Optical member, surface light source device and display device

Abstract

To sufficiently uniformize in-plane distribution of brightness while achieving reduction in thickness of a surface light source device.SOLUTION: An optical member 30 includes, in this order, a light reflection sheet 40 including a light reflection part 45 in which a reflection rate of light of a specific wavelength incident at an incident angle of 0° is 80% or more, and a reflection rate of light of a specific wavelength incident at at least a part of an incident angle range larger than 45°in an absolute value is smaller than 50%, and an optical sheet 50 including an uneven surface 51 facing a light reflection sheet side. The optical sheet 50 includes a plurality of unit optical elements 55, each being formed as a convex part 53 or a concave part 54, on a light reflection sheet 40 side, The uneven surface 51 is formed by the plurality of unit optical elements 55.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] A surface light source device is known as a device that emits light in a planar manner. As disclosed in Patent Document 1, a surface light source device can be used as a backlight for a liquid crystal display device. Patent Document 1 discloses a direct-type surface light source device in which a light source faces a diffusion member. In a direct-type surface light source device, unevenness in brightness occurs due to the arrangement of the light source. This unevenness in brightness becomes more noticeable when the surface light source device is made thinner. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6299811 Summary of the Invention [Problem to be solved by the invention]

[0004] In the prior art, it has not been possible to sufficiently uniform the in-plane distribution of brightness while reducing the thickness of the surface light source device. The present invention has been made in consideration of this point. The object of the present invention is to sufficiently uniform the in-plane distribution of brightness while reducing the thickness of the surface light source device. [Means for solving the problem]

[0005] The optical member according to the present invention comprises: a light reflecting sheet including a light reflecting portion having a reflectance of a specific wavelength incident at an incident angle of 0° that is greater than a reflectance of the specific wavelength incident at an incident angle greater than 0°; an optical sheet including an uneven surface facing the light reflecting sheet, The optical sheet includes a plurality of unit optical elements, each of which is formed as a convex portion or a concave portion, on the side of the light reflecting sheet, The uneven surface is formed by the plurality of unit optical elements.

[0006] In the optical member according to the present invention, The angle that the peak emission direction from the light reflecting sheet of light that is incident on the light reflecting portion at the minimum incident angle at which the transmittance of light of the specific wavelength in the light reflecting portion is half of the maximum value forms with respect to the stacking direction of the light reflecting sheet and the optical sheet is defined as a specific emission angle θx (°), The unit optical element includes an element surface that forms the uneven surface, The element surface may be inclined with respect to the stacking direction at an angle smaller than the specific emission angle θx (°).

[0007] In the optical member according to the present invention, The unit optical element includes an element surface that forms the uneven surface, The element surfaces may be inclined at an angle of less than 45° with respect to a lamination direction of the light reflecting sheet and the optical sheet.

[0008] In the optical member according to the present invention, A specific emission angle θx (°) is an angle formed by a peak emission direction from the light reflecting sheet of light incident on the light reflecting portion at a minimum incident angle at which the transmittance of light of the specific wavelength in the light reflecting portion is half of the maximum value, with respect to a stacking direction of the light reflecting sheet and the optical sheet; The sum of an element surface that is included in the unit optical element and forms the uneven surface and an inclination angle θs (°) that is an angle with respect to the stacking direction may be 80° or more and 100° or less.

[0009] In the optical member according to the present invention, the reflectance at the light reflecting portion for light of a specific wavelength incident at an incident angle of 0° may be 80% or more, and the reflectance at the light reflecting portion for light of a specific wavelength incident at at least some incident angles greater than 45° in absolute value may be less than 50%.

[0010] In the optical element according to the present invention, the reflectance of light of the specific wavelength incident at an incident angle of 0° or more and 30° or less at the light reflecting portion may be 80% or more, more preferably 90% or more, and even more preferably 95% or more.

[0011] In the optical element according to the present invention, the reflectance of light of the specific wavelength incident at an incident angle of 0° or more and 45° or less at the light reflecting portion may be 80% or more, more preferably 85% or more, and even more preferably 90% or more.

[0012] In the optical element according to the present invention, the reflectance at the light reflecting portion of light of the specific wavelength incident at an incident angle of 45° or more and 75° or less, more preferably the reflectance at the light reflecting portion of light of the specific wavelength incident at an incident angle of 50° or more and 60° or less, may be 50%.

[0013] In the optical element according to the present invention, the reflectance at the light reflecting portion of light of the specific wavelength having an incident angle of 45° or more and 75° or less, more preferably the reflectance at the light reflecting portion of light of the specific wavelength having an incident angle of 50° or more and 60° or less, may be gradually decreased as the absolute value of the incident angle increases.

[0014] In the optical member according to the present invention, the reflectance at the light reflecting portion of the light having the specific wavelength and an incident angle of 50° or more may be gradually decreased as the incident angle increases.

[0015] In the optical member according to the present invention, the reflectance of the light of the specific wavelength at the light reflecting portion may be gradually decreased as the angle of incidence increases.

[0016] The optical member according to the present invention may further include a wavelength conversion sheet that emits light having a wavelength different from that of the incident light, on the opposite side of the optical sheet to the light reflecting sheet.

[0017] The optical member according to the present invention may further include a reflective polarizing plate on the side of the optical sheet opposite to the light reflecting sheet.

[0018] A first surface light source device according to the present invention comprises: Any of the optical members according to the present invention described above; A light source that emits light to be incident on the optical member.

[0019] A second surface light source device according to the present invention is Any of the optical members according to the present invention described above; The light source substrate has a reflective layer facing the optical member and a light source that emits light incident on the optical member.

[0020] In the first and second surface light source devices of the present invention, the reflective layer may have a glossiness of 70 or more.

[0021] In the first and second surface light source devices according to the present invention, A direction in which half the peak brightness is obtained in a brightness angle distribution on a surface of the light reflecting sheet facing the optical sheet, obtained in a state where components on the optical sheet side of the light reflecting sheet are removed, forms an angle with respect to the lamination direction of the light reflecting sheet and the optical sheet, and the angle is defined as a half-value angle θh (°). The unit optical element includes an element surface that forms the uneven surface, The element surface may be inclined with respect to the stacking direction at an angle smaller than the half-value angle θh (°).

[0022] In the first and second surface light source devices according to the present invention, a half-value angle θh (°), which is the minimum value of the angle formed by a direction in which half the peak brightness is obtained in a brightness angle distribution on a surface of the light reflecting sheet facing the optical sheet, obtained in a state in which components on the optical sheet side of the light reflecting sheet are removed, with respect to the stacking direction of the light reflecting sheet and the optical sheet; An inclination angle θs (°) that is an angle that an element surface that is included in the unit optical element and forms the uneven surface makes with respect to the stacking direction; The sum of these may be equal to or greater than 80° and equal to or less than 100°.

[0023] The display device according to the present invention comprises: Any one of the above-mentioned surface light source devices according to the present invention; The surface light source device and a display panel are laminated together. Effect of the Invention

[0024] According to the present invention, it is possible to sufficiently uniform the in-plane distribution of brightness while reducing the thickness of the surface light source device. [Brief description of the drawings]

[0025] [Figure 1] FIG. 1 is a diagram for explaining an embodiment of the present invention, and is a perspective view showing a display device and a surface light source device. [Diagram 2] FIG. 2 is a vertical sectional view of the surface light source device of FIG. [Diagram 3] FIG. 3 is a plan view showing a light source substrate included in the surface light source device of FIG. 2, and shows an example of an arrangement of a plurality of light sources. [Figure 4] FIG. 4 is a cross-sectional view showing a light source substrate included in the surface light source device of FIG. 2, and shows an example of the configuration of the light source substrate. [Diagram 5] FIG. 5 is a graph showing an example of optical characteristics of a light reflecting portion of a light reflecting sheet of an optical member that can be included in the surface light source device of FIG. 2, and is a graph for explaining the reflection angle dependency of reflectance and transmittance. [Figure 6] FIG. 6 is a graph corresponding to FIG. 5, and shows optical characteristics of the light reflecting portion different from those of FIG. [Figure 7A] FIG. 7A is a graph corresponding to FIG. 5, and shows optical characteristics of the light reflecting portion different from those of FIGS. [Figure 7B] FIG. 7B is an enlarged graph of a portion of the graph of FIG. 7A. [Figure 8A] 8A is a cross-sectional view showing an example of an optical sheet of an optical member that can be included in the surface light source device of FIG. [Figure 8B] 8B is a cross-sectional view showing another example of an optical sheet of an optical member that can be included in the surface light source device of FIG. [Figure 9A] FIG. 9A is a plan view showing an example of a specific configuration of an optical sheet that can be included in the surface light source device of FIG. [Figure 9B] FIG. 9B is a perspective view showing a unit optical element of the optical sheet of FIG. 9A. [Figure 10] FIG. 10 is a plan view showing another example of a specific configuration of an optical sheet that can be included in the surface light source device of FIG. [Figure 11A] FIG. 11A is a plan view showing still another example of a specific configuration of an optical sheet that can be included in the surface light source device of FIG. [Figure 11B] FIG. 11B is a perspective view showing a unit optical element of the optical sheet of FIG. 11A. [Figure 12A] 12A is a plan view showing still another example of a specific configuration of an optical sheet that can be included in the surface light source device of FIG. [Figure 12B] FIG. 12B is a perspective view showing a unit optical element of the optical sheet of FIG. 12A. [Figure 13] FIG. 13 is a vertical cross-sectional view showing the surface light source device, and is a diagram for explaining the functions of the optical member and the surface light source device. [Figure 14] FIG. 14 is a vertical cross-sectional view showing the surface light source device, and is a diagram for explaining the functions of the optical member and the surface light source device. [Figure 15] FIG. 15 is a vertical cross-sectional view showing the surface light source device, and is a diagram for explaining the functions of the optical member and the surface light source device. [Figure 16] FIG. 16 is a vertical cross-sectional view showing an optical member, illustrating the function of an optical sheet. [Figure 17] FIG. 17 shows the results of a simulation in which the in-plane distribution of illuminance of the surface light source device according to Sample 1 is calculated. [Figure 18]FIG. 18 shows the results of a simulation in which the in-plane distribution of illuminance of the surface light source device according to Sample 2 is calculated. [Figure 19] FIG. 19 shows the results of a simulation in which the in-plane distribution of illuminance of the surface light source device according to Sample 3 is calculated. [Figure 20] FIG. 20 shows the results of a simulation in which the in-plane distribution of illuminance of the surface light source device of Sample 4 is calculated. [Figure 21] FIG. 21 shows the results of a simulation in which the in-plane distribution of illuminance of the surface light source device of Sample 5 is calculated. [Figure 22] FIG. 22 shows the results of a simulation in which the in-plane distribution of illuminance of the surface light source device of sample 6 is calculated. [Diagram 23] FIG. 23 shows the results of a simulation in which the in-plane distribution of illuminance of the surface light source device of Sample 7 is calculated. [Figure 24] FIG. 24 shows the results of a simulation in which the in-plane distribution of illuminance of the surface light source device of sample 8 is calculated. [Diagram 25] FIG. 25 shows the results of a simulation in which the in-plane distribution of illuminance of the surface light source device of Sample 9 is calculated. [Figure 26] FIG. 26 shows the results of a simulation in which the in-plane distribution of illuminance of the surface light source device of sample 10 is calculated. [Figure 27] FIG. 27 shows the results of a simulation in which the in-plane distribution of illuminance of the surface light source device of Sample 11 is calculated. [Figure 28] FIG. 28 shows the results of a simulation in which the in-plane distribution of illuminance of the surface light source device of Sample 12 is calculated. [Figure 29] FIG. 29 shows the results of a simulation in which the in-plane distribution of illuminance of the surface light source device of Sample 13 is calculated. [Diagram 30] FIG. 30 shows the results of a simulation in which the in-plane distribution of illuminance of the surface light source device of Sample 14 is calculated. [Diagram 31] FIG. 31 shows the results of a simulation in which the in-plane distribution of illuminance of the surface light source device of Sample 15 is calculated. [Diagram 32]FIG. 32 is a graph showing an example of the luminance angular distribution on the light output side surface of the light reflecting sheet in the surface light source device of FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. In the drawings attached to this specification, the scale and aspect ratios are appropriately changed and exaggerated from those of the actual objects for the convenience of illustration and understanding. In addition, configurations shown in some drawings may be omitted in other drawings.

[0027] In this specification, the terms "sheet," "film," and "plate" are not distinguished from one another solely on the basis of differences in name. For example, "sheet" is a concept that includes members that can be called "film" or "plate," and is not distinguished solely on the basis of differences in name.

[0028] 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. Also, 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.

[0029] Furthermore, terms used in this specification that specify shapes, geometric conditions, and the degree thereof, such as "parallel," "orthogonal," and "same," as well as values ​​of length and angle, are not to be bound by strict meanings, but are to be interpreted to include the range of degrees to which similar functions can be expected.

[0030] In order to clarify the directional relationships between the drawings, some of the drawings use arrows to indicate the first direction D1, the second direction D2, and the stacking direction D3 as directions common to the drawings. The tip of the arrow is one side of each of the directions D1, D2, and D3. An arrow pointing into the paper in a direction perpendicular to the paper surface of the drawing is indicated by a symbol with an X in a circle, as shown in Figure 2, for example. An arrow pointing out from the paper in a direction perpendicular to the paper surface of the drawing is indicated by a symbol with a dot in a circle, as shown in Figure 3, for example.

