JP2003162916A - Planar light source device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a planar light source device prevented unevenness of brightness and loss of light even if a point light source is used. <P>SOLUTION: A stick 30 is placed between a light guide 2 and point light sources 1a and 1b. These point light sources 1a and 1b are opposed to the planes of incidence 301a and 301b, respectively, so that their light axes 5a and 5b cross each other. The light beams from the point light sources 1a and 1b enter the light guide 2 at the plane of incidence 21 through the stick 30 and are reflected at the backside of the light guide 2 and emitted at the light emission face. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a light source having a plurality of L's.
The present invention relates to a surface light source device mainly using a back light or a front light of a liquid crystal display panel using an ED (light emitting diode).

[0002]

2. Description of the Related Art As a surface light source device for a backlight or front light of a liquid crystal display panel used for a liquid crystal display device, an edge light type device using a transparent flat plate as a light guide is known. The liquid crystal display device includes a transmissive type and a reflective type, and the transmissive liquid crystal display device is provided with a backlight which is an illuminating device that illuminates the liquid crystal display panel from the back surface. On the other hand, the reflection type liquid crystal display device is provided with an illuminating device for illuminating the liquid crystal display panel from the surface, a so-called front light.

Further, in the light guide used in the above edge light type surface light source device, light incident from an incident surface which is a side end surface of the light guide is refracted or reflected by the shape of the light guide, and the light is guided to the incident surface. Light is emitted from the emission surface by being evenly dispersed on the emission surface having a relatively large area and being approximately vertical.

In recent years, portable electronic devices, downsizing, low power consumption, and the like have been demanded. Therefore, as the edge light type surface light source device, a light emitting diode (LED), which consumes less power than a conventional cold cathode tube lamp, has been noticed and put into practical use. However, since each LED has a smaller amount of emitted light than the conventional cold cathode fluorescent lamp and the like, a plurality of LEDs are used for one surface light source device. A conventional surface light source device using LEDs will be described with reference to the drawings.

FIG. 5 is a schematic plan view showing a schematic structure of a conventional backlight surface light source device. FIG. 5 shows a state as viewed from the light emitting surface side of the light guide 2. This surface light source device includes LEDs 1e and 1f which are point light sources,
These LEDs 1e and 1f are arranged so as to face an incident surface 21 provided at one edge portion of the light guide 2. That is,
Light extension of LEDs 1e and 1f Optical axes 5e and 5 extending upward
Put each LED 1e, 1f into the light emitting surface 1 so that f becomes parallel.
1e and 11f are arranged on the same straight line. In the figure, the arrows on the optical axes 5e and 5f indicate the LEDs.
The traveling direction of each light emitted from 1e and 1f is shown. The light emitted from the LEDs 1e and 1f is emitted from the light emitting surfaces 11e and 11f of the LEDs 1e and 1f, respectively, and is incident on the incident surface 21 (edge portion) of the light guide 2.

Then, the light incident from the incident surface 21 of the light guide 2 is uniformly propagated throughout the light guide 2, and a part of the propagated light is reflected on the back surface of the light guide 2. (Not shown) forms diffuse reflected light, which is emitted as diffused light from the exit surface of the light guide 2 (the surface side of the paper in FIG. 5).

The edge light type light guide 2 used as a light source of a liquid crystal display panel is widely used because the thickness of the light guide 2 can be reduced and the structure can be simplified.

By the way, the two LEDs 1e and 1f are arranged in parallel and adjacent to the incident surface 21 of the light guide 2e.
Therefore, in the conventional surface light source device, as shown by the broken lines in FIG. 5, bright regions 7e and 7f of the light incident on the light guide 2 from the LEDs 1e and 1f, and these regions 7e and 7f.
A dark area 22 of light, which is indicated by a diagonal line, is present between. In particular, the closer the light guide body 2 is to the entrance surface 21, the darker the dark area 22 becomes, and the darker the light exit area 8 becomes, the more uneven the brightness is.

