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Technical Information
Lighting Glossary


ANSI (American National Standards Institute) The organization that develops voluntary guidelines and product performance standards for the electrical and other industries.
Accent Lighting
Directional lighting used to highlight a particular object or area.

Alternating Current (AC)
Electron flow that periodically reverses polarity and direction of travel through a circuit.
Ambient LIghting
The overall lighting in an area or room.

Ampere (amp)
A standard unit of measurement of electrical current. Amps = Watts/ Voltage

Inert gas used in incandescent and fluorescent lalmp types. In incandescent light sources, argon retards evaporation of the filament.
Average Rated Life
An average rating, in hours, indicating when 50% of a large 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 lamps when performing lamp life testing procedures; every lamp type has a unique mortality curve that depicts its average rated life.

A device used with an electric-discharge lamp to obtain the necessary circuit conditions (voltage, current and waveform) for starting and operating; all fluorescent and HID light sources require a ballast for proper operation.

Ballast Factor (BF)
The measured ability of a particular ballast to produce light from the lamp(s) it powers; ballast factor is derived by dividing the lumen output of the same lamp(s) on a reference ballast.

Beam Angle
The angle between the two directions for which the intensity (candlepower) is 50% of the maximum intensity as measured in a plane through the nominal beam center line.

Beam Spread
In any plane, the angle between the two directions in the plane in which the candlepower is equal to a stated percent of the maximum candlepower in the beam.

Term for electrical light source or lamp; the outer shell of the lamp.

Bulb Darkening
Darkening or discoloration of an incandescent lamp due to tungsten particles collecting on the inside of the glass as the filament burns and diminishes over its life.

Unit measurement of luminous intensity.

The luminous intensity of a light source expressed in candelas.

Cathode Guard
Metal band encircling the cathode of a fluorescent lamp, used to collect the evaportating particles from the cathode, greatly reducing end-blackening.

The aspect of color that includes consideraton of its dominant wavelength and purity.

Color Corrected
Refers to a lamp with a special phosphor or coating to give it a color rendering profile like natural daylight.

Color Rendering Index (CRI)
A measurement to rate a lamps ability to render an objects color. The higher the CRI, on a scale of 0-100, the more true to life colors appear, as they would in natural daylight.

Color Spectrum
The visible light spectrum, ranging between 380 (violet) and 770 (red) nanometers in the electromagnetic spectrum.

Color Temperature
The actual color of a light source, also referred to as Correlated Color Temperature (CCT), measured in degrees Kelvin (K). Typical color temperature are:
2700K Incandescent
3000K Halogen
3500K Fluorescent - Warm White
4100K Fluorescent - Cool White
5000K Fluorescent - White Light
6500K Fluorescent - Daylight 

Cove Lighting
Refers to light sources mounted above a ledge or in a recess that distribute light upward for ambient lighting.

A measure of the rate of flow of electricity, expressed in amperes (A).

Design Lumens
Lumen value at 40% of rated average life.

The even redirection or spreading of light by a lens or diffuser.

Down Lighting
A directed lighting unit, usually small, that aims the light downward. Can be recessed, surface mounted or suspended.

Referes to the efficiency of a light source expressed in lumens per watt (LPW). The light source may be a lamp or luminaire.

Electric Discharge Lamp
A light source that produces light by passing a current between electrodes through a vapor or gas. Includes fluorescent and high intensity discharge lamps.

Elliptical Reflector
Incandescent lamp with a reflector shell which is elliptically-shaped. Focuses light immediately in front of the lamp which reduces absorption and increased efficiency.

End Blackening
Darkening around the ends of a fluorescent tube caused by particles evaportating from the cathode and adhering to the glass. Lamps made with cathode guards greatly reduce this occurrence.

Energy Policy Act (EPACT)
Energy legislation passed by Congress in 1992 mandating labeling and minimum energy efficiency requirements for many commonly used incandescent and fluorescent lamps.

Energy Survey
Systematic cost comparison of an existing system to a proposed system, accounting for electrical, material, maintenance and labor costs.

Markings on the glass envelope or shell of a lamp designating product description, logo and/or brand name.

The total light which comes off of a surface. Exitance is dependent upon the illuminance on and reflectance of the surface.

Fixture, usually recessed, which can be rotated to point in a desired direction.

Wire used in incandescent lamps, usually made of tungsten and often coiled, that emits light when heated by an electrical current.

