JP3988801B2 - Surface light source device - Google Patents

Description

  The present invention relates to a surface light source device. In particular, the present invention relates to a surface light source device used as a backlight or a front light of a liquid crystal display device or the like.

  Backlights and frontlights that use light-emitting diodes (LEDs) as light sources have features such as a small light source, long life, high efficiency, and no need for a dedicated power supply. Often used as illumination for liquid crystal display devices. Of these features, two points are particularly important: high efficiency and small size. This is because if the surface light source device becomes highly efficient, the light emitting surface of the surface light source device becomes brighter, and the image of the liquid crystal display device becomes easier to see. Furthermore, when the efficiency is high, the surface light source device has low power consumption, and the battery life becomes long. Further, if the surface light source device is not miniaturized, the portable device cannot be miniaturized. For this purpose, the area of the portion that does not emit light must be reduced and the thickness must be reduced.

  Further, when used as a display of a portable device or the like, it is only necessary to be able to see the display from the front side, and it is not necessary to see the display from an oblique direction. Therefore, the light emitted from the surface light source device does not need a wide finger characteristic, and in order to improve the efficiency of the surface light source device, a certain amount of light is emitted in the direction of the normal line standing on the light emitting surface of the surface light source device. It is desirable to emit light only in the direction with the spread.

  First, an exploded perspective view and a sectional view of a surface light source device having a general structure are shown in FIGS. The surface light source device 1 is used as a backlight, and 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 made of a transparent resin having a large refractive index, such as polycarbonate resin or methacrylic resin. A diffusion pattern 5 is 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 configured by mounting a plurality of light emitting diodes 7 on the circuit board 6 and faces the side surface (light incident surface 2 a) of the light guide plate 2. The reflection plate 4 is formed of a white resin sheet, and both side portions are attached to the lower surface of the light guide plate 2 by a double-sided tape 8.

  In such a surface light source device 1, as shown in FIG. 2, the light emitted from the light emitting unit 3 and guided to the inside of the light guide plate 2 from the light incident surface 2 a is the upper surface of the light guide plate 2 (light emission). It proceeds while repeating regular reflection between the surface 2b) and the lower surface. And if it injects into the diffusion pattern 5, it will be diffusely reflected, and if it injects into the light-projection surface 2b at an angle smaller than the critical angle of total reflection, the light will be radiate | emitted outside from the light-projection surface 2b. Further, the light that has passed through the portion where the diffusion pattern 5 on the lower surface of the light guide plate 2 does not exist is reflected by the reflecting plate 4 and returns to the inside of the light guide plate 2 again, so that loss of light quantity from the lower surface of the light guide plate 2 is prevented.

  However, although the surface light source device 1 having such a structure is simple, the light use efficiency is poor due to the structure, and only about 20% of the light emitted from the light emitting diode 7 is emitted from the light guide plate 2. The light could not be emitted from the surface 2b.

  Furthermore, in the surface light source device 1 having such a structure, in order to direct light emitted in a direction nearly parallel to the light emitting surface 2b of the light guide plate 2 in a direction perpendicular to the light emitting surface 2b, FIG. As shown, since the diffuser plate 9 is used on the light guide plate 2, the thickness of the surface light source device 1 is increased, and it is difficult to reduce the size of the surface light source device 1. In addition, when the diffuser plate 9 is used, the light that has passed through the diffuser plate 9 becomes Lambertian light, and since the finger characteristics are wide, the front luminance is lowered and the light use efficiency is reduced.

  Further, in the surface light source device 1 having the structure as shown in FIG. 1, since the light emitting unit 3 on which the plurality of light emitting diodes 7 are mounted is used, it is difficult to reduce the size of the light emitting unit 3, and the surface light source device 1 is consumed. Electric power cannot be reduced.

  On the other hand, surface light source devices using light-emitting diodes are used in highly portable products such as mobile phones and PDAs because of their small size and light weight. The surface light source device used for this is also strongly desired to reduce power consumption. For this reason, the number of light emitting diodes to be used is decreasing.

  Therefore, a surface light source device 11 having a structure as shown in FIG. 4 using one light emitting diode has been proposed (Japanese Patent Laid-Open No. 11-231320: Patent Document 1). In the surface light source device 11, a light emitting diode 12 is disposed by facing a light emitting diode 14 at an end of a wedge-shaped rod-shaped member 13, and the light emitting unit 12 is opposed to a light incident surface 15 a of a light guide plate 15. Arranged. The light guide plate 15 also has a wedge shape, and a diffuse reflection sheet 17 is provided on the lower surface of the light guide plate 15 for diffusing and reflecting leakage light from the lower surface of the light guide plate 15 and returning the light into the light guide plate 15. The diffusion plate 18 and the prism sheet 19 are overlapped with each other so as to face the emission surface 15b. A prism-like pattern 16 is formed on the light incident surface 15 a of the light guide plate 15.

  According to such a surface light source device 11, since it can be driven by one light emitting diode 14, the light use efficiency of the light source is improved. However, since the light is diffused by the diffuse reflection sheet 17 and the diffuser plate 18, the directivity is widened as shown in FIG. 5, and the efficiency of the surface light source device 11 as a whole is not sufficient due to the reduction of directivity. It was. Furthermore, since the diffusion plate 18 and the prism sheet 19 are stacked on the light guide plate 15, the thickness of the surface light source device 1 is increased, and the light source 12 is increased by the rod-shaped member 13, which makes it difficult to reduce the size.

  Further, another surface light source device 21 using one light emitting diode is shown in FIG. This is because a single light emitting diode 23 is arranged facing the center of the light incident surface 22 a of the light guide plate 22, and a concealed diffusion pattern 24 centered on the light emitting diode 23 is concentrically formed on the lower surface of the light guide plate 22. Each diffusion pattern 24 extends in a direction orthogonal to the direction connecting to the light emitting diodes 23.

  Thus, in the surface light source device 21, the light emitted from the light emitting diode 23 enters the light guide plate 22 from the light incident surface 22 a and travels inside the light guide plate 22. As shown in FIG. 7, the light hitting the diffusion pattern 24 in the light guide plate 22 is reflected at the interface of the diffusion pattern 24, is emitted toward the light emission surface 22b on the surface of the light guide plate 22, and is emitted to the light emission surface 22b. On the other hand, only light incident at an incident angle smaller than the critical angle of total reflection is emitted to the outside from the light exit surface 22b.

  However, the diffusion pattern 24 is uniform in the circumferential direction centered on the light source, and the traveling direction of light does not change in plan view even when it hits the diffusion pattern 24, and the light diffusion is performed in the circumferential direction centered on the light source. There is no effect. Therefore, the uniformity of the light in the circumferential direction is determined only by the light amount distribution of the light source in the circumferential direction or the light amount distribution of light entering the light guide plate from the light incident surface.

  As a result, the surface light source device 21 has a narrow finger light characteristic in the circumferential direction. Therefore, the directivity of light emitted from the light guide plate 22 is extremely narrow in the width direction of the light guide plate 22 as shown in FIG. It was wide in the direction. For this reason, a diffusion plate that softens the directivity in the width direction is indispensable, and the thickness of the surface light source device 21 is increased. Further, since the diffusion plate diffuses not only in the width direction but also in the length direction, the directivity in the longitudinal direction is extremely deteriorated, and the luminance in the vertical direction is lowered.

  Next, a surface light source device 31 used as a front light is shown in FIG. In the surface light source device 31, a plurality of slits 33 are formed on the upper surface of the light guide plate 32 with a material or air different from that of the light guide plate 32, and a linear light source 34 such as a cold cathode tube is opposed to the side surface of the light guide plate 32. It is arranged. Thus, the light that has exited from the linear light source 34 and entered the light guide plate 32 is totally reflected by the slit 33, exits from the lower surface of the light guide plate 32, and is reflected by the reflective liquid crystal display panel 35, whereby the light guide plate 32. Then, the light passes through the slit 33 and is emitted from the upper surface of the light guide plate 32.

  However, in such a surface light source device 31, the number of slits 33 cannot be increased so much that the light utilization efficiency is low, and the slits 33 must be formed inside the light guide plate 32, so that it is difficult to manufacture. there were.

  Similarly, there is also proposed a front light surface light source device in which a plurality of island regions having different refractive indices are formed inside a light guide plate (Japanese Patent Laid-Open No. 7-199184: Patent Document 2). The utilization efficiency was not sufficient, and the production was difficult.

  In addition, as another surface light source device for a front light, a light guide plate that gradually decreases in a stepped manner as the distance from the light source is used (Japanese Patent Laid-Open No. 10-326515: Patent Document 3). A prism sheet is provided on the lower surface of the light guide plate (Japanese Patent Laid-Open No. 10-301109: Patent Document 4), and a concave-convex pattern having a rectangular cross section is formed on the lower surface of the light guide plate (Japanese Patent Laid-Open No. 10-123518: Patent Document 5). ), A wedge-shaped light guide plate provided with a V-groove groove on the upper surface (Japanese Patent Application Laid-Open No. 11-64641: Patent Document 6).

  Although such a surface light source device has a relatively simple structure, the light use efficiency is still insufficient and the screen is dark.

Japanese Patent Laid-Open No. 11-231320 JP 7-199184 A Japanese Patent Laid-Open No. 10-326515 JP-A-10-301109 JP-A-10-123518 JP-A-11-64641

  An object of the present invention is to provide a surface light source device capable of effectively preventing shining.

  A first surface light source device according to the present invention is a surface light source device including a light source and a light guide plate that spreads light introduced from the light source over almost the entire light emitting surface and emits the light from the light emitting surface. The light source has a plurality of peaks in its wavelength spectrum, and the light guide plate is formed with an antireflection film on its light exit surface, and the antireflection film has a minimum value of reflectance wavelength dependency with respect to normal incident light. There are a plurality of locations, and the maximum wavelength difference between the minimum values at the locations is greater than the maximum wavelength difference between the peaks of the light source.

  According to the first surface light source device, even when the wavelength spectrum of the light source has a plurality of peaks like a light-emitting diode, the maximum wavelength of the plurality of minimum values of the reflectance wavelength dependency with respect to the normal incident light of the antireflection film. If the difference is made larger than the maximum wavelength difference of the plurality of peaks of the light source, it is possible to effectively suppress the light caused by the light from the light source.

The second surface light source device according to the present invention is a surface light source device comprising: a light source; and a light guide plate that spreads light introduced from the light source over substantially the entire light emitting surface and emits the light from the light emitting surface. the light emitting surface of the light guide plate a plurality of concave patterns on the opposite side is formed, that different anti-reflection film having reflection characteristics from each other on the surface of the light emitting surface and the opposite side of the light guide plate is formed It is a feature.

  According to the second surface light source device, since the antireflection films having different reflection characteristics are formed on the light emitting surface of the light guide plate and the surface on the opposite side, an appropriate film thickness is set according to the front and back of the light guide plate. By making the selection, it is possible to effectively suppress screen shine when used in the image display device. For example, the thickness of the antireflection film can be determined so as to prevent reflection of external light on the surface on which the concave pattern is formed, and reflection by light source light can be suppressed on the surface opposite to the concave pattern. . This surface light source device is particularly effective when used as a front light.

The second surface light source device according to the present invention is a surface light source device comprising: a light source; and a light guide plate that spreads light introduced from the light source over substantially the entire light emitting surface and emits the light from the light emitting surface. light guide plate, the light emitting surface is formed a plurality of concave patterns on the opposite side from that of the light emitting surface anti-reflection film is formed on the opposite side, the anti-reflection film is not concave pattern flat The film thickness of the antireflection film at the boundary between the surface and the concave pattern is different from the film thickness of the antireflection film on the flat surface.