[0031] 1 to 28 are diagrams for explaining an embodiment. FIG. 1 is a perspective view that shows a display device 10 as an application example of a surface light source device 20 and an optical member 30. The display device 10 is a device that displays, for example, moving images, still images, text information, or an image composed of a combination of these on a display panel 15. The display device 10 can be used, for example, as a liquid crystal display device mounted on a vehicle. The display device 10 can also be used for various purposes, such as advertising, presentations, television images, and display of various information, indoors or outdoors. The display device 10 shown in FIG. 1 has a surface light source device 20 having a light-emitting surface 20a, and a display panel 15 arranged opposite the light-emitting surface 20a.

[0032] FIG. 2 is a vertical cross-sectional view showing the surface light source device 20. As shown in FIG. 2, the surface light source device 20 has, as main components, a light source 23 and an optical member 30 that adjusts the optical path of the light emitted from the light source 23. The optical member 30 is disposed facing the light source 23. The optical member 30 includes a light reflecting sheet 40 and an optical sheet 50 that are stacked in a stacking direction D3. 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 diffuses the light emitted from the light source 23. The diffusion in the optical member 30 eliminates unevenness in brightness caused by the presence of the light source 23. As a result, the illuminance at each position on the light-emitting side surface 30b of the optical member 30, or the illuminance at each position on a virtual light-receiving surface parallel to the light-emitting side surface 30b located in the vicinity of the light-emitting side surface 30b, is made uniform. In particular, the optical member 30 described in this embodiment is devised to sufficiently uniform the in-plane distribution of brightness while reducing the thickness of the surface light source device 20. Note that "illuminance of the light-emitting side surface 30b" used in the following description means "illuminance on the light-emitting side surface 30b" or "illuminance on a virtual light-receiving surface parallel to the light-emitting side surface 30b located in the vicinity of the light-emitting side surface 30b."

[0033] Hereinafter, a display device 10, a surface light source device 20, and an optical member 30 according to an embodiment will be described with reference to specific examples shown in the drawings.

[0034] First, the display panel 15 of the display device 10 will be described. As shown in Fig. 1, the display panel 15 is stacked with the surface light source device 20 in the stacking direction D3, and is disposed facing the light emitting surface 20a of the surface light source device 20. The display panel 15 has a display surface 15a on which an image is displayed. The display surface 15a faces the opposite side to the surface light source device 20 in the stacking direction D3, that is, toward the observer. In the illustrated example, the display panel 15 is formed in a rectangular shape when viewed from the stacking direction D3 of the display panel 15, that is, when viewed in a plan view from the front direction.

[0035] The display panel 15 is configured as, for example, a transmissive liquid crystal display panel. The display panel 15 forms an image on the display surface 15a by adjusting the transmittance of the display panel 15 for each pixel. The display panel 15 includes a liquid crystal layer having a liquid crystal material. The light transmittance of the display panel 15 changes according to the strength of the electric field applied to the liquid crystal layer.

[0036] As an example of such a display panel 15, a liquid crystal display panel having a pair of polarizing plates and a liquid crystal cell (liquid crystal layer) arranged between the pair of polarizing plates can be used. In this liquid crystal display panel, the polarizing plate has a polarizer that has a function of decomposing incident light into two orthogonal polarized components, transmitting the polarized component in one direction, and absorbing the polarized component in the other direction orthogonal to the one direction. The liquid crystal cell has a pair of support plates and liquid crystal arranged between the pair of support plates. The liquid crystal cell is designed so that an electric field can be applied to each region forming one pixel. The orientation of the liquid crystal in the liquid crystal cell to which an electric field is applied changes, and affects the polarization state of the incident light. As an example, a polarized component in a specific direction rotates its polarization direction by 90° when passing through a liquid crystal cell to which an electric field is not applied. The polarized component in a specific direction maintains its polarization direction when passing through a liquid crystal cell to which an electric field is applied. This makes it possible to control the transmission and light blocking of a pair of polarizing plates arranged on both sides of the liquid crystal cell depending on whether or not an electric field is applied to the liquid crystal cell.

[0037] Next, the surface light source device 20 will be described. The surface light source device 20 has a light-emitting surface 20a that emits planar light. This surface light source device 20 is configured as a so-called direct-type backlight. That is, the light source 23 is provided in an area that overlaps with the light-emitting surface 20a when projected in the stacking direction D3. In the illustrated example, the normal direction of the display panel 15, the normal direction of the display surface 15a, the normal direction of the light-emitting surface 20a, the normal direction of the optical member 30, the normal direction of the light reflecting sheet 40 and the optical sheet 50 included in the optical member 30, and the normal directions of the light source substrate 22 and the support substrate 25, which will be described later, are parallel to each other and coincide with the stacking direction D3 in which the light reflecting sheet 40 and the optical sheet 50 are stacked. The stacking direction D3 is also called the front direction.

[0038] The light source 23 has a light-emitting element that emits light. As the light-emitting element, a light-emitting diode, also referred to as LED, can typically be used. The size of the light-emitting diode used as the light source 23 is not particularly limited. However, from the viewpoint of making the image of the light source 23 less noticeable, it is preferable to use a small light-emitting diode, for example, a mini LED or a micro LED. Specifically, the length WL1, WL2 of one side of the light source 23 having a rectangular shape when observed from the stacking direction D3 shown in FIG. 3 is preferably 0.5 mm, and more preferably 0.2 mm or less.

[0039] The emission wavelength of the light source 23 may be appropriately selected depending on the application of the surface light source device 20. For example, the surface light source device 20 may have a light-emitting element that emits blue light and a light-emitting element that emits yellow light, and generate white light. The surface light source device 20 may also have a light-emitting element that emits blue light, a light-emitting element that emits green light, and a light-emitting element that emits red light, and generate white light. In addition, when a plurality of light-emitting elements are provided, one light source 23 may include a plurality of types of light-emitting elements arranged in close proximity to each other, or may include only a single light-emitting element. In other words, a plurality of types of light sources 23 having different emission wavelengths may be used.

[0040] As a specific example shown in the figure, the light source 23 may include a light emitting diode that emits blue light with a wavelength of 450 nm as a light emitting element. In such an example, a light emitting diode with high output can be used as the light source 23. On the other hand, by using an element that can change the wavelength, such as a phosphor, in the optical member 30, it is also possible to make the light emitting surface 20a emit white light.

[0041] As an example, the light source 23 may be configured only by 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 or a lens that adjusts the light distribution from the light emitting element, or may include a phosphor that absorbs the light from the light emitting element and emits light of a different wavelength.

[0042] The light distribution characteristic of the light source 23 is not particularly limited. As the light distribution characteristic of the light source 23, a Lambertian light distribution can typically be adopted. In the case of a Lambertian light distribution, in the emission intensity distribution from the light source 23 directed to the stacking direction D3, the highest peak intensity is obtained in the stacking direction D3 which is the optical axis, and an intensity of half the peak intensity is obtained in a direction inclined by 60° from the optical axis. On the other hand, the light distribution characteristic of the light source 23 may be sufficiently diffused, and in the emission luminous intensity distribution of the light source 23 directed to the stacking direction D3 and having an optical axis aligned with the stacking direction D3, a peak luminous intensity may be obtained in a direction other than the stacking direction D3. For example, the bud wing light distribution disclosed in Patent Document 1 (JP6299811B) may be used as the light distribution characteristic of the light source 23.

[0043] As shown in the figure, the surface light source device 20 may have a plurality of light sources 23. As another example, the surface light source device 20 may have only a single light source 23. The number of light sources 23 is appropriately selected according to the purpose of the surface light source device 20, the area of ​​the light-emitting surface 20a, and the like. From the viewpoint of eliminating unevenness in brightness caused by the arrangement of the light sources 23, it is preferable that the plurality of light sources 23 included in the surface light source device 20 are regularly arranged on a surface perpendicular to the stacking direction D3. As an example of a regular arrangement of the light sources 23, a honeycomb arrangement in which the light sources 23 are arranged at a constant pitch in each of three directions inclined at 60° to each other can be adopted. As an example of a regular arrangement of the light sources 23, a square arrangement in which the light sources 23 are arranged at a constant pitch in each of two directions perpendicular to each other can be adopted.

[0044] In the example shown in Fig. 3, the light sources 23 are arranged at a constant pitch in each of a first direction D1 and a second direction D2 perpendicular to each other. In the example shown, the arrangement pitch PL1 in the first direction D1 and the light distribution pitch PL2 of the light sources 23 in the second direction D2 are the same, but this is not limited thereto, and the arrangement pitch PL1 and the arrangement pitch PL2 may be different. Here, 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.

[0045] Furthermore, the light source 23 may be configured to emit only P-polarized light when it enters the optical member 30. P-polarized light refers to light that vibrates in a direction parallel to the incident surface including the traveling direction of the light when it enters the optical member 30 and the normal direction to the light-entering side surface 30a of the optical member 30. By having the light source 23 emit only P-polarized light, when a dielectric multilayer film described later is used for the light reflecting sheet 40, the transmittance of light incident at a large incident angle can be sufficiently increased, and the optical member 30 can be given the desired optical characteristics. This makes it possible to effectively uniform the in-plane distribution of illuminance on the light-exiting side surface 30b of the optical member 30.

[0046] Here, the incident angle is the angle (°) that the traveling direction of the incident light makes with respect to the normal direction of a sheet-like member or the like into which the light is incident. The exit angle is the angle (°) that the traveling direction of the exiting light makes with respect to the normal direction of a sheet-like member or the like from which the light exits. The incident angle (°) and the exit angle (°) are each specified as an angle value between 0° and 90°.

[0047] The illustrated surface light source device 20 further includes a support substrate 25 that supports the light sources 23, in addition to the light sources 23 and the optical members 30. The light sources 23 and the support substrate 25 form a light source substrate 22. The support substrate 25 supports the multiple light sources 23 from the side opposite the optical members 30 in the stacking direction D3. The support substrate 25 is a sheet-like member. The support substrate 25 includes a circuit that supplies power to the light sources 23. The support substrate 25 has optical reflectivity that reflects light toward the optical members 30. The optical reflectivity is not particularly limited as long as it is exhibited for light of a specific wavelength emitted from the light sources 23.

[0048] As a specific configuration, as shown in Fig. 4, the support substrate 25 has a sheet-shaped substrate body 26, and a reflective layer 27 and wiring 28 provided on the substrate body 26. The substrate body 26 spreads in a direction perpendicular to the lamination direction D3. The substrate body 26 is preferably insulating. The substrate body 26 may be a spreading resin film, for example, a polyethylene terephthalate film.

[0049] The reflective layer 27 is laminated on the substrate body 26 from the optical member 30 side in the lamination direction D3. The reflective layer 27 covers the area on the substrate body 26 where the light source 23 is not arranged. The reflective layer 27 is reflective to light of a specific wavelength emitted from the light source 23 or to light used for emission in the surface light source device 20. The reflectivity of the reflective layer 27 may be regular reflection, also called specular reflection, may be diffuse reflection, or may be anisotropic diffuse reflection. From the viewpoint of uniforming the in-plane distribution of illuminance in combination with other configurations of the surface light source device 20, it is preferable that the glossiness of the reflective surface of the reflective layer 27 (the surface facing the optical member 30) is 70 or more. Here, the glossiness is a value measured using a gloss meter (VG7000) manufactured by Nippon Denshoku Kogyo Co., Ltd. at an incident angle of 20° in accordance with JISZ8741. The reflective layer 27 may be a metal layer laminated on the substrate body 26, or may be a reflective diffractive optical element.

[0050] The wiring 28 is electrically connected to the light source 23. The wiring 28 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 28 may be located between the substrate body 26 and the reflective layer 27, as shown in FIG.

[0051] As shown by the two-dot chain line in FIG. 2, the light sources 23 may be covered with a sealant 24. The sealants 24 are arranged corresponding to the respective light sources 23. Therefore, the sealants 24 are arranged two-dimensionally like the light sources 23 when observed from the stacking direction D3. In the illustrated example, the light sources 23 are covered with the sealant 24 on the surface facing the optical member 30 and on the side surface. The sealant 24 is fixed to the support substrate 25. The portion where the light sources 23 and the wiring 28 are electrically connected is also covered with the sealant 24. As a material for the sealant 24, for example, a thermosetting resin such as a silicone resin or an epoxy resin, or a thermoplastic resin such as an olefin resin can be used.

[0052] In the example shown in FIG. 2, the optical member 30 is disposed on the sealing material 24. That is, the optical member 30 is supported by the sealing material 24 and is spaced from the light source 23 and the support substrate 25 in the stacking direction D3. The sealing material 24 may be bonded to the optical member 30 by adhesion, adhesion, welding, or the like. Note that the distance DX shown in FIG. 2 is the separation distance between the light source 23 and the optical member 30 along the stacking direction D3. In other words, the distance DX refers to the distance along the stacking direction D3 between the surface of the light source 23 facing the optical member 30 and the light-entering side surface 30a of the optical member 30.

