Study on Planar Lighting Systems Using Remote Phosphor Wavelength Conversion

• Main Authors: Huang, Hsin-Tao, 黃信道
• Other Authors: Tsai, Chuang-Chuang
• Format: Others
• Language: en_US
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/95052327335239085396

博士 === 國立交通大學 === 光電工程學系 === 99 === This study investigates planar lighting that is based on remote phosphor conversion to solve the problems of color deviation, non-uniform light distribution and low luminance efficiency of LED lighting. The LED is an emerging solid state light source that could potentially replace traditional light sources, and the interest in the use of LEDs for general illumination has been rapidly increasing. The point-type lighting of LEDs demands a focus on illumination performance, and understanding of the features of uniformity, light distribution and efficiency when LEDs are used in planar lighting. Conventional white LEDs is not simultaneously satisfactory in all these respects. This study focuses on LED devices using "conformal phosphor coating, CPC" and LED lighting module using "remote phosphor coating, RPC" method. Eventually, a dual-sided display system was produced to realize the color and optics performance as compared to conventional planar lighting systems. The results of this study reveal that the placement and arrangement of phosphors critically determine both the luminous efficiency and the color deviation. Since the phosphor in a conventional LED package is in contact with the LED die, a significant fraction of the blue light is backscattered by the phosphor and lost by absorption by the LED chips. Additionally, the high temperature of an operating wLEDs causes thermal quenching, reducing the light radiation efficiency of the phosphor and InGaN blue LEDs. Therefore, the placing of phosphor remote to the LED chip has been explored to analyze the luminous efficiency and color deviation of lighting module. The study of CPC by the pulsed spray (PS) method to an array of blue LED devices is investigated. PS can yield a wide range of color temperatures (Tc) from 2500 K to 9500 K with high color accuracy. Unlike other coating approaches, PS is a mechanical spray-based, environmentally friendly method that does not produce harmful ionic pollution in chemical reactions. In an investigation of RPC, a planar lighting module of blue LEDs was utilized to excite a yellow phosphor film. The phosphor film herein acts simultaneously as a wavelength converter and a light diffuser simultaneously. The proposed configuration yields a lower color deviation than a conventional wLEDs lighting system, and a uniform luminous distribution, from an ultra-slim structure. Most importantly, the configuration does not include a conventional diffuser plate or light guide plate (LGP). Accordingly, an RPC lighting system with excellent optical performance can be realized in a compact module. Hence, an ultraviolet (UV)-excited flat lighting (UFL) system, comprising a RPC is examined. An R/G/B trichromatic RPC is excited using a 254 nm UV light to achieve high color rendering and high luminous backlighting in a slim TFT-LCD display. A UFL system provides symmetrical dual-sided illumination without conventional optical reflectors. Furthermore, UFL exploits the thermal radiation mechanism to release the large amount of heat that is produced by the illumination system, preventing thermal accumulation. These characteristics of the UFL scheme were studied and compared with those of conventional lighting. A dual-sided display based on UFL lighting has potential for use in digital signage or public information displays, for example. This present investigation provides clear evidence of the low color deviation of LED devices. The color analysis and optics of an LED lighting module are studied. The findings are important since they suggest that a dual-sided display system with thermal radiation was low color deviation, high luminous efficiency and a compact mechanism design. The RPC scheme is environmentally friendly that does not involve chemical reactions that generate pollution. RPC lighting performs excellently in LED planar lighting systems.