The LED works on the principle of electroluminescence, a phenomenon that occurs whenever current is passed through a LED. Actually a LED is a light emitting diode, consisting of two different regions, but to the normal eye it appears as a very small size semiconductor chip located at the center of the bulb. Now these two regions – the p- type (consisting of holes) and n-type (consisting of electrons) are separated by a junction, known as the potential barrier, which prevents the flow of electrons and holes across it. Only when a sufficient amount of current is passed through the junction, the electrons from n side and holes from the p side cross the junction and recombine with other. Upon recombination, the energy is emitted due to difference in energy levels of the electron and holes. It is this energy , which is visible in the form of photons of light.
Color and Amount of light The color of light emitted by the LED is determined by the energy band gap difference between the hole and electrons present in the LED. For different applications, different types of material are used to construct LEDs having different electron hole energy band gap difference e.g. Aluminum gallium arsenide (AlGaAs) for red light, Gallium arsenide phosphide (GaAsP) for orange and Gallium(III) phosphide (GaP) for green light etc. The amount of light emitted by the LED is dependent on the voltage applied across it as well as the material used for its construction. For different applications, LEDs emitting different amount of light are available.
Difference between conventional bulbs and LEDs In an incandescent bulb, the light is emitted only after the filament gets enough heated up. While in a LED, the process of light emission is altogether different . Here the chip itself isn’t getting white hot, it’s simply producing light directly from the current that’s passing through it. Here no energy is wasted in getting the chip heated up, but the light is emitted because of an electronic process. Also the whole structure is contained in an epoxy, so that there are no air gap left that is why the name solid state lighting is given to LED lighting devices.
LEDs work on small dc voltages, but the power supply available at home or office is ac, so an electronic driver needs to be put between the LED and the AC supply. Also some lens or glasses can be used to focus or disperse the light in a particular way as per the requirement. The whole thing, that is the LEDs, the driver circuit and lens are encapsulated together to give the final structure to the lighting device.
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