Therefore, in order to eliminate the uneven brightness in FIG. 5, there has been proposed a surface light source device provided with means for reflecting the light from the point light source and converting it into a linear light source. Figure 6
It is a schematic plan view which shows the schematic structure of the conventional surface light source device comprised so that the light from a point light source may be reflected and changed into a linear light source.

This surface light source device is, as shown in FIG.
A second light guide body called a rod-shaped light guide body 31 is arranged on the incident surface 21 side of the light guide body 2. The rod-shaped light guide 31 is usually in the shape of a quadrangular prism, and the incident surfaces 311g and 311h arranged at both ends of the rod-shaped light guide 31 in the long axis direction.
The light incident from the bottom surface 314 of the rod-shaped light guide 31 is
Alternatively, the light is reflected by the back surface 313 facing the emission surface 312.
That is, the rod-shaped light guide 31 includes the LEDs 1e, 1f.
It is possible to convert the point light source into a linear light source by uniformly and separately emitting the light from the output surface 312.

As shown in FIG. 6, in the rod-shaped light guide 31, LEDs 1g and 1h, which are point light sources, are arranged near both ends in the long axis direction, and these LEDs 1g and 1h are arranged.
Can be emitted as linear light from the emission surface 312 that is substantially perpendicular to the incident end faces 311g and 311h. Specifically, the light beams 6g10 and 6h10 vertically emitted from the LEDs 1g and 1h, which are light sources, are emitted from the rod-shaped light guide 31.
The light rays 6g1 traveling toward the incident surface 21 of the light guide 2 are largely changed by being reflected by the fine concavo-convex shape provided on the bottom side surface 314 (the surface parallel to the paper surface in FIG. 6).
1 and 6h11.

Further, the light rays 6g20, 6h20 obliquely emitted from the respective LEDs 1e, 1f into the rod-shaped light guide 31 are reflected by the fine irregular shapes provided on the back surface 313 inside the rod-shaped light guide 31 to make it large. The directions are changed so that the light beams 6g21 and 6h21 are directed toward the light guide 2. In this way, the directions of the light rays from the LEDs 1e and 1f are largely changed within the rod-shaped light guide 31, and the emission surface 31 of the rod-shaped light guide 31 is changed.
The light is linearly dispersed and emitted from 2 to enter the light guide 2. Note that, in FIG. 6, the fine concavo-convex shape serving as the reflecting surface provided on the bottom side surface 314 (surface parallel to the paper surface) and the back surface 313 of the rod-shaped light guide 31 is omitted.

Therefore, in the conventional surface light source device as shown in FIG. 6, the light regions 7g and 7h from the LEDs 1e and 1f are dispersed and spread, but as described above, they are emitted from the light source. The light guide 31
Therefore, there is a problem that the loss of light is large as compared with the surface light source device in which the light from the light source is directly incident on the light guide.

[0014]

In a surface light source device using LEDs as a light source, a plurality of LEDs, which are light sources, are
When the light guides are arranged side by side so that their optical axes extending in the vertical direction are parallel to each other, the adjacent L on the side closer to the incident surface of the light guide body.
There is a problem in that there is a difference in brightness between the extension portions of the ED and the extension portions between the LEDs, and unevenness in the brightness of the image is noticeable.

Further, in a surface light source device in which a rod-shaped light guide is used and LEDs are arranged on both ends of the rod-shaped light guide in the long axis direction, the direction of the light beam emitted from the LED is directed inside the rod-shaped light guide. Make a big change. Therefore, there is a drawback that the loss of light becomes large.

An object of the present invention is to solve the problems of the uneven brightness and the loss of light, which are the problems of the above-mentioned prior art, and to provide a bright surface light source device with less uneven brightness.

[0017]

SUMMARY OF THE INVENTION The present invention is a surface light source device comprising a plurality of point light sources, and a light guide body which allows light from the point light sources to enter from an incident surface and to exit from an outgoing surface.
A plurality of the point light sources are arranged on the incident surface side of the light guide so that the optical axes of at least two of the point light sources intersect with each other.

