There are many words which are used when it comes to Lighting that many people may not completely understand.  The goal of this glossary is to provide definitions for several of these words to eliminate any potential confusion.  Simply click on the letter associated with the terms you’re looking for the definition of and you’ll be directed to all listings under that letter.

Accent Lighting – Concentrated light on a subject which highlights it and causes it to stand out from its surrounding. Depending on degree of drama desired, accent light should minimally be 10x the general light or ambient light.

A-Line Lamp – Bulbs with a spherical shape tapered to a narrow neck. Includes A15, A19, A21 and A23.

Alternating Current (AC) – The flow of an electric charge that has alternated or reversed in direction.

Amalgam – An amalgam is an alloy made of a metal mixed with mercury.

Ambient Lighting – Ambient lighting is your basic, general overhead lighting.

Ampere (Amp) – A unit expressing the rate of flow of electric current.

ANSI (American National Standards Institute) – The organization that develops voluntary guidelines and produces performance standards for the electrical and other industries.

Anode – The electrode through which current flows into a polarized device.  Traditional polarized devices are, but are not limited to, fluorescent lamps and diodes.

Area Lighting – A light pattern designed to cover more than a single object.  Area lighting can encompass lighting layers such as ambient or task, and is typically accomplished using one or more spot and floodlights.

Argon – Argon is a noble gas used in low pressure gas discharge lamps (similar to Neon Lamps).  Argon lamps typically emit a blue color and require mercury to make the color brighter.

Average Rated Life – An average rating, in hours, indicating when 50% of a large group of lamps have failed, when operated at nominal lamp voltage and current; manufacturers use 3 hours per start for fluorescent lamps and 10 hours per start for HID lamps when performing lamp life testing procedures; every lamp type has a unique mortality curve that depicts its average rated life. For Photo-Optic specialty lamps, average rated life refers to the operating period after which on statistical average, 50% of the lamps will perform within their specified values.

Audible Noise (Sound) – All fluorescent lamp ballasts produce some noise. Most brand ballasts are sound rated A (up to 75% quieter than magnetic types) and are acceptable for most applications. Care should be taken when mounting the ballast to reduce vibration.

Backlighting – Illuminating the subject from the back to create a glowing effect.

Baffle – The baffle is the trim in recessed lighting devices, often used to soften effects of light, commonly used in homes and offices.

Ballast – A device used with an electric discharge lamp to obtain the necessary circuit conditions (voltage, current and waveform) for starting and operating a lamp. All fluorescent and HID light sources require a ballast for proper operation. Dimming ballasts are special ballasts which, when used together with a dimmer, will vary the light output of a lamp. Photo-Optic discharge lamps are either designed for AC operation (sine wave and/or square wave with recommended operational frequencies below 1KHz) or DC operation (current regulated or power regulated). Please see lamp specifications for correct ballast or electronic control gear selection.

Ballast Basics – Ballasts have two primary functions: 1) start the lamp and 2) control operation of the lamp once it has started. High frequency electronic ballasts operate lamps more efficiently and eliminate the hum and visible flicker normally associated with standard magnetic ballasts. Electronic ballasts also typically have better power quality than magnetic ballasts.

Ballast Factor (BF) – The measured ability of a particular ballast to produce light from the lamp(s) it powers; ballast factor is derived by dividing the lumen output of a particular lamp/ballast combination by the lumen output of the same lamp(s) on a reference ballast.

Ballast Life – Ballasts have an average life expectancy. To maximize life, ambient temperature should be kept as low as possible. It is also important to maintain effective dissipation of heat using the lighting fixture as a heatsink for the ballast enclosure.

Ballast Types – There are three types of lighting ballasts: 1) Magnetic: an inefficient device that uses a core and coil assembly transformer to perform the minimum functions required to start and operate the lamp; 2) Hybrid or “low frequency electronic”: essentially a magnetic ballast with a few electronic components that switch off voltage to the lamp coil once the lamp has started. A minimal increase in efficiency is obtained via more expensive magnetic core material and the absence of power to the lamp coils during operation; 3) High frequency electronic: a ballast that operates lamps at frequencies above 20,000 Hz. Maximum efficiency is obtained through the use of electronic circuitry and optimum lamp operating characteristics.

Base – The lamp base mechanically holds the lamp in place in the application. The lamp base directly or indirectly (via a cable or lead-in wires) conducts electricity from the circuit to the lamp and can be designed to dissipate heat. Lamp bases should be operated within specified temperature ranges.

Basket Troffer – A recessed fixture which uses a special basket to diffuse the light.

Bayonet Base – Bulb base-type using two locking pins on either side of the base to hold it securely in place.  So named because it was most famously used as a quick connection method for bayonets on rifles.

Beam Angle – The angle between the two directions for which the intensity (candlepower) is 50% of the maximum intensity as measured in a plane through the nominal beam centerline (center beam candlepower or CBCP).

Beam Pattern – Light pattern of hot and cool spots emitted by a light source.  Pattern is determined by beam angle and physical shape of lamp or fixture.  Typical light patterns include a center hot spot or halo light.

Beam Spread – In any plane, the angle between the two directions in the plane in which the candlepower is equal to a stated percent of the maximum candlepower in the beam.

Binning – Separation of LED chips based on relative color or color temperature by production bins.

Black Light – A coated light bulb which emits light only in the ultra-violet and near ultra-violet spectrums.

Bollard – A post used for navigation, traffic control, or pathway lighting.

Brick Light – Light fixture designed to be recessed into brick-work.

Brightness – (See Luminance.)

Bulb – Hard, soft or quartz glass enclosure, which can contain a vacuum, elemental inert gas or metal and a means of light generation (filament or electrodes).

Cable Lighting System – A track mounting system which uses conductive cables in place of rails.  Two cables, one hot and the other neutral, are used as both fixture supports and power sources for the lights.

Canadian Standards Association (CSA) – Organization that provides product testing and certification services for a variety of products.  A CSA certification indicates that a product meets the minimum requirements for Canadian or U.S. standards necessary for that type of product.

Candela (cd) – The unit of measure indicating the luminous intensity (candlepower) of a light source in a specific direction; any given light source will have many different intensities, depending upon the direction considered.

Candelabra – Decorative light bulbs usually used in chandeliers. Also known as torpedo bulbs.

Candlepower – Candlepower, measured in candelas , is a unit of measurement that stands for the luminous intensity going in a specific direction from a light source. The latter, usually seen on reflector-type bulbs, is most important when the actual “punch” of the concentrated beam of light is more important than how much of an area it illuminates.

