Lighting Glossary

These commonly used lighting design terms are defined in plain English, so that homeowners, designers and contractors can communicate more clearly.

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.

Ambient 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.

The amount of electrical current through a conductive source.

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

Five digit numbering system in national use for designing lamp types.

Device that transforms electrical energy used by fluorescent, mercury vapor, high and low pressure sodium, or metal halide lamps so the proper amount of power is provided to the lamp.

Beam Spread
The diameter of the pattern of light produced by a lamp or lamp and luminaire together.

Below Grade
Recessed below ground level.

Black Hole
Refers to an opening or window in a room that appears to be empty darkness, especially at night, because there is insufficient illumination at the other side to light up the objects or features framed by the opening.

Bridge System
Two wire, low voltage cable system.

Candle Power
A measure of intensity of light related to lumens.

Cold Cathode
A neon-like electric-discharge light source primarily used for illumination (neon is often used for signage or as an art form). Cold cathode can sometimes be used where fluorescent tubes would be too large or too hard to re-lamp.

Color Rendering Index (CRI)
A scale used to measure how well a lamp illuminates an object's color tones as compared with the color of daylight.

Color Corrected
The addition of phosphors in a lamp to create better CRI

Decorative Luminaire
Luminaire designed to please the eye and provide focal illumination.

The reduction of the amount of wattage used to prevent overheating. Related to ganging of dimmers.

Diffusion Filters
Glass lenses used to widen and soften light output.

A control that regulates light levels.

Dimming Ballast
Device used with fluorescent lamps to control the light level. May also apply to H.I.D. sources.

Measurement of the efficiency of a light source.

An independent testing facility, similar to U.L.

Fade Rate
Rate at which light levels decrease.

Fiber optics
A illuminating system composed of a lamp source, fiber, and output optics used to remotely light an area or object.

Glass or metal accessory used to alter beam patterns.

Fish Tape
Mechanical device used to pull wires in tight spaces or conduit.

Fluorescent Lamp
A very energy
efficient type of lamp that produces light through the activation of the phosphor coating on the inside surface of a glass envelope. These lamps come in may shapes, wattages, and colors.

Foot Candle
A measurement of the total light reaching a surface. One lumen falling on one square foot of surface produces the illumination of one foot candle.

Framing Projector
A luminaire that can be adjusted to precisely frame an object with light.

Grouping two or more controls in one enclosure.

Glare/Glare Factor
A source of uncomfortably bright light that becomes the focus of attention rather than what it was meant to illuminate.

An incandescent lamp containing halogen gas which recycles the tungsten.

Hard Wire
Method of luminaire installation using a junction box.

High Pressure Sodium
An H.I.D. lamp that uses sodium vapor as the light producing element. It produces a yellow orange light.

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.

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 a very inefficient source of illumination.

Junction Box
Enclosure for joining wires behind walls or ceilings.

A measure of color temperature.

A measurement of electrical usage. A thousand watts equals one kilowatt.

What the lighting industry technically calls a light bulb. A glass envelope with gas, coating, or filament that glows when electricity is applied.

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

A metal or plastic accessory used on a luminaire to help prevent glare.

Low Pressure Sodium
A discharge lamp that uses sodium vapor as the light-producing element. It produces an orange-grey light.

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.

A unit of light power from a light source: the rate at which light falls on one square foot of surface area one foot away from a light source on one candlepower or on candela.

The complete light luminaire with all parts and lamps (bulbs) necessary for positioning and obtaining power supply.

Mercury Lamp
An H.I.D. lamp where the light emission is radiated mainly from mercury. It can be clear, phosphor-coated, or self-ballasted. It produces a bluish light.

Metal Halide Lamp
An H.I.D. lamp where the light comes from radiation from metal halide. It produces the whitest light of the H.I.D. sources.

Mirror Reflector MR16/MR11
Miniature tungsten halogen lamps with a variety of beam spreads and wattages. It is controlled by mirrored facets positioned in the reflector.

Motion Sensor
Control which activates luminaires when movement occurs.

A glass vacuum tube filled with neon gas and phosphors formed into signs, letters or shapes.

Open Hearth Effect
Lighting that creates the feeling of a glowing fire.

Panic Switch
An on/off switch to activate security lighting, usually located by the bed for emergencies.

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, which holds up in severe weather conditions.

Photo-Pigment Bleaching
Mirror like reflection of the sun on a surface causing glare.

A control device that activates luminaires depending on surrounding light levels.

Planetarium Effect
Too many holes in the ceiling from an over abundance of recessed fixtures.

R Lamp
An incandescent source with a built in reflecting surface.

The ratio of light reflected from a surface

Reflected Ceiling Plan
A lighting plan drawn from the floor looking at the ceiling above.

RLM Reflectors
A luminaire designed to reflect light down and prevent upward light transmission.

Spread Lens
A glass lenses accessory used to diffuse and widen beam patterns.

Stake Lights
Luminaires mounted on a stake to go into the ground or a planter.

Swiss Cheese Effect
Too many holes in the ceiling from an over abundance of recessed fixtures.

Controls for electrical devices.

Task Lighting
Illumination designed for a work surface so good light, free of shadows and glare, is present.

Control devices to activate luminaires at set timed intervals.

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

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

An independent testing company. Underwriters Laboratory.

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

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

Voltage Drop
The decrease of light output in fixtures further from the transformer in low voltage lighting systems.

White Light
Usually refers to light with a color temperature between 5000-6250 degrees Kelvin and composed of the whole visible light spectrum. This light allows all colors in the spectrum on an object's surface to be reflected, providing good color-rendering qualities. Daylight is the most commonly referred to source of white light.

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.