Liquid crystal cells – elements and systems – Particular structure – Particular illumination
Patent
1996-06-04
1998-10-06
Sikes, William L.
Liquid crystal cells, elements and systems
Particular structure
Particular illumination
62 63, G02F 11335
Patent
active
058185550
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a surface light source device, more particularly a surface light source device suitably used for back light systems of liquid crystal displays.
BACKGROUND OF THE INVENTION
A conventional surface light source device has a construction, for instance, as shown in FIG. 1, where a linear light source 1 such as a discharge tube, a light conducting member 2 made of a transparent material, a light diffusing plate 3, and a light reflecting member 4 are provided. The surface 2c of the light conducting member 2 is found on the side where the light reflecting member 4; and on the surface 2c, is printed a pattern 6 in white ink.
In the conventional surface light source device, a light emitted from the light source 1 is made incident upon the light conducting member 2, and then the light travels inside the light conducting member 2 being fully reflected by both the surfaces 2b and 2c, which are found on the light diffusing plate 3 side and the light reflecting member 4 side of the light conducting member, respectively. While, the light traveling inside the light conducting member is emitted from the surface 2b thereof, which is provided on the light diffusing plate 3 side of the light conducting member. The emitted light goes through the light diffusing plate 3 and then become a diffused light to constitute the surface light source.
However, in the conventional surface light source device, the light is absorbed by the white ink, etc., and thus all the light being emitted from the light emitting surface 2b of the light conducting member 2 is decreased. Therefore, the light cannot be used effectively so that only a dark surface light source device is obtained.
Another conventional surface light source device using a light conducting member is known which has the same construction as that of the device shown in FIG. 1, where the pattern is formed on the rear surface 2c of the light conducting member 2 (the surface provided on the light reflecting member 4 side of the light conducting member) by using transparent ink in which fine spherical silicon grains are mixed. It should be noted that the ink looks half-transparent because of the mixture of the silicon grains. Such a surface light source device is known where the pattern is printed on the surface 2c of the light conducting member 2 by using the half-transparent ink having spherical silicon grains therein.
In such a surface light source device using a light conducting member, only a little light is absorbed by the ink. Therefore, the amount of the light emitted from the surface 2b of the light conducting member 2 is increased as a whole. In this surface light source device, a brightness distribution, with respect to an angle .theta., which is formed between the light emitted from the light emitting surface 2b of the light conducting member 2 (the light L diffused by the light diffusing plate 3) and a direction perpendicular to the light emitting surface (the direction N in FIG. 1), varies depending upon the particle diameter of the silicon grains and the amount of the grains to be mixed in the ink. However, in any case, a sufficient brightness cannot be obtained in the direction perpendicular to the surface 2b of the light conducting member 2 (.theta.=0 degree) or in the similar direction thereof.
In liquid crystal display devices, observation is generally conducted in a direction perpendicular to the liquid crystal display plate or in a similar direction thereof. Therefore, even if the surface light source device having a light conducting member, on which the pattern is printed by using the transparent ink with said silicon grains mixed therein, is used in the liquid crystal display device as a back light system thereof, there would be a drawback in that a sufficient amount of light cannot be obtained in a direction where the observation is conducted.
Further, in the above-mentioned conventional surface light source device using a light conducting member, since the light is diffused by fine light diffusing por
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patent: 5550657 (1996-08-01), Tanaka et al.
patent: 5572411 (1996-11-01), Watai et al.
patent: 5584556 (1996-12-01), Yokoyama et al.
patent: 5627926 (1997-05-01), Nakamura et al.
Arai Takayuki
Ishikawa Tsuyoshi
Ohta Tetsufumi
Yokoyama Kazuaki
Enplas Corporation
Ngo Julie
Sikes William L.
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