A RED light-emitting diode (LED) is a semiconductor light source. LEDs are used as indicator lamps in many devices and are increasingly used for other lighting.
When a light-emitting diode is switched on, electrons are able to recombine with holes within the device, releasing energy in the form of photons. This effect is called electroluminescence and the color of the light (corresponding to the energy of the photon) is determined by the energy band gap of the semiconductor. An LED is often small in area (less than 1 mm2), and integrated optical components may be used to shape its radiation pattern. LEDs present many advantages over incandescent light sources including lower energy consumption, longer lifetime, improved physical robustness, smaller size, and faster switching. However, LEDs powerful enough for room lighting are relatively expensive and require more precise current and heat management than compact lamp sources of comparable output.
Bare uncoated semiconductors such as silicon exhibit a very high refractive index relative to open air, which prevents passage of photons at sharp angles relative to the air-contacting surface of the semiconductor.
Internal reflections can escape through other crystalline faces, if the incidence angle is low enough and the crystal is sufficiently transparent to not re-absorb the photon emission. But for a simple square LED with 90-degree angled surfaces on all sides, the faces all act as equal angle mirrors. In this case the light cannot escape and is lost as waste heat in the crystal.
·Efficiency: LEDs emit more light per watt than incandescent light bulbs. The efficiency of LED lighting fixtures is not affected by shape and size, unlike fluorescent light bulbs or tubes.
·Color: LEDs can emit light of an intended color without using any color filters
·Size: LEDs can be very small (smaller than 2 mm) and are easily attached to printed circuit boards.
·On/Off time: LEDs light up very quickly
·Cycling: LEDs are ideal for uses subject to frequent on-off cycling,.
·Dimming: LEDs can very easily be dimmed either by pulse-width modulation or lowering the forward current..
· Cool light: In contrast to most light sources, LEDs radiate very little heat in the form of IR that can cause damage to sensitive objects or fabrics
·Lifetime: LEDs can have a relatively long useful life.
·Shock resistance: LEDs, being solid-state components, are difficult to damage with external shock.
· Focus: The solid package of the LED can be designed to focus its light