About 60 years ago, people have understood the basic knowledge that semiconductor materials can produce light. In 1962, Nick Holonyak Jr. of General Electric Company developed the first practical visible light-emitting diode. LED is the abbreviation of light emitting diode. Its basic structure is a piece of electroluminescent semiconductor material, placed on a shelf with leads, and then sealed with epoxy resin around it, that is, solid packaging. Therefore, it can protect the inner core wire, so the LED has good shock resistance.
Initially, LEDs were used as indicating light sources for instruments and meters. Later, LEDs of various light colors were widely used in traffic lights and large-area display screens, 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 originally used as a light source, which produces 2000 lumens of white light. After passing through the red filter, 90% of the light is lost, leaving only 200 lumens of red light. In the newly designed lamp, Lumileds uses 18 red LED light sources, including circuit loss, and consumes a total of 14 watts of power to produce the same light effect. Automobile signal lights are also an important field of application of LED light sources.
LED, Light Emitting Diode, is a solid-state semiconductor device that converts electricity directly into light. The heart of LED is the wafer of a semiconductor. One end of the wafer is attached to a support. One is the negative pole, and the other one is connected to the positive pole of the power supply, so that the whole wafer is encapsulated by epoxy resin. Semiconductor wafer is made up of two parts. One part is P-type semiconductor, hole occupying an leading position in it. The other part is N-type semiconductor, here mainly being electron. But these two kinds of semiconductors couple together, between them, form a "P-N junction". When electric current acts on this chip by wire time, electron will be pushed to P district. And in P district, electron is with hole recombination, then will send energy with the form of photon. That is the principle of LED luminescence. And the wavelength of light, i.e. the color of light, is determined by the material forming P-N junction.