Ultimate Lighting Glossary



An abbreviation for alternating current, which refers to a power source that changes polarity multiple times per second, with a frequency of either 50 Hz or 60 Hz, depending on the country.

Accent Lighting 

Lighting that produces a narrow beam of light, designed to highlight specific decorative features or objects, making them stand out from their surroundings. In retail settings, accent lighting can be used to draw attention to particular products and make them more attractive.


A device used to change the type of plug on a lighting fixture to fit a different outlet.

Ambient Lighting

General lighting used to provide overall visibility in a built environment, including both artificial and natural lighting, but not task or accent lighting.


The unit of measurement 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.


An abbreviation for Ampere.

Amp Calculations 

The process of determining the current drawn by a lighting fixture or circuit consisting of multiple fixtures. Once the current draw in amperes is known, it is possible to size the wire for the lighting circuit and select appropriate electrical protection devices.

Angle of Light 

The angle between the orientation of a light source and the viewing direction. This term is commonly used in theatrical lighting to describe the angle between the stage lighting direction and the viewer's line of sight.

Anglepoise lamp

A type of desk lamp with a flexible arm that can be adjusted to direct light in a specific direction.

Angle of Incidence

The angle at which light strikes a surface.

Angle of Reflection

The angle at which light bounces off a surface.

Angle of Refraction

The angle at which light bends as it passes through a transparent medium.

Anti-corrosion coating

A coating applied to metal surfaces to prevent corrosion.


A part of a light fixture that extends from the base or body of the fixture and holds the light source.


The opening in a lighting fixture through which light is emitted.


The intended use of a lighting product, such as residential, retail, hospitality, healthcare, or high-bay industrial lighting.

Arc Lamp 

Any lamp that uses an electric arc between two electrodes to produce light. Arc lamps typically stimulate a gas, making it glow and generating light output.

Architectural Lighting 

Decorative lighting that is integrated into a building's design and construction, while also providing ambient lighting.


A chemical element and one of the noble gases. It is used in the bulbs of incandescent lamps to prevent filament oxidation. Argon can also be used in gas-discharge lamps to produce violet or blue light when mixed with mercury.

Asymmetrical Light Distribution

The distribution of light that is uneven or irregular.

Automatic Lighting 

A system that uses sensors to automatically turn lights on and off.

Average Lamp Life

The expected lifespan of a light bulb, usually measured in hours.



The output of outdoor fixtures that emits lighting opposite to the intended direction, which is typically unwanted. When pole lamps in a parking lot emit backlight towards neighboring homes or apartments, it can cause disturbance for the property owners.

Note that backlighting is a distinct lighting technique that illuminates an object from behind to produce a desirable glow effect.


A type of accent lighting designed to illuminate an object from behind to create an attractive glow effect around its edges. Backlighting is often used to highlight works of art.

Note that backlight is an undesirable lighting effect that can be produced by outdoor fixtures, and should not be confused with backlighting.


A component that blocks direct sight of a lighting source, made from either an opaque or translucent material.


A component essential for fluorescent and HID lighting fixtures, regulating the voltage and electric current provided to the lamp during ignition and operation to prevent overheating or premature failure. Ballasts can be magnetic or electronic, depending on their internal construction.

Ballast Factor (BF) 

A value that describes how a ballast affects the rated lighting output of a lamp. For instance, 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).

Bar Light

A type of lighting fixture that consists of a long, narrow bar with multiple bulbs.


The part of a lamp that connects to the lighting fixture, supplying both physical support and electric power for the lamp. A lamp and fixture must have matching bases for them to be used together. The bases of most residential lamps use either a screw or multiple pins.

Note that a lamp can have more than one base, such as fluorescent tubes that have one on each end.

Base Temperature 

The maximum allowable temperature of a lamp base that must be considered when designing the lighting fixture.


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

Bayonet Cap (BC) 

A type of light bulb base that has two pins that fit into corresponding slots in the socket.

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 spreads its lighting into a wider cone.

Bi-Pin Base 

A lamp base that uses two pins.

See Ballast.

Black Light 

A type of light that emits ultraviolet radiation and is used to make certain materials fluoresce.

Blue Light 

Light with a short wavelength that appears blue to the human eye.


A type of outdoor lighting fixture that features a short and broad post with a lamp on top. Bollards provide both outdoor lighting and decoration.

