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See alternating current


Awards for Design Excellence (ADEX) is the largest and most prestigious awards program for product design of furniture fixtures (including light fixtures), and finishes. It is sponsored by Design Journal, the trade publication for interior designers, architects, and facility managers. Each category has potential for three award levels: platinum, gold, or silver. An anonymous panel of professionals representing a cross section of the design industry conducts all voting for the ADEX Awards.


See American National Standards Institute

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 room, area, or space. 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.


Genuine alabaster is a very fine variety of crystalline gypsum (hydrous calcium sulfate) found in nature. It is translucent and its color is often white, pearly, or silky colorless but it, more often than not, has subtle reddish-brown bands of iron oxide 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. Real alabaster is expensive simply because quarrying it is costly and there is huge amount of waste when it is shaped, finished, and polished. Genuine alabaster is a minimum of 3/8in thick and weighs at least twice as much as imitations and has translucent and dark bands that are completely random in shape, size, and location. Since alabaster is a soft, porous stone it should be treated gently and never cleaned with detergents or abrasives. Instead, wipe alabaster with a slightly damp (not wet), soft cloth. Furthermore, heating alabaster for long periods of time with a high-wattage light bulb may drive out the residual water in the alabaster and turn it completely white.

A-Line Lamp

The type of incandescent light bulb that is generally used in most indoor residential lighting applications. By January 1, 2014 the most common standard screw-base incandescent household (A-line) light bulbs will be phased out in the U.S. Clear, frosted, soft white, and daylight light bulbs will be phased out but specialty colors and shapes will not be. The new standards for these light bulbs are technology neutral so any technology that can meet the new energy-efficiency standards can be used - including fluorescent, halogen IR, high-efficiency incandescent, LEDs, and any technologies still to be developed.

Alternating Current (AC)

The flow of electricity (electric current) in a circuit that frequently alternates direction every second. In the USA, the standard frequency of alternating current is 60 Hz (hertz or cycles/second) and AC (as opposed to direct current) is generally the method for delivering electric power to homes and buildings.


An alloy of mercury which is an upgrade from traditional liquid mercury. Since it gives better mercury vapor control in the glass envelope the lamps that use amalgam perform better over a wider variety of temperatures and operating positions.

Ambient Lighting

General lighting that usually lights up an entire room or space.

American National Standards Institute (ANSI)

Founded in 1918, ANSI is a private, non-profit organization that sets guidelines and standards to be used in a variety of industries, including electrical for such devices as ballasts, lamps, and light fixtures (see


See ampere

Ampere (Amp)

A standard unit of measurement for electric current adopted in 1881. One ampere equals one coulomb of electric charge passing a given point in one second. Amperes are sometimes abbreviated as "amps" or simply "A" and are often represented in electrical formulae by the letter, "I", as in V = I x R (volts = amperes x ohms). This unit is named after Andrè-Marie Ampère, a French physicist, who lived during 1775-1836 and is considered to be the "father of electrodynamics".

Area Lighting

A landscape lighting term that refers to the lighting of large landscaped areas, usually with floodlights.


An inert gas used in incandescent and fluorescent lamps. In incandescent lamps argon retards the evaporation of the filament and, thereby, lengthens the average rated life of the lamp.



See ballast factor


Lighting that illuminates an object from behind. The object to be illuminated is placed between the intended viewer and the light source. If the object is opaque, backlighting can cause the edges to "glow". With translucent objects (such as stained glass), backlighting illuminates the object by passing light through it. Backlighting is commonly used to accent artwork, photos, advertisements, or signage.


In lighting this is usually a grooved surface that deflects and controls the "flow" of light to soften it and minimize reflected glare. Baffle trims (sometimes called step baffle trims or stepped baffle trims), made of plastic or metal, are often integral parts of recessed downlights. They are often colored a flat black to absorb some of the light but can have other finishes such as flat white, brushed copper, or brushed nickel.


An electrical device used with fluorescent and HID lamps to supply sufficient voltage to start and operate the lamp but then limit the current during operation.

Ballast Factor (BF)

A ratio of the actual lumen output for a lamp using ballast to the lumen output for a lamp-ballast system under test conditions established by the American National Standards Institute (ANSI). The higher the ballast factor, generally the more wattage being used by the light fixture.

