A-lamp: An A-lamp is what most individuals think of when they hear the term “light bulb.” A19 is the most common form factor used in residential applications. Most of these are what are known as medium screw-base A19 lamps, which describes the sockets with which the lamps are compatible. These include most typical incandescent lamps and many compact fluorescent lamps.
avoided cost: The incremental cost to an electric power producer of generating or purchasing a unit of electricity or capacity or both.
ballast: An electronic device that converts incoming electricity to the proper voltage and current required to start and maintain the operation of a lamp.
bandgap: The energy gap between a semiconductor’s valence and conduction bands. The valence band is the highest energy level occupied by an electron, while the conduction band is the lowest unoccupied level. External energy is necessary to excite an electron through the bandgap from the valence band to the conduction band.
binning: General term for the production and sorting methodologies used by LED makers to ensure that the LEDs they manufacture conform to stated specifications for forward voltage, color, and luminous flux. (Philips Color Kinetics, 2010)
Btu: The British thermal unit is the traditional standard of measure for the quantity of heat required to raise the temperature of 1 lb of water by 1°F.
candela (cd): The SI unit of luminous intensity (i.e., flux per unit solid angle). A common candle will typically have luminous flux of about 1 candela.
chromaticity: The color of emitted light as perceived by the human visual system. The most common system for specifying and communicating chromaticity is with CIE 1931 (x,y) chromaticity coordinates.
color quality: The combination of chromaticity and color rendering properties of a light source that users judge to be pleasing.
color rendering: The appearance of colored objects illuminated by a source.
color rendering index (CRI): The internationally accepted metric for the evaluation of a light source’s color rendering abilities. The calculation of the CRI requires only the spectral power distribution of the light source of interest.
The appearance of a predefined set of reflective samples is compared when illuminated by the test source and when illuminated by a reference illuminant.
conduction band: See band gap.
control circuitry: Electronic components designed to control a power source by adjusting output voltage, current, or duty cycle to switch or otherwise control the amount and characteristics of the electrical energy delivered to a device. Control circuitry does not include a power source. (ANSI and IES, 2010)
cool white: Light described as “cool” has a coordinated color temperature (CCT) at the high end of the CCT spectrum. It is usually perceived as slightly blue.
correlated color temperature (CCT): The temperature of the blackbody radiator whose emitted light would appear to most closely match that of the source.
die: A small block of light-emitting semiconducting material on which a functional LED circuit is fabricated. (ANSI and IES, 2010)
dimmer: A device capable of adjusting the level of light output from a lamp.
downlight: A small, direct lighting unit that directs light downward and can be recessed, surface mounted, or suspended. (ANSI and IES, 2010)
driver: A device comprised of a power source and control circuitry designed to operate an LED package (component), array (module), or lamp. (ANSI and IES, 2010)
electroluminescence: The emission of light from a phosphor excited by an electromagnetic field. (ANSI and IES, 2010)
encapsulant: A material used for encapsulating a device. In the case of LEDs, the encapsulant typically surrounds
energy gap: See band gap.
epitaxy: The growth of one thin film layer using the crystalline structure of the preceding layer as a template.
exciton: An excitation of a molecule when an excited electron and hole are loosely bound together. This excitation is mobile and eventually decays by the recombination of the electron and the hole.
fluorescence: The emission of light as a result of, and only during, the absorption of radiation of shorter wavelengths. (ANSI and IES, 2010)
fluorescent lamp: A tubular electric lamp that is coated on its inner surface with a phosphor and that contains mercury vapor whose bombardment by electrons from the cathode provides ultraviolet light, which causes the phosphor to emit visible light either of a selected color or closely approximating daylight. (California Energy Commission, 2002)
footcandle (ftc): A lumen per square foot; a unit of illuminance. While commonly used, it is not an SI unit. The corresponding SI unit is lux.
glare: The sensation produced by luminances within the visual field that are sufficiently greater than the luminance to which the eyes are adapted; it may cause annoyance, discomfort, or loss in visual performance or visibility. (ANSI and IES, 2010)
halogen lamp: A type of incandescent lamps in which the tungsten filament has been enclosed in a capsule containing a halogen gas, typically bromine.
high-intensity discharge (HID) lamps: Electric lamps with tubes filled with gas and metal salts. The gas initiates an arc, which evaporates the metal salts, forming a plasma. These lamps are generally used to light large spaces or roadways. Mercury, metal halide, and high-pressure sodium lamps are examples of specific types of HID lamps.
