JP2012123936A - Plane light source device, and three-dimensional display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a plane light source device, which is used for a three-dimensional display device, capable of lessening a difference (darkness difference) of apparent intensity between a right eye and a left eye and a difference (luminance unevenness) of apparent light-emitting intensity on a screen.SOLUTION: In the plane light source device, a left-side light source 23a and a right-side light source 23b are arranged respectively on opposite light-incident end faces of a light guide plate 22. An emitting pattern 25a for making light emitted from the left-side light source 23a emit from a light emitting surface 26 and a light emitting pattern 25b for making light emitted from the right-side light source 23b emit from the light emitting surface 26 are formed on a back surface of the light guide plate 22. When peak intensity of the light emitted from an end on a left-side light source 23a (right-side light source 23b) side of a light-emitting region at the time of lighting up the left-side light source 23a is set to be Ia1 (Ia2) and peak intensity of the light emitted from an end at the left-side light source 23a (right side light source 23b) side of the light emitting region at the time of lighting up the right-side light source 23b is set to be Ib1 (Ib2), the relationship of both peak intensity becomes Ia1>Ib1 (Ia2<Ib2).

Description

  The present invention relates to a surface light source device and a stereoscopic display device. Specifically, the present invention relates to a stereoscopic display device for three-dimensionally displaying images and videos, and a surface light source device used for the stereoscopic display device.

  As a stereoscopic display device for displaying so-called three-dimensional images, there are a method using observation glasses and a method using no glasses. However, in the method of using eyeglasses, since the observer must wear the eyeglasses on the head, it is troublesome and may cause discomfort to the observer. Therefore, a method that does not use glasses is desired as a stereoscopic display device.

  1A and 1B are schematic diagrams illustrating the principle of a stereoscopic display device that does not use glasses. In this stereoscopic display device 11, the left light source 13 a is disposed facing the left light incident end surface of the flat light guide plate 12, and the right light source 13 b is disposed facing the right light incident end surface of the light guide plate 12. . Although not shown in the drawing, on the back surface or the front surface (light emitting surface 16) of the light guide plate 12, a large number of lights for emitting light from the left light source 13a and entering the light guide plate 12 from the light emitting surface 16 of the light guide plate 12 are provided. There are formed a minute emission pattern and a number of minute emission patterns for emitting light from the right light source 13 b and entering the light guide plate 12 from the light emission surface 16 of the light guide plate 12. A prism sheet 14 is disposed on the front surface of the light guide plate 12, and a liquid crystal panel 15 is disposed on the front surface thereof. In this specification, unless otherwise specified, left and right refer to the left and right of an observer observing a stereoscopic display device.

  The liquid crystal panel 15 alternately displays the right eye image and the left eye image in a time-division manner, and the right light source 13b emits light in synchronization with the right eye image (at this time, the left light source 13a is turned off). The left light source 13a emits light in synchronization with the image for the left eye (the right light source 13b is turned off at this time). As shown in FIG. 1A, when the right light source 13b emits light, the light Lb of the right light source 13b that has entered the light guide plate 12 is totally reflected by the emission pattern on the back surface, thereby causing the light exit surface 16 to be reflected. Are collected in the direction of the right eye 17 b by being refracted by the prism sheet 14. Therefore, the light Lb emitted from the light emitting surface 16 is converted into an image for the right eye by the liquid crystal panel 15 and enters the right eye 17b of the observer.

  Similarly, when the left light source 13a emits light, as shown in FIG. 1B, the light La of the left light source 13a that enters the light guide plate 12 is totally reflected by the emission pattern on the back surface. The light is emitted from the emission surface 16 and refracted by the prism sheet 14 to be collected in the direction of the left eye 17a. Therefore, the light La emitted from the light emitting surface 16 is converted into an image for the left eye by the liquid crystal panel 15 and enters the left eye 17a of the observer. As a result, the observer views the right eye image and the left eye image separately with the right eye 17b and the left eye 17a, respectively, and the stereoscopic image is recognized by the observer. An example of such a stereoscopic display device is disclosed in Patent Document 1.

  The stereoscopic display device as described above is designed so that the in-plane front intensity is uniform without uneven luminance on the light exit surface 16. That is, the emission pattern for emitting the light from the right light source 13b is determined so that the emission intensity is almost uniform over the entire emission region as shown by the straight line To in FIG. The distribution is determined so that the pattern density increases as the distance from the right light source 13b increases. Specifically, the pattern density of the emission pattern for emitting the light from the right light source 13b is determined according to the distribution curve Gb in FIG. Similarly, the emission pattern for emitting the light from the left light source 13a is also distributed so that the emission intensity is almost uniform over the entire emission region as shown by the straight line To in FIG. The distribution is determined so that the pattern density increases as the distance from the left light source 13a increases. Specifically, the pattern density of the emission pattern for emitting the light from the left light source 13a is determined according to the distribution curve Ga in FIG. Note that the pattern density of the emission pattern is a total value of the areas projected on the back surface of the light guide plate of the emission pattern included in the unit area. Further, the right end in FIG. 2 is an end on the right light source side in the light emitting region, and the left end is an end on the left light source side in the light emitting region (the same applies hereinafter). For example, Patent Document 2 discloses that the emission intensity of the surface light source device is made uniform by increasing the pattern density of the emission pattern as the distance from the light source increases.

Japanese Patent No. 4545464 JP 2003-232933 A

  However, the visual field sensitivity of a person is not uniform, and the visual field sensitivity is high in the direction in which the line of sight is directed, but the visual field sensitivity rapidly decreases as the line of sight deviates. Therefore, when the left eye and the right eye are looking at the same position on the screen, even if the left eye image emission intensity and the right eye image emission intensity at the same position are the same, the left eye and right eye The way you perceive brightness is different, and there is a physiological contrast between the left and right eyes. Moreover, the degree of the difference in brightness differs depending on the position on the screen. As a result, the recognition degree of the left-eye image and the recognition degree of the right-eye image are different, resulting in insufficient stereoscopic effects and uneven brightness on the screen.

  The reason for this will be described with reference to FIG. FIG. 3A shows a surface light source device without a liquid crystal panel. In the case of a stereoscopic display device, since the eye position is fixed with respect to the screen for observation, the direction of the line of sight CL of the left eye 17a of the observer (the direction of the line of sight is expressed by a two-dot chain line) and It is assumed that the direction of the line of sight CR is fixed so as to face the center of the prism sheet 14. Now, consider the light Lb emitted from the point P located in the right region of the light emitting region and incident on the right eye 17b, and the light La emitted from the same point P and incident on the left eye 17a. Since the direction of the line of sight CR of the right eye 17b and the direction of the line of sight CL of the left eye 17a are inclined in the opposite direction, the angle Lb formed by the light Lb entering the right eye 17b and the line of sight CR is φb, and the light La entering the left eye 17a. If the angle formed by the line of sight CL is φa, there is a relationship of φb> φa. In this way, the light Lb is more out of the line of sight than the light La, so even if the light Lb and the light La have the same light emission intensity, the apparent light emission intensity that the observer feels visually is the same. The light Lb is smaller than the light La (that is, the light Lb feels darker). Further, considering the light Lb and the light La emitted from the point on the left side of the light emitting region, the situation is opposite to that in FIG. 3A, so even if the light emission intensities of the light Lb and the light La are equal, the observation is performed. The apparent light emission intensity that a person feels visually is greater for the light Lb than for the light La (that is, the light Lb feels brighter).

  Therefore, even if the conventional surface light source device is manufactured so that the light emission intensity of the light emitting area is uniform as shown in FIG. 2A, the image for the left eye is more than the image for the right eye in the right area. Is recognized brightly, and the right-eye image is recognized brighter than the left-eye image in the left region. Therefore, when used in a stereoscopic display device, the balance between the image for the right eye and the image for the left eye is lost, and the effect of stereoscopic vision is reduced.

  As shown in FIG. 3A, the light Lb entering the right eye 17b from the point P at the distance X as measured from the right end (the end on the right light source 13b side) of the light guide plate 12, and the light La entering the left eye 17a. The apparent light emission intensities of the lights Lb and La that are visually perceived by the observer in consideration of the visual field sensitivity of the observer are represented by Jb and Ja, respectively. A curve Sg in FIG. 3B is obtained by obtaining an apparent emission intensity ratio Jb / Ja at a point P at a distance X from the right end. However, in calculating the apparent emission intensity ratio, the optical emission intensity of the light Lb and the light La is assumed to be equal.

  Thus, even if the surface light source device is designed so that the optical emission intensities of the light Lb and the light La are equal, the apparent emission intensity ratio Jb / Ja felt by the observer is as shown in FIG. As a result, the stereoscopic image becomes difficult to see.

  In addition, even when the left eye image is observed with the left eye (or the right eye image is observed with the right eye), there is a difference in brightness between the left side region and the right side region of the light emitting region due to visual field sensitivity. Arise. The reason for this will be described with reference to FIG. Now, let Lb2 be the light exiting from the point P2 in the right region and entering the right eye 17b, and Lb1 be the light exiting from the point P1 in the left region and entering the right eye 17b. The angle formed by the light Lb2 and the line of sight CR φb2 is larger than an angle φb1 formed by the light Lb1 and the line of sight CR. Therefore, even if the optical emission intensities of the light Lb2 and the light Lb1 are equal, the apparent light emission intensity Jb2 of the light Lb2 is smaller than the apparent light emission intensity Jb1 of the light Lb1. Accordingly, the right-eye image is dark in the right region and bright in the left region, and the brightness balance is lost or luminance unevenness occurs on the left and right. In particular, the screen becomes very dark at the right end. For the same reason, the left-eye image is dark in the left region and bright in the right region, and the brightness balance is lost and luminance unevenness occurs on the left and right sides, and the screen is particularly dark at the left end.

