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Glossary A-lamp: An A-lamp is what most individuals think of when color rendering: The appearance of colored objects illumi- they hear the term “light bulb.” A19 is the most com- nated by a source. mon form factor used in residential applications. Most color rendering index (CRI): The internationally accepted of these are what are known as medium screw-base A19 metric for the evaluation of a light source’s color render- lamps, which describes the sockets with which the lamps ing abilities. The calculation of the CRI requires only the are compatible. These include most typical incandescent spectral power distribution of the light source of interest. lamps and many compact fluorescent lamps. The appearance of a predefined set of reflective samples avoided cost: The incremental cost to an electric power is compared when illuminated by the test source and producer of generating or purchasing a unit of electricity when illuminated by a reference illuminant. or capacity or both. conduction band: See band gap. ballast: An electronic device that converts incoming elec­ control circuitry: Electronic components designed to con- tricity to the proper voltage and current required to start trol a power source by adjusting output voltage, current, and maintain the operation of a lamp. or duty cycle to switch or otherwise control the amount bandgap: The energy gap between a semiconductor’s and characteristics of the electrical energy delivered to valence and conduction bands. The valence band is the a device. Control circuitry does not include a power highest energy level occupied by an electron, while the source. (ANSI and IES, 2010) conduction band is the lowest unoccupied level. External cool white: Light described as “cool” has a coordinated color energy is necessary to excite an electron through the temperature (CCT) at the high end of the CCT spectrum. bandgap from the valence band to the conduction band. It is usually perceived as slightly blue. binning: General term for the production and sorting meth- correlated color temperature (CCT): The temperature odologies used by LED makers to ensure that the LEDs of the blackbody radiator whose emitted light would they manufacture conform to stated specifications for appear to most closely match that of the source. forward voltage, color, and luminous flux. (Philips Color die: A small block of light-emitting semiconducting material Kinetics, 2010) on which a functional LED circuit is fabricated. (ANSI Btu: The British thermal unit is the traditional standard of and IES, 2010) measure for the quantity of heat required to raise the dimmer: A device capable of adjusting the level of light temperature of 1 lb of water by 1°F. output from a lamp. candela (cd): The SI unit of luminous intensity (i.e., flux per downlight: A small, direct lighting unit that directs light unit solid angle). A common candle will typically have downward and can be recessed, surface mounted, or luminous flux of about 1 candela. suspended. (ANSI and IES, 2010) chromaticity: The color of emitted light as perceived by driver: A device comprised of a power source and control the human visual system. The most common system for circuitry designed to operate an LED package (compo- specifying and communicating chromaticity is with CIE nent), array (module), or lamp. (ANSI and IES, 2010) 1931 (x,y) chromaticity coordinates. electroluminescence: The emission of light from a phos- color quality: The combination of chromaticity and color phor excited by an electromagnetic field. (ANSI and rendering properties of a light source that users judge IES, 2010) to be pleasing. encapsulant: A material used for encapsulating a device. In the case of LEDs, the encapsulant typically surrounds 113

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114 ASSESSMENT OF ADVANCED SOLID-STATE LIGHTING the chip and must be capable of withstanding constant lamp: A replaceable component that produces light. The optical radiation and elevated operating temperatures term lamp can refer to an incandescent bulb, a CFL bulb, without loss of transparency. or an LED replacement bulb. energy gap: See band gap. light-emitting diode (LED): A p-n junction semiconduc- epitaxy: The growth of one thin film layer using the crystal- tor device that emits optical radiation under an applied line structure of the preceding layer as a template. voltage. The optical emission may be in the ultraviolet exciton: An excitation of a molecule when an excited elec- or infrared wavelength regions as well as visible light. tron and hole are loosely bound together. This excitation (Industrial Fiber Optics, 2004) is mobile and eventually decays by the recombination of LED array: An assembly of LED packages or dies that are the electron and the hole. intended to connect to an LED driver, created by mount- fluorescence: The emission of light as a result of, and only ing and interconnecting individual LED devices on a during, the absorption of radiation of shorter wave- printed circuit board, which is then connected thermally lengths. (ANSI and IES, 2010) to the heat sink. fluorescent lamp: A tubular electric lamp that is coated LED package: The LED package is the structure in which on its inner surface with a phosphor and that contains the LED chip is mounted and through which access to mercury vapor whose bombardment by electrons from the LED terminals is provided. The assembly typically the cathode provides ultraviolet light, which causes the includes one