Glossary of Lighting Terms - Lampetia

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We've compiled a list of terms and their definitions to better help you navigate the sometimes confusing world of Lighting.

We include in this glossary of definitions for a number of the basic Lighting terms and words used in the home, commercial lighting, horticultural lighting and light therapy community. For further information and formal definitions, see discussions in standard dictionaries, encyclopedias, the IES Lighting Handbook, and other lighting industry books.

Note that some of these definitions are quite subjective, and are offered here as a guidance, not as a formal definition.


A-bulbs: Is a standard. That's a regular light bulb. It can have either a little base, called a C or candelabra base or a bigger base called either an E or Edison base or an M or medium base. There are also intermediate or European base sockets. (If you have one of these, go buy an adapter. A little metal ring that goes into the socket will make a C base bulb fit and then you won't have to go searching for bulbs anymore).

Accent Lamp: Portable lamp that usually has a shade from 9" to 14" wide and height no taller than 24".

Accent Lighting: Is lighting that emphasizes an area of or an object in a room. This lighting adds to the drama or style of a room by highlighting certain aspects of a room's decor.

Adaptation: The process by which the retina of the eye becomes accustomed to more or less light than it was exposed to during an immediately preceding period. It results in a change in the sensitivity of the eye to light.

Adjustable Lamp: Portable lamp that has an adjustable height or width or shade position.

Alternating Current (AC): Electron flow that periodically reverses polarity and direction of travel through a circuit.

Ambient Lighting: The general lighting present in an area excluding task lighting and accent lighting but including general lighting and daylight streaming in.

Ampere (amp): A standard unit of measurement of electrical current. Amps = Watts/ Voltage.

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

Arc Tube: A completely sealed quartz or ceramic tube where the electrical discharge (arc) occurs and light is generated.

Argon: Inert gas used in incandescent and fluorescent lamp types. In incandescent light sources, argon retards evaporation of the filament.

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.


Baffle: A single opaque or translucent element to shield a source from direct view at certain angles, or to absorb unwanted light.

Ballast: A device that, by means of resistance, inductance, capacitance or electronic elements, singly or in combination, controls the current, voltage and waveform to the required values for proper lamp starting and operation. An auxiliary piece of equipment required to start and to properly control the flow of current to gas discharge light sources such as fluorescent and high intensity discharge (HID) lamps. Typically, magnetic ballasts (also called electromagnetic ballasts) contain copper windings on an iron core while electronic ballasts are smaller and more efficient and contain electronic components.

Ballast Characteristic Curve: The curve of lamp wattage vs. lamp voltage over a range of normal lamp voltages when a HID ballast is operated at a given supply voltage.

Ballast Efficacy Factor (BEF): Defined as ballast factor divided by input watts. The value is used to evaluate various lighting systems based on light output and power input. The BEF can only be used to compare systems operating the same type and quantity of lamps.

Ballast Factor (BF): This is the percentage of a lamp's rated lumen output that can be expected when operated on a specific, commercially available ballast. Note that the "rated output" is sometimes measured on a reference ballast unlike ones that actually operate the lamp in the field.

Ballast Power Factor: Power consumed by the lamp and ballast (watts) divided by the product of line voltage and line current (‘volt-amps’ or ‘VA’); It is a measure of power quality and of concern to utilities.

Ballast Hum: Sound generated by the vibration of laminations in the iron core of the transformer or inductor present in the ballast.

Ballast Losses: Power or energy dissipated in the ballast as heat and not converted to lamp energy.

Bankers Lamp: Portable desk lamp with an oblong shade that is usually adjustable.

Base: Stabilizing body of a lamp constructed from various materials such as metal, brass, porcelain, resin or wood.

Base or Socket: The socket is the receptacle connected to the electrical supply; the base is the end of the lamp that fits into the socket. There are many types of bases used in lamps, screw bases being the most common for incandescent and HID lamps, while bi-pin bases are common for linear fluorescent lamps. Sample Base Types.

Base Temperature (Maximum): The maximum operating temperature permitted for the base in Celsius. Fixture manufacturers need to ensure that these conditions are satisfied in their fixture.

Bayonet: A style of bulb base which uses keyways instead of threads to connect the bulb to the fixture base. The bulb is locked in place by pushing it down and turning it clockwise.

Beam Angle: 
1.) 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).

2.) The angular dimension of the cone of light from reflectorized lamps (such as R and PAR types) encompassing the central part of the beam out to the angle where the intensity is 50% of maximum. The beam angle sometimes called "beam spread" is often part of the ordering code for the reflectorized lamps. Example: The 50PAR30/HIR/NFL25 is a 50 watt PAR30 narrow flood lamp with a beam angle of 25 degrees.

Beam Lumens: The total lumens present within the portion of the beam contained in the beam angle.

Beam Spread (in any plane): The angle between the two directions in the plane in which the candlepower is equal to a stated percent (usually ten percent) of the maximum candlepower in the beam.

Beveled Glass: Clear glass, with edges that have been ground and polished to an angle other than 90 degrees.

Billiard or Oblong Pendant: Rectangular or oval shaped shade that is typically suited for suspension over a billiard table, kitchen island or counter.

Bi-Pin: Any base with two metal pins for electrical contact. This is the typical base for a fluorescent tube of 1 to 4 feet in length. It consists of 2 prong contacts which connect into the fixture. Medium bi-pins are used with type T-8 and T-12 tubular fluorescent lamps, and miniature bi-pins are used for tubular T-5 fluorescent lamps.

Blackbody: A hot body with an incandescent black surface at a certain temperature used as a standard for comparison. Note that a black surface is the best radiator possible. A tungsten filament will emit slightly less radiation than a blackbody at the same temperature.

Black Light: A popular term referring to a light source emitting mostly near UV (320 to 400 nm) and very little visible light.

Blacktop: Whether or not the top of the miniature lamp has a blacktop coating. The coating is used to control unwanted brightness or glare.

Bollard: A short, thick post with a light at its top, used for grounds and outdoor walkway lighting.

Bottom Exit (BE): (LFL plug-in ballasts) A configuration with leads or a wire-trap on the bottom or base of the ballast. This type of configuration is usually used when the ballast is mounted onto a junction box plate. Bottom Exit Studs (BES): (LFL plug-in ballasts) A configuration with screw studs mounted on the base plate or bottom of the ballast. The screws are 3/8" inches long with a #8-32 thread size (#8-32 nut). They are mounted on a two inch center. The studs are usually used to mount the ballast directly onto a junction box plate.

Bulb: A loose way of referring to a lamp. "Bulb" refers to the outer glass bulb containing the light source.

Bulb Darkening: The darkening or discoloration of an incandescent lamp due to tungsten particles collecting on the inside of the glass as the filament burns and diminishes over its life.

Bulb finish: The coating, if any, that is applied to the inside surface of the bulb. Finishes are either clear, phosphor coated, or diffuse.

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

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

Bulging Reflector (BR): May be used as a substitute for incandescent R lamps. They are also not to be used outside in open fixtures.

Burning Position: The position or orientation in which lamps operate.

Bridge Arm Lamp: Table or floor lamp with an arm supporting a single shade.

Brightness: Brightness can refer to any of several technical terms used in lighting and is, therefore, ambiguous (See LUMINANCE).

BTL: The distance from ballast to lamp.

Buffet Lamp: Portable lamp, usually tall and slender and suitable for use on a buffet, with height generally no taller than 36".


Canadian Energy Standards: Indicates ballast complies with Canadian Energy Standards and meets the requirements of CAN/CSA C654-M91.

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

Candela: Unit measurement of luminous intensity.

Candela (cd): The measure of luminous intensity of a source in a given direction. The term has been retained from the early days of lighting when a standard candle of a fixed size and composition was defined as producing one candela in every direction. A plot of intensity versus direction is called a candela distribution curve and is often provided for reflectorized lamps and for luminaires with a lamp operating in them.

Candlepower: An obsolete term for luminous intensity; current practice is to refer to this simply as candelas.

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.

Candlepower Distribution Curve: A curve, generally polar, representing the variation of luminous intensity of a lamp or luminaire in a plane through the light center.

Canopy: The part of a fixture that mounts to the ceiling or wall and covers the junction box to which the fixture attaches.

Cathedral Glass: Transparent single color sheet glass, with smooth or textured surfaces. Chandelier Surface mounted ceiling fixture with lighted arms.

Cathode: Metal filaments that emit electrons in a fluorescent lamp. Negatively charged free electrons emitted by the cathode are attracted to the positive electrode (anode), creating an electric current between the electrodes.

Cathode Guard: Metal band encircling the cathode of a fluorescent lamp, used to collect the evaporating particles from the cathode, greatly reducing end-blackening.

Cathode Resistance: Resistance of the cathode in a Fluorescent lamp. It is measured "cold" before the lamp is turned on (Rc) or "hot" after the lamp is turned on (Rh). The ratio of the hot resistance to the cold resistance is also measured (Rh/Rc).

CCT: Correlated color temperature; a measure of the color appearance of a white light source. CCT is measured on the Kelvin absolute temperature scale. White lighting products are most commonly available from 2700K (warm white) to 5000K (cool white).

Center Beam Candlepower (CBCP): Refers to the luminous intensity at the center of the beam of a blown or pressed reflector lamp (such as a PAR lamp). Measured in candelas.

Ceramic Metal Halide (CMH®): A type of metal halide lamp that uses a ceramic material for the arc tube instead of glass quartz, resulting in better color rendering (>80 CRI) and improved lumen maintenance. GE ConstantColor® CMH® lamps feature a 3-piece arc tube design that delivers excellent color consistency and lamp reliability.

CFL Light Bulbs: Compact Fluorescent Lighting, creates light by passing electricity through a tube containing gases. This reaction produces ultraviolet light that is transformed into visible light by the phosphor coating inside the tune.  CFLs use approximately 50 to 80% less energy than incandescent bulbs and last 10 times as long. They also run 75% cooler. CFL bulbs contain mercury, which is considered a toxic metal. While present in small amounts, burned out or broken bulbs must be treated as hazardous  waste material when disposed of. 

ChromaFit: A GE brand name for metal halide lamps designed to operate on HPS ballasts, allowing a user to switch from the yellowish color of HPS to the white color of metal halide without changing ballasts. These products are available in both quartz metal halide and ceramic metal halide (CMH) versions.

1.) Measure to identify the color of a light source, typically expressed as (x,y) coordinates on a chromaticity chart (See COLOR TEMPERATURE).

2.) The dominant or complementary wavelength and purity aspects of the color taken together, or of the aspects specified by the chromaticity coordinates of the color taken together. It describes the properties of light related to hue and saturation, but not luminance (brightness).