  The present invention has been made in view of the technical problems as described above, and an object of the present invention is to make an apparent appearance between the right eye and the left eye in a surface light source device used for a stereoscopic display device. The purpose is to reduce the difference in intensity (light / dark difference). Another object of the present invention is to reduce a difference in apparent light emission intensity (such as luminance unevenness) on a screen in a surface light source device used in a stereoscopic display device.

A first surface light source device according to the present invention includes a light guide plate that guides light incident from a pair of opposing light incident end surfaces and emits the light from a light exit surface, and one light incident end surface of the light incident end surfaces. A first light source that makes light incident on the light guide plate, a second light source that makes light incident on the light guide plate from the other light incident end surface of the light incident end surfaces, and the light exit surface of the light guide plate In the surface light source device including the prism sheet disposed in a manner, the peak intensity of the light emitted from the end of the light emitting region on the first light source side when the first light source is turned on is denoted by Ia1 and the first light source. When the peak intensity of light emitted from the end of the light emitting region on the first light source side when the light source 2 is turned on is Ib1
Ia1> Ib1
When the first light source is turned on, the peak intensity of light emitted from the end of the light emitting region on the second light source side is Ia2, and when the second light source is turned on, the second light emitting region. When the peak intensity of the light emitted from the end on the light source side is Ib2,
Ia2 <Ib2
It is characterized by becoming.

  In the first surface light source device of the present invention, the apparent light emission intensity at the edge of the image when the first light source is turned on, and the edge of the image when the second light source is turned on Therefore, the difference in brightness between the right eye and the left eye when viewing the screen is reduced, and the visibility of the stereoscopic image is improved.

A second surface light source device according to the present invention includes a first light guide plate that guides incident light and emits it from the light exit surface, and a second light guide plate that guides incident light and emits it from the light exit surface. A light guide plate; a first light source for allowing light to enter the first light guide plate from a light incident end surface of the first light guide plate; and a light source end surface of the second light guide plate to the second light guide plate. A second light source for allowing light to enter and a prism sheet, and the first light guide plate and the second light guide plate are overlapped with each other such that their light incident end faces are located on opposite sides, In a surface light source device in which a prism sheet is disposed so as to face a light emitting surface of a light guide plate located on the front side of one light guide plate and the second light guide plate, a light emitting region when the first light source is turned on The peak intensity of light emitted from the end on the first light source side is Ia1, and the second light source is turned on When the peak intensity of the light emitted from the end of the first light source side of the light-emitting region and Ib1 when the,
Ia1> Ib1
When the first light source is turned on, the peak intensity of light emitted from the end of the light emitting region on the second light source side is Ia2, and when the second light source is turned on, the second light emitting region. When the peak intensity of the light emitted from the end on the light source side is Ib2,
Ia2 <Ib2
It is characterized by becoming.

  In the second surface light source device of the present invention, the apparent light emission intensity at the edge of the image when the first light source is turned on, and the edge of the image when the second light source is turned on Therefore, the difference in brightness between the right eye and the left eye when viewing the screen is reduced, and the visibility of the stereoscopic image is improved.

In one embodiment of the first or second surface light source device of the present invention, when the first light source is turned on, the peak intensity of light emitted from an arbitrary light emitting point in the light emitting region is Ia, and the peak intensity Ia is The angle formed by the light with respect to the normal line set at the light emitting point is θa, and when the second light source is turned on, the peak intensity of light emitted from the same light emitting point in the light emitting region is Ib, and the peak intensity Ib When the angle formed by the light with respect to the normal line set at the light emitting point is θb,
If | θa | <| θb |, then Ia> Ib
In the case of | θa |> | θb |, Ia <Ib
It has become. According to this embodiment, the difference between the apparent light emission intensity in the image when the first light source is turned on and the apparent light emission intensity in the image when the second light source is turned on is small. The difference in contrast between the right eye and the left eye is reduced in almost the entire screen, and the visibility of the stereoscopic image is improved. In this embodiment, the angles θa and θb and the peak intensities Ia and Ib are
In the case of | θa | <| θb |, 1.0 <Ia / Ib <3.5
In the case of | θa |> | θb |, 1.0 <Ib / Ia <3.5
It is preferable that

In another embodiment of the first or second surface light source device of the present invention, the peak intensity of light emitted from the end of the light emitting region on the first light source side when the first light source is turned on is expressed as Ia1. When the peak intensity of the light emitted from the end of the light emitting region on the second light source side when the first light source is turned on is Ia2.
Ia1> Ia2
When the second light source is turned on, the peak intensity of light emitted from the end of the light emitting region on the second light source side is Ib2, and the light emitting region is turned on when the second light source is turned on. When the peak intensity of the light emitted from the end on the first light source side is Ib1,
Ib2> Ib1
This condition is met. According to such an embodiment, it is possible to reduce the difference in apparent light emission intensity at both ends of the image when the first light source is turned on. Further, it is possible to reduce the difference in the apparent light emission intensity at both ends of the image when the second light source is turned on. Therefore, luminance unevenness of the image can be reduced and the image can be easily viewed. In this embodiment, the peak intensities Ia1 and Ia2 are
1.0 <Ia1 / Ia2 <3.5
And the peak intensities Ib1 and Ib2 are
1.0 <Ib2 / Ib1 <3.5
It is preferable that this condition is satisfied.

  In another embodiment of the first surface light source device according to the present invention, the light emitted from the first light source is emitted to the light emitting surface of the light guide plate or the surface facing the light emitting surface. A first emission pattern for emitting from a surface and a second emission pattern for emitting light incident from the second light source from the light emission surface are formed. In this embodiment, by adjusting the distribution of each emission pattern, the apparent light emission intensity (ratio) when the first light source is turned on and the apparent light emission intensity (ratio) when the second light source is turned on. ) To have desired characteristics.

  In another embodiment of the second surface light source device according to the present invention, the light incident from the first light source is incident on the light emitting surface of the first light guide plate or the surface facing the light emitting surface. A first light emission pattern for emitting light from the light output surface of the first light guide plate is formed, and the second light source is formed on the light output surface of the second light guide plate or on the surface facing the light output surface. A second emission pattern for emitting the light incident from the light emission surface of the second light guide plate is formed. In this embodiment, by adjusting the distribution of each emission pattern, the apparent light emission intensity (ratio) when the first light source is turned on and the apparent light emission intensity (ratio) when the second light source is turned on. ) To have desired characteristics.

  The first emission pattern in this embodiment of the first or second surface light source device has a pattern density that increases in a non-linear function as the distance from the first light source increases, and in the direction away from the first light source. The increase rate of the pattern density is always positive, and the increase rate is gradually increased as the distance from the first light source increases, and the second emission pattern is separated from the second light source. The pattern density increases in a nonlinear function as the distance increases, the increase rate of the pattern density in the direction away from the second light source is always positive, and the increase rate increases gradually as the distance from the second light source increases. You may arrange | position so that it may become.

  Further, it is assumed that the first emission pattern is arranged to emit light having a uniform emission intensity from the light emission surface in a region farther from the first light source than the center of the light emission region. The increase rate of the pattern density of the first emission pattern in the direction farther from the first light source is smaller than the distribution of the pattern density of the emission pattern, and the second emission pattern is smaller than the center of the light emitting region. In the region far from the second light source, the second light source is more than the distribution of the pattern density of the second emission pattern that is assumed to be arranged so as to emit light having a uniform emission intensity from the light emission surface. The increasing rate of the pattern density of the second emission pattern in the direction far from the distance may be small.

  Further, the first emission pattern has a constant increase rate of the pattern density of the first emission pattern in a direction farther from the first light source in a region farther from the first light source than the center of the light emitting region. The second emission pattern has a constant rate of increase in pattern density of the second emission pattern in a direction farther from the second light source in a region farther from the second light source than the center of the light emitting region. It may be.

  The first emission pattern in yet another embodiment of the first or second surface light source device according to the present invention is the first emission pattern in a region closer to the first light source than the center of the light emitting region. The pattern density of the first emission pattern decreases with increasing distance from the light source, and the first emission pattern with increasing distance from the first light source in an area farther from the first light source than the center of the light emitting area. The pattern density of the second emission pattern increases as the distance from the second light source increases in the region closer to the second light source than the center of the light emitting region. In the region farther from the second light source than the center of the light emitting region, the pattern density of the second emission pattern decreases as the distance from the second light source increases. It is pressurized.

  Furthermore, in another embodiment of the second surface light source device according to the present invention, the thickness of the first light guide plate is opposite to the light incident end surface from the light incident end surface facing the first light source. The thickness of the second light guide plate gradually decreases toward the end surface, and the thickness of the second light guide plate gradually decreases from the light incident end surface facing the second light source toward the end surface opposite to the light incident end surface. According to such an embodiment, by adjusting the thickness of each light guide plate, the apparent light emission intensity (ratio) when the first light source is turned on, or the apparent light emission intensity (when the second light source is turned on) ( Ratio) to the desired characteristics.

