Enhancement of luminous efficiency by hybrid structure for warm white light-emitting diodes

Chin-Wei Sher,Kuo-Ju Chen,Mei-Tan Wang,Jie-Ru Li,Bing-Cheng Lin,Hau-Vei Han,Min-Hsiung Shih,Jung-Min Hwang,Hao-Chung Kuo,Chien-Chung Lin,Chien-Chung Fu,Kuan-Yu Wang

doi:10.1186/2196-1107-1-9

Abstract

Abstract This study demonstrates the hybrid structure with high lumen efficiency and uniform angular-dependent correlated color temperature (CCT) for warm white LED. Compared to the conventional structures, the hybrid structure combines the advantage of the two different fabrication methods including dispense and pulse spray method together, which can produce the high quality lighting source. The experimental results indicate that the hybrid structure yielded higher lumen efficiency than conventional phosphor structure because of the gradual refractive index difference from the coating layer to the dispense layer. Moreover, the CCT deviations of the hybrid phosphor structure could be reduced to 65 K in range of -70 to 70 degrees. This is attributed to the uniform color mixing of the blue, yellow and red band in the hybrid phosphor structure. In addition, the chromaticity coordinate shift compared to the hybrid structure with the dispense structure are almost the same at a current regulation from 20 mA to 500 mA. We believe that the technology of the hybrid structure with high lumen efficiency and uniform angular-dependent CCT is suitable for in the general lighting application.

Highlights

White light-emitting diodes (WLEDs) have been widely applied in the daily life because of their advantages of the small size, high efficiency, and long lifetime, which can be categorized as the environment-friendly lighting sources [1,2,3]
For the conformal-type phosphor structure, there are 60% backscattering lights reflected to the package [21] and these back-scattering photons are susceptible to reabsorption by the blue chip and reducing the luminous efficiency
In this study, the hybrid phosphor structure with high lumen efficiency and uniform angular-dependent correlated color temperature (CCT) is demonstrated for the warm white LED

Summary

Introduction

White light-emitting diodes (WLEDs) have been widely applied in the daily life because of their advantages of the small size, high efficiency, and long lifetime, which can be categorized as the environment-friendly lighting sources [1,2,3]. For the conformal-type phosphor structure, there are 60% backscattering lights reflected to the package [21] and these back-scattering photons are susceptible to reabsorption by the blue chip and reducing the luminous efficiency To solve these problems, the hybrid structure [22] and the dual-layer phosphor structure [23] are employed to enhance the lumen output due to the reduced back light inside the package. The hybrid structure [22] and the dual-layer phosphor structure [23] are employed to enhance the lumen output due to the reduced back light inside the package From these past experiences, it is essential to reduce the backscattering light issue when the concentration of the phosphor increased, especially in the warm white LED

Methods

Results

Conclusion