用LED实现高亮度超薄型背光源的设计方法

近年来随着LED产业的发展,LED光源在背光应用领域也在不断拓展。本文主要从LED直下式背光源的结构特点探讨,如何提高亮度和均匀性,用光学软件模拟了用大功率白光LED实现高亮度和均匀性的背光模组,用实验数据验证了最初理论结果。并对LED直下式结构模组和LED侧入式结构模组的优缺点进行了对比和全面分析,及直下式LED背光结构在背光源系统的各个领域广泛应用的必然性。     

车用LED照明技术及现状分析

随着汽车工业的快速发展,对汽车节能减排及安全性能的要求越来越高,汽车照明系统的节能与安全问题已成为该领域研究的热点.作为第四代车用光源,LED有很多优于其他传统光源的特点.为此分析了车用LED照明的可行性和先进性,介绍了其典型的驱动电路,并着重研究了LED以及AFS在汽车前照灯上应用现状.介绍了车用LED照明面临的问题及应对措施,并对其未来发展进行了展望.     

视觉检测的LED光源自适应亮度控制系统

照明光源的亮度控制视觉检测中的一个难题,为了使视觉检测系统获取优质图像,本文采用嵌入式ARM做控制器,利用亮度传感器采集环境亮度,通过实验研究图像采集图像灰度值与光照强度的关系,获取高质图像需要的合理亮度阈值,作为图像采集时LED光源亮度调节的参照,通过软件调节驱动LED的PWM信号,实现自适应调整LED光源亮度。     

LED呈别样生机，照明为最大驱动力

众所周知,LED被称为第四代照明光源或绿色光源,具有节能、环保、寿命长、体积小等特点,可以广泛应用于各种指示、显示、装饰、背光源、普通照明和城市夜景等领域。近年来,世界上一些经济发达国家围绕LED的研制展开了激烈的技术竞赛。美国从2000年起投资54L美元实施“国家半导体照明计划”,欧盟也在2000年7月宣布启动类似的“彩虹计划”。     

富士施乐LED光源彩色扫描仪技术获日本照明技术大奖

正富士施乐宣布其采用白色LED光源的彩色扫描仪技术,获得日本照明工程协会颁发的2011照明技术大奖。该技术是由富士施乐与其子公司富士施乐高科技株式会社共同研发的。富士施乐多款彩色数码多功能机均采用了白色LED光源技术的扫描仪。这一创新应用,成功克服了普通LED灯亮度不均且有色差的问题,只需1/3的能耗即能获得超过传统设备氙气灯1.5倍的亮度。     

大功率LED的驱动电器

随着光电技术的不断发展，LED的功率已经做到或超过了1W，由于其具有发光亮度大、发光效率高、使用寿命长、体积小、比普通节能灯及荧光灯更加节约能源等优点，故在各种固态照明、照相机的闪光光源、汽车内外照明等诸多方面得到了广泛的应用，因此，本人整理了如下一些电路．供同行在设计大功率LED驱动电路时参考。     

湿度对液晶显示器背光源光学亮度的影响

背光源(BackLight)是位于液晶显示器(LCD)背后的一种光源,它的发光效果将直接影响到液晶显示模块(LCM)视觉效果。在背光源的生产中常运用高温高湿的方法对背光源进行老化测试。本文主要研究了在一定温度下(50℃)湿度的变化对背光源亮度的影响。通过研究发现,在温度不变的情况下,随着湿度的升高,背光源的亮度衰减率占比逐渐增大。     

显示设备

对于LCD厂商来说，提高亮度和色彩表现的主要着眼点就是改良背光源。在这个领域，CCFL冷阴极荧光灯是绝对的主流，但是此时难以做到亮度均匀，而且令LCD的厚度无法控制。为此，LED背光技术成为LCD领域的关注焦点，它是一种平面状的光源，可以很好地控制亮度均匀性而且简化了LCD背光结构。     

LED影院新成员

LED光源色域广是投影业内共识,相比传统光源,LED在色彩表现上有着较强的优势,也非常适合家用投影机。只是由于LED光源在亮度性能上一直没有较大突破,因此我们很少能见到采用LED光源的影院级家用投影机。     

