Liquid crystal cells – elements and systems – Particular structure – Particular illumination
Reexamination Certificate
2000-02-04
2003-08-12
Ngo, Julie (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Particular illumination
C349S064000, C349S112000, C362S035000
Reexamination Certificate
active
06606133
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a light diffusing sheet used in a back light unit for a liquid crystal display and a back light unit using the light diffusing sheet.
2. Description of the Related Art
For liquid crystal displays, a back light system in which a back surface of a liquid crystal layer is illuminated to thereby emit light has spread, and the back light unit is provided on a lower surface side of the liquid crystal layer. In general, as shown in
FIG. 6
, a back light unit
10
comprises a linear lamp
11
as alight source, a light guiding plate
12
placed such that its ends are adapted to those of the lamp
11
, a light diffusing sheet
13
provided on a front-surface side of the light guiding plate
12
, and a prism sheet
14
provided on a front-surface side of the light diffusing sheet
13
. Although one prism sheet
14
is shown in
FIG. 6
, two prism sheets
14
may be provided such that prism portions
14
a
of one of the two prism sheets
14
are perpendicular to those of the other.
A function of the back light unit
10
will now be described. Light rays emitted from the lamp
11
enter the light guiding plate
12
, are reflected by reflection dots or a reflection sheet provided on a back surface of the light guiding plate
12
and side surfaces thereof, and emanate from a surface thereof. Then, the light rays emanating from the light guiding plate
12
enter the light diffusing sheet
13
, are diffused therein, and emanate from a surface thereof. Thereafter, the light rays emanating from the light diffusing sheet
13
enter the prism sheet
14
, and emanate from a surface thereof, thereby illuminating the entire surface of the liquid crystal layer (not shown) provided above.
Luminance distributions of the light rays emanating from the surface of the light guiding plate
12
, when viewed in a direction perpendicular to the lamp
11
and in a direction parallel to the lamp
11
, differ from each other. For instance, as shown in
FIG. 7
, in some light guiding plates
12
, the luminance distribution in the direction perpendicular to the lamp
11
has a high peak diagonally above on an opposite side of the lamp
11
, and the luminance distribution in the direction parallel to the lamp
11
has right and left peaks diagonally above that are relatively lower than that of the luminance distribution in the direction perpendicular to the lamp
11
.
Specific examples of the conventional light diffusing sheet
13
are as follows:
(a) A binder in which a light diffusing material such as beads is dispersed is applied to a surface of abase sheet to form a light diffusing layer with the light diffusing material dispersed therein on the surface(see Utility Model Application Publication Hei. No.
5-73602
).
(b) When forming a synthetic resin sheet, a plurality of convex regions and concave regions are formed on a surface thereof by embossing and the like.
Since the above-described conventional light diffusing sheet
13
exhibits a light diffusing ability because of the light diffusing material such as the dispersed beads or the convex regions and concave regions on the surface thereof, the light diffusing ability is the same over the entire surface and in all directions of the sheet.
For this reason, if the diffusing ability of the light diffusing sheet
13
is adapted to either the luminance distribution in the direction perpendicular to the lamp
11
or the luminance distribution in the direction parallel to the lamp
11
and thereby the amount of light emanating in a normal direction (normal direction of respective sheets disposed parallel to one another) in the luminance distribution in one direction is increased, then the amount of light emanating in the normal direction in the luminance distribution in the other direction is not increased. In a case where the luminance distribution of the light rays emanating from the light guiding plate
12
is that shown in
FIG. 7
, if the diffusing ability of the light diffusing sheet
13
is adapted to the luminance distribution in the direction perpendicular to the lamp
11
that has the high peak diagonally above and thereby a peak light is refracted to some degrees toward the normal direction without greatly dispersing it, then the luminance distribution in the direction parallel to the lamp
11
that is relatively low and has the right and left peaks diagonally above is almost the same as the distribution in which the light rays emanate from the surface of the light guiding plate
12
, and consequently, the amount of the light emanating in the normal direction remains small.
Conversely, if the diffusing ability of the light diffusing sheet
13
is adapted to the luminance distribution in the direction parallel to the lamp
11
that is relatively low and has the right and left peaks diagonally above to be thereby enhanced for the purpose of increasing the amount of the light emanating in the normal direction, then a strong peak light in the luminance distribution in the direction perpendicular to the lamp
11
is greatly dispersed, and thereby the amount of light emanating in the normal direction is reduced.
SUMMARY OF THE INVENTION
The present invention is directed to solving the above problems, and an object of the present invention is to provide a light diffusing sheet capable of changing a backward and forward diffusing ability and a right and left diffusing ability to be adapted to luminance distribution in a direction perpendicular to a lamp and luminance distribution in a direction parallel to the lamp, and thereby increasing light emanating in a normal direction in either direction, and a back light unit using the light diffusing sheet.
In one aspect of the present invention, a light diffusing sheet for use in a back light unit for a liquid crystal display includes light diffusing means which has a backward and forward diffusing ability and a right and left diffusing ability that differ from each other. The expression “backward and forward diffusing ability” as used herein refers to a diffusing ability of light rays on a backward and forward plane perpendicular to the sheet surface. The expression “right and left diffusing ability” as used herein refers to a light diffusing ability of light rays on a right and left plane perpendicular to the sheet surface. For convention purposes herein, the backward and forward plane and the backward and forward direction may be considered as extending along the direction B, in the drawings, and the right and left plane and the right and left direction may be considered as extending along the direction A. These directions are examples, however. As illustrated and described, the right and left direction may be considered a first direction and the backward and forward direction may be considered a second direction that is different than the first direction. In an example, the first and second direction may be perpendicular to one another.
With this configuration, the light diffusing means enables to set the backward and forward diffusing ability and the right and left diffusing ability so that they differ from each other. Hence, when a back light unit comprising a)a liner lamp; b) a light guiding plate provided along the lamp for guiding light rays emitted from the lamp to a surface side of the sheet; and c) a light diffusing sheet provided on a surface side of the light guiding plate, uses the above light diffusing sheet as the light diffusing sheet, the diffusing ability of the light diffusing sheet can be adapted to both the luminance distribution in the direction perpendicular to the lamp and the luminance distribution in the direction parallel to it, and the amount of light emanating in the normal direction can be increased in the luminance distribution in either direction. Therefore, in case of the emanating light rays of the light guiding plate represented by luminance distribution the direction perpendicular to the lamp that has a relatively high peak diagonally above on an opposite side of the lamp and luminance distributi
Keiwa Inc.
Marshall Gerstein & Borun
Ngo Julie
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