LED Technology Glossary | LED Technical Reference

LED Technology Glossary

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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 produces white light.
AlGaAs
One of the material systems for manufacturing LEDs that produce light in the red and amber portions of the visible light spectrum.
AllnGaP
The preferred LED (Light Emitting Diode) chip technology containing Aluminum, Indium, Gallium, and Phosphorous to produce red, orange and amber-colors.
Ambient Temperature (Ta)
The air temperature surrounding the device.
American National Standards Institute (ANSI)
A non-profit organization that develops voluntary consensus standards and conformity assessment systems for products, services, processes, systems, and personnel in the United States.
Ampere (Amp)
The unit for measuring rate of flow of electrical current: Current (Amps) = Power (Watts) / Voltage (Volts)
ANSI Binning
The system defined by the American National Standards Institute for the binning specifications for light emitting diodes.
Bin (Binning)
The systematic dividing of distribution of performance parameters (Flux, Wavelength or CCT, and Vf) in to small finite groupings that may be selected to optimize assembly performance.
Black Body / Black Body Radiator
An object that absorbs all electromagnetic radiation falling on it. Because it reflects no light, a black body appears black. As a black body is heated to incandescence, it radiates light in a sequence of colors, from red to orange to yellow to white to blue, depending on its temperature. This color sequence describes a curve within a color space, known as the black-body curve.
Black Body Curve
A curve within a color space describing the sequence of colors emitted by a black-body radiator at different temperatures.
Brightness
Often used incorrectly with respect to illumination as a synonym for luminous flux, an objective measurement of the visible power of a light source. The term is correctly used when describing screen brightness in a display or television. (see Nits).
Case Temperature
The temperature measured at the LED package or case.
CCT - See Correlated Color Temperature.
Chip - See LED chip.
Chromaticity
An objective specification of the quality of a color, independent of its luminance, and as determined by its or saturation and hue.
CIE - See International Commission on Illumination.
CIE 1931 Color Space
A color space created by the International Commission on Illumination (CIE) in 1931 to define the entire gamut of colors visible to the average viewer.
CIE Chromaticity Diagram
A horseshoe shaped line connecting the chromaticities of the spectrum of colors. (See Color Definition, Chroma).
Color Definition
The color of uniformly illuminated objects described using three terms:

Hue: Describes the situation when the appearance of different colors is similar (e.g. matching blues and pinks).

Lightness: Describes a range of grayness between black and white.

Chroma: Describes the degree of departure from gray of the same lightness and increasing color (e.g. red, redder, pure red).

Color Gamut
The range of colors within the CIE Chromaticity Diagram included when combining different sources.
Color Model
An abstract mathematical model describing the way colors can be represented as groups of values or color components. RGB (Red-Green-Blue) is a color model with three color components, and CMYK (Cyan-Magenta-Yellow and Key (Black)) is a color model with four color components.
Color Rendering
A general expression for the effect of a light source on the color appearance of objects.
Color Rendering Index (CRI)
A measure of the degree of color shift objects undergo when illuminated by the light source as compared with those same objects when illuminated by a reference source of comparable color temperature. The reference source has a CRI of 100.
Color Spectrum / Visible Spectrum
The visible spectrum is the portion of the electromagnetic spectrum that is visible to the human eye, typically between 390nm and 750nm.
Color temperature
The description used to describe the effect of heating an object until it glows incandescently, the emitted radiation, and apparent color, changes proportional to the temperature; easily envisioned when considering hot metal in a forge that glows red, then orange, and then white as the temperature increases.
Conformal Phosphor Coating
Phosphor application process that uniformly coats the LED chip with phosphor.
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.
Cool White
A description of a range of correlated color temperatures.
Correlated Color Temperature (CCT)
The absolute temperature of a blackbody whose chromaticity most nearly resembles that of the light source. Usually specified in Kelvin (K). The lower the Kelvin temperature, the warmer the light feels, or appears.
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).
Die
Chip: light emitting semiconductor.
Diffuser
An object with irregularities on a surface causing scattered reflections.
