JP3651238B2 - Surface light source device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
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]
[Prior 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 polycarbonate resin or methacrylic resin. A large number of diffusion patterns 5 are formed on the lower surface of the light guide plate 2 by concavo-convex processing or dot printing of diffuse reflection ink. ing. The light emitting unit 3 is a component in which a so-called point light source 7 such as a plurality of light emitting diodes (LEDs) is mounted on a circuit board 6, and faces the 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 both side portions are attached to the lower surface of the light guide plate 2 by a double-sided tape 9.
[0003]
As shown in FIG. 2, the light f emitted from the light emitting unit 3 and guided to the inside of the light guide plate 2 from the light incident end face 8 is totally reflected inside the light guide plate 2 to be inside the light guide plate 2. Be trapped. The light f inside the light guide plate 2 is diffused and reflected when entering the diffusion pattern 5, and the light f reflected toward the light emitting surface 10 at an angle smaller than the critical angle of total reflection is extracted from the light emitting surface 10 to the outside. . Further, the light f that has passed through the portion where the diffusion pattern 5 does not exist on the lower surface of the light guide plate 2 is reflected by the reflecting plate 4 and returns to the inside of the light guide plate 2 again, thereby preventing light loss from the lower surface of the light guide plate 2.
[0004]
In order to make the light emission luminance uniform in the entire light emitting area in such a surface light source device 1, as shown in FIG. 3A, the light f incident into the light guide plate 2 from the light incident end face 8 is used as the light guide plate. 2 It is necessary to scatter the light with the diffusion pattern 5 on the lower surface so that the light f is uniformly scattered throughout the light emission region. 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 to the light emission surface 10 side and the light emission surface 10. The inclination and the inclination direction of the diffusion pattern 5 are varied so that a part of the light f emitted from the outside and reflected by the diffusion pattern 5 changes the light traveling direction in the light guide plate 2.
[0005]
In the surface light source device 1 in which the diffusion pattern 5 as described above is formed, the light f inside the light guide plate 2 is gradually and uniformly diffused by repeating scattering in the diffusion pattern 5, so that it is separated from the light emitting unit 3. The luminance distribution is relatively uniform in the region. However, as shown in FIG. 4A, the light guide plate 2 shines brightly in the region a immediately 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. 4B shows a change in luminance in the vicinity of the light incident end face 8 along the line C1-C1 in FIG. 4A. In the vicinity of the light emitting unit 3, the direction parallel to the light incident end face 8 is shown. The variation in luminance increases along the line, and the ratio of the luminance change may reach several to ten times.
[0006]
The reason why the luminance in the intermediate region B in front of the point light source 7 is lower than the luminance in the region B immediately before the point light source 7 is that there is little light guided to the intermediate region B in front of the point light source 7. The reason why the amount of light guided to the intermediate region 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 and directed forward at the light incident end face 8 when entering the light, and the effect of diffusing the light f in the width direction (point light source arrangement direction) by the diffusion pattern 5 in the vicinity of the light incident end face 8 is also sufficiently expressed. It is due to things that are not.
[0007]
Here, if the diffusion effect of the diffusion pattern 5 in front of the point light source 7 is increased and the light incident on the front of the point light source 7 is bent in the width direction, the luminance in the intermediate region B in front of the point light source 7 is improved. At the same time, since the amount of light directed to the light exit surface 10 in the area immediately preceding the point light source 7 also increases, the luminance in the area immediately preceding the point light source 7 also increases, and the luminance variation is not improved.
[0008]
FIG. 4C shows a change in luminance in a region far from the light incident end face 8 along the line C2-C2 in FIG. 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 is drastically reduced at both ends. That is, the corner C on the side opposite to the light incident end face 8 of the light guide plate 2 becomes dark. As shown in FIG. 6A, the light f from the four point light sources 7 reaches other than the corner C on the C2-C2 line in FIG. As shown in FIG. 6 (b), the light f from the two point light sources 7 located far from the corner C is difficult to reach, so the brightness is lowered and darkened at the corner C. is there.
[0009]
In order to solve this and make the luminance distribution uniform at the position of the C2-C2 line, if the diffusion in the width direction by the diffusion pattern 5 is increased from the point light source 7 to the C2-C2 line. However, if the diffusion by the diffusion pattern 5 is increased, the light f is emitted to the outside from the light emitting surface 10 until reaching the C2-C2 line, and the leakage of the light f from both side surfaces of the light guide plate 2 is also large. Accordingly, the light f reaching the position of the C2-C2 line is reduced, and the entire position of the C2-C2 line is darkened.