Barn Doors

Two or four adjustable opaque plates attached to the front of a luminaire, such as a track fixture or a theatrical spotlight, which are used to shape and focus the light on a designated area, such as a framed work of art or a stage scene


The portion of a lamp (light bulb) that provides a means of physically and electrically connecting the lamp to a socket or lampholder within a luminaire

Basket Troffer

A troffer whose light sources are concealed by curved opaque shielding called "baskets", which are often perforated with a pattern of small holes. This type of troffer provides both direct lighting through the perforations and indirect lighting by bouncing light up from the basket and then off the upper light-colored opaque parts of the troffer.

Bayonet Base

A type of lamp base with pins that serve to lock the lamp into slots in the lamp socket of a luminaire. The bayonet base got its name from the method used by soldiers to mount bayonets on their rifles.

Beam Pattern

Synonymous with Beam Spread

Beam Spread

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


The process of sorting LEDs into a variety of groups based on certain performance characteristics such as color temperature and lumen output. LED manufacturers use binning to manage the slight variations that arise in LEDs during the manufacturing process.


An outdoor luminaire that is a short (usually about 2-4 feet in height) but very sturdy vertical post with the light source located at or near the top. Bollards are typically used to light walkways in commercial settings.

Brick Light

A light fixture (usually the size of a brick) that can be recessed in a brick wall with its face parallel to the surface of the brick surface in order to light a walkway, a step, a landing, or a path.


A colloquial term for a lamp. In the lighting industry, the term, bulb, refers only to the glass envelope of the lamp. Some lighting professionals contemptuously refer to "bulbs" as those things that are planted in the ground.



See center beam candle power


See Certified Ballast Manufacturers Association


See cold cathode fluorescent lamp


See color temperature


See Candela


See compact fluorescent lamp


See Commission on Illumination


See color quality scale


See color rendering index


See Canadian Standards Association

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 taut parallel metal cables.

Canadian Standards Association

Like UL and ETL in the USA, the CSA is a not-for-profit membership-based association serving business, industry, government, and consumers in Canada and the global marketplace. It is an organization that works in Canada and around the world to develop safety standards that address real needs, such as enhancing public safety and health, advancing the quality of life, and helping to preserve the environment. (see


A unit of light measurement that refers to the luminous intensity from a light source in a specific direction.


An obsolete term that has been replaced by the candela, a unit of measurement that refers to the luminous intensity from a light source in a specific direction.


An electrode that emits electrons. A fluorescent lamp cathode emits or discharges electrons to the cathode at the other end of the lamp.

Cathode Guard

A metal band encircling the cathode of a fluorescent lamp, used to collect the evaporating particles from the cathode, greatly reducing the end-blackening of the glass envelope.

Cave Effect

A lighting effect caused by parabolic recessed troffers with a high cut-off angle that leaves the upper part of the room's walls relatively unlit and noticeably darker than the lower part of the walls.

Center Beam Candle Power

A measure of the luminous intensity at the center of the beam of a reflector lamp measured in candelas.

Certified Ballast Manufacturers Association

An association that tests and certifies ballasts that match the standards established by the American National Standards Institute (ANSI).


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


A type of fluorescent lamp that is made up of a circular tube of glass; when placed in a light fixture the ballast that powers this type of lamp is usually located in the center of the circline lamp.


A pathway for the flow of electrons, including capacitors, resistors, and/or transistors, connected by wires through which electrical current flows. If there is only one path for the current, the circuit is called a "Series Circuit". If there are multiple paths, the circuit is called a "Parallel Circuit".

Cold Cathode

A cathode (an electrode that emits electrons) that is not independently heated.

Cold Cathode Fluorescent Lamp (CCFL)

A type of fluorescent lamp in which the cathode (an electron-emitting electrode inside the lamp) is not independently heated although the cathode can become quite hot once the CCFL has been operating. Screw-in CCFLs come in several different wattages (present range is 3W to 18W) and several different shapes (spiral, globe, reflector, A-line, torpedo) and are generally characterized by a very narrow glass tube envelope (2mm-4mm in diameter), a longer rated life than compact fluorescent lamps (often 25,000 hours), and a very good range of dimmability (down to 30%).