Book Light

A small, portable light fixture designed to be used for reading.

BUG Rating 

An acronym for backlight, uplight, and glare, the BUG rating is a system 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).

The BUG rating system uses a scale from 0 to 5 to indicate the degree of each effect, where 0 minimizes the effect and 5 indicates it is uncontrolled. The best possible BUG rating is B0 U0 G0, while the worst is B5 U5 G5.


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

Burn Position 

The specific operating position for which a lamp is designed. For example, some lamps can only function in the base-up position. Lamps used in positions they are not designed for may have reduced performance or experience short-term failure.



A term used to describe the enclosure of a recessed downlight.

Candela (cd) 

A unit of measurement for luminous intensity, indicating the amount of light emitted in a specific direction. The lumen (lm) is another unit used to measure the total lighting output of a lamp or fixture without specifying a direction.


A measure of the intensity of light emitted by a light source in a specific direction.


The emission of light by a material as a result of being heated.

Cave Effect 

A phenomenon that occurs when lighting fixtures emit light only downward, resulting in minimal light being reflected upward towards the ceiling or upper wall areas. The cave effect is typically undesired as it creates a gloomy and cavernous feeling within indoor spaces.


The part of a lighting fixture that covers the outlet box and wiring connections, which can have decorative features.

Carbon filament

A type of filament used in early incandescent light bulbs.

Ceiling Cavity 

The area above lighting fixtures within a room.

Ceiling Grid Lighting

A type of lighting design that uses a grid of light fixtures installed in a suspended ceiling.

Ceiling Light 

A type of light fixture that is mounted to the ceiling.


The International Lighting Commission (French: Commission internationale de l’éclairage) is an authoritative global organization in the lighting industry.


A decorative light that hangs from the ceiling and typically features several branch-like parts that hold lights or candles. The term originates from the word "chandler," meaning candle maker.

Circline Lamp 

A subtype of fluorescent lamp that consists of a fluorescent tube bent into a circular shape, typically with the ballast located in the middle.

Circuit Breaker 

An electrical protection device located within a distribution board that automatically interrupts current if an overload or fault is detected. Each lighting circuit is connected to a circuit breaker.

Cluster Pendant

A lighting fixture that consists of multiple pendant lights grouped together in a single fixture.

Coefficient of Utilization (CU) 

The fraction of a lamp’s luminous output that reaches the work plane, affected by factors such as the fixture’s luminous efficiency, room geometry, and colors.

Cold Cathode Fluorescent Lamp (CCFL) 

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

Colour Rendering Index (CRI) 

A metric used to describe how accurately 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. High CRI lamps are important in high-end interior design to enhance the visibility of décor and fine details.

Colour Temperature 

A measurement of the color appearance of a light source, typically measured in Kelvins.

Concealed Lighting 

Lighting that is hidden or not directly visible, such as lights that are recessed into a ceiling or wall.

Continuous Dimming 

A method of dimming 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 with a bent tube shape that reduces space requirements, often featuring built-in ballasts and screw bases to replace incandescent and halogen bulbs directly.

Cool White 

A light source with a correlated color temperature of approximately 4100K, lacking the characteristic yellow hue of incandescent bulbs or warm white LED lamps.

Cornice Lighting 

Fluorescent lighting installed into a soffit at the top corner of a wall, where it meets the ceiling.

Correlated Color Temperature (CCT) 

The correlated color temperature (CCT) is a measure of the color output of a light source, while the color rendering index (CRI) describes how faithfully the light source represents the color of other objects. Some common CCT values include:

  • 2700K: warm yellowish hue for creating relaxing and cozy environments
  • 4000K: neutral white tone for a balance between relaxation and focus
  • 6500K: slightly bluish hue for an energizing effect

Although often abbreviated as color temperature, it's important to note that the CCT doesn't represent the actual temperature of the lamp but rather the temperature required to make a black body emit light with the same color. For instance, an LED bulb with a CCT of 5000K emits light in the same color as a black body heated to 5000K, but the LED bulb itself doesn't reach that temperature.

Cove Lighting 

Cove lighting is a type of lighting that directs its output towards the ceiling and is installed in ledges to hide individual fixtures. It is often used for decorative purposes because it can highlight the edges of walls and ceiling features.

Crest Factor 

The ratio of the maximum lamp current to the average operating current in a ballast is called the crest factor. Lamps typically have a longer lifespan when the crest factor is lower.

