Optical member, surface light source device, and display device

Abstract

To provide an optical member for sufficiently uniformizing in-plane distribution of brightness, a surface light source device using the member, and a display device.SOLUTION: An optical member 30 includes: a first wavelength selection sheet 40, a second wavelength selection sheet 50, and a wavelength conversion sheet 60 overlapping in a first direction D1. The second wavelength selection sheet 50 is positioned on a light-incident side in the first direction D1 of the wavelength conversion sheet 60. The wavelength conversion sheet 60 has a wavelength conversion agent which absorbs primary light and discharges secondary light having a longer wavelength than that of the primary light. The first wavelength selection sheet 40 has a first wavelength selection section. The second wavelength selection sheet 50 has a second wavelength selection section. Transmittance of primary light of the first wavelength selection section is lower than that of secondary light of the first wavelength selection section. Transmittance of secondary light of the second wavelength selection section is lower than that of primary light of the second wavelength selection section.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to an optical member, a surface light source device, and a display device. [Background technology]

[0002] Patent Document 1 discloses a surface light source device that emits light in a planar manner. The surface light source device may be used as a backlight for a liquid crystal display device. The surface light source device of Patent Document 1 is a direct type. In the surface light source device of Patent Document 1, the light source faces the optical member directly. In a direct type surface light source device, uneven brightness occurs due to the arrangement of the light source. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP6299811B Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present disclosure is to achieve a sufficiently uniform in-plane brightness distribution. [Means for solving the problem]

[0005] A first optical member according to an embodiment of the present disclosure includes: A first wavelength selective sheet, a second wavelength selective sheet, and a wavelength conversion sheet are stacked in a first direction, the second wavelength selection sheet is located on a light incident side of the wavelength conversion sheet in the first direction, the wavelength conversion sheet includes a wavelength conversion agent that absorbs primary light and emits secondary light having a longer wavelength than the primary light, the first wavelength selective sheet includes a first wavelength selecting portion, the second wavelength selective sheet includes a second wavelength selective portion, a transmittance of the primary light of the first wavelength selection unit is lower than a transmittance of the secondary light of the first wavelength selection unit, The transmittance of the secondary light from the second wavelength selection section is lower than the transmittance of the primary light from the second wavelength selection section.

[0006] A second optical member according to an embodiment of the present disclosure includes: A first wavelength selective sheet, a second wavelength selective sheet, and a wavelength conversion sheet are stacked in a first direction, the second wavelength selection sheet is located on a light incident side of the wavelength conversion sheet in the first direction, the wavelength conversion sheet includes a wavelength conversion agent that absorbs primary light and emits secondary light having a longer wavelength than the primary light, the first wavelength selection sheet includes the first wavelength selection portion, the second wavelength selective sheet includes the second wavelength selecting portion, a reflectance of the primary light of the first wavelength selection unit is higher than a reflectance of the secondary light of the first wavelength selection unit, an optical member, wherein the reflectance of the secondary light from the second wavelength selection portion is higher than the reflectance of the primary light from the second wavelength selection portion.

[0007] A surface light source device according to an embodiment of the present disclosure includes: Any optical member according to an embodiment of the present disclosure; and a light source located on the light incident side of the optical member in the first direction.

[0008] A display device according to an embodiment of the present disclosure includes: A surface light source device according to any one of the embodiments of the present disclosure; The surface light source device includes a display panel overlapped with the surface light source device. Effect of the Invention

[0009] According to the present disclosure, it is possible to sufficiently uniform the in-plane distribution of brightness while reducing the thickness of the surface light source device. [Brief description of the drawings]

[0010] [Figure 1]FIG. 1 is a diagram for explaining an embodiment of the present invention, and is a perspective view showing a display device and a surface light source device. [Diagram 2] FIG. 2 is a vertical cross-sectional view of the surface light source device shown in FIG. 1, showing an optical member and a light source substrate that can be included in the surface light source device. [Diagram 3] FIG. 3 is a plan view showing the light source substrate shown in FIG. 2, illustrating an example of an arrangement of a plurality of light sources. [Figure 4] FIG. 4 is a cross-sectional view showing the light source substrate shown in FIG. 2, illustrating an example of the light source substrate. [Diagram 5] FIG. 5 is a vertical cross-sectional view showing an example of an arrangement of a first wavelength-selective sheet, a second wavelength-selective sheet, and a wavelength conversion sheet that can be included in the optical member shown in FIG. [Figure 6] FIG. 6 is a vertical sectional view showing a specific example of the wavelength conversion sheet shown in FIG. [Figure 7] FIG. 7 is a graph showing a specific example of optical characteristics of the first wavelength selecting portion that can be included in the first wavelength selecting sheet shown in FIG. [Figure 8] FIG. 8 is a graph showing a specific example of optical characteristics of the first wavelength selecting portion that can be included in the first wavelength selecting sheet shown in FIG. [Figure 9] FIG. 9 is a graph showing a specific example of optical characteristics of the second wavelength selecting portion that can be included in the second wavelength selecting sheet shown in FIG. [Figure 10] FIG. 10 is a perspective view showing an example of a prism sheet that can be included in the optical member shown in FIG. [Figure 11A] 11A is a diagram showing a modified example of the optical member, and is a vertical cross-sectional view showing an example of an optical sheet that can be included in the optical member shown in FIG. [Figure 11B] 1. FIG. 11B is a diagram illustrating a modified example of the optical member, and is a vertical cross-sectional view illustrating another example of an optical sheet that can be included in the optical member illustrated in FIG. [Figure 12A] FIG. 12A is a plan view showing an example of an arrangement of unit optical elements that can be included in the optical sheet shown in FIGS. 11A and 11B. [Figure 12B]FIG. 12B is a perspective view showing a specific example of the unit optical element shown in FIG. 12A. [Figure 12C] FIG. 12C is a diagram corresponding to FIG. 12A and shows another example of the arrangement of unit optical elements. [Figure 13] FIG. 13 is a cross-sectional view illustrating the function of the optical sheet shown in FIGS. 11A and 11B. [Figure 14] FIG. 14 corresponds to FIG. 5 and shows a modified example of the optical member. [Figure 15] FIG. 15 corresponds to FIG. 5 and shows another modified example of the optical member. [Figure 16] FIG. 16 is a vertical sectional view showing an example of a wavelength conversion sheet that can be included in the optical member shown in FIGS. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] One embodiment of the present disclosure is as follows. <1> ~ <16> Regarding.

[0012] <1> A first wavelength selective sheet, a second wavelength selective sheet, and a wavelength conversion sheet are stacked in a first direction, the second wavelength selection sheet is located on a light incident side of the wavelength conversion sheet in the first direction, the wavelength conversion sheet includes a wavelength conversion agent that absorbs primary light and emits secondary light having a longer wavelength than the primary light, the first wavelength selective sheet includes a first wavelength selecting portion, the second wavelength selective sheet includes a second wavelength selective portion, a transmittance of the primary light of the first wavelength selection unit is lower than a transmittance of the secondary light of the first wavelength selection unit, an optical member, wherein the transmittance of the secondary light from the second wavelength selection portion is lower than the transmittance of the primary light from the second wavelength selection portion.

[0013] <2> a reflectance of the primary light of the first wavelength selection unit is higher than a reflectance of the secondary light of the first wavelength selection unit, The reflectance of the secondary light of the second wavelength selection unit is higher than the reflectance of the primary light of the second wavelength selection unit. <1> The optical member according to claim 1.

[0014] <3> A first wavelength selective sheet, a second wavelength selective sheet, and a wavelength conversion sheet are stacked in a first direction, the second wavelength selection sheet is located on a light incident side of the wavelength conversion sheet in the first direction, the wavelength conversion sheet includes a wavelength conversion agent that absorbs primary light and emits secondary light having a longer wavelength than the primary light, the first wavelength selection sheet includes the first wavelength selection portion, the second wavelength selective sheet includes the second wavelength selecting portion, a reflectance of the primary light of the first wavelength selection unit is higher than a reflectance of the secondary light of the first wavelength selection unit, an optical member, wherein the reflectance of the secondary light from the second wavelength selection portion is higher than the reflectance of the primary light from the second wavelength selection portion.

[0015] <4> a transmittance of the primary light of the second wavelength selection unit is higher than a transmittance of the primary light of the first wavelength selection unit, The transmittance of the secondary light of the first wavelength selection unit is higher than the transmittance of the secondary light of the second wavelength selection unit. <1> ~ <3> 13. The optical member according to claim 12 .

[0016] <5> a reflectance of the primary light of the second wavelength selection unit is lower than a reflectance of the primary light of the first wavelength selection unit, The reflectance of the secondary light of the first wavelength selection unit is lower than the reflectance of the secondary light of the second wavelength selection unit. <1> ~ <4> 13. The optical member according to claim 12 .

[0017] <6> the wavelength conversion sheet is located on a light incident side of the first wavelength selection sheet in the first direction, <1> ~ <5> 13. The optical member according to claim 12 .

[0018] <7> the first wavelength selection sheet is located on a light incident side of the wavelength conversion sheet in the first direction; <1> ~ <5> 13. The optical member according to claim 12 .

[0019] <8> a transmittance of the first wavelength selection unit for the primary light incident on the first wavelength selection unit at an incident angle greater than 0° is greater than a transmittance of the first wavelength selection unit for the primary light incident on the first wavelength selection unit at an incident angle of 0°; <1> ~ <7> 13. The optical member according to claim 12 .

[0020] <9> The first wavelength selection portion includes a dielectric multilayer film. <1> ~ <8> 13. The optical member according to claim 12 .

[0021] <10> further comprising an optical sheet located on a light exit side of the first wavelength selection sheet in the first direction, the optical sheet includes an uneven surface facing a light-entering side in the first direction, The optical sheet includes a plurality of unit optical elements that constitute the uneven surface. <1> ~ <9> 13. The optical member according to claim 12 .

[0022] <11> the wavelength conversion sheet includes a wavelength converting portion including the wavelength conversion agent, and an optical element portion located on a light incident side of the wavelength converting portion in the first direction, the wavelength conversion sheet includes an uneven surface facing a light incident side in the first direction, The optical element unit includes a plurality of unit optical elements that constitute the concave-convex surface. <1> ~ <10> 13. The optical member according to claim 12 .

[0023] <12> a reflective polarizing plate overlapping the first wavelength selective sheet, the second wavelength selective sheet, and the wavelength conversion sheet; the reflective polarizing plate is located on a light exit side of the first wavelength selective sheet, the second wavelength selective sheet, and the wavelength conversion sheet in the first direction; <1> ~ <11> 13. The optical member according to claim 12 .

[0024] <13> a prism sheet overlapping the first wavelength selection sheet, the second wavelength selection sheet, and the wavelength conversion sheet; the prism sheet is located on a light exit side in the first direction of the first wavelength selection sheet, the second wavelength selection sheet, and the wavelength conversion sheet; <1> ~ <12> 13. The optical member according to claim 12 .

[0025] <14> <1> ~ <13> An optical member according to any one of claims 1 to 4, a light source located on the light incident side of the optical member in the first direction.

[0026] <15> <1> ~ <13> An optical member according to any one of claims 1 to 4, A surface light source device comprising: a light source substrate including a reflective layer located on the light-entering side of the optical member in the first direction; and a light source that emits light incident on the optical member.

[0027] <16> <14> or <15> The surface light source device according to claim 1, A display device comprising the surface light source device and a display panel overlapped therewith.

[0028] Hereinafter, several embodiments of the present disclosure will be described with reference to the drawings. In the drawings attached to this specification, the scale and the aspect ratio are appropriately changed and exaggerated from those of the actual objects for the convenience of illustration and understanding. Configurations shown in some drawings may be omitted in other drawings.

[0029] Terms that specify shapes or geometric conditions and their degrees, such as "parallel," "orthogonal," and "same," as well as values ​​of lengths and angles, are not limited to their strict meanings, but are interpreted to include the range within which similar functions can be expected.

[0030] Terms such as "sheet," "film," and "plate" are not distinguished from one another solely on the basis of differences in name. For example, an "optical sheet" cannot be distinguished from a member called an optical film or an optical plate solely on the basis of differences in name.

[0031] The normal direction of a sheet-like (sheet-like, plate-like) member refers to the direction parallel to the normal or perpendicular line to the sheet surface of the target sheet-like (film-like, plate-like) member. "Sheet surface (film surface, plate surface)" refers to the surface that coincides with the planar direction of the target sheet-like (film-like, plate-like) member when the target sheet-like (film-like, plate-like) member is viewed overall and globally.

[0032] A plurality of upper limit candidates and a plurality of lower limit candidates for a numerical range may be described in separate sentences. In this description, the numerical range may be formed by combining any one of the upper limit candidates and any one of the lower limit candidates. As an example, consider the description "Parameter B may be A1 or more, A2 or more, or A3 or more. Parameter B may be A4 or less, A5 or less, or A6 or less." In this example, the numerical range of parameter B may be A1 or more and A4 or less, A1 or more and A5 or less, A1 or more and A6 or less, A2 or more and A4 or less, A2 or more and A5 or less, A2 or more and A6 or less, A3 or more and A4 or less, A3 or more and A5 or less, or A3 or more and A6 or less.

[0033] In order to clarify the relationship between directions between the drawings, some drawings show a common first direction D1, a second direction D2, and a third direction D3 by arrows with common symbols. The tip side of the arrow is the first side of each direction. The side opposite the tip of the arrow is the second side of each direction. An arrow pointing into the paper in a direction perpendicular to the paper surface of the drawing is shown by a symbol with an x ​​in a circle, as shown in FIG. 2, for example. An arrow pointing out from the paper in a direction perpendicular to the paper surface of the drawing is shown by a symbol with a dot in a circle, as shown in FIG. 3, for example.

[0034] 1 to 16 are diagrams for explaining an embodiment. FIG. 1 is a perspective view that shows a surface light source device 20 and a display device 10 as an application example of an optical member 30. The display device 10 may display, for example, a moving image, a still image, text information, or an image composed of a combination of these. The display device 10 may be used for various purposes, such as advertisements, presentations, television images, and display of various information, indoors or outdoors. The display device 10 may be used, for example, as a liquid crystal display device for vehicle installation. The display device 10 shown in FIG. 1 includes a surface light source device 20 having a light-emitting surface 20a, and a display panel 15 facing the light-emitting surface 20a.

[0035] FIG. 2 is a vertical cross-sectional view showing a specific example of the surface light source device 20. As shown in FIG. 2, the surface light source device 20 includes, as main components, a light source 23 and an optical member 30 that adjusts the optical path of the light emitted from the light source 23. The optical member 30 faces the light source 23. The optical member 30 is a sheet-like member. The optical member 30 faces the light source 23 in its normal direction. The optical member 30 is a diffusion member that diffuses the light emitted from the light source 23. The optical member 30 can effectively suppress the in-plane variation in illuminance caused by the arrangement of the light source 23. The diffusion by the optical member 30 can effectively uniform the illuminance at each position on the light-emitting side surface 30b of the optical member 30, or the illuminance at each position on a virtual light-receiving surface parallel to the light-emitting side surface 30b located in the vicinity of the light-emitting side surface 30b.

