Surface light source device and display device

Abstract

To achieve thinness of a plane light source device by reducing an amount of wavelength conversion material.SOLUTION: An optical member includes: a selection transmission sheet 40 that includes a selection transmission part; and a wavelength conversion sheet 60 that includes a first surface serving as a selection transmission sheet side, and a second surface facing the first surface. Transmittance of the selection transmission part as for light of a specific wavelength to be incident upon the selection transmission part at a certain angle of incidence larger than 0° is larger than that of the selection transmission part as for light of the specific wavelength to be incident upon the selection transmission part at the angle of incidence of 0°. The second surface includes a rugged surface. The wavelength conversion sheet includes a wavelength conversion agent that absorbs primary light and emits secondary light. The secondary light has a wavelength different from the primary light.SELECTED DRAWING: Figure 5

Description

[Technical Field]

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

[0002] As disclosed in Patent Document 1, a surface light source device having a monochromatic light source is known. The surface light source device of Patent Document 1 includes a fluorescent layer containing a wavelength conversion agent. When light from the light source collides with the wavelength conversion agent, the wavelength conversion agent absorbs the light from the light source and emits light of a different wavelength. By incorporating a sufficient amount of wavelength conversion agent into the fluorescent layer, the emitted color can be adjusted. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-519232 Summary of the Invention [Problem to be solved by the invention]

[0004] If the amount of wavelength conversion agent can be reduced, it is possible to reduce the thickness of optical members and surface light source devices. An object of the present disclosure is to reduce the amount of wavelength conversion agent. [Means for solving the problem]

[0005] A first optical member according to an embodiment of the present disclosure includes: a selectively permeable sheet including a selectively permeable portion; a wavelength conversion sheet including a first surface facing the selective transmission sheet and a second surface facing the first surface, the transmittance of the selective transmission portion for light of a specific wavelength that is incident on the selective transmission portion at an incident angle greater than 0° is greater than the transmittance of the selective transmission portion for light of the specific wavelength that is incident on the selective transmission portion at an incident angle of 0°; the second surface includes a textured surface; the wavelength conversion sheet includes a wavelength conversion agent that absorbs primary light and emits secondary light, The secondary light has a wavelength different from that of the primary light.

[0006] In the first optical member according to the embodiment of the present disclosure, the selective transmission sheet may be bonded to the wavelength conversion sheet.

[0007] A first optical member according to an embodiment of the present disclosure includes: Further provided is a light diffusion sheet bonded to the selective transmission sheet, The selective transmission sheet may be located between the light diffusion sheet and the wavelength conversion sheet.

[0008] A second optical member according to an embodiment of the present disclosure includes: A light diffusion sheet; a wavelength conversion sheet including a first surface facing the light diffusion sheet and a second surface facing the first surface, the second surface includes a textured surface; the wavelength conversion sheet includes a wavelength conversion agent that absorbs primary light and emits secondary light, The secondary light has a wavelength different from that of the primary light.

[0009] In the first and second optical members according to an embodiment of the present disclosure, the wavelength conversion sheet includes an optical element portion including the uneven surface, The optical element section may include a plurality of unit optical elements that form the concave-convex surface.

[0010] In the first and second optical members according to an embodiment of the present disclosure, the wavelength conversion agent includes a first conversion agent that absorbs the primary light and emits a first secondary light, and a second conversion agent that absorbs the primary light and emits a second secondary light; the wavelength of the second secondary light is longer than the wavelength of the first secondary light; The wavelength of the first secondary light may be longer than the wavelength of the primary light.

[0011] In the first and second optical members according to an embodiment of the present disclosure, the wavelength conversion sheet includes a wavelength converting portion containing the wavelength converting agent, a first barrier layer and a second barrier layer overlapped with the wavelength converting portion, and an optical element portion overlapped with the second barrier layer and including the uneven surface, the wavelength converting portion is located between the first barrier layer and the second barrier layer, The second barrier layer may be located between the wavelength converting portion and the optical element portion.

[0012] A first surface light source device according to an embodiment of the present disclosure includes: one of a first and a second optical member according to an embodiment of the present disclosure; and a light source facing the optical member.

[0013] A second surface light source device according to an embodiment of the present disclosure includes: one of a first and a second optical member according to an embodiment of the present disclosure; The light source substrate includes a reflective layer facing the optical member and a light source that emits light incident on the optical member.

[0014] The first and second surface light source devices according to the embodiment of the present disclosure include: Further comprising a reflective polarizing plate superimposed on the optical member, The optical member may be located between the light source and the reflective polarizer.

[0015] The first and second surface light source devices according to the embodiment of the present disclosure include: Further, an optical sheet is provided overlaid on the optical member, The optical member may be located between the light source and the optical sheet.

[0016] A display device according to an embodiment of the present disclosure includes: one of the first and second surface light source devices according to an embodiment of the present disclosure; The display device includes a display panel overlapped with the surface light source device.

[0017] A first wavelength conversion sheet according to an embodiment of the present disclosure includes: a wavelength conversion sheet to be used by being superimposed on a selective transmission sheet including a selective transmission portion having a transmittance of light of a specific wavelength incident at an incident angle larger than 0° that is larger than the transmittance of light of the specific wavelength incident at an incident angle of 0°, a first surface that faces the selective permeation sheet; a second surface opposite to the first surface; a wavelength converting agent located between the first surface and the second surface, an optical element portion that configures the second surface is provided; the optical element unit includes a plurality of unit optical elements, the second surface includes a concave-convex surface formed by a plurality of unit optical elements, the wavelength conversion agent absorbs primary light of the specific wavelength and emits secondary light; The secondary light has a wavelength different from the specific wavelength.

[0018] A first wavelength conversion sheet according to an embodiment of the present disclosure includes: A first surface that faces the light source; a second surface opposite to the first surface; a wavelength converting agent located between the first surface and the second surface, an optical element portion that configures the second surface is provided; the optical element unit includes a plurality of unit optical elements, the second surface includes a concave-convex surface formed by a plurality of unit optical elements, the wavelength conversion agent absorbs the primary light emitted from the light source and emits the secondary light; The secondary light has a wavelength different from that of the primary light. [Effects of the Invention]

[0019] According to the present disclosure, the amount of wavelength conversion agent can be reduced. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1 is a diagram for explaining an embodiment, and is a perspective view showing a display device and a surface light source device. [Figure 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. [Figure 3] FIG. 3 is a plan view showing the light source substrate shown in FIG. 2, illustrating an example of the 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 configuration of the light source substrate. [Figure 5] FIG. 5 is a cross-sectional view showing an example of the configuration of the optical member shown in FIG. [Figure 6] FIG. 6 is a perspective view showing a light diffusion sheet that can be included in the surface light source device shown in FIG. 5, and shows an example of a unit diffusion element of the light diffusion sheet. [Figure 7] FIG. 7 is a graph showing an example of the optical characteristics of a selective transmission portion that can be included in the optical sheet shown in FIG. [Figure 8A] FIG. 8A is a cross-sectional view showing an example of a wavelength conversion sheet that can be included in the optical member shown in FIG. [Figure 8B] FIG. 8B is a cross-sectional view showing another example of a wavelength conversion sheet that can be included in the optical member shown in FIG. [Figure 9] FIG. 9 is a vertical cross-sectional view showing an example of a wavelength converting portion that can be included in the wavelength converting sheet shown in FIGS. 8A and 8B. [Figure 10A] FIG. 10A is a plan view showing an example of an optical element section that can be included in the wavelength conversion sheet shown in FIGS. 8A and 8B, and shows the arrangement of unit optical elements that can be included in the optical element section. [Figure 10B] FIG. 10B is a perspective view showing a specific example of the unit optical element shown in FIG. 10A. [Figure 10C] FIG. 10C is a diagram corresponding to FIG. 10A, and shows another example of the arrangement of unit optical elements. [Figure 11A]FIG. 11A is a plan view showing another example of an optical element section that can be included in the wavelength conversion sheet shown in FIGS. 8A and 8B, and shows the arrangement of unit optical elements that can be included in the optical element section. [Figure 11B] FIG. 11B is a perspective view showing a specific example of the unit optical element shown in FIG. 11A. [Figure 12] FIG. 12 is a perspective view showing an example of an optical sheet that can be included in the surface light source device shown in FIG. [Figure 13] FIG. 13 is a diagram illustrating the function of the wavelength conversion sheet that can be included in the optical member shown in FIG. [Figure 14] FIG. 14 is a view corresponding to FIG. 5 and is a vertical cross-sectional view showing another example of the optical member. [Figure 15] FIG. 15 is a diagram showing the in-plane distribution of radiation intensity on the light emitting surface of the surface light source device according to Example 1. As shown in FIG. [Figure 16] FIG. 16 is a diagram showing the in-plane distribution of radiation intensity on the light-emitting surface of the surface light source device according to Comparative Example 1. As shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0021] An embodiment of the present invention will be described below with reference to the drawings. In the drawings accompanying this specification, the scale and aspect ratios have been appropriately changed and exaggerated from those of the actual objects for the sake of ease of illustration and understanding. Configurations shown in some drawings may be omitted in other drawings.

[0022] In this specification, terms that specify shapes, geometric conditions, and their degrees, such as "parallel," "orthogonal," and "identical," as well as values ​​of lengths and angles, are not limited to their strict meanings, but are interpreted to include a range within which similar functions can be expected.

[0023] In this specification, terms such as "sheet," "film," and "plate" are not distinguished from one another solely on the basis of differences in name. For example, a "wavelength conversion sheet" cannot be distinguished from a member called a wavelength conversion film or a wavelength conversion plate solely on the basis of differences in name. A "selective transmission sheet" cannot be distinguished from a member called a selective transmission film or a selective transmission plate solely on the basis of differences in name.

