Title: Illumination device and liquid crystal display device
Abstract: An illumination device includes a light source and a planar illuminator for emitting light of the light source portion from one surface thereby to illuminate a liquid crystal panel. The planar illuminator has a reflection surface, on which minute concavo-convex shapes are substantially randomly formed. Surface emission is performed by diffuse reflecting the light irradiated from the light source portion by the reflection surface.
Patent Number: 6,971,782 Issued on 12/06/2005 to Nagakubo, et al.
| Inventors:
|
Nagakubo; Hideaki (Fukushima-ken, JP);
Sato; Norikazu (Fukushima-ken, JP)
|
| Assignee:
|
Alps Electric Co., Ltd. (Tokyo, JP)
|
| Appl. No.:
|
716374 |
| Filed:
|
November 18, 2003 |
Foreign Application Priority Data
| Nov 19, 2002[JP] | 2002-334994 |
| Current U.S. Class: |
362/625; 362/626; 362/600; 362/623; 362/348 |
| Intern'l Class: |
F21V 007/04 |
| Field of Search: |
362/31,600,606,607,608,623,625,626,297,342,348
349/67,62
|
References Cited [Referenced By]
U.S. Patent Documents
| 4779137 | Oct., 1988 | Tojo et al.
| |
| 4874228 | Oct., 1989 | Aho et al.
| |
| 6181396 | Jan., 2001 | Kanoh et al.
| |
| 6213625 | Apr., 2001 | Leadford et al.
| |
| 6692137 | Feb., 2004 | Blanchard.
| |
| 6755546 | Jun., 2004 | Ohkawa.
| |
| 2003/0227768 | Dec., 2003 | Hara et al.
| |
| 2004/0105157 | Jun., 2004 | Matsushita et al.
| |
| Foreign Patent Documents |
| 3277178 | Sep., 2001 | JP.
| |
Primary Examiner: Husar; Stephen
Assistant Examiner: Ton; Anabel
Attorney, Agent or Firm: Brinks Hofer Gilson & Lione
Claims
1. An illumination device, comprising:
a light source; and
a planar illuminator for illuminating an illuminated object by emitting light
of the light source from one surface,
wherein the planar illuminator has a reflection surface, on which minute concavo-convex
shapes are substantially randomly formed,
wherein the light irradiated from the light source is diffusively reflected by
the reflection surface thereby to perform surface emission,
wherein the light source is arranged at a side of the planar illuminator, and
wherein a reflection surface of the planar illuminator is a tilted surface that
rises as the reflection surface becomes more distant from the light source.
2. The illumination device according to claim 1, wherein a prism-shaped prism
sheet is disposed between the reflection surface of the planar illuminator and
the illuminated object.
3. The illumination device according to claim 2, wherein the prism sheet controls
the directivity of at least two light components, which travels in different directions
in plan view.
4. The illumination device according to claim 3, wherein the prism sheet has
a prism shape where a plurality of polypyramid-shaped or conical protrusions is formed.
5. The illumination device according to claim 4, wherein the vertical angle of
the polypyramid-shaped or conical protrusion is in the range of 70° to 110°.
6. The illumination device according to claim 4, wherein a vertical angle of
the polypyramid-shaped or conical protrusion is in the range of 80° to 100°.
7. The illumination device according to claim 4, wherein the protrusion has any
one of a quadrangular pyramid, a hexangular pyramid, and an octangular pyramid shape.
8. The illumination device according to claim 1, wherein the light source is
a cold cathode fluorescence lamp.
9. The illumination device according to claim 1, wherein the light source is
an LED or an LED array.
10. The illumination device according to claim 1,
wherein the light source comprises a substantially rod-shaped light guider and
a light emitting element disposed at an end of the longitudinal direction of the
light guider,
wherein the light guider introduces light of the light emitting element from
one end thereof to the inside thereof and emits the light to an emission surface
disposed on one side,
wherein a side opposite to the emission surface of the light guider is curved, and
wherein a plurality of grooves extended to the peripheral direction of the light
guider is formed along the curve.
11. The illumination device according to claim 10, wherein the pitches of the
plurality of grooves formed in the light guider gradually become narrower from
the side where the light emitting element is disposed and the depths of the grooves
gradually become deeper.
12. A liquid crystal display device, wherein the illumination device according
to claim 1 is disposed in the rear side of the liquid crystal panel.
13. An illumination device, comprising:
a light source; and
a planar illuminator for illuminating an illuminated object by emitting light
of the light source from one surface,
wherein the planar illuminator has a reflection surface, on which minute concavo-convex
shapes are substantially randomly formed,
wherein the light irradiated from the light source is diffusively reflected by
the reflection surface thereby to perform surface emission, and
wherein a prism-shaped prism sheet is disposed between the reflection surface
of the planar illuminator and the illuminated object.
14. The illumination device according to claim 13, wherein the prism sheet controls
directivity of at least two light components, which travels in different directions
in plan view.
15. The illumination device according to claim 14, wherein the prism sheet has
a prism shape where a plurality of polypyramid-shaped or conical protrusions is formed.
16. The illumination device according to claim 15, wherein a vertical angle of
the polypyramid-shaped or conical protrusion is in the range of 70° to 110°.
17. The illumination device according to claim 15, wherein a vertical angle of
the polypyramid-shaped or conical protrusion is in the range of 80° to 100°.
18. The illumination device according to claim 15, wherein the protrusions have
any one of a quadrangular pyramid, a hexangular pyramid, and an octangular pyramid shape.
19. The illumination device according to claim 13, wherein the light source is
a cold cathode fluorescence lamp.