  According to the third surface light source device, the thickness of the antireflection film at the boundary portion between the concave pattern and the flat surface is different from that of the flat surface on the surface opposite to the light emitting surface of the light guide plate. On the flat surface other than the pattern, the film thickness of the antireflection film is determined so as to prevent reflection of external light, and the film thickness of the antireflection film is determined so as to suppress reflection by the light source light at the boundary portion of the edge of the concave pattern. For example, by selecting an appropriate film thickness depending on the location, it is possible to effectively suppress the shine. Further, it is possible to more easily suppress illuminance due to outside light and illuminance due to light source light than by changing the material of the antireflection film. This surface light source device is particularly effective when used as a front light.

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

  In portable devices such as mobile phones, a display (liquid crystal display device) is often viewed by one person, and a wide viewing angle is not required. According to the experiment, when watching the screen of a mobile device while walking, if the light is emitted only within 10 ° when measured from the direction perpendicular to the screen, the screen flickers every time the screen viewing direction fluctuates and it is difficult to see. It was confirmed that if the direction in which the light was emitted was about 20 ° as measured from the direction perpendicular to the screen, it was easy to see, and that 30 ° or more was sufficient.

  From this result, it can be seen that the light emitted outside 20 ° to 30 ° as measured from the direction perpendicular to the screen is lost and the visibility of the liquid crystal display device is lowered. In other words, in order to improve the light use efficiency of the surface light source device and improve the visibility of the liquid crystal display device, the directivity of light emitted from the surface light source device is wider than about 10 °, and 20 to 30 °. It can be said that it may be narrower than the degree.

  However, the directivity of light emitted from the light guide plate can be easily increased by using a diffusion plate, but it is difficult to reduce the directivity. By using a prism sheet, it is possible to align the light direction, but once the emission direction has spread, it is difficult to align the light in a narrow range using the prism sheet, and the thickness of the surface light source device is not increased. In addition, it is desirable not to use a prism sheet.

  Therefore, in order to produce a surface light source device with excellent efficiency and visibility, the light emitted from the light guide plate is within 20 ° measured from the normal line standing on the light emitting surface without using a prism sheet. In addition, the higher the ratio of light emitted within 30 °, the better, and it is preferable that at least 1/2 or more, preferably 2/3 or more of light is emitted into the angular region.

  As shown in FIG. 10, the direction of light emitted from the surface light source device is a normal line (hereinafter referred to as the z-axis direction) standing on the light emission surface of the surface light source device 41 (light guide plate). The direction parallel to the pair of sides of the surface light source device is referred to as the x-axis direction, and the direction parallel to the remaining pair of sides is referred to as the y-axis direction. For example, the direction within θ = 30 ° refers to all directions within θ = 30 ° from the z-axis, and refers to the emission direction of light emitted toward the hatched region in FIG. As an example, as shown in FIG. 11, in the case of a surface light source device that emits light so as to be approximately Lambertian light in the zx plane, it is within 30 ° when viewed from a direction perpendicular to the zx plane. However, almost all light is contained within 30 ° when viewed from a direction perpendicular to the yz plane. In such a case, in the sense used in this specification, it does not mean that most of the light is emitted in a direction within 30 °. That is, in this specification, for example, when light is emitted in a direction within 30 °, it must be emitted in a direction within 30 ° from the z-axis as viewed from all directions as well as when viewed from one direction. I must.

  FIG. 12A shows the directivity characteristics of the light that is mostly emitted from the surface light source device 41 within θ. Considering the ideal directivity characteristics of the light emitted from the surface light source device 41, FIG. As shown in FIG. 12B, it is desirable that the luminance is uniform in a range inside θ = 20 ° to 30 ° (40 ° to 60 ° in full width), and that no light is emitted in other directions. By realizing such directivity, even if the viewing direction changes (even if the screen angle fluctuates), the luminance of the image does not change and flickers. In addition, the brightness is constant despite the difference in viewing angle between the center and the edge of the screen. As a result, the screen becomes easy to see.

Such an ideal directivity characteristic is a rectangular characteristic as shown by a two-dot chain line in FIG. 13 when the horizontal axis represents the emission angle and the vertical axis represents the luminance. It is difficult to accurately realize such directivity. However, even if such ideal directivity characteristics cannot be obtained, the emitted light is emitted in a direction (z-axis direction) substantially perpendicular to the light emitting surface, and is 1/2 of the maximum luminance in the luminance angle distribution of the emitted light. As shown in FIG. 14, more than half of all the emitted light is included in the angle region, and the width of this angle region (full width angle) is Δθx and Δθy in the x direction and y direction, respectively. At least 30 ° ≦ Δθx ≦ 70 °
30 ° ≦ Δθy ≦ 70 °
To achieve good directivity, and
40 ° ≦ Δθx ≦ 60 °
40 ° ≦ Δθy ≦ 60 °
If so, desirable directivity characteristics can be obtained.

  Next, consider the case of the surface light source device 41 used as a front light. In the case of the front light type surface light source device 41, it is necessary to consider the relationship with the reflected light angle characteristic of the reflective liquid crystal display panel 42. Here, the reflected light angle characteristic of the reflective liquid crystal display panel 42 refers to the angle dependency of the reflected light intensity when parallel light is incident on the reflective liquid crystal display panel 42 as shown in FIG. FIGS. 16A, 16B, 16C, and 16D show the directivity characteristics of the front light type surface light source device 41, and the directivity characteristics gradually become wider from (A) to (D). FIGS. 16A, 16B, 16C, and 16D show the reflected light angle characteristics of the reflective liquid crystal display panel 42, and FIGS. 16A, 16B, and 16C show directivity characteristics (A). (B) Corresponds to (C) and (D).

  As shown in FIG. 16, the reflected light intensity angle characteristic of the liquid crystal display panel 42 gradually becomes gentle as the directivity characteristic of the surface light source device 41 becomes wider. When the directivity characteristic of the surface light source device 41 becomes wider than the reflected light intensity angle characteristic of the liquid crystal display panel 42 as shown in FIGS. 16D and 16D, FIGS. (C) Compared with the case where the directivity characteristic of the surface light source device 41 is narrower than the reflected light intensity angle characteristic of the liquid crystal display panel 42 as in (c), the vertical component of the light reflected by the liquid crystal display panel 42 The strength of is reduced.

  In the case shown in FIG. 16, among the light emitted from the surface light source device 41, the light emitted from the axis perpendicular to the liquid crystal display panel 42 at an angle outside 30 ° is substantially equal. It has become a loss.

  Therefore, in the case of the front light type surface light source device 41, within the angle range of the full width at half maximum of the reflected light intensity angle distribution of the reflective liquid crystal display panel 42, more than half of the emitted light of the surface light source device 41, preferably It is desirable to narrow the directivity so that 2/3 or more light is emitted. However, the full width at half maximum of the reflected light intensity angle distribution of the reflective liquid crystal display panel 42 is an angle between two points that is a half value of the maximum value as shown in FIG. Since the directivity characteristic of 41 may have a sharp peak at the center, as shown in FIG. 17B, the intensity is 1 / of the intensity at a position deviated from the central peak position, for example, at a position about 5 ° away from the peak. The angle between two points that is 2 is called the full width at half maximum.

(First embodiment)
In the following, various embodiments of the surface light source device having characteristics close to the ideal directional characteristics as described above will be described. First, FIG. 18 is an exploded perspective view showing the structure of a backlight type surface light source device 43 according to an embodiment of the present invention. The surface light source device 43 includes a transparent light guide plate 44 and a light emitting unit 45 disposed to face the light incident surface 44 a of the light guide plate 44. The light guide plate 44 is formed into a rectangular flat plate with a transparent resin having a high refractive index (for example, polycarbonate resin, methacrylic resin, etc.), and a plurality of diffusion patterns extending substantially the entire length in the width direction on the lower surface thereof. 46. The diffusion pattern 46 has a substantially right triangle shape in cross section, the light source side is a deflection inclined surface 46a, and the back surface (re-incident surface) 44b is a substantially vertical surface. The diffusion pattern 46 is formed by engraving the lower surface of the light guide plate 44, and is formed at a distance from each other, but the distance between the diffusion patterns 46 decreases as the distance from the light incident surface 44a increases. Yes.

  The light emitting unit 45 is disposed so as to face a wedge-shaped light guide (hereinafter referred to as a wedge-shaped light guide) 47 formed of a transparent resin having a high refractive index and a side end surface of the wedge-shaped light guide 47. A small light source (hereinafter referred to as a point light source) 48, a specular reflection plate 49 disposed on the back surface of the wedge-shaped light guide 47, and a prism sheet 50 disposed on the front surface of the wedge-shaped light guide 47. . Here, the point light source 48 is formed by sealing one or a plurality of light emitting diodes in a transparent resin. The transparent resin is covered with a white resin except for the front surface, and the light emitted from the light emitting diodes is directly Alternatively, after being reflected by the inner surface of the white resin, it is efficiently emitted forward (see FIG. 80).

  Light (Lambertian light) emitted from the point light source 48 enters the wedge-shaped light guide 47 from the side end face of the wedge-shaped light guide 47. As shown in FIG. 19, the light incident on the wedge-shaped light guide 47 is reflected on the front surface (light emitting surface) 47 a and the back surface of the wedge-shaped light guide 47, so that the inside of the wedge-shaped light guide 47. The angle of incidence on the front surface 47a becomes smaller each time the light is reflected by the back surface of the wedge-shaped light guide 47, and the angle of incidence on the front surface 47a of the wedge-shaped light guide 47 becomes smaller than the critical angle of total reflection. The light is emitted from the front surface 47a of the wedge-shaped light guide 47 to the outside. Further, as indicated by a broken line in FIG. 19, the light emitted to the outside from the back surface of the wedge-shaped light guide 47 is reflected by the specular reflection plate 49 and returns into the wedge-shaped light guide 47 again, and the wedge-shaped light guide The light is emitted from the front surface 47 a of the body 47. In this way, the light emitted from the front surface 47a of the wedge-shaped light guide 47 is aligned in a direction substantially parallel to the front surface 47a of the wedge-shaped light guide 47 (substantially the negative direction of the x axis).

  The prism sheet 50 disposed on the front surface 47a of the wedge-shaped light guide 47 is also formed of a transparent resin having a high refractive index (for example, a transparent resin having a refractive index of 1.59). A prism 50a is arranged. Each prism 50a has a triangular cross section with an apex angle of 40 °, and extends in the vertical direction (thickness direction of the light guide plate 44). Thus, after the light emitted from the front surface 47a of the wedge-shaped light guide 47 is refracted through the prism 50a as described above, after being deflected in a direction substantially perpendicular to the prism sheet 50, The light is incident almost vertically into the light guide plate 44 from the light incident surface 44a. Therefore, according to the light emitting unit 45, the light emitted from the point light source 48 can be emitted while being spread over almost the entire length of the prism sheet 50, and the point light source 48 can be converted into a so-called linear light source.

