Glossary of Lighting Terms

“A” TYPE LAMP  Term used to describe the bulb’s shape.  This type of bulb is most commonly used as a standard for residential applications.  LAMP is another name commonly used for bulb. 

ACCENT LIGHTING   Term used to emphasize the direction of light on a particular object or field of view.  ( AKA directional lighting )

ALTERNATING CURRENT (AC) AC Current changes its polarity as travels through a conductor.  Typically AC current is measured in cycles per second or hertz.  In the USA the rate is 60hz but 50hz in Europe and other parts of the world.

AMBIENT LIGHTING  Term used to describe lighting that produces general illumination.

AMPERE (AMP)  Unit for measuring the rate and flow of an electrical current.

ANSI CODE   Stands for American National Standards Institute which offers standards for the physical, electrical, and performance characteristics of lamps, ballasts, luminaries, and other lighting and electrical equipment.  There standards are voluntary.

APPLICATION   AKA “lighting application,” which refers to the use of the particular lamp ( Example:  High-Bay industrial application or Ceiling Retail lighting). 

ARC   Term used to describe a high intensity electrical discharge occurring between two electrodes in a gaseous medium, usually accompanied by the generation of heat and the emission of light. 

ARC LAMP  A light source containing an arc (see above). Also called a discharge lamp, or an arc discharge lamp.

AVERAGE RATED LAMP LIFE  A median value of life expectancy. The average rated life is determined by burning a group of lamps until 50% are still burning and 50% have burned out.

BAFFLE  An opaque or translucent element that shields a light source from direct view at certain angles or absorbs unwanted light.

 BALLAST  A device used with electric-discharge lamps (fluorescent, mercury vapor, sodium vapor and other HIDs [High Intensity Discharge]) to obtain the necessary circuit conditions (voltage, current, and waveform) by controlling the flow of the electrical current.

BASE   This is the part of a bulb that provides a connection to the fixture when it is inserted into a socket.  Bases come in many different sizes and styles.

BEAM SPREAD  (a.k.a. BEAM ANGLE) For reflector and PAR lamps, the total angle of the beam (in degrees) to where the intensity of the beam falls to 50% of the light value at the center of the beam.

BI-PIN BASE   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 T8 and T12 tubular fluorescent lamps, and miniature bi-pins are used for tubular T5 fluorescent lamps.

BLACKBODY  A theoretical body used in the lighting industry as a standard for establishing “color” and spectral qualities of lamps. A perfect blackbody, when its temperature has risen to 3500˚K, would give out light of a certain color; at 4500˚K it would give a whiter color, and at 5500˚K still a whiter color.

BRIGHTNESS   Commonly used as a reference to the degree of apparent lightness of a surface-its brilliancy or concentration of candlepower; from an engineering perspective, brightness is a subjective measurement and should not be used (see luminance).

BULB   The outer jacket or envelope of a lamp.

BEAM SPREAD   (a.k.a. BEAM ANGLE) For reflector and PAR lamps, the total angle of the beam (in degrees) to where the intensity of the beam falls to 50% of the light value at the center of the beam.

BI-PIN BASE   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 T8 and T12 tubular fluorescent lamps, and miniature bi-pins are used for tubular T5 fluorescent lamps.

BLACKBODY   A theoretical body used in the lighting industry as a standard for establishing “color” and spectral qualities of lamps. A perfect blackbody, when its temperature has risen to 3500˚K, would give out light of a certain color; at 4500˚K it would give a whiter color, and at 5500˚K still a whiter color.

BRIGHTNESS   Commonly used as a reference to the degree of apparent lightness of a surface-its brilliancy or concentration of candlepower; from an engineering perspective, brightness is a subjective measurement and should not be used (see luminance).

BULB The outer jacket or envelope of a lamp.

CANDELA   The international unit (SI) of luminous intensity of a light source in a given direction. A term from the early days of lighting that is still used today, it evaluated the intensity of light sources based on comparison to a standard candle of fixed size and composition.

