The way of white LED light-emitting diodes can be mainly divided into single crystal type and polycrystalline type according to the number of LED light-emitting diodes used.
One is a polycrystalline type, that is, white light is formed by using two or more complementary two-color LED light-emitting diodes or mixing light of three primary color LED light-emitting diodes. The use of a polycrystalline type to generate white light, because different color LED light-emitting diodes have different driving voltages, light-emitting outputs, temperature characteristics, and lifetimes, so white light is produced in a manner using polycrystalline LED light-emitting diodes. The way in which white LEDs produce white light is complicated, and because of the large number of LED light-emitting diodes, the cost of polycrystalline LEDs is also high; if a single crystal type is used, only a single-color LED light-emitting diode element can be used, and The design on the drive circuit will be easier.
The other is a single crystal type, that is, a single-color LED light-emitting diode plus a corresponding phosphor, just like the fluorescent light of the fluorescent lamp, the LED light-emitting diode is used to excite the fluorescent light. Two methods are usually used, one is that the blue LED light emitting diode excites the yellow phosphor to generate white light, and the other is that the ultraviolet light LED excites the RGB three-wavelength phosphor to generate white light. Many manufacturers are mainly engaged in the research of white LEDs. They usually start development and mass production from blue LEDs. After the technology of blue LEDs, they will start to develop white LEDs. However, the most commonly used blue LEDs use yellow phosphors to generate white light, but The luminous efficiency of blue LEDs to emit white light is still insufficient. Many manufacturers have begun to develop toward ultraviolet LEDs in other directions. Ultraviolet LEDs and RGB three-wavelength phosphors are used to achieve white light effects. The luminous efficiency is better than blue light. A lot on it. The method of ultraviolet LED plus RGB three-wavelength phosphor is the key technology in the high-efficiency phosphor synthesis method, which is a technique for how to effectively attach the phosphor to the crystal grains.
The principle of illumination of white LEDs is slightly different from that of other LEDs. There are currently two illumination modes that enable the LED to emit white light. One is a white light-emitting diode using a two-wavelength blue light + yellow light-emitting mode, the basic part of which is a blue light-emitting diode, and a blue light-emitting diode chip is covered with a phosphor layer, when the blue light-emitting diode chip Some of the emitted blue light is absorbed by the phosphor when it passes through the phosphor, and becomes yellow light. The yellow light is mixed with the blue light transmitted through the phosphor to emit white light. For example, some white light-emitting diodes emit light that is pure white, while some emit light that is white-blue.
The other is a full-color light-emitting diode using three-wavelength blue light + green light + red light-emitting mode, which encapsulates three red, green and blue light-emitting diodes in the same tube, and the light mixing of the three primary colors is also White light can be produced, but since the cost of making full-color LEDs is relatively high, it is generally not necessary to use full-color LEDs to make illuminations. Full-color LEDs are mainly used to make full-color displays with full color. Light-emitting diodes make lighting that greatly increase the cost of the product.