Ballast - A device used to operate fluorescent and HID lamps. The ballast provides the necessary starting voltage, while limiting and regulating the lamp current during operation.

Ballast Cycling - Undesirable condition whereby the ballast turns lamps on and off (cycles) due to the overheating of the thermal switch inside the ballast. This may be due to incorrect lamps, improper voltage being supplied, high ambient temperature around the fixture, or the early stage of ballast failure.

Candela - Unit of luminous intensity, describing the intensity of a light source in a specific direction.

Candlepower - A measure of luminous intensity of a light source in a specific direction, measured in candelas (see above).

CBM - Certified Ballast Manufacturers Association; the CBM label indicates that the ballast has been tested to meet ANSI specifications.

Color Rendering index (CRI) - A scale for the effect of a light source on the color appearance of an object in comparison with the color appearance under a reference light source. Expressed on a scale from 0 to 100, where 100 is no color shift. In general, a low CRI rating indicates that the colors of objects will appear unnatural under that particular light source.

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Color Temperature - The color temperature is a specification of the color appearance of a light source, relating the color to a reference source that is heated to a particular temperature, measured by the thermal unit Kelvin. The measurement can also be described as the "warmth" or "coolness" of a light source. Generally, sources below 3500K are considered "warm;" while those above 4000K are considered "cool" sources.

Compact Fluorescent - A small fluorescent lamp that is often used as an alternative to incandescent lighting. The lamp life is about 1O times longer than incandescent lamps and is 3-4 times more efficacious. Also referred to as PLI DL, CFL or BIAX lamps.

CRI - See Color Rendering index.

Cut-Off Angle - The angle from a fixture's vertical axis at which a reflector, louver or other shielding device cuts off direct visibility of a lamp. it is the complementary angle of the shielding angle.

CW - Designation for the cool-white halophosphor used in fluorescent lamps. Cool-white lamps have a CRI rating of 62 and a color temperature of about 4200K.

Daylight Compensation - A dimming system controlled by a photocell that reduces the output of the lamps when daylight is present. As daylight levels increase, lamp intensity decreases. An energy-saving technique used in areas with significant daylight contribution.

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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.

Down light - A type of ceiling luminaries usually fully recessed, where most of the light is directed downward. May feature an open reflector and/or shielding device.

Electro luminescent - 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).

Electronic Ballast - A ballast that uses semiconductor components to increase the frequency of fluorescent lamp operation-typically in the 20-40 kHz range. Smaller inductive components are used to provide the lamp current control. Fluorescent system efficiency is increased due to high frequency lamp operation.

Electronic Dimming Ballast - A variable output electronic fluorescent ballast.

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 ballasts can no longer be manufactured.

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

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Flicker - Variation in light intensity due to 60 Hz operation. Can cause eyestrain and fatigue due to stroboscopic effects.

Fluorescent Lamp - A light source consisting of a tube filled with argon, along with krypton or other inert gas. When electrical current is applied, the resulting arc emits ultraviolet radiation that excites the phosphors on the inside of the lamp wall, causing them to radiate visible light.

Foot candle (fc) - The English unit of measurement of the illuminance (or light level) on a surface. One foot candle is equal to one lumen per square foot.

Glare - The effect of brightness or differences in brightness within the visual field sufficiently hiah to cause annoyance, discomfort or loss of visual performance.

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Halogen - See Tungsten Halogen Lamp.

HID - Abbreviation for High Intensity Discharge. Generic term used to describe mercury vapor, metal halide, high pressure sodium and (informally) low pressure sodium light sources and luminaries.

High-Bay - Pertains to the type of lighting in an industrial application where the ceiling is 20 ft. or higher. Also describes the application itself.

High-Output - A lamp or ballast designed to operate at higher currents (8OOmA) and produce more light.

High-Pressure Sodium Lamp (HPS) - A high-intensity discharge (HID) lamp whose light is produced by radiation from sodium vapor (and mercury).

Hot Restart (or Hot Restrike) - A phenomenon of re-striking the arc in an HID light source after a momentary power loss. Hot restart occurs after the arc tube has cooled a sufficient amount.

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IESNA - Abbreviation for Illumination Engineering Society of North America.

Illuminance - A photometric term that quantifies light incident on a surface or plane. Illuminance is commonly referred to as light level. it is expressed as lumens per square foot (foot candles), or lumens per square meter (lux).

Instant Start - A fluorescent circuit that ignites the lamp instantly with a very high starting voltage from the ballast. Instant start lamps have single-pin bases.

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Lamp Lumen Depreciation (LLD) Factor - A factor that represents the reduction of lamp lumen output over time. The factor is commonly used as a multiplier to the initial lumen rating in illuminance calculations, which compensates for the lumen depreciation.

Lay-In Troffer - A fluorescent fixture; usually a 2'x4' fixture that sets or "lays" into a specific ceiling grid.

Lens - A transparent or translucent medium that alters the directional characteristics of light passing through it. Usually made of glass or acrylic.

Lighting upgrade - A term which can apply to either an energy efficiency or light level improvement project.

Load Shedding - A lighting control strategy for selectively reducing the output of light fixtures on a temporary basis as a means to reduce peak demand charges.

Louver - Grid type of optical assembly used to control light distribution from a fixture. Can range from small-cell plastic to large-cell anodized aluminum louvers used in parabolic fluorescent fixtures.