20. The illumination device according to claim 13, wherein the light source is
an LED or an LED array.
21. The illumination device according to claim 13,
wherein the light source comprises a substantially rod-shaped light guider and
a light emitting element disposed at an end of a longitudinal direction of the
light guider,
wherein the light guider introduces light of the light emitting element from
one end thereof to an inside thereof and emits the light to an emission surface
disposed on one side,
wherein a side opposite to the emission surface of the light guider is curved, and
wherein a plurality of grooves extended to a peripheral direction of the light
guider is formed along the curve.
22. The illumination device according to claim 21, wherein pitches of the plurality
of grooves formed in the light guider gradually become narrower from a side where
the light emitting element is disposed and depths of the grooves gradually become deeper.
23. A liquid crystal display device, wherein the illumination device according
to claim 13 is disposed in the rear side of the liquid crystal panel.
24. An illumination device, comprising:
a light source; and
a planar illuminator for illuminating an illuminated object by emitting light
of the light source from one surface,
wherein the planar illuminator has a reflection surface, on which minute concavo-convex
shapes are substantially randomly formed,
wherein the light irradiated from the light source is diffusively reflected by
the reflection surface thereby to perform surface emission,
wherein the light source comprises a substantially rod-shaped light guider and
a light emitting element disposed at an end of a longitudinal direction of the
light guider,
wherein the light guider introduces light of the light emitting element from
one end thereof to an inside thereof and emits the light to an emission surface
disposed on one side,
wherein a side opposite to the emission surface of the light guider is curved, and
wherein a plurality of grooves extended to a peripheral direction of the light
guider is formed along the curve.
25. The illumination device according to claim 24, wherein pitches of the plurality
of grooves formed in the light guider gradually become narrower from a side where
the light emitting element is disposed and depths of the grooves gradually become deeper.
26. The illumination device according to claim 24, wherein a prism-shaped prism
sheet is disposed between the reflection surface of the planar illuminator and
the illuminated object and the prism sheet controls directivity of at least two
light components, which travels in different directions in plan view.
27. The illumination device according to claim 26, wherein the prism sheet has
a prism shape where a plurality of polypyramid-shaped or conical protrusions is formed.
28. The illumination device according to claim 27, wherein a vertical angle of
the polypyramid-shaped or conical protrusion is in the range of 70° to 110°.
29. The illumination device according to claim 27, wherein a vertical angle of
the polypyramid-shaped or conical protrusion is in the range of 80° to 100°.
30. The illumination device according to claim 27, wherein the protrusions have
any one of a quadrangular pyramid, a hexangular pyramid, and an octangular pyramid shape.
31. The illumination device according to claim 24, wherein the light source is
a cold cathode fluorescence lamp.
32. The illumination device according to claim 24, wherein the light source is
an LED or an LED array.
33. A liquid crystal display device, wherein the illumination device according
to claim 24 is disposed in the rear side of the liquid crystal panel.
Description
This application claims the benefit of priority to Japanese Patent Application
2002-334994, filed on Nov. 19, 2002.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an illumination device and a liquid crystal
display device.
2. Description of the Related Art
Illumination device such as a frontlight and a backlight used for liquid
crystal display device basically include a light guide plate and a light source
disposed on the side section of the light guide plate. Light incident from the
side sections of the light guide plates is reflected by a prism formed on the opposite
sides to the emission surfaces of the light guide plates and is emitted from the
emission surfaces. As a result, the illumination devices illuminate illuminated
objects such as liquid crystal panels. It is suggested that the traveling direction
of the light incident on the liquid crystal panels be controlled and that display
brightness be improved by disposing prism sheets between the light guide plates
and the liquid crystal panels (for example, Patent Document 1).
FIG. 15 illustrates an example of a section of a liquid crystal display device
having the above structure. The liquid crystal display device illustrated in FIG.
15 includes a liquid crystal panel 110 and a backlight 120 disposed
in the rear side of (below the liquid crystal panel in FIG. 15) the liquid crystal
panel 110. The liquid crystal panel 110 is transmissive type with
no reflection layer or transflective type with a reflection layer partially disposed
in a pixel region. In the backlight 120, reference numerals 122 and
123 denote a light guide plate and a cold cathode fluorescence lamp. A plurality
of grooves 124 having wedge-shaped sections are formed at a lower surface
122
b of the light guide plate 122. A light scattering plate
126 and two prism sheets 127 are arranged between the light guide
plate 122 and the liquid crystal panel 110.
[Patent Document 1]
Japanese Patent No. 3277178
The backlight 120 included in the liquid crystal display device illustrated
in FIG. 15 guides the light emitted from the cold cathode fluorescence lamp 123
to the inside of the light guide plate 122 and reflects the light transmitted
to the inside the light guide plate 122 from the internal surfaces of the
grooves 124, thereby to emit light to the liquid crystal panel 110.
The light emitted from the top face of the light guide plate 122 is scattered
by the light scattering plate 126 and changes the traveling direction thereof
by the two prism sheets 127 so that the traveling direction can be changed
substantially perpendicular to the liquid crystal panel 110 thereby to be
incident on the liquid crystal panel 110. As a result, the,light is used
as display light.
The structure of the backlight 120 illustrated in FIG. 15 is currently
and commonly used. However, in such a kind of backlight, a large amount of components
emitted at an angle so as to deviate from the direction perpendicular to the light
guide plate 122 is included in the light emitted from the light guide plate
122 to the liquid crystal panel 110. Therefore, there is a problem
in that the utilization efficiency of the light emitted from the backlight 120
decreases. In order to solve the above problem, the prism sheets 127 for
directing the light emitted from the backlight 120 toward the direction
perpendicular to the light guide plate are arranged between the light guide plate
122 and the liquid crystal panel 110. However, in a structure where
a plurality of optical devices is laminated, it is difficult to make the liquid
crystal display device light. Also, the manufacturing cost increases due to an
increase in the number of parts of liquid crystal display device. In particular,
the prism sheet is extremely expensive, which is a factor for increasing the price
of the conventional backlight systems.