[0053] Next, the optical member 30 will be described. The optical member 30 has a light reflecting sheet 40 and an optical sheet 50 in this order. That is, the light reflecting sheet 40 is located on the light entrance side of the light to be adjusted by the optical member 30, relative to the optical sheet 50. The optical sheet 50 is located on the light exit side of the light to be diffused by the optical member 30, relative to the light reflecting sheet 40. In the example shown in FIG. 2, the optical member 30 is configured in a sheet shape extending in a first direction D1 and a second direction D2 perpendicular to the stacking direction D3. Both the light reflecting sheet 40 and the optical sheet 50 are sheet-like members extending in a first direction D1 and a second direction D2 perpendicular to the stacking direction D3. The light reflecting sheet 40 forms the light entrance side 30a of the optical member 30, and the optical sheet 50 forms the light exit side 30b of the optical member 30. The light reflecting sheet 40 and the optical sheet 50 may be joined to each other, may be simply in contact with each other and not joined, and may be spaced from each other.

[0054] First, the light reflecting sheet 40 will be described. The light reflecting sheet 40 directly faces the light source substrate 22 in the stacking direction D3. The light reflecting sheet 40 includes a light reflecting portion 45. The light reflecting sheet 40 may be composed of only the light reflecting portion 45, as in the illustrated example. As another example, the light reflecting sheet 40 may have the light reflecting portion 45 and a diffusion portion or the like provided on at least one of the light entrance side and the light exit side of the light reflecting portion 45.

[0055] The light reflecting portion 45 has a reflection characteristic in which the reflectance of the light emitted from the light source 23 or the light used for emission in the surface light source device 20 at the light reflecting portion 45 is lower when the incident angle is other than 0° than when the incident angle is 0°. That is, the reflectance of the light of a specific wavelength incident at an incident angle of 0° at the light reflecting portion 45 is higher than the reflectance of the light of a specific wavelength incident at an incident angle greater than 0° at the light reflecting portion 45. The light reflecting portion 45 has a transmission characteristic in which the transmittance of the light emitted from the light source 23 or the light used for emission in the surface light source device 20 at the light reflecting portion 45 is higher when the incident angle is other than 0° than when the incident angle is 0°. That is, the transmittance of the light of a specific wavelength incident at an incident angle of 0° at the light reflecting portion 45 is lower than the transmittance of the light of a specific wavelength incident at an incident angle greater than 0° at the light reflecting portion 45.

[0056] Preferably, the light reflecting portion 45 reflects light of a specific wavelength incident at an incident angle of 0° with a reflectance of 80% or more. The light reflecting portion 45 transmits light of a specific wavelength incident at an incident angle of 0° with a transmittance of less than 20%. Moreover, the light reflecting portion 45 reflects at least a part of light of a specific wavelength incident at an incident angle greater than 45° with a reflectance lower than 50%. The light reflecting portion 45 transmits at least a part of light of a specific wavelength incident at an incident angle greater than 45° with a transmittance of 50% or more. That is, the light reflecting portion 45 has a reflectance dependent on the incident angle. Moreover, the light reflecting portion 45 has a transmittance dependent on the incident angle.

[0057] Here, FIG. 5 is a graph showing an example of the reflection characteristic and transmission characteristic of the light reflecting portion 45 according to the incidence angle. In the characteristics shown in FIG. 5, the reflectance of the light of the specific wavelength in the light reflecting portion 45 increases as the incidence angle decreases. More specifically, the reflectance of the light of the specific wavelength incident at an incidence angle of 60° or less is preferably 50% or more and less than 100%, more preferably 80% or more and less than 100%, and particularly preferably 90% or more and less than 100%. In addition, the reflectance of the light of the specific wavelength incident at an incidence angle of 0° in the light reflecting portion 45 is preferably 80% or more and less than 100%, more preferably 90% or more and less than 100%, and particularly preferably 95% or more and less than 100%. According to such reflection characteristic, in combination with the optical characteristic of the optical sheet 50 described later, it is possible to effectively prevent the illuminance in the area directly above the light source 23 from becoming too high, and effectively uniform the in-plane distribution of the illuminance.

[0058] In the characteristics shown in FIG. 5, the transmittance of light of a specific wavelength in the light reflecting section 45 increases as the incident angle increases. More specifically, the total light transmittance of light of a specific wavelength incident at an incident angle of 70° or more and less than 90° is preferably 30% or more, more preferably 40% or more, and particularly preferably 50% or more. In a region separated from the light source 23 in a direction perpendicular to the stacking direction D3, the amount of light traveling in a direction inclined relative to the stacking direction D3 is relatively large. Therefore, according to the light reflecting section 45 having the optical characteristics shown in FIG. 5, the illuminance in the region separated from the light source 23 can be increased, and the in-plane distribution of the illuminance can be effectively uniformed.

[0059] The light of the specific wavelength can be appropriately set depending on the application of the surface light source device 20 and the optical member 30. Typically, the light emitted from the light source 23 or the light used for emission in the surface light source device 20 can be the light of the specific wavelength. On the other hand, it is also preferable that the light of the specific wavelength is visible light. Here, "visible light" means light having a wavelength of 380 nm or more and 780 nm or less.

[0060] The reflectance of the light reflecting portion 45 and the light reflecting sheet 40 is a value measured using a variable angle photometer (goniophotometer) GP-200 manufactured by Murakami Color Research Laboratory Co., Ltd. The transmittance of the light reflecting portion 45 and the light reflecting sheet 40 is a total light transmittance measured in accordance with JIS K7361-1:1997. The transmittance of the light reflecting portion 45 and the light reflecting sheet 40 is a value measured using a variable angle photometer (goniophotometer) GP-200 manufactured by Murakami Color Research Laboratory Co., Ltd. When measuring the reflectance and transmittance of the light reflecting portion 45 and the light reflecting sheet 40 using the variable angle photometer (goniophotometer) GP-200, the light beam aperture is set to φ20 (mm) and the light receiving opening angle is set to 1°.

[0061] Fig. 6 shows optical characteristics of the light reflecting portion 45 different from those in Fig. 5. It is a graph showing the reflection characteristics and transmission characteristics of the light reflecting portion 45 for blue light having a wavelength of 450 nm. In the graph of Fig. 6, the horizontal axis shows the incidence angle (°) with positive and negative values ​​in order to distinguish the direction of incidence with respect to the stacking direction D3.

[0062] 6, the reflectance of the light reflecting portion 45 for light of a specific wavelength incident at an absolute angle of incidence of 0° to 30° is preferably 80% or more, more preferably 90% or more, and even more preferably 95% or more. Furthermore, the reflectance of the light reflecting portion 45 for light of a specific wavelength incident at an absolute angle of incidence of 0° to 45° is preferably 80% or more, more preferably 85% or more, and even more preferably 90% or more. Such reflection characteristics, in combination with the optical characteristics of the optical sheet 50 described later, can effectively prevent the illuminance in the area directly above the light source 23 from becoming too high, and can effectively uniform the in-plane distribution of the illuminance.

[0063] 6, the transmittance of light of a specific wavelength having an absolute incident angle of 0° or more and 30° or less through the light reflecting portion 45 may be less than 20%, less than 10%, or less than 5%. The transmittance of light of a specific wavelength having an absolute incident angle of 0° or more and 45° or less through the light reflecting portion 45 may be less than 20%, less than 15%, or less than 10%. Such transmission characteristics, in combination with the optical characteristics of the optical sheet 50 described below, can effectively prevent the illuminance in the area directly above the light source 23 from becoming too high, and effectively uniform the in-plane distribution of the illuminance.

[0064] As shown in FIG. 6, it is preferable that the reflectance of the light reflecting portion 45 of the light of a specific wavelength incident at an incident angle of 45° or more and 75° or less in absolute value is 50%. More preferably, it is preferable that the reflectance of the light reflecting portion 45 of the light of a specific wavelength incident at an incident angle of 50° or more and 60° or less in absolute value is 50%. It is also preferable that the reflectance of the light reflecting portion 45 of the light of a specific wavelength whose absolute value of the incident angle is 45° or more and 75° or less, more preferably the reflectance of the light reflecting portion 45 of the light of a specific wavelength whose absolute value of the incident angle is 50° or more and 60° or less, gradually decreases with an increase in the absolute value of the incident angle. Furthermore, it is preferable that the reflectance of the light reflecting portion 45 of the light of a specific wavelength whose absolute value of the incident angle is 50° or more gradually decreases with an increase in the absolute value of the incident angle. According to the light reflecting portion 45 having the optical characteristics shown in FIG. 6, the illuminance in the area away from the light source 23 can be increased, and the in-plane distribution of the illuminance can be effectively uniformed.

[0065] As shown in FIG. 6, it is preferable that the transmittance of the light reflecting portion 45 of the light of the specific wavelength incident at a certain incident angle of 45° or more and 75° or less in absolute value is 50%. More preferably, it is preferable that the transmittance of the light reflecting portion 45 of the light of the specific wavelength incident at a certain incident angle of 50° or more and 60° or less in absolute value is 50%. It is also preferable that the transmittance of the light reflecting portion 45 of the light of the specific wavelength whose absolute value of the incident angle is 45° or more and 75° or less, more preferably the transmittance of the light reflecting portion 45 of the light of the specific wavelength whose absolute value of the incident angle is 50° or more and 60° or less, gradually increases with an increase in the absolute value of the incident angle. Furthermore, it is preferable that the transmittance of the light reflecting portion 45 of the light of the specific wavelength whose absolute value of the incident angle is 50° or more gradually increases with an increase in the absolute value of the incident angle. According to the light reflecting portion 45 having the optical characteristics shown in FIG. 6, the illuminance in the area away from the light source 23 can be increased, and the in-plane distribution of the illuminance can be effectively uniformed.

[0066] Figures 7A and 7B are graphs showing still another example of the optical characteristics of the light reflecting portion 45. The light reflecting portion 45 having the optical characteristics shown in Figures 7A and 7B is different from the light reflecting portion 45 having the optical characteristics shown in Figure 5, and is also different from the light reflecting portion 45 having the optical characteristics shown in Figure 6. Figures 7A and 7B are graphs showing the transmission characteristics of the light reflecting portion 45 for light having a wavelength of 450 nm, which is blue light.

[0067] 7A and 7B, the transmittance of light of a specific wavelength having an absolute incident angle of 0° or more and 30° or less through the light reflecting portion 45 may be less than 15%, less than 8%, or less than 3%. The transmittance of light of a specific wavelength having an absolute incident angle of 0° or more and 45° or less through the light reflecting portion 45 may be less than 50%, less than 40%, or less than 30%. Such transmission characteristics, in combination with the optical characteristics of the optical sheet 50 described later, can effectively prevent the illuminance in the area directly above the light source 23 from becoming too high, and effectively uniform the in-plane distribution of the illuminance.

[0068] The reflectance of light of a specific wavelength having an absolute incident angle of 0° or more and 30° or less at the light reflecting portion 45 may be 85% or more, 92% or more, or 97% or more. The reflectance of light of a specific wavelength having an absolute incident angle of 0° or more and 45° or less at the light reflecting portion 45 may be 50% or more, 60% or more, or 70% or more. Such reflection characteristics, in combination with the optical characteristics of the optical sheet 50 described later, can effectively prevent the illuminance in the area directly above the light source 23 from becoming too high, and effectively uniform the in-plane distribution of the illuminance.

[0069] As shown in FIG. 7A and FIG. 7B, the transmittance of the light reflecting portion 45 of the light of a specific wavelength incident at an incident angle of 40° or more and 60° or less in absolute value may be 50%. The transmittance of the light reflecting portion 45 of the light of a specific wavelength incident at an incident angle of 45° or more and 55° or less in absolute value may be 50%. As the absolute value of the incident angle increases in a range of 30° or more and 60° or less, the transmittance of the light of the specific wavelength may increase in the light reflecting portion 45 of the light of the specific wavelength. As the absolute value of the incident angle increases in a range of 50° or less, the transmittance of the light reflecting portion 45 of the light of the specific wavelength may increase. In the region separated from the light source 23 in the direction perpendicular to the stacking direction D3, the amount of light traveling in a direction inclined with respect to the stacking direction D3 is relatively large. Therefore, according to the light reflecting portion 45 having such transmission characteristics, the illuminance in the region separated from the light source 23 can be increased by combining it with the optical sheet 50 described later, and the in-plane distribution of the illuminance can be effectively uniformed.

[0070] As shown in FIG. 7A and FIG. 7B, the reflectance of the light reflecting portion 45 of the light of a specific wavelength incident at an incident angle of 40° or more and 60° or less in absolute value may be 50%. The reflectance of the light reflecting portion 45 of the light of a specific wavelength incident at an incident angle of 45° or more and 55° or less in absolute value may be 50%. As the absolute value of the incident angle increases in a range of 30° or more and 60° or less, the reflectance of the light of the specific wavelength at the light reflecting portion 45 may decrease. As the absolute value of the incident angle increases in a range of 50° or less, the reflectance of the light of the specific wavelength at the light reflecting portion 45 may decrease. In the region separated from the light source 23 in a direction perpendicular to the stacking direction D3, the amount of light traveling in a direction inclined with respect to the stacking direction D3 is relatively large. Therefore, according to the light reflecting portion 45 having such reflection characteristics, the illuminance in the region separated from the light source 23 can be increased by combining it with the optical sheet 50 described later, and the in-plane distribution of the illuminance can be effectively uniformed.

[0071] The light reflecting portion 45 is not particularly limited as long as it has a reflectance and a transmittance that depend on the incident angle. A reflective volume hologram, a cholesteric liquid crystal structure layer, a retroreflective film, or a reflective diffractive optical element can be used as the light reflecting portion 45. A member that ensures the reflectance and the transmittance that depend on the incident angle by a physical structure can also be used as the light reflecting portion 45. In particular, a dielectric multilayer film that has a relatively high degree of freedom in designing the reflection characteristics and the transmission characteristics is suitable as the light reflecting portion 45.

