Lighting Reference Glossary


Bulborama invites you to browse the glossary below, which contains definitions of some common terms used throughout the lighting industry.



Acronym for alternating current, which describes a source where the voltage changes polarity multiple times per second, with a frequency of 50 Hz or 60 Hz depending on the country.

Accent Lighting

Lighting that focuses its output in a narrow beam, drawing attention to specific decorative features or objects, making them stand out from their surroundings. Accent lighting is also useful in retail applications, where it can be used to draw attention to specific products and make them seem more appealing.


American Lighting Association, a trade association that encompasses the USA, Canada and the Caribbean, focusing on residential lighting. ALA members include manufacturers, event organizers and designers.

Ambient Lighting

General lighting used to provide visibility in a built environment. Ambient lighting includes both artificial and natural lighting, and does not include task lighting and accent lighting.


Measurement unit for electric current. In lighting installations, wiring and protections are calculated based on the amperes drawn by the lighting circuits, as well as their rated voltage.


See Ampere.

Amp Calculations

Procedure of determining the current drawn by a lighting fixture or a circuit consisting of multiple fixtures. Once the current drawn in amperes is known, it is possible to size the wire for the lighting circuit, as well as electrical protection devices.

Angle of Light

Angle between the orientation of a light source and the viewing direction. For example, the angle of light is 0° when looking at a downlight directly from below, and increases progressively as the viewer steps away from it.

The term is commonly used in theatrical lighting, to describe the angle between the stage lighting direction and the viewer’s line of sight.


American National Standards Institute, a publisher of standards for US products and services. ANSI also coordinates national and international standards, allowing US products and services to be used elsewhere.

ANSI Ballast

A ballast that complies with ANSI standards.

See Ballast.


The intended use of a lighting product. Residential, retail, hospitality, healthcare and high-bay industrial are all examples of lighting applications.

Arc Lamp

Any lamp that establishes an electric arc between two electrodes. Arc lamps generally stimulate a gas, making it glow and generating a lighting output.

Architectural Lighting

Decorative lighting that is part of a building’s design and construction. It also provides ambient lighting as a secondary function.


A chemical element, and one of the noble gases. It is used inside the bulbs of incandescent lamps to prevent oxidation of their filaments. Argon can also be used in gas-discharge lamps to emit violet light, or blue if mixed with mercury.




The lighting output of outdoor fixtures that is emitted opposite to the intended direction, generally an undesirable effect. For example, if the pole lamps in a parking lot emit backlight towards adjacent homes or apartments, it can be bothersome for the property owners.

Backlight should not to be confused with backlighting, an accent lighting technique.


Lighting designed to illuminate an object from behind, which causes an appealing glow effect around its edges. Backlighting is a type of accent lighting, and is commonly used to draw attention to works of art.

Backlighting should not to be confused with backlight, an undesirable lighting effect that can be produced by outdoor fixtures.


An opaque or translucent component that blocks direct sight of a lighting source.


A component required by fluorescent and HID lighting fixtures. It controls the voltage and electric current provided to the lamp during ignition and operation, preventing overheating or premature failure. Depending on their internal construction, ballasts can be either magnetic or electronic.

Ballast Factor (BF)

Value that describes how a ballast affects the rated lighting output of a lamp. For example, a 3000-lumen lamp connected to a ballast with a BF of 0.90 or 90% will produce 2700 lumens (3000 lm x 90% = 2700 lm).


The part of a lamp that connects to the lighting fixture, providing both physical support and electric power for the lamp. A lamp and fixture can only be used together if the lamp base matches the fixture socket. The bases of most residential lamps use either a screw or multiple pins.

A lamp can have more than one base: for example, fluorescent tubes have one on each end.

Base Temperature

Maximum allowable temperature of a lamp base, which must be considered when designing the lighting fixture.


A type of lamp base that connects with the socket using keyways instead of threads.

Beam Angle

Also known as beam spread, the beam angle is a value that describes the downward light cone emitted by a lighting fixture with a reflector. The beam angle is measured between the downward direction, where the lamp provides maximum lighting intensity, and the direction in which intensity drops to 50%. In other words, a lamp with a large beam angle spread its lighting into a wider cone.

Bi-Pin Base

A lamp base that uses two pins, as implied by its name.

See Ballast.


A type of lighting fixture commonly used outdoors, consisting of a short and broad post with a lamp on top. Bollards generally accomplish a double function, providing both outdoor lighting and decoration.

BUG Rating

BUG is an acronym for backlight, uplight and glare, and the term was developed by the Illuminating Engineering Society (IES) and International Dark-Sky Association (IDA) to describe the amount of light emitted by a fixture in unwanted directions.

  • Backlight is directed behind the luminaire.
  • Uplight is directed upwards.
  • Glare causes a visual impairment (See Glare).

In the BUG rating, these effects are indicated in a scale from 0 to 5, where 0 indicates the effect is minimized and 5 indicates it is not controlled at all. Therefore, the best possible BUG rating is B0 U0 G0, and the worst possible rating is B5 U5 G5.


