JPH11260132A - Surface light source device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the loss of light and to increase and unify the brightness by projecting a convex portion from an outer peripheral face of a light guide plate and mounting a reflector on the convex portion of the light guide plate. SOLUTION: An adhesion piece 44 of a reflecting face 28 is attached to a protrusion part 43 mounted on a corner at a side far from a light incidence end face 23 of a light guide plate 22 by a pressure sensitive adhesive double coated tape 29, on the occasion, the protrusion part 43 is located between the prism portions 32, and shaded by the adjacent prism 32, to reduce the loss of light. The protrusion part 43 is farthest from a point light source 25, and the possibility that the light is outgone to the outside from a light outgoing face by the time when the light reaches the protrusion part 43, is high, so that the loss of light can be further reduced by adhering the reflector 28 on this part. The adhesion piece 44 of the reflector 28 is also adhered to a protrusion part 42 mounted on a corner at the light incidence end face 23 side, but the protrusion part 42 is projected from the light incidence end face 23, so that the light of the point light source 25 does not reach the protrusion part 42 to prevent the loss of light.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001] The present invention relates to a surface light source device. Specifically, the present invention relates to a surface light source device used for a liquid crystal display device, a lighting device, and the like.

[0002]

2. Description of the Related Art (Conventional surface light source device using point light source) A conventional surface light source device 1 is shown in an exploded perspective view of FIG. 1 and a sectional view of FIG. The surface light source device 1 includes a light guide plate 2 for confining light, a light emitting unit 3 and a reflection plate 4.
The light guide plate 2 is formed of a transparent resin having a large refractive index such as a polycarbonate resin or a methacryl resin, and a large number of diffusion patterns 5 are formed on the lower surface of the light guide plate 2 by uneven processing, dot printing of diffuse reflection ink, or the like. ing. The light emitting unit 3 includes a plurality of light emitting diodes (LE
A light source 7 such as D) is mounted, and faces a side surface (light incident end surface 8) of the light guide plate 2. The reflection plate 4 is formed of, for example, a white resin sheet having a high reflectance, and has both sides adhered to the lower surface of the light guide plate 2 by a double-sided tape 9.

As shown in FIG. 2, the light f emitted from the light emitting section 3 and guided from the light incident end face 8 into the light guide plate 2 is totally reflected inside the light guide plate 2 so that 2 is trapped inside. When the light f inside the light guide plate 2 is incident on the diffusion pattern 5, the light f is diffusely reflected, and the light f reflected at an angle smaller than the critical angle of total reflection toward the light emission surface 10 is extracted to the outside from the light emission surface 10. . Further, the light f transmitted through a portion of the lower surface of the light guide plate 2 where the diffusion pattern 5 does not exist is reflected by the reflection plate 4 and returns to the inside of the light guide plate 2 again, so that loss of light amount from the lower surface of the light guide plate 2 is prevented.

In order to make the light emission luminance uniform over the entire light emitting area in such a surface light source device 1, as shown in FIG. 3A, light f incident on the light guide plate 2 from the light incident end face 8 is used. Needs to be scattered by the diffusion pattern 5 on the lower surface of the light guide plate 2 to uniformly scatter the light f over the entire light emission area. Therefore, when the diffusion pattern 5 is provided on the lower surface of the light guide plate 2, as shown in FIG. 3B, a part of the light f reflected by the diffusion pattern 5 is reflected toward the light emission surface 10 and The inclination and the inclination direction of the diffusion pattern 5 are varied so that a part of the light f emitted from the light source and reflected by the diffusion pattern 5 changes the light traveling direction in the light guide plate 2.

In the surface light source device 1 in which the diffusion pattern 5 is formed as described above, the light f inside the light guide plate 2 is diffused uniformly by repeating the scattering in the diffusion pattern 5, so that the light emitting portion In a region away from 3, the luminance distribution is relatively uniform. However, as shown in FIG. 4A, the light guide plate 2 shines brightly in the region A just before the point light source 7, and the light guide plate 2 becomes dark in the intermediate region B in front of the point light source 7 on the light incident end face 8 side. FIG. 4B shows a change in luminance near the light incident end face 8 along the line C1-C1 in FIG. 4A, and a direction parallel to the light incident end face 8 near the light emitting unit 3. Along with the variation in brightness is large,
The ratio of the luminance change may reach several times to several tens times.

