Lighting Terminology

Lighting Terminology


Accent Lighting: Focusing light on a particular space or object. Intended to create visual interest in an area or object.   

Alternating Current (AC): Electric Current in which the flow of electric charge reverses direction at regular intervals.  

Amps (A): Standard Unit of  Measurement of electric current. 


Ballast: A device used to regulate current and voltage to start and operate a lamp. Ballasts are used with HID and Fluorescent light sources.

Ballast Factor: Indicates the percentage of rated light output and power that can be expected of a lamp. The higher the ballast factor that great the light output and the greater the power consumption

Beam Angle: The Angle between the two planes of light where the intensity is at least 50% of the maximum intensity at center beam. 


Candela (cd):  Measurement of luminous intensity of a source in a given direction. 

Center Beam Candle Power (CBCP): Luminous intensity at the center of a light source beam

Color Rendering Index (CRI): A Measure of a light sources ability to show colors accurately. The Scale is from 1 to 100.  The sun is considered 100. 

Color Temperature: Correlated Color Temperature (CCT).  A measurement of hue of the light produced by a source.


Diffuser: A device used to alter light by scattering it in order to create softer light with minimal glare

Dimmer: A device used to control the light output of a light source. 

Direct Current: Electrical current that flows in only one direction without cycling.  DC current is most commonly used with batteries and PV cells. 

Driver: Electrical or electronic circuit that controls other components.  In LED Lighting Systems, the driver regulates the power to the LEDs.


Efficacy: Lumens per Watt of a light source

Electromagnetic Interference: Disruption of an electronic device by an external source by electromagnetic induction, electrostatic coupling, or conduction. 

Electronic Ballast: Ballast composed of electronic components instead of the core-and-coil transformer.  Electronic ballasts do not experience as much power loss as magnetic ballast.


Fluorescent Lamp: Low-Pressure Mercury-Vapor-Gas-Discharge Lamp that uses fluorescence to produce visible light. Fluorescent lamps require a ballast for current and voltage regulation. 

Footcandle (fc): Unit of Measurement for Illuminance. One footcandle is equal to one lumen per square foot.


Glare: Glare is a visual sensation caused by excessive brightness.  It can be discomforting or disabling.


Halogen Lamp: Halogen Lamp is a type of incandescent lamp that incorporates halogen in order to increase the average life and light output of the light source. 

Heat Sink: Device incorporated in LED Lighting Systems to disperse heat away from the LED diode.   

Hertz (Hz): The standard unit of measurement for frequency. One Hz equals one cycle per second. 

High Bay: Type of Light Fixture typically used for commercial and industrial applications with high ceilings (>20 ft). 

High-Intensity Discharge Lamp: HID Lamps. The family of electrical gas-discharge lamps that produce light by means of an electrical arc.  

High-Pressure Sodium Lamp (HPS): Type of High-Intensity Discharge Lamp. Frequently used in street and outdoor lighting applications.


Illuminance: Measured in Lux or Footcandles,  Illuminance is the total luminous flux on a surface.  

Ingress Protection (IP) Ratings: Measurement of environmental protection for electronic equipment. Utilizes two numbers. First Digit rates ingress of solid objects. Second digit rates ingress of liquids. 

Initial Lumens: The total luminous flux of a light source at the beginning of its life. 


Kelvin Temperature (K): Unit of measurement of the Correlated Color Temperature of a light source.


Lamp Base: The Portion of a lamp that connects to the luminaire socket and power.

Light Emitting Diode (LED): A semiconductor device that emits light as electrical current passes through it. Light-emitting diodes are more efficient than other light sources and offer exceptionally long life

LM-79: Testing standards for performance characteristics of LED lamps and luminaires. 

LM-80: Testing standards for the lumen maintenance for LED packages and arrays. 

Lumen: Standard unit of measurement of luminous flux. Used to measure the total quantity of visible light emitted by a light source. 

Luminaire: Light Fixture. A complete unit consisting of lamp, ballast, reflectors, lens, and other parts.

Luminaire Efficiency: Lumens emitted by a light fixture compared to lumens emitted by the lamp source used in the fixture. 

Lux: SI unit to measure illuminance. One lux equals one lumen per square meter. 


Magnetic Ballast: Often Called "Core-and-Coil" ballast. Magnetic ballasts contain a magnetic core with copper windings. Magnetic ballast typically have greater power losses than electronic ballasts. 

Mean Lumens: Average luminous flux produced by a light source over the duration of its rated life. 

Medium Base: E26 Screw-in Base. Also know as Edison Base

Mercury Vapor Lamp: High-intensity discharge lamp that generates light by passing an electric arc through vaporized mercury

Metal Halide Lamp: High-intensity discharge lamp that generates light by passing an electric arc through a mixture of mercury and metal halide gases. 

Mogul Base: E39 Screw-in Base. Common base for HID lamp sources. 




PAR Lamp: Parabolic Aluminized Reflector Lamp. A precision-pressed glass reflector lamp which can use a variety of technologies including incandescent, halogen, or HID. The three most popular sizes are PAR20, PAR30, and PAR38. 

Photocell: Light Control that turns a light source on/off depending on daylight

PL lamp: Alternative name for Plug-in Compact Fluorescent. New LED PL lamps are an option now as well.  

Power Factor: The ratio of real to apparent power supplied to a circuit. Power factor can range from 0 to 1.



Radio Frequency Interference: A form of Electromagnetic Interference in the radio frequency spectrum.

Reflection: Light bouncing off a Medium. 

Refraction: Bending of light as it passes through a medium. The bending in light is a result of the change of speed as it passes from one medium to the next. 

Restrike Time: The time it takes for a lamp to reach full brightness after being turned off and back on. 

Retrofit: Upgrading old and inefficient technology with new equipment to improve the efficiency of a light system.



Transformer:  An electrical device that transfers electricity from one voltage to another. Step down transformers takes a higher voltage to a lower voltage. Step-up transformers take lower voltage to a higher voltage.



Voltage: Potential Difference in charge between two points in an electrical field. Measured in Volts (V). 

Voltage Drop: Loss of voltage caused by resistance. Voltage Drops can be created by too long or too thin wire.


Wall Sconce: Decorative Style Luminaire commonly hung on walls.

Watt: Standard unit of measurement for power. One Watt Equals one Volt-Amp.