Home-lighting glossary


Accent lighting: Lighting that, because of its relatively narrow beam of light, highlights a specific object it is pointed toward. Track lighting over a home photo gallery is one example of accent lighting.


Ambient lighting: Broad, general lighting made available in a built setting. This includes both natural and artificial lighting. Think of it as the lighting that sets the tone, or ambiance, of the space (vs. accent or task types of lighting).


Angle of light: The angle created from a light source to a direction of view.


Architectural lighting: Another term for decorative lighting, usually purposefully created as part of a building design (vs. happening organically). Its secondary function: to provide ambient light so as to create a specific ambiance.


Backlighting: Lighting intended to illuminate an object from behind, creating a glow that surrounds the object. It is a type of accent lighting.


Baffle: A translucent or opaque device in a luminaire used to block direct view of the source of lighting.


Ballast: Required in fluorescent and HID luminaires, a ballast controls the voltage and electric current sent to the light source when the fixture is first turned on and during operation. The goal: prevent overheating or early light failure. (Note: LED lights require a driver.) Ballasts are either electronic or magnetic.


Base (of a bulb): The part of a light bulb that connects the lighted portion, or casing, of the bulb to the light socket of a luminaire. The standard household bulb has a threaded, screw-type base known as an “e” type (for Thomas Edison, the creator of the light bulb).


Bayonet: A type of light bulb base that connects with the luminaire socket using connectors instead of the “e”-type threaded screws. A bayonet base locks in the socket by pushing and turning clockwise.


Beam angle: The measurable spread of a cone of light emitted by a luminaire, typically one with a reflector. It is also called “beam spread.”


Bi-pin base: The portion of a bulb that uses two pins for making a connection.


Bulb: A transparent or frosted glass or plastic casing that contains the filament, LED or other original source of light.


Can / Can lighting: Another name for the housing of a recessed downlight, or slang for the downlight itself.


Cave effect: The dark portion of a room directly above certain down-facing luminaires, where no light is emitted. Also called a ceiling cavity. A standard lamp shade reduces this effect because light is emitted upward through the shade.


Canopy: The usually decorative portion of a luminaire that covers the wiring and other non-decorative features.


Chandelier: From the word “chandler,” or “candle maker.” A decorative (even designer-inspired) luminaire that hangs from the ceiling. A traditional chandelier has many “branches” running from the center of the fixture and holding many lights for maximum lighting effect. More modern chandeliers emphasize the overall luminaire design as much or more than the amount of light output.


Circuit breaker: A device offering protection from electrical current; normally found within a distribution board inside a home. Lighting circuits are all connected to a circuit breaker, which automatically interrupts the flow of current when detecting an overload or fault.


Color-rendering index (CRI): A measure of how well a source of light renders the true, naturally lit colors of an environment and objects. The sun, with its natural-light-source CRI of 100, is the benchmark used in the measurement. For artificial lighting, the higher the CRI, the more accurate the light source.


Continuous dimming: A method of “smooth” dimming, whereby light output can be adjusted at any level between 0 percent (off) and 100-percent output, with no incremental stepping.


Compact fluorescent lamp (CFL): Fluorescent light bulbs designed to produce light from a compact form and shape and, typically, to replace, one-to-one, incandescent and halogen bulbs.


Cool white: A light source with a correlated-color temperature well above 2700K, typically around 4000K, without a yellow-glow factor.


Cornice lighting: Decorative lighting (typically fluorescent or LED) built into a room’s soffit for special effects.


Correlated-color temperature (CCT): The color output of a source of light, with useful values from 2700K (warm, yellowish light) to 6500K (a cool, bluish light). Other commercialized values include 3000K, 4000K and 5000K, with K meaning “Kelvin,” a measure of indexed temperature (vs. real operating temperature). The lower the Kelvin temperature, the more relaxing the effect of the light is said to be.


Cove lighting: A type of lighting meant to eliminate the cave effect, as it directs its light output toward the ceiling. Often used decoratively to emphasize wall or ceiling features.


Daylight harvesting: The purposeful use of devices such as skylights, picture windows, clerstory windows, etc., to capture natural light and to reduce the use of artificial light, thus saving energy. Daylight harvesting creates appealing indoor spaces that have a natural feel.


Daylight bulb: A light bulb with a correlated-color temperature, or CCT, value close to 100, or an artificial-light output comparable to daylight. The CCT value typically is between 5500K and 6500K.


DC, or direct current: A term used to describe a power supply with a same-direction flow of electricity, such as that of drivers for LED lighting.


Diffused light: Light that passes through a filter of sorts (a translucent or frosted diffuser) and is, therefore, indirect. Such light is often more uniform and softer than direct lighting; shadows are minimized.


Dimmer / dimmer switch: A device that lowers the output of a light source by controlling the amount of supplied power, either manually or via a timer. NOTE: Not all lighting works with all dimmers; LED lighting often requires LED-compatible dimmers.


Direct lighting: Lighting that reaches up to 90 percent or more of its intended reach (vs. indirect lighting that is diffused).


Downlight: A luminaire, typically small, that directs the light output downward. They come in recessed, surface-mounted or pendant forms.


Driver: An electronic device that lowers direct-current voltage so that it is appropriate for LED lighting. Some drivers are built into an LED luminaire; others are made to be external (like fluorescent-lighting ballasts).


Efficiency (of lighting): The measurement of how well (efficiently) a light source can convert electrical power into visible light; measured in watts (not to be confused with efficacy, or how well a light source converts watts of power into desired lumens).


Energy Star: A joint sustainability and energy-savings program sponsored by the U.S. Department of Energy and the Environmental Protection Agency. Products (particularly lighting) with an ENERGY STAR rating are recognized for their energy efficiency.


