Influence Of Phosphor Settling On Optical Consistency Of High-Power LED

Comparing with the traditional light sources, light-emitting diodes (LED) have better illumination effects and better efficiency; it is regarded to be the next generation illumination technology. The optical consistency is a key factor in the LED packaging industry, which decides the quality of produced LEDs. It includes the consistency of brightness and light colors. So far, the optical consistency of white LED is not good. Individual LED modules may deviate from the target optical performance due to many reasons, as one of these reasons, the settling of phosphor in packaging process will be investigated and discussed in this thesis.We illustrated the process of LED packaging, especially the procedure of phosphor dispensing. It is perceived that the phosphor settling in the packaging process may influence the optical consistency. Then some basic optical knowledge was introduced, including colorimetry, photometry, and illumination. Afterward, the phosphor settling problem was analyzed and investigated in details.The settling theory was studied, and the change of phosphor concentration before silicone cured was measured by UV-VIS spectrophotometer, it was proved that the settling does exist, and the concentration changes about 1% in every five minutes. In order to specify the distribution of the phosphor, a simulation of phosphor settling procedures was done.A new modeling method that divided the phosphor coating layer into three parts was presented. By using the Mie scattering theory, the deviation of color temperature caused by settling was simulated and calculated with commercial software. The results showed that the color temperature and the brightness deviation are very small.According to the dispending time of practical manufacturing process, we did some experiments by partially-packaged LED modules. The experimental results demonstrated that the phosphor settling happened in the packaging process can not greatly affect the color consistency.It is expected that the work could be valuable in LED optical consistency study and packaging industry.