Luminaire without lamps.

Fluorescent Lamp
A glass tube coated on the inside with a fluorescent substance that gives off light when mecury vapor in the tube is excited by a stream of electrons from the cathode.

Footcandle (FC)
A unit of measurement of direct illumination. One footcandle is equal to one lumen per square inch.

Full Spectrum
Broad spectrum light source capable of producing colors throughout the entire range of the visible spectrum; simulating actual sunlight. High CRI's and Kelvin temperatures ranging between 5500 and 5900.

General Lighting
Uniform light throughout an area, with no special provisions for task lighting or accent lighting.

Halogen Cycle
A regenerative cycle of tunsten and halogen atoms which prevents blackening of the lamp envelope during the life of the lamp.

Luminaire for a track-lighting system.

High Intensity Discharge (HID) Lamp
Metal Halide, High Pressure Sodium, Low Pressure Sodium and Mercury Vapor lamp types.

High Output Fluorescent (HO)
Fluorescent lamps designed to be used with an 800 milliampere ballast. Able to operate at low temperatures (down to zero) and still produce high light levels.

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.

High Voltage
Voltages of 208 or higher.

Light arriving at a surface, expressed in lumens per unit area; 1 lumen per square foot equals 1 footcandle, while 1 lumen per square meters equals 1 lux.

The results of the use of light.

Incandescent Lamp
A light source that produces light by the heating of a filament by an electric current.

Inches to Millimeters Conversion
To calculate the metric equivalent of inches in millimeters (mm), multiply inches by 25.4.

Indirect Lighting
Luminaires that distribute 90 - 100 percent of their light upward to be reflected by the ceiling.

Radiant energy in the wavelength range of about 770 to 1100 nanometers (nm). Energy in this range is not visible to the naked eye, but can be sensed by the skin. Applications include heat lamps, photography, medical therapy, and industry.

Instant Start
A type of fluorescent lamp-ballast circuit designed to start fluorescent lamps as soon as the power is applied. Originally, instant-start circuits were developed to eliminate separate mechanical starter devices. Slimline fluorescent lamps operate only on instant start circuits.

The light emitted from a source. Intensity varies given the direction at which one views the source. Intensity does not vary with distance.

Kelvin Temperature
See color temperature.

Kilowatt (kw)
A measure of electrical power equal to 1000 watts.

Kilwatt Hour (kwh)
The standard measurement of electrical energy consumption. 1000 watts of electricity used in one hour. Also the typical billing unit used by electrical utilities.

A heavy inert gas used in incandescent lamps which allows the filament to glow hotter and brighter and last longer.

Lighting industry term used for a light bulb.

Lamp Dimensions
Bulb designations consist of a letter(s) to indicate shape and a number to indicate the diameter in eighths of an inch.

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

Radiant energy that is capable of producing a visual sensation.

Light Center Length (L.C.L.)
The distance from a reference point, usually the bottom of the lamp base, to the center of the light source (filament).

Light Loss Factor
Used to calculate or project the performance of a lighting system after a given period of time under certain conditions; includes environmental conditions, such as temperature, voltage, dust and/or dirt and lamp depreciation.

An assembly of slats or crosspieces in a lighting fixture, used to control light intensity and glare.

Low Pressure Sodium (SOX) High Intensity Discharge lamp which uses pressurized sodium vapor to produce light.

International unit (SI) of luminous flux or quantity of light. Expresses quantity of light regardless of direction.

Lumen Depreciation
The gradual decline in light output from a light source over time. Due to filament deterioration and bulb darkening.

Lumen Maintenance
A measurement of how a lamp maintains its light output over time.

Lumens Per Watt (LPW)
A measurement of the efficancy (efficiency) of a light source. The number achieved by dividing lumens produced by watts consumed.

A complete lighting unit including lamps, housing, lens and ballast if required. All the necessary components to make what we commonly refer to as a "fixture".

Luminance (L)
Light reflected in a particular direction; the photometric quantity most closely associated with brightness perception, measured in units of luminous intensity (candelas) per unit area (square feet or square meters).

Lux (lx)
A unit of illuminance equal to 1 lumen per square meter.

Maximum Overall Length (M.O.L)
The overall length of a lamp, from the top tof the shell to the bottom of the base.
Mean Lumens
The average light output of a lamp over its rated life.

