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NLPIP Glossary

The terms and definitions have been grouped in alphabetical order. Please make a selection below to display the terms in that group, ie: selecting the E-H button will display all terms beginning with E, F, G and H.

If the results do not display the term you are looking for, please use the form on the FAQ page to suggest additional Glossary terms.

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A-lampThe incandescent lamp most commonly used in North American households. The "A" designation refers to the lamp's bulbous shape.
active powerthe system input power (in watts) for a lamp-ballast combination.
amalgamAn alloy of mercury with other metals. Some CFLs use a mercury amalgam rather than standard mercury. An amalgam keeps mercury pressure in the discharge near its optimal value as lamp temperature changes. Amalgam lamps can produce more than 90 percent of maximum light output over a wide temperature range, but they can take longer to reach their full light output when started.
ambient temperatureThe 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.
amplitudeThe maximum absolute value attained by a periodic wave.
ANSI codeAmerican National Standards Institute (ANSI) code that indicates the electrical operating designation of the lamp, which must match that of the ballast.
apertureThe diameter in the opening of a downlight, in inches (in.). Sometimes manufacturers will round up to the next whole-inch increment.
aperture diameterThe diameter of a reflector cone opening, expressed in inches.
apparent powerThe product of root-mean-square (rms) voltage and rms current.
applicationThe use to which a lighting system will be put; for example, a lamp may be intended for indoor residential applications.
arc tubeAn envelope, usually quartz or ceramic that contains the arc of a discharge light source.
average rated lifeThe 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.
ballastA 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 accessThe opening through which the ballast in a luminaire can be installed or replaced, either through the aperture or from above the luminaire.
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 lifeThe 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.
barn doorsTypically, four adjustable shields that are attached to the face of the luminaire to reduce glare.
beam angleThe angle at which luminous intensity is 50 percent of the maximum intensity.
beam appearanceThe description of a beam’s image on a wall as determined by subjective visual evaluations.
beam appearanceThe 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 spreadThe 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 switchingControl of light source intensity at two discrete levels in addition to off.
binTo sort or classify light sources (such as light emitting diodes) into groups according to their luminous intensity or color appearance.
blackbody radiatorA temperature radiator of uniform temperature whose radiant output in all parts of the spectrum is the maximum obtainable from any temperature radiator at the same temperature. Such a radiator is called a blackbody because it absorbs all the radiant energy that falls upon it. All other temperature radiators can be classed as non-blackbodies. Non-blackbodies radiate less in some or all wavelength intervals than a blackbody of the same size and the same temperature.
Brewster's angleThe incident angle of light on the surface of a medium for which the reflected and transmitted light are perpendicular to each other. This angle depends on the refractive index of the medium. It defines the angle of maximum polarization for a medium.
brownout circuitryFor 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 designationAn 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 finishThe coating, if any, that is applied to the inside surface of the bulb. Finishes are either clear, phosphor coated, or diffuse.
candelaThe Systeme International d'Unities (SI) of luminous intensity. One candela is one lumen per steradian. Formerly, candle.
capacitorA 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 ballastAn 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.
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).
CIEAbbreviated as CIE from its French title Commission Internationale de l'Eclairage, the International Commission on Illumination is a technical, scientific, and cultural organization devoted to international cooperation and exchange of information among its member countries on matters relating to the science and art of lighting.
coefficient of utilization (CU)Coefficient of utilization is the ratio of the luminous flux (lumens) received on a plane to the light output (lumens) of the lamps. Coefficient of utilization depends on luminaire efficiency, distribution of light from the luminaire, size and shape of the room, and reflectances of surfaces in the room. Specifiers use the coefficient of utilization to evaluate how effectively a luminaire delivers light to a workplane.
color appearanceThe resultant color perception that includes the effects of spectrum, background contrast, chromatic adaptation, color constancy, brightness, size and saturation.
color consistencyThe measure of how close in color appearance random samples of a lamp or source tend to be.
color matchingThe action of making a color appear the same as a given color. Often used as a method of evaluating the ability of a light source to render colors faithfully.
color renderingA general expression for the effect of a light source on the color appearance of objects in conscious or subconscious comparison with their color appearance under a reference light source.
color rendering index (CRI)A rating index commonly used to represent how well a light source renders the colors of objects that it illuminates. For a CRI value of 100, the maximum value, the colors of objects can be expected to be seen as they would appear under an incandescent or daylight spectrum of the same correlated color temperature (CCT). Sources with CRI values less than 50 are generally regarded as rendering colors poorly, that is, colors may appear unnatural.
