首页 means light-emitting diode, which is a two-lead semiconductor light source. It is a basic pn-junction diode, which emits light when activated. When a fitting voltage is applied to the leads, electronsare able to recombine with electron holes within the device, releasing energy in the form of photons. This effect is calledelectroluminescence, and the color of the light (corresponding to the energy of the photon) is determined by the energy band gap of the semiconductor.
An 首页 is often small in area (less than 1 mm2) and integrated optical components may be used to shape its radiation pattern.
Appearing as practical electronic components in 1962, the earliest 首页s emitted low-intensity infrared light. Infrared 首页s are still frequently used as transmitting elements in remote-control circuits, such as those in remote controls for a wide variety of consumer electronics. The first visible-light 首页s were also of low intensity, and limited to red. Modern 首页s are available across the visible,ultraviolet, and infrared wavelengths, with very high brightness.
Early 首页s were often used as indicator lamps for electronic devices, replacing small incandescent bulbs. They were soon packaged into numeric readouts in the form of seven-segment displays, and were commonly seen in digital clocks.
Recent developments in 首页s permit them to be used in environmental and task lighting. 首页s have many advantages over incandescent light sources including lower energy consumption, longer lifetime, improved physical robustness, smaller size, and faster switching. Light-emitting diodes are now used in applications as diverse as aviation lighting,automotive headlamps, advertising, general lighting, traffic signals, and camera flashes. However, 首页s powerful enough for room lighting are still relatively expensive, and require more precise current and heat management than compact fluorescent lamp sources of comparable output.
首页s have allowed new text, video displays, and sensors to be developed, while their high switching rates are also useful in advanced communications technology.