  Note that part of the light transmitted through the prism sheet 50 may become stray light due to molding errors such as roundness of the apex of the prism cross section of the prism sheet 50 and Fresnel reflection. Therefore, at least half or more of the light emitted from the point light source 48 is deflected by the prism sheet 50 and incident on the light guide plate 44 at a desired angle (in this embodiment, a direction perpendicular to the light incident surface 44a). In this case, it is desirable that the ratio of the light emitted from the front surface 47 a of the wedge-shaped light guide 47 to be substantially parallel to the front surface 47 a is 2/3 or more with respect to the total emitted light from the point light source 48.

  For comparison, when a diffuse reflection plate is used on the back surface of the wedge-shaped light guide 47 instead of the regular reflection plate 49, the light is emitted from the front surface 47a of the wedge-shaped light guide 47 along the front surface 47a. The light is less than half of the total amount of light emitted from the point light source 48. The reason for this is that light leaking from the back surface of the wedge-shaped light guide body 47 hits the diffuse reflector and is reflected in a substantially Lambertian distribution, as shown by the broken line in FIG. This is because almost no light is emitted along 47a (almost in the negative direction of the x-axis).

  Although it has been described that the light source 45 having the structure as in this embodiment can convert a point light source into a linear light source, the direction of light emitted from the linear light source can be made substantially uniform. FIG. 20 shows a configuration in which a specular reflection plate having no diffusing action and having an incident angle and an output angle equal to each other is arranged on the back surface of the wedge-shaped light guide 47, and the emitted light from the wedge-shaped light guide 47 is reflected on the front surface 47a ( The result of measuring the relationship between the angle α (refer to FIG. 19) formed with the negative direction of the x-axis and the intensity of light in that direction is shown. FIG. 21 shows an angle α formed by the light emitted from the wedge-shaped light guide 47 and its front surface 47a (the negative direction of the x axis) when the specular reflection plate on the back surface of the wedge-shaped light guide 47 is replaced with a diffuse reflection plate. The result of having measured the relationship between (refer FIG. 19) and the light intensity in the direction is shown. In this measurement, a wedge-shaped light guide 47 having a length of 30 mm, a thickness of 1 mm, and a width of a side surface facing the point light source 48 of 2 mm, a refractive index of 1.53, and a regular reflection plate or diffuse reflection having a length of about 30 mm. A plate was used. The measurement was performed with the prism sheet 50 removed.

  In the graphs shown in FIGS. 20 and 21, the light intensity (energy) in the α direction is emitted in the α direction on a plane perpendicular to the front surface 47a of the wedge-shaped light guide 47 (xy plane in FIG. 22). This is not an angular distribution of the intensity of the light, but all the emitted light from the front surface 47a is projected onto the plane, and represents the intensity of the light included in the unit angle (dα = 1) in the α direction at that time. is there.

  As can be seen from FIG. 20, even when a specular reflector is used, the light intensity is maximized in a direction of about 30 °, and 98% of the total light amount is concentrated in the range of 0 ° to 40 °. Yes. When this is deflected by the prism sheet 50 and the light guide plate 44 is also incident, even if a loss due to the manufacturing error of the prism sheet 5 occurs about 10%, 80% or more of light is seen from above (z-axis direction). It is aligned in the range of ± 13 °. On the other hand, as shown in FIG. 21, when a highly diffusible reflector as normally used is used, only 52% of the light is concentrated in the range of 0 ° to 40 °. In addition, if a loss due to the prism sheet 50 is added, the directivity cannot be reduced inside the light guide plate 44.

  Therefore, according to such a light emitting unit 45, it is possible to emit light over a long region like a linear light source using a point light source 48 such as a light emitting diode and a wedge-shaped light guide 47, and from the point light source. The emitted Lambertian light can be arranged almost uniformly and emitted as light having a narrow directivity.

  Thus, the light incident on the light guide plate 44 from the light incident surface 44a repeats total reflection between the upper surface (light emitting surface 44b) and the lower surface of the light guide plate 44, and is close to the light emitting unit 45 in the light guide plate 44. Proceed to the far side. When the light enters the triangular diffusion pattern 46 provided on the bottom surface of the light guide plate 44, a part of the light is reflected by the diffusion pattern 46 and emitted from the light emission surface 44b. Since such a triangular diffusion pattern 46 is elongated in the x-axis direction, the directivity of light in the x-axis direction does not change even if it is reflected by the diffusion pattern 46. Accordingly, the light having a narrow directivity in the x-axis direction aligned by the light emitting unit 45 is kept in a narrow directivity in the x-axis direction even after being reflected by the diffusion pattern 46 and emitted in the z-axis direction. On the other hand, the light propagating in the light guide plate 44 spreads in the z-axis direction, but when this spread is reflected in the z-axis direction by the diffusion pattern 46, it spreads in the y-axis direction. However, the spread in the y-axis direction can be narrowed by limiting the angle of the light reflected by the diffusion pattern, and the directivity in the y-axis direction of the light emitted from the light exit surface 44b is introduced. The directivity in the z-axis direction inside the optical plate 44 can be made narrower. In a typical example, the directivity when the light emitted from the light exit surface 44b of the light guide plate 44 is viewed from the x-axis direction is approximately within a range of about 55 ° in the entire width centering on the z-axis direction. When viewed from the direction, the directivity falls within a range of about 25 ° in the entire width around the z-axis direction.

  Therefore, according to the surface light source device 43, light can be emitted in a direction perpendicular to the surface light source device 43 without using a prism sheet or the like, and the directivity characteristic thereof can be narrowed. Directional characteristics close to the characteristics can be realized. And since the prism sheet is not used, the surface light source device 43 can be reduced in cost and the surface light source device 43 can be made thin.

  On the other hand, in the method of increasing the directivity of light by overlapping two prism sheets whose pattern directions are orthogonal to each other, the directivity characteristic of light becomes a pattern as shown by a broken line in FIG. And even if the directivity of the light before entering the prism sheet is ± 30 °, after passing through the two overlapping prism sheets, more than half of the light is emitted within the range of ± 20 °. I couldn't.

  Further, in this surface light source device 43, the distance between the diffusion patterns 46 is widened in the region close to the light emitting unit 45, and the distance between the diffusion patterns 46 is gradually shortened away from the light emitting unit 45. The luminance of the entire surface 44b is made uniform.

  Next, the function of the diffusion pattern 46 having a triangular cross section will be described in detail. Now, the directivity of light before entering the diffusion pattern 46 is narrow only in the x-axis direction as shown in FIG. 23 (a), narrow in the z-axis direction as shown in FIG. 23 (b), and FIG. As shown in (c), a thing narrow in the x-axis direction and the z-axis direction is considered. Among these, the case as shown in FIG. 23C is excluded because the directivity is not narrow as shown in FIGS. 23A and 23B in any direction.

  Next, consider a case where light having a narrow directivity is incident on the diffusion pattern 46 only in the z-axis direction as shown in FIG. In this case, as shown in FIG. 24, when all the light incident on the diffusion pattern 46 is totally reflected by the deflection inclined surface 46a of the diffusion pattern 46, the directivity of the light reflected by the diffusion pattern 46 does not change. In particular, the directivity in the x-axis direction is not narrowed. Therefore, as shown in FIGS. 25A and 25B, the inclination angle of the deflection inclined surface 46a of the diffusion pattern 46 is increased so that a part of the light is reflected by the diffusion pattern 46 and a part of the light is transmitted. Then, the light totally reflected by the deflection inclined surface 46a of the diffusion pattern 46 is emitted in a direction greatly inclined with respect to the z axis, and is transmitted through the deflection inclined surface 46a of the diffusion pattern 46 as shown in FIG. The light re-entered from the back surface 46b changes its angle when it re-enters, and the directivity in the z-axis direction is lost. Therefore, with light having a narrow directivity only in the z-axis direction as shown in FIG. 23B, it is extremely difficult to narrow the directivity in the x-axis direction.

  On the other hand, as shown in FIG. 23A, when light having a narrow directivity only in the x-axis direction is incident on the deflection inclined surface 46a of the diffusion pattern 46 having a triangular cross section long in the x-axis direction, for example, before the incidence. Even if it has a relatively large spread in the z-axis direction as shown in FIG. 27A, a part of the light is totally reflected by the deflection inclined surface 46a of the diffusion pattern 46 as shown in FIG. If part of the light is transmitted through the deflection inclined surface 46a and re-entered from the back surface 46b as shown in FIG. 27C, the region of the light reflected by the diffusion pattern 46 can be limited to a part. Therefore, the directivity in the y-axis direction of the light that is totally reflected by the diffusion pattern 46 and is emitted from the light exit surface 44b can be reduced. Moreover, by setting the inclination angle of the deflection inclined surface 46a of the diffusion pattern 46 to an appropriate value, the light reflected by the diffusion pattern 46 is emitted in a direction (z-axis direction) substantially perpendicular to the light emission surface 44b. Can also be done easily. On the other hand, since the diffusion pattern 46 extends uniformly in the x-axis direction, directivity does not increase in the x-axis direction even if the diffusion pattern 46 is totally reflected. In addition, as shown in FIG. 27C, the light transmitted through the deflection inclined surface 46a of the diffusion pattern 46 and re-entered from the back surface 46b changes in the angle of traveling in the yz plane, but originally has no directivity in the z direction. Therefore, the directivity in the z-axis direction does not increase. The light L2 at the center in FIG. 27A represents light incident on the deflection inclined surface 46a of the diffusion pattern 46 at an angle slightly larger than or slightly smaller than the critical angle of total reflection. Yes.

  In the description using FIG. 23A and FIG. 27, the case where there is no light spreading in the x-axis direction has been described, but in reality, the light emitted from the light emitting unit 45 is somewhat spread in the x-axis direction. Yes. For example, when considering the spatial frequency when the light propagating in the light guide plate 44 is viewed from the y-axis direction, it is considered that the light is concentrated in the shaded area in FIG. Here, the light on the center line j parallel to the z-axis direction is light guided in the yz plane, and the light on the i-line parallel to it indicates light inclined more in the x-axis direction. ing. When the diffusion pattern 46 extends completely parallel to the x-axis and the deflection inclined surface 46a and the back surface 46b of the diffusion pattern 46 extend parallel to each other in plan view, the diffusion pattern 46 reflects or transmits the light. The spatial frequency of light in the x-axis direction does not change. For this reason, in the xy plane, the traveling direction of the light in the light guide plate 44 does not change unless light is emitted, the light on the i line only moves on the i line, and the light on the j line only moves on the j line.

  Accordingly, if the directivity in the x-axis direction is narrowed by the light emitting unit 45 and then the directivity in the y-axis direction is narrowed by reflecting this light with the diffusion pattern 46, the light is emitted from the surface light source device 43 in the z-axis direction. The directed light has a narrow directivity in both the x-axis direction and the y-axis direction, and as a result, it becomes possible to emit light having a narrow directivity in all directions as shown in FIG.

  By the way, in order to set the directivity in the x-axis direction of the light emitted from the light guide plate 44 to ± 20 ° or less, the directivity in the x-axis direction in the light guide plate 44 needs to be ± 13 ° or less. This number of ± 13 ° or less is calculated by setting the refractive index of the light guide plate 44 as 1.53, but the transparent resin that can be used for the light guide plate 44 has a refractive index of about 1.4 to 1.65. Within that range, the directivity angle in the x-axis direction required in the light guide plate 44 does not change much. Further, even if the refractive index further changes, the value of 13 ° or less practically does not change so much. Therefore, this value may be targeted in designing the light emitting unit 45.

