Lighting Glossary

Accent Lighting: lighting that is used to accent or highlight a particular object such as a work of art. To be effective accent lighting should be approximately four or five times the level of ambient light in the area. House plants can be accented by aiming an uplight at the wall behind the plant, creating a dramatic silhouette of the plant against the wall. To learn more about this topic click Accent Lighting.

Alabaster: genuine alabaster is a very fine variety of gypsum (hydrous calcium sulfate) found in nature. It is translucent and its color is often white, pearly, or silky colorless but it sometimes has subtle reddish-brown bands running through it. It is often used for decorative objects such as light fixtures or figurines. Some light fixtures use faux alabaster, which is usually man-made glass. Both genuine and faux alabaster can be very attractive. The faux alabaster is generally much less expensive while real alabaster can lose some of its coloration over time.

Ambient Lighting: general lighting that usually lights up an entire space

Base: the portion of the lamp (light bulb) that provides a means of physically connecting the lamp to a socket or lampholder.

Beam Spread: a measure of the spread of light from a reflectorized light source, a special-shaped lamp with a reflective coating inside the bulb to direct the light forward. The beam spread may be very narrow (narrow spot), very wide (wide flood), or something in-between (narrow flood, for example). Examples of "reflectorized light sources" are MR11, MR16, PAR20, PAR30, PAR38, R40, ER30, and BR30 lamps.

Cable Lighting System: a low voltage lighting system where the mechanism holding the light fixtures and conducting electricity to those fixtures is a pair of cables.

Cathode: an electrode that emits electrons. A fluorescent lamp cathode emits or discharges electrons to the cathode at the other end of the lamp (light bulb).

Chandelier: a chandelier is often the focal point of the dining room. As such it should be hung about 30 inches above the tabletop and should be at least 6 inches narrower than the table on each side.

Colored Glass Filter: this term means that the glass is formed with the color in the glass as opposed to the color being coated on the surface. This is accomplished by mixing various metal oxides in the glass composition. These colored glass filters are primarily used for aesthetic purposes in lighting. They are not designed for the precise control of the spectral bands, as are optical color filters (dichroic filters).

Color Rendering Index (CRI): a measure of a lamp’s ability to render colors accurately. The scale ranges from 1 (low pressure sodium) to 100 (the sun). A CRI of 85 is considered to be very good.

Color Temperature: a measure of the color appearance of a light source which helps describe the apparent "warmth" (reddish) or "coolness" (bluish) of that light source. Generally, light sources below 3200K are considered "warm;" while those above 4000K are considered "cool" light sources. The color temperature of a lamp has nothing to do with how hot the lamp will get or how much heat is given off by the lamp. The letter, K, stands for Kelvin.

Compact Fluorescent Lamp (CFL): a generic name used for a whole family of small, single-ended fluorescent lamps with a folded, bridged, or spiral glass tube design and with high color rendering (CRI > 80) and a long life (> 8,000 hours).

Cornice Lighting: a lighting system comprised of light sources shielded by a panel parallel to the wall and attached to the ceiling and distributing light over the wall.

Cove Lighting: a lighting system comprised of light sources shielded by a ledge or recess, and distributing light over the ceiling and possibly the upper part of the wall.

Dimmer: a device in an electrical circuit used for varying the brightness of lamps in a lighting installation. Dimming controls are ideal for almost any type of room because they can change the amount of lighting to suit each mood or activity and they can help you look good. The use of dimmers with incandescent, xenon, and halogen light sources also increases the life of the lamps and decreases the use of electrical energy.

Direct Current: electric current without alterations. DC current is usually supplied by a battery, a transformer, or photovoltaic cells.

Downlight: a small light fixture recessed into the ceiling that usually concentrates the light in a downward direction. Synonyms: recessed downlight, “can”, recessed can.

Filament: a tungsten wire that incandesces or lights up when an electric current runs through it.

Flexible Track Lighting System: a low voltage or a line voltage lighting system where the suspended track (sometimes called a monorail) holding the light fixtures in place and also conducting electricity to those fixtures can be bent into creative shapes.

Fluorescent Lamp: a low-pressure mercury electric-discharge lamp (light bulb) in which a phosphor coating on the inside of the glass tubing transforms some of the ultraviolet energy created inside the lamp into visible light.

General Lighting: substantially uniform lighting of a space without providing for special local lighting requirements like task lighting or accent lighting.

Glare: direct glare is caused by light coming directly to the eye from a light source. Indirect glare is light reflected from a surface in the direction of the eye. Both can harm vision and cause visual discomfort or disability.

Halogen Lamp: a type of incandescent lamp (light bulb) that contains halogen gases (such as iodine, chlorine, bromine, and fluorine), which slow the evaporation of the tungsten filament. Also, sometimes called a tungsten halogen lamp or a quartz lamp. The glass envelope that surrounds the filament of a halogen lamp should not be touched with bare hands. The natural oil from human hands will only help to shorten the life of halogen lamps. If you should accidentally touch the glass bulb, you should thoroughly remove your fingerprints with methylated spirit (denatured alcohol).

Hard Wired: technically means that the light fixture is permanently connected to an electrical source. The light fixture is not hard-wired if it gets power via a cord & plug.

HID Lamp: high intensity discharge (HID) lamps (light bulbs) have a longer life and provide more light (lumens) per watt than most other light sources. Available in mercury vapor, metal halide, high pressure sodium, and low pressure sodium types.

Incandescence: light emission by a heated filament.

Incandescent Lamp: lamp (light bulb) in which light is produced by means of an element heated to the point of incandescence by the passage of an electric current.