Digital Addressable Lighting Interface (DALI)
A digital communications protocol for controlling and dimming lighting fixtures, originally developed in Europe.
Direct-View Lighting Fixtures
Lighting fixtures intended for viewing, rather than for illumination. For example, arrays of direct-view fixtures or nodes are used in large-scale video displays, traffic signals, and signage applications.
Directional Light Source
A light source that emits light only in the direction it is pointed or oriented.
DMX
A digital communications protocol for controlling lighting fixtures, originally developed to control stage lighting.
Driver
Electronics used to power illumination sources.
Efficacy
The light output of a light source divided by the total electrical power input to that source, expressed in lumens per watt (lm/W).
Efficiency - See Luminous efficiency.
ELV-type Dimmer
An electronic low voltage dimmer, used to dim LED lighting fixtures with electronic transformers.
Epoxy
Organic polymer frequently used for a dome or lens, often prone to optical decay over time, resulting in poor lumen maintenance. High quality LEDs such as LUXEON contain no epoxy in the optical system and deliver superior lumen maintenance.
Eye-sensitivity Curve - See spectral luminous efficiency function.
Flux / Luminous Flux
Luminous flux is the measure of the perceived power of light, adjusted to reflect the varying sensitivity of the human eye to different wavelengths of light
Forward voltage
LEDs are current driven devices. If an external current is passed through the device, a forward voltage will be developed across the diode.
FR4
A widely accepted printed circuit board (PCB) material which is fiberglass reinforced epoxy laminates that are flame retardant.
Freedom From Binning
Describes the case where the entire production of white LEDs can be described by a single CCT and within a declared number of MacAdam ellipses. No subdivision or color binning of the LEDs is required for use in the intended application.
Ghosting
An effect that occurs when lighting fixtures in the OFF state faintly glow as a result of residual voltage in the circuit.
Goniophotometer
A photometric device for testing the luminous intensity distribution, efficiency, and luminous flux of luminaires.
Heat Sink
A part of the thermal system that conducts or convects heat away from sensitive components, such as LEDs and electronics.
High Power LED
A high power LED, sometimes referred to as a power LED, is one that is driven at a current of 350 mA or higher.
High-brightness
High-brightness is a term that is often applied to an LED but has no measured meaning and does not indicate any level of performance.
Hot / Cold Factor
The relative light output performance at a temperature compared to the light output at a nominal or test temperature. For LUXEON products this is the relative light output at 100C Tj compared to 25C Tj. For “Hot Tested” products like LUXEON A it is the relative light output at 100C Tj compared to 85C Tj.
Hot Testing
LED performance testing and specification at an elevated temperature of 85°C.
IES / IESNA - See Illuminating Engineering Society.
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).
Illuminating Engineering Society of North America (IES)
The recognized technical authority on illumination, communicating information on all aspects of good lighting practice to its members, to the lighting community, and to consumers through a variety of programs, publications, and services.
Inboard Power Integration
An approach to power management that integrates the power supply directly into a fixture’s circuitry, creating an efficient power stage that consolidates line voltage conversion and LED current regulation.
Infrared (Near)
Electromagnetic radiation with wavelength range from 700 nm – 3000 nm.
InGaN LED
The preferred LED (Light Emitting Diode) semiconductor material system containing Indium, Gallium, and Nitrogen to produce green, blue and white-colored LED light sources.
Integrating Sphere
A device used for a variety of optical, photometric, or radiometric measurements.
Junction Temperature
Junction temperature, noted as Tj, is the temperature of the LED’s active region.
Kelvin Temperature
Term and symbol (K) used to indicate the comparative color appearance of a light source when compared to a theoretical blackbody. Yellowish incandescent lamps are 3000K. Fluorescent light sources range from 3000K to 7500K and higher.
Kelvin Temperature
Term and symbol (K) used to indicate the comparative color appearance of a light source when compared to a theoretical blackbody. Yellowish incandescent lamps are 3000K. Fluorescent light sources range from 3000K to 7500K and higher.
Leading Edge Dimmer
A type of dimmer that regulates power to lamps by delaying the leading edge of each half-cycle of AC power. Compatible with many LED fixtures.