  Further, when the center of the light traveling direction (center of spread of ± 13 ° or less) is parallel to the y-axis direction, the diffusion pattern 46 may be parallel to the x-axis direction as described above. 30, when the center of the light traveling direction is inclined with respect to the y-axis direction, in order to correct it, the extending direction of the diffusion pattern 46 is also inclined with respect to the x-axis direction, The traveling direction of light and the direction in which the diffusion pattern 46 extends may be set to be perpendicular to each other in plan view (in the xy plane).

  However, in such a surface light source device, since the directivity of light traveling inside the light guide plate 44 is very narrow, when the center of the light traveling direction is inclined from the y-axis direction, FIG. As shown, the corner D of the light guide plate 44 becomes dark. Therefore, in such a light guide plate having a rectangular light emitting area, the center of the light traveling direction is within ± 13 ° from the direction perpendicular to the light incident surface 44a or at least from the direction perpendicular to the light incident surface 44a. Is desirable. The diffusion pattern 46 also has a direction perpendicular to the light emitting surface 44b of the surface light source device 41 within the range of ± 13 ° even if the center of the light traveling direction and the diffusion pattern 46 are not completely perpendicular. Is included in the angle range of the emitted light ± 20 °.

  When inspecting the directional characteristics of light in the light guide plate 44, as shown in FIG. 31, the light guide plate 44 is cut along a plane parallel to the z axis and substantially perpendicular to the light traveling direction, and the cut surface. If the angular intensity distribution of the light emitted from CC is measured, the angular intensity distribution in the light guide plate 44 can be calculated from Snell's law.

  Next, the shape and design method of each diffusion pattern will be described. When the diffusion pattern 46 is disposed substantially perpendicular to the light traveling direction in the light guide plate 44, the diffusion pattern 46 is preferably a pattern having a right-angled triangular cross section as described above. In the case of the diffusion pattern 51 formed with a curved surface as shown in FIG. 32, the deflection direction of the light differs depending on the position where the light is reflected, and the angle range of the emitted light is widened. Therefore, a pattern in which the cross section perpendicular to the length direction is a curved surface is not desirable. In the case of the diffusion pattern 52 having a saw blade shape as shown in FIG. 33, the light transmitted through the diffusion pattern 52 is not emitted in a direction perpendicular to the light emission surface 44b, but is emitted in all useless directions. . Accordingly, such a sawtooth pattern diffusion pattern 52 is also not preferable.

  On the other hand, in the case of the diffusion pattern 46 having a right-angled triangular cross section in which the back surface 46b is perpendicular to the lower surface of the light guide plate 44, the light totally reflected by the deflection inclined surface 46a as shown in FIG. Even when all the light is reflected, it is reflected while maintaining the directivity, and when a part of the light is transmitted through the diffusion pattern 46, the directivity is narrowed. As shown in FIG. 34B, the light transmitted through the diffusion pattern 46 can also be totally reflected by another diffusion pattern 46 after re-entering from the back surface 46b without impairing the directivity. The back surface 46b is preferably perpendicular to the lower surface of the light guide plate 44, but is slightly inclined because it is difficult to remove the mold during molding.

  However, even in the case of such a diffusion pattern 46 having a right-angled triangular cross section, when the direction of light in the light guide plate is not uniform as viewed from above (the spread in the x-axis direction is large), The percentage of light that strikes vertically decreases and the light that strikes diagonally increases. Light that strikes obliquely when viewed from above has a larger incident angle on the diffusion pattern 46 than light that strikes vertically, and the ratio of reflection is increased. That is, the effect of re-incident in the diffusion pattern 46 (the effect of narrowing the directivity without reducing the light utilization efficiency) is reduced. Therefore, in the diffusion pattern 46 having a right-angled triangular cross section, in order to enhance the effect of the diffusion pattern 46, the light traveling direction is aligned in the light guide plate 44 and diffused at right angles to the traveling direction. It is necessary to arrange the pattern 46. Alternatively, in the case of this embodiment, it is assumed that the directivity in the x-axis direction is narrowed by the light emitting unit 45.

  Consider the inclination angle γ of the deflection inclined surface 46 a in the diffusion pattern 46. FIG. 35 shows the angular distribution of the emitted light intensity when the inclination angle γ is 45 °, 55 °, and 65 °. The horizontal axis indicates the outgoing angle ε of the outgoing light shown in FIG. 36, and the vertical axis indicates the outgoing light. Represents strength. In FIG. 35, the luminous intensity is large when the emission angle ε is negative, as shown in FIGS. 37 (a) and 37 (b), the light having a large emission angle has less light hitting the deflection inclined surface 46a. Is due to. Alternatively, when viewed in the yz plane, the light in the light guide plate 44 that is substantially parallel to the deflection inclined surface 46a has zero outgoing light intensity (there is often no such light), and such an angle. This is because as the distance from the distance increases, that is, as the emission angle ε decreases (increases on the minus side), the intensity of the output light increases. Referring to FIG. 35, when the inclination angle γ = 55 °, the emission angle ε is minus and the angle range of the emitted light is slightly small. However, the intensity is large, so the emission angle ε is minus and plus. Balanced.

  FIG. 38A shows the diffusion characteristics of a reflective liquid crystal display panel having a diffusion action of about 25 °, and FIG. 38B shows the outgoing light angle of a surface light source device having a diffusion pattern 46 with an inclination angle γ = 55 °. FIG. 38 (c) shows the characteristics when the light of the surface light source device having the characteristics as shown in FIG. 38 (b) is incident on the reflective liquid crystal display panel having the characteristics as shown in FIG. 38 (a). The angle characteristic of light emitted from the reflective liquid crystal display panel is shown. As shown here, when light is emitted from a surface light source device having a diffusion pattern 46 having an inclination angle γ = 55 ° to a reflective liquid crystal display panel having a diffusion action of about 25 °, the emitted light is displayed on the liquid crystal display. It becomes the maximum in the vertical axis direction of the panel, and the optimum emission direction can be obtained. On the other hand, when the inclination angle γ is outside the range of 45 ° to 65 °, light is not emitted in the direction (z-axis direction) perpendicular to the light emitting surface 44b, and a prism sheet or the like is required. Therefore, the inclination angle γ of the deflection inclined surface 46a of the diffusion pattern 46 is preferably in the range of 45 ° to 65 °.

  Next, the angle δ of the back surface 46b of the diffusion pattern 46 is considered. As shown in FIG. 39, if the angle δ of the back surface 46b is too small, the diffusion pattern 46 has a saw-tooth shape, so that the light that has passed through the deflection inclined surface 46a of the diffusion pattern 46 and re-entered from the back surface 46b Before hitting the diffusion pattern 46, the light enters the light emitting surface 44b and is emitted along the light emitting surface 44b, resulting in a loss. Therefore, the angle δ of the back surface 46b is preferably large, and is preferably at least larger than the inclination angle γ of the deflection inclined surface 46a (γ <δ).

  As shown in FIG. 40, when the angle δ of the back surface 46b is small, the light transmitted through the deflection inclined surface 46a is likely to leak from the light guide plate 46, but as shown by the broken line in FIG. 40, the angle δ of the back surface 46b. As the angle approaches 90 °, the proportion of light re-entered from the back surface 46b increases. On the other hand, when the angle δ exceeds 90 °, the light guide plate 44 cannot be formed. Therefore, the angle δ of the back surface 46b is preferably in the range of 80 ° to 90 ° as a guide, and more preferably 85 to 90 °.

  41A, 41B, and 41C show the configuration of a conventional light emitting unit. As the configuration of the light emitting unit, (i) as shown in FIG. 41 (a), a point light source 53 such as a light emitting diode is converted into a linear light source by a light guide 54 or the like, and is expanded in a planar shape. (Ii) As shown in FIG. 41 (b), the point light sources 53 are arranged at equal intervals to form a pseudo linear light source, and the light is spread in a planar shape. (Iii) FIG. 41 (c) As shown in the figure, there are three types, that is, a configuration in which the light emitted from the point light source 48 is directly expanded into a planar shape.

  In order to improve the directivity at each point on the light guide plate 55 when viewed from the upper surface of the light guide plate 55, the configuration (iii) can be realized relatively easily. However, in this case, there is a problem that the amount of light leaking from the side surface of the light guide plate 55 increases at P2 and P3 in FIG. In addition, in the corner P1 of the light guide plate 55, the required light quantity is very large compared to the positions P2 and P3, but in practice, it is difficult to increase the light quantity guided in the P1 direction compared to P2 and P3. . Therefore, in practice, by increasing the amount of light leakage at the locations P2 and P3, it is necessary to equalize the brightness of the locations P1 and P3 with the brightness of the locations P1 and to equalize the brightness at P2 and P3. The amount of light leakage increases and efficiency decreases.

  On the other hand, in the structures such as (i) and (ii), attention is paid only to equalizing the in-plane luminance, and the directivity of light emitted from the light guide plate 55 is increased. It was not considered. In particular, the point that the brightness of the light emitted from the light guide plate 55 is made uniform in a range of ± 10 ° to 30 ° is not found in any of (i), (ii), and (iii), and is not included in the present invention. It is unique.

(Second Embodiment)
Next, the case of the front light type surface light source device 56 will be described. In this case, as shown in FIG. 42, the light guide plate 44 is provided on the upper surface of the reflective liquid crystal display panel 57, and the light emitting surface 44 b is located on the lower surface of the light guide plate 44. The light emitting unit 45 converts light emitted from a point light source such as a light emitting diode into a linear shape and causes the light to enter the light guide plate 44 from the light incident surface 44a. Thus, when the light that has entered the light guide plate 44 is totally reflected by the light guide plate 46, the light is emitted from the light exit surface 44 b directly below and is disposed below the surface light source device 53. 57 is illuminated. The light reflected by the reflective liquid crystal display panel 57 returns again into the light guide plate 44 and is emitted upward through the light guide plate 46.

  In the case of the surface light source device 56 used as a front light in this manner, as shown in FIG. 43, if roundness occurs at the apex of the diffusion pattern 46 having a triangular shape or the boundary between the back surface 46b and the bottom surface, Is directly emitted toward the observer, and the contrast of light including the image reflected by the reflective liquid crystal display panel 54 is lowered. For this reason, it is preferable that the curvature radii R1 and R2 of these portions are small. However, even if the radii of curvature R1 and R2 of the mold for molding the light guide plate 46 are made small, there is a possibility that the roundness may be added during molding. Depending on slight molding conditions (for example, resin lot variations, etc.) Variations between individuals and variations due to location occur, which is not preferable. Therefore, in order to suppress this variation, it is preferable to add a slight curvature to the mold from the beginning. From the molding limit, R1 and R2 are set to 0.25 μm or more, and in order to suppress a decrease in contrast, At least 1/3 or less of the height T of the diffusion pattern 46 is preferable, and more preferably 1/5 or less.

(Third embodiment)
FIG. 44 is a plan view showing the structure of a surface light source device 58 according to still another embodiment of the present invention. The feature of this embodiment is that the diffusion pattern 46 is not connected over the entire length of the light guide plate 44 as in the first embodiment, and the short diffusion pattern 46 is dispersed throughout the light guide plate 44. The distribution density of the diffusion pattern 46 is small on the side close to the light emitting unit 45, and the distribution density of the diffusion pattern 46 increases as the distance from the light emitting unit 45 increases. If the diffusion pattern 46 is shortened and dispersed in this manner, the degree of freedom of arrangement of the diffusion pattern 46 increases, so that the luminance distribution of light emitted from the light guide plate 44 can be made uniform.