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 (which is a dichroic filter). 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 Quality Scale (CQS)

An alternative to the Color Rendering Index (CRI). The CQS measures a light source's ability to render colors. The CQS was designed by the NIST to evaluate LEDs. The scale uses 15 color samples of deeper color compared to the CRI, which uses 8 pastel colors.

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 or hue 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. This term is also referred to as the Correlated Color Temperature (CCT).

Here is some information to help you better understand how color temperature can effect your mood and the best applications for certain color temps.

  • 2700K - Friendly, Personal, Intimate - Home, Libraries, Restaurants
  • 3500K - Friendly, Inviting, Non-threatening - New Offices, Public Reception Areas
  • 4100K - Neat, Clean, Efficient - Older Offices, Classrooms, Mass Merchandisers
  • 5000K - Bright, Alert, Exacting Coloration - Graphics, Jewelry Stores, Medical Exam Areas, Photography

Different types of lights sources produce particular color temperatures.

  • 1600K - Sunrise or Sunset
  • 1800K - Candlelight & Gaslight
  • 2800K - Household Incandescent Lamp
  • 3000K - Warm White Fluorescent Lamp
  • 3500K - Neutral White Fluorescent Lamp
  • 4100K - Cool White Fluorescent Lamp
  • 5000K - Professional Light Booth
  • 5200K - Bright Midday Sun
  • 6500K - Heavily Overcast Sky

Commission on Illumination (CIE)

The International Commission on Illumination is a nonprofit that is "devoted to worldwide cooperation and the exchange on all matters relating to the science and art of light and lighting, colour and vision, photobiology and image technology." One of the CIE's achievements is the development of the Color Rendering Index (CRI). (see

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). To learn more about this topic click CFL Information.


A device that controls a lighting system. A control can take the form of a dimmer, switch, or an occupancy sensor.

Core and Coil Ballast

Another term for a magnetic ballast or electromagnetic ballast

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 and down the wall.

Correlated Color Temperature (CCT)

See color temperature

Coulomb (C)

The standard unit of electric charge, named after Charles-Augustin de Coulomb, a French physicist who developed Coulomb's law. A coulomb is equal to the charge transported in 1 second by 1 ampere.

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.

Cross Lighting

Illumination of an object from two light sources opposite of each other.


The Canadian Standards Association, like UL and ETL in the USA, is a not-for-profit membership-based association serving business, industry, government, and consumers in Canada and the global marketplace. It is an organization that works in Canada and around the world to develop safety standards that address real needs, such as enhancing public safety and health, advancing the quality of life, and helping to preserve the environment.


The rate of flow of electric charge in a conductor, which is measured in amperes or amps.

Cut-Off Angle

The position at which a viewer can no longer see the lamp in a fixture. The cut-off angle is measured from the base of the fixture to the point at which the lamp cannot be viewed. An angle of 45 degrees or less is considered "sharp", meaning the lamp is quickly hidden as one moves away from a fixture. The cut-off angle is important when considering glare.



See direct current

Daisey Chain

See series circuit

Desk Lamp

A portable lamp that usually sits on a desk and provides task lighting for any work done on the desktop.

Dichroic Filter

A material that splits visible light into different wavelengths, allowing for precise control of the spectral band. Dichroic filters are coated on the glass and only allow certain wavelengths or colors to pass through. Dichroic filters are different from colored glass filters, which are used mostly for aesthetic purposes.

Dichroic Reflector

A reflector or filter that transmits certain wavelengths but reflects other wavelengths. In lighting fixtures, dichroic reflectors often transmit infrared light out of the rear of the fixture while reflecting visible light through the front, resulting in cooler visible light.


To spread out or scatter the light coming from light fixtures in order to "soften" it and minimize direct glare. This is often accomplished by using diffusers that are translucent in nature such as frosted glass, linear spread lenses, solite lenses, or spread lenses.


A transparent or translucent piece of glass, silicone, or plastic designed to control light by scattering or diffusing it in order to create softer light without much glare.


Any lighting product (light fixture or light bulb) that is designated as dimmable can be dimmed if the correct dimming device (such as a dimmer) is used to decrease or increase the amount of light that light fixture gives off.


A device in an electrical circuit used for varying the brightness of light bulbs 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 electricity.

