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Lighting Glossary

Amperes (“Amps”)

A measure of electrical current. In incandescent lamps, the current is related to voltage and power as follows: Current (Amps) = Power (Watts) / Voltage (Volts)

Accent light

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


Lighting Glossary

Shades can be made of either alabaster stone or alabaster glass. Alabaster stone is much like marble in that it is quarried, cut and made into shades and bowls. It creates a warm, rich look, with each piece being completely unique. Stone is very expensive, however, so many lighting pieces recreate the look with more affordable alabaster glass.


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


Lighting Glossary

Part of the fixture that blocks light to prevent glare and control brightness. Baffles may be integral blades, plates or grooves or an accessory. Baffles are often painted black to absorb light.


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

Bathbar Lighting

Lighting Glossary

These fixtures supply task lighting, while supplementing the general lighting provided by ceiling fixtures. Similar to lighting in theater dressing rooms, these softly glowing lights are most often arranged in a row / bar fashion to provide excellent lighting for shaving and grooming.

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

For reflector type lamps. The total angle of the directed beam (in degrees horizontal or vertical) to where the intensity of the beam falls to 50% or 10% of the maximum candlepower value as indicated.

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

Hand blown glass is created by artisans who blow air into a molten balloon of glass. The artisan’s skill determines the shape and texture of the finished piece.


Lighting Glossary

Lights mounted on short, heavy piers or posts. They are used mostly for larger residences and campus settings.


The glass outer envelope component of a lamp.

Bulb Material or Coating

The type of glass (or quartz) used in the glass envelope surrounding the light source. The material can also have coatings applied to achieve particular performances.

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.


This is the part of the ceiling fixture that covers the electrical box where the electrical connections are made.

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

Light built into a cove, a shelf or ledge at the upper part of a wall, to illuminate the ceiling. Typically fluorescent, cold cathode or low voltage strip. Xenon or Halogen.

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

ULC listing for fixtures used in a moist unexposed area, such as a bathroom or porch area.

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.”


Light control device that spreads light by scattering it. Opal glass and plastic, etched glass, fabric and paper shades act as diffusers.


Control that varies the output of the light source by reducing the voltage or current to the lamp.

Dimming Ballast

Special fluorescent lamp ballast, which when used with a dimmer control, permits varying light output.


The light output of a light source divided by the total power input to that source. It is expressed in lumens per watt.

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.


Floodlights create a widespread distribution of light, perfect for illuminating a wall, sign or large object. A floodlight should be well shielded with an accessory louver or shield to avoid stray light and glare. You can also use plants to block unwanted light.

Fluorescent Lamp

A high efficiency lamp using an electric discharge through low pressure mercury vapor to produce ultra-violet (UV) energy. The UV excites phosphor materials applied as a thin layer on the inside of a glass tube which makes up the structure of the lamp. The phosphors transform the UV to invisible light.

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

Directional light at an acute angle, which emphasized texture. The sources of grazing light must be close to the surface.

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

Insulated Ceiling Fixture. Recessed downlight suitable for direct burial in thermal insulation. Called type IC.


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

Lighting that directs all or most light upward for ambient or general illumination; comfortable illumination with few shadows. Typical fixtures include uplight cans, fluorescent lighting aimed up, track lights aimed up and torchiere’s.

In-Ground Uplights

These outdoor accent lights provide maximum concealment because the source is recessed into the ground. Both line and low voltage sources are available.

Instant Start

A type of fluorescent lamp-ballast circuit designed to start fluorescent lamps as soon as the power is applied. Originally, instant-start circuits were developed to eliminate separate mechanical starter devices. Slimline fluorescent lamps operate only on instant start circuits.

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.


Scientific unit of temperature. Color temperature is measured on the Kelvin scale.


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


Radiant energy which can be sensed or seen by the human eye. Visible light is measured in lumens.

