Surface light source device, transmissive display device

Abstract

To provide a surface light source device which inhibits unevenness in brightness even with a small number of point light sources, and to provide a transmissive display device.SOLUTION: A surface light source device 10 comprises: a light source substrate 11 in which point light sources 12 are arranged on one surface; and a light guide plate 14 formed with multiple recessed parts 141 which are open to the light source substrate 11 side. The recessed parts 141 have a shape which becomes smaller from the light source substrate 11 side to the light emitting side along a thickness direction of the light guide plate 14, and include: first recessed parts 141A which are provided at positions corresponding to the point light sources 12 when viewed in a direction perpendicular to a plate surface of the light guide plate 14 and in each of which at least part of the point light source exists, and second recessed parts 141B respectively provided at positions which do not correspond to the point light sources 12. Two or more second recessed parts 141B are located between adjacent first recessed parts 141A. An opening 143 of each recessed part 141 has a polygonal shape. A direction orthogonal to each side of the polygonal shape of the opening 143 intersects with at least one of arrangement directions of the point light sources 12 when viewed in a direction orthogonal to the plate surface of the light guide plate 14.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a surface light source device and a transmissive display device. [Background technology]

[0002] Conventionally, there has been known a transmissive display device that displays an image by illuminating a transmissive display unit such as an LCD (Liquid Crystal Display) panel from behind with a surface light source device (backlight). In recent years, the use of small point light sources such as LEDs as the light source unit of surface light source devices has been increasing, and a device in which a light source substrate on which point light sources are arranged is disposed directly below a light guide plate is also widely known (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-97974 Summary of the Invention [Problem to be solved by the invention]

[0004] Generally, the light emitted from an LED is more directional than the light emitted from conventional fluorescent tubes, etc., so in a direct-type surface light source device in which the light source substrate is placed directly below the light guide plate, there is a large difference in brightness between the area directly above the point light source and the area between the point light sources. To solve this problem, there are methods to improve brightness unevenness by increasing the thickness of the light guide plate or using multiple optical sheets, but these methods make it difficult to make the surface light source device thinner. Another method is to increase the number of arranged light sources, but this has the problem of increasing the production cost of the surface light source device. For example, in Patent Document 1, a recess is provided at a position on the light guide plate corresponding to the light source, and the light source is placed within the recess, thereby reducing the light emitted directly above the light source, but this does not sufficiently improve brightness unevenness.

[0005] An object of the present invention is to provide a surface light source device and a transmissive display device in which brightness unevenness is suppressed even with a small number of point light sources. [Means for solving the problem]

[0006] The present invention solves the above-mentioned problems by the following means: For ease of understanding, the following description will be given with reference to the corresponding embodiments of the present invention, but the present invention is not limited to these. The first invention is a surface light source device comprising a light source substrate (11) on one side of which point light sources (12) are arranged, and a light guide plate (14) located on the light output side of the light source substrate and having formed thereon a plurality of recesses (141) that open to the light source substrate side, wherein the recesses have a shape that becomes smaller from the light source substrate side toward the light output side along the thickness direction of the light guide plate, and a first recess is provided at a position corresponding to the point light source when viewed from a direction perpendicular to the plate surface of the light guide plate, and at least a part of the point light source is contained therein. a first recess (141A) and a second recess (141B) provided at a position not corresponding to the point light source, wherein two or more of the second recesses are located between adjacent first recesses, an opening (143) of the recess has a polygonal shape when viewed from a direction perpendicular to the plate surface of the light guide plate, and a direction perpendicular to each side of the polygonal shape of the opening when viewed from a direction perpendicular to the plate surface of the light guide plate intersects with at least one of the arrangement directions (d1, d2) of the point light sources. The second invention is a surface light source device (10) characterized in that, in the surface light source device of the first invention, each side (144) of the opening forms an angle α (where 0°<α<90°) with at least one of the arrangement directions of the point light sources, and satisfies sinφ>W / (2×d), where φ is the angle between a line perpendicular to the center point of the side and the arrangement direction of the point light sources, d is the arrangement pitch of the recesses (141) in the arrangement direction of the point light sources, and W is the dimension of one side of the opening. The third invention is a surface light source device (10) characterized in that, in the surface light source device of the first or second invention, the point light sources (12) and the recesses (141) are arranged along a first direction (d1) and a second direction (d2) that are parallel to the plate surface direction of the light source substrate (11) and perpendicular to each other, the opening (143) has a square shape when viewed from a direction perpendicular to the plate surface of the light guide plate (14), and one side (144) of the opening forms an angle of 45° with respect to the arrangement direction of the point light sources. A fourth invention is a surface light source device comprising a light source substrate (11) on one side of which point light sources (12) are arranged, and a light guide plate (14) located on the light output side of the light source substrate and having a plurality of recesses (141) formed therein that open to the light source substrate side, wherein the recesses have a shape that becomes smaller from the light source substrate side to the light output side along the thickness direction of the light guide plate, and when viewed from a direction perpendicular to the plate surface of the light guide plate, the recesses are provided at positions corresponding to the point light sources and contain at least a part of the point light source, and and a second recess (141B) formed in the recess, two or more of the second recesses are located between adjacent first recesses, the opening of the recess has a shape in which three or more first curves (144a) having a large radius of curvature and three or more second curves (144b) having a smaller radius of curvature than the first curves are alternately arranged when viewed from a direction perpendicular to the plate surface of the light guide plate, and a normal to a point that is the center of the first curve of the recess intersects with at least one of the arrangement directions of the point light sources when viewed from a direction perpendicular to the plate surface of the light guide plate. A fifth invention is a surface light source device characterized in that, in the surface light source device of the fourth invention, the opening (143) can be approximated to a polygonal shape when viewed from a direction perpendicular to the plate surface of the light guide plate (14), the tangent to the point at the center of the first curve (144a) of the opening forms an angle α (where 0°<α<90°) with at least one of the arrangement directions (d1, d2) of the point light sources, and the angle that the normal to the point at the center of the first curve forms with the arrangement direction of the point light sources is φ, the arrangement pitch of the recesses in the arrangement direction of the point light sources is d, and the dimension of one side of the polygonal shape to which the opening is approximated satisfies sinφ>W / (2×d). The sixth invention is a surface light source device characterized in that, in the surface light source device of the fourth or fifth invention, the point light sources (12) and the recesses (141) are arranged along a first direction (d1) and a second direction (d2) that are parallel to the plate surface direction of the light source substrate (11) and perpendicular to each other, and the openings (143) are arranged such that, when viewed from a direction perpendicular to the plate surface of the light guide plate, four first curves (144a) and four second curves (144b) are alternately arranged, and the tangent to the central point of the first curve forms an angle of 45° with respect to the arrangement direction of the point light sources. The seventh invention is a surface light source device (10) characterized in that, in any one of the first to sixth inventions, the point light sources (12) are arranged along a first direction (d1) and a second direction (d2) that are parallel to the plate surface direction of the light source substrate (11) and perpendicular to each other, and the ratio P0 / P1 of the arrangement pitch P0 of the point light sources to the arrangement pitch P1 of the recesses in the arrangement direction of the point light sources satisfies 3≦P0 / P1≦8. The eighth invention is a surface light source device (10) characterized in that, in any one of the first to seventh inventions, when the depth of the recess (141) in the thickness direction of the light guide plate (14) is S1 and the distance between the recess and the nearest recess in a direction passing through the center of one side (144) of the opening and perpendicular to that side is P2, S1≦P2 is satisfied. A ninth invention is a surface light source device (10) characterized in that, in any one of the first to eighth inventions, the angle θ that the side surface (142) of the recess (141) makes with the plate surface direction of the light guide plate (14) satisfies the equation θ0-asin(sinθ0 / n)=asin(1 / n), where n is the refractive index of the light guide plate, and when viewed from a direction perpendicular to the plate surface of the light guide plate, θ≧θ0 is satisfied in 50% or more of the area corresponding to the first recess 141A. A tenth aspect of the present invention is a transmissive display device (1) comprising a surface light source device (10) according to any one of the first to ninth aspects of the present invention, and a transmissive display unit (20) arranged on the light output side of the surface light source device. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a surface light source device and a transmissive display device in which brightness unevenness is suppressed even when a small number of point light sources are used. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a diagram illustrating a transmissive display device 1 according to an embodiment. [Figure 2] 3A and 3B are diagrams illustrating recesses 141 of a light guide plate 14 according to the embodiment. [Figure 3] 10 is a diagram showing the positional relationship between a recess 141 of a light guide plate 14 and a point light source 12 according to the embodiment. [Figure 4] 10A and 10B are diagrams showing other forms of the recess 141. FIG. [Figure 5] 3A to 3C are diagrams illustrating the state of light traveling inside a light guide plate 14 according to an embodiment. [Figure 6] 10 is a diagram for explaining the positions of a point light source 12 and a recess 141 when measuring the illuminance in the surface light source device of sample 7. FIG. [Figure 7] FIG. 10 is a diagram showing the results of a simulation of brightness in the surface light source device of Sample 1. [Figure 8] FIG. 10 is a diagram showing the results of a simulation of brightness in the surface light source device of Sample 2. [Figure 9] FIG. 10 is a diagram showing the results of a simulation of brightness in the surface light source device of Sample 3. [Figure 10] FIG. 10 is a diagram showing the results of a simulation of brightness in the surface light source device of Sample 4. [Figure 11] FIG. 10 is a diagram showing the results of a simulation of brightness in the surface light source device of Sample 5. [Figure 12] FIG. 10 is a diagram showing the results of a simulation of brightness in the surface light source device of Sample 6. [Figure 13] FIG. 10 is a diagram showing the results of a simulation of brightness in the surface light source device of Sample 7. [Figure 14] FIG. 10 is a diagram showing the results of a simulation of brightness in the surface light source device of Sample 8. [Figure 15]FIG. 10 is a diagram showing the results of a simulation of brightness in the surface light source device of Sample 9. [Figure 16] 10A and 10B are diagrams illustrating another embodiment of a method for arranging recesses 141. FIG. [Figure 17] 10A and 10B show variations of the opening 143. FIG. [Figure 18] 10 is a diagram illustrating the inclination direction of a side 144 of an opening 143. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present invention will be described with reference to the drawings, etc. Note that the drawings shown below, including Fig. 1, are schematic diagrams, and the size and shape of each part are appropriately exaggerated to facilitate understanding. In this specification, terms specifying shapes or geometric conditions, such as parallel and orthogonal, are intended to include not only their strict meanings but also states that perform similar optical functions and have an error that can be considered as parallel or orthogonal. Furthermore, the numerical values such as dimensions of each component and the names of materials described in this specification are merely examples of embodiments, and are not limited to these, and may be selected and used as appropriate.

