Explore the key elements behind light quality - phosphors

White LED has high luminous efficiency, low power consumption, small size, long life, no harmful substances such as mercury and lead, no infrared and ultraviolet rays, etc. It is recognized as the fourth generation of green energy-saving and environmental protection light source. With the increasing emphasis on energy conservation and environmental protection, white LEDs have replaced traditional light sources into the general lighting market and have become a major trend in the lighting industry.

At present, there are mainly two ways to prepare white LEDs. One is to obtain white light by mixing "red light chip + green light chip + blue light chip (RGB)", and the other is to obtain "blue light chip + phosphor". White light, while the latter dominates white LEDs. For this main packaging method, the quality of the phosphor determines the color temperature, color rendering index, color uniformity and luminous flux of the light source. Recently, people have higher and higher requirements for the light quality of white LED light sources. In particular, the requirements for indicators such as blue light hazard, glare and color rendering are becoming more and more strict. How can phosphors meet the needs of high-quality light sources?

The light quality of the light source is a comprehensive evaluation, which needs to consider various parameter indexes such as color temperature, color coordinates (color preference), Ra, R1-R15 (especially R9), color saturation, application requirements, etc. The key factor of the parameter indicator is the phosphor. At present, there are eight major series of commercially available LED phosphors on the market: YAG yellow powder with emission peak range from 545 nm to 580 nm, GaYAG yellow green powder with 522 nm to 545 nm, LuAG green powder with 520 nm to 545 nm, and silicic acid of 515 nm to 575 nm. Salt green powder/yellow powder, silicate orange powder at 580 nm-600 nm, nitride red powder at 612 nm-675 nm, oxynitride blue-green powder at 490 nm-500 nm, and fluoride system red powder at 629 nm-632 nm . These commercial phosphors have different parameters such as emission peak, color coordinate, half-width, excitation efficiency, particle size, and surface smoothness, and their applications have their own advantages. In layman's terms, this is like a colored pen for painting. A blue LED is like a paper, and a phosphor is like a colored pen. You can get a color temperature, color coordinates, Ra, R1-R15 (especially R9). ), NTSC, light uniformity and other parameters are not the same as the beautiful "glorious painting".

1. Effect of spectral range of phosphor excitation on light quality

The most fundamental meaning of LED phosphors is to achieve light conversion, that is, to convert blue light into visible light of other wavelengths, and its conversion efficiency is closely related to its excitation spectrum. Figures 1 - 5 are the excitation spectra of some phosphors:

The excitation spectrum of the phosphor determines the conversion efficiency of the 440nm-470nm blue LED chip . As shown in the figure, some of the phosphors commonly found on the market only contain the wavelength range of the blue LED chip, but not all The series of phosphors have the strongest excitation in the wavelength range of the blue LED chip, which means that some phosphors can only be excited by the blue LED chip, rather than the best excitation application, so when using high-efficiency phosphors, It is necessary to select according to the matching of the wavelength of the blue chip and the excitation wavelength of the phosphor.

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