Bitesize has changed! We're updating subjects as fast as we can. Visit our new site to find Bitesize guides and clips - and tell us what you think!

Design & Technology


Light-emitting diode (LED)

A white LED light

A light-emitting diode (LED) is a special kind of diode that glows when electricity passes through it. Most LEDs are made from a semi-conducting material called gallium arsenide phosphide.

LEDs can be bought in a range of colours. They can also be bought in forms that will switch between two colours (bi-colour), three colours (tri-colour) or emit infra-red light.

In common with all diodes, the LED will only allow current to pass in one direction. The cathode is normally indicated by a flat side on the casing and the anode is normally indicated by a slightly longer leg. The current required to power an LED is usually around 20 mA.

Seven-segment LED displays

Seven-segment LCD alarm clock

A seven-segment LED is a special type of LED display used in digital clocks, video recorders and microwave ovens.

Other output devices

  • Like LEDs and seven-segment displays, lamps also convert electricity into light.
  • Piezo sounders, buzzers, bells, loudspeakers and sirens are used to convert electricity into sound.
  • Microphones convert sound into electricity.
  • Solenoids are used to convert electricity into linear movement.
  • Motors convert electricity into rotary movement.

Back to Electronics index

BBC © 2014 The BBC is not responsible for the content of external sites. Read more.

This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.