Glossary of Lighting Terms

Absorption - Refers to a measure of the amount of light absorbed by an object, instead of being reflected. Dark colored and matte surfaces are least likely to reflect light.

Accent Lighting - Lighting directed at a particular object in order to focus attention upon it.

ADA (Americans with Disabilities Act) - ADA-compliant fixtures cannot extend more than 4" from the wall.

AMPERE : The standard unit of measurement for electric current which is equal to one coulomb per second. It defines the quantity of electrons moving past a given point in a circuit during a specific period. Amp is the standard abbreviation.

ANSI: Abbreviation for American National Standards Institute.

Ambiant (General) Lighting - The soft indirect light that fills the volume of a room with illumination. It softens shadows on people's faces and creates an inviting glow in the room.

Amperage - The amount of electrical current through a conductive source.

Angle of Reflectance - The angle at which a light source hits a reflective surface equals the angle at which the resulting glare is reflected back.

ARM - A decorative-shaped tube or casting that is used to support a socket. An arm usually has socket wires running through it.

Back Plate -  The part of a fixture that mounts to a wall or vertical surface.

Ballast - Device that Provides the proper starting and operating electrical condition to power one or more fluorescent or HID lamps. There are two types of ballasts available, magnetic and electronic.

Bulb - What everyone calls it except the lighting industry which calls it a ‘Lamp'.

Candela - Unit of luminous intensity, describing the intensity of a light source in a specific direction.

Candela Distribution - A curve, often on polar coordinates, illustrating the variation of luminous intensity of a lamp or luminaire in a plane through the light center.

Candle Power - A measure of luminous intensity of a light source in a specific direction, measured in candelas.

Canopy - The decorative plate that attaches to the ceiling to cover the junction box.

CBM: Abbreviation for Certified Ballast Manufacturers Association.

CEC: Abbreviation for California Energy Commission.

Chandelier - A multi-arm, decorative, often ornate ceiling light fixture that holds a number of bulbs.

Collection - A group of matching fixtures and/or lamps that together can bring a unified look to a home or room.

Color Temperature - The appearance of white light, in terms of "warmth" or "coolness" of a light bulb. It is measured by the thermal unit Kelvin (K). Warm color corresponds to lower color temperatures below 3200K and cool colors to warm color temperatures are considered above 4000K.

Color Rendering Index (CRI) - A measure of how light sources render colors compared to sunlight. This measurement of quality is more important then color temperature. The higher (to 100) the CRI, the better and more accurate the color rendering, given the color temperature of the lamp.

Compact Fluorescent - A small fluorescent lamp that is often used as an alternative to incandescent lighting. The light bulb lasts about 10 times longer than a standard incandescent bulb or lamp and is 3-4 times more efficient. Commonly referred to as a CFL, PL, Twin-Tube, or BIAX lamps.

Contrast - The relationship between the luminance of an object and its background.

Cool - The color of the bulb that creates a sterile glow. Bluish Green colors are considered cool.


Design Voltage - The standard light bulb is 120 volts. Light bulbs with a higher voltage number have lower output and efficiency. 

Diffuser - A covering or shade over a light or lamp that generally softens or scatters the light and is usually used to eliminate hot spots and glare. Can be made from a variety of materials (glass, plastic, fabric, etc.) and in a variety of colors.
Dimmer - A control that regulates light levels.

Dimming Ballast - a ballast designed to allow the use of dimmers.

Efficacy - Measurement of the efficiency of a light source which compares light output to energy consumption. Efficacy is measured in lumens per watt. Efficacy is similar to the term efficiency, but is expressed in different units. If a 100-watt bulb produces 9000 lumens, then the efficacy is 90 lumens per watt.

Energy Usage - The electrical power of a bulb measured in watts.  This is usually listed on the light bulb.

Extension (EXT.) -  The depth of a wall light fixture (sconce or bath). The measurement from the wall to the farthest point away from the wall.

Energy-Saving Lamp - A lower wattage lamp or bulb, generally producing fewer lumens or output.

Family - Same as Collection - A group of matching fixtures and/or lamps that together can bring a unified look to a home or room.


Filters - Glass or metal accessory used to alter beam patterns or introduce/change colors.

Finial - A small finishing ornament at the crown or bottom of a fixture.

Fixture - A light that is permanently attached or wired directly into a junction box.  Chandeliers, bath lights and wall sconces are examples of ‘ fixtures'.

Fluorescent Lamp - A light source consisting of a tube filled with argon, along with krypton or other inert gas. When electrical current is applied, the resulting arc emits ultraviolet radiation that excites the phosphors inside the lamp wall, causing them to radiate visible light.

Flush-Mount - Attach directly to the ceiling with no gap between the light and ceiling.

FootCandle - The English unit of measurement for the intensity of illumination reaching a particular surface. One uniformly distributed lumen falling on one square foot of surface produces the illumination of one foot candle. (FC) is the standard abbreviation.

Glare - Excessive brightness or illumination from a direct light source affecting someone's visual impact. This can impair visibility.

