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Why do LEDs emit different colors of light

LED is the abbreviation of Light Emitting Diode in English. Like a diode, it has a PN junction, which has unidirectional conductivity. A forward voltage is applied to the pins at both ends of the PN junction. Holes and free electrons meet to produce recombination. A certain amount of energy.

This energy is either presented in the form of heat or in the form of light emission. Light-emitting diodes are presented in the form of light emission. Of course, the light-emitting diodes will also generate heat. Ordinary diodes cannot emit light.

There is not much difference between light-emitting diodes and diodes. Light-emitting diodes are doped with some compounds in the PN junction: gallium, arsenic, phosphorus, nitrogen and so on. These compounds are doped into the P and N areas, and then pins are added, and the epoxy resin is used to wrap them up, which is strong and shock-resistant.

Why do you want to dope with different compounds? In order to emit different colors of light. At present, LEDs are popular because of their high efficiency. Many people think that this is a new technology. In fact, the earliest LEDs have existed for more than 50 years. In 1962, Laomei developed light-emitting diodes.

Many friends think that the light emitted by the LED is white, but it is actually red, but the brightness is very weak. When gallium arsenide is doped, the LED emits red. Of course, it is not for the purpose of developing red light to make the LED emit red light. , Was later bought by HP as indicator light, which is why many indicator lights are red.

With the development of science and technology, some other colors slowly appeared: doped with gallium phosphide to make the LED emit green light, doped with silicon carbide to make the LED emit yellow light, and so on.

In 1993, Shuji Nakamura, an electronic engineering expert in Japan, successfully invented the high-brightness blue LED. In 2014, he “invented the high-brightness blue light-emitting diode and brought an energy-saving and bright white light source.” Hiroshi Amano, Yuki Akasaki and Nakamura Shuji jointly won the Nobel Prize in Physics.

Isn't it a bit ignorant, why the blue light-emitting diode was invented and brought a white light source. Many light sources in nature are made by mixing multiple colors, while white light is made by mixing red, green and blue.

Before Shuji Nakamura invented the blue light-emitting diode, he invented the red and green light-emitting diodes. After the emergence of the blue LED, the three primary colors were mixed together, and a high-brightness white light source came out. This method produced a white light source. The cost is relatively high, the three primary colors need to be mixed, and the production process is also complicated. But the efficiency is high and the white color gamut is wide.

Now that the production technology is advanced, white light LEDs are rarely manufactured using this method. Of course, there are other methods to emit white light. For example, blue LED chips are smeared with yellow phosphor, which looks white to our naked eyes.

Some friends have to ask again, why did Shuji Nakamura win the Nobel Prize in Physics? How could he not be issued to the inventor of the red light-emitting diode or the inventor of the green light-emitting diode? Their contributions are also great, why? What about the inventor who invented the blue light-emitting diode after so long?

Because it is very difficult to make blue LEDs, other inventors gave up continuing research because of the manufacturing process. Shuji Nakamura insisted on continuing research and development. The emergence of blue light-emitting diodes, mixed with yellow phosphors, pushed LEDs to the lighting industry. .

The emergence of blue light-emitting diodes gathered the three primary colors and realized a full-color display in the display. The mixed white light source realizes the use of LED as a lighting source. So blue LED has important meaning in LED lighting.

Many colors are either based on three primary colors or a mixture of two primary colors, or a single primary color plus phosphor emits different colors of light. Of the two ways to achieve white light, the most widely used is currently in blue LEDs. Yellow phosphor is added on the basis.

Each color corresponds to its own wavelength. What is a wavelength? Take a rope and shake it up and down, there will be a wave shape, and the wavelength is the distance between two adjacent wave tops, in nanometers. The wavelength is related to the different impurities and voltage doped.

A friend asked how many kinds of light can one LED emit, what is the operation? There is an LED chip that emits two colors in this light-emitting diode. There are three pins. One of the three pins is a common terminal, a common anode or a common cathode. Take the red and green LEDs as an example, connect the common terminal and the red LED. The other pin emits a red light, and when the green pin and the common terminal are connected, it emits a green light. When the two colors are connected at the same time, the red and green lights are mixed, and a yellow light is emitted.

After this kind of LED is integrated, it is widely used in display screens. It is more common in railway stations, train schedules on railway stations, and used in traffic lights, etc.

There is also a flashing version of the LED. Now there are LEDs on the market that flash by themselves, called self-flashing LEDs. It has a flicker control circuit inside, and it will flicker as long as it is connected to the working voltage. If your friends are interested, use a PCB board to make an oscillation circuit composed of resistors and capacitors, and the flicker frequency is not high.

LED lighting has a wide range of applications and high efficiency, occupying the main market, but the efficiency drops sharply due to high temperature, and the heat generation is also large. This is why the LED lamp has a radiator. Under normal circumstances, the LED life span is as long as 50,000. An hour can last five or six years. Incandescent lamps have slowly withdrawn from the stage of history. Will other lighting hardware squeeze the LED down in the future? Friends, please leave a message to discuss.


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