As described above, the luminance in the intermediate area B in front of the point light source 7 is lower than the luminance in the area A immediately before the point light source 7 because:
This is because the amount of light guided to the intermediate area b in front of the point light source 7 is small. The reason why the amount of light guided to the intermediate area b in front of the point light source 7 is small is that the light f emitted from the point light source (light emitting diode) 7 is concentrated forward as shown in FIG.
The light f is refracted by the light incident end face 8 when the light f is incident on the light guide plate 2 and directed forward, and the effect of diffusing the light f in the width direction (point light source arrangement direction) by the diffusion pattern 5 near the light incident end face 8 is also provided. It is due to the fact that it is not sufficiently revealed.

Here, by increasing the diffusion effect of the diffusion pattern 5 in front of the point light source 7 and bending the light incident in front of the point light source 7 in the width direction, the luminance in the intermediate area b in front of the point light source 7 becomes At the same time, the amount of light going to the light emitting surface 10 in the region A immediately before the point light source 7 also increases, so that the luminance in the region A immediately before the point light source 7 also increases, and the luminance variation is not improved.

FIG. 4 (c) is a diagram showing the state of C2-- in FIG. 4 (a).
It shows a change in luminance in a region along the line C2 far from the light incident end face 8. On the side far from the light incident end face 8, the change in luminance is small and the uniformity of luminance is high, but the luminance sharply decreases at both ends. That is, the corner c of the light guide plate 2 opposite to the light incident end face 8 becomes dark. This is shown in FIG.
6 (a) except for the corner C on the line C2-C2.
As shown in FIG. 6, light f from the four point light sources 7 arrives, but as shown in FIG. 6B, two points located far from the corner C are reached to the corner C. This is because the light f from the light source 7 is hard to reach, so that the brightness decreases at the corner C and the image becomes dark.

In order to solve this problem and to make the luminance distribution at the position of the line C2-C2 uniform, the point light source 7 needs
The diffusion in the width direction by the diffusion pattern 5 may be increased before reaching the line, but if the diffusion by the diffusion pattern 5 is increased, the light f is emitted from the light exit surface 10 to the outside until the light reaches the C2-C2 line. The light f is emitted, and the leakage of the light f from both side surfaces of the light guide plate 2 increases, so that the light f reaching the position of the C2-C2 line decreases, and the entire position of the C2-C2 line becomes dark.

As described above, although the surface light source device is required to have a uniform luminance distribution, the surface light source device having a plurality of light sources has a problem in that the shape, density, diffusion effect, and the like of the diffusion pattern are reduced. Even if devised, it is difficult to make the luminance distribution uniform.

(Surface light source device using one point light source) On the other hand, a backlight type liquid crystal display device is thin and lightweight, so that it is a portable information terminal such as an electronic notebook, a portable personal computer, or a portable telephone such as a mobile phone. It is used as a display device for products with strong characteristics. In the case of using such a highly portable product, a long battery life is strongly demanded from the viewpoint of improving portability, and a backlight used in this display device is also required to have low power consumption. I have.

For this reason, a point light source (light emitting diode) of a surface light source device used as a backlight is used with high efficiency, and power consumption is reduced by reducing the number of point light sources used. Such a surface light source device 11
Ultimately, a small light source (light emitting diode) as shown in FIG. 7, that is, one point light source 7 is used.

However, when the number of point light sources is reduced in this manner, the luminance variation of the surface light source device increases,
For example, in the surface light source device 11 using one point light source 7, as shown in FIG. 7, the luminance is very large in the area A immediately before the point light source 7, and the luminance is It drops and darkens.

Therefore, in a surface light source device, particularly a surface light source device used as a backlight of a liquid crystal display device,
It is required that the number of point light sources used be as small as possible and that the uniformity of the luminance distribution be as high as possible.

[0015]

SUMMARY OF THE INVENTION (Prior Art Example) Therefore, the inventors of the present invention have developed a surface light source device capable of minimizing the number of point light sources used and increasing the uniformity of luminance distribution. (Hereinafter referred to as a prior art example). For example, like a surface light source device 21 shown in FIG. 8, a point light source 25 such as an LED (in this specification, the light incident end surface 23 is located at the center of one end surface (light incident end surface 23) of the light guide plate 22. A light source smaller than the width is referred to as a point light source), and a large number of diffusion patterns 24 are provided in order to make the luminance on the light emitting surface 26 (see FIG. 9) uniform.
Are provided on the lower surface of the light guide plate 22, a reflective plate is overlapped on the lower surface of the light guide plate 22, and a semi-transmissive plate 27 is overlapped on the light emitting surface 26. The diffusion patterns 24 are arranged radially around the point light source 25 over the entire lower surface of the light guide plate 22.