[0024] In this specification, the normal direction of a sheet-like (sheet-like, plate-like) member refers to the normal direction to the sheet surface of the target sheet-like (film-like, plate-like) member. The "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.

[0025] To clarify the relationship between directions between drawings, several drawings use arrows with the same symbol to indicate the first direction D1, the second direction D2, and the third direction D3 as common directions. The tip of the arrow is the first side of each direction. The opposite side of the arrow is the second side of each direction. For example, as shown in Figure 2, a symbol with an x ​​in a circle indicates an arrow pointing into the paper in a direction perpendicular to the paper surface of the drawing. For example, as shown in Figure 3, a symbol with a dot in a circle indicates an arrow pointing toward the paper in a direction perpendicular to the paper surface of the drawing.

[0026] 1 to 14 are diagrams illustrating an embodiment. FIG. 1 is a perspective view schematically illustrating 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, moving images, still images, text information, or an image composed of a combination of these. The display device 10 may be used for various purposes, such as advertising, presentations, television images, and display of various information, indoors or outdoors. The display device 10 may be used, for example, as an in-vehicle liquid crystal display device. 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.

[0027] FIG. 2 is a longitudinal cross-sectional view showing a specific example of a surface light source device 20. As shown in FIG. 2, the surface light source device 20 includes, as its main components, a light source 23 and an optical member 30 that adjusts the optical path of 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 in-plane variations in illuminance caused by the arrangement of the light source 23. 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 near the light-emitting side surface 30b.

[0028] The display device 10, surface light source device 20, and optical member 30 according to one embodiment will be described below with reference to specific examples shown in the drawings.

[0029] As shown in FIG. 1 , the display panel 15 is overlapped with the surface light source device 20 in the third direction D3. The display panel 15 is disposed facing 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, which is the surface facing the opposite side to the surface light source device 20 in the third direction D3, i.e., the first side. In the illustrated example, the display panel 15 is flat. The display panel 15 extends in a first direction D1 and a second direction D2 perpendicular to the third direction D3. The display panel 15 has a rectangular shape when observed from the third direction D3.

[0030] Display panel 15 is configured as, for example, a transmissive liquid crystal display panel. A portion of the light incident from surface light source device 20 passes through display panel 15, which is a liquid crystal display panel, to display an image on display surface 15a. Display panel 15 includes a liquid crystal layer containing a liquid crystal material. The light transmittance of display panel 15 changes depending on the strength of the electric field applied to the liquid crystal layer.

[0031] 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 is 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 is provided within a region that overlaps with the optical member 30 when projected in the third direction D3.

[0032] The surface light source device 20 shown in Fig. 2 includes a light source substrate 22 including a light source 23, an optical member 30, a first optical sheet 81, a second optical sheet 82, and a reflective polarizing plate 85. The light source substrate 22, the optical member 30, the first optical sheet 81, the second optical sheet 82, and the reflective polarizing plate 85 are stacked in this order in the third direction D3. The light source substrate 22, the optical member 30, the first optical sheet 81, the second optical sheet 82, and the reflective polarizing plate 85 are sheet-shaped. The light source substrate 22, the optical member 30, the first optical sheet 81, the second optical sheet 82, and the reflective polarizing plate 85 extend in the first direction D1 and the second direction D2.

[0033] The light source substrate 22 includes 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 the third direction D3.

[0034] The light source 23 has a light-emitting element that emits light. The light-emitting element may be a light-emitting diode (LED). The size of the light-emitting diode is not particularly limited. To make the image of the light source 23 less noticeable, a small light-emitting diode, such as a mini LED or a micro LED, may be used. Specifically, the lengths WL1 and WL2 of one side of the rectangular light source 23 when observed from the third direction D3 shown in FIG. 3 may be 0.5 mm or less, or 0.2 mm or less.

[0035] The emission wavelength of the light source 23 can be selected appropriately depending on the application of the surface light source device 20. The light emitted from the light source 23 is absorbed as primary light LA ​​by a wavelength conversion agent 67 described below. Therefore, the emission wavelength of the light source 23 can be selected appropriately 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.

[0036] 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 whose optical axis is aligned with the third direction D3 may be configured to obtain a peak luminous intensity in a direction other than the third direction D3. For example, the light source 23 may have a bud wing light distribution as disclosed in JP6299811B. As an example, the light source 23 may be configured only with a light-emitting element. As another example, the light source 23 may include, in addition to the light-emitting element, optical elements such as a cover and a lens that adjust the light distribution from the light-emitting element.

[0037] 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. From the viewpoint of suppressing 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 plane perpendicular to the third direction D3. As an example of a regular arrangement of the light sources 23, a honeycomb arrangement or a square arrangement may be adopted. In a 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 a square arrangement, the light sources 23 may be arranged at a constant pitch in each of two directions perpendicular to each other.

[0038] In the example shown in FIG. 3, the multiple light sources 23 are arranged at a constant pitch in each of a first direction D1 and a second direction D2 that are perpendicular to each other. In the example shown, the arrangement pitch PL1 of the light sources 23 in the first direction D1 and the arrangement pitch PL2 of the light sources 23 in the second direction D2 are the same. The arrangement pitch PL1 and the arrangement pitch PL2 may be different. In the example shown, the first direction D1 and the second direction D2 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.

[0039] Next, the support substrate 25 that constitutes the light source substrate 22 together with the plurality of light sources 23 will be described. The support substrate 25 supports the plurality of light sources 23 from the second side in the third direction D3. The support substrate 25 is sheet-shaped. The support substrate 25 may include a circuit that supplies power to the light sources 23. The support substrate 25 may have optical reflectivity that reflects light toward the optical member 30.

[0040] The support substrate 25 shown in FIG. 4 includes a sheet-like substrate body 26, and a reflective layer 27 and wiring 29 provided on the substrate body 26. The substrate body 26 extends in a first direction D1 and a second direction D2. The substrate body 26 may be insulating. The substrate body 26 may be a resin film, for example, a polyethylene terephthalate film. The wiring 29 is electrically connected to the light source 23. The wiring 29 is 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.

[0041] The reflective layer 27 is laminated on the substrate body 26 from the optical member 30 side. The reflective layer 27 covers the area of ​​the substrate body 26 where the light source 23 is not disposed. The reflective layer 27 is reflective to light of a specific wavelength emitted by the light source 23 or to light used for emission in the surface light source device 20. The reflection by the reflective layer 27 may be regular reflection, also known as specular reflection, diffuse reflection, or anisotropic diffuse reflection. The reflective layer 27 having diffuse reflectivity may include a white reflective layer containing white particles such as silicon dioxide. The reflective layer 27 may be a metal layer laminated on the substrate body 26, or a reflective diffractive optical element.

[0042] The optical member 30 includes a selective transmission sheet 40 and a wavelength conversion sheet 60, in this order. The selective transmission sheet 40 and the wavelength conversion sheet 60 are stacked in the third direction D3. That is, the third direction D3 is the stacking direction of the selective transmission sheet 40 and the wavelength conversion sheet 60. The selective transmission sheet 40 is located on the second side of the wavelength conversion sheet 60 in the third direction D3. The wavelength conversion sheet 60 is located on the first side of the selective transmission sheet 40 in the third direction D3. The selective transmission sheet 40 and the wavelength conversion sheet 60 may be bonded to each other. The selective transmission sheet 40 and the wavelength conversion sheet 60 may simply be in contact with each other and not bonded to each other. The selective transmission sheet 40 and the wavelength conversion sheet 60 may be separated from each other.

[0043] In the illustrated example, the selective transmission sheet 40 and the wavelength conversion sheet 60 both extend in the first direction D1 and the second direction D2. In the illustrated example, the wavelength conversion sheet 60 forms the light-emitting side surface 30b of the optical member 30. The light-emitting side surface 30b faces a first side, which is the viewer side, in the third direction D3. The illustrated optical member 30 further includes a light diffusion sheet 50. The light diffusion sheet 50 is located on a second side, which is the light source side and is opposite the viewer side in the third direction D3, from the selective transmission sheet 40. The wavelength conversion sheet 60 forms the light-incident side surface 30a of the optical member 30. The light-incident side surface 30a faces the second side in the third direction D3. The illustrated light diffusion sheet 50 is bonded to the selective transmission sheet 40. The light diffusion sheet 50 does not have to be bonded to the selective transmission sheet 40. The light diffusion sheet 50 may be provided separately from the optical member 30.

[0044] The light diffusion sheet 50 changes the traveling direction of light emitted from the light source 23. The light diffusion sheet 50 has a light diffusion function that diffuses light. The light diffusion sheet 50 may include a resin binder and a light diffusion component dispersed in the resin binder. Examples of the light diffusion component include a metal compound, a porous substance containing gas, resin beads surrounding a metal compound, white fine particles, and simple air bubbles. The light diffusion sheet 50 may include a diffractive optical element. The light diffusion sheet 50 may be a layer including a matte surface. The light diffusion sheet 50 may include a microlens or a linear array lens. The light diffusion sheet 50 may be omitted from the selective transmission sheet 40.

[0045] The light diffusion sheet 50 includes a first surface 50a and a second surface 50b. The first surface 50a faces the second side in the third direction D3. The first surface 50a constitutes the light incident side surface 30a. The second surface 50b faces the first side in the third direction D3. The light diffusion sheet 50 is bonded to the selective transmission sheet 40 at the second surface 50b. The light diffusion sheet 50 may be bonded directly to the selective transmission sheet 40. The light diffusion sheet 50 may be bonded to the selective transmission sheet 40 via a bonding layer such as an adhesive layer or a bonding layer.