A transparent casing that contains a light source, generally made from glass.

Burn Position

The operating position for which a lamp is designed. For example, some lamps can only operate in the base-up position. Lamps operating in positions for which they are not designed generally suffer reduced performance or short-term failure.



Common term for the housing of a recessed downlight.

Candela (cd)

Measurement unit for luminous intensity, which is the amount of light emitted in a particular direction. Not to be confused with the lumen (lm), measurement unit for the total lighting output of a lamp or fixture, without describing a particular direction.

Cave Effect

An effect that occurs when lighting fixtures direct all of their lighting downward and little or no light is reflected back up towards the ceiling or upper wall portions. The cave effect is generally unwanted because it makes indoor spaces feel ominous, like the interior of a cavern.


Part of a lighting fixture that covers the outlet box and wiring connections. Canopies often have decorative features.


Certified Ballast Manufacturers Association, an organization that certifies ballasts as required by ANSI standards. Ballasts with the CBM seal have a guaranteed minimum ballast factor of 0.85 (See Ballast Factor).

Ceiling Cavity

The portion of a room that is above the lighting fixtures.


International Lighting Commission (French: Commission internationale de l’éclairage), an authoritative organization in the lighting industry across the globe.


Derived from "chandler" (candle maker), a chandelier is a designer/decorative light that hangs from the ceiling and consists of several branch-like parts that host lights or candles.

Circline Lamp

A subtype of fluorescent lamp where a fluorescent tube is bent into a circular shape, and where the ballast is typically located in the middle.

Circuit Breaker

Electrical protection device that is normally located within a distribution board. Each lighting circuit is connected to a circuit breaker, and it interrupts current automatically if an overload or fault is detected.

Coefficient of Utilization (CU)

The fraction of a lamp’s luminous output that reaches the work plane. The CU is influenced by the luminous efficiency of the fixture, as well as room geometry and colors.

Cold Cathode Fluorescent Lamp (CCFL)

A fluorescent lamp that emits electrons without heating its electrodes, applying only a high voltage (conventional fluorescent lamps use voltage and heating). CCFLs tend to be less efficient than conventional fluorescent lamps, but offer a service life of over 60,000 hours, comparable to that of LED lighting.

Color Rendering Index (CRI)

A metric used to describe how faithfully a light source can render the true colors of objects and spaces, where natural light sources like the sun have a perfect index of 100. Using lamps with a high CRI value is very important in high-end interior design, as they enhance the visibility of décor and fine details.

Continuous Dimming

Dimming method where the lamp output can be adjusted at any level between OFF and 100% output, without incremental steps.

See Dimmer.

Compact Fluorescent Lamp (CFL)

A type of fluorescent lamp where the tube is bent into a compact shape to reduce space requirements, hence its name. CFLs often have a built-in ballast and screw bases, allowing them to replace incandescent and halogen bulbs directly.

Cool White

A light source with a correlated color temperature of around 4100K. The term comes from the fact that light sources at this color temperature value do not have the characteristic yellow hue of incandescent bulbs or warm white LED lamps.

Cornice Lighting

Fluorescent light built into a soffit at the top corner of a wall (i.e., where the wall meets the ceiling).

Correlated Color Temperature (CCT)

Unlike the CRI, which describes how faithfully a light source represents other objects, the correlated color temperature (CCT) describes the color output of the lamp itself. Some common CCT values include:

  • 2700K, with a warm tinge of yellow that creates appealing and relaxing environments
  • 4000K, a neutral white tone that strikes just the right balance between relaxation and concentration
  • 6500K, with a slight tinge of blue, which has an energizing effect

Although the correct technical term is correlated color temperature, it is often shortened to only color temperature. It is also important to note that the CCT is not the real operating temperature of a lamp - it is the temperature to which you would have to heat a black body to make it glow with the same color. For example, an LED bulb with a CCT of 5000K glows in the same color as a black body heated to a real temperature of 5000K, but the LED bulb itself does not reach that temperature.

Cove Lighting

A type of lighting that generally directs it output towards the ceiling, and where individual fixtures are hidden in ledges. Cove lighting is often used for decorative purposes because it can emphasize the borders of walls, as well as ceiling features.

Crest Factor

In a ballast, the ratio of maximum lamp current to average operating current. The service life of lamps tends to be extended as the crest factor becomes lower.

Cutoff Angle

Viewing angle beyond with it is no longer possible to see a light source directly, measured from the direction exactly below the lamp (nadir).



Acronym for Digitally Addressable Lighting Interface, a communication protocol for lighting automation.

Daylight Harvesting

A lighting design strategy that maximizes the use of natural light to reduce energy costs and create indoor spaces that feel natural and appealing.

Daylight Lamp

A lamp with a CCT value comparable to that of daylight, generally between 5500K and 6500K. It is important to note that the term does not refer to actual daylight, but rather artificial lighting that replicates its color.


Acronym for Direct Current. Used to describe a power supply where the flow of electricity always takes place in the same direction, such as that provided to LED arrays by their drivers.