[0036] Hereinafter, a display device 10, a surface light source device 20, and an optical member 30 according to an embodiment will be described with reference to specific examples shown in the drawings.

[0037] As shown in FIG. 1, the display panel 15 is overlapped with the surface light source device 20 in the first direction D1. The display panel 15 faces the light emitting surface 20a of the surface light source device 20. The display panel 15 includes a display surface 15a on which an image is displayed, as a surface facing the opposite side to the surface light source device 20 in the first direction D1, i.e., the first side. In the illustrated example, the display panel 15 is flat. The display panel 15 may extend in a second direction D2 and a third direction D3 perpendicular to the first direction D1. The display panel 15 may have a rectangular shape when observed from the first direction D1. The second direction D2 and the third direction D3 are perpendicular to each other.

[0038] The display panel 15 may be configured as, for example, a transmissive liquid crystal display panel. A part of the light incident from the surface light source device 20 passes through the display panel 15, which is a liquid crystal display panel, to display an image on the display surface 15a. The display panel 15 includes a liquid crystal layer having a liquid crystal material. The light transmittance of the display panel 15 changes depending on the strength of the electric field applied to the liquid crystal layer.

[0039] The surface light source device 20 includes a light emitting surface 20a that emits light in a planar manner. The surface light source device 20 may be configured as a direct-type backlight. The surface light source device 20 includes a light source 23 and an optical member 30. The light source 23 may be provided in a region that overlaps with the optical member 30 when projected in the first direction D1.

[0040] The surface light source device 20 shown in Fig. 2 includes a light source substrate 22 including a light source 23. The light source substrate 22 and the optical member 30 are stacked in this order in a first direction D1. In the first direction D1, the optical member 30 is located between the light source substrate 22 and the display panel 15. The light source substrate 22 and the optical member 30 are sheet-shaped. The light source substrate 22 and the optical member 30 may extend in a second direction D2 and a third direction D3.

[0041] The light source substrate 22 may include a light source 23 and a support substrate 25. In the illustrated example, the light source substrate 22 has a rectangular shape when viewed from a first direction D1.

[0042] The light source 23 includes a light-emitting element that emits light. A light-emitting diode, denoted as LED, may be used as the light-emitting element. The size of the light-emitting diode is not particularly limited. In order to make the image of the light source 23 less noticeable, a small light-emitting diode, for example, a mini LED or a micro LED, may be used. Specifically, the length WL1, WL2 of one side of the light source 23 having a rectangular shape when observed from the first direction D1 shown in FIG. 3 may be 0.5 mm or less, or 0.2 mm or less.

[0043] The wavelength of the light emitted from the light source 23 is defined as the emission wavelength. The emission wavelength may be appropriately selected depending on the application of the surface light source device 20. The light emitted from the light source 23 may be absorbed as primary light LA ​​by a wavelength conversion agent 67 described below. The emission wavelength of the light source 23 may be appropriately selected depending on the optical characteristics of the wavelength conversion agent 67. In the illustrated example, the light source 23 emits blue light. The wavelength of the light emitted from the light source 23 may be 430 nm or more and 500 nm or less.

[0044] The light distribution characteristic of the light source 23 is not particularly limited. The light distribution characteristic of the light source 23 may be a Lambertian light distribution. On the other hand, the light emission luminous intensity distribution of the light source 23 may be configured to obtain a peak luminous intensity in a direction other than the first direction D1. For example, the light source 23 may have a bud wing light distribution disclosed in JP6299811B. As an example, the light source 23 may be composed of only light-emitting elements. As another example, the light source 23 may include optical elements such as a cover and a lens that adjust the light distribution from the light-emitting elements, in addition to the light-emitting elements.

[0045] As in the illustrated surface light source device 20, the light source substrate 22 may include a plurality of light sources 23. The number of light sources 23 is appropriately selected depending on the application of the surface light source device 20, the area of ​​the light-emitting surface 20a, and the like. In order to suppress unevenness in brightness due to the arrangement of the light sources 23, the plurality of light sources 23 included in the surface light source device 20 may be regularly arranged on a surface perpendicular to the first direction D1. As an example of a regular arrangement of the light sources 23, a honeycomb arrangement or a square arrangement may be adopted. In the honeycomb arrangement, the light sources 23 may be arranged at a constant pitch in each of three directions inclined at 60° to each other. In the square arrangement, the light sources 23 may be arranged at a constant pitch in each of two directions perpendicular to each other.

[0046] In the example shown in Fig. 3, the multiple light sources 23 are arranged at a constant pitch in each of the second direction D2 and the third direction D3 which are perpendicular to each other. In the example shown, the arrangement pitch PL1 of the light sources 23 in the second direction D2 and the arrangement pitch PL2 of the light sources 23 in the third direction D3 are the same. The arrangement pitch PL1 and the arrangement pitch PL2 may be different. In the example shown, the second direction D2 and the third direction D3 are parallel to the side edges of the rectangular surface light source device 20 and the optical member 30, respectively. The arrangement pitch PL1 and the arrangement pitch PL2 may each be 0.2 mm or more and 10 mm or less.

[0047] The support substrate 25 constituting the light source substrate 22 together with the plurality of light sources 23 will be described. The support substrate 25 may support the plurality of light sources 23 from the second side in the first direction D1. The support substrate 25 may be sheet-shaped. The support substrate 25 may include a circuit that supplies power to the light sources 23. The support substrate 25 may have light reflectivity that reflects light toward the optical member 30.

[0048] The support substrate 25 shown in FIG. 4 includes a sheet-shaped substrate body 26, and a reflective layer 27 and wiring 29 provided on the substrate body 26. The substrate body 26 may extend in the second direction D2 and the third direction D3. The substrate body 26 may have insulating properties. The substrate body 26 may be a resin film, for example, a polyethylene terephthalate film. The wiring 29 may be electrically connected to the light source 23. The wiring 29 may be electrically connected to a terminal (not shown) of the light source 23 via solder or the like. When the substrate body 26 and the reflective layer 27 are insulating, the wiring 29 may be located between the substrate body 26 and the reflective layer 27 as shown in FIG. 4.

[0049] The reflective layer 27 is laminated on the substrate body 26 from the second side in the first direction. The reflective layer 27 may cover an area on the substrate body 26 where the light source 23 is not arranged. The reflective layer 27 may have reflectivity for light of a specific wavelength emitted by the light source 23 or for light used for emission in the surface light source device 20. The reflection in the reflective layer 27 may be regular reflection, also called specular reflection, diffuse reflection, or anisotropic diffuse reflection. The reflective layer 27 having diffuse reflectivity may include an uneven surface. The reflective layer 27 may be formed of a white reflective layer containing white particles such as titanium oxide or silicon dioxide, thereby imparting diffuse reflectivity to the reflective layer 27. The reflective layer 27 may be a metal layer laminated on the substrate body 26, or a reflective diffractive optical element.

[0050] The optical member 30 will now be described. The optical member 30 adjusts the optical path of the light emitted from the light source 23.

[0051] 2, light from the light source 23 enters the optical member 30 from the second side in the first direction D1. After the optical path of the light is adjusted by the optical member 30, the light exits the optical member 30 to the first side in the first direction D1. With respect to the optical member 30, the second side in the first direction D1 is the light entering side. With respect to the optical member 30, the first side in the first direction D1 is the light exiting side.

[0052] 2, the optical member 30 includes a light incident side surface 30a and a light exiting side surface 30b. The light incident side surface 30a faces the light incident side in the first direction D1. The light exiting side surface 30b faces the light exiting side in the first direction D1.

[0053] 2 and 5, the optical member 30 includes a first wavelength selection sheet 40, a second wavelength selection sheet 50, and a wavelength conversion sheet 60. The first wavelength selection sheet 40, the second wavelength selection sheet 50, and the wavelength conversion sheet 60 are stacked in a first direction D1. The first direction D1 is the stacking direction of the first wavelength selection sheet 40, the second wavelength selection sheet 50, and the wavelength conversion sheet 60. The second wavelength selection sheet 50 is located on the light incident side of the wavelength conversion sheet 60 in the first direction D1.

[0054] As shown in Fig. 5, the wavelength conversion sheet 60 may be located on the light-entering side in the first direction D1 of the first wavelength selection sheet 40. In the example shown in Fig. 5, the optical member 30 includes the second wavelength selection sheet 50, the wavelength conversion sheet 60, and the first wavelength selection sheet 40, in this order from the light-entering side to the light-outgoing side in the first direction D1. The wavelength conversion sheet 60 is located between the first wavelength selection sheet 40 and the second wavelength selection sheet 50 in the first direction D1.

[0055] As described later, the first wavelength selection sheet 40 may be located on the light entrance side in the first direction D1 of the wavelength conversion sheet 60. The first wavelength selection sheet 40 may be located on the light exit side in the first direction D1 of the second wavelength selection sheet 50. The first wavelength selection sheet 40 may be located on the light entrance side in the first direction D1 of the second wavelength selection sheet 50.

[0056] The first wavelength selection sheet 40, the second wavelength selection sheet 50, and the wavelength conversion sheet 60 may be in a sheet shape. The first direction D1 may be a normal direction of the first wavelength selection sheet 40, the second wavelength selection sheet 50, and the wavelength conversion sheet 60. The first wavelength selection sheet 40, the second wavelength selection sheet 50, and the wavelength conversion sheet 60 may extend in the second direction D2 and the third direction D3.

[0057] Among the multiple sheets included in the optical member 30, two sheets adjacent in the first direction D1 may be joined to each other. Two sheets adjacent in the first direction D1 may be in contact with each other. In this example, two sheets adjacent in the first direction D1 may simply be in contact with each other and not be joined to each other. Two sheets adjacent in the first direction D1 may be separated from each other in the first direction D1.

[0058] The wavelength conversion sheet 60 has a function of converting the wavelength of incident light. The wavelength conversion sheet 60 converts the wavelength of a part of the incident light. The wavelength conversion sheet 60 includes a wavelength conversion agent 67. The wavelength conversion agent 67 absorbs the primary light LA ​​and emits secondary light LB. The wavelength of the secondary light LB is longer than the wavelength of the primary light LA.

[0059] 5 and 6, the wavelength conversion sheet 60 may include a first surface 60a and a second surface 60b. The first surface 60a faces the light-entering side in the first direction D1. The second surface 60b faces the light-emitting side in the first direction D1. The first surface 60a and the second surface 60b may be a pair of main surfaces of the sheet-like wavelength conversion sheet 60. The first surface 60a and the second surface 60b may be parallel flat surfaces. The first surface 60a and the second surface 60b may be perpendicular to the first direction D1.

[0060] As shown in Fig. 6, the wavelength conversion sheet 60 may include a first barrier layer 63, a wavelength converting portion 65, and a second barrier layer 64 in this order. The first barrier layer 63, the wavelength converting portion 65, and the second barrier layer 64 are stacked in this order in a first direction D1. The first barrier layer 63, the wavelength converting portion 65, and the second barrier layer 64 are positioned in this order from the light incident side to the light output side in the first direction D1. The first barrier layer 63, the wavelength converting portion 65, and the second barrier layer 64 are sheet-shaped. The first barrier layer 63, the wavelength converting portion 65, and the second barrier layer 64 extend in the second direction D2 and the third direction D3.

[0061] 6, the wavelength converting portion 65 includes a first surface 65a and a second surface 65b. The first surface 65a faces the light-entering side in the first direction D1. The second surface 65b faces the light-emitting side in the first direction D1. The wavelength converting portion 65 may include a base material portion 66 that holds a wavelength conversion agent 67. A resin may be used as the base material portion 66. Examples of the resin that constitutes the base material portion 66 include a thermoplastic resin, a cured product of a thermosetting resin composition, and a cured product of an ionizing radiation curable resin composition.

[0062] The wavelength conversion agent 67 absorbs the primary light LA ​​of a certain wavelength and emits secondary light LB having a wavelength longer than the wavelength of the primary light LA. Quantum dots or phosphors may be used as the wavelength conversion agent 67. The wavelength of the primary light LA ​​may be the wavelength of the light emitted from the light source 23. In other words, the light emitted from the light source 23 may include the primary light LA ​​of a certain wavelength.

[0063] A quantum dot is a nanometer-sized semiconductor particle. A quantum dot may be composed of one type of semiconductor compound. A quantum dot may be composed of two or more types of semiconductor compounds. A quantum dot may have a core-shell structure having, for example, a core made of a semiconductor compound and a shell made of a semiconductor compound different from the core.

[0064] Examples of the material of the core of the quantum dot include II-VI group semiconductor compounds such as MgS, MgSe, MgTe, CaS, CaSe, CaTe, SrS, SrSe, SrTe, BaS, BaSe, BaTe, ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, HgS, HgSe and HgTe. Examples of the material of the core of the quantum dot include III-V group semiconductor compounds such as AlN, AlP, AlAs, AlSb, GaAs, GaP, GaN, GaSb, InN, InAs, InP, InSb, TiN, TiP, TiAs and TiSb. Examples of the material of the core of the quantum dot include semiconductor compounds such as IV group semiconductors such as Si, Ge and Pb, or semiconductor crystals containing semiconductors.

[0065] When using core-shell quantum dots, a semiconductor constituting the shell may be a material having a higher band gap than the semiconductor compound forming the core. In this case, excitons are confined in the core, and the luminous efficiency of the quantum dots can be improved. Examples of core-shell structures (core / shell) having such a band gap relationship include CdSe / ZnS, CdSe / ZnSe, CdSe / CdS, CdTe / CdS, InP / ZnS, Gap / ZnS, Si / ZnS, InN / GaN, InP / CdSSe, InP / ZnSeTe, InGaP / ZnSe, InGaP / ZnS, Si / AlP, InP / ZnSTe, InGaP / ZnSTe, InGaP / ZnSSe, etc.

[0066] The size of the quantum dots is adjusted in consideration of the desired wavelength of the secondary light LB. As the particle diameter of the quantum dots becomes smaller, the energy band gap becomes larger. As the crystal size becomes smaller, the emission of the quantum dots shifts to the blue side, that is, to the higher energy side. The wavelength of the secondary light LB can be adjusted by changing the size of the quantum dots. The average particle diameter of the quantum dots may be 20 nm or less, 0.5 nm or more and 20 nm or less, or 1 nm or more and 10 nm or less. The shape, dispersion state, etc. of the quantum dots are identified by a transmission electron microscope (TEM). The crystal structure and particle diameter of the quantum dots are identified by X-ray crystal diffraction (XRD).

[0067] The wavelength conversion section 65 may include a plurality of quantum dots with different emission wavelengths as the wavelength conversion agent 67. By adjusting the content of each quantum dot, the color of the light emitted from the surface light source device 20 can be adjusted. In the example shown in FIG. 6, the wavelength conversion agent 67 includes a first conversion agent 67A and a second conversion agent 67B. The first conversion agent 67A and the second conversion agent 67B have different sizes. The first conversion agent 67A and the second conversion agent 67B emit light with different wavelengths.