3.) The aspect of color that includes consideration of its dominant wavelength and purity.

CIE: Abbreviated as CIE from its French title Commission International de l'Eclairage, the International Commission on Illumination is a technical, scientific, and cultural organization devoted to international cooperation and exchange of information among its member countries on matters relating to the science and art of lighting.

Circle E: Designates a ballast meets or exceeds the requirements of Public Law 100-357 establishing standards of efficiency.

Class P Thermal Protector: A switching device sensitive to current and heat that automatically disconnects ballast if the temperature exceeds UL temperature limitations.

Coefficient of utilization (CU): Coefficient of utilization is the ratio of the luminous flux (lumens) received on a plane to the light output (lumens) of the lamps. Coefficient of utilization depends on luminaire efficiency, distribution of light from the luminaire, size and shape of the room, and reflectance of surfaces in the room. Specifies use the coefficient of utilization to evaluate how effectively a luminaire delivers light to a work plane.

Coil: Windings of copper or aluminum wire surrounding the steel core in ballast. Also refers to the entire assembly comprising the inductor or transformer.

Compact Fluorescent Lamp (CFL): The general term applied to fluorescent lamps that are single-ended and that have smaller diameter tubes that are bent to form a compact shape. Some CFLs have integral ballasts and medium or candelabra screw bases for easy replacement of incandescent lamps (See INTEGRAL, SELF-BALLASTED LAMPS).

Cold Start Time: The amount of time from the application of ballast voltage to ignition of the arc discharge.

Color appearance: The resultant color perception that includes the effects of spectrum, background contrast, chromatic adaptation, color constancy, brightness, size and saturation.

Color consistency: The measure of how close in color appearance random samples of a lamp or source tend to be.

Color Corrected: Refers to a lamp with a special phosphor or coating to give it a color rendering profile like natural daylight.

Color matching: The action of making a color appear the same as a given color. Often used as a method of evaluating the ability of a light source to render colors faithfully.

Color Rendering: A general expression for the effect of a light source on the color appearance of objects in conscious or subconscious comparison with their color appearance under a reference light source.

Color Rendering Indicator: Draws attention to the fact that this is a lamp with high color rendering, which helps objects and persons illuminated to appear more true to life.

Color Rendering index (CRI):
 1.) Unit: Ra, A measure of a light source’s ability to render colors relative to a standard of 100. A rating index commonly used to represent how well a light source renders the colors of objects that it illuminates. For a CRI value of 100, the maximum value, the colors of objects can be expected to be seen as they would appear under an incandescent or daylight spectrum of the same correlated color temperature (CCT). Sources with CRI values less than 50 are generally regarded as rendering colors poorly, that is, colors may appear unnatural. On a scale of 0 - 100, the higher the number, the better the color rendering. Select a lamp with CRI of 85+ where color matching/selection is occurring, such as vanity lighting and closets; 80+ for pleasant appearance of people and food, such as in the kitchen and living room; 70+ for office areas; 50+ for work areas, garage and storage areas.

2.) A measurement to rate a lamps ability to render an objects color. The higher the CRI, on a scale of 0-100, the more true to life colors appear, as they would in natural daylight.

Color rendition: How colors appear when illuminated by a light source. Color rendition is generally considered to be a more important lighting quality than color temperature. Most objects are not a single color, but a combination of many colors. Light sources that are deficient in certain colors may change the apparent color of an object. The Color Rendition Index (CRI) is a 1–100 scale that measures a light source's ability to render colors the same way sunlight does. The top value of the CRI scale (100) is based on illumination by a 100-watt incandescent light bulb. A light source with a CRI of 80 or higher is considered acceptable for most indoor residential applications.

Color shift: The change in a lamp’s correlated color temperature (CCT) at 40% of the lamp’s rated life, in kelvin (K).

Color Spectrum: The visible light spectrum, ranging between 380 (violet) and 770 (red) nanometers in the electromagnetic spectrum.


Color stability: The ability of a lamp or light source to maintain its color rendering and color appearance properties over its life. The color properties of some discharge light sources may tend to shift over the life of the lamp.

Color Spectrum: The visible light spectrum, ranging between 380 (violet) and 770 (red) nanometers in the electromagnetic spectrum.

Color Temperature:  Unit K (Kelvin), the actual color of a light source, also referred to as Correlated Color Temperature (CCT), measured in degrees Kelvin (K). Commonly referred to as Kelvin temperature, color temperature is the visual warmth or coolness of a lamp. The lower the Kelvin temperature, the visually warmer the color; the higher the Kelvin temperature, the visually cooler the color. A lamp with a Kelvin temperature of 2700K is considered a warm source (Warm White). Lamps with a Kelvin temperature of 4100K and higher are considered cool sources (Cool White).

Typical color temperature are: 

  • 2700K Incandescent
  • 3000K Halogen
  • 3500K Fluorescent - Warm White
  • 4100K Fluorescent - Cool White
  • 5000K Fluorescent - White Light (white with a little blue)
  • 6500K Fluorescent - Daylight 

The color of the light source. By convention, yellow-red colors (like the flames of a fire) are considered warm, and blue-green colors (like light from an overcast sky) are considered cool. Color temperature is measured in Kelvin (K) temperature. Confusingly, higher Kelvin temperatures (3600–5500 K) are what we consider cool and lower color temperatures (2700–3000 K) are considered warm. Cool light is preferred for visual tasks because it produces higher contrast than warm light. Warm light is preferred for living spaces because it is more flattering to skin tones and clothing. A color temperature of 2700–3600 K is generally recommended for most indoor general and task lighting applications.

Color Temperature (Correlated Color Temperature-CCT): A number indicating the degree of "yellowness" or "blueness" of a white light source. Measured in kelvins, CCT represents the temperature an incandescent object (like a filament) must reach to mimic the color of the lamp. Yellowish-white ("warm") sources, like incandescent lamps, have lower color temperatures in the 2700K-3000K range; white and bluish-white ("cool") sources, such as cool white (4100K) and natural daylight (6000K), have higher color temperatures. The higher the color temperature the whiter, or bluer, the light will be (See CHROMATICITY).

Color variation: Lamps of the same type made by the same manufacturer may exhibit a certain degree of variation in color, even when operated under the same conditions and seasoned for the same about of time.

Combined uncertainty: Combined uncertainty is calculated by finding the sum of the squares of sample random variability (standard deviation) and laboratory measurement uncertainty and taking the square root of that sum.

Compact Fluorescent Lamp (CFL): The general term applied to fluorescent lamps that are single-ended and that have smaller diameter tubes that are bent to form a compact shape. Some CFLs have integral ballasts and medium or candelabra screw bases for easy replacement of incandescent lamps.

Compatible ballasts: An abbreviated list of common ballasts that will provide the necessary circuitry for a photo sensor to operate correctly. Other ballasts may also be compatible; contact the photo sensor manufacturer for details.

Conduction: The process of removing heat from an object via physical contact with other objects or materials, usually metals.

Constant Color®: A GE Registered name for lamp families which show very little color shift over life. Generally applies to GE's PRECISE MR-16 and GE's CMH (Ceramic Metal Halide) lamps.

Constant-wattage autotransformer (CWA): The most common type of ballast used for HID lamps, it maintains a constant power (wattage) supply to the lamp when system input voltage fluctuates. A magnetic autotransformer lead ballast circuit incorporating a capacitor in series with the lamp; compared to other ballasts, the CWA regulates over a wider input voltage range, holding lamp current nearly constant.

Constant Wattage Isolated (CWI) Ballast: A magnetic lead ballast circuit incorporating a fully-isolated secondary winding; it has a capacitor in series with the lamp and the same performance features as the CWA ballast

Continuous dimming: Control of a light source's intensity to practically any value within a given operating range.

Continuously variable signal: A signal that communicates data that can have a theoretically unlimited number of possible values between two end points. Examples include voltage, temperature, and il luminance.

Contrast: Also known as luminance contrast, it is the relationship between the luminance of an object and its immediate background.

Control signal range: The range of the electrical signal (in volts) that a control device uses to signal the dimming level to a ballast.

Convection: The process of removing heat from an object through the surrounding air.

Cool White: A term loosely used to denote a color temperature of around 4100 K. The Cool White (CW) designation is used specifically for T12 and other fluorescent lamps using halo phosphors and having a CRI of 62.

Copper foil: Narrow strips of copper tape used to wrap the edges of glass pieces that have been cut to fit a pattern. When wrapped, solder is applied, bonding the glass pieces together.

Core: Component of electromagnetic ballast that is surrounded by the coil. Core is comprised of steel laminations or solid ferrite material.

Core & Coil Ballast: A ballast that uses a "Core & Coil" assembly to operate fluorescent or HID lamps. Refers to copper windings on a steel core.

Correlated color temperature (CCT): The perceived "color" of the light emitted by a lamp expressed in Kelvin (K) units. A specification for white light sources used to describe the dominant color tone along the dimension from warm (yellows and reds) to cool (blue). Lamps with a CCT rating below 3200 K are usually considered warm sources, whereas those with a CCT above 4000 K usually considered cool in appearance. Temperatures in between are considered neutral in appearance. Technically, CCT extends the practice of using temperature, in kelvins (K), for specifying the spectrum of light sources other than blackbody radiators. Incandescent lamps and daylight closely approximate the spectra of black body radiators at different temperatures and can be designated by the corresponding temperature of a blackbody radiator. The spectra of fluorescent and LED sources, however, differ substantially from black body radiators yet they can have a color appearance similar to a blackbody radiator of a particular temperature as given by CCT.

Cost of Light: Usually refers to the cost of operating and maintaining a lighting system on an ongoing basis. The 88-8-4 rule states that (typically) 88% is the cost of electricity, 8% is labor and only 4% is the cost of lamps.

Cove Lighting: Refers to light sources mounted above a ledge or in a recess that distribute light upward for ambient lighting. Light built into a cove, a shelf or ledge at the upper part of a wall, to illuminate the ceiling. Typically fluorescent, cold cathode or low voltage strip.

CovRguard®: A special plastic shielding on the outside of tubular fluorescent lamps that effectively contains shattered glass particles if the lamp is broken. Such protection is mandated in many industries and locations, e.g. food packaging.

Crest Factor (Lamp Current Crest Factor): Ratio of peak to RMS for any AC waveform. Crest factor can refer to voltage crest factor or current crest factor.

CRI: Color rendering index; a measure of how a light source renders colors of objects, compared to a “perfect” reference light source. CRI is given as a number from 0 to 100, with 100 being equivalent to the reference source. Lumen Maintenance – the percentage of initial light output produced by a light source at some percentage of rated useful life (usually 100% for LED and 40% for source types characterized by sudden failure).