[0010] Furthermore, in this specification, the terms plate, sheet, etc. are used, but in general, these are used in the order of thickness, that is, plate, sheet, film, and so on, and this specification follows suit. However, since there is no technical significance in this distinction, these terms can be used interchangeably as appropriate. In this specification, the term "sheet surface" refers to the surface of each sheet-like member that is in the planar direction of the sheet when viewed as a whole, and this definition is used throughout this specification and the claims. The same applies to plate surfaces, etc.

[0011] (Embodiment) 1 is a diagram illustrating a transmissive display device 1 according to this embodiment. Fig. 1 shows an enlarged view of a portion of a cross section of the transmissive display device 1 (a cross section parallel to a first direction d1 and a third direction d3, which will be described later). The transmissive display device 1 of this embodiment includes an LCD panel 20 and a surface light source device 10. The transmissive display device 1 illuminates the LCD panel 20 from the rear side with the surface light source device 10, and displays image information formed on the LCD panel 20. For ease of understanding, in the following figures including Figure 1 and the following description, when the transmissive display device 1 is in use, two directions that are parallel to the screen of the transmissive display device 1 and perpendicular to each other are referred to as the first direction d1 and the second direction d2, and the direction perpendicular to the screen of the transmissive display device 1 (thickness direction of the transmissive display device 1) is referred to as the third direction d3. In this embodiment, as an example, the first direction d1 is the vertical direction of the screen, and the second direction d2 is the horizontal direction of the screen.

[0012] The screen of the transmissive display device 1 corresponds to the surface (hereinafter referred to as the display surface) 20a of the LCD panel 20 closest to the viewer (light output side). The "front direction" of the transmissive display device 1 is a direction perpendicular to the display surface 20a, parallel to the third direction d3, and coincides with a direction perpendicular to the plate surface of the light guide plate 14 described later. The display surface 20a of the transmissive display device 1 is parallel to the plate surface of the light guide plate 14 described later and the surface of sheets such as the optical sheet 15.

[0013] The LCD panel 20 is a substantially plate-shaped member formed by a transmissive liquid crystal display element, and is a transmissive display unit that forms video information on its display surface 20a. The LCD panel 20 has a rectangular shape when viewed from the front of the transmissive display device 1, with two sides parallel to a first direction d1 and two sides parallel to a second direction d2.

[0014] The surface light source device 10 is a device that illuminates the LCD panel 20 from the rear side, and is a so-called direct type surface light source device (backlight). The surface light source device 10 of this embodiment includes a light source substrate 11, a point light source 12, a reflective layer 13, a light guide plate 14, and optical sheets 15, 16, and 17.

[0015] The light source substrate 11 is a substrate on which point light sources 12 are arranged on one surface (the surface on the light guide plate 14 side), and is provided with wiring and the like (not shown) for supplying power for the point light sources 12 to emit light. The point light sources 12 are point-like light sources arranged at predetermined intervals on the light output side (light guide plate 14 side) of the light source substrate 11. For example, an LED (Light Emitting Diode) light source is used as the point light source 12. The LED used as the point light source 12 in this embodiment emits blue light. Note that the point light source 12 may be a light emitting element other than an LED.

[0016] As shown in Figure 2(b) described later, the point light source 12 has an example in which its shape when viewed from the thickness direction (third direction d3) of the light source substrate 11 is circular, but is not limited to this and may have a rectangular or other polygonal shape. In this embodiment, the point light sources 12 are arranged on one surface of the light source substrate 11 along a first direction d1 and a second direction d2. As shown in Fig. 3, which will be described later, the arrangement pitch of the point light sources 12 (first recesses 141A, which will be described later) in the first direction d1 is equal to the arrangement pitch in the second direction d2, which is assumed to be P0. The first direction d1 and the second direction d2 in this embodiment are parallel to the plate surface of the light source substrate 11 and, as described above, are perpendicular to each other.

[0017] The light guide plate 14 is a light-transmitting plate-like member provided on the light output side (LCD panel 20 side) of the light source substrate 11. The light guide plate 14 has a surface 14a on the light source substrate 11 side and a light output surface 14b on the LCD panel 20 side (light output side), and has multiple concave shapes (hereinafter referred to as recesses 141) that open onto the surface 14a on the light source substrate 11 side arranged at predetermined intervals. Light emitted from the point light source 12 enters the light guide plate 14, is guided within the light guide plate 14, and is emitted from the light output surface 14b. The light guide plate 14 is a member that guides light so that the brightness on the light output surface 14b is uniform.