Direct Current (DC)

An electric current that flows in only one direction without changes, cycling or alterations. DC current is usually supplied by a battery, a DC transformer, or photovoltaic (PV) cells.

Direct Glare

A type of glare or excessive brightness that travels straight from a light source directly into the viewer's eye rather than being reflected off another surface (indirect glare). Glare hinders visibility and contributes to eyestrain. Direct glare can sometimes be attributed to a poorly designed light fixture, and a light fixture that produces an unusual amount of direct glare is sometimes called a "glare bomb".

Discharge Tube

A tube (usually made of glass) that contains gas or a metal vapor that ionizes when (voltage is applied, resulting in the emission of light. Many different gases are used in discharge tubes, including xenon, neon, argon, mercury, and sodium.

Double-ended Lamp

A lamp that has 2 bases or points of electrical and physical connection that provide extra stability in rough service applications.


A small light fixture recessed into the ceiling that usually concentrates the light in a downward direction. Synonyms: recessed downlight, "can", recessed can, high hat, pot light.

Driver, LED

An electronic device that acts as the power supply for LEDs. A driver regulates the current in order to maintain steady lumen output and prevent variation.



See electroluminescent


See Energy Policy Act


See electron stimulated luminescence


ETL, like Underwriters Laboratories, Inc. (UL), is an independent, not-for-profit product safety testing and certification organization. Throughout its long history its name has changed several times. Thomas A. Edison established the Lamp Testing Bureau in 1896. In 1904 Edison renamed his Lamp Testing Bureau the Electrical Testing Laboratories (ETL). In 1977 ETL officially changed its corporate name to ETL Testing Laboratories and in 1996 ETL was renamed the Intertek Testing Services, Ltd. (NOTE: ETL Testing Laboratories, originally organized by the Edison Illuminating Companies, has been conducting electrical performance and reliability tests since 1896. Intertek Testing Services (ITS), which acquired ETL Testing Laboratories from Inchcape in 1996, is recognized by OSHA as a Nationally Recognized Testing Laboratory (NRTL) just as Underwriters Laboratories (UL), the Canadian Standards Association (CSA) and several other independent organizations are recognized. A federal law passed in 1988 established the NRTL program to eliminate provisions that explicitly required or implied that product certification be performed only by standard-writing companies such as UL. Since each NRTL must meet the same OSHA requirements of competency, NRTLs recognized for the same product safety test standard are considered as equivalent in their capability to certify to that standard.) (see


A measurement of efficiency used to compare light output to energy consumption. Efficacy is measured in lumens per watt (similar to miles/gallon for a motor vehicle). A 100-watt light source that produces 1750 lumens of light has an efficacy of 17.5 lumens per watt (L/W).

Efficacy for certain light sources:

  • Edison's first lamp - 1.4 L/W
  • Incandescent Lamps - 10-40 L/W
  • Fluorescent Lamps - 35-100 L/W
  • Mercury Vapor Lamps - 50-60 L/W
  • Metal Halide Lamps - 80-125 L/W
  • High Pressure Sodium Lamps - 100-140 L/W
  • Theoretical max for white light - 225 L/W


An electrical conductor used to make contact with a nonmetallic part of an electrical circuit or light bulb (e.g., a semiconductor, an electrolyte, or the gases found in the glass envelope of a light bulb).

Electroluminescent (EL)

A phosphorous material that emits light or "glows" when current passes through it.

Electromagnetic Ballast

Synonymous with magnetic ballast

Electromagnetic Spectrum

An entire "spectrum" of radiant energy arranged by wavelength and frequency, including radio waves (long wavelength with low frequency), microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays, and gamma-rays (short wavelength with high frequency).


A subatomic particle with a negative electric charge. Electricity is the movement of electrons in an electrical circuit.

Electronic Ballast

A type of ballast with electronic components that increases the standard operating frequency of electricity from 60 cycles per second (the U.S. standard) to 20 kHz (20,000 cycles/second) or higher. This increase in operating frequency is important for greatly reducing the stroboscopic effect or flickering that is associated with fluorescent lamps. Electronic ballasts are an improvement over magnetic ballasts because they are quieter, lighter in weight, and more efficient in converting electrical energy into light energy while producing less heat.

