What is LED Lighting?

A light-emitting diode (LED) is a semiconductor device that emits incoherent narrow-spectrum light when electrically biased in the forward direction. This effect is a form of electroluminescence. The color of the emitted light depends on the chemical composition of the semiconducting material used, and can be near-ultraviolet, visible or infrared.

LED Technology

Physical function
An LED is a special type of semiconductor diode. Like a normal diode, it consists of a chip of semiconducting material impregnated, or doped, with impurities to create a structure called a p-n junction. As in other diodes, current flows easily from the p-side, or anode to the n-side, or cathode, but not in the reverse direction. Charge-carriers - electrons and electron holes flow into the junction from electrodes with different voltages. When an electron meets a hole, it falls into a lower energy level, and releases energy in the form of a photon as it does so.

The wavelength of the light emitted, and therefore its color, depends on the band gap energy of the materials forming the p-n junction. In silicon or germanium diodes, the electrons and holes recombine by a non-radiative transition which produces no optical emission, because these are indirect bandgap materials. The materials used for an LED have a direct band gap with energies corresponding to near-infrared, visible or near-ultraviolet light.

Advantages of using LEDs

LEDs are capable of emitting light of an intended color without the use of color filters that traditional lighting methods require.
The shape of the LED package allows light to be focused. Incandescent and fluorescent sources often require an external reflector to collect light and direct it in a useable manner.
LEDs are insensitive to vibration and shocks, unlike incandescent and discharge sources.
LEDs are built inside solid cases that protect them, making them hard to break and extremely durable.
LEDs have an extremely long life span: typically ten years, twice as long as the best fluorescent bulbs and twenty times longer than the best incandescent bulbs. (Incandescent bulbs can also be made to last an extremely long time by running at lower than normal voltage, but only at a huge cost in efficiency; LEDs have a long life when operated at their rated power.)
Further, LEDs fail by dimming over time, rather than the abrupt burn-out of incandescent bulbs.
LEDs give off less heat than incandescent light bulbs with similar light output.
LEDs light up very quickly. An illumination LED will achieve full brightness in approximately 0.01 seconds, 10 times faster than an incandescent light bulb (0.1 second), and many times faster than a compact fluorescent lamp, which starts to come on after 0.5 seconds or 1 second, but does not achieve full brightness for 30 seconds or more. A typical red indicator LED will achieve full brightness in microseconds, or possibly less if it's used for communication devices.