Low-Pressure Sodium Lamp (LPS) - A low-pressure discharge lamp in which light is produced by radiation from sodium vapor. Considered a monochromatic light source (most colors are rendered as gray).

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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 - A unit of light flow, or luminous flux. The lumen rating of a lamp is a measure of the total light output of the lamp.

Lumen Maintenance Control - An energy-saving lighting control strategy in which a photocell is used with a dimming system to provide a fixed light level over the maintenance cycle.

Luminaries - A complete lighting unit consisting of a lamp or lamps, along with the parts designed to distribute the light, hold the lamps and connect the lamps to a power source. Also called a fixture.

Luminance - A photometric term that quantifies brightness of a light source or of a surface that is illuminated and reflects light. It is expressed as foot lamberts (English units) or candelas per square meter (metric units).

Lux - The metric unit of measure for illuminance of a surface. one lux is equal to one lumen per square meter. One lux equals 0.093 foot candles.

Maintained Foot candles - Foot candles calculated through application of light loss factors.

Mercury Vapor Lamp - A type of HID lamp in which the major portion of the light is produced by radiation from mercury vapor. Emits a blue-green cast of light. Available in clear and phosphor coated lamps.

Metal Halide Lamp - A type of HID lamp in which the major portion of the light is produced by radiation of metal halide and mercury vapors in the arc tube. Available in clear and phosphor-coated lamps.

MRI 6 - 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.

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Occupancy Sensor - Control device that turns lights off after the space becomes unoccupied. May be ultrasonic, infrared, combination or other type.

PAR Lamp - A Parabolic Aluminized Reflector lamp. An incandescent, metal halide or compact fluorescent lamp used to redirect light from the source using a parabolic reflector. Lamps are available with flood or spot distributions.

Parabolic Luminaire - A popular type of fluorescent fixture which has a louver composed of aluminum baffles that are curved in a parabolic shape. The resultant light distribution produced by this shape provides reduced glare, better light control, and is considered to have greater aesthetic appeal.

Paracube - A metallic coated plastic louver made up of small squares. Often used to replace the lens in an installed troffer to enhance its appearance. The paracube is visually comfortable, but the luminaire efficiency is lowered. Also used in rooms with computer screens because of their glare-reducing qualities.

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

Positive Cash Flow - when referred to as part of a lighting upgrade, this is a comparison of estimated savings to cost. With 100 percent project financing it is possible to have an immediate positive cash flow once the project starts.

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Rapid Start (RS) - The most popular fluorescent lamp/ballast combination used today. This ballast is designed to quickly and efficiently preheat lamp cathodes to start the lamp. Uses a "bi pin" base.

Reflectance - The ratio of light reflected from a surface to the light incident on the surface. Reflectance's are often used for lighting calculations. The reflectance of a dark carpet is around 20 percent, and a clean white wall is roughly 50 to 60 percent.

Reflector - The part of a light fixture that shrouds the lamps and redirects some of the light emitted from the lamp.

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.

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

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Shared Savings - A project where a building owner pays a lighting contractor a portion of the savings realized through the installation of energy efficiency products at the owner¹s facility. The term of the program varies based on existing technology currently in use.

Snap-Back - The potential or real situation where an energy-efficiency upgrade could be replaced with the original type of equipment. Installations that are subject to snap-back are not permanent.

Spacing Criterion - The maximum recommended distance that interior fixtures should be spaced to ensure uniform illumination on the workplane. The height of the luminaire above the work plane multiplied by the spacing criterion equals the recommended maximum center-to-center luminaire spacing.

Specular - Mirrored or polished surface. The angle of reflection is equal to the angle of incidence. This word is used to describe the finish of the material used in some louvers and reflectors.

Stroboscopic Effect - Condition where rotating machinery or other rapidly moving objects appear to be standing still due to the alternating current supplied to light sources. Sometimes called "strobe effect."

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T8 Lamp - Industry standard for a fluorescent lamp that is eight one-eights (one inch) in diameter. Other typical sizes include T10 (1.25 inches) and T12 (1.5 inches) in diameter. The Color Rendering Index (CRI) is usually higher than a standard T12 lamp.

T12 Lamp - Industry standard for a fluorescent lamp that is 12 one-eighths (1.5 inches) in diameter. Other typical sizes include T10 (1.25 inches) and T8 (1 inch) lamps.

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 - The lighting, or amount of light, that falls on a given visual task.

Troffer - The term used to refer to a recessed fluorescent light fixture (combination of trough and coffer).

Tungsten Halogen Lamps - A gas-filled tungsten filament incandescent lamp with a lamp envelope made of quartz to withstand the high temperature. This lamp contains a certain proportion of halogens, namely iodine, chlorine, bromine and fluorine that slows down the evaporation of the tungsten. Also commonly referred to as a quartz lamp.

Twin-Tube - See Compact Fluorescent Lamp.

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Underwriters Laboratories (UL) Inc. - 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.

Vandal-Resistant - Fixtures with rugged housings, break-resistant type shielding and tamperproof screws.

Very High output - A fluorescent lamp that operates at a "very high" current (15OOmA), producing more light output than a "high output" lamp (8OOmA) or standard output lamp (43OmA).

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