Surface light source device and 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 Art

[0002] Conventionally, a transmissive display device is known in which a transmissive display unit such as an LCD (Liquid Crystal Display) panel is illuminated from the back by a surface light source device (backlight) to display an image. In recent years, the use of small dot-like light sources such as LEDs as the light source unit of the surface light source device has been progressing, and a configuration 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

Summary of the Invention

Problems to be Solved by the Invention

[0004] Generally, since the light emitted from an LED has higher directivity than the light emitted from a conventional fluorescent tube or the like, in a direct-type surface light source device in which a light source substrate is disposed directly below a light guide plate, the difference in brightness between directly above the point light source and the region between the point light sources is large. To solve this problem, there are methods such as increasing the thickness of the light guide plate or using a plurality of optical sheets to improve brightness unevenness, but it has been difficult to reduce the thickness of the surface light source device. In addition, there is also a method of increasing the number of light sources to be arranged, but there are problems such as an increase in the production cost of the surface light source device. For example, in Patent Document 1, a concave shape is provided at a position corresponding to the light source of the light guide plate, and the light source is disposed in the concave shape, thereby reducing the light emitted directly above the light source, but the improvement of brightness unevenness is insufficient.

[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 Problems

[0006] The present invention solves the above problems by the following means. For ease of understanding, reference numerals corresponding to embodiments of the present invention are used for explanation, but the present invention is not limited thereto. A first invention is a surface light source device including a light source substrate (11) on which point light sources (12) are arranged on one side, and a light guide plate (14) located on the light-emitting side of the light source substrate and having a plurality of recesses (141) that open to the light source substrate side. The recesses have a shape that becomes smaller as they go from the light source substrate side to the light-emitting side along the thickness direction of the light guide plate. When viewed from a direction perpendicular to the plate surface of the light guide plate, the recesses include a first recess (141A) provided at a position corresponding to the point light source and at least partially containing the point light source, and a second recess (141B) provided at a position not corresponding to the point light source. Two or more of the second recesses are located between adjacent first recesses. The 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 intersects at least one of the arrangement directions (d1, d2) of the point light sources when viewed from a direction orthogonal to the plate surface of the light guide plate. The surface light source device (10) is characterized by this. A second invention is the surface light source device according to the first invention, wherein 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. When the angle formed by a straight line perpendicular to the midpoint of the side and the arrangement direction of the point light source is φ, the arrangement pitch of the recesses (141) in the arrangement direction of the point light sources (12) is d, and the dimension of one side of the opening is W, sin φ > W / (2 × d) is satisfied. The surface light source device (10) is characterized by this. The third invention is a surface light source device of the first invention or the second invention, wherein the point light source (12) and the concave portion (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 the arrangement direction of the point light source. The surface light source device (10) is characterized by this. The fourth invention is a surface light source device including a light source substrate (11) having point light sources (12) arranged on one side, and a light guide plate (14) located on the light-emitting side of the light source substrate and having a plurality of concave portions (141) opening to the light source substrate side. The concave portions have a shape that becomes smaller as they go from the light source substrate side to the light-emitting side along the thickness direction of the light guide plate. When viewed from a direction perpendicular to the plate surface of the light guide plate, it has a first concave portion (141A) provided at a position corresponding to the point light source and at least a part of the point light source is located therein, and a second concave portion (141B) provided at a position not corresponding to the point light source. Between adjacent first concave portions, two or more second concave portions are located. The opening of the concave portion has a shape in which three or more first curves (144a) with a large radius of curvature and second curves (144b) with 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. When viewed from a direction orthogonal to the plate surface of the light guide plate, the normal line at the center of the first curve of the concave portion intersects at least one of the arrangement directions of the point light sources. The surface light source device is characterized by this. The fifth invention is a surface light source device of the fourth invention. When 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 line at the center point 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. Let the angle formed by the normal line at the center point of the first curve and the arrangement direction of the point light sources be φ, the arrangement pitch of the concave portions in the arrangement direction of the point light sources be d, and the dimension of one side of the polygonal shape approximated by the opening be W. Then, it is characterized by satisfying sinφ > W / (2×d). The sixth invention is a surface light source device of the fourth or fifth invention, wherein the point light source (12) and the concave portion (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. When viewed from a direction perpendicular to the plate surface of the light guide plate, four of the first curves (144a) and the second curves (144b) are alternately arranged, and the tangent line of the point at the center of the first curve forms an angle of 45° with the arrangement direction of the point light sources. This is a surface light source device characterized by this. The seventh invention is a surface light source device according to any one of the first to sixth inventions, wherein 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 concave portions in the arrangement direction of the point light sources satisfies 3 ≤ P0 / P1 ≤ 8. This is a surface light source device (10) characterized by this. The eighth invention is a surface light source device according to any one of the first to seventh inventions. When the depth of the concave portion (141) in the thickness direction of the light guide plate (14) is S1, and the distance between the point passing through the center of one side (144) of the concave portion and the opening portion and the nearest concave portion in the direction perpendicular to that side is P2, it satisfies S1 ≤ P2. This is a surface light source device (10) characterized by this. The ninth invention is a surface light source device according to any one of the first to eighth inventions. When the angle θ formed by the side surface (142) of the concave portion (141) and the plate surface direction of the light guide plate (14) satisfies the formula θ0 - asin(sinθ0 / n) = asin(1 / n) for an angle θ0, when viewed from a direction perpendicular to the plate surface of the light guide plate, in more than 50% of the region corresponding to the first concave portion 141A, θ ≥ θ0. This is a surface light source device (10) characterized by this. The tenth invention is a transmissive display device (1) comprising any one of the surface light source devices (10) according to the first to ninth inventions and a transmissive display portion (20) arranged on the light-emitting side of the surface light source device.

Advantages of the Invention

[0007] According to the present invention, it is possible to achieve an effect of providing 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.