  In this embodiment, the thickness of the first light guide plate changes more slowly than the change in thickness assumed to emit light of uniform light emission intensity from the light exit surface of the light guide plate, and the second The thickness of the light guide plate may change more slowly than the change in thickness assumed to emit light with uniform light emission intensity from the light exit surface of the light guide plate. Furthermore, the thickness of the first light guide plate and the thickness of the second light guide plate may be uniformly thin at a constant rate.

  Further, in such an embodiment, the thickness reduction rate decreases as the thickness of the first light guide plate approaches the end portion far from the first light source, and the thickness of the second light guide plate is The decreasing rate of thickness may become small as it approaches the end part far from the second light source.

  Still another embodiment of the second surface light source device according to the present invention is such that the thickness of the first light guide plate is changed from a light incident end surface facing the first light source to an end surface opposite to the light incident end surface. The thickness of the second light guide plate gradually increases toward the end surface of the end portion, and the thickness of the second light guide plate is opposite to the second light source. The thickness may gradually decrease from the light end surface toward the end surface opposite to the light incident end surface, and may gradually increase in thickness toward the end surface of the end portion on the side far from the second light source. In this embodiment, the thickness of the first light guide plate and the second light guide plate may gradually increase in a region where the thickness is gradually increased.

  The stereoscopic display device according to the present invention is characterized in that an optical sheet and a liquid crystal panel are arranged in front of the first or second surface light source device of the present invention. In such a stereoscopic display device, the apparent light emission intensity can be made uniform, so that the quality of the stereoscopic image can be improved.

  The means for solving the above-described problems in the present invention has a feature in which the above-described constituent elements are appropriately combined, and the present invention enables many variations by combining such constituent elements. .

1A and 1B are schematic views for explaining the principle of a stereoscopic display device. FIG. 2A is a diagram illustrating a distribution of light emission intensity in a light emission region of a conventional surface light source device used in a stereoscopic display device. FIG. 2B shows the pattern density distribution of the emission pattern for emitting light from the left light source from the light emission surface and the pattern density distribution of the emission pattern for emitting light from the right light source from the light emission surface. FIG. FIG. 3A is a diagram for explaining the reason why the apparent light emission intensity felt by the right eye differs from the apparent light emission intensity felt by the left eye. FIG. 3B is a diagram showing a change in the ratio of the apparent light emission intensity felt by the right eye to the apparent light emission intensity felt by the left eye. FIG. 4 is a diagram for explaining the reason why the apparent light emission intensity distributions of the light emitted from the left region of the light emitting region and the light emitted from the right region are different. FIG. 5 is a schematic cross-sectional view of the surface light source device according to Embodiment 1 of the present invention. 6A and 6B are schematic cross-sectional views of a light guide plate used in the surface light source device of Embodiment 1, and FIG. 6A is a total reflection of light emitted from the right light source. FIG. 6B shows an emission pattern for totally reflecting light emitted from the left light source. FIG. 7A is a diagram illustrating an example of an emission pattern provided on the back surface of the light guide plate. FIG. 7B and FIG. 7C are a perspective view and a cross-sectional view of the emission pattern. FIG. 8A is a diagram illustrating another example of the emission pattern provided on the back surface of the light guide plate. FIG. 8B and FIG. 8C are a perspective view and a cross-sectional view of the emission pattern. FIG. 9A is a diagram showing still another example of the emission pattern provided on the back surface of the light guide plate. FIG. 9B and FIG. 9C are a perspective view and a cross-sectional view of the emission pattern. FIG. 10A is a diagram showing still another example of the emission pattern provided on the back surface of the light guide plate. 10B and 10C are a perspective view and a cross-sectional view of the emission pattern. FIG. 11 is a detailed view showing the cross-sectional shape and optical action of the optical sheet. FIG. 12 is a schematic cross-sectional view illustrating a stereoscopic display device using the surface light source device according to the first embodiment. FIG. 13A is a diagram showing the relationship between the position of the light emitting point in the light emitting region of the surface light source device and the optical light emission intensity of each light emitting point. FIG. 13B is a diagram showing the relationship between the position in the light guide plate and the pattern density of the emission pattern. FIG. 14 is a schematic diagram showing the relationship between the position of the light emitting point and the apparent light emission intensity in a conventional surface light source device. FIG. 15 is a diagram showing the relationship between the position of the light emitting point in the light emitting region and the apparent light emission intensity ratio. FIG. 16A is a diagram showing human visual field sensitivity. FIG. 16B is a diagram showing visual field sensitivity approximated by an exponential function. FIG. 17 is a diagram showing a pattern density distribution curve of the emission pattern. FIG. 18 is a diagram showing the relationship between the position of the light emitting point in the light emitting region and the optical emission intensity. FIG. 19 is a diagram showing the relationship between the position of the light emitting point in the light emitting region and the apparent light emission intensity ratio. FIG. 20A is a diagram showing a pattern density distribution curve of the emission pattern. FIG. 20B is a diagram illustrating the relationship between the position of the light emitting point in the light emitting region and the apparent light emission intensity ratio. FIG. 21 is a diagram for explaining Embodiment 2 of the present invention, in which the angle formed between the peak direction of light emitted from the light emitting region and the direction of the normal line set at the light emitting point is described. FIG. 22A is a diagram showing a pattern density distribution of emission patterns in the light guide plate. FIG. 22B is a diagram showing the relationship between the position of the light emitting point in the light emitting region and the apparent light emission intensity ratio. 23A and 23B are diagrams for explaining the third embodiment of the present invention. FIG. 23A shows the pattern density distribution of the emission pattern, and FIG. 23B shows the apparent light emission intensity. FIG. FIG. 24 is a schematic view of a surface light source device according to Embodiment 4 of the present invention. FIG. 25A is a rear view showing an emission pattern formed on one light guide plate in the surface light source device of the fourth embodiment. FIG. 25 (B) is a back view showing another emission pattern formed on one light guide plate in the surface light source device of Embodiment 4. FIG. FIG. 25C is a rear view showing still another emission pattern formed on one light guide plate in the surface light source device of the fourth embodiment. FIG. 25D is a rear view showing still another emission pattern formed on one light guide plate in the surface light source device of the fourth embodiment. FIG. 26A is a rear view showing still another emission pattern formed on one light guide plate in the surface light source device of Embodiment 4. FIG. FIG. 26B is a back view showing still another emission pattern formed on one light guide plate in the surface light source device of the fourth embodiment. FIG. 26C is a back view showing still another emission pattern formed on one light guide plate in the surface light source device of the fourth embodiment. FIG. 26D is a rear view showing still another emission pattern formed on one light guide plate in the surface light source device of the fourth embodiment. FIG. 25A is a rear view showing an emission pattern formed on one light guide plate in the surface light source device of the fourth embodiment. FIG. 27A is a diagram illustrating a change in the thickness of the light guide plate in the surface light source device of the fourth embodiment. FIG. 27B is a diagram showing a change in the apparent light emission intensity ratio in the surface light source device. FIG. 28A is a diagram illustrating a change in the thickness of the light guide plate in the modification of the fourth embodiment. FIG. 27B is a diagram showing a change in the apparent light emission intensity ratio in the modified example. FIG. 29A is a diagram for explaining Embodiment 5 of the present invention, FIG. 29A is a diagram showing a change in the thickness of the light guide plate, and FIG. 29B is an apparent light emission intensity. FIG. FIG. 30 is a schematic view of a surface light source device according to Embodiment 6 of the present invention.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. However, the present invention is not limited to the following embodiments, and various design changes can be made without departing from the gist of the present invention.

[First Embodiment]
(Surface light source device)
Hereinafter, the surface light source device 21 according to the first embodiment will be described with reference to FIG. In the surface light source device 21, one or a plurality of left light sources 23 a are arranged to face the left light incident end face of the flat light guide plate 22, and one piece faces the right light incident end face of the light guide plate 22. Alternatively, a plurality of right light sources 23b are arranged. The light guide plate 22 is formed into a flat plate shape using a light-transmitting resin having a high refractive index such as polycarbonate resin or polymethyl methacrylate resin.

  Both the left light source 23a and the right light source 23b are constituted by LED light sources that emit white light. The left light source 23 a is disposed with its light exit window facing the left light incident end surface of the light guide plate 22. Similarly, the right light source 23 b is disposed with its light exit window facing the right light incident end surface of the light guide plate 22. The left light source 23a and the right light source 23b are controlled so as to be alternately turned on and off at regular intervals. As the left light source 23a and the right light source 23b, a cold cathode ray tube may be used instead of the LED light source.

  On the back surface of the light guide plate 22, a large number of minute emission patterns 25 a for emitting light from the left light source 23 a and entering the light guide plate 22 from the front surface (light emission surface 26) of the light guide plate 22, and the right light source A large number of minute emission patterns 25 b are formed for emitting the light exiting from 23 b and entering the light guide plate 22 from the light exit surface 26 of the light guide plate 22. The emission pattern 25a and the emission pattern 25b are formed on the back surface of the light guide plate 22 so as to have a substantially predetermined pattern density distribution.