Cutoff Angle 

The cutoff angle is the viewing angle beyond which a light source can no longer be seen directly. It is measured from the direction directly below the lamp (nadir).


A communication protocol for lighting automation, which stands for Digitally Addressable Lighting Interface.

Daylight Harvesting 

A lighting design technique that utilizes natural light to reduce energy costs and create a more natural and inviting indoor environment.

Daylight Lamp 

A type of lamp that has a correlated color temperature (CCT) similar to that of daylight, typically between 5500K and 6500K. It is important to note that daylight lamps are not actual daylight, but rather artificial lighting designed to mimic its color.


Direct current, which is a type of power supply where the flow of electricity always goes in the same direction. DC is commonly used to power LED arrays through their drivers.

Deck Light 

A type of outdoor light fixture that is designed to be mounted to a deck or patio.

Desk Lamp 

A compact and portable lighting fixture used for task lighting on a desk.

Diffused Light 

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


A piece of glass or acrylic that scatters light from a bulb to create a more uniform distribution and reduce glare.


A term used to describe a lamp or fixture that can have its lighting output adjusted using a dimmer.

See Dimmer.


A device that controls the power supplied to a lamp, allowing for adjustable lighting output. Dimmers provide customizable and energy-saving lighting options, but 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 travels directly from the source to the desired area of illumination.

Directed Light 

Light produced by a point source, resulting in a concentrated output that highlights edges and shadows. Directed light can cause glare when viewed directly.

Discharge Lamp 

A type of light fixture that uses an electric arc to produce light, such as a metal halide or high-pressure sodium lamp.


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


An electronic device that converts the main supply voltage into a lower DC voltage suitable for LED lighting. Some LED lamps have built-in drivers, while others require an external driver, similar to the ballasts used by fluorescent and HID lamps.

Dusk-to-dawn Sensor

A sensor that turns on outdoor lights at dusk and turns them off at dawn, saving energy and providing security.

Edge Lit LED 

An LED fixture that utilizes a transparent acrylic pattern with etched dots, lines or patterns to refract the light uniformly in all directions. The panel is surrounded by an array of LEDs.

Edison Screw

A type of threaded socket used for light bulbs, named after its inventor Thomas Edison.


The measure of how effectively a lighting fixture can convert electric power into lighting, expressed in lumens per watt. This is akin to 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.


The conversion ratio between lighting power output and electric power input, measured in watts. It is 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 is a more useful concept in lighting design.


The process of producing light by passing an electric current through a material.

Electromagnetic Ballast 

Also known as a magnetic ballast.

Electronic Ballast 

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

Electronic Transformer 

An electronic version of a transformer that is smaller and lighter than magnetic transformers. It employs electronic switching and special dimmers to step the line voltage down to the lamp voltage.

Ellipsoidal Reflector Lamp (ER Lamp) 

This soft glass lamp gathers and reflects light through a barrel situated approximately 2" in front of the fixture.

Emergency Lighting 

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

Energy Star 

A certification program for energy-efficient lighting products.



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

Flat Panel Top LED 

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


A repeated blinking of a lamp caused by power supply issues, or a faulty ballast or driver.


High-power lighting fixtures typically used outdoors to emphasize specific objects or areas, using HID bulbs or their LED equivalents.


The emission of light by a material as a result of being excited by another source of light.

Fluorescent Lamp 

One of the main types of lighting that is more efficient than incandescent and halogen bulbs, but outclassed by LED lighting. It 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 type of fluorescent lamp that is tubular 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, with the most common being 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) 

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

Fresnel Lens 

A type of lens used in lighting fixtures to focus or diffuse light.

Frosted Lens 

A translucent white lens that diffuses the output of a lamp.

Gas-Discharge Lamp 

A type of light fixture that uses a gas-filled tube to produce light.


A device (often a downlight) used to mount and adjust lighting fixtures, typically allowing for adjustable angles and directions of light.


Visual impairment caused by a bright source of light, either directly visible or reflected by a surface. Two types of glare are discomfort glare and disability glare. Discomfort glare causes an instinctive reaction to close the eyes and look away, while disability glare impairs vision but does not cause the same reaction as discomfort glare.

Grow Light

A type of lighting designed specifically for growing plants indoors, typically using high-intensity discharge (HID) lamps or light-emitting diodes (LEDs).

