What device uses a semiconductor junction to emit light when electric current passes through it?

A light-emitting diode emits light when electric current passes through a semiconductor junction.

A light-emitting diode, usually called an LED, is a semiconductor device based on a p–n junction. When it is forward-biased, electrons and holes recombine near the junction. The released energy can appear as photons, producing electroluminescence.

The color depends largely on the semiconductor’s band gap. Different materials and structures produce infrared, visible, or ultraviolet emission. White LEDs commonly combine a blue LED with a phosphor that converts part of the light into longer wavelengths, creating a broad white appearance.

LEDs are efficient, compact, durable, and fast-switching, so they are used in indicators, displays, lighting, optical communications, and remote controls. An LED is not the same as a photodiode: a photodiode primarily converts incoming light into electrical current.