JPH11250714A - Surface light source device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent diffusion patterns from being seen raising in the vicinity of a point light source in a surface light source device uniformly dispersing light emitted from one point light source through dispersion patterns so as to radiate in uniform luminance from a light radiating face. SOLUTION: In this surface light source device, one point light source 40 is arranged on one side end face of a light guide plate 32, and diffusion patterns 36 are formed on the bottom face of the light guide plate 32. The diffusion patterns 36 are arrayed fan-like centering the point light source 40, the pattern densities of the diffusion patterns 36 are set to be large near the point light source 40, and the diffusion pattern densities are set to be gradually smaller as approaching the point light source 40. Further perspective angles being seen respective diffusion patterns 36 from the point light source 40 are set to be large far from the point light source 40, and are set to be gradually smaller as approaching the point light source 40.

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.

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). This is because, for example, as in a surface light source device 21 shown in FIG. 8, a point light source 25 such as an LED (in the present specification, the width of the light incident end face) is located at the center of one end face (light incident end face 23) of the light guide plate 22. A light source smaller than the light source is referred to as a point light source), and a large number of diffusion patterns 24 are provided on the lower surface of the light guide plate 22 in order to make the luminance on the light emission surface 26 uniform. Are repeated.
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 a region near the point light source 25, as shown in FIG. 10A, the diffusion pattern 24 having the same cross-sectional shape is formed with a small pattern density.
Since the intensity of the light f is low in a region away from the point light source 25, as shown in FIG. 9A, the diffusion pattern 24 having the same cross-sectional shape is formed with a large pattern density, so that a uniform luminance can be obtained. Light plate is realized.

However, such a surface light source device 21
In this case, the pattern density of the diffusion pattern 24 is small near the point light source 25, and the diffusion pattern 24 is sparse. Therefore, as shown in FIG. A problem arose. When the diffusion pattern 24 emerges in this manner, when used as a backlight of a liquid crystal display device, characters on the display screen are difficult to see or the display screen is not beautiful.

The present invention has been made in view of the above-mentioned prior art example, and has as its object to prevent a diffusion pattern from appearing in the vicinity of a point light source and improve the quality of a surface light source device. To make it happen.

[0019]

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 large number of diffusion patterns formed on the opposite surface, and a surface light source device including a light source smaller than the width of the light incident surface for causing light to enter the light guide plate from the light incident surface,
The angle at which each of the diffusion patterns is viewed from the light source is
It is characterized in that it is smaller in a region closer to the light source than in a region distant from the light source.

If the expected angle at which the diffusion pattern is viewed from the light source in a region close to the light source is made small, it is necessary to make the luminance distribution uniform. Pattern spacing in the direction can be reduced. Therefore, the interval between the diffusion patterns can be reduced even in the vicinity of the light source, and the diffusion patterns can be prevented from being seen on the surface of the light guide plate.

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, expanding the light into a planar shape, and emitting the light from the light exit surface, and a side opposite to the light exit surface of the light guide plate. A surface light source device comprising: a plurality of diffusion patterns formed on the surface of the light source, and a light source for causing light to enter the light guide plate from the light incident surface, the light source being smaller than the width of the light incident surface. The angle at which the individual diffusion patterns are viewed from is smaller in a region closer to the light source than in a region distant from the light source, and at least in the vicinity of the light source, the diffusion pattern is random in a circumferential direction around the light source. It is characterized by being arranged in.

If the angle at which the diffusion pattern is viewed in a region close to the light source is reduced, the interval between the diffusion patterns in the circumferential direction is increased, and a dark portion may be generated. The occurrence of such dark areas 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, expanding the light into a planar shape, and emitting the light from the light exit surface, and a side opposite to the light exit surface of the light guide plate. A large number of diffusion patterns recessed in the surface of the surface, and a surface light source device 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, The width of the cross section of the diffusion pattern in the direction connecting with the light source is wider in a region closer to the light source than in a region distant from the light source.

