Lighting Glossary

Amperes (“Amps”)


Accent light

Directional lighting designed to emphasize a particular object or to draw attention to a part of the field of view.




A finish produced by electrochemically brightening and anodizing a special high purity aluminum alloy. It is used to provide reflectors with a highly specular permanent finish, resistant to corrosion and abrasion. Alzak® is a registered trademark of the Aluminum Company of America (ALCOA).

Ambient light

Electric and/or natural lighting throughout a space that produces uniform general illumination.


American wire gauge. Identifies gauges of electric wire from 46 to 4.0




A magnetic or electronic device used to control the starting and operation of discharge lamps.

Bathbar Lighting


Beam Angle

The angular dimension of the cone of light from the reflectorized lamps (such as R and PAR types) encompassing the central part of the beam out of the angle where the intensity is 50% of maximum. The beam angle sometimes called the “beam spread” is often part of the ordering code of reflectorized lamps. Example: The GE Lamp 50PAR30/HIR/NFL25° is a 50 watt PAR30 narrow flood lamp with a beam angle of 25 degrees. Generally, beam angles 25 degrees and greater are considered Flood, while angles less than 25 degrees are considered Spots.

Beam Spread


Blinding glare

Glare that is so intense that, for an appreciable length of time after it has been removed, no object can be seen.

Blown Glass





The glass outer envelope component of a lamp.

Bulb Material or Coating


Bulb [size]

Bulb shape followed by its size (the maximum diameter of the bulb expressed in eighths of an inch). For Compact Fluorescent products, “S”, “D”, “T”, and “Q” are used to represent Single, Double, Triple and Quad Biax® sizes. The code also includes a reference such as T4 to represent the size of the tube. Rectangular headlamps are designated as “Rect” and the number of millimeters horizontally.

Canadian Standards Association (CSA)

An organization that writes standards and tests lighting equipment for performance as well as electrical and fire safety. Canadian provincial laws generally require that all products sold for consumer use in Canada have CSA or equivalent approval.

Candela (cd)

The international unit (SI) of luminous intensity. The term has been retained from the early days of lighting when a standard candle of a fixed size and composition was used as a basis for evaluating the intensity of other light sources.


Luminous intensity expressed in candelas. Plots of luminous intensity called candlepower distribution curves are used to indicate the intensity distribution characteristics of reflector type lamps.



Center Beam Candlepower (CBCP)

For reflector type lamps. Center Beam Candlepower is the intensity (candelas) at the center or maximum intensity of the beam.

Coefficient of utilization (CU)

The ratio of lumens from a luminaire received on the work plane to the total quantity of lumens emitted by the lamps of that luminaire.

Colour rendering index CRI

A measurement of the amount of colour shift that objects undergo when lighted by a light source as compared with the colour of those same objects when seen under a reference light source of comparable colour temperature. CRI values generally range from 0 to 100.

Colour Temperature

3000K fluorescent lamps offer a warm colour impression, which many people prefer for low light levels. You can also use warm colour fluorescent lamps to blend with incandescent and halogen sources for a more “residential” ambiance. A colour coordinated 3000K MasterColour Metal Halide lamp is also available. 3500K fluorescent lamps offer a neutral colour impression. They are the most commonly chosen today for offices and create a familiar and comfortable ambiance. 3500K PL lamps can be used in sconces and downlights to achieve consistent colour in all luminaires.

4100K fluorescent lamps offer a cool colour impression. They are often chosen to effect an atmosphere of cool efficiency and modernity. These lamps also look less yellow when a space enjoys substantial daylight. The coolest lamps (5000K and higher) are used only for special colour-sensitive tasks. Note, however, the impression of colour in electric lighting is culturally biased. For example, cool colours are preferred in Asian communities.Maintaining consistent colour treatment throughout a room keeps the appearance of the lighting clean, orderly, and unobtrusive.

Compact PL lamps, colour coordinated with primary linear fluorescent’s, can be used in wall sconces and downlights to achieve a consistent colour effect. While you could specify fluorescent lamps of different colours for different areas (executive offices or conference areas, for example), limiting the variety of lamps used also simplifies maintenance (especially where lamps could be mistakenly installed).