Desk Lamp

A compact fixture used for task lighting on a desk, and which is generally portable.

Diffused Light

Light produced by an extended surface, either directly or through reflection. Diffused light provides a uniform and soft distribution that minimizes shadows.


A piece of glass or acrylic that has the purpose of scattering the light from a bulb, which results makes lighting more uniform and eliminates glare.


Adjective used to describe a lamp or fixture whose lighting output can be modulated with a dimmer.

See Dimmer.


A device that regulates the lighting output of a lamp by controlling the power supplied. Dimmers can be used to make indoor environments more customizable and personal, and are also useful to save energy. It is important to note that not all lamps are compatible with dimmers, and incompatible types may be damaged.

Direct Lighting

Lighting where more than 90% of the light goes directly from the source to the area you wish to illuminate.

Directed Light

Light produced by point surfaces, which results in a concentrated output that accentuates edges and shadows. Directed light normally causes glare when the sources is viewed directly.


A compact lighting fixture that directs its output downward, hence its name. Downlights can be recessed, surface-mounted or pendant.


Piece of electronic equipment that transforms the main supply voltage into a lower DC voltage that is appropriate for LED lighting. Some LED lamps have a built-in driver, while others require one to be connected externally, just like the ballasts used by fluorescent and HID lamps.


Edge Lit LED

A type of LED fixture that uses a transparent acrylic pattern with etched dots, lines or patterns. The panel is encircled by an array of LEDs, and the etched pattern refracts the light uniformly in all directions.


Describes how effectively a lighting fixture can convert electric power into lighting, measured in lumens per watt. This is like the gas mileage of a sports car, where the lighting output can be compared to miles traveled, and the electric power input is like fuel consumption.


Conversion ratio between lighting power output and electric power input, measuring both quantities in watts. Not to be confused with efficacy, which describes the ratio between lumen output and watts consumed.

Since lumens describe lighting output better than watts, efficacy tends to be a much more useful concept in lighting design.

Electromagnetic Ballast

See Magnetic Ballast.

Electronic Ballast

A subtype of ballast that uses power electronics to provide a high-frequency voltage and controlled current for fluorescent lamps. Electronic ballasts are lighter and more efficient than magnetic ballasts, and they eliminate humming and flickering issues.

Electronic Transformer

Smaller and lighter than magnetic transformers, electronic versions use electronic switching and special dimmers to step the line voltage down to the lamp voltage.

Ellipsoidal Reflector Lamp (ER Lamp)

This soft glass lamp collects and reflects light through a barrel about 2" in front of the fixture.

Emergency Lighting

Lighting designed to provide visibility when the normal lighting system fails, for example during blackouts. Emergency lighting is equipped with batteries, allowing it to operate long enough for a building to be evacuated.

Energy Star

An energy savings and sustainability program by the US Department of Energy and Environmental Protection Agency. Lighting products with the ENERGY STAR have been tested for superior energy efficiency.


Energy Policy Act, a 1992 law that established minimum efficacy requirements for incandescent and fluorescent lamps, a well as labeling requirements.



The wire coil that is heated to produce lighting in incandescent and halogen lamps, normally made from tungsten.

Flat Panel Top LED

A low-profile LED fixture that uses an edge-lit panel, designed to replace linear and parabolic fluorescent fixtures. This fixture type is available in recessed, surface-mounted and pendant versions.


A phenomenon where a lamp blinks repeatedly, often caused by power supply issues, or a faulty ballast or driver.


High-power lighting fixtures that typically use HID bulbs or their LED equivalents. They are generally used outdoors to emphasize specific objects or areas.

Fluorescent Lamp

One of the main types of lighting, far more efficient than incandescent and halogen bulbs, but outclassed by LED lighting. A fluorescent lamp uses electrodes to stimulate mercury vapor and produce ultraviolet (UV) radiation, which in turn stimulates the phosphor coating of the lamp to produce visible light.

Fluorescent Tube

A specific type of fluorescent lamp that has a tubular shape and comes equipped with pins at its ends, to be connected to the voltage output of a magnetic or electronic ballast. Fluorescent tubes are designated by the letter “T” followed by a number indicating its diameter in 1/8ths of an inch:

  • T12 = 12/8” or 1.5”
  • T8 = 8/8” or 1.0”
  • T5 = 5/8" or 0.625”

Fluorescent tubes come in standard lengths, where the some of the most common are 24” (2’), 48” (4’) and 96” (8’).

Flush Mount Lighting / Flush Mount LED Lights

This kind of lighting is mounted to the ceiling with little or no gap between the ceiling and the light.

Focused Light

See Direct Light.

Foot-candle (fc)

Measurement unit for illuminance, or lumens per unit of area. One foot-candle is equivalent to one lumen per square foot (See Illuminance).

Frosted Lens

A white lens that is translucent but not transparent, which diffuses the output of a lamp.