[0046] In the example shown in Figures 5 and 6, the first surface 50a of the light diffusion sheet 50 is an uneven surface 51. The light diffusion sheet 50 includes a sheet-like main body 52 and a plurality of unit diffusion elements 55, each formed as a convex portion 53 or a concave portion. The unit diffusion elements 55 are elements that change the direction of light travel by refraction, reflection, etc. The unit diffusion elements 55 are a concept that includes elements called unit shape elements, unit prisms, unit lenses, and unit optical elements. The unit diffusion elements 55 are provided on the main body 52. ​​The unit diffusion elements 55 face the light source substrate 22. The uneven surface 51 is formed by the plurality of unit diffusion elements 55.

[0047] The light diffusion sheet 50 shown in FIG. 5 includes a plurality of protrusions 53 provided on a main body 52. ​​In the examples shown in FIGS. 5 and 6, the plurality of protrusions 53 are arranged two-dimensionally. That is, the protrusions 53 are arranged in two or more non-parallel directions. The plurality of protrusions 53 may be arranged adjacent to each other without any gaps. The light diffusion sheet 50 may also include a plurality of recesses provided on the main body 52. ​​The plurality of recesses may be arranged two-dimensionally. The plurality of recesses may be arranged adjacent to each other without any gaps. Each unit diffusion element 55 shown in FIGS. 5 and 6 includes an element surface 56 inclined with respect to the third direction D3. The element surface 56 defines the unit diffusion element 55. The uneven surface 51 of the light diffusion sheet 50 is formed by the element surfaces 56 of the unit diffusion elements 55.

[0048] The optical characteristics of the light diffusion sheet 50 are affected by the inclination angle of the element surface 56 of the unit diffusion element 55. Therefore, the configuration of the unit diffusion element 55 can be adjusted appropriately based on the optical characteristics required for the surface light source device 20 and the optical member 30. For example, the inclination angles of the multiple element surfaces 56 included in one unit diffusion element 55 may be different from each other or the same. The light diffusion sheet 50 may include unit diffusion elements 55 that differ in at least one of the shape and orientation, or may include only unit diffusion elements 55 that are identical to each other.

[0049] The plurality of unit diffusion elements 55 included in the light diffusion sheet 50 are preferably arranged two-dimensionally. In this example, the element surfaces 56 of the unit diffusion elements 55 included in the light diffusion sheet 50 face various directions. As a result, the two-dimensionally arranged unit diffusion elements 55 in the light diffusion sheet 50 can guide light in various directions. That is, the light can be guided in multiple non-parallel directions, effectively homogenizing the in-plane illuminance distribution. Each unit diffusion element 55 may be configured with rotational symmetry about an axis parallel to the third direction D3. For example, each unit diffusion element 55 may be configured with three-fold, four-fold, or six-fold rotational symmetry about the axis parallel to the third direction D3. The plurality of unit diffusion elements 55 may be arranged irregularly or regularly.

[0050] FIG. 6 shows a specific example of unit diffusing elements 55 in a light diffusing sheet 50. In the example shown in FIG. 6, the multiple unit diffusing elements 55 are arranged in a square configuration. The multiple unit diffusing elements 55 are arranged at a regular pitch in the first direction D1. The multiple unit diffusing elements 55 are arranged at a regular pitch in the second direction D2. The unit diffusing elements 55 may be arranged in directions inclined to the first direction D1 and the second direction D2. For example, the multiple unit diffusing elements 55 may be arranged at a regular pitch in two directions inclined at ±45° with respect to the first direction D1. The arrangement pitches of the unit diffusing elements 55 in the two directions may be the same or different. The arrangement pitch of the unit diffusing elements 55 may be 0.05 mm or more and 1 mm or less, or 0.1 mm or more and 0.5 mm or less. As shown in FIG. 6, the unit diffusing elements 55 may be configured as a quadrangular pyramidal convex portion 53 or concave portion having a square base. The height or depth in the third direction D3 of each unit diffusion element 55 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. The unit diffusion elements 55 shown in Figures 5 and 6 can be produced by embossing or resin molding.

[0051] The selective transmission sheet 40 includes a selective transmission portion 45. The transmission and reflection characteristics of the selective transmission portion 45 depend on the angle of incidence. The reflectance and transmittance of the selective transmission portion 45 change depending on the angle of incidence. The angle of incidence refers to the angle (°) between the direction of propagation of incident light and the normal direction of a sheet-like member or other member on which the light is incident.

[0052] The selective permeation sheet 40 includes a first surface 40a and a second surface 40b. The first surface 40a faces the second side in the third direction D3. The second surface 40b faces the first side in the third direction D3. The illustrated selective permeation sheet 40 is composed only of a selective permeation section 45. This selective permeation section 45 constitutes the first surface 40a and the second surface 40b. The selective permeation sheet 40 may include a protective film that protects the selective permeation section 45. In this example, the protective film may constitute the first surface 40a and the second surface 40b.

[0053] The transmittance of the selective transmission portion 45 for light of a specific wavelength incident on the selective transmission portion 45 at an incident angle of 0° is lower than the transmittance of the selective transmission portion 45 for light of a specific wavelength incident on the selective transmission portion 45 at an incident angle greater than 0°. In other words, the transmittance of the selective transmission portion 45 for light of a specific wavelength incident perpendicularly is lower than the transmittance of the selective transmission portion 45 for light of a specific wavelength incident on the selective transmission portion 45 from at least one oblique direction. The reflectance of the selective transmission portion 45 for light of a specific wavelength incident on the selective transmission portion 45 at an incident angle of 0° is higher than the reflectance of the selective transmission portion 45 for light of a specific wavelength incident on the selective transmission portion 45 at an incident angle greater than 0°. In other words, the reflectance of the selective transmission portion 45 for light of a specific wavelength incident perpendicularly is higher than the reflectance of the selective transmission portion 45 for light of a specific wavelength incident on the selective transmission portion 45 from at least one oblique direction. The selective transmission portion 45 can also be referred to as a selective reflection sheet or a light reflection sheet.

[0054] The selective transmission portion 45 may have various transmission and reflection characteristics.

[0055] The transmittance of the selective transmission portion 45 for light of a specific wavelength incident at an incident angle of 0° may be less than 5%, less than 3%, or less than 1%. The reflectance of the selective transmission portion 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.

[0056] The transmittance of the selective transmission portion 45 for light of a specific wavelength that is incident on the selective transmission portion 45 at an incident angle of 0° or more and 30° or less in absolute value may be half or less of the maximum transmittance of the selective transmission portion 45, may be 1 / 5 or less of the maximum transmittance of the selective transmission portion 45, or may be 1 / 10 or less of the maximum transmittance of the selective transmission portion 45. The transmittance of the selective transmission portion 45 for light of a specific wavelength that is incident on the selective transmission portion 45 at an incident angle of 0° or more and 45° or less in absolute value may be half or less of the maximum transmittance of the selective transmission portion 45, may be 1 / 5 or less of the maximum transmittance of the selective transmission portion 45, or may be 1 / 10 or less of the maximum transmittance of the selective transmission portion 45.

[0057] The transmittance of the selective transmission portion 45 for light of a specific wavelength that is incident on the selective transmission portion 45 at an incident angle of 0° or more and 30° or less in absolute value may be less than 10%, less than 5%, or less than 1%. The transmittance of the selective transmission portion 45 for light of a specific wavelength that is incident on the selective transmission portion 45 at an incident angle of 0° or more and 40° or less in absolute value may be less than 10%, less than 5%, or less than 1%. The transmittance of the selective transmission portion 45 for light of a specific wavelength that is incident on the selective transmission portion 45 at an incident angle of 0° or more and 45° or less in absolute value may be less than 15%, less than 10%, or less than 5%. The transmittance of the selective transmission portion 45 for light of a specific wavelength that is incident on the selective transmission portion 45 at an incident angle of 0° or more and 50° or less in absolute value may be less than 15%, less than 10%, or less than 5%.

[0058] The incident angle at which the maximum transmittance of the selective transmission section 45 is obtained may be, in absolute value, 50° or more, 55° or more, or 60° or more. The incident angle at which the maximum transmittance of the selective transmission section 45 is obtained may be, in absolute value, 80° or less, 75° or less, or 70° or less.

[0059] Fig. 7 is a graph showing an example of the optical characteristics of the selective transmission portion 45. As shown in Fig. 7, the transmittance of the selective transmission portion 45 for light of a specific wavelength having an incident angle of 0° or more and 30° or less in absolute value may be less than 15%, less than 8%, or less than 3%. The transmittance of the selective transmission portion 45 for light of a specific wavelength having an incident angle of 0° or more and 50° or less in absolute value may be less than 15%, less than 10%, or less than 5%.

[0060] The reflectance of the selective transmission portion 45 for light of a specific wavelength having an incident angle of 0° or more and 30° or less in absolute value may be 85% or more, 92% or more, or 97% or more. The reflectance of the selective transmission portion 45 for light of a specific wavelength having 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.

[0061] 7, the transmittance of the selective transmission portion 45 for light of a specific wavelength incident at an incident angle whose absolute value is between 60° and 70° may be 50%. As the absolute value of the incident angle increases within a range between 0° and 65°, the transmittance of the selective transmission portion 45 for light of a specific wavelength may increase.

[0062] The reflectance of the selective transmission portion 45 for light of a specific wavelength incident at an incident angle whose absolute value is 60° or more and 70° or less may be 50%. As the absolute value of the incident angle increases within a range of 0° or more and 65° or less, the reflectance of the selective transmission portion 45 for light of a specific wavelength may decrease.

[0063] The optical characteristics of the selective transmission section 45 described here are based on the assumption that the first surface 45a and the second surface 45b of the selective transmission section 45 are parallel and that the first surface 45a and the second surface 45b are adjacent to an air layer.

