Since 1968, when the GaAsP red light emitting diode (LED) has achieved 1 lm/ W by nitrogen doping,LED research has developed rapidly. In 1985, the liquid phase epitaxy method was adopted to make the luminescence intensity of Al GaAs LED exceed 1 CD [1] for the first time.

The research on InGaAlP quaternary materials in the early 1990s not only greatly improved the efficiency of LED, but also extended the spectrum of high-brightness LED from red light to yellow light and yellow-green light [2 ~ 4]. In the mid-1990s,Nakamura et Al. [5,6] successfully prepared high-brightness InGaN/ Al GaN double heterojunction blue light LED and InGaN quantum well ultraviolet LED using MOCVD method. The emergence of Gan-based blue light LED and its rapid improvement in efficiency enable LED to form a complete light system of three primary colors, and make the development of white light LED possible. There are two main technical approaches to achieve white LED: first, the red, green and blue primary colors are mixed to generate white light; second, the white light is achieved by the conversion of phosphor powder, of which the latter is the majority [7-11].
With the continuous improvement of the power and efficiency of white LED,LED is striding forward from indicator and display field to lighting field, and will become the third generation lighting source after incandescent lamp and fluorescent lamp. Although high-power white LED is the current research hotspot, there are still problems such as low luminous efficiency, poor spatial chromaticity uniformity and high cost for lighting. In addition, although LED is recognized as a highly reliable semiconductor product, there are still insufficient reports on life test data of high-power LED. This paper has studied