Electronic Transformer

A type of transformer that includes an inverter, which allows for a substantially smaller size compared to a magnetic transformer with comparable wattage. The inverter causes the current to alternate at a frequency of 20-50 kHz. The higher the frequency, the smaller the transformer can be. The transformer "transforms" line voltage (usually 120-277 volts) into low voltage (usually 12 or 24 volts). Light fixture manufacturers often incorporate built-in electronic transformers in the fixture design because of their small size. Note: due to its very high frequency the voltage of electronic transformers can not be measured with standard voltmeters; instead, a "true RMS" voltmeter with sufficient range should be used.

Electron Stimulated Luminescence

ESL is an entirely new, energy efficient lighting technology that uses accelerated electrons to stimulate phosphor to create light, making the surface of the light bulb "glow". It is not a type of incandescent, fluorescent, or LED light source. - an emerging light source that does not require filaments, plasma, or mercury to operate. Accelerated electrons travel over an area inside a phosphor-coated bulb, causing the surface to glow. The developer of this new technology, Vu1, claims the lamp is energy efficient, creates similar quality light of incandescent bulbs, and is much cheaper to produce than LEDs.

Elliptical Lens

Synonymous with linear spread lens

Elongated Lens

Synonymous with linear spread lens

Emergency Lighting

Lighting used when the normal lighting fails.

End Blackening

Darkening of the glass envelope around the ends of a fluorescent lamp caused by particles evaporating (literally boiling off) from the cathode and adhering to the glass. Fluorescent lamps made with cathode guards greatly reduce this occurrence.

Energy Policy Act (EPACT)

Energy legislation originally passed by the US Congress in 1992, and updated periodically, mandating labeling and minimum energy efficiency requirements for many commonly used lighting products like lamps and ballasts.


A government-backed program (a joint program between the U.S. Environmental Protection Agency and the U.S. Department of Energy) helping businesses and consumers protect the environment through superior energy efficiency. If a lighting product is ENERGY STAR® compliant, that means it has passed stringent testing by the government and is considered to be energy efficient. ENERGY STAR® qualified products can be identified by a label on the packaging. The U.S. Environmental Protection Agency has established the following guidelines for determining the product specifications necessary to qualify for the ENERGY STAR® label.

  • Product categories must contribute significant energy savings nationwide.
  • Qualified products must deliver the features and performance demanded by consumers, in addition to increased energy efficiency.
  • If the qualified product costs more than a conventional, less-efficient counterpart, purchasers will recover their investment in increased energy efficiency through utility bill savings, within a reasonable period of time.
  • Energy efficiency can be achieved through broadly available, non-proprietary technologies offered by more than one manufacturer.
  • Product energy consumption and performance can be measured and verified with testing.
  • Labeling would effectively differentiate products and be visible for purchasers.

ER Lamp

A type of incandescent reflector lamp with the reflector shaped like an ellipsoid (a 3-dimensional ellipse) with the lamp's filament located at one of the two foci of the ellipsoid so that the light is focused directly in front of the lamp at the second foci.

Eyeball Trim

A recessed trim (part of a recessed downlight) that can be rotated to point the light in almost any desired direction.



See foot-candle


See foot-lambert


The metal or plastic plate installed over an on/off switch, dimmer, or receptacle, which covers the wall opening and protects the wiring inside the junction box.

Fiber Optic

A type of transparent cable, usually made of plastic or glass, that transmits light. Fibers can be used in lighting to create distinct effects.


A tungsten wire that incandesces or lights up when an electric current passes through it.


A piece of plastic or glass designed to transmit a certain narrow range of light (wavelength) while reflecting or absorbing the wavelengths of light that are not transmitted. See colored glass filter and dichroic filter.

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, sometimes to enhance or emulate the architecture of the space.


A broad-beamed high intensity light fixture.

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.

Foot-Candle (fc)

The USA unit of measurement of lighting level (illumination or the amount of light reaching a subject) and sometimes spelled footcandle. The international unit of measurement of lighting level (Illumination) is the lux (lx). The relationship between the lux and the foot-candle is 1 fc = 10.76 lux.


A unit of luminance in the USA which is now rarely used; the brightness of a surface which emits or reflects 1 lumen per square foot of its surface. The brightness of the face of an exit sign is sometimes reported in foot-lamberts.

Four-Way Switch

A wall switch that allows three switches to control one lighting system. Whenever you flip one of the four-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.

