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A 3-letter code assigned by the American National Standards Institute (ANSI) that provides a system of assuring mechanical and electrical interchangeability among similarly coded lamps from various manufacturers.

Arc Tube

A completely sealed quartz or ceramic tube where the electrical discharge (arc) occurs and light is generated.

Average Rated Life

An average rating, in hours, indicating when 50% of a group of lamps have failed when operated at nominal lamp voltage and current.  Manufacturers use 3 hours per start for fluorescent lamps and 10 hours per start for HID (High Intensity Discharge) lamps when performing lamp life testing procedures.  Every lamp has a unique mortality curve that depicts its average rated life.


Baffle (Fixture)

A mechanism that regulates the flow of light in a fixture.


The ballast is an electrical device that performs two basic functions:
1) Provides the starting voltage and
2) Limits the current to sustain lamp operation.


The end of the lamp that fits into the socket.


A style of bulb base which uses keyways instead of threads to connect the bulb to the fixture base.  The bulb is locked in place by pushing it down and turning it clockwise.

Beam Spread

The angle over which the intensity of the beam drops to 50% of its peak intensity, measured in degrees.


Any base with two metal pins for electrical contact.

Black Light

A popular term referring to a light source emitting near ultraviolet light and a minimum amount of visible light.


A common term for a “lamp”; specifically, the glass outer shell of the lamp.


Candela (cd)

The quantity of light emitted by a lamp in one direction, or the luminous intensity of the light in that direction.


The intensity or strength of the beam in a given direction expressed in candelas.

Color Rendering Index (CRI)

Color rendering is the ability of a light source to produce color in objects.  The CRI is expressed on a scale from 0-100, the higher the CRI, the more vibrant colors appear.

Color Temperature

Originally, a term used to describe the “whiteness” of incandescent lamp light.  Color temperature is directly related to the physical temperature of the filament in incandescent lamps, so the Kelvin (K) (absolute) temperature scale is used to describe it.  A low color temperature implies a warmer color light (more yellow/red) while high color temperature implies a cooler light (more blue).

Compact Fluorescent Lamp (CFL)

The general term applied to fluorescent lamps that are single-ended and have smaller diameter tubes bent into a compact shape.
            •           2 Pin CFL — A type of CFL that has a glow bottle starter built into
                        the base of the lamp and operates with an electromagnetic ballast.
            •           4 Pin CFL — A type of CFL that typically operates with electronic
                        ballasts and the starting circuit is within the ballast.
            •           Self Ballasted – A type of CFL with a built-in ballast and screw-in
                        base used as a direct replacement for incandescent lamps.

Cool White

Reference to the color tone or appearance of light produced by a fluorescent lamp for a specific Kelvin color temperature (4000K, 4100K).

Core & Coil Ballast

A type of ballast associated with the operation of High Intensity Discharge (HID) lamps.  See Ballast.


Damp Location (Fixtures)

Fixtures which are suitable for use in partially protected locations or interior locations subject to moderate degrees of moisture.


Reference to the color tone or appearance of light produced by a lamp for a specific Kelvin color temperature (5000K).  The bluish white appearance of this lamp is similar to natural daylight. 

Dichroic Reflector

A reflector that projects light forward while deflecting heat backward, toward the socket.


The ability of the lamp lumens to be varied while maintaining reliability.



Efficiency of a light source expressed in lumens per watt (LPW or lm/W).

Enclosed Fixtures

Fixtures which have a lens to protect the lamp and contain glass particles, should the lamp rupture.

Energy Policy Act (EPACT)

Energy legislation passed by the U.S. Congress in 1992 which includes lamp labeling and minimum energy efficacy requirements for many commonly used incandescent and fluorescent lamp types.

Energy Star

Energy Star was introduced by the U.S. Environmental Protection Agency in 1992 as a voluntary labeling program designed to identify and promote energy-efficient products that reduce carbon dioxide emissions.  The EPA partnered with the U.S. Department of Energy in 1996 to promote the Energy Star label.