CANDELABRA BASE  An E12 screw-in style lamp base, 7/16” (12 mm) in diameter, that is commonly found on decorative lamps and used in decorative fixtures, such as ceiling fans and chandeliers.

CATHODE   A cathode is an electrode in a linear fluorescent lamp that emits electrons to the cathode at the opposite end of the lamp to create light.

COLOR RENDERING INDEX (CRI)  Because colors appear differently under different light sources, the Color Rendering Index (CRI) measures a lamp’s ability to render colors most naturally. It measures the degree of color shift objects undergo when illuminated by a light source as compared with those same objects when illuminated by a reference source of comparable color temperature. CRI is measured on a scale of 0 to 100, with daylight being 100. Generally, the higher the CRI, the better the colors appear. The color rendering property of lamps is extremely important to many consumers, especially retail stores, museums, galleries, etc.

COLOR SPECTRUM  All the radiant energy wavelengths that make human sight possible. The visible wavelengths include all colors and are measured in nanometers.

COMPACT FLUORESCENT LAMP (CFL) The general term applied to fluorescent lamps that are single-ended and have smaller diameter tubes that are bent to form a compact shape. With the exception of plug-in lamps, CFLs have integral ballasts for easy replacement of incandescent lamps.

CONTRAST The difference in brightness (luminance) of an object and its background.

COOL WHITE   A term loosely used to denote a color temperature of around 4100K.

CORRELATED COLOR TEMPERATURE (C.C.T.)  Describes the apparent color, or chromaticity, of a light source measured in degrees Kelvin (K). The higher the color temperature, the visually cooler, or bluer, the light appears. Typical color temperatures are: 2700K (incandescent), 4100K (cool white fluorescent), and 5000K (daylight fluorescent).

COST OF LIGHT  A term typically used to describe the total cost for bringing light to a given area. The Cost of Light includes the cost of the electricity to power the bulb, the labor to change the bulb, and the cost of the bulb itself. On average, traditional lighting electricity makes up 88%, the labor 8%, and the bulb 4% of every dollar spent on lighting. LEDs use approximately 80% less energy than incandescent bulbs.

DEPARTMENT OF ENERGY (DOE)  U.S. government agency which regulates energy-related issues.

DESCRIPTION   The lamp’s identifying description. It typically includes the lamp shape and size.

DIFFUSED LIGHTING Lighting on a work area or an object that does not come from one particular direction.

DIMMER  A device used to control the intensity of light emitted by a luminaire by controlling the voltage or current available to it.

DIODE  A device attached to a wire that reduces the influx current.

DIRECT CURRENT (DC)  Electric current that flows continuously in only one direction from positive to negative.

DIRECT LIGHTING   Lighting that distributes 90-100% of the emitted light in the general direction of the surface to be illuminated. The term usually refers to light emitted in a downward direction.

DESIGN LIGHTS CONSORTIUM  The DLC — a collaboration of utility companies and regional energy efficiency organizations — is committed to raising awareness of the benefits of efficient lighting in commercial buildings.

DOWNLIGHT  A small, direct lighting unit which directs the light downwards and can be recessed, surface mounted, or suspended.

EFFICACY OR LUMINOUS EFFICACY   A measurement of a lamp’s ability to convert electrical power (watts) into visible light (lumens) and is expressed in terms of light output compared to the energy consumed.

 EFFICIENCY   An entire lighting system’s quality of light output compared to the energy consumed.

 ELECTRICAL DISCHARGE   A condition under which a gas becomes electrically conducting and capable of transmitting current, usually accompanied by the emission of radiation. An electric spark in air is an example of an electrical discharge.

ELECTROMAGNETIC BALLAST  A ballast used with discharge lamps that consists primarily of transformer-like copper windings on a steel or iron core.

ELECTROMAGNETIC INTERFERENCE (EMI)  High frequency electronic ballasts and other electronic devices can produce a small amount of radio waves which can interfere with radio and TV. Federally mandated requirements for EMI levels must be met before an electronic device is considered FCC compliant.