Brief Description of Drawings

[0008]

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Embodiments for Carrying Out the Invention

[0009] Hereinafter, embodiments of the present invention will be described with reference to the drawings and the like. Note that each of the drawings shown below, including FIG. 1, is a schematically shown diagram, and the size and shape of each part are appropriately exaggerated for easy understanding. In this specification, with respect to terms specifying shapes and geometric conditions, such as terms like parallel and orthogonal, in addition to their strict meanings, states having errors to the extent that they can exhibit similar optical functions and can be regarded as parallel or orthogonal are also included. Also, the numerical values such as the dimensions of each member described in this specification and the material names, etc. are examples as embodiments, and are not limited thereto, and may be appropriately selected and used.

[0010] Also, in this specification, words such as plate and sheet are used, but in general usage, in the order of increasing thickness, they are used in the order of plate, sheet, and film, and this specification also follows that usage. However, since there is no technical meaning in such a distinction, these words can be replaced as appropriate. Also, in this specification, the sheet surface refers to the surface in the planar direction of the sheet when the entire sheet-like member is viewed as a whole, and the same definition is used in this specification and in the claims. The same applies to the plate surface and the like.

[0011] (Embodiment) FIG. 1 is a diagram for explaining the transmissive display device 1 of the present embodiment. In FIG. 1, a part of a cross section (a cross section parallel to the first direction d1 and the third direction d3 described later) of the transmissive display device 1 is shown enlarged. The transmissive display device 1 of the present 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 back side with the surface light source device 10 and displays video information formed on the LCD panel 20. In the following figures including FIG. 1 and the following description, for ease of understanding, in the usage state of the transmissive display device 1, two directions parallel to the screen of the transmissive display device 1 and perpendicular to each other are defined as the first direction d1 and the second direction d2, and the direction perpendicular to the screen of the transmissive display device 1 (the thickness direction of the transmissive display device 1) is defined as the third direction d3. In the present embodiment, as an example, it is assumed that 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 on the observer side (light-emitting side) of the LCD panel 20. The "front direction" of the transmissive display device 1 is the direction perpendicular to this display surface 20a, parallel to the third direction d3, and coincides with the direction perpendicular to the plate surface of the light guide plate 14 described later. Also, the display surface 20a of the transmissive display device 1 is parallel to the plate surface of the light guide plate 14 and the sheet surfaces such as the optical sheet 15 described later.

[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 outer shape and the display surface 20a of the LCD panel 20 are rectangular when viewed from the front direction of the transmissive display device 1, and have two sides parallel to the first direction d1 and two sides parallel to the second direction d2.

[0014] The surface light source device 10 is a device that illuminates the LCD panel 20 from the back side, and is a so-called direct-lit surface light source device (backlight). The surface light source device 10 of this embodiment includes a light source substrate 11, point light sources 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 the point light sources 12 are arranged on one side (the surface on the light guide plate 14 side), and wiring (not shown) and the like for supplying power for the point light sources 12 to emit light are formed. The point light sources 12 are dot-like light sources arranged at a predetermined interval on the light-emitting side (the light guide plate 14 side) surface of the light source substrate 11. For example, LED (Light Emitting Diode) light sources are used as the point light sources 12. The LEDs used for the point light sources 12 in this embodiment emit blue light. Note that light-emitting elements other than LEDs may be used as the point light sources 12.

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

[0017] The light guide plate 14 is a translucent plate-like member provided on the light-emitting side (the 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-emitting surface 14b on the LCD panel 20 side (the light-emitting side), and a plurality of concave shapes (hereinafter referred to as recesses 141) that open to the surface 14a on the light source substrate 11 side are arranged at a predetermined interval. The light emitted from the point light sources 12 enters the light guide plate 14, is guided inside the light guide plate 14, and is emitted from the light-emitting surface 14b. The light guide plate 14 is a member that guides light so that the brightness at the light-emitting surface 14b becomes uniform.

[0018] This light guide plate 14 may be formed of a transparent resin mainly composed of one or more of, for example, acrylic resin, polystyrene resin, polycarbonate resin, polyethylene terephthalate resin, polyacrylonitrile resin, etc. Further, for example, a shape portion having a recess 141 may be formed on the surface on the light source substrate 11 side of a base material layer formed of the above-described transparent resin with a UV-curable resin having translucency such as urethane acrylate, polyester acrylate, or epoxy acrylate. Furthermore, the entire light guide plate 14 may be formed of a UV-curable resin. In the present embodiment, the thickness of the light guide plate 14 is set to S0.

[0019] FIG. 2 is a diagram for explaining the recess 141 of the light guide plate 14 of the present embodiment. In FIG. 2(a), as in FIG. 1, a part of the cross section of the surface light source device 10 parallel to the first direction d1 and the third direction d3 is enlarged and shown. Further, FIG. 2(b) is a view of the recess 141 and the point light source 12 seen along the direction (third direction d3) perpendicular to the plate surface of the light guide plate 14. For easy understanding, in FIG. 2(a), the optical sheets 15, 16, and 17 are omitted, and in FIG. 2(b), the reflection layer 13 and the optical sheets 15, 16, and 17 are omitted. FIG. 3 is a diagram showing the positional relationship between the recess 141 of the light guide plate 14 of the present embodiment and the point light source 12. In FIG. 3, for easy understanding, only the light guide plate 14 is shown as seen from the observer side in the direction (third direction d3) perpendicular to the plate surface of the light guide plate 14, and the recess 141 (first recess 141A) corresponding to the point light source 12 is hatched. In FIG. 3, as an example, the case where there are four recesses 141 (second recesses 141B) between the point light sources 12 (first recesses 141A) is described as an example.

