JPH11232918A - Surface light source device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the nonuniformity of a luminance caused by the total reflection of light in a light guide plate through the edge of the light guide plate. SOLUTION: Among the bottom face of a light guide plate 42, a diffusion pattern 46 for irradiating light from a light-irradiating face in uniform luminance is provided in an effective area 58 (for example, an area corresponding to the screen of a liquid crystal display panel). A scattering pattern 63 is provided in a non-effective area 59 (for example, an area outside the screen of the liquid crystal display panel), so that the light entering the non-effective area 59 is prevented from being regularly reflected again onto the effective area 58.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[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.

However, in such a surface light source device 1, even if a diffusion pattern is arranged so as to make the luminance distribution uniform, as shown in FIG. The light guide plate 2 glows brightly in the region b, 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. 3B shows a change in luminance near the light incident end face 8 along the line C1-C1 in FIG. 3A, and a direction parallel to the light incident end face 8 near the light emitting section 3. And the variation of the luminance is several times higher
In some cases, it can be ten times larger.

FIG. 3 (c) is a diagram showing the C2-
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.

Accordingly, although the surface light source device is required to have a uniform luminance distribution, in the surface light source device having a plurality of light sources, even if the shape, density, diffusion effect and the like of the diffusion pattern are devised. It has been 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 phone 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 also highly efficient, and power consumption is reduced by reducing the number of point light sources used. Such a surface light source device 11
Ultimately, a single point light source 7 (light emitting diode) as shown in FIG. 4 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. 4, the luminance is very large in the area B immediately before the point light source 7, and the luminance is high in the four corners C of the light guide plate 2. 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.

[0011]

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). In this surface light source device 21, for example, as shown in FIG. 5, a point light source 24 such as an LED is arranged at the center of one end surface (light incident end surface 23) of a light guide plate 22, and the luminance on a light emitting surface 25 is made uniform. For this purpose, a large number of diffusion patterns 26 are provided on the lower surface of the light guide plate 22. These diffusion patterns 26 are formed on the light guide plate 2 around the point light source 21.
4 are radially arranged on the entire lower surface of the light source 4 and do not have a light diffusion function in a circumferential direction around the point light source 24.

The pitch of each of the diffusion patterns 26 decreases as the distance from the point light source 24 increases, and the density of the diffusion patterns gradually increases as the distance from the point light source 24 increases. This is because, as the distance from the point light source 24 increases, the amount of light gradually coming out of the light exit surface 25 and reaching the point light source 24 decreases, and the spread of the light increases as the distance from the point light source 24 increases. Since the light is weakened, the probability that the light is reflected toward the light exit surface 25 increases with the distance, thereby realizing the surface light source device 21 with uniform luminance.

However, in such a surface light source device 21 using only one small (or concentrated at one place) point light source 24, the light is emitted from the point light source 24 and introduced into the light guide plate 22. Since the density of the diffusion pattern 26 is designed in accordance with the light intensity when the reflected light propagates through the light guide plate 22, as shown in FIGS. When the light f reaches the end face of the light guide plate 22 and undergoes total reflection, the light f that has been totally reflected and returned to the inside of the light guide plate 22 is diffused again by the diffusion pattern 26 and is emitted from the light exit surface 25 near the end face. For this reason, there is a problem that the luminance distribution of the surface light source device 21 becomes non-uniform, and particularly the edges and corners of the light guide plate 22 shine brightly. In the figure, 27 is a liquid crystal display panel, and 28 is a reflection sheet.

The present invention has been made in view of the above-mentioned drawbacks of the conventional example, and has as its object to reduce the brightness distribution caused by the total reflection of light in the light guide plate at the edge of the light guide plate. The purpose is to suppress non-uniformity.

[0015]

According to a first aspect of the present invention, there is provided a surface light source device for confining light introduced from a light incident surface, expanding the light into a planar shape, and emitting the light from a light exit surface, and a light exit surface of the light guide plate. A surface light source device comprising: a diffusion pattern formed on an opposite surface; and a light source for allowing light to enter the light guide plate from the light incident surface and having a small size compared to the width of the light incident surface. In the light plate, a means for scattering light reaching the ineffective area is provided in an ineffective area located outside an effective area for emitting light used as a light source.

