How To Get White Light Source With LED

    LED light-emitting diode is a solid-state semiconductor device that can convert electrical energy into visible light, which can directly convert electricity into light. The heart of the LED is a semiconductor chip, one end of the chip is attached to a bracket, one end is the negative electrode, and the other end is connected to the positive electrode of the power supply so that the entire chip is encapsulated by epoxy resin. The wavelength of light, which is also the color of light, is determined by the material that forms the P-N junction.

    At first, LED was used as an indicator light source 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 a 12-inch red traffic light as an example. In the United States, a long-life, low-efficiency 140-watt incandescent lamp is used as the light source, which produces 2000 lumens of white light. After the red filter, 90% of the light is lost, leaving only 200 lumens of red light.

    For general lighting, people need more white light sources. In 1998, the LED that emits white light was successfully developed. This LED is made by encapsulating GaN chips and YAG together. The GaN chip emits blue light (λp=465nm, Wd=30nm), and the YAG phosphor powder containing Ce3+ sintered at high temperature emits yellow light after being excited by this blue light, with a peak value of 550nLED lamp m. The blue LED substrate is mounted in a bowl-shaped reflective cavity, covered with a thin layer of resin mixed with YAG, about 200-500 nm. Part of the blue light emitted by the LED substrate is absorbed by the phosphor, and the other part of the blue light is mixed with the yellow light emitted by the phosphor to obtain white light. For InGaN/YAG white LEDs, by changing the chemical composition of the YAG phosphor and adjusting the thickness of the phosphor layer, various colors of white light with a color temperature of 3500-10000K can be obtained. This method of obtaining white light through blue LEDs has the advantages of simple structure, low cost, and high technical maturity, so it is widely used.

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