[0068] As a specific example, the light source 23 may emit blue light having a wavelength of 430 nm or more and 500 nm or less. The first conversion agent 67A may absorb the primary light LA ​​from the light source 23 and emit green light having a wavelength of 500 nm or more and 600 nm or less as the first secondary light LB1. The second conversion agent 67B may absorb the primary light LA ​​from the light source 23 and emit red light having a wavelength of 600 nm or more and 750 nm or less as the second secondary light LB2. According to this example, the surface light source device 20 can emit light of various colors by additive color mixing of the first secondary light LB1, the second secondary light LB2, and the primary light LA ​​that has not been wavelength-converted by the wavelength conversion unit 65. By adjusting the contents of the first conversion agent 67A and the second conversion agent 67B, the surface light source device 20 can emit white light.

[0069] The wavelength converting portion 65 may contain a light diffusing component that diffuses transmitted light. The light diffusing component may be dispersed in the base material portion 66. Examples of the light diffusing component include a metal compound, a porous substance containing gas, resin beads surrounding a metal compound, white fine particles, and simple air bubbles.

[0070] In the illustrated example, the wavelength conversion agent 67 includes a first conversion agent 67A that absorbs the primary light LA ​​and emits a first secondary light LB1, and a second conversion agent 67B that absorbs the primary light LA ​​and emits a second secondary light LB2. In this example, the wavelength of the second secondary light LB2 is longer than the wavelength of the first secondary light LB1.

[0071] The first barrier layer 63 is bonded to a first surface 65a of the wavelength converting portion 65. The second barrier layer 64 is bonded to a second surface 65b of the wavelength converting portion 65. The first barrier layer 63 constitutes the first surface 60a of the wavelength converting sheet 60. The second barrier layer 64 constitutes the second surface 60b of the wavelength converting sheet 60. The first barrier layer 63 and the second barrier layer 64 have the function of protecting the wavelength converting agent 67 from oxygen and moisture.

[0072] The first barrier layer 63 and the second barrier layer 64 may have oxygen barrier properties. In this example, the oxygen permeability of the first barrier layer 63 and the second barrier layer 64 is 1.0 cc / (m 2·day·atm) or less is acceptable, and 5.0×10 -1 cc / (m 2 ·day·atm) or less. The oxygen permeability is a value measured in accordance with JIS K7126-2:2006 "Appendix A (Regulations): Test method for oxygen gas permeability by electrolytic sensor method" under conditions of temperature 23°C and relative humidity difference 90%RH. The oxygen permeability measuring device may be "OX-TRAN 2 / 20" manufactured by MOCON, USA.

[0073] The first barrier layer 63 and the second barrier layer 64 may have water vapor barrier properties. In this example, the water vapor permeability of the first barrier layer 63 and the second barrier layer 64 is 1.0 g / (m 2 24h) or less is also acceptable, 5.0×10 -1 g / (m 2 The water vapor permeability is a value measured in an environment with a temperature of 40°C and a relative humidity difference of 90% RH in accordance with JIS K7129-2:2019. The water vapor permeability measuring device may be a PERMATRAN-w 3 / 33 manufactured by MOCON, USA.

[0074] The first barrier layer 63 and the second barrier layer 64 can be produced using a material capable of exhibiting barrier properties by a physical vapor deposition (PVD) method such as a sputtering method or an ion plating method, a deposition method such as a chemical vapor deposition (CVD) method, or a coating method such as roll coating or spin coating. As the material, an inorganic oxide, a metal, a sol-gel material, or the like may be used. As the inorganic oxide, silicon oxide (SiO x ), aluminum oxide (Al n O m ), titanium oxide (TiO2), yttrium oxide, boron oxide (B2O3), calcium oxide (CaO), silicon carbide oxide (SiO x N y C z Examples of the metal include Ti, Al, Mg, Zr, etc. Examples of the sol-gel material include siloxane-based sol-gel materials.

[0075] The first wavelength selection sheet 40 includes a first wavelength selection portion 45. The transmittance of the first wavelength selection portion 45 has wavelength dependency. The transmittance of the first wavelength selection portion 45 changes depending on the wavelength. The transmission characteristics of the first wavelength selection portion 45 are adjusted so that the transmittance changes depending on the wavelength.

[0076] The reflectance of the first wavelength selecting section 45 may have wavelength dependency. The reflectance of the first wavelength selecting section 45 may change depending on the wavelength. The reflection characteristics of the first wavelength selecting section 45 may be adjusted so that the reflectance changes depending on the wavelength. The transmittance of the first wavelength selecting section 45 may change depending on the wavelength due to the reflectance changing depending on the wavelength.

[0077] 5, the first wavelength selection sheet 40 may include a first surface 40a and a second surface 40b. The first surface 40a faces the light-entering side in the first direction D1. The second surface 40b faces the light-emitting side in the first direction D1. The first surface 40a and the second surface 40b may be a pair of main surfaces of the sheet-like first wavelength selection sheet 40. The first surface 40a and the second surface 40b may be parallel flat surfaces. The first surface 40a and the second surface 40b may be perpendicular to the first direction D1.

[0078] The first wavelength selection sheet 40 may include only the first wavelength selection portion 45. The first wavelength selection sheet 40 may be composed of only the first wavelength selection portion 45. As shown in FIG. 5, the first wavelength selection portion 45 may include a first surface 45a and a second surface 45b. The first surface 45a is oriented toward the light-entering side in the first direction D1. The second surface 45b is oriented toward the light-emitting side in the first direction D1. The first surface 45a and the second surface 45b may be a pair of main surfaces of the sheet-like first wavelength selection portion 45. The first surface 45a and the second surface 45b may be parallel flat surfaces. The first surface 45a and the second surface 45b may be perpendicular to the first direction D1. The first surface 45a of the first wavelength selection portion 45 may constitute the first surface 40a of the first wavelength selection sheet 40. The second surface 45b of the first wavelength selection portion 45 may constitute the second surface 40b of the first wavelength selection sheet 40.

[0079] The first wavelength selection section 45 may reflect the low wavelength region of the visible light wavelength range. The first wavelength selection section 45 may transmit the high wavelength region of the visible light wavelength range. The first wavelength selection section 45 may function as a high-pass filter. Visible light means light having a wavelength of 380 nm or more and 780 nm or less. The visible light wavelength range is 380 nm or more and 780 nm or less.

[0080] The transmittance of the primary light LA ​​of the first wavelength selecting unit 45 may be lower than the transmittance of the secondary light LB of the first wavelength selecting unit 45. The transmittance of the first wavelength selecting unit 45 for the light emitted from the light source 23 may be lower than the transmittance of the first wavelength selecting unit 45 for the light emitted from the light source 23 and whose wavelength has been converted by the wavelength converting unit 65. In the example shown in FIG. 6, the transmittance of the primary light LA ​​of the first wavelength selecting unit 45 may be lower than the transmittance of the first secondary light LB1 of the first wavelength selecting unit 45. The transmittance of the primary light LA ​​of the first wavelength selecting unit 45 may be lower than the transmittance of the second secondary light LB2 of the first wavelength selecting unit 45.

[0081] The transmittance of the first wavelength selection unit 45 for light having a wavelength of 430 nm or more and 500 nm or less may be lower than the transmittance of the first wavelength selection unit 45 for light having a wavelength of 500 nm or more and 600 nm or less. The transmittance of the first wavelength selection unit 45 for light having a wavelength of 430 nm or more and 500 nm or less may be lower than the transmittance of the first wavelength selection unit 45 for light having a wavelength of 600 nm or more and 750 nm or less.

[0082] The transmittance of the first wavelength selection unit 45 for blue light may be lower than the transmittance of the first wavelength selection unit 45 for green light. The transmittance of the first wavelength selection unit 45 for blue light may be lower than the transmittance of the first wavelength selection unit 45 for red light.

[0083] The transmittance of the first wavelength selection unit 45 may decrease as the wavelength becomes shorter in the wavelength range of 500 nm or more and 550 nm or less. The transmittance of the first wavelength selection unit 45 may decrease as the wavelength becomes shorter in the wavelength range of 475 nm or more and 575 nm or less. The transmittance of the first wavelength selection unit 45 may decrease as the wavelength becomes shorter in the wavelength range of 450 nm or more and 600 nm or less. The transmittance of the first wavelength selection unit 45 may decrease as the wavelength becomes shorter in the wavelength range of 430 nm or more and 750 nm or less.

[0084] In the wavelength range of 430 nm or more and 500 nm or less, the transmittance of the first wavelength selection unit 45 may be 20% or less, 15% or less, 10% or less, or 5% or less. In the wavelength range of 430 nm or more and 500 nm or less, the transmittance of the first wavelength selection unit 45 may be 0% or more, or may be greater than 0%.

[0085] In the wavelength range of 550 nm or more and 700 nm or less, the transmittance of the first wavelength selection unit 45 may be 50% or more, 60% or more, 70% or more, or 80% or more. In the wavelength range of 550 nm or more and 700 nm or less, the transmittance of the first wavelength selection unit 45 may be 100% or less, or may be less than 100%.

[0086] The reflectance of the primary light LA ​​of the first wavelength selecting unit 45 may be higher than the reflectance of the secondary light LB of the first wavelength selecting unit 45. The reflectance of the first wavelength selecting unit 45 for the light emitted from the light source 23 may be higher than the reflectance of the first wavelength selecting unit 45 for the light emitted from the light source 23 and whose wavelength has been converted by the wavelength converting unit 65. The reflectance of the primary light LA ​​of the first wavelength selecting unit 45 may be higher than the reflectance of the first secondary light LB1 of the first wavelength selecting unit 45. The reflectance of the primary light LA ​​of the first wavelength selecting unit 45 may be higher than the reflectance of the second secondary light LB2 of the first wavelength selecting unit 45.

[0087] The reflectance of the first wavelength selection unit 45 for light having a wavelength of 430 nm or more and 500 nm or less may be higher than the reflectance of the first wavelength selection unit 45 for light having a wavelength of 500 nm or more and 600 nm or less. The reflectance of the first wavelength selection unit 45 for light having a wavelength of 430 nm or more and 500 nm or less may be higher than the reflectance of the first wavelength selection unit 45 for light having a wavelength of 600 nm or more and 750 nm or less.

[0088] The reflectance of the first wavelength selecting unit 45 for blue light may be higher than the reflectance of the first wavelength selecting unit 45 for green light. The reflectance of the first wavelength selecting unit 45 for blue light may be higher than the reflectance of the first wavelength selecting unit 45 for red light.

[0089] The reflectance of the first wavelength selection unit 45 may increase as the wavelength becomes shorter in the wavelength range of 500 nm or more and 550 nm or less. The reflectance of the first wavelength selection unit 45 may increase as the wavelength becomes shorter in the wavelength range of 475 nm or more and 575 nm or less. The reflectance of the first wavelength selection unit 45 may increase as the wavelength becomes shorter in the wavelength range of 450 nm or more and 600 nm or less. The reflectance of the first wavelength selection unit 45 may increase as the wavelength becomes shorter in the wavelength range of 430 nm or more and 750 nm or less.

[0090] In the wavelength range of 430 nm or more and 500 nm or less, the reflectance of the first wavelength selection portion 45 may be 80% or more, 85% or more, 90% or more, or 95% or more. In the wavelength range of 430 nm or more and 500 nm or less, the reflectance of the first wavelength selection portion 45 may be 100% or less, or may be less than 100%.

[0091] In the wavelength range of 550 nm or more and 700 nm or less, the reflectance of the first wavelength selection portion 45 may be 50% or less, 40% or less, 30% or less, or 20% or less. In the wavelength range of 550 nm or more and 700 nm or less, the reflectance of the first wavelength selection portion 45 may be 0% or more, or may be greater than 0%.

[0092] Fig. 7 is a graph showing a specific example of the transmission characteristics of the first wavelength selection section 45. Fig. 7 shows a specific example of the spectral transmittance of the first wavelength selection section 45. In the graph of Fig. 7, the vertical axis represents the spectral transmittance (%). In the graph of Fig. 7, the horizontal axis represents the wavelength (nm).

[0093] The optical characteristics of the first wavelength selection section 45, i.e., the transmission characteristics and reflection characteristics of the first wavelength selection section 45, are assumed to be such that the first surface 45a and the second surface 45b are parallel and that the first surface 45a and the second surface 45b are adjacent to an air layer.

[0094] The transmittance (%) of the first wavelength selection unit 45 for each wavelength and the reflectance (%) of the first wavelength selection unit 45 for each wavelength are values ​​measured in accordance with JIS Z 8722:2009. The transmittance is measured at an incident angle of 0°. The geometric condition of irradiation and reception when measuring the transmittance is the geometric condition f specified in JIS Z8722:2009. The reflectance is measured using method b using a one-path spectrophotometer specified in JIS Z 8722:2009. The reflectance is measured at an incident angle of 5°. The geometric condition of irradiation and reception when measuring the reflectance is the geometric condition d specified in JIS Z8722:2009.

[0095] The incident angle refers to the angle (°) between the normal direction of the sheet-like member into which the light enters and the direction of travel of the incident light. The exit angle refers to the angle (°) between the normal direction of the sheet-like member into which the light exits and the direction of travel of the exiting light.

[0096] Examples of the first wavelength selection unit 45 having the above-mentioned optical characteristics include a dielectric multilayer film 46, a reflective volume hologram, a cholesteric liquid crystal structure layer, a retroreflective film, and a reflective diffractive optical element. The dielectric multilayer film is excellent in that it has a relatively high degree of freedom in designing the reflection characteristics and transmission characteristics. The optical characteristics shown in FIG. 7 and FIG. 8 described later are examples of the optical characteristics of the dielectric multilayer film 46.

[0097] The dielectric multilayer film 46 constituting the first wavelength selection section 45 may include low-refractive index layers and high-refractive index layers having different refractive indices, which are alternately stacked. The low-refractive index layers and high-refractive index layers may be layers of inorganic compounds or resin layers. The multilayer film constituting the dielectric multilayer film 46 may include a protective film on one side or both sides. The material of the protective film may be polyethylene terephthalate or polyethylene naphthalate. The thickness of the protective film may be 5 μm or more. A co-extrusion method or the like may be adopted as a method for manufacturing the dielectric multilayer film. More specifically, the dielectric multilayer film 46 may be manufactured according to the manufacturing method of a laminated film described in JP2008-200861A. A commercially available laminated film may be used as the dielectric multilayer film. Examples of commercially available dielectric multilayer films include Picasus (registered trademark) manufactured by Toray Industries, Inc. and ESR manufactured by 3M.

[0098] The transmission characteristics and reflection characteristics of the first wavelength selection unit 45 may have incidence angle dependency. The transmission characteristics and reflection characteristics of the first wavelength selection unit 45 may change depending on the incidence angle. The transmission characteristics of the first wavelength selection unit 45 may be adjusted so that the transmittance changes depending on the incidence angle. The reflection characteristics of the first wavelength selection unit 45 may be adjusted so that the reflectance changes depending on the incidence angle.

