JP4505755B2 - Diffuser and surface light source device - Google Patents

Description

  The present invention relates to a diffuser plate and a surface light source device, and more particularly to a surface light source device used as a backlight for a liquid crystal display panel and the like, and a diffuser plate used for the surface light source device.

  The surface light source device is used as a backlight of a transmissive liquid crystal display panel. A liquid crystal display panel generates an image by transmitting or blocking light for each pixel, but the liquid crystal display panel itself does not have a function of emitting light, so a surface light source device for backlight Need.

  FIG. 1 is an exploded perspective view showing the structure of a conventional surface light source device 1, and FIG. 2 is a sectional view thereof. 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 high refractive index such as polycarbonate resin or methacrylic resin, and a diffusion pattern 5 is formed on the back surface thereof by concavo-convex processing or dot printing of diffuse reflection ink. The light emitting unit 3 has a plurality of light emitting diodes (LEDs) 7 mounted on the front surface of the circuit board 6, and faces the side surface (light incident side 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 is attached to the lower surface of the light guide plate 2 with a double-sided tape 9.

  Therefore, in this surface light source device 1, as shown in FIG. 2, the light p emitted from the light emitting unit 3 and guided to the inside of the light guide plate 2 from the light incident side surface 8 is reflected on the surface of the light guide plate 2. By repeating total reflection with the back surface, the light is confined in the light guide plate 2 and propagates away from the light emitting unit 3. The light p propagating through the light guide plate 2 in this way enters the back surface of the light guide plate 2 and is diffusely reflected by the diffusion pattern 5. At this time, the light p propagates to the surface of the light guide plate 2 (light emitting surface 10). The light p reflected at an angle smaller than the critical angle of total reflection is emitted from the light emitting surface 10 to the outside of the light guide plate 2. On the other hand, the light p emitted from the back surface of the light guide plate 2 through a portion where the diffusion pattern 5 on the lower surface of the light guide plate 2 does not exist is reflected by the reflection plate 4 and returns to the inside of the light guide plate 2. Be trapped. Therefore, the light loss from the back surface of the light guide plate 2 is prevented by the reflection plate 4.

  The light emitted from the light emitting surface 10 of the light guide plate 2 in this way is emitted from a medium having a large refractive index to a medium having a small refractive index, so that the light is emitted just past the light emitting surface 10 as shown in FIG. The Hereinafter, assuming that the x axis is defined along the width direction of the incident side surface 8, the y axis is defined in the direction perpendicular to the incident side surface 8, and the z axis is defined in the direction perpendicular to the light emitting surface 10, the light emitting surface 10. The light emitted from the light becomes light having an elongated directivity profile extending substantially in the y-axis direction. In this state, when viewed from the direction (z-axis direction) perpendicular to the light emitting surface 10, the light emitting surface 10 of the surface light source device 1 appears dark. Therefore, in general, as shown in FIG. 3, a diffusion plate 11 having a relatively large diffusion degree is disposed on the light emitting surface 10, and the light emitted from the light emitting surface 10 is diffused by the diffusion plate 11. Thus, the peak direction of the light directivity profile is oriented in the z-axis direction perpendicular to the light exit surface 10.

  Alternatively, when a higher directivity than that in the case of FIG. 3 is required, the prism sheet 13 is used as shown in FIG. That is, the prism sheet 13 is disposed on the light emitting surface 10 of the light guide plate 2, and the diffusion plates 12 and 14 are disposed on the front and back sides of the prism sheet 13, respectively. In this case, the light emitted from the light emitting surface 10 is diffused by the diffusion plate 12 and the directionality of the light is made closer to the vertical direction, and then directed to the vertical direction by the prism sheet 13 and further diffused. The light is diffused by the plate 14 and emitted in a direction perpendicular to the light emitting surface 10. Here, the function of the diffusion plate 12 is to make the light incident on the prism sheet 13 at an angle such that the light passing through the prism sheet 13 faces the z-axis direction. Further, as shown in FIG. 4, the light that has passed through the prism sheet 13 has an angle at which almost no light is emitted in an oblique direction (the angle α at which the light intensity is minimum). In this direction, the image of the liquid crystal display panel is displayed. Since the light is diffused by the diffusion plate 14, the light is also distributed in the direction α, so that an image can be seen over a wide range centering on the z-axis direction. Furthermore, the diffusion plates 12 and 14 and the prism sheet 13 also have a function of preventing the diffusion pattern 5 formed on the lower surface of the light guide plate 2 from being seen from the front.

  In the surface light source device using the LED as described above, the power consumption is significantly reduced as compared with the surface light source device using the cold cathode tube. However, surface light source devices using LEDs are used for products with high portability such as mobile information terminals such as mobile phones and PDAs (Personal Digital Assitance) because of their small size and light weight. In order to improve convenience at the time, there is a strong demand for a long life of the power supply, and a reduction in power consumption is required. Therefore, low power consumption is also strongly desired for surface light source devices (backlights) used in these products. For this reason, more efficient LED is used for the surface light source device, and the number of light emitting elements used is decreasing with the improvement of the light emitting efficiency of the light emitting elements.

  However, in the surface light source device 1 as shown in FIG. 1 having the light emitting unit 3 in which a plurality of LEDs 7 are arranged in a line to form a linear light source, if the number of LEDs 7 is reduced, the light emitting surface (light emitting surface) becomes darker or the luminance is increased. Since unevenness increases, there is a limit in reducing the number of LEDs 7, and there is a limit in reducing power consumption.

  FIG. 5 shows a surface light source device 21 having a light emitting unit 23 in which several (preferably one) light emitting elements such as LEDs are gathered at one place to be a point light source. In this surface light source device 21, a point light source-like light emitting portion 23 is disposed so as to face a side surface (light incident surface 22 a) of a light guide plate 22 made of a transparent resin having a high refractive index such as polycarbonate resin or methacrylic resin. ing. On the lower surface of the light guide plate 22, a large number of diffusion patterns 24 are arranged on a concentric arc centered on the light emitting portion 23. Each diffusion pattern 24 is recessed on the lower surface of the light guide plate 22 in a circular arc shape and extends along the circumferential direction of a concentric circular arc centered on the light emitting portion 23. The reflection surface of the pattern 24 is orthogonal to the direction connecting the light emitting portion 23 and the diffusion pattern 24 (this direction is the r-axis direction) in plan view. Further, the diffusion pattern 24 is formed so that the pattern density gradually increases as the distance from the light emitting unit 23 increases.