In a method of guiding the light from the cold cathode fluorescence lamp 123
to the inside of the light guide plate 122 and reflecting the light from
the grooves 124 of the light guide plate 122, some components of
the light may be lost inside light guide plate 122. Therefore, it is difficult
to improve the utilization efficiency of light.
SUMMARY OF THE INVENTION
Accordingly, in order to solve the above problems, it is an object of
the present invention to provide an illumination device capable of being manufactured
at small expenses and of being easily made lightwieght, thereby not creating loss
of light.
An illumination device according to the present invention comprises a light source
and a planar illuminator for illuminating an illuminated object by emitting light
of the light source from one surface, the planar illuminator has a reflection surface,
on which minute concavo-convex shapes are substantially randomly formed, and light
irradiated from the light source is diffusively reflected by the reflection surface
thereby to perform surface emission.
The illumination device having the above structure illuminates the illuminated
object such as a liquid crystal panel by reflecting the light illuminated from
the light source by the planar illuminator having the reflection surface for diffusing
and reflecting incident light. In a conventional illumination device, as illustrated
in FIG. 15, in order to use light from a linear light source or a point light source
as a planar light source, a transparent light guide plate 122 is used. However,
a molded product such as acrylic resin is used as the light guide plate. In particular,
when the illumination device is enlarged, significant increase in the weight of
the illumination device is caused. In the illumination device according to the
present invention, the planar illuminator having diffusively reflection functions
caused by minute concavo-convex shapes is used for making a linear light source
or a point light source as a planar light source. Therefore, in order to obtain
the function as the planar illuminator, at least the reflection surface is preferably
included. As a result, it is possible to easily make the illumination device thin.
Also, it is possible to make the illumination device light.
In the illumination device according to the present invention, the light source
is arranged at a side of the planar illuminator, and a reflection surface of the
planar illuminator is a tilted surface that rises as the reflection surface becomes
more distant from the light source.
According to the above structure, it is possible to provide an illumination
device which can be used instead of the conventional backlight, in which the light
source is disposed on the side section of the light guide plate that is a planar
light emitting portion. In the above structure, the light emitted from the light
source is transferred in the air and reaches the reflection surface of the planar
illuminator. The light is diffusively reflected on the reflection surface and,
at the same time, the direction of the light changes to travel over the planar
illuminator, thereby to illuminate the illuminated object.
In the illumination device according to the present invention, a prism-shaped
prism sheet is disposed between the reflection surface of the planar illuminator
and an illuminated object.
According to the above structure, it is possible to condense the illumination
light diffusively reflected on the reflection surface and incident on the illuminated
object to a predetermined direction. Therefore, it is possible to improve substantial
illumination brightness.
In the illumination device according to the present invention, the prism sheet
controls the directivity of at least two light components, which travels in different
directions in plan view.
According to the structure, it is possible to further increase the concentration
of the illumination light and thereby to further improve the brightness of the
condensed light. Therefore, it is possible to obtain illumination light having
higher brightness.
In the illumination device according to the present invention, the prism sheet
has a prism shape where a plurality of polypyramid-shaped or conical protrusions
is formed.
According to the above structure, it is possible to efficiently condense
light components having a plurality of traveling directions in a plane to a predetermined
direction and to substantially obtain illumination light having high brightness.
In the illumination device according to the present invention, the vertical angle
of the polypyramid-shaped or conical protrusion is in the range of 70° to
110° and the vertical angle of the polypyramid-shaped or conical protrusion
is in the range of 80° to 100°.
It is possible to efficiently emit light components having a plurality of traveling
directions in a plane to a direction perpendicular to the prism sheet by making
the vertical angle of the protrusion be in the above range. In particular, when
the illuminated object is the liquid crystal panel, it is possible to form a liquid
crystal display device capable of displaying image with high brightness.
In the illumination device according to the present invention, the protrusion
has any one of a quadrangular pyramid, a hexangular pyramid, and an octangular pyramid.
According to the above structure, it is possible to provide an illumination
device, by which it is possible to uniformly control directivity of the light components
that pass through the prism sheet within the prism face and to improve uniformity
of the emitted light.
In the illumination device according to the present invention, the light source
is a cold cathode fluorescence lamp and the light source is an LED or an LED array.
There is not limited in the light source applied to the illumination device according
to the present invention. Any light source used as the conventional back or frontlight
may be used. In order to make the illumination device thin and lightweight, it
is preferable to use a light source with the LED (a light emitting diode).
In the illumination device according to the present invention, the light source
comprises a substantially rod-shaped light guider and a light emitting element
disposed at the end of the longitudinal direction of the light guider, the light
guider introduces light of the light emitting element from one end thereof to the
inside thereof and emits the light to an emission surface disposed on one side,
a side opposite to the emission surface of the light guider is curved, and a plurality
of grooves extended to the peripheral direction of the light guide is formed along
the curve.
According to the above structure, it is possible to change the light emitting
element that is the point light source into the linear light source by the light
guider and thereby to irradiate the planar illuminator. Therefore, it is possible
to provide an illumination device, in which the point light source is used and
the amount of the light emitted from a light emission surface is uniform.