According to the above arrangement, the optical axes of the plurality of point light sources intersect. Therefore, as compared with the case where the optical axes of a plurality of point light sources are made parallel, the bright region of the light incident on the light guide from the point light sources comes closer to the incident surface side of the light guide, and the light guide It is possible to reduce the dark region of light formed on the side close to the incident surface, and as a result, it is possible to obtain a surface light source device with less uneven brightness.

Further, according to the present invention, a second light guide is disposed between the incident surface of the light guide and the plurality of point light sources, and the second light guide faces the point light sources. A light incident surface is provided, and the tangential directions of at least two light incident surfaces may intersect.

Further, according to the present invention, an incident surface of the light guide may be formed so as to face the point light source, and tangential directions of at least two incident surfaces may intersect.

According to the above structure, a second light guide or the like for changing the light from the point light source to enter the light guide is provided between the point light source and the light guide. It is not necessary to provide the surface light source device in which the light guide body and the second light guide body can be integrated and the luminance unevenness is small.

Further, according to the present invention, light diffusing means for diffusing the light from the point light source may be provided in at least a portion of the incident surface where the light is incident from the point light source.

According to the above construction, the light diffusing means such as the concave-convex shape and the arcuate concave portion can diffuse the traveling direction of the light from the light source and widen the traveling direction of the light to enter the light guide. Therefore, it is possible to more efficiently reduce the dark area.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic plan view showing a first embodiment utilizing the present invention and showing a schematic configuration of a surface light source device used as a backlight. This FIG. 1 shows a point light source L as seen from the incident surface side of the light guide 2.
The arrangement configuration of the EDs 1a and 1b, the light guide 2, and the second light guide (stick) 30 is shown. LED1a,
For 1b, a white light emitting diode or the like is used.

The light guide 2 is constructed in the same manner as the above-mentioned conventional example, and is composed of a planar light guide made of a translucent thermoplastic resin such as an acrylic resin or a polycarbonate resin having a wedge-shaped cross section. It The light incident from the incident surface 21 of the light guide 2 is uniformly propagated throughout the light guide 2, and a part of the propagated light is reflected by a light reflection member (not shown) on the back surface of the light guide 2. The diffused reflected light is emitted as diffused light from the exit surface of the light guide 2 (the surface side of the paper in FIG. 1). Reflecting members (not shown) are provided on the three side surfaces of the light guide body 2 other than the light incident surface 21 to prevent light from leaking from the outer peripheral surface of the light guide body 2.

The stick 30 is made of a light guide body made of a transparent thermoplastic resin such as an acrylic resin or a polycarbonate resin, like the light guide body 2.

In the above surface light source device, as shown in FIG.
The two LEDs 1a and 1b, which are light sources, are arranged so as to face the incident surfaces 301a and 301b of the stick 30, respectively.
Further, the LE is set so that the optical axes 5a and 5b are intersected with each other.
D1a and 1b are not parallel but are arranged at an appropriate angle.

Then, as shown in FIG. 1, in the present invention,
A stick 30 is provided between the light guide 2 and the LEDs 1a and 1b. The stick 30 is different from the rectangular prism shape, and is formed in a mountain shape in which the incident surfaces 301a and 301b of the stick facing the incident surfaces 11a and 11b of the LEDs 1a and 1b form an angle. Therefore, the LED
The main light rays emitted from 1a and 1b can be directly incident on the light guide 2 through the stick 30 without largely changing the direction due to reflection or the like in the stick 30.

The light from the LEDs 1a, 1b is emitted from the emission surfaces 11a, 11b of the LEDs 1a, 1b, passes through the incident surfaces 301a, 301b of the stick 30 inside the stick 30, and is incident on the light guide 2. It is incident on the surface 21.

In FIG. 1, the arrows on the optical axes 5a and 5b extending in the vertical direction of the LEDs 1a and 1b indicate the traveling directions of the light emitted from the light source. The light incident from the incident surface 21 of the light guide 2 is reflected by the reflection member or the light reflection surface and propagated uniformly throughout the entire light guide 2, and the light exit surface of the light guide 2 (in FIG. 1). Emits diffused light from the front side of the paper.

