Absorption The dissipation of light within a surface or medium; A process by which incident radiant flux is converted to another form of energy, usually (and ultimately) heat.

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

Accommodation The process by which the eye changes focus from one distance to another.

Acrylic Material used in fixture lenses; may tend to yellow with age.

A-lamp The incandescent lamp most commonly used in North American households. The "A" designation refers to the lamp's bulbous shape.

Alternating Current (AC) Flow of electricity which cycles or alternates direction many times per second. The number of cycles per second is referred to as frequency. Most common frequency used in this country is 60 Hertz (cycles per second).

Ambient Lighting Electric and/or natural lighting throughout a space that produces uniform general illumination as opposed to task lighting or the lighting of the object one is looking at).

Ambient temperature The temperature of the surrounding air that comes into contact with the lamp and ballast. Ambient temperature affects the light output and active power of fluorescent lamp/ballast systems. Each fluorescent lamp-ballast system has an optimum ambient temperature at which it produces maximum light output. Higher or lower temperatures reduce light output. For purposes of lamp/ballast tests, ambient temperature is measured at a point no more than 1 meter (3.3 feet) from the lamp and at the same height as the lamp.

Amperes (amps or A) The unit of measurement of electric current

Amplitude The maximum absolute value attained by a periodic wave.

Anodizing An electrolytic process for converting an aluminum surface to aluminum oxide. Anodizing creates an incredibly hard, transparent finish that is physically part of the metal and highly resistant to corrosion. Anodized finishes are generally colorless, but may be dyed in a variety of colors (see also Architectural Class 1 Anodizing.

ANSI American National Standards Institute. A professional organization made up of representatives from manufacturers, safety protection agencies, and consumers. ANSI publishes testing standards for products and components.

Apparent power The product of root-mean-square (rms) voltage and rms current.

Application The use to which a lighting system will be put; for example, a lamp may be intended for indoor residential applications.

Arc tube An envelope, usually quartz or ceramic that contains the arc of a discharge light source.

Argon Inert gas used in incandescent and fluorescent lamps. In incandescents, helps retard evaporation of the tungsten filament.

Asymmetric Distribution A non-symmetric distribution of light. The luminous intensity may be more pronounced in one direction.

Average rated life The number of hours at which half of a large group of product samples fail under standard test conditions. Rated life is a median value; any lamp or group of lamps may vary from the published rated life.

Baffle An opaque or translucent element that serves to shield a light source from direct view at certain angles, or serves to absorb unwanted light

Ballast A device required by electric-discharge light sources such as fluorescent or HID lamps to regulate voltage and current supplied to the lamp during start and throughout operation.

Ballast efficacy factor (BEF) Sometimes called ballast efficiency factor, ballast efficacy factor is the ratio of the ballast factor to the active power (in watts), usually expressed as a percent. It is used as a relative measurement of the system efficacy of the fluorescent lamp/ballast combination.

Ballast factor (BF) The ratio of the light output of a fluorescent lamp or lamps operated on a ballast to the light output of the lamp(s) operated on a standard (reference) ballast. Ballast factor depends on both the ballast and the lamp type; a single ballast can have several ballast factors depending on lamp type.

Ballast rated life The number of hours at which half of a group of ballasts fail under standard test conditions. Rated life is a median value of life expectancy; any ballast, or group of ballasts, may vary from the published rated life.

Base The end of the lamp that inserts into lamp socket; The end (or ends) of a lamp that makes electrical and mounting connections with the luminaire.

Beam angle The angle at which luminous intensity is 50 percent of the maximum intensity.

Beam appearance The description of the beam's image on a wall as determined by subjective visual evaluations of each lamp. The descriptive categories used are smooth, cloud, two-contour, ripple, and variegated.

Beam spread The width of a light beam, expressed in degrees. The beam of light from a reflector-type lamp (PAR, R, ER, or MR) can be thought of as a cone. The beam spread is the angular width of the cone. Common beam spreads are known as spot, narrow, narrow flood, and flood.

Bi-level switching Control of light source intensity at two discrete levels in addition to off.

Brightness The degree of apparent lightness of a surface: its brilliancy; concentration of candlepower. Brightness is produced by either a self-luminous object, by light energy transmitted through objects or by reflection. Unit of measurement of brightness is the footlambert. (fl). Luminance.

