Glossary of Lighting Terms

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American National Standards Institute (ANSI):
A consensus organization which coordinates voluntary standards for the physical, electrical and performance characteristics of lamps, ballasts, luminaires and other lighting and electrical equipment.

Amps: A measure of electrical current. In incandescent lamps, amps are related to voltage and power as follows: Current (Amps) = Power (Watts) / Voltage (Volts)

Apparent Color Temperature: Used to describe the degree of "whiteness" for fluorescent and high intensity discharge lamps.

Average Rated Life: The median time it takes for a lamp to burn out.  Based upon continuous testing lamps in laboratories, the 1,000 hour rating is the point in time when 50% of the test samples have burned out and 50% are still burning. Average life ratings are based on closely controlled laboratory test of lamps, at their rated voltage, over a long period of production time. Average Rated Life is not necessarily the same as service life; mechanical shock & vibration, voltage fluctuation, temperature and other environmental factors may result in shorter service life. Therefore, as with any average value, some individual lamps may operate longer and some may operate shorter than their Average Rated Life.

An auxiliary piece of equipment required to start and to operate gas discharge light sources like fluorescent and high intensity discharge (HID) types.  This device converts electrical current to the right quantity of voltage required to start the lamp safely and efficiently. Magnetic: Least expensive option but are heavier than electronic ballasts, require a few seconds to light and often produce a low hum. Electronic: Usually lightweight, allow the lamp to start instantly, and consume significantly less energy.

Beam Angle: Indicates the spread of the beam of light. The smaller the number, the tighter and more intense the beam.  Same as beam spread measured at 50% of the maximum intensity. This angular dimension of the cone of light from the reflectorized lamps (such as R and PAR types) encompasses the central part of the beam out to the angle where the intensity is 50% of maximum.

Beam Spread: A measure of the angular spread of light from reflectorized lamps such as R and PAR types, typically including the central part of the beam within 50% of the maximum .

Candela (CD)
: The International System (SI) unit of luminous intensity. The term has evolved from considering a standard candle as the basis of evaluating the intensity of other light sources. Sometimes the term candlepower is used to describe the relative intensity of a source.

Candlepower: A measure of intensity of light in a given direction (see Candela).

Center Beam Candlepower: A photometric measurement taken at the beam center of a fully illuminated lamp. This measurement is typically the brightest point, in terms of lumens, of a given beam spread.

Coefficient of Utilisation: A percent of initial lamp lumens that reaches the work plane as determined by surface reflectance’s, room shape, and fixture efficiency.

Color Rendering: Defines how light from the lamps affects the colors of objects being illuminated

CRI: Color Rendering Index (CRI) is a term used to describe the extent to which an artificial light source is able to render the "true" color of objects as seen by natural outdoor. The closer the CRI of a lamp is to 100, the more "true" it renders colors. 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 higher color rendering indexes generally appear more true to life.

Color Temperature: Color temperature is a measure of the visual "whiteness" of a source and is expressed in degrees K. (Kelvin). Red/orange/yellow colors and light sources from this side of the spectrum are described as a warm, with a low color temperature (incandescents). Colors and light sources toward the blue end with a high color temperature are referred to as cool (natural daylight).

Compact Fluorescent Lamp: The general term applied to families of smaller diameter fluorescent lamps, some of which have built-in ballasts and BC or ES caps for easy replacement of incandescent lamps. Use advanced 'electronic' technology to produce a highly efficient and compact light using a fraction of the electricity of ordinary incandescent bulbs. These bulbs use about one-fifth to a quarter of the electricity of standard bulbs and last up to ten times as long.

The measurement of the lamp's diameter.

Dimmable: An electrical device that enables you to vary the light output of the lamp.

The ratio of light output (lumens) to input power (watts), expressed in lumens per watt. Used in measuring the amount of light given off by a light source. The higher the lumen efficacy, the more efficient the source is at producing light.

Electromagnetic Spectrum: An orderly arrangement of radiant energy by wavelength or frequency.

Energy: The electric power input, measured in kilowatt-hours (kwh).

Energy saving lightbulb: Uses advanced 'electronic' technology to produce a highly efficient and compact light using a fraction of the electricity of ordinary incandescent bulbs. These bulbs use about one-fifth to a quarter of the electricity of standard bulbs and last up to ten times as long.

Federal Communications Commission:
A U.S. Federal agency that is charged with regulating emissions in the radio frequency portion of the electromagnetic spectrum.

Filament: Very thin coiled wire used in incandescent lamps which is heated by an electric current to produce light.

Fluorescent Lamp: A lamp in which electric discharge of ultraviolet energy excites a fluorescing coating (phosphor) and transforms some of that energy to visible light. This lamp uses less electricity and last for a longer time than incandescents.
click here to view color temperature scale diagram

Footcandle: A measurement of the quantity of light falling onto a surface or subject. One footcandle is equal to one lumen per square foot. One footcandle equals 10 lux.

Frosted: Internal Frosting of the glass of the bulb


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. This lamp produces twice as much light and lasts twice as long as a conventional incandescent bulb of the same wattage.

High-Intensity Discharge Lamp (HID): General term for a mercury, metal halide or high-pressure sodium lamp.

HIR LAMPS: HIR lamps are a new form of high efficiency tungsten halogen lamp. By coating the filament tube, it reflects the infrared back onto the filament, reducing the power needed to keep the filament hot.

The quantity of light (foot-candles or lux) at a point on a surface.

Incandescent Lamp: A light source which generates light utilizing a thin filament wire (usually of tungsten) heated to white heat by an electric current passing through it. Incandescent lamps are the oldest form of electric lighting technology.