In the illumination device according to the present invention, the reflection
surface is formed on the tilted surface that rises according to the distance as
the tilted surface becomes far from the light guider. Therefore, in the emission
characteristics of the light guider, main components are preferably distributed
to the front direction of an emission surface. It is preferable that the amount
of the components emitted from the front of the emission surface to the vertical
direction of the emission surface be relatively small. According to the light guider
having the above structure, it is possible to easily obtain emitted light having
the related distribution.
In the illumination device according to the present invention, the pitches of
the plurality of grooves formed in the light guide gradually become narrower from
the side where the light emitting element is disposed and the depths of the grooves
gradually become deeper.
According to the above structure, it is possible to provide an illumination
device capable of making uniform the distribution of the amount of emitted light
to a direction, to which the light guider is extended and of obtaining uniform
illumination light in a surface of the planar illuminator.
In the liquid crystal device according to the present invention, the illumination
device according to the claims is disposed in the rear side of the liquid crystal
panel. According to the above structure, it is possible to provide a thin and light
liquid crystal display device capable of displaying images with high brightness
by including the illumination device according to the present invention capable
of being easily made thin and light.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of a liquid crystal display device according to
an embodiment of the present invention;
FIG. 2 is a sectional view of the liquid crystal display device illustrated
in FIG. 1;
FIG. 3 is a partial perspective view illustrating an enlargement of a reflection
surface of a planar illuminator illustrated in FIG. 1;
FIG. 4 is a perspective view of a light guider 17 illustrated in FIG. 1;
FIG. 5 is a perspective view of a prism sheet that can be used as optical means
illustrated in FIG. 1;
FIG. 6 illustrates a section of a concave portion according to a first example
of shape;
FIG. 7 illustrates reflection characteristics of a reflection surface having
the concave portion illustrated in FIG. 6;
FIG. 8 is a perspective view of a concave portion according to a second example
of shape;
FIG. 9 is a sectional view along the longitudinal section X illustrated in FIG. 8;
FIG. 10 illustrates reflection characteristics of a reflection surface having
the concave portions illustrated in FIGS. 8 and 9;
FIG. 11 is a perspective view illustrating a concave portion according to a
third example of shape;
FIG. 12 is a sectional view along the longitudinal section X illustrated in
FIG. 11;
FIG. 13 is a sectional view along the longitudinal section Y illustrated in
FIG. 11;
FIG. 14 illustrates reflection characteristics of a reflection surface having
the concave portions illustrated in FIGS. 11 to 13; and
FIG. 15 is a sectional view illustrating an example of a conventional liquid
crystal display device.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
An embodiment of the present invention will now be described with reference to drawings.
FIG. 1 is a perspective view of a liquid crystal display device according to
an embodiment of the present invention. FIG. 2 is a sectional view of the liquid
crystal display device illustrated in FIG. 1. The liquid crystal display device
according to the embodiment, as illustrated in FIGS. 1 and 2, includes a liquid
crystal panel
20 and a backlight (an illumination device)
10 arranged
on the rear side of (below the liquid crystal panel in Figure) the liquid crystal
panel
20. In the liquid crystal display device according to the present
embodiment, optical means
30 having a light diffusing function or a directivity
controlling function is arranged between the liquid crystal panel
20 and
the backlight
10.
The backlight
10 includes a planar illuminator
12 having a reflection
surface
12b formed at its upper surface, and a light source portion
(a light source)
13 arranged on a light source arranging portion
12a
disposed at the end of the upper surface. The liquid crystal panel
20
is a transmissive or transflective liquid crystal display device that includes
an upper substrate
21 and a lower substrate
22 arranged to face each
other. Pixels (not shown) are formed in a matrix.
In the liquid crystal display device having the above structure, the planar illuminator
12 is arranged on the rear side of the liquid crystal panel
20. The
planar illuminator
12 reflects the light emitted from the light source portion
13, thereby to illuminate the liquid crystal panel
20 and to recognize
images displayed on the liquid crystal panel
20. Also, under the periphery
where the external light such as sunlight is incident, the external light may be
reflected by the reflection surface
12b of the planar illuminator
12, thereby to be used as display light.
If the liquid crystal panel
20 is transflective type, it is possible to
display images by reflecting the external light by a reflection layer formed in
the liquid crystal panel
20.
Structures of the respective portions of the liquid crystal display device
according to the embodiment will now be described in detail.
<Backlight>
The backlight
10 according to the present embodiment, as illustrated in
FIGS. 1 and 2, includes the planar illuminator
12 and the light source portion
13 disposed at the side end of the planar illuminator
12 as main
components. The planar illuminator
12 has the reflection surface
12b
tilted so as to rise from the light source arranging portion
12a
for arranging the light source portion
13 to a side that faces the side,
on which the light source arranging portion
12a is formed. A plurality
of minute concave portions
14 is randomly and continuously formed on the
reflection surface
12b. As illustrated in FIG. 2, the thickness H
of the planar illuminator
12 at the end of the facing side formed thicker
than the thickness h of the planar illuminator
12 in the light source arranging
portion
12a. The surface of the light source arranging portion
12a
is substantially a flat plane in the planar illuminator
12 according
to the embodiment. The planar illuminator
12 is obtained by forming a metal
reflection film such as Al and Ag in one side of transparent resin such as polycarbonate
resin mixed with Ti particles and acrylic resin.
FIG. 3 is a partial perspective view illustrating an enlargement of the reflection
surface
12b of the planar illuminator
12 illustrated in FIG.
1. As illustrated in FIG. 3, the plurality of concave portions
14 having
substantially spherical concave surfaces is formed on the surface of the planar
illuminator
12. In the illustrated example, the adjacent concave portions
14 are continuously formed so as to partially overlap each other.
