The traditional incandescent bulbs are obsolete these days due to its high power consumption and less efficiency. The CFL (Compact Fluorescent Lamp) has replaced incandescent bulbs. But the latest light emitting technology called LED or Light Emitting Diode is proved to be the most energy efficient and produces pure monochromatic light.
LED or Light Emitting Diode is actually a PN junction diode made of semiconductors. Under certain condition of PN junction diode, called forward bias condition, current starts flowing through the diode and produces energy by emitting photon particles which result in producing light.
How LED Works?
P-type semiconductors containing positively charged carriers called holes while N-type semiconductors containing negatively charged carriers called electrons are joined together. No current flows through the PN junction diode until voltage is applied in the forward biased condition.
When proper voltage is applied under forward biased condition current starts flowing. The electrons and the holes which move in opposite direction recombine when they come nearby. As free electrons are at higher energy level than the positively charged holes, when they combine electrons fall into lower energy levels and hence electrons release energy in the form of photon emission. This photon emission is responsible for the light generation and this effect is termed as electroluminescence.
The wavelength or the color of the light emitted depends on the band gap energy of semiconductors used for manufacturing the diode. Silicon and germanium made P-N junction results with no light due to non-radiative transition.
For producing infrared light Gallium arsenide (GaAs) semiconductor is used. Indium gallium nitride (InGaN) is used for producing ultraviolet light.
Common uses of LED
1. Light source- LED bulbs and tube lights are very common these days due to its energy efficiency and its long life.
2. LED Screen- LCD and TFT screens are replaced by the latest LED screens. More energy efficient LED television and monitor screens are popular these days.
3. Indicators- Nowadays LEDs are used for indication purpose in traffic signals or railway signals or even used in many electronic devices due to its clear visibility occurring due to the emission of monochromatic light.