Candlepower Distribution – A curve that represents the variation in luminous intensity (expressed in candelas) in a plane through the light center of a lamp or luminaire; each lamp or lamp/luminaire combination has a unique set of candlepower distributions that indicate how light will be spread.

Cathode – The electrode through which current flows out of a polarized device.  Traditional polarized devices are, but are not limited to, fluorescent lamps and diodes.

Cathode Guard – Specialized device for fluorescent lamps.  The cathode guard is a metal band  surrounding the cathode in a fluorescent.  This band collects evaporating particles to prevent end blackening in the lamp.

Cave Effect – The cave-like shadow appearance on walls and ceiling caused by direct downlights.

Certified Ballast Manufacturers Association (CBM) – Association for certification and testing of ballasts to ensure compliance with the standards of the American National Standard Institute.

Center Beam Candlepower (CBCP) – The intensity of light produced at the center of a reflector lamp beam, expressed in candelas.

Circuit – A closed loop, typically an electrical device.

Class of Lamp – Incandescent lamps are classified as type B or type C. The type B lamp is one in which the filament operates in a vacuum. The type C lamp is one in which the filament operates in an atmosphere of inert gas. For gas-filled lamps which can be operated in any position, the lumen maintenance is best when lamps are operated base up. For the vacuum type lamps which have no restrictions on operating position, the lumen maintenance is the same in all operating positions.

Cold Cathode – A cathode that is not heated by a filament.

Cold Cathode Fluorescent Lamp (CCFL) – Fluorescent lamp that uses a cold cathode.

Color Quality Scale (CQS) – A color rendering index which uses the CIELAB color space to measure how well a light reproduces colors on an illuminated object.

Color Rendering Index (CRI) – The Color Rendering Index (CRI) measures the effect a light source has on the perceived color of objects and surfaces. High CRI light makes virtually all colors look natural and vibrant. Low CRI causes some colors to appear washed out or even to take on a completely different hue.

Color Temperature (CT) – Color temperature, which is measured in Kelvin, indicates whether a lamp has a warm, midrange or cool color appearance. “Warm” light sources have a low color temperature (2000-3000K) and feature more light in the red/orange/yellow range. Light with a higher color temperature (>5000K) features more blue light and is referred to as “cool.”

Colored Glass Filter – A glass insert used to filter out a portion of the visible color spectrum from a light source.

Compact Fluorescent Lamps (CFL) – Compact fluorescent lamps employ small diameter tubes that are bent so they begin and end in a single base. This allows them to be produced in a wide variety of configurations, greatly extending the applications for fluorescent lighting.

Constant Wattage Autotransformer (CWA) – Employing two coils, this HID ballast is less efficient than reactor types, but has better voltage regulation. Most popular type in use.

Core and Coil Ballast – Some of the first lighting ballasts used to operate MH lamps were electromagnetic ballasts with a bulky, heavy, magnetic core of laminated steel plates wrapped in copper windings.

Cornice Lighting – Indirect lighting using a light recessed within crown molding.

Correlated Color Temperature (CCT) – A specification of the color appearance of a lamp, relating its color to that of a reference source, black body radiator, heated to a particular temperature, measured in degrees Kelvin (K); CCT generally measures the “warmth” or “coolness” of light source appearance.

Coulomb – Coulombs are units of electrical charge. Defined as the charge by a constant current.

Cove Lighting – Indirect lighting with lights built into ledges, recesses, ceilings, or high walls.

Cross Lighting – Technique using two opposing light sources (typically one in front and one behind) for dramatic effect.

Current – A measure of the rate of flow of electricity, expressed in amperes (A).

Cut Off Angle – The angle between a direction directly beneath a lamp (the nadir) to the point where the lamp or light source can no longer be seen.

Daisey Chain – Daisy-chaining is a wiring setup where devices are linked together sequentially, with only the first device physically connecting to the power source.

Dichroic Filter – Thin-film filter, or interference filter is an accurate color filter used to selectively pass light of a small range of colors while reflecting other colors.

Dichroic Reflector – Commonly found and used behind a light source to reflect light forward while allowing infrared light to pass the back of the lamp. This results in a beam that is cooler in thermal temperature.

Diffuse – To scatter or spread out light in an even pattern.

Diffuser – A device that scatters or spreads out light.

Dimmable – Capable of being reduced in intensity.

Dimmer – A device that allows you to vary the brightness or color temperature of an electrical light.

Direct Current (DC) – The unidirectional flow of an electric charge.

Direct Glare – A bright, non-reflected light that obscures or impairs vision.

Double-Ended – Lamps that have two bases opposite one another for series electrical connection, mechanical mounting and heat dissipation.

Directional Lighting – Illumination on the work plane or on an object predominantly from a single direction.

Discharge Tube – An insulated, thermally resistant glass or quartz envelope filled with a gas that can be electrically charged by internal electrodes.

Double-Ended Lamp – Lamps that have two bases opposite one another for series electrical connection, mechanical mounting and heat dissipation.

Downlight – A fixture or lamp that is designed to point illumination downwards.

Driver – Electronics used to power illumination sources. Ballast.

Driver, LED – A self contained power supply used to power LEDs.

Efficacy – The rate at which a lamp is able to convert power (watts) into light (lumens), expressed in lumens per watt (LPW or lm/W). See also LPW Performance.

Electrode – An electrical conductor that makes contact with a nonmetallic portion of a circuit (such as an electrollytic fluid, vacuum, or semiconductor).

Electrodeless Lamp – See Induction Lamp

Electroluminescent (EL) – Optical and electrical phenomenon where a material emits light in response to the the passage of an electrical current or to a strong electric field.

Electromagnetic Ballast – A current controlling device that is typically used for HID and fluorescent lamps.

Electromagnetic Spectrum – The range of possible frequencies of electromagnetic radiation.

Electron Stimulated Luminescence (ESL) – Light produced by fluorescent phosphors when hit by a beam of electrons.  A process known as cathodolumiescence.

Electronic Ballast – A current controlling device for fluorescent lamps which first converts the voltage frequency from 60 cycles to 20KHz or higher.

Electromagnetic Spectrum – The range of possible frequencies of electromagnetic radiation.

Electron Stimulated Luminescence (ESL) – Light produced by fluorescent phosphors when hit by a beam of electrons.  A process known as cathodolumiescence.

Electronic Ballast – A current controlling device for fluorescent lamps which first converts the voltage frequency from 60 cycles to 20KHz or higher.