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

[0021] The recess 141 of the present embodiment has a square pyramid shape having four side surfaces 142 that are inclined with respect to the thickness direction of the light guide plate 14, with the opening 143 on the surface 14a side as the bottom surface, 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 emitting surface 14b side along the thickness direction (third direction d3) of the light guide plate 14. As shown in FIG. 2(a), the recess 141 of the present 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. The opening 143 of the present embodiment has a square shape, and the side surfaces 142 have an isosceles triangle shape. Conventionally, such a recess 141 is formed in a conical shape or a truncated conical shape. However, in the present embodiment, from the viewpoints of ease of forming the recess 141, improvement in accuracy of dimensions and the like, and reduction of brightness unevenness, the recess 141 has a square pyramid shape with the opening 143 having a square shape.

[0022] As shown in FIG. 2(b), in this recess 141, the four sides 144 forming the square shape of the opening 143 all intersect with respect to the first direction d1 and the second direction d2 which are the arrangement directions of the point light sources 12, forming an angle α. FIG. 2(b) shows an example where the angle α = 45°.

[0023] FIG. 4 is a diagram showing another form of the recess 141. In FIG. 4(a), similar to FIG. 2, 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 is shown. In FIGS. 4(b) and 4(c), cross-sections passing through the center of the opening 143 and parallel to the third direction d3 and a direction forming a 45° angle with respect to the first direction d1 and the second direction d2 (a direction orthogonal to the side 144) are shown. As shown in Fig. 4(a), the recess 141 may have a frustum of a square pyramid shape having a top surface on the light-emitting surface 14b side. At this time, the top surface may be a flat surface or a curved surface convex toward the light-emitting surface 14b side. Further, as shown in Fig. 4(b), the recess 141 may have a so-called bell shape in cross section, and the side surface 142 may be a concave curved surface, or as shown in Fig. 4(c), the side surface 142 may be a curved surface convex toward the opening 143 side in the cross section shown in Fig. 4(c).

[0024] Returning to Fig. 2, the depth of the recess 141 (dimension in the thickness direction of the light guide plate 14) is S1, and it is assumed that one side dimension of the opening 143 on the surface 14a of the recess 141 is S3 and the diagonal dimension of the opening 143 (maximum dimension of the opening 143) is S2. Also, in the cross section shown in Fig. 2(a), let the angle formed by the side surface 142 of the recess 141 and the plate surface direction of the light guide plate 14 be θ.

[0025] As shown in Figs. 2 and 3, among the plurality of recesses 141 formed in the light guide plate 14, when viewed from a direction (third direction d3) perpendicular to the plate surface of the light guide plate 14, there are recesses 141 provided at positions corresponding to the point light source 12 and having the point light source 12 therein, and recesses 141 provided at positions not corresponding to the point light source 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 the present embodiment, the first recess 141A and the second recess 141B have the same shape and size.

[0026] As shown in Fig. 3, in the present embodiment, the point light source 12 and the recesses 141 are arranged at arrangement pitches P0 and P1 along the first direction d1 and the second direction d2, respectively. Also, in the present embodiment, the opening 143 has a square shape, and the angle α formed by the side 144 of the opening 143 with respect to the arrangement direction of the point light sources 12 is α = 45°. Therefore, the virtual straight lines (the straight lines B1 and B2 shown by the broken lines in the first recess 141A in the upper left of the drawing in FIG. 3) obtained by extending the diagonal lines of the square shape of the opening 143 of the first recess 141A are parallel to the first direction d1 and the second direction d2 which are the arrangement directions of the recess 141 and the point light sources 12, respectively, and the closest other first recesses 141A (point light sources 12) are located on these straight lines B1 and B2. Also, on the virtual straight lines (the straight lines C1 and C2 shown by the dashed-dotted lines in the first recess 141A in the upper left of the drawing in FIG. 3) passing through the midpoints of the sides 144 of the opening 143 and perpendicular to the sides 144, the closest other first recesses 141A (point light sources 12) are not located, and the second-closest first recesses 141A (point light sources 12) are located.

[0027] Here, when the recess 141 has a conical shape, the amount of light incident from the first recess 141A into the light guide plate 14 is substantially uniform along the circumferential direction of the circular shape of the opening 143 when viewed from the direction (the third direction d3) perpendicular to the plate surface of the light guide plate 14. On the other hand, the recess 141 of the present embodiment has a quadrangular pyramid shape, and when viewed from the thickness direction of the light guide plate 14 (the direction perpendicular to the plate surface, the third direction d3), the light incident from the first recess 141A into the light guide plate 14 and traveling in the light guide plate 14 is not uniform in its light amount along the outer peripheral direction of the opening 143.

[0028] In this embodiment, most of the light incident on 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 incident on the light guide plate 14 from the corner is small. That is, when viewed from the direction perpendicular to the plate surface of the light guide plate 14 (the third direction d3), the direction in which the corners of the opening 143 face (the extension directions of the straight lines B1 and B2 which are the extensions of the diagonals of the opening 143 of the first recess 141A in the upper left of the drawing shown in FIG. 3, and the direction in which the closest other point light source 12 is located) has a smaller amount of light than other directions. On the other hand, the amount of light traveling in the direction where the closest other point light source 12 is not located (the directions along the straight lines C1 and C2 passing through the midpoints of the sides of the opening 143 of the first recess 141A in the upper left of the drawing shown in FIG. 3) is larger.

