An LED (Light Emitting Diode) is a relatively new light source in the market even though the technology itself is old, having been discovered at the beginning of the 1900s soon after Edison invented the light bulb. However, its significance wasn’t realised at the time. The 1960s saw the use of the first red diodes, but it wasn’t until the 2000s that we started using them as light sources on a large scale.
Light emitting diodes have no filament, gas, glass bulb or any moving parts, unlike other light sources. Light emitting diodes contain a special semiconductor that emits light when a current is passed through the diode.
Depending on which elements the semiconductor contains, it glows in different colours, red, green, yellow, ultraviolet and blue. To protect against external impingement, and to enable an electrical connection, the diode is sealed in a casing that provides an angle of illumination of 140–180 degrees.
White light is created using phosphor technology in the same way as for fluorescent lamps – a blue or ultraviolet diode is coated in a yellow or orange fluorescent powder (phosphor) that transforms some of the radiation into yellow light, so that the end result is a white light.