Tungsten wire positioned inside a bulb which generates light when heated.

Fluorescent Lamp

A high efficiency lamp utilizing an electric discharge through low pressure mercury vapor to produce ultraviolet (UV) energy.  The UV excites phosphor materials applied as a thin layer on the inside of a glass tube which makes up the structure of the lamp.  The phosphors transform the UV to visible light.


A unit of illuminance or light falling onto a surface.  One footcandle is equal to 1 lumen per square foot (1m/ft2). One footcandle = 10.674 lux.

Full Spectrum

A marketing term typically associated with light sources that are similar to some forms of natural daylight (5000K and above, 90+CRI).



Excessive brightness that may be caused by either direct or indirect viewing of a light source.


Halogen Lamp

A short name for tungsten-halogen lamp.  Halogen lamps are high pressure incandescent lamps containing halogen gases such as iodine or bromine which allow the filaments to be operated at higher temperatures and higher efficacies.  A high-temperature chemical reaction, involving tungsten and the halogen gas, recycles evaporated particles of tungsten back onto the filament surface.

High Bay Lighting

Pertains to the type of lighting in an industrial situation where the ceiling is 25 feet or higher.

High Intensity Discharge (HID) Lamp

A lamp containing a filled arc tube in which the active element becomes vaporized (a gaseous state) and is discharged into the arc stream to produce light.

High Output/Very High Output (HO, VHO) Lamp

Designation for lamps generating more light than standard lamps, in extreme operating conditions.

High Pressure Sodium (HPS) Lamp

HPS lamps are high intensity discharge light sources which produce light by an electrical discharge through sodium vapor operating at relatively high pressures and temperatures.



An electronic device providing a high voltage pulse to initiate an electrical discharge.

Incandescent Lamp

A lamp in which light is produced by a filament heated to incandescence by an electrical current.

Infrared Radiation

Electromagnetic energy radiated in the wavelength range of about 770 to 1106 nanometers.  Energy in this range cannot be seen by the human eye, but can be sensed as heat by the skin.

Initial vs. Mean Lumens

The measured luminous output of a new light source versus the output at 40% of lamp life.

Instant Start

A lamp starting method in which lamps are started by high voltage input with no preheating of lamp filaments.  Some rapid start lamps are designed so that they may be instantly started.



The Kelvin unit is the basis of all temperature measurement. In lighting, Kelvin is the unit of measure for Color Temperature used to indicate the color of light produced from a source.


A measure of electrical power equal to 1000 watts.

Kilowatt Hour (kWh)

A unit of electrical power consumed over a period of time.  1000 Watts used for one hour equals one kilowatt-hour.



The term used to refer to the complete light source package including the inner parts as well as the outer bulb or tube.  “Lamp,” of course, is also commonly used to refer to a type of small fixture such as a table lamp.


Light Emitting Diode. A semiconductor diode that emits light when an electric current is applied in the forward direction of the device.


A glass or plastic element used in luminaries to change the direction and control the distribution of light.

Light Pollution

Light that is directed to areas where it is not needed or desired.

Low Pressure Sodium

A lamp that produces light by the flow of an electric current through a sodium vapor at low pressure.  This combination of sodium and low pressure produces a yellow monochromatic light.


A unit of measure used to describe the amount of light a lamp emits.

Lumen Deprecation

The term for the gradual decline in a source’s light output due to the gradual deterioration of the filament.

Lumens Per Watt

A ratio expressing luminous efficacy of a light source.

Lumen Maintenance

A measure of how well a lamp maintains its light output over time.


A complete lighting unit consisting of a lamp (or lamps), together with the parts designed to distribute the light, position and protect lamps and connect them to the power supply.


A unit of illuminance equal to one lumen per square meter.


