Tech Notes

LED GLOSSARY

Ambient Temperature (Ta) The air temperature surrounding the device.

Ampere (Amp)
The unit for measuring rate of flow of electrical current: Current (Amps) = Power (Watts) / Voltage (Volts)

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.

Case Temperature
The temperature measured at the LED package or case.

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 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.

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.

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.

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.

Heat Sink
A part of the thermal system that conducts or convects heat away from sensitive components, such as LEDs and electronics.

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).

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

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.

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.

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

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

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.

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.

Thermal Resistance (K/W)
The property of a material's ability to conduct heat.

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.