In this surface light source device, since the light reaching the non-effective area is scattered, it is possible to prevent the light from being totally reflected and returning to the effective area as in the prior art example, and the luminance distribution is non-uniform. Can be suppressed.

According to a second aspect of the present invention, in the surface light source device, a light guide plate for confining the light introduced from the light incident surface, spreading the light in a planar shape, and emitting the light from the light emission surface, and the opposite side of the light guide plate from the light emission surface. And a diffusion pattern formed on the surface of the light guide plate, and a light source having a light source smaller than the width of the light incident surface for allowing light to enter the light guide plate from the light incident surface. Among these, a feature is provided in a non-effective area located outside an effective area for emitting light used as a light source, for absorbing light reaching the non-effective area.

In this surface light source device, since the light reaching the non-effective area is absorbed, it is possible to prevent the light from returning from the non-effective area to the effective area again, and to prevent the luminance distribution from becoming non-uniform. Can be suppressed.

According to a third aspect of the present invention, in the surface light source device, a light guide plate for confining the light introduced from the light incident surface, spreading the light into a planar shape, and emitting the light from the light exit surface, and the opposite side of the light guide plate from the light exit surface. And a diffusion pattern formed on the surface of the light guide plate, and a light source having a light source smaller than the width of the light incident surface for allowing light to enter the light guide plate from the light incident surface. Among them, in the non-effective area located outside the effective area for emitting light used as a light source, means for transmitting light reaching the non-effective area to the outside of the light guide plate in the non-effective area is provided. Features.

In this surface light source device, light that has reached the ineffective area is transmitted and exits from the ineffective area.
Light can be prevented from returning from the ineffective area to the effective area again,
Non-uniformity of the luminance distribution can be suppressed.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) FIG. 7 is an exploded perspective view showing a surface light source device 41 according to one embodiment of the present invention, which is composed of a light guide plate 42, a light emitting unit 43, and a reflection plate 44. It is configured. The light guide plate 42 is formed of a transparent resin material having a large refractive index, such as polycarbonate resin or methacrylic resin. The upper surface of the light guide plate 42 is a light emission surface 45, and a large number of diffusion patterns 46 are provided on the lower surface. Have been. On both sides of the lower surface of the light guide plate 42, there are provided groove-shaped reflector holding portions 47, and a stopper 49 hangs downward on an end surface of the light guide plate 42 opposite to the light incident end surface 48. Have been.

In the light emitting section 43, a light emitting diode chip (LED chip) constituting the point light source 51 is accommodated in an outer case 50 made of white resin having a high reflectance. At the point light source mounting position, an outer case 50 is opened, and a transparent resin 52 is molded in the opening to seal the point light source 51.

A pair of elastic pieces 53 project from the light incident end face 48 of the light guide plate 42 by integral molding, and engaging claws 54 project from the inner surfaces of the distal ends of both elastic pieces 53. On the other hand, on both side surfaces of the outer case 50, side grooves 55 are provided so as to fit the elastic pieces 53 exactly. Thus, the light emitting portion 43 is sandwiched between the elastic pieces 53 so as to receive the elastic pieces 53 in the side grooves 55, and is held so as not to fall off by engaging the engaging claws 54 of the elastic pieces 53 with the back surface. ing.

In the center of the light incident end face 48 of the light guide plate 42, a light coupling recess 56 is formed. In the light emitting section 43, from the upper edge and the lower edge of the opening of the outer case 50, a light reflecting wall 57 having a shape matching the optical coupling concave portion 56 extends so as to fit into the optical coupling concave portion 56 of the light guide plate 42. . The light-emitting portion 43 is disposed to face the light-incident end face 48 of the light guide plate 42, and the light-reflecting wall 5
7 and the transparent resin 52 therebetween are stuck.

Here, the light coupling recess 56 optically controls the refraction direction of light emitted from the point light source 51 and guided into the light guide plate 42. Light of a light amount proportional to the light guide plate area in the azimuth is distributed to each azimuth, and the light reaches the four corners of the light guide plate 42.

The reflection plate 44 is formed of a material having a high surface reflectance, for example, a hard or relatively soft white plastic sheet. The reflection plate 44 is held on the lower surface of the light guide plate 42 by inserting both sides into the reflection plate holding portion 47.