[0018] The light guide plate 14 may be formed from a transparent resin containing one or more of, for example, acrylic resin, polystyrene resin, polycarbonate resin, polyethylene terephthalate resin, polyacrylonitrile resin, etc. as a main component. Alternatively, for example, a base layer formed from the above-mentioned transparent resin may have a shape portion having recesses 141 formed from a light-transmitting ultraviolet-curable resin such as urethane acrylate, polyester acrylate, or epoxy acrylate on the surface facing the light source substrate 11. Furthermore, the entire light guide plate 14 may be formed from an ultraviolet-curable resin. In this embodiment, the thickness of the light guide plate 14 is set to S0.

[0019] 2 is a diagram illustrating the recess 141 of the light guide plate 14 of this embodiment. Similar to FIG. 1, FIG. 2(a) shows an enlarged view of a portion of the cross section of the surface light source device 10 parallel to the first direction d1 and the third direction d3. FIG. 2(b) is a view of the recess 141 and the point light source 12 viewed in a direction perpendicular to the plate surface of the light guide plate 14 (third direction d3). For ease of understanding, the optical sheets 15, 16, and 17 are omitted from FIG. 2(a), and the reflective layer 13 and the optical sheets 15, 16, and 17 are omitted from FIG. 2(b). 3 is a diagram showing the positional relationship between the recesses 141 of the light guide plate 14 of this embodiment and the point light sources 12. For ease of understanding, FIG. 3 shows only the light guide plate 14 as viewed from the observer's side in a direction perpendicular to the plate surface of the light guide plate 14 (third direction d3), and the recesses 141 (first recesses 141A) corresponding to the point light sources 12 are shaded. Note that FIG. 3 illustrates, as an example, a case where there are four recesses 141 (second recesses 141B) between the point light sources 12 (first recesses 141A).

[0020] The recess 141 has a recessed shape that opens to the surface 14a on the light source substrate 11 side. The recesses 141 of this embodiment are arranged on the surface 14a along the first direction d1 and the second direction d2. In this embodiment, the arrangement pitch of the recesses 141 in the first direction d1 and the arrangement pitch in the second direction d2 are equal to P1. The arrangement pitch P1 of the recesses 141 is smaller than the arrangement pitch P0 of the point light sources 12.

[0021] The recess 141 of this embodiment has a quadrangular pyramid shape with an opening 143 on the surface 14a side as a bottom surface and four side surfaces 142 that are inclined with respect to the thickness direction of the light guide plate 14, and the area of the opening portion in a plane parallel to the plate surface of the light guide plate 14 gradually decreases toward the light output surface 14b along the thickness direction (third direction d3) of the light guide plate 14. As shown in Fig. 2(a), the recess 141 of this embodiment has a triangular cross-sectional shape in a cross section parallel to the thickness direction (third direction d3) of the light guide plate 14 and the arrangement direction of the recesses 141. In this embodiment, the opening 143 is square-shaped, and the side surface 142 is an isosceles triangle. Conventionally, such recesses 141 are formed in a conical or truncated conical shape, but in this embodiment, the opening 143 is formed in a quadrangular pyramid shape, which is a square shape, from the standpoints of ease of formation of the recesses 141, improved accuracy of dimensions, etc., and reduction of uneven brightness.

[0022] 2(b), the recess 141 has four sides 144 that form the square shape of the opening 143, each of which intersects with the first direction d1 and the second direction d2 that are the arrangement directions of the point light sources 12, forming an angle α. In FIG. 2(b), an example is shown in which the angle α is 45°.

[0023] Fig. 4 is a diagram showing another embodiment of the recess 141. Fig. 4(a) shows the cross-sectional shape of the recess 141 in a cross section passing through the center of the opening 143 and parallel to the first direction d1 and the third direction d3, as in Fig. 2, and Figs. 4(b) and (c) show cross sections passing through the center of the opening 143 and parallel to the direction forming 45° with the first direction d1 and the second direction d2 (the direction perpendicular to the side 144) and the third direction d3. As shown in Fig. 4(a), the recess 141 may have a truncated quadrangular pyramid shape with the apex facing the light-emitting surface 14b. In this case, the apex may be flat or may be a curved surface that is convex toward the light-emitting surface 14b. As shown in Fig. 4(b), the recess 141 may have a cross-sectional shape that is a so-called bell shape and the side surface 142 has a concave curved surface, or as shown in Fig. 4(c), the side surface 142 may have a curved surface that is convex toward the opening 143 in the cross section shown in Fig. 4(c).

[0024] Returning to Figure 2, the depth of recess 141 (the dimension in the thickness direction of light guide plate 14) is S1, the dimension of one side of opening 143 on surface 14a of recess 141 is S3, and the dimension of the diagonal of opening 143 (the maximum dimension of opening 143) is S2. In addition, in the cross section shown in FIG. 2(a), the angle formed by the side surface 142 of the recess 141 and the plate surface direction of the light guide plate 14 is defined as θ.

[0025] As shown in Figures 2 and 3, the multiple recesses 141 formed in the light guide plate 14 include recesses 141 that are located at positions corresponding to the point light sources 12 and have point light sources 12 inside them, when viewed from a direction perpendicular to the plate surface of the light guide plate 14 (third direction d3), and recesses 141 that are located at positions that do not correspond to the point light sources 12. Here, the recess 141 provided at a position corresponding to the point light source 12 and having the point light source 12 therein is referred to as a first recess 141A, and the recess 141 provided at a position not corresponding to the point light source 12 and not having the point light source 12 therein is referred to as a second recess 141B. In this embodiment, the first recess 141A and the second recess 141B have the same shape and size.

[0026] As shown in FIG. 3, in this embodiment, the point light sources 12 and the recesses 141 are arranged along the first direction d1 and the second direction d2 at arrangement pitches P0 and P1, respectively. In this embodiment, the opening 143 has a square shape, and the angle α that the side 144 of the opening 143 makes with the arrangement direction of the point light sources 12 is α=45°. Therefore, imaginary lines extending the diagonal lines of the square shape of the opening 143 of the first recess 141A (the dashed lines B1 and B2 in the first recess 141A at the upper left in FIG. 3) are parallel to the first direction d1 and the second direction d2 that are the arrangement directions of the recess 141 and the point light sources 12, respectively, and the nearest other first recess 141A (point light source 12) is located on these lines B1 and B2. Furthermore, on the imaginary line (the lines C1 and C2 shown by the dashed lines in the upper left first recess 141A in Figure 3) that passes through the midpoint of the side 144 of the opening 143 and is perpendicular to that side 144, the closest other first recess 141A (point light source 12) is not located, but the second closest first recess 141A (point light source 12) is located.

[0027] Here, when the recess 141 has a conical shape, the amount of light entering the light guide plate 14 from the first recess 141A is approximately uniform along the circular circumferential direction of the opening 143 when viewed from a direction perpendicular to the plate surface of the light guide plate 14 (third direction d3). In contrast, the recess 141 in this embodiment has a quadrangular pyramid shape, and when viewed from the thickness direction of the light guide plate 14 (a direction perpendicular to the plate surface, the third direction d3), the amount of light that enters the light guide plate 14 from the first recess 141A and travels through the light guide plate 14 is not uniform along the outer periphery of the opening 143.