Hard Light 

A light source that casts sharp shadows on objects. Typically, direct lighting from a focused source creates hard light. Examples of hard light sources include:

  • The sun on a clear day
  • A camera flash
  • Highly directional lighting fixtures like floodlights and spotlights 

See Soft Light.

Halogen Lamp

An improved version of incandescent lamps. The filament in a halogen lamp is surrounded by halogen gas, making it more efficient than traditional incandescent lamps by around 25%.

Heat sink 

A component of a lamp or luminaire that effectively dissipates heat. Heat sinks are usually made of materials with high thermal conductivity and have a fin-like design, maximizing their surface area in contact with the air.

High-Bay Lighting 

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

See low-bay lighting.

High-Efficiency Plasma (HEP) 

A new lighting technology that uses radiofrequency to stimulate gas and create a small but very bright ball of plasma. HEP lighting has a high efficacy, over 90 lumens per watt, and perfect color rendition with a CRI of 100. Although the technology has recently become commercially available, it has not achieved a market share comparable to that of LED.

High-Intensity Discharge (HID) Lamp 

A type of light fixture that uses an electric arc to produce light, such as a metal halide or high-pressure sodium lamp. All types of HID lamps operate at high temperatures and generate lighting by exciting an enclosed gas with an electric arc.

High-Output (HO) Lamp 

Fluorescent tubes with 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 high voltage and offer naturally diffused or scattered light.


High-pressure sodium, a subtype of HID lighting that generates light by exciting sodium vapor. HPS lamps have a warm yellow hue and are commonly used in cobra-head street lights.


The International Association of Lighting Designers is a global organization that promotes best practices in lighting design and provides training and scholarships.


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


Illuminance is the luminous flux on a surface per unit of area. The illuminance requirements of built environments are determined by their intended purpose. The two common units of measurement are Lux, which is equivalent to one lumen per square meter, and Foot-candle, which is equivalent to one lumen per square foot. Higher illuminance levels make surfaces appear brighter to the human eye and improve visibility.


Illumination refers to the use of lighting for practical or artistic purposes.


Incandescence is the light produced by heating a material. Examples include the glow of a candle, an incandescent filament lamp, and a shooting star.

Incandescent Lamp 

An incandescent lamp is a type of lamp with a tungsten filament that glows when it carries current. It has a perfect color-rendering index of 100, which is comparable to that of the sun. However, it is one of the least efficient types of lighting.

Indirect Lighting 

Indirect lighting is a 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 

An induction lamp is a type of gas-discharge lighting that uses microwaves or radiofrequency instead of electrodes to stimulate the gas. Induction lighting has a much longer service life than HID or fluorescent lighting because there are no electrodes subject to wear each time the lamp is activated.

Infrared (IR) Light 

Light with a wavelength longer than visible light that is not visible to the human eye.

Ingress Protection (IP) Rating

A rating system that indicates the degree of protection provided by a lighting fixture against dust and moisture.

Initial Lumens 

Initial lumens refer to the lighting output of a new lamp, which diminishes with use. See Mean Lumens.

Instant Start Ballast 

An instant start ballast is 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 

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

Integrated Lighting Fixture 

An integrated lighting fixture is 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 

Interior soffit lighting or soffit light fixtures are lights for portions of the ceiling that are lower than the primary surface, such as the fixtures installed above the kitchen sink or on a beam or the underside of a balcony.

International Dark-Sky Association (IDA) 

The International Dark-Sky Association is an international authority on light pollution and environmentally responsible outdoor lighting. Its main goal is to preserve night sky visibility throughout the world.

Ingress Protection (IP) Rating

The Ingress Protection (IP) rating is a code consisting of two digits that represent the level of resistance of a lighting fixture to solid particles and liquids. A higher IP rating indicates greater protection. The first digit indicates the degree of protection against solids, while the second digit indicates the level of protection against liquids. For instance, an IP67 rating provides greater protection than an IP54 rating.


Junction Box 

A box used to connect wiring for a lighting fixture to the building's electrical system.

Kelvin (K)

A unit of measurement for temperature. In the lighting industry, it is commonly used to indicate the correlated color temperature (CCT) of light sources.

Kilowatt (kW)

A unit of measurement for electric power, equivalent to 1000 watts. It should not be confused with kilowatt-hour.

See Watt.

Kilowatt-hour (kWh)

A unit of measurement for energy consumption. 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. It should not be confused with kilowatt.