illuminance: The total luminous flux incident on a surface per unit area. Commonly referred to as brightness, it indicates how bright an illuminated space is. Illuminance depends on the luminous flux of the light sources, their distances from the illuminated surface, and some of the reflectance properties of nearby surfaces.
incandescence: The self-emission of radiant energy in the visible spectrum, due to the thermal excitation of atoms or molecules. (ANSI and IES, 2010)
incandescent lamp: A light source that generates light by passing an electric current through a thin filament wire (usually tungsten) to a temperature of approximately 2,500-3,000 kelvin (K) where the filament glows or incandesces.
internal quantum efficiency (IQE): The percentage of photons generated relative to the current (of electrons or holes) injected into a device.
lamp: A replaceable component that produces light. The term lamp can refer to an incandescent bulb, a CFL bulb, or an LED replacement bulb.
light-emitting diode (LED): A p-n junction semiconductor device that emits optical radiation under an applied voltage. The optical emission may be in the ultraviolet or infrared wavelength regions as well as visible light. (Industrial Fiber Optics, 2004)
LED array: An assembly of LED packages or dies that are intended to connect to an LED driver, created by mounting and interconnecting individual LED devices on a printed circuit board, which is then connected thermally to the heat sink.
LED package: The LED package is the structure in which the LED chip is mounted and through which access to the LED terminals is provided. The assembly typically includes one or more LED dies with electrical connections and may include an optical element as well as thermal, mechanical, and electrical interfaces. (ANSI and IES, 2010)
LED lamp, integrated: An integrated assembly composed of LED packages or LED arrays, LED driver, ANSI standard base and other optical, thermal, mechanical, and electrical components. The device is intended to connect directly to the branch circuit through a corresponding ANSI standard socket. (ANSI and IES, 2010)
LED lamp, non-integrated: An assembly comprised of an LED array or LED packages and ANSI standard base. The device is intended to connect to the LED driver of an LED luminaire through an ANSI standard socket and not to the branch circuit directly. (ANSI and IES, 2010)
LED light engine: An integrated assembly comprised of LED packages or LED arrays, LED driver, and other optical, thermal, mechanical, and electrical components. The device is intended to connect directly to the branch circuit through a custom connector compatible with the LED luminaire for which it was designed and does not use an ANSI standard base. (ANSI and IES, 2010)
lighting power density (LPD): The spatial average power consumption of the installed luminaires in a building or in a space. It is expressed in units of Watts per square feet of floor area (W/ft2).
lumen (lm): A measure of the amount of light, or luminous flux, emitted by a source per unit time.
lumen maintenance: The relationship between temperature, operating time, and light output.
luminance: A measure of the amount of light per unit area of a surface. The luminance of an illuminated object is dependent on both the incident illuminance and the reflectance of the object. Luminance is the common measure of the intensity of displays. Lighting products available in variable-sized flat forms, such as sheets or tapes, often report luminance because luminous flux depends on the surface area of the product.
luminous flux: The quantity of visible light emitted by a source per unit time. Luminous flux is measured in lumens.
luminous intensity: The luminous flux per unit solid angle (i.e., in a specific direction) expressed in candela. Luminous intensity magnitude results from luminous flux being redirected by a reflector or magnified by a lens.
lux (lx): A lux is defined as a lumen per square meter and is the SI unit of illuminance.
Metal Organic Chemical Vapor Deposition (MOCVD): A method used for the growth of single crystal materials. During MOCVD, the wafer/substrate is exposed to metal-organic precursor gases (e.g., ammonia, trimethylgallium, and trimethylaluminum) at elevated temperatures. These gases then react, depositing a high-quality film (e.g., AlGaN) on the substrate.
N-type material: A semiconductor rich in (negativelycharged) electrons.
organic light-emitting diode (OLED): Organic (carbonbased) molecules can behave similarly to inorganic semiconductors; an OLED is an LED made from an organic semiconductor. In contrast to an LED, which is a point source, OLEDs are made in sheets and act as a diffuse area light source. In addition to lighting, they are used prominently in displays for TVs and cell phones.
organic vapor phase deposition: A method of deposition wherein an organic material is heated in the presence of an inert carrier gas. The carrier gas is saturated by the evaporated organic material before flowing toward the substrate onto which the organic molecules are then deposited.
