Basically Light Emitting Diode (LED) is a semi-conductor device. It emits energy photons when powered. Frequency of emitting photon depends on construction of LED. Generally it is used for visible light & Infrared light. For visible light LED wave length varies from 700 nano-meter (red light) to 400 nano-meter (blue light) and for Infrared wave length is more than 830 nano meter. Infrared LED also called IRED (infrared-emitting diode). Generally LEDs are designed for monochrome Light. That’s the reason we get a sharp single color light from any LED.
Construction and working of a Light Emitting Diode (LED)
As mentioned earlier LED is a semiconductor device. It works only in forward bias mode. In this mode, free electrons from n-type material and free holes from p-type material moves towards junction. Here in junction free holes accept free electrons. This phenomenon also called recombination. In this process, energy release from p-n junction area. This energy is nothing but light. In ordinary Diodes it is in form of heat.
Here in LED intensity of light is depends on band gaps of free electrons. If band gap is large it emits high intensity light and if band gap is small there will be low intensity light. In fact intensity and color of LED depends on material used for LED construction. Here in list, material and its LED color is given.
Construction of LED is different from a normal diode. However it is a type of diode but its p-n junction is covered with transparent plastic and epoxy material. Its junction has a reflected cavity as shown in figure. Its function is to reflect all light rays in to outward direction. And its transparent plastic resin works as a lens and create a parallel beam of light.
Here a in picture from IEEE, construction of LED is clearly shown. P-n junction is situated in side reflective cavity. And cavity is covered with transparent plastic resin. Anvil work as cathode terminal and a thin anode wire is connected with post. Here p-n junction is sandwich between positive and negative terminal.
Key points of LED s
- LED can be switched ON and OFF at very high frequency. Its operating time is very less (approx. 1 Nano-sec)
- Low operating Power (required only few mW for 5mm LED)
- Very High Efficiency (compared to other light bulbs) because there is no heat generation during operation.
- Long life as compared to other conventional devices.
- Monochromatic (single wave length) light emission.
Now LED s are used in many application, It from a simple indication to Optical fiber transmitter. It is used in kids toy and also in aviation system. So finally we can say LED s are playing a vital role in our life.