[0010]
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 been devised with respect to the shape and density of the diffusion pattern, the diffusion effect, and the like. However, it has been difficult to make the luminance distribution uniform.
[0011]
(A surface light source device using one point light source)
On the other hand, the backlight type liquid crystal display device is thin and lightweight, and thus is used as a display device for portable information terminals such as electronic notebooks and portable personal computers, and highly portable products such as cellular phones. When used in such highly portable products, there is a strong demand for longer battery life from the standpoint of improving portability, and the backlight used in this display device is also required to reduce power consumption. Yes.
[0012]
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 to be used. Such a surface light source device 11 ultimately uses a small light source (light emitting diode) as shown in FIG.
[0013]
However, when the number of point light sources is reduced in this way, 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. The luminance is very large in the area a immediately before the light source 7, and the luminance is lowered and darkened at the four corners C of the light guide plate 2.
[0014]
Accordingly, 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 to reduce the number of point light sources to be used as much as possible and to make the luminance distribution as uniform as possible. .
[0015]
[Problems to be solved by the invention]
(Prior art example)
Therefore, the inventors of the present invention have proposed a structure of a surface light source device that can reduce the number of point light sources to be used as much as possible and can increase the uniformity of the luminance distribution (hereinafter referred to as prior art). Called example). For example, as in the surface light source device 21 shown in FIG. 8, the light source plate 22 has a point light source 25 (in this specification, the width of the light incident end face in the center of one end face (light incident end face 23)). In order to make the luminance on the light exit surface 26 uniform, a large number of diffusion patterns 24 are provided on the lower surface of the light guide plate 22, and the translucent plate 27 is provided on the light exit surface 26. Are piled up. These diffusion patterns 24 are arranged in a radial pattern on the entire lower surface of the light guide plate 22 with the point light source 25 as the center.
[0016]
Further, the pitch between the diffusion patterns 24 decreases as the distance from the point light source 25 increases, and the diffusion pattern density 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 that is gradually emitted from the light emitting surface 26 and reaches the point light source 25 decreases, and as the distance from the point light source 25 increases, the light f spreads. Since the light f becomes larger and the light f becomes weaker, the probability that the light f is reflected toward the light emitting surface 26 increases with the distance. That is, since the light intensity is strong in the area close to 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. Since the intensity of the light f is weak, as shown in FIG. 9A, the light guide plate with uniform luminance is realized by forming the diffusion pattern 24 having the same cross-sectional shape with a large pattern density.
[0017]
However, in such a surface light source device 21, the pattern density of the diffusion pattern 24 is small in the vicinity of the point light source 25, and the diffusion pattern 24 becomes sparse. Therefore, as shown in FIG. This causes a problem that the diffusion pattern 24 appears to be raised. When the diffusion pattern 24 emerges in this way, when used as a backlight of a liquid crystal display device, characters on the display screen become difficult to see or the display screen becomes unbeautiful.
[0018]
  The present invention has been made in view of the above prior art examples, and its object is to provide a surface as shown in FIG. 8 in which diffusion patterns are arranged concentrically along a circumferential direction centering on a point light source. In the light source device, the pattern density increases as the distance from the point light source increases in order to make the luminance distribution uniform.LikeIn the case where a diffusion pattern is arranged on the surface, the diffusion pattern is prevented from appearing in the vicinity of the point light source, and the quality of the surface light source device is improved.
[0019]
DISCLOSURE OF THE INVENTION
  The surface light source device according to claim 1 confines light introduced from the light incident surface, spreads the light into a planar shape and emits the light from the light exit surface, and a surface opposite to the light exit surface of the light guide plate. In a surface light source device comprising a large number of formed diffusion patterns and a light source smaller than the width of the light incident surface for making light enter the light guide plate from the light incident surface, the diffusion pattern is: The pattern density increases as the distance from the light source increases, and along the circumferential direction around the light source.DiscretelyArranged,The length of each diffusion pattern in the circumferential direction around the light source is determined from the light source.The viewing angle is smaller in the area closer to the light source than in the area away from the light source.The diffusion pattern located at least in the vicinity of the light source is randomly displaced in the circumferential direction around the light source from a line segment connecting the light source and the center of the diffusion pattern farthest from the light source.It is characterized by that.