If the width of the cross section of the diffusion pattern is widened in a region near the light source, it is necessary to make the luminance distribution uniform, and the diffusion pattern density can be increased in the region near the light source.
Therefore, the interval between the diffusion patterns can be reduced even in the vicinity of the light source, and the diffusion patterns can be prevented from being seen on the surface of the light guide plate.

According to a fourth 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 a side opposite to the light exit surface of the light guide plate. A large number of diffusion patterns recessed in the surface of the surface, and a surface light source device 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, The height of the diffusion pattern in the direction connecting with the light source,
It is characterized in that it is lower in a region closer to the light source than in a region distant from the light source.

If the diffusion pattern is lowered in a region near the light source, the luminance distribution needs to be uniform, and the diffusion pattern density can be increased in the region near the light source. Therefore, the interval between the diffusion patterns can be reduced even in the vicinity of the light source, and the diffusion patterns can be prevented from being seen on the surface of the light guide plate.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) FIG. 12 is an exploded perspective view showing a surface light source device 31 according to one embodiment of the present invention, which is composed of a light guide plate 32, a light emitting section 33, and a reflector 34. It is configured. The light guide plate 32 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 32 is a light emitting surface 35, and a large number of diffusion patterns 36 are recessed on the lower surface. Have been. On both sides of the lower surface of the light guide plate 32, groove-shaped reflector holding portions 37 are provided, and a stopper 38 is hung downward on an end surface of the light guide plate 32 opposite to the light incident end surface. ing.

In the light emitting section 33, a light emitting diode chip (LED chip) constituting a point light source 40 is housed in an outer case 39 made of white resin having high reflectivity. At the point light source mounting position, an outer case 39 is opened, and a transparent resin 47 is molded in the opening to seal the point light source 40.

A pair of elastic pieces 41 protrude from the light incident end face 44 of the light guide plate 32 by integral molding, and engaging claws 42 project from the inner surfaces of the distal ends of both elastic pieces 41. On the other hand, side grooves 43 are provided on both side surfaces of the outer case 39 so that the elastic pieces 41 fit exactly. Thus, the light emitting portion 33 is sandwiched between the elastic pieces 41 so as to receive the elastic pieces 41 in the side grooves 43, and is held so as not to fall off by engaging the engaging claws 42 of the elastic pieces 41 with the back surface. ing.

A light coupling recess 45 is formed at the center of the light incident end face 44 of the light guide plate 32. In the light emitting section 33, from the upper edge and the lower edge of the opening of the outer case 39, a light reflecting wall 46 having a shape matching the light coupling recess 45 extends so as to fit into the light coupling recess 45 of the light guide plate 32. . The light-emitting portion 33 is opposed to the light-coupling recess 45 of the light guide plate 32, and the light-reflecting wall 4 of the light-emitting portion 33 is provided in the light-coupling recess 45.
6 and the transparent resin 47 in between.

Here, the light coupling recess 45 optically controls the refraction direction of light emitted from the point light source 40 and guided into the light guide plate 32. Light of a light amount proportional to the area of the light guide plate in the azimuth (the area of the fan-shaped region C) is distributed to each azimuth, and the light reaches the four corners of the light guide plate 32.

The reflector 34 is made of a material having a high surface reflectance, for example, a hard or relatively soft white plastic sheet. The reflection plate 34 is held on the lower surface of the light guide plate 32 by inserting both sides into the reflection plate holding portion 37.

The upper surface of the light guide plate 32 (light emitting surface 35)
Is overlaid with a semi-transparent plate 48 (FIG. 15B).