ELECTROMAGNETIC SPECTRUM  A continuum of electric and magnetic radiation encompassing all wavelengths: visible, ultra-violet, and infra-red light.

ELECTRONIC BALLAST A ballast that uses solid state electronic components and typically operates fluorescent lamps at frequencies in the range of 25-35 kHz. The benefits are increased lamp efficacy, reduced ballast losses, and lighter, smaller ballasts compared to electromagnetic ballasts. Electronic ballasts may also be used with HID (high intensity discharge) lamps.

EMISSION COATING An oxide coating deposited on a cathode that emits electrons when heated.

ENCLOSED-RATED HID  An HID lamp that must be used in enclosed luminaires. These lamps are designated by ANSI as type-E. The medium base lamps that are enclosed rated have a smaller neck at the base of the lamp. Mogul base lamps that are "protected" have a longer tip on the base that meets ANSI designation 

ENERGY ANALYSIS   A formula which measures the current cost of lighting as compared to the cost of lighting with an upgraded system to show the money saved in energy costs.

ENERGY POLICY ACT (EPACT)  The Energy Policy Act of 1992 mandated efficiency standards for many of the industry’s most popular lamp types. It eliminated the production of certain inefficient lamps, established minimum energy efficacy standards, and outlined labeling laws for certain lamps.

ENERGY STAR  Some lamps have earned the ENERGY STAR designation. They meet strict energy efficiency guidelines set by the EPA and the U.S. Department of Energy.

FILAMENT   The threadlike tungsten wire that lights up when an electric current runs through it. The filament is what makes an incandescent lamp light up. There are different filament types, which are designated by a prefix letter that indicates whether the wire is straight (S), coiled (C), or coiled coil (CC) and a number to indicate the arrangement of the filament on the support.

FINISH  The color, or finish, on the glass shell or lens of the lamp. Typically clear, white, or frost.

FLICKER The periodic variation in light level caused by AC operation that can lead to strobe effects.

FLOOD  A designation of a lamp’s beam spread. A flood lamp produces a wider beam angle of light to illuminate a larger area.

FLUORESCENCE   The emission of light as the result of the absorption of radiation of shorter wavelengths. Fluorescence occurs only while energy is being absorbed by the fluorescing material.

FLUORESCENT LAMP  A low pressure mercury, electric discharge lamp in which a fluorescing coating (phosphors) transforms some of the ultraviolet energy into light. Fluorescent lighting produces many different color tones, ranging from cool to warm, and is more diffuse than other light sources, making it excellent for general lighting.

FLUX Continuous flow of luminous energy.

FOOTCANDLE (FC)  The unit of illumination-one footcandle is one lumen per square foot.

GENERAL LIGHTING  Lighting designed to provide a substantially uniform level of illumination throughout an area.

GLARE   When light is brighter than the light to which the eyes are adapted to, it can cause a glare which is annoying, uncomfortable, and can lower visibility.

GLOBE  A decorative lamp with a ball-shaped bulb that is used primarily in bathroom and kitchen fixtures.

GREEN LIGHT PROGRAM  Initiated by the E.P.A. in 1991 to encourage companies to become Green Light allies by retrofitting their facilities with energy-efficient products.

GROUP RELAMPING  Replacing an entire group of lamps at a specified time, even if all of them haven’t burned out. This is the correct method for replacing HID lamps.

GU24 BASE  A type of lamp base that has two pins that are 24 mm apart. GU24 bases were specially designed for energy efficient lamps, such as CFLs, to guarantee energy savings in a light fixture. Incandescent and halogen lamps are not manufactured with GU24 bases; therefore, a fixture with GU24 sockets can only accept energy efficient lamps.

HIGH-BAY LIGHTING  Lighting designed for (typically) industrial locations with a ceiling height of 25 feet and above.