Mean Lumens

The average light output of a lamp over its rated life.  For fluorescent and metal halide lamps, mean lumen ratings are measured at 40% of rated lamp life.  For mercury, high pressure sodium, and incandescent lamps, mean lumen ratings are measured at 50% of rated lamp life.

Medium Base

Usually refers to the screw base typically used in household incandescent lamps.

Mercury Vapor Lamp

A high intensity discharge light source operating at a relatively high pressure (about 1 atmosphere) and temperature in which most of the light is produced by radiation from excited mercury vapor.  Phosphor coatings on some lamp types add additional light and improve color rendering.

Metal Halide Lamp

A high intensity discharge light source in which the light is produced by the radiation from mercury, plus halides of metals such as sodium, scandium, indium and dysprosium.  Some lamp types may also utilize phosphor coatings.

Mogul Base

A large screw base that is approximately 1.5" in diameter.

Multi-tap Ballast

A ballast that is able to function on more than one voltage.



A rare earth element used in glass that filters out the excessive yellow part of the light spectrum to which our eyes are most sensitive.


Open Rated Lamp (Medium Base)

Designed for open luminaries. Lamp has a narrower neck than standard medium base lamps in order to fit into an exclusionary medium base (EX26) socket.

Open Rated Lamp (Mogul Base)

Designed with a extended contact pin on the bottom of the base.  Lamps should be used with an open fixture mogul socket (EX39) which prevents electrical contact if a non open rated lamp is used.

Operating Position

The position in which a lamp is designed to operate for maximum performance and safety.


Parabolic Aluminized Reflector (PAR) Lamp

A type of incandescent lamp made of heavy glass that controls its light beam by a reflector and lens, typically used in floodlighting.

Photocontrol (Photocell)

A device used to detect light levels, which controls the electrical operation of a light fixture when changes occur.

Power Factor

The ratio of the actual power being consumed by a lamp or circuit to the apparent power being consumed.

Preheat Lamp

A fluorescent lamp in which the filament must be heated by use of a starter before the arc is created.  These lamps are typically operated with electromagnetic ballasts.

Programmed Rapid Start

A lamp starting method which preheats the lamp filaments, while not allowing the lamp to ignite, and then applies the open circuit voltage to start the lamp.  The user may experience a half to one second delay after turning on the lamps while the preheating takes place.

Pulse Start Lamp

A specifically designed metal halide lamp that requires a high voltage pulse for starting and has improved lumen maintenance. 


Quad Tube

Generally refers to a compact fluorescent lamp containing 2 U-shaped tubes.


Rapid Start

A lamp starting method in which lamp filaments are heated while open circuit voltage (OCV) is applied to facilitate lamp ignition.

Rated Life — See Average Rated Life.


Reflector Lamp

An incandescent, compact fluorescent or HID lamp with a built-in reflecting surface.  Incandescent and HID versions are made from a single piece of blow-molded soft or hard glass.  CFL versions may be one piece or may be designed so that the inner lamp can be replaced.

Restart or Restrike Time

The amount of time from return of power after an interruption to the point of lamp ignition.



A glass cylinder that surrounds the arc tube in open fixture rated metal halide lamps.  The shroud is designed to contain hot arc tube particles and glass bulb breakage, should a rupture occur.


UL (Underwriters’ Laboratories, Inc.)

Laboratory that sets safety standards for building materials, electrical appliances and other products.



A measure of electric potential, expressed in volts.  Voltage can be thought of as being analogous to the pressure in a waterline.


Warm White

Reference to the color tone or appearance of light produced by a fluorescent lamp for a specific Kelvin color temperature (2700K).

Warm-Up Time

The amount of time from ignition of the lamp to 90% light output.


A unit of electrical power.  Lamps are rated in watts to indicate their power consumption. 

Wet Location Fixture

Fixtures which are suitable for use in wet locations because their construction or installation prevents water from entering or accumulating in wireways, lampholders or other electrical parts.