Electronic Transformer – A device used to convert voltage via induction by first increasing the frequency using an inverter.  Electronic transformers are typically smaller in size compared to traditional transformers.

Elliptical Lens – An elliptically shaped lens.  The design produces an asymmetrical light distribution in a single direction.  Also known as a Linear Spread Lens.

Elongated Lens – An elongated shaped lens.  The design produces an asymmetrical light distribution in a single direction.  Also known as a Linear Spread Lens.

EMI/RFI – Electronic Ballasts contain circuits that limit electrical noise conducted onto the power line or radiated through the air, otherwise referred to as EMI/RFI. Many of our ballasts comply with FCC 47 CFR Part 18, non-consumer limits for commercial applications. Ballasts for residential application must meet consumer limits. We have a complete line of magnetic ballasts for residential use.

End Blackening – A darkening of the ends of  a fluorescent lamp caused by deposits of particles evaporating from the cathode.

Energy – A measure of work done by an electrical system over a given period of time, often expressed in kilowatt-hours (kWh).

Energy Independence and Security Act (EISA) – The Energy Independence and Security Act (EISA) of 2007 was passed to increase the standards for lighting product efficiency.

Energy Policy Act (EPACT) – Legislation enacted by the US Congress in 1992 regarding the labeling and energy requirements for lamps and ballasts.

ENERGY STAR® – Organization responsible for setting international standards for energy efficiency for consumer products.

ER Lamp – An ellipsoidal reflector spotlight is a stage light that collects and directs light through a barrel and lens to maximize light output.  Colloquially known as a Leko or Shakespeare light.

Eyeball Trim – Trim kit for a recessed light that grants the lamp an adjustable angle.

Faceplate – A cover, plate, or bezel placed on the front of an object that is usually replaceable or cosmetic.  Examples include the covers on light switches, electrical outlets, and the masks used by life-like humanoid robots.

Fiber Optic – Glass or plastic fibers used to transmit data in the form of light.  A bundle of fibers is typically used to preserve data integrity.

Filament – A tungsten wire purposely positioned inside a lamp bulb, that when heated electrically generates radiation in the visible, infrared and ultraviolet ranges. Tungsten material is most often used, as it has great tensile strength, is very durable, and can be heated very near its melting point without evaporating rapidly. Lamp filaments are offered in a variety of designs optimized for specific applications.

Filter – A device, bounded by a system, whose designated purpose consists of the selective impedence, removal, or discretionary selection, of specific objects deemed undesirable for the end product of the initially stated system. This is regardless of if the stated product, process, or concept consists of an electromagnetic field; light color, spectral frequency, or angle; set of concepts or terms; or heterogeneous mixture containing excess particulates such as dirt, plastic, wood, or metals.

Fixture – (See Luminaire.)

Flexible Track Lighting System – Suspended track lighting system with a flexible rail to allow for custom fixture designs.

Floodlight – A reflector lamp with a relatively wide beam pattern. Also a luminaire consisting of lamp and reflector at fixed distance providing a wide field of illumination.

Fluorescent Lamp – A low pressure mercury vapor discharge light source. The electric discharge generates ultra-violet (UV) energy, which is absorbed by a phosphor and converted to visible light.

Footcandle (fc) – A unit of illumination equal to 1 lumen per square foot.

Foot-Lambert (fL) – Luminance unit used in the US that is equal to 1/π candela per square foot.

Four-Way Switch – An intermediate switch used to expand the number of control locations within a room.

Frequency – The number of times per second that an alternating current system reverses from positive to negative and back to positive, expressed in cycles per second or hertz (Hz).

Fresnel Lens – A compact lens allowing for construction of a large aperature lens with a short focal length that’s much thinner than a conventional lens.

Frosted Lens – A slightly opaque lens used to create a softer, more diffused light.

Ganging – Process of arranging multiple electrical devices or machines together to work in coordination.

Gel – Colored, heat resistant plastic used to color a light source.  Used for stage lighting.

General Lighting (Ambient Lighting) – Lighting designed to deliver a predominately uniform level of light throughout an area.

Glare – A strong or dazzling light that obscures vision.

Glare Bomb – A streetlight which casts light upward or sideways creating glare or excess light pollution.

Glow to Arc Transition – In order to achieve full rated lamp life, a ballast should start a lamp so that the time from when the lamp begins to glow to the time the lamp arc strikes should be as short as possible. Instant start ballasts typically accomplish this task within 50 millisecond.

Gobo – A stencil or template which is placed in front of a light source to control the pattern of light emitted by the fixture.

Ground – The common return path for current in an electrical circuit.

Grounding – The ballast case and fixture must always be grounded. The grounding helps assure safety, proper lamp starting, and acceptable EMI/RFI performance. Install ballast in accordance with national and local electric codes.

Halogen Cycle – Chemical process where the halogen gas within a lamp’s envelope  redeposits the evaporated tungsten back onto the filament, prolonging lamp-life and preventing clouding of the envelope.

Halogen IR Lamp (HIR) – Halogen lamp coated to reduce heat output, improving efficiency.

Halogen Lamps – High pressure tungsten filament lamps containing halogen gases. The halogen gases allow the filaments to operate at higher efficacies than incandescent lamps. Halogen lamps also provide brighter, whiter light with better color characteristics, longer service life and improved energy efficiency.

Hardwired – A device with electrical wire leads already permanently attached.

Harmonic – An electrical frequency that is an integer multiple of the fundamental frequency; for example, if 60 Hz is the fundamental frequency, then 120 Hz is the second harmonic and 180 Hz is the third harmonic. Some electronic devices, such as ballasts or power supplies, can cause harmonic distortion, directly affecting power quality.

Harp – Metal component on the frame of a portable or desk lamp that holds the shade in place.

Heat Sink – A passive heat exchanger used in electronic systems to collect and disperse heat away from sensitive components.  Typically made up of several separated fins or blades to increase surface area.

Hertz (Hz) – A unit of frequency equal to one cycle per second; see frequency.

High Bay Light Fixture – Designed for high ceilings (typically above 25 feet), high bay fixtures are used most often in factories, warehouses and gymnasiums.

High-Intensity Discharge (HID) Lamps – Lamps in which an arc passing between two electrodes in a pressurized tube causes various metallic additives to vaporize and release large amounts of light. All HID lamps offer outstanding energy efficiency and service life. Metal halide lamps also offer good to excellent color rendering index (CRI).

