Optics 101

What is an LED?

Light emitting diodes (LEDs) are devices that convert electricity into light. The uses of LEDs has evolved into a source of major lighting technology.

LEDs provide advantages such as high energy efficiency, durability, non-toxicity and long life. LEDs were invented during the 1960s. By varying the type of material used for the LED, it can emit different wavelengths in the infrared, visible and ultraviolet regions of the spectrum.

Working Principle and Spectral Output

LEDs work based on solid-state electronics. A diode is made up of alternate layers of electron rich (n) and electron deficient (p) materials, forming a number of p-n junctions. When sufficient power is supplied to the junction, electrons of the n-region are excited and generate light through photon emission.

The light emitted by LEDs varies with the type of semiconductor material used for its construction. The various wavelengths produced by LEDs along with the corresponding semiconductor material are listed below:

  • Infrared (>760 nm) – gallium arsenide and aluminum gallium arsenide
  • Visible spectrum – gallium arsenide phosphide, indium gallium arsenide, zinc selenide, indium gallium nitride
  • Ultraviolet (<400 nm) – aluminum nitride, aluminum gallium nitride, diamond.

Construction and Types of LEDs

LEDs are semiconductor diodes made from a host of semiconductor materials. Like any other diode they consist of p-n junction. LEDs are classified based on the application they are used for, the various LED types are listed below:

  • Miniature
  • High power
  • Custom designs
  • Alphanumeric


Some of the typical applications of LEDs are given below:

  • Traffic signal array
  • Television remote controls
  • Lighting
  • Medical devices and monitors
  • Toys
  • Displays, sign boards and indicators
  • Optocouplers and optoisolators


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