Filament: The tungsten-based, coiled or straight wire that, when heated by an electric current, produces a glow in incandescent or halogen light bulbs.


Flicker: The repeated blinking of a light source, typically caused by problems in the power supply or by a bad driver or ballast.


Flood light: High-output luminaire that most often uses HID or equivalent LED bulbs to provide outdoor lighting.


Fluorescent bulb: A type of light bulb that uses electrodes to stimulate mercury vapor and, thus, produce ultraviolet (UV) radiation. This UV radiation then stimulates the phosphor coating of the bulb to produce visible light. Fluorescent lighting, which comes in many sizes and shapes, is significantly more efficient than incandescent lighting but significantly less efficient than LED lighting.


Flush-mount lighting / flush-mount LED lighting: A type of luminaire that is mounted directly to the surface of a ceiling or wall.


Foot-candle (fc): Foot candle measures illuminance, or lumens; one foot-candle equals one lumen per square foot.


Glare: Impairment of vision created by an unusually bright source of light, either directly or as a result of reflection.


Hard light: A source of light that creates sharp-edged shadows, typically the result of direct lighting. Is unlike soft light, which is from an indirect source of light, that creates soft-edged shadows.


Halogen lamp: A type of improved incandescent light bulb. The (tungsten) filament of a halogen bulb is contained in halogen gas inside the casing, making the bulb about 25 percent more efficient than the non-halogen incandescent bulb.


Heat sink: The device on an LED luminaire used to dissipate heat. This is done through a fin-like shape that maximizes the surface area of the heat sink, or by a hollow metal core. Both sit beneath the lighted part of the bulb and draw heat from the bulb.


Illuminance: A measure of illumination, or luminous flux, on a surface (per unit of area). Built environments require certain illuminance based on their purpose (higher, for example, in a medical exam room than in a restaurant; they key is how light the room is perceived by the human eye). Two common measures of illuminance are lux, which equals one lumen per square meter, and foot-candle, which equals one lumen per square foot.


Illumination: The use of lighting, either for utilitarian purposes or for aesthetics.


Incandescent bulb: A type of light bulb that works by glowing when electrical current is carried through its filament, typically made of tungsten. While it is a relatively inefficient type of lighting, incandescent lighting has a color-rendering index (CRI) of 100, which is considered ideal because it is most comparable to the CRI of the sun.


Indirect lighting: A lighting technique that uses the reflective output of a lighting source onto a surface (vs. the lighting source directly aimed at the surface).


Initial lumens: The illuminance or lighting output of a new light bulb; this diminishes with use of the bulb over time.


Instant-start ballast: A type of ballast for fluorescent lighting when a high-voltage pulse is applied to the bulb; the start is instant with no preheating of the electrodes required. Such an instant start, however, reduces the lifespan of fluorescent bulbs (compared to non-instant-start ballasts). 


Insulated ceiling fixture: Luminaire that can be installed into a ceiling plane and in proximity to insulation because of their low wattage and relatively low heat output.


Interior-soffit lighting / soffit-light fixtures: Typically decorative lighting fixtures that fit into non-flush environments to provide the offset with lighting. For example, in a soffit of a tray ceiling or on the underside of a balcony.


Kelvin (K): A measurement unit for the (non-heat) temperature of a light source; also referred to as correlated-color temperature (CCT).


Kilowatt (kW): A measurement unit for electric power, which is equivalent to 1000 watts. Often confused with kilowatt-hour, below.


Kilowatt-hour (kWh): A measurement unit for the consumption of energy (via a one-kilowatt appliance running for an hour of time). For home/residential purposes, electric power bills are often calculated according to the monthly consumption of kilowatt-hours.


Lamp: Another word for light bulb, not to be confused with a desk or table lamp.


Lamp lumen depreciation (LLD): The reduction in initial-lumen output of a lighting source over time and with use.


Layering light: An approach to interior design that combines several lighting types to set a certain mood or aesthetic in the space.


LED: The acronym for light-emitting diode, which is a solid-state lighting component that emits a glow when the component is exposed to a current of electricity. LED lighting is more energy-efficient than other available types of lighting (incandescent, halogen, HID, fluorescent, etc.).


Lens: The part of a light bulb or luminaire, typically glass or plastic, that helps to disperse the light output. It typically covers the light source and it designed to distribute the light in a specific manner.


Light bulb: The light source, typically. For information about light bulbs, click here.


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.


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


Low-voltage fixtures, or 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.


Lumen: Measure of the light output of lamps or luminaires. What’s most important are the total lumens emitted relative to their spatial distribution (their efficacy). If lighting were a car, think of lumens as gas mileage and watts as gas 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.


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. The term is used more often by industry professional than by consumers.


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.


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.


Mounting height
Depending on the application, mounting height can have two possible definitions: Distance between the bottom of the fixture and the work plane; and 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.


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.


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 (the common household flood light).


Pendant light / pendant fixture
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.


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.


Recessed lighting / recessed fixture
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 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.


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


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.


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 lighting fixtures
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.


Smart lighting
Lighting that uses the latest in technology to provide a superior range of energy efficiency and environmental control and monitoring.


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


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, or lighting fixtures with lens or diffusers.


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


SSL: An acronym for solid state lighting.


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


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.


Thermal management: Controlling the operating temperature of the product through design. Examples include heat sinks & air flow.


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.


Transformer: Transformers make it possible to use low-voltage lighting; they “dim,” or convert, line voltage down to an acceptable voltage for low-voltage lighting.


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 sockets.


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


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, or (previously) incandescent versions.


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.


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


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.


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


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).