  A reflection sheet 28 is disposed on the back surface of the light guide plate 22. The reflection sheet 28 is made of a highly reflective material such as a white resin sheet or a metal foil, reflects light leaked from the back surface of the light guide plate 22 and re-enters the light guide plate 22. Increase light utilization efficiency by reducing light. An optical sheet 24 is disposed on the front surface of the light guide plate 22. The optical sheet 24 collects light for generating an image for the left eye emitted from the light emitting surface 26 of the light guide plate 22 toward the left eye 27a of the observer, and the right eye emitted from the light emitting surface 26. The light for generating the image for use is collected toward the viewer's right eye 27b.

  FIG. 6A is a schematic view showing only the emission pattern 25b for reflecting the light Lb from the right light source 23b out of the emission patterns 25a and 25b. FIG. 6B is a schematic diagram showing only the emission pattern 25a for reflecting the light La from the left light source 23a. The emission pattern 25b is formed so that the pattern density increases as the distance from the right light source 23b increases. The emission pattern 25a is formed so that the pattern density increases as the distance from the left light source 23a increases. The light beams Lb and La emitted from the light sources 23b and 23a are guided in the light guide plate 22 while being totally reflected between the front surface and the back surface of the light guide plate 22, and the light Lb is totally reflected by the output pattern 25b. As a result, the light La is emitted from the light emission surface 26 by being totally reflected by the emission pattern 25a.

  As the above-described emission patterns 25a and 25b, those having various shapes are conceivable. 7 to 10 show some of them. The emission patterns 25a and 25b may be concave patterns in which the back surface of the light guide plate 22 is partially recessed, or may be convex patterns in which the back surface of the light guide plate 22 is partially protruded. Only the ones are shown.

  FIGS. 7B and 7C are a perspective view and a cross-sectional view showing the emission patterns 25a and 25b having a triangular prism shape, and FIG. 7A is a concave view of the emission patterns 25a and 25b on the back surface. It is the reverse view of the light guide plate 22 which was made. In the emission patterns 25a and 25b, the light Lb and La are totally reflected by the flat slopes facing the light sources 23a and 23b, and the emission patterns 25a and 25b are opposite to each other. It is arranged on the lower surface of the light guide plate 22.

  FIGS. 8B and 8C are a perspective view and a cross-sectional view showing the emission patterns 25a and 25b having a triangular pyramid shape, and FIG. 8A is a drawing in which the emission patterns 25a and 25b are recessed on the back surface. It is the reverse view of the light guide plate 22 which was made. In the emission patterns 25a and 25b, the light Lb and La are totally reflected by the two inclined surfaces facing the light sources 23a and 23b, so that the light Lb and La are diffused also in the width direction of the light guide plate 22. be able to.

  9B and 9C are a perspective view and a cross-sectional view showing the emission patterns 25a and 25b each having a quadrangular pyramid shape, and FIG. 9A is a drawing in which the emission patterns 25a and 25b are recessed on the back surface. It is the reverse view of the light guide plate 22 which was made. Also in the emission patterns 25a and 25b, the light Lb and La are totally reflected by the two inclined surfaces facing the light sources 23a and 23b, so that the lights Lb and La are diffused also in the width direction of the light guide plate 22. be able to.

  FIGS. 10B and 10C are a perspective view and a cross-sectional view showing the spherical emission patterns 25a and 25b, and FIG. 10A has the emission patterns 25a and 25b recessed on the back surface. 4 is a rear view of the light guide plate 22. FIG. The points in FIGS. 10A, 10B, and 10C indicate the positions of the vertices of the emission patterns 25a and 25b. The emission patterns 25a and 25b have a substantially elliptical shape that is long in the direction perpendicular to the light incident end face of the light guide plate 22. However, in the emission pattern 25a, the position of the apex is biased away from the left light source 23a. In the emission pattern 25b, the position of the apex is biased in the direction away from the right light source 23b.

  Here, the light emission patterns 25 a and 25 b are provided on the back surface of the light guide plate 22 and totally reflect the light guided through the light guide plate 22 toward the light output surface 26 and emit light from the light output surface 26. However, the emission pattern may be provided on the front surface (light emission surface 26) of the light guide plate (the same applies to other embodiments). When the emission pattern is provided on the front surface of the light guide plate, the light incident on the emission pattern provided on the front surface of the light guide plate passes through the front surface (output pattern) of the light guide plate and is emitted forward from the light emission surface 26. Is done.

  FIG. 11 is a detailed view showing the shape of the optical sheet 24. A prism row 24a in which fine triangular prisms are arranged is formed on the back surface of the optical sheet 24, and a lens row 24b in which fine cylindrical lenses are arranged is formed on the front surface. The prism row 24 a and the lens row 24 b have a uniform cross-sectional shape perpendicular to the width direction of the light guide plate 22, and are arranged at a constant pitch along the length direction of the light guide plate 22. However, the array pitch p2 of the lens array 24b is slightly larger than the array pitch p1 of the prism array 24a. The prism row 24 a is arranged to be symmetric with respect to a vertical plane passing through the center of the optical sheet 24, and the lens row 24 b is also arranged to be symmetric with respect to a vertical plane passing through the center of the optical sheet 24.

  When the left light source 23a is turned on, the light emitted from the left light source 23a is emitted obliquely forward from the light emitting surface 26 of the light guide plate 22 as left illumination light La having the same peak intensity direction. As shown in FIG. 11, the direction of La is bent by the optical sheet 24 so as to converge on the left eye 27 a of the observer located at a predetermined distance from the surface light source device 21. Similarly, when the right light source 23b is turned on, the light emitted from the right light source 23b is emitted obliquely forward from the light emitting surface 26 of the light guide plate 22 as the right illumination light Lb having the same peak intensity direction. The direction of the light Lb is bent by the optical sheet 24 so as to converge on the observer's right eye 27b.

  At this time, the light beams Lb and La that are transmitted through the optical sheet 24 are bent in the light beam direction by the prism array 24a, and are further bent in the light beam direction by the lens array 24b when transmitted through the lens array 24b. It is made to converge to the assumed position of the eye 27b.

  In addition, as the optical sheet 24, the lens row | line | column is not provided in the front surface but the front surface may become the flat surface.

(3D display device)
FIG. 12 shows a structure of a stereoscopic display device 31 using the surface light source device 21. In this stereoscopic display device 31, the optical sheet 24 is stacked on the front surface of the light guide plate 22, and the rim sheet 32 is attached to the surface light source device 21 from the front surface. The rim sheet 32 is a light-absorbing member formed of black adhesive tape or the like, and an area corresponding to the light emitting area of the light guide plate 22 is opened and covers the periphery of the front surface of the light guide plate 22. Further, a liquid crystal panel 33 is stacked in front of the opening of the rim sheet 32.

  The image for left eye / right eye on the liquid crystal panel 33 and the on / off of the light sources 23 a and 23 b are synchronously controlled by the synchronous drive device 34. The synchronous drive device 34 displays the left-eye image and the right-eye image alternately on the liquid crystal panel 33 in a short cycle such that the observer cannot recognize the switching between the left and right images, and synchronizes with the left-eye image on the liquid crystal panel 33. Then, the left light source 23a is turned on (the right light source 23b is turned off), and the right light source 23b is turned on (the left light source 23a is turned off) in synchronization with the image for the right eye.

  When the right light source 23b is turned on, the light Lb emitted from the right light source 23b is emitted obliquely forward from the light guide plate 22 as right illumination light having a uniform peak intensity direction. The light Lb emitted from the light guide plate 22 is bent by the optical sheet 24 so that the light transmitted through each pixel gathers on the observer's right eye 27b located at a predetermined distance from the liquid crystal panel 33, and then the liquid crystal panel 33. Is incident on. The light Lb passes through the liquid crystal panel 33 to be converted into an image for the right eye and is recognized by the observer's right eye 27b.

  Similarly, when the left light source 23a is turned on, the light La emitted from the left light source 23a is emitted obliquely forward from the light guide plate 22 as left illumination light having the same peak intensity direction. The light La emitted from the light guide plate 22 is incident on the liquid crystal panel 33 after being bent in the direction by the optical sheet 24 so that the light transmitted through each pixel is collected in the left eye 27a of the observer. This light La is converted into an image for the left eye by passing through the liquid crystal panel 33 and is recognized by the left eye 27a of the observer.

  Thus, the left eye image and the right eye image are alternately sent to the left eye 27a and the right eye 27b of the observer, but the observer recognizes the right eye image and the left eye image at the same time by the afterimage effect. A 3D image (stereoscopic image) is recognized. In this stereoscopic display device 31, since the surface light source device 21 is used, the left-eye image and the right-eye image are perceived to have substantially the same brightness, and a stereoscopic image with a stereoscopic effect in which left and right are balanced is recognized. be able to.

(Features of Embodiment 1)
In this surface light source device 21, the difference in apparent light emission intensity is reduced by the following configuration. This will be described with reference to FIG. 5, FIG. 13, FIG. 14 and FIG. FIG. 13A shows the relationship between the position of the light emitting point in the light emitting region (surface of the optical sheet) of the surface light source device and the optical emission intensity of each light emitting point. FIG. 13B shows the relationship between the position in the light guide plate and the pattern density of the emission pattern. FIG. 14 is a schematic diagram showing the relationship between the position of the light emission point and the apparent light emission intensity in the conventional surface light source device. FIG. 15 shows the relationship between the position of the light emitting point in the light emitting region and the apparent light emission intensity ratio. Here, the right end is the end on the right light source 23b side in the light emitting region, and the left end is the end on the left light source 23a side in the light emitting region. The optical emission intensity is a physical emission intensity measured by a measuring instrument with respect to the emission intensity as perceived by an observer.