Framing Projector

A light fixture with a lens and adjustable shutters, which allow the fixture to "project" a beam of accent lighting with a variable size in order to light a well-defined area such as a hanging frame of artwork.


The number of occurrences of a repeating event per unit of time - the number of times something occurs per unit of time. The standard unit for frequency is the Hertz, or 1 cycle per second.

Fresnel Lens

(Pronounced fray-nell) A special type of lens developed by the French physicist Augustin-Jean Fresnel for lighthouses. Compared to a conventional bulky lens, a Fresnel lens is much thinner, lighter in weight, larger, and flatter.

Frosted Lens

A white translucent lens that creates a soft (diffused) light.



The technique of installing two or more on/off switches, dimmers or electrical receptacles side by side in one wall junction box.


A transparent, heat-resistant, colored piece of plastic that is used to add color to a light source and is often used in theatrical lighting.

General Lighting

Substantially uniform lighting of a space without providing for special local lighting requirements like task lighting or accent lighting.


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.

Glare Bomb

A light fixture that obviously produces way too much glare.


A thin metal stencil with a cut-out pattern that produces an image projected onto a surface when a light beam is directed through it.


An electrical connection that is literally connected to "ground" (the earth) directly or indirectly so that any spurious electrical current developing within the circuit or light fixture can pass to the earth harmlessly.



See high output


See hertz

Halogen Cycle

A regenerative cycle of tungsten and halogen atoms, which helps minimize the evaporation of tungsten atoms from the filament of a halogen lamp and the blackening of the glass envelope during the life of the lamp.

Halogen IR Lamp

A type of halogen lamp that has a reflective dichroic coating on the inner glass bulb that reflects infrared (heat) energy back to the filament, causing an increase in the output of light without an increase in the wattage supplied to the lamp.

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).


Technically means that the light fixture is permanently connected to an electrical source. The light fixture is not hardwired if it gets power via a cord & plug.


on a portable lamp the metal frame that holds the shade in place - the metal wire component on a fixture that supports the lamp shade.

Heat Sink

A component found in well-designed LED light fixtures that lowers the temperature of the LEDs by dissipating their heat. Heat sinks are also found in other electronic devices such as computers and lasers. They are often made of aluminum and have grooves, fins, and sometimes a fan.

Hertz (Hz)

The standard unit of measurement for frequency (how many times something occurs in a unit of time), usually how many cycles occur in 1 second. Named after German physicist, Heinrich Hertz, the unit was first established in 1930. In lighting, Hz is the unit used to measure alternating current.

HID Lamp

See high intensity discharge lamp

High Bay Light Fixture

An indoor luminaire designed for and used in spaces with very high ceilings (25ft or higher) like factories, warehouses, and gymnasiums. Also see low bay light fixture.

High Intensity Discharge Lamp (HID Lamp)

A lamp that has a longer life and provides more light (lumens) per watt than most other light sources. HID lamps are available in mercury vapor, metal halide, high pressure sodium, and low pressure sodium types.

High Output (HO)

A fluorescent lamp designed to use high levels of current (800 milliamperes), which corresponds with an increase in lumen output. HO fluorescent lamps are able to operate at low temperatures (down to 0F) and still produce high light levels.

High Pressure Sodium Lamp (HPS Lamp)

A high intensity discharge (HID) light bulb that illuminates by radiation from sodium vapor producing a yellowish color rendering, when supplied with electricity from a ballast. This type of light bulb is often used in street lights and is available with clear or phosphor coated glass envelopes. Often abbreviated as HPS lamps they are considered to be quite efficient producing about 100 lumens/watt.

HIR Lamp

See halogen IR lamp

Household Wire

"Household wire" is the term that is sometimes used to refer to the "non-metallic sheathed electrical cable" that is used behind all of the walls and ceilings in a home to connect the electrical panel to switches, junction boxes, ceiling fans, electrical outlets, exhaust fans, and light fixtures. The term, "Romex" is often incorrectly used as a generic term to refer to any "non-metallic sheathed electrical cable" just like the brand name Kleenex is often incorrectly used to refer to any brand of tissue. ROMEX® is a trademark of the Southwire Company which refers to their specific brand of "non-metalic sheathed electrical cable". The non-metallic sheathing is the outside rubber insulation around the entire cable. The cable inside the sheathing is usually made up of 3 wires: one wire with white insulation (neutral wire), one wire with black insulation (power wire), and one copper wire with no insulation (ground wire). The size of the non-metallic sheathed electrical cable that is used to connect lighting fixtures in a home 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.

