Lighting Glossary

Common lighting terms and definitions


ANSI (American National Standards Institute)

The organization that develops voluntary guidelines and produces performance standards for the electrical and other industries.

Average Rated Life

An average rating, in hours, indicating when 50% of a large group of lamps has failed (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 operation. All fluorescent and HID light sources require a ballast for proper operation. Dimming ballasts are special ballasts which, when used together with a dimmer, will vary the light output of a lamp.

Ballast Efficacy Factor (BEF)

Ballast factor divided by input power (watts). Used to compare ballast efficiency.

Ballast Factor

The measured ability of a particular ballast to produce light from the lamp(s) it powers. The number is calculated by dividing the lumen output of a particular lamp/ballast combination by the lumen output of the same lamps(s) on a reference ballast. Click here to read a more detailed article explaining how the ballast factor affects fluorescent tubes.

Beam Angle

Beam angle is defined as the angle of light emitted from a lamp. The angle is measured between two directions for which the light intensity (candlepower) is 50 percent of maximum intensity. The wider the beam angle, the less intense the light.

Beam Spread

If beam angle is the angle lumens are emitted from a light source, beam spread is the range of the surface illuminated, expressed in distance. To calculate beam spread, multiply beam angle by 0.18 by distance of surface from light source. Beam spread does not account for field spread –– the outmost area illuminated by a light source.

Base Down

A base down lamp must be inserted into a socket with the base of the lamp pointing down (vertical orientation). This is a common specification for HID lighting.

Base Up

A base up lamp must be inserted into a socket with the base of the lamp pointing up (vertical orientation). This is a common specification for HID lighting. For example, if the socket is in the ceiling, pointed toward the floor, the lamp will be base up.


Candela (cd)

The unit of luminous intensity (candlepower) of a light source in a specific direction.


The negatively charged electrode by which electrons enter an electrical device.

Center Beam Candlepower (CBCP)

The intensity of light at the center of a reflector lamp beam (expressed in candelas).

Color Pumping

This advancement in LED lighting essentially boosts the output of a certain spectrum of light. Lighting with color pumping technology enhances the perceived colors of the items displayed under its light.

Color Quality Scale (CQS)

A complimentary metric to Color Rendering Index that provides a gauge of the quality of light produced by a light source based on 15 color swatches.

Color Rendering Index (CRI)

Measures the visual effect a light source has on the perceived color of objects it illuminates. High CRI light generally makes colors look natural and vibrant. Low CRI causes some colors to appear washed out or even to take on a completely different hue. Click here to download a Guide to Color Rendering Index.

Color Shifting

This happens in fluorescent or HID lamps as the chemical balance becomes unbalanced and causes the lamp to shift to a pink, green, orange, or purple tint. The longer fluorescents burn, the more likely it is that the chemical properties will shift and cause an imbalanced reaction, making the fluorescence less white and less bright than it once was.

Color Temperature

Is measured in Kelvin and indicates whether a lamp has a warm, midrange or cool color appearance. Warm light sources, such as incandescent lamps, have a low color temperature (2000-3000K) and feature more light in the red/orange/yellow range. Cool light sources, such as some HID or fluorescent lamps, have a high color temperature (>5000K) and feature more light in the blue range.


A measure of the rate of flow of electricity expressed in amperes.

Custom Rebate

Custom lighting rebate programs offer incentives for projects which do not meet the requirements of the existing instant or prescriptive rebate programs. These rebate programs may also offer more lucrative incentives on the same applications, but there are typically a lot of variables and complexities to sort through to get to those larger incentives.


Delivered Lumens

Light arriving at a surface, expressed in lumens per unit area. One lumen per square foot equals one footcandle, while one lumen per square meter equals one lux.

DLC Listed

DLC is a rating system that identifies, through testing and manufacturer data, which lighting products are generally regarded as being acceptable for their intended use.

Double Ended

Lamps that have two bases opposite one another. These are often designed for series electrical connections, mechanical mounting and heat dissipation.