[0099] The transmittance of the first wavelength selection unit 45 for light of a specific wavelength incident on the first wavelength selection unit 45 at an incident angle of 0° may be smaller than the transmittance of the first wavelength selection unit 45 for light of a specific wavelength incident on the first wavelength selection unit 45 at an incident angle larger than 0°. In other words, the transmittance of the first wavelength selection unit 45 for specific wavelength light incident perpendicularly may be smaller than the transmittance of the first wavelength selection unit 45 for specific wavelength light incident on the first wavelength selection unit 45 from at least one oblique direction.

[0100] The light of the specific wavelength can be appropriately set depending on the application of the surface light source device 20 and the optical member 30. The light of the specific wavelength may be light having a wavelength of 430 nm or more and 500 nm or less. The light of the specific wavelength may be light emitted from the light source 23.

[0101] The reflectance of the first wavelength selection unit 45 for light of a specific wavelength incident on the first wavelength selection unit 45 at an incident angle of 0° may be higher than the reflectance of the first wavelength selection unit 45 for light of a specific wavelength incident on the first wavelength selection unit 45 at an incident angle greater than 0°. In other words, the reflectance of the first wavelength selection unit 45 for light of a specific wavelength incident perpendicularly may be higher than the reflectance of the first wavelength selection unit 45 for light of a specific wavelength incident on the first wavelength selection unit 45 from at least one oblique direction.

[0102] The transmittance of the first wavelength selection unit 45 for light of a specific wavelength incident at an incident angle of 0° may be 5% or less, 3% or less, or 1% or less. The reflectance of the first wavelength selection unit 45 for light of a specific wavelength incident at an incident angle of 0° may be 95% or more, 97% or more, or 99% or more.

[0103] The transmittance of the first wavelength selection unit 45 for light of a specific wavelength incident on the first wavelength selection unit 45 at an incident angle of 0° or more and 40° or less in absolute value may be ½ or less, ⅕ or less, or 1 / 10 or less of the maximum transmittance of the first wavelength selection unit 45. The transmittance of the first wavelength selection unit 45 for light of a specific wavelength incident on the first wavelength selection unit 45 at an incident angle of 0° or more and 45° or less in absolute value may be ½ or less, ⅕ or less, or 1 / 10 or less of the maximum transmittance of the first wavelength selection unit 45. The transmittance of the first wavelength selection unit 45 for light of a specific wavelength incident on the first wavelength selection unit 45 at an incident angle of 0° or more and 50° or less in absolute value may be ½ or less, ⅕ or less, or 1 / 10 or less of the maximum transmittance of the first wavelength selection unit 45.

[0104] The transmittance of the first wavelength selection unit 45 for light of a specific wavelength incident on the first wavelength selection unit 45 at an incident angle of 0° or more and 40° or less in absolute value may be 10% or less, 5% or less, or 1% or less. The transmittance of the first wavelength selection unit 45 for light of a specific wavelength incident on the first wavelength selection unit 45 at an incident angle of 0° or more and 45° or less in absolute value may be 10% or less, 5% or less, or 1% or less. The transmittance of the first wavelength selection unit 45 for light of a specific wavelength incident on the first wavelength selection unit 45 at an incident angle of 0° or more and 50° or less in absolute value may be 15% or less, 10% or less, or 5% or less.

[0105] The reflectance of the first wavelength selection unit 45 for light of a specific wavelength incident on the first wavelength selection unit 45 at an incident angle of 0° or more and 40° or less in absolute value may be 90% or more, 95% or more, or 99% or more. The reflectance of the first wavelength selection unit 45 for light of a specific wavelength incident on the first wavelength selection unit 45 at an incident angle of 0° or more and 45° or less in absolute value may be 90% or more, 95% or more, or 99% or more. The reflectance of the first wavelength selection unit 45 for light of a specific wavelength incident on the first wavelength selection unit 45 at an incident angle of 0° or more and 50° or less in absolute value may be 85% or more, 90% or more, or 95% or more.

[0106] The maximum value of the transmittance of the first wavelength selection unit 45 for light of a specific wavelength may be 30% or more, 40% or more, or 45% or more. The maximum value of the transmittance of the first wavelength selection unit 45 for light of a specific wavelength may be 100% or less, less than 100%, or 50% or less. The incident angle at which the maximum value of the transmittance of the first wavelength selection unit 45 for light of a specific wavelength is obtained may be 50° or more, 60° or more, or 65° or more in absolute value. The incident angle at which the maximum value of the transmittance of the first wavelength selection unit 45 for light of a specific wavelength is obtained may be 80° or less, or 75° or less in absolute value.

[0107] The minimum value of the reflectance of the first wavelength selection unit 45 for light of a specific wavelength may be 30% or more, 40% or more, or 45% or more. The minimum value of the reflectance of the first wavelength selection unit 45 for light of a specific wavelength may be 100% or less, less than 100%, or 70% or less. The incident angle at which the minimum value of the reflectance of the first wavelength selection unit 45 for light of a specific wavelength is obtained may be 50° or more, 60° or more, or 65° or more in absolute value. The incident angle at which the minimum value of the reflectance of the first wavelength selection unit 45 for light of a specific wavelength is obtained may be 80° or less, or 75° or less in absolute value.

[0108] Fig. 8 is a graph showing a specific example of the transmission characteristics of the first wavelength selection unit 45. The graph in Fig. 8 shows the relationship between the spectral transmittance and the angle of incidence for light with a wavelength of 450 nm. In the graph in Fig. 8, the vertical axis represents the spectral transmittance (%) for light with a wavelength of 450 nm. In the graph in Fig. 8, the horizontal axis represents the angle of incidence (°).

[0109] The optical characteristics of the first wavelength selection section 45, i.e., the transmission characteristics and reflection characteristics of the first wavelength selection section 45, are assumed to be such that the first surface 45a and the second surface 45b are parallel and that the first surface 45a and the second surface 45b are adjacent to an air layer.

[0110] The transmittance (%) of the first wavelength selection unit 45 at each incident angle (°) for a specific wavelength is a value measured in accordance with JIS Z 8722: 2009. The geometric conditions of irradiation and reception when measuring the transmittance at each incident angle (°) are the geometric conditions f specified in JIS Z 8722: 2009, except for selecting the incident angle.

[0111] The reflectance (%) of the first wavelength selection unit 45 at each incident angle (°) for a specific wavelength shall be a value measured in accordance with JIS Z 8722:2009. In measuring the reflectance, method b using a spectrophotometer with one optical path as specified in JIS Z 8722:2009 shall be adopted. The incident angle shall be 5° for measuring the reflectance. The geometric conditions of irradiation and reception when measuring the reflectance at each incident angle (°) shall be the geometric conditions d as specified in JIS Z8722:2009, except for the selection of the incident angle.

[0112] Optical characteristics that exhibit wavelength dependence as well as incidence angle dependence can be realized by a dielectric multilayer film 46, a reflective volume hologram, a cholesteric liquid crystal structure layer, a retroreflective film, a reflective diffractive optical element, etc. Dielectric multilayer films are excellent in that they offer a relatively high degree of freedom in designing the reflection and transmission characteristics. The optical characteristics shown in FIG. 7 and FIG. 8, which will be described later, are optical characteristics investigated for the same dielectric multilayer film 46.

[0113] The second wavelength selection sheet 50 includes a second wavelength selection portion 55. The transmittance of the second wavelength selection portion 55 has wavelength dependency. The transmittance of the second wavelength selection portion 55 changes depending on the wavelength. The transmission characteristics of the second wavelength selection portion 55 are adjusted so that the transmittance changes depending on the wavelength.

[0114] The reflectance of the second wavelength selecting section 55 may have wavelength dependency. The reflectance of the second wavelength selecting section 55 may change depending on the wavelength. The reflection characteristics of the second wavelength selecting section 55 may be adjusted so that the reflectance changes depending on the wavelength. The transmittance of the second wavelength selecting section 55 may change depending on the wavelength due to the reflectance changing depending on the wavelength.

[0115] As shown in FIG. 5, the second wavelength selection sheet 50 may include a first surface 50a and a second surface 50b. The first surface 50a faces the light-entering side in the first direction D1. The second surface 50b faces the light-emitting side in the first direction D1. The first surface 50a and the second surface 50b may be a pair of main surfaces of a sheet-like second wavelength selection sheet 50. The first surface 50a of the second wavelength selection sheet 50 may constitute the light-entering side surface 30a of the optical member 30. The first surface 50a and the second surface 50b may be parallel flat surfaces. The first surface 50a and the second surface 50b may be perpendicular to the first direction D1.

[0116] The second wavelength selective sheet 50 may include only the second wavelength selective portion 55. The second wavelength selective sheet 50 may be composed of only the second wavelength selective portion 55. As shown in FIG. 5, the second wavelength selective portion 55 may include a first surface 55a and a second surface 55b. The first surface 55a is oriented toward the light incident side in the first direction D1. The second surface 55b is oriented toward the light exiting side in the first direction D1. The first surface 55a and the second surface 55b may be a pair of main surfaces of the sheet-like second wavelength selective portion 55. The first surface 55a and the second surface 55b may be parallel flat surfaces. The first surface 55a and the second surface 55b may be orthogonal to the first direction D1. The first surface 55a of the second wavelength selective portion 55 may constitute the first surface 50a of the second wavelength selective sheet 50. The first surface 55a of the second wavelength selective portion 55 may constitute the light incident side surface 30a of the optical member 30. The second surface 55b of the second wavelength selecting portion 55 may constitute the second surface 50b of the second wavelength selecting sheet 50.

[0117] The second wavelength selection section 55 may reflect a high wavelength region in the visible light wavelength range. The second wavelength selection section 55 may transmit a low wavelength region in the visible light wavelength range. The second wavelength selection section 55 may function as a high-pass filter.

[0118] The transmittance of the secondary light LB of the second wavelength selecting unit 55 may be lower than the transmittance of the primary light LA ​​of the second wavelength selecting unit 55. The transmittance of the second wavelength selecting unit 55 for the light emitted from the light source 23 and whose wavelength has been converted by the wavelength converting unit 65 may be lower than the transmittance of the second wavelength selecting unit 55 for the light emitted from the light source 23. In the example shown in FIG. 6, the transmittance of the first secondary light LB1 of the second wavelength selecting unit 55 may be lower than the transmittance of the primary light LA ​​of the second wavelength selecting unit 55. The transmittance of the second secondary light LB2 of the second wavelength selecting unit 55 may be lower than the transmittance of the primary light LA ​​of the second wavelength selecting unit 55.

[0119] The transmittance of the second wavelength selection unit 55 for light having a wavelength of 500 nm or more and 600 nm or less may be lower than the transmittance of the second wavelength selection unit 55 for light having a wavelength of 430 nm or more and 500 nm or less. The transmittance of the second wavelength selection unit 55 for light having a wavelength of 600 nm or more and 750 nm or less may be lower than the transmittance of the second wavelength selection unit 55 for light having a wavelength of 430 nm or more and 500 nm or less.

[0120] The transmittance of the second wavelength selection unit 55 for green light may be lower than the transmittance of the second wavelength selection unit 55 for blue light. The transmittance of the second wavelength selection unit 55 for red light may be lower than the transmittance of the second wavelength selection unit 55 for blue light.

[0121] The transmittance of the second wavelength selection unit 55 may decrease as the wavelength becomes longer in the wavelength range of 450 nm or more and 500 nm or less. The transmittance of the second wavelength selection unit 55 may decrease as the wavelength becomes longer in the wavelength range of 425 nm or more and 525 nm or less. The transmittance of the second wavelength selection unit 55 may decrease as the wavelength becomes longer in the wavelength range of 430 nm or more and 600 nm or less. The transmittance of the second wavelength selection unit 55 may decrease as the wavelength becomes longer in the wavelength range of 430 nm or more and 750 nm or less.

[0122] In the wavelength range of 500 nm or more and 750 nm or less, the transmittance of the second wavelength selection portion 55 may be 20% or less, 15% or less, 10% or less, or 5% or less. In the wavelength range of 500 nm or more and 700 nm or less, the transmittance of the second wavelength selection portion 55 may be 0% or more, or may be greater than 0%.

[0123] In the wavelength range of 430 nm or more and 465 nm or less, the transmittance of the second wavelength selection portion 55 may be 20% or more, 30% or more, 35% or more, or 40% or more. In the wavelength range of 430 nm or more and 465 nm or less, the transmittance of the second wavelength selection portion 55 may be 100% or less, or may be less than 100%.

[0124] The reflectance of the secondary light LB of the second wavelength selecting unit 55 may be higher than the reflectance of the primary light LA ​​of the second wavelength selecting unit 55. The reflectance of the second wavelength selecting unit 55 for the light emitted from the light source 23 and whose wavelength has been converted by the wavelength converting unit 65 may be higher than the reflectance of the second wavelength selecting unit 55 for the light emitted from the light source 23. In the example shown in FIG. 6, the reflectance of the first secondary light LB1 of the second wavelength selecting unit 55 may be higher than the reflectance of the primary light LA ​​of the second wavelength selecting unit 55. The reflectance of the second secondary light LB2 of the second wavelength selecting unit 55 may be higher than the reflectance of the primary light LA ​​of the second wavelength selecting unit 55.

[0125] The reflectance of the second wavelength selection unit 55 for light having a wavelength of 500 nm or more and 600 nm or less may be higher than the reflectance of the second wavelength selection unit 55 for light having a wavelength of 430 nm or more and 500 nm or less. The reflectance of the second wavelength selection unit 55 for light having a wavelength of 600 nm or more and 750 nm or less may be higher than the reflectance of the second wavelength selection unit 55 for light having a wavelength of 430 nm or more and 500 nm or less.

[0126] The reflectance of the second wavelength selection unit 55 for green light may be higher than the reflectance of the second wavelength selection unit 55 for blue light. The reflectance of the second wavelength selection unit 55 for red light may be higher than the reflectance of the second wavelength selection unit 55 for blue light.

[0127] The reflectance of the second wavelength selection unit 55 may increase as the wavelength becomes longer in the wavelength range of 450 nm or more and 500 nm or less. The reflectance of the second wavelength selection unit 55 may increase as the wavelength becomes longer in the wavelength range of 425 nm or more and 525 nm or less. The reflectance of the second wavelength selection unit 55 may increase as the wavelength becomes longer in the wavelength range of 430 nm or more and 600 nm or less. The reflectance of the second wavelength selection unit 55 may increase as the wavelength becomes longer in the wavelength range of 430 nm or more and 750 nm or less.

[0128] In the wavelength range of 500 nm or more and 750 nm or less, the reflectance of the second wavelength selection portion 55 may be 80% or more, 85% or more, 90% or more, or 95% or more. In the wavelength range of 500 nm or more and 700 nm or less, the reflectance of the second wavelength selection portion 55 may be 100% or less, or may be less than 100%.

[0129] In the wavelength range of 430 nm or more and 465 nm or less, the reflectance of the second wavelength selection portion 55 may be 80% or less, 70% or less, 65% or less, or 60% or less. In the wavelength range of 430 nm or more and 465 nm or less, the reflectance of the second wavelength selection portion 55 may be 0% or more, or may be greater than 0%.

