LED (Light Emitting Diodes) are solid-state semiconductor devices that convert electrical energy directly into light. The heart of an LED ia a semiconductor chip of which one side is bonded to the top of reflector cup often called the anvil. The anvil carries the negative current. The other side of the semiconductor is connected with a micro wire often referred to as the whisker which supplies the positive current. This assembly is encapsulated in such a way as the upper half of the epoxy resin encapsulation is precisely shaped and acts as a lens to alter the beam angle or divergence.
Since the light output of individual light-emitting diodes is small compared to incandescent and compact fluorescent lamps, multiple diodes are often used together. In recent years, as diode technology has improved, high power light-emitting diodes with higher lumen output are making it possible to replace other lamps with LED lamps. One high power LED chip used in some commercial LED lights can emit 7,527 lumens while using only 100 watts. LED lamps can be made interchangeable with other types of lamps. Diodes are energized by direct current (DC) electrical power integrated with internal circuits power driver to deliver standard AC voltage. LEDs are damaged by being run at higher temperatures, so LED lamps typically include heat management elements such as heat sinks and cooling fins.
The LED consists of a chip of semiconducting material doped with impurities to create 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 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. The wavelength of the light emitted, and thus 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 band gap materials. The materials used for the LED have a direct band gap with energies corresponding to near-infrared, visible or near-ultraviolet light. LED development began with infrared and red devices made with gallium arsenide. Advances in materials science have enabled making devices with ever-shorter wavelengths, emitting light in a variety of colors such as ultraviolet and blue LEDs, white LEDs, RGB LEDs, and phosphoric based white LEDs.