LED Technology

How LEDs Work?

The term solid state refers to the fact that light in an LED is actually emitted from a solid object - a block of semiconductor - rather than from a vacuum or gas tube, as is the case in traditional incandescent or CFL lamps.

LEDs are closely related to computer technology than they are to traditional forms of lighting, as an LED is basically a semiconductor. In an incandescent lamp, a tungsten filament is heated by electric current until it glows or emits light. In a fluorescent lamp, an electric arc excites mercury atoms, which emit ultraviolet (UV) radiation. After striking the phosphor coating on the inside of glass tubes, the UV radiation is converted and emitted as visible light.

LEDs are electronic devices that permit current to flow in only one direction. The diode is formed by bringing two slightly different materials together to form a PN junction (positive - negative). In a PN junction, the P side contains excess positive charge (holes, indicating the absence of electrons) while the N side contains excess negative charge (electrons).

A simplified PN junction diagram.

When a forward voltage is applied to the semiconducting element forming the PN junction, electrons move from the N area toward the P area and holes move toward the N area. Near the junction, the electrons and holes combine. As this occurs, energy is released in the form of a photon (light) that is emitted by the LED. The specific wavelength or color emitted by the LED depends on the materials used to make the diode.

LEDs are very versatile due to their ability to emit nearly all spectrums of light. This has led to their nearly universal adoption as a light source for a wide range of applications from: status indicator lights, to traffic signals, to today’s advanced direct replacement LED light sources.