[0130] The transmittance of the second wavelength selection unit 55 for the primary light LA ​​may be higher than the transmittance of the first wavelength selection unit 45 for the primary light LA. The transmittance of the second wavelength selection unit 55 for the light emitted from the light source 23 may be higher than the transmittance of the first wavelength selection unit 45 for the light emitted from the light source 23. The transmittance of the second wavelength selection unit 55 for light having a wavelength of 430 nm or more and 500 nm or less may be higher than the transmittance of the first wavelength selection unit 45 for light having a wavelength of 430 nm or more and 500 nm or less. The transmittance of the second wavelength selection unit 55 for blue light may be higher than the transmittance of the first wavelength selection unit 45 for blue light.

[0131] The reflectance of the second wavelength selecting unit 55 for the primary light LA ​​may be lower than the reflectance of the first wavelength selecting unit 45 for the primary light LA. The reflectance of the second wavelength selecting unit 55 for the light emitted from the light source 23 may be lower than the reflectance of the first wavelength selecting unit 45 for the light emitted from the light source 23. The reflectance of the second wavelength selecting unit 55 for light having a wavelength of 430 nm or more and 500 nm or less may be lower than the reflectance of the first wavelength selecting unit 45 for light having a wavelength of 430 nm or more and 500 nm or less. The reflectance of the second wavelength selecting unit 55 for blue light may be lower than the reflectance of the first wavelength selecting unit 45 for blue light.

[0132] The transmittance of the secondary light LB of the first wavelength selecting unit 45 may be higher than the transmittance of the secondary light LB of the second wavelength selecting unit 55. The transmittance of the first wavelength selecting unit 45 for light emitted from the light source 23 and wavelength-converted by the wavelength converting unit 65 may be higher than the transmittance of the second wavelength selecting unit 55 for light emitted from the light source 23 and wavelength-converted by the wavelength converting unit 65. In the example shown in FIG. 6, the transmittance of the first secondary light LB1 of the first wavelength selecting unit 45 may be higher than the transmittance of the first secondary light LB1 of the second wavelength selecting unit 55. The transmittance of the second secondary light LB2 of the first wavelength selecting unit 45 may be higher than the transmittance of the second secondary light LB2 of the second wavelength selecting unit 55.

[0133] The transmittance of the first wavelength selection section 45 for light having a wavelength of 500 nm or more and 750 nm or less may be higher than the transmittance of the second wavelength selection section 55 for light having a wavelength of 500 nm or more and 750 nm or less. The transmittance of the first wavelength selection section 45 for light having a wavelength of 500 nm or more and 600 nm or less may be higher than the transmittance of the second wavelength selection section 55 for light having a wavelength of 500 nm or more and 600 nm or less. The transmittance of the first wavelength selection section 45 for green light may be higher than the transmittance of the second wavelength selection section 55 for green light. The transmittance of the first wavelength selection section 45 for light having a wavelength of 600 nm or more and 750 nm or less may be higher than the transmittance of the second wavelength selection section 55 for light having a wavelength of 600 nm or more and 750 nm or less. The transmittance of the first wavelength selection section 45 for red light may be higher than the transmittance of the second wavelength selection section 55 for red light.

[0134] The reflectance of the secondary light LB of the first wavelength selecting unit 45 may be lower than the reflectance of the secondary light LB of the second wavelength selecting unit 55. The reflectance of the first wavelength selecting unit 45 for light emitted from the light source 23 and wavelength-converted by the wavelength converting unit 65 may be lower than the reflectance of the second wavelength selecting unit 55 for light emitted from the light source 23 and wavelength-converted by the wavelength converting unit 65. In the example shown in FIG. 6, the reflectance of the first secondary light LB1 of the first wavelength selecting unit 45 may be lower than the reflectance of the first secondary light LB1 of the second wavelength selecting unit 55. The reflectance of the second secondary light LB2 of the first wavelength selecting unit 45 may be lower than the reflectance of the second secondary light LB2 of the second wavelength selecting unit 55.

[0135] The reflectance of the first wavelength selection unit 45 for light having a wavelength of 500 nm or more and 750 nm or less may be lower than the reflectance of the second wavelength selection unit 55 for light having a wavelength of 500 nm or more and 750 nm or less. The reflectance of the first wavelength selection unit 45 for light having a wavelength of 500 nm or more and 600 nm or less may be lower than the reflectance of the second wavelength selection unit 55 for light having a wavelength of 500 nm or more and 600 nm or less. The reflectance of the first wavelength selection unit 45 for green light may be lower than the reflectance of the second wavelength selection unit 55 for green light. The reflectance of the first wavelength selection unit 45 for light having a wavelength of 600 nm or more and 750 nm or less may be lower than the reflectance of the second wavelength selection unit 55 for light having a wavelength of 600 nm or more and 750 nm or less. The reflectance of the first wavelength selection unit 45 for red light may be lower than the reflectance of the second wavelength selection unit 55 for red light.

[0136] Fig. 9 is a graph showing a specific example of the transmission characteristics of the second wavelength selection section 55. Fig. 9 shows a specific example of the spectral transmittance of the second wavelength selection section 55. In the graph of Fig. 9, the vertical axis represents the spectral transmittance (%). In the graph of Fig. 9, the horizontal axis represents the wavelength (nm).

[0137] The optical characteristics of the second wavelength selection section 55, i.e., the transmission characteristics and reflection characteristics of the second wavelength selection section 55, are assumed to be such that the first surface 55a and the second surface 55b are parallel and that the first surface 55a and the second surface 55b are adjacent to an air layer.

[0138] The method for measuring the transmittance (%) of the second wavelength selection unit 55 is the same as the method for measuring the transmittance (%) of the first wavelength selection unit 45 described above. The method for measuring the reflectance (%) of the second wavelength selection unit 55 is the same as the method for measuring the reflectance (%) of the first wavelength selection unit 45 described above.

[0139] Examples of the second wavelength selection unit 55 having the above-mentioned optical characteristics include a dielectric multilayer film 56, a reflective volume hologram, a cholesteric liquid crystal structure layer, a retroreflective film, and a reflective diffractive optical element. The dielectric multilayer film is excellent in that it has a relatively high degree of freedom in designing the reflection characteristics and transmission characteristics. The optical characteristics shown in FIG. 9 are an example of the optical characteristics of the dielectric multilayer film 56.

[0140] The dielectric multilayer film 56 constituting the second wavelength selection section 55 may have a similar configuration to the dielectric multilayer film 46 constituting the first wavelength selection section 45, except for the optical characteristics. The dielectric multilayer film 56 constituting the second wavelength selection section 55 may be manufactured by a similar method to the dielectric multilayer film 46 constituting the first wavelength selection section 45.

[0141] The transmission characteristics and reflection characteristics of the second wavelength selection section 55 may have incidence angle dependency. The transmission characteristics and reflection characteristics of the second wavelength selection section 55 may change depending on the incidence angle. The transmission characteristics of the second wavelength selection section 55 may be adjusted so that the transmittance changes depending on the incidence angle. The reflection characteristics of the second wavelength selection section 55 may be adjusted so that the reflectance changes depending on the incidence angle.

[0142] 2, the optical member 30 may further include components in addition to the first wavelength selection sheet 40, the second wavelength selection sheet 50, and the wavelength conversion sheet 60. The optical member 30 may include a light control sheet that exerts optical effects such as reflection, refraction, and diffraction on the incident light. The light control sheet may have a function appropriate for the application of the optical member 30 and the surface light source device 20.

[0143] The optical member 30 shown in FIG. 2 further includes a first prism sheet 91, a second prism sheet 92, and a reflective polarizing plate 95 as light control sheets. The first prism sheet 91, the second prism sheet 92, and the reflective polarizing plate 95 are stacked in the first direction D1 with the above-mentioned sheets 40, 50, and 60 included in the optical member 30. The first prism sheet 91, the second prism sheet 92, and the reflective polarizing plate 95 may be located on the light output side of the above-mentioned sheets 40, 50, and 60 in the first direction D1. The first prism sheet 91, the second prism sheet 92, and the reflective polarizing plate 95 may be located in this order from the light input side to the light output side in the first direction D1. As shown in FIG. 2, the reflective polarizing plate 95 may constitute the light output side surface 30b of the optical member 30. The reflective polarizing plate 95 may constitute the light emitting surface 20a. The first prism sheet 91, the second prism sheet 92, and the reflective polarizing plate 95 may be sheet-like members extending in the second direction D2 and the third direction D3.

[0144] FIG. 10 shows a specific example of the first prism sheet 91 and the second prism sheet 92. The prism sheets 91 and 92 may include a sheet-like main body 93 and a plurality of unit prisms 94 provided on the main body 93. The unit prisms 94 may extend linearly in a direction perpendicular to the arrangement direction of the plurality of unit prisms 94. The first prism sheet 91 and the second prism sheet 92 may be prism sheets in which the unit prisms 94 are linearly arranged. FIG. 10 shows the linearly arranged unit prisms 94. The unit prisms 94 shown in FIG. 10 mainly adjust the luminance angle distribution in a plane parallel to both the arrangement direction of the unit prisms 94 and the first direction D1. Therefore, the illustrated first prism sheet 91 and the illustrated second prism sheet 92 may be incorporated into the optical member 30 such that the arrangement directions of the unit prisms 94 are non-parallel. For example, the arrangement direction of the unit prisms 94 of the first prism sheet 91 may be perpendicular to the arrangement direction of the unit prisms 94 of the second prism sheet 92 .

[0145] The prism sheet shown in Fig. 10 may be "BEF" (registered trademark) available from 3M, USA. The prism sheet shown in Fig. 10 bends the traveling direction of the transmitted light so that the angle between the traveling direction of the transmitted light and the first direction D1 becomes small. The prism sheet shown in Fig. 10 functions as a light collecting sheet.

[0146] The reflective polarizing plate 95 transmits one linearly polarized component and reflects the other linearly polarized component. The reflective polarizing plate 95 can selectively transmit light of a linearly polarized component that can transmit a polarizing plate located on the surface light source device 20 side of the display panel 15. The light reflected by the reflective polarizing plate 95 can change its polarization state by subsequent reflection or the like and enter the reflective polarizing plate 95 again. This can improve the utilization efficiency of the light emitted from the light source 23. The reflective polarizing plate 95 may be "DBEF" (registered trademark) available from 3M Corporation of the United States. The reflective polarizing plate 95 may be a high-brightness polarizing sheet "WRPS" available from Shinwa Intertek Corporation of Korea, a wire grid polarizer, or the like.

[0147] Next, the operation of the surface light source device 20 having the above configuration when generating surface light will be described.

[0148] As shown in Fig. 2, the light source 23 emits primary light LA. The primary light LA ​​is, for example, blue light. The wavelength of the blue primary light LA ​​may be 430 nm or more and 500 nm or less. The light L21, L22 emitted from the light source 23 travels toward the optical member 30. The optical member 30 includes a light-entering side surface 30a facing the light-entering side (second side) in the first direction D1. The light L21, L22 passes through the light-entering side surface 30a.

[0149] As shown in FIG. 2, the light L21, L22 incident on the optical member 30 first travels through the second wavelength selective sheet 50. The second wavelength selective sheet 50 includes a second wavelength selective portion 55 having the above-mentioned optical characteristics. The transmittance of the primary light LA ​​of the second wavelength selective portion 55 is higher than the transmittance of the secondary light LB of the second wavelength selective portion 55. As shown in FIG. 9, the transmittance of the second wavelength selective portion 55 is high for light having a wavelength of 430 nm or more and 500 nm or less. The reflectance of the primary light LA ​​of the second wavelength selective portion 55 is lower than the reflectance of the secondary light LB of the second wavelength selective portion 55. The reflectance of the second wavelength selective portion 55 for light having a wavelength of 430 nm or more and 500 nm or less is low. Therefore, the primary light LA ​​emitted from the light source 23 passes through the second wavelength selective sheet 50 with high transmittance.

[0150] A part of the primary light LA ​​may be reflected by the second wavelength selection sheet 50. This light may be reflected by the reflective layer 27 of the support substrate 25 with high reflectance. The light reflected by the reflective layer 27 travels toward the first side in the first direction D1. The light reflected by the reflective layer 27 may re-enter the optical member 30 while traveling in a direction perpendicular to the first direction D1. The presence of such light promotes diffusion of the primary light LA, making it possible to suppress unevenness in brightness caused by the primary light LA.

[0151] The light L21 and L22 transmitted through the second wavelength selection sheet 50 enters the wavelength conversion sheet 60. As shown in Fig. 6, the wavelength conversion sheet 60 includes, from the light incident side in the first direction D1, a first barrier layer 63, a wavelength converting portion 65, and a second barrier layer 64. The light incident on the wavelength conversion sheet 60 passes through the first barrier layer 63 and travels to the wavelength converting portion 65.

[0152] As shown in FIG. 6, the wavelength conversion unit 65 includes a wavelength conversion agent 67. A portion of the light traveling through the wavelength conversion unit 65 collides with the wavelength conversion agent 67. The wavelength conversion agent 67 absorbs the primary light LA ​​emitted from the light source 23 and emits secondary light LB with a different wavelength. The wavelength of the secondary light LB is longer than the wavelength of the primary light LA. In the illustrated example, the wavelength conversion unit 65 includes a first conversion agent 67A and a second conversion agent 67B. The first conversion agent 67A absorbs a portion L61 of the blue primary light LA ​​and emits a first secondary light LB1 of green. The second conversion agent 67B absorbs a portion L62 of the blue primary light LA ​​and emits a second secondary light LB2 of red. As shown in FIG. 6, a portion L63 of the primary light LA ​​does not enter the wavelength conversion agent 67 and passes through the wavelength conversion unit 65.

[0153] The light that has passed through the wavelength converting portion 65 further passes through the second barrier layer 64 and is emitted from the wavelength converting sheet 60.

[0154] The light L23, L24 transmitted through the wavelength conversion sheet 60 travels toward the first wavelength selection sheet 40. The light L23, L24 traveling toward the first wavelength selection sheet 40 includes the primary light LA ​​and the secondary light LB. The first wavelength selection sheet 40 includes the first wavelength selection portion 45 having the above-mentioned optical characteristics.

[0155] The transmittance of the secondary light LB of the first wavelength selection unit 45 is higher than the transmittance of the primary light LA ​​of the first wavelength selection unit 45. The transmittance of the first secondary light LB1 of the first wavelength selection unit 45 is higher than the transmittance of the primary light LA ​​of the first wavelength selection unit 45. The transmittance of the second secondary light LB2 of the first wavelength selection unit 45 is higher than the transmittance of the primary light LA ​​of the first wavelength selection unit 45.

[0156] The first wavelength selection section 45 has high transmittance for light with a wavelength of 500 nm or more and 750 nm or less. The first wavelength selection section 45 has high transmittance for light with a wavelength of 500 nm or more and 600 nm or less. The first wavelength selection section 45 has high transmittance for green light as the first secondary light LB1. The first wavelength selection section 45 has high transmittance for light with a wavelength of 600 nm or more and 750 nm or less. The first wavelength selection section 45 has high transmittance for red light as the second secondary light LB2.