[0028] In this embodiment, most of the light entering the light guide plate 14 from the first recess 141A enters the light guide plate 14 from the side surface 142 of the recess 141, and the amount of light entering the light guide plate 14 from the corners is small. That is, when viewed from a direction perpendicular to the plate surface of the light guide plate 14 (third direction d3), the amount of light heading in the direction toward the corners of the opening 143 (the extension direction of straight lines B1 and B2, which are extensions of the diagonal lines of the opening 143 of the first recess 141A at the upper left in FIG. 3 , and the direction toward which the nearest other point light source 12 is located) is smaller than the amount of light heading in other directions. In contrast, the amount of light heading in the direction toward which the nearest other point light source 12 is not located (the direction along straight lines C1 and C2, which pass through the midpoints of the sides of the opening 143 of the first recess 141A at the upper left in FIG. 3 ) is greater.

[0029] Therefore, from the viewpoint of reducing brightness unevenness, as mentioned above, it is preferable that the angle α is α>0°, it is more preferable that α satisfies the following (Equation 1), and it is most preferable that α=45° while satisfying (Equation 1). When the angle α satisfies α>0°, the amount of light incident from the point light sources 12 into the light guide plate 14 that travels in a direction that forms an angle with the arrangement direction of the point light sources 12 can be increased.

[0030] Furthermore, it is preferable that the angle α satisfies the following (Equation 2). Fig. 18 is a diagram illustrating the inclination direction of the side 144 of the opening 143. Fig. 18 shows, as an example, an example in which the recesses 141 are arranged in a square, as in this embodiment. In Fig. 18, the arrangement pitch d of the recesses 141 in the arrangement direction of the point light sources 12 is defined as, W is the length of the side 144 of the opening 143 of the recess 141, and φ is the angle formed by a line perpendicular to the center point of the side 144 and the arrangement direction of the point light sources 12. In this case, it is preferable that the angle φ satisfies the following (Equation 1). sinφ>W / (2×d) (Equation 1) When the angle φ satisfies the above (Equation 1), a straight line passing through the midpoint of a side of the opening 143 and perpendicular to that side (for example, lines C1 and C2 shown in Figure 3) does not reach the recess 141 closest to that recess 141 in the arrangement direction of the point light sources 12.

[0031] In this embodiment, the point light sources 12 and recesses 141 are arranged in a square, the openings 143 are square-shaped, the arrangement pitch P1 of the recesses 141 in the arrangement direction of the point light sources 12 corresponds to the above dimension d, the length S3 of the side 144 of the recess 141 corresponds to the above dimension W, and the angle α corresponds to the above angle φ, so the above (Equation 1) becomes as follows: sinα>S3 / (2×P1) (Formula 2) In this embodiment, by making the angle α satisfy the above (Equation 2), it is possible to reduce the amount of light that enters the light guide plate 14 from the side surface 142 of the first recess 141A in which the point light source 12 is located and is totally reflected by the side surface of the recess 141 (second recess 141B) closest to this first recess 141A at the shortest distance, thereby reducing uneven brightness caused by only the area near the point light source 12 being bright.

[0032] Furthermore, in this embodiment, angle α satisfies the above (Equation 2), and further, α=45°. Therefore, a direction passing through the midpoint of side 144 of opening 143 and perpendicular to side 144 forms an angle of 45° with first direction d1 and second direction d2, which are the arrangement directions of point light sources 12. In addition, the corners of opening 143 are oriented in the direction along the arrangement direction of point light sources 12, and straight lines B1 and B2 shown in FIG. 3 are parallel to the arrangement direction of point light sources 12. By adopting such a configuration, it is possible to significantly reduce the amount of light that enters the light guide plate 14 from the side surface 142 of the first recess 141A containing the point light source 12 and is totally reflected by the side surface of another recess 141 (second recess 141B) that is closest to the first recess 141A at the shortest distance in the arrangement direction of the point light sources 12, and to more effectively reduce uneven brightness caused by only the vicinity of the point light source 12 becoming bright. Furthermore, by adopting such a configuration, it is possible to improve the brightness of the region D (see FIG. 3) that is the center of the unit lattice formed by the arranged recesses 141, and to reduce uneven brightness.

[0033] Furthermore, from the viewpoint of reducing unevenness in brightness on the light exit surface 14b of the light guide plate 14, it is preferable that the recess 141 satisfy the following conditions. In the arrangement direction of the point light sources 12, the ratio P0 / P1 of the arrangement pitch P0 of the point light sources 12 (the arrangement pitch of the first recesses 141A) to the arrangement pitch P1 of the recesses 141 preferably satisfies 3≦P0 / P1≦8, and more preferably P0 / P1=5. That is, in the arrangement direction of the point light sources 12, the number of second recesses 141B arranged between adjacent first recesses 141A (between adjacent point light sources 12) is preferably 2 to 7, and more preferably 4.

[0034] By making the ratio P0 / P1 satisfy the above range, it is possible to reduce uneven brightness on the light output surface 14b of the light guide plate 14, where only the areas directly above or near the point light sources 12 are bright and the areas corresponding to the center between adjacent point light sources 12 are dark. When P0 / P1>8 (when eight or more second recesses 141B are arranged between adjacent point light sources 12 in the arrangement direction of the point light sources 12), the amount of light emitted from the areas on the light output surface 14b directly above or in the vicinity of the second recesses 141B located near the point light sources 12 increases, the brightness of these areas increases, and the brightness of the area in the center between adjacent point light sources 12 decreases, resulting in uneven brightness.

[0035] On the other hand, if P0 / P1<3 and, for example, one second recess 141B is arranged between adjacent point light sources 12 in the arrangement direction of the point light sources 12 (if P0 / P1=2), the area between the recess 141 corresponding to the point light source 12 (first recess 141A) and the recess 141 not corresponding to the point light source 12 (second recess 141B) will be dark, resulting in a difference in brightness. Also, if P0 / P1<3 and, for example, there are no second recesses 141B arranged between adjacent point light sources 12 in the arrangement direction of the point light sources 12 (if P0 / P1=1), only the areas directly above or near the point light sources 12 on the light output surface 14b of the light guide plate 14 will be bright, while the area corresponding to the center between the adjacent point light sources 12 will be dark, resulting in brightness unevenness. Furthermore, in these cases, in order to improve brightness unevenness, it becomes necessary to reduce the arrangement pitch P0 of the point light sources 12 and increase the number of point light sources 12, which is undesirable.

[0036] Furthermore, in this embodiment, from the viewpoint of reducing unevenness in brightness, it is preferable that the depth S1 of the recess 141 satisfies S1≦P2, where P2 is the distance between the first recess 141A and the recess 141 (second recess 141B) that is closest in a direction passing through the midpoint of the side 144 of the first recess 141A and perpendicular to this side 144. This distance P2 is the distance between the center of the opening 143 of the first recess 141A and the center of the opening 143 of the recess 141 (second recess 141B) that is closest to the first recess 141A (see FIG. 3).

[0037] When S1>P2, the recesses 141 are too close to each other, so most of the light that enters the light guide plate 14 from the first recess 141A corresponding to the point light source 12 passes through the midpoint of the side 144 of the first recess 141A, is totally reflected by the side surface of the second recess 141B that is closest in the direction perpendicular to the side 144, and is emitted from the light output surface 14b. As a result, the area directly above and near the point light source 12 (first recess 141A) becomes significantly brighter than other areas, resulting in uneven brightness. Therefore, from the viewpoint of improving brightness unevenness, it is preferable that the depth S1 of the recess 141 and the distance P2 between the first recess 141A and the recess 141 (second recess 141B) closest to the first recess 141A in a direction passing through the midpoint of the side 144 of the first recess 141A and perpendicular to the side 144 satisfy S1≦P2.