High Output (HO) – Fluorescent lamp with higher than average lumen output.  These fluorescents are designed to higher current levels (roughly 800 milliamperes) and can operate in lower temperatures.

High Pressure Sodium Lamp (HPS) – A sodium-vapor lamp which uses an amalgamation of mercury and metallic sodium to generate an arc-light.  HPS lamps are extremely efficient but have poor color rendering.

Household Wire – While typically incorrectly referred to by the term “Romex” (a brand of household wire), non-metallic sheathed electrical cable is the rubber-insulated electrical cable used for most in-home wiring.  Household wiring is usually 14/2 with a ground wire, as it’s comprised of three separate 14-gauge wires, sheathed in rubber insulation.

Illuminance – Light arriving at a surface, expressed in lumens per unit area; 1 lumen per square foot equals 1 footcandle, while 1 lumen per square meter equals 1 lux.

Illuminating Engineering Society (IES) – The recognized technical authority on illumination, the Illuminating Engineering Society of North America (IES) ensures the disemmination of up-to-date lighting information to its members through programs, publications and services.  As a premiere source of lighting industry news and information, IES publishes nearly 100 technical publications and work in conjunction with a variety of other organizations for further reach.  IES’s outreach programs include instructional courses, documentation, and general information publications.

Illumination – A secondary term for illuminance, illumination means “lighting” or “light.”

Illuminator – A light source.

Incandescence – Incandescence is the emission of electromagnetic radiation from a source by heat.  This EM radiation includes visibile light.  In simpler terms, incandescent light is generated by heating an object until it glows.

Incandescent Lamp – A light source using the principle of incandescence. When an electric current passes through a filament wire (usually tungsten), the heated wire glows. Filaments of standard incandescent lamps are enclosed in a vacuum or gas-filled bulb. They provide low initial cost, good color rendition and excellent optical control.

Indirect Glare – While glare is caused directly by a vibrant light source, indirect glare is when a strong light is reflected off a secondary surface to impair the vision of the viewer.

Indirect Lighting – Lighting an object by reflecting a strong source off of a secondary object such as a wall or ceiling.

Induction Lamp – A gas-discharge lamp, similar in construction to a fluorescent, which uses an electromagnetic field to excite the gas.  The gas generates illumination through electrical inducation instead of the more traditional internal electrodes.

Infrared (IR) – Electromagnetic radiation with wavelengths longer than those of visible light.  This spectrum of the EM band extends from 700 nm to 1 mm.

Infrared Radiation – See Infrared.

Initial Lumens – is a measure of how much light the lamp is emitting near the beginning of its life.

Input Voltage – Power supply voltage required for proper operation of fluorescent or HID ballast.

Instant Start (IS) – Instant start ballasts apply high voltage across the lamp with no preheating of the cathode. This is the most energy efficient starting method for fluorescent lamp ballasting because they provide maximum energy savings and start lamps without delay or flashing. IS ballasts use 1.5 to 2 watts less per lamp than rapid start ballast. Other IS ballast benefits typically include parallel lamp circuitry, longer remote wiring distance, easier installation due to less complicated wiring, and capability to start lamps at 0 degrees (versus 50 degrees F for rapid start).

Instant Start (IS) –  Instant start ballasts apply high voltage across the lamp with no preheating of the cathode. This is the most energy efficient starting method for fluorescent lamp ballasting because they provide maximum energy savings and start lamps without delay or flashing. IS ballasts use 1.5 to 2 watts less per lamp than rapid start ballast. Other IS ballast benefits typically include parallel lamp circuitry, longer remote wiring distance, easier installation due to less complicated wiring, and capability to start lamps at 0 degrees (versus 50 degrees F for rapid start).

International Dark-Sky Association (IDA) – Founded in 1988, the International Dark-Sky Association works to reduce light pollution across the world.  They focus on promoting the idea that cities should light only what they need when they need it and work with both cities and manufacturers to develop new systems and technologies to reduce overall light pollution.

Inverse Square Law – In lighting, this law states that the illumination of a light source is inversely proportional to the square of the distance from the source.  In short, the further you are from the source, the dimmer the light on an object.

Inverter – An electronic device that converts direct current (DC) into alternating current (AC).

IP Ratings – Ingress protection (IP) ratings identify what material(s) the rated item is protected from.  The first number identifies solid objects while the second number identifies liquids.

Junction Box – A container to house electrical connections.

Kelvin Temperature Scale – See Kelvin.

Kelvin (K) – A unit of absolute temperature equal to 1/273.16 of the absolute temperature of the triple point of water. One kelvin degree is equal to one Celsius degree. In lighting, Kelvin is the unit of measure for Color Temperature. (See – Color Temperature)

Kilowatt (Kw) – Scaled unit measurement for wattage.  Equal to 1,000 watts.

Kilowatt Hour (kWh) – The measure of electrical energy from which electricity billing is determined. For example, at the rate of $0.11 oer kWh, a 100-watt lamp operating for 2000 hours will cost $22.00 (100×2000/1000 = 200kWh x.11 = 22.00).

Knockout – Sections that can be easily removed or knocked out from a panel.  Typical uses are in junction boxes to allow for cables to pass through the sides or back.

Krypton – One of the noble gases.  Atomic number 36.  This inert gas is used in krypton lamps and as part of many fluorescent lights.

Lamp – Manufactured light source, synonymous with light bulb; the three broad categories of electric lamps are incandescent, fluorescent and high-intensity discharge.

Lamp Current Crest Factor (LCCF) – The ratio of peak lamp current to the RMS (average) lamp current. Lamp manufacturers require a LCCF of less than 1.70 in order to achieve full lamp life.

Lamp Dimensions –  Bulb designations consist of a letter or letters to indicate shape and a number to indicate the approximate diameter in eighths of an inch.

Lamp Disposal – When disposing of spent lamps, always consult federal, state, local and/or provincial hazardous waste disposal rules and regulations to ensure proper disposal.

Lamp Flicker – Cyclic variation in output of a light source. High frequency electronic ballasts provide a minimal level of lamp flicker. Lamp flicker from magnetic ballasts may cause eye fatigue for some people.

Lamp Fuse – Wire or device designed to protect a lamp from over-voltage or over-current conditions. Photo-Optic lamps are fused in their applications to prevent lamp overpowering. Certain lamps contain their own internal fuse. Please ensure lamps in your specific application are fused with respect to their power source.

Lamp Lumen Depreciation Factor (LLDF) – The multiplier to be used in illumination calculations to relate the initial rated output of light sources to the anticipated minimum rated output based on the relamping program to be used. (See Lumen Depreciation and Mean Lumens.)