Current (I): A measure of the flow of electricity, expressed in amperes (A).

Current Crest Factor: The ratio of the peak-to-rms value of lamp current; metal halide magnetic ballast values range from 1.5 to 1.8.

Current Type (AC/DC): Whether the operational voltage is based on Alternating Current or Direct Current.


Damp Location: UL listing for fixtures used in a moist unexposed area, such as a bathroom or porch area.

Daylight: Is the combination of all direct and indirect sunlight outdoors during the daytime (and perhaps twilight). This includes direct sunlight, diffuse sky radiation, and (often) both of these reflected from the Earth and terrestrial objects.

Daylight Harvesting: Lighting design for building interiors that makes of daylight as a way of reducing energy consumption.

Dark Sky (IDA): A non-profit member organization that teaches others how to preserve the night sky through factsheets, law references, pictures, and web resources.

Dark-sky movement: The dark-sky movement is a campaign by people who want to reduce light pollution so people can see the stars, to reduce the effects of unnatural lighting on the environment, and to cut down on energy usage.

Daylight Lamp: A lamp resembling the color of daylight, typically with a color temperature of 5500 K to 6500K

Degree of polarization: A measure of the amount of light polarization ranging from 0 to 100 percent.

Department of Transportation (DOT) Type: The US Department of Transportation lamp number stamped in the glass lens or on the base of headlamps.

Design Lumens: Lumen value at 40% of rated average life.

Desk Lamp: Portable lamp, usually with a downward task light.

Diamond Precise®: Diamond Precise is the GE trade name for its line-voltage MR16 ConstantColor® halogen lamp. An integral ballast and a medium screw base enable Diamond Precise lamps to operate on standard (120 volt) circuits. The MR16 technology of Diamond Precise allows a tighter, more intense beam than can be attained by the 50-watt PAR20 and R20 types it's designed to replace, even though the lumen output is significantly less by comparison.

Dichroic Reflector (or Filter): A reflector (or filter) that reflects one region of the spectrum while allowing the other region(s) to pass through. A reflector lamp with a dichroic reflector will have a "cool beam" i.e. most of the heat has been removed from the beam by allowing it to pass through the reflector while the light has been reflected.

Dichroic coating (dichroic filter): A multi-layer coating that transmits certain wavelengths and reflects those not transmitted.

Diffusion: The even redirection or spreading of light by a lens or diffuser.

Diffuse Lighting: Light that is not predominantly incident from any particular direction.

Diffuser material: Diffusers scatter the light from a luminaire in all directions. Most diffusers in commodity residential-grade luminaires are made of plastic, usually acrylic or polycarbonate. Other materials include glass and alabaster.

Dimmable: Whether or not the lamp lumens can be varied while maintaining reliability.

Dimmer, Dimming Control: A device used to lower the light output of a source, usually by reducing the wattage it is being operated at. Dimming controls are increasing in popularity as energy conserving devices.

Dimming ballast: A device that provides the ability to adjust light levels by reducing the lamp current. Most dimming ballasts are electronic.

Direct light: Light emitted by a luminaire in the general direction of the task to be illuminated. The term usually refers to light emitted in a downward direction.

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

Direct luminaire: A luminaire that emits light in the general direction of the task to be illuminated. The term usually refers to luminaires that emit light in a downward direction.

Direct up light: Light emitted upward direction by a luminaire.

Disability glare: A type of glare that causes a loss of visibility from stray light being scattered within the eye.

Discomfort glare: The sensation of annoyance or even pain induced by overly bright sources.

Distance Between Legs: For U-shaped Fluorescent lamps, this measurement is the average distance between the inner walls of the legs.

Distance Between Leg Centers: For U-shaped Fluorescent lamps, this measurement is the average distance between the centers of each leg.

Distance Outside Legs: For U-shaped Fluorescent lamps, this measurement is the average distance to the outside of each leg.

Down Lighting: A directed lighting unit, usually small, that aims the light downward. Can be recessed, surface mounted or suspended.

Dynamic outdoor lighting: Outdoor lighting that varies light level or other characteristics automatically and precisely in response to factors such as vacancy or the type of use of an outdoor location.


ECE R37 Code: European Common Market Regulation 37 standard lamp number.

Eccentricity (Maximum): In High Intensity Discharge lamps the Bulb to Arc Angle is the angle off of center between electrodes and bulb. The Bulb to Base Angle is the angle off of center that the bulb is from the base.

Ecolux®: A term for GE lamps that have reduced mercury content and pass the TCLP test (See TCLP TEST).

Economic Life: Unit: hours,  the hours of operation a lamp is designed to provide in terms of optimum light output, aesthetic quality, and economic energy consumption. The "economic life" of lamps is generally defined as 60% of the lamp’s rated life. For example. outdoor lighting bulbs are designed as 70 percent to the rated life, and indoor lighting bulbs are 80%.

Edison Thomas - In the late 1880s, Nikola Tesla and Thomas Edison became adversaries in part because of Edison's failed promotion of direct current (DC) for electric power distribution over the more efficient alternating current advocated by Tesla and Westinghouse. Until Tesla invented the induction motor, AC's advantages for long distance high voltage transmission were counterbalanced by the inability to operate motors on AC. As a result of the "War of Currents", Shortly before he died, Edison said that his biggest mistake had been in trying to develop direct current, rather than the superior alternating current system that Tesla had put within his grasp.

Efficacy: The ratio of light output (in lumens) to input power (in watts), expressed as lumens per watt (LPW). The light source may be a lamp or luminaire.

Electric Discharge Lamp: A light source that produces light by passing a current between electrodes through a vapor or gas. Includes fluorescent and high intensity discharge lamps.

Electrode preheat current: The current flowing through a lamp's electrodes to heat them during starting.

Electrodes: The structure that serves as the electric terminals at each end of electric discharge lamps.

Electromagnetic interference (EMI): The interference of unwanted electromagnetic signals with desirable signals. Electromagnetic interference may be transmitted in two ways: radiated through space or conducted by wiring. The 

Electronic ballast: A ballast that uses electronic components instead of a magnetic core and coil to operate fluorescent lamps. Electronic ballasts operate lamps at 20 to 60 kHz, which results in 
reduced flicker and noise and increased efficacy compared with ballasts that operate lamps at 60 Hz.

Elliptical Reflector: Incandescent lamp with a reflector shell which is elliptically-shaped. Focuses light immediately in front of the lamp which reduces absorption and increased efficiency.

Emergency options: Refers to options available when exit signs are operated on a non-utility power supply such as a generator, a central battery unit that operates several exit signs, or an individual rechargeable battery. Options include whether or not the exit sign increases the brightness of the light source if the utility-supplied power fails.

End Blackening: Darkening around the ends of a fluorescent tube caused by particles evaporating from the cathode and adhering to the glass. Lamps made with cathode guards greatly reduce this occurrence.

End Foot Candles (EFC): A measure of that portion of the total light output of a T-2 lamp that passes through a .250" orifice placed at the end of the lamp. 

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

Energy Policy Act (EPACT): Energy legislation passed by Congress in 1992 mandating labeling and minimum energy efficiency requirements for many commonly used incandescent and fluorescent lamps.

Energy Survey: Systematic cost comparison of an existing system to a proposed system, accounting for electrical, material, maintenance and labor costs.

Enhancing Reflections: Reflections which enhance appearance described in such terms as sparkling, glittering, etc.

Etch: Markings on the glass envelope or shell of a lamp designating product description, logo and/or brand name.

Etched Glass: The use of hydrofluoric acid or sand blasting to create a matte finish or a specific design on glass.

Exitance: The total light which comes off of a surface. Exitance is dependent upon the illuminance on and reflectance of the surface.

Eyeball: Fixture, usually recessed, which can be rotated to point in a desired direction.

Ewave: A wave composed of perpendicular electric and magnetic fields. The wave propagates in a direction perpendicular to both fields.


Fan Light: A glass shade that can be used on a ceiling fan.

Federal Communications Commission (FCC): Sets electromagnetic interference limits on fluorescent lighting systems in FCC Part 18.

Fenestration: Any opening or arrangement of openings or windows (normally filled with media for light control) for the admission of daylight or for the transmission of electric from one room to another room.

Field of view: The area covered by an occupancy sensor, often reported (for wall-mounted sensors) as a horizontal field of view or (for ceiling-mounted sensors) as the solid angle of the cone-shaped coverage area.

Filament: Wire used in incandescent lamps, usually made of tungsten and often coiled, that emits light when heated by an electrical current.

Filter: A device that allows currents at certain frequencies to pass while those at other frequencies are blocked. Filters reduce conducted electromagnetic waves by grounding the current or by increasing the impedance to a specific frequency.

Finial: Decorative detail on the top of a lamp or the very bottom of a chandelier.

Finish: The decorative color of hardware achieved by painting or plating base or fixture materials.

Fireplace Screen: Decorative screen that covers the opening of a fireplace while not in use.

Fire screen: Functional fireproof screen that covers the opening of a fireplace while in use.

Fixture: A complete lighting unit consisting of lamp or lamps and the parts designed to distribute the light, position and protect the lamp(s), and connect the lamp(s) to the power supply. (Also referred to as luminaire.) - complete lighting unit usually consisting of socket, housing, shade, and connection to electrical power.

Fixture Requirements: The type of fixture a lamp requires; i.e., enclosed or open rated.

Fixture: See luminaire.

Flicker: A rapid and continuous change in light levels caused by the modulation of the light output from fluorescent lamps.

Floodlight: A reflectorized lamp whose emitted beam pattern is enlarging. Also a luminaire consisting of lamp and reflector at fixed distance providing a wide field of illumination. 

Floor Lamp: Portable lamp with a shade that directs light downward and a height usually taller than 48".

Fluorescent Lamp: A low pressure mercury electric discharge lamp, tubular in shape in which a fluorescent coating (phosphor) transforms ultraviolet energy into visible light.

Flush mount: Surface mounted ceiling fixture with three inches or less between the shade and the ceiling.

Foot candle (fc): A unit of illuminance equal to 1 lumen per square foot. he unit is defined as the amount of illumination the inside surface of a 1-foot radius sphere would be receiving if there were a uniform point source of one candela in the exact center of the sphere.

Formed Body Arc Tube: Precisely reproducible ellipsoidal arc tube formed by pressurizing molten quartz inside a mold; produces arc tubes with higher efficacy and improved color uniformity.

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).

Full cutoff luminaire: IESNA classification that describes a luminaire having a light distribution in which zero candela intensity occurs at or above an angle of 90° above nadir. Additionally, the candela per 1000 lamp lumens does not numerically exceed 100 (10%) at or above a vertical angle of 80° above nadir. This applies to all lateral angles around the luminaire.