[0020]
  The diffusion pattern in the surface light source device according to claim 1 is discretely arranged along a circumferential direction centering on the light source so that the pattern density increases as the distance from the light source increases. Since each of the diffusion patterns has a circumferential length around the light source, the angle seen from the light source is smaller in a region closer to the light source than in a region away from the light source.In order to make the luminance distribution uniform, the pattern interval in the direction viewed from the light source can be reduced without changing the diffusion pattern density in the region close to 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 appearing on the surface of the light guide plate.
[0021]
  Further, if the angle at which the diffusion pattern is viewed in the region close to the light source is reduced, the distance between the diffusion patterns in the circumferential direction may be widened, and a dark portion may be generated. However, in the surface light source device according to claim 1, Since the diffusion pattern located in the vicinity of the light source is randomly deviated in the circumferential direction around the light source from the line segment connecting the light source and the center of the diffusion pattern farthest from the light source. Generation of dark parts can be suppressed.
[0027]
DETAILED DESCRIPTION OF THE INVENTION
(First embodiment)
FIG. 12 is an exploded perspective view showing a surface light source device 31 according to an embodiment of the present invention, which includes a light guide plate 32, a light emitting unit 33, and a reflection plate 34. 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 number of diffusion patterns 36 are recessed on the lower surface. Has been. On both sides of the lower surface of the light guide plate 32, groove-shaped reflection plate holding portions 37 are provided, and a stopper 38 is suspended downward on the end surface of the light guide plate 32 opposite to the light incident end surface. ing.
[0028]
In the light emitting unit 33, a light emitting diode chip (LED chip) constituting the point light source 40 is housed in an exterior case 39 made of a white resin having a high reflectance. At the point light source mounting position, an exterior case 39 is opened, and the point light source 40 is sealed by molding a transparent resin 47 in the opening.
[0029]
A pair of elastic pieces 41 protrude from the light incident end face 44 of the light guide plate 32 by integral molding, and an engaging claw 42 protrudes from the inner surfaces of the distal end portions of both elastic pieces 41. On the other hand, side grooves 43 are provided in the both side surfaces of the outer case 39 so that the elastic pieces 41 can be received exactly. Thus, the light emitting portion 33 is sandwiched between the elastic pieces 41 so that the elastic piece 41 is accommodated in the side groove 43, and is held so as not to fall off by engaging the engaging claw 42 of the elastic piece 41 with the back surface. ing.
[0030]
An optical coupling recess 45 is formed in the center of the light incident end face 44 of the light guide plate 32. In the light emitting unit 33, a light reflecting wall 46 having a shape matching the light coupling recess 45 extends from the upper and lower edges of the opening of the outer case 39 so as to fit into the light coupling recess 45 of the light guide plate 32. . The light-emitting portion 33 is disposed opposite to the light coupling recess 45 of the light guide plate 32, and the light reflecting wall 46 of the light-emitting portion 33 and the transparent resin 47 therebetween fit into the light coupling recess 45.
[0031]
Here, the optical coupling recess 45 optically controls the refraction direction of the light emitted from the point light source 40 and guided to the inside of the light guide plate 32, and guides light in each direction around the point light source 40. A light amount proportional to the area of the light plate (the area of the fan-shaped region C) is distributed to each direction, and the light reaches the four corners of the light guide plate 32.
[0032]
The reflector 34 is made of a material having a high surface reflectance, and is made of, for example, a hard or relatively soft white plastic sheet. The reflecting plate 34 is held on the lower surface of the light guide plate 32 by inserting both side portions into the reflecting plate holding portion 37.
[0033]
In addition, a semi-transmissive plate 48 is overlaid on the upper surface (light emitting surface 35) of the light guide plate 32 (FIG. 15B).
[0034]
The arrangement of the diffusion pattern 36 provided on the lower surface of the light guide plate 32 is shown in FIG. Each diffusion pattern 36 recessed in the lower surface of the light guide plate 32 has a semi-cylindrical shape, and from the vicinity of the point light source 40 to the edge of the light guide plate 32 in a fan-shaped region C centered on the point light source 40. It is arranged. Each of the diffusion patterns 36 is arranged such that the length direction forms an angle of 90 ° with respect to the direction connecting to the point light source 40, and has a diffusing action in the circumferential direction around the point light source 40. Not done. Moreover, the length of each diffusion pattern 36 is gradually shortened from the far side to the near side with respect to the point light source 40, and further, the length of each diffusion pattern 36 is estimated with the point light source 40 as the center. The angle gradually decreases 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.