Light Emitting Diode (LED) – A solid state semiconductor device that converts electrical energy directly into light. On its most basic level, a semiconductor is comprised of two regions. The p-region contains positive electrical charges while the n-region contains negative electrical charges. When voltage is applied and current begins to flow, the electrons move across the n region into the p region. The process of an electron moving through the p-n junction releases energy. The dispersion of this energy produces photons with visible wavelengths.

Lamp Dimensions – Bulb designations consist of a letter or letters to indicate shape and a number to indicate the approximate diameter in eighths of an inch.

LED Driver – See “Driver.”

Lens – A glass or plastic element used in luminaires to change the direction and control the distribution of light rays.

Lensed Troffer – Any troffer that uses a lens to focus or diffuse its light.

Life-Cycle Cost – The cost of ownership of a product over its lifetime, or “buy-to-bin.”

Light – Radiant energy that is capable of producing a visual sensation.

Light Bulb – Often ascribed to the incandescent light, a light bulb is any of a number of bulb-shaped light sources.  Light bulbs come in many shapes and sizes and use multiple source types, including incandescent, fluorescent, LED, and HID.

Light Center Length (LCL) – Light Center Length is the distance from a reference point on a lamp base (usually the eyelet) to the center of the light source. For high intensity discharge lamps, it is the distance from the center of the filament or center of the arc to the point shown below for the base indicated:

•              All Screw Bases: Bottom base contact

•              Medium and Mogul Prefocus: Top of base pin

•              Medium BiPost: Bottom of bulb

•              Bayonet Candelabra and Medium Bayonet: Top of base pins

•              SC or DC Prefocus: Plane of locating bosses of prefocusing collar

•              Mini-Can: Intersection of 45 degree taper with max. diameter of base

Light Emitting Diode (LED) –  A solid state semiconductor device that converts electrical energy directly into light. On its most basic level, a semiconductor is comprised of two regions. The p-region contains positive electrical charges while the n-region contains negative electrical charges. When voltage is applied and current begins to flow, the electrons move across the n region into the p region. The process of an electron moving through the p-n junction releases energy. The dispersion of this energy produces photons with visible wavelengths.

Light Emitting Plasma (LEP) – LEP lamps are a type of electrodeless, gas-discharge lamp which uses radio frequency (RF) power to excite the gas an generate a light producing (emitting) plasma.

Light Fixture – A lighted piece of furniture that is immobile.  Used for illumination.

Light Loss Factor (LLF) – A factor used in calculating illuminance after a given period of time and under given conditions. It takes into account temperature and voltage variations, dirt accumulation on luminaire and room surfaces, lamp depreciation, maintenance procedures and atmosphere conditions. Formerly called maintenance factor.

Light Source – Origination point for light. Typically a light fixture or bulb. May also refer to type of light such as incandescent or LED.

Light Trespass – When lighting is poorly controlled and allows unwanted light to shine onto property and windows.

Lighting Facts Label – FTC mandated label that outlines specifications for the light source.  Details include lumen output, energy cost, life expectancy, appearance, wattage, and mercury content.

Line Voltage – Also known as mains electricity, is the general-purpose building electricity line.  For the US, this value is usually 120 volts.

Linear Spread Lens – Elongates any beam of light that passes through it by diverging light on only a single axis, creating an asymmetrical light pattern.

LM-79 – Photometric test system for solid state lighting.  The LM-79 test focuses on performance characterists of SSL technology.  Input voltage, current, power, and the power factor of the lamp are all tested and compared with lumen output and luminous flux.

LM-80 – Another photometric test system for purposes of comparison between lamps.  See LM-79.

Louver – A blind or shutter, typically made up of angled slats that can be opened or closed.

Low Bay Light Fixture – Fixture used for large areas with low ceilings.  Low-bay fixtures typically use a diffuser lens to disperse light and mitigate glare from the powerful lamps used inside.

Low Pressure Sodium Lamp – An arc lamp which uses a solid sodium base as an illuminator.  LPS lamps are extremely energy efficient, but have very poor color rendering, making them useful for street lamps and security lighting.

Low Temperature Starting – Instant start and programmed rapid start electronic ballasts have the capability to start fluorescent lamps at temperatures down to 0°F providing the following conditions are met: 1. The ballast is operated at rated nominal line voltage; 2. Ballast cannot be tandem/remote wired for low temperature starting applications. Please note, starting time may increase at 0°F ambient temperatures. Enclosed fixtures are recommended as fluorescent lamps have reduced light output at cooler ambient temperatures. (See specifications for each model’s starting temperature rating.)

Low Voltage – A relative measurement depending on your state and country.  Low voltage lighting is typically 24 volts or lower.  Low voltage as an industry standard describes anything that is not regulated by High Voltage Safety codes (anything less than 1000V AC or 1500V DC).

LPW Performance – Lumens Per Watt. The number of lumens produced by a light source for each watt of electrical power supplied to the light source. Also see Efficacy.

Lumen (lm) – A unit of luminous flux; overall light output; quantity of light, expressed in lumens. For example, a dinner candle provides about 12 lumens and a 60-watt soft white incandescent lamp provides about 840 lumens.

Lumens (mean) –  The amount of lumens the bulb produces at 50 percent of its life.

Lumen Depreciation – The decrease in lumen output of a light source over time; every lamp type has a unique lumen depreciation curve (sometimes called a lumen maintenance curve) depicting the pattern of decreasing light output. See Lamp Lumen Depreciation Factor, LLDF and Mean Lumens.


Lumen Maintenance – The opposite of Lumen Depreciation; lumen maintenance compares the initial lumen output to an estimated output at a future time.

Luminaire – A light fixture; the complete lighting unit, including lamp, reflector, ballast, socket, wiring, diffuser and housing.

Luminaire Efficiency – The ratio of luminous flux (lumens) emitted by a luminaire to that emitted by the lamp or lamps used therein.

Luminance (L) – Light reflected in a particular direction; the photometric quantity most closely associated with brightness perception, measured in units of luminous intensity (candelas) per unit area (square feet or square meters).

Luminous Efficacy – The expression of efficiency in converting power (watts) into light (lumens). Expressed as lumens per watt or l/w.

Luminous Flux – The amount of energy radiated in visible wavelengths (visible spectrum) per unit of time.

Lux (lx) – A unit of illuminance equal to 1 lumen per square meter.