The pitch between the diffusion patterns 24 decreases as the distance from the point light source 25 increases, and the density of the diffusion patterns gradually increases as the distance from the point light source 25 increases. This is because, as the distance from the point light source 25 increases, the amount of the light f gradually emitted from the light exit surface 26 and reaches the point light source 25 decreases, and the spread of the light f increases as the distance from the point light source 25 increases. The probability that the light f is reflected toward the light exit surface 26 increases with the distance because the light f becomes weaker as the distance increases. That is, since the light intensity is high in the area near the point light source 25, the diffusion pattern 24 having the same cross-sectional shape is formed with a small pattern density as shown in FIG. FIG. 9
As shown in (1), a light guide plate 22 having a uniform luminance is realized by forming a diffusion pattern 24 having the same cross-sectional shape with a large pattern density.

However, such a surface light source device 21
In this case, a light amount loss occurs due to leakage of light from the outer peripheral surface of the light guide plate 22, which causes a decrease in luminance.
As a device capable of preventing light from leaking from the outer peripheral surface of the light guide plate 22, a surface light source device 31 as shown in FIG. 11 has been proposed.

In the surface light source device 31, the light guide plate 2
A plurality of prism portions 32 are formed on the three outer peripheral surfaces of 2, respectively. As shown in FIG.
The sides 33a and 33b are composed of two sides 33a and 33
b is approximately 45 with respect to the direction of the point light source 25.
It has a degree inclination κ and forms an angle of about 90 degrees with each other.

Thus, as shown in FIG.
The light f emitted from the light source 5 and reaching the outer peripheral surface inside the light guide plate 22 is totally reflected twice by the prism part 32 and is returned and reflected in the original direction. Therefore, light does not leak from the outer peripheral surface of the light guide plate 22 to cause loss, and the brightness of the light guide plate 22 can be increased.

When a linear light source is used, light enters the prism section 32 from various directions.
2 cannot be expected to have the effect of totally reflecting the light and preventing the light from leaking to the outside. However, when the point light sources 25 are used, the prism units 32 have the point light sources 25 from a certain direction.
, The light from the point light source 25 can be efficiently totally reflected so as not to leak to the outside.

However, the reflecting plate 28 for reflecting the light leaking from the lower surface of the light guide plate 22 to the light guide plate 22 is provided in FIG.
As shown in (a), both sides are adhered to the lower surface of the light guide plate 22 by the double-sided tape 29. Therefore, in such an improved prior art example, as shown in FIGS. 13A and 13B, the light f confined in the light guide plate 22 is scattered when the light f hits the double-sided tape 29, and the light f Despite the provision of the prism portion 32, there is an inconvenience that the light f does not return from the outer peripheral surface of the light guide plate 22 toward the light source.

The present invention has been made in view of the above-mentioned prior art example, and an object of the present invention is to suppress a loss of light by optimizing a position where a reflection plate is attached to a light guide plate. An object of the present invention is to achieve high brightness and uniformity of a surface light source device.

[0023]

According to a first aspect of the present invention, there is provided a surface light source device, comprising: a light source; a light guide plate for introducing light from the light source from a light incident surface and confining the light therein to emit from a light exit surface; And a reflector installed on the surface to be provided, in a surface light source device having a prism portion having an apex angle of about 90 degrees on the outer peripheral surface of the light guide plate, the convex portion protrudes from the outer peripheral surface of the light guide plate,
It is characterized in that the reflection plate is attached to a convex portion of the light guide plate.

In the surface light source device according to the first aspect,
Since the reflection plate is attached by the convex portion provided on the light guide plate, the prism portion is hardly affected by the attachment of the reflection plate. Therefore, loss of light can be suppressed, and high brightness and uniformity of the surface light source device can be achieved.

According to a second aspect of the present invention, there is provided a surface light source device comprising: a light source;
A surface light source device comprising: a light guide plate for introducing light from the light source from a light incident surface and confining the light from the light incident surface and emitting the light from a light emission surface; and a reflector provided on a surface facing the light guide plate. A through hole is formed in a part of the light plate, and a prism portion having an apex angle of about 90 degrees is provided at an edge of the through hole on the light source side,
The light guide plate is characterized in that the reflector is attached to a portion of the light guide plate which is shaded by the through hole when viewed from the light source.

