Ambient Temperature (Ta)

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)

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.


Often used incorrectly with respect to illumination as a synonym for luminous flux, an objective measurement of the visible power of a light source.

Case Temperature

The temperature measured at the LED package or case.


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


See International Commission on Illumination.

Color Definition

The color of uniformly illuminated objects described using three terms:

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.


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.

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).


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.


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.

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.


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 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 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.

Hot Testing

LED performance testing and specification at an elevated temperature of 85°C.


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.


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.

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/LED Module

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 distribute 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.

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 Output

The total lumens emitted of 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.

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).

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.

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.

Power Factor

The active power divided by the apparent power.

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. Compare photometry.

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.

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.

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.

Thermal management

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

Thermal Resistance (K/W)

The property of a material’s ability to conduct heat.

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.

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 3000K and 3500K, usually perceived a slightly yellow.


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