Visual impairment caused by a bright source of light, directly visible or reflected by a surface. There are two types of glare:

  • Discomfort glare causes an instinctive reaction to close the eyes and look away. This is the type of glare felt when exposed to a potent HID light or when the sun is directly visible through a window.
  • Disability glare impairs vision, but does not cause the same reaction as discomfort glare. If a light source gets reflected on your laptop screen, for example, it does not bother your eyes but distinguishing objects on the screen may be impossible.


Hard Light

A light source that creates shadows with a very sharp edge when cast on objects. Direct lighting from a concentrated source is generally hard light, and some examples are:

  • The sun in a day with clear skies.
  • A camera flash.
  • Highly directional lighting fixtures such as floodlights and spotlights.

See Soft Light.

Halogen Lamp

An improved version of incandescent lamps, where the glowing filament is contained in halogen gas, hence its name. Halogen lamps are around 25% more efficient than their incandescent counterparts.

Heat sink

A lamp or luminaire component that is used to dissipate heat effectively. Heat sinks normally use materials with a high thermal conductivity and have a fin-like geometry so that their surface area in contact with the air is maximized.


Acronym for high-intensity discharge, a type of lighting often used for industrial and outdoor settings due to its powerful output. Some examples of HID lighting are mercury-vapor, metal-halide, xenon, high-pressure sodium and low-pressure sodium lamps.

All types of HID lamps produce lighting by stimulating an enclosed gas with an electric arc, and therefore they operate at high temperatures.

High-Bay Lighting

Lighting systems designed for ceiling heights of 25’ or more, commonly found in sports complexes, warehouses or industrial locations.

See low-bay lighting.

High-Efficiency Plasma (HEP)

An emerging lighting technology that uses radiofrequency to stimulate a contained gas and create a small but very bright ball of plasma. HEP lighting offers a very high efficacy (over 90 lumens per watt) and perfect color rendition (CRI = 100).

The technology became commercial very recently, however, and has not achieved a market share comparable to that of LED.

High-Output (HO) Lamp

Fluorescent tubes with a higher lumen output and rated power than conventional fluorescent tubes. For example, a normal 48” T5 tube may consume 28 watts and provide 2400 lumens, while an HO version may consume 54 watts and provide 5000 lumens.

High Voltage Lamps

Lamps that function at a high voltage and offer naturally diffused or scattered light.


Acronym for high-pressure sodium, a subtype of HID lighting where excited sodium vapor is the source of light. The lighting output of HPS lamps is characterized by its warm yellow hue, and they are commonly used in cobra-head street lights.



International Association of Lighting Designers, a global association that promotes best practices in lighting design, while providing training and scholarships.


Institute of Electrical and Electronics Engineers, a global professional association with over 400,000 members. The IEEE is a technical authority that has published many standards and recommended practices for the electrical and electronic fields.


Illuminating Engineering Society of North America, a technical authority in the lighting industry, with dozens of publications to its credit. IESNA has members and recognition throughout the world.


The luminous flux on a surface, per unit of area. The illuminance requirements of built environments are determined by their intended purpose, and there are two common units of measurement:

  • Lux - Equivalent to one lumen per square meter.
  • Foot-candle - Equivalent to one lumen per square foot.

Higher illuminance levels make surfaces appear brighter to the human eye and improve visibility.


The use of lighting for practical or artistic purposes.


Light produced by heating a material; Examples include the glow of a candle, an incandescent filament lamp, a shooting star, etc.

Incandescent Lamp

A type of lamp with a tungsten filament that glows when it carries current. Incandescent lighting has a perfect color-rendering index of 100, comparable to that of the sun, but is among the least efficient types of lighting.

Indirect Lighting

Lighting technique based on reflecting the output of a lamp on surfaces. An example is the lighting provided by torchiere fixtures, which emit their beam towards the ceiling to be reflected back down.

Induction Lamp

A type of gas-discharge lighting where the gas is not stimulated directly by electrodes, like in fluorescent or HID lighting, and where microwaves or radiofrequency are used instead. Induction lighting has a much longer service life than HID or fluorescent lighting because there are no electrodes being subject to wear each time the lamp is activated.

Initial Lumens

Lighting output of a new lamp, which diminishes with use.

See Mean Lumens.

Instant Start Ballast

A type of fluorescent lighting ballast that applies a high-voltage pulse to the lamp, making it start instantly without preheating the electrodes. The drawback of instant-start ballasts is that they reduce the service life of lamps: electrode material is expelled each time the lamp is started, blackening its edges and causing eventual failure.

Insulated Ceiling (IC) Fixture

These lighting fixtures are installed into the ceiling and are in direct contact with insulation. They have a lower wattage and emit less heat.

Integrated Lighting Fixture

A type of lighting fixture that offers superior energy efficiency, by using a specially-designed LED array and internal geometry. Integrated lighting fixtures are generally more efficient than lamp-based LED fixtures, but they make retrofits more expensive because the entire fixture must be replaced, not only the lamps and ballasts.

Interior Soffit Lighting / Soffit Light Fixtures

Lights for portions of the ceiling that are lower than the primary surface; for example, the fixtures installed above the kitchen sink or on a beam or the underside of a balcony.