[0029] Therefore, from the viewpoint of reducing brightness unevenness, as described above, the angle α is preferably α > 0°, more preferably satisfies the following (Equation 1), and most preferably satisfies (Equation 1) and α = 45°. By the angle α satisfying α > 0°, among the light incident on the light guide plate 14 from the point light source 12, the light traveling in the direction forming an angle with respect to 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 for explaining the inclination direction of the side 144 of the opening 143. In FIG. 18, as an example, the recesses 141 are shown as being arranged in a square array 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, the length W of the side 144 of the opening 143 of the recess 141, and the angle formed by the straight line orthogonal to the center point of the side 144 with the arrangement direction of the point light sources 12 are defined as φ. At this time, 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), the straight line passing through the midpoint of the side of the opening 143 and orthogonal to the side (for example, the straight lines C1 and C2 shown in FIG. 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 the concave portions 141 are arranged in a square array, the opening 143 has a square shape, the arrangement pitch P1 of the concave portions 141 in the arrangement direction of the point light sources 12 corresponds to the dimension d, the length S3 of the side 144 of the concave portion 141 corresponds to the dimension W, and the angle α corresponds to the angle φ. Therefore, the above (Equation 1) becomes as follows. sinα > S3 / (2×P1) ···(Equation 2) In this embodiment, by satisfying the above (Equation 2) for the angle α, the light incident from the side surface 142 of the first concave portion 141A in which the point light source 12 is located into the light guide plate 14 can reduce the amount of light that is totally reflected by the side surface of the concave portion 141 (second concave portion 141B) closest to the first concave portion 141A at the shortest distance, and can reduce the brightness unevenness caused by only the vicinity of the point light source 12 becoming bright.

[0032] Furthermore, in this embodiment, the angle α satisfies the above (Equation 2), and further α = 45°. Therefore, the direction passing through the midpoint of the side 144 of the opening 143 and perpendicular to the side 144 forms a 45° angle with the first direction d1 and the second direction d2 which are the arrangement directions of the point light sources 12. Also, the corners of the opening 143 face in the direction along the arrangement direction of the point light sources 12, and the straight lines B1 and B2 shown in FIG. 3 are parallel to the arrangement direction of the point light sources 12. By adopting such a configuration, the amount of light that is totally reflected by the side surface of another concave portion 141 (second concave portion 141B) closest to the first concave portion 141A in which the point light source 12 is located at the shortest distance in the arrangement direction of the point light source 12 from the side surface 142 of the first concave portion 141A entering the light guide plate 14 can be significantly suppressed, and the brightness unevenness caused by only the vicinity of the point light source 12 becoming bright can be more effectively reduced. Also, by adopting such a configuration, the brightness of the region D (see FIG. 3) at the center of the unit lattice formed by the arranged concave portions 141 can be improved, and the brightness unevenness can be reduced.

[0033] Also, from the viewpoint of reducing the brightness unevenness on the light emitting surface 14b of the light guide plate 14, it is preferable that the concave portion 141 satisfies 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 the second recesses 141B arranged between adjacent first recesses 141A (between adjacent point light sources 12) is preferably 2 or more and 7 or less, and more preferably 4.

[0034] By the ratio P0 / P1 satisfying the above range, brightness unevenness can be reduced in which only the regions directly above or in the vicinity of the point light sources 12 are bright and the region corresponding to the center between adjacent point light sources 12 is dark on the light-emitting surface 14b of the light guide plate 14. When P0 / P1 > 8 (when 8 or more second recesses 141B are arranged between adjacent point light sources 12 in the arrangement direction of the point light sources 12), the light emission from the regions directly above or in the vicinity of the second recesses 141B located in the vicinity of the point light sources 12 becomes large on the light-emitting surface 14b, the brightness of these regions becomes large, the brightness in the region at the center between adjacent point light sources 12 decreases, and brightness unevenness occurs.

[0035] On the other hand, when P0 / P1 < 3, for example, when 1 second recess 141B is arranged between adjacent point light sources 12 in the arrangement direction of the point light sources 12 (when P0 / P1 = 2), the region between the recess 141 (first recess 141A) corresponding to the point light source 12 and the recess 141 (second recess 141B) not corresponding to the point light source 12 becomes dark, and a difference in brightness occurs. Further, when P0 / P1 < 3, for example, when the number of the second recesses 141B arranged between adjacent point light sources 12 is 0 in the arrangement direction of the point light sources 12 (when P0 / P1 = 1), only the regions directly above or in the vicinity of the point light sources 12 are bright and the region corresponding to the center between adjacent point light sources 12 is dark on the light-emitting surface 14b of the light guide plate 14, and brightness unevenness occurs. Furthermore, in these cases, in order to improve the brightness unevenness, it is necessary to reduce the arrangement pitch P0 of the point light sources 12 and increase the number of the point light sources 12, which is not preferable.

[0036] Also, in the present embodiment, from the viewpoint of reducing brightness unevenness, when the depth S1 of the recess 141 is such that the distance to the recess 141 (second recess 141B) closest in the direction orthogonal to the side 144 of the first recess 141A through the midpoint of the side 144 of the first recess 141A is P2, it is preferable that S1 ≤ P2. 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 closest recess 141 (second recess 141B) (see FIG. 3).

[0037] When S1 > P2, since the recesses 141 are too close to each other, most of the light incident from the first recess 141A corresponding to the point light source 12 into the light guide plate 14 is totally reflected by the side surface of the second recess 141B closest in the direction orthogonal to the side 144 through the midpoint of the side 144 of the first recess 141A and exits from the light emitting surface 14b. As a result, the area directly above or in the vicinity of the point light source 12 (first recess 141A) becomes significantly brighter than other regions, resulting in brightness unevenness. 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 in the direction perpendicular to the side 144 through the midpoint of the side 144 of the first recess 141A satisfy S1 ≤ P2.

[0038] In the present embodiment, it is preferable for the recess 141 to further satisfy the following conditions from the viewpoint of reducing brightness unevenness. That is, when the refractive index of the light guide plate 14 is n, it is preferable that the angle θ formed by the side surface 142 of the recess 141 and the plate surface direction (main surface direction) of the light guide plate 14 is equal to or greater than an angle θ0 satisfying the following (Equation 3). θ0 - asin(sinθ0 / n) = asin(1 / n) ···(Equation 3) When the angle θ satisfies θ ≥ θ0, the light emitted from the point light source 12 in the direction perpendicular to the plate surface of the light guide plate 14 (third direction d3) is refracted by the side surface 142 when entering the light guide plate 14 and enters the light emitting surface 14b at an angle greater than or equal to the critical angle and is totally reflected. Thereby, the light from the point light source 12 can be guided into the light guide plate 14.

