JP2003059321A - Flat light source illuminating object - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flat light source, especially a backlight for a liquid crystal display device, minimizing the light loss in a liquid crystal panel. SOLUTION: This flat light source has a light source; a light guide plate leading the light thereinto from the end face opposite to the light source and diffusing the light, and reflecting the light on a reflection face to project the reflected light to the outside; and a prism sheet transmitting the reflected light and projecting the transmitted light as projection light in the normal direction to illuminate an object. A vertical angle of each microprism of the prism sheet is 65-75 deg., and the microprisms are disposed face down.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light source, and a light guide plate which introduces light from an end surface facing the light source into the inside and diffuses the light, reflects the light at a reflecting surface and projects the reflected light to the outside. The present invention relates to a planar light source having a prism sheet that transmits this reflected light and projects it as projection light in the normal direction to illuminate the illuminated object. In particular, in such a planar light source, the illuminated object is The present invention relates to a planar light source that illuminates an illuminated object that is intended to illuminate the illuminated object brighter by increasing the amount of light to be emitted.

[0002]

2. Description of the Related Art A planar light source used as a front light or a back light of a liquid crystal display device is already known. A planar light source used as a front light or a back light of this liquid crystal display device introduces light from a light source and an end surface facing the light source into the inside to diffuse the light, and reflects the light at a reflecting surface to reflect the reflected light. It is configured to have a light guide plate that projects to the outside, and a prism sheet that transmits the reflected light and projects it as projection light in the normal direction to irradiate a liquid crystal panel that is an illuminated object.

In a normal front light or backlight, a commercially available light guide plate or prism sheet is often used in combination, and the light guide plate and prism sheet are not necessarily the optimum combination. Often, the light projected from the LED, which is the light source, is not used to the maximum extent, and the amount of light that illuminates the illuminated object such as the liquid crystal panel with the planar light source is equal to that of the light projected from the LED that is the light source. Often only a part.

The present invention and the prior art will be described below by taking a backlight of a liquid crystal display device as an example. FIG. 4 is a sectional view schematically showing an outline of a backlight of a conventional liquid crystal display device. As shown in FIG. 4, in a backlight 20 of a conventional liquid crystal display device, light projected from a light source 21, such as an LED (light emitting diode), has an end face 22 a of a light guide plate 22 arranged to face the light source 21. Introduced internally from
The light that is repeatedly reflected and diffused inside the light guide plate 22 and is reflected by the reflection surface 22b on the lower surface of the light guide plate 22 and directed upward is projected from the upper surface 22c of the light guide plate 22 to the outside.

The light projected from the light guide plate 22 to the outside is refracted when it is received by the prism sheet 23 and becomes a light toward a liquid crystal panel (not shown), and is illuminated from the upper surface of the prism sheet 23 as illumination light. It is projected on the body (a liquid crystal panel (not shown)). The reflection sheet 24 disposed below the light guide plate 22 is for reflecting the light leaked from the lower surface of the light guide plate 22 and returning it to the light guide plate 22 again.

FIG. 5 is an explanatory view schematically showing the locus of light incident on the inside of the light guide plate. As shown in FIG. 5, a stepped prism or a V-groove prism (not shown) is formed as a reflecting surface 22b on the lower surface of the light guide plate 22, so that the light enters the light guide plate 22 from the end surface 22a. The light emitted from the light source 21 is reflected by the reflecting surface 22b, goes upward, is refracted by the upper surface 22c, and is reflected by a normal line perpendicular to the upper surface 22c of the light guide plate 22, as shown by a ray A in FIG. And is projected in a direction inclined by an angle θ. Then, this light is directed to the light guide plate 22 and the micro-prism 23a arranged downward of the prism sheet 23 (see FIG. 4).
When refracted, the light is refracted again and is projected as illumination light from the upper surface of the prism sheet 23 toward a liquid crystal panel (not shown) which is an illuminated object.

Here, the light beam B is the upper surface 22 of the light guide plate 22.
After being totally reflected by c, the reflecting surface 22 on the lower surface of the light guide plate 22 is again formed.
The light reflected by b is directed upward, and is refracted by the upper surface 22c to show the light projected from the upper surface 22c of the light guide plate 22.
Shows an example of light that is repeatedly reflected between the upper surface 22 c and the lower reflective surface 22 b of the light guide plate 22 and diffused inside the light guide plate 22. Further, in this embodiment, since the reflecting surface 22b of the stepped prism formed as the reflecting surface 22b on the lower surface of the light guide plate 22 is inclined, the angle of the reflected light becomes closer to a vertical angle each time it is reflected. The light having an angle projected from the upper surface 22c is projected upward from the upper surface 22c.