Full Spectrum: Broad spectrum light source capable of producing colors throughout the entire range of the visible spectrum; simulating actual sunlight. High CRI's and Kelvin temperatures ranging between 5500 and 5900.

Full-spectrum color index (FSCI): A mathematical transformation of full-spectrum index into a zero to 100 scale, where the resulting values are directly comparable to color rendering index. An equal energy spectrum is defined as having an FSCI value of 100, a “standard warm white” fluorescent lamp has an FSCI value of 50, and a monochromatic light source (e.g., low pressure sodium) has an FSCI value of 0.

Full-spectrum index (FSI): A mathematical measure of how much a light source's spectrum deviates from an equal energy spectrum, based on the slope of its cumulative spectrum.

Fully shielded luminaire: A luminaire that emits no direct up light, but which has no limitation on the intensity in the region between 80° and 90°.

Fundamental: The component of a periodic wave that has the lowest frequency. It is also called the first-order harmonic.


Gamut area: A measure of color rendering based upon volume in color space. It is the range of colors achievable on a given color reproduction medium (or present in an image on that medium) under a given set of viewing conditions.

Gas-discharge lamps: An electric lamp that produces light from gas atoms excited by an electric current.

GE Edison™: GE's trademark for a wide range of lighting products.

GE Edison Award: An annual competition where lighting designers submit their best projects. The entries are judged by an international panel and awards are presented at a banquet accompanying Light Fair, the North American trade show for the lighting industry.

General Lighting: Designed to provide a substantially uniform illuminance throughout an area, exclusive of any provision for special local requirements.

Glare: The sensation produced by luminance within the visual field that are sufficiently greater than the luminance to which the eyes are adapted, which causes annoyance, discomfort, or loss in visual performance and visibility.

Glass Jewel: Piece of hot glass that is press-molded into a jewel like shape.

Glow current: The flow of electrons away from a rapid-start lamp's electrodes during preheating. The higher the glow current, the faster the electrodes' emissive coating degrades, increasing lamp-end darkening and reducing lamp life.

Glue Chip Glass: Texture created on the surface of glass by applying hot glue, which after drying contracts and chips the glass surface resulting in a natural pattern, like frost on a window pane.

Granite Glass: A texture with the appearance of granite that is applied to hot glass sheets with an embossed roller.

Grounded: A circuit or metal object that is connected to the earth at one or more points. Done mostly for safety, grounding also reduces electromagnetic waves.


Halo-phosphors: Also referred to as halophosphates. Phosphors are the white powder inside fluorescent lamps that fluoresces (emits visible light) when excited by the ultraviolet radiation produced by the mercury vapor that is energized by the electric arc sustained inside the lamp. Phosphors are used to achieve high efficacy, good color rendering, and low lamp lumen depreciation. Halo-phosphors, however, are limited in their ability to provide a high color rendering index without sacrificing light output and are often mixed with other phosphors.

Halogen cycle: Halogen incandescent lamps are in the same family as standard incandescent lamps. The basic operating principle is the same, except that chemicals called halogens are introduced in the gas fill. When electricity passes through the lamp's filament, it is heated until it glows and emits light. In this process, tungsten from the filament evaporates and, over the life of the lamp, causes the glass bulb wall to slowly blacken and the filament to disintegrate until the lamp fails. Halogens remove evaporated tungsten from the glass wall and redeposit it back onto the filament. As a result, tungsten does not build up on the bulb, so the light output does not degrade as rapidly.

Halogen lamp: An incandescent lamp that uses a halogen fill gas. Halogen lamps have higher rated efficacies and longer lives than standard incandescent A-lamps.

Halophosphates: The class of phosphors commonly used in fluorescent lamps. Halophosphates are limited in their ability to provide a high color rendering index without sacrificing light output. Standard T12 lamps containing halophosphates are the most common and least expensive fluorescent lamps, but United States federal regulations require that all fluorescent lamps must meet minimum efficacy and CRI standards, and 40-watt T12 halophosphate lamps do not meet these standards. T8 lamps usually contain both halophosphates and rare-earth phosphors.

Hand Rubbed: Process of hand rubbing to achieve a desired finish.

Hardware: Any component that supports the shade and or socket.

1.) For a distorted waveform, a component of the wave with a frequency that is an integer multiple of the fundamental.

2.) Distortions of a periodic sinusoidal waveform represented as a harmonic series of sinusoidal waveforms of different amplitude and phase. A harmonic series is a group of different frequency waveforms that are multiples of the lowest or fundamental frequency.

Harmonic distortion: Distorted wave shapes contain components with frequencies that are multiples of the fundamental frequency. These higher frequency components are known as harmonics.

Head: Luminaire for a track-lighting system.

Heat sinking: Adding a material, usually metal, adjacent to an object in order to cool it through conduction.

HID: High Intensity Discharge lamps; includes metal halide, mercury vapor and high pressure sodium.

High-intensity discharge (HID): 
An electric lamp that produces light directly from an arc discharge under high pressure. Metal halide, high-pressure sodium, and mercury vapor are types of HID lamps.

High-Power-Factor (HPF) Ballast: A ballast designed so that the input power factor is not less than 90% when the ballast is operated at the rated supply voltage using an appropriate reference lamp.

High-pressure sodium (HPS): A high-intensity discharge lamp type that uses sodium under high pressure as the primary light-producing element. HPS lamps produce light with a correlated color temperature (CCT) of approximately 2000 kelvins, although CCTs for lamps having higher CRI values range from 2200 to 2700 kelvins. Standard lamps have a CRI value of 22; others have CRI values from 60 to 80. HPS lamps are among the most efficacious light sources, with efficacies as high as 150 lumens per watt, although those with higher CRI values have efficacies as low as 25 lumens per watt.

High Pressure Sodium (HPS) Lamp: HPS lamps are high intensity discharge light sources which produce light by an electrical discharge through sodium vapor operating at relatively high pressures and temperatures.

High Output Fluorescent (HO): Fluorescent lamps designed to be used with an 800 milliampere ballast. Able to operate at low temperatures (down to zero) and still produce high light levels.

High Reactance Autotransformer (HX) Ballast: An autotransformer lag circuit that uses a magnetic shunt path between primary and secondary coils to control reactance; has operating characteristics similar to those of a reactor and has input taps to accept a wide range of supply voltages.

High-wattage compact fluorescent lamp:  Abbreviated as HW-CFL, sometimes called "high lumen CFLs", these lamps are a larger cousin to regular CFLs, usually much larger in size and with higher wattages and light output.

Horizontal illuminance: The average density of luminous flux incident on a horizontal surface, measured in foot candles (fc) or lux (lx). One fc equals 10.76 lx.

Horizontal rotation range: The total angular horizontal rotation of the lamp-reflector assembly.

Hot Restart or Restrike Time: The time from lamp extinction after a supply voltage interruption to lamp re-start.

Hue: The attribute of a light source or illuminated object that determines whether it is red, yellow, green, blue, or the like.

Hybrid Ballast: A Venture lag (magnetic) ballast designed with a low current crest factor for improved lamp performance.


Igniter: A device, either by itself or in association with other components, that generates voltage pulses to start discharge lamps.

 Symbol E, Unit: lux (Lm/m2),  the unit of illuminance in the International System of Units (SI). It is defined in terms of lumens per meter squared (lm/m 2 ). Lux equals -  Lumens divided by Square Meter.

Impedance: A measure of the total opposition to current flow in an alternating current circuit. The unit of impedance is the ohm Ω .

Incandescent Lamp: A light source that produces light by the heating of a filament by an electric current.

Inches to Millimeters Conversion: To calculate the metric equivalent of inches in millimeters (mm), multiply inches by 25.4.

Incident angle: The angle between a ray of light reaching a surface and a line normal (perpendicular) to that surface.

Indirect lighting: Light arriving at a surface after reflecting from one or more surfaces (usually walls and/or ceilings) that are not part of the luminaire.

Infrared radiation: Any radiant energy within the wavelength range of 770 to 106 nanometers is considered infrared energy.(1 nanometer = 1 billionth of a meter, or 1 X 10-9 m).

Initial light output: A lamp's light output, in lumens, after 100 hours of seasoning.

Instant start: A method of starting fluorescent lamps in which the voltage that is applied across the electrodes to strike the electric arc is up to twice as high as it is with other starting methods. The higher voltage is necessary because the electrodes are not heated prior to starting. This method starts the lamps without flashing. It is more energy efficient than rapid or preheat starting, but results in greater wear on the electrodes during starting. The life of instant-start lamps that are switched on and off frequently may be reduced by as much as 25 percent relative to rapid-start operation. However, for longer burning cycles (such as 12 hours per start), there may be no difference in lamp life for different starting methods.

Intensity (luminous intensity): Total luminous flux within a given solid angle, in units of candelas, or lumens per steradian.

International Dark-Sky Association (IDA): Established in 1988, the International Dark-Sky Association is an educational, environmental 501(c)(3) nonprofit dedicated to protecting and preserving the nighttime environment and our heritage of dark skies through quality outdoor lighting.  With thousands of members in more than 70 countries, IDA is the leading authority concerning the problems and solutions related to light pollution.

Interoperability: The ability to communicate such information as temperature, illuminance levels, status of security devices, and occupancy among building systems and their controls.

Inverted Pendant: Chain hung ceiling fixture with open end of shade facing toward the ceiling.

IP (INTERNATIONAL PROJECTION) followed by two numbers, e.g. IP65. The first digit in the rating is the protection against contact and foreign bodies. The second digit in the rating is the water protection factor.

Iridescent Glass: Glass with a colorful shimmering effect created when a layer of metallic oxide is bonded to hot glass.

Island Pendant: Ceiling fixture usually multi-shaded, horizontally hung and generally best suited for a kitchen island or billiard table.

Isotemperature: A set of coordinates within which all points have the same temperature. In a color space diagram, isotemperature lines represent lights with identical correlated color temperatures.


Jadestone: Durable, compact thinly cut stone with luminous color that can be shaped and constructed with the copperfoil technique.

Junction temperature: For light emitting diodes, the temperature of the light-emitting portion of the device (see PN junction), which is inversely correlated with its light output.


Kelvin Temperature Term and symbol (K): Used to indicate the comparative color appearance of a light source when compared to a theoretical blackbody. Yellowish incandescent lamps are 3000K. Fluorescent light sources range from 3000K to 7500K and higher.

K-factor: A measurement that quantifies the effect of non-linear equipment, such as lighting ballasts, on an electrical system. Lighting systems should be designed so that the transformer rating is sufficient for the ballast used (typically K-factor

Kilowatt (kw): A measure of electrical power equal to 1000 watts.