[0157] The reflectance of the secondary light LB of the first wavelength selecting unit 45 is lower than the reflectance of the primary light LA ​​of the first wavelength selecting unit 45. The reflectance of the first secondary light LB1 of the first wavelength selecting unit 45 is lower than the reflectance of the primary light LA ​​of the first wavelength selecting unit 45. The reflectance of the second secondary light LB2 of the first wavelength selecting unit 45 is lower than the reflectance of the primary light LA ​​of the first wavelength selecting unit 45.

[0158] The first wavelength selection unit 45 has low reflectance for light with a wavelength of 500 nm or more and 750 nm or less. The first wavelength selection unit 45 has low reflectance for light with a wavelength of 500 nm or more and 600 nm or less. The first wavelength selection unit 45 has low reflectance for green light as the first secondary light LB1. The first wavelength selection unit 45 has low reflectance for light with a wavelength of 600 nm or more and 750 nm or less. The first wavelength selection unit 45 has low reflectance for red light as the second secondary light LB2.

[0159] Due to the above optical characteristics of the first wavelength selection portion 45 regarding the secondary light LB, the light L24 emitted from the light source 23 and whose wavelength is converted by the wavelength conversion sheet 60 passes through the first wavelength selection sheet 40 with high transmittance.

[0160] The transmittance of the primary light LA ​​of the first wavelength selection section 45 is lower than the transmittance of the secondary light LB of the first wavelength selection section 45. The transmittance of the primary light LA ​​of the first wavelength selection section 45 is lower than the transmittance of the first secondary light LB1 of the first wavelength selection section 45. The transmittance of the primary light LA ​​of the first wavelength selection section 45 is lower than the transmittance of the second secondary light LB2 of the first wavelength selection section 45. The transmittance of the first wavelength selection section 45 for light with a wavelength of 430 nm or more and 500 nm or less is low. The transmittance of the first wavelength selection section 45 for blue light as the primary light LA ​​is low.

[0161] The reflectance of the primary light LA ​​of the first wavelength selection section 45 is higher than the reflectance of the secondary light LB of the first wavelength selection section 45. The reflectance of the primary light LA ​​of the first wavelength selection section 45 is higher than the reflectance of the first secondary light LB1 of the first wavelength selection section 45. The reflectance of the primary light LA ​​of the first wavelength selection section 45 is higher than the reflectance of the second secondary light LB2 of the first wavelength selection section 45. The reflectance of the first wavelength selection section 45 is high for light with a wavelength of 430 nm or more and 500 nm or less. The reflectance of the first wavelength selection section 45 is high for blue light as the primary light LA.

[0162] The light L25 as the primary light LA ​​reflected by the first wavelength selection unit 45 travels toward the second side in the first direction D1, as shown in FIG. 2. A part of the light is reflected by the wavelength conversion sheet 60 or the second wavelength selection sheet 50. The remaining light L25 passes through the wavelength conversion sheet 60 and the second wavelength selection sheet 50 and travels toward the light source substrate 22. The light L25 can be reflected with high reflectance by the reflective layer 27 of the support substrate 25. The light reflected by the reflective layer 27 etc. travels toward the first side in the first direction D1.

[0163] The light L25 as the primary light LA ​​reflected by the first wavelength selection unit 45 may re-enter the first wavelength selection sheet 40 while traveling in a direction perpendicular to the first direction D1. Due to the reflection of the primary light LA ​​by the first wavelength selection sheet 40, the light emitted from one light source 23 may re-enter the first wavelength selection sheet 40 in an intermediate region away from the light source 23 in a direction perpendicular to the first direction D1. This makes it possible to prevent the light emitting surface 20a from becoming too dark in the intermediate region facing the intermediate position between two adjacent light sources.

[0164] In this way, the reflection of the primary light LA ​​at the first wavelength selection unit 45 can promote the diffusion of the primary light LA. The in-plane distribution of brightness caused by the primary light LA ​​can be effectively uniformed. Since the primary light LA ​​is diffused, the in-plane distribution of color can also be effectively uniformed.

[0165] As described above, the selective transmittance or selective reflectance of the first wavelength selection portion 45 according to the wavelength can suppress the in-plane variation in brightness according to the arrangement of the light sources 23. This makes it possible to effectively uniform the illuminance at each position on the second surface 40b of the first wavelength selection sheet 40.

[0166] By effectively uniforming the in-plane distribution of brightness and color, the distance in the first direction D1 between the optical member 30 and the light source 23 can be shortened, and the thickness of the surface light source device 20 can be reduced. The area in which light emitted from one light source 23 spreads uniformly can be widened. The number of light sources 23 used in combination with the optical member 30 can be reduced. The distance between adjacent light sources 23 can be shortened.

[0167] In the example shown in FIG. 2 and FIG. 4, the wavelength conversion sheet 60 is located on the light-entering side in the first direction D1 of the first wavelength selection sheet 40. Therefore, the light reflected by the first wavelength selection sheet 40 is incident on the first wavelength selection sheet 40. That is, the wavelength conversion agent 67 is located in the circulation path of the primary light LA ​​for uniformizing the in-plane distribution of brightness. Therefore, the wavelength conversion agent 67 contained in the wavelength conversion sheet 60 can be efficiently used. By saving the wavelength conversion agent 67, the total amount of the wavelength conversion agent 67 contained in the wavelength conversion sheet 60 can be reduced. The thickness of the wavelength conversion sheet 60 can be reduced. With the reduction in the thickness of the wavelength conversion sheet 60, the thickness of the surface light source device 20 can also be reduced.

[0168] The optical characteristics of the first wavelength selection section 45 may have the incidence angle dependency as described above.

[0169] For example, the transmittance of the first wavelength selection unit 45 for the primary light LA ​​incident on the first wavelength selection unit 45 at an incident angle greater than 0° may be higher than the transmittance of the first wavelength selection unit 45 for the primary light LA ​​incident on the first wavelength selection unit 45 at an incident angle of 0°. The transmittance of the first wavelength selection unit 45 for the primary light LA ​​incident on the first wavelength selection unit 45 at an incident angle greater than 0° may be higher than for the primary light LA ​​incident on the first wavelength selection unit 45 at an incident angle of 0°.

[0170] The reflectance of the first wavelength selection unit 45 for the primary light LA ​​incident on the first wavelength selection unit 45 at an incident angle greater than 0° may be lower than the reflectance of the first wavelength selection unit 45 for the primary light LA ​​incident on the first wavelength selection unit 45 at an incident angle of 0°. The reflectance of the first wavelength selection unit 45 for the primary light LA ​​incident on the first wavelength selection unit 45 at an incident angle greater than 0° may be lower than for the primary light LA ​​incident on the first wavelength selection unit 45 at an incident angle of 0°.

[0171] The transmittance of the first wavelength selection unit 45 for light of a specific wavelength incident on the first wavelength selection unit 45 at an incident angle of 0°, the transmittance of the first wavelength selection unit 45 for light of a specific wavelength incident on the first wavelength selection unit 45 at an incident angle of 30°, and the transmittance of the first wavelength selection unit 45 for light of a specific wavelength incident on the first wavelength selection unit 45 at an incident angle of 60° may increase in this order. The transmittance of the first wavelength selection unit 45 for light of a specific wavelength incident on the first wavelength selection unit 45 at incident angles of 0°, 10°, 20°, 30°, 40°, 50°, and 60° may gradually increase as the incident angle increases.

[0172] The reflectance of the first wavelength selection unit 45 for light of a specific wavelength incident on the first wavelength selection unit 45 at an incident angle of 0°, the reflectance of the first wavelength selection unit 45 for light of a specific wavelength incident on the first wavelength selection unit 45 at an incident angle of 30°, and the reflectance of the first wavelength selection unit 45 for light of a specific wavelength incident on the first wavelength selection unit 45 at an incident angle of 60° may decrease in this order. The reflectance of the first wavelength selection unit 45 for light of a specific wavelength incident on the first wavelength selection unit 45 at incident angles of 0°, 10°, 20°, 30°, 40°, 50°, and 60° may gradually decrease as the incident angle increases.

[0173] The specific wavelength may be a wavelength of 430 nm or more and 500 nm or less. The specific wavelength may be the wavelength of the primary light LA. The specific wavelength may be the wavelength of the light emitted from the light source 23.

[0174] The area including the position facing the light source 23 in the first direction D1 and the periphery of the position is defined as the directly above area. A large amount of primary light LA ​​is directly incident on this directly above area from the light source 23. The angle of incidence of the primary light LA ​​on the directly above area is relatively small. Therefore, the light L23 as the primary light LA ​​emitted from the light source 23 and proceeding to the first wavelength selection unit 45 is reflected with a high reflectance in the directly above area due to the optical characteristics of the first wavelength selection unit 45 having the incidence angle dependency. This makes it possible to prevent the light emitting surface 20a from becoming too bright in the directly above area.

[0175] As described above, the selective transmittance or selective reflectance of the first wavelength selection portion 45 according to the incident angle can further suppress the in-plane variation in brightness according to the arrangement of the light sources 23. This makes it possible to more effectively uniform the illuminance at each position on the second surface 40b of the first wavelength selection sheet 40.

[0176] By effectively uniforming the in-plane distribution of brightness and color, the distance (length in the first direction) between the optical member 30 and the light source 23 can be shortened, and the thickness of the surface light source device 20 can be reduced. The area in which light emitted from one light source 23 spreads uniformly can be widened. The number of light sources 23 used in combination with the optical member 30 can be reduced. The distance between adjacent light sources 23 can be shortened.

[0177] The angle between the traveling direction of the primary light LA ​​and the first direction D1 tends to be small in the directly above region directly above the light source 23. The angle between the traveling direction of the primary light LA ​​and the first direction D1 tends to be large in the intermediate region away from the light source 23 in the direction perpendicular to the first direction D1. Due to this tendency, the optical path length of the primary light LA ​​in the wavelength conversion sheet 60 is short in the directly above region. Therefore, in the directly above region where the amount of the primary light LA ​​is likely to be large, the probability that the primary light LA ​​is wavelength-converted by the wavelength conversion agent 67 is low. In the intermediate region where the amount of the primary light LA ​​is likely to be small, the optical path length of the primary light LA ​​in the wavelength conversion sheet 60 is long. Therefore, in the intermediate region, the probability that the primary light LA ​​is wavelength-converted by the wavelength conversion agent 67 is high. This makes it possible to suppress in-plane variation in color.

[0178] The light L24 and L25 transmitted through the first wavelength selection sheet 40 are transmitted through the first prism sheet 91, the second prism sheet 92, and the reflective polarizing plate 95, and are emitted from the light emitting surface 20a of the surface light source device 20. In this manner, the light emitting surface 20a of the surface light source device 20 emits light.

[0179] Incidentally, as shown in Fig. 6, the traveling direction of the secondary light LB emitted from the wavelength conversion agent 67 does not depend on the traveling direction of the primary light LA, L61, L62 before being absorbed by the wavelength conversion agent 67. As shown in Fig. 6, the secondary light LB is emitted in a wide angle range from the wavelength conversion agent 67. As shown in Fig. 2, a part of the secondary light LB travels toward the second side (light incident side) in the first direction D1.

[0180] In this embodiment, the second wavelength selection sheet 50 is disposed on the light incident side in the first direction D1 of the wavelength conversion sheet 60. The optical characteristics of the second wavelength selection sheet 50 have wavelength dependency.

[0181] The reflectance of the secondary light LB of the second wavelength selecting section 55 is higher than the reflectance of the primary light LA ​​of the second wavelength selecting section 55. The reflectance of the first secondary light LB1 of the second wavelength selecting section 55 is higher than the reflectance of the primary light LA ​​of the second wavelength selecting section 55. The reflectance of the second secondary light LB2 of the second wavelength selecting section 55 is higher than the reflectance of the primary light LA ​​of the second wavelength selecting section 55.

[0182] The second wavelength selection section 55 has high reflectance for light with a wavelength of 500 nm or more and 750 nm or less. The second wavelength selection section 55 has high reflectance for light with a wavelength of 500 nm or more and 600 nm or less. The second wavelength selection section 55 has high reflectance for green light as the first secondary light LB1. The second wavelength selection section 55 has high reflectance for light with a wavelength of 600 nm or more and 750 nm or less. The second wavelength selection section 55 has high reflectance for red light as the second secondary light LB2.

[0183] The transmittance of the secondary light LB of the second wavelength selection unit 55 is lower than the transmittance of the primary light LA ​​of the second wavelength selection unit 55. The transmittance of the first secondary light LB1 of the second wavelength selection unit 55 is lower than the transmittance of the primary light LA ​​of the second wavelength selection unit 55. The transmittance of the second secondary light LB2 of the second wavelength selection unit 55 is lower than the transmittance of the primary light LA ​​of the second wavelength selection unit 55.

[0184] The second wavelength selection section 55 has a low transmittance for light with a wavelength of 500 nm or more and 750 nm or less. The second wavelength selection section 55 has a low transmittance for light with a wavelength of 500 nm or more and 600 nm or less. The second wavelength selection section 55 has a low transmittance for green light as the first secondary light LB1. The second wavelength selection section 55 has a low transmittance for light with a wavelength of 600 nm or more and 750 nm or less. The second wavelength selection section 555 has a low transmittance for red light as the second secondary light LB2.

[0185] That is, the second wavelength selection sheet 50 selectively reflects the secondary light LB with high reflectance and selectively transmits the primary light LA ​​with high transmittance. Therefore, the light L26 as the secondary light LB emitted from the wavelength conversion agent 67 to the light incident side in the first direction D1 is reflected by the second wavelength selection sheet 50. The light L26 reflected by the second wavelength selection sheet 50 can transmit through the wavelength conversion sheet 60 and the first wavelength selection sheet 40 to the light output side in the first direction D1.

[0186] In this way, the second wavelength selection sheet 50 located on the light-entering side in the first direction D1 of the wavelength conversion sheet 60 can direct the secondary light LB toward the light-entering side to the light-outgoing side. This can prevent the secondary light LB from becoming stray light or being lost due to absorption, etc. The utilization efficiency of the secondary light LB can be improved.

[0187] The light L26 reflected by the wavelength conversion sheet 60 and re-entering the first wavelength selection sheet 40 travels in a direction perpendicular to the first direction D1. By effectively utilizing such light L26 in the surface light source device 20, the diffusion of the secondary light LB can be promoted. This makes it possible to effectively uniformize the in-plane distribution of brightness. In addition, it is possible to effectively uniformize the in-plane distribution of color. By effectively uniformizing the in-plane distribution of brightness and color, it is possible to shorten the distance along the first direction D1 between the optical member 30 and the light source 23, thereby reducing the thickness of the surface light source device 20. It is possible to widen the area in which the light emitted from one light source 23 spreads uniformly. It is possible to reduce the number of light sources 23 used in combination with the optical member 30. It is possible to shorten the distance between adjacent light sources 23.

[0188] Furthermore, since the efficiency of use of the secondary light LB increases, the efficiency of use of the wavelength conversion agent 67 also increases. This makes it possible to save the wavelength conversion agent 67 contained in the wavelength conversion sheet 60. The thickness of the wavelength conversion sheet 60 can be reduced, and therefore the thickness of the surface light source device 20 can also be reduced.