The shape of the reflection surface
12b illustrated in FIGS. 1
and 3 is an example. It is preferable that the shape, the depth, and the pitch
of the concave portions
14 be appropriately changed so as to obtain appropriate
reflection characteristics in accordance with the structure of the light source
portion
13 assembled with the planar illuminator
12 or the structure
of the illuminated object assembled with the backlight
10. The shapes applied
to the concave portions
14 will now be described.
According to the embodiment, the light source arranging portion
12a
is a substantially flat plane. However, the region of the reflection surface
12b, in which the concavo-convex shapes are formed, may be extended
to the light source arranging portion
12a.
The distance between the planar illuminator
12 and the optical means
30
disposed in the liquid crystal panel
20 may be appropriately diffused by
the sizes of the backlight
10 and the liquid crystal panel
20. For
example, when the planar illuminator
12 is arranged on the rear side of
the liquid crystal panel
20 of about 2 to 4 inches, the distance is about
1 to 3 mm in the light source arranging portion
12a and is about
0.5 to 1 μm at the end of the side that faces the light source arranging
portion
12a. It is possible to easily adjust the distance by adjusting
the thicknesses H and h of the planar illuminator
12, which are illustrated
in FIG. 2.
FIG. 4 is a perspective view illustrating the light source portion
13
illustrated in FIGS. 1 and 2 in more detail. The light source portion
13
illustrated in FIG. 4 includes a light guider
17 formed of substantially
rod-shaped transparent resin and a light-emitting element
15 such as a white
LED arranged in a section
17a of the light guider
17. as main components
As illustrated in FIG. 4, one side (the rear side in Figure) of the light guider
17 is an emission surface
17b. The side opposite to the emission
surface
17b is curved. A plurality of grooves
18 with wedge-shaped
sections is formed along the curved surface so as-to extend to the peripheral direction
of the light guider. As illustrated in FIG. 4, the grooves
18 are formed
shallow to have the wide pitch in the section
17a where the light
emitting element is disposed and are formed deeper to have a narrower pitch from
the section
17a toward the direction where the light guider extends.
The light source portion
13 introduces the light emitted from the light
emitting element
15 from the section
17a to the inside of
the light guider
17, reflects the light transferred from the inside the
light guider
17 by the plurality of grooves
18 formed in the side
surface opposite to the emission surface
17b, and emits the reflected
light from the emission surface
17b. In the light source portion
13 according to the present embodiment, the grooves
18 are formed
so that the pitch and the depth thereof are controlled as mentioned above. Therefore,
it is possible to uniformly emit light in the direction extending to the light
guider
17 of the emission surface
17b. Since the side opposite
to the emission surface
17b is curved, the distribution of the light
emitted from the emission surface
17b in the thickness direction
of the light guider is optimal when the light source portion
13 is assembled
with the planar illuminator
12. To be more specific, the main components
of the light emitted from the emission surface
17b are emitted to
the front direction with respect to the emission surface
17b. The
amount of the components emitted to the vertical tilted direction in the direction
of the thickness of the light guider
17 is small. (In FIG. 2, most of the
light emitted from the emission surface
17b is emitted to be almost
vertical to the emission surface
17b. Therefore, the amount of the
light emitted from the emission surface
17b to the illustrated tilted
direction is relatively small.)
According to the present embodiment, the light source portion
13
is formed by assembling the light-emitting element
15 of the point light
source with the rod-shaped light guider
17. However, instead of the light
source portion
13, the light emission direction directs toward the reflection
surface
12b so that an LED array (an element obtained by arranging
a plurality of LEDs on a line or a surface) is disposed. A cold cathode fluorescence
lamp
123 illustrated in FIG. 15 may be used.
In the backlight
10 having the above structure according to the present
embodiment, as illustrated in FIG. 2, the light emitted from the light source portion
13 to the inside of the planar illuminator
12 is diffusively reflected
by the reflection surface
12b of the planar illuminator
12.
Therefore, the backlight
10 can uniformly illuminate the liquid crystal
panel
20. The backlight
10 according to the present embodiment does
not allow the light of the cold cathode fluorescence lamp
123 that is a
light source to transfer inside the light guide plate
122 as the conventional
backlight
120 illustrated in FIG. 15 does but reflects the light transferred
in the air by the planar illuminator
12 thereby to illuminate-the liquid
crystal panel
20. Therefore, loss of light does not occur inside the light
guide plate structurally. As a result, it is possible to use the light emitted
from the light source portion
13 as illumination light with high efficiency
and thereby to perform illumination with high brightness.
According to the present embodiment, the thicknesses of the planar illuminator
12 vary in the plane so that the reflection surface
12b is
tilted. In order to obtain function of the backlight
10 according to the
embodiment, the planar illuminator
12 preferably has only the reflection
surface
12b. A thin planar illuminator slowly curved along the reflection
shape
12b may be used. When the thin planar illuminator is used,
it is possible to easily make the backlight
10 thin and light and thereby
to easily make the liquid crystal display device thin and light.
<Shape of Reflection Surface of Planar Illuminator>
The shape of the reflection surface
12b of the planar illuminator
12 illustrated in FIG. 1 will now be described with reference to FIGS. 6
to 14.
[First Example of Shape]
FIG. 6 is a sectional view illustrating a first example of the shape of the
concave portions
14 formed on the reflection surface
12b illustrated
in FIG. 3. FIG. 7 illustrates the reflection characteristic of the reflection surface
12b including the concave portions
14 having the shape illustrated
in FIG. 6.
