Diffuser, method for manufacturing a diffuser, surface light source device, display device, and dielectric multilayer film

Abstract

To achieve a sufficiently uniform in-plane brightness distribution while reducing the thickness of a surface light source device. [Solution] The surface light source device 20 has a light diffusion section 50 and a light reflection section 70 in this order. The light diffusion section 50 has light transparency and light diffusion properties. The light reflection section 70 has a reflectance of 80% or more for light of a specific wavelength that is incident at an incident angle of 0°. The light reflection section 70 has a reflectance of less than 50% for at least a part of the specific wavelength that is incident at an incident angle greater than 45° in absolute value.

Description

Technical Field

[0001] The present disclosure relates to a diffusion member, a method for manufacturing a diffusion member, a surface light source device, a display device, and a dielectric multilayer film.

Background Art

[0002] Patent Document 1 discloses a surface light source device that emits light in a planar shape. The surface light source device may be used as a backlight for a liquid crystal display device. The surface light source device of Patent Document 1 is a direct-type, and the light source faces the diffusion member. In a direct-type surface light source device, unevenness in brightness occurs due to the arrangement of the light sources. When the surface light source device is thinned, the non-uniformity of brightness becomes remarkable.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the prior art, while attempting to thin the surface light source device, sufficient uniformization of the in-plane distribution of brightness has not been achieved. An object of the present disclosure is to sufficiently uniformize the in-plane distribution of brightness while attempting to thin the surface light source device.

Means for Solving the Problems

[0005] The first diffusion member according to the present disclosure is a light diffusion part having light transmissivity and light diffusibility, a light reflection part having a reflectance of 80% or more for light of a specific wavelength incident at an incident angle of 0°, and a reflectance of less than 50% for at least a part of the light of the specific wavelength incident at an incident angle having an absolute value greater than 45°, provided in this order.

[0006] The second diffusion member according to the present disclosure is A light-diffusing section having light-transmitting and light-diffusing properties, The device comprises, in this order, a light-reflecting section whose transmittance to light of a specific wavelength incident at an incident angle of 0° is lower than the transmittance to light of the same specific wavelength incident at a certain incident angle greater than 0°.

[0007] In the first and second diffusion members according to this disclosure, the specific wavelength may be 450 nm.

[0008] In the first and second diffusion members according to this disclosure, when a light ray is incident on the light diffusion portion at an incident angle of 0°, the radiant intensity on the side of the light diffusion portion facing the light reflection portion may have a peak at an exit angle other than 0°.

[0009] In the first and second diffusion members according to this disclosure, when a light ray is incident on the light diffusion portion at an incident angle of 0°, the radiation intensity on the side of the light diffusion portion facing the light reflection portion may be such that, in an angular distribution within any plane including the emission direction where the emission angle is 0°, the emission angle has a peak at emission angles other than 0°.

[0010] In the first and second diffusion members according to this disclosure, the absolute value of the emission angle having the peak of the radiation intensity may be 30° or more and 60° or less.

[0011] In the first and second diffusion members according to this disclosure, the absolute value of the exit angle of 90% or more of the light incident on the light diffusion portion at an incident angle of 0° may be 30° or more and 60° or less.

[0012] In the first and second diffusion members of this disclosure, If the absolute value of the emission angle having the peak of the radiation intensity is defined as the peak angle, The reflectance of light of a specific wavelength incident on the light reflecting portion at an incident angle that is 0° or more in absolute value and less than or equal to the peak angle may be 80% or more.

[0013] In the first and second diffusion members according to this disclosure, the light diffusion portion may be formed as an uneven surface that forms the surface of the light reflection portion.

[0014] In the first and second diffusion members according to this disclosure, the light diffusion portion may have an uneven surface facing away from the light reflecting portion and may be joined to the light reflecting portion.

[0015] In the first and second diffusion members according to this disclosure, the light diffusion portion may include an optical sheet having an uneven surface with light-diffusing properties on the side of the light reflecting portion in the stacking direction in which the light diffusion portion and the light reflecting portion are stacked.

[0016] In the first and second diffusion members according to this disclosure, the light diffusion portion may include an optical sheet having an uneven surface with light-diffusing properties on the side opposite to the light-reflecting portion in the stacking direction in which the light diffusion portion and the light-reflecting portion are stacked.

[0017] In the first and second diffusion members according to this disclosure, the light diffusion portion may include an optical sheet having light-diffusing uneven surfaces on both sides in the lamination direction in which the light diffusion portion and the light reflection portion are laminated.

[0018] In the first and second diffusion members according to this disclosure, the light diffusion portion may include a plurality of optical sheets having light-diffusing properties.

[0019] The first and second diffusion members according to this disclosure may further include a thermoplastic resin layer provided on the side of the light diffusion portion opposite to the light reflection portion.

[0020] In the first and second diffusion members according to this disclosure, the thermoplastic resin layer may include a thermoplastic resin and low refractive index particles having a refractive index lower than that of the material constituting the light diffusion portion.

[0021] In the first and second diffusion members of this disclosure, The thermoplastic resin layer includes a first layer spaced apart from the light diffusion portion and a second layer positioned between the first layer and the light diffusion portion. The low refractive index particles may be included only in the second layer of the first layer and the second layer.