[0039] In addition, as shown in FIGS. 4(b) and 4(c), when the angle θ formed by the tangential direction of the side surface 142 and the plate surface direction of the light guide plate 14 changes, when viewing the light guide plate 14 from the thickness direction (the third direction d3), in more than 50% of the region corresponding to the concave portion 141 (the first concave portion 141A) where the point light source 12 is located, it is preferable that the angle θ formed by the side surface 142 and the plate surface of the light guide plate 14 is equal to or greater than the angle θ0. When the above conditions are not satisfied, the light emitted from the point light source 12 is refracted at the side surface 142 and travels inside the light guide plate 14, and enters the light emitting surface 14b directly above the point light source 12 or in its vicinity at an angle smaller than the critical angle and is emitted from the light emitting surface 14b. Only directly above the point light source 12 or in its vicinity becomes bright, which is not preferable.

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

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

[0042] Returning to FIG. 1, the optical sheets 15, 16, and 17 are optical members disposed 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 its traveling direction. In the present embodiment, an example in which three optical sheets are arranged will be described, but the type, number, etc. may be appropriately changed according to the characteristics of the point light source 12 and the like. The optical sheet 15 is disposed on the side of the LCD panel 20 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 this QD sheet, the blue light emitted from the point light source 12 is converted into white light.

[0043] The optical sheet 16 is disposed closer to the LCD panel 20 than the optical sheet 15 and is a prism sheet in which unit prism shapes are arranged on one side. The optical sheet 16 of the present embodiment has convex unit prisms 161 with a triangular cross-sectional shape arranged on the surface on the side of the LCD panel 20 (light-emitting side). When the light emitted from the light guide plate 14 enters 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, the optical sheet 16 has a function of returning it to the side of the light guide plate 14 by total reflection at the two inclined surfaces 162 of the unit prism 161. When the light emitted from the light guide plate 14 enters 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, it is refracted and emitted at the inclined surface 162. That is, the optical sheet 16 has an effect of directing the light in the front direction. The optical sheet 16 of the present embodiment is a prism sheet in which the unit prisms 161 having the second direction d2 (horizontal direction of the screen) as the ridge line direction are arranged along the first direction d1 (vertical direction of the screen).

[0044] The optical sheet 17 is a reflective polarizing sheet that transmits the polarization component in the direction parallel to its transmission axis and reflects the polarization component in the direction parallel to the reflection axis orthogonal to its transmission axis. This optical sheet 17 has the function of reflecting the light of the polarization component that would otherwise be absorbed by the polarizing plate in the LCD panel 20 toward the light guide plate 14 side and transmitting the light of the polarization component that passes through the polarizing plate in the LCD panel 20. Thereby, the utilization efficiency of the light emitted from the light guide plate 14 can be improved.

[0045] In the present embodiment, as an example, the optical sheet 16 is shown as a prism sheet in which the unit prisms 161 having the second direction d2 as the ridge line direction are arranged in the first direction d1. However, the present invention is not limited to this, and according to the usage environment of the display device and the desired optical performance, it may be a prism sheet in which the unit prisms 161 having the first direction d1 as the ridge line direction are arranged in the second direction. Further, 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 first direction d1 as the ridge line direction are arranged in the second direction, or may include a sheet having a diffusing action or the like. The optical sheet disposed between the light guide plate 14 and the LCD panel 20 may be appropriately selected according to the usage environment of the surface light source device 10 or the transmissive display device 1 and the desired optical performance.

[0046] FIG. 5 is a diagram for explaining the state of light traveling in the light guide plate 14 of the present embodiment. In FIG. 5, for ease of understanding, only the light source substrate 11, the point light source 12, the reflection layer 13, and the light guide plate 14 are shown. Further, in FIG. 5, a part of the cross section parallel to the thickness direction of the light guide plate 14 and the arrangement direction of the recesses 141 is enlarged and shown. The light emitted from the point light source 12 enters the light guide plate 14 from the side surface 142 of the concave portion 141 (the first concave portion 141A), and is guided through the light guide plate 14 while undergoing total reflection at the light exit surface 14b of the light guide plate 14 and the surface 14a on the light source substrate 11 side. Then, for example, the light L1 undergoes total reflection at the side surface 142 of another concave portion 141 (the second concave portion 141B in FIG. 5) and exits from the light exit surface 14b. Also, for example, the light L2 enters the concave portion 141 from the side surface 142 of another adjacent concave portion 141 (the second concave portion 141B in FIG. 5), is reflected by the reflection layer 13 provided on the light source substrate 11, etc., re-enters the light guide plate 14 from the side surface 142 of the concave portion 141, is guided through the light guide plate 14, etc., undergoes total reflection at the side surface 142 of another concave portion 141 (the second concave portion 141B) and exits from the light exit 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 through the light guide plate 14, and undergoes total reflection at the light exit surface 14b near the point light source 12. Therefore, the amount of light exiting from the light exit surface 14b directly above or near the point light source 12 is suppressed. Also, according to this embodiment, a part of the light guided through the light guide plate 14 undergoes total reflection at the side surface 142 of the concave portion 141 (the second concave portion 141B) provided at a position not corresponding to the point light source 12, that is, between adjacent point light sources 12, and exits from the light exit surface 14b directly above or near that concave portion 141 (the second concave portion 141B), thereby increasing the brightness of that region. That is, that concave portion 141 (the second concave portion 141B) becomes a pseudo light source. Therefore, according to this embodiment, in the arrangement direction of the point light sources 12, two or more second concave portions 141B are arranged between adjacent point light sources 12, and a plurality of pseudo light sources (the second concave portions 141B) are located between the point light sources 12. Therefore, even if the number of point light sources 12 is small, uneven brightness of the surface light source device and the transmissive display device can be effectively reduced.

