Liquid crystal display apparatuses have increasingly replaced cathode-ray tube (CRT) display apparatuses. Such liquid crystal display apparatuses have advantages in features such as energy saving, reduced thickness, lightweight, and the like. For their advantages, the liquid crystal display apparatuses have been widely used in liquid crystal display televisions, monitors, mobile phones, and the like. One way to further utilize such advantages of the liquid crystal display apparatuses is to improve an illumination apparatus (a so-called backlight) provided behind a liquid crystal display apparatus.
Illumination apparatuses can be generally classified into a side light type (also known as edge light type) and a direct backlight type. According to the side light type, light guide plates are provided behind a liquid crystal panel and light sources are provided to lateral edges of the respective light guide plates. A light source emits light which is then reflected in a light guide plate such that the liquid crystal display panel is irradiated with the light indirectly and uniformly. This configuration makes it possible to realize an illumination apparatus having a reduced thickness and good luminance uniformity although having a low luminance. Thus, an illumination apparatus of the side light type is mainly used in a medium-to-small-size liquid crystal display of a mobile phone, a laptop personal computer, or the like.
According to the direct backlight, on the other hand, a plurality of light sources are provided behind a liquid crystal display panel so as to directly illuminate the liquid crystal display panel. This makes it easier for even a large screen to have a high luminance. Therefore, an illumination apparatus of the direct backlight type is mainly used in a large-size liquid crystal display of 20 inches or more. However, of illumination apparatus of the direct backlight type, a currently-available one has a thickness in a range of approximately 20 mm to 40 mm. This results in a barrier to a further reduction in thickness of a display.
A further reduction in thickness of a large-size liquid crystal display can be attained by providing light sources and a liquid crystal display panel closer to each other. In this case, however, it is impossible for an illumination apparatus to have luminance uniformity unless a larger number of light sources are provided. Such an increase in the number of light sources leads to higher cost. In such circumstances, there is a demand for development of a thin illumination apparatus in which good luminance uniformity can be obtained without causing an increase in the number of light sources.
In order to solve such problems, it has been attempted to (i) reduce a thickness of a large-size liquid crystal display by employing an illumination apparatus in which a plurality of light guide units are provided and to (ii) improve a luminance uniformity of an illumination apparatus by providing a spacer or the like so as to secure a space between an optical member and a light emitting surface of the illumination apparatus.
Patent literature 1 discloses a configuration in which a protrusion part 118p is provided, on a light emitting surface 118a of a light guide plate 118, above a boundary between corresponding two of light guide plates 118A, 118B, and 118C so as to extend in a direction parallel with a direction in which a parallel trench 118f extends (see (a) of FIG. 10). The protrusion part 118p has a shape similar to an ellipse cut in halves. Thus, an upper portion of the protrusion part 118p is rounded. The protrusion part 118p has a given height and width and extends in the direction parallel with the direction in which the parallel trench 118f extends. The given height of the protrusion part 118p is not limited to a specific one, provided that luminance unevenness of the light emitting surface 118a of the light guide plate 118 can be fully reduced by a film member provided above the light guide plate 118. Neither a location nor the number of the protrusion part 118p is limited to a specific one shown in (a) of FIG. 10. Instead, it is described in the patent literature 1 that any number of the protrusion parts 118p can be provided at any location. Also, a plurality of lenticular lenses 134 are provided, on the light emitting surface 118a, above the parallel trench 118f in which a light source 112 is provided. Further, a reflecting sheet 122 is provided so as to cover an inclined surface (a rear surface in (a) of FIG. 10) of the light guide plate 118.
It is described in the patent literature 1 as follows. Specifically, the protrusion part 118p which is provided on the light emitting surface 118a is used as a spacer whereby an optical member (such as a prism sheet or a diffusing sheet) is away, by a predetermined distance, from a flat part of the light emitting surface 118a. According to this configuration, light emitted from the light emitting surface 118a travels toward the optical member, while overlapping in multiple directions. As such, the light which is to irradiate the optical member is uniformized. This can realize a surface light source apparatus advantageous in view of luminance uniformity.
Patent literature 2 describes a surface light source apparatus 285 configured as shown in (b) of FIG. 10. According to the surface light source apparatus 285, light guide plates 213a, 213b, and 213c, each of which causes surface emission of light emitted from a corresponding one of light sources 211a, 211b, and 211c, are provided independently from each other. Reflecting sheets 214a, 214b, and 214c are provided so as to cover inclined surfaces (rear surfaces in (b) of FIG. 10) of the light guides plates 213a, 213b, and 213c, respectively. A light-shielding layer 241 is provided to a thinnest part of a rear end of each of the light guide plates 213a and 213b. Further, a transparent plate 278 is stacked, above top surfaces of the light guide plates 213a, 213b, and 213c, via an adhesive layer 272a. A diffusing plate 276 is stacked, above the transparent plate 278, via an adhesive layer 272b. According to the configuration, the transparent plate 278 which is thick in thickness is provided between (i) the light guide plates 213a, 213b, and 213c and (ii) the diffusing plate 276, so that (i) the light guide plates 213a, 213b, and 213c and (ii) the diffusing plate 276 are sufficiently away from each other. This can uniformize a light amount unevenness such as a bright line or a dark spot. It is therefore possible to realize a surface light apparatus excellent in view of luminance evenness.
Citation List
Patent Literature 1
Japanese Patent Application Publication, Tokukai, No. 2006-302687 A (Publication Date: Nov. 2, 2006)
Patent Literature 2
Japanese Patent Application Publication, Tokukai, No. 2001-312916 A (Publication Date: Nov. 9, 2001)
Patent Literature 3
Japanese Patent Application Publication, Tokukai, No. 2006-134748 A (Publication Date: May 25, 2006)
Patent Literature 4
Japanese Patent Application Publication, Tokukai, No. 2006-100225 A (Publication Date: Apr. 13, 2006)
Patent Literature 5
Japanese Patent Application Publication, Tokukai, No. 2001-75096 A (Publication Date: Mar. 23, 2001)