, and data equipment.

Power Supply Unit.

The amount of electrical power required by a touring show in a venue.

Plastic insulating tape used for taping cables to bars and for securing coiled cables. Neater and cheaper than Gaffa tape. Also known as LX tape.

(Pyro) Chemical explosive or flammable firework effects with a manual detonation. Usually electrically fired with special designed fail-safe equipment. There are many different variations of pyrotechnic effects available. The categories are as follows:

    Theatrical Flash - a flash and a cloud of smoke
    Maroon: produces a very loud bang. Must only be detonated inside a bomb tank covered with a protective mesh.
    Gerb: version of the Roman Candle firework, throwing a shower of sparks into the air. Possibly named from the French "Gerbe" meaning a sheaf of wheat, due to it's shape.
    All pyrotechnics should be used with close reference to local licensing laws, and the manufacturer's instructions. Professional advice should be sought before the first use of effects. Some territories only permit licenced pyrotechnicians to use these devices.


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