Term Definition
Accent Lighting Directional lighting to emphasize a particular object or to draw attention to a part of the field of view.

Absorption The dissipation of light within a surface or medium.

Accommodation The process by which the eye changes focus from one distance to another.

Adaptation The process by which the visual system becomes
accustomed to more or less light than it was exposed to during an immediately preceding period. It results in a change in the sensitivity of the eye to light.

Alternating Current (AC) Flow of electricity which cycles or alternates direction many times per second. The number of cycles per second is referred to as frequency. Most common frequency used in this country is 60 Hertz (cycles per second).
Ambient Lighting Background or fill light in a space.

Amperes (amps or A) The unit of measurement of electric current.

Back Lighting The illumination provided for scenery in off-stage areas visible to the audience.

Baffle An opaque or translucent element that serves to shield a light source from direct view at certain angles, or serves to absorb unwanted light.

Ballast An auxiliary device consisting of induction windings wound around a metal core and sometimes includes a capacitor for power correction. It is used with fluorescent and HID lamps to provide the necessary starting voltage and to limit the current during operation.

"Batwing" Distribution Candlepower and distribution which serves to reduce glare and veiling reflections by having its maximum output in the 30° to 60° zone.

Candela The unit of measurement of luminous intensity of a light source in a given direction.
Candlepower Luminous intensity expressed in candelas.

Candlepower
Distribution Curve		 A curve, generally polar, representing the variation of luminous intensity of a lamp or luminaire in a plane through the light center.

Cavity Ratio A number indicating cavity proportions calculated from length, width and height.
Class "P" Ballast Contains a thermal protective device which deactivates the ballast when the case reaches a certain critical temperature. The device resets automatically when the case temperature drops to a lower temperature.

Coefficient of
Utilization (CU)		 The ratio of the luminous flux (lumens) from a luminaire calculated as received on the work-plane to the luminous flux emitted by the luminaires lamps alone.