Light Emitting Diodes

• Light-emitting diodes (LEDs) have succeeded the incandescent bulbs and fluorescent lamps of previous centuries as the world’s light-source of choice.

What is a diode?

• A diode is an electronic component about 5 mm wide.
• It has two points of contact, or terminals, called its anode and cathode.
• A diode’s primary purpose is to allow current to flow in only one direction.
• It achieves this using a p-n junction.
  • A p-n junction is made of two materials laid next to each other.
  • One material is a p-type material: its primary charge-carriers are holes.
  • The other is an n-type material: its primary charge-carriers are electrons.

About LEDs

• An LED is a diode that emits light.
• Inside the diode’s p-n junction, the electrons have more energy than the holes.
• When an electron meets and occupies a hole, it releases energy into its surroundings.
• If the frequency of this energy is in the visible part of the electromagnetic spectrum, the diode will be seen to emit light.
• The overall phenomenon is called
• Since LEDs can produce all three primary colours – red, green, and blue – different LEDs can be combined on a display board to produce a large variety of colours.
• LEDs have several applications in industry, consumer electronics, and household appliances: from smartphones to TV screens, from signboards to ‘feeding’ plants light in greenhouses, from barcode scanners to monitoring air quality.