HIGH INTENSITY DISCHARGE (HID)   LAMP A general term for mercury, metal halide, high-pressure sodium, or xenon lamps. HID lamps contain compact arc tubes which enclose various gases and metal salts operating at relatively high pressures and temperatures.

HIGH OUTPUT (HO)  A fluorescent lamp designed for use with an 800 milliampere ballast. These lamps usually operate at low temperatures near zero and still produce high quality light.

HIGH PRESSURE SODIUM (HPS)   LAMPS A clear or coated high-intensity discharge lamp in which light is produced by an electrical discharge through sodium vapor operating at relatively high pressures and temperatures. HPS lamps are highly efficient and produce a warm, golden color. They are commonly used to light large areas such as roadways, offices, shopping malls, reception areas, parks, and commercial and industrial areas.

HIGH VOLTAGE Voltage of 208 and higher.

HOT RESTART TIME  The amount of time from a momentary power interruption to return to full light output.

HUE  The attribute that determines whether a color is red, yellow, green, blue, etc.

IGNITOR  A device that generates voltage pulses to start discharge lamps without preheating the electrodes.

ILLUMINANCE The density of light on a surface or lumens/area; measured in footcandles or lux.

INDIRECT LIGHTING Lighting an area with fixtures that distribute 90-100% of the light upward.

INFRA-RED  Radiant energy with wavelengths of 770 to 1106 nanometers, which cannot be seen by the human eye but can be felt as heat on the skin. Applications include photography, industrial drying or baking, medical heat therapy, food heating, etc.

INITIAL LUMENS A measurement of a lamp’s lumen output the moment the lamp is burned for the first time.

INSTANT START OR INSTANT RESTRIKE  Refers to fluorescent lamps that start instantly without preheating the cathodes and without the need of starters. “Instant Start” lamps have coiled heat cathodes in contrast to “Cold Cathode” lamps. Both, however, start cold and instantly. A higher voltage ballast is required for instant start lamps than for pre-heat. “Instant Starts” differ from “rapid start” lamps and cannot be used in “rapid start” fixtures.

INTENSITY A shortening of the terms luminous intensity and radiant intensity. Often mistaken to mean level of illumination.

JUNCTION BOX   A metal box in which circuit wiring is spliced to provide power to lighting fixtures without using an electrical circuit.

KELVIN TEMPERATURE (K)  A unit of temperature starting from absolute zero, parallel to the Celsius (or Centigrade) scale. 0˚ C is 273˚ K. Kelvin temperature is used to indicate the comparative color appearance of a light source compared to a theoretical blackbody.

KILOWATT (KW)  The measure of electrical power equal to 1000 watts.

KILOWATT HOUR (KWH)  The standard measure of electrical energy and the typical billing unit used for electricity use. Example: A 100-watt lamp operated for 10 hours consumes 1000 watt-hours (100 x 10) or one kilowatt-hour. If the utility charges $.10/kWh, then the electricity cost for the 10 hours of operation would be 10 cents (1 x $.10).

KRYPTON  A very heavy, inert gas which permits the filament in an incandescent lamp to glow hotter and brighter, while still providing long life.

LAMP  The term used to refer to the complete light source package, including the inner parts as well as the outer bulb or tube. “Lamp”, of course, is also commonly used to refer to a type of small light fixture, such as a table lamp.

LAMP 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.

LEED LEED stands for Leadership in Energy and Environmental Design. The United States Green Building Council (USGBC) created LEED as a rating system for the design, construction, and operation of buildings in an environmentally friendly way. LEED promotes a whole-building approach to sustainability by recognizing performance in five key areas of human and environmental health: sustainable site development, water savings, energy efficiency, materials selection, and indoor environmental quality.

LENS A glass or plastic element used in fixtures and lamps to control the distribution of light rays. The lens is what makes a spot lamp’s beam narrower and a flood lamp’s beam wider.

LIFE TEST A test in which lamps are operated under a specified length of time for the purpose of obtaining information on lamp life.