LED - See Light Emitting Diode.
LED Array
An assembly of LED packages or dies on a printed circuit board or substrate, possibly with optical elements and additional thermal, mechanical, and electrical interfaces that are intended to connect to the load side of an LED driver.
LED Chip (Chip)
The light producing semiconductor device that may or may not be incorporated into an LED.
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.
LED Light Engine
An integrated assembly comprised of LEDs or LED arrays, LED driver, and other optical, thermal, mechanical, and electrical components.
LED Luminaire
A complete lighting unit consisting of LED-based light emitting elements and a matched driver together with parts to distribut light, to position and protect the light emitting elements, and to connect the unit to a branch circuit. The LED based light emitting elements may take the form of LED packages, (components), LED arrays (modules) LED Light Engine, or LED lamps. The LED luminaire is intended to connect directly to a branch circuit.
LED Module - See LED array.
Light Emitting Diode (LED)
A Light Emitting Diode (LED) is a solid-state semiconductor device that converts electrical energy directly into light. On its most basic level, the semiconductor is comprised of two regions. The p-region contains positive electrical charges while the n-region contains negative electrical charges. When voltage is applied and current begins to flow, the electrons move across the n region into the p region. The process of an electron moving through the p-n junction releases energy. The dispersion of this energy produces photons with visible wavelengths.
Light output - See luminous flux.
Lumen (lm)
The international (SI) unit of luminous flux or quantity of light and equals the amount of light that is spread over a square foot of surface by one candle power when all parts of the surface are exactly one foot from the light source. For example, a dinner candle provides about 12 lumens
Lumen Depreciation
Describes the percentage of light lost relative to the initial lumen output. See lumen maintenance for more information.
Lumen Maintenance
The luminous flux at a give time in the life of the LED. This is expressed as a percentage of the intial luminous flux.
Lumen Maintenance Curve
A graph illustrating the predicted average light output behavior over time of a single LED or solution.
Lumen Output
The total lumens emitted of a light source, system, or solution.
Luminaire
A lighting fixture complete with installed lamps and other accessories.
Luminous Efficiency
The percentage of total lamp lumens that a lighting fixture, luminaire, or system emits, minus any blocked or wasted light.
Luminous Flux - See Flux.
Lumiramic
This Philips proprietary phosphor system embeds phosphor in a ceramic platelet that can be mass manufactured with very high degrees of uniformity and consistency.
Lux (lx)
The SI (International) unit of illuminance, or luminous flux incident on a unit area, frequently defined as one lumen per square meter (lm/m2).
MacAdam Ellipse
A MacAdam ellipse is the region on a chromaticity diagram which contains all colors which are indistinguishable, to the average human eye, from the color at the center of the ellipse.
Material System
The material, such as aluminum indium gallium phosphide (AlInGaP) and indium gallium nitride (InGaN), used within an LED to produce light of a specific color.
MCPCB
A widely accepted Printed Circuit Board (PCB) material with a Metal Core (MC) for better thermal performance.
Nits
Measurement of display screen brightness. 1 nit = 1 cd/m2.
NTSC Color Space
The range of colors within the CIE Chromaticity Diagram included when combining phosphor based RGB sources in CRTs such a televisions and computer monitors.
Onboard Power Integration
An approach to power management that integrates the power supply into a fixture’s housing, eliminating the need for an external power supply.
Organic Light-emitting Diodes (OLED)
Organic light-emitting diodes (OLEDs) are based on organic (carbon based) materials. In contrast to LEDs, which are small point sources, OLEDs are made in sheets which provide a diffuse area light source. OLED technology is developing rapidly and is increasingly used in display applications such as cell phones and PDA screens. However, OLEDs are still some years away from becoming a practical general illumination source. Additional advancements are needed in light output, color, efficiency, cost, and lifetime.
P-N Junction
Area on an LED chip where the positively and negatively charged regions meet. When current is applied, the electrons move across the n region into the p region. The process of an electron moving through the p-n junction releases energy. The dispersion of this energy produces photons with visible wavelengths. In short, the area on a chip where light is produced.
