(N/A) Design: An $LED$ is a heavily doped $p-n$ junction diode. It is encapsulated in a transparent cover so that the emitted light can escape. It is operated under forward bias.
Working: When the diode is forward-biased,electrons are injected from the $n$-region to the $p$-region,and holes are injected from the $p$-region to the $n$-region. Near the junction boundary,the concentration of these minority carriers increases. These excess minority carriers recombine with majority carriers near the junction. During this recombination,energy is released in the form of photons. The energy of the emitted photons is approximately equal to or slightly less than the band gap energy $(E_g)$. As forward current increases,the intensity of light increases,reaches a maximum,and then decreases due to heating effects.
Uses: $LED$s are used in remote controls,optical communication,traffic signals,decorative lighting,and displays.
Benefits: $LED$s have low operational voltage,fast action,no warm-up time required,long life,ruggedness,and they are available in different colors.