  As shown in the comparative explanatory diagram of FIG. 45, when the outgoing light from the light exit surface 44b has strong directivity in the x-axis direction and spreads in the y-axis direction, the directivity in the x-axis direction is widened. In this case, for example, it is necessary to dispose the weak diffuser plate on the light guide plate 44 to diffuse the emitted light and widen the directivity in the x-axis direction, which increases the size of the surface light source device.

  Therefore, in the embodiment of FIG. 44, by providing a diffusion pattern 59 for slightly diffusing light in the x-axis direction on the light incident surface 44a of the light guide plate 44, directivity in the x-axis direction and directivity in the y-axis direction are provided. It is adjusted so that the sex is almost equal. As the diffusion pattern 59, for example, a prismatic pattern can be used. As described above, since the directivity of the emitted light is preferably at least 10 ° or more, when the directivity in the x-axis direction is smaller than 10 °, the directivity in the x-axis direction is obtained by using such means. The property can be about 10 ° or more.

(Fourth embodiment)
In addition, the surface light source device 60 shown in FIG. 46 is configured so that the light directivity in the x-axis direction can be widened by the diffusion pattern 46. That is, even in the surface light source device 60, the short diffusion pattern 46 is dispersed throughout the light guide plate 44. The diffusion pattern 46 is not linear, but loosely undulates along the longitudinal direction as shown in FIG. Therefore, the reflection direction of the incident light is slightly different depending on the position on the diffusion pattern 46, and the emitted light can be spread in a direction orthogonal to the light traveling direction. For example, when the maximum angle formed between the tangent drawn to the diffusion pattern 46 and the x-axis direction is φ = 13 °, the directivity of the light reflected by the diffusion pattern 46 can be increased by about ± 20 °.

  Further, even if the individual diffusion patterns 46 themselves are not wavy, as shown in FIG. 48, if the respective diffusion patterns 46 are arranged in different directions, the effect of expanding the directivity of the emitted light as a whole is obtained. can get.

  In the diffusion pattern 46 as shown in FIG. 47, the directivity differs depending on which position of the diffusion pattern 46 the maximum tangent angle is, and in the diffusion pattern 46 as shown in FIG. 48, which diffusion pattern 46 is most inclined. . However, by designing the diffusion pattern 46 as shown in FIG. 47 so that the slope of each portion exists at a constant ratio from the maximum value to 0, the slope of each diffusion pattern 46 in the diffusion pattern 46 as shown in FIG. The angular distribution of the emitted light can be made uniform by designing it to be distributed substantially uniformly. Further, the luminance in the direction perpendicular to the light exit surface can be reduced by eliminating the region perpendicular to the light traveling direction and the respective diffusion patterns 46 in a plan view or by reducing the ratio.

  Now, the light having a very narrow directivity in the x-axis direction in the light guide plate 44 (FIG. 23A) is totally reflected by the diffusion pattern 46 as shown in FIG. Think about realizing. As described above, it is desirable that the ideal light guide plate outgoing light angle distribution is constant within a certain range as described above, and zero otherwise. When the light traveling inside the light guide plate 44 is aligned in one direction as viewed from the z-axis direction, it can be realized by wobbling the diffusion pattern 46 as shown in FIG. Consider light L4, L5, and L6 that are totally reflected by hitting the e portion, the f portion, and the g portion of the diffusion pattern 46 that is wavy in an S shape as shown in FIG. Since the diffusion pattern 46 is perpendicular to the light L4 hitting the e portion in plan view, the totally reflected light L4 is emitted in the z and y planes as shown in FIG. The figure which looked at this from the z-axis is shown to Fig.51 (a). In FIG. 51A, the reflected light L4 is parallel to the y axis.

  On the other hand, of the light L5 and L6 totally reflected upon hitting the f portion and the g portion of the diffusion pattern 46, the light reflected in the negative direction of the y axis is separated from the light of the L4 and reflected in the positive direction of the y axis. Light approaches L4 light. Specifically, out of the light L6 reflected at the point g, the light reflected in the negative direction of the y-axis like the light ray C1 shown in FIG. However, the light reflected in the positive direction of the y-axis like the light ray C2 is far away from the light of L4 because the deflection angle when reflected by the diffusion pattern 46 is small. There is nothing. Therefore, when viewed from the z-axis direction, the lights L5 and L6 reflected at the f point and the g point are emitted while spreading in the direction shown in FIG. Therefore, when light is reflected between the point f and the point g of the diffusion pattern 46 as shown in FIG. 49, the light shown in FIG. 51A is emitted after being emitted in the z-axis direction. Expanded to the region between L5 and L6.

  Further, when the light is incident substantially parallel to the deflection inclined surface 46a when viewed from the x-axis direction, the lights L4 and L6 coincide with each other, and the light L4 and L6 are separated as the angle with respect to the deflection inclined surface 46a increases. For this reason, the larger the angle with respect to the deflection inclined surface 46a, the smaller the amount of light per unit angle in the x-axis direction. However, as described above, considering only the light rays on L4, L5, or L6, the amount of light that is originally reflected by the diffusion pattern 46 is the intensity when the light is substantially parallel to the deflection inclined surface 46a of the diffusion pattern 46. Becomes zero and the amount of reflected light increases as the angle with respect to the deflection inclined surface 46a increases. As a result of canceling these two effects, the light becomes uniform in the region surrounded by A1, B1, B2, A2, C2, and C1 in FIG. 52, that is, in the angle range where the light is emitted. In this directivity characteristic, the exit angle is −22 ° to + 37 ° in the y-axis direction, and the exit angle is −25 ° to + 25 ° in the x-axis direction. Therefore, Δθy = 59 ° and Δθx = 50 °, and almost 100% of light is emitted in this range.

  Even when the diffusion pattern 46 is wavy in this way, the light transmitted through the deflection inclined surface 46a of the diffusion pattern 46 and re-entered from the back surface 46b when viewed from the direction perpendicular to the light incident surface 44a. The light traveling direction is hardly changed before and after passing through the diffusion pattern 46. For this purpose, if the deflection inclined surface 46a and the back surface 46b are made parallel to each other when viewed from the direction perpendicular to the light incident surface 44a, the light travels substantially before and after transmitting through the diffusion pattern 46. The direction will be the same.

(Fifth embodiment)
FIG. 53 shows a surface light source device 61 used as a backlight according to still another embodiment of the present invention. In this surface light source device 61, a regular reflection plate 62 is disposed in parallel to the back surface of a wedge-shaped light guide plate 44, and a prism sheet 63 is provided so as to face the light emitting surface 44 b of the light guide plate 44. The wedge-shaped light guide plate 44 has an inclined rear surface, and the inclination angle is, for example, η = 1.52 °. The size of the light guide plate is, for example, a length of 30 mm, a thickness of the light incident surface 44a of 1 mm, and a tip thickness of 0.2 mm. In such a light guide plate 44, it seems that the diffusion pattern 46 does not appear at first glance, but the back surface and the light incident surface 44a are not parallel, and the entire lower surface is considered to be one diffusion pattern 46. In the case shown in FIG. 53, the prism sheet 63 in which prisms having apex angles of 40 ° or more are arranged is arranged with the pattern surface facing outward, but the pattern surface faces the light incident surface 44a of the light guide plate 44. In this case, the apex angle of the prism is not limited to 40 °. The light emitting unit 45 converts the light from a point light source such as a light emitting diode into a linear light source and emits it. For example, a wedge-shaped light guide 47, a point light source 48, a regular reflection plate 49, and a prism sheet. The light emitting unit 45 as described in the first embodiment consisting of 50 can be used. The back surface of the light guide plate 44 is not flat and may be curved.

  Accordingly, the light emitted from the light emitting unit 45 and incident on the light guide plate 44 from the light incident surface 44a is gradually reflected at the back surface (diffusion pattern 46) and reflected at the light exit surface 44b and the back surface. When the incident angle incident on the light incident surface 44a exceeds the critical angle of total reflection, the light is emitted from the light emitting surface 44b. Further, as shown in FIG. 54, the light emitted from the back surface of the light guide plate 44 is specularly reflected without being diffused by the specular reflection plate 62, and reenters the light guide plate 44 without changing the direction of the light. Is done. As shown in FIG. 54, the light emitted from the light emitting surface 44b is emitted along the light emitting surface 44b, then deflected by the prism sheet 63 and emitted in a direction perpendicular to the light emitting surface 44b.

  Here, most of the light emitted from the light guide plate 44 is emitted along the y-axis when viewed from the x-axis direction (or when viewed from the yz plane). 99% of the light is concentrated within an angle of ρ = 0 to 40 °. Therefore, most of the light deflected by the prism sheet 63 is concentrated within a range of ± 20 ° with respect to the z axis perpendicular to the light exit surface 44b of the light guide plate 44 when viewed from the x-axis direction. Yes.

  In the light emitting unit 45 as described in the first embodiment, when viewed from the z-axis direction, light emitted from the light emitting unit 45 is 80% or more of light within a range of ± 13 ° with respect to the y axis. Therefore, the light emitted from the light guide plate 44 is also concentrated by 80% or more in a range of ± 20 ° with respect to the z axis when viewed from the y-axis direction.

  Therefore, the emitted light from the prism sheet 63 is emitted almost in parallel with the z-axis, does not spread in the x-axis direction and the y-axis direction, and very high directivity is obtained.

  Further, it is necessary to use the regular reflection plate 62 as a reflection plate for reflecting leakage light, and it goes without saying that a high directivity cannot be obtained with a diffusion type reflection plate. The amount of light emitted substantially parallel to the light exit surface is affected by the regular reflection quality and reflectance of the regular reflection plate 62. It is desirable to use a regular reflection plate 62 that emits at least 2/3 or more of light in the angle range of ρ = 0 ° to 40 ° from the light exit surface 44b, and this amount of light is transmitted from the light exit surface 44b. If emitted, 50% or more of light can be emitted in the z-axis direction even after passing through the prism sheet 63. FIG. 55 and FIG. 56 show the intensity angle characteristics of light emitted from the light guide plate 44 when a diffusive reflection plate is used on the back surface of the light guide plate 44 and when a regular reflection plate is used. . Also from this measurement data, when the specular reflection plate 62 is used, most of the light is included in the range of ρ = 0 ° to 30 °, whereas when the diffuse reflection plate is used, ρ It can be seen that considerable light is emitted even in the range of ≧ 30 °.

  The cross-sectional shape of the light guide plate 44 used in this embodiment is not limited to a wedge shape, and for example, as shown in FIG. 57, a prism pattern 64 may be provided on the back surface. In the case of this light guide plate 44, the directivity equivalent to the wedge-shaped light guide plate 44 can be obtained if the inclination angle γ of the prismatic pattern 64 on the back surface is set to 10 ° or less. However, the inclination angle γ is preferably 5 ° or less, and particularly preferably 2 ° or more and 5 ° or less. Further, the inclination angle γ of the prism pattern 64 does not need to be uniform, and may be relatively small on the light incident surface side, and gradually increase toward the tip side.

  Further, as in the light guide plate 44 shown in FIG. 58, a prism-like pattern 64 may be provided only at the front end portion of the wedge-shaped plate. Here, the inclination angle γs of the prismatic pattern 64 is larger than the inclination angle γ of the wedge-shaped portion, for example, γ = 2 ° and γs = 3 °.

