A Glossary of Terms Commonly Used in the Lighting Industry

ALTERNATING CURRENT (AC): Current that changes its direction of flow through a conductor, going first one way, then the other. The usual rate used is 60 alternations (60 times each way) per second.

AMPERE (AMP): The unit for measuring rate of flow of electrical current.

ARC TUBE: A quartz tube in which a current traverses a gas between two electrodes.

ARGON: An inert (will not unite with any other elements to form chemical compounds) gas used in incandescent and fluorescent lamps. In incandescent lamps it helps to retard evaporation of tungsten filament.

BALLAST: A part of every fluorescent lamp fixture. It is a circuit that controls the rate of flow of electrical current through a fluorescent lamp. Also used for mercury vapor, sodium vapor and other HID sources. (HID - High intensity discharge)

BEAM CANDLEPOWER: A measurement of beam intensity from reflector lamps as opposed to overall lumens of non-reflector lamps.

BLACKBODY: A theoretical body used by the lighting industry as a standard for establishing the "color" and spectral qualities of lamps. A perfect blackbody, when its temperature has risen to 3500K would give out light of a certain color; at 4500K it would give a whiter color, and at 5500K a still whiter color.

BULB DARKENING: The darkening of an incandescent lamp caused by small particles of tungsten that evaporate from the filament and deposit on the bulb as the filament burns.

CANDLEPOWER (CP): Candlepower is a measurement of light intensity. It is used as a measurement of beam intensity at various angles from reflector lamps or fixtures.

CATHODE: A cathode is an electrode that emits or gives off electrons - the type of electrode in a fluorescent lamp. The fluorescent lamp cathode emits or discharges electrons to the cathode (acting also as anode) at the opposite end of the lamp.

COLOR RENDERING INDEX (CRI): A rating method by which fluorescent, or any other light source, is evaluated according to its ability to impart color to colored objects, with natural outdoor light having a CRI of 100. Cool White has a CRI of 62, Vita-Lite has a CRI of 91.

COLOR SPECTRUM: All the radiant energy wave lengths that make human sight possible. The visible wave lengths include all colors and are measured in nanometers.

DIRECT CURRENT (DC): Electric current without alternations - that flows in one direction only. Duro-Test has direct current fluorescents available in 20-watt Daylite. DC does not affect incandescents adversely. High voltage Fluormerics (230v or higher) can be used on DC. Should be utilized with polarity switches.

EMISSION COATING: An oxide coating deposited on a cathode that emits electrons when heated.

FILAMENT: The threadlike tungsten wire that incandesces or lights up when an electric current runs though it. The light source in an incandescent lamp.

FOOTCANDLE: The unit of illumination: one footcandle is one lumen per square foot.

FLUORESCENCE: Light resulting from the action of ultraviolet or other forms of energy on phosphors. Fluorescence occurs only while energy is being absorbed by the fluorescing material.

HIGH BAY: High ceiling, usually in an industrial plant. Because of height, it may be hard to reach for lamp changers without special ladders or scaffolding. Usually above 20 ft.

H.I.D.: Any class of high-intensity-discharge lamps, such as mercury vapor, metal halide, high pressure sodium, xenon and Optimarc.

HIGH OUTPUT (HO): A fluorescent lamp designed for use with an 800 milliampere ballast. Will usually operate at low temperatures near zero and still produce high light output.

HIGH VOLTAGE: Voltage of 208 and higher.

INCANDESCENCE: Light emission by a heated filament or coil.

INFRA-RED: Radiant energy with wave lengths that are longer than the wave lengths of the visible spectrum. Applications include photography, drying or baking materials in industry, medical heat therapy, heating food, etc.

INSTANT START: Refers to fluorescent lamps that start instantly - without pre-heating of cathodes, and without the need of starters. "Instant Start" lamps have coiled hot cathodes in contrast to "Cold Cathode" lamps. Both, however, start cold and instantly. A higher voltage ballast is required for instant start lamps than for pre-heat. Instant starts differ from rapid start lamps and cannot be used in rapid start fixtures.

KELVIN TEMPERATURE: Term used to indicate the comparative color appearance of a light source compared to a theoretical blackbody. Yellowish incandescent lamps are 3000K. Fluorescents range from 3000K to 7500K.

KILOWATT: One thousand watts. KILOWATT HOUR: One thousand watts of electric energy consumed in one hour. For example; one 1000-watt lamp or ten 100-watt lamps burning for one hour.

KRYPTON: A very heavy, inert (will not unite with any other elements to form chemical compounds) gas which permits the filament in an incandescent lamp to glow hotter and brighter while still providing long life.

LOUVER: A frame fitted with slats or cross pieces that is fitted into an opening of a light fixture. For lighting fixtures, the cross pieces in louvers act to reduce glare from exposed lamps. May also improve appearance of fixtures, although they sometimes reduce light output somewhat.

LUMEN (LM): The amount of light that is spread over a square foot of surface by one candle when all parts of the surface are exactly one foot from the one candle light source.

LUMEN MAINTENANCE CURVE: This curve shows the loss of light output against the life of the lamp.

LUMINAIRE: A lighting fixture complete with lamps installed.

NORTH LIGHT: Scattered (not direct sunlight) light from the north sky at noon. About 7500K.

PREHEAT: A fluorescent system, which requires starters. With this system several seconds of heating time are necessary between the time the circuit is turned on and the time the lamp produces light.

RAPID START: A fluorescent system, which does not require starters and usually requires 1 to 2 seconds to start. Current flows continuously through the electrodes keeping them hot and electron emissive.

SPECTRAL DISTRIBUTION CHARTS: The term "spectral distribution" refers to the various wave lengths (colors) of light emitted by a lamp, and to the intensity or power of the various wave lengths.

STARTER: A starting switch needed for preheat fluorescent fixtures to "start" or light a lamp. It preheats the lamp cathodes and also provides a powerful electrical "kick" to jump the current through the lamp from cathode to cathode.

ULTRA-HIGH OUTPUT (UHO): A fluorescent lamp, which operates with a 1,500 milliampere ballast. It is used whenever higher footcandle levels are needed, using fewer lamps. Also called VHO - Very High Output or SHO - Super High Output. Power-Groove T-17 bulbs use the 1500 ma. ballasts.

ULTRAVIOLET: Radiant energy of wave lengths shorter than the wave lengths of visible light. "Ultra" means beyond; so ultraviolet rays are beyond the violet end of the spectrum; that is, beyond the range of sight.

VISIBLE SPECTRUM: The complete range of energy wavelengths that activate human eyesight.

WATT: The unit of electrical power as used by an electrical device during its operation. The more lumens per watt, the higher a bulb's efficiency.