[0022] In the first and second diffusion members according to the present disclosure, the thickness of the second layer may be thinner than the thickness of the first layer.

[0023] In the first and second diffusion members according to the present disclosure, the light diffusion portion may include a thermoplastic resin layer having an uneven surface having light diffusibility on the side of the light reflection portion in the stacking direction in which the light diffusion portion and the light reflection portion are stacked.

[0024] In the first and second diffusion members according to the present disclosure, voids may be provided on both sides of the light diffusion portion in the stacking direction in which the light diffusion portion and the light reflection portion are stacked.

[0025] In the first and second diffusion members according to the present disclosure, the light diffusion portion may include a diffusion main body portion including an uneven surface and a reflection covering portion that covers the uneven surface while maintaining the unevenness of the uneven surface to form a reflection surface.

[0026] In the first and second diffusion members according to the present disclosure, the light diffusion portion includes a plurality of element light diffusion portions arranged in a direction perpendicular to the stacking direction in which the light diffusion portion and the light reflection portion are stacked, the side end surfaces of the plurality of element light diffusion portions may be colored dark.

[0027] In the first and second diffusion members according to the present disclosure, the light diffusion portion includes a plurality of element light diffusion portions arranged in a direction perpendicular to the stacking direction in which the light diffusion portion and the light reflection portion are stacked, at least a part of the boundary between two adjacent element light diffusion portions may include a curve in an observation from the stacking direction.

[0028] In the first and second diffusion members of this disclosure, The light diffusion section includes a microlens having a plurality of unit optical elements, The unit optical element may include an element surface having a normal direction inclined at an angle greater than 45° with respect to the stacking direction in which the light diffusing portion and the light reflecting portion are stacked.

[0029] In the first and second diffusion members of this disclosure, The light diffusion section includes a microlens having a plurality of unit optical elements, The unit optical element may include a curved element surface.

[0030] In the first and second diffusion members of this disclosure, The light diffusion section includes a microlens having a plurality of unit optical elements, When observed from the stacking direction in which the light-diffusing portion and the light-reflecting portion are stacked, the unit optical element may have dimensions smaller than a 0.6 mm square.

[0031] In the first and second diffusion members of this disclosure, The light diffusion section includes a microlens having a plurality of unit optical elements, An indicator may be provided showing the direction in which the light-diffusing section should be positioned.

[0032] In the first and second diffusion members of this disclosure, The light diffusion section includes a microlens having a plurality of unit optical elements, The unit optical element may include an element surface formed as a matte surface.

[0033] In the first and second diffusion members according to this disclosure, the reflectance at the light reflection portion for light of a specific wavelength incident at an incident angle of 0° or more and 30° or less in absolute value may be 80% or more, more preferably 90% or more, and even more preferably 95% or more.

[0034] In the first and second diffusion members according to this disclosure, the reflectance at the light reflection portion for light of a specific wavelength incident at an incident angle of 0° or more and 45° or less in absolute value may be 80% or more, more preferably 85% or more, and even more preferably 90% or more.

[0035] In the first and second diffusion members according to this disclosure, the reflectance at the light reflection portion for light of a specific wavelength incident at an incident angle of 45° or more and 75° or less in absolute value, and more preferably the reflectance at the light reflection portion for light of a specific wavelength incident at an incident angle of 50° or more and 60° or less in absolute value, may be set to 50%.

[0036] In the first and second diffusion members according to this disclosure, the reflectance at the light reflection portion for light of a specific wavelength with an absolute value of the angle of incidence of 45° or more and 75° or less, and more preferably the reflectance at the light reflection portion for light of a specific wavelength with an absolute value of the angle of incidence of 50° or more and 60° or less, may be made to gradually decrease with increasing absolute value of the angle of incidence.

[0037] In the first and second diffusion members according to this disclosure, the reflectance at the light reflection portion for light of a specific wavelength with an absolute value of the incident angle of 50° or more may be such that it gradually decreases with increasing absolute value of the incident angle.

[0038] In the first and second diffusing members according to this disclosure, the reflectance of light of the specific wavelength at the light reflecting portion may gradually decrease with increasing absolute value of the incident angle.

[0039] In the first and second diffusion members according to this disclosure, the light-reflecting portion may have a matte surface facing the light-diffusing portion.

[0040] The first and second diffusion members according to this disclosure may further comprise optical element portions provided on the side of the light-reflecting portion opposite to the light-diffusing portion and having an uneven surface on the side opposite to the light-reflecting portion.

[0041] The third diffusion member according to this disclosure is A light-diffusing section having light-transmitting and light-diffusing properties, A light-reflecting portion in which the transmittance of light of a specific wavelength incident at an incident angle of 0° is lower than the transmittance of light of the same specific wavelength incident at an incident angle greater than 0°, The optical element portion having an uneven surface on the side opposite to the light-reflecting portion is provided in this order.

[0042] In the first to third diffusion members according to this disclosure, the uneven surface may include element surfaces having a normal direction inclined at an angle of 25° or less with respect to the stacking direction in which the light reflecting portion and the optical element portion are stacked.