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

120 volt distribution is used mostly for lighting mounted to the outside of a house or for post-top lanterns along a drive or path. Line voltage landscape lighting can provide more light and handle greater distances than low voltage systems, but the installation is less flexible and more costly.

Low Voltage Fixtures

Recessed track, task, decorative or landscape fixtures for low voltage lamps. A transformer is required for these fixtures and may by integrated, local or remote.

Low Voltage Housing

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

Low Voltage Lamps

Incandescent lamps that operate at 6, 12 or 24 volts. Low voltage lamps require a step-down transformer to reduce the voltage from the normal household 120 volts.

Low Voltage Lighting System

A type of lighting that operates on 12-volt current rather than the standard 120 volts. Power is supplied by a transformer, which is itself connected to 120-volt power.


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

The ratio of total lumens emitted by a luminaire to those emitted by the lamp or lamps used.

Luminous Efficacy

The light output of a light source divided by the total power input to that source. It is expressed in lumens per watt.

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

Control that uses passive infrared or ultrasonic detection to sense whether someone is present or not, and to turn a light on or off appropriately. Commonly used in outdoor flood or spot fixtures. “Automatic On” sensors turn lights on when presence; “Manual On” sensors require you to press a switch. Both types turn lights off automatically when they no longer sense a presence.

Milk Glass

Milk Glass is a term used by glass-makers for opaque white glass. The German term is milch-glass, the Italian term is lattimo (from latte, milk) and the French term is blanc-de-lait (milk white) or verre-de-lait. Milk glass looks like white porcelain. The opaque white colour is usually made with tin oxide. During the 17th and 18th centuries it was very popular, and during that period it was often decorated with enamel painting. Semi-opaque white glass was also made using ashes of calcined bones, and this kind of glass is called by names such as opal, opaline, or milk-and-water glass.

MR Lamp

Lighting Glossary

Multi-facet reflector lamp, of which the most popular is MR16. MR lamps surround a halogen capsule with a computer-designed glass, or metal reflector with many surfaces or facets. These compact lamps require a glass cover, either integral or with the fixture.

Murano Glass

Lighting Glossary

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)

Bulbs used to control the level of light more precisely. They provide about four times the light of General Service (A) bulbs and are used in recessed and track lighting. Weatherproof casings make them suitable for outdoor spot and flood lighting fixtures.

PAR Lamps

Lighting Glossary

Parabolic Aluminized Reflector Lamp. Constructed of hard glass with a separate back reflector and front legs that are fused together. PAR lamps may be line or low voltage and can be used unprotected outdoors.


Pavers are luminous elements mounted in the ground of a patio or pathway. They act like lighted paving stones, marking a path. Some pavers are designed to replace individual bricks, others are imbedded in concrete.

Pendant Lights

Pendants can provide both general and task lighting. With shades or globes to avoid glare, they can be suspended from the ceiling over dinette table, kitchen counters or work areas. When used over end or night tables they free up space normally occupied by table lamps. The addition of a dimmer control allows you to alter the intensity of the light to suit your mood or time of day.

Pendant Mounted

Pendant mount on a chain, stem, cable or wire, and hand down into space. The word also refers to a style of hanging fixture with a single, central luminous element (like a cone, globe or dish), distinguished from a chandelier, which typically has several arms or luminous elements.


Recessed downlight that includes a faceplate with a small aperture used for inconspicuous accent lights.

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

Outdoor fixtures used to mark the entrance to a property, define a driveway or light a garden pathway.

Quad-Tube Lamp

Single-ended compact fluorescent lamp consisting of two twin tubes on a single base.

Quad-Tube Lamp

Quartz Lamp Or quartz halogen. Term derives from the quartz glass that encloses the filament and halogen gas. Quartz glass can withstand the high pressure of the halogen lamp, but it transmits more UV radiation than ordinary hard glass. Touching the quartz glass with bare hands leaves an oily residue that greatly reduces lamp life.

R Lamp (BR Lamp)

Reflector Lamp. Soft-glass reflectorized lamp with a generally smooth light distribution.