Initial Lumens: Light output of a lamp

Instant On: A type of fluorescent lamp-ballast circuit designed to start fluorescent lamps as soon as the power is applied.


A measure of how yellow, blue or white the light from a bulb will look to the human eye. Lower kelvin rated bulbs will appear more yellowish, while higher kelvin bulbs appear to be bluer. A bulb with a kelvin rating of between 5000 to 6500 is comparable to mid-day sun.

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

Lamp Efficiency
: Measure of light output per watt of input. The more efficient the lamp, the lower the cost of lighting.

Light: Radiant energy which can be seen or sensed by the human eye. Visible light is measured in lumens or candlepower.

Light Center Length: This dimension defines the location of the filament to the lamp base. It is measured from the geometric center of the filament to a specified point of, or plane through, the base.

Lumens: A lumen is a measure of the amount of light produced by a lamp. A lamp's light output rating expresses the total amount of light emitted in all directions per unit time.  

Lumen Maintenance: A measure of how a lamp maintains its light output over time. It is often expressed as percent initial lumens vs. percent rated life.

Lumens Per Watt: A measurement of the efficacy of a light source in terms of the light produces by the power consumed. For example a 100 watt lamp producing 1750 lumens give 17.5 lumens per watt.

Luminaire: The international term for 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.

Luminaire Efficiency: The ratio of lumens emitted by a Luminaire to those emitted by the lamp or lamps used.

Luminance: Measurable quantity (candelas per square inch or per square meter) which is related to perceived brightness.

Lux: The ratio of lumens to surface. Measures the light that actually reaches the target. Lux varies depending upon how far away the target is from the light source and other environmental factors such as wall color, reflectors, etc. This is the SI (International System) unit of illumination. Generally, one lumen uniformly distributed over an area of one square meter.


: A unit of wavelength equal to 10-9 meter.


Parabolic Aluminized Reflector (PAR)
: A type of incandescent lamp of heavy glass that controls its light beam by a reflector and lens. This bulb emits light in only one direction, control light more precisely and produce about four times the light of standard incandescents. They are often are used in recessed and track lighting.

Phosphor: A coating, deposited on the inner bulb surface of fluorescent lamp types. Phosphors are designed to absorb short wavelength ultraviolet radiation and to transform and emit it as visible light.

Power Factor (PF): A measure of how efficiently a device uses power. Power factor may range from 0 to 1, with 1 being the ideal. A device that converts all the power supplied to it by the power utility into watts is said to have a power factor of 1. Devices with PF greater than or equal to 0.90 are referred to as High Power Factor (HPF) devices, whereas devices with PF less than 0.60 are referred to as low power factor devices.. Incandescent lamps always have power factors close to 1.0 because they are simple “resistive” loads. The ballast used determines the power factor of a discharge lamp system. “High” power factor usually means a rating of 0.9 or greater. The power factor of “core and coil” electromagnetic ballasts may be as low as 0.5 – 0.6.


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. The reflector is a specific functional shape to concentrate the light in one direction.

Silver Bowl / Crowned Silver:
Refers to the finish of the bulb being silver at the crown. They are a form of reflector lamp for use with a special type of reflector luminaire. The reflector coating on the top half of the sphere of the lamp prevents any direct forward light from the filament and reflects it backwards onto the luminaire reflector.

Soft glow / Opal: A fine white powder coating which produces a more even brightness than pearl where diffusion of the light is important.

Spotlight: Beam of light projected onto a particular object or location.

Striplight: Tubular shaped incandescent lightbulb used in bathroom shaver lights, picture lights and under-cupboard lighting. (See also Fluorescent Lamps)

Total Harmonic Distortion (THD):
A measure of the distortion of the sine wave on alternation current (ac) systems cause by higher order waves superimposed on the fundamental (usually 60 Hz.) frequency of the system. THD is expressed in percent and may refer to individual electrical loads (such as ballast) or a total electrical circuit or system in a building. The ANSI recommendation is for THD to be no greater than 32% although some electrical utilities may require lower THD’s on some systems. Excessive THD’s on electrical systems can cause efficiency losses as well as overheating and deterioration of system components.

Ultraviolet (UV) Radiation
: For practical purposes, any radiant energy within the range of 100-380 nanometers. Wavelengths 180-220nm produce ozone; 220-300nm bactericidal (germicidal); 280-320nm erythemal (reddening of human skin); and 320-400nm secondary luminance (blacklight). The international Commission on Illumination (CIE) defines UV-A (315-400 NM); UV-B (280-315 nm) and UV-C (100-280).

Underwriters Laboratories (UL): A private organization which tests and lists electrical (and other) equipment for electrical and fire safety according to recognized UL and other standards. A UL listing is not an indication of overall performance. Lamps are not UL listed except for compact fluorescent lamp assemblies – those with screw bases and built-in ballasts.

: A unit of measure of the potential difference in an electric circuit (a lamp's voltage should match the voltage rating of the circuit on which it operates.)

Voltage: A measurement of the electromotive force in an electrical circuit or device expressed in volts. The voltage of a circuit is the electrical pressure it provides. In an incandescent lamp, voltage designates the supply voltage to which the lamp should be connected, and is related to current and power as follows: Voltage (Volts) = Power (Watts) / Current (Amps).

: The amount of electricity consumed by a lamp. Lamps are rated in watts to indicate their power consumption. Power consumed over time equals the electrical energy used. For Incandescent lamps, Watts is related to voltage and amps as follows: Power (Watts) = Voltage (Volts) x Current (Amps).





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