(A) study of maximizing the light extraction efficiency of a monolithic backlight unit for liquid crystal displays

Abstract

In this thesis, a simple method for improving the light efficiency for a monolithic backlight unit (BLU) for liquid crystal (LC) display is proposed, and experimentally verified. Since the LC display was proposed, the market and its usage have been rapidly grown. Nowadays, it is one of the most popular types of display in the flat panel display field. Because it does not emit or radiate any light, an external light source is required. A BLU is a very important component in the LC display as the external light source. BLU can be categorized into two types: direct-lit type and edge-lit type. For the mobile application such as cellular phone and small multimedia player, edge-lit type BLU is mostly used. This edge-lit type BLU requires many optical sheets to correct the light radiation, which is originally inclined toward the far-end side from the source, toward the normal direction. To reduce the number of the sheets, the light guiding plate (LGP) should extract the light toward normal direction. The pattern shape on the top surface of the LGP decides the angular luminance profile of the BLU. Among many types of the pattern shape, pattern having negative sidewall slope is effective to extract the light toward the vertical direction. However, the maximum density of the pattern with negative slope is limited because its top width is greater than that of the bottom. Less than 10 percent of the top area of the LGP is used for the pattern area; therefore its light efficiency is very low. A straight line pattern can be a simple solution for enlarge the pattern area. Using the bar pattern, the amount of the extracted light can be maximized. However, the significant bright lines from the light source positioned at one side of the LGP cannot be avoided when straight line pattern is employed. In other words, the angular luminance distribution is not toward the normal direction. In this research, the characteristic of the pattern with negative sidewall slope is di...