  Even in the surface light source device 21, when the light emitting unit 23 emits light, the light emitted from the light emitting unit 23 enters the light guide plate 22 from the light incident surface 22 a and is totally reflected by the upper and lower surfaces of the light guide plate 22. The light propagates farther from the light emitting unit 23 while repeating the above. The light diffused and reflected by the diffusion pattern 24 on the lower surface of the light guide plate 22 while propagating through the light guide plate 22 enters the upper surface of the light guide plate 22 at an incident angle smaller than the critical angle of total reflection. The light is emitted from the upper surface (light emission surface). However, in such a surface light source device 21, light diffusely reflected by the diffusion pattern 24 is diffused in the zr plane, but not diffused in the xy plane, and is reflected by the diffusion pattern 24 when viewed from the z-axis direction. Continue straight ahead. For this reason, the amount of light emitted in an arbitrary direction centered on the light emitting unit 23 does not change even when diffused by the diffusion pattern 24, and the amount of light transmitted to each direction within the light guide plate 22 is emitted from the light emitting unit 23 to each direction. It depends on the amount of light emitted. Therefore, according to such a surface light source device 21, light is emitted from the light emitting unit 23 by making light of a light amount corresponding to the distance that the direction passes through the light guide plate 22 enter each direction in the light guide plate 22. The entire surface can be illuminated uniformly, and by combining it with a transmissive liquid crystal display panel, it is possible to produce a liquid crystal display device that is easy to see from a wide range of directions, and also contributes to the reduction of power consumption of the liquid crystal display device. can do.

Japanese Patent Laid-Open No. 11-84111

  When there is a possibility that a plurality of people can view the screen at the same time, such as a notebook computer, the screen must be seen from a wide direction, and a surface light source device with a wide directivity of the emitted light is required. However, mobile devices such as mobile phones are premised on personal use, and conversely, it is preferable to narrow the directivity so that it cannot be seen by neighboring people in a train or the like. In particular, a surface light source device that does not emit light in an oblique direction is desired.

  Further, when no light is emitted in the oblique direction, there is no extra emitted light, and the power consumption can be further reduced. Or the light of a light emission part can be gathered in the front, and front brightness can be made high, and efficiency (= brightness / power consumption) of a surface light source device can be made high anyway.

  However, if a diffusion plate is used as in the surface light source device 1 as in the first conventional example, light is inevitably emitted in all directions, and it is difficult to narrow the range of light emitted from the liquid crystal display device. Met.

  Moreover, in the surface light source device 21 as in the second conventional example, the light traveling direction is directly converted into a direction perpendicular to the light guide plate 22 while spreading the light emitted from the light emitting unit 23 throughout the light guide plate 22. In other words, since the light is only emitted from the light exit surface, there has been no particular effort to narrow the light directivity angle.

  In addition, in the surface light source device 21 as in the second conventional example, when viewed obliquely from above, radial luminance unevenness (bright line) R centering on the light emitting portion 23 is partially as shown in FIG. It was visible. For this reason, when used in a liquid crystal display device or the like, there is a problem that depending on the viewing direction, the luminance unevenness R prevents the image from being viewed and the quality of the image display device or the like is degraded.

  The present invention has been made in view of the above-described conventional problems, and an object of the present invention is to provide a diffusion plate capable of reducing radial luminance unevenness generated in a surface light source device using a point light source. There is to do.

The first diffusion plate according to the present invention has a plurality of concave and convex portions that are long in one direction whose surface shape changes in a concentric direction centering on a point determined as a light emitting position, and the short direction of each concave and convex portion is The concavity is directed concentrically with respect to the point, the length of the uneven portion in the longitudinal direction is shorter than the length of the side of the surface, and the uneven portion is formed discontinuously in the radial direction centered on the point. It is characterized by being.

In the first diffusion plate according to the present invention, the surface has a plurality of concave and convex portions that are long in one direction whose surface shape changes in a concentric direction centering on a point determined as the light emission position. The hand direction is concentric with respect to the point, the length of the uneven portion in the longitudinal direction is shorter than the length of the side of the surface, and the uneven portion is not in the radial direction centered on the point. Since it is formed continuously, the direction in which the full width at half maximum of the light emitted from the light exit surface of the light guide plate is oriented concentrically with respect to the point determined as the light emission position (that is, the position of the point light source) By combining the light guide plate and the diffuser plate, the difference in directivity (full width at half maximum) due to the direction of light emitted from the light guide plate and transmitted through the diffuser plate is reduced. As a result, in the surface light source device using this diffusing plate, radial luminance unevenness is reduced. Further, in the liquid crystal display device in which the liquid crystal display panel and the surface light source device are combined, it is easy to see the screen from an arbitrary direction on the front side.

The second diffusion plate according to the present invention includes a plurality of ring-shaped regions concentrically divided around a point determined as a light emission position, and a surface shape in a concentric direction centering on the point in each of the regions. And has a concavo-convex pattern consisting of a plurality of concavo-convex portions arranged in a concentric direction at a constant period on the surface, and the period of the concavo-convex pattern is different between adjacent ring-shaped regions. It is said.

The second diffuser plate according to the present invention has a plurality of annular zones concentrically centered around a point defined as the light emitting position, and the irregularities formed in each annular zone. Since the surface shape changes in a concentric direction centering on a point determined as the light emitting position, the direction in which the full width at half maximum of the light emitted from the light emitting surface of the light guide plate is narrow is a predetermined one point (for example, a point light source) If the light guide plate and this diffuser plate are combined, the directivity (full width at half maximum) due to the direction of the light emitted from the light guide plate and transmitted through the diffuser plate can be reduced. The difference becomes smaller. As a result, in the surface light source device using this diffusing plate, radial luminance unevenness is reduced. Further, in the liquid crystal display device in which the liquid crystal display panel and the surface light source device are combined, it is easy to see the screen from an arbitrary direction on the front side.
Furthermore, since the period of the concavo-convex pattern is different between adjacent ring-shaped areas, small moiré fringes can be generated by the concavo-convex pattern, thereby preventing the generation of large moiré fringes between the areas. be able to.
In the second diffusing plate according to the present invention, the concavo-convex pattern may have a cross-sectional wave shape, a triangular wave shape, a trapezoidal shape, or a cylindrical lens shape.

The surface light source device according to the present invention is arranged to face a point light source, a light guide plate that spreads light introduced from the point light source into a planar shape and emits the light from the light exit surface, and a light exit surface of the light guide plate. It is characterized by comprising the diffusion plate according to the present invention . According to such a surface light source device, it becomes possible to reduce the difference in directivity (full width at half maximum) due to the direction of light emitted from the light guide plate and transmitted through the diffuser plate, so that radial luminance unevenness can be reduced. become. Further, in a liquid crystal display device in which a liquid crystal display panel and the surface light source device are combined, the screen can be easily viewed from an arbitrary direction on the front side.

  It should be noted that the above-described components of the present invention can be combined as much as possible.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

(First embodiment)
FIG. 7 is an exploded perspective view showing the structure of the surface light source device 31 according to the first embodiment of the present invention, and FIG. 8 is a schematic sectional view thereof. The surface light source device 31 mainly includes a light guide plate 32, a light emitting unit 33, a reflection plate 34, and a diffusion prism sheet 35. The light guide plate 32 is formed in a rectangular flat plate shape using a transparent resin such as polycarbonate resin or methacrylic resin, and a light diffusion pattern 36 is provided on the back surface. A light incident surface 37 is formed at one corner portion of the light guide plate 32 by cutting the corner portion obliquely in plan view.