The rate at which a lamp is able to convert power (watts) into light (lumens), expressed in lumens per watt (LPW or lm/W).

Energy Star

A rating symbol by the U.S. Department of Energy and Environmental Protection Agency that labels a product as energy-efficient.

ETL Listing

ETL (Electrical Testing Labs) is another electrical safety certification. ETL tests products to the same safety standards as UL listing. Like with UL, an ETL mark signifies a product’s safety for the public.



A tungsten wire positioned inside an incandescent or halogen lamp, that when heated electrically generates radiation in the visible, infrared and ultraviolet ranges.

Fluorescent Lamp

A low pressure mercury vapor discharge light source. The electric discharge generates ultraviolet (UV) energy, which is absorbed by a phosphor and converted to visible light.

Footcandle (fc)

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


Group Relamp

Changing out all of the light bulbs in an area at one time instead of replacing them as they burn out individually.


Halogen Lamps

High-pressure tungsten filament lamps containing halogen gasses. The halogen gasses allow the filaments to operate at higher efficacies than incandescent lamps. Halogen lamps also provide brighter, whiter light with better color characteristics, longer life and improved energy efficiency.

High Intensity Discharge (HID)

Lamps in which an arc passing between two electrodes in a pressurized tube causes various metallic additives to vaporize and release large amounts of light. All HID lamps offer good energy efficiency and life.



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


Lamps that generate light by the application of electrical current to a tungsten filament.

Indoor Positioning

Technology that allows retail shoppers and staff to find products based on location services emitting from light fixtures.

Instant Start (IS)

Instant start ballasts apply high voltage across a lamp with no preheating of the cathode. This is the most energy-efficient starting method for fluorescent lamps. IS Ballasts generally use 1.5 to 2 watts less per lamp than rapid start ballasts. Other IS ballast benefits typically include parallel lamp circuitry, longer remote wiring distance, easier installation and capability to start lamps at colder temperatures than rapid start ballasts.



Just like watts, kilowatts is a measure of how much energy something will consume. Going from watts (W) to kilowatts (kW) is a pretty straightforward calculation: 1 kW is equal to 1,000 W.

Kilowatt Hour

A way to measure how much energy is used over time. Calculate kilowatt hours by multiplying the kW of energy consumption by the total number of hours the lighting has been operated. Click here to learn more about kilowatt vs. kilowatt-hour.


LED Conversion/LED Retrofit

The process of replacing inefficient lamps to more efficient, LED lighting.

LED Driver

A driver is typically built into an LED lamp and controls all electricity that flows to the diode. The driver is responsible for many functions of the lamp including, converting the electrical current to DC, dimming the lamp, and responding to voltage changes.

Lighting as a Service (LaaS)

Instead of shelling out the capital investment for a lighting upgrade at the beginning of your project, your lighting service provider will come out and install and warranty your new long-life, high-efficiency lighting system on their dime. Then, with a portion of the money you save on reduced energy bills, you budget a monthly payment for your lighting. It’s effectively a way to get the advantage of the lighting upgrade you’ve been considering and making it cash-flow positive from day one. Learn more about lighting as a service here.

Lighting Audit

A lighting audit will give you a better handle on the expected project cost and return on investment. Additionally, it will give you a clearer picture of installation conditions, minimizing surprises when it’s time to install. Check out our detailed article explaining the types of audits we recommend.

Light Emitting Diode (LED)

Semiconductor devices that produce visible light when an electrical currency passes through them.

Light Center Length (LCL)

The distance from a specified reference point on a lamp base to its light center.

Lumen Depreciation

The decrease in lumen output of a light source over time. Every lamp type has a unique lumen depreciation curve depicting the pattern of decreasing light output.

Lumens (lm)

A unit of luminous flux. This measurement expresses the overall light output or quantity of light produced.


The complete lighting unit (“fixture”), including lamp, reflector, ballast, socket, wiring, diffuser and housing.

Luminaire Efficiency

The ratio of luminous flux emitted by a luminaire to that emitted by the lamp or lamps used within.