Lamp: a light source such as an incandescent, halogen, or fluorescent lamp. A lamp is sometimes called a “light bulb” or simply a “bulb”.

Layers of Light: layers of light in a given space are created by introducing task lighting (lighting by which people perform tasks), accent lighting (lighting used to highlight specific objects), decorative lighting (lighting created by very attractive light sources), and general lighting (lighting that fills the space). This technique can eliminate ugly shadows in the room and on your face.

LED: light emitting diode. A small electronic device that lights up when electricity is passed through it. LEDs are quite energy-efficient and have very long lives. They can be red, green, blue or white in color. To learn more about this topic click LED Fixtures.

Light Fixture: a complete lighting unit consisting of a lamp (light bulb) or lamps, a housing, and a connection to the source of electrical power.

Light Trespass: also known as "spill light". Light that is emitted into an unintended area.

Line Voltage: usually 120 volts

Louver: a type of “screen” made of translucent or opaque material and geometrically designed to prevent lamps from being viewed directly within a given angle. Louvers are intended to minimize direct or indirect glare.

Low Voltage: usually 12 volts but sometimes 24 volts.

Lumen: a unit of measure used to describe the amount of light that a light source produces or emits.

Pendant: pendants can provide both task and general lighting. Equipped with shades or globes to avoid glare, they are suspended from the ceiling over dinette tables, game tables, kitchen counters, or other work areas. When used over end tables or night tables, they free up the space occupied by table lamps. In general, pendants should be hung about 30 inches above the tabletop and be about 12 inches narrower than the table on all sides.

Portable Lamp: a table lamp, floor lamp, pharmacy lamp, or reading lamp which can be easily moved and plugged into an outlet.

Recessed Downlight: a small light fixture recessed into the ceiling that usually concentrates the light in a downward direction. Synonyms: downlight, can, recessed can. To learn more about this topic click Recessed Lighting.

Romex Wire: Romex wire is used throughout your household behind walls to wire your entire house. It usually is made up of 3 wires: one wire with white insulation, one wire with black insulation, and one copper wire with no insulation and white insulation around all 3 wires holding them together. The Romex wire that is used to connect lighting fixtures is usually described as "14/2 with ground" (although this may vary with geographical location). The "14/2" refers to the two insulated wires that are 14 gauge in size and the "ground" refers to the uninsulated copper wire.

Sconce: an ornamental light fixture attached to a wall. Synonym: wall sconce. Not to be confused with a scone, which is a flat, round cake of wheat flour.

Single-Pole Switch: a standard on/off wall switch that is the only switch that controls one or more light fixtures in a single circuit.

Sky Glow: also, known as "light pollution". The "haze" or "glow" that surrounds highly populated areas and reduces the ability to view the nighttime sky. Specifically, light that enters the sky from an outdoor lighting system by indirect light reflected from atmospheric particles such as fog, dust, or smog.

Task Lighting: lighting that is specifically installed to light an area where a task is performed.

Three-Way Switch: a wall switch that allows two switches like this to control one lighting system. Whenever you flip one of the three-way switches in a given circuit, the light changes its state; that is, if the light was on, it then turns off and if the light was off, it then turns on.

Transformer: an electrical device that transforms the line voltage of a facility (usually 120 volts for residential settings or 277 volts for commercial settings) into the voltage that a low voltage lighting system requires (12 volts or 24 volts). To learn more about this topic click Transformers.

Translucent: a term that describes a material that transmits some visible light usually with some distortion. A frosted piece of glass, a stained glass window, and paper are all examples of translucent materials.

Transparent: a term that describes a material that transmits most, if not all, of the visible light incident upon it with very little, if any, distortion. A typical glass window pane, the air, and clear plexiglas are all examples of transparent materials.

Troffer: a large recessed light fixture that often uses several fluorescent lamps, measures 24in by 48in, and is usually installed with the opening flush with the ceiling.

UL: Underwriters Laboratories, Inc., like Electrical Testing Laboratory (ETL), is an independent, not-for-profit product safety testing and certification organization. The UL symbol with the letter, "C", and the letters, "US", indicate that the lighting product is UL listed in both Canada and the United States.

Uplight: the percentage of lamp lumens directed from a light fixture at or above 90 degrees.

Wall Grazing: a lighting term that refers to the dramatic highlight and shadow effects on surfaces such as draperies, stone, and brick. Grazing creates easily distinguishable high and low levels of light on the surface.

Wall Sconce: a light fixture affixed to the wall and usually decorative in nature.

Wall Washing: a lighting technique that produces a relatively smooth, even level of illumination on the wall and reduces the texture of the surface.

Wattage: the amount of electrical power consumed by a lamp or light fixture measured in “watts”. One watt is equal to the power dissipated by 1 ampere of electrical current flowing across a resistance of 1 ohm or the power produced by 1 ampere of electrical current under an electromotive force of 1 volt. One horsepower is equal to 746 watts.
Formulae: watts = volts x amps, P = V x I, electrical power = electromotive force x electric current.

Xenon Lamp: a type of incandescent lamp that contains xenon gas in the glass envelope. The primary reason that this is done is to lengthen the average rated life of the lamp. Depending on the lamp a typical xenon lamp may have a rated life of 10,000 hours whereas a similar halogen lamp may have a rated life of 2,000 hours. Unlike halogen lamps, xenon lamps may be touched with bare hands without affecting the rated life of the lamp. Xenon lamps also operate at cooler temperatures than halogen lamps. Like halogen lamps, xenon lamps may be dimmed.