直下式發光二極體背光板設計

Abstract

在寬螢幕、數位化及高畫質的未來電視需求中，液晶顯示器(LCD Display)不僅由於解析度高、純數位化的特性成為下一世代電視的當然候選人外，更因其具有厚度薄、重量輕與高亮度的優點，使其成為最具有競爭優勢的競逐者之一。現今的液晶顯示器都使用冷陰極管(CCFL)作為發光光源，但由於螢光材料的特性問題，其顯示的色彩範圍不及傳統陰極射線管（CRT）顯示器，並且由於冷陰極管內部含汞，無論在製造過程與回收處理上皆對環境汙染的衝擊甚大。若改以發光二極體（LED）為光源，液晶顯示器之色域將可以提升到與CRT相同，甚至超 越CRT型顯示器。

本論文主要著重在利用發光二極體設計液晶背光模組，工作重點為利用朗伯型（Lambertian）發光二極體，藉由二次光學修正其光出射場形為側發射光場(Side-emitting)，並進行其光源擺設位置、相對面積密度與背光模組出射面之光均勻度，甚至混色效果的關連性探討，以期得到針對不同模組尺寸大小的最佳化參數。並且在更進一步的容忍度模擬分析中，探究了在實際操作上我們所設計的背光模組對於元件故障的承受能力。在我們的研究成果中，利用OSLO設計了一個能將朗伯型LED轉換成側射場型的光學模粒，並利用TracePro進行背光模組的光機模型之建構與模擬，並分析均勻度與混光的效果。針對我們的最佳化設計，我們得到了約92％的均勻度與極好的混光能力，並且具有極高的容忍度。

In the demand of the future display, wide screen size, full digitalization and high definition are the most crucial requirements. Liquid crystal device (LCD) display undoubtedly may be taken as one of the potential candidate owing to its extra high resolution and pure digitalization and moreover, it might be the most competitive since it is of thin, light and high brightness. The present LCD displays commonly utilize the Cold Cathode Fluorescent Lamp (CCFL) as the light source, however due to the luminant characteristic of phosphor the chromatic range where the display can show is smaller than that of CRT display. And also, it will be an eco-threat whenever in the phase of manufacturing and recycling since mercury is not avoidable in fabrication of CCFL. Altering the light source to light emitting device (LED) is a good solution to enhance the color range to the level of CRT display, or moreover, better than CRT display.

In this thesis, we concentrated on the design of back-light module with LEDs. To achieve a better uniformity of illumination and color mixing quality, an optical element was designed to shape emitting field of the Lambertian LED to side-emitting distribution and on the basis of the modification of emitting field of light source, the correlation between the optical performances on the exit surface of back-light module, including uniformity and chromatic mixing quality, and the design parameters, such as the locations of LEDs and the relative density corresponding to different sizes were explored. Consequently, the optimal design parameters were obtained. In the further analysis of tolerance, we studied the bearing capability of the proposed design under the assumption of specified devices malfunctioned. We also designed an optical element being able to reshape the emitting field from Lambertian distribution to side-emitting with the assistance of OSLO and built the complete model of back-light model in TracePro and furthermore, simulated it. We have obtained the uniformity about 92% within whole exit surface of back-light module in which good color mixing quality and great tolerance have been verified by numerical simulations.