HPS Lamp

See high pressure sodium lamp



See International Dark-Sky Association


See Illuminating Engineering Society of North America


The total luminous flux incident on a surface per unit area; a measure of how much of the incident light illuminates the surface; measured in lux or foot-candles.


See illuminance

Illuminating Engineering Society of North America (IESNA)

founded in 1906, the Illuminating Engineering Society of North America is a non-profit organization made up of lighting professional members that seeks to "improve the lighted environment by bringing together those with lighting knowledge and by translating that knowledge into actions that benefit the public." (see


A device that produces light for a fiber optic lighting system, which also is made up of fiber optic fibers and sometimes fixtures used at the ends of the fibers to direct the light in a specified manner. The light source used in an illuminator is usually an MR halogen lamp, an MR metal halide lamp, or an LED lamp.


Emission of visible light by any heated object (e.g., molten steel, a hot branding iron, or the filament of a lit light bulb).

Incandescent Lamp

A lamp in which light is produced by the passage of an electric current through a tungsten filament which is heated to the point of incandescence.

Indirect Glare

glare or excessive brightness reflected off another surface separate from the light source. Indirect glare, sometimes referred to as reflected glare, can be a reflection off a computer or television screen or even a magazine. Similar to direct glare, the light source should be considered when trying to prevent indirect glare.

Indirect Lighting

lighting that uses luminaires to direct most, if not all, of the light toward the ceiling or wall, providing soft, glare-free illumination without seeing the luminaire directly.

Induction Lamp

A special type of fluorescent lamp that uses electricity to generate an electromagnetic field that causes the gaseous mercury atoms inside the glass envelope to emit ultraviolet radiation, which in turn, is converted to visible light by the phosphor coating on the inside of the glass envelope. Induction lamps have no electrodes and, therefore, have longer rated lamp lives than standard fluorescent lamps because the deterioration of the tungsten filaments in a standard fluorescent lamp is usually the main cause of a fluorescent lamp to stop working.

Infrared Radiation

A type of invisible radiation for which the wavelengths are longer (about 770 nm to 1100 nm) and frequency lower than those for visible radiation (The visible spectrum is made up of red, orange, yellow, green, blue, indigo, and violet - ROYGBIV, for short.)

Initial Lumens

The luminous output of a brand new lamp.

Instant Start

refers to fluorescent lamps that start instantly without pre-heating the cathodes and without the need for starters.

International Dark-Sky Association (IDA)

Incorporated in 1988, the International Dark-Sky Association is a USA-based, non-profit organization that is dedicated to eliminating light pollution (excessive artificial light) in order to protect ecosystems, save energy, and allow for a star-filled night time sky that is easily visible with the naked human eye (see

Inverse Square Law

A law that states that the illuminance (E) at a point on a plane perpendicular to the line joining the point and a source is inversely proportional to the square of the distance (d) between the source and the plane, E = I/d2. This means, for example, that if the distance between a light source and the object being lit is doubled or tripled, that the object being lit receives 1/4 or 1/9 illumination (respectively) as it did originally.


An electrical device that changes direct current into alternating current. Inverters are an integral part of electronic transformers.

IP Ratings

Ingress Protection (IP) ratings, developed by the European Committee for Electro Technical Standardization, are used to specify the environmental protection an enclosure provides to the electrical equipment inside that enclosure. An IP rating normally has two numbers associated with it: (1) protection from solid objects or materials (like dust) and (2) protection from liquids (like water).

Example: With an IP rating of IP54, the "5" describes the level of protection from solid objects (protected against dust limited ingress with no harmful deposit) and the "4" describes the level of protection from liquids (protection against water sprayed from all directions with limited ingress permitted). An "X" can be used for one of the digits if there is only one class of protection, e.g., IPX1 describes only the level of protection from liquids (protection against vertically falling drops of water, e.g., condensation).