  Although not shown in the drawings, the light emitting unit 33 is one in which one or several LEDs are sealed in a transparent mold resin, and a surface other than the front surface of the mold resin is covered with a white resin. Is emitted from the front surface of the light emitting section 33 directly or after being reflected at the interface between the mold resin and the white resin. The light emitting unit 33 is disposed at a position where the front surface thereof faces the light incident surface 37 of the light guide plate 32.

  An arrangement of the light diffusion patterns 36 formed on the light guide plate 32 is shown in FIG. In the description of the embodiment of the present invention, the z-axis is defined in a direction perpendicular to the surface of the light guide plate 32, and the x-axis and the y-axis are defined in directions parallel to two sides adjacent to the light incident surface 37, respectively. . Further, when considering light propagating in an arbitrary direction or considering reflection at an arbitrary light diffusion pattern 36, a direction parallel to the surface of the light guide plate 32 within a plane that includes the propagating light beam and is perpendicular to the light guide plate 32 It is also assumed that the r axis is defined in the direction parallel to the surface of the light guide plate 32 in a plane perpendicular to the light guide plate 32 including the direction connecting the light emitting portion 33 and the light diffusion pattern 36. Further, an angle formed by the x axis and the r axis is θ.

  The light diffusion patterns 36 formed on the lower surface of the light guide plate 32 are arranged on a concentric arc centering on the light emitting portion 33 (particularly, the internal LED), and each light diffusion pattern 36 is guided. The optical plate 22 is formed in a straight line by recessing the back surface of the asymmetrical triangular cross section. In the light diffusion pattern 36 having a triangular cross section, the inclination angle of the slope closer to the light emitting portion 33 is preferably within 20 °. Each light diffusion pattern 36 extends linearly along the circumferential direction of the arc centered on the light emitting portion 33, and the reflection surface of each light diffusion pattern 36 is viewed in plan view (viewed from the z-axis direction). And perpendicular to the direction (r-axis direction) connecting the light emitting portion 33 and the light diffusion pattern 36. The light diffusion pattern 36 is formed so that the pattern density gradually increases as the distance from the light emitting unit 33 increases. However, in the vicinity of the light emitting portion 23, the pattern density of the diffusion pattern 24 may be substantially uniform. The light incident surface 37 of the light guide plate 22 may be formed with an optical element 44 such as a lens or a prism in order to control the alignment pattern of light entering the light guide plate 32 from the light emitting unit 33.

  The reflecting plate 34 has a surface subjected to mirror finishing by Ag plating, and is disposed so as to face the entire back surface of the light guide plate 22.

  The diffusion prism sheet 35 is obtained by forming a transparent uneven diffusion plate 39 on the surface of a transparent plastic sheet 38 and forming a transparent prism sheet 40 on the back surface of the plastic sheet 38. The uneven diffusion plate 39 and the prism sheet 40 are obtained by dropping an ultraviolet curable resin on the upper surface of the plastic sheet 38 and pressing the ultraviolet curable resin with a stamper to spread the ultraviolet curable resin between the stamper and the plastic sheet 38. It is formed by irradiating an ultraviolet curable resin with ultraviolet rays and curing it (Photo Polymerization method).

  FIGS. 10A, 10B and 10C are explanatory views for explaining the structure of the uneven diffusion plate 39. FIG. As shown in FIG. 10A, the uneven diffusion plate 39 is a pattern in which repeated patterns 41 are arranged periodically in the horizontal and vertical directions with almost no gap. Further, as shown in FIG. 10B, the repetitive pattern 41 is a pattern in which convex portions 42 having a conical shape with blunt apexes as shown in FIG. The vertical and horizontal widths H and W of one repeating pattern 41 are larger than the pixel size of the liquid crystal display panel in order to prevent moire fringes, and both are preferably 100 μm or more and 1 mm or less. Further, it is desirable that the convex portions 42 constituting the repetitive pattern 41 have irregular dimensions and have an outer diameter D of 5 μm or more and 30 μm or less (particularly, about 10 μm is preferable).

  Since the uneven diffusion plate 39 has a special diffusion characteristic, the uneven shape of the pattern must be accurately controlled. In that case, if one uneven pattern is arranged periodically, all the uneven patterns have the same shape, so that all the uneven patterns can be produced in the same way and an accurate uneven shape can be formed. However, in such a method, moire fringes are generated on the screen of the liquid crystal display device, and pixels are easily noticeable. On the other hand, if the concave / convex pattern is to be arranged at random, the shape and size of the concave / convex pattern must be changed one by one, making it difficult to produce an accurate shape. In addition, the characteristics of the uneven diffusion plate may change depending on the location. Therefore, in the uneven diffusion plate 39 of the present invention, a convex pattern 42 having a random shape and size is randomly arranged to form a repetitive pattern 41, and the repetitive pattern 41 is periodically arranged to obtain moire fringes and the like. The pattern production of the uneven diffusion plate 39 is facilitated while suppressing the generation.

  FIG. 11 is a perspective view showing the structure of the prism sheet 40 from the back side. The prism sheet 40 is formed by concentrically arranging arcuate prisms 43 (amplitude prisms 43 are exaggeratedly drawn in FIG. 11) having a triangular asymmetric cross section. 43 is formed in an arc shape around the position where the LED of the light emitting unit 33 is arranged.

  The uneven diffusion plate 39 and the prism sheet 40 do not need to be integrally formed as in this embodiment, and may be formed separately and arranged with a gap therebetween. However, as in this embodiment, the one formed integrally with the plastic sheet 38 is advantageous in that the overall thickness is reduced and the cost is reduced.

  Next, the behavior of the light p in the surface light source device 31 will be described with reference to FIGS. 12 and 13A and 13B. 12 is a diagram showing the behavior of light when viewed from obliquely above the light guide plate 32, FIG. 13A is a diagram for explaining the behavior of light in the cross section (zr plane) of the light guide plate 32, and FIG. ) Is an enlarged view of a portion X in FIG. The light p emitted from the light emitting unit 33 enters the light guide plate 32 from the light incident surface 37. The light p incident on the light guide plate 32 from the light incident surface 37 spreads radially in the light guide plate 32. At this time, the amount of light in each direction of the light p spreading in the light guide plate 32 is the light amount of the light guide plate 32 in each direction. It is desirable to design the optical element 44 provided on the light incident surface 37 so as to be proportional to the area. Specifically, as shown in FIG. 14, the amount of light emitted from the side of the light guide plate 32 (side in the x-axis direction) within the range of the spread Δθ located in any direction of θ is within this range. It is desirable to be proportional to the area of the light guide plate included in Δθ (the area of the area shown by hatching in FIG. 14), thereby making the luminance distribution of the surface light source device 31 in each direction uniform. it can.