The conventional surface light source device is designed so that the optical emission intensity is uniform over the entire emission region as indicated by a straight line To shown in FIG. For this reason, in the conventional surface light source device, the emission pattern for totally reflecting the light from the right light source is provided with a pattern density distribution as indicated by Gb in FIG. The output pattern for reflection is provided in a pattern density distribution as indicated by Ga in FIG. 13B (see FIG. 2B). However, considering the human visual field sensitivity as described above, in the case of the conventional surface light source device, as shown in FIG. 14, the right side of the light Lb2 emitted from the right end of the light emitting region when the right light source is turned on, as shown in FIG. If the apparent light emission intensity felt by the eye is Jb2, and the apparent light emission intensity felt by the left eye of the light La2 emitted from the right end when the left light source is turned on is Ja2,
Jb2 <Ja2
It has become. Similarly, the apparent emission intensity felt by the right eye of the light Lb1 emitted from the left end when the right light source is turned on is Jb1, and the apparent light intensity felt by the left eye of the light La1 emitted from the left end when the left light source is turned on. If the emission intensity is Ja1,
Jb1> Ja1
It has become. Therefore, the light emission intensity of the image for the right eye felt by the right eye is different from the light emission intensity of the image for the left eye felt by the left eye, and the effect of stereoscopic vision is reduced.

Further, in the case of the conventional surface light source device, as shown in FIG. 14, when the right light source is turned on, the apparent light emission intensity Jb2 and Jb1 of light emitted from both ends of the light emitting region is between
Jb2 <Jb1
There is a relationship between the apparent light emission intensities Ja2 and Ja1 of light emitted from both ends of the light emitting region when the left light source is turned on,
Ja2> Ja1
There is a relationship. Therefore, even when the left light source is turned on or when the right light source is turned on, the visually perceived light emission intensity is different between the right and left portions of the light emitting region, resulting in uneven brightness on the screen.

Therefore, in order to reduce the apparent intensity difference between the right eye image and the left eye image,
Jb2 = Ja2 and Jb1 = Ja1
It is necessary to bring it closer to this state. For that purpose, the optical emission intensity of the light Lb2 in the peak direction emitted from the right end of the light emitting region when the right light source is turned on is Ib2, and the light La2 in the peak direction emitted from the right end when the left light source is turned on. When the optical emission intensity is Ia2,
Ib2> Ia2
And it is sufficient. Similarly, the optical emission intensity of the peak direction light Lb1 emitted from the left end when the right light source is turned on is Ib1, and the optical emission intensity of the peak direction light La1 emitted from the left end when the left light source is turned on. Is Ia1,
Ib1 <Ia1
And it is sufficient. After all, in order to reduce the apparent intensity difference between the right eye image and the left eye image,
Ib2> Ia2 and Ib1 <Ia1 ... Condition (1)
And it is sufficient.

  If this condition (1) is satisfied, the optical emission intensities Ia2 and Ib1 are smaller than Ib2 and Ia1, respectively, and the apparent emission intensities Ja2 and Jb1 in FIG. The difference between Ja1 and Jb1 is reduced, and the difference between the apparent light emission intensities Jb2 and Ja2 at the right end is also reduced. As a result, the difference in apparent light emission intensity at the left and right ends of the light emitting area is reduced, and the stereoscopic effect when observed with the left eye and the right eye is increased.

In addition, in order to reduce the feeling that the right and left areas of the light emitting area feel different in intensity when only the left light source (or only the right light source) is turned on,
Jb2 = Jb1 and Ja2 = Ja1
It is necessary to be close to the state. For that purpose, optical emission intensities Ib1 and Ib2 at the left and right ends when the right light source is turned on, and optical emission intensities Ia1 and Ia2 at the left and right ends when the left light source is turned on,
Ib2> Ib1 and Ia2 <Ia1 ... Condition (2)
What should be done.

  If this condition (2) is satisfied, the optical emission intensities Ib1 and Ia2 will be smaller than Ib2 and Ia1, respectively, and the apparent emission intensities Jb1 and Ja2 in FIG. The difference between the apparent light emission intensities Jb1 and Jb2 is reduced, and the difference between the apparent light emission intensities Ja2 and Ja1 when the left light source is turned on is also reduced. As a result, when only the right light source is turned on or only the left light source is turned on, the intensity difference between the left and right regions of the light emitting region is reduced.

Therefore, it is understood that the above condition (1) and the above condition (2) should be satisfied in order to improve the quality of the stereoscopic image observed by the observer. That is,
Ib2> Ia2
Ib1 <Ia1
Ib1 <Ib2
Ia1> Ia2
It is sufficient to satisfy the following four expressions simultaneously.

In order to satisfy the above conditions (1) and (2), for example, as shown in FIG.
Ia2 = Ib1 <Ia1 = Ib2
The optical emission intensities at the left and right ends are determined so that the optical emission intensity Ia in the light emission region of the light La emitted from the left light source 23a is represented by a straight line connecting the emission intensities Ia2 and Ia1 at the both ends. The optical emission intensity Ib in the emission region of the light Lb emitted from the light source 23b may be represented by a straight line connecting the emission intensity Ib2 and Ib1 at both ends. In order to realize such a change in optical emission intensity, the pattern density of the emission pattern 25b (the total pattern projection area per unit area on the back surface of the light guide plate) is represented by a distribution curve Db in FIG. And the pattern density of the emission pattern 25a may be determined as shown by the distribution curve Da in FIG. That is, for the emission pattern 25b for reflecting the light from the right light source 23b, with respect to the pattern density distribution curve Gb in the case where the optical emission intensity is made uniform in the emission region (the outer shape and size of the light guide plate). Assuming that the emission efficiency is the same), the pattern density is increased on the side closer to the right light source 23b as in the distribution curve Db, and the pattern density is decreased on the side far from the right light source 23b. Similarly, the output pattern 25a for reflecting the light from the left light source 23a is close to the left light source 23a as shown by the distribution curve Da with respect to the pattern density distribution curve Ga that makes the optical emission intensity uniform. The pattern density is increased on the side, and the pattern density is decreased on the side far from the left light source 23a.

  As a result, the apparent light emission intensities Ja and Jb become smaller on the side closer to the light sources 23a and 23b, and become larger on the side far from the light sources 23a and 23b, and the apparent light emission intensity ratio Jb / Ja is shown in FIG. It becomes like the curve Sd. Therefore, in the case of the conventional example in which the optical emission intensity is made uniform, the apparent emission intensity ratio Jb / Ja changes greatly as shown by the curve Sg, which is ideal as shown by the curve Sd. It becomes close to Jb / Ja = 1, which is an apparent emission intensity ratio.

FIG. 15 shows the relationship between the position of the light emitting point in the light emitting region and the apparent light emission intensity ratio. The relationship between the human visual field sensitivity, that is, the visual field angle φ (the angle formed by the incident direction of the light to be recognized and the direction of the line of sight) and the physiological visual field sensitivity has a characteristic as shown in FIG. However, in obtaining the apparent emission intensity ratio in FIG. 16, the visual field sensitivity K (φ) in FIG.
K (φ) = exp (−α · | φ |)
Where α = 0.71
(This is shown in FIG. 16B).

  If the pattern density of the emission pattern is set to the distribution curves Da and Db, the following advantages can be obtained. The difference in brightness between the images recognized by the right eye and the left eye is reduced, making it easier to view a stereoscopic image, and the brightness difference and luminance unevenness on the left and right of the screen are reduced, improving the image quality. Further, since the change in the pattern density of the emission patterns 25a and 25b is reduced and the maximum value of the pattern density is reduced (see FIG. 13B), the light guide plate 22 can be easily manufactured. Furthermore, since the maximum value of the density of the emission pattern to be formed becomes small, the emission efficiency from the light guide plate can be improved. In addition, since the light emitted from the light sources 23a and 23b does not easily reach the opposite end face of the light guide plate 22, the return light is reduced and crosstalk is less likely to occur when used in a stereoscopic display device.

  An emission pattern distribution curve Mb shown in FIG. 17 represents another distribution of the emission pattern 25b. If the pattern density is made larger than the distribution curve So in the region close to the light source as shown by the distribution curve Db in FIG. Can be small. Therefore, the pattern density is gentler than the distribution curve Db of the pattern density, and the pattern density is larger than the distribution curve Db in the region near the right light source 23b, and the pattern density is smaller than the distribution curve Db in the region far from the right light source 23b. Consider 17 distribution curves Mb. When the pattern density is further moderated as shown by the curve Mb, the emitted light increases near the right light source 23b, and the emitted light decreases near the right light source 23b. Therefore, as shown in FIG. 18, the optical emission intensity Tm corresponding to the pattern density distribution curve Mb changes more rapidly than the optical emission intensity Td corresponding to the pattern density distribution Db.