or more LED dies with electrical connec- phosphor to emit visible light either of a selected color tions and may include an optical element as well as or closely approximating daylight. (California Energy thermal, mechanical, and electrical interfaces. (ANSI Commission, 2002) and IES, 2010) footcandle (ftc): A lumen per square foot; a unit of illumi- LED lamp, integrated: An integrated assembly composed nance. While commonly used, it is not an SI unit. The of LED packages or LED arrays, LED driver, ANSI corresponding SI unit is lux. standard base and other optical, thermal, mechanical, glare: The sensation produced by luminances within the and electrical components. The device is intended to visual field that are sufficiently greater than the lumi- connect directly to the branch circuit through a corre- nance to which the eyes are adapted; it may cause sponding ANSI standard socket. (ANSI and IES, 2010) annoyance, discomfort, or loss in visual performance LED lamp, non-integrated: An assembly comprised of an or visibility. (ANSI and IES, 2010) LED array or LED packages and ANSI standard base. halogen lamp: A type of incandescent lamps in which the The device is intended to connect to the LED driver of tungsten filament has been enclosed in a capsule con- an LED luminaire through an ANSI standard socket and taining a halogen gas, typically bromine. not to the branch circuit directly. (ANSI and IES, 2010) high-intensity discharge (HID) lamps: Electric lamps with LED light engine: An integrated assembly comprised of tubes filled with gas and metal salts. The gas initiates an arc, LED packages or LED arrays, LED driver, and other which evaporates the metal salts, forming a plasma. These optical, thermal, mechanical, and electrical components. lamps are generally used to light large spaces or roadways. The device is intended to connect directly to the branch Mercury, metal halide, and high-pressure sodium lamps are circuit through a custom connector compatible with the examples of specific types of HID lamps. LED luminaire for which it was designed and does not illuminance: The total luminous flux incident on a surface use an ANSI standard base. (ANSI and IES, 2010) per unit area. Commonly referred to as brightness, it lighting power density (LPD): The spatial average power indicates how bright an illuminated space is. Illumi- consumption of the installed luminaires in a building or nance depends on the luminous flux of the light sources, in a space. It is expressed in units of Watts per square their distances from the illuminated surface, and some of feet of floor area (W/ft2). the reflectance properties of nearby surfaces. lumen (lm): A measure of the amount of light, or luminous incandescence: The self-emission of radiant energy in the flux, emitted by a source per unit time. visible spectrum, due to the thermal excitation of atoms lumen maintenance: The relationship between temperature, or molecules. (ANSI and IES, 2010) operating time, and light output. incandescent lamp: A light source that generates light by luminance: A measure of the amount of light per unit area passing an electric current through a thin filament wire of a surface. The luminance of an illuminated object (usually tungsten) to a temperature of approximately is dependent on both the incident illuminance and the 2,500-3,000 kelvin (K) where the filament glows or reflectance of the object. Luminance is the common incandesces. measure of the intensity of displays. Lighting products internal quantum efficiency (IQE): The percentage of available in variable-sized flat forms, such as sheets or photons generated relative to the current (of electrons tapes, often report luminance because luminous flux or holes) injected into a device. depends on the surface area of the product.

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GLOSSARY 115 luminous efficacy: The luminous efficacy of a lamp is the of maintaining a constant level of illuminance in an ratio of the luminous flux to the total electrical power environment. consumed by the lamp. pop-on effect: A rapid increase in brightness before dim- luminous flux: The quantity of visible light emitted by a ming. Pop-on effects occur either (1) when lights do source per unit time. Luminous flux is measured in not turn on to their pre-set dimming level but first come lumens. on (near) full and then dim down automatically to the luminous intensity: The luminous flux per unit solid angle preset level, in the case of a preset dimming control; (i.e., in a specific direction) expressed in candela. Lumi- or (2) when lights do not turn on at the low end, but nous intensity magnitude results from luminous flux require the dimmer to be raised to a relatively high level being redirected by a reflector or magnified by a lens. to start the lamp, before dimming to a lower level can lux (lx): A lux is defined as a lumen per square meter and is be achieved, in the case of a slider or rotary dimmer. the SI unit of illuminance. power factor (PF): The ratio of electrical power dissipated Metal Organic Chemical Vapor Deposition (MOCVD): by a piece of equipment to the line power drawn. A method used for the growth of single crystal materi- power quality: The degree to which an electrical system als. During MOCVD, the wafer/substrate is exposed to functions as intended, with low levels of electrical noise metal-organic precursor gases (e.g., ammonia, trimeth- and steady voltage output up to a specified load. ylgallium, and trimethylaluminum) at elevated tempera- power