  The light p incident on the light guide plate 32 travels in the direction away from the light emitting unit 33 (r-axis direction) while repeating total reflection on the upper and lower surfaces of the light guide plate 32. Each time the light p incident on the lower surface of the light guide plate 32 is reflected by the light diffusion pattern 36 having a triangular cross section, the incident angle γ to the upper surface (light output surface 45) of the light guide plate 32 becomes smaller. Then, the light p incident at an incident angle γ smaller than the critical angle of total reflection passes through the light exit surface 45 and is emitted to the outside of the light guide plate 32 along the light exit surface 45. Since all the light diffusion patterns 36 are arranged so as to be orthogonal to the direction connecting the light emitting portion 33 and each light diffusion pattern 36, the light p propagating in the light guide plate 32 is diffused by the light diffusion pattern 36. However, the light p is diffused in a plane (zr plane) perpendicular to the light guide plate 32 including the direction connecting the light emitting portion 33 and the light diffusion pattern 36, but in the plane (xy plane) of the light guide plate 32. Then go straight without spreading.

  On the other hand, the light p transmitted through the lower surface without being reflected by the lower surface of the light guide plate 32 is regularly reflected by the reflection plate 34 facing the lower surface of the light guide plate 32 and returns to the light guide plate 32. Propagate inside.

  As a result, the range of light emitted from the light emitting surface 45 of the light guide plate 32 is considerably limited. If the inclination angle β of the light diffusion pattern 36 having a triangular cross section is 12 °, for example, the light emission The light emission direction φ in the zr plane perpendicular to the surface 45 is about 45 ° to 90 °.

  In this way, the light emitted from the light emitting surface 45 of the light guide plate 32 does not spread in the θ direction, and the directivity angle Δφ in the φ direction is limited, so that the light has a fairly narrow directivity. In this way, light having a small spread and strong directivity emitted along the light exit surface 45 is bent in a direction perpendicular to the light exit surface 45 by passing through the prism sheet 40 of the diffusion prism sheet 35. Then, it is diffused by the uneven diffusion plate 39 of the diffusion prism sheet 35, and the directivity is expanded.

  Next, the function of the diffusion prism sheet 35 will be described. First, for comparison, let us consider a case where light is emitted in a direction perpendicular to the light emission surface without using the diffusion prism sheet 35. In order to emit light vertically without using the diffusion prism sheet 35, the light must be emitted in the vertical direction by the light diffusion pattern of the light guide plate. In order to emit light vertically by the light diffusion pattern, as shown in FIG. 15, it is necessary to increase the inclination angle of the slope of the light diffusion pattern 36A, and the inclination angle β of the slope closer to the light emitting portion 33 is The inclination angle ρ of the slope on the side far from the light emitting portion 33 is 85 °. FIG. 16 is a diagram showing the directivity in the zr plane when the light guide plate 32A having the light diffusion pattern 36A as shown in FIG. 15 is used, and the horizontal axis is an angle measured from the z axis in the zr plane. φ indicates the light intensity. As can be seen from FIG. 16, the directivity in this case is asymmetric between the side closer to the light emitting unit 33 (φ <0) and the side farther from the light emitting unit 33 (φ> 0), and the side farther from the light emitting unit 33. It ’s pretty broad. Incidentally, the angle φ (half-value width) at which the intensity becomes half of the peak value is about −13 ° on the side closer to the light source, and is about 26 ° on the side far from the light source. The half-value width of light intensity in a plane perpendicular to the zr plane and parallel to the z-axis is about 5 ° (see FIG. 18).

  FIG. 17 shows light having directivity as shown in FIG. As shown in FIG. 17, the light emitted from the light emitting surface 45A (the hatched area represents the light emitting area. The same applies hereinafter) extends in the range of Δφ in the φ direction. In the ω direction, it extends in the range of Δω (in the plane zθ plane perpendicular to the zr plane and including the z axis, the angle formed with the z axis is ω, and the directivity angle of light in the ω direction is Δω), φ The directivity angle Δφ in the direction is considerably wider than the directivity angle Δω in the ω direction. Moreover, as shown in FIG. 17, the light emitted from the light exit surface 45A after propagating in the light guide plate 32A in the r1 direction, and the light emitted from the light exit surface 45A after propagating in the light guide plate 32A in the r2 direction Then, the direction of the wide directivity angle Δφ is different. Therefore, when the surface light source device is viewed from the direction of the point P, the light propagating in the r1 direction can be seen in the light guide plate 32A, but the light propagating in the r2 direction cannot be seen, and the light guide plate 32A is shown in FIG. Such radial luminance unevenness R can be seen.

  Even when a diffusion plate was placed on the light guide plate 32A of the comparative example as shown in FIG. 15, the radial luminance unevenness did not disappear. Further, in such a light guide plate 32A, the amount of light included in the range of φ = ± 10 ° is about 30% of the whole, and in order to reduce radial luminance unevenness, a diffusion plate is provided on the light guide plate 32A. As a result, the light emission efficiency suddenly decreased.

  On the other hand, when the prism sheet 40 is placed on the light guide plate 32, it is not necessary to emit light in the vertical direction by the light diffusion pattern 36, and the light emitted along the light emitting surface 45 is emitted from the prism sheet 40. Will be bent in the vertical direction. FIG. 18 is a diagram showing the directivity in the ω direction and the directivity in the φ direction of light transmitted through the prism sheet 40 placed on the light guide plate 32, and both show symmetrical profiles. As can be seen from FIG. 18, the angle at which the light intensity becomes half of the peak value (half-value width) is about 5 ° in the ω direction, and about 15 ° in the φ direction, and no prism sheet is used. Compared with the comparative example, the light directivity angle Δφ in the φ direction is narrower.

  As described above, when the prism sheet 40 composed of the arc-shaped prism 43 centering on the light emitting unit 33 is used, the directivity of light passing through the prism sheet 40 does not change in the ω direction as shown in FIG. In the φ direction, light is collected and the directivity in the φ direction is narrowed. Therefore, the difference Δφ−Δω between the directivity angle Δω in the ω direction and the directivity angle Δφ in the φ direction becomes small, and radial luminance unevenness is reduced.

  However, in actuality, the prism sheet 40 alone cannot sufficiently reduce the difference between the directivity in the ω direction and the directivity in the φ direction (the full width at half maximum in the ω direction is 10 °, and the full width at half maximum in the φ direction). Is 30 °, and there is a difference of 20 ° in the full width at half maximum.) Even though the radial luminance unevenness is reduced, the luminance unevenness still appears strong. Further, the spread of light in the ω direction (half-value width) is as narrow as about 5 °, and it cannot be used for general purposes unless the light is further spread in the ω direction.