FIG. 8 shows an arrangement of the diffusion pattern 46 provided on the lower surface of the light guide plate 42. The light guide plate 42 can be divided into an effective area 58 and a non-effective area 59. The effective area 58 is, as shown in FIG. 9, an image display area 61 of a liquid crystal display panel 60 mounted on the surface light source device 41.
The light corresponding to (screen) is emitted from this portion, passes through the image display area 61 of the liquid crystal display panel 60, and is used for image display. On the other hand, the non-effective area 59 is the area outside the image display area 61 of the liquid crystal display panel 60,
For example, a portion corresponding to the frame portion 62, and light emitted from the portion does not pass through the image display surface 61 of the liquid crystal display panel 60.

In the effective area 58, each diffusion pattern 46 is formed in a concave shape in a semi-cylindrical shape.
Are arranged radially around the center. In addition, each of the diffusion patterns 46 is disposed so that the length direction forms an angle of 90 ° with the direction connecting to the point light source 51, and has a diffusion action in the circumferential direction around the point light source 51. I haven't. Moreover, the pattern density of the diffusion pattern 46 is large on the side far from the point light source 51 so that the luminance distribution of the light guide plate 42 is uniform, and the diffusion pattern density gradually increases as the point light source 51 is approached. Has become smaller.

On the other hand, in the non-effective area 59, a scattering pattern 63 composed of a concavo-convex pattern (for example, a size of about 10 μm) is provided on the entire lower surface of the light guide plate 42. It is desirable that the pattern density of the scattering pattern 63 be as high as possible.

Thus, as shown in FIG.
8 propagates in the effective area 58 in the diffusion pattern 46.
Are uniformly emitted from the light exit surface 45 by the light f
Are strongly scattered by the scattering pattern 63 in the non-effective area 59. Therefore, the light in the non-effective area 59 is transmitted to the light guide plate 4.
2 can be prevented from being totally reflected and returning to the effective area 58, and the luminance distribution of the surface light source device 41 can be made more uniform.

The scattering pattern 63 of the non-effective area 59
May be an arbitrary one, and may be a concave / convex pattern or groove recessed on the lower surface of the light guide plate 42, a printing layer of diffuse reflection ink, or FIG.
What is necessary is just a scattering pattern such as a graining process such as a zero scattering pattern 63.

(Second Embodiment) FIG. 11 is a partially cutaway sectional view of a light guide plate 42 used in a surface light source device 71 according to another embodiment of the present invention. In this embodiment,
In the non-effective area 59, scattering patterns 63 are provided on the upper and lower surfaces of the light guide plate 42, respectively. Therefore, light entering the non-effective area 59 from the effective area 58 is transmitted to the non-effective area 5.
Since the light is scattered by both of the upper and lower scattering patterns 63, the totally reflected light can be more effectively prevented from returning to the effective area 58 of the light guide plate 42 to make the luminance distribution non-uniform.

(Third Embodiment) FIG. 12 is a partially broken sectional view of a light guide plate 42 used in a surface light source device 72 according to still another embodiment of the present invention. In this embodiment, the scattering material 73 is dispersed in the light guide plate 42 in the non-effective area 59. The scattering substance 73 is a resin powder, a resin bead, a metal powder or the like having a different refractive index from that of the light guide plate material, and it is desirable to disperse as fine a substance as possible (about 10 μm) at a high density.

When the scattering material 73 is dispersed in the non-effective area 59 in this way, the light f entering the non-effective area 59 from the effective area 58 is scattered by the scattering substance and totally reflected by the end face of the light guide plate 42. Return to the effective area 58 is suppressed, and unevenness of the luminance distribution can be prevented.

(Fourth Embodiment) FIG. 13 is a partially broken sectional view of a light guide plate 42 used in a surface light source device 74 according to still another embodiment of the present invention. In this embodiment, a scattering pattern 75 made of a concavo-convex pattern or texture is formed on an end face (three outer peripheral faces) of the light guide plate 42 except for the light incident end face 48. It is desirable that the scattering pattern 75 has a pattern density as high as possible. Light guide plate 4
If the scattering pattern 75 is provided on the end face of the light emitting element 2, the light that has reached the non-effective area 59 is scattered without being totally reflected on the end face. It is prevented from causing.

