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White LEDs: There are three main types of natural spect […]
White LEDs: There are three main types of natural spectrum white LEDs:
The first is a relatively mature and commercialized blue chip + yellow phosphor to obtain white light. This white light has the lowest cost, but the shift of the blue light crystal wavelength, the change of intensity and the change of the thickness of the phosphor coating will be Affects the uniformity of white light, and the spectrum is narrower in band shape, color is incomplete, color temperature is high, color rendering is low, and the light is not soft and uncoordinated to the eyes. The human eye is most adapted to the sunlight. The continuous spectrum of incandescent lamps is the best. The color temperature is 2500K and the color rendering index is 100. Therefore, this white light needs to be improved, such as adding a multi-lighting process to improve the spectrum to make it continuous and wide enough.
The second type is ultraviolet or violet chip + red, blue and green phosphors to obtain white light. The principle of illumination is similar to that of fluorescent lamps. This method has better color rendering, and UV-LED does not participate in white color matching, so UV- The fluctuation of the wavelength and intensity of the LED is not particularly sensitive to the white light that is dispensed, and the white light of acceptable color temperature and color rendering can be modulated by the selection and ratio of the phosphors of the respective colors. However, there is also a problem that the effective conversion efficiency of the phosphor used is low, and in particular, the efficiency of the red phosphor needs to be greatly improved. Such phosphors have poor luminous stability, large light decay, selection of phosphor wavelengths for phosphors, difficulty in UV-LED fabrication, and development of anti-UV packaging materials.
The third is to use the three primary color principle to mix RGB three ultra-high brightness LEDs into white light. The advantage of this method is that white light can be directly dispensed without conversion of the phosphor, which is better than avoiding the loss of phosphor conversion. In addition to the luminous efficiency, the luminous intensity of the red, green and blue LEDs can be separately controlled to achieve a full-color color-changing effect (variable color temperature), and a better color rendering property can be obtained by selecting the wavelength and intensity of the LED. However, the problem with this method is that the conversion efficiency of green light is low, the light mixing is difficult, and the design of the driving circuit is complicated. In addition, since these three light colors are all heat sources, the heat dissipation problem is three times that of other package forms, which increases the difficulty in use. Polarized LEDs and three-wavelength full-color white LEDs will be the future direction.