[0043] In the first to third diffusion members according to this disclosure, the optical element portion may be joined to the light reflecting portion.

[0044] In the first to third diffusion members according to this disclosure, the optical element portion may include a microlens having a plurality of unit optical elements.

[0045] In the first to third diffusion members of this disclosure, The optical element portion may include a microlens having a plurality of unit optical elements. The unit optical element may be a convex portion that protrudes on the side opposite to the light-reflecting portion.

[0046] In the first to third diffusion members of this disclosure, The optical element portion may include a microlens having a plurality of unit optical elements. The unit optical element may include an element surface having a normal direction inclined at an angle of 25° or less with respect to the stacking direction in which the light reflecting portion and the optical element portion are stacked. The element surface may form the uneven surface.

[0047] In the first to third diffusion members of this disclosure, The optical element portion may include a microlens having a plurality of unit optical elements. The unit optical element includes a curved element surface, and the element surface may form the uneven surface.

[0048] In the first to third diffusion members of this disclosure, The optical element portion may include a microlens having a plurality of unit optical elements. When observed from the stacking direction in which the optical element portion and the light reflecting portion are stacked, the unit optical element may have dimensions smaller than a 1.5 mm square.

[0049] In the first to third diffusion members of this disclosure, The optical element portion may include a microlens having a plurality of unit optical elements. The unit optical element includes an element surface formed as a matte surface, and the element surface may form the uneven surface.

[0050] In the first to third diffusion members of this disclosure, The optical element portion may have a plurality of unit optical elements arranged in one direction. Each unit optical element may extend linearly in a direction nonparallel to the aforementioned one direction.

[0051] In the first to third diffusion members of this disclosure, The optical element portion may have a plurality of unit optical elements arranged in one direction. Each unit optical element may extend linearly in a direction nonparallel to the aforementioned one direction. The unit optical element may also be a convex portion that protrudes on the side opposite to the light-reflecting portion.

[0052] In the first to third diffusion members of this disclosure, The optical element portion may have a plurality of unit optical elements arranged in one direction. Each unit optical element may extend linearly in a direction nonparallel to the aforementioned one direction. The unit optical element may include an element surface having a normal direction inclined at an angle of 25° or less with respect to the stacking direction in which the light-reflecting portion and the optical element portion are stacked.

[0053] In the first to third diffusion members of this disclosure, The optical element portion may have a plurality of unit optical elements arranged in one direction. Each unit optical element may extend linearly in a direction nonparallel to the aforementioned one direction. The unit optical element includes a curved element surface, and the element surface may form the uneven surface.

[0054] In the first to third diffusion members of this disclosure, The optical element portion may have a plurality of unit optical elements arranged in one direction. Each unit optical element may extend linearly in a direction nonparallel to the aforementioned one direction. The unit optical element includes an element surface formed as a matte surface, and the element surface may form the uneven surface.

[0055] The surface light source device disclosed herein is Any of the first and third diffusion members described above in this disclosure, The system comprises a light source that emits light incident on the diffusing member.

[0056] In the surface light source device according to this disclosure, the light emitted from the light source may be P-polarized.

[0057] In the surface light source device according to this disclosure, The aforementioned light source includes a plurality of light sources arranged in a regular pattern, At least one of the light diffusion section and the optical element section may include a microlens having a plurality of unit optical elements arranged in a direction nonparallel to the arrangement direction of the plurality of light sources.

[0058] In the surface light source device according to this disclosure, At least one of the light diffusion portion and the optical element portion includes a microlens having a plurality of unit optical elements. In observation from the stacking direction in which the light diffusing portion and the light reflecting portion are stacked, the dimension of the unit optical element along any direction may be three times or less the dimension of the light source along that direction.

[0059] In the surface light source device according to this disclosure, The aforementioned light source includes a plurality of light sources arranged in a regular pattern, At least one of the light diffusion portion and the optical element portion includes a microlens having a plurality of unit optical elements. The unit optical element may include an element surface having a normal direction that is non-parallel to the arrangement direction of the plurality of light sources when observed from the stacking direction in which the light diffusing portion and the light reflecting portion are stacked.

[0060] The surface light source device disclosed herein is The system further comprises a support substrate that supports the light source from the opposite side of the diffusion member, The diffusion member may further include a thermoplastic resin layer provided on the support substrate side of the light diffusion portion.

[0061] The surface light source device disclosed herein is The system further comprises a support substrate that supports the light source from the opposite side of the diffusion member, The diffusion member may further include a thermoplastic resin layer provided on the support substrate side of the light diffusion portion.

[0062] In the surface light source device according to this disclosure, The thermoplastic resin layer is provided with a recess on the side facing the support substrate. The light source may be positioned within the recess, spaced apart from the thermoplastic resin layer.

[0063] The surface light source device disclosed herein is A support substrate that supports the light source from the opposite side of the diffusion member, A bead located between the support substrate and the diffusion member, The system may further include a binder for fixing the beads to the support substrate.

[0064] The surface light source device disclosed herein is A support substrate that supports the light source from the opposite side of the diffusion member, The system may further include a void-forming layer located between the support substrate and the diffusion member, and having a plurality of voids.

