top of page
LED Glossary of Terms
A   B   C   D   E   F   G   H   I   J   K     M   N     P   Q   R             X   Y   Z


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.


One of the material systems for manufacturing LEDs that produce light in the red and amber portions of the visible light spectrum.


The preferred LED chip technology containing aluminum, indium, gallium, and phosphorus to produce red, orange, and amber colors.

Ambient Temperature (Ta)

The air temperature surrounding the device.

American National Standards Institute (ANSI)

A nonprofit 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 (LEDs).


Bin (Binning)

The systematic dividing of performance parameters (Flux, Wavelength or CCT, and Vf) into 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.


An objective measurement of the visible power of a light source. Understandably, people often use the word incorrectly by referring to illumination as a synonym for luminous flux. Actually, the correct way to use “brightness” is when describing screen brightness in a display or television (see Nits).


Case Temperature

The temperature measured at the LED package or case.


See Correlated Color Temperature.


See LED Chip.


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


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:


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


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


Describes a range of grayness between black and white.

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-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, compared to 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 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, then white as the temperature increases.

Conformal Phosphor Coating

Phosphor application process that uniformly coats the LED chip with phosphor.


A device that controls the output of color-changing and tunable white lighting fixtures. Controllers typically have software components for configuring fixtures, 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 black body 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.


See Color Rendering Index.



See Digital Addressable Lighting Interface.

Delivered Light

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

Die Chip

A light-emitting semiconductor.


An object with irregularities on a surface that cause 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.


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


Electronics used to power illumination sources.



The light output of a light source divided by the total electrical power input to that source; expressed in lumens per watt (lm/W).


See Luminous Efficiency.

ELV-Type Dimmer

An electronic low-voltage dimmer, used to dim LED lighting fixtures with electronic transformers.


An organic polymer frequently used for a dome or lens; often prone to optical decay over time, which results 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 (FR4)

A widely accepted printed circuit board (PCB) material which is flame-retardant, fiberglass-reinforced epoxy laminates.

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.



An effect that occurs when lighting fixtures in the OFF state faintly glow as a result of residual voltage in the circuit.


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-brightness is a term that is often applied to an LED but has no measured meaning and does not indicate any level of performance.

High-Power LED/Power LED

An LED that is driven at a current of 350 mA or higher.

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.



See Illuminating Engineering Society of North America.


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. The IES communicates information on all aspects of good lighting practice to its members, the lighting community, and 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 wavelengths ranging from 700 nm - 3000 nm.


The preferred LED semiconductor material system containing indium, gallium, and nitrogen to produce green, blue, and white LED light sources.

Integrating Sphere

A device used for a variety of optical, photometric, or radiometric measurements.


Junction Temperature (Tj)

The temperature of the LED's active region.


Kelvin Temperature (K)

Refers to the comparative color appearance of a light source when compared to a theoretical black body. Yellow incandescent lamps are 3,000K. Fluorescent light sources range from 3,000K to 7,500K 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.


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; an 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. An LED luminaire distributes light; positions and protects the light-emitting elements; and connects the unit to a branch circuit. The 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 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 Flux/Luminous Flux.

Lumen (lm)

The international (SI) unit of luminous flux, or quantity of light; 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

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; expressed as a percentage of the initial 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 from a light source, system, or solution.


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/Luminous Flux.


This Philips proprietary phosphor system embeds phosphor in a ceramic platelet that can be mass manufactured with high 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

The region on a chromaticity diagram that contains all colors, which the average human eye cannot distinguish 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.


A widely accepted Printed Circuit Board (PCB) material with a Metal Core (MC) for better thermal performance.



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 (cathode ray tubes) such as 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)

Based on organic (carbon-based) materials. In contrast to LEDs, which are small point sources, OLEDs are made in sheets that provide a diffuse area light source. OLED technology is developing rapidly and is increasingly used in display applications such as cell phones and PDA (personal digital assistant) 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

The 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 (light).

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 (Phosphor Converted) Amber

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.


A coating of phosphorescent material which photons from a royal blue LED pass through, causing those photons to exit with a differently colored property.

Phosphor Conversion

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.


See Radiometry.

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.


The measurement of radiant energy (including light) in terms of absolute power. This differs from photometry, which is the measurement of light in terms of its perceived brightness to the human eye.

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.



See Standard Deviation of Color Matching.


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.


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 five or more SDCM steps is readily visible.


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.



See Ambient Temperature.


See Case Temperature.

Thermal Management

Controlling the operating temperature of the product through design; examples includes heat sinks and improved airflow.

Thermal Pad Temperature (Tp)

The measured temperature of the thermal pad during testing. The thermal pad aides in the conduction of heat away from the component being cooled and into the heat sink. For more information, refer to LUXEON® Rebel and LUXEON® Rebel ES Assembly and Handling Guide application brief 32.

Thermal Resistance (K/W)

A material's ability to conduct heat.


See Junction Temperature.


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.


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.



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 3,000K and 3,500K, usually perceived as a slight yellow.


The unit of electrical power used by an electrical device during its operation. Many lamps come with ratings 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.


Zero Emissions

An energy source that does not produce any gas or release any harmful gases directly into the environment. LED lighting can help reduce our carbon footprint and get one step closer to our zero emissions goal.

bottom of page