Brownout circuitry For exit signs, brownout circuitry is designed to switch the sign over to battery supply if the voltage of the utility-supplied power drops below a specified value. Brownout circuitry is an option for some signs.

Bulb The outer jacket or envelope of a lamp.

Bulb Darkening The darkening of an incandescent lamp caused by small particles of tungsten that evaporate from the filament and deposit on the bulb as the filament burns.

Bulb designation An abbreviation of the shape and size of a lamp's outer envelope. The letter or letters indicate the shape and the numbers indicate the bulb's maximum diameter in eighths of an inch.

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

Burning Position The position in which lamps are designed to he objected.

Candela (cd) The unit of measurement of luminous intensity of a light source in a given direction

Candlepower Luminous intensity expressed in candelas.

Capacitor A device used in electric circuitry to temporarily store electrical charge in the form of an electrostatic field. In lighting, a capacitor is used to smooth out alternating current from the power supply.

Cathode-disconnect ballast An electromagnetic ballast that disconnects the electrode-heating circuit after the lamps are started. Cathode-disconnect ballasts operate lamps at 60 hertz; they are sometimes called "hybrid" or "low-frequency electronic" ballasts. They operate lamps at lower power than other magnetic ballasts that produce similar light output.

Ceiling Cavity Ratio A numerical relationship of the vertical distance between luminaire mounting height and ceiling height to room width and length. It is used with the Zonal Cavity method of calculating average illumination levels.

Center beam candlepower (CBCP) Center beam candlepower is the luminous intensity at the center of a beam, expressed in candelas (cd).

Chromaticity 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).

Circuit Breaker Resettable safety device to prevent excess current flow.

Class "P" Ballast Contains a thermal protective device which deactivates the ballast when the case reaches a certain critical temperature. The device resets automatically when the case temperature drops to a lower temperature

Coefficient of Utilization (CU) A ratio representing the portion of light emitted by a luminaire in any particular installation that actually gets down to the work plane. The coefficient of utilization thus indicates the combined efficiency of the luminaire, room proportions and room finish reflectances. The ratio of the luminous flux (lumens) from a luminaire is calculated as received on the work-plane to the luminous flux emitted by the luminaire's lamps alone

Cold Cathode Lamp An electric-discharge lamp whose mode of operation is that of a glow discharge

Color Rendering Index (CRI) Measure of the degree of color shift objects undergo when illuminated by the light source as compared with the color of those same objects when illuminated by a reference source of comparable color temperature; a quality of the light. It is a measure of the lamp's ability to "render" colors accurately.

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 Same as the "visible light" spectrum: electromagnetic energy between 380 (violet) and 770 (red) nanometers, which can be seen by the human eye.

Compact Fluorescent Lamp(CFL) A small fluorescent lamp that is often used as an alternative to incandescent lighting. The lamp life is about 10 times longer than incandescent lamps and is 3-4 times more efficacious. Also referred to as PLI DL, CFL or BIAX lamps.

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

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

Cone Reflector Parabolic reflector that directs light downward thereby eliminating brightness at high angles

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.

Continuous dimming Control of a light source's intensity without abrupt transitions.

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 illuminance.

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

Contrast Rendition Factor (CRF) The ratio of visual task contrast with a given lighting environment to the contrast with sphere illumination. Contrast measured under sphere illumination is defined as 1.00.

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 Beam Lamps Incandescent PAR lamps that use a special coating (dichronic interference filter) on the reflectorized portion of the bulb to allow heat to pass out the back while reflecting only visible energy to the task, thereby providing a "cool beam" of light.

Correlated color temperature (CCT) A specification of the apparent color of a light source relative to the color appearance of an ideal incandescent source held at a particular temperature and measured on the Kelvin (K) scale. The CCT rating for a lamp is a general indication of the warmth or coolness of its appearance. As CCT increases, the appearance of the source shifts from reddish white toward bluish white; therefore, the higher the color temperature, the cooler the color appearance. 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.

Cosine distribution A property of a light source such that its luminous intensity in a particular direction is proportional to the cosine of the angle from the normal to the source.

Cove Lighting Refers to light sources mounted above a ledge or in a recess (usually around the perimeter of a room) that distribute light upward for ambient lighting.

CSA Canadian Standards Association.