[0189] The second wavelength selection sheet 50 may be disposed adjacent to the wavelength conversion sheet 60 from the light entrance side in the first direction D1. Other components may not be disposed between the second wavelength selection sheet 50 and the wavelength conversion sheet 60. According to this example, the second wavelength selection sheet 50 located on the light entrance side of the wavelength conversion sheet 60 reflects the secondary light LB, and thus the improvement in the utilization efficiency of the secondary light LB becomes more remarkable. The stably improved utilization efficiency of the secondary light LB promotes the diffusion of the secondary light LB more stably. As a result, the in-plane distribution of brightness can be more effectively uniformed, and the in-plane distribution of color can be more effectively uniformed.

[0190] As described above, the optical member 30 according to this embodiment includes a first wavelength selection sheet 40, a second wavelength selection sheet 50, and a wavelength conversion sheet 60, which are stacked in the first direction D1. The second wavelength selection sheet 50 is located on the light incident side of the wavelength conversion sheet 60 in the first direction D1. The wavelength conversion sheet 60 includes a wavelength conversion agent 67. The wavelength conversion agent 67 absorbs the primary light LA ​​and emits secondary light LB having a longer wavelength than the primary light LA. The first wavelength selection sheet 40 includes a first wavelength selection portion 45. The second wavelength selection sheet 50 includes a second wavelength selection portion 55.

[0191] In this optical member 30, the transmittance of the primary light LA ​​of the first wavelength selecting section 45 may be lower than the transmittance of the secondary light LB of the first wavelength selecting section 45. The transmittance of the secondary light LB of the second wavelength selecting section 55 may be lower than the transmittance of the primary light LA ​​of the second wavelength selecting section 55. In this optical member 30, the reflectance of the primary light LA ​​of the first wavelength selecting section 45 may be higher than the reflectance of the secondary light LB of the first wavelength selecting section 45. The reflectance of the secondary light LB of the second wavelength selecting section 55 may be higher than the reflectance of the primary light LA ​​of the second wavelength selecting section 55.

[0192] According to this embodiment, the second wavelength selection sheet 50 located on the light-entering side in the first direction D1 of the wavelength conversion sheet 60 can direct the secondary light LB toward the light-entering side to the light-outgoing side. Therefore, the secondary light LB can be prevented from becoming stray light or being lost due to absorption. The efficiency of use of the secondary light LB can be improved. In addition, the diffusion of the secondary light LB can be promoted. As a result, the in-plane distribution of brightness can be more effectively uniformed, and the in-plane distribution of color can be more effectively uniformed. By effectively uniforming the in-plane distribution of brightness and color, the distance between the optical member 30 and the light source 23 along the first direction D1 can be shortened, and the thickness of the surface light source device 20 can be reduced. The area in which the light emitted from one light source 23 spreads uniformly can be widened. The number of light sources 23 used in combination with the optical member 30 can be reduced. The distance between adjacent light sources 23 can be shortened.

[0193] Moreover, since the loss of the secondary light LB can be suppressed, it is possible to improve the utilization efficiency of the wavelength conversion agent 67. It is possible to save the wavelength conversion agent 67 contained in the wavelength conversion sheet 60. By reducing the amount of the wavelength conversion agent, the thickness of the optical member 30 can be reduced, and further the thickness of the surface light source device 20 can also be reduced.

[0194] In a specific example of this embodiment, the transmittance of the primary light LA ​​of the second wavelength selecting section 55 may be higher than the transmittance of the primary light LA ​​of the first wavelength selecting section 45. The transmittance of the secondary light LB of the first wavelength selecting section 45 may be higher than the transmittance of the secondary light LB of the second wavelength selecting section 55. In a specific example of this embodiment, the reflectance of the primary light LA ​​of the second wavelength selecting section 55 may be lower than the reflectance of the primary light LA ​​of the first wavelength selecting section 45. The reflectance of the secondary light LB of the first wavelength selecting section 45 may be lower than the reflectance of the secondary light LB of the second wavelength selecting section 55.

[0195] According to such optical characteristics, the efficiency of use of the light from the light source can be improved by increasing the transmittance of the second wavelength selection unit 55 for the primary light LA. The efficiency of use of the secondary light can be improved by increasing the transmittance of the first wavelength selection sheet 40 for the secondary light LB. The improved efficiency of use of the secondary light can further save the wavelength conversion agent 67. The in-plane distribution of brightness can be more effectively uniformed. Accordingly, the distance between the optical member 30 and the light source 23 in the first direction D1 can be further shortened, and the thickness of the surface light source device 20 can be further reduced. The area in which the light emitted from one light source 23 spreads uniformly can be widened. The number of light sources 23 used in combination with the optical member 30 can be further reduced. The distance between adjacent light sources 23 can be further shortened.

[0196] In a specific example of the present embodiment, the wavelength conversion sheet 60 may be located on the light-entering side of the first wavelength selection sheet 40 in the first direction D1. With such an arrangement, the primary light LA ​​transmitted through the wavelength conversion sheet 60 can be reflected by the first wavelength selection sheet 40 with high reflectance. The primary light LA ​​reflected by the first wavelength selection sheet 40 can be re-incident on the wavelength conversion sheet 60. Therefore, the wavelength conversion agent 67 contained in the wavelength conversion sheet 60 can be used more efficiently. The wavelength conversion agent 67 contained in the wavelength conversion sheet 60 can be further saved.

[0197] In a specific example of the present embodiment, the transmittance of the first wavelength selection unit 45 for the primary light LA ​​incident on the first wavelength selection unit 45 at an incident angle greater than 0° may be greater than the transmittance of the first wavelength selection unit 45 for the primary light LA ​​incident on the first wavelength selection unit 45 at an incident angle of 0°. This optical characteristic further promotes the diffusion of the primary light LA, and more effectively uniforms the in-plane brightness distribution and the in-plane color distribution. Accordingly, the distance between the optical member 30 and the light source 23 in the first direction D1 can be further shortened, and the thickness of the surface light source device 20 can be further reduced. The area in which the light emitted from one light source 23 spreads uniformly can be widened. The number of light sources 23 used in combination with the optical member 30 can be further reduced. The distance between adjacent light sources 23 can be further shortened.

[0198] Although one embodiment has been described with reference to a specific example, the above-mentioned specific example does not limit the embodiment. The above-mentioned embodiment can be embodied in various other specific examples, and various omissions, substitutions, changes, additions, etc. can be made without departing from the spirit of the embodiment.

[0199] An example of the modification will be described below with reference to the drawings. In the following description and the drawings used in the following description, parts that can be configured similarly to the above-mentioned specific example are designated by the same reference numerals as those used for the corresponding parts in the above-mentioned specific example, and duplicated descriptions will be omitted.

[0200] As described above, the optical member 30 may further include components in addition to the first wavelength selection sheet 40, the second wavelength selection sheet 50, and the wavelength conversion sheet 60. The optical member 30 may include a light control sheet that exerts optical effects such as reflection, refraction, and diffraction on the incident light. The light control sheet may have a function appropriate for the application of the optical member 30 and the surface light source device 20.

[0201] 11A and 11B, the optical member 30 may further include an optical sheet 80. The optical sheet 80 may be located on the light exit side in the first direction D1 of the first wavelength selection sheet 40. The optical sheet 80 may include an uneven surface 81 facing the light entrance side in the first direction D1.

[0202] As shown in FIG. 11A and FIG. 11B, the optical sheet 80 may include a first surface 80a and a second surface 80b. The first surface 80a faces the light-entering side in the first direction D1. The second surface 80b faces the light-emitting side in the first direction D1. The first surface 80a and the second surface 80b may be a pair of main surfaces of the sheet-like optical sheet 80. In the illustrated example, the first surface 80a includes an uneven surface 81. The uneven surface 81 faces the wavelength conversion sheet 60. The second surface 80b includes a flat surface. The illustrated second surface 80b is a flat surface over the entire surface. The second surface 80b may be a surface perpendicular to the first direction D1. In the illustrated example, the optical sheet 80 is located between the first wavelength selection sheet 40 and a first prism sheet 91 described later in the first direction D1.

[0203] 11A and 11B, the optical sheet 80 includes a plurality of unit optical elements 85 each formed as a convex portion 83 or a concave portion 84. The unit optical elements 85 are elements that change the traveling direction of light by refraction, reflection, or the like. The unit optical elements 85 are a concept that includes elements called unit shape elements, unit prisms, and unit lenses. The unit optical elements 85 may directly face the first wavelength selection sheet 40. The unit optical elements 85 form an uneven surface (prism surface) 81.

[0204] The optical sheet 80 shown in Fig. 11A includes a sheet-like main body 82 and a plurality of convex portions 83 provided on the main body 82. In the example shown in Fig. 11A, the plurality of convex portions 83 may be provided adjacent to each other with no gaps. The optical sheet 80 shown in Fig. 11B includes a main body 82 having a plurality of concave portions 84 provided on a surface serving as the light-entering side in the first direction D1. In the example shown in Fig. 11B, the plurality of concave portions 84 may be provided adjacent to each other with no gaps.

[0205] 11A and 11B, the unit optical elements 85 have element surfaces 86 that are inclined with respect to the first direction D1. The unit optical elements 85 are defined by the element surfaces 86. The concave-convex surface (prism surface) 81 of the optical sheet 80 is constituted by the element surfaces (element prism surfaces) 86 of the unit optical elements (unit prisms) 85.

[0206] The optical characteristics of the uneven surface 81 are affected by the inclination angle of the element surface 86 of the unit optical element 85. Therefore, the cross-sectional shape of the unit optical element 85 can be appropriately adjusted based on the optical characteristics required for the surface light source device 20 and the optical member 30. The inclination angles of the element surfaces 86 included in one unit optical element 85 may be different from each other or may be the same. The optical sheet 80 may include unit optical elements 85 that are different in at least one of the shape and the orientation, or may include only unit optical elements 85 that are identical to each other. The optical sheet 80 may include both unit optical elements 85 as convex portions 83 and unit optical elements 85 as concave portions 84.

[0207] 11A and 11B, the element surface (element prism surface) 86 may be curved to some extent. The unit optical element 85 may have an outer shape of a part of a sphere such as a hemisphere, or may have an outer shape of a part of a spheroid.

[0208] The plurality of unit optical elements 85 may be two-dimensionally arranged. According to this example, the element surfaces 86 of the unit optical elements 85 included in the optical sheet 80 face various directions. As a result, the optical sheet 80 can guide light in various directions by the two-dimensionally arranged unit optical elements 85. That is, the light can be guided in a plurality of non-parallel directions, and the in-plane distribution of illuminance can be effectively uniformed. Each unit optical element 85 may be configured to be rotationally symmetric about an axis parallel to the first direction D1. For example, each unit optical element 85 may be configured to be three-fold, four-fold, or six-fold symmetric about an axis parallel to the first direction D1.

[0209] The plurality of unit optical elements 85 may be arranged irregularly or regularly. Regularly arranging the plurality of unit optical elements 85 can facilitate the design of the optical sheet 80. Regularly arranging the plurality of unit optical elements 85 can facilitate the arrangement of the unit optical elements 85 without gaps.

[0210] If the dimensions of the unit optical elements 85 are large when observed from the first direction D1, unevenness in brightness due to the shape of the unit optical elements 85 is easily visible. From the viewpoint of suppressing such defects, the maximum length of the unit optical elements 85 in the direction perpendicular to the first direction D1 may be 1.5 mm or less, 1 mm or less, or 0.5 mm or less. The arrangement pitch of the unit optical elements 85 may be 0.01 mm or more and 1.5 mm or less. Furthermore, from the viewpoint of effectively uniforming the in-plane distribution of illuminance on the light-emitting side surface 30b of the optical member 30 when applied to the surface light source device 20, the arrangement pitch of the unit optical elements 85 may be 0.05 mm or more and 1 mm or less, or 0.1 mm or more and 0.5 mm or less. The height or depth of the unit optical elements 85 in the first direction D1 may be 0.025 mm or more and 0.5 mm or less, or 0.05 mm or more and 0.25 mm or less.

[0211] 12A and 12B show specific examples of unit optical elements 85 included in the optical sheet 80. In the example shown in FIG. 12A and FIG. 12B, the arrangement of the unit optical elements 85 is a square arrangement. The unit optical elements 85 are arranged at a constant pitch in the second direction D2. The unit optical elements 85 are also arranged at a constant pitch in the third direction D3. The arrangement pitch in the second direction D2 and the arrangement pitch in the third direction D3 may be the same or different. In the example shown in FIG. 12A and FIG. 12B, the unit optical elements 85 may be arranged closely together with no gaps. In the illustrated example, the arrangement pitch in the second direction D2 and the arrangement pitch in the third direction D3 are the same.

[0212] The unit optical elements 85 may be arranged in directions inclined to the second direction D2 and the third direction D3. For example, in the example shown in Fig. 12C, a plurality of unit optical elements 85 are arranged at a constant pitch in two directions inclined at ±45° with respect to the second direction D2. The arrangement of Fig. 12C can be applied to the unit optical elements 85 shown in Fig. 12B. According to this example, the element surface 86 is oriented in two directions inclined at ±45° with respect to the second direction D2, and light can be spread in these two directions.

[0213] The optical sheet 80 shown in FIGS. 11A to 12C can be produced by embossing or resin molding.

[0214] Next, the function of the optical sheet 80 will be described. The optical sheet 80 can selectively reflect the primary light LA ​​at the second surface 80b with high reflectance. By selectively reflecting the primary light LA ​​with high reflectance by the optical sheet 80, diffusion of the primary light LA ​​is promoted. This makes it possible to more effectively uniform the in-plane distribution of brightness and the in-plane distribution of color.

[0215] The primary light LA ​​and the secondary light LB are incident on the optical sheet 80. When the primary light LA ​​is incident on the optical sheet 80, it travels in a direction within a narrow angle range according to the transmission characteristics of the first wavelength selection sheet 40. In an example in which the optical characteristics of the optical sheet 80 have the above-mentioned incidence angle dependency, the primary light LA ​​travels in a direction greatly inclined with respect to the first direction D1.

[0216] 13, light L131 as primary light LA ​​incident on the optical sheet 80 is likely to be incident on element surfaces 86 that are inclined with respect to the first direction D1, among element surfaces 86 constituting the uneven surface 81, from the traveling direction side. The traveling direction of this light L131 is not greatly bent due to refraction at the uneven surface 81 when it is incident on the optical sheet 80. That is, the primary light LA ​​can maintain a traveling direction that is very greatly inclined with respect to the first direction D1 within the optical sheet 80.

[0217] As a result, the incident angle θy on the flat second surface 80b of the optical sheet 80 becomes large. As a result, the primary light LA ​​that has not been wavelength converted by the wavelength conversion agent 67 is reflected at the second surface 80b with a high reflectance. Furthermore, since the incident angle θy becomes large, the primary light LA ​​can be totally reflected at the second surface 80b.

[0218] In FIG. 13, in order to facilitate understanding of the optical action regarding the optical path within the wavelength conversion sheet 60, the optical sheet 80 is shown to have a small thickness.