[0064] The light of a specific wavelength can be set appropriately depending on the application of the surface light source device 20 and the optical member 30. The light emitted from the light source 23 may be light of a specific wavelength. The light of a specific wavelength may be visible light. "Visible light" means light with a wavelength of 380 nm or more and 780 nm or less.

[0065] The reflectance of the selective transmission portion 45 is a value measured using a goniophotometer GP-200 manufactured by Murakami Color Research Laboratory Co., Ltd. The transmittance of the selective transmission portion 45 is a total light transmittance measured in accordance with JIS K7361-1:1997. The transmittance of the selective transmission portion 45 is a value measured using a goniophotometer GP-200 manufactured by Murakami Color Research Laboratory Co., Ltd.

[0066] The selective transmission section 45 is not particularly limited as long as it has incident angle dependency of reflectance and incident angle dependency of transmittance. The selective transmission section 45 may include a dielectric multilayer film, a reflective volume hologram, a cholesteric liquid crystal structure layer, a retroreflective film, or a reflective diffractive optical element. A dielectric multilayer film is advantageous in that it allows a relatively high degree of freedom in designing its reflection and transmission characteristics. The transmission characteristics shown in Figures 6A and 6B are examples of the transmission characteristics of a dielectric multilayer film. The selective transmission section 45 may include a reflective structure that is structurally imparted with incident angle dependency of reflectance and incident angle dependency of transmittance. A reflective structure is advantageous in that it has low wavelength dependency.

[0067] The dielectric multilayer film constituting the selective transmission section 45 may include alternately stacked low-refractive index layers and high-refractive index layers with different refractive indices. 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 may have a protective film on one or both sides. The protective film may be made of 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 used as a manufacturing method for the dielectric multilayer film. Specifically, the manufacturing method for the laminated film described in JP2008-200861A may be used. 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.

[0068] 8A and 8B, the wavelength conversion sheet 60 includes a first surface 60a and a second surface 60b. The first surface 60a faces a second side in the third direction D3. The second surface 60b faces a first side in the third direction D3. The second surface 60b includes an uneven surface 61. The wavelength conversion sheet 60 includes a wavelength conversion agent 67. The wavelength conversion agent 67 absorbs primary light and emits secondary light having a different wavelength from the primary light.

[0069] The illustrated second surface 60b is an uneven surface 61 over its entire surface. The illustrated wavelength conversion sheet 60 is bonded to the selective transmission sheet 40 via the first surface 60a. The wavelength conversion sheet 60 may be bonded directly to the second surface 50b of the light diffusion sheet 50. As shown in FIG. 9 , the light diffusion sheet 50 may be bonded to the second surface 50b of the selective transmission sheet 40 via a bonding layer 35 such as an adhesive layer or a bonding layer.

[0070] 8A and 8B, the wavelength conversion sheet 60 includes a first barrier layer 63, a wavelength converting portion 65, a second barrier layer 64, and an optical element portion 70. The first barrier layer 63, the wavelength converting portion 65, the second barrier layer 64, and the optical element portion 70 are stacked in this order in the third direction D3. The first barrier layer 63, the wavelength converting portion 65, the second barrier layer 64, and the optical element portion 70 are arranged in this order from the first side to the second side in the third direction D3. The first barrier layer 63, the wavelength converting portion 65, the second barrier layer 64, and the optical element portion 70 are sheet-shaped. The first barrier layer 63, the wavelength converting portion 65, the second barrier layer 64, and the optical element portion 70 extend in the first direction D1 and the second direction D2.

[0071] 8A and 8B, the wavelength converting portion 65 includes a first surface 65a and a second surface 65b. The first surface 65a faces a second side in the third direction D3. The second surface 65b faces a first side in the third direction D3. The wavelength converting portion 65 is bonded to the first barrier layer 63 at the first surface 65a. The wavelength converting portion 65 is bonded to the second barrier layer 64 at the second surface 65b.

[0072] The wavelength converting portion 65 may include a base material portion 66 that holds a wavelength converting agent 67. A resin may be used as the base material portion 66. Examples of resins that may form 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.

[0073] The wavelength conversion agent 67 absorbs primary light LA ​​of a certain wavelength and emits secondary light LB having a wavelength different from 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 primary light LA ​​of a certain wavelength.

[0074] Quantum dots are nanometer-sized particles of semiconductors. Quantum dots may be composed of one type of semiconductor compound. Quantum dots may also be composed of two or more types of semiconductor compounds. Quantum dots may have, for example, a core-shell structure having a core made of a semiconductor compound and a shell made of a semiconductor compound different from the core.

[0075] Examples of quantum dot core materials include II-VI 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 quantum dot core materials include III-V semiconductor compounds such as AlN, AlP, AlAs, AlSb, GaAs, GaP, GaN, GaSb, InN, InAs, InP, InSb, TiN, TiP, TiAs, and TiSb. Examples of quantum dot core materials include semiconductor compounds or semiconductor-containing semiconductor crystals, such as Group IV semiconductors such as Si, Ge, and Pb.

[0076] When using core-shell quantum dots, the semiconductor constituting the shell may be a material with a higher band gap than the semiconductor compound constituting the core. In this case, excitons are confined in the core, improving the luminous efficiency of the quantum dots. Examples of core-shell structures (core / shell) with 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, and InGaP / ZnSSe.

[0077] The size of the quantum dots is adjusted taking into account the desired wavelength of the secondary light LB. As the particle diameter of quantum dots decreases, the energy band gap increases. As the crystal size decreases, the emission of quantum dots shifts toward the blue side, i.e., toward higher energy. 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 to 20 nm, or 1 nm to 10 nm. The shape, dispersion state, etc. of the quantum dots are identified using a transmission electron microscope (TEM). The crystal structure and particle size of the quantum dots are identified using X-ray crystal diffraction (XRD).

[0078] The wavelength converting section 65 may include a plurality of quantum dots with different emission wavelengths as the wavelength converting agent 67. By adjusting the content of each quantum dot, it is possible to adjust the color of light emitted from the surface light source device 20. In the example shown in FIG. 9, the wavelength converting agent 67 includes a first converting agent 67A and a second converting agent 67B. The first converting agent 67A and the second converting agent 67B have different sizes. The first converting agent 67A and the second converting agent 67B emit light with different wavelengths.

[0079] As a specific example, the light source 23 may emit blue light having a wavelength of 430 nm to 500 nm. 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 to 600 nm 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 to 750 nm as the second secondary light LB2. According to this example, the surface light source device 20 can emit light of various colors through 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.

[0080] 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.

[0081] The first barrier layer 63 is bonded to a first surface 65a of the wavelength converting portion 65. The first barrier layer 63 constitutes the first surface 60a. The second barrier layer 64 is bonded to a second surface 65b of the wavelength converting portion 65. 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.

[0082] 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 1.0×10 under the conditions of 23° C. and 90% relative humidity. -1 cc / m 2 / day / atm or less is acceptable, 1.0 × 10 -2 cc / m 2 / day / atm or less. The oxygen permeability can be measured using an oxygen gas permeability measuring device (OX-TRAN 2 / 21, manufactured by MOCON).

[0083] The first barrier layer 63 and the second barrier layer 64 may have water vapor barrier properties. In this example, the water vapor transmission rate of the first barrier layer 63 and the second barrier layer 64 is 1.0×10 under the conditions of 40° C. and 90% relative humidity. -1 g / m 2 / day or less is acceptable, 1.0 × 10 -2 g / m 2 The water vapor transmission rate can be measured using a water vapor transmission rate measuring device (DELTAPERM (manufactured by Technolox)).

[0084] The first barrier layer 63 and the second barrier layer 64 can be formed using a material capable of exhibiting barrier properties by a physical vapor deposition (PVD) method such as sputtering or ion plating, a vapor deposition method such as chemical vapor deposition (CVD), or a coating method such as roll coating or spin coating. Materials that can be used include inorganic oxides, metals, sol-gel materials, and the like. Examples of inorganic oxides include silicon oxide (SiO x ), aluminum oxide (Al n O m ), titanium oxide (TiO2), yttrium oxide, boron oxide (B2O3), calcium oxide (CaO), silicon oxynitride carbide (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.

[0085] The optical element unit 70 includes a first surface 70a and a second surface 70b. The first surface 70a faces a second side in the third direction D3. The second surface 70b faces a first side in the third direction D3. The optical element unit 70 is bonded to the second barrier layer 64 at the first surface 70a. The second surface 70b constitutes the second surface 60b. The second surface 70b constitutes the light-emitting side surface 30b of the optical member 30. The second surface 70b includes an uneven surface 61.

[0086] In the example shown in FIGS. 8A and 8B, the optical element section 70 includes a plurality of unit optical elements 75, each formed as a convex portion 73 or a concave portion 74. The unit optical elements 75 are elements that change the traveling direction of light by refraction, reflection, or the like. The unit optical elements 75 are a concept that includes elements called unit shape elements, unit prisms, and unit lenses. The unit optical elements 75 constitute the first surface 60a. The unit optical elements 75 form the concave-convex surface 61.

[0087] The optical element unit 70 shown in Fig. 8A includes a sheet-like main body 72 and a plurality of protrusions 73 provided on the main body 72. In the example shown in Fig. 8A, the plurality of protrusions 73 may be provided adjacent to each other with no gaps between them. The optical element unit 70 shown in Fig. 8B includes a main body 72 provided with a plurality of recesses 74. In the example shown in Fig. 8B, the plurality of recesses 74 may be provided adjacent to each other with no gaps between them.

[0088] 8A and 8B, the unit optical elements 75 have element surfaces 76 that are inclined with respect to the third direction D3. The unit optical elements 75 are defined by the element surfaces 76. The uneven surface 61 of the wavelength conversion sheet 60 is formed by the element surfaces 76 of the unit optical elements 75.