[0038] In this embodiment, it is preferable that the recess 141 further satisfies the following conditions from the viewpoint of reducing uneven brightness. That is, assuming that the refractive index of light guide plate 14 is n, it is preferable that the angle θ formed between side surface 142 of recess 141 and the plate surface direction (main surface direction) of light guide plate 14 is equal to or larger than θ0, which satisfies the following (Equation 3). θ0-asin(sinθ0 / n)=asin(1 / n) (Equation 3) When the angle θ is θ≧θ0, the light emitted from the point light source 12 in a direction perpendicular to the plate surface of the light guide plate 14 (third direction d3) is refracted at the side surface 142 when it enters the light guide plate 14, and is totally reflected when it enters the light output surface 14b at an angle equal to or greater than the critical angle. This allows the light from the point light source 12 to be guided into the light guide plate 14.

[0039] 4(b) and (c), when the angle θ formed between the tangent direction of the side surface 142 and the plate surface direction of the light guide plate 14 changes, it is preferable that when the light guide plate 14 is viewed from the thickness direction (third direction d3), the angle θ formed between the side surface 142 and the plate surface of the light guide plate 14 is equal to or greater than the above-mentioned angle θ0 in 50% or more of the area corresponding to the recess 141 (first recess 141A) in which the point light source 12 is located. If the above conditions are not satisfied, the light emitted from the point light source 12 will be refracted at the side surface 142, travel inside the light guide plate 14, and be incident on the light output surface 14b directly above the point light source 12 or in the vicinity thereof at an angle smaller than the critical angle, and will be emitted from the light output surface 14b, which will undesirably brighten only the area directly above the point light source 12 or in the vicinity thereof.

[0040] In addition, in order to prevent the area directly above the point light source 12 from becoming too bright, when the light guide plate 14 is viewed from the thickness direction (third direction d3), in the area corresponding to the recess 141 (first recess 141A) in which the point light source 12 is located, a reflective layer or the like (not shown) may be formed on the side surface 142 so that the transmittance is 50% or less in the area where the angle θ between the side surface 142 and the plate surface of the light guide plate 14 is smaller than the angle θ0.

[0041] The reflective layer 13 is formed in a region between adjacent point light sources 12 (first recesses 141A) on the light source substrate 11. There is a gap between the surface of the reflective layer 13 on the light guide plate 14 side and the surface 14a of the light guide plate 14, and air is present therein. The reflective layer 13 has a function of reflecting light emitted from the surface 14 a of the light guide plate 14 toward the light source substrate 11 side and returning it to the light guide plate 14 . The reflective layer 13 is, for example, a layer formed of a white resin layer or the like with high reflectivity, and a sheet-like member made of white resin or the like may be used. The reflective layer 13 may also be formed of a dielectric multilayer film with high light reflectivity. The reflective layer 13 may also be a layer formed of a metal or the like with high reflectivity. Furthermore, the reflective layer 13 may be a layer with high diffuse reflectivity or a layer with high specular reflectivity.

[0042] 1, the optical sheets 15, 16, and 17 are optical members arranged on the light-emitting side of the light guide plate 14 (i.e., between the light guide plate 14 and the LCD panel 20), and have various optical functions such as diffusing the light emitted from the light-emitting surface 14b of the light guide plate 14 and controlling the direction of travel of the light. In this embodiment, an example in which three optical sheets are arranged will be described, but the type and number of optical sheets may be changed as appropriate depending on the characteristics of the point light source 12, etc. The optical sheet 15 is disposed on the LCD panel 20 side of the light guide plate 14 and is a so-called QD sheet (quantum dot sheet). By passing through the optical sheet 15, which is a QD sheet, the blue light emitted from the point light source 12 is converted into white light.

[0043] Optical sheet 16 is disposed closer to LCD panel 20 than optical sheet 15, and is a prism sheet having unit prism shapes arranged on one side. Optical sheet 16 of this embodiment has convex unit prisms 161 with triangular cross-sections arranged on the surface facing LCD panel 20 (light output side). This optical sheet 16 has a function of returning light toward the light guide plate 14 by total reflection at two inclined surfaces 162 of the unit prisms 161 when the light emitted from the light guide plate 14 is incident on the optical sheet 16 at an incident angle that forms a large angle with respect to the front direction (third direction d3) of the transmissive display device 1. On the other hand, when the light emitted from the light guide plate 14 is incident on the optical sheet 16 at an incident angle that forms a small angle with respect to the front direction (third direction d3) of the transmissive display device 1, the light is refracted at the inclined surfaces 162 and emitted. In other words, the optical sheet 16 has a function of directing light toward the front direction. The optical sheet 16 of this embodiment is a prism sheet in which unit prisms 161, whose ridgelines extend in the second direction d2 (horizontal direction of the screen), are arranged along the first direction d1 (vertical direction of the screen).

[0044] Optical sheet 17 is a reflective polarizing sheet that transmits polarized light components parallel to its transmission axis and reflects polarized light components parallel to its reflection axis, which is perpendicular to the transmission axis. This optical sheet 17 has the function of reflecting polarized light components that would otherwise be absorbed by the polarizing plate in LCD panel 20 toward light guide plate 14, and transmitting polarized light components that pass through the polarizing plate in LCD panel 20. This improves the utilization efficiency of light emitted from light guide plate 14.

[0045] In this embodiment, the optical sheet 16 is shown as an example of a prism sheet in which unit prisms 161 with their ridgeline direction in the second direction d2 are arranged in the first direction d1, but this is not limited to this, and the optical sheet 16 may be a prism sheet in which unit prisms 161 with their ridgeline direction in the first direction d1 are arranged in the second direction depending on the usage environment of the display device and the desired optical performance. In addition to the optical sheet 16, the surface light source device 10 may further include a prism sheet in which unit prisms having the ridge direction in the first direction d1 are arranged in a second direction, or may include a sheet with a diffusing effect. The optical sheet disposed between the light guide plate 14 and the LCD panel 20 may be selected appropriately depending on the environment in which the surface light source device 10 and the transmissive display device 1 are used and the desired optical performance.

[0046] Fig. 5 is a diagram illustrating the state of light traveling inside the light guide plate 14 of this embodiment. For ease of understanding, Fig. 5 shows only the light source substrate 11, the point light source 12, the reflective layer 13, and the light guide plate 14. Fig. 5 also shows an enlarged portion of a cross section parallel to the thickness direction of the light guide plate 14 and the arrangement direction of the recesses 141. Light emitted from the point light source 12 enters the light guide plate 14 from the side surface 142 of the recess 141 (first recess 141A) and is guided through the light guide plate 14 while being totally reflected by the light output surface 14b of the light guide plate 14 and the surface 14a on the light source substrate 11 side. Then, for example, light L1 is totally reflected by the side surface 142 of another recess 141 (second recess 141B in FIG. 5) and is emitted from the light output surface 14b. Furthermore, for example, light L2 enters the recess 141 from the side surface 142 of another adjacent recess 141 (the second recess 141B in Figure 5), is reflected by the reflective layer 13 provided on the light source substrate 11, etc., enters the light guide plate 14 again from the side surface 142 of the recess 141, is guided within the light guide plate 14, etc., is totally reflected by the side surface 142 of the other recess 141 (the second recess 141B), and is emitted from the light output surface 14b.