LIGHT  Radiant energy that can be sensed or seen by the human eye. Visible light is measured in lumens.

LIGHT SOURCE COLOR The color of the light emitted by a source.

LIGHTING FACTS   is a program of the U.S. Department of Energy that showcases LED products for general illumination from manufacturers who commit to testing products and reporting performance results according to industry standards.

L70   L70 is the point at which the LED's lumen output is at 70% of the original rated amount. L70 of 30,000 hours means that the tested LEDs produce 70% of the initial light output at 30,000 hours. If an LED has L50 of 30,000 hours, its lumen output decays faster than one with L70 of 30,000 hours.

LM-79   is an approved method for taking electrical and photometric measurements of SSL products. It covers total flux (light output), electrical power, efficacy, chromaticity, and intensity distribution. The five required metrics on the LED Lighting Facts label come from LM-79 test results.

LM-80    is an approved method for measuring the lumen maintenance of LED packages, arrays, and modules (i.e., the LED light source) at various temperatures. It specifies a minimum testing period of 6,000 hours, although 10,000 hours is preferred, and it requires testing at a minimum of 1,000-hour increments. LM-80 provides no determination or estimate of expected life or lumen maintenance beyond the test data, which, even with 10,000 hours of testing, falls far short of the claimed lifetimes of most SSL products on the market today

LUMEN The amount of light that is spread over a square foot of the surface by one candle when all parts of the surface are exactly one foot from the one-candle light source.

LUMEN DEPRICIATION   As a lamp burns, the amount of light (lumens) produced slowly decreases. For example, in incandescent lamps, the evaporating tungsten gathers on the inside of the bulb wall, causing it to darken. This lets less light through, causing lumen depreciation.

LUMEN GLAZE A proprietary coating applied to all Neolite lamps prior to the phosphor. Lumen Glaze flushes out impurities from the inner glass tube and acts as a sealant to prevent any remaining impurities from deteriorating the phosphor coating. It also acts as an adhesive to improve phosphor adherence to the glass tube. This increases the lumen maintenance and lumen output of Neolite lamps.

LUMEN MAINTENANCE A measure of how well a lamp maintains its light output over time.

LUMINAIRE   A complete lighting unit consisting of a lamp(s), ballast(s), and fixture as required together with the parts designed to distribute the light, position and protect the lamps, and connect them to the power supply. MEDIUM BASE A screw-in base, often referred to as a standard base because it is the most common. This is an E26 base, measuring 1” (26 mm) in diameter.

LUMINAIRE EFFICIENCY  The ratio of total lumens emitted by a luminaire to those emitted by the lamp(s) used.

LUMINANCE  A complicated mathematical definition of photometric brightness involving the intensity and direction of light. Simply, luminance is the amount of light reflected or transmitted by an object.

LUX  The SI unit of illuminance. One lux is one lumen per square meter (lm/m2).

MAINTENANCE FACTOR  A factor used to calculate 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 atmospheric conditions.

MEDIUM BASE  A screw-in base, often referred to as a standard base because it is the most common. This is an E26 base, measuring 1” (26 mm) in diameter.

MERCURY VAPOR  An HID lamp operating at a relatively high pressure and temperature in which the major portion of the light is produced by radiation from excited mercury vapor. Includes clear, phosphor-coated, and self-ballasted lamps. Phosphor-coated lamps add additional light and improve color rendering. Mercury lamps are the oldest of the HID family, and while not as energy efficient as other HID lamps, are commonly used where color rendering is not critical, especially in parking lot, roadway, security, and landscape lighting.

METAL HALIDE  An HID light source in which the major portion of the light is produced by the radiation from mercury plus halides of metals such as sodium, scandium, indium, and dysprosium. Metal halide lamps tend to be very efficient and produce a crisp, white light with excellent color-rendering properties. They are commonly used in outdoor lighting installations such as floodlighting and sports stadium lighting, as well as indoors in retail stores, lobbies, and other commercial and public spaces.