According to the present example, it is preferable that the concave portion
14 be randomly formed so that the depth thereof is in the range of 0.1 μm
to 3 μm. It is preferable that the pitch between the adjacent concave portions
14 be randomly set in the range of 5 μm to 100 μm. The tilt
angle of the inside surface of the concave portion
14 is preferably set
in the range of -18° to +18°. The depth of the concave portion is the
distance between the reflection surface
12b of the portion where
the concave portions are not formed and the bottom of the concave portion. The
pitch between the adjacent concave portions is the distance between the centers
of the concave portions that are circular in a plane. As illustrated in FIG. 6,
when a minute range where the width of an arbitrary portion inside the concave
portion
14 is, for example, 0.5 μm is obtained, the tilt angle of
the inside surface of the concave portion is an angle θc of a tilted surface
in the minute range with a level surface (the surface of a base). For example,
in FIG. 6, positive and negative of the angle θc is defined such that the
right tilted surface is positive and the left tilted surface is negative with respect
to a normal line formed on the reflection surface
12b where the concave
portions are not formed.
In the present example of shape, in particular, it is very important that the
distribution of the tilt angles inside the concave portion
14 is in the
range of -18° to +18° and that the pitch between the adjacent concave
portions
14 is randomly set for all of the directions of a plane. If the
pitch between the adjacent concave portions
14 has regularity, interference
color of light is generated thereby to color the reflected light. When the distribution
of the tilt angles inside the concave portion
14 exceeds the range of -18°
to +18°, the diffusion angle of the reflected light is too large. Therefore,
reflection intensity deteriorates and images cannot be displayed with high brightness.
(The diffusion angle of the reflection angle is 55° or more in the air.)
When the depth of the concave portion
14 is less than 0.1 μm, it
cannot obtain a large enough light diffusion effect by forming the concave portion
in the reflection surface. When the depth of the concave portion
14 is larger
than 3 μm, the pitch must be made large in order to obtain the enough light
diffusion effect, which may cause moiré fringes.
When the pitch between the adjacent concave portions
14 is less than
5 μm, processing time is extremely long. There is a problem in that a shape
that enables a desired reflection characteristic to be obtained cannot be formed
and interference light is generated. The pitch between the adjacent concave portions
14 is preferably in the range of 5 μm to 100 μm.
FIG. 7 illustrates a relationship between a light-receiving angle (unit: °)
and brightness (a reflectivity, unit: %) when light is irradiated at an incident
angle 30° with respect to the normal line direction of the planar illuminator
12 according to the embodiment and the light-receiving angle is changed
from the perpendicular position (0°: the normal line direction) to 60°
on the basis of 30° which is the regular reflection direction 30° with
the display surface. As illustrated in FIG. 7, it is possible to obtain almost
uniform reflectivity in a large light-receiving angle range that is symmetrical
with respect to the regular reflection direction. In particular, the reflectivity
is almost uniform in the light-receiving angle range of ±10° on the basis
of the regular reflection direction. Therefore, it is suggested to display images
with almost equal brightness in any direction in the viewing angle range.
The reflectivity can be made almost uniform in the wide light-receiving angle
range that is symmetrical with respect to the regular reflection direction because
the depth or the pitch of the concave portion
14 illustrated in FIG. 3 is
limited to the above-mentioned range and because the internal surface of the concave
portion
14 forms a part of a spherical surface. That is, the tilt angle
of the internal surface of the concave portion
14, which controls the reflectivity
of light is controlled to a uniform range because the depth and the pitch of the
concave portion
14 are limited. Therefore, it is possible to limit the reflection
efficiency of the reflection surface
12b to a uniform range. As a
result, it is possible to control the light emission direction of the backlight
and thereby to improve the brightness of a desired direction compared with the
brightness in a conventional art without using the prism sheet that is essential
to the backlight system in the conventional art.
[Second Example of Shape]
In the backlight
10 according to the present embodiment, it is possible
to use a reflection surface having the reflection characteristic where a reflection
brightness distribution is asymmetrical with respect to the regular reflection
direction as well as the reflection surface
12b having the reflection
characteristic where the reflection brightness distribution is almost symmetrical
with respect to the regular reflection direction. The reflection surface having
such a reflection characteristic will now be described with reference to FIGS.
8 and 9.
The reflection surface having the above reflection characteristic can be formed
by changing the shape of the internal surface of the concave portion
14
illustrated in FIG. 3. That is, the reflection surface according to the present
example has a structure where the plurality of concave portions
14 is formed
on the reflection surface so as to be adjacent to and overlap each other like in
the reflection surface
12b according to the foregoing embodiment,
which is illustrated in the perspective view of FIG. 3. That is, only the shape
of the internal surface of the concave portion
14 varies.
FIGS. 8 and 9 illustrate one of the concave portions
14 in accordance
with the present example, which illustrates a reflection brightness distribution
asymmetric with respect to the regular reflection direction. FIG. 8 is a perspective
diagram. FIG. 9 is a sectional view illustrating the specific longitudinal section
X illustrated in FIG. 8.
In the specific longitudinal section X of the concave portion
14 illustrated
in FIG. 8, the shape of the internal surface of the concave portion
14 consists
of a first curve A that extends from a periphery S
1 of the concave portion
14 to the deepest point D and a second curve B that extends from the deepest
point D of the concave portion to another periphery S
2 so as to be continuous
to the first curve A. In the two curves, the tilt angle with the reflection film
surface S is 0° in the deepest point D. The two curves are connected to each
other. 'The tilt angle' is an angle with respect to the level surface (the reflection
film surface S of the portion where the concave portions are not formed) of a tangent
line in an arbitrary position of the internal surface of the concave portion in
the specific longitudinal section.
