Lighting Terminology for Dummies

Lighting Terminology for Dummies

By OEO 2024 • Jan 8th 2018

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.

Amp (A): Standard unit of measurement of electric current, the strenght of an electric current. Watts divided by volts.


Ballast: A device which provides the necessary starting voltage and appropriate current to a fluorescent or high intensity discharge (HID) luminaire. It's a device used to regulate current and voltage to start and operate a lamp. 

Ballast Factor: Indicates the percentage of rated light output and power that can be expected of a lamp. 

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): The ability of a light source to accurately render an object's color in comparison with a natural light source. Measured on a scale of 1 to 100, with 100 being the ideal, or natural sunlight. 

Color Temperature: Correlated Color Temperature (CCT). A measurement of hue of the light produced by a source. A specification of the apparent color of a light source relative to the color appearance of an ideal incadescent source held at a particular temperature and measured on the kelvin (K) sacale. The CCT rating for a lamp is a general indication of the "warmth" or "coolness" of its appearance. As CCT increases, the appearance of the source shifts from reddish white toward bluish white; therefore, the higher the color temperature, the cooler the color appearance. Lamps with a CCT rating below 3500K usually are considered "warm" sources, wheras those with a CCT above 4000K usually are considered "cool" in appearance. See also Kelvin.

Diffuser: A light control device that spreads light by scattering it. They are often used to alter light it in order to create softer light with minimal glare.

Dimmer: A device used to control the light output of a light source by reducing the voltage or current to the 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. 

Direct Replacement: it's as simple as Plug-N-Play! Direct replacement LED lamps from OEO screw into your existing fixture without the need to rewire or upgrade while helping to save you up to 84% on energy costs. 

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


Efficacy: The ratio of light output (lumens) of a lamp to input power (watts). Simply put, efficacy is conveyed as "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. 

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). Common in big box retail, industrial, warehouse and manufacturing spaces.

High Intensity Discharge Lamp (HID): A family of electrical gas-discharge lamps that produce light by means of electrical arc. Includes high pressure sodium (HPS), pulse start metal halide (PSMH), and metal halide (MH) lamps.

High Pressure Sodium Lamp (HPS): Type of high intensity discharge lamp. Frequently used in street and outdoor lighting applications. 

Illuminance: Light arriving on a surface, measured in Lux or foot candles. Illuminance is expressed in lumes per unit area; 1 lumen per square foot equals 1 foot candle, while 1 lumen per square meter equals 1 Lux.

Input Watts: The total wattage required by a lighting source (including ballast and lamp if applicable) in a luminaire. 

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

Instant Start: A method of starting fluorescent lamps without preheating the electrodes. Instant-start ballasts cause the electric arc to strike between the lamp's electrodes by supplying a high initial voltage to the lamps.  

Kelvin Temperature (K): A numerical scale used to describe the color of light. Light with a lower Kelvin rating will have a more yellow tint, wile light with a higher Kelvin rating will have a bluer tint.  See Correlated Color Temperature (CCT).

Kilowatt: 1000 watts.

Kilowatt Hour: 1000 watts used continuously for one hour.   


Lamp: Otherwise know as a "light bulb", it's a device that emits light produced by electricity (such as an incadescent, fluorescent, HID, halogen, or LED bulb). 

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

Lamp Disposal: Refers to the proper recycling of lamps containing mercury or other hazardous materials.

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 

Lens: A glass or plastic element used in luminaires to seal a fixture or control the existing light.

Low Bay: Lighting used in industrial or commercial applications where the ceiling height is 20 feet or less. Common in big box retail, industrial, gymnasium settings.

Lumen: A unit measurement of the rate at which a light source produces light. 

Lumen Depreciation: The decrease in lumen output of a light source over time; every lamp and luminaire has a unique lumen depreciation curve (sometimes called the lumen maintenance curve) depicting the pattern of decreasing light output.

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


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. 

Metal Halide (MH): A high intensity discharge lamp that generates light by passing an electric arc through a mixture of mercury and metal halide gases. 


Occupancy Sensor: A device which activates a light source upon sensing motion or the presence of a person.

PAR Lamp: PAR stands for parabolic aluminum reflector, used in recessed or track lighting.

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

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

Power Quality: The degree to shich current and voltage wave forms conform to a sinusoidal shape and are in synchronous phase wich each other. Poor power quality results when the wave forms are distorted and/or out of phase and can interfere with data communications, cause inefficient operation or failure of other electrical equipment on the same supply line, and result in excessive current in electrical distribution lines. 

PSMH: Pulse start metal halide.



Rapid Start: A method of starting fluorescent lamps in which the electrodes are heated prior to starting, using a starter that is an integral part of the ballast. By heating the electrodes before starting the lamps, the voltage required to strike the electric arc between the electrodes is reduced.

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. 



T5: 5/8" diameter fluorescent or LED tube lamp. "T" stands for tubular, while the number "5" stands for the 5 in 5/8" diameter.

T8: 8/8" or 1" diameter fluorescent or LED tube lamp. "T" stands for tubular, while the number "8" stands for the numerator in 8/8" diameter.

T12: 12/8" or 1 1/5" diameter fluorescent tube lamp. "T" stands for tubular, while the number "12" stands for the 12 in 12/8" diameter.

Troffer: A recessed luminaire shaped like an inverted trough used to enclose and reflect a light source. For use in suspended ceilings; derived from the words "trough" and "coffer".



Voltage (V): The potential for energy to move. 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 thick wire.  

Wall Pack: The most widely used commercial outdoor lighting fixtures used today. Wall packs are powerful light fixtures that are installed in outdoor locations of commercial buildings. 

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

Wattage: The amount of electricity consumed by a bulb.