Rated Lamp Life

The point in hours where 50% of a lamp type initially started will still be functioning.

Recessed Fixture

A fixture mounted in the ceiling. With downlights, only the aperture and trim are visible from below. With fluorescent troffers and luminous ceilings, only the light shield is visible. Recessed fixtures provide direct downlighting and are highly effective used as wall washers, to accent painting, or to highlight architectural or home décor points of interest.

Recessed Lighting

Recessed Lighting is installed above the ceiling. Only the aperture or opening of the light shows. Recessed downlights are the most popular form of architectural lighting fixture because they blend into almost any décor and provide a range of lighting effects.

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.


Lighting Glossary

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.”)


Specific setting for a group of dimmers channels or zone. A multi-scene control allows you to select the different setting by pushing a button.


Wall bracket fixture derived from the form of a candelabra, often with exposed or decorative light sources.


An opaque or translucent covering on luminaries and portable lamps to shield the light source. Redirects the light and enhances decoration.

Shade Measurement

Measure in this order: Top across, bottom across, slant of the sides, height.


Accent lighting technique that creates a dramatic outline by back lighting. Also used in landscape lighting.

Slide Dimmers

Slide dimmers operate via a slide toggle, providing a full-range of manual dimming control. Some are equipped with a touch-button that allows you to return to the previous lighting level. Others have an indicator light that glows in the dark for easy location.

Sloped Ceilings

The flexibility of track lighting can be a major help when trying to light from a sloped ceiling. Most recessed fixtures cannot be aimed to light art on an adjacent wall, while track lighting fixtures allow you to do so easily.


In architecture, the underside of an overhead component, such as an arch, cornice, beam or balcony. Often used to describe an area of the ceiling that drops below the primary surface.

Spot Lamp

Reflectorized lamp with a narrow light distribution.

Step Lights

Step Lights are recessed into walls and stairs so they illuminate the treads of stairs or pathways. An eye shield is often used to block direct view of the light source.


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

Dimmer that works with a three-way switch for control from two locations; turns on/off and dims at the dimmer, but only turns on/off at the switch.

Three-Way Lamp

Incandescent lamp with two filaments that provides three levels of light when sequentially switched.

Three-Way Switch

Operates a fixture from two locations. Also called a three-pole switch. Also called a “three-pole switch” because it is connected to three wires; “hot” in, “switched” out and a “traveler” to the other 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.


Device that turns lights on and off at pre-programmed times.


Indirect floor lamp that sends all, or most, of its light upward.


A device used to raise (step up) or lower (step down) the electric voltage. For example, many halogen ceiling fixtures require a transformer, most commonly hidden in the wall during installation, to function properly. Step down transformers reduce household voltage (120 volts) to low voltage used in accent and landscape lighting. Larger transformers reduce high voltage used for efficient power distribution to safe and flexible household voltage. Input voltage is on the primary tap; output voltage on the secondary tap.

U Lamp

Linear, double-ended fluorescent lamp, usually T8 or T12, bent into a “U” shape.

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.


Unit of electrical force or pressure. Household voltage in the United States, nominally 120 volts, varies between 110 and 125 volts.

Voltage Drop

Difference in voltage along a circuit. Voltage drop becomes a problem with low voltage wiring and small cable, reducing the intensity of the lights at the far end of the cable.

Wall Grazing

A lighting technique in which light is aimed down a wall for a grazing effect. For dramatic shadows, especially on textured surfaces such as brick, draperies or stone, mount the lights 6 to 12 inches from the wall, with the fixtures the same distance apart and aimed downward.

Wall Washing

A lighting technique in which a wall is evenly washed with light. For most surfaces, mount the track 2 to 3 feet from the wall on ceiling up to 9 feet high. Mount between 3 and 4 feet on ceilings between 9 and 11 feet high. Space the fixtures the same distance apart for even light distribution.


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.

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