source: A transformer, power supply, battery, or other tures. These gases then react, depositing a high-quality device capable of providing current, voltage, or power film (e.g., AlGaN) on the substrate. within its design limits. This device contains no addi- N-type material: A semiconductor rich in (negatively- tional control capabilities. (ANSI and IES, 2010) charged) electrons. power supply: An electronic device capable of providing organic light-emitting diode (OLED): Organic (carbon- and controlling current, voltage, or power within design based) molecules can behave similarly to inorganic limits. (ANSI and IES, 2010) semiconductors; an OLED is an LED made from an quantum well: A layered structure designed to confine organic semiconductor. In contrast to an LED, which is electrons or holes to a plane. a point source, OLEDs are made in sheets and act as a remote phosphor: A remote phosphor is a phosphor that is diffuse area light source. In addition to lighting, they are not put in intimate contact with the LED chip but rather used prominently in displays for TVs and cell phones. secondary optics for the packaged LED. organic vapor phase deposition: A method of deposition retrofit luminaire: A luminaire with an integrated lamp. wherein an organic material is heated in the presence They are designed to fit into the spaces occupied by of an inert carrier gas. The carrier gas is saturated by existing luminaires, but require complete removal of the the evaporated organic material before flowing toward existing luminaire for installation. the substrate onto which the organic molecules are then roll-to-roll processing: The process of creating a large deposited. quantity of electronic devices on a flexible substrate. P-type material: A semiconductor rich in (positively- This manufacturing process is typically imagined for charged) holes. OLEDs and organic photovoltaics to drive the cost p-n junction diode: When a p- and n-type semiconductor down, because both technologies are capable of being come in contact, they create a junction known as a diode. grown at low temperatures onto flexible substrates. The diode will selectively pass current from one material semiconductor: A semiconductor is a material characterized to the other. In an inorganic LED, the diode structure by its ability to conduct a small electrical current. Intrin- creates a region at the junction interface where electrons sically, it has far fewer carriers than a metal and is typi- recombine radiatively with holes and emit light. cally doped with other materials to pass large currents. performance bins: See binning. skyglow: The result of blue light being absorbed or scattered phosphor: A material that absorbs and re-emits light at a in the atmosphere resulting in a loss of visibility of the lower energy. Phosphor coatings are commonly used night sky, which is of special concern to the astronomy with LEDs—for example, a blue LED coated with a community. y ­ ellow phosphor will emit both blue light (from the Spectral Luminous Efficiency Function (Vλ): A model LED) and yellow light (from the phosphor after absorb- depicting the relationship between wavelength of light ing some of the LED’s light), which can appear white. and the relative sensitivity of the human visual system. Common phosphors used in LEDs include rare-earth thermal coefficient of expansion: The rate at which a mate- doped yttrium aluminum garnets, or YAG:RE. rial expands/contracts as it is heated/cooled. photobiology: Photobiology is the study of the effect of light total harmonic distortion (THD): The amount of distor- on biological organisms. tion on the voltage supply line at frequencies above the photosensor: A device capable of detecting the amount fundamental (60 Hz) carrier frequency. A high THD of light present. In lighting, it is often used as a way (>33 percent) causes problems in three-phase power

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116 ASSESSMENT OF ADVANCED SOLID-STATE LIGHTING systems, because usually the dominant harmonic current warm white: Light described as “warm” has a coordinated is the third harmonic. The third harmonic currents add color temperature (CCT) at the low end of the CCT in the neutral wire of the electrical system and in cases spectrum. It is usually perceived as slightly yellow. of high THD one can have a situation where the current flowing in the neutral wire exceeds the rating of the wire, REFERENCES causing overheating. troffer: A long, recessed lighting unit usually installed with ANSI (American National Standards Institute) and IES (Illuminating Engi- the opening flush with the ceiling. (ANSI and IES, 2010) neering Society). 2010. Nomenclature and Definitions for Illuminating Engineering. New York: ANSI and IES. vacuum thermal evaporation: A method of deposition in California Energy Commission. 2002. Energy Quest. Glossary of ­ nergy E which a material is heated in vacuum, evaporating from Terms. Available at the source and then condensing on the substrate. U ­ pdated May 20, 2002. valence band: See band gap. Industrial Fiber Optics. 2004. Fiber Optic Lab Manual: Fifth Edition. visible spectrum: The band of electromagnetic radiation Tempe, Ariz.: Industrial Fiber Optics, Inc. Philips Color Kinetics. 2010. LED Lighting Explained: Understanding LED that can be detected by the human eye, encompassing Sources, Fixtures, Applications, and Opportunities. Burlington, Mass.: wavelengths between 380 nm (violet) and 750 nm (red). Philips Solid-State Lighting Solutions, Inc.