A variety of colorful LEDs

LED is the abbreviation for a light emitting diode, an electronic device that lights up when electricity is passed through it. Traditionally, LEDs were red but other colors have become possible since the mid 1990s. LEDs can be very small, have low power consumption and heating, and can have very long lifetimes.

The physical principle of light production is very much like that of the excited hydrogen atom: electrons excited away from the ground state emit photons (light) as they return back to their lowest energy state. The colors emitted depend on the electron energy levels (and hence the materials) as well as phosphorescent coating placed around the LED. The electrons in the LED are made to enter excited states by driving a current through the LED. The materials used in LEDs are two types of semiconductors placed together to form a diode junction.