  As shown in FIG. 20, in a surface light source device 31B using a linear light source 33B such as a cold cathode tube or a light emitting unit 3 in FIG. 1, light is emitted along the surface of the light guide plate 32B, and this is used as a prism sheet. A method of deflecting in the vertical direction at 40B has been proposed (for example, JP-A-11-84111). In this case, the direction in which the prism 43B of the prism sheet 40B extends is parallel to the linear light source 33B, and as shown in FIG. 21, the directivity angle Δφx in the x-axis direction parallel to the prism 43B is orthogonal to the prism 43B. It was considerably wider than the directivity angle Δφy in the y-axis direction, and the directivity angle anisotropy was large. However, in such a surface light source device 31B, since the direction of anisotropy of the directivity angle does not change depending on the position on the light emitting surface 45B, no radial luminance unevenness has occurred.

  On the other hand, in the surface light source device 31 of the present invention, the light emitted radially from the light source 33 having the point light source shape is diffusely reflected by the light diffusion pattern 36 formed concentrically on the lower surface of the light guide plate 32. Therefore, the directivity anisotropy of the emitted light differs depending on the position on the light emitting surface 45, and radial luminance unevenness occurs. That is, the radial luminance unevenness is a problem peculiar to the surface light source device having the point light source-like light emitting portion 33 and the concentric light diffusion pattern 36, and the present invention intends to improve such luminance unevenness.

  In the surface light source device 31B shown in FIG. 20, the directivity of light is wide in the prism length direction (x-axis direction) of the prism sheet 40B, whereas in the surface light source device 31 of the present invention, the prism is The directivity of light is narrow in the prism length direction (θ direction) of the sheet 40, which is completely opposite to the surface light source device 31B. In other words, in the method of the present invention, it is necessary to widen the directivity of light in the prism length direction and narrow it in the direction perpendicular thereto, but in this way, the surface light source device 31B in FIG. The directivity increases, and extra light increases in the prism length direction, and the opposite result that the required viewing angle cannot be obtained in the direction perpendicular thereto. As described above, the present invention is intended to solve the problems occurring in the surface light source device of the original system.

Below, the effect of the uneven | corrugated diffuser plate 39 used for the surface light source device 31 of this invention is demonstrated. For comparison, first, a case where a general diffusion plate that is normally used is used as the uneven diffusion plate will be described. As a general diffusing plate, the directivity when parallel light is vertically incident is as shown in FIG. 22 (the full width at half maximum is 10 °). When this general diffusion plate was placed on the prism sheet 40, the directivities in the ω direction and the φ direction were as shown in FIG. Here, ω refers to the angle formed with the z-axis in the zθ plane, and φ refers to the angle formed with the z-axis in the zr plane. The full width at half maximum Δω and Δφ in the ω direction and φ direction are respectively Δω = 20 °
Δφ = 33 °
And the difference is
Δφ−Δω = 13 °
Thus, the difference in full width at half maximum is reduced by 38% compared to the case of the prism sheet 40 alone. For this reason, although the radial luminance unevenness is reduced to some extent, the luminance unevenness is still visible. Considering the light actually emitted in the effective direction, about 23% of the light is included in the full width at half maximum Δω = 20 °. That is, 77% of light is wasted. Further, when ω = 2.5 ° away from the vertical direction, the luminance is reduced by nearly 20%, and there is a problem that the luminance appears to be different between the left and right eyes and is difficult to see.

On the other hand, the directivity when parallel light is vertically incident on the uneven diffusion plate 39 as shown in FIG. 10 is as shown in FIG. When this uneven diffusion plate 39 is placed on the prism sheet 40, the directivities in the ω direction and the φ direction are as shown in FIG. That is, the full widths at half maximum Δω and Δφ in the ω direction and φ direction are respectively Δω = 20 °
Δφ = 29 °
And the difference is
Δφ−Δω = 9 °
Thus, the difference in full width at half maximum is reduced by 58% compared to the case of the prism sheet 40 alone. For this reason, radial luminance unevenness can be considerably reduced. Further, the amount of light included in the full width at half maximum Δω = 20 ° in the narrowest direction is about 30% of the total amount of light, and the useless light is reduced to 70%. For this reason, the luminance in the vertical direction is improved by about 20% as compared with a general diffusion plate, and the luminance reduction rate at a position away from ω = 5 ° from the vertical direction is less than 10%. The difficulty of seeing due to unevenness has been almost eliminated.

  The reason for this will be explained. The light emitted from the light guide plate 32 has a slightly gentle profile as shown in FIG. On the other hand, when the diffusion characteristic (directivity with respect to perpendicular incident light) of the uneven diffusion plate has a gentle profile like the light emitted from the light guide plate as shown in FIG. The light that exits and passes through the uneven diffusion plate becomes even smoother, and its profile is as shown in FIG. 26 (b) ′ (just like the phenomenon that the center is sharpened by autocorrelation). With such directivity, if the light is spread to some extent in the ω direction, very strong diffusion is required and spread in the φ direction, and Δφ−Δω is not so small. In addition, useless light in an oblique direction also increases.

  On the other hand, as shown in FIG. 26 (c), when the diffusing characteristic of the uneven diffusion plate is close to a rectangle, the profile of light that has passed through the uneven diffusion plate from the light guide plate is shown in FIG. 26 (c) ′. It becomes close to a rectangle as shown. While Δω greatly spreads with such relatively small diffusion, Δφ does not spread so much, so Δφ−Δω becomes small. For example, the directivity angle Δω in the ω direction of the light guide plate (shown in FIG. 27B) is sufficiently larger than the directivity angle Δφ in the φ direction of the light guide plate (shown in FIG. 27B ′). When a diffusion plate having diffusion characteristics as shown in FIG. 27A is placed on the light guide plate, the directivity angle Δω of light transmitted through the uneven diffusion plate in the ω direction is as shown in FIG. It depends on the directivity of the diffusion plate having a diffusion characteristic wider than the directivity angle of the light emitted from the light guide plate. On the other hand, in the φ direction, the directivity of the light emitted from the light guide plate is originally widened as shown in FIG. 27 (b) ′. Therefore, the directivity of the light transmitted through the uneven diffusion plate is as shown in FIG. c) As shown at ', the half width is not changed, only the center and the edge become slightly gentle. Therefore, when the directivity angle of light emitted from the light guide plate is narrow in the ω direction and wide in the φ direction, there is an effect of reducing Δφ−Δω by using a diffusion plate with small diffusion.

  Furthermore, as shown in FIG. 26 (d), in the case of diffusion characteristics having peaks on both sides across the direction perpendicular to the light guide plate, the profile of the light that has exited the light guide plate and passed through the uneven diffusion plate Is closer to a rectangle as shown in FIG. 26 (d) ', and the proportion of light that falls within the required angle increases.

