Illumination – Light fiber – rod – or pipe – Illuminating or display apparatus
Reexamination Certificate
2000-10-20
2002-09-24
Cariaso, Alan (Department: 2875)
Illumination
Light fiber, rod, or pipe
Illuminating or display apparatus
C362S035000, C362S330000, C362S339000, C362S224000, C349S065000
Reexamination Certificate
active
06454452
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to backlights for liquid crystal display devices.
2. Description of the Related Art
FIG. 27
is a cross section of a conventional backlight for a liquid crystal display device (see for example
Liquid Crystal Display Technology.
edited by Shoichi Matsumoto, Sangyo Tosho, p. 255). As shown in
FIG. 27
, the backlight includes a cold cathode fluorescent lamp (CCFL)
101
, a reflecting mirror
102
, a light guide plate
103
, a reflecting white dot pattern
110
having scattering dot elements regularly arranged to radially scatter light, a reflecting sheet
107
, a prism sheet
111
, and a scattering sheet
112
.
The backlight operates as described below: CCFL
101
emits light, which is directly or via reflection provided by reflecting mirror
102
incident on light guide plate
103
via a receiving end plane
120
and propagates through the light guide plate in repeated total reflection provided by a bottom plane
122
and an output plane
121
before the light emanates from output plane
121
. When white scattering dot
110
, provided in bottom plane
122
of the light guide plate, receives light, the light scatters, passes through bottom plane
122
and thus emanates outside light guide plate
103
. The light emanating from bottom plane
122
is reflected by reflecting sheet
7
and is thus incident on bottom plane
122
and repeats the total reflection described above before it emanates from output plane
121
. The light emanating from the light guide plate has its distribution adjusted by one or two sheets of prism sheet
111
and scattering sheet
112
for eliminating a small uneven distribution of light and irradiates a liquid crystal panel (not shown) arranged in front of the backlight.
Such a backlight uses scattering dot
110
to extract light. As such, the exact light emanating from the light guide plate has a distribution having a large angle and it thus does not always have a direction in which it is visually recognized. As such, prism sheet
111
is required to effectively collect light to allow the light to have an adjusted distribution collected in the direction in which the light is visually recognized. As such, one or two sheets of expensive prism sheet
111
are required, as described above, which increases the number of members of the backlight and complicates the fabrication process.
In order to minimize the number of members of a backlight, there has been proposed a guide light plate having an optical prism integrated thereto, as shown in
FIG. 28
(Japanese Patent Laying-Open No. 10-282342). With reference to
FIG. 28
, among the members as described above, light guide plate
103
includes a reflecting, grooved portion
104
extending in a direction in which the receiving end plane extends, corresponding to a hollow space in the form of a wedge extending in the direction of a depth of the light guide plate, and an uneven portion
106
in the form of a prism having a plurality of parallel ridges extending in a direction orthogonal to receiving end plane
120
.
Light incident on light guide plate
103
via receiving end plane
120
repeats total reflection as it propagates through the light guide plate. When a reflecting hollowed portion receives light on its oblique plane closer to the receiving end plane it reflects the light upwards. The reflected light does not have the conditions for total reflection and thus emanates from output plane
121
without total reflection. Output plane
121
has an uneven portion in the form of a prism to provide a narrow distribution of light. As such, a prism sheet can be dispensed with in controlling a distribution of emanating light. In such a configuration as above, a hollowed portion in the form of a wedge is required to have a shape controlled to correspond to its position in the light guide plate to provide a uniform distribution in density of emanating light over different points in the light guide plate.
Since the conventional backlight is configured as above, it requires a large number of independent members to allow emanating light to have an appropriate distribution. As such it is costly. Furthermore, the backlight using the conventional light guide plate having an optical prism integrated therein has a reflecting hollowed portion in the form of a wedge regularly arranged and it thus hardly provides emanating light with a spatially uniform intensity.
SUMMARY OF THE INVENTION
The present invention contemplates a highly efficient, low-cost backlight capable of providing appropriate light distribution and providing control to allow emanating light to have a spatially uniform intensity.
The present invention provides a backlight for a liquid crystal display device including a rod-shaped light source supplying light for light radiation for displaying information on a liquid crystal panel and a flat light guide plate having a side receiving end surface parallel to the rod-shaped light source, an output surface arranged opposite and parallel to the liquid crystal panel, and a bottom surface facing the output surface in parallel. The bottom surface is provided with a reflecting prism having a reflecting hollowed portion in a form of a wedge extending along the receiving end surface and a dividing flat portion in a form of a strip extending orthogonal to the reflecting hollowed portion in the form of a wedge to divide the reflecting hollowed portion in the form of a wedge.
The backlight thus configured has a dividing flat portion dividing a reflecting plane in the form of a wedge providing reflection. As such, a prism sheet or the like can be dispensed with and a light guide plate suffices to emanate light having an appropriate light distribution. Furthermore, if its output surface is provided with a collecting prism, an uneven portion in the form of a prism of the output surface can effectively collect light to achieve high level of brightness. Furthermore, light emanating from the light guide plate can have a spatial distribution in intensity adjusted from example by changing both the reflecting hollowed portion in the form of a wedge in depth and the reflecting hollowed portion in the form of a wedge in width and the flat portion in width to consider their respective distances from the receiving end surface. As such, the backlight can be configured of a reduced number of members and hence at low cost to provide spatially uniform distribution and appropriate light distribution. More specifically, the above effect is obtained by gradually increasing in depth the reflecting hollowed portion in the wedge to consider its distance from the receiving end surface and by gradually decreasing in width the dividing flat portion to consider its distance from the receiving end surface. Thus the above effect can be readily achieved.
Desirably in the backlight the output surface is provided with a collecting prism having an uneven portion in the form of a prism with a plurality of parallel ridges extending in a direction orthogonal to the receiving end surface.
The output surface with a collecting prism arranged therein can provide high level of brightness in addition to appropriate distribution of light provided via a reflecting prism.
Furthermore, the present backlight can have the dividing flat portion in the form of a strip having a width that varies depending on its distance from the receiving end surface.
If the reflecting hollowed portion in the form of a wedge is changed only in depth to provide emanating light having spatially uniform distribution, the hollowed portion in a vicinity of the receiving end surface is required to have as extremely minute a height as approximately several &mgr;m. In contrast, if it is combined with a dividing flat portion of a strip having a variable width, then the reflecting hollowed portion in the vicinity of the receiving end surface can have a depth that is readily processed and the backlight can thus be readily manufactured. Furthermore, conventionally, as seen in a direction parallel to the receiving end
Inoue Mitsuo
Iwasaki Naoko
Matsumoto Sadayuki
Oda Kyoichiro
Sasagawa Tomohiro
Cariaso Alan
Leydig , Voit & Mayer, Ltd.
Mitsubishi Denki & Kabushiki Kaisha
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