[0072] A multilayer film of an inorganic compound in which inorganic layers having different refractive indexes are alternately laminated can be used as the dielectric multilayer film constituting the light reflecting portion 45. As another example, a resin multilayer film in which resin layers having different refractive indexes are alternately laminated can also be used as the light reflecting portion 45.

[0073] The dielectric multilayer film as the multilayer film of inorganic compounds can be obtained by alternately laminating high refractive index inorganic layers and low refractive index inorganic layers by, for example, a CVD method, a sputtering method, a vacuum deposition method, or a wet coating method. The thickness of the multilayer film of inorganic compounds can be 0.5 μm or more and 10 μm or less. The refractive index of the inorganic compound contained in the high refractive index inorganic layer can be 1.7 or more and 2.5 or less. Examples of the inorganic compound contained in the high refractive index inorganic layer include those mainly composed of titanium oxide, zirconium oxide, tantalum pentoxide, niobium pentoxide, lanthanum oxide, yttrium oxide, zinc oxide, zinc sulfide, and indium oxide, and those containing small amounts of titanium oxide, tin oxide, cerium oxide, and the like. In addition, the refractive index of the inorganic compound contained in the low refractive index inorganic layer can be 1.2 or more and 1.6 or less. Examples of the inorganic compound contained in the low refractive index inorganic layer include silica, alumina, lanthanum fluoride, magnesium fluoride, and sodium aluminum hexafluoride.

[0074] The dielectric multilayer film as a resin multilayer film contains many layers of, for example, thermoplastic resin or thermosetting resin. Thermoplastic resin is particularly preferable because of its excellent moldability. Various additives such as antioxidants, antistatic agents, crystal nucleating agents, inorganic particles, organic particles, viscosity reducing agents, heat stabilizers, lubricants, infrared absorbing agents, ultraviolet absorbing agents, doping agents for adjusting the refractive index, etc. may be added to the resin layers.

[0075] Of the resin layers having different refractive indices, the difference in the in-plane average refractive index between the high refractive index resin layer and the low refractive index resin layer is preferably 0.03 or more, more preferably 0.05 or more, and even more preferably 0.1 or more. If the difference in the in-plane average refractive index is too small, sufficient reflectance may not be obtained.

[0076] The difference between the in-plane average refractive index and the thickness direction refractive index of the high refractive index resin layer is preferably 0.03 or more. The difference between the in-plane average refractive index and the thickness direction refractive index of the low refractive index resin layer is preferably 0.03 or less. In this case, even if the incident angle increases, the reflectance of the reflection peak is unlikely to decrease.

[0077] The number of high-refractive index resin layers and low-refractive index resin layers is adjusted according to the reflection characteristics and transmission characteristics required for the light reflecting portion 45. For example, the high-refractive index resin layers and low-refractive index resin layers can be alternately stacked in 30 layers or more, or 200 layers or more. The total number of high-refractive index resin layers and low-refractive index resin layers can be, for example, 600 layers or more. If the number of layers is too small, sufficient reflectance may not be obtained. Also, by having the number of layers in the above range, the desired reflectance can be easily obtained.

[0078] The resin multilayer film constituting the dielectric multilayer film preferably has a surface layer containing polyethylene terephthalate or polyethylene naphthalate with a thickness of 3 μm or more on at least one side. In particular, the resin multilayer film constituting the dielectric multilayer film preferably has the above surface layer on both sides. In addition, the thickness of the surface layer is more preferably 5 μm or more. By having the above surface layer, the surface of the resin multilayer film can be protected.

[0079] Examples of methods for producing the resin multilayer film constituting the dielectric multilayer film include co-extrusion, etc. Specifically, reference can be made to the method for producing a laminated film described in JP-A-2008-200861.

[0080] In addition, a commercially available laminated film can be used as the resin multilayer film constituting the dielectric multilayer film. Specific examples include PICASUS (registered trademark) manufactured by Toray Industries, Inc. and ESR manufactured by 3M.

[0081] Incidentally, the reflection or transmission in the light reflecting sheet 40 may be given diffusivity. The light reflecting sheet 40 may include a diffusing portion on the light source 23 side of the light reflecting portion 45, together with the light reflecting portion 45. The light reflecting sheet 40 may include a diffusing portion on the optical sheet 50 side of the light reflecting portion 45, together with the light reflecting portion 45. As the diffusing portion, a layer having a matte surface or a lens layer can be used. The lens layer may include a microlens or a linear array lens.

[0082] Next, a description will be given of the optical sheet 50. The optical sheet 50 is laminated on the light reflecting sheet 40 from the side opposite to the light source 23 in the lamination direction D3.

[0083] As described above, the reflection characteristics of the light reflecting sheet 40 have incidence angle dependency. The light reflecting sheet 40 typically reflects light with a low incidence angle and turns the traveling direction of the light back to the stacking direction D3. The traveling direction of the light transmitted through the light reflecting sheet 40 is mainly in a direction within an angle range that is greatly inclined with respect to the stacking direction D3 due to the reflection characteristics and transmission characteristics of the light reflecting sheet 40. The optical sheet 50 reinforces or complements the reflection characteristics at the light reflecting portion 45 of the light reflecting sheet 40. The optical sheet 50 is given a characteristic of selectively reflecting light traveling in a direction with a smaller inclination angle with respect to the stacking direction D3 within this angle range. The selective reflection function of the optical sheet 50 can reinforce and complement the reflection characteristics of the light reflecting sheet 40 that depend on the incidence angle. Such cooperation between the optical sheet 50 and the light reflecting sheet 40 can effectively uniform the in-plane distribution of illuminance.

[0084] Similarly, the optical sheet 50 is given a property of selectively transmitting light traveling in a direction with a larger inclination angle with respect to the stacking direction D3 out of the light transmitted through the light reflecting sheet 40. Furthermore, the optical sheet 50 bends the traveling direction of the light transmitted through the optical sheet 50 so that the inclination angle with respect to the stacking direction D3 becomes smaller. Due to such a light collecting function of the optical sheet 50, the burden of optical path correction for the light transmitted through the optical sheet 50 is reduced, and the utilization efficiency of the light transmitted through the optical sheet 50 can be improved.

[0085] As a specific configuration, the optical sheet 50 includes an uneven surface 51 facing the light reflecting sheet 40. In the example shown in FIG. 8A and FIG. 8B, the optical sheet 50 includes the uneven surface 51 facing the light reflecting sheet 40 and a flat surface facing the opposite side to the light reflecting sheet 40. The optical sheet 50 has a light incident side surface 50a and a light exiting side surface 50b. Of these, the light incident side surface 50a is the uneven surface 51. The light exiting side surface 50b is a flat surface. The optical sheet 50 includes a plurality of unit optical elements 55 each formed as a convex portion 53 or a concave portion 54. The unit optical element 55 is an element that changes the traveling direction of light by refraction, reflection, etc. The unit optical element 55 is a concept that includes elements called unit shape elements, unit prisms, and unit lenses. The unit optical elements 55 are provided facing the light reflecting sheet 40. The uneven surface 51 is formed by the plurality of unit optical elements 55.

[0086] The optical sheet 50 shown in Fig. 8A has a sheet-like main body 52 and a plurality of convex portions 53 provided on the surface of the main body 52 facing the light reflecting sheet 40. In the example shown in Fig. 8A, the plurality of convex portions 53 are provided adjacent to each other with no gaps. The optical sheet 50 shown in Fig. 8B has a sheet-like main body 52 with a plurality of concave portions 54 provided on the surface facing the light reflecting sheet 40. In the example shown in Fig. 8B, the plurality of concave portions 54 are provided adjacent to each other with no gaps.

[0087] 8A and 8B, the unit optical elements 55 have element surfaces 56 that are inclined with respect to the stacking direction D3. The unit optical elements 55 are defined by the element surfaces 56. The concave-convex surface 51 of the optical sheet 50 is formed by the element surfaces 56 of the unit optical elements 55.

[0088] The optical characteristics of the optical sheet 50 are affected by the inclination angle of the element surface 56 of the unit optical element 55. Therefore, the cross-sectional shape of the unit optical element 55 can be appropriately adjusted 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 element surfaces 56 included in one unit optical element 55 may be different from each other or may be the same. Furthermore, the optical sheet 50 may include unit optical elements 55 that are different in at least one of the shape and orientation, or may include only unit optical elements 55 that are identical to each other.

[0089] Also, unlike the examples shown in Figs. 8A and 8B, the element surface 56 may be curved to some extent. Alternatively, the unit optical element 55 may have an outer shape of a part of a sphere such as a hemisphere, or may have an outer shape of a part of a spheroid. When the unit optical element 55 includes a curved element surface 56, the optical path of light incident on the optical sheet 50 can be bent in various directions by reflection or refraction. This makes it possible to more effectively uniform the in-plane distribution of illuminance. Also, it is possible to effectively smooth the change in the luminance angle distribution.

[0090] The plurality of unit optical elements 55 included in the optical sheet 50 are preferably arranged two-dimensionally. According to this example, the element surfaces 56 of the unit optical elements 55 included in the optical sheet 50 face various directions. As a result, the optical sheet 50 can guide light in various directions by the two-dimensionally arranged unit optical elements 55. That is, the light can be guided in a plurality of non-parallel directions, and the in-plane distribution of illuminance can be made uniform. Each unit optical element 55 may be configured to be rotationally symmetric about an axis parallel to the stacking direction D3. For example, each unit optical element 55 may be configured to be three-fold, four-fold, or six-fold symmetric about the stacking direction D3.

[0091] The plurality of unit optical elements 55 may be arranged irregularly or regularly. By regularly arranging the plurality of unit optical elements 55, it is possible to facilitate the design of the optical sheet 50. Furthermore, by regularly arranging the plurality of unit optical elements 55, it is possible to easily arrange the unit optical elements 55 closely together without any gaps.

[0092] However, if the dimensions of the unit optical elements 55 are large when observed from the stacking direction D3, unevenness in brightness due to the shape of the unit optical elements 55 becomes visible. From the viewpoint of preventing such a defect, the maximum length of the unit optical elements 55 in the direction perpendicular to the stacking direction D3 is preferably 1.5 mm or less, more preferably 1 mm or less, and even more preferably 0.5 mm or less. Accordingly, the arrangement pitch of the unit optical elements 55 can be set to 0.01 mm or more and 1.5 mm or less. Furthermore, from the viewpoint of effectively uniforming the in-plane distribution of illuminance on the light-emitting side surface 30b of the optical member 30 when applied to the surface light source device 20, the arrangement pitch of the unit optical elements 55 is preferably 0.05 mm or more and 1 mm or less, and more preferably 0.1 mm or more and 0.5 mm or less. In addition, the height or depth of the unit optical elements 55 in the stacking direction D3 is preferably 0.025 mm or more and 0.5 mm or less, and can be set to 0.05 mm or more and 0.25 mm or less.

[0093] 9A to 12B, a number of specific examples of the optical sheet 50 will be described. In particular, the optical sheet 50 shown in Fig. 10 and Fig. 9B is the subject of a simulation to be described later.

[0094] First, in the example shown in FIG. 9A and FIG. 9B, the arrangement of the plurality of unit optical elements 55 is a square arrangement. The plurality of unit optical elements 55 are arranged at a constant pitch in the first direction D1. The plurality of unit optical elements 55 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 FIG. 9A and FIG. 9B, the plurality of unit optical elements 55 are arranged closely packed 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 and are 0.1 mm. As shown in FIG. 9A and FIG. 9B, the unit optical elements 55 are configured as a convex portion 53 or a concave portion 54 having a quadrangular pyramid shape with a square base.

[0095] Next, in the example shown in FIG. 10, the arrangement of the multiple unit optical elements 55 is a square arrangement. The multiple unit optical elements 55 are arranged at a constant pitch in two directions inclined at ±45° with respect to the first direction D1. The arrangement pitch in each direction may be the same or different. In the illustrated example, the arrangement pitch of the unit optical elements 55 in the two directions can be the same and 0.1 mm. As the unit optical elements 55 of the optical sheet 50 shown in FIG. 10, the convex portion 53 or the concave portion 54 having a quadrangular pyramid shape shown in FIG. 9B can be adopted. According to this example, the element surface 56 faces two directions inclined at ±45° with respect to the first direction D1, and light can be spread in these two directions. The optical sheet 50 of FIG. 10 using the unit optical elements 55 shown in FIG. 9B is the subject of a simulation to be described later.

[0096] In the example shown in FIG. 11A and FIG. 11B, the arrangement of the unit optical elements 55 is a square arrangement. The unit optical elements 55 are arranged at a constant pitch in the first direction D1. The unit optical elements 55 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 FIG. 11A and FIG. 11B, the unit optical elements 55 are closely packed with no gaps. In the illustrated example, the arrangement pitch in the first direction D1 and the arrangement pitch in the second direction D2 may be the same and may be 0.1 mm. The height or depth of each unit optical element 55 in the stacking direction D3 may be 0.09 mm.

