luminous efficacy: The luminous efficacy of a lamp is the ratio of the luminous flux to the total electrical power consumed by the lamp.

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

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