[0047] As described above, according to this embodiment, the light emitted from the point light source 12 is refracted at the side surface 142, enters the light guide plate 14, and is guided within the light guide plate 14, and is totally reflected at the light output surface 14b in the vicinity of the point light source 12. Therefore, the amount of light emitted from the light output surface 14b directly above the point light source 12 or in the vicinity thereof is reduced. Furthermore, according to this embodiment, a portion of the light guided within the light guide plate 14 is totally reflected at a position not corresponding to a point light source 12, i.e., at the side surface 142 of a recess 141 (second recess 141B) provided between adjacent point light sources 12, and is emitted from the light-emitting surface 14b directly above or in the vicinity of the recess 141 (second recess 141B), thereby increasing the brightness of that region. In other words, the recess 141 (second recess 141B) serves as a pseudo light source. Therefore, according to this embodiment, two or more second recesses 141B are arranged between adjacent point light sources 12 in the arrangement direction of the point light sources 12, and multiple pseudo light sources (second recesses 141B) are located between the point light sources 12, so that even if there are only a small number of point light sources 12, brightness unevenness in the surface light source device and the transmissive display device can be effectively reduced.

[0048] In this embodiment, the recess 141 has a quadrangular pyramid shape with the square opening 143 as the base, and the side 144 forms an angle α (where α>0°) with respect to the arrangement direction of the point light sources 12, and this angle α satisfies sin α>S3 / (2×P1). This makes it possible to reduce the amount of light traveling in the direction toward the corner of the opening 143 (the direction toward the nearest other point light source 12) when viewed from the direction perpendicular to the plate surface of the light guide plate 14 (the third direction d3). This makes it possible to allow more light to travel from the first recess 141A corresponding to the point light source 12 in a direction different from the direction toward which the nearest point light source 12 (first recess 141A) is located in the arrangement direction of the point light sources 12, i.e., in a direction toward which the nearest point light source 12 is not located (in this embodiment, the direction along the straight lines C1 and C2 in the first recess 141A at the upper left in FIG. 3 ), thereby further reducing brightness unevenness. In addition, in this embodiment, α=45°, which further enhances the above effect.

[0049] Furthermore, in this embodiment, the ratio P0 / P1 of the arrangement pitch P0 of the point light sources 12 to the arrangement pitch of the recesses 141 in the arrangement direction of the point light sources 12 satisfies the above-mentioned preferred range (3≦P0 / P1≦8), so that the brightness can be improved in the region between adjacent point light sources 12 on the light output surface 14b of the light guide plate 14 (particularly, the region at the center between the point light sources 12). This reduces the difference in brightness between the region directly above or near the point light source 12 and the region between adjacent point light sources 12 (particularly, the region at the center between the point light sources 12), thereby improving brightness uniformity on the light output surface 14b of the light guide plate 14, i.e., improving the brightness uniformity of the surface light source device 10. This also makes it possible to increase the arrangement interval between the point light sources 12 and reduce the number of point light sources 12 used. Therefore, according to this embodiment, the number of point light sources 12 used can be reduced, and uneven brightness on the light output surface 14b of the light guide plate 14, and therefore uneven brightness on the light output surface of the surface light source device 10, can be reduced. Furthermore, according to this embodiment, the recesses 141 are quadrangular pyramidal in shape with the openings 143 being square, and therefore can be formed more accurately and easily than when the recesses 141 are conical. Generally, such light guide plate 14 is formed using a molding die having protrusions that form the recesses 141. Forming protrusions in the shape of quadrangular pyramids is easier than forming protrusions in the shape of cones.

[0050] On the other hand, in a conventional light guide plate in which recesses are formed only at positions corresponding to point light sources, the brightness is high only in the areas directly above and near the point light sources on the light output surface of the light guide plate, and the areas between the point light sources (especially the central areas between the point light sources 12) are dark, which tends to result in uneven brightness. In order to eliminate this brightness unevenness, for example, if the thickness of the light guide plate is increased, the brightness of the area between the point light sources will improve, but this is not preferable from the viewpoint of making the surface light source device or the transmissive display device thinner, lighter, reducing production costs, etc. Furthermore, increasing the number of point light sources in order to eliminate brightness unevenness is not preferable from the viewpoint of reducing production costs and power consumption, etc. As described above, the surface light source device 10 of this embodiment can solve these problems and significantly improve brightness unevenness.

[0051] (Sample evaluation) Here, surface light source devices of samples 1 to 7, which differ in the shape of recesses 141 of light guide plate 14, etc., were prepared, and the brightness (illuminance) at the light output surface of surface light source device 10 was calculated by simulation. Note that the surface light source devices of the samples used in the simulation did not include optical sheets 15 to 17, and the light output surface of surface light source device 10 was light output surface 14b of light guide plate 14.

[0052] 6 is a diagram illustrating the positions of point light sources 12 and recesses 141 when measuring illuminance in the surface light source device of sample 7. In FIG. 6, recesses 141 (first recesses 141A) corresponding to point light sources 12 are indicated by hatching. Note that FIG. 6 shows the position of recesses 141 in measurement region M in the surface light source device of sample 7 as an example, but in the surface light source devices of samples 1 to 6, the positions of recesses 141 in measurement region M are the same, but the shape and the angle (angle α) that sides 144 of openings 143 make with the arrangement direction of point light sources 12 are different from those in the surface light source device of sample 7.

[0053] The measurement area M of the surface light source device of each sample used for the simulation was a 6 mm square area on the light output surface 14b of the light guide plate 14, centered on the point light source 12 (first recess 141A) as shown in Fig. 6. Note that Fig. 6 shows the position of the recess 141 in the measurement area M of the sample 7. In a measurement area M on the light-emitting surface of the surface light source device of each sample (samples 1 to 7), illuminance was calculated at approximately 0.286 mm intervals from the center of the measurement area M along straight lines K1 and K2 shown by dashed lines in Fig. 6. Straight line K1 is parallel to the first direction d1, and straight line K2 is parallel to the second direction d2, and both straight lines pass through the center of the point light source 12 (first recess 141A) located at the center of the measurement area M.

[0054] The surface light source devices 10 of samples 1 to 7 have in common that the arrangement pitch P0 of the point light sources 12 (first recesses 141A) is 6.0 mm, the thickness S0 of the light guide plate 14 is 0.675 mm, the refractive index of the light guide plate 14 is 1.49, and the arrangement pitch of the recesses 141 is 1.2 mm. In addition, the surface light source device of sample 1 has a recess 141 that is conical in shape and an opening 143 that forms the bottom surface that is circular in shape, while the surface light source devices 10 of samples 2 to 7 have a recess 141 that is quadrangular pyramid in shape and an opening 143 that forms the bottom surface that is square in shape.

[0055] Regarding the dimensions of each part, in surface light source device 10 of sample 1, depth S1 of recess 141 is 0.225 mm, and diameter of opening 143 of recess 141 is 0.03 mm. Angle θ between side surface 142 and the plate surface direction of light guide plate 14 is 82.5. In surface light source devices 10 of samples 2 to 7, depth S1 of recess 141 is 0.19 mm, one side of opening 143 of recess 141 is 0.05 mm, and angle θ=82.5° between side surface 142 and the plate surface direction of light guide plate 14. In surface light source devices 10 of samples 2 to 7, angle α between side 144 of recess 141 and the arrangement direction of recesses 141 is 0°, 10°, 20°, 30°, 40°, and 45°, respectively. In each of these sample surface light source devices, the point light source 12 was turned on, and the presence or absence of brightness unevenness was evaluated based on the illuminance distribution within the measurement region M of the light-emitting surface 14b.