Halogen - An incandescent lamp containing halogen gas which recycles the tungsten.

Hard Wire - Method of luminaire installation using a junction box.

HCWO (Height from Center of Wall Opening) - The measurement from the top of the fixture to the center of the outlet box when installed.

High Intensity Discharge (H.I.D.) Lamp - A category of lamp that emits light through electricity activating pressurized gas in a bulb. Mercury vapor, metal halide, and high pressure sodium lamps are all H.I.D. sources. They are bright and energy-efficient light sources used mainly in exterior environments.

Housing - Enclosure for recessed sockets and trim above the ceiling.

Incandescent Lamp - The traditional type of light bulb that produces light through electricity causing a filament to glow. It is not a very efficient source of illumination.

Inverted pendant - An ornamental hanging fixture with no multiple arms where the glass or diffuser opening is facing the ceiling.

Junction Box - an enclosure that houses electric wires or cables that are joined together and protects the connections. Junction boxes are also sometimes called ‘Gang boxes' or ‘Splitter boxes'.

Kelvin - The common unit of measure for the color temperature of a light source. The higher the Kelvin the cooler the light . Most standard light bulbs range from 2700K (Kelvin) to 6500K.  A standard 60-watt light bulb is 2700K, giving it what is called a warm or soft color.  The higher the Kelvin the closer the bulb color gets to being white. Very high Kelvin bulbs give off a bluish-white light.

Lamp - What the lighting industry technically calls a light bulb. A glass envelope with gas, coating, or filament that glows when electricity is applied. What everyone else calls a table or floor lamp.

L.E.D. - Abbreviation Light Emitting Diode.  This are long lasting and energy efficient bulbs consuming low wattage.

Lens -  Transparent or translucent medium that alters the directional characteristics of light passing through it. Usually made of glass or acrylic.

Life - The estimated time a light bulb will last.

Light Layering - It takes more then one light to properly illuminate a room. There should always be three layers of light. Overhead Lighting, Task Lighting and Accent Lighting. Adds depth and dimension to any room.

Light Output - This is how much light a bulb can produce.  Usually listed in Lumens which is the measurement light power or emission. A standard 100-watt bulb would produce 1750 lumens. 

Line-Voltage - The 110-120-volt household current, generally standard in North America.

Low-Voltage Lighting - System that uses less than 50-volt current (commonly 12-volt), instead of 110-120-volt, the standard household current. A transformer is used to convert the electrical power to the appropriate voltage.

Lumen - It is the measure of the "perceived power" of light.

Metal Halide - A type of high intensity discharge (HID) lamp in which most of the light is produced by radiation of metal halide and mercury vapors in the arc tube. Available in clear and phosphor-coated lamps.

MR-16 - A low-voltage quartz reflector lamp or bulb. Diameter is 2 inches. Typically the lamp and reflector are in one unit, which directs a sharp, precise beam of light.

PAR Lamps - Lamps (bulbs) with parabolic aluminized reflectors that give exacting beam control. There are a number of beam patterns to choose from, ranging from wide flood to very narrow spot. PAR lamps can be used outdoors due to their thick glass in flood light or spot light distributions, which holds up in severe weather conditions.

PAR 36 - A PAR lamp that is 36 1/8's of an inch in diameter with a parabolic shaped reflector (See PAR Lamp).

Pendant -An ornamental hanging fixture with no multiple arms where the glass or diffuser opening faces down.

Portable - A light or lamp that is simply plugged into an outlet and can easily be picked up and moved. Table lamps and floor lamps are examples of ‘ portables'

Sconce - A decorative lighting fixture with a flat side to be hung on a wall, that holds candles or lights.

Semi Flush - A light fixture which attaches to the ceiling with a stem or part that creates a gap between the fixture and ceiling.

Switches - Controls for electrical devices.

T - Diameter of a bulb.  A T12 bulb would be 12/8 of an inch or 1 ½ inches wide. Certain light fixtures have specific requirements for certain width bulbs.

Task Lighting - Illumination designed for a work surface to provide good light, free of shadows and glare. One of the three layers of lighting. 

Timers - Control devices to activate luminaires at set timed intervals.

Torchiere - a tall floor lamp with a bowl-shaped glass that diffuses the light or directs it upward.

Transformer - A device which can raise or lower electrical voltage, generally used for low voltage lights.

Tungsten-Halogen - A tungsten incandescent lamp (bulb) which contains gas and burns hotter and brighter than standard incandescent lamps.

UL - An independent 3rd party testing company. Underwriters Laboratory.

Veiling Reflection - A mirror like reflection of a bright source on a shiny surface.

Voltage - A measurement of the pressure of electricity going through a wire.

Voltage Drop - The decrease in voltage between the source and the load due to resistance in the wire(s).

Warm - A bulb color with a soft white glow. Yellowish colors are considered warm.

Watt - Unit of electrical power or energy used by a bulb.

Xenon - An inert gas used as a component in certain lamps to produce a cooler color temperature than standard incandescent. It is often used in applications where halogen may normally be specified, because of a longer lamp life and lower pressure.