华硕预言：千万比一对比度将成显示器标准

我们知道现在流行的LED背光和普通的液晶显示器最大的差别在于背光源的差别。普通液晶显示器采用的是CCFL冷光灯管,而LED背光采用LED（发光二极管）作为背光源。LED背光除了在能效和亮度呈现的均匀性方面有一定的优势外,在背光变化速度方面也快于CCFL背光。随着LED技术的日渐成熟,LED背光亮度变化速度更快,液晶显示器动态比的高度数据也不断被厂商刷新。     

Brightness management in a direct LED backlight for LCD TVs

Abstract— A method of calculating the luminance and luminance uniformity of a bottom LED backlight is proposed and demonstrated. Both the power consumption and brightness uniformity as a function of screen brightness, screen size, backlight thickness, transmittance of the LCD panel, reflective cavity efficiency, gain, cone angle of the enhancement films, LED array configuration, and the average luminous flux, radiation pattern, and input power of individual LEDs. Moreover, a 42‐in. LCD TV using this backlight design approach was fabricated. The bottom backlight incorporates an array of RGGB 4‐in‐1 multi‐chip LEDs within a highly reflective box behind a diffuser and a dual brightness‐enhancement film. The brightness uniformity can be predicted within an accuracy of 94% and the luminance level within an accuracy of 96%.     

Optimizing angular placements of the LEDs in a LCD backlight module for maximizing optical efficiency

This study aims to optimize angular placements of the LEDs with novel cone-shaped caps for achieving high optical efficiency in an ultra-thin, directly-lit RGB LED backlight unit (BLU) for large-sized LCD-TVs. This novel lens cap is used as a diffuser with the purpose to gain higher efficiency and provide satisfactory uniformity over a display panel. To this aim, the outer surface of the novel lens is coated with aluminum for mirroring effects to reflect most of the LED emitted light horizontally and then reflect the light at the BLU boundaries, finally to the output plane. Since the emitted white light from LEDs result from color-mixing of three individual RGB chips in a LED package, the addition of the LED cap however deteriorates the aforementioned expected color mixing. The optimal design on angular placements of LEDs presented in this study for satisfactory color-mixing and emission uniformity is achieved by necessary optics simulations via TracePro, followed by utilizing an intelligent numerical optimization technique, genetic algorithm (GA). The design parameters for GA optimization are different combinations of LED placement angles in a backlight module. Favorable color balance is shown achievable in terms of high low color difference resulted. Finally, experiments are conducted, which successfully validate the expected performance of color balance and emission uniformity for a novel cone-shaped LED lens with optimized angular placements in a large-area backlight module.     

LED backlighting for LCD HDTV

Light‐emitting diodes (LEDs) are used today for backlighting of small displays such as PDAs and mobile phones. We show in this paper that a new LED technology can be used for high‐demanding display‐backlighting applications such as LCD HDTV. Using this new type of emitter, called a Luxeon? Power Light Source, a brightness higher than an edge‐lit CCFL backlight can be achieved, while compared to a direct‐lit CCFL backlight the thickness is lower and the uniformity is better. With on‐going improvements in LED performance over the coming years, LED backlights will reach and even outperform the brightness performance of direct‐lit backlights while maintaining the benefits of edge‐lit solutions at even higher brightness levels.     

Gradually tapered light pipes for illumination of LED projectors

Abstract— LEDs are totally different from classical light sources: they have a different shape, radiation pattern, driving requirements, etc. Therefore, the illumination engine, which determines the brightness and uniformity of the system, has to be redesigned for LED‐based projectors. A compact illumination system based on gradually tapered light pipes (GTLP) will be presented. The GTLP collects, reshapes, and uniformizes the light flux from the LED to illuminate the light‐valve uniformly. The design and the simulations have been completed. The result is a uniformly illuminated rectangular beam at the end of the pipe with an efficiency of 81.1%. Afterwards, the light pipe was fabricated, and the experimentally measured efficiency is 76.9%, which demonstrates a successful manufacturing process. Finally, two recycling techniques to enhance the brightness have been applied and these enhancements were experimentally observed.     