[0056] 7 to 13 are diagrams showing the results of a brightness simulation for the surface light source devices of Samples 1 to 7. In FIGS. 7 to 13, (a) is an image showing the brightness distribution in measurement region M of light-emitting surface 14b when point light source 12 is turned on, (b) is a graph showing the illuminance along line K2 in measurement region M, (c) is a graph showing the illuminance along line K1 in measurement region M, and (d) is a histogram of the brightness distribution in (a). In the graphs shown in (b) of FIGS. 7 to 13, the vertical axis represents illuminance (lux) and the horizontal axis represents the distance (mm) from the center of measurement region M (the center of point light source 12), and in the graph shown in (c), the horizontal axis represents illuminance (lux) and the vertical axis represents the distance (mm) from the center of measurement region M (the center of point light source 12).

[0057] [Table 1]

[0058] Table 1 shows the results of evaluating the shape, arrangement pitch P1, angle α, etc. of the recesses 141 of the light guide plate 14 in the surface light source devices of Samples 1 to 7, and the difference in brightness between the area directly above or near the recesses 141 and the other area between the recesses 141 in the measurement area M of the light output surface 14b. Here, the "area between the recesses 141" refers to the central area between adjacent recesses 141 in the arrangement direction, or area D (see FIGS. 3 and 6) that is the center of the unit lattice formed by the arranged recesses 141. In Table 1, with regard to the difference in brightness between the area directly above or near recess 141 and the area between other recesses, if it is sufficiently small it is indicated as good by "◎", if it is within the allowable range it is indicated as acceptable by "◯", and if it is larger than the allowable range it is indicated as unacceptable by "×".

[0059] As shown in Figures 7 to 13, in the surface light source devices of samples 1 to 7, the difference in brightness between the area directly above and near the point light source 12 on the light output surface 14b and the area between adjacent point light sources 12 (especially the area in the center between the point light sources 12, which is the outer edge of the measurement area M) is improved.

[0060] In samples 2 to 7 in which the recesses 141 are pyramidal, the difference in brightness between the area between the recesses 141 and the area directly above or near the recesses 141 decreases as the angle α that the side 144 makes with the arrangement direction increases. For example, in the surface light source device of sample 2 (angle α=0°), as shown in FIG. 8, bright vertical and horizontal regions appear near recess 141 along side 144, and the difference with the darkness of the region corresponding to region D (the region at the center of the unit lattice formed by recess 141) is very large, which is undesirable.

[0061] However, as the angle α increased, the vertical and horizontal bright regions as described above were eliminated, and in the surface light source devices of Samples 3 to 7, brightness unevenness was reduced to a level equal to or greater than that of Sample 1, in which the recesses 141 were conical. In particular, in the surface light source device of Sample 7 shown in FIG. 13 (angle α = 45°), the difference in brightness between the region directly above and near the recesses 141 and the other regions between the recesses 141 was significantly reduced. Furthermore, in the surface light source devices of Samples 3 to 7, as the angle α increased and approached 45°, the region at the center of the unit lattice formed by the recesses 141 (region D shown in FIGS. 3 and 6) became brighter, and the difference in brightness with other regions became smaller. In the surface light source devices of Samples 3 to 7, the improvement in brightness of region D was more effective than in Sample 1, which had a conical shape. Furthermore, in the surface light source device of Sample 7, the difference in brightness between the region directly above and near the recesses 141 and the other regions between the recesses 141 was significantly reduced among the surface light source devices of Samples 1 to 7.

[0062] Next, samples 8 and 9 were prepared which had different magnitude relationships between the depth S1 of the recess 141 and the distance P2 between the first recess 141A and the recess 141 (second recess 141B) closest to the first recess 141A in a direction passing through the midpoint of the side 144 of the first recess 141A and perpendicular to this side 144, and brightness measurements were performed by simulation in the same manner as samples 1 to 7 described above, and the brightness unevenness was evaluated. In Samples 8 and 9, the recesses 141 are arranged in a square within the measurement region M, similar to Sample 7 shown in Fig. 6, with a first recess 141A (point light source 12) located at the center. The recesses 141 of the light guide plates 14 of Samples 8 and 9 are in the shape of a truncated quadrangular pyramid, with the openings 143 being square, and the sides 144 of the openings 143 forming an angle α of 45° with respect to the arrangement direction of the point light sources 12. In Samples 8 and 9, the dimension of one side of the square of the top surface of the recess 141 closest to the light output surface 14b is 10% of the dimension of the side 144 of the opening 143 which forms the bottom surface.

[0063] In Samples 8 and 9, the thickness S0 of the light guide plate 14 was 1.0 mm, the dimension S3 of the side 144 of the opening 143 of the recess 141 was 0.2 mm, and the depth S1 of the recess 141 was 0.72 mm. The arrangement pitch P1 of the recesses 141 in Sample 8 was 1.2 mm, and the arrangement pitch P1 of the recesses 141 in Sample 9 was 1.0 mm. In Samples 8 and 9, the angle θ between the side 142 and the plate surface direction of the light guide plate 14 was 82.5 mm. Furthermore, the distance P2 for sample 8 is 0.85 mm, and the distance P2 for sample 9 is 0.7 mm. Therefore, the surface light source device of sample 8 satisfies S1≦P2, and the surface light source device of sample 9 satisfies S1>P2.

[0064] 14 and 15 show the results of a brightness simulation for the surface light source devices of Samples 8 and 9. In FIGS. 14 and 15, (a) is an image showing the brightness distribution in measurement area M of light-emitting surface 14b when point light source 12 is turned on, (b) is a graph showing the illuminance along line K2 in measurement area M, (c) is a graph showing the illuminance along line K1 in measurement area M, and (d) is a histogram of the brightness distribution in (a). In the graphs shown in (b) of FIGS. 14 and 15, the vertical axis represents illuminance (lux) and the horizontal axis represents the distance (mm) from the center of measurement area M (the center of point light source 12), and in the graph shown in (c), the horizontal axis represents illuminance (lux) and the vertical axis represents the distance (mm) from the center of measurement area M (the center of point light source 12). 14 and 15, in the surface light source device of sample 9, where S1>P2, the area directly above and near the point light source 12 was significantly brighter than other areas, resulting in a large difference in brightness. In contrast, in the surface light source device of sample 8, where S1≦P2 was satisfied, the brightness directly above and near the point light source 12 was suppressed, and the difference in brightness was reduced. As a result, the surface light source device of sample 8, where S1≦P2 was satisfied, had less uneven brightness than the surface light source device of sample 9, where S1>P2.

[0065] (Other embodiments) In the above embodiment, the recesses 141 are arranged in a square pattern, but the arrangement is not limited to this, and may be a staggered pattern as shown in FIG. 16, which will be described later. Fig. 16 is a diagram illustrating another embodiment of a method for arranging the recesses 141. Like Fig. 3, Fig. 16 shows the light guide plate 14 as viewed from a direction perpendicular to the plate surface of the light guide plate 14 (the thickness direction of the light guide plate 14, the third direction d3). 16, the point light sources 12 (first recesses 141A) are arranged in the first direction d1 and the second direction at an arrangement pitch P0, as in the embodiment described above, in a so-called square arrangement. However, the recesses 141 are arranged in a form in which they are further arranged at positions shifted by half a pitch (P1 / 2) in the first direction d1 and half a pitch (P1 / 2) in the second direction in the square arrangement shown in FIG. 3 of the embodiment described above. Even with this configuration, brightness unevenness can be sufficiently eliminated, as in the above-described embodiment. Furthermore, since the recess 141 is located at a position corresponding to the region D shown in Figure 3, brightness unevenness can be further improved.

