LED (Light Emitting Diode), a light-emitting diode, is a solid-state semiconductor device that converts electrical energy into visible light, which converts electricity directly into light. The heart of an LED is a semiconductor wafer with one end attached to a holder On the one end is negative, the other end connected to the positive power supply, so that the entire chip is encapsulated by epoxy resin. The semiconductor wafer is made up of two parts, one part is a P-type semiconductor, in which holes are dominant and the other end is a N-type semiconductor, mostly electrons here. However, when the two semiconductors are connected, a PN junction is formed between them. When a current is applied to the wafer through the wire, the electrons are pushed into the P region. The electrons in the P region recombine with the holes, and then they emit energy in the form of photons. This is the principle of LED light. The wavelength of light, which is the color of light, is determined by the material that forms the PN junction. 
Initially used as a LED instrumentation light source, then a variety of light-colored LED lights in traffic lights and large-scale display has been widely used, resulting in good economic and social benefits. Take the 12-inch red traffic light as an example. In the United States, a long-life, low-efficiency 140-watt incandescent lamp was used as the light source, which produced 2,000 lumens of white light. After the red filter, the light loss of 90%, leaving only 200 lumens of red light. In the newly designed lamp, Lumileds company uses 18 red LED light source, including the circuit loss, a total of 14 watts of power consumption, can produce the same luminous efficiency. Automotive semaphores are also an important area of LED light source applications.