The process of bonding thin layers of material together to create a stronger and more stable composite material.


A component of a lighting fixture that emits light. It may come with a standard base that fits into sockets in compatible fixtures, and may have a built-in ballast or driver or be connected to an external one.

Lamp Lumen Depreciation (LLD)

A reduction in the luminous output of a lamp as it ages.


The part of a lighting fixture that supports and powers a lamp with a matching base.


A decorative cover or shade used to diffuse or direct the light emitted by a light bulb.


A type of light source that produces a narrow, intense beam of light.

Layering Light

An interior design approach that combines different types of lighting to create a specific mood or ambience.


Light-emitting diode, a solid-state component that emits light when electricity passes through it. LED lighting is known for its energy efficiency, design flexibility, and range of available colors.

LED Array 

A group of LEDs mounted on a printed circuit board to produce a lighting output.


A lamp or luminaire component used to disperse the lighting output to achieve the desired distribution pattern.

Lensed Troffer

A troffer-type luminaire covered by a lens to produce uniform lighting distribution and eliminate glare.

Light Loss Factor (LLF)

A factor used in lighting design to account for luminous output degradation over time. The LLF takes into account reflector or lens degradation, dust accumulation, lamp degradation due to voltage surges or heat, etc.

Light Pollution

Any unwanted lighting output that 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 aesthetic effect of a downlighting plan. Downlights closest to the wall create light scallops, adding visual appeal to a room.

Light Transformer

Also known as dimmer switches, electrical devices used to adjust circuit voltage to make the light dimmer or brighter.

Lighting Fixture

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

Lighting Plan

A plan that outlines the placement and types of lighting fixtures to be used in a space.

Linear Lighting

Multiple LEDs aligned in a single strip to create uninterrupted lines of directional 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', similar to high-bay lighting.

Low Voltage Fixtures/Lamps/Track

Lighting fixtures or lamps that operate at a lower voltage than standard household voltage, requiring a step-down transformer.


Low-pressure sodium, a subtype of HID lighting where excited sodium vapor is the source of light, known for its high efficacy but poor color rendering performance.

Lumen (lm)

The unit used to measure the total amount of light emitted by a lamp or fixture, and its spatial distribution.

Lumen Maintenance Life

A metric used to describe how long it takes for a lighting product to diminish to a specific percentage of its initial value.

Lumens per Watt

The light output per unit of energy consumption, reflecting the lighting system's efficacy.

Lumens to Watts

A calculation that divides the luminous flux in lumens by the luminous efficacy in lumens per watt to determine power usage.


A lighting fixture that includes various components such as the lamp, ballast or driver, wiring, reflectors, lens, and other necessary elements to produce light.

Luminaire Dirt Depreciation (LDD)

A gradual reduction in the output of a luminaire caused by the accumulation of dust.

Luminaire Efficiency

The proportion of lumens produced by a complete luminaire to those emitted by its lamps. Some amount of light is lost due to internal geometric features and reflection. Note that this is different from luminous efficacy.


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

Luminous Ceiling

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

Luminous Efficacy

See Efficacy.

Luminous Flux

The total output emitted by a light source, measured in lumens. It describes the total lighting output of a lighting fixture without considering direction. Note that this is different from luminous intensity.

Luminous Intensity

The lighting emission in a specific direction, measured in candelas. Luminous intensity changes depending on the viewing angle. Note that this is different from luminous flux.


A unit of measurement for illuminance, or lumens per unit of area. One lux is equal to one lumen per square meter. Achieving an appropriate illuminance level is a crucial component of lighting design depending on the application.


Magnetic Ballast

A type of ballast that regulates the power supply to a fluorescent lamp using a ferromagnetic core similar to that of a transformer. Magnetic ballasts are heavier and less efficient than electronic ballasts and can cause flickering or humming.

Mean Lumens

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

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 lighting output by stimulating mercury vapor. It may use a phosphor coating to enhance lighting performance and is commonly used in outdoor and industrial lighting applications.

Metal Halide (MH)

A subtype of HID lamp that produces lighting output by stimulating vaporized metal-halide compounds. Like mercury lamps, MH lamps are commonly used in outdoor and industrial settings. Ceramic metal halide is a subtype of MH lamp where the arc tube is made from a ceramic material instead of quartz glass, improving 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 light source with a single wavelength, such as the dull yellow lighting of low-pressure sodium lamps.