[0035]
  Here, in the prior art example (FIG. 8), the reason why the diffusion pattern 24 is raised near the point light source 25 and can be seen from the light emitting surface 26 will be considered. In the prior art example, each diffusion pattern 24 has the same cross section, and its length is proportional to the distance from the point light source 25. Therefore, the angle at which the length of each diffusion pattern 24 is estimated 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, the distance between the diffusion patterns 24 in the portion away from the point light source 25 is as shown in FIG.ShortIn the portion close to the point light source 40, the distance between the diffusion patterns 24 islongIt has become.
[0036]
Since the pattern density of the diffusion pattern 24 is large in the region away from the point light source 25 in this way, in the prior art example, as shown in FIG. 9A, the light f reflected by the diffusion pattern 24 is as shown in FIG. However, when this is diffused by the semi-transmissive plate 27, it becomes a luminance distribution as shown by a thick line β1 in FIG. 9B, and the luminance distribution is almost uniform at any position. It is made uniform. On the other hand, since the pattern density of the diffusion pattern 24 is small in the region close to the point light source 25, as shown in FIG. 10A, the light reflected by the diffusion pattern 24 is a thin line α2 in FIG. It has such a luminance distribution. However, since the distance between the diffusion patterns 24 is too long, even if it is diffused by the semi-transmissive plate 27, it is not sufficiently uniformed, resulting in a luminance distribution as shown by the 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. 10B, and is constant at an arbitrary portion of the light guide plate 32. It has become.
[0037]
On the other hand, in the present embodiment, as shown in FIG. 14B, the angle θ1 at which the length of the diffusion pattern 36 located near the point light source 40 is expected is the diffusion pattern 36 away from the point light source 40. Is smaller than the angle θ2 (which is equal to that in the prior art example) (that is, the length of the diffusion pattern 36 is shorter near the point light source 40 than in the prior art example). Therefore, if the luminance distribution is made uniform throughout the light guide plate 32, the distance between the diffusion patterns 36 can be made smaller in the vicinity of the point light source 40 than in the prior art example without changing the diffusion pattern density. 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 that in the case of the prior art example.
[0038]
As a result, in the region away from the point light source 40, as shown in FIG. 16A, the light reflected by the diffusion pattern 36 has a luminance distribution as shown by the thin line α3 in FIG. However, when this is diffused by the semi-transmissive plate 48, the luminance distribution becomes as shown by the thick line β3 in FIG. 16B, and the luminance distribution is made uniform so as to be almost uniform at any position. In the region close to the point light source 40, the distance between the diffusion patterns 36 is shorter than that in the prior art example. Therefore, as shown in FIG. 17A, the light reflected by the diffusion pattern 36 is as shown in FIG. Has a luminance distribution like a thin line α4, and is uniformed when diffused by the semi-transmissive plate 48, resulting in a luminance distribution like the thick line β4 in FIG. 7B. The contrast between the bright part and the dark part is recognized by the naked eye. become unable. In particular, it has been found from the experimental results that if the distance between the diffusion patterns 36 is set to 0.2 mm or less, it cannot be seen.
[0039]
(Second Embodiment)
FIG. 18 is a partially omitted schematic view showing the diffusion pattern 36 on the lower surface of the light guide plate 32 used in the 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 is gradually narrowed as the distance from the point light source 40 is shortened, but the center of each diffusion pattern 36 is It was located on the bisector γ of the sector area C. The second embodiment is similar in that the expected angle of the length of the diffusion pattern 36 with respect to the light source position is gradually narrowed as the distance from the point light source 40 is shortened. However, the center of the diffusion pattern 36 is randomly displaced in the circumferential direction around the point light source 40 from the bisector γ of the sector region C so that it does not protrude from the sector region C. In particular, the arrangement of the diffusion pattern 36 is made random in the vicinity of the point light source 40.
[0040]
When the diffusion pattern 36 is orderly positioned on the bisector γ of the sector region C, the length of the diffusion pattern 36 becomes shorter in the vicinity of the point light source 40 than the expansion of the sector region C, thereby causing the sector region. A region without the diffusion pattern 36 is generated on the boundary of C, and as a result, a dark portion E as shown in FIG. 19 is generated. In the second embodiment, the arrangement of the diffusion pattern 36 in the vicinity of the point light source 40 is randomized in the circumferential direction, thereby suppressing the occurrence of such a dark portion.
[0041]
Although not shown, each diffusion pattern 36 may be displaced in the circumferential direction around the point light source 40 beyond the sector region C.