Magnetic Ballast – Voltage or current regulator for a lamp which magnetic induction instead of solid-state electronics.

Magnetic Induction – Process where voltage is added to a line or circuit by means of a magnetic field instead of electrical conduction.

Magnetic Transformer – Voltage conversion unit used to step up (increase) or step down (decrease) voltage on a line using magnetic induction.

Maximum Case Temperature – All electronic ballasts have a maximum allowable case temperature. Applications in which the case temperature exceeds this maximum void all warranties.

Maximum Overall Length (MOL) – The total length of a lamp, from top of bulb to bottom of base.

Mean Lumens – Lumen output of a light source after the source has been used. Mean lumen values for fluorescent and HID lamps are typically measured at 40% of their rated lives. Most high pressure sodium and mercury lamps are measured at 50% of their rated lives. All measurements are made on ANSI reference ballasts. Mean lumens are not typically measured for incandescent and tungsten halogen lamps.

Mercury – An element with the symbol Hg and atomic number 80.  Mercury is toxic if directly exposed to large quantities of the metal; however, it’s ability to form an amalgam with many elements has made it extremely useful.  Mercury is an essential part of arc and fluorescent lamps since mercury vapor in a lamp creates a path for electricity to follow.

Mercury Vapor Lamp – An arc lamp which uses mercury vapor as an electrical conductor.  The arc is contained in a small internal envelope, while the outer lamp is designed for thermal and ultraviolet radiation protection.

Mesopic Vision – The combination of photopic and scotopic vision (day and night vision) used in low light conditions.

Metal Halide Lamp (MH) – An arc lamp which uses a combination of mercury vapor and metal halides (bromine or iodine compounds) for the electric arc.

Motion Sensor – An electronic device designed to detect motion.  Motion sensors typically use optical, microwave, or acoustic sensors to detect differences within a room and trigger an electrical device as a response.

 Multifaceted Reflector (MR) – A reflector base bulb, typically with bi-pin or GU bases.  MR bulbs are designated by MR# where the # equals the distance between pins in eighths of an inch (e.g. MR16 is an MR bulb with a spacing of 16 eights of an inch or 2 inches).

Multi-Location Control – Multi-location dimmers can be used with accessory dimmers (Smart Remotes) for full control of the lights from up to 10 locations.

NAED – A five-digit number used to identify a specific lamp. This NAED number in this catalog is labeled Product Number and should be used when ordering products. NAED is the abbreviation for National Association of Electrical Distributors.

Nanometer (nm) – A unit of length equal to 10-9 meters; commonly used as a unit of wavelength.

National Association of Electrical Distributors (NAED ) – NAED is the abbreviation for National Association of Electrical Distributors, a non-profit organization dedicated to service and protection of electrical product distribution.  A five-digit number used to identify a specific lamp. This NAED number in this catalog is labeled Product Number and should be used when ordering products.

National Association of Independent Lighting Distributors (NAILD) – A  distributor of lighting technology, specification, and installation resources for commercial lighting specialist distributors and manufacturers.

National Electric Code (NEC) – Regional standards for safe installation of electrical wiring and equipment.

National Electrical Manufacturers Association (NEMA) – National association responsible for many of the electrical standards used by manufacturers.

National Institute of Standards and Technology (NIST) – Organization designed to promote innovation and industrial competition through advancing measurement science, standards, and technology.

Neodymium – Chemical element with an atomic number of 60 and the symbol Nd.

Neon – Chemical element with an atomic number of 10 and the symbol Ne.  A noble gas used in Neon lamps.

Nominal Length – A measurement of fluorescent lamp length based on the length of the lamp plus the proper allowance for standard lamp  holders.

Nominal Watts – Wattage used to describe a lamp. Also see Power and Watt.

Occupancy Sensor – See “Motion Sensor”.

OFR – Abbreviation for “ozone free” technology. Lamps with the designation OFR do not generate ozone during operation.

OLED – OLEDs are comprised of mainly organic materials, making them an environmentally friendly light source that can easily be recycled. Free of ultra violet rays, unlike LEDs.

Open Circuit – A non-closed circuit, preventing electrical current from flowing.  Circuits can be open due to an electrical break, or due to a switch forcing the circuit open.

Open Circuit Voltage (OCV) – Open Circuit Voltage measured across the socket the lamp screws into, with the ballast powered on. It is dangerous to stick a voltmeter into such a socket without precise knowledge of the ballast because exceedingly high voltages could be present.

Operating Position – Some lamps are specified/ designed to be operated in certain positions, i.e., horizontal or base up. Lamps may be operated in any position unless otherwise indicated.

Optics – The behaviors and properties of light.

Ordering Abbreviation – Provides a shorthand description of the lamp, using a unique code which can be used when ordering a lamp if the Product Number is not known. An example would be: CF15EL/R30/830/MED, which translates to a 15-watt Soft White DULUX® EL reflector electronic self-ballasted compact fluorescent lamp with an R30 reflector, 82CRI, 3000K color temperature and a medium screw base.

Outlet – In building wiring, a socket wire appliances or electrical equipment can connect to line or main voltage.

PAR Lamps – Pressed aluminized reflector lamp, with the outer bulb formed from two pressed glass parts that are fused or sealed together. PAR lamps may be incandescent, halogen, or HID types.

Parabolic Troffer – A troffer fixture that includes a parabolic lens to reduce glare by shielding the lamp from view.

Parallel Circuit – A circuit consisting of two or more parallel paths through which voltage can flow between source and ground.

Parallel vs. Series – Wiring configurations for ballasts. Ballasts with parallel lamp circuitry have the benefit of companion lamps remaining lit, even if one of the lamps operated by the ballast should fail. Systems with series lamp wiring (magnetic ballasts and many rapid start electronic types) result in all lamps operated on the ballast going out if one should fail.

Passive Infrared (PIR) – A device that measures infrared light from objects in its field of view.  Typically used for motion and occupancy sensors.

Path Light – Fixtures and lights used for pathway illumination.

Pendant – A free-hanging light fixture.

Phosphor – A substance that exhibits luminescence, usually caused from exposure to ultraviolet light.

Photocell – A transducer used to detect and measure light and other radiations.

Photometry – The science of measuring visible light in units that are weighted according to the sensitivity of the human eye known as the Visual Wavelength factor. Photometric theory does not address how we perceive colors.

Photo-Optic Specialty Lamps – Photo-Optic specialty lamps employ a variety of technologies to meet the very precise levels of performance required by the entertainment industry, science, medical and other high-tech fields.

