lichtdiodes

Light-emitting diodes, or LEDs, are semiconductor devices that emit light when forward biased. The term lichtdiode is the German equivalent. LEDs rely on electroluminescence at a p-n junction: electrons from the n-type region recombine with holes in the p-type region in an active layer, releasing photons. The color of the light depends on the energy bandgap of the semiconductor material.

Common materials include gallium arsenide (GaAs), gallium phosphide (GaP), gallium nitride (GaN) and their alloys. By varying the composition, LEDs can emit red, green, blue, infrared and ultraviolet light. White light is typically produced by a blue or near-ultraviolet LED with a phosphor coating that converts part of the emission to longer wavelengths, or by combining multiple color emitters.

LEDs are fabricated as small packages containing a die, electrical contacts, encapsulation, and often a phosphor layer. Efficient heat dissipation and thermal management extend light output and lifetime. Modern white LEDs achieve high luminous efficacy and long lifetimes, often tens of thousands of hours.

History and impact: LEDs were developed from early red devices in the 1960s; bright blue GaN-based LEDs were demonstrated in the 1990s, enabling practical white lighting. The advancement supported widespread adoption of energy-efficient lighting and was recognized with a Nobel Prize in Physics in 2014 for Nakamura, Akasaki and Amano.

Applications include general illumination, displays, signage, backlighting and automotive lighting. Benefits include high energy efficiency, long life, compact size and robustness; limitations include higher upfront cost and, for some white LEDs, incomplete color rendering with traditional lighting. LEDs also avoid mercury, reducing environmental impact compared with some fluorescent lamps.