[0065] The display device according to this disclosure comprises any of the surface light source devices according to this disclosure described above.

[0066] The first light-reflecting portion according to this disclosure is A light-reflecting part used in combination with a light-diffusing part having light-diffusing properties, The reflectance of light of a specific wavelength incident at an incident angle of 0° is 80% or more, and the reflectance of at least some of the light of the same specific wavelength incident at an incident angle greater than 45° in absolute value is less than 50%.

[0067] The second light-reflecting portion according to this disclosure is A light-reflecting part used in combination with a light-diffusing part having light-diffusing properties, The transmittance of light of a specific wavelength incident at an incident angle of 0° is lower than the transmittance of light of the same specific wavelength incident at an incident angle greater than 0°.

[0068] The first dielectric multilayer film according to this disclosure is A dielectric multilayer film used in combination with at least one of a diffractive optical element and a microlens, The reflectance of light of a specific wavelength incident at an incident angle of 0° is 80% or more, and the reflectance of at least some of the light of the same specific wavelength incident at an incident angle greater than 45° in absolute value is less than 50%.

[0069] The second dielectric multilayer film according to this disclosure is A dielectric multilayer film used in combination with at least one of a diffractive optical element and a microlens, The transmittance of light of a specific wavelength incident at an incident angle of 0° is lower than the transmittance of light of the same specific wavelength incident at an incident angle greater than 0°.

[0070] The method for manufacturing the first diffusion member according to this disclosure is: A step of curing the resin composition by irradiating the resin composition located between the mold and the light-reflecting part with ionizing radiation, The process includes a step of peeling the mold from the light-diffusing portion laminated with the light-reflecting portion, which is made of a cured product of the resin composition.

[0071] The method for manufacturing the second diffusion member according to this disclosure is: A step of curing the resin composition by irradiating the resin composition located between the mold and the dielectric multilayer film with ionizing radiation, The process includes a step of peeling the mold off a microlens or diffractive optical element made of a cured product of the resin composition and laminated with the dielectric multilayer film.

[0072] The method for manufacturing the third diffusion member according to this disclosure is: A step of curing a resin composition applied to one surface of a dielectric multilayer film to form a light-diffusing portion having an uneven surface on the dielectric multilayer film, The process includes a step of curing a resin composition applied to the other surface of a dielectric multilayer film to form an optical element portion having an uneven surface on the dielectric multilayer film. [Effects of the Invention]

[0073] According to the present invention, it is possible to make the surface light source device thinner while ensuring a sufficiently uniform distribution of brightness within the plane. [Brief explanation of the drawing]

