1. Field of the Invention
The present invention relates to a high-luminance surface illumination device using a laser light as a light source and a liquid crystal display device using such a surface illumination device.
2. Description of the Background Art
In a liquid crystal display device used in a display panel or the like, a surface illumination device is used as backlight illumination. A light source such as a discharge tube or a light-emitting diode (LED) is generally used in the surface illumination device. In recent years, in order to realize the higher luminance of the entire surfaces of such display panels, surface illumination devices have been used which employ a multitude of LED light sources of red light (R-light), green light (G-light) and blue light (B-light) from which strong monochromatic lights with high luminance can be obtained. A display device including a surface illumination device employing a multitude of LED light sources has been put into practical use. There is also an ongoing development of display devices including surface illumination devices employing laser light sources as strong monochromatic light sources with high luminance.
For a surface illumination device used in a large-size display device, strong monochromatic lights with high luminance are required and, at the same time, ingenuity to uniformly irradiate lights from light sources is required to eliminate luminance nonuniformity on the entire surface of a display panel. The surface illumination device used in the large-size display device is also required to have a thin shape and a smaller size except a screen.
As an example of such an illumination device, there has been proposed an illumination display device capable of improving the visibility of a displayed shape by making illumination by a light source with strong directivity such as a LED uniform (see, for example, Japanese Unexamined Patent Publication No. 2003-186427). Specifically, this illumination display device is constructed such that light is emitted from the LED arranged at the bottom of a lamp housing to a lightguide arranged above. Parts of the light which cannot be directly emitted to the lightguide are introduced to the lightguide by using the inner side wall of the lamp housing as a reflecting surface. By efficiently introducing the light from the LED to the lightguide in this way, illumination on the lightguide is made uniform.
As an illumination device similarly employing LEDs with strong directivity, the one disclosed, for example, in Japanese Unexamined Patent Publication No. 2005-353816 has been proposed. In this illumination device, lights from the LEDs are efficiently introduced to a lightguide by a tapered rod with a small light intensity loss. The tapered rod is an optical component having a side surface as a full reflecting surface for fully reflecting the incident illumination light and an emergent end surface having a larger area than an incident end surface and adapted to emit the illumination light fully reflected by the side surface. In other words, this illumination device is designed to make the illumination light on the lightguide uniform by introducing substantially the total amount of the lights from the LEDs by way of the tapered rod.
There has been also proposed an illumination optical device constructed such that a uniform intensity distribution can be obtained to perform a uniform exposure by disposing a fly's eye lens having a magnification corresponding to the light intensity distribution of an excimer laser before a diffuser (see, for example, Japanese Unexamined Patent Publication No. 63-60442).
On the other hand, a proposal has also been made for light irradiation apparatuses and image forming apparatuses of the type for scanning a laser light to realize a light source suitable for the respective apparatuses by changing the intensity distribution of the laser light.
In linear light irradiation apparatuses in the fields of measuring and cutting work, an optical member called “cylindrical lens” has been proposed as disclosed, for example, in Japanese Unexamined Patent Publication No. 2004-170884. In the cylindrical lens, at least one of an incident surface and an emergent surface is a cylindrical surface. By emitting laser lights from a plurality of laser light sources to this cylindrical lens, the light intensities of the respective laser light sources are added, whereby a linear light with an increased light intensity can be obtained.
For example, as in an image forming apparatus disclosed in Japanese Unexamined Patent Publication No. H08-111749, it has been proposed that a laser light is transmitted to a photoconductive member substantially without changing its beam diameter and an intensity change of the laser light is electrically compensated to scan a laser light with constant intensity and beam diameter on the photoconductive member by devising an optical construction.
Here, the visibility of images is improved by making the luminance of the display panel surface uniform with high luminance in the entire panel. On the other hand, image characteristics upon viewing images can be improved if only the luminance of the display panel central part where viewer's attentions are generally concentrated is increased instead of making the luminance of the entire display panel uniform. Further, power consumption can be reduced since it is not necessary to increase the luminance of the entire display panel. In other words, image characteristics can be efficiently improved by locally increasing the luminance in the part of the display panel where attentions are concentrated. Specifically, for a display such as an advertising screen installed at such a high position that viewers look up, visibility is thought to be improved by locally increasing the luminance in an upper part of the screen more distant from the viewers as compared to the case where the luminance of the entire screen is made uniform.
However, in the above respective prior art technologies, no consideration was made concerning a construction for introducing a laser light such that the luminance of a luminous surface comes to have a desired distribution. Neither disclose the above respective prior art technologies a construction for realizing both an adjustment of the luminance of the luminous surface to a desired distribution and a reduction in laser light loss.