International Dark-Sky Association (IDA)

An international authority on light pollution and environmentally responsible outdoor lighting. Their main goal is to preserve night sky visibility throughout the world.

Ingress Protection (IP) Rating

Ingress Protection rating, a two-digit code that indicates the resistance of a lighting fixture to solid particles and liquids, where higher digits indicate enhanced protection. The first digit indicates protection against solids, and the second indicates the protection degree against liquids.

For example, an IP67 rating indicates a higher degree of protection than an IP54 rating.


Kelvin (K)

Measurement unit for temperature, although in the lighting industry it is more commonly used to indicate the correlated color temperature (CCT) of light sources.

Kilowatt (kW)

Measurement unit for electric power, equivalent to 1000 watts. This term should not be confused with kilowatt-hour.

See Watt.

Kilowatt-hour (kWh)

Measurement unit for energy consumption. As implied by its name, it is equivalent to the amount of energy consumed by a one-kilowatt appliance running for one hour. Electric utility bills are often calculated based on kilowatt-hour consumption per month. This term should not be confused with kilowatt.



The process of fusing together thin sheets of material so that the composite material is stronger and more stable.


The specific component of a lighting fixture that emits light. They generally come with standard bases that fit into the sockets found in compatible fixtures. Some lamps have built-in ballasts or drivers, while others are connected to an external one contained in the fixture.

Lamp Lumen Depreciation (LLD)

A progressive reduction in the luminous output of a lamp throughout it service life.


The part of a lighting fixture that provides support and power for a lamp with a matching base.

Layering Light

An interior design approach where several types of lighting are combined to achieve a specific ambience or mood.


Acronym for light-emitting diode, a solid-state component that emits light when exposed to electric current. LED lighting represents the state-of-the-art in the industry, outclassing most other types of lighting in terms of energy efficiency, design flexibility and colors of light available.

LED Array

A group of LEDs mounted on a printed circuit board, capable of producing a lighting output.


Leadership in Energy and Environmental Design, a resource efficiency certification framework for buildings, developed by the US Green Building Council.


Lamp or luminaire component that has the goal of dispersing the lighting output so that the desired distribution pattern is achieved.

Lensed Troffer

A troffer-type luminaire that is covered by a lens, making the lighting distribution more uniform and eliminating glare.

Light Loss Factor (LLF)

A factor used in lighting design to account of the degradation in luminous output over time. The LLF accounts for many aspects such as reflector or lens degradation, dust accumulation, lamp degradation due to voltage surges or heat, etc.

For example, if the LLF is 0.80 and a room needs 40,000 lumens, the lighting system will be designed to provide 50,000 initial lumens (50,000 lm x 0.80 = 40,000 lm).

Light Pollution

Any lighting output emitted in unwanted directions, which may have negative consequences. An example of light pollution is when parking lot fixtures emit bright light sideways, exposing drivers to glare.

Light Scallops

An effect of a downlighting plan. The downlights that are closest to the wall create light scallops and add aesthetic value to a room.

Light Transformer

Also referred to as dimmer switches, light transformers are electrical devices that are used to change the voltage of a circuit to make the light dimmer or brighter.

Lighting Fixture

See Luminaire.

Linear Lighting

Multiple LEDs (light-emitting diodes) aligned in a single strip and used for creating uninterrupted lines of directional lighting.


IESNA standard that establishes the procedure to test the photometric and electrical properties of LED lighting.


IESNA standard that establishes the procedure to test the lifespan of LED lighting.


A translucent or opaque screen that blocks direct visibility of a light source and eliminates glare.

Low-Bay Lighting

Lighting systems designed for ceiling heights below 25’.

See high-bay lighting.

Low Voltage Fixtures / Low Voltage Lamps

Lights that operate at a lower voltage than the standard household voltage. These incandescent lamps need a step-down transformer to bring the voltage down from 120 to 6, 12 or 24 volts.

Low Voltage Track

As the name suggests, this is a track that functions at a low voltage using a step-down transformer.


Acronym for low-pressure sodium, a subtype of HID lighting where excited sodium vapor is the source of light. LPS lights have a very high efficacy, but their color rendering performance is very poor. This limits their use to some outdoor applications where the CRI is not important.


Measurement unit for the lighting output of lamps or fixtures. The total lumens emitted and their spatial distribution are of paramount importance when creating appealing and luxurious indoor spaces. In lighting, lumens can be compared to miles traveled and watts can be compared to fuel consumption.

Lumen Maintenance Life

A metric used to describe the time in which the output of a lighting product diminishes to a specific percentage of its initial value. The lumen maintenance life is measured in hours and displayed by the letter L plus two digits. For example, the following lumen maintenance life would describe a product whose output decreases to 70% after 60,000 hours of use:

  • L70 = 60,000 hours

Lumens per Watt

Lumens Per Watt (LPW) is the light output per unit of energy consumption and it reflects the lighting system's efficacy.