(Fifth Embodiment) FIG. 14 is a perspective view showing the shape of a light guide plate 42 used in a surface light source device according to still another embodiment of the present invention. In this embodiment, the corner of the light guide plate 42 farther from the light incident end face 48 is obliquely cut in the non-effective area to form the chamfered portion 7.
6 are formed. In the case of the rectangular light guide plate 42, the chamfered portion 76 is formed by obliquely cutting the end face region where the angle of incidence of the light from the point light source 51 is larger than the critical angle of total reflection and the light is totally reflected. I have. Light f emitted from the point light source 51
Is not diffused in the circumferential direction by the diffusion pattern 46, so that the light f entering the non-effective area 59 from the effective area 58
The part which is totally reflected by the end face of the light guide plate 42 and easily returns to the effective area 58 is a corner far from the point light source 51 (see FIG. 5). In this embodiment, since this corner is cut obliquely, the light f incident on the corner passes through the chamfered portion 76 to the outside of the light guide plate 42 without being totally reflected at the end face of the light guide plate 42. Therefore, it is possible to prevent the brightness distribution from returning to the effective area 58 again and becoming uneven.

It should be noted that the angle of the chamfered portion 76 is
It is preferable that the cut angle is such that the light emitted from the light enters the chamfered portion 76 perpendicularly (in a plan view).

(Sixth Embodiment) When one of the length and the width of the light guide plate 42 is longer than the other (in the case of the vertical or horizontal length), the incident angle of the light incident on the end face is totally reflected. 14 and the total reflection area becomes longer, and if this area is obliquely cut as shown in FIG. 14, there is a possibility that the effective area 58 may be cut.

The light guide plate 42 shown in FIG. 15 is an embodiment which is effective in such a case. The region where the total reflection occurs on the end face of the light guide plate 42 is cut obliquely in a piecewise manner. A plurality of surfaces 77 perpendicular to the connecting direction;
And a surface 78 parallel to the connecting direction. Therefore, even when the light guide plate 42 is vertically long or horizontally long, it is possible to prevent the cut area from entering the effective area 58 and prevent total reflection of light at the end face of the light guide plate 42.

(Seventh Embodiment) FIG. 16 is a perspective view showing the shape of a light guide plate 42 used in a surface light source device according to still another embodiment of the present invention. In this embodiment, in the non-effective area 59 of the light guide plate 42, the light guide plate 4
The inclined surface 79 is formed by making the three outer peripheral surfaces except the light incident end face 48 of the second 2 oblique (for example, setting the angle θ in FIG. 17 to 60 ° or more).

When the light guide plate 42 is formed in such a shape, as shown in FIG. 17, the light f entering from the effective area 58 to the non-effective area 59 is totally reflected by the inclined surface 79 of the light guide plate 42 so as to be guided. It is possible to prevent light emitted from the upper surface (non-effective area 59) of the light plate 42 from returning to the effective area 58 again.

(Eighth Embodiment) FIG. 18 is a perspective view showing the shape of a light guide plate 42 used in a surface light source device 81 according to still another embodiment of the present invention. In this embodiment, in the non-effective area 59 of the light guide plate 42, the light absorbing layer 82 formed of a resin having a high light absorbing property such as a black resin.
The upper surface, the lower surface, and the outer peripheral end surface of the light guide plate 42 are covered with this. Therefore, light that has entered the non-effective area 59 from the effective area 58 is absorbed by the light absorbing layer 82 and can be prevented from returning to the effective area 58 again.

However, when the light absorbing layer is attached to the edge of the light guide plate 42, an air layer (gap) is formed between the end of the light absorbing layer 82 and the light guide plate 42 due to a manufacturing error of the light absorbing layer 82 or the light guide plate 42. When 82 c occurs, light may be reflected toward the effective area 58 by this air layer. Therefore, in the surface light source device 83 shown in FIG. 19, of the light absorbing layer 82 covering the edge of the light guide plate 42 with the non-effective area 59, the side 82 on the upper surface side
a and the length of the side 82b on the lower surface side is made different. For example, if the upper side 82a is shorter than the lower side 82b, the light f reflected by the air layer 82c generated on the upper side 82a is absorbed by the lower side 82b. Therefore, if the light absorbing layer 82 is manufactured such that the air layer 82c is formed on the shorter side 82a and the shorter side 82a has a tolerance slightly shorter than the design value, the light absorbing layer 82 and the light guide plate 4 are formed.
Even when the air layer 82c is generated between the light emitting device and the second edge, it is possible to make it difficult for light to return to the effective area 58.