color rendering index (CRI)A rating index commonly used to represent how well a light source renders the colors of objects that it illuminates. For a CRI value of 100, the maximum value, the colors of objects can be expected to be seen as they would appear under an incandescent or daylight spectrum of the same correlated color temperature (CCT). Sources with CRI values less than 50 are generally regarded as rendering colors poorly, that is, colors may appear unnatural.
color shiftThe change in a lamp’s correlated color temperature (CCT) at 40% of the lamp’s rated life, in kelvin (K).
color stabilityThe ability of a lamp or light source to maintain its color rendering and color appearance properties over its life. The color properties of some discharge light sources may tend to shift over the life of the lamp.
color variationLamps of the same type made by the same manufacturer may exhibit a certain degree of variation in color, even when operated under the same conditions and seasoned for the same about of time.
combined uncertaintyCombined uncertainty is calculated by finding the sum of the squares of sample random variability (standard deviation) and laboratory measurement uncertainty and taking the square root of that sum.
compact fluorescent lamp (CFL)A family of single-ended fluorescent-discharge light sources with small-diameter [16-millimeter (5/8-inch) or less] tubes.
compatible ballastsAn 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.
conductionThe process of removing heat from an object via physical contact with other objects or materials, usually metals.
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 dimmingControl of a light source's intensity to practically any value within a given operating range.
continuously variable signalA signal that communicates data that can have a theoretically unlimited number of possible values between two end points. Examples include voltage, temperature, and illuminance.
contrastAlso known as luminance contrast, it is the relationship between the luminances of an object and its immediate background.
control signal rangeThe range of the electrical signal (in volts) that a control device uses to signal the dimming level to a ballast.
convectionThe process of removing heat from an object through the surrounding air.
correlated color temperature (CCT)A specification for white light sources used to describe the dominant color tone along the dimension from warm (yellows and reds) to cool (blue). Lamps with a CCT rating below 3200 K are usually considered warm sources, whereas those with a CCT above 4000 K usually considered cool in appearance. Temperatures in between are considered neutral in appearance. Technically, CCT extends the practice of using temperature, in kelvins (K), for specifying the spectrum of light sources other than blackbody radiators. Incandescent lamps and daylight closely approximate the spectra of black body radiators at different temperatures and can be designated by the corresponding temperature of a blackbody radiator. The spectra of fluorescent and LED sources, however, differ substantially from black body radiators yet they can have a color appearance similar to a blackbody radiator of a particular temperature as given by CCT.
cosine distributionA 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.
CSACanadian 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 THDA measure of the degree to which the current waveform deviates from sinusoidal, expressed as a percentage. See total harmonic distortion (THD).
cutoff angleThe angle of light distribution from a luminaire, measured upward from nadir, between the vertical axis and the first line at which the bare source (lamp) is not visible.
cutoff classificationThe classification system of the Illuminating Engineering Society of North America (IESNA) that describes the light distribution of anoutdoor luminiare. Cutoff classifications define the luminous intensity limits in two illumination zones that occur within the range of 80° to 180° above nadir. North America (IESNA) that describes the light distribution of an outdoor luminaire. Cutoff classifications define the luminous intensity limits in two illumination zones that occur within the range of 80° to 180° above nadir.
cutoff luminaireIESNA classification that describes a luminaire having a light distribution in which the candela per 1000 lamp lumens does not numerically exceed 25 (2.5%) at or above an angle of 90° above nadir, and 100 (10%) at or above a vertical angle of 80° above nadir. This applies to all lateral angles around the luminaire.
degree of polarizationA 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 materialDiffusers 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.
dimming ballastA device that provides the ability to adjust light levels by reducing the lamp current. Most dimming ballasts are electronic.
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.
direct lightLight emitted by a luminaire in the general direction of the task to be illuminated. The term usually refers to light emitted in a downward direction.
direct luminaireA luminaire that emits light in the general direction of the task to be illuminated. The term usually refers to luminaires that emit light in a downward direction.
direct uplightLight emitted upward by a luminaire.
disability glareA type of glare that causes a loss of visibility from stray light being scattered within the eye.
discomfort glareThe sensation of annoyance or even pain induced by overly bright sources.
distributed control systemA 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.
driverFor light emitting diodes, a device that regulates the voltage and current powering the source.
dynamic outdoor lightingOutdoor lighting that varies light level or other characteristics automatically and precisely in response to factors such as vacancy or the type of use of an outdoor location.

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