Lumens to Watts

The power (P) in watts (W) can be calculated by dividing the luminous flux (ΦV) in lumens (lm) by the luminous efficacy (η) in lumens per watt (lm/W).


A complete and functional lighting fixture. A luminaire includes the lamp, the ballast or driver, internal wiring, reflectors, lens and any additional components required to deliver light.

Luminaire Dirt Depreciation (LDD)

Progressive reduction in the output of a luminaire due to dust accumulation.

Luminaire Efficiency

The ratio between the lumens emitted by a complete luminaire to those emitted by the lamps within. A portion of lighting is always lost due to internal geometric features and reflection.

Not to be confused with luminous efficacy.


The brightness of an object or surface, as perceived by human eyesight from a specific direction. Luminance is measured in candelas per square meter (cd/m2). It is important to note than luminance changes depending on the viewing angle, and high luminance values are the direct cause of glare.

Luminous Ceiling

An uninterrupted plane of translucent ceiling panels with diffusing, fluorescent strip lights.

Luminous Efficacy

See Efficacy.

Luminous Flux

Total output emitted by a light source, measured in lumens. The luminous flux describes the total lighting output of a lighting fixture without considering direction. Not to be confused with luminous intensity.

Luminous Intensity

Lighting emission in a specific direction, measured in candelas. Luminous intensity changes depending on the viewing angle. Not to be confused with luminous flux.


Measurement unit for illuminance, or lumens per unit of area. One lux is equivalent to one lumen per square meter.

A key component of lighting designed is achieving a suitable illuminance level depending on the application at hand.


Magnetic Ballast

A type of ballast that uses a ferromagnetic core, similar to that of a transformer, to regulate the power supply provided to a fluorescent lamp. Magnetic ballast are heavier and less efficient than their electronic counterparts, and issues with flickering or humming are common.

Mean Lumens

Lighting output of a lamp or luminaire at 40 percent of its service life.

See Initial Lumens.

Medium Base

Also known as E26 or standard base, it is the screw-shaped base used by most residential light bulbs.

Mercury Lamp

A subtype of HID lamp that produces its lighting output by stimulating mercury vapor, hence its name. Mercury lamps may use a phosphor coating to enhance lighting performance, and are commonly used in outdoor and industrial lighting applications.

Metal Halide (MH)

A subtype of HID lamp that produces its lighting output by stimulating vaporized metal-halide compounds, hence its name. Like mercury lamps, MH lamps are commonly used in outdoor and industrial setting.

Ceramic metal halide is a subtype of MH lamp, where the arc tube is made from a ceramic material instead of quartz glass. This improves the color rendering index of the lamp.

Mogul Base

Also known as E39 base, it is larger than the medium E26 base and commonly used by HID lamps. Some LED replacement lamps for HID fixtures are compatible with the same types of ballasts and include a mogul base to use the same socket.

Monochromatic Light

A source of light whose output only has one wavelength. The dull yellow lighting of low-pressure sodium lamps is an example of monochromatic light.

Mounting Height

Depending on the application, mounting height can have two possible definitions:

  • Distance between the bottom of the fixture and the work plane.
  • Distance between the bottom of the fixture and the ground.

MR Lamp

MR is an acronym for multifaceted reflector, a component used to shape the output of a light bulb into a directional beam. MR lamps typically use incandescent, halogen or HID bulbs, and there are also LED replacements available. MR lamps are available with both screw bases and pin bases.

The MR designation is followed by a numerical value indicating the lamp diameter in 1/8ths of an inch, where two of the most common types are MR11 and MR16.



National Association of Innovative Lighting Distributors, a lighting industry association that provides ongoing training, a discussion forum, networking, business intelligence and information services.


National Electric Code,a publication by the National Fire Protection Association, which establishes the requirements for fireproof electrical installations.


National Electrical Manufacturers Association, a US-based electrical industry association that develops technical standards to ensure product quality and uniformity.

NEMA Enclosure Type

A numeric code that describes the degree of protection offered by an enclosure, according to the NEMA 250-214 standard. For example:

  • NEMA 2 = Indoor use, protection against falling dirt and light splashing of water.
  • NEMA 3R = Indoor or outdoor use, dirt protection, resistant to rain and snow.
  • NEMA 4X = Indoor or outdoor use, dust-tight, water-proof (including hosedown) and corrosion-proof.
  • NEMA 6P = All NEMA 4X benefits, and also submersible.


National Institute of Standards and Technology, a US-based physical science laboratory that is a technical authority on standards, measurements and technology.


Occupancy Sensor

A device that uses infrared or ultrasonic radiation, or sound, to detect the presence of humans and switch the lights accordingly. Occupancy sensors are an effective energy-saving measure.


Acronym for organic light-emitting diodes, flexible polymers based on organic carbon molecules, where the light source is spread across a surface as opposed to a point source.

Opal Glass

Semi-translucent white glass that owes its milky finish to the ingredients added to clear glass. It is used for diffusing light.

Opaque Material

A material that completely blocks visible light.