METRIC CONVERSION  To convert inches to millimeters use the formula: inches X 25.4001=millimeters.

MOGUL BASE  An E39 screw base, 1 ½” (39 mm) in diameter used on larger lamps.

MR16  A line of low voltage compact reflector lamps used for accent and spot lighting.

NANOMETER (NM) A unit of wavelength equal to 10-9 m.

OBJECT COLOR  The color of the light reflected or transmitted by an object when illuminated by a standard light source.

O.E.M.  Standard term for an Original Equipment Manufacturer. LITETRONICS has many O.E.M. customers who purchase our lamps to use as part of complete lighting systems that they manufacture.

OPEN-RATED HID  An HID lamp that can be operated in open or enclosed luminaires. These lamps are designated by ANSI as type-O.

OPERATING CURRENT Current, in amps, consumed by a lamp at rated watts.

OPERATING TEMPERATURE  Refers to the temperature of the environment around a lamp that may affect the operation of the lamp.

OPERATING VOLTAGE Voltage at rated watts after the lamp warms.

PAR LAMP   PAR is an acronym for parabolic aluminized reflector. The reflector, in a parabola shape, is aluminized to reflect the light and then covered with a lens to control the light beam. PAR lamps offer excellent beam control, come in a variety of beam patterns from spot to wide flood, and can be used outdoors unprotected because they are made of “hard” glass that can withstand adverse weather.

PHOTOCELL  An electronic device that uses light to regulate the flow of current in automatic control systems. When the photocell detects light, current is not allowed to flow and the lamp remains off. When the photocell does not detect light, current is allowed through and the lamp is turned on. Some photocells work as dimmers; the photocell will allow a variable amount of current to flow depending on how much light is detected. Other photocells work as total on/off switches.

PULSE START An HID ballast with a high voltage igniter to start the lamp.

QUALITY OF LIGHT  Favorable distribution of light in a visual environment. It is determined by measuring visual performance, visual comfort, ease of seeing, safety, and aesthetics for the specific visual tasks involved.

QUANTITY PER CASE Number of product units packed in a master case.

R WARNING   A federally mandated (Federal Standard 21 CFR 1040.3) warning which must be printed on all metal halide and mercury lamp packaging and catalogs because both lamps produce enough ultraviolet radiation to cause negative biological effects.

RADIANT ENERGY Energy traveling in the form of electromagnetic waves. It is measured in units of energy such as joules, ergs or kilowatt hours.

RAPID START CIRCUIT  A fluorescent system that does not require starters and usually requires 1 to 2 seconds to start. Current flows continuously through the electrodes, keeping them hot and electrons emissive.

RATED LAMP LIFE(AVERAGE LIFE) The point, in hours, where 50% of the lamps initially started will still be operating. Life may also be based on the average time before the lamp produces a certain amount of light.

RECESSED LIGHTING  A fixture that has been built into the ceiling so that the bottom edge of the fixture is flush to the ceiling.

REFLECTION Light striking a surface is either absorbed, transmitted, or reflected. Reflected light bounces off of a surface. Specular reflection means the rays strike and leave the surface at equal angles. Diffuse reflection leaves a surface in all directions.

REFLECTOR LAMP A light source with a built-in reflecting surface.

SOFT LIGHT Diffuse illumination that produces soft-edged, poorly defined shadows.

SPECTRAL POWER DISTRIBUTION (SPD) A graph of the radiant power emitted by a light source as a function of a wavelength.

SPEED OF LIGHT The speed of all radiant energy, including light: approximately 186,000 miles per second.

STARTER A starting switch needed for preheat fluorescent fixtures to “start” or light a lamp. It preheats the lamp cathodes and also provides a powerful electrical “kick” to jump the current through the lamp from cathode to cathode.

SURFACE MOUNTED  A type of fixture that is mounted on some type of surface, such as on a wall or under a cabinet.