[0048] Further, in the present embodiment, the concave portion 141 has a quadrangular pyramid shape with an opening 143 having a square shape as the bottom surface, and its side 144 forms an angle α (where α > 0°) with the arrangement direction of the point light sources 12, and this angle α satisfies sinα > S3 / (2×P1). Thereby, when viewed from the direction (the third direction d3) orthogonal to the plate surface of the light guide plate 14, the amount of light traveling toward the direction in which the corners of the opening 143 face (the direction in which the other closest point light source 12 is located) can be suppressed, and from the first concave portion 141A corresponding to the point light source 12, in a direction different from the direction in which the closest point light source 12 (the first concave portion 141A) is located in the arrangement direction of the point light sources 12, that is, in a direction in which the closest point light source 12 is not located (in the present embodiment, in the first concave portion 141A in the upper left of the drawing in FIG. 3, the directions along the straight lines C1 and C2), more light can be made to travel, so that brightness unevenness can be further reduced. Further, in the present embodiment, since α = 45°, the above effect can be further enhanced.

[0049] Further, in the present embodiment, 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 to the arrangement pitch of the concave portions 141 satisfies the above-described preferable range (3 ≤ P0 / P1 ≤ 8). Therefore, on the light-emitting surface 14b of the light guide plate 14, the brightness in the region between adjacent point light sources 12 (particularly, the region at the center between the point light sources 12) can be improved. Thereby, the difference in brightness between the region directly above or in the vicinity of 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) can be reduced, and the brightness unevenness on the light-emitting surface 14b of the light guide plate 14, that is, the uniformity of the brightness of the surface light source device 10 can be improved. Further, thereby, the arrangement interval of the point light sources 12 can be widened and the number of point light sources 12 used can be reduced. Therefore, according to the present embodiment, the number of point light sources 12 used can be suppressed, and the brightness unevenness on the light-emitting surface 14b of the light guide plate 14, and thus the brightness unevenness on the light-emitting surface of the surface light source device 10 can be suppressed. Further, according to the present embodiment, since the concave portion 141 has a quadrangular pyramid shape with the opening portion 143 having a square shape, the concave portion 141 can be formed more accurately and easily compared to the case of having a conical shape. Generally, such a light guide plate 14 is formed using a mold having a convex portion for shaping the concave portion 141. Forming a convex portion having a quadrangular pyramid shape is easier than forming a convex portion having a conical shape.

[0050] On the other hand, in a light guide plate in which concave portions are formed only at positions corresponding to conventional point light sources, uneven brightness occurs on the light emitting surface of the light guide plate, where the brightness increases only in the region directly above or in the vicinity of the point light sources, and the region between the point light sources (especially the central region between the point light sources 12) becomes dark. In order to eliminate this brightness unevenness, for example, if the thickness of the light guide plate is increased, the brightness of the region between the point light sources improves, but this is not preferable from the viewpoints of thinning, weight reduction, and production cost reduction of the surface light source device and the transmissive display device. Also, increasing the number of point light sources to eliminate brightness unevenness is not preferable from the viewpoints of production cost reduction and power consumption reduction. The surface light source device 10 of the present embodiment solves these problems as described above and can significantly improve brightness unevenness.

[0051] (Evaluation by Samples) Here, surface light source devices of Samples 1 to 7 with different shapes etc. of the concave portions 141 of the light guide plate 14 were prepared, and the brightness (illuminance) on the light emitting surface of the surface light source device 10 was calculated by simulation. Note that the surface light source devices of each sample used in the simulation do not include the optical sheets 15 to 17, and the light emitting surface of the surface light source device 10 is the light emitting surface 14b of the light guide plate 14.

[0052] FIG. 6 is a diagram for explaining the positions of the point light source 12 and the recess 141 during the illuminance measurement in the surface light source device of the sample 7. In FIG. 6, the recess 141 (the first recess 141A) corresponding to the point light source 12 is shown with hatching. Note that in FIG. 6, as an example, the position of the recess 141 in the measurement region M of the surface light source device of the sample 7 is shown. However, in the surface light source devices of samples 1 to 6, although the position of the recess 141 in the measurement region M is the same, its shape and the angle (angle α) formed by the side 144 of the opening 143 with the arrangement direction of the point light sources 12 are different from those of the surface light source device of the sample 7.

[0053] The measurement region M of the surface light source device of each sample for which the simulation was performed is on the light-emitting surface 14b of the light guide plate 14 and is a 6 mm square region centered on the point light source 12 (the first recess 141A) as shown in FIG. 6. Note that in FIG. 6, the position of the recess 141 in the measurement region M of the sample 7 is shown. In the measurement region M on the light-emitting surface of the surface light source device of each sample (samples 1 to 7), the illuminance was calculated at approximately every 0.286 mm from the center of the measurement region M along the straight lines K1 and K2 shown by the broken lines in FIG. 6. The straight line K1 is parallel to the first direction d1, and the straight line K2 is parallel to the second direction d2. Both straight lines pass through the center of the point light source 12 (the first recess 141A) located at the center of the measurement region 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 (the 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. Also, in the surface light source device of the sample 1, the shape of the recess 141 is conical, and the opening 143 serving as the bottom surface is circular. However, in the surface light source devices 10 of samples 2 to 7, the shape of the recess 141 is square pyramidal, and the opening 143 serving as the bottom surface is square.