The angle θ of the light projected from the upper surface 22c of the light guide plate 22 toward the prism sheet 23 with respect to the normal line N is about 60 when the conventional light guide plate 22 is used. In this case, the apex angle of the micro prisms 23a of the prism sheet 23 is 60 ° to 63 °, as shown in an enlarged view on the upper side of FIG. .

FIG. 6 shows a computer simulation of the locus of light incident on the light guide plate when the apex angle of the micro prism is 60 °. When the trajectory of the light incident on the light guide plate 22 is simulated by a computer and drawn, as shown in FIG. 6, the apex angle of the micro prism is 60.
It was revealed that when the angle was °, the light was projected on the liquid crystal panel 25 as light in a direction slightly tilted to the left from the normal line perpendicular to the upper surface of the prism sheet 23. The light that passes through the liquid crystal panel 25 as the illumination light becomes a component in the normal direction of the light projected from the prism sheet 23 onto the liquid crystal panel 25. Therefore, from the result of simulation, the apex angle of the micro prism is set to 60 °. Therefore, the liquid crystal panel 2
The light projected on 5 is projected as light inclined by about 10 ° to 25 °, and as a result, about 1.5% to about 10% of the light projected from the prism sheet 23 is lost.

[0010]

SUMMARY OF THE INVENTION The present invention solves these problems of the prior art, and the light incident on the light guide plate, reflected by the lower reflecting surface and transmitted through the prism sheet is substantially parallel to the normal line. It is intended to provide a planar light source that illuminates an object to be illuminated, which is configured to be projected onto a prism. More specifically, the prism is incident on a light guide plate and reflected by a reflection surface on the lower surface. An object of the present invention is to provide a backlight of a liquid crystal display device in which light transmitted through a sheet is projected substantially parallel to a normal line to minimize light loss in a liquid crystal panel.

[0011]

SUMMARY OF THE INVENTION The present invention solves the problems of the prior art as described above, and introduces light from the light source and the end surface facing the light source into the inside, diffuses and reflects the light. A planar light source having a light guide plate that reflects light on a surface and projects reflected light to the outside, and a prism sheet that transmits the reflected light and projects it as projection light in a normal direction to illuminate an illuminated object The planar light source for illuminating an illuminated object is characterized in that the apex angle of the micro prism of the prism sheet is 65 ° to 75 ° and the micro prism is arranged downward. Here, it is preferable that the illuminated body is a liquid crystal panel and the planar light source is a backlight that illuminates the liquid crystal panel.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The details of the present invention will be described below with reference to the drawings illustrating an embodiment. FIG. 1 is a sectional view schematically showing an embodiment of a planar light source for illuminating an object to be illuminated according to the present invention, particularly a backlight of a liquid crystal display device. Here, the backlight 1 of the liquid crystal display device of the present invention is an LED.
The light guide plate 3 has a light source 2 formed of (light emitting diode) and the like, and the prism sheet 4 approaches the upper surface of the light guide plate 3 and
As in the prior art, the reflector 5 is arranged close to the lower surface.

As in the backlight of the conventional liquid crystal display device, the light projected from the light source 2 such as an LED (light emitting diode) is emitted from the end surface 3a of the light guide plate 3 arranged facing the light source 2. Just like the light guide plate 22 that is introduced inside and described as the prior art in FIG. 5, total reflection is repeatedly performed between the upper surface 3c and the lower reflection surface 3b of the light guide plate 3 and diffused inside the light guide plate 3. At the same time, the light reflected by the reflection surface 3b on the lower surface of the light guide plate 3 and having a more nearly vertical angle is refracted and projected from the light guide plate 3 to the outside, and refracted again by the microprisms 4a of the prism sheet 4 and the liquid crystal It is projected as illumination light toward a panel (not shown). In addition, the reflection sheet 5 arranged below the light guide plate 3
Is also for reflecting the light leaked from the lower surface of the light guide plate 3 and returning it to the light guide plate 3 again.