In the surface light source device according to the second aspect,
Since the reflector is attached to the light guide plate behind the prism provided at the edge of the through hole, the prism is not affected by the attachment of the reflector. Therefore, loss of light can be suppressed, and high brightness and uniformity of the surface light source device can be achieved.

According to a third aspect of the present invention, there is provided a surface light source device comprising: a light source;
A light guide plate that emits light from the light exit surface by diffusing and reflecting the light from the light source from the light incident surface through the light incident surface and diffusing and reflecting the light with a diffusion pattern, and a reflector plate provided on a surface facing the light guide plate. A surface light source device provided with a prism portion having an apex angle of approximately 90 degrees on an outer peripheral surface of the light guide plate, wherein a straight line connecting the light source and the light incident surface side end of the diffusion pattern forming region of the light guide plate is used. This is characterized in that the reflection plate is attached to a region on the light incident surface side.

According to a third aspect of the present invention, in the surface light source device, the reflector is attached to the light guide plate in a region closer to the light incident surface than a straight line connecting the light source and the end of the diffusion pattern forming region on the light incident surface side. . Since the light reflected by the diffusion pattern hardly reaches this region, there is little possibility that the prism portion is affected by the attachment of the reflection plate. Therefore, the loss of light is suppressed,
High brightness and uniformity of the surface light source device can be achieved.

[0029]

(First Embodiment) FIG. 14 is a plan view showing a surface light source device 41 according to one embodiment of the present invention. Even in the surface light source device 41, the light guide plate 22 formed of polycarbonate resin, methacrylic resin, or the like is used.
A point light source 25 such as a light emitting diode is disposed at the center of the light incident end face 23 of the light guide plate 23. On the lower surface of the light guide plate 22, a diffusion pattern (not shown: see FIG. ) Are arranged. Further, on the outer peripheral surface of the light guide plate 22, there are provided a large number of prism portions 32 having a vertex angle of about 45 degrees for returning the light from the point light source 25 to the original direction (see FIG. 12). Further, from the four corners of the light guide plate 22, convex portions 42 and 43 each having a substantially rectangular shape are bulged.
Reflecting plate 28 formed of a white resin sheet or the like
Are formed in a rectangular shape slightly smaller than the light guide plate 22 so as not to cover the prism part 32, as shown in FIGS. 14 and 15, and the projections 42,
An adhesive piece 44 is extended so as to overlap the lower surface 43.
The reflection plate 28 is disposed so as to face the lower surface of the light guide plate 22, and the adhesive pieces 44 at the four corners are connected to the projections 42 of the light guide plate 22.
The lower surface 43 is adhered with a double-sided tape 29.

The convex portion 43 provided at the corner of the light guide plate 22 farther from the light incident end face 23 has a double-sided tape 29.
Although the adhesive piece 44 of the reflection plate 28 is adhered by this, the convex portion 43 is located between the prism portions 32 and, as shown in FIG. Light loss is reduced. In addition, since the convex portion 43 is farthest from the point light source 25 and the probability that the light f is emitted to the outside from the light emitting surface before reaching the convex portion 43 is high, the reflecting plate 28 should be bonded at this portion. Thus, light loss can be reduced. The adhesive piece 44 of the reflector 28 is also adhered to the convex portion 42 provided at the corner on the light incident end face 23 side.
Is protruded from the light incident end face 23, so that the light of the point light source 25 does not reach here, and therefore, no light loss occurs. Therefore, loss of light due to scattering by the double-sided tape 29 to which the reflection plate 28 is attached can be reduced, and a decrease in luminance of the surface light source device 41 can be suppressed. However, when the reflection plate 28 overlaps below the point light source 25, light leaking downward between the point light source 25 and the light incident end face 23 is reflected by the reflection plate 28 and leaks upward, and becomes partially bright. The reflection plate 28 does not fall below the point light source 25.

The reflecting plate 28 shown in FIG.
17, the reflection plate 28 may be cut along the contour of the prism portion 32 to have the same shape as the light guide plate 22, as in the reflection plate 28 shown in FIG. However, also in this case, the reflection plate 28 is set so as not to extend below the point light source 25.

(Second Embodiment) In a surface light source device 45 of this embodiment, as shown in FIG. 18, no projection 42 is provided on the light incident end face 23 side, and the point light source 25 and the diffusion pattern forming area 46 are formed. In a region closer to the light incident end face 23 than a straight line 47 connecting the ends on the light incident end face 23 side, the reflecting plate 28 is attached to the lower surface of the light guide plate 22 with a double-sided tape 29. Since the light of the point light source 25 hardly reaches this attachment position, the reflection of the light by the prism portion 32 is not hindered.