Two approaches to derive LED driving signals for high‐dynamic‐range LCD backlights

Abstract— The LED‐array backlight technique dramatically enhances the dynamic range of an LCD and hence extends its ability to present images with high reality. This is achieved by modulating LEDs individually, thus providing an area‐adaptive backlight for the display. The spatial overlap of light from the LED (crosstalk) occurs due to the diffusion screen placed between the backlight and LCD layer. However, the crosstalk is not only a blessing for supplying high brightness but is also a curse for causing potential artifacts, making the derivation of an LED driving signal a challenging task. This paper formulates the problem into two mathematical models: an iterative de‐convolution approach and a linear optimization approach. Algorithms for solving these two models are provided. The first approach provides instantaneous and satisfactory results except for high‐intensity highlights in the image. The linear optimization method conquers this drawback, but requires much more computation, possibly requiring preprocessing of the target, and also introduces undesired artifacts. These two approaches are extensively evaluated by building an image database composed of 161 high‐dynamic‐range images.     

A novel lens cap designed for the RGB LEDs installed in an ultra‐thin and directly lit backlight unit of large‐sized LCD TVs

Abstract— The objective of this study is to design a novel cone‐shaped lens cap on LEDs in order to achieve high optical efficiency in an ultra‐thin directly lit RGB LED backlight unit (BLU) for large‐sized LCD TVs. The use of the novel lens cap could play the role of a diffuser, a low light‐efficiency component in a BLU, in order to gain higher efficiency and simultaneously provide satisfactory uniformity in light distribution. The novel cone‐shaped lens is coated with aluminum on the outside surface of the cone for mirroring effects to reflect most of the LED emitted light horizontally and then reflect the light at the BLU boundaries, and then, finally to the output plane. In this way, bright spots on the output plane of the BLU can be avoided, leading to increased uniformity. Simulations were conducted to design and optimize varied aspects of the designed lens and BLU, including the cone angle of the proposed lens and the LED spacing (pitch). To further achieve color balance, a known Genetic Algorithm is used to search for the optimal angular placement of each RGB LED, resulting in better color balance. Finally, a prototype BLU for large‐sized 37‐in. LCD TVs with the proposed lens was built to verify the expected performance.     

Locally pixel‐compensated backlight dimming on LED‐backlit LCD TV

Abstract— The pixel brightness of an LCD panel perceived by a user is the product of the backlight brightness and the panel transmittance. In conventional LCD panels, the backlight brightness is constant and always at peak luminance. This design suffers from light leakage and power waste problems at dark scenes. This paper presents a new LCD system, which uses locally pixel‐compensated backlight dimming (PCBD). The proposed method combines backlight control and pixel processing for reducing light leakage and power consumption while keeping the image at the original brightness. Backlight luminance is dimmed locally in the dark‐image region, and pixel values are compensated synchronously according to the luminance profile of dimmed backlight. By reducing the light leakage, a static contrast of over 20,000:1 has been achieved on a large‐sized LCD panel with the proposed PCBD method. No obvious artifacts have been noticed as well. The power consumption of the panel can also be greatly reduced, depending on various video content. The PCBD method could be widely used for developing state‐of‐the‐art LCD panels with LED backlights.     

Backlight unit with double‐surface light emission using a single micro‐structured lightguide plate

Abstract— A novel illumination system for a liquid‐crystal‐display (LCD) module used in a dual‐display cellular phone has been developed. A double‐surface light‐emitting backlight uses a single light‐guide plate to illuminate both LCDs. A single lightguide, two prism sheets, and four light‐emitting diodes (LED) were used in the new structure, compared with ten components and two sets of light sources with six LEDs in the current backlight. The thickness and power consumption of the new backlight were reduced by a factor of 0.59 and 0.67, respectively.     

Wide gamut LCD using locally dimmable four‐primary‐color LED backlight

This paper proposes a wide gamut LCD using locally dimmable four‐primary‐color (4PC) LED backlight. Although the color gamut of LCDs has been improved in recent years, it is insufficient to reproduce all the colors in the real world. The objective of this paper is to propose a wide gamut LCD that reproduces all the colors in the real world while keeping the cost increases to a minimum. We evaluated the color gamut reproduced by LEDs of multiple primary colors and selected cyan as the optimal color to be added to the three primary colors to reproduce all the colors in the real world. Therefore, we designed an LED backlight consisting of an additional only‐cyan LED with three‐primary‐color LEDs and developed a prototype LCD with 4PC LED backlight. Furthermore, we developed a local dimming algorithm for the 4PC LED backlight. As a result, we confirmed that the prototype LCD with the 4PC LED backlight is able to cover almost all the colors in the real world and also able to display natural images with highly saturated colors by local dimming.