Here, in the planar light source for illuminating the object to be illuminated of the present invention, the apex angle of the microprisms 4a of the prism sheet 4 is 65 ° to 7 °, as shown in an enlarged view on the upper side of FIG.
It is formed at 5 ° and is arranged so that the micro prism 4a faces downward. And the micro prism 4a
By forming the apex angle of the prism sheet in this way, as shown in FIGS. 2 and 3, the illumination light projected from the prism sheet 4 to the liquid crystal panel 6 which is the illuminated object is reflected by the prism sheet 4.
The light can be almost perpendicular to the upper surface of the.

2 and 3 are diagrams in which the locus of light incident on the light guide plate 3 is simulated by a computer when the apex angles of the micro prisms are 65 ° and 70 °. As shown in the drawing, the illumination light projected from the prism sheet 4 onto the liquid crystal panel 6 which is the object to be illuminated is slightly tilted to the left in the embodiment of FIG. 2 in which the apex angle of the micro prism is 65 °, In the embodiment of FIG. 3 in which the apex angle of the micro prism is 70 °, the light tends to be tilted slightly to the right, but the light is almost perpendicular to the upper surface of the prism sheet 4. As is clear from the figure, this inclination angle is about 15 ° at the maximum, and the light transmitted through the liquid crystal panel 6 as the illumination light has a loss of 4% or less of the light projected from the prism sheet 4. be able to.

Further, according to the result of this simulation, it is clear that the optimum apex angle of the micro prism is between 65 ° and 70 °, and the apex angle is close to 70 °, and the apex angle is 70 °. By setting the angle in the range of 65 ° to 75 ° centered at, the loss of light that passes through the liquid crystal panel 6 as the illumination light can be reduced to a few percent or less, and can be reduced to a substantially negligible level.

As described above, the planar light source for illuminating the object to be illuminated according to the present invention, particularly the backlight of the liquid crystal display device as the embodiment, has an apex angle of the micro prism of the prism sheet of 65 ° to 75 °. The present invention is not limited to the method described in the above-mentioned embodiment, and various changes and improvements can be made without departing from the scope of the present invention. Of course you can.

[0018]

The surface light source for illuminating the object to be illuminated of the present invention,
In particular, the backlight of the liquid crystal display device as an example,
As described above, by setting the apex angle of the micro-prisms of the prism sheet to 65 ° to 75 °, the loss of light that passes through the liquid crystal panel as illumination light is reduced to such an extent that it can be substantially ignored. It is possible to provide a backlight of a liquid crystal display device in which light loss in the liquid crystal panel is minimized.

[Brief description of drawings]

FIG. 1 is a sectional view schematically showing an embodiment of a planar light source for illuminating an object to be illuminated of the present invention, particularly a backlight of a liquid crystal display device.

FIG. 2 is a diagram obtained by simulating with a computer the trajectory of light incident on a light guide plate when the apex angle of the micro prism is 65 °.

FIG. 3 is a computer simulation diagram of the trajectory of light incident on the light guide plate when the apex angle of the micro prism is 70 °.

FIG. 4 is a cross-sectional view schematically showing an outline of a backlight in a conventional liquid crystal display device.

FIG. 5 is an explanatory diagram schematically showing the locus of light incident on the inside of the light guide plate.

FIG. 6 is a diagram in which a computer simulates the locus of light incident on the light guide plate when the apex angle of the micro prism is 60 °.

[Explanation of symbols]

1 Backlight of liquid crystal display 2 light sources 3 Light guide plate 3a end face 3b Reflective surface 3c upper surface 4 prism sheet 4a Micro prism 5 Reflective sheet 6 LCD panel

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) G02F 1/1335 520 G02F 1/1335 520 1/13357 1/13357 G09F 9/00 324 G09F 9/00 324 336 336J // F21Y 101: 02 F21Y 101: 02

Claims (2)

[Claims] 1. A light source, a light guide plate for introducing and diffusing light from an end surface facing the light source, reflecting the light on a reflecting surface and projecting the reflected light to the outside, and transmitting the reflected light. And a prism sheet for illuminating an object to be illuminated by projecting light as projection light in a normal direction, the apex angle of the microprisms of the prism sheet is 65 °.
A planar light source for illuminating an object to be illuminated, characterized in that the micro-prism is arranged downward, at an angle of ˜75 °. 2. The planar light source for illuminating an illuminated object according to claim 1, wherein the illuminated object is a liquid crystal panel, and the planar light source is a backlight for illuminating the liquid crystal panel.