[0089] The optical characteristics of the uneven surface 61 are affected by the inclination angle of the element surfaces 76 of the unit optical elements 75. Therefore, the cross-sectional shape of the unit optical elements 75 can be adjusted appropriately based on the optical characteristics required of the surface light source device 20 and the optical member 30. The inclination angles of the multiple element surfaces 56 included in one unit optical element 75 may be different from each other or the same. The optical element section 70 may include unit optical elements 75 that differ in at least one of shape and orientation, or may include only unit optical elements 75 that are identical to each other.

[0090] 8A and 8B, the element surface 76 may be somewhat curved. The unit optical element 75 may have an outer shape of a portion of a sphere, such as a hemisphere, or may have an outer shape of a portion of a spheroid.

[0091] The plurality of unit diffusion elements 55 may be arranged two-dimensionally. In this example, the element surfaces 76 of the unit optical elements 75 included in the optical element unit 70 face various directions. As a result, the optical element unit 70 can guide light in various directions using the two-dimensionally arranged unit optical elements 75. That is, it is possible to guide light in a plurality of non-parallel directions, thereby effectively homogenizing the in-plane distribution of illuminance. Each unit optical element 75 may be configured with rotational symmetry about an axis parallel to the third direction D3. For example, each unit optical element 75 may be configured with three-fold rotational symmetry, four-fold symmetry, or six-fold symmetry about an axis parallel to the third direction D3.

[0092] The plurality of unit optical elements 75 may be arranged irregularly or regularly. Regularly arranging the plurality of unit optical elements 75 can facilitate the design of the optical element section 70. Regularly arranging the plurality of unit optical elements 75 makes it easy to arrange the unit optical elements 75 closely together without any gaps.

[0093] If the dimensions of the unit optical elements 75 are large when viewed from the third direction D3, uneven brightness due to the shape of the unit optical elements 75 becomes more visible. To prevent such problems, the maximum length of the unit optical elements 75 in a direction perpendicular to the stacking direction D3 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 75 may be 0.01 mm or more and 1.5 mm or less. Furthermore, to effectively uniform the in-plane illuminance distribution 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 75 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 75 in the third direction D3 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.

[0094] 10A and 10B show a specific example of a unit optical element 75 included in the optical element section 70. In the example shown in FIGS. 10A and 10B, the multiple unit optical elements 75 are arranged in a square configuration. The multiple unit optical elements 75 are arranged at a constant pitch in the first direction D1. The multiple unit optical elements 75 are also arranged at a constant pitch in the second direction D2. The arrangement pitch in the first direction D1 and the arrangement pitch in the second direction D2 may be the same or different. In the example shown in FIGS. 10A and 10B, the multiple unit optical elements 75 may be arranged closely together with no gaps. In the illustrated example, the arrangement pitch in the first direction D1 and the arrangement pitch in the second direction D2 are the same.

[0095] The unit optical elements 75 may be arranged in directions inclined in the first direction D1 and the second direction D2. For example, in the example shown in Fig. 10C, a plurality of unit optical elements 75 are arranged at a constant pitch in two directions inclined at ±45° with respect to the first direction D1. The arrangement of Fig. 10C can be applied to the unit optical elements 75 shown in Fig. 10B. According to this example, the element surfaces 76 face two directions inclined at ±45° with respect to the first direction D1, and light can be spread in these two directions.

[0096] 11A and 11B show other specific examples of unit optical elements 75 included in the optical element section 70. In the example of the optical element section 70 shown in FIGS. 11A and 11B, unit optical elements 75 having the same bottom shape are arranged in four orientations. As a result, multiple unit optical elements 75 having the same bottom shape and orientation are arranged at a constant pitch in each of the first direction D1 and the second direction D2. The arrangement pitches in the two directions may be the same or different. In the example shown, the arrangement pitches in the two directions are the same. The unit optical elements 75 have a triangular pyramid shape whose base is a right-angled isosceles triangle.

[0097] 8A to 11B can be produced by embossing or resin molding. The optical element section 70 including the unit optical elements 75 may be bonded to the second barrier layer 64 via a bonding layer including a pressure-sensitive adhesive or adhesive. The optical element section 70 including the unit optical elements 75 may be produced on the second barrier layer 64.

[0098] As described above, the surface light source device 20 includes the first optical sheet 81, the second optical sheet 82, and the reflective polarizing plate 85, which are superimposed on the optical member 30.

[0099] The first optical sheet 81 and the second optical sheet 82 exert optical effects such as reflection, refraction, and diffraction on incident light. The first optical sheet 81 and the second optical sheet 82 may have functions appropriate for the applications of the optical member 30 and the surface light source device 20.

[0100] 12 shows a specific example of the first optical sheet 81 and the second optical sheet 82. The first optical sheet 81 and the second optical sheet 82 shown in FIG. 12 are prism sheets including a plurality of linearly extending unit prisms 84. The prism sheets include a sheet-like main body 83 and a plurality of unit prisms 84 provided on the main body 83. The unit prisms 84 may extend linearly in a direction perpendicular to the arrangement direction of the plurality of unit prisms 84. In other words, the first optical sheet 81 and the second optical sheet 82 are prism sheets in which the unit prisms 84 are linearly arranged.

[0101] The linearly arranged unit prisms 84 shown in FIG. 12 mainly adjust the luminance angular distribution in a plane parallel to both the arrangement direction of the unit prisms 84 and the third direction D3. Therefore, the first optical sheet 81 and the second optical sheet 82 may be incorporated into the optical member 30 such that the arrangement directions of the unit prisms 84 are non-parallel. For example, the arrangement direction of the unit prisms 84 of the first optical sheet 81 may be perpendicular to the arrangement direction of the unit prisms 84 of the second optical sheet 82. The prism sheet shown in FIG. 12 may be "BEF" (registered trademark) available from 3M Company, USA.

[0102] The reflective polarizing plate 85 transmits one linearly polarized component and reflects the other linearly polarized component. The reflective polarizing plate 85 can selectively transmit light of a linearly polarized component that can be transmitted through 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 85 can change its polarization state through subsequent reflection or the like and re-enter the reflective polarizing plate 85. This improves the utilization efficiency of light emitted from the light source 23. The reflective polarizing plate 85 may be "DBEF" (registered trademark) available from 3M Corporation in the United States. The reflective polarizing plate 85 may also be a high-brightness polarizing sheet "WRPS" available from Shinwa Intertek Co., Ltd. in Korea, a wire grid polarizer, or the like.

[0103] Next, the operation of the surface light source device 20 having the above configuration when generating surface light will be described.

[0104] 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 emitted from the light source 23 travels toward the optical member 30. As shown in FIG. 5, the primary light LA ​​from the light source 23 is incident on the light diffusion sheet 50 of the optical member 30. The light diffusion sheet 50 has a light diffusion function. In the illustrated example, the first surface 50a of the light diffusion sheet 50, which constitutes the light incident side surface 30a of the optical member 30, is an uneven surface 51. As shown in FIG. 5, the light L51 changes its traveling direction when it enters the light diffusion sheet 50.

[0105] The primary light LA ​​from the light source 23 passes through the light diffusion sheet 50 and enters the selective transmission portion 45 of the selective transmission sheet 40. The transmittance of the selective transmission portion 45 depends on the angle of incidence. The transmittance of the selective transmission portion 45 for the primary light LA ​​incident at an angle of incidence greater than 0° is greater than the transmittance of the selective transmission portion 45 for the primary light LA ​​incident at an angle of incidence of 0°. According to the optical characteristics shown in FIG. 7, the transmittance of the selective transmission portion 45 for light incident on the selective transmission portion 45 at an angle of incidence of 0° is 1% or less. Furthermore, the transmittance of the selective transmission portion 45 for light incident on the selective transmission portion 45 at an absolute angle of incidence of 0° or more and 40° or less is less than half the maximum transmittance of the selective transmission portion 45. Furthermore, as the angle of incidence increases within a wide range of absolute values ​​of 0° or more and 65° or less, the transmittance of the selective transmission portion 45 increases. When the angle of incidence is in the absolute value range of 0° or more and 30° or less, the transmittance is 5% or less. That is, light that is inclined with respect to the third direction D3 can be transmitted through the selective transmission portion 45 with a higher transmittance than light that travels in the third direction D3.

[0106] The region facing the light source 23 in the third direction D3 and the surrounding region adjacent to this region are referred to as the directly above region. A large amount of light is directly incident on this directly above region from the light source 23. However, the angle of incidence of light on the directly above region is small. Therefore, light L21 emitted from the light source 23 and traveling to the selective transmission sheet 40 is reflected with high reflectance in the directly above region. In the directly above region, light passes through the selective transmission sheet 40 with low transmittance. This prevents the light-emitting surface 20a from becoming too bright in the directly above region.

[0107] As shown in FIG. 5, most of the light L52 reflected by the selective transmission portion 45 passes through the light diffusion sheet 50 and proceeds toward the light source substrate 22. This light L52 is diffused by the light diffusion sheet 50. As a result, the light L22, L52 can proceed in a direction significantly inclined with respect to the third direction D3. As shown in FIG. 2, the light L22 is reflected by the reflective layer 27 of the light source substrate 22. As a result of this reflection, the light L23 reflected by the reflective layer 27 proceeds toward the optical member 30 in the third direction D3. As shown in FIG. 2, the light L23 re-enters the optical member 30 at a position away from the light source 23 in the first direction D1 or the second direction D2 orthogonal to the third direction D3.

[0108] The light diffusion sheet 50 can change the traveling direction of the light L23 that re-enters the optical member 30 to a direction that is greatly inclined with respect to the third direction D3. The light L24 diffused by the light diffusion sheet 50 can be transmitted through the selective transmission sheet 40 with high transmittance in a spaced apart region that is separated from the light source 23 in a direction perpendicular to the third direction D3. This can prevent the light-emitting surface 20a from becoming too dark in the spaced apart region.

