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Light-emitting diode (LED) is a semiconductor device that emits light when forward biased. The light is produced by electroluminescence as electrons recombine with holes in a pn junction, releasing energy in the form of photons. The color of the emitted light is determined by the bandgap of the semiconductor material.

LEDs are typically built from III-V compound semiconductors, such as gallium arsenide for red and gallium nitride for blue and green. White light is usually produced with blue or near-ultraviolet LEDs coated with phosphor, or by combining multiple LEDs in RGB configurations. The development of bright blue LEDs in the 1990s enabled practical white-light LEDs and earned the researchers Isamu Akasaki, Hiroshi Amano, and Shuji Nakamura the Nobel Prize in Physics in 2014.

Operation and performance: A current-limiting driver is required; LEDs are efficient but sensitive to heat, so thermal management extends life. Modern white LEDs achieve high luminous efficacy, with values varying by design and application, and typical lifetimes ranging from tens of thousands to over 100,000 hours with gradual lumen depreciation.

LEDs offer high efficiency, long life, compact size, and robustness, leading to widespread use in general illumination, displays, signage, automotive lighting, and indicators. They present some challenges, including color rendering dependent on phosphor design, the need for proper heat sinking, and concerns about blue-light exposure in some applications.