Kilowatt Hour (kwh): The standard measurement of electrical energy consumption. 1000 watts of electricity used in one hour. Also the typical billing unit used by electrical utilities.

Krypton: A heavy inert gas used in incandescent lamps which allows the filament to glow hotter and brighter and last longer.


Lag Ballast: A magnetic ballast having a lagging lamp current with respect to the supply voltage. Current limiting is primarily inductive; holds lamp power reasonably constant with respect to lamp voltage variations.

Lamp: A radiant light source. The light source, or 'lamp' determines the light level, color, fixture spacing and energy use.

Lamp base position: The location of the lamp socket, either in the center of the top of the ballast or on the side of the ballast. Modular ballasts for circular compact fluorescent lamps (CFLs) have a lamp socket located at the end of a wiring harness.

Lamp current: The current flowing between a lamp's electrodes during operation.

Lamp Dimensions: Bulb designations consist of a letter(s) to indicate shape and a number to indicate the diameter in eighths of an inch.

Lamp efficacy: The ratio of the light output of a lamp (lumens) to its active power (watts), expressed as lumens per watt (LPW). Lamp electrode voltage: Voltage to the electrodes to operate a lamp.

Lamp envelope: The shape of either the bare lamp or the capsule surrounding the lamp. Common shapes include quad, triple tube, four-tube, coiled tube, A-line, circular, square, globe, capsule (bullet), reflector, and decorative.

Lamp life: 
1.) The median life span of a very large number of lamps (also known as the average rated life). Half of the lamps in a sample are likely to fail before the rated lamp life, and half are likely to survive beyond the rated lamp life. For discharge light sources, such as fluorescent and HID lamps, lamp life depends on the number of starts and the duration of the operating cycle each time the lamp is started.

2.) The number of hours at which half of a large group of lamps have failed when operated under standard testing conditions.

Lamp lumen depreciation (LLD): The reduction in lamp light output that progressively occurs during lamp life. Or the decrease in lumen (light) output of a lamp (bulb) over time.

Lamp operating current: Current flowing through a lamp during normal operation.

Lamp Power: The power consumed by a lamp after warm-up, measured in watts.

Lamp Power Factor: Power consumed by the lamp divided by the product of RMS lamp volts and RMS lamp current; It is less than unity on magnetic ballasts operating at 50 or 60 Hz.

Lamp quantity and type: The number of lamps (in parentheses) used by the luminaire, followed by a generic designation indicating the type.

Lamp Regulation: The ratio of lamp power to lamp voltage often expressed in graphical format.

Lamp rated life: The number of operating hours at which half of a large group of product samples are expected to fail. The rated life is a median value of life expectancy; individual lamp life may vary considerably from the published rated life and operating conditions (e.g., temperature, hours per start) may affect actual life because rated life is based on standard test conditions. In addition, the way a product fails can vary by technology. For example, incandescent lamps abruptly stop producing any light while LEDs are considered to have failed when their light output drops below a certain fraction of the initial level.

Lamp shield type: The material used in a luminaire to shield the lamp from the environment. Lamp shields are required by Underwriters Laboratories for some lamp types.

Lamp starting current: Current flowing through a lamp during starting operation.

Lamp Voltage: The RMS voltage at which lamps operate when they are fully warmed up.

Lead Ballast: A magnetic ballast having a leading lamp current with respect to the supply voltage; current limiting is accomplished by means of an inductor as well as a capacitor connected in series with the lamp; this includes CWA and CWI ballasts.

L.E.D.: LED means light emitting diode. LEDs are a solid state device and do not require heating of a filament to create light. Rather, electricity is passed through a chemical compound that is excited and that generates light.

LED: Lighting stands for Light Emitting Diodes. LEDs are small light sources that become illuminated by the movement of electrons through a semiconductor material. A PN junction device that gives off light radiation when biased in the forward direction. LEDs are cool to the touch and 90% of the energy they consume is given off in the form of light, with less than 10% given off as heat. They use up to 90% less energy than incandescent bulbs. LEDs are rated to last between 35,000-50,000 hours, which is at least 20 times that of an incandescent bulb. LEDs, however, don't "burn out" as an incandescent or CFL bulb would. The lifetime of an SSL lamp is generally considered to be the point where the light output has declined to 70% of its initial output, measured in lumens. So instead of burning out after 35,000 hours, the bulb will only be slightly dimmer. 

LEDs: Are not bulbs or lamps in the true sense of the word and application. LEDs require a lot of work to make them ready to be used by the consumer. They need to be placed on a circuit board or other material that will allow electricity to pass through it at a specific voltage and current, and with components required to operate them at specific voltages such as 12vdc, 24vdc or 120vac. They do not come ready to plug into a 12volt or 120 volt power source. These are LEDs.

LED - Light from crystals

LED Bar: Refers to a solid strip of material on which LEDs have been soldered to, along with resistors and other components.

that a specific product requires to make them operate at the stated operating voltage. The Bars are usually an enclosed strip 
of LEDs. Enclosures are plastics, or aluminum, or metal composites with various types of lens/cover plates.

LED Cluster or Array: A group of LEDs set in a square, rectangular or linear pattern, and formatted to be operated at a specific voltage. They will always include two wires called leads. One is positive, the other negative.

LED Drivers: are current control devices that replace the need for resistors. LED Drivers respond to the changing input voltage while maintaining a constant amount of current (output power) to the LED as its electrical properties change with temperature. 

LED Lighting: A general term used by those who do not know the specific type or category of LED lighting they are after. LED lighting includes LED bulbs and fixtures, flashlights, strips, clusters and other LED light sources.

LED Life: Since LED's do not rely on replaceable bulbs, the LED Life refers to the number hours an LED can be used before needing to be replaced. Typically, LED life reaches 100,000 hours.

LED Strip: LED Strips are usually printed circuit boards with LEDs soldered to the board. The strip can be rigid, or flexible and without any enclosure to protect the LED and circuit. 

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

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

Light Center Length (L.C.L.): The distance from a reference point, usually the bottom of the lamp base, to the center of the light source (filament). Also the distance from the center of the visible arc discharge to the bottom contact of the base.

Light loss: The reduced light output caused by a circuit-level power reducer expressed as a percentage of the light output without the circuit-level power reducer. (Full system output minus reduced output with a lighting-circuit power reducer divided by the full system output times 100).

Light Loss Factor (LLF): Used to calculate or project the performance of a lighting system after a given period of time under certain conditions; includes environmental conditions, such as temperature, voltage, dust and/or dirt and lamp depreciation. Normally in a residence, .8 is used, meaning that the maintained or average lumen output of the system will be 80% of the initial output due to dirt and age. However, LLF can be more or less than .8, depending on the operating conditions of the system.

Light pollution: An unwanted consequence of outdoor lighting that includes such effects as sky glow, light trespass, and glare.

Light power density (LPD): Sometimes referred to as power density. A measurement of the ratio of light output in an area and the electric power used to produce that light. LPD is determined by dividing the total light output by the total wattage consumed and is measured in lumens per watt.

Light trespass: A undesirable condition in which exterior light is cast where it is not wanted.

Line Regulation: The ratio of lamp power to ballast input voltage often expressed as a percentage.

Line voltage: The voltage supplied by the electric power infrastructure, typically 110-120 Vac at 60 Hz for homes in North America.

Load capacity: The maximum total power that can be connected to an occupancy sensor.

Load shedding: The practice of turning off electrical devices during peak energy demand hours to reduce building energy use.

Louver: A fixed shield, usually divided into small cells, that is attached to the face of a luminaire to reduce direct glare.

Low battery voltage disconnect: Indicates whether or not an exit sign has a circuit that is designed to disconnect the battery after it is discharged. This circuit prevents damage to the battery. Lead acid and lead calcium batteries need this circuit, but nickel cadmium batteries do not.low-voltage circuit protectionProtection for a ballast’s low-voltage control circuit from high voltage spikes. Does not apply to high-voltage controls.

Low Pressure Sodium (SOX): High Intensity Discharge lamp which uses pressurized sodium vapor to produce light.

Low Voltage: With LEDs, that means 12vDC 24VDC or 48VDC, as opposed to 110/120vac which is high voltage. With LEDs, low voltage is commonly 12 VDC sometimes at 24 VDC. To run these low voltage lights, power will have to be sent to the light through a power supply/transformer/adapter that is hooked up to 110/120/240 VAC power lines. The actual voltage reaching  the light will be at 12VDC.

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):

1.) The amount of light that a bulb produces. Unit of output; t "Luminous flux." A lamp's light output rating expresses the total amount of light emitted in all directions per unit time. Ratings of initial light output provided by manufacturers express the total light output after 100 hours of operation. Unit of light flow or “Luminous Flux.” All lamps have a rated lumen output.

2.) International unit (SI) of luminous flux or quantity of light. Expresses quantity of light regardless of direction.

Lumen depreciation: The decrease in lumen output that occurs as a lamp is operated, until failure. Also referred to as lamp lumen depreciation (LLD).

lumen maintenance: The ability of a lamp to retain its light output over time. Greater lumen maintenance means a lamp will remain brighter longer. The opposite of lumen maintenance is lumen depreciation, which represents the reduction of lumen output over time. Lamp lumen depreciation factor (LLD) is commonly used as a multiplier to the initial lumen rating in illuminance calculations to compensate for the lumen depreciation. The LLD factor is a dimensionless value between 0 and 1.

Lumen maintenance: The lumens produced by a light source at any given time during its operating life as a percentage of its lumens at the beginning of life.

Lumens Per Watt (LPW): See Efficacy

Luminaire: A complete lighting unit consisting of a lamp or lamps and the parts designed to distribute the light, to position and protect the lamp(s), and to connect the lamp(s) to the power supply. (referred to as a fixture.)

Luminaire angle: The vertical (altitude) angle used in luminaire photometry to express the direction of the light output being measured. Light coming straight down is at 0° (the nadir).

Luminaire efficacy: The ratio of the measured light output of a luminaire to its active power, expressed in lumens per watt (LPW) and or (lm/W).

Luminance: Unit: Lm / w, The photometric quantity most closely associated with the perception of brightness, measured in units of luminous intensity (candelas) per unit area (square feet or square meter).

Luminance contrast: Luminance contrast quantifies the relative brightness of an object against its background. It can range from zero and one. The closer the luminance contrast is to one, the greater the relative brightness of the object against its background.

Luminous efficiency: Visual efficacy of visible radiation, a function of the spectral distribution of the source radiation in accordance with the “spectral luminous efficiency curve,’’ usually for the light-adapted eye or photopic vision, or in some instances for the dark-adapted eye or scotopic vision.