Motion Sensor 

A device used to detect motion and trigger lighting or other systems.

Mounting Height

Depending on the application, the term "mounting height" can have two possible meanings:

  1. The distance between the bottom of a fixture and the work plane.
  2. The distance between the bottom of a fixture and the ground.

MR Lamp

The acronym "MR" stands for multifaceted reflector, a component that shapes the output of a light bulb into a directional beam. Incandescent, halogen, or HID bulbs are commonly used for MR lamps, with LED replacements also available. MR lamps can have screw bases or pin bases.

The "MR" designation is followed by a numerical value that indicates the lamp's diameter in 1/8ths of an inch. Two of the most common types are MR11 and MR16.


Neon Lamp 

A type of gas-discharge lamp that produces a glowing light by exciting neon gas.


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.


Organic light-emitting diodes are flexible polymers based on organic carbon molecules. 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.

Optical Fiber 

A type of fiber-optic cable used to transmit light signals.


PAR Lamp 

A directional light bulb that shapes its output into a beam. PAR lamps can use incandescent, halogen, HID, or LED bulbs with screw or pin bases. The diameter of the lamp is indicated by a numerical value following the PAR acronym (e.g. PAR20, PAR30, PAR38).

Parabolic Reflector 

A type of reflector used in lighting fixtures to direct light in a specific direction.


A type of louver with a parabolic shape.

Pendant Light / Pendant Fixture / Pendant Lamp 

A lighting fixture that hangs from the ceiling and often includes a shade to prevent glare. Pendant lights are suitable for both general and task lighting.


A device that detects changes in light levels and can be used to trigger lighting or other systems.


The measurement of light and its properties.

Photopic Lumens 

The amount of luminous output that activates the cones in human eyes responsible for daytime vision.

Post Light 

An outdoor lighting fixture that sits on top of a pole and produces a specific lighting pattern through its reflective housing.

Power Factor (PF) 

The ratio of real power to apparent power drawn by electrical devices. A low PF can result in additional charges from the electric utility company.

Programmed Start Ballast 

A ballast that preheats the electrodes of a fluorescent lamp before igniting it, extending the lamp's service life.

Pull Down Light Fixture Parts 

A recessed downlight that can be pulled down from the ceiling to aim at different angles.

Pulse Start Ballast 

A ballast used with HID lighting that minimizes electrode damage by using controlled voltage pulses to ignite the lamp.



Energy transmission in the form of waves, including visible and invisible light.

Rapid Start Ballast 

A type of ballast for fluorescent lamps that preheats electrodes and applies voltage simultaneously, resulting in intermediate electrode damage and service life.

Rated Lamp Life 

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

Recessed Can / Recessed Lighting / Recessed Fixture / Recessed Luminaire 

A cylindrical lighting fixture embedded in a ceiling that appears as if the light is shining from an elevated hole.

Reflectance / Reflective Lamp Shade / Reflective Lighting Fixtures 

The ratio of reflected light to incident light on a surface. A reflective lamp or fixture directs all its light downward.


An internal component of many lamps and luminaires that reflects light to provide a specific lighting distribution.

Restrike Time 

The time required for an HID lamp to achieve full brightness after being turned off.


An upgrade to a lighting system to improve energy efficiency and site safety.


A color model that uses red, green, and blue light to create a wide range of colors.

Room Utilization Factor 

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



The color intensity of objects under a light source compared to natural lighting. If colors appear more vibrant, the light source is saturating them. Conversely, if colors appear muted, the light source is desaturating them.


A decorative lighting fixture mounted on a wall.

Scotopic Lumens 

The luminous output that activates the rods in human eyes responsible for night vision.

Scotopic/Photopic (S/P) Ratio 

The ratio of scotopic to photopic lumens for a specific light source. A higher S/P ratio indicates better simulation of human eyesight, resulting in lower power consumption for achieving desired lighting levels.

Self-Ballasted Lamp 

A lamp with an integrated ballast for direct connection to the supply voltage. CFL bulbs with a screw base are a common example.

Semi Flush 

A ceiling lighting fixture with a stem that separates the light from the ceiling.


A screen that blocks direct view of a light source, typically using opaque or translucent materials.

Shadow Casting Light Fixtures 

Lamps designed to cast intricate geometrical or abstract patterns of light and shadows on surrounding surfaces.