(Third Embodiment) FIG. 19 is a plan view showing a surface light source device 48 according to still another embodiment of the present invention. In this embodiment, a through-hole 49 is formed in the edge of the light guide plate 22 farther from the light incident end face 23, and the edge of the through-hole 49 closer to the point light source 25 has an apex angle of approximately 90 degrees. A prism portion 50 is provided, and a reflection plate 28 is adhered to the light guide plate 22 by a double-sided tape 29 in a portion that is shaded by the through hole 49 when viewed from the point light source 25. When the reflecting plate 28 is stuck behind the prism portion 32 in this manner, the reflection of the light by the prism portion 50 is not hindered by the sticking of the reflecting plate 28, and the brightness distribution can be kept uniform.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view showing a conventional surface light source device.

FIG. 2 is a schematic sectional view of the above surface light source device.

FIGS. 3 (a) and 3 (b) are views for explaining the operation of the above surface light source device.

4A is a diagram illustrating a problem of the surface light source device according to the first embodiment, FIG. 4B is a diagram illustrating a change in luminance along a line C1-C1 in FIG. 4A, and FIG. FIG. 7 is a diagram showing a change in luminance along the line C2-C2 of FIG.

FIG. 5 is a diagram illustrating the reason why the problem of the surface light source device occurs.

FIGS. 6A and 6B are diagrams for explaining the reason why the problem of the surface light source device occurs.

FIG. 7 is a diagram showing a surface light source device using one point light source.

FIG. 8 is a diagram showing a diffusion pattern of a light guide plate used in a prior art example.

FIG. 9 is a diagram showing a cross section of the light guide plate of the above light guide plate in a region far from the point light source and the behavior of light there.

FIG. 10 is a diagram showing a cross section in a region near the point light source of the above light guide plate and a behavior of light there.

FIG. 11 is a plan view showing an improved prior art example.

FIG. 12 is an operation explanatory view of the prior art example.

FIGS. 13 (a) and 13 (b) are a plan view and an enlarged cross-sectional view, respectively, showing a part of the prior art example.

FIG. 14 is a plan view showing a surface light source device according to an embodiment of the present invention.

FIG. 15 is a plan view showing a reflector used in the surface light source device of the above.

FIG. 16 is an operation explanatory view of the above surface light source device.

FIG. 17 is a plan view showing another embodiment of the reflection plate.

FIG. 18 is a plan view showing a surface light source device according to still another embodiment of the present invention.

FIG. 19 is a plan view showing a surface light source device according to still another embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 22 light guide plate 23 light incident end surface 24 diffusion pattern 25 point light source 26 light emission surface 28 reflection plate 29 double-sided tape 32, 50 prism portion 42, 43 convex portion 46 diffusion pattern formation region 49 through hole

Claims (3)

[Claims] 1. A light source comprising: a light source; a light guide plate for introducing light from the light source from a light incident surface and confining the light from the light incident surface and emitting the light from a light emitting surface; and a reflecting plate provided on a surface facing the light guide plate. In a surface light source device provided with a prism portion having an apex angle of about 90 degrees on an outer peripheral surface of the light guide plate, a convex portion is projected from the outer peripheral surface of the light guide plate, and the reflection plate is attached to the convex portion of the light guide plate. A surface light source device characterized by the above-mentioned. 2. A light source comprising: a light source; a light guide plate for introducing light from the light source from a light incident surface to confine the light from the light incident surface and emitting the light from a light emitting surface; and a reflecting plate provided on a surface facing the light guide plate. In the surface light source device, a through hole is formed in a part of the light guide plate, and a prism portion having an apex angle of about 90 degrees is provided at an edge of the through hole on the light source side, and the light guide plate is viewed from the light source. A surface light source device, wherein the reflection plate is attached to a portion that is shaded by a through hole. 3. A light source, a light guide plate for introducing light from the light source from a light incident surface, confining the light inside, and diffusing and reflecting the light from a light emitting surface through a diffusion pattern, and a surface facing the light guide plate. A light source provided in the light guide plate, wherein the light guide plate has a prism portion having an apex angle of approximately 90 degrees on an outer peripheral surface of the light guide plate. In the area closer to the light incident surface than the straight line connecting the surface side ends,
A surface light source device, wherein the reflection plate is attached.