Current crest factor (CCF) Defined as the peak current divided by the root-mean-square (rms) current of a lamp. Current crest factor ranges from 1 to infinity. ANSI requires current crest factor to be less than 1.7. Lamp manufacturers usually will not warranty their lamps when operated on a ballast having a current crest factor greater than 1.7.

Current THD A measure of the degree to which the current waveform deviates from sinusoidal, expressed as a percentage. See total harmonic distortion (THD).

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

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

Diffuser A translucent piece of glass or plastic sheet that shields the light source in a fixture. The light transmitted throughout the diffuser will be redirected and scattered.

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.

Diffusion The scattering, spreading or redirection of light in an even manner, by a lens, to achieve some intended effect such as reduced glare.

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

Direct Current (DC) Flow of electricity continuously in one direction from positive to negative.

Direct digital control (DDC) The technology used by the components of a distributed control system. Direct digital control modules exchange digitally encoded signals with each other, indicating the status of devices connected to the network and executing commands when appropriate. Each module contains a programmable microprocessor, hardware for at least one type of network connection, and some means of detecting or changing a device's status.

Discharge Lamp A lamp in which light (or radiant energy near the visible spectrum) is produced by the passage of an electric current through a vapor or a gas.

Distributed control system A control system in which the computing hardware and software are contained in a network of control modules or multi-circuit control panels physically distributed throughout the facility.

Distribution Panel Box containing circuit breakers or fuses where power is distributed to branch circuits.

Driver For light emitting diodes, a device that regulates the voltage and current powering the source.

Efficacy The ratio of the light output of a lamp (lumens) to its active power (watts), expressed as lumens per watt.

Electric Discharge Lamp A light source that produces light by passing a current between electrodes through a vapor or gas; includes fluorescent, high intensity discharge, and other 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.

Electroluminescence The emmision of light from a phosphor excited by an electromagnetic field. An example: a light source technology used in exit signs that provides uniform brightness, long lamp life (approximately eight years), while consuming very little energy (less than one watt per lamp). The emmision of light from a phosphor excited by an electromagnetic field.

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

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

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.

Electronic Dimming Ballast A variable output electronic fluorescent ballast.

Emission Coating An oxide coating deposited on a cathode that emits electrons when heated.

Emissivity/Emittance The ratio of radiance (for directional emissivity) or radiant exitance (for hemispherical emissivity) of an element of surface on a temperature radiator to that of a blackbody at the same temperature. By Kirchoff's Law, for a given wavelength of the electromagnetic spectrum, emissivity of a surface equals its absorptivity (and is the reciprocal of its reflectivity).

End Blackening Darkening around the ends of a fluorescent tube caused by the emitter paste on the electrodes evaporating and collecting on the glass.

Energy-Saving Ballast A type of magnetic ballast designed so that the components operate more efficiently, cooler and longer than a "standard magnetic" ballast. By U.S. law, standard magnetic ballast's can no longer be manufactured.

Energy-Saving Lamp A lower wattage lamp, generally producing fewer lumens.

EPA Effective Projected Area; A value given to outdoor pole mounted lighting equipment based on fixture surface area and shape. Used in outdoor applications to calculate wind loading data to determine proper pole size necessary to support fixture.

Equivalent Sphere Illumination (ESI) The level of sphere illumination which would produce task visibility equivalent to that produced by a specific lighting environment. Suppose a task at a given location and direction of view within a specific lightings system has l00 fc of illumination. Suppose this same task is now viewed under sphere lighting and the sphere lighting level is adjusted so that the task visibility is the same under the sphere lighting as it was under the lighting system. Suppose the lighting level at the task from the sphere lighting is 50 fc for equal visibility. Then the Equivalent Sphere Illumination of the task under the lighting system would be 50 ESI fc.

ER (Elliptical Reflector) Lamp whose reflector focuses the light about 2" ahead of the bulb, reducing light loss when used in deep baffle downlights.

Etch Logo, brand name, and product information that appears on glass envelope of lamp.

Extended Life Lamps Incandescent lamps that have an average rated life of 2500 or more hours and reduced light output compared to standard general service lamps of the same wattage.

Filament Wire element, often coiled, in a lamp that becomes incandescent and emits light when heated by an electric current.

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.)

