This invention relates to a liquid crystal display apparatus using a liquid crystal display panel, more particularly, to a liquid crystal display apparatus including back light structure.
Liquid crystal display apparatus are used for displays of various kinds of electronic devices such as lap-top computers, word processors and televisions because liquid crystal display apparatus contribute to the miniaturization and low electric consumption of electronic device. Liquid crystal display apparatus are generally divided into two types. One is reflection type equipped with no light source. The other is back light type equipped with light source. The present invention relates to the latter.
Regarding the back light type of liquid crystal display, there are the behind illumination type as shown in FIG. 2 and the side illumination type as shown in FIG. 3. In the behind illumination type as shown in FIG. 2, light sources 4 each comprising a bar-like light emitter such as a cold cathode fluorescent tube (CCFT() are disposed behind a liquid crystal display panel 1. A diffusion plate 2 is disposed between the light sources 4 and the liquid crystal display panel 1. The liquid crystal display panel 1 is uniformly illuminated by the light diffused by the diffusion plate 2. In this behind i illumination type of liquid crystal display apparatus, although the luminance of the liquid crystal display panel 1 is good, it is hard to decrease the thickness of display apparatus. An example of this type is disclosed in JP-A-57-13478 (1982).
In the side illumination type as shown in FIG. 3, light sources 4 such as CCFTs are located at both sides of a liquid crystal display panel 1. The light from each light source 4 is introduced in the lateral direction by a light introduction plate 3 made of glass or transparent synthetic resin. The liquid crystal display panel 1 is illuminated by the light diffused by the light introduction plate 3. This side illumination type has the drawback that the luminance of the liquid crystal display panel 1 is low. The luminance of this type of apparatus is nearly half that of the behind illumination type described above. In the side illumination type, however, the thickness of display apparatus can be decreased by more than 30% in comparison with the behind illumination type. For this reason, this side illumination type is employed in notebook computers given attention in recent years. An example of this type is disclosed in JP-A-1-277817 (1987).