A light-emitting diode is a semiconductor diode that produces light as an electrical current passes through it. The diode is formed by bringing an excess positive charge and an excess negative charge together, releasing energy in the form of light.
LEDs are available in several colors, but not white. White light is produced by mixing several colors together and covering them with a yellow phosphor material to create bulbs for use in homes and businesses. LEDs are more efficient than incandescent and fluorescent bulbs because they produce directional light, which is sometimes undesirable for household uses. To compensate, the bulb housing is engineered to reflect the light in all directions.
Unlike incandescent bulbs, which release 90 percent of their energy as heat, LEDs do not radiate heat into the surrounding environment. In order to prevent the diode from overheating and burning out, a thermal management system is added. This passive device, called a heat sink, absorbs and dissipates the heat, lengthening the life of the LED.
Instead of burning out, LEDs typically experience lumen depreciation, where the amount of light produced decreases over time. The lifetime of an LED bulb is calculated by the amount of time it takes for the light output of the diode to decrease by 30 percent.