Light Emitting Diode

A light emitting diode, often abbreviated LED, is a semiconductor diode that emits light when it is forward-biased. LEDs of many different colors are available, based on the wavelength of the light being emitted by the diode. Apart from LEDs that emit light visible to the human eye, special LEDs that emit ultra-violet (UV) or infra-red (IR) light are also available.

Advantages

Light emitting diodes are advantageous as they are energy efficient, cheap, reliable and robust.

Power dissipation

Many LEDs used in e.g. consumer electronics have power dissipation on the order of tens of milliwatts, while the same figure for very bright power LEDs is on the order of watt.

Lifetime of LEDs

Manufacturers of LEDs state own lifetime figures for their products measured using various test fixtures and criteria, causing confusion regarding the actual meaning and comparability of the figures. It is important to remember that LEDs fail differently from incandescent lamps in that they usually do not suddenly fail, but rather become dimmer with increasing age. It is thus reasonable to rate the lifetime of LEDs based on the time required for the unit's output light intensity to drop to a certain percentage of the initial output. In many cases, this figure is thousands - if not tens of thousands - of hours.

Lifetime is lengthened through proper electrical and thermal design of the LED fixture. For example, power LEDs that dissipate a relatively large amount of power will heat up unless the excess heat is conducted away from the fixture. Additionally, LEDs are rated for a maximum current that should not be exceeded as this may shorten the lifetime of the unit.

Applications

LEDs are used in an ever increasing number of applications. LEDs that emit visible lights are commonly used as indication lights, e.g. in electronic equipment, but are also used in LED traffic lights and indoor lighting. Infra-red LEDs are commonly used in remote controls and other communication equipment.