[0109] As described above, the combination of the diffusion function of the light diffusion sheet 50 and the selective transmission function of the selective transmission sections 45 according to the incident angle can suppress in-plane variations 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 selective transmission sheet 40.

[0110] 8A , the wavelength conversion sheet 60 includes, from the second side in the third direction D3, a first barrier layer 63, a wavelength converting portion 65, a second barrier layer 64, and an optical element portion 70. Light emitted from the selective transmission sheet 40 passes through the first barrier layer 63 of the wavelength conversion sheet 60 and proceeds toward the wavelength converting portion 65.

[0111] As shown in FIG. 9 , the wavelength converting portion 65 includes a wavelength converting agent 67. A portion of the light traveling through the wavelength converting portion 65 collides with the wavelength converting agent 67. The wavelength converting agent 67 absorbs the primary light LA ​​emitted from the light source 23 and emits secondary light LB of a different wavelength. In the illustrated example, the wavelength converting portion 65 includes a first converting agent 67A and a second converting agent 67B. The first converting agent 67A absorbs a portion L91 of the blue primary light LA ​​and emits a green first secondary light LB1. The second converting agent 67B absorbs a portion L92 of the blue primary light LA ​​and emits a red second secondary light LB2.

[0112] Most of the light L24 (see FIG. 2) traveling through the wavelength conversion sheet 60 travels in a direction significantly inclined with respect to the third direction D3 due to the transmission characteristics of the selective transmission section 45. Therefore, even if the thickness of the wavelength conversion section 65 is reduced, the optical path length of the light L24 within the wavelength conversion section 65 becomes long. This makes it easier for the light L24 to enter the wavelength conversion agent 67 within the wavelength conversion sheet 60. Since the wavelength conversion agent 67 can be used efficiently, the content of the wavelength conversion agent 67 in the selective transmission section 45 can be reduced.

[0113] As shown in FIG. 9, a portion L93 of the primary light LA ​​does not enter the wavelength conversion agent 67 and reaches the second surface 60b.

[0114] As shown in FIG. 8A , light L81 that has passed through the wavelength conversion section 65 passes through the second barrier layer 64 and proceeds to the optical element section 70. The optical element section 70 includes a plurality of unit optical elements 75. The optical element section 70 provides a concave-convex surface 61 on the second surface 60b of the wavelength conversion sheet 60. The concave-convex surface 61 is formed by element surfaces 76 of the unit optical elements 75. The second surface 60b forms the light-emitting side surface 30b. The light L81 is refracted by the concave-convex surface 61 and is emitted from the optical member 30.

[0115] As shown in FIG. 8A , in the illustrated example, refraction at the element surfaces 76 that constitute the light-emitting side surface 30b reduces the angle that the traveling direction forms with respect to the third direction D3. That is, the element surfaces 76 of the optical element unit 70 exert a light-condensing function on the emitted light. The light-condensing function of the optical element unit 70 reduces the burden of optical path correction for light that has passed through the optical member 30. Therefore, the utilization efficiency of the light that has passed through the optical member 30 can be improved. Furthermore, the number and thickness of components incorporated into the surface light source device 20 can be reduced, allowing the surface light source device 20 to be made thinner.

[0116] In this manner, light L25 (see FIG. 2), such as primary light LA, first secondary light LB1, and second secondary light LB2, can be emitted from the optical member 30 to the first side in the third direction D3. The light L25 emitted from the optical member 30 passes through the first optical sheet 81, the second optical sheet 82, and the reflective polarizing plate 85, and is 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.

[0117] As shown in FIGS. 2 and 13 , the light beams L26, L131, and L132 incident on the second surface 60b of the wavelength conversion sheet 60 may be reflected by the second surface 60b. The light beams L26, L131, and L132 reflected by the second surface 60b travel toward the second side in the third direction D3. These light beams may be reflected by any interface, for example, the surface of the reflective layer 27, to turn back in the third direction D3 and re-enter the light-emitting side surface 30b. These light beams travel in the first direction D1 or the second direction D2 perpendicular to the third direction D3 until they reach the light-emitting side surface 30b again. Therefore, by utilizing the reflection on the light-emitting side surface 30b, it is possible to more effectively suppress in-plane variations in brightness due to the arrangement of the light source 23. That is, the wavelength conversion sheet 60 reinforces or complements the incident-angle-dependent optical characteristics of the selective transmission portion 45, thereby further uniforming the in-plane illuminance distribution.

[0118] In FIG. 13 , the thickness of the wavelength conversion sheet 60 is shown thin to facilitate understanding of the optical effects related to the optical path within the wavelength conversion sheet 60. Also, the wavelength conversion agent 67 is not shown in FIG. 13 . In reality, the wavelength conversion agent 67 is provided between the first surface 60a and the second surface 60b of the wavelength conversion sheet 60. By utilizing reflection from the second surface 60b of the wavelength conversion sheet 60, the wavelength conversion agent 67 is positioned within the circulating optical path of the light emitted from the light source 23. In particular, the wavelength conversion agent 67 is dispersed within the wavelength conversion sheet 60, which folds back the traveling direction in the third direction D3 within the circulating optical path. Therefore, within the wavelength conversion sheet 60 containing the wavelength conversion agent 67, the light travels in a direction inclined with respect to the third direction D3. The optical path length within the wavelength conversion sheet 60 is significantly longer. This significantly improves the utilization efficiency of the wavelength conversion agent 67 and significantly reduces the content of the wavelength conversion agent 67 in the wavelength conversion portion 65. For example, the thickness of the wavelength converting portion 65 can be reduced, and the thickness in the third direction D3 of the optical member 30 and the surface light source device 20 can be reduced. The density of the wavelength converting agent 67 in the wavelength converting portion 65 can be reduced.

[0119] In the illustrated wavelength converting section 65, the wavelength converting agent 67 is dispersed in the base material section 66. The refractive index of the base material section 66 may be smaller than the refractive index of the optical element section 70. The refractive index of the base material section 66 may be smaller than the refractive index of the selective transmission section 45. By setting the refractive index in this way, light in the wavelength converting section 65 travels in a direction more inclined with respect to the third direction D3. This makes it possible to ensure a longer optical path length in the wavelength converting section 65. Therefore, the content of the wavelength converting agent 67 in the wavelength converting section 65 can be reduced. The thickness of the wavelength converting section 65 can be made thinner.

[0120] In the wavelength conversion sheet 60, a barrier layer may not be provided on the side end surfaces of the wavelength conversion portion 65. In this example, deterioration of the wavelength conversion agent 67 located near the side end surfaces may progress, causing a change in color at the peripheral portion of the wavelength conversion portion 65. According to the present embodiment, the content of the wavelength conversion agent 67 in the wavelength conversion portion 65 can be reduced as described above. Therefore, the area ratio of the wavelength conversion agent 67 per unit area when projected in the third direction D3 can be reduced. This makes it possible to suppress a change in color at the peripheral portion even when a barrier layer is not provided on the side end surfaces of the wavelength conversion portion 65.

[0121] Here, the transmittance of the selective transmission portion 45, which is a dielectric multilayer film, increases for light with wavelengths longer than the specific wavelength. More specifically, the angle of incidence at which the transmittance begins to increase decreases for light with longer wavelengths. The selective transmission property of the selective transmission portion 45, which depends on the angle of incidence, weakens for light with wavelengths longer than the specific wavelength. Therefore, the selective transmission portion 45 cannot effectively exhibit selective transmission property that depends on the angle of incidence for secondary light LB having a wavelength longer than the specific wavelength. In other words, the selective transmission portion 45 cannot reflect the secondary light LB, just like the primary light LA.

[0122] Therefore, from the viewpoint of sufficiently uniforming the in-plane distribution of illuminance, it is preferable to convert the primary light LA ​​into secondary light LB after uniforming the in-plane distribution of illuminance by sufficiently circulating the primary light LA ​​between the optical member 30 and the light source substrate 22. That is, from the viewpoint of suppressing in-plane variations in brightness, it is preferable to reduce the content of the wavelength conversion agent 67 in the selective transmission part 45, which is in the circulating light path.

[0123] Furthermore, the primary light LA ​​may be selectively reflected at the light-emitting side surface 30b. The reflectance of the primary light LA ​​at the light-emitting side surface 30b may be greater than the reflectance of the secondary light LB at the light-emitting side surface 30b. As shown in FIG. 9, 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 ​​before being absorbed by the wavelength conversion agent 67. As shown in FIG. 9, the secondary light LB is emitted from the wavelength conversion agent 67 over a wide angular range. The angular distribution of the luminance resulting from the secondary light LB is somewhat uniform on the second surface 65b of the wavelength conversion unit 65. That is, the traveling direction angle of the secondary light LB is dispersed within a wide angular range. On the other hand, the traveling direction angle of the primary light LA ​​depends on the transmission characteristics of the selective transmission unit 45 and falls within a relatively narrow angular range. The incident angle (°) shown in FIG. 7 is the incident angle from an air layer with a refractive index of 1. Here, it is assumed that the refractive index of transparent resins commonly used in optical components is 1.4 to 1.7. It is assumed that the selective transmission portion 45 intensively transmits light from the air layer with an incident angle of 45° to 70°. In this reference assumption, the angle (°) of the traveling direction of light that passes through the selective transmission portion 45 and travels through the resin, i.e., the angle (°) between the traveling direction and the third direction D3, is approximately 25° to 40°. The inclination angle θp (°) of the element surfaces 76 that constitute the light-emitting side surface 30b may be adjusted so that the primary light LA ​​at this limited traveling direction angle is reflected by the light-emitting side surface 30b.