Luminous flux: Symbol Φ, Unit: lumen( Lm), Luminous radiant power, measured in lumens. The overall light output of a lamp or luminaire. The rate of flow of light per unit of time, especially the flux of visible light expressed in lumens. Luminous flux in lumens = Radiant power (watts) x 683 lumens/watt x luminous efficacy.

Luminous intensity: Symbol I, Unit: Candela cd, The luminous flux on a small surface centered on and normal to the direction divided by the solid angle (in steradians) that the surface subtends at the source. Luminous intensity can be expressed in candelas or in lumens per steradian.

Lux (lx): A measure of illuminance in lumens per square meter. One lux equals 0.093 foot candle.


Matte Surface: A non-glossy dull surface as opposed to a shiny (specular) surface. Light reflected from a matte surface is diffuse.

Maximum Overall Length (M.O.L): The overall length of a lamp, from the top of the shell to the bottom of the base. Mean Lumens: The average light output of a lamp over its rated life.

MCD: or Millicandela, is used to rank/denote the brightness of an LED. 1000mcd is equal to one Candela. The higher the mcd number, the brighter the light the LED emits. 

Mean Lumens: Light output at 40% of rated lamp life.

Mean Spherical Candela (MSCD): The average value of the luminous intensity of a light source in all directions. To convert MSCD to Lumens, multiply by 4? (12.57). 

Medium pin: Referring to the lamp base pin diameters. Often referencing fluorescent lamps (T-8F and T-12F). 

Mercury Vapor Lamp: A high intensity discharge light source operating at a relatively high pressure (about 1 atmosphere) and temperature in which most of the light is produced by radiation from excited mercury vapor. Phosphor coating on some lamp types add additional light and improve color rendering.

Metal Halide Lamp: A high intensity light source in which the light is produced by the radiation from mercury, plus halides or metals such as sodium, scandium, indium and dysprosium. Some lamp types may also utilize phosphor coatings.

Mica: A natural mineral bonded with shellac to create a light diffuser, usually available in Silver or Amber colors.

Micro Mini Lamp: Portable table lamp that usually has a shade 4" or smaller and height no taller than 6".

Mini Lamp: Portable table lamp that generally has a shade of 4" to 8" wide and height usually no taller than 15".

Mini Pendant: Surface mounted one light fixture consisting of a single pole or chain, extending from the ceiling canopy with shade no larger than 10" in diameter.

Mini Window: Lighted miniature tabletop glass window suspended from a frame.

Modeling: The effect of using highly directional light to create form through shadows and highlights.

MTBF - Mean Time Between Failures: A calculation of ballast life based on thermal conditions, component values, and circuit characteristics used to develop relative predictions of ballast life. 


Nanometer (nm): or nm. Used to measure the wavelengths of light. The lower the wavelength e.g. 400nm the bluer and stronger the light source. Longer wavelengths above 600nm are red. Above 680nm, they fall into the Infrared category, which is colorless to our eyes. White LEDs have no specific wavelength. They are measured by the color of white against the chromaticity scale. 

National Electrical Code
Sets out standards for wiring and electrical devices. The NEC requirements are widely followed by local jurisdictions.

National Electrical Manufacturers Association. Includes lamp, electrical device and larger fixture manufacturers. NEMA develops consensus ratings and designations for various products.

Neodymium: Full spectrum incandescent lamps. Also known as daylight or natural light. Uses a colored glass shell to filter out yellow light produced by standard incandescent lamps.

Night Light: Small portable light that plugs directly into an electrical outlet.

Nominal Length: A measurement for Fluorescent lamp length, based on the length of the lamp plus an allowance for luminaires lamp holders.

Normal (Low) Power-Factor (NPF) Ballast: A ballast designed so that the input power factor is less than 90% when the ballast is operated at the rated supply voltage using a reference lamp.

Nominal Watts
The power rating of lamps, as published by lamp manufacturers.


Ohm's Law: A scientific law which states that current (amperes) in a circuit depends on resistance (ohms) and applied electromotive force (volts). Current (I) = Voltage (E) / Resistance (R).

Opalescent Glass: Glass that incorporates white, or opal glass, into the color mix.

Open Circuit Current (Line): The RMS current measured at the input terminals of a ballast with lamp removed or inoperative.

Open Circuit Voltage, Ballast (OCV): The voltage across the output terminals of a ballast when no load is connected (RMS, unless otherwise stated).

Open Rated Lamp (Medium Base): Designed for open luminaires; has a narrower neck than standard medium base lamps in order to fit into an exclusionary E26 medium socket.

Open Rated Lamp (Mogul Base): Designed with an extended contact pin on the bottom of the base; should be used with an open fixture mogul sockets (EX39) which prevents electrical contact if a non-O-rated lamp is used.

Operating Current (Line): The RMS current measured at the input terminals of a ballast which is operating a reference lamp.

Operating Life: usually refers to the number of hours a specific type of LED is expected to be operational. With high powered LEDs, that usually means life after it loses 10-15% or more rated output after 1000 or more hours of run time. 


Parabolic Aluminized Reflector (PAR): These bulbs may be used indoors in recessed or track lighting indoors. They are also suitable for outdoor use in spot and flood fixtures. They provide halogen light and are more efficient than R or PAR lamps. The light is whiter, brighter and the bulbs last longer. There are more beam spreads available, so you can direct the light exactly where you want it for indoor or outdoor accent lighting. These bulbs are weather proof and can be used outside in un-protected fixtures.

PAR Lamp: PAR is an acronym for parabolic aluminized reflector. A PAR lamp which may utilize either an incandescent filament, a halogen filament tube or HID arc tube is a precision pressed-glass reflector lamp. PAR lamps rely on both the internal reflector and prisms in the lens for the control of the light beam.

Parallel vs. series: 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 competitors' electronic types) result in all lamps operated on the ballast going out if one should fail. 

Patina: Coloration of metal finish due to aging or from a solution applied to metal to change its color.

Printed circuit board: Made from various materials including fiberglass and aluminum. The pcb has an electrical circuit imprinted in silver etching. That circuit says how the LED will operate. The Printed circuit board, or PCB is also the platform by which LEDs are employed in various applications. It can be a rigid board or flexible to twistable. 

Peak Lead Ballast: A CWA ballast that produces a highly peaked open circuit voltage wave shape and a peaked current wave shape.

Pendalog: Element that hangs from a shade, base or hardware, usually crystal but can be made of various materials.

Pendant: Ceiling fixture that usually features a shade larger than 10" in diameter. suspended by a single pole or chain extending from the ceiling canopy.

Phosphor: An inorganic chemical compound processed into a powder and depositied on the inner glass surface of fluorescent tubes and some mercury and metal-halide lamps. Phosphors are designed to absorb short wavelength ultraviolet radiation and to transform and emit it as visible light.

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

Photometrics: Measurement of the properties of light, especially luminous intensity.

Photopic Light: Describes lumen values measured using the high luminance eye sensitivity function centered at 555 nm (yellow-green).

Photopic Vision: Refers to vision involving the cones of the eye; used in reference to the adaptation of the eye to illuminance of more than 3.4 candelas per square meter.

P-N Junction: Area on an LED chip where the positively and negatively charged regions meet. When Voltage is applied and current begins to flow, the electrons move across the n region and into the p region. This process releases energy, the dispersion of which creates visible wavelengths. More simply, the area on the chip which produces light.

Position Oriented Mogul Base (POMB): Used with horizontal operating lamps; has an alignment pin in the base for proper lamp orientation when installed into a EP39 socket.

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 (V-A).

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 Supply: A Transformer and Voltage adapter apply to the electrical conversion of 110/120/240VAC line power into 12VDC or 24 DCV that will then be applied directly to the LED light product. Power Supplies are rated according to the current/amperage load capacity each will handle. It is an electrical or electro-mechanical device and is sometimes referred to as a LED Driver. 

Pulse Start CWA Ballast: A CWA ballast using an igniter to start the lamp.

Pulse Start Lamp: Specially designed metal halide lamp that requires a high voltage pulse for starting; has improved lumen maintenance and not starter electrode (probe).

Preheat: A fluorescent lamp-ballast circuit where the electrodes are heated or warmed by an auxiliary switch or starter before the lamps light up.

PWM: Pulse Width Modulation with regards to LEDs means that the LED will be pulsed or strobed at a rate so fast that the eye will see the light as being constantly on. In fact it is not. This pulsing or turning the LED on and off lowers the potential heat stress on the chemical that makes the light, thus allowing the LED to perform longer than anticipated. 


Quality of Lighting: Pertains to the distribution of luminance in a visual environment. The term is used in a positive sense and implies that all luminance's contribute favorably to visual performance, visual comfort, ease of seeing, safety and esthetics for the specific visual tasks involved.

Quantity of Light: The product of the luminous flux by the time it is maintained. It is the time integral of luminous flux.


Rated Life: The number of operating hours at which 50% of the lamps will still be operating.

Rated Supply Voltage: The input voltage for which a ballast is designed to operate and to which performance characteristics are referred.

R lamp: A common reflector lamp. An incandescent filament or electric discharge lamp in which the sides of the outer blown-glass bulb are coated with a reflecting material so as to direct the light. The light-transmitting region may be clear, frosted, or patterned.

Rapid start: A method of starting fluorescent lamps in which the electrodes are heated prior to starting, using a starter that is an integral part of the ballast. Heating the electrodes before starting the lamps reduces the voltage required to strike the electric arc between the electrodes. A rapid-start system starts smoothly, without flashing.

Rare-earth phosphors: A group of phosphors containing rare-earth elements. Rare-earth phosphors are used in fluorescent lamps to achieve high efficacy and better color rendering. They produce light in very narrow wavelength bands.

Rated average lamp life: Also referred to as lamp rated life. Lamps are tested in controlled settings and the point at which 50% of a given sample burns out is listed as the lamps’ rated average lamp life.

Rated lamp life: The number of hours at which half of a group of product samples fail. The rated life is a median value of life expectancy; any lamp or group of lamps may vary from the published rated life. 

Rated life: Is based on standard test conditions.

Rated light output: The sum of the initial rated lamp lumens of the lamp(s) that were supplied with the luminaire.

Rated light output from lamp(s): The sum of the initial rated lamp lumens of the lamp(s) that were supplied with the luminaire.

Rated lumen:Also referred to as rated light output from lamp in lumens. Lumen refers to a unit measurement of the rate at which a lamp produces light. A lamp’s light output rating expresses the total amount of light emitted in all directions per unit time. Manufacturers rate their lamps’ initial light output after 100 hours of operation.

Reactor Ballast: A lag ballast with a single input voltage tap.

RE70: Designation referring to lamps that use rare-earth phosphors and have color-rendering index values of 70-79.