  In the case where the light emission intensity, the pattern density, etc. are illustrated, only the light emitted from the right light source 23b and the emission pattern 25b are shown in FIG. The light emission intensity of the light emitted from the left light source 23a, the pattern density of the emission pattern 25a, and the like appear symmetrically with respect to the light emitted from the right light source 23b and the emission pattern 25b, and thus are not illustrated.

  Furthermore, it is assumed that the emission intensity of the left light source 23a and the right light source 23b is equal, the emission pattern 25a and the emission pattern 25b are formed to have a symmetrical distribution, and the visual field sensitivity of the observer is shown in FIG. Thus, in the surface light source device formed so that the pattern density of the emission pattern 25b becomes the distribution curve Mb when approximated by an exponential function, the apparent emission intensity ratio Jb / Ja becomes the curve Sm of FIG. .

  When the apparent light emission intensity ratio is represented by the curve Sm, the optical light emission intensity of the light Lb2 emitted from the right end of the light emission region and entering the right eye 27b when the right light source 23b is turned on is defined as Ib2. When the optical emission intensity of the light La2 emitted from the right end of the light emitting region and entering the left eye 27a when the left light source 23a is turned on is Ia2, this ratio Ib2 / Ia2 is about 2 (for example, Ib2 is In the case of about 30,000 nits and Ia2 of about 15,000 nits), the apparent light emission intensity emitted from the right end of the light emitting region becomes almost equal and there is no difference in brightness.

However, it can be seen from the curve Sm in FIG. 19 that if the emission pattern distribution curve becomes too gradual, the apparent emission intensity ratio Jb / Ja deviates from the straight line of Jb / Ja = 1. That is, when the optical emission intensity ratio Ib2 / Ia2 is about 3.5 (for example, Ib2 is about 30,000 nits and Ia2 is about 10,500 nits), the light emission efficiency is improved, but The light / dark difference at the right end is the same as when the optical emission intensity is made uniform over the entire light emitting region, and light emitted from the right end of the light emitting region causes a light / dark difference between the right eye and the left eye. Therefore, in the right region, the ratio of optical emission intensity is
1.0 <Ib2 / Ia2 <3.5 ... Condition (3)
Is desirable. Similarly, the optical emission intensity of the light Lb1 emitted from the left end of the light emitting area when the right light source 23b is turned on and entering the right eye 27b is Ib1, and emitted from the left end of the light emitting area when the left light source 23a is turned on. When the optical emission intensity of the light La1 entering the left eye 27a is Ia1, the ratio of the optical emission intensity in the left area of the emission area is
1.0 <Ia1 / Ib1 <3.5 ... Condition (4)
Is desirable.

Further, regarding the optical emission intensity Ia1 and Ia2 of the light emitted from the left end and the right end of the light emitting region when the left light source 23a is turned on,
1.0 <Ia1 / Ia2 <3.5 ... Condition (5)
It is preferable to satisfy the condition. Similarly, for the optical emission intensities Ib1 and Ib2 of the light emitted from the left end and the right end of the light emitting region when the right light source 23b is turned on,
1.0 <Ib2 / Ib1 <3.5 ... Condition (6)
It is desirable to satisfy the condition. This is because if Ia1 / Ia2 in condition (5) or Ib2 / Ib1 in condition (6) exceeds 3.5, the end near the light source that emits light is too bright.

  An emission pattern distribution curve Eb shown in FIG. 20 represents yet another distribution of the emission pattern 25b. A distribution curve Gb shown in FIG. 20A is a pattern density distribution curve of the emission pattern for the right light source when the optical emission intensity is designed to be uniform throughout the emission region. In this distribution curve Gb, the differential value (increase rate) is always positive, and the differential value increases as the distance from the right light source increases (that is, the second-order differential value is positive). When the differential value is used, the differential value of the pattern density of the emission pattern 25b is a differential value related to the distance measured from the right end to the left end, but the differential value of the pattern density of the emission pattern 25a is from the left end to the right end. This is the differential value related to the distance measured.

  The distribution curve Eb in FIG. 20A matches the distribution curve Gb except for the end portion on the side far from the right light source 23b, but the differential value is constant at the end portion on the side far from the right light source 23b. Yes. When the pattern density of the emission pattern 25b is defined as a distribution curve Eb and the pattern density of the emission pattern 25a is determined to be a symmetric curve with respect to the distribution curve Eb, the apparent emission intensity ratio Jb / Ja is Compared with the characteristic (curve Sg) in which the curve Se of 20 (B) is designed and the optical emission intensity distribution is designed to be uniform, the difference in apparent emission intensity at both ends of the emission region is reduced. be able to. Moreover, since the maximum value of the pattern density at the end of the light emitting region can be reduced, the light guide plate 22 can be easily manufactured.

[Second Embodiment]
As a condition for reducing the difference between the light emission intensity recognized by the right eye and the light emission intensity recognized by the left eye, the condition (1) considers only the light emitted from the left and right ends of the light emitting area. However, the following conditions can be obtained for the entire light emitting region.

  When light is emitted from the left half of the light emitting area as in the light emitting point P1 of FIG. 21, the optical emission intensity at the light emitting point P1 is the same when the left light source 23a is lit and when the right light source 23b is lit. The emission intensity Jb felt by the right eye 27b is larger than the emission intensity Ja felt by the left eye 27a. Therefore, when the light emitting point is the left half of the light emitting area, the optical emission intensity Ia when the left light source 23a is turned on is larger than the optical emission intensity Ib when the right light source 23b is turned on. You can do it. On the other hand, when light is emitted from the right half of the light emitting area as in the light emitting point P2 in FIG. 21, the optical emission intensity at the light emitting point P2 is different between when the left light source 23a is turned on and when the right light source 23b is turned on. If they are equal, the light emission intensity Jb felt by the right eye 27b is smaller than the light emission intensity Ja felt by the left eye 27a. Therefore, when the light emitting point is the right half of the light emitting region, the optical emission intensity Ia when the left light source 23a is turned on is smaller than the optical emission intensity Ib when the right light source 23b is turned on. You can do it.

  On the other hand, the angle formed by the normal direction set up at a certain light emitting point and the peak intensity direction of the light La coming out of the light emitting point and entering the left eye 27a is θa, and the normal direction and the light emitting point are emitted from the light emitting point to the right eye 27b. When the angle formed by the peak intensity direction of the incoming light Lb is θb, there is a relationship of | θa | <| θb | in the case of the light emitting point P1 in the left half of the light emitting region. In the case of the light emitting point P2 in the right half of the light emitting region, there is a relationship of | θa |> | θb |.

Therefore, if an attempt is made to reduce the difference in the apparent light emission intensity in the entire light emitting region, at any light emitting point in the light emitting region,
If | θa | <| θb | (left region), then Ia> Ib
If | θa |> | θb | (right side region), then Ia <Ib ... condition (7)
What should be done.

In order to improve the quality of the stereoscopic image observed by the observer, the condition (2) described in the first embodiment may be satisfied together with the condition (7). That is,
If | θa | <| θb | (left region), then Ia> Ib
If | θa |> | θb | (right region), then Ia <Ib
Ib1 <Ib2
Ia1> Ia2
It is sufficient to satisfy the following four expressions simultaneously.

  A distribution curve Fb of the emission pattern 25b shown in FIG. 22A represents a change in pattern density of the emission pattern 25b that satisfies the conditions (2) and (7). The curve Fb coincides with the curve Gb at a portion close to the right light source 23b, but its differential value is slightly smaller than the curve Gb on the side far from the right light source 23b (left side region). Therefore, the curve Fb changes more slowly than the curve Gb on the side far from the right light source 23b, and is along the curve Gb on the side where the pattern density is small. When the pattern density of the emission pattern 25b is determined as a curve Fb and the pattern density of the emission pattern 25a is determined to be a curve symmetrical to the curve Fb, the apparent emission intensity ratio Jb / Ja is as shown in FIG. B) curve Sf is obtained, and good characteristics very close to the ideal case of Jb / Ja = 1 are obtained.

  Even in such a case, the brightness difference between the images recognized by the right eye and the left eye is reduced, making it easier to see the stereoscopic image, and the brightness difference between the left and right sides of the screen and the luminance unevenness are reduced, thereby improving the image quality. Moreover, since the maximum value of the pattern density at the end of the light emitting region can be reduced, the light guide plate 22 can be easily manufactured. Furthermore, since the maximum value of the density of the emission pattern to be formed becomes small, the emission efficiency from the light guide plate can be improved. In addition, since the light emitted from the light sources 23a and 23b does not easily reach the opposite end face of the light guide plate 22, the return light is reduced and crosstalk is less likely to occur when used in a stereoscopic display device.

In the case of the second embodiment, it is preferable that the same conditions as the above conditions (3) and (4) are satisfied at an arbitrary light emitting point. That is, when the left light source 23a is turned on, the peak intensity of the light La emitted from an arbitrary light emitting point in the light emitting region and entering the left eye 27a is set to Ia, and the light having the peak intensity Ia is set to the normal line set at the light emitting point. The angle formed with respect to θa is θa, and when the right light source 23b is turned on, the peak intensity of the light Lb emitted from the same light emitting point of the light emitting region and entering the right eye 27b is Ib, and the light of the peak intensity Ib is the light emitting point. When the angle formed with respect to the raised normal is θb,
In the case of | θa | <| θb |, 1.0 <Ia / Ib <3.5
In the case of | θa |> | θb |, 1.0 <Ib / Ia <3.5
It is preferable that

[Third Embodiment]
FIG. 23 is a diagram for explaining the third embodiment of the present invention. The distribution curve Nb shown in FIG. 23A represents the pattern density of the emission pattern 25b provided on the light guide plate 22, and FIG. (B) represents the apparent light emission intensity.