[0074] [Figure 1] Figure 1 is a diagram illustrating a first specific example of one embodiment, and is a perspective view showing a display device and a surface light source device. [Figure 2] Figure 2 is a longitudinal cross-sectional view of the surface light source device shown in Figure 1. [Figure 3] Figure 3 is a plan view showing the multiple light sources of the surface light source device shown in Figure 2. [Figure 4] Figure 4 is a graph illustrating the diffusion characteristics of the light-diffusing portion of a diffusion member that may be included in the surface light source device of Figure 2, and shows the angular distribution of radiant intensity. [Figure 5] Figure 5 is a perspective view showing the light diffusion portion of a diffusion member that may be included in the surface light source device of Figure 2, and is a diagram for explaining the light diffusion characteristics of the diffractive optical element that forms the light diffusion portion. [Figure 6] Figure 6 is a graph illustrating the light diffusion characteristics of the diffractive optical element shown in Figure 5, and it shows the angular distribution of radiant intensity. [Figure 7] Figure 7 is a longitudinal cross-sectional view showing a diffractive optical element that may be included in the surface light source device of Figure 2. [Figure 8] Figure 8 is a plan view showing a diffractive optical element that may be included in the surface light source device shown in Figure 2. [Figure 9] Figure 9 is a longitudinal cross-sectional view showing an example of a microlens that may be included in the surface light source device of Figure 2. [Figure 10] Figure 10 is a longitudinal cross-sectional view showing another example of a microlens that may be included in the surface light source device of Figure 2. [Figure 11] Figure 11 is a longitudinal cross-sectional view showing yet another example of a microlens that may be included in the surface light source device of Figure 2. [Figure 12] Figure 12 is a longitudinal cross-sectional view showing yet another example of a microlens that may be included in the surface light source device of Figure 2. [Figure 13A] Figure 13A is a plan view showing an example of a specific configuration of a microlens that may be included in the surface light source device shown in Figure 2. [Figure 13B] Figure 13B is a perspective view showing the unit optical element of the microlens in Figure 13A. [Figure 14A] Figure 14A is a plan view showing another example of a specific configuration of microlenses that may be included in the surface light source device of Figure 2. [Figure 14B] Figure 14B is a perspective view showing the unit optical element of the microlens in Figure 14A. [Figure 15A] Figure 15A is a plan view showing an example of a specific configuration of a microlens that may be included in the surface light source device shown in Figure 2. [Figure 15B] Figure 15B is a perspective view showing the unit optical element of the microlens in Figure 15A. [Figure 16A] Figure 16A is a plan view showing an example of a specific configuration of a microlens that may be included in the surface light source device shown in Figure 2. [Figure 16B] Figure 16B is a perspective view showing the unit optical element of the microlens in Figure 16A. [Figure 17] Figure 17 is a graph showing an example of the optical properties of the light-reflecting portion of a diffuser that may be included in the surface light source device of Figure 2, and is a graph intended to explain the dependence of reflectance and transmittance on the reflection angle. [Figure 18] Figure 18 is a graph showing another example of the optical properties of the light-reflecting portion of a diffuser that may be included in the surface light source device of Figure 2. [Figure 19] Figure 19 is a graph showing yet another example of the optical properties of the light-reflecting part that may be included in the surface light source device of Figure 2. [Figure 20] Figure 20 is an enlarged view of a portion of the graph in Figure 19. [Figure 21] Figure 21 is a longitudinal cross-sectional view showing an example of a reflective structure that may be included in the surface light source device of Figure 2. [Figure 22] Figure 22 is a plan view showing the reflective structure in Figure 21. [Figure 23] Figure 23 is a longitudinal cross-sectional view showing another example of a reflective structure that may be included in the surface light source device of Figure 2. [Figure 24] Figure 24 is a plan view showing the reflective structure in Figure 23. [Figure 25] Figure 25 is a vertical cross-sectional view showing a surface light source device, and is a diagram for explaining the operation of the diffusion member and the surface light source device. [Figure 26] Figure 26 is a longitudinal cross-sectional view of the area light source device corresponding to Figure 2, and is a diagram for explaining the operation of the diffusion member and the area light source device. [Figure 27] Figure 27 is a longitudinal cross-sectional view of the area light source device corresponding to Figure 2, and is a diagram for explaining the operation of the diffusion member and the area light source device. [Figure 28]Figure 28 is a longitudinal cross-sectional view of the area light source device corresponding to Figure 2, and is a diagram for explaining the operation of the diffusion member and the area light source device. [Figure 29A] Figure 29A shows the simulation results of the in-plane illuminance distribution of the surface light source device for Sample 1. [Figure 29B] Figure 29B shows the simulation results of the in-plane illuminance distribution of the surface light source device for Sample 2. [Figure 29C] Figure 29C shows the simulation results of the in-plane illuminance distribution of the surface light source device for Sample 3. [Figure 29D] Figure 29D shows the simulation results of the in-plane illuminance distribution of the surface light source device for Sample 4. [Figure 29E] Figure 29E shows the simulation results of the in-plane illuminance distribution of the surface light source device for Sample 5. [Figure 29F] Figure 29F shows the simulation results of the in-plane illuminance distribution of the surface light source device for sample 6. [Figure 29G] Figure 29G shows the simulation results of the in-plane illuminance distribution of the surface light source device for Sample 7. [Figure 30] Figure 30 is a diagram illustrating a second specific example of one embodiment, and is a longitudinal cross-sectional view showing an example of a diffusion member that may be included in the surface light source device of Figure 2. [Figure 31A] Figure 31A is a longitudinal cross-sectional view showing an example of a microlens that may be included in the optical element portion of the diffusion member in Figure 30. [Figure 31B] Figure 31B is a longitudinal cross-sectional view showing another example of a microlens that may be included in the optical element portion of the diffusion member in Figure 30. [Figure 32] Figure 32 is a perspective view showing another example of the optical element portion of the diffusion member shown in Figure 30. [Figure 33] Figure 33 is a vertical cross-sectional view of a surface light source device corresponding to Figure 2, and is a diagram illustrating the operation of the diffusion member and the surface light source device. [Figure 34]Figure 34 is a longitudinal cross-sectional view of the area light source device corresponding to Figure 2, and is a diagram illustrating the operation of the diffusion member and the area light source device. [Figure 35] Figure 35 is a vertical cross-sectional view of a surface light source device corresponding to Figure 2, and is a diagram illustrating the operation of the diffusion member and the surface light source device. [Figure 36] Figure 36 is a vertical cross-sectional view of a surface light source device corresponding to Figure 2, and illustrates the operation of the diffusion member and the surface light source device. [Figure 37] Figure 37 is a longitudinal cross-sectional view of the optical element, corresponding to Figure 31A, and is a diagram illustrating the operation of the optical element. [Figure 38] Figure 38 is a longitudinal cross-sectional view of a surface light source device corresponding to Figure 2, illustrating an example in which the diffusion member includes a thermoplastic resin layer. [Figure 39] Figure 39 is a longitudinal cross-sectional view of a surface light source device corresponding to Figure 2, illustrating an example in which the diffusion member includes a thermoplastic resin layer. [Figure 40] Figure 40 is a longitudinal cross-sectional view of a surface light source device corresponding to Figure 2, illustrating an example in which the diffusion member includes a thermoplastic resin layer. [Figure 41] Figure 41 is a longitudinal cross-sectional view of a surface light source device corresponding to Figure 2, illustrating an example in which the surface light source device includes beads. [Figure 42] Figure 42 is a longitudinal cross-sectional view of a surface light source device corresponding to Figure 2, illustrating an example in which the surface light source device includes a void-forming layer. [Figure 43] Figure 43 is a side view illustrating an example of a method for manufacturing the light-diffusing portion and optical element portion that may be included in the diffusion member of Figure 2 or Figure 30. [Figure 44] Figure 44 illustrates an example of the layer configuration of the light-diffusing portion that may be included in the diffusion member of Figure 2 or Figure 30. [Figure 45] Figure 45 illustrates another example of a method for manufacturing the light-diffusing portion and optical element portion that may be included in the diffusion member of Figure 2 or Figure 30. [Figure 46] Figure 46 is a diagram illustrating an example of the layer configuration of the light-diffusing portion that may be included in the diffusion member of Figure 2 or Figure 30. [Figure 47]Figure 47 illustrates an example of the layer configuration of the light-diffusing portion that may be included in the diffusion member of Figure 2 or Figure 30. [Figure 48] Figure 48 illustrates an example of the layer configuration of the light-diffusing portion that may be included in the diffusion member of Figure 2 or Figure 30. [Figure 49] Figure 49 illustrates an example of the layer configuration of the light-diffusing portion that may be included in the diffusion member of Figure 2 or Figure 30. [Figure 50] Figure 50 illustrates an example of the layer configuration of the optical element portion that may be included in the diffusion member of Figure 30. [Figure 51] Figure 51 illustrates an example of the layer configuration of the light-diffusing portion that may be included in the diffusion member of Figure 2 or Figure 30. [Figure 52] Figure 52 is a plan view illustrating an example in which the diffusion member of Figure 2 or Figure 30 includes multiple elemental diffusion sections or multiple elemental optical sections. [Figure 53] Figure 53 is a perspective view showing the element diffusion section and element optics section of Figure 52. [Figure 54] Figure 54 is a plan view illustrating an example in which the diffusion member of Figure 2 or Figure 30 includes multiple elemental diffusion sections or multiple elemental optical sections. [Figure 55] Figure 55 is a longitudinal cross-sectional view of a microlens corresponding to Figures 9 to 12, and illustrates one modified example of a microlens. [Figure 56] Figure 56 shows the in-plane distribution of radiant intensity on the light-emitting surface of the surface light source device according to Example 1. [Figure 57] Figure 57 shows the in-plane distribution of radiant intensity on the light-emitting surface of the surface light source device according to Example 2. [Figure 58] Figure 58 shows the in-plane distribution of radiant intensity on the light-emitting surface of the surface light source device according to Example 3. [Figure 59] Figure 59 shows the in-plane distribution of radiant intensity on the light-emitting surface of the surface light source device according to Example 4. [Figure 60] Figure 60 shows the in-plane distribution of radiant intensity on the light-emitting surface of the surface light source device according to Example 5. [Figure 61]Figure 61 shows the in-plane distribution of radiant intensity on the light-emitting surface of the surface light source device according to Example 6. [Figure 62] Figure 62 shows the in-plane distribution of radiant intensity on the light-emitting surface of the surface light source device according to Comparative Example 1. [Modes for carrying out the invention]