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

Floodlighting A system designed for lighting a scene or object to a luminance greater than its surroundings. It may be for utility, advertising or decorative purposes

Fluorescent Lamp A low-pressure mercury electric-discharge lamp in which a fluorescing coating (phosphor) transforms some of the ultraviolet energy generated by the discharge into light.

Flux Continuous flow of luminous energy

Foot Lambert (fl) A unit of luminance of a perfectly diffusing surface emitting or reflecting light at the rate of one lumen per square foot.

Footcandle (fc) The unit of illuminance when the foot is taken as the unit of length. It is the illuminance on a surface one square foot in area on which there is a uniformly distributed flux of one lumen.

Frequency The number of cycles completed by a periodic wave in a given unit of time. Frequency is commonly reported in cycles per second, or hertz (Hz).

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 uplight, but which has no limitation on the intensity in the region between 80? and 90?.

Fuse Replaceable safety device to prevent excess current flow.

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.

General Lighting Essentially uniform light throughout an area, with no special provisions for individual tasks or objects.

General Service Lamps "A" or "PS" incandescent lamps

Globe A transparent or translucent spherical lamp enclosure.

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.

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.

Grounding Connection of electric components to earth for safety

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.

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.

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

Harmonics 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.

Heat Extraction The process of removing heat from a luminaire by passing return air through the lamp cavity

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

High Intensity Discharge (HID) Lamp A discharge lamp in which the light producing arc is stabilized by wall temperature, and the arc tube has a bulb wall loading in excess of three watts per square centimeter. HID lamps include groups of lamps known as mercury, metal halide, and high pressure sodium.

High Output (HO) Fluorescent A fluorescent lamp designed for use with an 800 milliampere (MA) ballast; will usually operate at low temperatures (down to zero) while still producing high light levels.

High Pressure Sodium (HPS) Lamp High intensity discharge (HID) lamp in which light is produced by radiation from sodium vapor. Includes clear and diffuse-coated lamps. High pressure sodium lamps rely on an ignitor to send a high voltage pulse to the lamp electrodes in order to start the lamp. This results in a quick ignition time: 1 to 3 minutes. High pressure sodium systems provide higher efficiencies (lumens/watt), lumen maintenance, and greater component life than traditional metal halide systems, but similar to mercury vapor. The color rendering index (CRI) of these systems, however, is substantially less than metal halide and closer to that of mercury vapor lamps, 22 to 25. There are "color corrected" lamps available, but which are somewhat cost inhibitive, but will reach CRI values up to 65.

High Voltage Voltages of 208 and higher

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

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

Hot cathode lamp An electric dis-charge lamp whose mode of operation is that of an arc discharge. The cathodes may be heated by the discharge or by external means.

Hot Re-Start Time The amount of time from a momentary power interruption to return of full light output

IESNA Abbreviation for Illumination Engineering Society of North America.

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

Illuminance The amount of light (luminous flux) incident on a surface area. Illuminance is measured in footcandles (lumens/square foot) or lux (lumens/square meter). One footcandle equals 10.76 lux, although for convenience 10 lux commonly is used as the equivalent.

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 lamp in which light is produced by a filament heated to incandescence by an electric current

Indirect Lighting Luminaires that distribute 90-to-100 percent of their light upward to be reflected by the ceiling.

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 Fluorescent Lamp A fluorescent lamp designed for starting by a high voltage without preheating of the electrodes

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

Isolux Chart A series of lines plotted on any appropriate set of coordinates, each line connecting all the points on a surface having the same illumination.

Junction Box A metal box in which circuit wiring is spliced. It may also be used for mounting luminaires, switches or receptacles

Kelvin Color temperature is measured in degrees Kelvin, which indicathe hue of a specific type of light source. Higher temperatures indicate whiter, "cooler" colors, while lower temperatures indicate yellower, "warmer" colors.

Kilowatt (kw) A unit of electrical power, equal to 1000 watts.

Kilowatt-Hour (KWH) Unit of electrical power consumed over a period of time. KWH=watts/lOOOxhours used.

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

Lamp An artificial source of light (also a portable luminaire equipped with a cord and plug). Industry term for light bulb.

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 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 Rated life of a lamp, as established through laboratory testing during which a sample group of lamps is burned, including being subjected to a scheduled number of starts per day. The length of time required for half the lamps to fail is the rated lamp life.