PAR Lamp

PAR is an acronym for parabolic aluminized reflector, and it is used to shape the output of a light bulb into a directional beam. PAR lamps typically use incandescent, halogen or HID bulbs, and there are also LED replacements available. PAR lamps are available with both screw bases and pin bases.

The PAR designation is followed by a numerical value indicating the lamp diameter in 1/8ths of an inch. Some of the most common types are PAR20, PAR30 and PAR38.


Term used to describe a louver with a parabolic shape.

See Louver.

Pendant Light / Pendant Fixture / Pendant Lamp

A lighting fixture that is designed to hang from the ceiling, and which often uses a shade to prevent glare. Pendant lights can be used for both general and task lighting.


The measurement of light and its properties.

Photopic Lumens

The portion of luminous output that gets a response from the cones in human eyes, which are responsible for daytime vision.

Post Light

Lighting fixture used to provide outdoor area lighting, where the lamp is found on top of a pole, often with a reflective housing that achieves a characteristic lighting pattern.

Power Factor (PF)

Ratio of real power to apparent power drawn by lighting fixtures and other electrical devices. The real power is represented by the actual watts consumed, while the apparent power is the multiplication product of voltage and current, measured in volt-amperes. Electric utility companies normally apply additional charges if the power factor of a building drops below a specified level.

Programmed Start Ballast

A ballast that preheats the electrodes of a fluorescent lamp before igniting it, which reduces their wear over time and extends the service life of the lamp. Preheating is accomplished by applying a very low voltage that is high enough to raise the temperature of electrodes, but without causing the lamp to ignite.

Pull Down Light Fixture Parts

Utilizing retractable functionality, this recessed downlight pulls down from the ceiling to aim at various angles.

Pulse Start Ballast

A type of ballast used with HID lighting, which uses a series of controlled voltage pulses to ignite the lamp, minimizing damage to the electrodes each time the lamp is turned on.



Energy transmission in the form of waves. Light is a form of radiation, including infrared and ultraviolet light, which are invisible for humans.

Rapid Start Ballast

A type of ballast for fluorescent lamps, which preheats the electrodes and applies voltage simultaneously. This type of ballast is faster than an programmed start ballast, but slower than an instant start ballast. The resulting electrode damage when the lamp is started is intermediate between that of instant start ballast (high damage) and programmed start ballast (low damage), and the resulting service life is also intermediate as a result.

Rated Lamp Life

The time it takes for 50 percent of the lamps in a batch to reach the end of their service life.


A cash incentive for a purchase. In the USA, many states have rebate programs for energy-efficient technologies (e.g. LED lighting) or renewable energy systems (e.g. solar panels)

Recessed Can

A specific type of lighting fixture with a cylindrical shape that is embedded in the ceiling, hence its name.

Recessed Lighting / Recessed Fixture / Recessed Luminaire

Also known as pot light, canister light or downlight, recessed lighting fixtures or luminaires are installed into the openings in a ceiling, appearing as if the light is shining from an elevated hole.


A physical property of surfaces, equivalent to the ratio of reflected light to incident light.

Reflective Lamp Shade / Reflective Lighting Fixtures

A lamp or lighting fixture that produces directional beams. Reflective fixtures direct all the lighting downward (so that there is little or no reflection of light back in the opposite direction).


An internal component of many lamps and luminaires. It has a reflective surface and its geometry is specially designed to provide a specific lighting distribution. Reflectors are often used with lamps that emit light rays in every direction (HID, fluorescent, etc.) to concentrate their output in a specific direction.

Restrike Time

Time required by an HID lamp to achieve full brightness after it has been turned off.


A lighting system upgrade, generally with the goal of improving energy efficiency and site safety.

Room Utilization Factor

Ratio between the light that reaches the work plane and that emitted by the luminaires in the room.



The resulting “colorfulness” when objects are exposed to a light source, compared to that resulting from natural lighting. If the colors appear more intense, the light source saturates them; on the other hand, if colors are dulled, the light source desaturates them.


A wall-mounted lighting fixture, which generally has a decorative purpose.

Scotopic Lumens

The portion of luminous output that gets a response from the rods in human eyes, which are responsible for nighttime vision.

Scotopic/Photopic (S/P) Ratio

Ratio of scotopic to photopic lumens for a specific light source. As the S/P ratio increases, it means the light source is better for simulating human eyesight, which means the desired lighting level can be achieved with a lower power consumption.

Self-Ballasted Lamp

A lamp that has an integrated ballast, allowing direction connection to the supply voltage. CFL bulbs with a screw base are one of the best-known types.

Semi Flush

A ceiling lighting fixture that has a stem that separates (or creates a visible gap between) the light from the ceiling.


A screen that prevents a light source from being viewed directly. Shades generally use opaque or translucent materials.

Shadow Casting Light Fixtures

Lamps that are designed to cast light and shadows, creating intricate geometrical or abstract patterns on surrounding surfaces.


See lampholder.

Soft Light

A light source that creates gradual shadows, without a noticeable edge between lighted and dark areas. Soft light is generally created with diffuse lighting sources, such as:

  • The sun, when covered with clouds that diffuse its light.
  • Lighting fixtures with lens or diffusers.