  A distribution curve Db shown in FIG. 23A represents the distribution of a conventional emission pattern determined so that the optical emission intensity is uniform over the entire emission region. Since the observer's visual field sensitivity has the characteristics shown in FIG. 17A, if the optical emission intensity is uniform, the apparent emission intensity reflects the visual field sensitivity. In the example, the apparent light emission intensity distribution is as shown by a curve Qo in FIG.

  Therefore, in the third embodiment, the pattern density of the emission pattern is set to be the reciprocal of the curve representing the visual field sensitivity as the distribution curve Nb in FIG. As a result, the apparent light emission intensity is uniform over the entire light emitting region as shown by the straight line Qn shown in FIG. 23B, and the observer feels uniform brightness over the entire light emitting region.

[Fourth Embodiment]
FIG. 24 is a schematic view of a surface light source device 41 according to Embodiment 4 of the present invention. In this surface light source device 41, the substantially wedge-shaped light guide plates 22a and 22b that are gradually reduced in thickness from the light incident end surface toward the opposite end surface are overlapped so that the light incident end surfaces are located on the opposite side. It is matched. The left light source 23a faces the light incident end face of the light guide plate 22a, and the right light source 23b faces the light incident end face of the light guide plate 22b. Further, on the back surface of the light guide plate 22a, a minute emission pattern 25a for totally reflecting the light from the left light source 23a and emitting it from the light emission surface of the light guide plate 22a is provided with a uniform density. Also on the back surface of the light guide plate 22b, a minute emission pattern 25b for totally reflecting the light from the right light source 23ba and emitting it from the light exit surface of the light guide plate 22b is provided with a uniform density.

  The emission patterns 25b and 25a may be triangular prism-like or cylindrical lens-like emission patterns 25a extending over the entire width of the light guide plates 22b and 22a as shown in FIG. 25A. The output pattern 25a having a short triangular prism shape or cylindrical lens shape may be used. Further, spherical emission patterns 25b and 25a as shown in FIG. 25C and elliptical emission patterns 25b and 25a as shown in FIG. 25D may be used. Furthermore, it may be a triangular pyramid-shaped emission pattern 25b, 25a as shown in FIG. 26A or 26B, and a visual cone-shaped emission as shown in FIG. 26C or FIG. The patterns 25b and 25a may be used.

  Also in the surface light source device 41 having such a structure, the condition (1) and the condition (2) or the condition (7) is used in order to reduce the difference in the apparent light emission intensity felt by the right eye and the left eye. And Condition (2) may be satisfied.

  FIG. 27A is a diagram showing changes in the thickness of the light guide plates 22a and 22b in the surface light source device 41. FIG. FIG. 27B shows a change in the apparent light emission intensity ratio Jb / Ja in the light emission region. The straight line Hao in FIG. 27A is the thickness of the light guide plate 22a of the comparative example in which the thickness is designed so that the optical emission intensity of the light La emitted from the light emission surface of the light guide plate 22a is uniform in the light emission region. The straight line Hbo of the light guide plate 22b of the comparative example in which the thickness is designed so that the optical emission intensity of the light Lb emitted from the light exit surface of the light guide plate 22b is uniform in the light emission region It represents the change in thickness. In addition, Ha in FIG. 27 represents a change in the thickness of the light guide plate 22a in the fourth embodiment, and the thickness of the light guide plate 22a changes more slowly than the thickness of the light guide plate characterized by the change in thickness Hao, The region near the left light source 23a is thinner than the light guide plate having a thickness Hao, and the region far from the left light source 23a is thicker than the light guide plate having a thickness Hao. Similarly, Hb in FIG. 27 represents a change in the thickness of the light guide plate 22b in the fourth embodiment, and the thickness of the light guide plate 22b changes more slowly than the thickness of the light guide plate characterized by the change in thickness Hbo. The region near the right light source 23b is thinner than the light guide plate having a thickness Hbo, and the region far from the right light source 23b is thicker than the light guide plate having a thickness Hbo.

  As a result, in the comparative example, the optical emission intensity in the emission region is uniform (similar to the straight line To in FIG. 13), whereas the apparent emission intensity ratio Jb / Ja in the emission region is as shown in FIG. The curve Sg shown in (B) is obtained, and the change in the apparent light emission intensity ratio is large. On the other hand, in the case of the fourth embodiment, when the right light source 23b is turned on, the optical emission intensities Ib1 and Ib2 of the peak direction light Lb1 and Lb2 emitted from the left and right ends of the light emitting region, and the left light source 23a. Since the relationship between the optical emission intensities Ia1 and Ia2 of the light beams La1 and La2 in the peak direction emitted from the left end and the right end when the light is turned on is the same as the straight lines Ib and Ia in FIG. The apparent light emission intensity ratio Jb / Ja in the light emission region in the case of the surface light source device 4 of No. 4 is as shown by the curve Sh in FIG. 27B, and the change Sh of the apparent light emission intensity ratio is more gradual than Sg. Become. As a result, according to the surface light source device 41 of the fourth embodiment, the light emission intensity of the screen of the surface light source device 41 can be felt uniformly as viewed from the observer.

  Therefore, according to the fourth embodiment, the brightness difference between the images recognized by the right eye and the left eye is reduced, making it easier to see the stereoscopic image, and the brightness difference and luminance unevenness on the left and right sides of the screen are reduced, improving the image quality. To do. Moreover, since the change in the pattern density of the emission patterns 25a and 25b is reduced and the maximum value of the pattern density is reduced, the light guide plate 22 can be easily manufactured. Furthermore, since the maximum value of the density of the emission pattern to be formed becomes small, the emission efficiency from the light guide plate can be improved. In addition, since the light emitted from the light sources 23a and 23b does not easily reach the opposite end face of the light guide plate 22, the return light is reduced and crosstalk is less likely to occur when used in a stereoscopic display device.

  FIG. 28 shows a first modification and a second modification in which the thickness of the light guide plate 22b is changed (the light guide plate 22a is omitted). A curve H1b in FIG. 28A and a curve Sh1 in FIG. 28B show Modification Example 1 of this embodiment, and a curve H2b in FIG. 28A and a curve Sh2 in FIG. Modification 2 is shown.

  The thickness change Hb decreased linearly and had a constant slope. However, in the thickness change of Modification 1 represented by the curve H1b in FIG. 28A, the thickness change Hb was introduced as the distance from the right light source 23b increased. Although it is the same in that the thickness of the optical plate 22b decreases, in the case of H1b, the decreasing rate of the thickness decreases as the distance from the right light source 23b increases (the absolute value of the differential value of H1b decreases). . In this case, the apparent light emission intensity ratio Jb / Ja is as shown by a curve Sh1 in FIG. 28B, and approximates the curve Sh.

  In addition, in the thickness change of Modification 2 represented by the curve H2b in FIG. 28A, the reduction rate of the thickness gradually decreases (that is, the second-order differential value of the curve H2b is positive) and is far from the right light source 23b. In the region, the thickness has a minimum value, and in the region far from the right light source 23b, the thickness slightly increases. In this case, the apparent light emission intensity ratio Jb / Ja is as shown by a curve Sh2 in FIG.

[Fifth Embodiment]
FIG. 29 is a view for explaining the fifth embodiment of the present invention, and a curve Rb shown in FIG. 29A represents a change in the thickness of the light guide plate 22b, and FIG. Represents the emission intensity.

  A distribution curve Db shown in FIG. 29A represents the distribution of a conventional emission pattern determined so that the optical emission intensity is uniform over the entire emission region. Since the observer's visual field sensitivity has the characteristics shown in FIG. 17A, if the optical emission intensity is uniform, the apparent emission intensity reflects the visual field sensitivity. In the example, the apparent light emission intensity distribution is as shown by a curve Qo in FIG.

  Therefore, in the fifth embodiment, the thickness of the light guide plate 22b is set to be the reciprocal of the curve representing the visual field sensitivity as indicated by the curve Rb in FIG. As a result, the apparent light emission intensity becomes a straight line Qr shown in FIG. 29B, which is uniform over the entire light emitting area, and the observer feels uniform brightness over the entire light emitting area.

[Sixth Embodiment]
FIG. 30 is a schematic view of a surface light source device 51 according to Embodiment 6 of the present invention. In this embodiment, the apparent light emission intensity in the light emitting region is adjusted by adjusting the aperture ratio of the liquid crystal panel 33. In the surface light source device 51, the optical emission intensity on the surface of the optical sheet 24 may be uniform.

  When the optical emission intensity is uniform, as shown in FIG. 30A, when the right light source 23b is turned on and the right eye 27b is observing, the light exits from the left end and enters the right eye 27b. The optical emission intensity of Lb1 is larger than the optical emission intensity of the light Lb2 that exits from the right end and enters the right eye 27b. Therefore, in this embodiment, when the right image is displayed on the liquid crystal panel 33, the pixels at the left end portion of the screen are partially blocked from light (the pixels in the light blocking state are dispersed so that they cannot be seen). I will reduce it. As a result, since the amount of light entering the right eye 27b from the left end of the screen is reduced, the difference in apparent light emission intensity between the left end portion and the right end portion of the screen is reduced in the right eye 27b.