First IP Number - Protection Against Solid Objects
  • 0 - No special protection
  • 1 - Protected against solid objects up to 50 mm, e.g., accidental touch by person's hands.
  • 2 - Protected against solid objects up to 12 mm, e.g., person's fingers.
  • 3 - Protected against solid objects over 2.5 mm (tools and wires).
  • 4 - Protected against solid objects over 1 mm (tools, wires, and small wires).
  • 5 - Protected against dust limited ingress (no harmful deposit).
  • 6 - Totally protected against dust.
Second IP Number - Protection Against Liquids
  • 0 - No protection.
  • 1 - Protected against vertically falling drops of water, e.g., condensation.
  • 2 - Protected against direct sprays of water up to 15° from the vertical.
  • 3 - Protected against direct sprays of water up to 60° from the vertical.
  • 4 - Protected against water sprayed from all directions - limited ingress permitted.
  • 5 - Protected against low pressure jets of water from all directions - limited ingress.
  • 6 - Protected against temporary flooding of water, e.g., for use on ship decks - limited ingress permitted.
  • 7 - Protected against the effect of immersion between 15 cm and 100 cm.
  • 8 - Protected against long periods of immersion under pressure.


Junction Box

A plastic or metal container inside which all standard electrical wiring connections must be made. A junction box protects and conceals these electrical connections.



See kilowatt


See kilowatt hour

Kelvin Temperature Scale

A temperature scale that references to absolute zero (0 degrees Kelvin), which, in theory, is the absence of all thermal energy. In lighting, the Kelvin temperature scale is useful when describing the color temperature of a light source.

Kilowatt (kw)

A measure of electrical power equal to 1000 watts.

Kilowatt Hour (kWh)

The standard measurement of electrical energy equal to one kilowatt of electricity used over the period of one hour.


A perforated piece of metal (usually in the shape of a circle) on a metal box (like a junction box) that is removed with a punch and hammer to permit insertion of electrical wire like Romex wire.


An inert gas in incandescent lamps that allows the filament to glow hotter and brighter and last longer.



See lamp current crest factor


See light emitting diode


See Leadership in Energy and Environmental Design


See light emitting plasma


See lamp lumen depreciation


A lighting measurement standard published by the IES in 2008 that provides specific practices for testing LED performance. LM-79 covers testing procedures for determining how the color and light emitted from LEDs is perceived by people and how power is measured for LEDs.


A lighting measurement standard published by the IESNA in 2008 that provides specific practices for LED testing performance. LM-80 designates uniform test methods for measuring lumen maintenance for LEDs.


See lux


A light source such as an incandescent, halogen, xenon, fluorescent, or HID lamp. In everyday usage the terms, "light bulb" or "bulb", are usually used instead of the term, "lamp". In everyday usage the term, "lamp", usually refers to a portable lamp like a table lamp or a floor lamp but in the field of lighting the term, "lamp", refers to what most people call a "light bulb". Strictly speaking, the term, "bulb", refers to the glass envelope part of the "lamp".

Lamp Current Crest Factor (lccf)

The ratio of the peak or highest electric current to the average current for a ballast. A lamp current crest factor (lccf) above the maximum value set by a lamp manufacturer can shorten the lamp's life. The ANSI standard for lamp current crest factor is < 1.7


Synonymous with lamp socket

Lamp Lumen Depreciation (LLD)

As any lamp ages, it produces less and less light, the extent of which depends on the type of lamp in question. The value that indicates the lifetime decay of a lamp's lumen output as the lamp is operated over time is called lamp lumen depreciation. This is exactly why the published "initial lumens" for a lamp are always greater than the "mean lumens" for that same lamp. Some causes for lamp lumen depreciation may be the depletion of the incandescent filament over time, the accumulation of evaporated tungsten particles on the inside of the incandescent or fluorescent glass envelope, the photochemical degradation of the phosphor coating on the inside of a fluorescent glass tube, and the heat generated at the LED junction.

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 such as works of art), decorative lighting (lighting created by very attractive light sources such as chandeliers or mini pendants), and general lighting (lighting that fills the space). This technique (long favored by cameramen and cinematographers) can eliminate ugly shadows in the room and on your face.

Leadership in Energy and Environmental Design (LEED)

An internationally recognized green building certification system, providing third-party verification that a building or community was designed and built using strategies aimed at i

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