Liquid crystal cells – elements and systems – Particular structure – Particular illumination
Patent
1997-07-03
2000-01-04
Sikes, William L.
Liquid crystal cells, elements and systems
Particular structure
Particular illumination
349 61, 349 62, 349 64, 362 31, G02F 11335, F21V 704
Patent
active
060116021
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a lighting apparatus, a liquid crystal display system using the lighting apparatus, and electronic equipment using the lighting apparatus. Particularly, it relates to a lighting apparatus which can utilize light with improved efficiency.
BACKGROUND ART
(1) An example of a conventional liquid crystal display system is shown in FIG. 37. Such liquid crystal display system is generally provided with a dot-like printed layer, a white reflecting sheet or the like for irregular reflection at the back side of a light guide 1400, which guides the light from a light source 1401 to a liquid crystal display panel 1402, to obtain an uniform light intensity. In this case, since the light source emits light nondirectionally, the light can be uniformly diffused.
However, since the light is diffused, light directivity is lowered to lead to a low light intensity.
When the light intensity is increased, the light will be used inefficiently because the light is widely diffused, causing large power consumption. The lighting apparatus having such problems is not fit for long-time usage and not appropriate to portable electronic equipment.
When it is tried to lower the power consumption, however, the light intensity is also lowered.
(2) In order to solve these problems, it has been tried to increase directivity of the light from the light guide. Some known examples can be found in Japanese Patent Application Laid-open Nos. 5-089827, 6-067004, 6-130387,or the like. A prism array having fine prisms is used in these references to increase the light directivity. Each of the prisms has an apex which points the liquid crystal panel, and an apex angle is substantially 90.degree.. By supposing the light source to be the point light source, considering the optical path, and controlling the apex angle, the light directivity can be increased.
When a prism array is used, the light directivity can be increased. However, since part of the light is reflected at the prism array due to the total internal reflection and is returned to the light guide to lower the light intensity.
Moreover, when the liquid crystal display panel is viewed at an oblique angle, the display looks dark. In other words, a wide viewing angle range cannot be obtained. Such display system cannot be applied to a color television, for example, because a display of television requires a uniform and high light intensity and a wide viewing angle range.
(3) Another example of the liquid crystal display system which uses a prism array for increasing the light directivity is disclosed in Japanese Patent Application Laid-Open No. 2-17. Part of this system is shown in FIG. 38.
In this reference, the prism array efficiently changes the direction of most of the input light to a direction substantially perpendicular to the liquid crystal display panel, when the apex angle of each prism is 60.degree. and the normal to the liquid crystal display panel is in a position to halve the apex angle. In other words, each of prisms 1420p of a prism array 1420 has a vertical section which is an isosceles triangle, and its apex angle is 60.degree. (the angle .theta.=30.degree.), as shown in the figure. When light 1421r is output from the light guide at the angle .beta.=60.degree., an available maximum light intensity can be obtained. When the light 1421r is output at the angle .alpha.=70.degree., which is 10.degree. more than the angle .beta., or at the angle .gamma.=50.degree., which is 10.degree. less than the angle .beta., the light intensity is nearly half an available maximum value.
However, the light beam c which has been output at the angle .gamma. is then reflected at an output surface 1420e of the prism array 1420 toward the light guide 1421 by the total internal reflection. Consequently, the transmittance of the light with respect to the prism array is low, and the light cannot be utilized efficiently.
Moreover, there is another example of the prism array in the above reference. In order to output the light from the prism array at an ang
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Proceedings of the 15.sup.th International Display Research Conference, Asia Display '95, Oct. 16-18, 1995, "Reflective Cholesteric Polariser Improving the Light Yield of Back-and Side-Lighted Flat Panel Liquid Crystal Displays", D.J. Broer et al., pp. 735-738.
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Funamoto Tatsuaki
Miyashita Satoru
Yokoyama Osamu
Eisenhut Heidi L.
Seiko Epson Corporation
Sikes William L.
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