The tilt angle of the first curve A with the reflection film surface S is larger
than the tilt angle of the second curve B with the reflection film surface S. The
deepest point D deviates from the center ∘ of the concave portion
14
in the x-direction. That is, the average of the absolute value of the tilt angle
of the first curve A with respect to the reflection film surface S is larger than
the average of the absolute value of the tilt angle of the second curve B with
the reflection film surface S. In the plurality of concave portions
14 formed
on the surface of a diffusive reflector, the tilt angles of the first curves A
with the reflection film surfaces S are irregularly scattered in the range of 1°
to 89°. The averages of the absolute values of the tilt angles of the second
curves B with the reflection film surfaces S in the concave portions
14
are irregularly scattered in the range of 0.5° to 88°.
The tilt angles of the two curves slowly change. Therefore, the maximum tilt
angle δa of the first curve A (the absolute value) is larger than the maximum
tilt angle δb (the absolute value) of the second curve B. The tilt angle
of the deepest point D where the first curve A is connected to the second curve
B with the base surface is 0°. The first curve A whose tilt angle has a negative
value is slowly connected to the second curve B whose tilt angle has a positive value.
The maximum tilt angles δa in the plurality of concave portions
14
formed on the reflection surface
12b are irregularly scattered in
the range of 2° to 90°. However, the maximum tilt angles δa of
a large number of concave portions are irregularly scattered in the range of 4°
to 35°.
The concave surface of the concave portion
14 according to the present
example has a single minimum point D (a point on the surface where the tilt angle
is 0°). The depth d of the concave portion
14 is formed by the distance
between the minimum point D and the reflection film surface S of the base. The
depths d are irregularly scattered in the range of 0.1 μm to 3 μm with
respect to the plurality of concave portions
14.
According to the embodiment, the specific sections X in the plurality of
concave portions
14 are in the same direction. The first curves A are arranged
in the same direction. That is, the x-direction marked with the arrows in FIGS.
8 and 9 is directed to the same direction in any concave portions.
In the reflection surface
12b having such a structure, the first
curves A in the plurality of concave portions
14 are arranged in the same
direction. Therefore, the reflected light of the light incident from above the
slope of the x-direction x (on the side of the first curve) of FIG. 9 on the reflection
surface
12b is shifted more to the side of the normal line direction
of the reflection film surface S than to the regular reflection direction. To the
contrary, the reflected light of the light incident from above the slope opposite
to the x-direction (on the side of the second curve B) of FIG. 9 is shifted more
to the side of the normal line direction of the reflection film surface S than
to the regular reflection direction.
Therefore, in the total reflection characteristics of the specific longitudinal
section X, the reflectivity in the direction of light to be reflected by the surface
around the second curve B increases. As a result, it is possible to obtain reflection
characteristics where reflection efficiency in a specific direction is selectively improved.
According to the embodiment, the relationship between the light-receiving
angle of the reflection surface
12b and the reflection angle of the
plane of the reflection
12b is obtained the same as in the first
example. The result is illustrated in FIG. 10. A relationship between the light-receiving
angle and the reflectivity when the concave portion
14 having the section
shape illustrated in FIG. 6 is formed is also illustrated in FIG. 10. As illustrated
in FIG. 10, the reflectivity in the reflection angle smaller than the reflection
angle 30° which is the regular reflection direction of the incident angle
30° considered as the structure of the present example is largest. Therefore,
the reflectivity around the direction as its the peak increases.
According to the reflection surface
12b having such a structure,
it is possible to effectively reflect and scatter the light emitted from the light
source portion
13 and incident from the side on the reflection surface
12b
to a panel direction. Simultaneously, the light reflected from the reflection
surface
12b has directivity where the reflectivity thereof increases
in a specific direction. Therefore, the emission angle of the reflected light emitted
via the reflection surface
12b increases. Also, it is possible to
improve emission efficiency at a specific emission angle. As a result, it is possible
to control the light emission direction of the backlight without using the prism
sheet that is essential in the conventional art and thereby to improve the brightness
in a desired direction compared with that in the conventional art.
[Third Example of Shape]
A reflection surface having the following structure can be used as a reflection
surface having a reflection brightness distribution asymmetric with respect to
the regular reflection direction of incident light. The structure will now be described
as a third example of a shape.
In the present example, it is possible to change the shape of the internal surface
of the concave portion
14 illustrated in FIG. 3 like in the second example
of shape. That is, in the present example, the reflection surface
12b
also has the structure where the plurality of concave portions
14 is
formed on the reflection surface so as to be adjacent to and overlap each other
like in the reflection surface according to the embodiment, which is illustrated
in the perspective view of FIG. 3. Therefore, only the shape of the internal surface
of the concave portion
14 varies.
FIGS. 11 to 13 illustrate the internal shape of the concave portion
14
according to the present example.
FIG. 11 is a perspective view of the concave portion
14. FIG. 12 illustrates
a section along the X-axis (the longitudinal section X) of the concave portion
14. FIG. 13 illustrates a section along the Y-axis (the longitudinal section
Y) perpendicular to the X-axis of the concave portion
14.
As illustrated in FIG. 12, the shape of the internal surface of the concave portion
14 in the longitudinal section X consists of a first curve A′ that
extends from a periphery S
1 of the concave portion
14 to the deepest
point D and a second curve B′ that is connected to the first curve and extends
from the deepest point D of the concave portion
14 to another periphery
S
2. In FIG. 12, in the backward leaning first curve A′ and the forward
leaning second curve B′, the tilt angle with respect to the surface S of
the reflection film surface is 0° in the deepest point D. Therefore, the first
curve A′ is smoothly connected to the second curve B′.