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.
PC Amber (Phosphor Converted)
PC amber is a method of making amber colored LEDs from royal blue LED chips. It requires the use of special phosphors and results in a more reliable, less temperature sensitive, and more consistent amber LED.
Phosphor
A coating of phosphorescent material which photons from a royal blue LED pass through causing those photons to exit with a different color property.
Phosphor Conversion
This is the process by which photons from an LED chip are converted to a different color. White LEDs and some colored LEDs are made using phosphor conversion.
Planckian Black Body Locus
The line on the CIE Chromaticity Diagram that describes the color temperature of an object when heated from approximately 1,000K to more than 10,000K.
Power Factor
The active power divided by the apparent power (i.e., product of the rms input voltage and rms input current of a driver).
Power Factor Correction
In an electronic device, such as an LED lighting fixture, a system of inductors, capacitors, or voltage converters to adjust the power factor of electronic devices toward the ideal power factor of 1.0.
Pulse Width Modulation (PWM)
A method, used by LED drivers, to regulate the amount of energy 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.
Radiometry
The measurement of radiant energy (including light) in terms of absolute power. Compare photometry.
Remote Phosphor
A phosphor conversion technique in which photons from a royal blue LED pass through a phosphor material that is not attached to the LED chip.
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.
SDCM - See standard deviation of color matching.
SMDs
Surface-mount LEDs.
Solder Point Temperature (Ts)
Solder point temperature as specified by ENERGY STAR® and Philips Lumileds Application Brief 33.
Solid-state lighting
A description of the devices that do not contain moving parts or parts that can break, rupture, shatter, leak or contaminate the environment.
Spectral Luminous Efficiency Function
A bell-shaped curve describing the sensitivity of a human eye with normal vision to the spectrum of visible light. Also known as the eye-sensitivity curve.
sRGB
A Standard Default Color Space for the Internet created by Hewlett-Packard and Microsoft to support a standard color space within the Microsoft operating systems, HP products, and others.
Standard deviation of color matching (SDCM)
Describes the difference between two colors. A difference of one to three SDCM “steps” is virtually imperceptible, a difference of four SDCM steps is just noticeable, and a difference of more than four SDCM steps is readily visible.
Steradian
The standard unit of solid angle. Describes two-dimensional angular spans in three-dimensional space.
Subtractive Color Model
A color model that applies to reflective surfaces such as paints, dyes, and inks. Combining red, green, and blue in equal amounts produces black.
Ta - See Ambient Temperature
Tc - See Case Temperature
Thermal management
Controlling the operating temperature of the product through design, examples includes heat sinks and improved airflow.
Thermal Pad Temperature
The measured temperature of the thermal pad during tesing. The thermal pad aides in the conduction of heat away from the component being cooled and into the heatsink. For more information refer to LUXEON® Rebel and LUXEON® Rebel ES Assemby and Handling Guide application brief 32.
Thermal Resistance (K/W)
The property of a material's ability to conduct heat.
Tj - See Junction Temperature
Tp - See Thermal Pad Temperature
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.
Ts - See Solder Point Temperature.
Tunable White Light
White-light LED fixtures that combine channels of warm white and cool white LEDs to produce a range of color temperatures.
Ultraviolet (UV)
Electromagnetic radiation with wavelength shorter than that of visible light.
Useful Life
The amount of light a lighting fixture delivers in an application, minus any wasted light.
Volt
The term used to describe the electrical potential difference between oppositely charged conductors, for example there is a 1.5V potential between the top and bottom of an AAA battery.
Wall Plug Efficiency
This typically refers to the effectiveness of converting electrical power to light output. It is defined as the ratio of the radiant flux to the input electrical power.
Warm White
A description of light with a correlated color temperature between 3000K and 3500K, usually perceived a slightly yellow.
Watt
The unit of electrical power as used by an electrical device during its operation. Many lamps come with rating in watts to indicate their power consumption.
White Point
The Coordinated Color Temperature (CCT) defined by a line perpendicular to the Planckian Black Body Curve and intersecting the measured chromaticity.