[0097] As shown in Fig. 11B, the unit optical element 55 in this example is configured as a convex portion 53 or a concave portion 54 in the shape of a cone whose base is cut from all four sides. That is, the cones are arranged at an arrangement pitch shorter than the diameter of the cone base shown by the dotted line in Fig. 11A, and the overlapping portions of adjacent cones in the first direction D1 and the second direction D2 are cut out to produce each unit optical element 55. As a result, in the example shown in Figs. 11A and 11B, a plurality of unit optical elements 55 are arranged closely together with no gaps. Each unit optical element 55 can spread light radially when observed from the stacking direction D3.

[0098] In the example shown in FIG. 12A and FIG. 12B, the optical sheet 50 has two types of unit optical elements 55 with different bottom surface orientations. Each type of unit optical element 55 is arranged at a constant pitch in the second direction D2 and two directions inclined at ±60° with respect to the second direction. That is, the two types of unit optical elements 55 are arranged at a constant pitch in each of three directions inclined at 60° with respect to each other. The arrangement pitch in each direction may be the same or different, but in the illustrated example, the arrangement pitches of the unit optical elements 55 in the three directions are the same. The two types of unit optical elements 55 with different bottom surface orientations have the same bottom surface shape. The bottom surface shapes are both equilateral triangles, and when one unit optical element 55 is rotated by 60°, the orientation is also the same as that of the other unit optical element 55. 12A and 12B, the unit optical elements 55 are configured as convex portions 53 or concave portions 54 having a triangular pyramid shape with an equilateral triangular base. In the illustrated example, the length of one side of the base of the unit optical elements 55 may be 0.12 mm. The height or depth of each unit optical element 55 in the stacking direction D3 may be 0.08 mm.

[0099] In the specific example shown in FIGS. 9A to 12B, all of the perpendicular lines from the apex to the base of the cone forming the unit optical element 55 pass through the center of gravity of the base.

[0100] In addition, without being limited to the specific examples shown in FIG. 9A to FIG. 12B, the plurality of unit optical elements 55 may be arranged in one direction, and each unit optical element 55 may extend linearly in a direction non-parallel to the one direction. Typically, each unit optical element 55 may extend linearly in another direction perpendicular to the one direction. That is, the plurality of unit optical elements 55 may be linearly arranged. Also, a plurality of optical sheets 50 in which a plurality of unit optical elements 55 are linearly arranged may be stacked in the stacking direction D3 and included in the optical member 30. In this example, the arrangement direction of the unit optical elements 55 included in one optical sheet 50 may be non-parallel to the arrangement direction of the unit optical elements 55 included in the other optical sheets 50, and may be orthogonal in particular. The arrangement pitch of the linearly arranged unit optical elements 55 is preferably 0.01 mm or more and 1.5 mm or less, more preferably 0.05 mm or more and 1 mm or less, and even more preferably 0.1 mm or more and 0.5 mm or less. The height or depth of the linearly arranged unit optical elements 55 in the stacking direction D3 is preferably 0.005 mm or more and 0.75 mm or less, more preferably 0.025 mm or more and 0.5 mm or less, and even more preferably 0.05 mm or more and 0.25 mm or less. The cross-sectional shape of the linearly arranged unit optical elements 55 in a cross section perpendicular to the longitudinal direction is not particularly limited. The unit optical elements 55 may have a cross-sectional shape such as a triangular shape, a semicircular shape, or a semi-elliptical shape.

[0101] The optical sheet 50 having the above configuration is preferably formed using a transparent material since it serves as a light transmission path. For example, the optical sheet 50 can be formed from a transparent resin material by molding.

[0102] Next, the operation of generating planar light by the surface light source device 20 using the optical member 30 having the above configuration will be described mainly with reference to Figs. 13 to 16. In Figs. 13 to 15, the amount of light traveling in the direction of the arrow is represented by the thickness of the arrow. In the example shown in Figs. 13 to 15, the light reflecting sheet 40 is composed of only the light reflecting portion 45.

[0103] As shown in FIG. 13, first, light LP1 is emitted from the light source 23. In the examples shown in FIGS. 13 to 16, the light source 23 emits light LP1 with a wavelength of 450 nm, which is blue light. When a general light source 23 is used, a large amount of light LP1 is emitted toward the stacking direction D3. In the illustrated example, the light source 23 also emits light with a Lambertian light distribution. As a result, the luminance is highest in the stacking direction D3, and the luminance decreases as the inclination angle from the stacking direction D3 increases. As shown in FIG. 13, the light LP1 emitted from the light source 23 travels toward the light reflecting sheet 40 of the optical member 30.

[0104] The light reflecting portion 45 of the light reflecting sheet 40 reflects light incident at an incident angle of 0° with a reflectance of 80% or more. On the other hand, the light reflecting portion 45 reflects light incident at at least a part of the incident angle greater than 45° in absolute value with a reflectance of less than 50%. The light reflecting portion 45 typically has the reflection characteristics shown in FIG. 7A and FIG. 7B. Therefore, as shown in FIG. 14, the light reflecting sheet 40 reflects light traveling in a direction that is not greatly inclined with respect to the stacking direction D3. The light LP2 reflected by the light reflecting sheet 40 turns back the traveling direction in the stacking direction D3. That is, this light LP2 travels toward the support substrate 25. On the other hand, the light reflecting portion 45 of the light reflecting sheet 40 selectively transmits the light LP3 and LP4 that are very greatly inclined with respect to the stacking direction D3. The light LP3 and LP4 transmitted through the light reflecting sheet 40 travel toward the optical sheet 50.

[0105] The light LP2 reflected by the light reflecting sheet 40 is reflected by the reflecting layer 27 of the support substrate 25, as shown in FIG. 15. The reflected light LP5 by the reflecting layer 27 turns back again in the direction of travel in the stacking direction D3. That is, the reflected light LP5 by the reflecting layer 27 heads toward the optical sheet 50 of the optical member 30 again. In the illustrated example, the light LP5 reflected by the support substrate 25 is somewhat diffused. Therefore, when the reflected light LP5 re-enters the light reflecting sheet 40, a part of the light may be transmitted through the light reflecting sheet 40. The light reflected again by the light reflecting sheet 40 heads toward the support substrate 25 again.

[0106] Here, the position where the light LP5 re-enters the light reflecting sheet 40 after being reflected once by the light reflecting sheet 40 is farther away from the light source 23 in the direction perpendicular to the stacking direction D3 than the previous position of incidence on the light reflecting sheet 40. In general, in a direct-type surface light source device, a large amount of light tends to advance in the stacking direction in an area including a position directly facing the light source 23 and its periphery, making the area brighter. On the other hand, due to the reflection characteristics of the light reflecting sheet 40, such as selectively reflecting light with a small incident angle, the light reflecting sheet 40 can effectively prevent a large amount of light with a small incident angle from passing through the light reflecting sheet 40 in this area that tends to become brighter. In other words, due to the reflection characteristics of the light reflecting sheet 40, it is possible to suppress the illuminance in the area including a position directly facing the light source 23 and its periphery from becoming too high.

[0107] As shown in FIG. 15, the optical sheet 50 reflects a part LP3 of the incident light LP3 and LP4, and transmits a part LP4. The optical sheet 50 of the present embodiment reinforces or complements the reflection characteristics of the light reflecting sheet 40, which have an incidence angle dependency. That is, the light incident on the optical sheet 50 travels in a direction greatly inclined with respect to the stacking direction D3 due to the reflection characteristics of the light reflecting sheet 40. The optical sheet 50 selectively reflects light traveling in a direction with a relatively small inclination angle with respect to the stacking direction D3 among the light traveling in a direction within an angle range greatly inclined with respect to the stacking direction D3. Conversely, the optical sheet 50 selectively transmits light traveling in a direction with a relatively large inclination angle with respect to the stacking direction D3 among the light traveling in a direction within an angle range greatly inclined with respect to the stacking direction D3.

[0108] In the illustrated example, both the light LP3 and the light LP4 proceed in a direction greatly inclined with respect to the stacking direction D3. That is, the angles of incidence of the light LP3 and the light LP4 to the optical sheet 50 are large. As shown in FIG. 15, the light LP4 having a larger angle of incidence to the optical sheet 50 transmits through the optical sheet 50. On the other hand, the light LP3 having a relatively small angle of incidence is reflected by the optical sheet 50. The reflected light LP6 at the optical sheet 50 turns back its traveling direction in the stacking direction D3 and proceeds toward the support substrate 25. This light LP6 can re-enter the optical member 30 at a position separated from the light source 23 in a direction perpendicular to the stacking direction D3, similar to the reflected light LP2 described above.

[0109] The transmitted light LP7 transmitted through the optical sheet 50 is emitted from the light-emitting surface 20a formed by the light-emitting side surface 50b of the optical sheet 50. Since the light LP7 originally traveled in a direction greatly inclined with respect to the stacking direction D3, the light LP7 is emitted from the surface light source device 20 at a position separated from the light source 23 in the direction perpendicular to the stacking direction D3.

[0110] Similarly, light reflected by the optical member 30 and the reflective layer 27 of the support substrate 25 can also be emitted from the surface light source device 20 at a position spaced apart from the light source 23 in a direction perpendicular to the stacking direction D3. That is, the light emitted from the light source 23 can be effectively spread in a direction perpendicular to the stacking direction D3 due to the reflection characteristics of the optical member 30. This makes it possible to ensure sufficient brightness in an area spaced apart from the light source where brightness is likely to be insufficient.

[0111] In this manner, it is possible to effectively eliminate uneven brightness caused by the presence of the light source 23, and effectively uniform the illuminance on the light-emitting surface 20a. In particular, by reinforcing or complementing the reflective properties of the light-reflecting sheet 40 with the optical sheet 50, it is possible to guide light in a direction perpendicular to the stacking direction D3 while thinning the surface light source device 20. As a result, it is possible to effectively uniformize the illuminance at each position on the light-emitting side surface 30b of the optical member 30, that is, to effectively uniform the in-plane distribution of illuminance, while thinning the surface light source device.

[0112] Here, the optical function of the optical sheet 50 that reinforces or complements the reflection characteristics of the light reflecting sheet 40 will be described in more detail with reference to Fig. 16. As shown in Fig. 16, the optical sheet 50 according to this embodiment includes an uneven surface 51 as a light incident side surface 50a. The optical sheet 50 includes a plurality of unit optical elements 55 on the light incident side, each of which is formed as a convex portion 53 or a concave portion 54. The uneven surface 51 is formed by the plurality of unit optical elements 55.

[0113] 16, the traveling directions of the lights L161 and L162 traveling from the light reflecting sheet 40 to the optical sheet 50 are greatly inclined with respect to the stacking direction D3. Such lights L161 and L162 are likely to be incident on the element faces 56 that form the uneven surface 51 and are inclined with respect to the stacking direction D3 in the opposite direction to the traveling direction.

[0114] Among these, the light L161 that forms a relatively small angle with respect to the stacking direction D3 passes through the element faces 56 inclined in the opposite direction and tends to proceed toward the light-emitting side face 50b without entering other element faces 56. Next, this light L161 is reflected at the light-emitting side face 50b. The reflected light L161 can be emitted from the optical sheet 50 via the element faces 56 inclined in the opposite direction to the traveling direction with respect to the stacking direction D3. In this way, the optical sheet 50 exhibits a selective reflection characteristic that selectively reflects the light L161 that travels in a direction with a relatively small angle of inclination with respect to the stacking direction D3 among the incident light.

[0115] From the viewpoint of making the selective reflection characteristic of the optical sheet 50 more effective by uniforming the illuminance, it is preferable that the reflection on the light-emitting side surface 50b is total reflection. Considering the refractive index of transparent resin materials widely used in optical applications, when the incident angle of the light L161 on the light-emitting side surface 50b is greater than 45°, total reflection on the light-emitting side surface 50b is likely to occur. From this viewpoint, it is preferable that the traveling direction of the light incident on the optical sheet 50 is inclined by more than 45° with respect to the stacking direction D3. Therefore, it is preferable that the exit angle of the exiting light exiting from the light reflecting sheet 40 is also greater than 45°. Therefore, it is preferable that the reflectance of the light of a specific wavelength that is incident at an incident angle of 45° or less on the light reflecting sheet 40 is 50% or more. In addition, in the luminance angle distribution on the light-emitting side surface 40b of the light reflecting sheet 40, it is preferable that the luminance in the direction that forms an angle of 45° with respect to the stacking direction D3 is less than half of the peak luminance. More preferably, in the luminance angular distribution on the light-emitting side surface 40b, the luminance in a direction that is at or below 45° with respect to the stacking direction D3 is less than half of the peak luminance.

[0116] Here, the luminance angular distribution on the light-emitting side surface 40b is the distribution of luminance in each direction measured on the light-emitting side surface 40b after emitting light from the light source 23 in a state in which components on the optical sheet 50 side (observer side) of the light-reflecting sheet 40 are removed from the surface light source device 20. As an example, in the example shown in FIG. 2, the distribution of luminance in each direction measured on the light-emitting side surface 40b of the light-reflecting sheet 40 in a state in which the optical sheet 50 and a wavelength conversion sheet 71 and a reflective polarizing plate 72 shown by a two-dot chain line, which will be described later, are removed. The luminance angular distribution is measured using MB8 manufactured by Topcom Corporation. When measuring the luminance angular distribution, the distance from the luminance meter to the effective area to be measured by the luminance meter is 50 times or more the maximum length of the effective area. When measuring the luminance angular distribution, the projection angle of the luminance meter is 2°.

[0117] In order to expect total reflection at the light-emitting side surface 50b, the optical sheet 50 preferably has a flat surface as the light-emitting side surface 50b.