Lamp lumen depreciation (LLD) The reduction in lamp light output that progressively occurs during lamp life.

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

Lamp rated 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.

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 Wattage The power consumption of a lamp after warm up NOT including ballast losses

Lens Used in luminaires to redirect light into useful zones.

Lexan Brand name for polycarbonate material used in lenses that will not break or yellow.

Light Loss Factor (LLF) A factor used in calculating the level of illumination that takes into account such factors as dirt accumulation on luminaire and room surfaces, lamp depreciation, maintenance procedures and atmosphere conditions.

Light Output Amount of light produced by a light source such as a lamp. The unit most commonly used to measure light output is the lumen.

Light pollution Any adverse effect of manmade light. Often used to denote urban sky glow. "The wasted light that goes up into the sky."

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.

Line voltage The 110-120-volt household current, generally standard 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 Pressure Sodium Lamp A discharge lamp in which light is produced by radiation of sodium vapor at low pressure producing a single wavelength of visible energy, i.e. yellow.

Low-voltage circuit protection Protection for a ballast's low-voltage control circuit from high voltage spikes. Does not apply to high-voltage controls.

Low-Voltage Lamps A lamp-typically compact halogen-that provides both high intensity and good color rendition. Lamp operates at 12V and requires the use of a transformer. Popular lamps are MR11, MR16 and PAR36.

Lumen (lm) 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. Ratings of initial light output provided by manufacturers express the total light output after 100 hours of operation.

Lumens Per Watt Lumen (light) output divided by lamp watts consumed (i.e. amount of light for electricity used); also known as 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. (Also referred to as fixture.)

Luminaire Dirt Depreciation (LDD) The multiplier to be used in illuminance calculations to relate the initial illuminance provided by clean, new luminaires to the reduced illuminance that they will provide due to dirt collection on the luminaires at the time at which it is anticipated that cleaning procedures will be instituted.

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

Luminance The amount of light reflected or transmitted by an object.

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

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

Maximum ambient temperature The maximum ambient temperature for which a compact fluroescent lamp (CFL) product is warranted to achieve rated life.

Maximum ballast case temperature The maximum temperature of the ballast case for which the manufacturer?s life rating is valid.

Maximum relative light output Illuminance measured at a fixed distance from the lamps.

Medium Bi-Pin A type of connector commonly used on T-8 and T-12 fluorescent lamps. Two small pins protrude from the lamp ends, which are inserted into a socket in the fixture.

Mercury Lamp A high intensity discharge (HID) lamp in which the major portion of the light is produced by radiation from mercury. Includes clear, phosphor-coated and self-ballasted lamps.

Mercury vapor (MV) lamp A high-intensity discharge lamp type that uses mercury as the primary light-producing element. Mercury vapor lamps produce light with a CCT from 3000 to 7000 K. Mercury vapor lamps with clear outer bulbs have CRI values from 15 to 25, whereas phosphor-coated lamps have CRI values from 40 to 55. Mercury vapor lamps are less efficacious than other HID lamp types, typically producing only 30 to 65 LPW, but they have longer lamp lives and lower initial costs than other HID lamp types.

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

Miniature bi-pin A type of connector commonly used on T-5 lamps. Similar in design to but smaller than medium bi-pin connectors, it uses two small pins that protrude from the lamp ends and are inserted into a fixture socket.

Minimum ambient temperature The minimum temperature at which a compact fluorescent lamp (CFL) product is warranted to start.

Minimum dimmed level The lowest dimmed level achieved by a ballast, expressed as a percentage of that ballast?s maximum light output.

Minimum load requirement The minimum power required for an occupancy sensor to operate properly.

Minimum required efficacy The minimum lamp efficacy required by EPACT, expressed in lumens per watt (LPW).

Minimum starting temperature The minimum ambient temperature at which a ballast will reliably start fluorescent lamps.

MR16 A low-voltage quartz reflector lamp, only 2 inches in diameter. Typically the lamp and reflector are one unit, which directs a sharp, precise beam of light

Multitap A passive distribution component composed of a directional coupler and a splitter with two or more output connections.

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). Or: I = E/R

Open-circuit voltage The voltage applied across the output terminals of a ballast when no load is connected. Open-circuit voltage is the voltage applied across a lamp circuit to start the lamp. After starting, the voltage rapidly decreases and stabilizes at the operating voltage.

