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Glossary | Industrial Lighting Terms


A term used for the luminous intensity of a light source.The intensity in anyone direction from the standard candle is called one candela (formerly one candlepower; cpl).

Color Rendering Index (CRI)

A measurement of the color shift an object undergoes when illuminated by the light source, as compared to a reference source at the same color temperature. Color rendering is measured on an index from 0-100, with natural daylight and incandescent lighting both equal to 100. Objects and people viewed under lamps with a high color rendering index (CRI) appear more true to life.

Color Temperature

The chromaticity of an ideal "black body" when it is heated to a specific temperature in Kelvin (K). It is the measure of the color of light, not actual temperature.


A unit used in measuring direct illumination. It is defined as the illumination produced from a source of one candela at a point on a surface of one foot away and perpendicular to the source of light. One lumen per square foot.


The result of the use of light, illuminance, the density ofluminous flux on a surface, is usually measured in footcandles.

Inches to Metric Conversion

To calculate the metric equivalent of inches in millimeters (mm) use the following formula: inches x 25.4001 = millimeters.

Instant Start

A circuit used to start specially-designed fluorescent lamps without the aid of a starter. The circuit utilizes higher open circuit voltage than is required for the same length preheat lamps, to strike the arc instantly. This circuit is used today in slimline and cold cathode lamps. Instant start 40-watt bipin lamps are made with a short circuiting device built into the base.

Kilowatt (KW)

A larger unit of power, a thousand watts (watts x 1000 kilowatts).

Kilowatt Hour (KWH)

The measure of electrical usage from which electricity billing is determined. For example, a 100-watt bulb operated for 1000 hours would consume 100 kilowatt hours, (100 watt x 1000 hours = 100 KWH).At a billing rate of $0.10/KWH, this bulb would cost $10.00 (100 KWH x $0.10/KWH) to operate.

Lamp Dimensions

Bulb designations consist of a letter or letters to indicate the approximate diameter in eights of an inch.

Lamp Listing Sequence

Lamps are listed in wattage sequence within their groups.


The term generally applied to the visible energy from a source. Light is usually measured in lumens or candlepower. When light strikes a surface it is either absorbed, reflected or transmitted. Light is said to travel in straight lines.


The unit that expresses the total quantity of light given off by a source, regardless of direction. A lumen is defined as the amount of light falling on a surface of one square foot, every point of which is one foot away from a source of one candlepower. A uniform source of one candlepower placed in a sphere emits 12.57 lumens or mean spherical candela equals to 12.57 lumens.

Luminance or Brightness

The light emitted, transmitted or reflected from a unit area of the source of surface is its brightness. It is usually expressed in candles per square inch or Lamberts or foot Lamberts.

Lumens Per Watt (LPW)

A measure of the efficacy of a light source in terms of the light produced for the power consumed. For example, a 100-watt lamps producing 1750 lumens gives 17.5 lumens per watt.

Maximum Overall Length (MOL)

is measured from the top of the bulb to bottom of the base.
Nominal Length A measurement of fluorescent lamp length based on the length of the lamp plus the proper allowance for standard lamp holders.

Operating Position

Lamps may be operated in any position unless otherwise indicated.

Ordering Codes

The numbers shown in the order code column along with the descriptions should be used when placing orders. In a number of instances a lamp type may be available in different kinds of outer carton cases such as 24 or 120 pack. Each of these items is shown as a separate listing.


A circuit used in fluorescent lamps where the electrodes are heated or warmed to a glow stage, by an auxiliary switch or starter (can be a glow switch, thermal type or mechanical device like a push button) before the lamps are lighted. This system was used on the original fluorescent lamps and is still in use today.

Rapid Start

A circuit designed to start lamps by continuously heating or preheating the electrodes. This circuit is a modern version of the trigger start system and requires lamps designed for this circuit. In the rapid start two-lamp circuit, one end of each lamp is connected to a separate starting winding. The other end of each lamp is connected to a common winding. Except for slimline lamps, all modern fixtures using 40-watt and higher lamps are equipped with rapid start ballasts.

Rated Average Life

The operating life (hours) at which 50% of the lamps are still operating. Where a plus (+) is used in starting the life, survival rate is 67% at the started time.

Trigger Start

A circuit used to eliminate the starter and start the preheat lamp almost instantly. In this circuit, each electrode is connected to a separate winding in the ballasts so that the electrode is continuously heated. This circuit is primarily used on a 20-watt and lower wattage fluorescent lamps today.


Lamps listed are available only in the voltage shown.

Voltage (V or E)

A measurement of electromotive force or the pressure of electricity. This is analogous to the pressure in a water line; i.e. pounds per square inch. The voltage of a circuit is the electrical pressure it gives. In an incandescent lamp "voltage" designates the supply voltage to which the lamps should be connected. In other lamp types, it may refer to "operating voltage" of a lighted arc discharge lamp.

Watt (W)

Unit used to measure power consumption of a lamp.