Further, in FIG. 1, each LED 1a, 1b is
The bright areas of the emitted light of are the broken lines 7a,
7b, a dark area 20 of light is shown in the shaded portion on the incident surface 21 side of the light guide 2. The dark area 20 of the present embodiment is much smaller than the dark area 22 of the conventional surface light source device in which the optical axes of the LEDs are arranged in parallel as described in FIG. 5, for example. ing.

As described above, the optical axes 5 of the LEDs 1a and 1b are
Since a and 5b intersect as shown in FIG.
As compared with the conventional surface light source device in which the light sources are opposed to each other, it is possible to reduce changes in the direction of light rays from the point light source, reflection, and the like, and it is possible to efficiently suppress light loss. Further, in the present embodiment, the area 20 where the light is dark can be reduced as compared with the conventional surface light source device, and as a result, the surface light source device with less uneven brightness can be obtained. Incidentally, 23 is a central axis of the light guide 2.

FIG. 2 is a schematic plan view showing a schematic structure of a surface light source device according to the second embodiment of the present invention. In practice,
When the light from the LEDs 1a and 1b is incident on the light guide 2 from the stick 30, it is preferable that the light be spread to some extent. In the present embodiment, as shown in FIG. 2, a light diffusing unit for diffusing light is provided at the light incident portion on the light incident surfaces 301a and 301b side of the stick 30. In this embodiment, minute concavo-convex shapes 303a and 303b are provided as light diffusing means. As shown in FIG. 2, the uneven shapes 303a and 303b are
It can be formed by silk printing or a method of forming grain dots, and the uneven shapes 303a and 303b can be formed.
Can be a V-shaped groove.

Then, when the light from the LEDs 1a, 1b is incident on the stick 30, the uneven shapes 303a, 3b are formed.
By scattering the light on the surface of 03b, it is possible to spread the traveling direction of the light and make it enter the stick 30. As a result, brighter areas 7a, 7 of the light emitted by the LEDs 1a, 1b shown by the broken lines than in the first embodiment are obtained.
As b expands, the dark area 20 of light on the incident surface 21 side of the light guide 2 shown by the hatched portion becomes smaller.

Therefore, in this embodiment, the dark area 20 of light can be reduced as compared with the first embodiment, and as a result, a bright surface light source device with less uneven brightness can be obtained more efficiently. .

FIG. 3 is a schematic plan view showing a schematic configuration of a surface light source device according to the third embodiment of the present invention. In the present embodiment, as shown in FIG. 3, in the vicinity of the incident portion of the stick 30, an arc-shaped concave portion 30 as a light diffusing means.
4a and 304b are provided. These recesses 304a, 30
4b does not require the roughening process called the embossing process used in the second embodiment. Therefore, there are advantages that the processing means becomes easier and the processing cost can be saved.

Then, these recesses 304a, 304b
Is a concave lens effect that refracts the traveling direction of light from the LEDs 1a, 1b at the recesses 304a, 304b.
The advancing direction of light can be expanded and made to enter the stick 30. Therefore, the light is transmitted from the stick 30 to the light guide 2
It becomes possible to effectively spread the light when it is incident on. The shape of the recess is not limited to the above-mentioned arc shape, and may be any shape that has a concave lens effect and diffuses light. In the first to third embodiments described above, in order to spread the light beam from the point light source, it is possible to provide the emitting surface 302 of the stick 30 with a minute uneven shape.

FIG. 4 is a sectional view showing a fourth embodiment of the present invention and showing a schematic structure of a surface light source device utilizing the present invention. In this embodiment, the planar light guide 4 in which the stick 30 and the light guide 2 in the configuration of FIG.
Are arranged. Then, as in FIG. 3 above, each LED
Incident surfaces 41c and 41d of the light guide 4 facing 1c and 1d
Is a mountain shape with an appropriate angle. With this, each L
The EDs 1c and 1d are arranged so that the optical axes 5c and 5d extending in the light extension direction intersect.