  In order to widen the directivity of the emitted light in the θ direction or the ω direction, a method of bending along the θ direction as in the light diffusion pattern 36C shown in FIGS. 28A, 28B, and 28C is also considered. It is done. Here, the θ-axis is in a direction perpendicular to the zr plane. However, in such a method, as shown in FIG. 29, out of the light p deflected by hitting the light diffusion pattern 36C, the light hitting the light diffusion pattern 36C like the light p shown by the broken line in FIG. Although the light is emitted, it is emitted from the light guide plate 32C after being reflected by the light diffusion pattern 36C a plurality of times when the angle that hits the light diffusion pattern 36C first is small, such as the light p indicated by the solid line in FIG. There is a problem that the spread in the direction increases and the spread in the θ direction of the emitted light p increases as the distance from the light emitting portion 33C increases. In the surface light source device 31 of the present invention, the light diffusion pattern 36 has a linear shape, and thus there is no such problem.

  Further, in the case of the light diffusion pattern 36C as shown in FIGS. 28A, 28B, and 28C, when viewed from the direction perpendicular to the light guide plate 32C, after the light hits the light diffusion pattern 36C for the first time, Since the traveling direction is curved, it becomes difficult to design the uniform luminance. Therefore, the deflection angle in the θ direction by the light diffusion pattern 36C cannot be increased so much, and when this deflection angle is increased, the light is spread straight and emitted in a concentric pattern as considered in the present invention. It becomes different from the method of making it spread, and becomes a normal method of diffusing and spreading light. The deflection angle in the zr plane and the deflection angle in the xy plane should be about 4: 1 (preferably 10: 1) on average, but for the reasons described above, FIGS. ) With the light diffusion pattern 36C as shown in (c), it is difficult to realize such a deflection angle.

  In the above embodiment of the present invention, the light diffusion pattern 36 has a triangular cross section, but the cross sectional shape of the light diffusion pattern 36 has a circular arc shape or a semicircular cross section as shown in FIG. There is no problem. However, the light diffusion pattern 36 having a circular arc or semicircular cross section is not preferable because the directivity angle Δφ in the φ direction of the light emitted from the light exit surface 45 is widened. For the same reason, even in the case of the light diffusion pattern 36 having a triangular cross section, it is not preferable to mix the light diffusion patterns 36 having different inclination angles β. Further, instead of using the light diffusion pattern 36, the light in the light guide plate 32 may be emitted from the light emitting surface 45 by diffusing with a hologram or the like.

  As a method for emitting the light in the light guide plate 32 from the light emitting surface 45, a wedge-shaped light guide plate 32 that is thin on the side far from the light emitting portion 33 may be used as shown in FIG. However, in the light guide plate 32 having a rectangular shape in plan view, the area of the light guide plate that emits light varies depending on the θ direction (see FIG. 14), and the amount of light emitted from the light emitting unit 33 also varies depending on the direction (angle θ). It is impossible to make the light emitting surface 45 shine uniformly only by making 32 a wedge shape. If the light guide plate 32 is made to have a wedge shape to emit light uniformly, the planar shape of the light guide plate 32 must be a complicated shape. Therefore, even when the light guide plate 32 has a wedge shape, it is necessary to combine it with the light diffusion pattern 36.

(Second Embodiment)
FIG. 32 is a perspective view showing the structure of a surface light source device 51 according to another embodiment of the present invention. 33A is a plan view showing the uneven diffusion plate 53 of the diffusion prism sheet 52 used in the surface light source device 51, and FIG. 33B is an enlarged view of the Y portion of FIG. 33A. 33 (c) is a cross-sectional view taken along the line ZZ of FIG. 33 (b). In the surface light source device 51, the structures of the light guide plate 32, the light emitting unit 33, and the reflection plate 34 are the same as those described in the first embodiment.

  The diffusion prism sheet 52 has an uneven diffusion plate 53 formed on the front surface and a prism sheet 40 formed on the back surface. The prism sheet 40 is the same as that described in the first embodiment (see FIG. 11). It is. The uneven diffusion plate 53 diffuses light transmitted through the prism sheet 40 only in the ω direction. That is, as shown in FIG. 33A, the uneven diffusion plate 53 is divided into concentric ring-shaped regions 54a, 54b,... Having a width Λr with the light emitting portion 33 as the center, and each region 54a. , 54b,..., A sinusoidal concave / convex pattern 55 is formed along the θ direction with a period Λθ sufficiently smaller than the width Λr, as shown in FIGS. 54a, 54b,... Have a slightly different period Λθ. For example, the width of the regions 54a, 54b,... Is Λr = 100 μm, and the pattern period of the concave / convex pattern 55 is alternately changed to Λθ = 9 μm and Λθ = 10 μm. This is to intentionally generate small moire fringes in order to prevent visible moire fringes with a large period due to the uneven pattern 55 between adjacent regions 54a, 54b,. Of course, in order to suppress moire fringes, the width Λr of the regions 54a, 54b,... And the period Λθ of the concavo-convex pattern 55 may be randomly changed.

  Since the period Λθ changes at the boundary between the regions 54a, 54b,..., Light is slightly diffused in the φ direction in this vicinity, but by setting Λr >> Λθ, the diffusion in the φ direction is reduced and almost ω Directional diffusion can be achieved. Further, the cross-sectional shape of the concave / convex pattern 55 is not limited to a cross-sectional wave shape as shown in FIG. 33C, but may be a cross-sectional shape such as a triangular wave shape, a trapezoidal shape, or a cylindrical lens array shape.

  FIG. 34 is a diagram showing diffusion characteristics in the ω direction and φ direction when parallel light is incident on the uneven diffusion plate 53 used in this embodiment, and the horizontal axis is an angle measured from the z axis. (Ω, φ) is represented, and the vertical axis represents the light intensity. As can be seen from FIG. 34, the uneven diffusion plate 53 has a large diffusivity in the ω direction (full width at half maximum Δω = 20 °), but has almost no diffusibility in the φ direction.

FIG. 35 is a diagram showing the directivity angles of light in the ω direction and φ direction when the uneven diffusion plate 53 is placed on the light guide plate 32 as described in the first embodiment, and the horizontal axis is z. The angle (ω, φ) measured from the axis is represented, and the vertical axis represents the intensity of light emitted in each direction. As can be seen from FIG. 35, the light transmitted through the uneven diffusion plate 53 in this case has a full width at half maximum of Δω = 20 ° in the ω direction and a full width at half maximum of Δφ = 26 ° in the φ direction. The difference is Δφ−Δω = 6 °
As compared with the case of the prism sheet 40 alone, the difference in full width at half maximum is reduced by 71%. For this reason, radial luminance unevenness is hardly visible.

  In the characteristics shown in FIG. 35, the amount of light included in the range of the full width at half maximum Δω = 20 ° is 44% of the total amount of light, and unnecessary light is reduced to 56%. As a result, the luminance in the vertical direction in the surface light source device 51 is increased by 45% compared to a normal diffusion plate.

