기하 광학적 광선 추적법을 이용한 수평형 발광다이오드의 광특성 해석

Abstract

White light emitting diodes (LEDs) have attracted a great deal of attention in solid-state lighting applications due to their potential for energy savings, high efficiency, small size and long lifetime. The use of white LEDs for general illumination has recently grown rapidly with improvement of efficiency. However, the color of white light source is usually evaluated by two optical properties: the color rendering index (CRI) describes how well colors are reproduced by the light source and the correlated color temperature (CCT) describes how colors are falling close to the blackbody curve. In general, to create white light from LEDs, the approach of combination of wavelength down-converting cerium-doped yttrium garnet (YAG:Ce) yellow phosphor with blue LED have been adopted because they have benefit of relatively low cost as well as great stability over a wide range of temperature. However, some problems remain with phosphor converted white LEDs such as low CRI and high CCT by the absence of green and red spectrum. White LEDs must have a broadband spectrum to achieve a CRI of over 80, which is required for use in general and special illumination application. So, phosphors of two or more colors are required. So, we need to spend lots of time and cost to find the optimum weight percent of phosphors of two or more colors for improvement of CRI and control of CCT. In these works, we suggest the simple method to find optimum weight percent of phosphors of two or more colors to improve the CRI and control the CCT based on geometrical ray tracing method. First, we design the radiation pattern of blue LED chip and package by apodization method. Then, we simulate the emission spectrum and radiation pattern of white LED by adopting the yellow and red phosphors with various weight percent and compared them to experimental measured values. Finally, we suggest the various CCT and high CRI white LEDs by combination of yellow and red phosphors in blue LED.