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 coating on some lamp types add additional light and improve color rendering.

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

A unit of length equal to 10 to the -9th meters, or one billionth of a meter; commonly used as a unit of wavelength.

Full spectrum incandescent lamps. Also known as daylight or natural light. Uses a colored glass shell to filter out yellow light produced by standard incandescent lamps. see

Nominal Length
A measurement for Fluorescent lamp length, based on the length of the lamp plus an allowance for luminaires lamp holders.

Ohm's Law
A scientific law which states that current (amperes) in a circuit depends on resistance (ohms) and applied electromotive force (volts).
Current (I) = Voltage (E) / Resistance (R).

Operating Position
Lamps may be operated in any position unless otherwise noted.

PAR Lamp
PAR is an acronym for parabolic aluminized reflector. A PAR lamp which may utilize either an incandescent filament, a halogen filament tube or HID arc tube is a precision pressed-glass reflector lamp. PAR lamps rely on both the internal reflector and prisms in the lens for the control of the light beam.

An inorganic chemical compound processed into a powder and depositied on the inner glass surface of fluorescent tubes and some mercury and metal-halide lamps. Phosphors are designed to absorb short wavelength ultraviolet radiation and to transform and emit it as visible light.

Photopic Vision
Refers to vision involving the cones of the eye; used in reference to the adaptation of the eye to illuminance of more than 3.4 candelas per square meter.

Power Factor
A measurement indicating how efficiently a lighting system is using the power it is drawing. The ratio between power used (watts) and power being drawn from the line (volts-amperes). Expressed as a percent or range from 0 to 1.0. The higher the percent the more efficiently the power is being used. High power factors are ratings of 0.9 (90%) or higher. Incandescent lamps are close to 1.0, magnetic ballasts can be as low as 0.5.

A fluorescent lamp-ballast circuit where the electrodes are heated or warmed by an auxiliary switch or starter before the lamps light up.

Rapid Start
A fluorescent lamp-ballast circuit which utilizes continuous cathode heating, while the system is energized, to start and maintain lamp light output at efficient levels. Rapid start ballasts may be either electromagnetic, electronic or of hybrid designs. Full-range fluorescent lamp dimmming is only possible with rapid start systems.

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.

The bending of light rays.

A translucent fixture covering, such as a lens or diffuser that refracts or bends light rays.

A measure of resistance to flow of current, expressed in ohms.

Scotopic Vision
Sight involving the eye's rods, which respond to low levels of lighting, below .034 candela per square meter.

High Pressure Sodium abbreviation term.

Low Pressure Sodium abbreviation term.

Spectral Power Distribution
A graph of the radiant power emitted by a light source as a function of wavelength. SPD's provide a visual profile of the color characteristics of the light source throughtout the visible part of the spectrum.

A device used in conjunction with a ballast to start preheat fluorescent lamps.

The Toxicity Characteristic Leaching Procedure (TLCP) test, specified in the Resource Conservation and Recovery Act (RCRA) of 1990, is used to characterize fluorescent lamp waste as hazardous or nonhazardous waste. The TCLP test measures the ability of the mercury in a lamp to leach from a landfill into ground water under very aggressive and reactive conditions.

Total Harmonic Distortion
A measure of the distortion of an electrical wave form. Excessive THD may cause adverse effects to the electrical system.

Trigger Start
A circuit used that eliminates the starter and allows for instant starting of preheat lamps.

A long recessed lighting fixture, usually installed flush with the ceiling.

Radiant energy in the wavelength range of about 100 to 380 nanometers (nm). This light is invisible to the naked eye and is also known as black light.

Applications include:
Blacklight ................ 320-400 nm
Germicidal .............. 220-300 nm
Ozone-producing ... 180-220 nm 

Very High Output (VHO) Lamps
Fluorescent lamps designed to be used with a 1500 milliampere ballast.

Visible Spectrum
Radiant energy in the wavelength range of about 380 to 770 nanometers (nm). The light that can be seen by the naked eye and produces what we also call the "color spectrum".

The unit of electromotive force (emf). The difference in electrical potential that will cause a current of one ampere to flow through a resistance of one ohm.

Voltage Rating
The recommended operating voltage for a lamp.

A unit of electrical power. One watt is equal to one ampere of currrent flowing through one ohm of resistance.

Distance between two successive points of a periodic wave; the wavelegth of light are expressed in nanometers.