(Third embodiment)
FIG. 36 shows a cross-sectional shape in the zr plane of the prism sheet 56 of the uneven diffusion plate used in still another embodiment of the present invention. In this prism sheet 56, the directivity in the φ direction is narrowed by bending a slope (reflecting surface) 58 on the side far from the light emitting portion 33 of the slope in the prism cross section so as to project halfway, and the brightness in the vertical direction is reduced. As well as reducing radial brightness unevenness.

  FIG. 37 is a diagram showing the directivity in the φ direction of light transmitted through the prism sheet 56. The horizontal axis represents the angle φ measured from the z axis, and the vertical axis represents the light intensity. As shown in FIG. 36, the inclination angle δ = 74 ° of the inclined surface (incident surface) 57 near the light emitting portion 33, the inclination angle ε = 56 ° of the lower portion of the inclined surface 58 far from the light emitting portion 33, The prism sheet 56 has an upper inclination angle ζ = 59 °, a prism portion height T2 = 31.2 μm, and a slope height T1 = 18.7 μm above the protruding portion of the slope 58 far from the light emitting portion 33. This is the result of simulation. According to FIG. 37, the half-value width in the φ direction is Δφ / 2 = ± 11 °, and the half-value width is 25% smaller than the case where the middle of the slope 58 is not bent. Further, the light amount included in the range of the full width at half maximum Δφr = 20 ° is 48% of the total light amount, and the vertical efficiency is good.

The reason is considered as follows. As in the first embodiment, when the slope (reflecting surface) 38 on the side far from the light emitting unit 33 is a flat surface, the prism sheet 40 appears to shine when viewed from the vertical direction. As shown in FIG. 38, the other areas Sb and Sc are dark only in the area of Sa. Moreover, the light hitting the region Sb of the inclined surface 38 is deflected in an oblique direction as shown by a broken line in FIG. 38, which causes radial luminance unevenness and luminance reduction in the vertical direction. Therefore, in the case of the prism sheet 40 as shown in FIG.
Sa / So = 38% (However, So = Sa + Sb + Sc)
There was only.

On the other hand, when the inclined surface 58 is bent as in the prism sheet 56 of this embodiment, the light impinging on the region Sb of the inclined surface 58 is also deflected in the vertical direction as shown by the broken line in FIG. Therefore, problems such as luminance unevenness and luminance reduction in the vertical direction are solved. In other words, by expanding the area that appears bright when viewed from the direction perpendicular to the prism sheet 56 to Sa and Sb, radial luminance unevenness and a decrease in efficiency in the vertical direction can be suppressed. According to such a prism sheet 56, the ratio of the illuminated area is
(Sa + Sb) / So = 69% (However, So = Sa + Sb + Sc)
It becomes.

  When the light transmitted through the prism sheet and the uneven diffusion plate is viewed from the direction perpendicular to the surface light source device, if the area of the shining area exceeds 50% (preferably 60%), it is a considerably preferable characteristic as a surface light source device. Therefore, according to such a prism sheet, good characteristics can be obtained.

  Various other structures can be considered as the prism sheet structure for increasing the amount of light emitted in the vertical direction. What is shown in FIG. 40 is a prism sheet 59 in which a slope 58 far from the light emitting portion 33 is curved into a curved surface. Also, as in the prism sheet 60 shown in FIG. 41, the area of the region shining in the vertical direction can be increased by curving the slope 57 on the side close to the light emitting portion 33 in a convex shape.

  Further, as shown in the prism sheet 61 shown in FIG. 42, by increasing the inclination angle ε of the inclined surface 58 far from the light emitting unit 33, the light reflected to the light emitting unit 33 side by the inclined surface 58 is transmitted to the light emitting unit 33. By reflecting again at the near-side inclined surface 57, the light can be deflected in the vertical direction, thereby increasing the area of the region shining in the vertical direction. For example, when the inclination angle ε = 56 ° of the slope 58 far from the light emitting portion 33 and the inclination angle δ = 85 ° of the slope 57 closer to the light emitting portion 33, the directivity characteristics in the φ direction are shown in FIG. As shown, the half-value width Δφ / 2 is 11.5 °, which is about 21% smaller than the original case. Further, the light amount included in the range of the full width at half maximum Δφ = 20 ° is 51% of the total light amount, and the light use efficiency is improved. Furthermore, the area ratio of the region that appears to be shining when viewed from the vertical direction is 82%.

  Although not shown, the light source disposed in the surface light source device including the prism sheet in the present embodiment is not limited to a point light source, and may be a linear light source.

  Even in the case where a plurality of point light sources are arranged or in the case of a line light source (however, as described in Japanese Patent Laid-Open No. 11-84111, a case where a large amount of light is emitted also in the direction of the light source is excluded). This prism sheet may be effective when intentionally reducing the directivity of one side. The light emitted from the point light source as shown in the first embodiment is radially spread out from the light exit surface. It is not limited to the light guide plate to be emitted.

(Liquid crystal display device)
FIG. 44 is a schematic sectional view showing the structure of a liquid crystal display device using the surface light source device of the present invention. The liquid crystal display device 71 includes a transmissive liquid crystal display panel 80 and a surface light source device 72 according to the present invention. The surface light source device 72 has a diffusing prism sheet 73, a light guide plate 74, a reflecting plate 75, and a point light source. The light emitting unit 76 is configured.

  Thus, the light emitted from the light emitting unit 76 is introduced into the light guide plate 74 and spread throughout the light guide plate 74, and extends in a direction substantially along the light emission surface 77 from the light emission surface 77 of the light guide plate 74. Emitted. The light emitted from the light guide plate 74 is deflected in a direction perpendicular to the surface light source device 72 by passing through the uneven diffusion plate 78 of the diffusion prism sheet 73, and the directivity angle is widened by the prism sheet 79 of the diffusion prism sheet 73. After that, the liquid crystal display panel 80 is illuminated.

  As a result, luminance unevenness hardly occurs in the surface light source device 72, so that the screen of the liquid crystal display device 71 is easy to see. In addition, since the difference in directivity between the wide direction angle direction and the narrow direction angle direction can be reduced while keeping the directivity angle relatively narrow, the liquid crystal display device 71 is easy to see from the front, but from an oblique direction. It becomes difficult to see and directivity suitable for a portable terminal can be obtained. Further, since the difference in directivity in each direction becomes small, it is easy to see the screen from any direction.