Compact Fluorescent Lamp (CFL)

The general term applied to families of smaller diameter fluorescent lamps (e.g. the GE T4 and T5), some of which have built in ballasts and medium screw bases for easy replacement of incandescent lamps. Fluorescent bulbs use approximately 2/3 to 4/5 less electricity than regular incandescent bulbs with comparable lumen ratings and also last 20 times longer. They produce warm white tones that closely duplicate incandescent light.

Cosine Law

The law that the illuminance on any surface varies as the cosine of the angle of incidence. (The angle of incidence is the angle between the normal to the surface and the direction of the incident light.)

Cove Lighting


Cut-off angle

The critical viewing angle beyond which a source can no longer be seen because of an obstruction (such as a baffle or overhang).

Damp Location


Dichroic Coating

Film that reflects visible light and transmits infrared light. Reflector lamps with dichroic coatings, such as most MR16′s provide a cooler beam because most of the heat goes out the back. Dichroic PAR lamps are often called “cool beam.”





Dimming Ballast




Electronic Ballast

A short name for fluorescent high frequency electronic ballast. Electronic ballasts use solid state electronic components and typically operate fluorescent lamps at frequencies in the range of 25-35 kHz. The benefits are: increased lamp efficacy reduced ballast losses and lighter, smaller ballasts compared to electromagnetic ballasts. Electronic ballasts may also be used with HID lamps, but the circuits are quite different.



Fluorescent Lamp


G Lamp

Globe-shaped incandescent, generally for exposed use.


Glare is any unwanted light that causes discomfort, interference with vision, or eye fatigue. Direct glare is caused by light coming directly to the eye from a source or bright surface. Discomfort or reflected glare is light reflected from a surface in the direction of the eye.

Grazing Light


Halogen Lamp

A type of incandescent lamp 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). To learn more about this topic click on this link

High-Intensity Discharge (HID) Lamp

A general term for mercury, metal halide (GE Multi-Vapor, MXR or Arcstream) and high-pressure sodium (GE Lucalox) lamps. HID lamps contain compact arc tubes, which enclose various gases and metal salts operation at relatively high pressures and temperatures.

High-Pressure Sodium (HPS) Lamp

A generic name for GE’s Lucalox lamp. HPS lamps are high intensity discharge light sources, which produce light by an electrical discharge through sodium vapor operating at relatively high pressures and temperatures.

IC Fixture



The “density” of light(lumens/area) incident on a surface. Illuminance is measured in footcandles or lux.

Incandescent Lamp

A light source which generates light using a thin filament wire (usually tungsten) heated to white heat by an electric current passing through it.

Indirect Lighting


In-Ground Uplights


Instant Start


Inverse-square law

The law stating that the illuminance at a point on a surface varies directly with the intensity of a point source, and inversely as the square of the distance between that source and that surface.




The term used to refer to the complete light source package including the inner parts as well as the outer bulb or tube. “Lamp,” of course, is also commonly used to refer to the type of small light fixture such as a table lamp



Life [Average Rated]

The median time it takes for a lamp to burn out. For example, a 60-watt Soft White Bulb can be expected, on average, to burn for 1,000 hours. Based upon continuous testing of lamps in laboratories, the 1,000 hour rating is the point in time when 50% of the test samples have burned out and 50% are still burning. Unless otherwise noted Fluorescent and CFL life assumes 3 hours average operating time per start. Unless otherwise noted HID life assumes 10 hours average operating time per start

Line Voltage Systems


Low Voltage Fixtures


Low Voltage Housing

Recessed housing with an integral, or occasionally, remote transformer.

Low Voltage Lamps


Low Voltage Lighting System



The international (SI) unit of luminous flux or quantity of light. For example, a dinner candle provides about 12 lumens. A 60-Watt Soft White incandescent lamp provides 840 lumens.

Lumen Maintenance

A measure of how well a lamp maintains its lamp output as it ages. Lumen maintenance is usually provided as a curve.


A complete lighting unit consisting of a lamp (or lamps), ballast (or ballasts) as required together with the parts designed to distribute the light, position and protect the lamp and connect them to the power supply.

Luminaire Efficiency


Luminous Efficacy


Lux (lx)

The SI (International) unit of illuminance. One lux is equal to one lumen per square meter.