FIG. 13 shows an arrangement of the diffusion pattern 36 provided on the lower surface of the light guide plate 32. Each of the diffusion patterns 36 recessed on the lower surface of the light guide plate 32 has a semicylindrical shape, and extends from the vicinity of the point light source 40 to the edge of the light guide plate 32 in a sector C having a fixed angle around the point light source 40. Are arranged. In addition, each of the diffusion patterns 36 is disposed so that the length direction forms an angle of 90 ° with the direction connecting to the point light source 40, and has a diffusion action in the circumferential direction around the point light source 40. I haven't. In addition, the length of each diffusion pattern 36 is gradually reduced as the distance from the point light source 40 to the side closer to the light source 40 is further reduced, and further, the length of each diffusion pattern 36 around the point light source 40 is expected. The angle is also gradually reduced from the far side to the near side with respect to the point light source 40. Moreover, the pattern density of the diffusion pattern 36 is designed so that the luminance distribution of the light guide plate 32 is uniform.

Here, in the prior art example (FIG. 8), the diffusion pattern 24 emerges near the point light source 25 and
Consider the reason you can see from 6. In the prior art example, each diffusion pattern 24 had the same cross section, and its length was proportional to the distance from the point light source 25. Therefore, the angle at which the length of each diffusion pattern 24 is viewed from the point light source 25 is constant as shown in FIG. For this reason,
When the diffusion pattern 24 is provided so that the luminance distribution of the light guide plate 22 is uniform, as shown in FIG.
The distance between the diffusion patterns 24 is long at a portion away from 5, and the distance between the diffusion patterns 24 is short at a portion near the point light source 40.

Thus, in an area far from the point light source 25,
Since the pattern density of the diffusion pattern 24 is large, in the prior art example, as shown in FIG.
9 has a luminance distribution as shown by a thin line α1 in FIG. 9B, and when the light f is diffused by the semi-transmissive plate 27, a luminance distribution as shown by a thick line β1 in FIG. The luminance distribution is uniformed so as to be substantially uniform at any position. On the other hand, in an area near the point light source 25, the diffusion pattern 2
4 has a low pattern density, and as shown in FIG.
Has a luminance distribution like the thin line α2. However, since the distance between the diffusion patterns 24 is too long, this is
Are not sufficiently uniformized even when the light is diffused, and the luminance distribution becomes like a thick line β2 in FIG.
Incidentally, the average value of the luminance distribution indicated by the thick line β1 in FIG. 9B is equal to the average value of the luminance distribution indicated by the thick line β2 in FIG. It has become.

On the other hand, in the present embodiment, FIG.
As shown in FIG. 2B, the angle θ1 in view of the length of the diffusion pattern 36 located near the point light source 40 is
Angle θ2 that allows for the length of the diffusion pattern 36 away from 0
(That is, equal to that of the prior art example) (ie, the length of the diffusion pattern 36 is shorter near the point light source 40 than in the case of the prior art example). If the luminance distribution is made uniform, the interval between the diffusion patterns 36 can be made smaller in the vicinity of the point light source 40 than in the prior art without changing the density of the diffusion patterns. That is, in the vicinity of the point light source 40, as shown in comparison with FIGS. 15A and 15B, the interval between the diffusion patterns 36 is shorter than in the prior art.

As a result, in a region away from the point light source 40, as shown in FIG. 16A, the light reflected by the diffusion pattern 36 becomes the thin line α in FIG.
3 has a luminance distribution, but when this is diffused by the semi-transmissive plate 48, the luminance distribution becomes like a thick line β3 in FIG. 16B, and the luminance distribution is made uniform so that it becomes almost uniform at any position. Is done. In the region near the point light source 40, the interval between the diffusion patterns 36 is shorter than that in the prior art example. Therefore, as shown in FIG. 7 has a luminance distribution like a thin line α4, and is diffused by the
The luminance distribution is as shown by the thick line β4 in (b), and the contrast between the bright part and the dark part cannot be recognized by the naked eye. Especially,
According to the experimental results, it was found that if the interval between the diffusion patterns 36 was set to be equal to or less than 0.2 mm, the diffusion pattern 36 could not be seen.