Photopic Vision – The vision of the eye in well-lit conditions which allows for higher color perception.

Picture Light – A light fixture or luminaire used to illuminate pictures and other flat artistic works.  This fixture can be mounted to the frame, wall or ceiling above the object.

PL Lamp – Another term for a twin-tube CFL.

Polarized Plug – An electrical plug which features two different sized blades to ensure a single orientation for socket insertion.  A polarized plug is used on devices with set positive and negative sides.

Polycarbonate – A temperature and tamper-resistant plastic used in multiple applications.  Used often in lighting fixtures for high durability and excellent light transmission.

Portable Lamp – A luminaire that can be moved from place to place with relative ease.  Examples include table, floor, and desk lamps.

Power – The rate at which energy is taken from an electrical system or dissipated by a load, expressed in watts (W); power that is generated by a utility is typically expressed in volt-amperes (VA).

Power Factor – A measure of the effectiveness with which an electrical device converts volt amperes to watts; devices with power factors (>0.90) are “high power factor” devices.

Power Failure Memory – A feature of dimming controls that ensures the last selected light level will be preserved after a power outage.

Preheat – A class of fluorescents requiring a starter, which allows the lamp and filaments to be properly heated before allowing the ballast to supply the correct current flow.

Prismatic Lens – Uses perpendicular ribs along one side of the lens to send light in all directions evenly.  Also known as a spread lens.

Product Number – (See NAED.)

Programmed Start (PS) – A method of starting fluorescent lamps where cathode heat is applied prior to lamp ignition then removed or reduced once the lamp has ignited. Programmed Start ballasts maximize the number of lamp starting cycles while maintaining energy efficiency. This is the preferred mode of lamp starting for applications with occupancy sensors and several on/off cycles per day. Additionally, the lamps will strike reliably in cold conditions down to 0°F. This type of ballast may also be referred to as Programmed (Rapid) Start.

Quartz Halogen Lamp – See Halogen Lamp.

Quick Connector – A plastic wire connector with metal contacts on the insides.  Used to splice wires or create simple electrical connections by pushing an exposed or uninsulated wire into the connector.

R Lamp – A Reflector Lamp.

Radio Frequency Interference – Radio interference caused by high-frequency devices such as electronic ballasts.

Rapid Start (RS) – Rapid start ballasts apply a low filament voltage to preheat the cathodes. Simultaneously, a starting voltage (lower than that used in instant start) is also applied to strike the arc. When the cathodes are hot enough, the lamp will strike. The filament voltage continues to be applied throughout the operation of the lamp. Rapid start ballasts appear to have a slight turn on delay compared to instant start. They will typically not be able to start lamps reliably under 50°F.

Rated Average Life – The length of operation (in hours) at which point an average of 50% of a large sample of lamps will still be operational and 50% will not.

Receptacle – Reception point of an electrical outlet for power source.  Typically includes multiple sockets and a connection for grounding.

Recessed Downlight – A ceiling light which is recessed into rather than mounted to or hung from the ceiling.  Recessed lights typically consist of a housing, reflector, and trim, although many include a lens as well.

Reflectance – The ratio of reflected to source light on an object.

Reflection – Effect where light bounces off of another medium such as water or a mirror.

Reflector – A device used to redirect the light by the process of reflection. Photo-Optic reflector lamps utilize ellipsoidal (converging light rays) or parabolic (collimating light rays) reflectors. Dichroic coated reflectors are designed to reflect visible light and pass through unwanted infrared wavelengths.

Reflector Lamp – A conical incandescent lamp with an internal reflector on the base and sides of the envelope.  The reflective surface focuses light from the filament in a single direction.

Refraction – The bending of light as it passes through another medium.

Refractor – A transparent medium that refracts (bends) light.

Resistance (R) – A measure of resistance to flow of current, expressed in ohms (O).

Restrike Time – Amount of time taken by an HID lamp to reach full brilliance after having been turned off.

Retrofit – Replacing older equipment with better or more efficient devices.

RFI Suppression – A feature of dimming controls that reduces the amount of Radio Frequency Interference (RFI) caused by using solid-state dimmers near AM radios, telephones, intercoms and other RFI-sensitive radio components.

Reflector Luminaire Manufacturer (RLM) – A fixture designed to project light in only a downward direction.

Rope Light – A string of bulbs (either LED or incandescent) connected within a clear plastic tube.

Sconce – A candle or light source holder that is usually attached to a wall with an ornamental bracket.

Scotopic Vision – Vision of the eye when in low light conditions.

Seasonal Affective Disorder (SAD) – Seasonal depression that occurs at the same time every year.  Believed to be related to the lack of natural light exposure during the winter season.

Security Lighting – Outdoor lighting used to illuminate for safety purposes.  Security lighting consists of flood lights and street lamps and typically includes some kind of motion or occupancy sensor.

Self-Luminous Exit Sign – A non-electrical emergency-exit sign.  Self-luminous signs use a tritium gas to trigger luminescence from a phosphor-coated glass.

Semi-Specular – A reflective surface with a higher diffusion of light than fully reflective surfaces.

Series Circuit – A circuit where every component is connected in a linear manner between source and ground

Shielding – A general term to include all devices used to block, diffuse or redirect light rays, including baffles, louvers, shades, diffusers and lenses.

Shielding Angle – The horizontal angle through a fixture from which the lamp is visible.

Silhouetting – Lighting technique where an object is purposely silhouetted against a light source.

Single-Ended – Lamps having a single lamp base or point of electrical connection.

Single Pole Switch – A type of switch or lighting control that controls an outlet or lighting fixture from a single location.

Sky Glow – Reduction in night-sky visibility due to light pollution.  The hazy glow caused by excess light reflected into the sky above a city.

Snoot – A hollow cone with a high cut-off angle to reduce the beam angle of track lights, landscape lights, and spotlights.

Socket – The receiving point for an electrical plug or light bulb.  A socket can be any hollow space designed to fit a specific object.

Solid State Lighting (SSL) – Lighting technology that uses a semiconductor, organic, or polymer light-emitting diode (LED) to generate light.

Spacing Criterion – ISENA term which indicates the largest ratio of luminaire spacing to mounting height for maintaining even illumination of the work plane.

Sparkle Lighting – A light source which generates aesthetically beautiful sparkles, such as a star-filament bulb or chandelier.

Spectral Power Distribution (SPD) – A curve illustrating the distribution of radiant power produced by the lamp, at each wavelength across the spectrum.