[0075] Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. Note that, for the sake of illustration and ease of understanding, the scale and aspect ratios of the drawings attached to this specification have been appropriately altered and exaggerated from those of the actual objects. Furthermore, some components shown in some drawings are omitted in others.

[0076] In this specification, the terms “sheet,” “film,” and “board” are not distinguished from each other solely on the basis of name differences. For example, “sheet” is a concept that includes components that may be called “film” or “board,” and is not distinguished solely on the basis of name differences.

[0077] Furthermore, in this specification, the normal direction of a sheet-like (sheet-like, plate-like) member refers to the direction normal to the sheet surface of the sheet-like (film-like, plate-like) member in question. Also, the "sheet surface (film surface, plate surface)" refers to the surface that coincides with the planar direction of the sheet-like (film-like, plate-like) member in question when the sheet-like (film-like, plate-like) member in question is observed as a whole and from a broad perspective.

[0078] Furthermore, terms used herein to specify shapes, geometric conditions, and their degrees, such as "parallel," "perpendicular," and "identical," as well as values ​​of length and angle, should not be interpreted strictly, but rather to include a range that allows for the expectation of similar functionality.

[0079] To clarify the directional relationships between drawings, some drawings use arrows to indicate the first direction D1, the second direction D2, and the stacking direction D3 as common directions across the drawings. The tip of the arrow corresponds to one side of each direction D1, D2, and D3. For example, as shown in Figure 2, an arrow pointing towards the back of the drawing along a direction perpendicular to the drawing's surface is indicated by a symbol with an X inside a circle. For example, as shown in Figure 3, an arrow pointing towards the front of the drawing along a direction perpendicular to the drawing's surface is indicated by a symbol with a dot inside a circle.

[0080] Figures 1 to 62 are diagrams illustrating one embodiment. Of these, Figure 1 is a schematic perspective view showing a display device 10 as an application example of a surface light source device 20 and a diffusion member 40. The display device 10 displays images composed of, for example, moving images, still images, text information, or a combination thereof. The display device 10 can be used, for example, as an in-vehicle liquid crystal display device. The display device 10 can also be used for various purposes indoors or outdoors, such as displaying advertisements, presentations, television images, and various types of information. The display device 10 shown in Figure 1 comprises a surface light source device 20 having a light-emitting surface 20a and a display panel 15 arranged opposite the light-emitting surface 20a.