In place of the light absorbing layer 82 made of resin, FIG.
As in the case of the surface light source device 84 shown in FIG. 0, when the light absorbing tape 85 such as a black tape is attached to the outer peripheral surface of the light guide plate 42 in the non-effective area 59, light is effectively absorbed by a simple configuration. Total reflection to the region 58 can be prevented. Alternatively, as in the case of the surface light source device 86 shown in FIG. 21, the same applies when a highly light-absorbing paint 87 such as black paint is applied to the outer peripheral surface of the light guide plate 42 in the non-effective area 59.

[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.

3A is a diagram illustrating a problem of the surface light source device according to the first embodiment, FIG. 3B is a diagram illustrating a change in luminance along line C1-C1 in FIG. 3A, and FIG. FIG. 7 is a diagram showing a change in luminance along the line C2-C2 of FIG.

FIG. 4 is a diagram showing a surface light source device using one point light source.

FIG. 5 is a diagram showing a diffusion pattern of a light guide plate used in a prior art example.

FIG. 6 is a diagram for explaining a problem in the prior art example of the embodiment.

FIG. 7 is an exploded perspective view showing a surface light source device according to an embodiment of the present invention.

FIG. 8 is a diagram showing a diffusion pattern provided on a lower surface of a light guide plate used in the above surface light source device.

FIG. 9 is an operation explanatory view of the surface light source device according to the embodiment.

FIG. 10 is a partially broken sectional view showing a surface light source device according to another embodiment of the present invention.

FIG. 11 is a partially broken sectional view showing a surface light source device according to still another embodiment of the present invention.

FIG. 12 is a partially broken sectional view showing a surface light source device according to still another embodiment of the present invention.

FIG. 13 is a partially broken sectional view showing a surface light source device according to still another embodiment of the present invention.

FIG. 14 is a perspective view showing a light guide plate used in a surface light source device according to still another embodiment of the present invention.

FIG. 15 is a perspective view showing a light guide plate used in a surface light source device according to still another embodiment of the present invention.

FIG. 16 is a perspective view showing a light guide plate used in a surface light source device according to still another embodiment of the present invention.

FIG. 17 is an operation explanatory view of the embodiment.

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

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

FIG. 20 is a partially broken sectional view showing a surface light source device according to still another embodiment of the present invention.

FIG. 21 is a partially broken sectional view showing a surface light source device according to still another embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 42 light guide plate 46 diffusion pattern 51 point light source 58 effective area 59 ineffective area 63, 75 scattering pattern 73 scattering material 76 chamfered portion 82 light absorbing layer 85 light absorbing tape 87 paint with high light absorbing property

Claims (3)

[Claims] (1) confining light introduced from a light incident surface,
A light guide plate which is spread out in a plane and emitted from the light exit surface, a diffusion pattern formed on a surface opposite to the light exit surface of the light guide plate, and a light guide plate for allowing light to enter the light guide plate from the light incident surface. A light source device having a light source smaller than the width of the light incident surface, wherein the light guide plate has a non-effective area located outside an effective area for emitting light used as a light source. A surface light source device comprising means for scattering light reaching an effective area. 2. A method for confining light introduced from a light incident surface,
A light guide plate that is spread out in a planar shape and emitted from the light emission surface, a diffusion pattern formed on a surface of the light guide plate opposite to the light emission surface, and a light guide for allowing light to enter the light guide plate from the light incident surface. A light source device having a light source smaller than the width of the light incident surface, wherein the light guide plate has a non-effective area located outside an effective area for emitting light used as a light source. A surface light source device comprising means for absorbing light reaching an effective area. 3. A method for confining light introduced from a light incident surface,
A light guide plate that is spread out in a planar shape and emitted from the light emission surface, a diffusion pattern formed on a surface of the light guide plate opposite to the light emission surface, and a light guide for allowing light to enter the light guide plate from the light incident surface. A light source device having a light source smaller than the width of the light incident surface, wherein the light guide plate has a non-effective area located outside an effective area for emitting light used as a light source. A surface light source device comprising means for transmitting light reaching an effective area to the outside of the light guide plate in a non-effective area.