Light Diffuser Plates For LCD-TV Backlight Systems

A lighting system called direct type is usually employed for backlight systems in large size LCD-TVs. With this type of backlight system, a diffuser plate has to be mounted in order to blur the images of CCFLs and to hold several thin optical films. We have developed diffuser plates with properties which are specially optimized for this type of backlight system, and have released them onto the market. In this report, the properties that are required for diffuser plates and our R&D activity will be described.

Introduction The demand for television sets known as flat-panel displays (FPD) is expected to grow rapidly as shown in Fig. 1-a). What type of FPD will be dominant is still controversial, there are strong expectations for LCDTVs to be the market leader restraining other types of FPD like PDPs and projection TVs. At the same time, looking at it by size as shown in Fig. 1-b), the growth in 30 inch or larger size, particularly 40 inch class size will be remarkable, and there is an overall movement toward larger size. On the other hand, because liquid crystal displays do not emit the light by themselves, several light sources that illuminate the liquid crystal panel from its backside are necessary. This is what we call backlight systems. Sumitomo Chemical marketed a diffuser plate, which is set into these systems in 2001, ahead of other companies, and with further improvements, continues to maintain the largest share of the market to date. In this article, general properties that are required for the diffuser plates specially designed to adjust to the LCD-TV sets will be described. Then, some of the latest issues that have emerged from the demand for much larger size and cost reductions will also be discussed. Liquid Crystal Display Structure and Diffuser Plates As shown in Fig. 

2, there are several types of backlight systems that are used in liquid crystal displays Light Diffuser Plates for LCD-TV Backlight Systems A lighting system called direct type is usually employed for backlight systems in large size LCD-TVs. With this type of backlight system, a diffuser plate has to be mounted in order to blur the images of CCFLs and to hold several thin optical films. We have developed diffuser plates with properties which are specially optimized for this type of backlight system, and have released them onto the market. In this report, the properties that are required for diffuser plates and our R&D activity will be described. Sumitomo Chemical Co., Ltd.  1 Worldwide development of the number of TV set \

according to the size of the display. For applications like laptops and PC monitors, illumination systems known as “edge lit” are usually used. In these systems, linear light sources (normally Cold Cathode Fluorescent Lamp; CCFL) are placed at the edges of a highly transparent plastic plate called a light guide plate, within which the light propagates from one edge to the other edge in accordance with the TIR (Total Internal Reflection).White dots printed on the opposite surface to the emission surface scatter the light uniformly by adjusting the dot density. On the other hand, in larger displays like LCD-TVs, a large number of CCFL are required depending on the size of the screen to assure sufficient luminance. Since the number of CCFLs that can be accommodated in an edge is limited, an illumination system known as the “direct type” backlight system is adopted, where the illumination comes from directly behind the liquid crystal panel from multiple CCFLs. In this system, the images of the light sources can be seen through the panel as shown in Fig. 3-a). Therefore, a white opaque plate, called a diffuser plate, with a thickness of several millimeters is installed to hide the images of the light sources. Finally, as is shown in Fig. 4, several types of optically functional films, such as a diffuser film, prism film and brightness enhancement film, are used together with a diffuser plate in order to adjust the final optical performance