  The light emitting unit 45 is not limited to the configuration described in the first embodiment. However, as shown in FIG. 59, when a plurality of point light sources 65 such as light emitting diodes are opposed to the light exit surface 44b of the light guide plate 44, the directivity is high at first glance, but there is a lot of light that can be emitted in the lateral direction. Often appropriate. Alternatively, if the light flying in the lateral direction is bent so as to be parallel to the y-axis direction, the size in the z-axis direction becomes large. For this reason, it cannot be used as it is.

  Therefore, for example, a cylindrical lens 66 is placed between the point light source 65 and the light guide plate 44 as in the light emitting unit shown in FIG. 60, and the cylindrical lens 66 focuses light in the z-axis direction.

  Further, as shown in FIG. 61, a plurality of point light sources 65 such as light emitting diodes may be arranged and the back thereof may be covered with a concave mirror 67. In such a light emitting unit 45, light is emitted from the point light source 65 toward the concave mirror 67, and the light that is reflected by the concave mirror 67 and becomes substantially parallel light is incident on the light guide plate 44.

(Sixth embodiment)
FIG. 62 is a plan view showing a configuration of a surface light source device 68 according to still another embodiment of the present invention. The light guide plate 44 used in the surface light source device 68 is provided with a non-light emitting area 44d around a rectangular light emitting area 44c used as a light source. A light source 45 is integrally formed by accommodating a point light source 48 using a diode outside the light emitting region 44c at the end of the short side of the light guide plate 44 having a substantially rectangular shape. Further, the diffusion pattern 46 having a right-angled triangular section composed of the deflection inclined surface 46a and the back surface (re-incident surface) 46b is arranged concentrically with the point light source 48 as the center. The distance between the diffusion patterns 46 is relatively wide on the side close to the point light source 48 (the pattern density may be constant near the point light source), and the distance decreases as the distance from the point light source 48 increases. Thus, the brightness of the light exit surface 44b is made uniform. Further, when two or more light emitting diodes are used, a point light source is formed by collecting a plurality of light emitting diodes in one place. In FIG. 62, reference numeral 69 denotes a film wiring board (FPC) for supplying power to the point light source 48.

  The diffusion pattern 46 is arranged so that its length direction is substantially orthogonal to the direction connecting to the point light source 48, and the light totally reflected by the diffusion pattern 46 is emitted in a direction substantially perpendicular to the light emitting surface 44b, and diffused. Since the light passing through the pattern 46 is transmitted almost without changing the traveling direction, the direction of the light beam at each point is aligned in one direction at each point when viewed from directly above the light guide plate 44. Accordingly, when viewed from the direction perpendicular to the light exit surface 44b, the light emitted from the point light source 48 proceeds radially without being scattered in the lateral direction, and the light totally reflected by the diffusion pattern 46 is reflected by the light exit surface. 44b.

  Such a surface light source device 68 can be placed on the back surface of the transmissive liquid crystal display panel 70 and used as a backlight as shown in FIG. In that case, there is no need to have a reflector on the back surface of the light guide plate 44, but as shown in FIG. 63, a reflector plate 69 such as a regular reflector or a diffuse reflector is provided on the back surface of the light guide plate 44. Also good. However, when a diffusion plate is provided on the back surface of the light guide plate 44 (particularly when the directivity of the point light source 48 is narrow), it is necessary to use a plate having a sufficiently small diffusion action so as not to impair the directivity. .

  Such a surface light source device 68 can also be used as a front light by placing it on the front surface of a reflective liquid crystal display panel 71 as shown in FIG. In that case, as shown in FIG. 64, the light use efficiency is improved by providing antireflection films 72 on both the front and back surfaces of the light guide plate 44.

65A and 65B are a plan view and an enlarged cross-sectional view showing the shape of the diffusion pattern 46. FIG. The diffusion pattern 46 has a substantially uniform cross section in the length direction, and is disposed perpendicular to the traveling direction of the light beam. The diffusion pattern 46 used here is slightly wavy as shown in FIG. The diffusion pattern 46 is formed in a substantially right triangle shape by the deflection inclined surface 46a and the back surface 46b, and the inclination angle γ of the deflection inclined surface 46a and the inclination angle δ of the back surface 46b are:
γ <δ,
γ = 45 ° to 65 °
δ = 80 ° -90 °
Is desirable. For example, when the light guide plate 44 made of a transparent resin having a refractive index n = 1.53 is used, the light is emitted from the light guide plate 44 when the inclination angle γ of the deflection inclined surface 46a is 55 ° as shown in FIG. The light is emitted in the range of −25 ° to + 35 ° as viewed from the x-axis direction. This is because the light hitting the diffusion pattern 46 from below is reflected by the diffusion pattern 46, and the light hitting from the upper direction again from the back surface (re-incident slope) 46b as shown in FIG. 67. Re-entered inside.

  68 (a), (b), (c), and (d) show how the entire diffusion pattern 46 is arranged, FIG. 69 shows the change in pattern density (area ratio) in the radial direction, and FIG. 70 shows the pattern length. FIG. 71 shows a change in the number of patterns per unit area. r represents the distance from the light emitting part 45, and the diffusion pattern 46 has a density that increases as the distance from the light emitting part 45 increases as shown in FIG. This is to make the luminance of the light exit surface 44b uniform. As a method of gradually increasing the diffusion pattern density, it is possible to gradually increase the number of diffusion patterns per unit area, but in this embodiment, a plurality of light guide plates 44 are provided according to the distance from the light emitting unit 45. In each zone, as shown in FIG. 71, the number of diffusion patterns per unit area is constant and the number of diffusion patterns per unit area is increased stepwise for each zone. As shown at 70, the length of the diffusion pattern is gradually changed in each zone. In addition, the pattern length once becomes shorter at the zone boundary.

  68 (b), 68 (c), and 68 (d) specifically show the diffusion patterns at the locations a, b, and c in FIG. 68 (a), respectively. FIG. 68 (b) shows the region a closest to the light emitting portion 45, and the pitch in the radial direction and the circumferential direction of the diffusion pattern 46 are both 140 μm, and the inner diffusion pattern 46 and the outer diffusion pattern 46 Are not overlapped in the radial direction. FIG. 68 (c) shows the intermediate region B, in which both the pitch in the radial direction and the pitch in the circumferential direction of the diffusion pattern 46 are 70 μm, and there are two rows of the inner diffusion pattern 46 and the outer diffusion pattern 46. It overlaps one by one. FIG. 68D shows a region C far from the light emitting portion 45, where the pitch in the radial direction is 35 μm and the pitch in the circumferential direction is 140 μm. 68 (b), (c), and (d) show a linearly extending diffusion pattern, the wavy diffusion pattern as shown in FIG. 65 is shown in FIGS. 68 (b), (c), and (d). You may arrange as follows.

  In addition, the long side of the light guide plate opposite to the end where the light emitting unit 45 is disposed is straight, whereas the long side of the light guide plate near the light emitting unit 45 is cut diagonally by one or more steps. Has been. Similarly, in the vicinity of the light emitting part 45, the short side is also formed partly obliquely. If slopes 73 and 74 are provided on the long side and the short side near the light emitting part 45, respectively, as shown in FIG. 72, a part of the light emitted from the light emitting part 45 is combined with the long side slope part 73. Light can be sent to the corners of the light guide plate 44 (regions hatched in FIG. 72) after being totally reflected by the short-side slope portion 74. When the light emitting portion 45 is placed at the corner of the light guide plate 44, the other corner portions tend to be dark. With such a structure, the light totally reflected by the slope portions 73 and 74 is reflected on the light guide plate 44. By sending to the corner of the light emitting region 44c, the luminance distribution of the surface light source device 68 can be made more uniform, and the efficiency of the surface light source device 68 can be increased.

  When the fixed frame 75 is attached to the light guide plate 44 as shown in FIG. 73, the slope portions 73 of the light guide plate 44 are structured such that the slope portions 73 and 74 for reflecting light and the fixed frame 75 are in close contact with each other. , 74 may be easily scratched and the reflection characteristics may be impaired. In order to prevent this, a small convex pot 76 is provided in a part of or near the slopes 73 and 74 for reflecting light, and the light guide plate 44 is brought into contact with the fixed frame 75 by the convex pot 76. It is preferable that a gap be formed between the slope portions 73 and 74 and the fixed frame 75.

  Next, the antireflection film 72 will be described. When the surface light source device 68 is used as a front light, an antireflection film (AR coating) 72 for preventing light (light that is brightly reflected by light other than an image, for example, reflected light) By attaching to both surfaces of 44 or the surface on which the diffusion pattern 46 is formed, it is possible to prevent the light. However, as shown in FIG. 74, the anti-reflection film 72 prevents external light from being reflected by the surface of the light guide plate 44 (flat portion 44e). The light enters the flat portion 44e of the light guide plate 44 perpendicularly. On the other hand, as shown in FIG. 74, the light of the light emitting portion 45 that has passed through the deflection inclined surface 46a is incident obliquely on the rounded portion 44f at the boundary between the back surface 46b of the diffusion pattern 46 and the flat portion 44e. Reflected into the sky, it becomes a treasure.

  However, if the antireflection film 72 is formed to have a uniform film thickness to suppress the shine caused by external light, the light emitting portion that is obliquely incident on the rounded portion 44f at the boundary between the back surface 46b of the diffusion pattern 46 and the flat portion 44e. Like the light from 45, the effect on the light incident obliquely on the antireflection film 72 was weak. As shown in FIG. 75, assuming that the wavelength (light source wavelength) of the light emitted from the light emitting unit 45 is about 450 nm, the antireflection film 72 to be used has a substantially minimum reflectance at the wavelength as shown in FIG. Therefore, when light is obliquely incident and the converted wavelength is shortened, the reflectance is increased. Therefore, in order to prevent such light from the light from the light emitting portion 45, the film thickness of the antireflection film 72 at the rounded portion 44f at the boundary between the back surface 46b of the diffusion pattern 46 and the flat portion 44e is partially set. It is effective to increase the thickness.

  Thus, in order to partially increase the thickness of the antireflection film 72 in the rounded portion 44f at the end of the diffusion pattern 46, for example, as shown in FIG. 77, a vacuum deposition apparatus 77 for depositing the antireflection film 72 is used. If the light guide plate 44 is installed obliquely and the rounded portion 44 f faces the vapor deposition source 78, this can be done easily. Usually, since the antireflection film 72 deposited on the inclined portion is thin, by depositing the antireflection film 72 while the light guide plate 44 is inclined, the film thickness in the rounded portion 44f can be made thicker than the others. it can.

  As shown in FIG. 78, the light on the flat surface 44e on the diffusion pattern side of the light guide plate 44 is largely due to external light, whereas the light on the light exit surface 44b of the light guide plate 44 is shown in FIG. As shown in FIG. 5, the light L11 from the light emitting portion 45 is reflected by the deflection inclined surface 46a and further reflected by the light emitting surface 44b. These are noises for the image of the light L12 from the light emitting unit 45 reflected by the deflection inclined surface 46a and further reflected by the reflective liquid crystal display panel 71. Therefore, in order to prevent light from being reflected on the front and back of the light guide plate 44, the flat portion 44e on the surface on which the diffusion pattern 46 is formed has a normal antireflection film 72 (or the above-described one). Such an antireflection film 72) having a partially thick film may be formed, and an antireflection film 79 specialized for light from the light emitting portion 45 may be used on the light emitting surface 44b.