[0042]
(Third embodiment)
FIG. 20 is a partially omitted schematic view showing the diffusion pattern 36 on the lower surface of the light guide plate 32 used in the surface light source device 52 according to still another embodiment of the present invention. FIG. 21A is a sectional view on a bisector of the sector region C of FIG. FIG. 21B shows the case of the prior art for comparison. In this embodiment, the length of the diffusion pattern 36 is equal to the width of the sector region C as shown in FIG. That is, the angle at which the length of the diffusion pattern 36 is estimated from the point light source 40 is the same 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.
[0043]
FIGS. 22A and 22B show how light from the low diffusion pattern 36 and the high diffusion pattern 36 is diffused. As shown in this figure, when the height H of the diffusion pattern 36 decreases, the amount of light extracted from the light exit surface 35 decreases (the same effect as shortening the length of the diffusion pattern 36). If the height H of the diffusion pattern 36 is gradually lowered as it approaches the point light source 40, in order to make the luminance distribution uniform, as shown in FIGS. It is necessary to make the diffusion pattern density in the vicinity higher than in the case of the prior art example. For this reason, it is possible to prevent the diffusion pattern 36 in the vicinity of the point light source 40 from appearing to be raised.
[0044]
(Fourth embodiment)
FIG. 23 is a partially omitted schematic view showing the diffusion pattern 36 on the lower surface of the light guide plate 32 used in the surface light source device 53 according to still another embodiment of the present invention. FIG. 24A is a cross-sectional view of the sector region C in FIG. 23 on the bisector γ. FIG. 24B shows a case of the prior art for comparison. Also in this embodiment, the length of the diffusion pattern 36 is equal to the width of the sector region C as shown in FIG. That is, the angle at which the length of the diffusion pattern 36 is estimated from the point light source 40 is the same for all the diffusion patterns 36. As shown in FIG. 24A, in the cross section of the diffusion pattern 36, the height (H) of the diffusion pattern 36 is equal. However, the width (W) of the diffusion pattern 36 gradually increases as it approaches the point light source 40.
[0045]
FIGS. 25A and 25B show how the light f is diffused by the wide diffusion pattern 36 and the narrow diffusion pattern 36. As shown in this figure, when the width of the diffusion pattern 36 is widened, the amount of light extracted from the light emitting surface 35 is reduced (the same effect as shortening the length of the diffusion pattern 36). If the width of the diffusion pattern 36 is gradually increased toward 40, in order to make the luminance distribution uniform, the diffusion pattern density in the vicinity of the point light source 40 is preceded as shown in FIGS. 25 (a) and 25 (b). It needs to be higher than in the case of the technical example. For this reason, it is possible to prevent the diffusion pattern 36 in the vicinity of the point light source 40 from appearing to be raised.
[0046]
(Fifth embodiment)
In the first to fourth embodiments, when the prospective angle from the point light source 40 is reduced in the vicinity of the point light source 40, when the height H of the diffusion pattern 36 is reduced in the vicinity of the point light source 40, The case where the width W in the cross section of the diffusion pattern 36 is increased in the vicinity has been described. However, these embodiments can be implemented not only independently but also in combination with each other. For example, in the surface light source device 54 of the embodiment shown in FIG. 26, as the point light source 40 is approached, the width W in the cross section of the diffusion pattern 36 gradually increases and the height H gradually decreases.
[0047]
(Sixth embodiment)
As the diffusion pattern 36, in the above-described embodiments, the kamaboko shape as shown in FIG. 27A is used. However, the diffusion pattern 36 is not limited to this, and for example, a triangular prism-like diffusion pattern 36 as shown in FIG. Good. In the kamaboko-shaped diffusion pattern 36, the light incident on the surface is uniformly reflected over a wide range and is incident on the light emitting surface 35 at various incident angles, so that the luminance 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, an unnecessary slope can be eliminated (that is, the surface opposite to the point light source 40 is a vertical surface), so that the density of the diffusion pattern 36 can be increased, The emission rate can be increased, and there is an advantage that a highly efficient light guide plate 32 can be obtained.
[0048]
In the case of the triangular prism-shaped diffusion pattern 36, the cross-sectional shape of the diffusion pattern 36 is changed according to the distance from the point light source 40 as in the surface light source device 55 shown in FIG. The density of the diffusion pattern 36 in the vicinity 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 cross-sectional view of the above surface light source device.