RE80: Designation referring to lamps that use rare-earth phosphors and have color-rendering index values of 80-89. RE80 HLO, LL: An RE80 lamp with additional enhancements of high light output (HLO) and/or long life (LL).

RE90: Designation referring to lamps that use rare-earth phosphors and have color-rendering index values equal to or greater than 90. reactive power. Power that creates no useful work. It results when current is not in phase with voltage. It is calculated using the equation reactive power = V x A x sin(q) where q is the phase displacement angle.

Reference Ballast:: A ballast specially constructed to have certain prescribed characteristics for use in testing electric-discharge lamps and other ballasts.

Reflectance (rho): A measure of the ability of an object to reflect or absorb light, expressed as a unit less value between 0 and 1. A perfectly dark object has a reflectance of 0, and a perfectly white object has a reflectance of 1.

Reflection: The process by which flux leaves a surface or medium from the incident side.

Reflector: A device used to redirect the light by the process of reflection.

Refraction: The process by which the direction of a ray of light changes as it passes obliquely from one medium to another.

Refractor: A device used to redirect the luminous flux from a source, primarily by the process of refraction. Provides directional illumination. These are available as floods or spots. They are often used in recessed lights or track lights. They cannot be used outside unless they are used in a completely sealed waterproof fixture.

Regulated Lag Ballast: A lag ballast with a third coil for improved lamp power regulation.

Relative beam diameter (manufacturer): The normalized beam diameter based on manufacturer-supplied beam angles.

Relative beam diameter (NLPIP): The normalized beam diameter based on NLPIP-measured values.

Relative CBCP (manufacturer): The normalized center beam candlepower based on manufacturer-supplied values.

Relative system efficacy: The ratio of relative light output (RLO) to system active power. For each lamp type, relative system efficacy is normalized to the highest value at the maximum light output level, which is assigned a relative system efficacy value of 100%.

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

Restrike: To re-ignite the arc of a HID lamp.

Restrike time: The time required for a lamp to restrike, or start, and to return to 90% of its initial light output after the lamp is extinguished. Normally, HID lamps need to cool before they can be restarted.

Reverse Painted Glass: Paints are applied to the underside of glass, starting with the foreground and ending with the background.

RGB: RGB stands for Red, Blue, Green, the 3 primary colors that make white light and all other colors. It can be a pre-programmed 7 color automatically changing LED bar or strip that is non-adjustable. It also means a RGB color changing system that allow adjustment of color change frequency, strobing, chasing and other action modes. 

RGB color model: is an additive color model in which red, green, and blue light is added together in various ways to reproduce a broad array of colors. The name of the model comes from the initials of the three additive primary colors, red, green, and blue.

Ripple Glass: Texture that has the appearance of ripples that is applied to hot glass sheets with an embossed roller.

RMS current: Root-mean-square current, a value that quantifies the magnitude of a current that varies with time (as in ac circuits). RMS current is calculated as the square root of the squared values of current over one complete cycle. RMS current delivers the same power to a resistive load as an equivalent steady dc current.

Root-mean-square (RMS): The effective average value of a periodic quantity such as an alternating current or voltage wave, calculated by averaging the squared values of the amplitude over one period and taking the square root of that average.


Sconce: Typically, a one or two light fixture surface mounted to a wall.

Scotopic Light: Describes lumen values measured using the low luminance eye sensitivity function centered at 507 nm (blue-green).

Scotopic Vision: Sight involving the eye's rods, which respond to low levels of lighting, below .034 candela per square meter.

Sculpture: A lighted or unlighted decorative tabletop accessory.

Seedy Glass: Glass which contains trapped air bubbles, created with air or gas injected into the molten glass, prior to forming the sheet.

Semiconductor: A material whose electrical conductivity is between that of a conductor and an insulator; the conductivity of most semiconductors is temperature dependent.

Semi cut-off luminaire:IESNA classification that describes a luminaire light distribution in which the candela per 1000 lamp lumens does not numerically exceed 50 (5%) at or above an angle of 90° above nadir, and 200 (20%) at or above a vertical angle of 80° above nadir. This applies to all lateral angles around the luminaire.

Semi Flush: Surface mounted ceiling fixture with three inches or more between the shade and the ceiling.

Sensitivity adjustment: A trim potentiometer (sometimes called a "trim pot") or a set of dip switches used to refine the response function of a photo sensor. Some photosensors include a remote trim pot that allows for adjustment at a distance from the photo sensor housing.

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 complementary angle of the cut-off angle of a luminaire.

Shielding Blocking: An electric or magnetic field with a metallic substance. The incident field induces currents in the metallic substance, and these currents induce a field that opposes the incident field. Shielding reduces radiated electromagnetic waves. Electronic components, wires, lamps, and devices can all be shielded.

Short-Circuit Current (Ballast): The current at the output terminals of a ballast when the output is shorted (RMS, unless otherwise stated).

Shroud: A quartz cylinder surrounding the arc tube of a metal halide lamp; designed to reduce the damage to the outer bulb if an arc tube rupture occurs; usually required to pass the ANSI containment test of the O-rating.

Shower: Fixture with a ceiling pan that usually suspends 3 or more pendants.

Sky glow: (See Dark Sky)Brightening of the sky caused by outdoor lighting and natural atmospheric and celestial factors.

Skylight: A device similar to a window that is placed in a roof, allowing sunlight to enter a structure, thus reducing the need for electric lighting. Skylights can be used to reduce peak load demand by taking advantage of sunlight during the peak demand time of the day.

SMD/SMT: A type of low profile LED that is surface mounted to a PCB. These type LEDs are very powerful and range in lumen output from 35 up to 170 lumens. With the latest LED technology being applied today, these have shown to have the most promise in delivering light levels and coloring that we are used to having. Those SMD LEDs we talk about, use and sell are in the .5 watt, 1 watt, 3 watt and 5 watt power range. When you see a 7 watt or 9 watt LED light, it will contain 1 watt LEDs x 7, or 1 watt LEDs x 9, or 3 watt LEDs x 3. 

SON: High Pressure Sodium abbreviation term.

Sound rating: Magnetic ballasts sometimes produce a humming noise caused by vibration of the magnetic core. Electronic ballasts operate at high frequencies and are usually less noisy. Ballasts are rated from “A” to “F” based on their noise levels. Ratings define the range of ambient sound levels in which people will not notice the ballast noise. The higher the rating, the more noise that will be required to mask the ballast hum.

SOX: Low Pressure Sodium abbreviation term.

Spectral Power Distribution: A graph of the radiant power emitted by a light source as a function of wavelength. SPD's provide a visual profile of the color characteristics of the light source throughout the visible part of the spectrum.

Spectral power distribution (SPD): A representation of the radiant power emitted by a light source as a function of wavelength.

Specular angle: The reflected angle of light striking a surface, which is equal to and in the same plane as the incident angle.

Specular Surface: A shiny, highly polished surface which reflects light at an angle equal to that of the incident light.

Specular reflection: Light incident on a surface that is redirected at the specular angle. Glossy or shiny surfaces exhibit a high degree of specular reflection. Spill light that falls outside of the area intended to be lighted.

SSL: SSL means Solid State Lighting. It does not use heating of a thin fragile filament to create light. Rather it uses electrical current passing through a chemical that will get excited and thus emit light. 

Stained or Art Glass: Colored glass.

Standard deviation: A measure of the average distance of a set of data points from their mean. A set of data points that are all close to their mean will have a smaller standard deviation than a set of points that are further from their mean.

Standard Light Bulbs: An incandescent light bulb, create light by passing electricity through a metal filament, when the filament becomes hot enough it glows. 

Starting Current (Line): The RMS current measured through the input terminals of the ballast five to 15 seconds after the lamp has started.

Starting method: The method a ballast uses to start a lamp. For compact fluorescent lamps (CFLs), ballasts use one of three methods: preheat, instant start, or rapid start. Dimming electronic ballasts use one of these starting methods- rapid start, programmed start, or controlled rapid start. Incandescent bulbs give off about 90% of the energy they consume in the form of heat, leaving only 10% used to produce light. This equates to about 85 BTUs/hour. The average lifespan of an incandescent bulb is between 750 to 2500 hours.

Starting Pulse: A high-voltage, low-energy pulse superimposed on the open circuit voltage of some HID ballasts to aid in starting a lamp.

Starting time: The time it takes the lamp to start from the point at which voltage is applied to the lamp until stable operation.

Starter: A device used in conjunction with a ballast to start preheat fluorescent lamps.

Starting voltage: The voltage applied across the lamp during starting.

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

Steradian (sr): A unit of measure equal to the solid angle subtended at the center of a sphere by an area on the surface of the sphere equal to the square of the sphere radius. Substrate For light emitting diodes, the material on which the devices are constructed.

Supplementary Lighting:  Used to provide an additional quantity and quality of illumination that cannot be readily obtained by a general system and that supplements the general level usually for specific task requirements.

Supply voltage: The voltage, usually direct, applied by an external source to the circuit of an electrode.

Sustaining Voltage: The instantaneous voltage available to the lamp from the ballast at the time the lamp current passes through zero.

Swag: Pendant or chandelier with chain and wire that can drape across a ceiling to reach a hard mounted electrical box or plug into an electrical outlet Table Lamp Portable lamp usually with a shade having a 14” width or larger.

System efficacy: Also referred to as relative system efficacy, system efficacy is a measurement of a system's ability to convert electricity into light. Measured in lumens per watt (LPW), system efficacy is the ratio of the light output (in lumens) to the active power (in watts).

System Power: The power measured at the input terminals of a ballast while is operating a reference lamp.


Task Lighting/Lamp: A LED light used to specifically light a particular area used for work or reading. Typically found in the form of a desk, floor, or clamp-on lamp, it can be a high powered LED light in any form. 

TCLP Test: The Toxicity Characteristic Leaching Procedure (TLCP) test, specified in the Resource Conservation and Recovery Act (RCRA) of 1990, is used to characterize fluorescent lamp waste as hazardous or nonhazardous waste. The TCLP test measures the ability of the mercury in a lamp to leach from a landfill into ground water under very aggressive and reactive conditions.

Tesla (unit): This SI unit is named after Nikola Tesla. As with every SI unit whose name is derived from the proper name of a person, the first letter of its symbol is upper case (T). When an SI unit is spelled out in English.

tesla (symbol T): The unit of magnetic flux density in the International System of Units, equal to the magnitude of the magnetic field vector necessary to produce a force of one newton on a charge of one coulomb moving perpendicular to the direction of the magnetic field vector with a velocity of one meter per second. It is equivalent to one weber per square meter.