[0124] The inclination angle θp is the angle (°) between the element surface 76 and a plane perpendicular to the third direction D3. It is also possible that the element surface 76 is not flat. The inclination angle θp of the element surface 76 is determined at the center position of the element surface 76 in the third direction D3. For the element surface 76 as a convex portion 73, the inclination angle θp is determined at the center position in the third direction D3 between the base end of the element surface 76 connected to the main body portion 72 and the tip end furthest from the main body portion 72 in the third direction D3. For the element surface 76 as a concave portion 74, the inclination angle θp is determined at the center position in the stacking direction D3 between the base end (deepest portion) of the element surface 76 closest to the selectively permeable sheet 40 in the third direction D3 and the tip end (bank portion) furthest from the selectively permeable sheet 40 in the stacking direction D3.

[0125] 13 shows a light path that is bent back in the traveling direction in the third direction D3 by reflection from the element surface 76. Both light L131 and light L132 are incident on the first element surface 76A, which is inclined toward the same side as the traveling direction with respect to the third direction D3. The light L131 and L132 are reflected by the first element surface 76A. The inclination angle θp may be set so that the reflection from the first element surface 76A is total reflection. Assuming the above-mentioned reference conditions, the inclination angle θp may be 5° or more, 10° or more, or 15° or more.

[0126] The inclination angle θp may be set so that the light reflected by the first element surface 76A turns back in the third direction D3 toward the second side. Assuming the above-mentioned reference conditions, the inclination angle θp may be 35° or less, 30° or less, or 25° or less.

[0127] The light beams L131 and L132 then enter the second element surface 76B opposite the first element surface 76A. The light beam L131 is further reflected by the second element surface 76B. Due to the reflection by the second element surface 76B, the traveling direction of the light beam L131 turns back in the third direction D3 toward the second side. This reflection is preferably total reflection. The tilt angle θp may be set so that the reflection by the second element surface 76B is total reflection. Assuming the above-mentioned reference conditions, the tilt angle θp may be 38° or less, 35° or less, or 32° or less.

[0128] The light L132 is refracted at the second element surface 76B and is emitted from the unit optical element 75. Thereafter, the light L132 is incident on another adjacent unit optical element 75 via the third element surface 76C. Next, the light L132 is reflected by the fourth element surface 76D of the other unit optical element 75. Due to the reflection at the fourth element surface 76D, the traveling direction of the light L132 is turned back in the third direction D3 and directed toward the second side.

[0129] The traveling direction of the light L132 may be turned back in the third direction D3 toward the second side due to refraction at the second element surface 76B when it is emitted from the first unit optical element 75. The inclination angle θp may be set so that the traveling direction of the light is turned back in the third direction D3 toward the second side due to refraction at the second element surface 76B. Assuming the above-mentioned reference condition, the inclination angle θp may be 38° or less, 35° or less, or 32° or less. As another condition, the inclination angle θp may be set so that the light continues to travel toward the first side in the third direction D3 after refraction at the second element surface 76B, but the angle of the traveling direction becomes larger due to refraction at the second element surface 76B, like the light L132. In other words, the inclination angle θp may be set so that the light continues to travel toward the first side in the third direction D3 after being refracted at the second element surface 76B, but the refraction at the second element surface 76B causes the traveling direction of the light to be more inclined with respect to the third direction D3. Assuming the above-mentioned reference conditions, the inclination angle θp may be 55° or less, 50° or less, or 45° or less.

[0130] By setting the inclination angle θp of the element surfaces 76 as described above, the primary light LA, whose traveling direction angle has been adjusted by the selective transmission portion 45, can be selectively reflected by the light-emitting side surface 30b formed by the element surfaces 76. This makes it possible to more effectively uniform the illuminance distribution.

[0131] In the illustrated example, the wavelength conversion sheet 60 is bonded to the selective transmission sheet 40. This example improves the utilization efficiency of light emitted from the light source 23. FIG. 9 shows the optical path of light L94 assuming that a gap is provided between the wavelength conversion sheet 60 and the selective transmission sheet 40. In FIG. 9, light L94 and light L91 are emitted in the same direction from the selective transmission sheet 40. Light L94 entering the wavelength conversion sheet 60 from the gap is reflected by the first surface 60a of the wavelength conversion sheet 60. Depending on the transmission characteristics of the selective transmission portion 45, light L91 and L94 travel in directions significantly inclined with respect to the third direction D3. Therefore, light L94 is reflected with high reflectivity by the first surface 60a of the wavelength conversion sheet 60. Such light L94 becomes stray light and reduces the light utilization efficiency. In contrast to this, the angle of incidence on the first surface 60a of the wavelength conversion sheet 60 can be reduced by bonding the selective transmission sheet 40 and the wavelength conversion sheet 60 together, for example, via the bonding layer 35. This makes it possible to suppress reflection on the first surface 60a and improve the light utilization efficiency.

[0132] In the embodiment described above, the optical member 30 includes a selective transmission sheet 40 including a selective transmission portion 45, and a wavelength conversion sheet 60 including a first surface 60a facing the selective transmission sheet 40 and a second surface 60b facing the first surface 60a. The transmittance of the selective transmission portion 45 for light of a specific wavelength incident on the selective transmission portion 45 at an incident angle greater than 0° is greater than the transmittance of the selective transmission portion 45 for light of the specific wavelength incident on the selective transmission portion 45 at an incident angle of 0°. The second surface 60b includes a concave-convex surface 61. The wavelength conversion sheet 60 includes a wavelength conversion agent 67 that absorbs primary light LA ​​and emits secondary light LB. The secondary light LB has a wavelength different from that of the primary light LA.

[0133] According to the optical member 30 of this embodiment, the primary light LA ​​from the light source 23 can be reflected by the second surface 60b of the wavelength conversion sheet 60. That is, the second surface 60b can reflect light traveling toward the first side, which is the viewer side, in the third direction D3. Therefore, a circulating optical path along which the primary light LA ​​circulates can be formed between the second surface 60b of the wavelength conversion sheet 60 and the light source substrate 22, etc. According to this embodiment, the wavelength conversion agent 67 is contained in the wavelength conversion sheet 60, which turns back its traveling direction in the third direction D3. The primary light LA ​​travels in a direction inclined with respect to the third direction D3 within the wavelength conversion sheet 60, depending on the transmission characteristics of the selective transmission portion 45. Therefore, the content of the wavelength conversion agent 67 in the wavelength conversion sheet 60 can be significantly reduced. In fact, by reducing the content of the wavelength conversion agent 67 that emits secondary light LB in various directions, the circulation of the primary light LA ​​using reflection at the second surface 60b can be promoted. That is, by circulating the primary light LA, it is possible to suppress the in-plane variation in brightness caused by the arrangement of the light source 23, thereby suppressing the in-plane variation in illuminance, while significantly reducing the content of the wavelength conversion agent 67. It is also possible to make the optical member 30 and the surface light source device 20 thinner.

[0134] Although one embodiment has been described with reference to specific examples, the above-described specific examples do not limit the present invention. The above-described embodiment can be implemented with various other specific examples, and various omissions, substitutions, changes, additions, etc. can be made without departing from the spirit of the present invention.

[0135] For example, in the above-described surface light source device 20, a spacer may be disposed between the light source substrate 22 and the optical member 30. A transparent resin layer may be provided between the light source substrate 22 and the optical member 30, and the resin layer may function as a spacer. The resin layer may be formed of a thermoplastic resin. The resin layer may contain a light-diffusing component. Examples of the light-diffusing component include a metal compound, a porous substance containing a gas, resin beads surrounding a metal compound, white fine particles, simple air bubbles, and a crystalline interface.

[0136] For example, in the above-described specific example, one or more of first optical sheet 81, second optical sheet 82, and reflective polarizing plate 85 may be omitted from surface light source device 20. Furthermore, light diffusion sheet 50 may be omitted from optical member 30.

[0137] In another embodiment, the selective transmission sheet 40 may be omitted from the optical member 30. In this modification, the optical member 30 may include a light diffusion sheet 50 and a wavelength conversion sheet 60. The light diffusion sheet 50 and the wavelength conversion sheet 60 may be bonded to each other, as shown in FIG. 14 . In the example shown in FIG. 14 , the light diffusion sheet 50 includes a main body 52 and a plurality of unit diffusion elements 55. The light diffusion sheet 50 can exhibit a light diffusion function due to the uneven surface 51 formed by the element surfaces 56 of the unit diffusion elements 55. The main body 52 may contain a light diffusion component. Examples of light diffusion components include metal compounds, porous substances containing gas, resin beads surrounding metal compounds, white fine particles, simple air bubbles, and crystalline interfaces. In the optical member 30 shown in FIG. 14 , the light diffusion function of the light diffusion sheet 50 can cause the traveling direction of light incident on the wavelength conversion sheet 60 to be significantly inclined with respect to the third direction D3. Therefore, the amount of the wavelength conversion agent 67 contained in the wavelength conversion sheet 60 can be reduced, while effectively suppressing the in-plane variation in brightness. [Example]

[0138] The above-described embodiment will be described in more detail below using examples, but the above-described embodiment is not limited to these examples.

[0139] The surface light source devices of Example 1 and Comparative Example 1 were manufactured as follows.

