At present, GaN-based LEDs achieve white light mainly: […]
At present, GaN-based LEDs achieve white light mainly: blue LED + yellow phosphor, three-color LED to form white light, purple LED + three-color phosphor three ways. The most common way to form white light is to combine a blue LED chip with a phosphor that can be effectively excited by blue light to form a white LED. The LED emits blue light with a peak of 470 nm, and some blue light-emitting phosphors have a peak of 570 nm. The yellow-green light is at the mercy. Y l O :Ce white light occurs when the blue light transmitted from another portion is mixed with the yellow-green light generated by the stimulating phosphor. Most of the currently selected phosphors are rare earth-activated aluminates Y l O :Ce (YAG), which are yellow-green phosphors when they are excited by blue light. The method emits light, has high luminous power, is simple to prepare, and has sophisticated skills.
But the color changes with the angle. The light consistency is poor, and the lifespan of the phosphor and the LED are also inconsistent. As the time goes by, the color rendering index and the color temperature are changed, which affects the illuminating quality of the illuminating light source. The red, green and blue primary color LED chips or the three primary color LED tubes are used to complete the white light. The former is a three-chip type, and the latter is a three-lamp type. The red, green and blue LEDs are packaged in one tube, and the luminous efficiency can reach 20 lm/W. The luminous power is high and the color rendering is good. [31. However, the shortcoming of this method of forming white light is the driving circuit of LED. More complicated. The three-chip type three primary color mixing cost is higher, and because the light decay characteristics of the three types of red, green and blue LEDs are inconsistent, with the addition of the use time, the mixing ratio of the three colors of the LED device manufacturer will be changed. The color rendering index will also change the ultraviolet or violet LED to ignite the three primary color phosphors, resulting in white light. This method is simpler to obtain a white color with consistent color. Since the color is only determined by the ratio of the phosphor, in addition, a high color rendering index can be achieved. But the biggest difficulty is how to achieve high conversion power of three-color phosphors, especially high-efficiency red phosphors. And it is also important to avoid UV leakage.