  However, since the white light emitting diode has two peaks (450 nm, 550 nm) in the normal wavelength spectrum as shown in FIG. 79, it is necessary to suppress the reflectance at these two peaks. The light L11 reflected by the light emitting surface 44b has a little width in the antireflection film 79, and the obliquely incident light may have the reflectance characteristic of the antireflection film 79 shifted to a lower wavelength side than the case of normal incident light. Many. Therefore, it is desirable that the antireflection film 79 used on the back side has a reflectance in the visible range having two minimum values, and the interval between the two minimum values is wider than the interval between the peaks of the light emitted from the point light source 48. . Furthermore, it is more desirable that the two average values of the reflectance minimum values in the antireflection film 79 have longer wavelengths than the average value of the two peaks of the point light source 48.

  FIG. 80 is a cross-sectional view showing the structure of the light emitting unit 45 embedded in the end of the short side of the light guide plate 44. The light emitting unit 45 is obtained by sealing a light emitting diode chip 81 in a transparent resin 82 and covering a surface other than the front surface with a white transparent resin 83. The light emitting unit 45 is mounted on the film wiring board 84 and fixed by solder 85. Further, the film wiring board 84 is fixed to a reinforcing plate 86 made of glass epoxy resin. In the light source mounting portion 87 of the light guide plate 44, a hole 88 for receiving the light emitting portion 45 passes vertically, and a positioning pin 89 is projected on the lower surface of the light guide plate 44 in the vicinity of the light source mounting portion 87. Yes. On the other hand, the film wiring board 84 and the reinforcing plate 86 are provided with through holes 90 and 91 for passing the positioning pins 89.

  Then, an ultraviolet curable adhesive (or a thermosetting adhesive) 92 is applied to the lower surface of the light guide plate 44 around the base portion of the positioning pin 89, and the positioning pin 89 is attached to the film wiring board 84 and the reinforcing plate. The UV curable adhesive 92 is cured by irradiating ultraviolet rays after positioning the center of the light guide plate 44 in the thickness direction and the emission center of the light emitting portion 45 with a CCD camera or the like through the through holes 90 and 91 of 86. Then, the light guide plate 44 and the light emitting unit 45 are bonded together, and the positioning pins 89 are heat staked to the reinforcing plate 86.

  At this time, as shown in FIG. 80, the light emitting part 45 is formed by the protrusions 93 provided on the inner surface of the hole 88 of the light source mounting part 87 (which may be the back side, the front side, or both of the light emitting part 45). Positioning of the center may be performed. Although not shown, the light guide plate 44 is used with a stepped jig for positioning the upper surface of the light guide plate 44 and the upper surface of the light emitting unit 45 in a state where the light guide plate 44 and the light emitting unit 45 are turned upside down. And the center of the light emitting part 45 may be positioned. Further, instead of the film wiring board 84, a glass epoxy wiring board or a lead frame may be used.

  For example, in the case of a transmissive liquid crystal display device, the light guide plate 44 to which the light emitting section 45 is attached is as shown in FIG. 80, with the reinforcing plate 86 side up (or down). The end of the film wiring board 84 is connected to the heat sink 96. Further, the transmissive liquid crystal display panel 70 is overlaid on the light guide plate 44, and the end of the film wiring substrate 97 connected to the liquid crystal display panel 70 is also fixed to the heat sink 98 on the main substrate 94.

  When forming the rectangular light guide plate 44 as described above, if the rectangular light guide plate 44 is directly formed, the resin flow in the mold 98 is not uniform as shown in FIG. Therefore, it is difficult to achieve uniform pattern transferability over the entire surface, and the light guide plate is likely to warp. However, as shown in FIG. 83, a metal mold 98 is made larger than the light guide plate 44 to be manufactured, and a large light guide plate 99 having a sector shape or a semicircular shape is manufactured using the metal mold 98. The light guide plate 44 can be formed by appropriately cutting. If the large light guide plate 99 with good resin flowability is formed in this way and the desired light guide plate 44 is produced by cutting it, the flow of the resin will be reduced when the large light guide plate 99 is formed. Uniform in any direction, uniform pattern transferability over the entire surface can be achieved, and warpage of the light guide plate 44 is less likely to occur.

  The dimensions of the surface light source device shown in FIG. 62 are described. The length of the light guide plate 44 in the short side direction is 33 mm, the length in the long side direction is about 43 mm (about 47 mm including the light source mounting portion), and the thickness. Is 0.1 mm. The width of the non-light emitting area 44d of the light guide plate 44 is 0.2 mm. Further, the light emitting diode which is the point light source 48 has a width of about 25 mm and a depth of 1.3 mm.

  FIG. 84 shows a cellular phone 100 in which a reflection-side liquid crystal display device using the surface light source device 68 having the above structure is incorporated as a display 101. The mobile phone 100 includes a speaker 102 and an antenna 103 on a display 101, and an operation button (such as a dial) 104 below the display 101. FIG. 85 also shows a PDA 105 using the surface light source device 68 having the above structure as the display 106. This PDA has an operation button 107 under the display 106.

  In the cellular phone 100 and the PDA 105, the liquid crystal display screens of the displays 101 and 106 often use the entire front surface of the device, and are long and narrow in the vertical direction, and operation switches 104 and 107 above and below the displays 101 and 106, respectively. And a speaker 102 are often provided. For this reason, the use of the surface light source device 68 in which the light emitting unit 45 is placed at the end near the short side facilitates the component layout design and contributes to the miniaturization of the mobile phone 100 and the PDA 105. To do. In particular, in the case of the cellular phone 100, since the antenna 103 generates a high-frequency electromagnetic wave, an IC or a high-frequency circuit cannot be placed in the vicinity thereof, but a point light source such as a light emitting diode is affected by the high-frequency electromagnetic wave. Since it is difficult, the space can be effectively utilized by placing the light emitting unit 45 here.

(Seventh embodiment)
FIG. 86 is a diagram showing characteristics of a liquid crystal display device using a surface light source device according to still another embodiment of the present invention as a front light. FIG. 86A is a diagram showing an outgoing light intensity angle distribution of light emitted from the light guide plate 44 and shows a substantially flat characteristic. 86B to 86E are characteristics corresponding to the emitted light intensity characteristics shown in FIG. 86A. FIG. 86B is reflected from the lower surface of the light guide plate 44 and is reflected from the light emitting surface 44b. Intensity distribution of emitted light, FIG. 86C shows the diffusion characteristic of the liquid crystal display panel, FIG. 86D shows the intensity characteristic of the emitted light from the liquid crystal display panel, and FIG. Shows the S / N ratio at the time, and after being reflected by the liquid crystal display panel, the image emitted to the front side [(D) in the figure] and the noise light reflected by the lower surface of the light guide plate 44 and emitted to the front surface [ (B)] (see FIG. 78).

  Similarly, FIG. 86 (a) is a diagram showing an outgoing light intensity angle distribution of light emitted from the light guide plate 44, and shows a characteristic that is recessed substantially at the center. 86B to 86E are characteristics corresponding to the emitted light intensity characteristics of FIG. 86A, and FIG. 86B is an intensity distribution of light reflected by the light guide plate 44, and FIG. c) shows the diffusion characteristics of the liquid crystal display panel, FIG. 86 (d) shows the intensity of emitted light from the liquid crystal display panel, and FIG. 86 (e) shows the S / N ratio.

  The contrast of the liquid crystal display device when the surface light source is lit (no external light) is determined by the S / N between the reflected light (image) from the reflective liquid crystal display panel and the reflected light (light) from the light guide plate 44. The characteristic diagrams [86 (B), (b)] of the light emitted after being reflected by the light plate 44 are easily affected by the intensity distribution of the emitted light intensity of the light emitted from the light guide plate 44, whereas the liquid crystal display The images reflected by the panel [FIGS. 86D, 86D] are not easily affected by the intensity distribution of the outgoing light intensity of the light emitted from the light guide plate 44, and the spread thereof changes slightly due to the diffusion characteristics of the liquid crystal display panel. Even so, the characteristics do not change much.

  Therefore, as shown in FIGS. 86A to 86E, the S / N ratio in the vertical direction is increased by reducing the intensity of the light emitted in the vertical direction with respect to the light emitting surface 44b of the light guide plate 44. be able to.

  FIG. 87 is a plan view showing an example of the diffusion pattern 46 for realizing the characteristics shown in FIGS. 86 (a) to 86 (e). In this diffusion pattern 46, when the angle formed by the tangent line to the direction perpendicular to the light traveling direction inside the light guide plate 44 is ν, the region where the angle ν is almost zero is very small. Alternatively, it may be completely eliminated. With this structure, it is possible to reduce the light emitted in the direction perpendicular to the light exit surface 44b when viewed from the light traveling direction (y-axis direction), and to increase the S / N ratio in the vertical direction. .

(Eighth embodiment)
FIG. 88 (b) shows a surface light source device using a light guide plate provided with a diffusion pattern of the same shape as a whole. In such a surface light source device, the light is emitted from the light exit surface 44b regardless of the light exit position. The emission direction is evenly aligned. When actually observing the liquid crystal display device, the viewing angle differs depending on the location in the screen of the liquid crystal display device. For this reason, when the directivity of the light guide plate 44 is the same regardless of the place, the brightness looks different depending on the pixel position, and uneven luminance in the surface occurs. If a Fresnel lens or the like is placed on the light guide plate 44, this problem is solved, but the surface light source device becomes thicker.

  In such a case, the shape of the diffusion pattern 46 (inclination angle γ of the deflection inclined surface 46a) and the arrangement (inclination ν in the length direction of the diffusion pattern 46) are changed depending on the location in the light guide plate 44. What is necessary is just to change sex according to a place. That is, as shown in FIG. 88A, the diffusion pattern 46 is designed so that light is emitted in the central portion of the light guide plate 44 in a direction perpendicular to the light emission surface 44b, and light is emitted in the peripheral portion. If the emission direction from the surface 44b is directed to the central portion of the light guide plate 44, the diffusion pattern 46 can have the function of a Fresnel lens, and the entire screen appears to have the same brightness. The brightness can be made uniform.