(Second Embodiment) FIG. 18 is a partially omitted schematic view showing a diffusion pattern 36 on the lower surface of a light guide plate 32 used in a surface light source device 51 according to another embodiment of the present invention. In the first embodiment, the expected angle of the length of the diffusion pattern 36 with respect to the position of the point light source 40 gradually decreases as the distance from the point light source 40 decreases, but the center of each diffusion pattern 36 is It was located on the bisector γ of the sector C. In the second embodiment, the similarity is that the expected angle of the length of the diffusion pattern 36 with respect to the light source position gradually narrows as the distance from the point light source 40 decreases. Does not protrude from the fan-shaped area C, and the center of the diffusion pattern 36 is set on the point light source 40 from the bisector γ of the fan-shaped area C.
Are randomly displaced in the circumferential direction around the center. In particular, the arrangement of the diffusion patterns 36 near the point light source 40 is randomized.

When the diffusion pattern 36 is orderly positioned on the bisector γ of the sector C, the length of the diffusion pattern 36 becomes shorter in the vicinity of the point light source 40 as compared with the spread of the sector C. As a result, an area without the diffusion pattern 36 is generated on the boundary of the fan-shaped area C, so that a dark area E as shown in FIG. 19 is generated. In the second embodiment, the occurrence of such a dark portion E is suppressed by randomizing the arrangement of the diffusion patterns 36 in the vicinity of the point light source 40 in the circumferential direction.

Although not shown, each diffusion pattern 36
May be deviated in the circumferential direction around the point light source 40 beyond the fan-shaped area C.

(Third Embodiment) FIG. 20 is a partially omitted schematic view showing a diffusion pattern 36 on the lower surface of a light guide plate 32 used in a surface light source device 52 according to still another embodiment of the present invention. FIG. 21A is a cross-sectional view of the fan-shaped region C in FIG. 20 on a bisector. FIG. 21B shows a case of a prior art example for comparison. In this embodiment, as shown in FIG.
Is equal to the width of the sector area C. That is, the angle at which the length of the diffusion pattern 36 is viewed from the point light source 40 is equal for all the diffusion patterns 36. Further, as shown in FIG. 21A, in the cross section of the diffusion pattern 36, the width (W) of the diffusion pattern 36 is equal. However, the height (H) of the diffusion pattern 36 gradually decreases as it approaches the point light source 40.

FIGS. 22A and 22B show how the light of the low diffusion pattern 36 and the light of the high diffusion pattern 36 are diffused. As shown in FIG.
When the height H of the light source 6 decreases, the amount of light extracted from the light exit surface 35 decreases (the same effect as reducing the length of the diffusion pattern 36). If the height H is gradually reduced, it is necessary to make the luminance distribution uniform as shown in FIG.
As shown in (b), the diffusion pattern density in the vicinity of the point light source 40 needs to be higher than in the case of the prior art. Therefore, it is possible to prevent the diffusion pattern 36 in the vicinity of the point light source 40 from appearing and emerging.

(Fourth Embodiment) FIG. 23 is a partially omitted schematic view showing a diffusion pattern 36 on a lower surface of a light guide plate 32 used in a surface light source device 53 according to still another embodiment of the present invention. FIG. 24A is a cross-sectional view of the fan-shaped region C of FIG. 23 on the bisector γ. FIG. 24 (b)
Indicates the case of the prior art example for comparison. Also in this embodiment, as shown in FIG.
The length of 6 is equal to the width of the sector area C. That is, the angle at which the length of the diffusion pattern 36 is viewed from the point light source 40 is equal for all the diffusion patterns 36. Further, as shown in FIG. 24A, in the cross section of the diffusion pattern 36, the heights (H) of the diffusion patterns 36 are all equal. However, the width (W) of the diffusion pattern 36 gradually increases as it approaches the point light source 40.

