Illumination – Revolving
Reexamination Certificate
2001-12-12
2003-07-22
O'Shea, Sandra (Department: 2875)
Illumination
Revolving
C362S026000, C362S330000, C362S331000, C362S326000, C362S558000, C385S901000, C349S064000
Reexamination Certificate
active
06595652
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an edge-light type surface lighting device (e.g., an LCD panel lighting device) which is used for LCDs for, e.g., notebook personal computers and LCD TV sets.
2. Description of the Related Art
In recent years color LCDs have been widely used in various applications, including notebook personal computers, cellular phones and LCD TV sets. As information technology moves forward, LCDs have been required to have performance which fills particular needs in response to the increase in quantity of information to be managed, diversity of needs, and multimedia compatibility. A common challenge for manufacturers is to increase the brightness and the resolution of LCDs in order to meet such requirements.
LCDs are generally constructed in two parts: an LCD panel and a surface lighting device (back light unit). The construction of the surface lighting device can be divided roughly into two types: direct and edge light types. In the direct type, a light source (e.g., CCFL tubes) is placed under an emission plane. The Edge-light type of surface lighting devices use a straight lamp (CCFL lamp) along an end face of the LCD, two lamps on opposite end faces of the LCD, or L-shaped lamps along the opposite corners of the LCD. The edge-light type has become more widespread than the direct type because the edge-light type is advantageous for reducing the size of the LCD.
Mobile notebook personal computers and TV sets that adopt a color LCD generally use a battery (e.g., a rechargeable NiMH pack or a lithium-ion battery pack). The color LCD, especially the surface lighting device thereof, consumes most of the power of the battery. Accordingly, reducing power consumption of the surface lighting device as low as possible has been a significant challenge to manufacturers to extend battery life and improve the practical value of LCDs.
However, if a reduction in power consumption of the surface lighting device sacrifices the brightness thereof, the contrast becomes low, which is not preferable. It is desired to reduce power consumption of the surface lighting device while increasing the brightness thereof by improving optical efficiency of the surface lighting device.
In response to such a desire, a new type of surface lighting device has been developed. In this new type of surface lighting device, a lens unit is formed directly on a light exit surface of a light guiding plate (which serves an element of the surface lighting device), while a prism sheet, on which an array of prisms each having a triangular cross section is formed, is positioned on the light guiding plate so that the prism array faces the light guiding plate. According to this construction, light which is condensed by the lens unit that is formed on the light guiding plate is emitted obliquely from the light guiding plate and is subsequently directed toward the front of the device to thereby achieve a high brightness.
Another type of surface lighting device having a light guiding plate on which linear projections and depressions are formed to extend in a direction substantially perpendicular to the light incident surface of the light guiding plate has been developed. According to this structure, the spread of light in a direction parallel to the light incident surface of the light guiding plate is condensed by the lens effect that is produced by the linear projections and depressions to thereby achieve a high brightness.
If there is any defect on the screen of the LCD, the defect becomes an eyesore and thus is perceived as a serious defect since the user usually constantly looking at the screen. Such a defect can be in the form or, e.g., bright and dark streaks which occur in the vicinity of an end face of the light guiding plate. A part of the screen of the LCD which faces a non-light emitting portion of the surface lighting device, e.g., in the vicinity of either end of a straight lamp where an electrode portion thereof exits, is seen slightly darker than the remaining part of the screen, especially if the light guiding plate has a light incident surface which is longer than the length of a light emitting portion of the straight lamp.
In order to overcome this problem, it has been proposed that the light incident surface of the light guiding plate be formed as a mat surface so that the incident light thereon is diffused thereby to reduce the occurrence of the bright and dark streaks.
However, if the brightness of the surface lighting device is increased to meet the recent demand for the further enhancement of the brightness of LCDs, the aforementioned defect becomes more apparent.
In a typical edge-light type surface lighting device, a light bundle emitted from a straight lamp is made incident on an end face of a light guiding plate so as to exit from a light exit surface defined on one side of the light guiding plate. An LCD panel is positioned on the light exit surface with one or more diffusion sheets and/or prism sheets being positioned between the LCD panel and the light exit surface. Each prism sheet is a conventional optical element which is provided thereon with an array of minute parallel prism projections to have refractive and reflective functions. The light bundles emitted from the light exit surface of the light guiding plate are directed to the LCD panel via the prism sheet. Although one or two thicknesses of prism sheets are generally used, there is a limit of gathering the diffused light with the prism sheets.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a surface lighting device which illuminates an LCD panel entirely with less unevenness in luminance distribution. Another object of the present invention is to provide a surface lighting device with a high brightness which improves the quality of images indicated on an LCD panel.
To achieve the object mentioned above, according to an aspect of the present invention, a surface lighting device is provided, including a light guiding plate having a light incident surface formed at one end surface of the light guiding plate and a light exit surface formed on a front surface of the light guiding plate; an elongated light source which faces the light incident surface; a light source reflector which reflects light emitted from the elongated light source toward the light incident surface; a prism sheet, wherein an array of minute parallel prism projections is formed on a surface of the prism sheet, the prism sheet being positioned so that the array of minute parallel prism projections faces the light exit surface; a regular reflection type reflector positioned to face a rear surface of the light guiding plate; a light guiding device for guiding light emitted from the elongated light source to each of two portions of the light incident surface which respectively face opposite ends of the elongated light source; and a diffuser, formed on the light incident surface, which diffuses incident light thereon.
In an embodiment, a diffusion reflector is formed on the regular reflection type reflector, which diffuses part of incident light on the regular reflection type reflector.
In an embodiment, the light incident surface is inclined with respect to a plane normal to the light exit surface.
Preferably, the light guiding plate includes a first array of minute parallel prism projections formed on one of the front surface and the rear surface of the light guiding plate to extend in a first direction, and a second array of minute parallel prism projections formed on the other of the front surface and the rear surface of the light guiding plate to extend in a second direction perpendicular to the first direction.
Preferably, the above-mentioned first direction is parallel to an axial direction of the elongated light source.
In an embodiment, the light guiding plate has a substantially wedge shape cross section, wherein a thickness of the light guiding plate gradually decreases in a direction away from the light incident surface. A first angle between the light incident surface
Narumi Rika
Oda Masaharu
Tsuji Mitsuo
Alavi Ali
International Manufacturing and Engineering Services Co., Ltd.
McCormick Paulding & Huber LLP
O'Shea Sandra
LandOfFree
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