Tesla, Nikola 

 Nikola Tesla (Serbian: Никола Тесла; 10 July 1856 – 7 January 1943) was an inventor, mechanical and electrical engineer. He was an important contributor to the birth of commercial electricity, and is best known for his many revolutionary developments in the field of electromagnetism in the late 19th and early 20th centuries. Tesla's theoretical work formed the basis of modern alternating current (AC) electric power systems, including the polyphase system of electrical distribution and the AC motor. Nikola Tesla divulge to the United States government the secret of his 'teleforce,' (Energy beam weapon) of which he said, 'airplane motors would be melted at a great distances miles, so that an invisible strategic defense initiative began, would be built around the country against any future enemy attacks, using aircraft. Tesla's father was Milutin Tesla.

Thermal resistance (C/W): A measure of the heat transfer capacity of the LED. Lower resistance is preferred.

A - Style referring to Art Nouveau, Art Deco, Victorian or scenes of nature.
B - The copper-foil technique of stained glass assembly.
C - Opalescent glass invented by Louis Comfort Tiffany 1848-1933, son of Charles Lewis Tiffany, an American jeweler.

Time delay range: For motion sensors, the range of time that may be set for the interval between the last detected motion and the turning off of the lamps. Total harmonic distortion (THD): A measure of the degree to which a sinusoidal wave shape is distorted by harmonics, with higher values of THD indicating greater distortion Track head diameter. The size of the luminaire used in a track lighting system.

Tipless Arc Tube: An arc tube made without an auxiliary tube for dosing gases and other ingredients.

Torchieres: Portable floor lamp with a shade that directs light upward.

Total Harmonic Distortion: A measure of the distortion of an electrical wave form. Excessive THD may cause adverse effects to the electrical system.

Track luminaire options: Accessories available for track luminaires.

Track mounting: For track luminaires, the method by which the track is attached to the ceiling.

Transformer: Electrical devices with no moving parts, which change distribution voltages to higher or lower levels. When used with incandescent or halogen lamps, they typically step 120-V distribution downward to 12V, although 5.5V and 24-V models are also offered.

Transmission: The process by which incident flux leaves a surface or medium on a side other than the incident side, the characteristics of many materials such as glass, plastics and textiles.

Transmittance: The ratio of the flux transmitted by a medium to the incident flux.

Translucent Glass: Glass that allows light transmission while diffusing. Objects cannot be seen clearly through this glass.

Transients: For an alternating current circuit, a momentary voltage surge, often at amplitudes 10 to 20 times the normal voltage.

Trigger Start: A circuit used that eliminates the starter and allows for instant starting of preheat lamps.

Tri-light: A 3-way lamp. A lamp that uses a 3-way bulb to produce three levels of light in a low-medium-high configuration. A 3-way lamp requires a 3-way bulb and socket, and a 3-way 2-circuit switch.


Tri-level switching: Control of light source intensity at three discrete levels in addition to off.

Tri-phosphor: A mixture of three phosphors to convert ultraviolet radiation to visible light in fluorescent lamps; each of the phosphors emits light that is blue, green or red in appearance with the combination producing white light.

Tri-phosphors: Tri-phosphors are a blend of three narrow-band phosphors (red, blue, and green) that provide improved color rendition and higher light output versus some other types of phosphors.

Trim option: A decorative luminaire accessory.

Troffer: A long recessed lighting fixture, usually installed flush with the ceiling.

Turtleback: Molded glass tiles that are usually irregular in shape and thickness.


UL "Temp code": An Underwriters Laboratories (UL) alphabetic temperature code for ballasts which designates a range of temperature rise of wire over ambient temperature. The code is found on the label directly following the number 1029X, where X is the appropriate alphabetic character

Ultrasonic frequency: The frequency at which an ultrasonic sensor operates.

Ultraviolet: Any radiant energy within the wavelength range 100 to 400 nanometers is considered ultraviolet radiation (1 nanometer = 1 billionth of a meter, or 1 X 10-9 m).

Applications include:

  • Blacklight ................ 320-400 nm
  • Germicidal .............. 220-300 nm
  • Ozone-producing ... 180-220 nm

Uniformity: The degree of variation of illuminance over a given plane. Greater uniformity means less variation of illuminance. The uniformity ratio of illuminance is a measure of that variation expressed as either the ratio of the minimum to the maximum illuminance or the ratio of the minimum to the average illuminance.

Uplight: Light directed upward at greater than 90° above nadir. The source of up-light can be from a combination of direct up-light and reflected light.

UV-A: (380–315 nm), also called Long Wave or "blacklight" because it is invisible to the human eye. Can cause skin irritation and fading of fabrics. 

UV-B: (315–280 nm), also called Medium Wave radiation. Can cause severe damage to the skin and human eye through exposure. 

UV-C: (? 280 nm), also called Short Wave or "germicidal" for its ability to destroy even bacterial lifeforms. Extremely hazardous to all lifeforms due to its ability to cause immediate damage to cellular DNA. 


Vanity: Surface mounted wall fixture with three or more lights, usually used in the bathroom.

Veiling Reflections: Reflections which partially or totally obscure the details to be seen by reducing the contrast. 

Venting: Holes in the reflector assembly of a down light.

Vertical illuminance: The average density of luminous flux incident on a vertical surface, measured in footcandles (fc) or lux (lx). One fc equals 10.76 lx.

Very High Output (VHO) Lamps: Fluorescent lamps designed to be used with a 1500 milliampere ballast.

View Angle Degree: Also referred to as directivity, or the directional pattern of a LED light beam. The expressed degree dictates the width of the light beam and also controls to some extent, the light intensity of a LED. View angles range from 8 to 160 degrees, and are provided through the use of optics, special lenses made to colimate light to into a desired view angle. 

Visible Spectrum: Radiant energy in the wavelength range of about 380 to 770 nanometers (nm). The light that can be seen by the naked eye and produces what we also call the "color spectrum".

Visual Comfort Probability (VCP): A discomfort glare calculation that predicts the percent of observers positioned in the least favorable part of the room who would be expected to judge a condition to be comfortable. VCP rates the luminaire in its environment, taking into account such factors as illuminance level, room dimensions and reflectance's, luminaire type, size and light distribution, number and location of luminaires, and observer location and line of sight. The higher the VCP the more comfortable the environment.

Visual Field: The location of objects or points in a space where the head and eyes are kept fixed.

Visual Surround: All portions of the visual field except the visual task.

Visual performance:The quantitative assessment of the performance of a visual task, taking into consideration speed and accuracy.

Visual Task: Those details and objects which must be seen for the performance of a given activity, including the immediate background of the details or objects.

Volt: The unit of electromotive force (emf). The difference in electrical potential that will cause a current of one ampere to flow through a resistance of one ohm.

Voltage (E): A measure of electrical potential, expressed in volts (V).

Voltage drop: The difference between the voltages at the transmitting and receiving ends of a feeder, main, or service.

Voltage Rating: The recommended operating voltage for a lamp.

Voltage regulation: The change in output voltage that occurs when the load (at a specified power factor) is reduced from rated value to zero, with the primary impressed terminal voltage maintained constant.

Voltage Regulator(LED): A device which limits or controls and stabilizes the voltage being applied to a using unit such as LED lights and motors. Regulators also take higher voltages than required and reduces it to the working voltage that makes a specific product run correctly. In many instances a lack of a Voltage Regulator will allow higher voltage than a product can work with and will cause irreparable damage. 


Wall-washing: The practice of illuminating vertical surfaces, such as walls. Wall-washer luminaries are designed to illuminate vertical surfaces.

Warm-up time: The time it takes for a lamp to produce 90% of its initial light output when it is started, unless otherwise indicated.

Warm White: A description of light with a correlated color temperature between 3000K and 3500K, usually perceived a slightly yellow.

Washed: Process of lightly applying an accent finish by hand.

Watt (W): A unit of electrical power equal to 1 joule per second. The unit of electrical power as used by an electrical device during its operation. Many lamps come with rating in watts to indicate their power consumption. A light source with a higher lumen per watt value is more efficient.

Watt per LED: It can be confusing when two watt numbers are used in product specifications. For the application to smd high powered LEDs, the 1 watt, 3 watt, 5 watt, etc., refers to the power consumption of that specific LED installed in that product. The watt numbers expressed as light output are a comparison to an incandescent light bulb light output, e.g; a 60 watt light 
output is equal to a 60 watt incandescent light bulb. The Watt Output is equipment measured. Weatherproof: meaning the product will take water splashing and high humidity without deterioration to the LED or circuit. LED product cannot be submerged into water. 

Wavelength: The distance between two corresponding points of a given wave. Wavelengths of light are measured in nanometers (1 nanometer = 1 billionth of a meter, or 1 X 10-9 m). Electromagnetic energy is transmitted in the form of a sinusoidal wave. The wavelength is the physical distance covered by one cycle of this wave; it is inversely proportional to frequency.

Weight: The weight of a luminaire plus ballast (except for certain track luminaires with separately mounted ballasts, when the weight is that of the lamp and track head only). For modular compact fluorescent lamp (CFL) ballasts, the weight of the ballast without a lamp. For self-ballasted CFLs, "weight" indicates the total product weight.

White: White is defined by Kelvin Temperature or Degrees Kelvin. Most will say that a Kelvin Temperature of 6000k plus is white with a bluish tint. And let's say that 5000k -5500k is daylight/sunlight white. At 4200k-4500k, it is called cool white. At 2800-3300k, it's warm white, which is the color temperature most incandescent light bulbs emit. From 5500k on down the scale, the color becomes "warmer" due to the dominance of red and yellow hues. In the opposite direction, whites will have cooler colors like blues and green becoming more apparent, thus they are called cool whites.

White point: The Coordinated Color Temperature (CCT) defined by a line perpendicular to the Planckian Black Body Curve and intersecting the measured chromaticity.

Wispy Glass: Mixed opalescent glass with thin wisps of white or clear glass.

Working Distance: As a function of an elliptical reflector, light is collected and converged into a specific area a certain distance in front of the lamp. Lamp alignment can be provided for specific illumination and color qualities at the designated area.

Work Plane: The plane at which work usually is done, and on which the illuminance is specified and measured. Unless otherwise indicated, this is assumed to be a horizontal plane 0.76 meters (30 inches) above the floor.


X-bar: Color matching function x-bar, y-bar, z-bar are used to define the color-matching properties of the CIE 1931 standard observer. In 1931, CIE defined the color-matching functions x-bar, y-bar, z-bar in the wavelength range from 380nm to 780 nm at wavelength intervals of 5nm.


Zenith: In the lighting discipline, zenith is the angle pointing directly upward from the luminaire, or 180°. Zenith is opposite nadir. In astronomical usage, zenith is the highest point in the sky, directly above the observation point.