FIGS. 25 (a) and 25 (b) show how the light f from the wide diffusion pattern 36 and the narrow diffusion pattern 36 is diffused. As shown in this figure, if the width of the diffusion pattern 36 is increased, the amount of light extracted from the light exit surface 35 is reduced (the same effect as reducing the length of the diffusion pattern 36). If the width of the diffusion pattern 36 is gradually increased as it approaches 40, in order to make the luminance distribution uniform, the diffusion pattern density near the point light source 40 must be increased as shown in FIGS. Must be higher than in the technical case. Therefore, it is possible to prevent the diffusion pattern 36 in the vicinity of the point light source 40 from appearing and emerging.

(Fifth Embodiment) In the first to fourth embodiments, when the angle of view from the point light source 40 is reduced near the point light source 40, the diffusion pattern 36 near the point light source 40 is used.
When the height H is reduced, the width W in the cross section of the diffusion pattern 36 near the point light source 40 is increased. However, these embodiments can be implemented not only individually, but also in combination with each other. For example, in the surface light source device 54 of the embodiment shown in FIG. 26, the width W in the cross section of the diffusion pattern 36 gradually increases and the height H gradually decreases as the point light source 40 is approached.

(Sixth Embodiment) In each of the above-described embodiments, the diffusion pattern 36 has a semi-cylindrical shape as shown in FIG. 27A, but is not limited to this.
A triangular prism-shaped diffusion pattern 36 as shown in FIG.
The light incident on the surface of the semi-cylindrical diffusion pattern 36 is uniformly reflected over a wide range and is incident on the light exit surface 35 at various incident angles, so that the brightness of the entire light guide plate 32 can be made uniform. There is. On the other hand, in the triangular prism-shaped diffusion pattern 36, unnecessary slopes can be eliminated (that is, the surface opposite to the point light source 40 is made a vertical surface), so that the density of the diffusion patterns 36 can be increased, and There is an advantage that the emission rate can be increased and a highly efficient light guide plate 32 can be obtained.

In the case of the diffusion pattern 36 having a triangular prism shape, the cross-sectional shape of the diffusion pattern 36 is changed according to the distance from the point light source 40, as in a surface light source device 55 shown in FIG. The density of the diffusion pattern 36 near the light source 40 can be increased to prevent the diffusion pattern 36 from being seen.

[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.

9A is a diagram showing a cross section of the above light guide plate in a region far from the point light source and the behavior of light therethrough, and FIG. 9B is a diagram showing a luminance distribution of light emitted from the light guide plate and passing through the semi-transmissive plate. FIG. 9 is a diagram showing a luminance distribution of light after the light is applied.

10A is a diagram showing a cross section of the above light guide plate in a region near a point light source and the behavior of light there, and FIG. 10B is a diagram showing a luminance distribution of light emitted from the light guide plate and passing through a semi-transmissive plate. FIG. 9 is a diagram showing a luminance distribution of light after the light is applied.

FIG. 11 is a diagram for explaining a problem in the prior art example.

FIG. 12 is an exploded perspective view showing a surface light source device according to an embodiment of the present invention.

FIG. 13 is a diagram showing a diffusion pattern provided on the lower surface of a light guide plate used in the above surface light source device.

14A is a diagram showing a diffusion pattern in one fan-shaped region in the prior art example, and FIG. 14B is a diagram showing a diffusion pattern in one fan-shaped region in the embodiment of the present invention.

FIG. 15A is a diagram showing the arrangement of diffusion patterns and the behavior of light in a light guide plate in the prior art example, and FIG. 15B is a diagram showing the arrangement of diffusion patterns and light in the light guide plate in the same embodiment. It is a figure showing a behavior.

16A is a diagram showing a cross section of a light guide plate in a region far from a point light source and the behavior of light in the same embodiment, and FIG. 16B is a diagram illustrating a luminance distribution and semi-transmission of light emitted from the light guide plate. FIG. 4 is a diagram illustrating a luminance distribution of light after passing through a plate.