Specular Reflection – A standard reflection, as seen in mirrors or extremely polished surfaces.

Spill Light – Excess light spilling behind an spotlighted object.

Splice – A connection between two or more wires using a splice connector or terminal.

Spotlight – A luminaire using halogen/incandescent or a high intensity discharge (HID) lamp that produces a narrow beam angle designed to illuminate a specifically defined area. It can also be called a reflector lamp.

Spread Lens – See Prismatic Lens.

Starter – Electrical device used with a ballast for fluorescent or HID lamps.  The starter is used for the initial electric discharge before voltage regulation by the ballast.

Starting Temperature (Minimum) – The minimum ambient temperature at which the lamp will start reliably.

Starting Temperature (Maximum) – The maximum ambient temperature at which the lamp will start reliably.

Step Light – Low profile light fixture used to illuminate steps are stairs.

Sulfur Lamp – An electrodeless lamp which uses a sulfur-based plasma.

Tandem Wiring – Wiring two or more lamps or luminaires to a single ballast.

Task lighting – Lighting designed for a specific visible operation which requires higher light levels; most often characterized by proximity to that task.

TCLP Test (Toxicity Characteristic Leaching Procedure) – Federal EPA regulations (RCRA of 1990) have defined a TCLP test to determine whether wastes are to be treated as hazardous or non-hazardous.

Terminal Block – A fixed block of connection points for wires.  Allows for easy installation and removal of new devices within a system.

Three-Way Lamp – A light fixture which uses a 3-way light bulb to produce multiple light levels (low, medium, and high) without the use of a dimmer.

Three Way Switch – A type of switch or dimming control that is wired in tandem with another switch to control an outlet or lighting fixture from two locations.

Torchiere – A torch lamp, typically constructed as a lamp built onto a tall stand of wood or metal.

Total Harmonic Distortion (THD) – A measure of the distortion of an electrical wave form. Excessive THD (defined by ANSI as greater than 32%) may cause adverse effects to the electrical system. <20% THD ballasts are fine for most applications. However, in buildings with neutral problems caused by high THD loads such as computers, printers, DC supplies, etc., the <10% THD products can help reduce the overall % of Total Harmonic Distortion.

Total Life Hours – The total lifespan of an LED (Light Emitting Diode), usually 100,000 hours.

Track Lighting – A series of adjustable light fixtures suspended from a mounting rail or track.

Transformer – An electrical device by which alternating current of one voltage is changed to another voltage

Translucent – A material or object that is not transparent but allows light to pass through in a diffused manner, frosted glass is a translucent material.

Transmit – For waves and the electromagnetic spectrum, transmission consists of passing through a medium (such as glass or air) without changes in color.

Transparent – A clear material that transmits all or most of the light that hits it, without distortion.

Trigger Start – A circuit used to eliminate the starter and start the preheat lamp almost instantly. In this circuit each electrode is connected to a separate winding in the ballast so that the electrode is continuously heated.

Troffer – A recessed ceiling luminaire, larger than typical round or square can lights and designed to house fluorescent tubes.

Tube – The outer envelope of some lamps use a tube shape in place of a bulb.

Tungsten – A metallic element, symbol W with an atomic number of 74, that has a high melting point which makes it the best candidate for use a filament in incandescent lamps.

Tungsten Halogen Lamp – See Halogen Lamp.

Twin Tube – A compact fluorescent lamp which uses two parallel tubes for illumination.

U-Bend Lamp – A fluorescent lamp with a U-shaped glass tube

Ultraviolet Radiation (UV) – Wavelength of ultraviolet radiation that is outside of the human visual spectrum.  This is light with a wavelength between 400 and 100 nm.

Underwriters Laboratories (UL) – An independent science company which tests new products for safety and efficiency to provide a measurable system of standards and ratings for electrical devices.

Uniformity – The degree of variance in lighting over a given plane.  Higher uniformity means fewer variances in the light pattern.

Uplight – A light fixture or luminaire where the majority of the light source is projected at or above 90 degrees from the floor (up).

Uplighting – A technique using light directed upward for special effect on a room (to cancel out cave effect, to to add floor shadows, or to create a more intimate environment for example).

Usable Light Hours – The life of an LED (Light Emitting Diode) before light output is significantly reduced, usually 50,000 hours.

Valance Lighting – Light fixture built into a horizontal shield mounted above a window or at the top of a wall.  The lamp illuminates as both an up and a downlight.

Vandal Resistant – A light fixture that is resistant to damage and tampering.  Vandal resistant lights are usually made of a heavy-gauge metal and polycarbonate plastic diffuser.  The light source inside is protected from theft and damage since access is locked.  These fixtures are usually found in public spaces where vandalism is common.

Vanity Light – A light positioned around a mirror, usually paired with an opposing light.

Vapor-Tight Luminaire – Completed enclosed fixture with some form of sealing gasket to keep out vapors such as water or gas.

Visual Comfort Probability (VCP) – The percentage of observers who will find the glare from a lighting system to be acceptable. The higher this number, the more acceptable the system.

Very High Output (VHO) – A fluorescent lamp with a higher lumen output due to increased current draw.

Volt – The SI Unit for Voltage.

Voltage (V) – A measure of electrical potential, expressed in volts (V). Voltage is the “force” that pushes electrical current through a conductor.

Voltage Drop – The amount of voltage expended across a single component or device in a circuit.

Volumetric Troffer – A troffer fixture that distributes light more evenly than traditional troffers in order to eliminate the glare and the cave effect associated with parabolic troffers.

Wall Grazing – Using lighting to create dynamic accents out of light and shadows on a wall.

Wall Sconce – See Sconce.

Wall Washing – A lighting technique that evenly illuminates a wall.

Warranty – A statement of manufacturer warranty. Please see Customer Service page for more information.

Watt (W) – A unit of electrical power equal to 1 joule per second. Lamps are rated in watts to indicate power consumption. Also see Nominal watts.

Wattage – Amount of electrical power used across a specific device, component, or piece of equipment.

Wavelength – Distance between two successive points of a periodic wave; the wavelengths of light are typically expressed in nanometers (nm), or billionths of a meter.

Wire Nut – A screw-on cap used to easily splice two wires together.

Work Plane – The plane on which a task is performed.  Area illumination is designed around this horizontal plane.

Xenon Lamp – An incandescent lamp which uses xenon gas within the envelop to lengthen the average life the lamp.  Unlike halogen lamps, touching the bulb will not damage the lamp since xenon lamps operate at a cooler temperature than halogens.