See Hard Light.

Specular Reflection

Reflection from a surface that is smooth and shiny, such as metallic kitchenware.


Lighting fixture that produces a narrow downward beam, generally used for accent lighting or task lighting applications.


Acronym for solid state lighting, any type of lighting that uses LEDs to produce light, instead of incandescent filaments, ignited gas or plasma. SSL includes OLEDs.

Step Dimming

Dimming method that uses incremental and fixed lighting levels, as opposed to gradual dimming from to OFF to 100% output.

See Dimmer.

Strip Light

Flexible, dynamic and customizable, strip lights can be cut and stuck anywhere, according to project requirements.

Suspension Light / Suspension Fixture / Suspension Lamp

See Pendant Light / Pendant Fixture / Pendant Lamp

Swing Arm Lamp

Adjustable folding arm lamp that can be used to provide task lighting (lighting up a specific area). Also referred to as a floating arm lamp or balanced arm lamp.


Task Lighting

Lighting fixtures with the goal to improve visibility in an area where specific tasks will be carried out, hence their name. The use of under cabinet lights for food preparation areas in kitchens is an example of task lighting.

Total Cost of Ownership (TCO)

Cost of owning a lighting product over its entire lifetime. It includes the sales price, installation cost, energy consumption, maintenance, component replacements and decommissioning cost.


A floor lamp that uses a reflector on top a pole to direct its entire output upward, which is then reflected from the ceiling and walls.

Track Lighting

Lighting configuration where several fixtures are mounted on a common track, which provides them with power and allows each of them to be oriented in a different direction.

Translucent Material

A material that allows a partial transmission of light, generally diffusing it and eliminating glare. Frosted glass is an example of a translucent material.

Transparent Material

A material that allows most or all of the light incident on it to pass through. Clear glass is a translucent material.


A recessed lighting fixture, designed to be installed in an opening in the ceiling. Troffers typically have predetermined dimensions, such as 2’x2’ or 2’x4’.

Twin Tube

A type of CFL lamp where two parallel fluorescent tubes share the same base.


U-Bend Lamp

A type of fluorescent lamp where the tube is bent in a U shape, hence its name. U-bend lamps generally have two bases, one on each end, which attach to different lampholders.

UL Label

A label placed by Underwriters Laboratories, which means a product has been tested for fire safety and electrical safety.

Ultrasonic Sensor

An acoustic sensor that measures distances by sending and receiving ultrasonic signals.

Ultraviolet Light

A type of electromagnetic radiation, invisible to the human eye (i.e., beyond the visible spectrum) with a wavelength of 10 to 380 nanometers.

Under cabinet lighting

Installed under a cabinet or shelf, this lighting is used to produce localized lighting and can also serve as a night light. It can come in LED, fluorescent, incandescent versions.

Universal Product Code

A 12-digit code found in lighting products, which can be scanned at the point of sale.


Lighting method where an object or surface is lit from below, with a luminaire that directs its output upward. The applications of uplighting are generally decorative.


Valance Lighting

Lighting that is installed above the upper edge of windows, where an opaque panel blocks direct vision of the fixture and the light is directed upward and downward as a result.

Vandal-Resistant Fixture

A lighting fixture that is resistant to breaking or tampering, generally intended for outdoor public spaces.

Vanity Light

Lighting located above, below or to the sides of a bathroom mirror.

Vapor-Tight Fixture

A lighting fixture that is enclosed and gasketed to prevent the entrance of vapors or gases.


The electric potential difference between two contacts. Voltage drives electric current through lighting fixtures and other appliances, just like pressure drives the flow of water in plumbing installations.

Volumetric Troffer

A troffer that is specially designed for maximum optical performance, with a uniform lighting distribution that eliminates both glare and the cave effect.


Wall Grazing

Lighting effect where a wall with an irregular surface is illuminated so that there are both highlighted and shaded areas. This effect is only possible on walls with granular surfaces, such as those built from stone or exposed brick. The opposite effect is wall washing.

Wall Sconce

See Sconce.

Wall Washing

Lighting effect where a wall is illuminated so that surface irregularities are minimized, it seem smoother. The opposite effect is wall grazing.


Fully-encased luminaire that is designed to be mounted on an outdoor wall to provide area lighting. Wallpacks are available in HID, CFL and LED versions.

Warm White

White light that is characterized by a yellow tinge. The term is generally used for lighting with a correlated color temperature (CCT) of around 3000K.


Measurement unit for the electric power consumption of lighting fixtures, or any other appliance that runs with electricity. In lighting, lumens can be compared to miles traveled and watts can be compared to fuel consumption.

Watts to Lumens

To convert watts to lumens, multiply the power (P) in watts (W) with the luminous efficacy (η) in lumens per watt (lm/W).

Work Plane

The horizontal plane where activities are carried out, typically 30 inches above the floor. Lighting designs are generally based on providing a specified illumination level at the work plane.