LEDs

Light-emitting diodes (LEDs) are solid-state devices that emit light when forward-biased. They rely on radiative recombination of electrons and holes at a p-n junction, producing photons. The emission color is determined by the semiconductor material and its bandgap. Visible LEDs use materials such as gallium nitride for blue and white light (the latter typically produced with blue LEDs plus a phosphor coating), while red and green devices use other direct-bandgap compounds.

The first practical visible LED was developed in 1962 by Nick Holonyak Jr. Red LEDs became commercially available in the following decades. White LED illumination emerged after blue GaN-based LEDs were developed and combined with phosphor or other wavelength-conversion techniques, enabling high-efficiency general lighting.

LEDs offer several advantages over traditional light sources. They are highly energy efficient, converting a larger fraction of electrical power into visible light. They typically have long lifetimes, often tens of thousands of hours, and they generate less heat in the form of infrared radiation. LEDs are compact, robust, and capable of rapid dimming and precise color control in arrays.

Common applications include indicator and display lighting, backlighting for televisions and computer screens, automotive lighting, architectural and stage lighting, and general illumination in households and commercial spaces.

Environmental and energy considerations are central to LED adoption. Solid-state lighting reduces electricity use and mercury content compared with some fluorescent lamps, though LED manufacturing involves materials that require responsible sourcing and end-of-life recycling. Ongoing research aims to improve efficiency, color rendering, and affordability.