[0118] On the other hand, the light L162 that forms a relatively large angle with respect to the stacking direction D3 passes through an element surface 56 that is inclined in the opposite direction to the traveling direction of the light L162 with respect to the stacking direction D3 as the center, and is incident on another element surface 56 that faces the element surface 56. The light L162 is totally reflected by the other element surface 56, and the traveling direction of the light L162 is greatly bent. At this time, the traveling direction of the light L162 is bent so that the angle with respect to the stacking direction D3 becomes smaller. Therefore, the light L162 is emitted from the light-emitting surface 20a without being reflected by the light-emitting side surface 50b. In this way, the optical sheet 50 exhibits a selective transmission characteristic that selectively transmits the light L162 that travels in a direction with a relatively large inclination angle with respect to the stacking direction D3 among the incident light.

[0119] The selective reflection property and the selective transmission property of the optical sheet 50 can reinforce or complement the reflection property of the light reflecting sheet 40. That is, the combination of the light reflecting sheet 40 and the optical sheet 50 can effectively increase the angle that the traveling direction of light that can transmit through the optical member 30 makes with respect to the stacking direction D3. This makes it possible to sufficiently uniform the in-plane distribution of brightness while reducing the thickness of the surface light source device 20.

[0120] The light L162 passing through the optical sheet 50 is totally reflected at the element surface 56 and the traveling direction is greatly bent. Due to this reflection, the traveling direction of the light L162 changes from a direction greatly inclined with respect to the stacking direction D3 to a direction in which the angle with respect to the stacking direction D3 becomes smaller. That is, the angle that the traveling direction of the light L162 makes with respect to the stacking direction D3 is greatly reduced by the reflection of the light L162 at the element surface 56. That is, the optical sheet 50 exerts a function of concentrating the light emitted from the surface light source device 20 in the stacking direction D3. Due to such a concentrating function of the optical sheet 50, the burden of optical path correction for the light passing through the optical sheet 50 is reduced. As a result, the utilization efficiency of the light passing through the optical sheet 50 can be improved. In addition, the number and thickness of the optical members can be reduced, which can contribute to the thinning of the surface light source device 20.

[0121] As shown in FIG. 16, a part of light L163 traveling toward the optical sheet 50 is incident on an element surface 56 inclined toward the same side as the traveling direction with respect to the stacking direction D3. This phenomenon is likely to occur in the light L163 traveling in a direction that forms a relatively small angle with respect to the stacking direction D3 among the light incident on the optical sheet 50. As shown in FIG. 16, the traveling direction of this light L163 is refracted at the element surface 56, so that the angle with respect to the stacking direction D3 becomes small. Therefore, this light L163 is not reflected by the light-emitting side surface 50b, and is emitted from the optical sheet 50 through the light-emitting side surface 50b. That is, the presence of the light L163 that is incident on the element surface 56 inclined toward the same side as the traveling direction with respect to the stacking direction D3 makes the selective reflection characteristic and selective transmission characteristic of the optical sheet 50 weaker. Conversely, from the viewpoint of sharpening the selective reflection characteristic and selective transmission characteristic of the optical sheet 50, it is preferable to make this phenomenon less likely to occur.

[0122] From this viewpoint, it is preferable to set the inclination angle θs of the element surface 56 small with respect to the emission angle from the light reflecting sheet 40. Here, the inclination angle θs of the element surface 56 is the angle (°) that the element surface 56 forms with respect to the stacking direction D3 as shown in FIG. 16. The inclination angle θs (°) is specified as an angle value of 0° or more and 90° or less. As described above, light having an emission angle of more than 45° from the light reflecting sheet 40 is likely to be totally reflected by the light output side surface 50b of the optical sheet 50. From this point of view, it is preferable to set the inclination angle θs of the element surface 56 to 45° or less, more preferably less than 45°. According to this example, it is possible to effectively prevent the light that can be totally reflected by the light output side surface 50b from being incident on the element surface 56 inclined to the same side as the traveling direction with respect to the stacking direction D3.

[0123] The condition that the element surfaces 56 are inclined with respect to the stacking direction D3 at an inclination angle θs smaller than 45° may be satisfied by the inclination angle θs in at least a partial region of the element surfaces 56. In other words, this condition does not need to be satisfied in the entire region of the element surfaces 56. Preferably, this condition is satisfied in 70% or more of the region of the element surfaces 56. By satisfying this condition in 70% or more of the region of the element surfaces 56, the above-mentioned action and effect can be sufficiently achieved.

[0124] As another example, the inclination angle θs of the element surface 56 may be set in consideration of the specific emission angle θx (°). It is preferable to make the inclination angle θs smaller than the specific emission angle θx (°). Here, the specific emission angle θx (°) is the angle that the peak emission direction from the light reflecting sheet 40 of light incident at the minimum incidence angle θi at which the transmittance of light of a specific wavelength in the light reflecting section 45 is half the maximum transmittance is formed with respect to the stacking direction D3. In the optical characteristics shown in FIG. 5 to FIG. 7B, it can be said that the peak emission direction from the light reflecting sheet 40 of light incident on the light reflecting section 45 at the minimum incidence angle θi at which the transmittance is half the maximum transmittance is formed with respect to the stacking direction D3. In addition, the peak emission direction means the direction in which the luminance is the highest. When the light reflecting sheet 40 does not exhibit a diffusing function for the transmitted light, the specific exit angle θx (°) is the same as the minimum incident angle at which half the maximum transmittance of light of a specific wavelength is obtained in the light reflecting section 45 at which half the maximum transmittance is obtained. The specific exit angle θx (°) is specified as an angle value between 0° and 90°. By setting it in this manner, the selective reflection characteristic can be effectively used for light emitted from the light reflecting sheet 40 with a relatively small exit angle, and the light can be reflected by the light exit side surface 50b of the optical sheet 50.

[0125] The condition that the inclination angle θs of the element surface 56 is smaller than the specific emission angle θx may be satisfied by the inclination angle θs in at least a partial region of the element surface 56. In other words, this condition does not need to be satisfied in the entire region of the element surface 56. Preferably, this condition is satisfied in 70% or more of the region of the element surface 56. By satisfying this condition in 70% or more of the region of the element surface 56, the above-mentioned operational effects can be sufficiently achieved.

[0126] As another example, the inclination angle θs of the element surface 56 may be set in consideration of the luminance angle distribution on the light-emitting side surface 40b of the light-reflecting sheet 40. It is preferable to set the inclination angle θs smaller than the half-value angle θh of the luminance angle distribution. Here, the luminance angle distribution on the light-emitting side surface 40b of the light-reflecting sheet 40 is the distribution of luminance in each direction measured on the light-emitting side surface 40b by emitting light from the light source 23 in a state in which the components on the optical sheet 50 side (observer side) of the light-reflecting sheet 40 are removed from the surface light source device 20. An example of this luminance angle distribution is shown in FIG. 32. The half-value angle θh here is the minimum value of the magnitude (absolute value) of the angle formed by the direction in which half the peak luminance in the luminance angle distribution is obtained with respect to the stacking direction D3. The peak luminance on the light-emitting side surface 40b may occur at a relatively large angle, for example, around 45 to 60°, due to the selective transmission characteristics of the light-reflecting portion 45 of the light-reflecting sheet 40. The half-value angle here is the angle that the direction between the peak emission direction and the stacking direction D3 forms with respect to the stacking direction D3. This half-value angle θh (°) is specified as an angle value between 0° and 90°. By setting it in this manner, the selective reflection characteristic can be effectively used for light emitted from the light reflecting sheet 40 with a relatively small emission angle, and the light can be reflected by the light-emitting side surface 50b of the optical sheet 50.

[0127] The condition that the inclination angle θs of the element surface 56 is smaller than the half-value angle θh may be satisfied by the inclination angle θs in at least a partial region of the element surface 56. In other words, this condition does not need to be satisfied in the entire region of the element surface 56. Preferably, this condition is satisfied in 70% or more of the region of the element surface 56. By satisfying this condition in 70% or more of the region of the element surface 56, the above-mentioned operational effects can be sufficiently achieved.

[0128] In addition, from the viewpoint of making the selective reflection characteristic an effective characteristic by uniforming the illuminance, it is preferable that the reflection at the light output side surface 50b is total reflection. For this reason, as described above, it is preferable that the output angle of the output light from the light reflecting sheet 40 is greater than 45°. However, when the light is incident through the element surface 56, if the traveling direction of the light is significantly changed due to refraction at the element surface 56, it is assumed that the expected total reflection cannot be obtained. On the other hand, when the sum of the magnitude of the output angle of the light and the magnitude of the inclination angle θs of the element surface 56 that is the incident surface of the light is 90°, the light maintains the traveling direction when passing through the element surface 56. Then, after the inventors of the present invention have conducted intensive studies, it has been confirmed that the total reflection of the light at the light output side surface 50b can be effectively promoted by setting the sum of the magnitude of the output angle of the light and the magnitude of the inclination angle θs of the element surface 56 that is the incident surface of the light to be 80° or more and 100° or less.

[0129] For example, it is preferable that the sum of the above-mentioned specific emission angle θx (°) and the inclination angle θs (°) of the element surface 56 is 80° or more and 100° or less. Also, it is preferable that the sum of the above-mentioned half-value angle θh (°) and the inclination angle θs (°) of the element surface 56 is 80° or more and 100° or less. According to these examples, the selective reflection characteristic can be effectively used for light emitted from the light reflecting sheet 40 with a relatively small emission angle, so that the light can be totally reflected by the light-emitting side surface 50b of the optical sheet 50.

[0130] The condition that the sum of the inclination angle θs of the element surface 56 and the specific emission angle θx or the half-value angle θh is 80° or more and 100° or less may be satisfied by the inclination angle θs in at least a partial region of the element surface 56. In other words, this condition does not need to be satisfied in the entire region of the element surface 56. Preferably, this condition is satisfied in 70% or more of the region of the element surface 56. By satisfying this condition in 70% or more of the region of the element surface 56, the above-mentioned action and effect can be sufficiently achieved.

[0131] In addition, by setting the inclination angle θs (°) of the element surface 56 to 45° or less, total reflection at the light-emitting side surface 50b is promoted, and the selective reflection characteristic of the optical sheet 50 can be sharpened. On the other hand, if the inclination angle θs (°) is too small, the light passing through one element surface 56 is likely to be incident on another element surface 56 opposite to the one element surface 56. As shown in FIG. 16, such light L162 travels in a direction that is not greatly inclined to the stacking direction D3, and is emitted from the optical sheet 50 without being reflected by the light-emitting side surface 50b. As a result of extensive research by the present inventors, it has been confirmed that the inclination angle θs (°) in at least a part of the region of the element surface 56 is preferably greater than 25°, and more preferably greater than 30°. In addition, the above-mentioned condition that determines the lower limit value of the inclination angle θs of the element surface 56 may be satisfied by the inclination angle θs in at least a part of the region of the element surface 56. In other words, this condition does not need to be satisfied in the entire region of the element surface 56. Preferably, this condition is satisfied over 70% or more of the area of ​​the element surface 56. When this condition is satisfied over 70% or more of the area of ​​the element surface 56, the above-mentioned operational effects can be sufficiently exhibited.

[0132] The above has described the effects of the optical member 30 with reference to the example shown in Fig. 16. In the example shown in Fig. 16, the unit optical elements 55 are configured as convex portions 53, but unit optical elements 55 configured as concave portions 54 can also achieve the same effects.

[0133] Here, the results of a simulation carried out by the present inventors will be described. The simulation was carried out on the surface light source devices according to Samples 1 to 15. The simulation was carried out by ray tracing simulation using LightTools manufactured by Synopsys.

[0134] As the simulation targets, the configurations of Samples 1 to 15 will be described. Table 1 shows an overview of Samples 1 to 15.

[0135] [Table 1]

[0136] The surface light source device 20 according to the samples 1 to 15 includes a light source 23, a support substrate 25 supporting the light source 23, and an optical member 30 arranged facing the light source 23 and the support substrate 25 in the stacking direction D3. The light source 23, the support substrate 25, and the light reflecting sheet 40 included in the optical member 30 are common among the samples 1 to 15. The light source 23 is a light emitting diode that emits light with a wavelength of 450 nm and is arranged on the support substrate 25. The reflection on the surface of the reflective layer 27 of the support substrate 25 is partial diffuse reflection with a reflectance of 100%. The distance DX (see FIG. 2) along the stacking direction D3 from the surface of the light source 23 facing the optical member 30 to the light-entering side surface 30a of the optical member 30 facing the light source 23 is 0.5 mm. The light reflecting sheet 40 is a dielectric multilayer film having the reflection characteristics and transmission characteristics shown in FIG. 7A and FIG. 7B.

[0137] In the surface light source devices 20 according to Samples 1 to 12 as examples, the optical member 30 had a light reflecting sheet 40 and an optical sheet 50 in this order from the side of the light source 23 and the supporting substrate 25. The optical sheet 50 was arranged such that the uneven surface 51 formed by the unit optical elements 55 faced the light reflecting sheet 40. The refractive index of the material constituting the optical sheet 50 was 1.59.