[0081] Figure 2 is a longitudinal cross-sectional view showing a surface light source device 20 as a first specific example. As shown in Figure 2, the surface light source device 20 has, as its main components, a light source 22 and a diffusion member 40 that adjusts the optical path of the light emitted from the light source 22. The diffusion member 40 is positioned directly facing the light source 22. That is, the diffusion member 40 is a sheet-like member and faces the light source 22 in the direction normal to it. By diffusing the light emitted from the light source 22, the diffusion member 40 can effectively eliminate brightness unevenness caused by the presence of the light source 22. As a result, the illuminance at each position on the light-emitting side surface 40b of the diffusion member 40, or the illuminance at each position on a virtual light-receiving surface parallel to the light-emitting side surface 40b located near the light-emitting side surface 40b, can be made uniform. In particular, the diffusion member 40 described in this embodiment is designed to sufficiently uniformize the in-plane distribution of brightness while making the surface light source device 20 thinner.

[0082] In the following explanation, "illuminance on the light-emitting side 40b" refers to "illuminance on the light-emitting side 40b" or "illuminance on the light-receiving surface" as described above.

[0083] The following will describe the display device 10, the surface light source device 20, and the diffusion member 40 in one embodiment, with reference to the first specific example shown in the figure.

[0084] First, the display panel 15 of the display device 10 will be described. As shown in Figure 1, the display panel 15 is stacked with the surface light source device 20 in the stacking direction D3. The display panel 15 is positioned 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, which faces away from the surface light source device 20 in the stacking direction D3. In the illustrated example, the display panel 15 is formed in a rectangular shape when viewed from the stacking direction D3, that is, in a plan view from the front.

[0085] The display panel 15 is configured, for example, as a transmissive liquid crystal display panel. A portion of the light incident from the surface light source device 20 passes through the display panel 15 as a liquid crystal display panel, thereby displaying an image on the display surface 15a. The display panel 15 includes a liquid crystal layer having liquid crystal material. The light transmittance of the display panel 15 changes according to the intensity of the electric field applied to the liquid crystal layer.

[0086] As an example of the display panel 15, a liquid crystal display panel can be used that has a pair of polarizing plates and a liquid crystal cell (liquid crystal layer) disposed between the pair of polarizing plates. The polarizing plates have polarizers. The polarizers decompose incident light into two perpendicular polarization components. One polarization component is transmitted through the polarizer. The other polarization component, perpendicular to the first, is absorbed by the polarizer. The liquid crystal cell has a pair of support plates and liquid crystal disposed between the pair of support plates. The liquid crystal cell is configured so that an electric field can be applied to each region forming a single pixel. As an example, the orientation of the liquid crystal in a liquid crystal cell to which an electric field is applied changes. A polarization component in a specific direction that is emitted from the surface light source device 20 and has passed through the polarizing plate disposed on the surface light source device 20 side of the liquid crystal cell will, as an example, rotate its polarization direction by 90° when passing through a liquid crystal cell to which an electric field is not applied. The polarization component in a specific direction maintains its polarization direction when passing through a liquid crystal cell to which an electric field is applied. Whether a polarization component in a specific direction that has passed through one polarizing plate is further transmitted through the other polarizing plate, or absorbed and blocked by the other polarizing plate, can be controlled by whether or not an electric field is applied to the liquid crystal cell.

[0087] 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. The surface light source device 20 is configured as a direct-type backlight. In projection onto the stacking direction D3, the light source 22 is provided in the region that overlaps with the light-emitting surface 20a. 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 diffusion member 40, the normal directions of the light diffusion part 50, light reflection part 70, and optical element part 110 included in the diffusion member 40 (described later), and the normal direction of the support substrate 25 that supports the light source 22 (described later) are parallel to each other. In the illustrated example, these normal directions coincide with the stacking direction D3 and are also called the front direction.

[0088] The light source 22 has a light-emitting element that emits light. An example of a light-emitting element is a light-emitting diode. A light-emitting diode is also referred to as an LED. The dimensions of the light-emitting diode used as the light source 22 are not particularly limited. From the viewpoint of making the image of the light source 22 inconspicuous, a small light-emitting diode, such as a mini-LED or micro-LED, may be used. Specifically, the lengths of one side WL1, WL2 of the light source 22, which has a rectangular shape when observed from the stacking direction D3 shown in Figure 3, may preferably be 0.5 mm or less, and more preferably 0.2 mm or less.

[0089] The emission wavelength of the light source 22 can 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, thereby generating white light. Alternatively, the surface light source device 20 may 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, thereby generating white light. Furthermore, if multiple light-emitting elements are provided, a single light source 22 may include multiple types of light-emitting elements arranged in close proximity, or it may include only a single light-emitting element. In other words, multiple types of light sources 22 having different emission wavelengths may be used.