P-type material: A semiconductor rich in (positivelycharged) holes.
p-n junction diode: When a p- and n-type semiconductor come in contact, they create a junction known as a diode. The diode will selectively pass current from one material to the other. In an inorganic LED, the diode structure creates a region at the junction interface where electrons recombine radiatively with holes and emit light.
performance bins: See binning.
phosphor: A material that absorbs and re-emits light at a lower energy. Phosphor coatings are commonly used with LEDs—for example, a blue LED coated with a yellow phosphor will emit both blue light (from the LED) and yellow light (from the phosphor after absorbing some of the LED’s light), which can appear white. Common phosphors used in LEDs include rare-earth doped yttrium aluminum garnets, or YAG:RE.
photobiology: Photobiology is the study of the effect of light on biological organisms.
photosensor: A device capable of detecting the amount of light present. In lighting, it is often used as a way of maintaining a constant level of illuminance in an environment.
pop-on effect: A rapid increase in brightness before dimming. Pop-on effects occur either (1) when lights do not turn on to their pre-set dimming level but first come on (near) full and then dim down automatically to the preset level, in the case of a preset dimming control; or (2) when lights do not turn on at the low end, but require the dimmer to be raised to a relatively high level to start the lamp, before dimming to a lower level can be achieved, in the case of a slider or rotary dimmer.
power factor (PF): The ratio of electrical power dissipated by a piece of equipment to the line power drawn.
power quality: The degree to which an electrical system functions as intended, with low levels of electrical noise and steady voltage output up to a specified load.
power source: A transformer, power supply, battery, or other device capable of providing current, voltage, or power within its design limits. This device contains no additional control capabilities. (ANSI and IES, 2010)
power supply: An electronic device capable of providing and controlling current, voltage, or power within design limits. (ANSI and IES, 2010)
quantum well: A layered structure designed to confine electrons or holes to a plane.
remote phosphor: A remote phosphor is a phosphor that is not put in intimate contact with the LED chip but rather secondary optics for the packaged LED.
retrofit luminaire: A luminaire with an integrated lamp. They are designed to fit into the spaces occupied by existing luminaires, but require complete removal of the existing luminaire for installation.
roll-to-roll processing: The process of creating a large quantity of electronic devices on a flexible substrate. This manufacturing process is typically imagined for OLEDs and organic photovoltaics to drive the cost down, because both technologies are capable of being grown at low temperatures onto flexible substrates.
semiconductor: A semiconductor is a material characterized by its ability to conduct a small electrical current. Intrinsically, it has far fewer carriers than a metal and is typically doped with other materials to pass large currents.
skyglow: The result of blue light being absorbed or scattered in the atmosphere resulting in a loss of visibility of the night sky, which is of special concern to the astronomy community.
Spectral Luminous Efficiency Function (Vλ): A model depicting the relationship between wavelength of light and the relative sensitivity of the human visual system.
thermal coefficient of expansion: The rate at which a material expands/contracts as it is heated/cooled.
total harmonic distortion (THD): The amount of distortion on the voltage supply line at frequencies above the fundamental (60 Hz) carrier frequency. A high THD (>33 percent) causes problems in three-phase power
systems, because usually the dominant harmonic current is the third harmonic. The third harmonic currents add in the neutral wire of the electrical system and in cases of high THD one can have a situation where the current flowing in the neutral wire exceeds the rating of the wire, causing overheating.
troffer: A long, recessed lighting unit usually installed with the opening flush with the ceiling. (ANSI and IES, 2010)
vacuum thermal evaporation: A method of deposition in which a material is heated in vacuum, evaporating from the source and then condensing on the substrate.
valence band: See band gap.
visible spectrum: The band of electromagnetic radiation that can be detected by the human eye, encompassing wavelengths between 380 nm (violet) and 750 nm (red).
warm white: Light described as “warm” has a coordinated color temperature (CCT) at the low end of the CCT spectrum. It is usually perceived as slightly yellow.
ANSI (American National Standards Institute) and IES (Illuminating Engineering Society). 2010. Nomenclature and Definitions for Illuminating Engineering. New York: ANSI and IES.
California Energy Commission. 2002. Energy Quest. Glossary of Energy Terms. Available at http://energyquest.ca.gov/glossary/index.html. Updated May 20, 2002.
Industrial Fiber Optics. 2004. Fiber Optic Lab Manual: Fifth Edition. Tempe, Ariz.: Industrial Fiber Optics, Inc.
Philips Color Kinetics. 2010. LED Lighting Explained: Understanding LED Sources, Fixtures, Applications, and Opportunities. Burlington, Mass.: Philips Solid-State Lighting Solutions, Inc.