17A is a diagram showing a cross section of a light guide plate in a region near a point light source and the behavior of light in the above embodiment, and FIG. 17B is a diagram illustrating luminance distribution and semi-transmission of light emitted from the light guide plate. FIG. 4 is a diagram illustrating a luminance distribution of light after passing through a plate.

FIG. 18 is a plan view showing another embodiment of the present invention, which is a feature of an arrangement of a diffusion pattern in one fan-shaped region.

FIG. 19 is a diagram illustrating a problem that may occur in the first embodiment.

FIG. 20 is still another embodiment of the present invention and is a plan view showing an arrangement of diffusion patterns in one fan-shaped region.

FIG. 21 (a) is a diagram showing the arrangement of diffusion patterns and the behavior of light in a light guide plate in the above embodiment, and FIG. 21 (b) is the arrangement of the diffusion patterns and light distribution in a light guide plate in the prior art example. It is a figure showing a behavior.

22A is a diagram showing a cross section in a region near a point light source of a light guide plate and the behavior of light there in the embodiment of the present invention, and FIG. 22B is a diagram showing a cross section in a region far from the light guide plate and a cross section thereof. It is a figure showing the behavior of light.

FIG. 23 is a plan view showing an arrangement of a diffusion pattern in one fan-shaped region according to still another embodiment of the present invention.

FIG. 24 (a) is a diagram showing the arrangement of diffusion patterns and the behavior of light in a light guide plate in the above embodiment, and FIG. 24 (b) is a diagram showing the arrangement of diffusion patterns and light distribution in a light guide plate in a prior art example; It is a figure showing a behavior.

25A is a diagram showing a cross section in a region near a point light source of a light guide plate and a behavior of light there in the embodiment of the present invention, and FIG. 25B is a diagram showing a cross section in a region far from the light guide plate and a cross section thereof. It is a figure showing the behavior of light.

FIG. 26 is a cross-sectional view of yet another embodiment of the present invention.

27 (a) is a perspective view showing a semi-cylindrical diffusion pattern, and FIG. 27 (b) is a perspective view showing a triangular prism-shaped diffusion pattern.

FIG. 28 is a cross-sectional view of yet another embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 32 light guide plate 33 light emitting section 35 light emitting surface 36 diffusion pattern 40 point light source 44 light incidence end face 48 semi-transmissive plate θ1, θ2 expected angle of diffusion pattern viewed from light source H diffusion pattern height W diffusion pattern width C sector area

Claims (4)

[Claims] (1) 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 exit surface, a large number of diffusion patterns formed on a surface of the light guide plate opposite to the light exit surface, and light enters the light guide plate from the light incident surface. For, in a surface light source device provided with a light source smaller than the width of the light incident surface, the angle at which each diffusion pattern is viewed from the light source,
A surface light source device characterized in that it is smaller in a region closer to the light source than in a region distant from the light source. 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 exit surface, a large number of diffusion patterns formed on a surface of the light guide plate opposite to the light exit surface, and light enters the light guide plate from the light incident surface. For, in a surface light source device provided with a light source smaller than the width of the light incident surface, the angle at which each diffusion pattern is viewed from the light source,
A surface characterized by being smaller in a region closer to the light source than in a region away from the light source, and at least in the vicinity of the light source, the diffusion patterns are randomly arranged in a circumferential direction around the light source. Light source device. 3. A method for 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 large number of diffusion patterns recessed on a surface opposite to the light exit surface of the light guide plate, and light enters 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 width of the cross section of the diffusion pattern in the direction connecting with the light source is closer to the light source than to a region farther from the light source. A surface light source device characterized by being wider in a near area. 4. 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 large number of diffusion patterns recessed on a surface opposite to the light exit surface of the light guide plate, and light enters 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 height of the diffusion pattern in a direction connecting with the light source is closer to the light source than to a region apart from the light source. A surface light source device characterized by being lower in a region.