【作者】 秦宗；

【导师】 刘胜；

【作者基本信息】 华中科技大学 ， 机械制造及其自动化， 2013， 博士

【摘要】 目前,液晶显示器在平板显示器市场中占据统治性地位,其中,背光模组是液晶显示的重要组成部分。自2008年起,发光二极管(LED)背光以高光效、使用寿命长、显色性能良好、体积紧凑、不含汞等优势迅速取代传统的冷阴极管(CCFL)背光成为主流技术。LED背光模组按光源的位置可以分为侧下式和直下式两大类。考虑到两种背光模组的特点,本文将全阵列直下式LED背光用于大尺寸液晶显示器的背光模组,并对大尺寸高性能全阵列直下式LED背光模组的若干关键技术问题展开了研究。首先,在之前的基于Sparrow判据的广义朗伯型LED阵列照明系统的均匀照明条件研究的基础上,本文基于Sparrow判据研究了任意光型LED组成的阵列照明系统的均匀照明条件,首次发现对于某些宽出光角LED,阵列照明系统的照明均匀度随着LED间距或系统厚度做非单调变化。结合发现的反常均匀照明条件,本文给出了基于Sparrow判据的均匀照明LED阵列照明系统的一般性设计方法。然后,本文应用人眼视觉中的对比度敏感函数研究了LED阵列照明系统的均匀照明条件,重新推导了广义朗伯型与宽出光角LED阵列照明系统的均匀照明条件,发现所得最优结构参数比基于Sparrow判据得到的结果更准确、更实用,然后基于对比度敏感函数更系统的论述了正常和反常均匀照明条件。最后,本文又基于人眼视觉效应给出了均匀LED阵列照明系统的设计方法。背光用增亮膜在减小视角提高轴向亮度的同时会产生很高的光损耗,限制了背光模组亮度的进一步提升。为此,本文实际加工制作了一款19英寸直下式LED背光模组,并通过模拟仿真逐角度的研究了不同空间方向的光线穿过增亮膜时的透过率,得到了增亮膜“花瓣形”的空间透过率特性。然后,本文设计了一款自由曲面透镜,使得光源出光的角度范围与增亮膜的透过率特性相匹配,在不改变视角的前提下可以提高背光模组的轴向亮度。实验结果表明,在有扩散膜劣化光学效果的情况下,轴向亮度提升幅度达到了22.8%,视角只有非常轻微的下降。局部调光动态背光技术是高性能大尺寸全阵列直下LED背光的另一项关键技术,它可以提高输出画面的对比度并降低功耗。本文研究了背光源亮度确定、真实背光模拟、灰阶补偿这三个主要步骤在局部调光动态背光处理中的作用和相应的计算复杂度,分析了不同的调光算法和调光块数目对失真率和节能性能的影响,指出增大调光块数目是从本质上同时提高失真率和节能性能的唯一手段。本文提出了一种使用网格反光板的技术方案,使得真实背光模拟步骤可以被完全省略,从而降低了整体复杂度降低数倍并减弱了其与调光块数目的关联。借助网格反光板,本文使用了更多的调光块,且使用了一种与网格反光板技术方案相配套的临界溢出调光算法,失真率和节能性能都获得了显著提升。更多还原

【Abstract】 At present, flat panel display market is dominated by liquid crystal display (LCD). In an LCD, backlight module is an important component. Since2008, light emitting diodes (LED) backlight has rapidly taken the place of conventional cold cathode fluorescent lamp (CCFL) backlight due to its advantages including high luminous efficiency, long work life, high color rendering capacity, compact volume, nonuse of mercury etc., and become the mianstream technical solution. LED backlight module can be classified into edge and direct configurations according to the way light sources are placed. With the consideration of characteristics of these two types of configurations, full-array direct LED backlight was adopted for large-size LCD in this paper. Several key techniques of large-size full-array direct LED backlight module with high performance were investigated in this paper.Firstly, based on former research, in which uniform lighting condition for generalized Lambertian LED array lighting system was studied on the basis of Sparrow’s Criterion, uniform lighting condition for LED array lighting system made up by LEDs with arbitrary spatial radiation distribution was investigated. If certain types of LED with wide viewing angle were used, uniforimity of the LED array lighting system was demonstrated to vary non-monotonically with system thickness or LED pitch. By taking consideration of the abnormal uniformity condition demonstrated in this study, a general design method of LED array lighting system with uniform lighting was proposed based on Sparrow’s Criterion.Then contrast sensitivity function in human vision was adopted to investigate the uniformity condition of LED array lighting system, and uniform lighting condition for Lambertian and batwing type LED array lighting system were derived again. Optimum structural parameters achieved through contrast sensitivity function were found to be more accurate and practical than those achieved through Sparrow’s Criterion. Normal and abnormal uniformity condition were analyzed systematically based on contrast sensitivity function. Finally, design method of LED array lighting system with uniform lighting was proposed based on human vision.Significant light loss is produced by brightness enhancement films (BEF) while they increase the on-axis luminance by reducing the viewing angle in backlight module, which prevents on-axis luminance from being further increased. To solve this problem, a19inch direct LED backlight module was actually fabricated. Transmittances of the light propagating onto the BEF(s) with different spatial directions were investigated angle by angle via simulations and a petal-like spatial transmittance characteristic of BEF(s) was achieved. Then a type of freeform lens was designed to match up the angle range of the light emitting from LED and spatial transmittance characteristic of BEF(s). Resultantly, on-axis luminance can be significantly enhanced with approximately unchanging viewing angle. The experimental results showed that on-axis luminance was enhanced by22.8%while viewing angle was only reduced slightly even though a degree of optical performance degradation was caused by the diffuse film.Local dimming, which is another key technique of full-array direct LED backlight with high performance, can enhance the contrast ratio of output image and reduce the power consumption. Functions and corresponding computational complexity of three main process steps, as dimmed backlight determination, actual backlight distribution simulation and gray level compensation, in local dimming were detailedly investigated and effect of different diming algorithms and dimming block mumbers on performances of distortion and power consumption reduction were analyzed. Resultantly, increasing dimming block number was demonstrated to be the only way to essentially improve distortion and power consumption reduction performances simultaneously. In this paper, a technical solution adopting a type of gridded reflector was proposed to completely move away the process step of actual backlight distribution simulation, reduce the total computational complexity by several times and make total computational complexity considerably uncorrelated with dimming block number. With the aid of gridded reflector, more dimming blocks and an auxiliary dimming algorithm entitiled "critical exceeding method" proposed in this paper were utilized, which resulted in improved performances of distortion rate and power consumption reduction.更多还原