Principle of LED lights

- May 24, 2019-

  1. The LED lamp is an electroluminescent semiconductor material chip, which is solidified on the bracket with silver or white glue, and then the chip and the circuit board are connected with silver or gold wire, sealed around with epoxy resin to protect the internal core wire, and finally the shell is installed, so the LED lamp has a good seismic performance.

  2. Can blue light from LED lights damage your eyes?

    The tissue used to receive light in the human eye is called retina. If the blue light band of 400-500 nm in the light source is too bright, it may cause photochemical damage to the retina after the eyes look directly at the light source for a long time. There are two main types of damage: those caused by blue light reacting directly with visual pigments in visual photoreceptors, and those caused by blue light reacting with lipofuscin in retinal pigment epithelial cells.

    How do blue leds emit white light?

    Blue light photons are high in energy and can excite fluorescence. The blue light of blue LED is usually hit on the phosphor to produce yellow light. When the yellow light is excited by the blue light, they shoot out of the LED together. We feel that we see the white light, but in fact, this is just the composite light of blue and yellow mixed together.

    Is blue light harmful to the eyes?

    Human beings evolved in the solar system. According to the wien shift law of black body radiation, we can calculate that the central wavelength of sunlight is about 550nm, while the central wavelength of blue light LED is 465nm, which deviates from the central wavelength of sunlight. Therefore, from the perspective of evolution, our human eyes cannot accept "excessive" blue light.

  3. The principle :

    The LED, a solid-state semiconductor device that converts electrical energy into visible Light, is able to convert electricity directly into Light. The heart of the LED is a semiconductor wafer, one end of which is attached to a scaffold, one end is a negative pole, and the other end is connected to the positive pole of the power supply, so that the whole wafer is encapsulated by epoxy resin.

    A semiconductor chip is made up of two parts, a p-type semiconductor in which the holes dominate, and an n-type semiconductor in which the electrons dominate. But when these two semiconductors are connected, they form a p-n junction. When an electric current is applied to the chip through a wire, the electrons are pushed toward the p-region, where they recombine with the holes and then emit energy in the form of photons, which is how leds emit light. And the wavelength of the light, the color of the light, is determined by the material that forms the p-n junction.

    LED can directly emit red, yellow, blue, green, green, orange, purple, white light.

    At first LED was used as the indicating light source for instruments and meters, and later LED of various light colors was widely used in traffic lights and large-area display screens, resulting in good economic and social benefits. Take a 12-inch red traffic light, for example. In the United States, the long-life, low-light, low-efficiency 140-watt incandescent lamp was originally used as the light source, which produced 2,000 lumens of white light. With the red filter, 90% of the light is lost, leaving only 200 lumens of red light. For the new lamp, Lumileds USES 18 red LED lights that use a total of 14 watts, including circuit losses, to achieve the same luminous effect. The automobile signal light is also the LED light source application important domain.

    To general illume character, people needs white illuminant more. In 1998, white LED was successfully developed. The LED is made of GaN chip and yttrium aluminum garnet (YAG) encapsulated together. GaN chip emitting blue light (lambda p=465nm, Wd=30nm), high-temperature sintered YAG phosphors containing Ce3+ emit yellow light when stimulated by this blue light, with a peak value of 550nLED m. The blue LED substrate is mounted in a bowl-shaped reflecting chamber and covered with a thin layer of resin mixed with YAG, about 200-500nm. The blue light from the LED substrate is partly absorbed by the phosphor, and the other part is mixed with the yellow light from the phosphor to get white light.

    For InGaN/YAG white LED, white light with color temperature of 3500-10000k can be obtained by changing the chemical composition of YAG phosphor powder and adjusting the thickness of phosphor powder layer. This method of obtaining white light through blue LED is the most widely used due to its simple structure, low cost and high technology maturity.