[0219] On the other hand, the direction in which the secondary light LB is emitted from the wavelength conversion agent 67 does not depend on the direction of incidence on the wavelength conversion agent 67. Therefore, the secondary light LB is diffused light and cannot be reflected with a high reflectance by the second surface 80b.

[0220] As described above, by combining the transmission characteristic having the incidence angle dependency of the first wavelength selection sheet 40 that affects the emission direction of the primary light LA ​​with the uneven surface 81 of the optical sheet 80, the second surface 80b of the optical sheet 80 selectively reflects the primary light LA ​​with high reflectance. Therefore, the diffusion of the primary light LA ​​is further promoted, and the in-plane distribution of brightness and the in-plane distribution of color can be more effectively uniformed. Accordingly, the distance along the first direction D1 between the optical member 30 and the light source 23 can be further shortened, and the thickness of the surface light source device 20 can be further reduced. The area in which the light emitted from one light source 23 spreads uniformly can be widened. The number of light sources 23 used in combination with the optical member 30 can be further reduced. The distance between adjacent light sources 23 can be further shortened. In addition, the utilization efficiency of the wavelength conversion agent 67 can be further improved, and the content of the wavelength conversion agent 67 in the wavelength conversion section 65 can be further reduced.

[0221] The optical sheet 80 may be positioned adjacent to the first wavelength selection sheet 40 from the light output side in the first direction D1. The uneven surface 81 may directly face the first wavelength selection sheet 40. According to this example, the traveling direction of the primary light LA ​​when it is emitted from the wavelength conversion sheet 60 is stably maintained when it is incident on the optical sheet 80. Therefore, the optical sheet 80 can selectively reflect the primary light LA ​​with high reflectance more stably.

[0222] As another modification, the positions of the first wavelength selection sheet 40, the second wavelength selection sheet 50, and the wavelength conversion sheet 60 in the first direction D1 may be changed. As shown in Fig. 14 and Fig. 15, the second wavelength selection sheet 50 is located on the light entrance side of the wavelength conversion sheet 60 in the first direction D1. As shown in Fig. 14 and Fig. 15, the first wavelength selection sheet 40 is located on the light entrance side of the wavelength conversion sheet 60 in the first direction D1.

[0223] In the example shown in Fig. 14, the second wavelength selection sheet 50 is located on the light incident side in the first direction D1 of the first wavelength selection sheet 40. In the example shown in Fig. 14, the second wavelength selection sheet 50, the first wavelength selection sheet 40, and the wavelength conversion sheet 60 are located in this order from the light incident side to the light output side in the first direction D1. In the example shown in Fig. 14, the first wavelength selection sheet 40 is located between the second wavelength selection sheet 50 and the wavelength conversion sheet 60 in the first direction D1.

[0224] In the example shown in Fig. 15, the first wavelength selection sheet 40 is located on the light incident side in the first direction D1 of the second wavelength selection sheet 50. In the example shown in Fig. 15, the first wavelength selection sheet 40, the second wavelength selection sheet 50, and the wavelength conversion sheet 60 are located in this order from the light incident side to the light output side in the first direction D1. In the example shown in Fig. 15, the second wavelength selection sheet 50 is located between the first wavelength selection sheet 40 and the wavelength conversion sheet 60 in the first direction D1.

[0225] In the example shown in FIG. 14 and FIG. 15, the first wavelength selection sheet 40 is located on the light-entering side in the first direction D1 of the wavelength conversion sheet 60. The optical characteristics of the first wavelength selection sheet 40 may have the incidence angle dependency as described above. Since the wavelength conversion sheet 60 is located on the light-emitting side of the first wavelength selection sheet 40, the traveling direction of the primary light LA ​​traveling in the wavelength conversion sheet 60 is largely inclined with respect to the first direction D1. Therefore, the optical path length of the primary light LA ​​in the wavelength conversion sheet 60 can be secured to be long. This allows the wavelength conversion agent 67 to be used more efficiently. The amount of the wavelength conversion agent 67 contained in the wavelength conversion sheet 60 can be reduced.

[0226] The optical sheet 80 described above can be applied to the optical member 30 shown in Fig. 14 and Fig. 15. As shown in Fig. 16, the wavelength conversion sheet 60 may include a wavelength conversion section 65 and an optical element section 70 superimposed on the wavelength conversion section 65 in the first direction D1. The optical element section 70 is located on the light incident side of the wavelength conversion section 65 in the first direction D1. The optical element section 70 may be located adjacent to the wavelength conversion section 65 from the light incident side in the first direction D1.

[0227] This optical element portion 70 is configured similarly to the optical sheet 80. The wavelength conversion sheet 60 may include the above-mentioned optical sheet 80 as the optical element portion 70. The optical sheet 80 may be bonded to the wavelength conversion portion 65. The optical element portion 70 includes an uneven surface 81 facing the light incident side in the first direction D1. The uneven surface 81 may face the first wavelength selection sheet 40. The optical element portion 70 may include a plurality of unit optical elements 85 that form the uneven surface 81. In the example shown in FIG. 16, the primary light LA ​​can be selectively reflected at a high reflectance by the second surface 60b of the wavelength conversion sheet 60.

[0228] As another modification, as shown by a two-dot chain line in FIG. 2, the surface light source device 20 may include a thermoplastic resin layer 99 located between the light source substrate 22 and the optical member 30. The thermoplastic resin layer 99 may be in contact with the light source substrate 22. The thermoplastic resin layer 99 may be bonded to the light source substrate 22. The thermoplastic resin layer 99 may be in contact with the optical member 30. The thermoplastic resin layer 99 may be bonded to the optical member 30. The thermoplastic resin layer 99 may function as a spacer that maintains a constant distance between the light source substrate 22 and the optical member 30. The thermoplastic resin layer 99 may function as a protective layer that protects the light source 23 and the wiring 29 of the light source substrate 22. The thermoplastic resin layer 99 may function as a sealing layer that seals the light source 23 and the wiring 29 of the light source substrate 22.

[0229] <<Simulation>>

[0230] Here, the results of a simulation carried out by the present inventors will be described. The simulation was a ray tracing simulation using LightTools manufactured by Synopsys.

[0231] <Simulation model A> Model A, which was the subject of the simulation, was the surface light source device shown in Figures 1 and 2. That is, the surface light source device included a light source substrate and an optical member. The optical member included, in order from the light incident side in the first direction D1, a second wavelength selection sheet, a wavelength conversion sheet, a first wavelength selection sheet, a first prism sheet, a second prism sheet, and a reflective polarizing plate.

[0232] The light source substrate had blue micro light-emitting diodes arranged at a pitch of 6 mm in both the first and second directions. The distance DX (see FIG. 4) along the first direction D1 between the surface of the light source facing the optical member and the light-entering side surface of the optical member was set to eight different values: 0.8 mm, 1.0 mm, 2.0 mm, 3.0 mm, 5.0 mm, 6.0 mm, 7.0 mm, and 8.0 mm.

[0233] The first wavelength selection sheet included only the first wavelength selection portion. The first wavelength selection portion had the optical characteristics shown in Fig. 7 and Fig. 8. A pair of main surfaces of the first wavelength selection portion were parallel. The second wavelength selection sheet included only the second wavelength selection portion. The second wavelength selection portion had the optical characteristics shown in Fig. 9. A pair of main surfaces of the second wavelength selection portion were parallel.

[0234] The wavelength conversion sheet included a first barrier layer, a wavelength conversion portion, and a second barrier layer. The wavelength conversion portion included a base material and a wavelength conversion agent dispersed in the base material. The wavelength conversion agent included a first conversion agent that absorbs blue light from the light source and emits green light, and a second conversion agent that absorbs blue light from the light source and emits red light. The content of the wavelength conversion agent was determined by a ray tracing simulation using LightTools manufactured by Synopsys. In a simulation targeting a surface light source device, the content was determined to be an amount that can cause the light emitting surface to emit white light.

[0235] The model was created assuming that the first prism sheet and the second prism sheet 92 were "BEF" (registered trademark) available from 3M Corporation, USA. The model was created assuming that the reflective polarizing plate was "DBEF" (registered trademark) available from 3M Corporation, USA.

[0236] <Simulation model B> Model B, which was the subject of the simulation, differed from model A in that it did not include the first wavelength selection sheet and that the amount of the wavelength conversion agent was changed, but was otherwise similar to model A. The optical members of model B included, in order from the light incident side in the first direction D1, a second wavelength selection sheet, a wavelength conversion sheet, a first prism sheet, a second prism sheet, and a reflective polarizing plate.

[0237] In Model B, the amount of wavelength conversion agent was determined by a ray tracing simulation using LightTools made by Synopsys. In the simulation for a surface light source device, the amount was determined to be the amount that would allow the light emitting surface to emit white light. The amount of wavelength conversion agent required in Model B was 25 times that required in Model A.

[0238] <Simulation model C> Model C, which was the subject of the simulation, differed from model A in that it did not include the second wavelength selection sheet 50 and that the amount of the wavelength conversion agent was changed, but was otherwise similar to model A. The optical members of model C included, in order from the light incident side in the first direction D1, a wavelength conversion sheet, a first wavelength selection sheet, a first prism sheet, a second prism sheet, and a reflective polarizing plate.

[0239] In Model C, the amount of wavelength conversion agent was determined by a ray tracing simulation using LightTools made by Synopsys. In the simulation for a surface light source device, the amount was determined to be the amount that would allow the light emitting surface to emit white light. The amount of wavelength conversion agent required in Model C was six times that required in Model A.

[0240] A simulation was carried out to confirm the in-plane brightness distribution and the in-plane color distribution by changing the distance in the first direction between the light source and the optical member. The evaluation was carried out under the following conditions, and the evaluation results are shown in Table 1. Table 1 also shows the relative amounts of wavelength conversion agent required to make the light-emitting surface white in models A to C. A: No in-plane variation in brightness or in-plane variation in color was observed. B: At least one of the in-plane variations in brightness and in-plane variations in color was faintly confirmed. The in-plane variations were at a level that passed the inspection. C: At least one of the brightness and color variations was observed, and the position of the light source was clearly identified. This was to the extent that the product failed the inspection.

[0241] [Table 1] [Explanation of symbols]

[0242] D1: first direction, D2: second direction, D3: third direction, LA: primary light, LB: secondary light, LB1: first secondary light, LB2: second secondary light, 10: display device, 15: display panel, 15a: display surface, 20: surface light source device, 20a: light emitting surface, 22: light source substrate, 23: light source, 25: support substrate, 26: substrate body, 27: reflective layer, 29: wiring, 30: optical member, 30a: light incident side, 30b: light exit side, 40: first wavelength selective sheet, 40a: first surface, 40b: second surface, 45: first wavelength selective portion, 45a: first surface, 45b: second surface, 46: dielectric multilayer film, 50: second wavelength selective sheet, 50a: first surface, 50b: second surface, 55: second wavelength selective portion , 55a: first surface, 55b: second surface, 56: dielectric multilayer film, 60: wavelength conversion sheet, 60a: first surface, 60b: second surface, 63: first barrier layer, 64: second barrier layer, 65: wavelength conversion portion, 65a: first surface, 65b: second surface, 66: base material portion, 67: wavelength conversion agent, 67A: first conversion agent, 67B: second conversion agent, 70: optical element portion, 80: optical sheet, 80a: first surface, 80b: second surface, 81: uneven surface, 82: main body portion, 83: convex portion, 84: concave portion, 85: unit optical element, 86: element surface, 91: first prism sheet, 92: second prism sheet, 93: main body portion, 94: unit prism, 95: reflective polarizing plate, 99: thermoplastic resin layer

Claims

1. A first wavelength selective sheet, a second wavelength selective sheet, and a wavelength conversion sheet are stacked in a first direction, the second wavelength selection sheet is located on a light incident side of the wavelength conversion sheet in the first direction, the wavelength conversion sheet includes a wavelength conversion agent that absorbs primary light and emits secondary light having a longer wavelength than the primary light, the first wavelength selective sheet includes a first wavelength selecting portion, the second wavelength selective sheet includes a second wavelength selective portion, a transmittance of the primary light of the first wavelength selection unit is lower than a transmittance of the secondary light of the first wavelength selection unit, an optical member, wherein the transmittance of the secondary light from the second wavelength selection portion is lower than the transmittance of the primary light from the second wavelength selection portion.

2. a transmittance of the primary light of the second wavelength selection unit is higher than a transmittance of the primary light of the first wavelength selection unit, The optical member according to claim 1 , wherein a transmittance of the secondary light from the first wavelength selection portion is higher than a transmittance of the secondary light from the second wavelength selection portion.

3. The optical member according to claim 1 , wherein the wavelength conversion sheet is located on a light-entering side of the first wavelength selection sheet in the first direction.

4. 4. The optical element according to claim 3, wherein a transmittance of the first wavelength selection section for the primary light incident on the first wavelength selection section at an incident angle greater than 0° is greater than a transmittance of the first wavelength selection section for the primary light incident on the first wavelength selection section at an incident angle of 0°.

5. The optical member according to claim 1 , wherein the first wavelength selection sheet is located on a light-entering side of the wavelength conversion sheet in the first direction.

6. 6. The optical element according to claim 5, wherein the transmittance of the first wavelength selection section for the primary light incident on the first wavelength selection section at an incident angle greater than 0° is greater than the transmittance of the first wavelength selection section for the primary light incident on the first wavelength selection section at an incident angle of 0°.

7. an optical sheet located on a light output side of the first wavelength selection sheet in the first direction, the optical sheet includes an uneven surface facing a light incident side in the first direction, The optical member according to claim 4 , wherein the optical sheet includes a plurality of unit optical elements that constitute the uneven surface.

8. the wavelength conversion sheet includes a wavelength converting portion including the wavelength conversion agent and an optical element portion located on a light incident side of the wavelength converting portion in the first direction, the wavelength conversion sheet includes an uneven surface facing a light incident side in the first direction, The optical member according to claim 6 , wherein the optical element portion includes a plurality of unit optical elements that constitute the uneven surface.

9. a reflective polarizing plate superimposed on the first wavelength selective sheet, the second wavelength selective sheet, and the wavelength conversion sheet, The optical member according to claim 1 , wherein the reflective polarizing plate is located on a light exit side in the first direction of the first wavelength selective sheet, the second wavelength selective sheet, and the wavelength conversion sheet.

10. a prism sheet overlapping the first wavelength selection sheet, the second wavelength selection sheet, and the wavelength conversion sheet; The optical member according to claim 1 , wherein the prism sheet is located on a light exit side in the first direction of the first wavelength selection sheet, the second wavelength selection sheet, and the wavelength conversion sheet.

11. An optical member according to any one of claims 1 to 10; a light source located on a light incident side of the optical member in the first direction.

12. An optical member according to any one of claims 1 to 10; A surface light source device comprising: a light source substrate including a reflective layer located on the light-entering side of the optical member in the first direction; and a light source that emits light incident on the optical member.

13. The surface light source device according to claim 11 , A display device comprising the surface light source device and a display panel overlapped therewith.

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