Metal halide (MH) lamp

A high-intensity discharge lamp type that uses mercury and several halide additives as light-producing elements. Metal halide lamps have better color properties than other HID lamp types because the different additives produce more visible wavelengths, resulting in a more complete spectrum. Metal halide lamps are available with CCTs from 2300 to 5400 K and with CRI values from 60 to 93. Efficacies of metal halide lamps typically range from 75 to 125 LPW.

Motion Detector


Milk Glass


MR Lamp


Murano Glass

The key ingredients of Murano glass are silica sand, soda ash and red lead that are melted together to make it. In the process the materials are heated to 1,400 degrees Celsius, or 2,552 Fahrenheit, before being cooled to the 1,000-degree temperature that makes the molten glass pasty enough to be gathered in red-hot blobs on the glassmakers’ tools. Murano glass production dates back to the early Middle Ages in the Venetian Republic (now Venice, Italy).

Between the twelfth and the fourteenth Centuries the Venetian glass industry conquered all European and East Mediterranean markets with the force of its merchant fleet. In 1291 because of fire risks in the city, most of the houses being built of wood, it was decided to move the glass industry to Murano. Because of the importance of the industry to the local economy a law was proclaimed in 1441, that foreigners are to be totally excluded from the practice of glass art. Over the centuries many different techniques and innovations of the glass art, materials, and design have kept Murano Glass the top in the world in quality and design to this day.

Light fixtures that use Murano glass could be made anywhere and of any style for any room, what they all would have in common is that they have first quality glassware made in Italy.

Parabolic Reflector Bulbs (PAR)


PAR Lamps




Pendant Lights


Pendant Mounted




Portable Lamps

Portables, typically table or floor lamps, include a cord and plug. They are distinguished from fixtures, which are permanently fastened and electrified. Portables include table lamps, floor lamps and torchiere’s. Small specialty lamps, such as clip-on lights, can lights, adjustable task lights, desk and piano lights also classify as portable lamps.

Post-Top Fixtures


Quad-Tube Lamp


Quad-Tube Lamp


R Lamp (BR Lamp)


Rated Lamp Life


Recessed Fixture


Recessed Lighting


Reflector Lamp

An incandescent, compact fluorescent or HID lamp with a built in reflecting surface. Incandescent and HID versions are made from a single piece of blow-molded soft or hard glass. CFL versions may be one piece or may be designed so that the inner lamp can be replaced.


The arch or scallop-shaped pattern on a light fixture.


Scavo is a technique for producing an etched or corroded effect on the surface of glass, like it had been buried for a long time. (Translated from Italian, it means “unearthed.”)







Shade Measurement




Slide Dimmers


Sloped Ceilings




Spot Lamp

Reflectorized lamp with a narrow light distribution.

Step Lights



Tubular Lamp; may be incandescent, halogen or fluorescent.

Task light

Light that is directed to a specific surface or area to provide illumination for visual tasks.

Three-Way Dimmer


Three-Way Lamp


Three-Way Switch



Louis Comfort Tiffany (1848-1933) was the creative genius son of a famous New York jeweler. His flamboyant sumptuous lifestyle and family connections with the artistic world in Europe and America, coupled with his talent and dedication, took him to a leading position in the Art Nouveau movement. Today, of course, any piece of genuine Tiffany output is treasured and commands a relatively high price, and the museum-quality pieces reach astronomical figures at auction. Tiffany designed beautiful lamps, typically having ornate art nouveau bronze bases and leaded glass shades with floral designs.







U Lamp


Undercabinet Fixtures

Fixtures which are placed under a cabinet or room recess to provide task and accent lighting. Under kitchen cabinets they can light a countertop with task lighting. In a display cabinet they can be used to illuminate a prized collection. They include slim, energy-efficient fluorescent’s, miniature track lighting and strips of low-voltage mini-lights.



Voltage Drop


Wall Grazing


Wall Washing



A heavy, colorless, and relatively inert gaseous element that occurs in air as about one part in 20 million by volume A low heat, long life alternative to halogen bulbs, xenon bulbs do not emit harmful UV rays. Considerably safer due to less pressure in bulb vessel. Does not require tempered glass cover. Handling or dimming bulb does not affect bulb life.