It is a disassembled perspective view of the surface light source device which has the conventional general structure. It is sectional drawing of a surface light source device same as the above. It is a figure which shows the directional characteristic of a surface light source device same as the above. It is a disassembled perspective view of the surface light source device which has another conventional structure. It is a figure which shows the directional characteristic of a surface light source device same as the above. It is a top view which shows the structure of the conventional surface light source device of another structure. It is a figure which shows the shape and effect | action of a diffusion pattern of a surface light source device same as the above. It is a figure which shows the directional characteristic of a surface light source device same as the above. It is sectional drawing which shows the conventional front light type surface light source device. It is a figure for demonstrating the desirable directional characteristic in a surface light source device. It is a figure showing an example of the directional characteristic shown for a comparison. (A) is a characteristic diagram showing an example of desirable directivity, and (b) is a characteristic diagram showing an example of a more preferable directivity. FIG. 4 is a diagram illustrating ideal directivity characteristics, directivity characteristics when a prism sheet is used, and directivity characteristics from an x-axis direction and a y-axis direction when a diffusion pattern is used. It is the figure which represented the directivity characteristic of the light radiate | emitted from a surface light source device in three dimensions. It is the schematic which shows the combination (surface light source device) of a reflection type liquid crystal display panel and a front light type surface light source device. (A), (B), (C), and (D) are diagrams showing the directivity characteristics of the surface light source device, and (a), (b), (c), and (d) are the corresponding reflected light intensity angle characteristics of the reflective liquid crystal display panel. FIG. (A) is a figure explaining the full width at half maximum in the reflected light intensity angle distribution of a reflection type liquid crystal display panel, (b) is a figure explaining the full width at half maximum in the directivity of a surface light source device. It is a disassembled perspective view which shows the structure of the surface light source device by one Embodiment of this invention. It is a figure which shows the behavior of the planar light of the light emission part used for the surface light source device same as the above. It is a figure which shows the directional characteristic of the light radiate | emitted from the light emission part of FIG. 19 which used the regular reflection board for the back surface. FIG. 20 is a diagram showing directivity characteristics of emitted light when the back regular reflection plate is replaced with a diffuse reflection plate in the light emitting unit of FIG. 19. It is the figure explaining how to obtain | require the light intensity (energy) in the (alpha) direction in FIG.20 and FIG.21. (A) is a figure which shows the directional characteristic of the light spread in the thickness direction (z-axis direction) of the light-guide plate, (b) is a figure which shows the directional characteristic of the light spread in the width direction (x-axis direction) of the light-guide plate, (C) is a figure which shows the directional characteristic of the light which spread in the thickness direction and width direction (z-axis direction, x-axis direction) of the light-guide plate. It is a figure showing a mode that the direction of light changes, when the light which spreads in the width direction of the light-guide plate is totally reflected by the deflection | deviation inclined surface of a diffusion pattern. (A) (b) is a figure showing another mode that the direction of light changes when the light which spreads in the width direction of the light guide plate is totally reflected by the deflection inclined surface of the diffusion pattern. It is a figure which shows the behavior of the light which permeate | transmitted the deflection | deviation inclined surface of the diffusion pattern, and reentered into the light-guide plate from the back surface. (A) is a figure which shows the direction of the light before injecting into a diffused pattern, (b) is the figure which shows the direction of the light totally reflected by the deflection | deviation inclined surface of a diffused pattern, and the light after reflection, (c). FIG. 4 is a diagram showing the directions of light that is transmitted through the deflection inclined surface of the diffusion pattern and re-entered from the back surface and light after re-incident. It is a figure showing the spatial frequency of light when it sees from the advancing direction (y-axis direction) of the light in a light-guide plate. It is a figure which shows the directional characteristic of the light radiate | emitted from the light-projection surface of a surface light source device. It is a figure explaining how to provide a diffusion pattern in case light is introduced into the light guide plate from the light emitting portion obliquely. It is a figure explaining the method to test | inspect the directional characteristic of the light in a light-guide plate. It is a figure which shows the behavior of the reflected light in the cross-section circular arc-shaped diffusion pattern (comparative example). It is a figure which shows the behavior of the reflected light in the diffusion pattern (comparative example) which carried out saw-tooth shape. (A) is a figure which shows the behavior of the light totally reflected by the deflection | deviation inclined surface of the diffusion pattern of the cross-sectional right triangle shape, (b) is the light of the light which permeate | transmitted the front diffusion pattern and was reflected by the back diffusion pattern. It is a figure which shows a behavior. It is a figure which shows the relationship between the emission angle from a surface light source device, and light intensity when changing the angle of a deflection | deviation inclination angle into 45 degrees, 55 degrees, and 65 degrees. It is a figure which shows the definition of the inclination angle (gamma) of the deflection | deviation inclined surface in a diffusion pattern, the inclination angle (delta) of a back surface, and the output angle (epsilon) from a light-projection surface. (A) and (b) are diagrams for explaining the relationship between the emission angle and the light intensity shown in FIG. 35, and (a) shows a state in which light that is incident substantially horizontally is reflected by the deflection inclined surface. (B) shows a state in which light incident from below is reflected by the deflection inclined surface. (A) shows the diffusion characteristic of the reflective liquid crystal display panel, (b) shows the outgoing light intensity angle characteristic of the light guide plate, (c) shows the outgoing light intensity angle characteristic from the reflective liquid crystal display element. It is. It is a figure which shows the behavior of the light which permeate | transmitted the deflection | deviation inclined surface and re-entered from the back surface, when the inclination | tilt angle of the back surface of a diffusion pattern is small. It is a figure which shows the behavior of the light which permeate | transmitted the deflection | deviation inclined surface when the inclination | tilt angle of the back surface of a diffusion pattern is small. (A) is a schematic diagram showing a traveling direction of light introduced from a linear light source into the light guide plate, and (b) is a traveling light introduced into the light guide plate from a plurality of point light sources arranged at intervals. FIG. 6C is a schematic diagram showing a direction in which light introduced into a light guide plate from a plurality of point light sources arranged in a single location is shown. It is a schematic side view which shows the reflection type liquid crystal display device used with the surface light source device by another embodiment of this invention. It is an expanded sectional view which shows the diffusion pattern of the light-guide plate in a surface light source device same as the above. It is a schematic plan view of the surface light source device by further another embodiment of this invention. It is a figure which shows the directional characteristic of the light radiate | emitted from a surface light source device same as the above. It is a schematic plan view of the surface light source device by further another embodiment of this invention. It is an enlarged plan view of the diffusion pattern provided in the light guide plate of the same surface light source device. It is a modification of a diffusion pattern same as the above. It is a figure which shows the wavy diffusion pattern and the light which injects there. It is a figure which shows the directional characteristic of the light L4 reflected by the e point of FIG. (A) is a view of the directions of the lights L4, L5, and L6 reflected at points e, f, and g in FIG. 49 as viewed from the z-axis direction, and (b) is reflected by the deflection inclined surface. It is a figure which shows the light of C1, C2. It is a figure which shows the radiation | emission area | region of the light shown in FIG. It is a perspective view of the surface light source device by another embodiment of this invention. It is a side view which shows the behavior of the light in a surface light source device same as the above. It is a figure which shows the relationship between the angle which the direction (y-axis direction) parallel to a light-projection surface and an outgoing light make, and outgoing light intensity when a regular reflection board is used for the back surface of a light-guide plate. It is a figure which shows the relationship between the angle which the direction (y-axis direction) parallel to a light-projection surface and an outgoing light make, and outgoing light intensity when a diffused reflection board is used for the back surface of a light-guide plate. It is a schematic side view of the surface light source device using the light-guide plate in which the diffusion pattern of a different structure was formed. Furthermore, it is a schematic side view of the surface light source device using the light-guide plate in which the diffusion pattern of a different structure was formed. It is the schematic which shows the comparative example using a some point light source. It is the schematic perspective view partly fractured | ruptured which shows the comparative example using a some point light source and a cylindrical lens. It is a schematic plan view showing a surface light source device that emits light having a narrow directivity using a plurality of point light sources and a concave mirror. It is a top view which shows the surface light source device by another embodiment of this invention. FIG. 63 is a schematic side view showing a liquid crystal display device using the surface light source device of FIG. 62 as a backlight. FIG. 64 is a schematic side view showing a liquid crystal display device using the surface light source device of FIG. 62 as a front light. (A) is a top view which shows the wavy diffusion pattern, (b) is the JJ sectional view taken on the line of (a). It is a figure which shows the breadth of the light reflected by the deflection | deviation inclined surface of the diffusion pattern same as the above. It is a figure which shows the light which permeate | transmitted the diffusion pattern same as the above. (A) is a plan view of the light guide plate provided with the diffusion pattern same as above, (b) is an enlarged view of a portion of (a), (c) is an enlarged view of a portion of (a), and (d) is (a) FIG. It is a figure which shows the relationship between the distance from the light emission part (light source), and the pattern density of a diffusion pattern in the light guide plate same as the above. It is a figure which shows the relationship between the distance from a light emission part, and the pattern length of a diffusion pattern in the light guide plate same as the above. It is a figure which shows the relationship between the distance from a light emission part, and the pattern number density (pattern number / area) of a diffusion pattern in the light guide plate same as the above. It is the schematic for showing the structure for sending more light to the corner part of a light-projection surface in the surface light source device same as the above, and its effect | action. It is the schematic which shows the light-guide plate filled with the fixed frame. It is the partially broken expanded sectional view which shows the anti-reflective film formed in the pattern surface side of a light-guide plate same as the above. It is a figure which shows the relationship between the wavelength of a light emitting diode, and emitted light intensity. It is a figure which shows the relationship between the incident light wavelength and reflectance in an antireflection film. It is the schematic explaining the method for forming a thick anti-reflective film in the edge of a diffusion pattern. It is a figure which shows the antireflection film | membrane provided in the light which is reflected by the surface by the side of the pattern of a light-guide plate, a light-projection surface, etc., and the surface by the side of the pattern of a light-guide plate, and a light-projection surface. It is a figure which shows the emitted intensity wavelength characteristic of the light radiate | emitted from a white light emitting diode. It is sectional drawing which shows the structure of the light emission part attached to the light-guide plate. It is a side view which shows the liquid crystal display device mounted on the circuit board. It is a figure which shows the resin flow at the time of shape | molding a rectangular light-guide plate within the rectangular cavity of a metal mold | die. It is a figure explaining a mode that it shape | molds with the metal mold | die which has a cavity larger than the target light-guide plate and whose resin flow is smooth. It is a front view of a mobile phone. It is a front view of PDS. (A) (a) is a figure which shows the emitted light intensity distribution of the light radiate | emitted from a light-guide plate, (B) (b) is the intensity distribution of the light reflected from the lower surface of a light-guide plate and radiate | emitted from a light-projection surface. (C) and (c) are diagrams illustrating the diffusion characteristics of the liquid crystal display panel, (D) and (d) are diagrams illustrating the intensity characteristics of light emitted from the liquid crystal display panel, and (E) and (e) are the surface light source lightings. It is a figure which shows S / N ratio at the time. It is a top view which shows the diffusion pattern used with the surface light source device by another embodiment of this invention. (A) is the schematic of the surface light source device by another embodiment of this invention, (b) is a figure for comparing and explaining.

Explanation of symbols

44 Light guide plate 44a Light incident surface 44b Light exit surface 45 Light emitting portion 46 Diffusion pattern 46a Deflection inclined surface 46b Back surface (re-incident surface)
47 Wedge-shaped light guide 48 Point light source 72 Antireflection film

Claims (3)

In a surface light source device comprising a light source and a light guide plate that spreads light introduced from the light source over almost the entire light emitting surface and emits the light from the light emitting surface,
The light source has a plurality of peaks in its wavelength spectrum, and the light guide plate is formed with an antireflection film on its light exit surface, and the antireflection film has a minimum value of reflectance wavelength dependency with respect to normal incident light. A surface light source device characterized in that there are a plurality of locations, and the maximum wavelength difference of the minimum values of the plurality of locations is larger than the maximum wavelength difference of the plurality of peaks of the light source. In a surface light source device comprising a light source and a light guide plate that spreads light introduced from the light source over almost the entire light emitting surface and emits the light from the light emitting surface,
Said the light exit surface of the light guide plate a plurality of concave patterns on the opposite side is formed, different anti-reflection film having reflection characteristics from each other on the surface of the light emitting surface and the opposite side of the light guide plate is formed A surface light source device. In a surface light source device comprising a light source and a light guide plate that spreads light introduced from the light source over almost the entire light emitting surface and emits the light from the light emitting surface,
The light guide plate, the light emitting surface is formed a plurality of concave patterns on the opposite side from that of the light emitting surface anti-reflection film is formed on the opposite side, the anti-reflection film is not concave pattern A surface light source device, wherein a film thickness of an antireflection film at a boundary portion between a flat surface and a concave pattern is different from a film thickness of the antireflection film on the flat surface.

Images