[0055] Regarding the dimensions of each part, etc., in the surface light source device 10 of the sample 1, the depth S1 of the recess 141 is 0.225 mm, and the diameter of the opening 143 of the recess 141 is 0.03 mm. The angle θ formed by the side surface 142 with the plate surface direction of the light guide plate 14 is 82.5 degrees. For the surface light source devices 10 of Samples 2 to 7, the depth S1 of the recess 141 is 0.19 mm, one side of the opening 143 of the recess 141 is 0.05 mm, and the angle θ formed by the side surface 142 and the plate surface direction of the light guide plate 14 is 82.5°. For the surface light source devices 10 of Samples 2 to 7, the angle α formed by the side 144 of the recess 141 and the arrangement direction of the recesses 141 is 0°, 10°, 20°, 30°, 40°, and 45°, respectively. In the surface light source devices of these respective samples, the point light source 12 was lit, and the presence or absence of brightness unevenness was evaluated from the illuminance distribution within the measurement region M of the light exit surface 14b.

[0056] Figures 7 to 13 are diagrams showing the simulation results of the brightness of the surface light source devices of Samples 1 to 7. In Figures 7 to 13, the diagram of (a) is an image showing the brightness distribution of the measurement region M of the light exit surface 14b when the point light source 12 is lit, the diagram of (b) is a graph showing the illuminance along the straight line K2 of the measurement region M, the diagram of (c) is a graph showing the illuminance along the straight line K1 of the measurement region M, and (d) is a histogram of the brightness distribution in (a). In the graphs shown in the diagrams of (b) in Figures 7 to 13, the vertical axis represents the illuminance (lux), the horizontal axis represents the distance (mm) from the center of the measurement region M (the center of the point light source 12), and in the graphs shown in the diagram of (c), the horizontal axis represents the illuminance (lux), and the vertical axis represents the distance (mm) from the center of the measurement region M (the center of the 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 region directly above and in the vicinity of the recesses 141 and the region between the other recesses 141 in the measurement region M of the light exit surface 14b. Here, the "region between the recesses 141" refers to, that is, the central region between adjacent recesses 141 in the arrangement direction, or the central region D of the unit lattice composed of the arranged recesses 141 (see Figures 3 and 6). In Table 1, regarding the difference in brightness between the region directly above or in the vicinity of the recess 141 and the region between the other recesses, those with a sufficiently small difference are regarded as good and indicated by "◎", those within the allowable range are regarded as acceptable and indicated by "〇", and those greater than the allowable range are regarded as unacceptable and indicated by "×".

[0059] As shown in FIGS. 7 to 13, in the surface light source devices of Samples 1 to 7, the difference in brightness between the region directly above and in the vicinity of the point light source 12 on the light emitting surface 14b and the region between adjacent point light sources 12 (particularly, the region at the center between the point light sources 12 and which is the outer edge of the measurement region M) has been improved.

[0060] In Samples 2 to 7 where the recess 141 has a square pyramid shape, as the angle α formed by the side 144 with the arrangement direction increases, the difference in brightness between the region between the recesses 141 and the region directly above or in the vicinity of the recess 141 is reduced. For example, in the surface light source device of Sample 2 (angle α = 0°), as shown in FIG. 8, vertical and horizontal bright regions along the side 144 are generated in the vicinity of the recess 141, and the difference from the darkness of the region corresponding to the region D (the central region of the unit lattice formed by the recess 141) is extremely large, which is not preferable.

[0061] However, as the angle α increases, the vertical and horizontal bright regions as described above are eliminated, and in the surface light source devices of Samples 3 to 7, the brightness unevenness was reduced to the same level as or lower than that of Sample 1 in which the recess 141 has a conical shape. 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 or near the recess 141 and the region between the other recesses 141 was significantly reduced. Also, in the surface light source devices of Samples 3 to 7, as the angle α increases and approaches 45°, in particular, the region (region D shown in FIGS. 3 and 6) at the center of the unit lattice formed by the recess 141 becomes brighter, and the difference in brightness from other regions becomes smaller. Regarding the improvement in the brightness of such region D in the surface light source devices of Samples 3 to 7, the effect was greater than that of Sample 1 having a conical shape. And in the surface light source device of Sample 7, among the surface light source devices of Samples 1 to 7, the difference in brightness between the region directly above or near the recess 141 and the region between the other recesses 141 was significantly reduced the most.

[0062] Next, Samples 8 and 9 were prepared in which the relationship 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 in the direction orthogonal to the side 144 of the first recess 141A passing through the midpoint of the side 144 was different, and brightness measurement by simulation was performed in the same manner as Samples 1 to 7 described above, and the brightness unevenness was evaluated. Also in Samples 8 and 9, the recesses 141 are arranged in a square array within the measurement region M, and the first recess 141A (point light source 12) is located at the center thereof, similar to Sample 7 shown in FIG. 6 described above. The recesses 141 of the light guide plate 14 of Samples 8 and 9 have a frustum of a square pyramid shape, the opening 143 has a square shape, and its side 144 forms an angle α = 45° with respect to the arrangement direction of the point light sources 12. In these Samples 8 and 9, the dimension of one side of the square of the top surface on the light emitting surface 14b side of the recess 141 is 10% of the dimension of the side 144 of the opening 143 serving as the bottom surface.

[0063] In addition, in Samples 8 and 9, the thickness S0 of the light guide plate 14 is 1.0 mm, the dimension S3 of the side 144 of the opening 143 of the recess 141 is 0.2 mm, and the depth S1 of the recess 141 is 0.72 mm. The arrangement pitch P1 of the recesses 141 in Sample 8 is 1.2 mm, and the arrangement pitch P1 of the recesses 141 in Sample 9 is 1.0 mm. Further, in Samples 8 and 9, the angle θ formed by the side surface 142 with the plate surface direction of the light guide plate 14 is 82.5 degrees. In addition, the distance P2 in Sample 8 is 0.85 mm, and the distance P2 in Sample 9 is 0.7 mm. Therefore, in the surface light source device of Sample 8, S1 ≤ P2 is satisfied, and in the surface light source device of Sample 9, S1 > P2.