  Similarly, as shown in FIG. 30B, when the left light source 23a is turned on and the left eye 27a is observing, when the left image is displayed on the liquid crystal panel 33, the pixels at the right end of the screen are partially displayed. Therefore, the amount of transmitted light is reduced as a light blocking state. As a result, since the amount of light entering the left eye 27a from the right end of the screen is reduced, the difference in apparent light emission intensity between the left end portion and the right end portion of the screen is also reduced in the left eye 27a.

21, 41, 51 Surface light source device 22, 22a, 22b Light guide plate 23a Left light source 23b Right light source 24 Optical sheet 25a, 25b Output pattern 26 Light exit surface 27a Left eye 27b Right eye 31 Stereoscopic display device 33 Liquid crystal panel

Claims (19)

A light guide plate that guides light incident from a pair of opposing light incident end faces and emits the light from a light exit surface;
A first light source that causes light to be incident on the light guide plate from one of the light incident end surfaces;
A second light source that causes light to enter the light guide plate from the other light incident end surface of the light incident end surfaces;
In a surface light source device comprising a prism sheet disposed to face the light exit surface of the light guide plate,
When the first light source is turned on, the peak intensity of light emitted from the end of the light emitting region on the first light source side is Ia1, and when the second light source is turned on, the first light source in the light emitting region. When the peak intensity of the light emitted from the end on the side is Ib1,
Ia1> Ib1
And
When the first light source is turned on, the peak intensity of light emitted from the end of the light emitting region on the second light source side is Ia2, and when the second light source is turned on, the second light source in the light emitting region. When the peak intensity of the light emitted from the end on the side is Ib2,
Ia2 <Ib2
A surface light source device. A first light guide plate that guides incident light and emits the light from a light exit surface;
A second light guide plate that guides incident light and emits it from the light exit surface;
A first light source that causes light to be incident on the first light guide plate from a light incident end surface of the first light guide plate;
A second light source for causing light to enter the second light guide plate from a light incident end surface of the second light guide plate;
A prism sheet,
The first light guide plate and the second light guide plate are overlapped with each other so that the light incident end faces are located on opposite sides,
In the surface light source device in which the prism sheet is arranged to face the light emitting surface of the light guide plate located on the front side of the first light guide plate and the second light guide plate,
When the first light source is turned on, the peak intensity of light emitted from the end of the light emitting region on the first light source side is Ia1, and when the second light source is turned on, the first light source in the light emitting region. When the peak intensity of the light emitted from the end on the side is Ib1,
Ia1> Ib1
And
When the first light source is turned on, the peak intensity of light emitted from the end of the light emitting region on the second light source side is Ia2, and when the second light source is turned on, the second light source in the light emitting region. When the peak intensity of the light emitted from the end on the side is Ib2,
Ia2 <Ib2
A surface light source device. When the first light source is turned on, Ia represents the peak intensity of light emitted from an arbitrary light emitting point in the light emitting region, and θa represents the angle formed by the light having the peak intensity Ia with respect to the normal line set at the light emitting point. When the second light source is turned on, Ib represents the peak intensity of light emitted from the same light emitting point of the light emitting region, and θb represents the angle formed by the light having the peak intensity Ib with respect to the normal line set at the light emitting point. and when,
If | θa | <| θb |, then Ia> Ib
In the case of | θa |> | θb |, Ia <Ib
The surface light source device according to claim 1, wherein the surface light source device is configured as follows. The angles θa and θb and the peak intensities Ia and Ib are
In the case of | θa | <| θb |, 1.0 <Ia / Ib <3.5
In the case of | θa |> | θb |, 1.0 <Ib / Ia <3.5
The surface light source device according to claim 3, wherein When the first light source is turned on, the peak intensity of light emitted from the end of the light emitting region on the first light source side is Ia1, and when the first light source is turned on, the second light source in the light emitting region. When the peak intensity of the light emitted from the end on the side is Ia2,
Ia1> Ia2
And satisfy the condition
When the second light source is turned on, the peak intensity of light emitted from the end of the light emitting region on the second light source side is Ib2, and when the second light source is turned on, the first light source in the light emitting region When the peak intensity of the light emitted from the end on the side is Ib1,
Ib2> Ib1
The surface light source device according to claim 1, wherein the condition is satisfied. The peak intensities Ia1 and Ia2 are
1.0 <Ia1 / Ia2 <3.5
Satisfy the condition,
The peak intensities Ib1 and Ib2 are
1.0 <Ib2 / Ib1 <3.5
The surface light source device according to claim 5, wherein the condition is satisfied.   A first emission pattern for causing the light incident from the first light source to exit from the light exit surface on the light exit surface of the light guide plate or the surface facing the light exit surface, and the second light source The surface light source device according to claim 1, wherein a second emission pattern for emitting light incident from the light emission surface from the light emission surface is formed. A first light for emitting light incident from the first light source to the light exit surface of the first light guide plate or the surface facing the light exit surface from the light exit surface of the first light guide plate. An emission pattern is formed,
Second light for causing the light incident from the second light source to exit from the light exit surface of the second light guide plate to the light exit surface of the second light guide plate or the surface facing the light exit surface. The surface light source device according to claim 2, wherein an emission pattern is formed. In the first emission pattern, the pattern density increases in a nonlinear function as the distance from the first light source increases, the rate of increase in the pattern density in the direction away from the first light source is always positive, and The increase rate is gradually increased as the distance from the first light source increases.
In the second emission pattern, the pattern density increases in a nonlinear function as the distance from the second light source increases, the rate of increase in the pattern density in the direction away from the second light source is always positive, and The surface light source device according to claim 7 or 8, wherein the surface light source device is arranged so that the increase rate gradually increases as the distance from the second light source increases. The first emission pattern is assumed to be arranged so as to emit light having a uniform emission intensity from the light emission surface in a region farther from the first light source than the center of the light emission region. The increase rate of the pattern density of the first emission pattern in the direction farther from the first light source is smaller than the pattern density distribution of the pattern,
The second emission pattern is assumed to be arranged so as to emit light having a uniform emission intensity from the light emission surface in a region farther from the second light source than the center of the light emission region. 10. The surface light source device according to claim 9, wherein an increase rate of a pattern density of the second emission pattern in a direction farther from the second light source is smaller than a pattern density distribution of the pattern. The first emission pattern has a constant increase rate of the pattern density of the first emission pattern in a direction farther from the first light source in a region farther from the first light source than the center of the light emitting region,
The second emission pattern has a constant increase rate of the pattern density of the second emission pattern in a direction farther from the second light source in a region farther from the second light source than the center of the light emitting region. The surface light source device according to claim 9, wherein:   In the region closer to the first light source than the center of the light emitting region, the first emission pattern has a pattern density of the first emission pattern that decreases as the distance from the first light source increases. In an area farther from the first light source than the center, the pattern density of the first emission pattern increases as the distance from the first light source increases, and the second emission pattern becomes higher than the center of the light emission area. In the region close to the second light source, the pattern density of the second emission pattern decreases with increasing distance from the second light source, and in the region farther from the second light source than the center of the light emitting region, the second light source pattern density decreases. 9. The surface light source device according to claim 7, wherein a pattern density of the second emission pattern increases as the distance from the light source increases. The thickness of the first light guide plate gradually decreases from the light incident end surface facing the first light source toward the end surface opposite to the light incident end surface,
3. The thickness of the second light guide plate is gradually reduced from a light incident end face facing the second light source toward an end face opposite to the light incident end face. Surface light source device. The thickness of the first light guide plate changes more slowly than the thickness change assumed to emit light of uniform light emission intensity from the light exit surface of the light guide plate,
The thickness of the second light guide plate changes more gradually than a change in thickness assumed to emit light of uniform light emission intensity from the light exit surface of the light guide plate. 14. A surface light source device according to item 13.   The surface light source device according to claim 14, wherein the thickness of the first light guide plate and the thickness of the second light guide plate are uniformly thin at a constant rate. The thickness of the first light guide plate is such that the rate of decrease in thickness decreases as it approaches the end on the side farther from the first light source,
14. The surface light source device according to claim 13, wherein the thickness of the second light guide plate decreases as the thickness of the second light guide plate approaches an end portion farther from the second light source. The thickness of the first light guide plate gradually decreases from the light incident end surface facing the first light source toward the end surface opposite to the light incident end surface, and the end portion on the side far from the first light source The thickness gradually increases toward the end face of the end,
The thickness of the second light guide plate gradually decreases from the light incident end surface facing the second light source toward the end surface opposite to the light incident end surface, and the end portion on the side far from the second light source The surface light source device according to claim 2, wherein the surface light source device gradually increases in thickness toward the end surface of the end portion.   18. The surface light source device according to claim 17, wherein the thickness of the first light guide plate and the second light guide plate is gradually increased in a region where the thickness is gradually increased.   A three-dimensional display device comprising an optical sheet and a liquid crystal panel arranged in front of the surface light source device according to claim 1.

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