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    Lighting Terminology


    Lighting terms are easy to understand with this handy glossary.


    absolute photometry The standards method for testing the light output and light distribution of LED lighting fixtures.

    AMCA The Australian governing body for EMC compliance.

    additive color model A type of RGB color model that describes how different proportions of red, green and blue light combine to create colors. In the additive color model, combining red, green and blue light in equal amounts produces white light.

    AllnGaP The aluminum indium gallium phosphide material system for manufacturing red and amber high-brightness LEDs.

    ballast Solid-state electronic circuitry that provides the proper electrical conditions for starting and operating fluorescent lamps and HID lamps.

    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.

    brightness The subjective impression of the intensity of a light source. Often used incorrectly as a synonym for luminous flux, an objective measurement of the visible power of a light source.

    candela The standards unit of luminous intensity-power emitted by a light source in a particular direction, weighted by the spectral luminous efficiency function.

    C-Tick A regulatory marking usually followed by a "N" number relating to the suppliers declaration of conformity to relevant EMC standards.

    CCT See correlated color temperature

    CFL See compact fluorescent lamp

    chromaticity An objective specification of the quality of a color, independent of its luminance and as determined by its saturation and hue.

    color rendering index (CRI) The standards unit of luminous intensity-power emitted by a light source in a particular direction, weighted by the spectral luminous efficiency function.

    color temperature See correlated color temperature

    compact fluorescent lamp (CFL) A type of fluorescent lamp with relatively low power draw, often designed to replace an incandescent lamp.

    controller A device that controls the output of color-changing and tunable white lighting fixtures. Controllers typically have software components for configuring fixtures and designing and editing light shows, and hardware components for sending control data to fixtures.

    correlated color temperature Describes whether white light appears warm (reddish), neutral or cool (bluish), based on the appearance of light emitted by a black body heated to various temperatures in degrees Kelvin (K).

    CRI See color rendering index

    DALI See digital addressable lighting interface

    delivered light The amount of light a lighting fixture or lighting installation delivers to a target area or task surface, measured in footcandles (fc) or lux (lx).

    digital addressable lighting interface A digital communications protocol for controlling and dimming lighting fixtures, originally developed in Europe.

    DMXv A digital communications protocol for controlling lighting fixtures, originally developed to control stage lighting.

    efficacy The efficacy, or energy efficiency, of lighting fixtures is the amount of light produced (in lumens) per unit of energy consumed (in watts) or lm/W. Not to be confused with luminous efficiency.

    energy efficiency See efficacy

    forward voltagev Occurs when a negative charge is applied to the n-type side of a diode, allowing current to flow from the negatively-charged area to the positively-charged area.

    heat sink A feature of device that conducts or convects heat away from sensitive components, such as LEDs and electronics.

    HID lamp A type of electrical lamp which produces light by means of an electric arc between tungsten electrodes housed inside a translucent or transparent fused quartz or fused alumina arc tube.

    illuminance The intensity of light falling on a surface area. If the area is measured in square feet, the unit of illuminance is footcandles (fc). If measured in square meters, the unit of illuminance is lux (lx).

    illuminator-type LEDs High performance, high-power LEDs capable of providing functional illumination.

    indicator-type LEDs Inexpensive, low-power LEDs suitable for use as indicator lights in panel displays and electronic devices or instrument illumination in cars and computers.

    InGaN The indium gallium nitride material system for manufacturing green, blue and cyan high-brightness LEDs.

    junction The p-n junction in a diode, where positively charged and negatively charged materials exchange electrons, emitting photons and generating heat.

    junction temperature The temperature in the vicinity of an LED's p-n junction. Controlling junction temperatures is critical for achieving the optimal balance between lumen output and lumen maintenance.

    lamp The light source in a luminaire or lighting fixture.

    LED See light-emitting diode.

    LED driver An electronic circuit that converts input power into a current source-a source in which current remains constant despite fluctuations in voltage. An LED driver protects LEDs from normal voltage fluctuations, overvoltages, and voltage spikes.

    light emitting diode (LED) A semiconductor device that emits visible light of a certain color.

    light level See delivered light

    light output See luminous flux

    lumen The unit of measurement of luminous flux, the total energy that a light source emits across the visible wavelengths of light.

    lumen maintenance Describes how long a light source will retain a certain percentage of its initial lumen output. For instance, L50 is the length of time a light source retains 50% or more of its initial lumen output.

    lumen output The total lumens emitted by a lamp or luminaire.

    luminous efficiency The percentage of total lamp lumens that a conventional lighting fixture emits, minus any blocked or wasted light. By definition, LED lighting fixtures in which the LEDs are inseparable components have a luminous efficiency of 100%.

    luminous flux The total energy emitted by a light source across the visible wavelengths of light, measured in lumens.

    lux (lx) A unit of illuminance that measures the intensity of light falling on a surface area measured in square meters.

    material system The material, such as aluminum indium gallium phosphide (AllnGaP) and indium gallium nitride (InGaN), used within an LED to produce light of a specific color.

    nanometer (nm) The most common unit to describe the wavelength of light, equal to one billionth of a meter.

    n-type material In a diode's p-n semiconductor junction, n-type material is negatively charged. Atoms in the n-type material have extra electrons.

    phosphor A coating of phosphorescent material that absorbs light from a blue or UV LED and emits most of its output in the yellow range. The proper combination of a blue or UV LED and a phosphor coating generates white light.

    phosphor white A method of producing white light in a single LED by combining a short-wavelength LED, such as a blue or UV and a yellow phosphor coating. photon The basic unit of electromagnetic radiation, including visible white light.

    p-n junction The location within an LED where negatively charged (n-type) material "donates" extra electrons to positively charged (p-type) material, which "accepts" them, releasing energy in the form of photons.

    p-type material In a diode's p-n semiconductor junction, p-type material is positively charged. Atoms in the p-type material have electron holes-electrons missing from their outer rings.

    pulse width modulation (PWM) A method, used by most LED drivers, to regulate the amount of power to the LEDs. PWM turns LEDs on and off at high frequency, reducing total ON time to achieve a desired dimming level.

    radiant flux The total energy emitted by a light source across all wavelengths, measured in watts.

    remote phosphor A technique that separates the phosphor from the chip in a white-light LED, improving the extraction efficiency of emitted light.

    RGB color model An additive color model in which red, green and blue light are added together in different proportions to produce a broad range of colors, including white.

    RGB white A method of producing white light by combining the output from red, green and blue LEDs.

    trailing-edge dimmer A type of dimmer that regulates power to lamps by delaying the end of each half-cycle of AC power. Compatible with many LED fixtures.

    tunable white light White-light LED fixtures that combine channels of warm white and cool white LEDs to produce a range of color temperatures.

    useful life Refers to the lumen maintenance projections of the LED sources integrated into that fixture ñ the number of hours an LED lighting fixture will deliver a sufficient amount of light in a given application.

    ultraviolet ( UV) Electromagnetic radiation with wavelength shorter than that of visible light.

    watt (W) the unit of power required to drive a LED lighting system.