'The tilt angle' is an angle of a specific longitudinal section with the level
surface (here, the surface S of the reflection surface in the portion where the
concave portions are not formed) of a tangent line in an arbitrary position of
the internal surface of the concave portion.
The tilt angle of the first curve A′ with respect to the reflection film
surface S is larger than the tilt angle of the second curve B′. The deepest
point D deviates from the center ∘ of the concave portion
14 to the
direction (the x-direction) extended to the periphery thereof along the X-axis.
That is, the average of the absolute value of the tilt angle of the first curve
A′ is larger than the average of the absolute value of the tilt angle of
the second curve B′. The averages of the absolute values of the tilt angles
of the first curves A′ in the plurality of concave portions
14 are
irregularly scattered in the range of 2° to 90°. The averages of the
absolute values of the tilt angles of the second curves B′ in the plurality
of concave portions
14 are irregularly scattered in the range of 1°
to 89°.
As illustrated in FIG. 13, the internal surface of the concave portion
14
in the longitudinal section Y is symmetrical with respect to the center O of the
concave portion
14. In the periphery of the deepest point D of the concave
portion
14, a shallow curve E having a large radius of curvature, that is,
close to a straight line exists. On either side of the shallow curve E, deep curves
F and G having a small radius of curvature exist. The absolute values of the tilt
angles of the shallow curves E in the plurality of concave portions
14 formed
on the reflection surface
12b are mostly 10° or less. The absolute
values of the tilt angles of the deep curves F and G in the plurality of concave
portions
14 are irregularly scattered in the range of 2° to 90°.
The depths d of the deepest points D are irregularly scattered in the range of
0.1 μm to 3 μm.
In the present example, in the plurality of concave portions
14 formed
on the reflection surface
12b, the section directions that shape
the longitudinal sections X are the same. The section directions that shape the
longitudinal sections Y are the same. Simultaneously, the directions from the deepest
points D to the peripheries S
1 via the first curves A′ are the same.
That is, in the concave portions
14 formed on the reflection surface, the
x-direction marked with the arrows in FIGS. 11 and 12 are the same.
In the present example, the directions of the concave portions
14 formed
on the reflection surface
12b are the same. The directions from the
deepest points D to the peripheries S
1 via the first curves A′ are
the same. Therefore, in the reflection surface
12b, the reflected
light incident from above the slope of the x-direction (on the side of the first
curve A′) in FIGS. 11 and 12 is shifted more to the normal line direction
of the reflection film surface S than to the regular reflection direction.
To the contrary, the reflected light of the light incident from above the slope
of the direction (on the side of the second curve B′) opposite to the direction
x in FIGS. 11 and 12 is more shifted to the reflection film surface S than to the
regular reflection direction.
The longitudinal section Y that is at right angle to the longitudinal section
X includes the shallow curve E with the large radius of curvature and the deep
curves F and G with the small radius of curvature, which exist on both sides of
the shallow curve E. Therefore, it is possible to increase the reflectivity in
the regular reflection direction with respect to the reflection surface
12b.
As a result, as illustrated in FIG. 14, according to the total reflection characteristics
in the longitudinal section X, it is possible to secure enough reflectivity in
the regular reflection direction and to appropriately condense the reflected light
to a specific direction. FIG. 14 illustrates a relationship between the light-receiving
angle and the reflectivity in the reflection surface in the present example of
shape like in the first example of shape. According to the reflection characteristics
illustrated in the graph, the integrated value of the reflectivity in the reflection
angle range smaller than the regular reflection angle 30° is larger than the
integrated value of the reflectivity in the reflection angle range larger than
the regular reflection angle. Therefore, the reflection direction tends to be shifted
more to the normal line than to the regular reflection direction.
Therefore, according to the backlight including the reflection surface
12b, in which the concave portions
14 having the above structure
are formed, due to the reflection surface
12b having the above shape,
it is possible to effectively reflect and scatter the light emitted from the light
source portion
13 and incident from the side. The light reflected to the
reflection surface
12b has the directivity where the reflectivity
thereof in a specific direction increases. Therefore, the emission angle of the
reflected light emitted via the reflection surface
12b increases
and it is possible to improve the emission efficiency in a specific emission angle.
Therefore, it is possible to control the light emission direction of the backlight
without using the prism sheet essential in the conventional art and to improve
the brightness of a desired direction compared with that in the conventional art.
The shapes of the concave portions
14 illustrated in the examples of FIGS.
1 to 3 are examples of the shapes of the concavo-convex portions formed on the
reflection surface
12b of the planar illuminator
12 according
to the present invention. The scope of the present invention is not limited thereto.
<Optical Means>
For example, the prism sheet for controlling the directivity of the light reflected
to the reflection surface
12b of the planar illuminator
12
can be used as the optical means
30 illustrated in FIGS. 1 and 2. FIG. 5
is a perspective view of a prism sheet that is suitable for the optical means
30
according to the present embodiment. In the prism sheet
31 illustrated in
FIG. 5, quadrangular pyramid-shaped protrusions
32 are arranged on an upper
surface in Figure. The prism sheet
31 changes the main traveling direction
of the light incident from a lower surface thereby to condense the light to the
direction perpendicular to the prism sheet
31. When the prism sheet
31
is included as the optical means
30, it is possible to condense the light
emitted from the backlight
10 to the direction perpendicular to the liquid
crystal panel
20 and make the light incident on the liquid crystal panel
20 by the optical mean