[0140] Example 1 The surface light source device of Example 1 had the configuration shown in Figure 2. The surface light source device included a light source substrate including a light source, an optical element, a first optical sheet, a second optical sheet, and a reflective polarizing plate. The support substrate had a white reflective layer containing titanium oxide. Reflection from the reflective layer of the support substrate was diffuse reflection with a reflectance of 95%. The light sources were arranged in a square array on the support substrate as shown in Figure 3. The array pitch of the light sources in the first direction was 6 mm. The array pitch of the light sources in the second direction perpendicular to the first direction was 6 mm. Each light source was a light-emitting diode emitting blue light with a center wavelength of 450 nm. The planar shape of the light-emitting diode was a rectangle measuring 0.2 mm x 0.4 mm. The light-emitting diode was arranged on the support substrate so that its sides were aligned with the first and second directions. The distance along the third direction D3 from the surface of the light source facing the optical element to the light-incident side of the optical element was 0.5 mm.

[0141] In the surface light source device of Example 1, the optical member included a light diffusion sheet, a selective transmission sheet, and a wavelength conversion sheet, in this order from the second side in the third direction D3, as shown in FIG. 5 . The light diffusion sheet included a selective transmission portion. The light diffusion sheet and the wavelength conversion sheet were each bonded to the selective transmission portion. A dielectric multilayer film obtained from Toray Industries, Inc. was used for the selective transmission portion. The selective transmission portion had the transmission characteristics shown in FIG. 7 for light of 450 nm. The wavelength conversion sheet included a first barrier layer, a wavelength conversion portion, a second barrier layer, and an optical element portion, as shown in FIG. 8A . The light diffusion sheet and the optical element portion were molded by supplying an uncured ultraviolet-curable resin composition between a mold and a main body portion and curing it between the mold and the main body portion.

[0142] The optical element section included a main body and unit optical elements as convex portions arranged on the main body. The optical element section included unit optical elements having the shapes, arrangements, and other configurations described with reference to FIGS. 11A and 11B. As shown in FIG. 11A, unit optical elements of the same shape were arranged closely spaced on the surface of the main body, with the orientation of their bottom faces varied in four ways. Each unit optical element had a triangular pyramid shape and included three element faces. The bottom face of the unit optical element was a right-angled isosceles triangle. The element faces of the unit optical element included an equilateral element face extending from the equilateral side of the right-angled isosceles triangle shape that formed the base, and a base element face extending from the base of the right-angled isosceles triangle shape that formed the base. The lengths of the two equilateral sides of the right-angled isosceles triangle shape that formed the base were each 0.1 mm. The inclination angle θp of each equilateral element face was 45°. The inclination angle θp of the base element surface was 45°.

[0143] The light diffusion sheet included a sheet-like main body bonded to the selectively transmitting sheet and unit diffusion elements as recesses arranged on the main body. The light diffusion sheet included unit diffusion elements having the shape, arrangement, and other configurations described with reference to Figures 11A and 11B. As shown in Figure 11A, unit diffusion elements of the same shape were arranged closely on the surface of the main body, with the orientation of their bottom faces varied in four different directions. Each unit diffusion element had a triangular pyramid shape and included three element faces. The bottom face of the unit diffusion element was a right-angled isosceles triangle. The element faces of the unit diffusion element included an equilateral element face extending from the equilateral side of the right-angled isosceles triangle that formed the base, and a base element face extending from the base of the right-angled isosceles triangle that formed the base. The lengths of the two equilateral sides of the right-angled isosceles triangle that formed the base were each 0.1 mm. The inclination angle θp of each equilateral element face was 45°. The inclination angle θp of the base element surface was 45°. As a result, the concave-convex surface formed by the element surfaces of the unit diffusion elements was configured identically to the concave-convex surface formed by the element surfaces of the unit optical elements, except that the concave-convex surfaces were reversed.

[0144] QF-6000 available from Showa Denko Materials was used as the wavelength conversion section. Two sheets of brightness enhancement film BEF (registered trademark) available from 3M were used as the first and second optical sheets. For the first optical sheet, the longitudinal direction of the prisms extended in the second direction. For the second optical sheet, the longitudinal direction of the prisms extended in the first direction. For the reflective polarizing plate, brightness enhancement film DBEF (registered trademark) available from 3M was used.

[0145] In the surface light source device of Example 1, the distance along the third direction from the surface of the light source facing the optical member to the light-incident side surface of the optical member facing the light source was 0.5 mm.

[0146] <Comparative Example 1> In the surface light source device of Comparative Example 1, a laminate including a first barrier layer, a wavelength converting portion, and a second barrier layer was bonded to the selective transmission portion of the selective transmission sheet instead of the wavelength conversion sheet of Example 1. That is, in the surface light source device of Comparative Example 1, the optical element portion was omitted from the optical member of Example 1. Also, in the surface light source device of Comparative Example 1, the content of the wavelength conversion agent contained in the wavelength converting portion was set to 1.5 times the content of the wavelength conversion agent in Example 1. The surface light source device of Comparative Example 1 was otherwise identical to the surface light source device of Example 1.

[0147] <Evaluation> For the surface light source devices of Example 1 and Comparative Example 1, the distribution of radiant intensity on the light-emitting surface of the surface light source device was measured while the light source was emitting light. The radiant intensity measurement range was a circular evaluation area with a radius of 6 mm centered on one light source. The evaluation area was set so that the light source was located at the center of the evaluation area when observed from a third direction. The in-plane distribution of radiant intensity on the light-emitting surface of the surface light source devices of Example 1 and Comparative Example 1 is shown in Figures 15 and 16, respectively. Figures 15 and 16 indicate the magnitude of radiant intensity at each position within the evaluation area by the intensity of the color at that position. Positions with low radiant intensity are displayed in darker colors. In Figures 15 and 16, the black area indicates the outside of the evaluation area. In Figures 15 and 16, a circle centered on the light source is indicated by a white line. The white circle is superimposed on the radiant intensity distribution to indicate the center position of the light source.

[0148] For the surface light source device of Comparative Example 1 shown in Fig. 16, unevenness occurred in the radiation intensity distribution according to the arrangement of the light sources, and the positions of the light sources could be identified. Compared to the in-plane distribution of radiation intensity for the surface light source device of Comparative Example 1, the in-plane distribution of radiation intensity for the surface light source device of Example 1 was sufficiently uniform. For Example 1 shown in Fig. 15, the brightness distribution was uniform, making it difficult to identify the positions of the light sources. [Explanation of symbols]

[0149] 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 surface, 30b: light-emitting side surface, 35: bonding layer, 40: selective transmission sheet, 40a: first surface, 40b: second surface, 40b, 45: selective transmission portion, 45a: first surface, 45b: second surface, 46: dielectric multilayer film, 50: light diffusion sheet, 50a: first surface, 50b: second surface, 51: uneven surface, 52: main body portion, 53: convex portion, 55: unit diffusion element, 56: element surface, 60: wavelength conversion sheet, 60a: first surface, 60b: second surface, 61: uneven surface, 63: first barrier layer, 64: second barrier layer, 65: wavelength converting portion, 65a: first surface, 65b: second surface, 66: base material portion, 67: wavelength converting agent, 67A: first converting agent, 67B: second converting agent, 70: optical element portion, 70a: first surface, 70b: second surface, 72: main body portion, 73: convex portion, 74: concave portion, 75: unit optical element, 76: element surface, 76A: first element surface, 76B: second element surface, 81: first optical sheet, 82: second optical sheet, 85: reflective polarizing plate, D1: first direction, D2: second direction, D3: third direction, LA: primary light, LB: secondary light, LB1: first secondary light, LB2: second secondary light

Claims

1. An optical member; a light source facing the optical member in a third direction; a prism sheet overlapping the optical member in the third direction, the optical member is located between the light source and the prism sheet, The optical member is a selectively permeable sheet including a selectively permeable portion; a wavelength conversion sheet including a first surface facing the selective transmission sheet and a second surface facing the first surface, the transmittance of the selective transmission portion for light of a specific wavelength that is incident on the selective transmission portion at an incident angle greater than 0° is greater than the transmittance of the selective transmission portion for light of the specific wavelength that is incident on the selective transmission portion at an incident angle of 0°; the second surface includes an uneven surface; the wavelength conversion sheet includes a wavelength conversion agent that absorbs primary light and emits secondary light, the secondary light has a wavelength different from the wavelength of the primary light; the wavelength conversion sheet includes a wavelength converting portion containing the wavelength converting agent, a first barrier layer and a second barrier layer overlapped with the wavelength converting portion, and an optical element portion overlapped with the second barrier layer and including the uneven surface, the wavelength converting portion is located between the first barrier layer and the second barrier layer, the second barrier layer is located between the wavelength converting portion and the optical element portion; the optical element unit includes a plurality of unit prisms that form the concave-convex surface, the plurality of unit prisms are arranged in a first direction and a second direction that are non-parallel to each other; the unit prism includes a plurality of element surfaces that constitute the concave-convex surface, A surface light source device, wherein an inclination angle between the element surface and a plane perpendicular to the third direction is 5° or more and 38° or less.

2. The surface light source device according to claim 1 , wherein the selective transmission sheet is joined to the wavelength conversion sheet.

3. Further provided is a light diffusion sheet bonded to the selective transmission sheet, The surface light source device according to claim 1 , wherein the selective transmission sheet is located between the light diffusion sheet and the wavelength conversion sheet.

4. the wavelength conversion agent includes a first conversion agent that absorbs the primary light and emits a first secondary light, and a second conversion agent that absorbs the primary light and emits a second secondary light; the wavelength of the second secondary light is longer than the wavelength of the first secondary light; 4. The surface light source device according to claim 1, wherein the wavelength of the first secondary light is longer than the wavelength of the primary light.

5. A surface light source device described in any one of claims 1 to 4, comprising a light source substrate having a reflective layer facing the optical element and the light source.

6. Further comprising a reflective polarizing plate superimposed on the optical member, 6. The surface light source device according to claim 1, wherein the optical member is located between the light source and the reflective polarizing plate.

7. The surface light source device according to any one of claims 1 to 6, A display device comprising the surface light source device and a display panel superimposed thereon.

Images