Light-emitting diode

A light-emitting diode produces light through electroluminescence at a semiconductor junction. When the diode is forward-biased, electrons from the n-type region and holes from the p-type region enter the active region and recombine; the released energy can emerge as a photon. The photon energy, and therefore the approximate color, depends mainly on the semiconductor band gap.¹

Unlike an incandescent lamp, an LED does not heat a filament, and unlike a laser diode it generally emits relatively broad, non-coherent light. The basic device includes semiconductor layers, electrical contacts, a substrate, and optical packaging that directs or extracts the light. A current-limiting circuit is normally required because a small voltage change can produce a large current change.

LED color is determined chiefly by the composition of its semiconductor materials. Early commercial devices commonly used gallium arsenide phosphide and related compounds for red, orange, and yellow emission, while gallium nitride compounds enabled efficient blue and ultraviolet devices. Blue LEDs were a crucial advance because they made practical white solid-state lighting possible when combined with a phosphor or with red, green, and blue emitters.²

The first visible-spectrum LED was developed in the early 1960s, and Nick Holonyak Jr. demonstrated a practical visible red device. The 2014 Nobel Prize in Physics recognized Isamu Akasaki, Hiroshi Amano, and Shuji Nakamura for the development of efficient blue LEDs, whose manufacture required difficult advances in gallium nitride crystal growth and p-type doping.²

LEDs serve as indicators, displays, illumination sources, optical transmitters, and sensing components. Their small size and fast response support traffic signals, vehicle lamps, mobile-device screens, digital signage, remote controls, fiber-optic links, and machine-vision systems. In general lighting, LEDs are sold as lamps and luminaires rather than as bare junctions; drivers convert incoming power into the controlled current the devices require.³

White LEDs usually combine a blue or ultraviolet chip with a wavelength-converting phosphor, although multichip designs are also used. Performance is described by measures such as luminous efficacy, color-rendering properties, correlated color temperature, and useful life. Heat remains a central engineering concern: junction temperature affects output, color stability, reliability, and the rate of lumen depreciation.³

LEDs are not limited to visible lighting: related devices emit infrared radiation for remote controls and communications, while ultraviolet LEDs support specialized curing, analysis, and disinfection applications. Some LEDs are designed for narrow spectral bands, making them useful in plant lighting, fluorescence excitation, and optical measurement. Their rapid modulation also permits data transmission and visible-light communication, although illumination and communication requirements can conflict.

The apparent color of an LED can shift with drive current, temperature, optics, and phosphor aging. A white LED is therefore not a single spectral technology but a family of constructions with different trade-offs among efficiency, color quality, cost, and lifetime. Blue-rich light can also influence circadian physiology, so lighting design considers spectrum, timing, intensity, and exposure context rather than efficiency alone.⁴ Research into microLED displays, deep-ultraviolet emitters, and improved green emitters continues to address manufacturing and efficiency limits.⁵

Electroluminescence

Emission of light from a material as a result of an applied electric current or electric field.

p–n junction

The boundary between p-type and n-type semiconductor regions, forming the fundamental junction in a diode.

Phosphor

A wavelength-converting material that absorbs shorter-wavelength radiation and emits light at longer wavelengths.

Luminous efficacy

Visible-light output per unit of electrical power, commonly expressed in lumens per watt.