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


Unit of illumination equal to the direct illumination on a surface that is everywhere one meter from a uniform point source of one candle intensity or equal to one lumen per square meter.


Magnetic Ballast

An older ballast that regulates electricity incrementally. Typically, this causes a buzz or a hum.

Maximum Overall length (MOL)

The overall length of a lamp, from the top of the bulb to the bottom of its base.

Mean Lumens

Lumen output of a light source after the source has been used. Mean lumen values for fluorescent and HID lamps are typically measured at 40% of their rated lives. Most high-pressure sodium and mercury lamps are measured at 50% of their rated lives.

Metal Halide

An electrical lamp that produces light by an electric arc through a gaseous mixture of vaporized mercury and metal halides (compounds of metals with bromine or iodine). It is a type of high-intensity discharge (HID) gas discharge lamp.

Mirror Reflector

A smaller halogen lamp that has a mirrored reflector around the quartz capsule. This is often used in jewelry stores or homes as accent lighting.


Nominal Watts

Wattage of a particular lamp.

Non-Shunted Sockets

Non-shunted sockets have separate contacts –– or points of entry for the wires –– creating two tracks for the electrical current to travel. Non-shunted sockets have contacts that are not joined/connected. Click here to see a guide on when to use non-shunted sockets.


Operating position

Some lamps are specified or designed to be operated in certain positions, such as horizontal or base-up.


Planned Lighting Maintenance

A lighting maintenance plan designed to have a technician check lighting on a regular interval to check for outages or necessary repairs. This approach yields more consistent lighting within a facility.

Pressed Aluminized Reflector Lamp (PAR Lamp)

A lamp with the outer bulb formed from two pressed glass parts that are fused or sealed together. PAR lamps may be incandescent, halogen or HID types.

Point of Sale (POS) Rebate

Point of sale, or POS, rebates are often set around specific product types. This kind of rebate is issued when the corresponding materials are purchased. Click here to read about point of sale rebates.


The rate at which energy is taken from an electrical system or dissipated by a load expressed in watts.

Power Factor

A measure of the effectiveness with which an electrical device converts volt amperes to watts. Devices with power factors greater than .90 are considered “high power factor” devices.

Prescriptive Rebate

Prescriptive lighting rebate programs are not designed to be claimed instantly. The incentives are paid out based on the parameters correlating to the item sold. Click here to read about prescriptive rebates.


R9 Color Rendering Value

The R9 color rendering value produces strong, vibrant reds. Having a high R9 quality is important in restaurant, retail, hospital, and art gallery applications. Learn more about R9 color rendering value here.

Rapid Start (RS)

Rapid start ballasts apply a low filament voltage to preheat the cathodes in a lamp. When the cathodes are hot enough, a starting voltage is applied, and the lamp will “strike”. Typically, RS ballast will not be able to start lamps reliably at cold temperatures.


Single Ended

Lamps having a single lamp base or point of electrical connection.

Shunted Sockets

Shunted sockets feature internally connected electrical contacts. This provides a single track for the electrical current to travel from the ballast, through the tombstone, or socket, and to the lamp’s pins. Click here to see a guide on when to use shunted sockets.


Tube Lighting

Tube lighting is often known as fluorescent lighting or linear lighting. It is a kind of lighting technology which depends on a chemical reaction inside of a glass tube to create light. This chemical reaction involves gases and mercury vapor interacting, which produces an invisible UV light. That invisible UV light illuminates the phosphor powder coating the inside of the glass tube, emitting white “fluorescent” light. To learn more, visit this article.


UL Listing

UL is a global safety science company that tests the safety of products. When a product is UL listed UL has recognized that it meets a standard set of safety requirements. Click here to learn more about UL listing.



A measure of electrical potential expressed in volts. Voltage is the force that pushes electrical current through a conductor.


Watt (W)

A unit of electrical power equal to 1 joule per second. Lamps are rated in watts to indicate power consumption.

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