[0066] (Variations) The present invention is not limited to the above-described embodiments, and various modifications and changes are possible, and these are also within the scope of the present invention.

[0067] (1) In the present embodiment, the first direction d1 and the second direction d2 are perpendicular to each other. However, the angle between the first direction d1 and the second direction d2 may be an angle other than 90°.

[0068] (2) In this embodiment, an example has been given in which the arrangement pitch of the recesses 141 in the first direction d1 is equal to the arrangement pitch in the second direction d2, but this is not limited to this, and the arrangement pitch may be different in the two directions.

[0069] (3) In this embodiment, the point light source 12 emits blue light, but it may emit white light. In that case, the optical sheet 15 (QD sheet) may not be used.

[0070] (4) In this embodiment, the recess 141 has an example in which the opening 143 is square-shaped. However, this is not limited to this. For example, the opening 143 may have a polygonal shape with an even number of sides, such as a hexagonal shape or an octagonal shape.

[0071] (5) In this embodiment, the recess 141 may have a curved corner portion (the ridge portion between the side surfaces 142) of the opening 143, or the side 144 may have a convex curved shape (the side surfaces 142 may have a convex curved shape). Fig. 17 is a diagram showing a modified form of the opening 143. In Fig. 17, only the shape of the opening 143 is shown for ease of understanding. As shown in Fig. 17, opening 143 may have an equal number of first curves 144a with a large radius of curvature and second curves 144b with a smaller radius of curvature than first curves 144a, which are alternately arranged. Fig. 17 shows an example in which four first curves 144a and four second curves 144b are alternately arranged. The shape of opening 143 shown in Fig. 17 is a shape that approximates a polygonal shape such as a square.

[0072] In such a configuration, the tangent to the first curve 144a intersects with the arrangement direction of the point light sources 12 (first direction d1 and second direction d2) and forms an angle α (α>0°), and in particular, it is preferable from the viewpoint of reducing brightness unevenness that the angle α that the tangent to the central point of the first curve 144a makes with the arrangement direction of the point light sources 12 is α=45°. It is preferable that the first curve 144a and the second curve 144b have the same number of points, and that both be an even number of four or more. Furthermore, when the recess 141 is a pyramid, its apex (the point closest to the light-emitting surface) may be curved and convex toward the light-emitting surface, and when the recess 141 is a truncated pyramid, its apex (the surface closest to the light-emitting surface) may be curved and convex toward the light-emitting surface.

[0073] The present invention is not limited to the above-described embodiments and variations, and the present invention can be applied to various embodiments and variations. [Explanation of symbols]

[0074] 1 Transparent display device 10 surface light source device 11 Light source board 12 point light source 13 Reflective layer 14 Light guide plate 141 recess 141A First recess 141B Second recess 15 Optical Sheet 16 Optical Sheet 17 Optical Sheet 20 LCD panels

Claims

1. a light source substrate having point light sources arranged on one side thereof; a light guide plate located on the light output side of the light source substrate and having a plurality of recesses formed therein that open toward the light source substrate; A surface light source device comprising: The recessed portion is a shape that becomes smaller from the light source substrate side to the light output side along a thickness direction of the light guide plate, an opening of the recess has a square shape when viewed in a direction perpendicular to the plate surface of the light guide plate, and has a quadrangular pyramid shape having four side surfaces inclined with respect to the thickness direction of the light guide plate; a first recess provided at a position corresponding to the point light source and containing at least a part of the point light source when viewed from a direction perpendicular to a plate surface of the light guide plate, and a second recess provided at a position not corresponding to the point light source; Two or more of the second recesses are located between adjacent first recesses, a direction perpendicular to each side of the square shape of the opening portion when viewed from a direction perpendicular to the plate surface of the light guide plate intersects with at least one of the arrangement directions of the point light sources; the point light sources and the recesses are arranged along a first direction and a second direction that are parallel to a plate surface direction of the light source substrate and perpendicular to each other, a ratio P0 / P1 of an arrangement pitch P0 of the point light sources to an arrangement pitch P1 of the recesses in the arrangement direction of the point light sources satisfies 3≦P0 / P1≦8; the angle α formed by the sides of the square shape of the opening with respect to the arrangement direction of the point light sources satisfies 10°≦α≦45°; A surface light source device characterized by:

2. The surface light source device according to claim 1, When the angle formed by a line perpendicular to the center point of the side and the arrangement direction of the point light sources is φ, the arrangement pitch of the recesses in the arrangement direction of the point light sources is d, and the dimension of one side of the opening is W, sinφ>W / (2×d) To satisfy A surface light source device characterized by:

3. a light source substrate having point light sources arranged on one side thereof; a light guide plate located on the light output side of the light source substrate and having a plurality of recesses formed therein that open toward the light source substrate; A surface light source device comprising: The recessed portion is a shape that becomes smaller from the light source substrate side to the light output side along a thickness direction of the light guide plate, The light guide plate has an opening in which, when viewed from a direction perpendicular to a plate surface of the light guide plate, four first curves having a large radius of curvature and four second curves having a smaller radius of curvature than the first curves are alternately arranged, a first recess provided at a position corresponding to the point light source and containing at least a part of the point light source when viewed from a direction perpendicular to a plate surface of the light guide plate, and a second recess provided at a position not corresponding to the point light source; Two or more of the second recesses are located between adjacent first recesses, a normal to a center point of the first curve of the recess intersects with at least one of the arrangement directions of the point light sources when viewed from a direction orthogonal to the plate surface of the light guide plate; the point light sources and the recesses are arranged along a first direction and a second direction that are parallel to a plate surface direction of the light source substrate and perpendicular to each other, a ratio P0 / P1 of an arrangement pitch P0 of the point light sources to an arrangement pitch P1 of the recesses in the arrangement direction of the point light sources satisfies 3≦P0 / P1≦8; a tangent to a central point of the first curve forms an angle of 45° with respect to an arrangement direction of the point light sources; A surface light source device characterized by:

4. The surface light source device according to claim 3, the opening can approximate a polygonal shape when viewed from a direction perpendicular to the plate surface of the light guide plate, Let φ be the angle formed by the normal to the center point of the first curve and the arrangement direction of the point light sources, d be the arrangement pitch of the recesses in the arrangement direction of the point light sources, and W be the dimension of one side of the polygonal shape to which the opening is approximated, sinφ>W / (2×d) To satisfy A surface light source device characterized by:

5. In the surface light source device according to any one of claims 1, 2 and 4, When the depth of the recess in the thickness direction of the light guide plate is S1, and the distance between the recess and the nearest recess in a direction passing through the center of one side of the opening and perpendicular to that side is P2, S1≦P2 To satisfy A surface light source device characterized by:

6. The surface light source device according to any one of claims 1 to 5, The angle θ formed by the side surface of the recess with respect to the plate surface direction of the light guide plate is expressed as follows, where n is the refractive index of the light guide plate: θ ０ -asin(sinθ ０ / n=asinn(1nn) Angle θ that satisfies the formula ０ In contrast, in 50% or more of the region corresponding to the first recess, as viewed from a direction perpendicular to the plate surface of the light guide plate, θ≧θ ０ To satisfy A surface light source device characterized by:

7. The surface light source device according to any one of claims 1 to 6, a transmissive display unit disposed on the light output side of the surface light source device; A transmissive display device comprising:

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