[0138] For samples 1 to 11, an optical sheet 50 was used in which the unit optical elements 55 shown in FIG. 9B were arranged as shown in FIG. 10. The unit optical elements 55 were pyramids with a square base. One side of the square forming the base of the pyramid was 0.1 mm. The unit optical elements 55 were arranged without gaps. In samples 1 to 9, the unit optical elements 55 were convex portions 53. In samples 1 to 9, the inclination angles θs of the element surfaces 56 were set to different angles. Specifically, as shown in Table 1, the inclination angles θs of samples 1 to 9 were set to 70°, 60°, 55°, 50°, 45°, 40°, 35°, 30°, and 25°, respectively. For the unit optical elements 55 of sample 10, unit optical elements having the same configuration as the unit optical elements of sample 5 were used as the concave portions 54. In the unit optical element 55 of the sample 11, a unit optical element having the same configuration as the unit optical element of the sample 6 was used as the recess 54.

[0139] In sample 12, the optical sheet 50 had linearly arranged unit optical elements 55. The unit optical elements 55 were arranged with no gaps at an arrangement pitch of 0.1 mm. The unit optical elements 55 had a right-angled isosceles triangular shape in a cross section along the arrangement direction. Therefore, the inclination angle θs of the element surface 56 of the optical sheet 50 was set to 45°. In sample 12, the unit optical elements 55 were arranged in the first direction D1.

[0140] Surface light source device 20 according to Sample 13 was a comparative example that had a configuration in which optical sheet 50 was omitted from Samples 1-12.

[0141] The surface light source device 20 of Sample 14 is a comparative example in which the orientation of the optical sheet 50 in the stacking direction D3 is reversed in the surface light source device 20 of Sample 5. That is, in Sample 14, the unit optical elements 55 face the opposite side to the light reflecting sheet 40. Sample 14 was configured similarly to Sample 5 except for the orientation of the optical sheet 50 in the stacking direction D3.

[0142] The surface light source device 20 of Sample 15 is a comparative example in which the orientation of the optical sheet 50 in the stacking direction D3 is reversed from that of the surface light source device 20 of Sample 12. That is, in Sample 15, the unit optical elements 55 face the opposite side to the light reflecting sheet 40. Sample 12 was configured similarly to Sample 8, except for the orientation of the optical sheet 50 in the stacking direction D3.

[0143] For Samples 1 to 15, in a state where the light source 23 emits light, a light receiving surface was set as a virtual surface extending in the first direction D1 and the second direction D2 at a position 1 mm away from the surface of the optical sheet 50 facing the light reflecting sheet 40, and the illuminance at each position on the light receiving surface was simulated. The illuminance was calculated for an area on the light receiving surface having a length of 6 mm in the first direction D1 and 6 mm in the second direction D2, with the light source 23 at the center. In other words, the light source 23 was positioned at the center of the light receiving surface having an area of ​​6 mm x 6 mm when projected in the stacking direction D3. The in-plane distribution of the illuminance on the light receiving surface calculated for the surface light source devices 20 relating to Samples 1 to 15 is shown in Figs. 17 to 31, respectively.

[0144] 17 to 31 include diagrams showing the in-plane distribution of illuminance on a light receiving surface having an area of ​​6 mm x 6 mm. Also, FIG. 17 to FIG. 31 include graphs showing the illuminance distribution at each position on a straight line along the first direction D1 passing through a position facing the light source 23 in the third direction D3 on the light receiving surface. Furthermore, FIG. 17 to FIG. 31 include graphs showing the illuminance distribution at each position on a straight line along the second direction D2 passing through a position facing the light source 23 in the third direction D3 on the light surface. In the diagrams showing the in-plane distribution, the illuminance at each position on the light receiving surface is expressed by color, and the illuminance is high at positions with lighter colors. Also, the diagrams showing the in-plane distribution are provided with a scale showing the position on the light receiving surface, and the distance from the light source is shown in mm. The results shown in FIG. 17 to FIG. 31 show the relative illuminance at each position in each sample, and do not compare the illuminance between different samples.

[0145] According to the simulation results, samples 1 to 12 were able to uniformize the in-plane distribution of illuminance compared to samples 13 to 15. Samples 3 to 7, 10, and 11 were able to significantly uniformize the in-plane distribution of illuminance. Among them, samples 6, 7, and 11 had more uniform illuminance distribution. The above-mentioned specific emission angle θx of the light reflecting portion 45 constituting the light reflecting sheet 40 used for the simulation was 45°. The half-value angle θh of the luminance angle distribution on the light output side surface 40b of the light reflecting sheet 40 used for the surface light source device 20 used for the simulation was 45°. That is, the inclination angle θs at which the sum of the specific emission angle θx or the half-value angle θh is 80° or more and 100° or less is 35° or more and 55° or less, and the in-plane distribution of illuminance was significantly uniform for samples 3 to 7, 10, and 11 having this inclination angle θ. In particular, the illuminance distribution could be made more uniform for Samples 6, 7, and 11, which had an inclination angle θs of 35° or 40° smaller than the specific emission angle θx or half-value angle θh.

[0146] Samples 5 and 10 were comparable in terms of uniformity of the in-plane illuminance distribution. Similarly, Samples 6 and 11 were comparable in terms of uniformity of the in-plane illuminance distribution. Sample 12 was able to achieve a significantly uniform in-plane illuminance distribution compared to Sample 15.

[0147] In the embodiment described above, the optical member 30 includes the light reflecting sheet 40 and the optical sheet 50 in this order. The light reflecting sheet 40 includes a light reflecting portion 45. The reflectance of light of a specific wavelength incident at an incident angle of 0° at the light reflecting portion 45 is higher than the reflectance of light of a specific wavelength incident at an incident angle greater than 0°. The optical sheet 50 includes an uneven surface 51 facing the light reflecting sheet 40 side. The optical sheet 50 includes a plurality of unit optical elements 55, each of which is formed as a convex portion 53 or a concave portion 54 on the light reflecting sheet 40 side, forming the uneven surface 51.

[0148] When the optical member 30 according to this embodiment is applied to the surface light source device 20, the light from the light source 23 first enters the light reflecting sheet 40. A part of the light that enters the light reflecting sheet 40 is reflected by the light reflecting portion 45 of the light reflecting sheet 40. Here, the light reflecting portion 45 of the light reflecting sheet 40 selectively reflects light with a small incident angle and selectively transmits light with a large incident angle. In the region including the position directly facing the light source 23 and its periphery, a large amount of light tends to proceed in the stacking direction D3. In this region, the light reflecting sheet 40 can effectively prevent a large amount of light with a small incident angle from transmitting through the light reflecting sheet 40. The reflection characteristics of the light reflecting portion 45 of the light reflecting sheet 40 can suppress the illuminance in the region including the position directly facing the light source 23 and its periphery from becoming too high.

[0149] On the other hand, the light transmitted through the light reflecting sheet 40 travels in a direction greatly inclined with respect to the stacking direction D3 toward the optical sheet 50. Among the light incident on the optical sheet 50, light L161 (see FIG. 16) having a small inclination angle with respect to the stacking direction D3 is reflected at the light output side surface 50b of the optical sheet 50. The light output side surface 50b may be a flat surface. In particular, reflection at the flat surface of the optical sheet 50 can be total reflection without reflection loss. That is, the optical sheet 50 reinforces or complements the reflection characteristics of the light reflecting portion 45 of the light reflecting sheet 40. The optical characteristics of the optical sheet 50 can more effectively prevent the illuminance in the area including the position directly facing the light source 23 and its surroundings from becoming too high.

[0150] Of the light incident on the optical sheet 50, light having a small inclination angle with respect to the stacking direction D3 passes through one element surface 56 of the unit optical elements 55, and then enters another element surface 56 opposite the one element surface 56. This light L162 (see FIG. 16) is reflected by the other element surface 56 and bent in such a way that the angle it makes with respect to the stacking direction D3 becomes smaller. By reflecting the light incident on the optical sheet 50 by the element surface 56 in this manner, the light passing through the optical sheet 50 is concentrated in the stacking direction D3. The light collecting effect of the optical sheet 50 can improve the utilization efficiency of the light passing through the optical sheet 50.

[0151] The light reflected by the light reflecting sheet 40 or the optical sheet 50 may be reflected by the reflective layer 27 of the light source substrate 22 and enter the optical member 30 again. The position of incidence on the optical member 30 at this time is farther away from the light source 23 in the direction perpendicular to the stacking direction D3 than the previous position of incidence on the optical member 30. In this way, the light emitted from the light source 23 can be effectively spread in the direction perpendicular to the stacking direction D3 by reflection on the light reflecting sheet 40 or the optical sheet 50. This effectively eliminates unevenness in brightness caused by the presence of the light source 23. That is, the image of the light source 23 can be effectively made inconspicuous. In particular, by reinforcing or complementing the reflection characteristics of the light reflecting portion 45 of the light reflecting sheet 40 with the optical sheet 50, the surface light source device 20 can be made thinner while guiding the light in the direction perpendicular to the stacking direction D3. As a result, while the surface light source device 20 can be made thinner, the illuminance at each position on the light-emitting side surface 30b of the optical member 30 can be effectively uniformed, that is, the in-plane distribution of the illuminance can be effectively uniformed.

[0152] In one specific example of the embodiment described above, the unit optical element 55 includes an element surface 56 that forms the uneven surface 51. The element surface 56 is inclined with respect to the stacking direction D3 at an inclination angle θs smaller than 45°. The element surface 56 being inclined with respect to the stacking direction D3 at an inclination angle θs smaller than 45° means that the inclination angle θs in at least a part of the region of the element surface 56 satisfies this condition. That is, it is not necessary that this condition is satisfied in the entire region of the element surface 56. Preferably, this condition is satisfied in 70% or more of the region of the element surface 56. By satisfying this condition in 70% or more of the region of the element surface 56, the effect described below can be sufficiently achieved. According to this specific example, it is possible to suppress light traveling in a direction inclined by 45° or more with respect to the stacking direction D3 from being incident on an element surface inclined to the same side as the traveling direction of the light with respect to the stacking direction D3. That is, light traveling in a direction inclined by 45° or more with respect to the stacking direction D3 can be incident on the optical sheet 50 via the element surface 56 inclined with respect to the stacking direction D3 on the opposite side to the traveling direction of the light. When this light enters the optical sheet 50, the traveling direction does not change significantly due to refraction at the element surface 56. This effectively promotes reflection, particularly total reflection, at the light-emitting side surface 50b of the optical sheet 50 of the light traveling in a direction inclined at 45° or more with respect to the stacking direction D3. As a result, the optical function of the optical sheet 50 described above is more effectively exerted, and the in-plane distribution of illuminance can be effectively uniformed.

[0153] In one specific example of the embodiment described above, the element surface 56 is inclined with respect to the stacking direction D3 at an inclination angle θs smaller than the specific emission angle θx (°). Here, the specific emission angle θx (°) is the angle that the peak emission direction from the light reflecting sheet 40 of the light incident on the light reflecting portion 45 at the minimum incident angle at which the transmittance of light of a specific wavelength in the light reflecting portion 45 is half of the maximum value forms with respect to the stacking direction D3. Note that the element surface 56 is inclined with respect to the stacking direction D3 at an inclination angle θs smaller than the specific emission angle θx (°) means that at least a part of the element surface 56 satisfies this condition. In other words, it is not necessary that this condition is satisfied in the entire area of ​​the element surface 56. Preferably, this condition is satisfied in 70% or more of the element surface 56. By satisfying this condition in 70% or more of the element surface 56, the effect described below can be sufficiently achieved. According to this specific example, the light traveling in the peak emission direction is likely to travel toward the element surface 56 inclined with respect to the stacking direction D3 in the opposite direction to the traveling direction of the light. Here, the peak emission direction is a direction that is not greatly inclined with respect to the stacking direction D3 in the emission angle range of the light transmitted through the light reflecting sheet 40. Therefore, most of the emitted light from the light reflecting sheet 40 enters the optical sheet 50 through the element surface 56 inclined with respect to the stacking direction D3 in the opposite direction to the traveling direction of the light. Therefore, the optical function of the optical sheet 50 described above can be more effectively exhibited. That is, the light having a small inclination angle with respect to the stacking direction D3 can be reflected at a high rate on the light exiting side surface 50b of the optical sheet 50. In addition, the light transmitted through the optical sheet 50 can be effectively condensed in the stacking direction D3. As a result, the optical function of the optical sheet 50 described above can be more effectively exhibited, and the in-plane distribution of illuminance can be effectively uniformed. In addition, the light utilization efficiency can be improved.