According to this structure, it is not necessary to separately provide a stick for changing the light from the point light source and making it enter the light guide body, and the light guide body and the stick can be integrated. Therefore, by using the planar light guide 4, it is possible to prevent the light from the LEDs 1c and 1d incident on the stick from being emitted from the stick and re-entering the light guide, as compared with the configuration of FIG. Since it can be omitted, the light loss is reduced, and a bright surface light source device that illuminates an image with more uniform brightness can be obtained. Needless to say, the configuration of the planar light guide according to this embodiment can be applied to the first and second embodiments.

Also in this embodiment, the incident surface 4 of the light guide 4 is
It is possible to reduce the dark area of light formed on the side close to 1c and 41d, and to obtain a surface light source device with less uneven brightness.

Further, in each of the above embodiments, each LED 1
Since the bright regions 7a and 7b of the light from a and 1b overlap near the center line 22 of the light guide 2, the center of the light guide 2 becomes bright. Therefore, it becomes easy to provide a surface light source device that attaches importance to the brightness of the central portion of the image.

Although the surface light source device of the above-described embodiment is used for the backlight of the transmissive liquid crystal panel, it goes without saying that the present invention can be applied to the front light of the reflective liquid crystal display device.

Further, by using the surface light source device of the above-mentioned embodiment and the liquid crystal panel and applying the light emitted from the light guide to the liquid crystal panel, a display device including a transmissive liquid crystal display device or a reflective liquid crystal display device is provided. Can be configured. Further, the surface light source device of the present invention is not limited to the number of LEDs being two, and may be two or more, such as three or four, of which at least two or more are used. It suffices that the optical axes of the LEDs of (3) intersect.

[0044]

As described above, in the surface light source device of the present invention, by arranging each point light source so that the optical axes of the point light sources intersect, the surface light source device in which the optical axes of the point light sources are parallel to each other. Compared with the above, the dark area of light decreases as the bright area of the light guide approaches the incident surface. Therefore, according to the present invention, it is possible to provide a surface light source device in which the brightness of the screen is less uneven and the light is bright. Further, since the optical axes of the point light sources intersect, the central region of the light guide becomes bright, and it is possible to provide a surface light source device that places importance on the brightness of the central portion of the image.

[Brief description of drawings]

FIG. 1 is a schematic plan view showing a schematic configuration of a surface light source device according to the present invention.

FIG. 2 is a schematic plan view showing a schematic configuration of a surface light source device according to the present invention.

FIG. 3 is a schematic plan view showing a schematic configuration of a surface light source device according to the present invention.

FIG. 4 is a schematic plan view showing a schematic configuration of a surface light source device according to the present invention.

FIG. 5 is a schematic plan view showing a schematic configuration of a conventional surface light source device.

FIG. 6 is a schematic plan view showing a schematic configuration of a conventional surface light source device according to another example.

[Explanation of symbols]

1a LED (light emitting diode) 2 Light guide 3 sticks 4 Light guide 5a optical axis

Claims (4)

[Claims] 1. A surface light source device, comprising: a plurality of point light sources; and a light guide body that allows light from the point light sources to enter through an incident surface and exit through an exit surface, wherein at least two of the point light sources are provided. A surface light source device, wherein a plurality of the point light sources are arranged on an incident surface side of the light guide so that optical axes intersect with each other. 2. A second light guide is disposed between an incident surface of the light guide and a plurality of the point light sources, and light incident on the second light guide faces the point light sources, respectively. The surface light source device according to claim 1, wherein a surface is provided, and the tangential directions of at least two incident surfaces intersect each other. 3. The incident surface of the light guide is formed so as to face each of the point light sources, and the tangential directions of at least two incident surfaces intersect each other. The surface light source device according to. 4. The light diffusing means for diffusing light from the point light source is provided in at least a portion of the incident surface on which light is incident from the point light source. The surface light source device according to any one of claims.