Terminology of the Lighting World

Acrylic:    Material used in fixture lens that tends to yellow with age.
Alternating Current (AC): Current that changes its direction of flow through a conductor, going first one way then the other, the usual rate used in 60 alternations (60 times each way) per second.

Amps:    The rate of flow of the electricity along the line.

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 device required in all light sources, except incandescent, which operates when starting the lamp to obtain necessary circuit
conditions (voltage, current and waveform). It should be noted that a ballast consumes additional energy (from the lamp).

Base:    End(s) of a lamp that make contact with the electrical source.

Bulb:    Layman’s terms for lamp, actually the glass outer shell of a lamp.

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

Color Corrected:    Refers to a lamp that has a special phosphor or coating applied either internally or externally to alter the natural color rendering properties of the light source to be more true (to sunlight colors).


H.I.D High Intensity Discharge Lamp: Mercury vapor, metal halide, high pressure sodium lamps or any electric discharge lamp in which the light producing arc is stabilized by wall temperature and the arc tube has a bulb wall loading in excess of three watts per square centimeter.

High Bay:    High ceiling, usually in an industrial plant because of height. It may be hard to reach for lamp changes without special ladders or scaffolding (usually above twenty feet).

High Hat:    Recessed (usually into ceiling) incandescent fixture.

High Output (HO):     A fluorescent lamp designed for us with 800-milliampere ballast. Will usually operate at low temperatures (near zero) and still produce high light output.

High Pressure Sodium (HPS) Lamp:    High intensity discharge (HID) Lamp in which light is produced by radiation from sodium vapor operating a partial pressure. Also known as “Son.”

High Voltage:    Voltage of 208 and higher.

Incandescent:    First light source invented most common light source still used today. This is the only source that does not require a ballast.

Infrared:  Radiant energy with wavelengths that is longer than the wavelengths 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 preheating 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 interchanged.

Kilowatt:    Equals 1000 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.

Label law:    Effective in 1995, the FTC “Appliance Labeling Rule” has come to be known in the lighting industry as the “Label Law.” It applies to general service incandescent lamps (reflector and non-reflector), medium screw base compact fluorescent lamps and general service fluorescent lamps. Lamp labeling requirements were mandated by “EPACT.” The spirit of the law is to make the consumer aware of the efficiencies of products. In the lighting industry, this means to change the focus from thinking of watts used (measurement of energy) to thinking of lumens produced (measurement of light) or even better yet lumens-per-watt. In the case of the general service fluorescent products, an encircled “E” indicates that the product meets the standard.

Lamp:   Industry term for light bulb.


Lamp Life:   The rated life of any lamp is that which an independent laboratory has taken a sampling of one type of lamp (i.e. 100) and leaves them burning with a scheduled amount of starts per day. When 50% (i.e. 50) of the lamps burn out, this is said to be the rated life of that lamp.

Lens:    covering over lighting fixture that controls the light and/or protects the internal workings of a fixture. Can also be known as a reflector, fixture, or diffuser.

Lexan:    Brand name for polycarbonate material used for lens that will not break and will not yellow.

Louver: A frame fitted with slates 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 fixture.

Low Pressure Sodium (LPS) Lamp:    A discharge lamp in which light is produced by radiation from sodium vapor operating at a particular pressure. The most efficient light source delivering more lumens per watt than any other, also the only single color (yellow) light source. Also known as

Lumen: Measurement of the amount of light hitting an object.

Lumen Depreciation: All light sources except low pressure sodium decrease in lumen output as they are used. This is due to a gradual deterioration of the internal parts of the lamp and a blacking of the glass caused by the deterioration parts being deposited on it. This is called lumen depreciation different methods of manufacturing lamps.

Lumen Maintenance:  The factor used when doing calculations for a new lighting system that takes into account the effect of lumen depreciation (of the light source, fixture and surroundings).


Luminaire:    A luminaire is a complete lighting unit consisting of a light source together with the parts designed to distribute the light. These units are commonly referred to as lighting “fixture.”

Color Rendering Index (CRI):    A rating method by which any fluorescent is evaluated according to its variance from natural outdoor light, which as a CRI of 100. It is sometimes referred to as Chromatic Index.

Color Spectrum:     Same as the visible light spectrum. All the radiant energy wave lengths that make human sight possible. The visible wavelengths include all colors and are measured in nanometers.

Diffusion: The scattering of light is called diffusion. A light transmitting material, such as a white glass globe, is a diffuser. A diffuser will scatter light broadly in all directions.
Downlight: A small direct lighting unit that directs the light downward and can be recessed, surface mounted or suspended.



Efficacy:    The efficiency of a light source is known as the luminous efficacy, which is the ration of the total lumens produced by the source to the watts consumed by the source. This ratio is expressed in lumens per watt. For example, a 100 watt lamp produces 1290 lumens. Therefore, its efficacy is 1290/100 or 12.9 lumens per watt.

Efficiency of a Fixture:    The efficiency of a luminaire is the ration of lumens emitted by the luminaire to those emitted by the bare lamp. Realistically, only a portion of the lumens produced by bare lamp will actually leave the luminaire and reach the work-plane. The term used to describe this percentage is Coefficient of Utilization (CU). For example, if a particular luminaire has CU of .75, then 75 percent of the lumens produced by the lamp would reach the work-plane. The other 25 percent is lost (absorbed) by the luminaire’s surface area.

End Blackening:    The darkening of a fluorescent lamp bulb caused by small particles of mercury evaporating and depositing on the bulb as the lamp burns.

Energy Survey:    Synonymous with cost calculations, energy audit, energy savings and consist of the necessary calculations required to indicate the power and material costs of an existing lighting system versus a proposed lighting system.

Epact:    Energy Policy Act was enacted in 1992. The primaries focus was to insure the “appliances” being produced were efficient to operate (and not wasting energy). Specific products (many of the lamps sold in our industry) have minimum efficiency requirements, which are measured in “lumens-per-watt” (akin to mile per gallon). Different lamp types had different efficacy requirements, which take effect over a 10-20 year period (i.e. Fluorescent lamps were the first to take effect in 1994).

Etch:    Printing on outer glass bulb of lamp depicting brand name (if any) and usually watts, volts, rated life, phosphor blend (fluorescent).

Eyeball:    Fixture with either a partially recessed head or hung from track lighting system that can be pointed in any direction and resembles
an eyeball.

Filament:    Coiled wire that heats up. Creating light in an incandescent lamp.

Fluorescent:    Second light source invented, most common source used in indoor commercial installations today a low-pressure mercury electric-discharge lamp in which a fluorescing coating (phosphor) transforms some of the ultraviolet energy generated by the discharge into light.

Foot-Candle:    Measurement of light at a particular point.

Head:    Suspended portion of a track lighting system that contains the lamp.