[0154] In a specific example of the embodiment described above, the element surface 56 is inclined with respect to the stacking direction D3 at an inclination angle θs smaller than the half-value angle θh of the luminance angle distribution on the light-emitting side surface 40b of the light-reflecting sheet 40. Here, the luminance angle distribution on the light-emitting side surface 40b of the light-reflecting sheet 40 is the distribution of luminance in each direction measured on the light-emitting side surface 40b by emitting light from the light source 23 in a state in which components on the optical sheet 50 side (observer side) of the light-reflecting sheet 40 are removed from the surface light source device 20. The half-value angle θh is the minimum value of the angle formed with respect to the stacking direction D3 by a direction in which half the peak luminance in the luminance angle distribution is obtained. Note that the element surface 56 is inclined with respect to the stacking direction D3 at an inclination angle θs smaller than the half-value angle θh of the luminance angle distribution on the light-emitting side surface 40b of the light-reflecting sheet 40 means that the inclination angle θs in at least a part of the region of the element surface 56 satisfies this condition. In other words, it is not necessary for this condition to be satisfied in the entire region of the element surface 56. Preferably, this condition is satisfied in 70% or more of the element surface 56. By satisfying this condition in 70% or more of the element surface 56, the effect described below can be sufficiently achieved. According to this specific example, light traveling in a direction inclined by a half-value angle θh with respect to the stacking direction D3 is likely to travel toward the element surface 56 inclined with respect to the stacking direction D3 in the opposite direction to the traveling direction of the light. Here, the direction inclined by the half-value angle θh with respect to the stacking direction D3 is a direction that is not greatly inclined with respect to the stacking direction D3 within the emission angle range of the light transmitted through the light reflecting sheet 40. Therefore, most of the emitted light from the light reflecting sheet 40 enters the optical sheet 50 through the element surface 56 inclined with respect to the stacking direction D3 in the opposite direction to the traveling direction of the light. Therefore, the optical function of the optical sheet 50 described above can be more effectively exhibited. That is, light with a small inclination angle with respect to the stacking direction D3 can be reflected with high reflectance at the light-emitting side surface 50b of the optical sheet 50. Moreover, the light passing through the optical sheet 50 can be effectively condensed in the stacking direction D3. As a result, the optical function of the optical sheet 50 described above can be more effectively exhibited, and the in-plane distribution of illuminance can be effectively uniformed. Furthermore, the light utilization efficiency can be improved.

[0155] In one specific example of the embodiment described above, the sum of the specific emission angle θx and the inclination angle θs of the element surface 56 is set to 80° or more and 100° or less. The sum of the specific emission angle θx and the inclination angle θs of the element surface 56 is set to 80° or more and 100° or less, which means that the inclination angle θs in at least a part of the element surface 56 satisfies this condition. That is, it is not necessary for the entire area of ​​the element surface 56 to satisfy this condition. Preferably, this condition is satisfied in 70% or more of the element surface 56. By satisfying this condition in 70% or more of the element surface 56, the effect described below can be sufficiently achieved. According to this specific example, the incident angle of the light traveling in the peak emission direction on the element surface 56 can be reduced. Specifically, the light traveling in the peak emission direction can be incident on the element surface 56 at an incident angle of 10° or less. Such light can be incident on the optical sheet 50 without changing the traveling direction significantly due to refraction on the element surface 56. Here, the peak emission direction is a direction in which the inclination angle with respect to the stacking direction D3 is relatively small within the emission angle range of the light transmitted through the light reflecting sheet 40. Such light travels through the optical sheet 50 without changing its traveling direction, and is likely to reach the light-emitting side surface 50b. As a result, light with a small inclination angle θs with respect to the stacking direction D3 can be reflected with high reflectance on the light-emitting side surface of the optical sheet 50. By making the light-emitting side surface 50b a flat surface, the reflection efficiency can be further increased. It is also possible to cause the reflection on the light-emitting side surface 50b to be, in particular, total reflection.

[0156] In one specific example of the above-mentioned embodiment, the sum of the half-value angle θh of the luminance angle distribution on the light-emitting side surface 40b of the light-reflecting sheet 40 and the inclination angle θs of the element surface 56 is set to 80° or more and 100° or less. The sum of the half-value angle θh of the luminance angle distribution on the light-emitting side surface 40b of the light-reflecting sheet 40 and the inclination angle θs of the element surface 56 is set to 80° or more and 100° or less, which means that the inclination angle θs in at least a part of the element surface 56 satisfies this condition. That is, it is not necessary for the entire area of ​​the element surface 56 to satisfy this condition. Preferably, this condition is satisfied in 70% or more of the element surface 56. By satisfying this condition in 70% or more of the element surface 56, the effect described below can be sufficiently achieved. According to this specific example, the incident angle of the light traveling in the direction in which the half-value angle θh is obtained on the element surface 56 can be reduced. Specifically, the light traveling in the direction in which the half-value angle θh is obtained can be incident on the element surface 56 at an incident angle of 10° or less. Such light can enter the optical sheet 50 without changing its traveling direction significantly due to refraction at the element surface 56. Here, the peak emission direction is a direction in which the inclination angle with respect to the stacking direction D3 is relatively small within the emission angle range of the light transmitted through the light reflecting sheet 40. Such light then travels through the optical sheet 50 without changing its traveling direction, and is likely to reach the light-emitting side surface 50b. As a result, light with a small inclination angle θs with respect to the stacking direction D3 can be reflected with high reflectance, particularly total reflection, at the light-emitting side surface of the optical sheet 50.

[0157] Although one embodiment has been described with reference to a number of specific examples, these specific examples are not intended to limit the one embodiment. The one embodiment described above can be embodied in various other specific examples, and various omissions, substitutions, changes, additions, and the like can be made without departing from the spirit of the embodiment.

[0158] For example, as shown by the two-dot chain line in FIG. 2, the surface light source device 20 may further include other members in addition to the light source 23, the support substrate 25, and the optical member 30. Examples of other members added to the surface light source device 20 include a wavelength conversion sheet 71 and a reflective polarizing plate 72. The wavelength conversion sheet 71 has, for example, a phosphor, absorbs light from the light source 23, and emits light of a wavelength different from the wavelength of the absorbed light. For example, the light source 23 may emit blue light, and the wavelength conversion sheet 71 may convert a part of the blue light into red light and green light. According to this example, since it is only necessary to adjust the reflection characteristics of the light reflection sheet 40 to light in a limited wavelength range, it is possible to generate white surface light as the surface light source device 20 while imparting the light reflection sheet 40 with ideal reflection characteristics corresponding to the optical characteristics of the optical sheet 50. Furthermore, the reflective polarizing plate 72 transmits only the linearly polarized light component that can be used by the display panel 15, and reflects the linearly polarized light component that cannot be used by the display panel 15. The polarized components of the light reflected by the reflective polarizing plate can be changed into polarized components that can be used by the display panel 15 by reflection or the like in the subsequent optical path. The optical member 30 may include a member bonded to the display panel 15. That is, the member of the optical member 30 located closest to the light output side may be bonded to the display panel 15. [Explanation of symbols]

[0159] D1 1st direction D2 2nd direction D3 Stacking direction 10 Display device 15 Display Panel 15a Display surface 20 surface light source device 20a Light emitting surface 22 Light source board 23 Light source 24 Encapsulating materials 25 Support substrate 26 Board body 27 Reflective layer 28 Wiring 30 Optical Components 30a Light receiving side 30b Idemitsu side 40 Light reflective sheet 40a Light receiving side 40b Idemitsu side 45 Light reflecting part 50 Optical Sheet 50a Light receiving side 50b Idemitsu side 51 Uneven surface 52 Main body 53 Convex 54 Recess 55 Unit Optical Elements 56 Element Surfaces 71 Wavelength conversion sheet 72 Reflective polarizing plate

Claims

1. a light reflecting sheet including a light reflecting portion having a reflectance of a specific wavelength of light incident at an incident angle of 0° that is greater than a reflectance of the specific wavelength of light incident at an incident angle greater than 0°; an optical sheet including an uneven surface facing the light reflecting sheet, The optical sheet includes a plurality of unit optical elements, each of which is formed as a convex portion or a concave portion, on the side of the light reflecting sheet, the concave-convex surface is formed by the plurality of unit optical elements, When the peak emission direction of light incident on the light reflecting portion at the minimum incident angle at which the transmittance of light of the specific wavelength in the light reflecting portion is half of the maximum value, the angle formed by the peak emission direction from the light reflecting sheet with respect to the stacking direction of the light reflecting sheet and the optical sheet is defined as a specific emission angle θx (°), The unit optical element includes an element surface that forms the uneven surface, The optical member, wherein the element surface is inclined with respect to the stacking direction at an angle smaller than the specific emission angle θx (°).

2. The optical member according to claim 1 , wherein the element surfaces are inclined at an angle of less than 45° with respect to the stacking direction of the light reflecting sheet and the optical sheet.

3. The specific emission angle θx (°) is the angle that the element surface makes with respect to the stacking direction.

3. The method according to claim 1, wherein the sum of the inclination angle θs (°) is 80° or more and 100° or less. Optical components.

4. a light reflecting sheet including a light reflecting portion having a reflectance of a specific wavelength of light incident at an incident angle of 0° that is greater than a reflectance of the specific wavelength of light incident at an incident angle greater than 0°; an optical sheet including an uneven surface facing the light reflecting sheet, The optical sheet includes a plurality of unit optical elements, each of which is formed as a convex portion or a concave portion, on the side of the light reflecting sheet, the concave-convex surface is formed by the plurality of unit optical elements, A specific emission angle θx (°) is an angle formed by a peak emission direction from the light reflecting sheet of light incident on the light reflecting portion at a minimum incident angle at which the transmittance of light of the specific wavelength in the light reflecting portion is half of its maximum value, with respect to a stacking direction of the light reflecting sheet and the optical sheet; an inclination angle θs (°) that an element surface that is included in the unit optical element and forms the uneven surface forms with respect to the stacking direction, the sum of which is 80° or more and 100° or less.

5. 5. The optical member according to claim 1, further comprising a wavelength conversion sheet that emits light having a wavelength different from that of incident light, on a side of the optical sheet opposite to the light reflecting sheet.

6. a light reflecting sheet including a light reflecting portion having a reflectance of a specific wavelength of light incident at an incident angle of 0° that is greater than a reflectance of the specific wavelength of light incident at an incident angle greater than 0°; an optical sheet including an uneven surface facing the light reflecting sheet, The optical sheet includes a plurality of unit optical elements, each of which is formed as a convex portion or a concave portion, on the side of the light reflecting sheet, the concave-convex surface is formed by the plurality of unit optical elements, The optical member further comprises a wavelength conversion sheet that emits light having a wavelength different from that of incident light, on an opposite side of the optical sheet from the light reflecting sheet.

7. The optical member according to claim 1 , further comprising a reflective polarizing plate on the opposite side of the optical sheet to the light reflecting sheet.

8. An optical member according to any one of claims 1 to 7; a light source that emits light incident on the optical member.

9. An optical member according to any one of claims 1 to 7; A surface light source device comprising: a light source substrate having a reflective layer facing the optical member; and a light source that emits light incident on the optical member.

10. The surface light source device according to claim 9 , wherein the reflective layer has a glossiness of 70 or more.

11. A direction in which half the peak brightness is obtained in a brightness angle distribution on a surface of the light reflecting sheet facing the optical sheet, obtained in a state in which components on the optical sheet side of the light reflecting sheet are removed, forms an angle with respect to the lamination direction of the light reflecting sheet and the optical sheet, and the angle is defined as a half-value angle θh (°). The unit optical element includes an element surface that forms the uneven surface, 11. The surface light source device according to claim 8, wherein the element surfaces are inclined with respect to the stacking direction at an angle smaller than the half-value angle θh (°).

12. An optical member; A light source that emits light to be incident on the optical member, The optical member is a light reflecting sheet including a light reflecting portion having a reflectance of a specific wavelength of light incident at an incident angle of 0° that is greater than a reflectance of the specific wavelength of light incident at an incident angle greater than 0°; an optical sheet including an uneven surface facing the light reflecting sheet, The optical sheet includes a plurality of unit optical elements, each of which is formed as a convex portion or a concave portion, on the side of the light reflecting sheet, the concave-convex surface is formed by the plurality of unit optical elements, A direction in which half the peak brightness is obtained in a brightness angle distribution on a surface of the light reflecting sheet facing the optical sheet, obtained in a state in which components on the optical sheet side of the light reflecting sheet are removed, forms an angle with respect to the lamination direction of the light reflecting sheet and the optical sheet, and the angle is defined as a half-value angle θh (°). The unit optical element includes an element surface that forms the uneven surface, The element surface is inclined with respect to the lamination direction at an angle smaller than the half-value angle θh (°). A surface light source device.

13. a half-value angle θh (°), which is the minimum value of the angle formed by a direction in which half the peak brightness is obtained in a brightness angle distribution on a surface of the light reflecting sheet facing the optical sheet, obtained in a state in which components on the optical sheet side of the light reflecting sheet are removed, with respect to the stacking direction of the light reflecting sheet and the optical sheet; An inclination angle θs (°) that an element surface that is included in the unit optical element and forms the uneven surface forms with respect to the stacking direction; The surface light source device according to any one of claims 8 to 12, wherein the sum of the angles is 80° or more and 100° or less.

14. An optical member; A light source that emits light to be incident on the optical member, The optical member is a light reflecting sheet including a light reflecting portion having a reflectance of a specific wavelength of light incident at an incident angle of 0° that is greater than a reflectance of the specific wavelength of light incident at an incident angle greater than 0°; an optical sheet including an uneven surface facing the light reflecting sheet, The optical sheet includes a plurality of unit optical elements, each of which is formed as a convex portion or a concave portion, on the side of the light reflecting sheet, the concave-convex surface is formed by the plurality of unit optical elements, a half-value angle θh (°), which is the minimum value of the angle formed by a direction in which half the peak brightness is obtained in a brightness angle distribution on a surface of the light reflecting sheet facing the optical sheet, obtained in a state in which components on the optical sheet side of the light reflecting sheet are removed, with respect to the stacking direction of the light reflecting sheet and the optical sheet; An inclination angle θs (°) that an element surface that is included in the unit optical element and forms the uneven surface forms with respect to the stacking direction; The sum of the angles is 80° or more and 100° or less.

15. A surface light source device according to any one of claims 8 to 14, A display device comprising the surface light source device and a display panel laminated thereon.

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