Illumination – Revolving
Patent
1997-06-09
1999-03-30
Cariaso, Alan
Illumination
Revolving
362 26, 362330, 362333, 362339, 349 65, F21V 1304
Patent
active
058879641
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a surface light source device and a liquid crystal display, and more specifically, to a surface light source device utilizing a light guide plate made of light scattering and guiding material and a prism sheet, and a liquid crystal display with the surface light source device applied to back lighting.
BACKGROUND
A surface light source device utilizing a light guide plate made of light scattering and guiding material and a prism sheet has been proposed and applied to back lighting for a liquid crystal display and the like.
The prism sheet is a sheet-like member made of optical material, which has a surface provided with a large number of V-shaped groove rows, that is, a prism surface. It is known that this element has a function to alter the propagation-directional characteristics of luminous flux.
FIG. 1 shows the most general usage of a prism sheet in a surface light source device provided with a light guide plate made of light scattering and guiding material. Referring to FIG. 1, a light guide plate 1 made of light scattering and guiding material has a wedge-shaped section. The light scattering and guiding material may be obtained by uniformly distributing a substance of different refractive index in a matrix made of polymethyl methacrylate (PMMA), for instance.
The side end surface on the thick side of the light guide plate 1 serves as an incidence surface 2 and a light source element (a fluorescent lamp) L is disposed in the vicinity of the incidence surface.
A reflector 3 is disposed along one surface (a back surface 6) of the light guide plate 1. For the reflector 3, a regular-reflective silver foil sheet or a diffuse-reflective white sheet is used. An illumination flux is emitted from the other surface (an exiting surface 5) of the light guide plate 1. A prism sheet 4 is disposed on the outside of the exiting surface 5.
In FIG. 1, the gap between the prism sheet and the light guide plate 1, the pitch of prism rows and the depth of prism and others are exaggerated for the sake of illustration. One surface of the prism sheet 4 is composed of V-shaped prism surfaces 4a, 4b, and the other surface is a flat surface 4e.
In the prism sheet 4 disposed as shown in FIG. 1, the flat surface 4e faces the outside and serves as a luminant surface 4e, from which an illumination flux 4f is emitted. If a well-known liquid crystal display panel is disposed further outside the prism sheet 4, a liquid crystal display of back lighting type is constituted.
As the result of repetitive reflection occurring in the wedge-shaped section of the light guide plate 1, such a surface light source device shows excellent characteristics for the efficiency of light utilization and the uniformity in luminance.
Light introduced from the light source element L into the light guide plate 1 is guided toward an end surface 7 on the thin side, while being affected by a scattering action and a reflecting action in the light guide plate 1. In the process, the light is emitted little by little from the exiting surface 5. The light emitted from the exiting surface 5 has directivity according to the size of particles of different refractive index distributed in the light guide plate 1 (more generally speaking, according to the correlation distance in a structure having uneven refractive index). In other words, the illumination flux emitted from the exiting surface 5 assumes a parallel luminous flux.
The larger the size of the particles of different refractive index distributed in the light guide plate 1 is (more generally speaking, the more the correlation distance is), light emitted from the exiting surface 5 is parallelized more clearly. The preferential propagation direction (the main propagation direction of illumination flux) is generally inclined at an angle ranging from about 25.degree. to 300.degree. with respect to the exiting surface as viewed from the side of the incidence surface 2.
On the basis of the above fact, a description will now be given on a function to alter the propagation dire
REFERENCES:
patent: 4120018 (1978-10-01), Nagel
patent: 5136480 (1992-08-01), Pristash et al.
patent: 5396350 (1995-03-01), Beeson et al.
patent: 5408388 (1995-04-01), Kobayashi et al.
Higuchi Eizaburo
Koike Yasuhiro
Cariaso Alan
Koike Yasuhiro
Nitto Jushi Kogyo Kabushiki kaisha
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