Operating Current Current in amps consumed by a lamp at rated watts.

Operating cycle The frequency with which lamps are cycled on and off.

Operating electrode voltage The voltage that a ballast supplies to a lamp's electrodes.

Operating position The manufacturer-recommended operating position for a lamp.

Operating Voltage Voltage at rated watts after lamp fully warms

Outlet Box A metal box in which circuit wiring is spliced. It may also be used for mounting luminaires, switches or receptacles

PAR lamp An incandescent or tungsten-halogen incandescent lamp with a hard glass bulb and an interior reflecting surface, a precisely placed filament, and a lens to control beam spread. The lens is hermetically sealed to the reflector. Metal halide PAR-lamps are also now available.

Phosphors The white, powdered material coating the inside of the glass tube of a lamp. The phosphors fluoresce (emit visible light) when excited by the ultraviolet radiation produced by the mercury vapor that is energized by the electric arc sustained inside the lamp.

Photo sensor A device used to integrate an electric lighting system with a daylighting system so lights operate only when daylighting is insufficient.

Photocell A light sensing device used to control luminaires and dimmers in response to detected light levels.

PL Designation for a type of compact fluorescent lamp.

Plug-in Wiring Electrical distribution system which has quick-connect wiring connectors.

PN junction For light emitting diodes, the portion of the device where positive and negative charges combine to produce light.

Polarization The process by which the transverse vibrations of light waves are oriented in a specific plane. Polarization may be obtained by using either transmitting or reflecting media.

Polycarbonate Material used in lenses that will not break or yellow

POMB Position Oriented Mogul Base lampsfor horizontal burning positions

Power The power (in watts) used by a device to produce useful work (also called input power or active power). In lighting, it is the system input power (in watts) for a lamp and ballast combination. When referred to as benchtop active power, the measurement procedure follows ANSI standards, which include horizontally mounted bare lamp(s) at an ambient temperature of 25°C, 1°C, and air movement less than 5 feet per minute. The lamps are seasoned 100 hours before testing, and the measurements are conducted after lamp light output stabilizes.

Power factor (PF) The ratio of active power (in watts) to apparent power (in rms volt-amperes), power factor is a measure of how effectively an electric load converts power into useful work. Power factor (PF) is calculated using the equation PF = (active power) / [(rms voltage) x (rms current)]. Phase displacement and current distortion both reduce power factor. A power factor of 0.9 or greater indicates a high power factor ballast.

Power line carrier (PLC) A system that transmits high-frequency (50 to 500 kHz) analog or digital signals via the power lines of a building. These signals control devices such as luminaires or contain voice transmissions such as intercom messages. Some commercial and residential energy management systems also use power line carrier systems.

Power reduction efficiency factor A measure of the efficiency of a power reducer, representing the reduced light output in percent from a lighting-circuit power reducer divided by the reduced active power in percent from a lighting circuit power reducer.

Preheat Fluorescent Lamp A fluorescent lamp designed for operation in a circuit requiring a manual or automatic starting switch to preheat the electrodes in order to start the arc.

Preheat time For rapid-start lamps, the time from the onset of lamp current to the lamp arc's striking, during which the lamp electrodes are heated to ease starting.

Prismatic lens An optical component of a luminaire that is used to distribute the emitted light. It is usually a sheet of plastic with a pattern of pyramid-shaped refracting prisms on one side. Most ceiling-mounted luminaires in commercial buildings use prismatic lenses.

Programmed start Refers to a type of rapid start ballast that optimizes the starting process by waiting until the lamp?s electrodes have been heated to apply the starting voltage, thus easing the load to the electrode and extending lamp life. Standard rapid start ballasts heat the electrodes during the starting process to allow quicker starting without flicker.