Smart Light

A smart light is an advanced lighting system that can be controlled remotely via a mobile app, voice commands, or a smart home system. Smart lights can be turned on or off, dimmed, and even change color, temperature or brightness levels with the help of a mobile app or voice assistant.


A lampholder.

Sodium Vapor Lamp

A type of gas-discharge lamp that uses sodium vapor to produce light.

Soft Light 

A light source that creates gradual shadows without noticeable edges. Soft light is typically produced by diffuse lighting sources, such as diffusers or the sun when covered with clouds. See Hard Light.

Solar Light

A solar light is a lighting system that uses solar panels to convert sunlight into electricity, which is then stored in a battery and used to power an LED light source. Solar lights are typically self-contained and do not require external wiring or a power supply.

Spectral Power Distribution (SPD) 

A measure of the amount of light emitted by a light source at each wavelength.

Specular Reflection 

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


A lighting fixture that produces a narrow downward beam used for accent or task lighting.


Solid state lighting, a type of lighting that uses LEDs instead of incandescent filaments, ignited gas, or plasma. SSL includes OLEDs.

Step Dimming 

A dimming method that uses fixed incremental lighting levels, as opposed to gradual dimming from OFF to 100%. See Dimmer.

Strip Light 

A flexible and customizable lighting fixture that can be cut and installed according to project requirements.

Strobe Light 

A type of light source that produces flashes of light at regular intervals.

Suspension Light / Suspension Fixture / Suspension Lamp 

See Pendant Light / Pendant Fixture / Pendant Lamp.

Swing Arm Lamp 

An adjustable folding arm lamp used for task lighting.


Task Lighting 

Lighting fixtures that improve visibility for specific tasks, such as under cabinet lights for food preparation areas in kitchens.

Total Cost of Ownership (TCO) 

The cost of owning a lighting product over its lifetime, including sales price, installation, energy consumption, maintenance, component replacements, and decommissioning cost.


A floor lamp that directs its entire output upward using a reflector on top of a pole, reflected from the ceiling and walls.

Track Lighting 

A lighting configuration with several fixtures mounted on a common track, providing power and allowing orientation in different directions.


A device used to convert voltage from one level to another, typically used in lighting systems.

Translucent Material 

A material that partially transmits light, diffusing it and reducing glare. Frosted glass is an example.

Transparent Material 

A material that allows most or all of the incident light to pass through, such as clear glass.


A recessed lighting fixture installed in an opening in the ceiling with predetermined dimensions, such as 2’x2’ or 2’x4’.

Twin Tube 

A type of CFL lamp with two parallel fluorescent tubes sharing the same base.


U-Bend Lamp 

A fluorescent lamp with a tube bent in a U-shape. It has two bases that attach to different lampholders.

UL Label 

A label that indicates a product has been tested for fire and electrical safety by Underwriters Laboratories.

Ultrasonic Sensor 

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

Ultraviolet Light 

A type of invisible electromagnetic radiation with a wavelength of 10 to 380 nanometers.

Under Cabinet Lighting 

Lighting installed under a cabinet or shelf that provides localized lighting and can also function as a night light. It can be available in LED, fluorescent, or incandescent versions.

Universal Product Code 

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


A decorative lighting method that involves directing light upward toward an object or surface from below, using a luminaire.

Valance Lighting 

Lighting 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.

Vandal-Resistant Fixture 

A lighting fixture that is designed to resist breaking or tampering, typically for use in 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 that drives electric current through lighting fixtures and other appliances.

Volumetric Troffer 

A troffer with a uniform lighting distribution that eliminates both glare and the cave effect.


Wall Grazing 

A lighting effect that illuminates a wall with an irregular surface to create both highlighted and shaded areas. It is only possible on walls with granular surfaces such as stone or exposed brick.

Wall Sconce 

Also known as a sconce, it is a type of lighting fixture installed on a wall.

Wall Washing 

A lighting effect that illuminates a wall to minimize surface irregularities, making it appear smoother.


A fully-enclosed luminaire designed to be mounted on an outdoor wall to provide area lighting, available in HID, CFL, and LED versions.

Warm White 

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


A unit of measurement for the electric power consumption of lighting fixtures or any other appliance that runs on electricity.

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.


Xenon Lamp 

A type of gas-discharge lamp that uses xenon gas to produce light.