FIGS. 3A and 3B are operation explanatory views of the above surface light source device.
4A is a diagram for explaining a problem of the surface light source device same as the above, FIG. 4B is a diagram showing a change in luminance along the C1-C1 line in FIG. 4A, and FIG. 4C is a diagram in FIG. It is a figure which shows the change of the brightness | luminance along line C2-C2.
FIG. 5 is a diagram for explaining the reason why a problem occurs in the surface light source device of the above.
6 (a) and 6 (b) are diagrams for explaining the reason why the problem of the surface light source device same as above 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 light guide plate in the region far from the point light source and the behavior of light there, and FIG. 9B is a diagram showing the luminance distribution of light emitted from the light guide plate and passing through the semi-transmissive plate. It is a figure which shows the luminance distribution of the light after performing.
10A is a diagram showing a cross section of the light guide plate in the region near the point light source and the behavior of the light there, and FIG. 10B is a luminance distribution of light emitted from the light guide plate and passes through the semi-transmissive plate. It is a figure which shows the luminance distribution of the light after performing.
FIG. 11 is a diagram for explaining a problem in the above 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 view showing a diffusion pattern provided on the lower surface of the light guide plate used in the surface light source device same as above.
FIG. 14A is a diagram showing a diffusion pattern in one sector area in the prior art example, and FIG. 14B is a diagram showing a diffusion pattern in one sector area in the embodiment of the present invention.
15A is a diagram showing the arrangement of a diffusion pattern and the behavior of light in the light guide plate in the prior art example, and FIG. 15B is a diagram showing the arrangement of the diffusion pattern in the embodiment and the light in the light guide plate. It is a figure which shows behavior.
FIG. 16A is a diagram showing a cross section in a region far from the point light source of the light guide plate and the behavior of the light in the embodiment, and FIG. 16B is a luminance distribution and semi-transmission of the light emitted from the light guide plate. It is a figure which shows the luminance distribution of the light after passing a board.
FIG. 17A 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, and FIG. 17B is a luminance distribution and semi-transmission of light emitted from the light guide plate. It is a figure which shows the luminance distribution of the light after passing a board.
FIG. 18 is a plan view showing the characteristics of the arrangement of the diffusion pattern in one sector area according to another embodiment of the present invention.
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 the arrangement of diffusion patterns in one sector area.
FIG. 21A is a diagram showing the arrangement of the diffusion pattern and the behavior of light in the light guide plate in the above embodiment, and FIG. 21B is the diagram showing the arrangement of the diffusion pattern in the prior art example and the light in the light guide plate. It is a figure which shows behavior.
FIG. 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. It is a figure which shows the behavior of light.
FIG. 23 is still another embodiment of the present invention, and is a plan view showing the arrangement of diffusion patterns in one sector area.
FIG. 24A is a diagram showing the arrangement of the diffusion pattern and the behavior of light in the light guide plate in the embodiment, and FIG. 24B is the arrangement of the diffusion pattern in the prior art example and the light in the light guide plate. It is a figure which shows behavior.
FIG. 25A 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. 25B is a cross section in a region far from the light guide plate It is a figure which shows the behavior of light.
FIG. 26 is a cross-sectional view of yet another embodiment of the present invention.
FIG. 27A is a perspective view showing a kamaboko-shaped diffusion pattern, and FIG. 27B 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]
32 Light guide plate
33 Light emitting part
35 Light exit surface
36 Diffusion pattern
40 point light source
44 Light incident end face
48 translucent plate
θ1, θ2 Probable angle of diffusion pattern seen from light source
H Height of diffusion pattern
W Spread pattern width
C sector area

Claims (1)

A light guide plate that confines light introduced from the light incident surface, spreads the light into a planar shape, and emits the light from the light exit surface;
A number of diffusion patterns formed on the surface opposite to the light exit surface of the light guide plate;
In a surface light source device comprising a light source that is smaller than the width of the light incident surface for making light incident on the light guide plate from the light incident surface,
The diffusion pattern is discretely arranged along a circumferential direction centering on the light source so that the pattern density increases as the distance from the light source increases.
The angle in which the length of each of the diffusion patterns in the circumferential direction around the light source is viewed from the light source is smaller in the region closer to the light source than the region away from the light source ,
The diffusion pattern positioned at least in the vicinity of the light source is randomly displaced in a circumferential direction centered on the light source from a line segment connecting the light source and the center of the diffusion pattern farthest from the light source. A surface light source device.

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