Pulse start metal halide lamps Pulse start metal halide lamps incorporate a high voltage ignitor similar to the high pressure sodium. The result is a run up time of two minutes, one-half that of standard metal halide and equal to high pressure sodium. The restrike time is similarly affected, being cut by 80% down to three to four minutes. The efficiency (lumen/watt) of pulse start systems is anywhere from a 25% to 50% increase in lumens/watts, 90 to 110 up from probe start at 60-85. Lumen maintenance also increases by up to 30%, up to 85% from 65%. The change in color (color shift) of pulse start due to the improved crest factor and lamp wattage regulation is reduced by up to 2/3 of the comparable probe start metal halide or less than 200°K over the life of the lamp versus 600°K for probe start. A CRI of up to 85 represents a 30% improvement over traditional probe start metal halide sources (four times that of high pressure sodium). Finally, the high voltage ignitor allows a much colder starting temperature compared to standard metal halide units, -40°F/-40°C to -20°F/-30°C.

R Lamps Reflectorized lamps available in spot (clear face) and flood (frosted face).

Rapid Start Fluorescent Lamp A fluorescent lamp designed for operation with a ballast that provides a low-voltage winding for preheating the electrodes and initiating the arc without a starting switch or the application of high voltage.

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 Lamp Life The point in hours where 50% of lamps initially started will still be operating.

Rated light output 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.

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.

Reflectance Sometimes called reflectance factor. The ratio of reflected light to incident light (light falling on a surface). Reflectance is generally expressed in percent.

Reflector A piece of material with a reflective surface that directs radiant energy (light)in a desired direction.

Reflector Lamp A light source with an integral reflector, usually a silver or aluminum coating on the bulb.

Refraction The process by which the direction of a ray of light changes as it passes obliquely from one medium to another in which its speed is different

Relamping A project where the existing lighting fixtures at a facility are, as a group, cleaned and new lamps are installed. This is typically scheduled around projected life expectancy to reduce the day-to-day interruptions of failing aged lamps.

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.

Retrofit Refers to upgrading a fixture, room, building, etc., by installing new parts or equipment.

Romex A cable comprised of flexible plastic sheathing inside of which are two or more insulated wires for carrying electricity.

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

Semicutoff 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.

Shielding An arrangement of light-controlling material to prevent direct view of the light source.

SON Another term for a high pressure sodium (HPS) lamp

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 Another term for a low pressure sodium (LPS) lamp.

Spectral Energy Distribution (SED) Curves A plot of the level of energy at each wavelength of a light source.

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

Spectroradiometer An instrument capable of separating and measuring light waves.

Starter A device used in conjunction with a ballast to start electric-discharge lamps, usually older fluorescents.

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.

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

Starting voltage The voltage applied across the lamp during starting.

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.

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

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).

Tandem Wiring A wiring option in which a ballast is shared by two or more luminaires. This reduces material and energy costs. Also called "master-slave" wiring.

Task Lighting Lighting directed to a specific surface or area that provides illumination for visual tasks.

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.

Transformer device to raise or lower electric voltage.

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

Transmission The passage of light through a material.

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

Trim option A decorative luminaire accessory.

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.

Tungsten-Halogen Lamp A gas filled tungsten incandescent lamp containing a certain proportion of halogens

UL Underwriters Laboratory. An independent organization whose responsibilities include rigorous testing of electrical products. When products pass these tests, they can be labeled (and advertised) as "UL listed." UL tests for product safety only.

Ultrasonic frequency The frequency at which an ultrasonic sensor operates.

Ultraviolet Light (UV) Light that is shorter in wavelength and higher in frequency than visible violet light (literally beyond the violet light).

Underwriters Laboratory Commonly referred to as "UL". An independent organization whose responsibilities include rigorous testing of electrical products. When products pass these tests, they can be labeled (and advertised) as "UL listed." UL tests for product safety only.

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.

Venting Holes in the reflector assembly of a downlight.

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.

Visible Spectrum Electromagnetic energy between 380 (violet) and 770 (red) nanometers in wavelength, which can be seen by the human eye. Same as the "color spectrum."

Volt (V) The unit for measuring electric potential. It defines the force or pressure of electricity.

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. For example, a 120 volt lamp operated at 125 volts will lose 40 percent of its lamp life; conversely, operating that lamp at 115 volts will virtually double its life.

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.

Wall Wash Lighting A smooth even distribution of light over a wall.

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

Warm-up Time The amount of time from turn-on to 90% light output.

Watt (W) The unit for measuring electric power. It defines the power or energy consumed by an electrical device. The cost of operating an electrical device is determined by the watts it consumes times the hours of use. It is related to volts and amps by the following formula: Watts = Volts x Amps.

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)