It is a disassembled perspective view which shows the structure of the conventional surface light source device. It is sectional drawing of a surface light source device same as the above. It is a figure which shows the directivity of the light radiate | emitted from the light-projection surface of a light-guide plate in the surface light source device of FIG. 1, and the directivity of the light which permeate | transmitted the diffuser plate. In the surface light source device of FIG. 1, the directivity of light emitted from the light exit surface of the light guide plate, the directivity of light transmitted through the diffuser plate, the directivity of light transmitted through the prism sheet, and further transmitted through the diffuser plate It is a figure which shows the directivity of the light which performed. It is a schematic plan view which shows the structure of the conventional surface light source device which has a point light source-like light emission part. It is a figure which shows the radial brightness nonuniformity (bright line) which arises in the surface light source device same as the above. It is a disassembled perspective view which shows the structure of the surface light source device by the 1st Embodiment of this invention. It is a schematic sectional drawing of a surface light source device same as the above. It is a figure showing the arrangement | sequence of the light-diffusion pattern currently formed in the light-guide plate in the surface light source device same as the above. (A) is a partially broken plan view showing an uneven diffusion plate of a diffusion prism sheet used in the surface light source device of FIG. 7, (b) is a plan view of a repeating pattern constituting the uneven diffusion plate, (c) FIG. 4 is an enlarged perspective view of convex portions constituting a repetitive pattern. It is a perspective view from the back surface side which shows the prism sheet of the diffusion prism sheet used for the surface light source device of FIG. It is a schematic perspective view explaining the behavior of the light in the surface light source device of FIG. (A) is a schematic sectional drawing explaining the behavior of the light in a surface light source device same as the above, (b) is the X section enlarged view of (a). It is a figure explaining the relationship between the light quantity radiate | emitted in the range of (DELTA) (theta) from a light emission part, and the light-guide plate area in the range (DELTA) (theta). It is a figure explaining the structure of the light-diffusion pattern for radiating | emitting light perpendicularly | vertically from a light-projection surface. It is a figure which shows the directivity of the directivity of the light radiate | emitted from the light-guide plate in which the light diffusion pattern same as the above was formed. FIG. 16 is a perspective view illustrating the directivity of light emitted from the light guide plate of FIG. 15. It is a figure which shows the directivity of (omega) direction and the directivity of (phi) direction of the light which permeate | transmitted the prism sheet | seat like FIG. 11 set | placed on the light-guide plate. It is a perspective view which shows the directivity of light when a prism sheet like FIG. 11 is used. It is a perspective view which shows the surface light source device using a linear light source and a prism sheet, and its directivity. It is a perspective view which shows the directivity of the light radiate | emitted from a surface light source device same as the above. It is a figure which shows the directivity of a general diffuser. It is a figure which shows the directivity of (omega) direction and (phi) direction at the time of putting the diffusion plate same as the above on the prism sheet | seat of FIG. It is a figure which shows the directivity when parallel light makes normal incidence on the uneven | corrugated diffuser plate like FIG. It is a figure which shows the directivity of (omega) direction and (phi) direction at the time of putting the uneven | corrugated diffusion plate same as the above on the prism sheet | seat of FIG. (A) is a figure which shows the directivity of the light radiate | emitted from a light-guide plate, (b) (c) (d) is a figure which shows the diffusion characteristic of a diffusion plate, (b) '(c)' (d) ' It is a figure which shows the directivity of the light which each radiate | emitted from the light-guide plate and permeate | transmitted the diffuser plate which has the characteristic of (b) (c) (d). (A) is a figure which shows the spreading | diffusion characteristic of a diffuser plate, (b) (b) 'is a figure which shows the directivity of the light radiate | emitted from a light-guide plate, (c) is light which has directivity like (b). Is a diagram showing the directivity after passing through the diffusion plate having the characteristics of (a), (c) 'is a light having the directivity as in (b)' is transmitted through the diffusion plate having the characteristics of (a) It is a figure which shows the directivity after having performed. (A), (b), and (c) are the perspective view, the top view, and the side view which show the light-diffusion pattern of another form. It is a figure which shows the light radiate | emitted from the light-guide plate which has a light-diffusion pattern like FIG. It is sectional drawing which shows the light-diffusion pattern of another form. It is a perspective view of the surface light source device using the light guide plate of another form. It is a perspective view which shows the structure of the surface light source device by the 2nd Embodiment of this invention. (A) is a top view of the uneven | corrugated diffusion plate used for the surface light source device same as the above, (b) is the Y section enlarged view of (a), (c) is a ZZ line sectional view of (b). . It is a figure which shows the spreading | diffusion characteristic in the (omega) direction and (phi) direction when parallel light is made to inject perpendicularly into the uneven | corrugated diffusion plate used for the diffusion prism sheet same as the above. It is a figure which shows the directivity angle of the light in (omega) direction and (phi) direction when the uneven | corrugated diffuser plate which has a characteristic like FIG. 34 is set | placed on a light-guide plate. It is sectional drawing of the prism sheet of the uneven | corrugated diffuser plate used for the 3rd Embodiment of this invention. It is a figure showing the directivity in the (phi) direction of the light which permeate | transmitted the prism sheet same as the above. It is a figure which shows the behavior of the light in the prism sheet in which the slope far from a light emission part is a plane. It is a figure which shows the behavior of the light in the prism sheet | seat of FIG. 36 where the slope on the side far from a light emission part is bent. It is sectional drawing which fractured | ruptured partially which shows the prism sheet from which cross-sectional shape differs. It is a partially broken sectional view showing a prism sheet having a different sectional shape. Furthermore, it is sectional drawing which fractured | ruptured partially showing the prism sheet of a different cross-sectional shape. It is a figure which shows the directional characteristic of the light which permeate | transmitted the prism sheet same as the above. It is a schematic sectional drawing which shows the structure of a liquid crystal display device.

Explanation of symbols

32 Light guide plate 33 Light emitting portion 34 Reflector plate 40 Prism sheet 51 Surface light source device 52 Diffusion prism sheet 53 Concavity and convexity diffusion plates 54a, 54b,... Ring-shaped region 55 Sinusoidal concavity and convexity pattern

Claims (4)

The surface has a plurality of concavo-convex portions that are long in one direction whose surface shape changes in a concentric direction around the point determined as the light emission position, and the short direction of each concavo-convex portion faces the concentric direction with respect to the point, A diffusion plate, wherein a length of the uneven portion in a longitudinal direction is shorter than a length of a side of the surface, and the uneven portion is formed discontinuously in a radial direction centered on the point . A plurality of zonal regions concentrically divided around a point determined as a light emitting position, and the surface shape changes in a concentric direction centering on the point in each region, and concentric circles with a constant period A diffusing plate having a concavo-convex pattern composed of a plurality of concavo-convex portions arranged in a direction on the surface, and the period of the concavo-convex pattern being different between adjacent annular zones. The diffusing plate according to claim 2, wherein the concavo-convex pattern has a cross-sectional wave shape, a triangular wave shape, a trapezoidal shape, or a cylindrical lens shape. A point light source,
A light guide plate that spreads light introduced from the point light source into a planar shape and emits the light from a light exit surface;
The diffusing plate according to any one of claims 1 to 3, wherein the diffusing plate is disposed so as to face a light emitting surface of the light guide plate.
A surface light source device comprising:

Images