[0064] Figures 14 and 15 are diagrams showing the simulation results of the brightness of the surface light source devices of Samples 8 and 9. In Figures 14 and 15, the diagram of (a) is an image showing the brightness distribution of the measurement region M of the light emitting surface 14b when the point light source 12 is lit, the diagram of (b) is a graph showing the illuminance along the straight line K2 of the measurement region M, the diagram of (c) is a graph showing the illuminance along the straight line K1 of the measurement region M, and (d) is a histogram of the brightness distribution in (a). In the graphs shown in the diagrams of (b) in Figures 14 and 15, the vertical axis represents the illuminance (lux), the horizontal axis represents the distance (mm) from the center of the measurement region M (the center of the point light source 12), and in the graph shown in the diagram of (c), the horizontal axis represents the illuminance (lux), and the vertical axis represents the distance (mm) from the center of the measurement region M (the center of the point light source 12). As shown in Figures 14 and 15, in the surface light source device of Sample 9 where S1 > P2, the area directly above and in the vicinity of the point light source 12 becomes significantly brighter than other regions, and the difference in brightness is large. On the other hand, in the surface light source device of Sample 8 where S1 ≤ P2 is satisfied, the brightness directly above and in the vicinity of the point light source 12 is suppressed, and the difference in brightness is suppressed. As a result, the surface light source device of Sample 8 that satisfies S1 ≤ P2 has less brightness unevenness than the surface light source device of Sample 9 where S1 > P2.

[0065] (Other embodiments) In the above-described embodiment, the concave portions 141 were shown as being in a square array, but the present invention is not limited to this, and a so-called staggered array as shown in FIG. 16 described later may also be used. FIG. 16 is a diagram for explaining another embodiment of the arrangement method of the concave portions 141. In FIG. 16, similar to FIG. 3, the light guide plate 14 is shown 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). As shown in FIG. 16, the point light sources 12 (the first concave portions 141A) are arranged at an arrangement pitch P0 in the first direction d1 and the second direction as shown in the above-described embodiment, and are in a so-called square array. However, the concave portions 141 are also arranged at positions shifted by a half pitch (P1 / 2) in the first direction d1 and a half pitch (P1 / 2) in the second direction in the square array shown in FIG. 3 of the above-described embodiment. Even in such a form, similar to the above-described embodiment, brightness unevenness can be sufficiently eliminated. Further, since the concave portions 141 are located at positions corresponding to the region D shown in FIG. 3, brightness unevenness can be further improved.

[0066] (Modified Form) The present invention is not limited to the embodiments described above, 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 have been described by taking an example in which they are orthogonal, but the angle formed by the first direction and the second direction d2 may be other than 90°.

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

[0069] (3) In the present embodiment, the point light source 12 has been described by taking an example in which it emits blue light, but a point light source that emits white light may also be used. In that case, the optical sheet 15 (QD sheet) may not be used.

[0070] (4) In this embodiment, although an example in which the opening 143 of the concave portion 141 has a square shape is shown, the present invention is not limited thereto. 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 corner portion (ridge line portion between the side surfaces 142) of the opening 143 of the concave portion 141 may be a curved surface, or the side 144 may be a convex curve (the side surface 142 may be a convex curved surface). FIG. 17 is a diagram showing a deformed state of the opening 143. In FIG. 17, only the shape of the opening 143 is shown for easy understanding. As shown in FIG. 17, the opening 143 may have the same number of first curves 144a with a large radius of curvature and second curves 144b with a smaller radius of curvature than the first curves 144a, and these may be alternately arranged. In FIG. 17, as an example, an example in which four first curves 144a and four second curves 144b are alternately arranged is shown. The shape of the opening 143 shown in FIG. 17 is a shape approximated to a polygonal shape such as a square.

[0072] In such a case, the tangent line of the first curve 144a intersects the arrangement direction (the first direction d1 and the second direction d2) of the point light sources 12 and forms an angle α (α>0°). In particular, from the viewpoint of reducing brightness unevenness, it is preferable that the angle α formed by the tangent line of the point at the center of the first curve 144a with respect to the arrangement direction of the point light sources 12 is α = 45°. Note that the first curves 144a and the second curves 144b preferably have the same number and are both even numbers of 4 or more. Further, when the concave portion 141 is a pyramid, its top (the point closest to the light-emitting surface side) may be a convex curved surface or the like on the light-emitting surface side. When the concave portion 141 is a frustum of a pyramid, its top surface (the surface closest to the light-emitting surface side) may be a convex curved surface or the like on the light-emitting surface side.

[0073] Note that the present embodiment and the modified forms can be used in appropriate combination, but detailed description thereof will be omitted. Also, the present invention is not limited to the embodiments described above and the like.

Explanation of Reference Numerals

[0074] 1 Transmissive display device 10 Surface light source device 11 Light source substrate 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 panel

Claims

【Claim 1】 a light source substrate having point light sources arranged on one side; a light guide plate positioned on the light-emitting side of the light source substrate and having a plurality of recesses that open to the light source substrate side; A surface light source device comprising: The recesses are: shaped to become smaller as they extend from the light source substrate side toward the light-emitting side along the thickness direction of the light guide plate; when viewed from a direction perpendicular to the plate surface of the light guide plate, having a first recess provided at a position corresponding to the point light source and at least a part of the point light source being located therein, and a second recess provided at a position not corresponding to the point light source; two or more of the second recesses are positioned between adjacent first recesses; the opening of the recess is polygonal when viewed from a direction perpendicular to the plate surface of the light guide plate; when viewed from a direction orthogonal to the plate surface of the light guide plate, the direction orthogonal to each side of the polygonal shape of the opening intersects at least one of the arrangement directions of the point light sources; A surface light source device characterized by the above.

Images