SUSPENDED  Fixture that hangs down from the ceiling to bring the actual lamp part of the fixture closer to the surface to be illuminated.

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

The Energy Independence and Security Act (EISA) of 2007 was passed with the intention of moving the United States toward greater energy security, partly by increasing the standards for product efficiency. Section 321 of the Energy Independence and Security Act (EISA) establishes increased minimum energy efficiency standards for general service lamps. EISA does not ban incandescent light bulbs, but its minimum efficiency standards are high enough that the incandescent lamps most commonly used by consumers today will not meet the new requirements. Once implemented, the Act will essentially eliminate 40W, 60W, 75W, and 100W medium screw-base incandescent light bulbs. 

TCLP TEST Toxicity Characteristic Leaching Procedure 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 and/or lead in a lamp to leach from a landfill into groundwater.

TOTAL HARMONIC DISTORTION (THD)   A measure of the distortion caused by ballasts and other inductive loads of the input current on alternating current (AC) power systems caused by higher order harmonics of the fundamental frequency (60Hz in North America). THD is expressed in percent and may refer to individual electrical loads (such as ballast) or a total electrical circuit or system in a building. ANSI C82.77 recommends THD not exceed 32% for individual commercial electronic ballasts, although some electrical utilities may require lower THDs on some systems. Excessive THDs on electrical systems can cause efficiency losses, as well as overheating and deterioration of system components.

TM-21   provides guidelines for using LM-80 data to estimate the light source lumen maintenance beyond the LM-80 test period. LM-80 and TM-21 are designed to work hand-in-hand, with TM-21 using the LM-80 data, along with in-situ temperature performance data, to project the lumen maintenance of an LED light source.

TROFFER  A long, recessed lighting unit, usually installed in an opening in the ceiling.

ULTRAVIOLET (UV) RADIATION  Radiant energy of wavelengths shorter than the wavelengths of visible light. “Ultra” means beyond, so ultraviolet rays are beyond the violet end of the spectrum and, thus, beyond the range of sight. On the electromagnetic spectrum, UV radiation is within the wavelength range of 10-380.

UNDERWRITERS LABORATORIES (UL)   A private organization which tests and lists electrical equipment for electrical and fire safety according to recognized UL and other standards.

UNIVERSAL BURN  A notation indicating that a lamp can be burned base-up, base-down, or horizontally.

USEFUL LIFE  For LED light sources, one can define failure as when the LED can no longer produce a certain percentage of the initial light-output. For example, failure might be defined as when the light output of an LED reaches 70% or lower of the initial light output, this is the L70 rating on a product. At this point you can say the product is at the end of it's useful life, however the lamp may not be dead or out like incandescent bulbs. In other words, for a given period of time, if an LED produces insufficient light or no light, the LED is considered at failure.

VALANCE LIGHTING  Lighting from light sources on a wall typically above eye level, shielded by horizontal panels. The light may be upward or downward directed.

VOLT  A measure of “electrical pressure” between two points. The higher the voltage, the more current will be pushed through a resistor connected across the points. The volt specification of an incandescent lamp is the electrical “pressure” required to drive it at its designed point. The “voltage” of a ballast (e.g. 277 V) refers to the line voltage it must be connected to.

VOLTAGE  A measurement of the electromotive force in an electrical circuit or device expressed in volts. Voltage can be thought of as being analogous to the pressure in a waterline. Standard voltage in the U.S. is 110-120 (130 in some northwestern states). Standard voltage in Europe is 230-240.

WARM UP TIME The amount of time from turn-on to 90% light output.

WATT  The unit of electrical power used by an electrical device during its operation. Lamps are rated in watts to indicate their power consumption; power consumed over time equals the electrical energy used. It is related to volts and amps by the following formula: watts = volts X amps.

WAVELENGTH  Commonly measured in units of micrometers, nanometers, or angstroms. It is the distance between two successive points of a periodic wave, in the direction of propagation, at which the oscillation has the same phase.