[0090] As a specific example illustrated, the light source 22 may include a light-emitting diode that emits blue light with a wavelength of 450 nm as the light-emitting element. In this example, a light-emitting diode with high output can be used as the light source 22. On the other hand, it is also possible to emit white light by using an element that can change the wavelength, such as a phosphor.

[0091] As an example, the light source 22 may consist only of light-emitting elements. As another example, the light source 22 may include optical elements such as covers and lenses that adjust the light distribution from the light-emitting elements, in addition to the light-emitting elements, or it may include phosphors that absorb light from the light-emitting elements and emit light of different wavelengths.

[0092] The light distribution characteristics of the light source 22 are not particularly limited. The light distribution characteristics of the light source 22 may be Lambertsian. With Lambertsian distribution, in the emission intensity distribution from the light source 22 directed in the stacking direction D3, the highest peak intensity is obtained in the stacking direction D3, which is the optical axis, and half the peak intensity is obtained in the direction tilted 60° from the optical axis. As another example, the peak intensity may be obtained in directions other than the stacking direction D3. For example, the batwing light distribution disclosed in Patent Document 1 (JP6299811B) may be used as the light distribution characteristics of the light source 22.

[0093] The surface light source device 20 may have multiple light sources 22 or only a single light source 22. The number of light sources 22 is appropriately selected according to the application of the surface light source device 20 and the area of ​​the light-emitting surface 20a. From the viewpoint of eliminating brightness unevenness caused by the arrangement of the light sources 22, it is preferable that the multiple light sources 22 included in the surface light source device 20 are regularly arranged on a surface perpendicular to the stacking direction D3. For example, the multiple light sources 22 may be arranged in a honeycomb arrangement in which they are arranged at a constant pitch in each of three directions that are inclined at 60° to each other, or in a square arrangement in which they are arranged at a constant pitch in each of two directions that are perpendicular to each other.

[0094] In the example shown in Figure 3, the multiple light sources 22 are arranged at a constant pitch in each of the first direction D1 and the second direction D2, which are perpendicular to each other. In the illustrated example, the arrangement pitch PL1 in the first direction D1 and the light distribution pitch PL2 of the light sources 22 in the second direction D2 are the same. However, the arrangement pitch PL1 and arrangement pitch PL2 may be different, as shown in the example. In the illustrated example, 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 diffusion member 40, respectively. The arrangement pitch PL1 and arrangement pitch PL2 of the light sources 22 may be 0.2 mm or more and 10 mm or less, respectively.

[0095] Furthermore, the light source 22 may emit only P-polarized light when incident on the diffusion member 40. P-polarized light is light that vibrates on a plane that includes the direction of propagation of the light when incident on the diffusion member 40 and the direction normal to the light-receiving side surface 40a of the diffusion member 40. By having the light source 22 emit only P-polarized light, when the dielectric multilayer film described later is used as the light-reflecting part 70, the transmittance of light incident at a large incident angle can be made sufficiently high, thereby imparting the desired optical properties to the diffusion member 40. This makes it possible to effectively uniformize the in-plane distribution of illuminance on the light-emitting side surface 40b of the diffusion member 40.

[0096] Incidentally, the illustrated surface light source device 20 further includes a support substrate 25 that supports the light sources 22, in addition to the light sources 22 and the diffusion member 40. The support substrate 25 supports multiple light sources 22 from the opposite side of the diffusion member 40 in the stacking direction D3. The support substrate 25 includes a circuit that supplies power to the light sources 22. The support substrate 25 is a sheet-like material. The support substrate 25 has light reflectivity that reflects light and directs it toward the diffusion member 40. The light reflectivity of the support substrate 25 is not particularly limited as long as it is exhibited toward the light emitted from the light sources 22 or the light used for emission in the surface light source device 20. The light used for emission in the surface light source device 20 may include light emitted from the light sources 22 and wavelength converted, etc.

[0097] As a specific configuration, as shown in Figure 2, the device has a sheet-like substrate body 26, a reflective layer 27 laminated on the substrate body 26 from the side of the diffusion member 40 in the lamination direction D3, and wiring 28 electrically connected to the light source 22. The substrate body 26 extends in a direction perpendicular to the lamination direction D3, and the substrate body 26 is insulating. The reflective layer 27 is reflective to light emitted from the light source 22 or to light used for emission in the surface light source device 20. The reflectivity of the reflective layer 27 may be specular reflection, also called specular reflection, diffuse reflection, or anisotropic diffuse reflection. The substrate body 26 may be a resin film containing diffusion particles, for example, a white polyethylene terephthalate film. The reflective layer 27 may be a metal layer laminated on the substrate body 26, or a reflective diffractive optical element. The wiring 28 is electrically connected to terminals of the light source 22 (not shown) via solder or the like. If the substrate body 26 and the reflective layer 27 are insulating, it is preferable that the wiring 28 be located between the substrate body 26 and the reflective layer 27.

[0098] As shown by the dashed line in Figure 2, the light sources 22 may be covered with a sealing material 23. The sealing material 23 is provided corresponding to each light source 22. In the examples shown in Figures 2 and 3, the sealing material 23 is arranged in a two-dimensional manner, similar to the light sources 22. In the illustrated examples, the light sources 22 are covered with the sealing material 23 on the surface facing the diffusion member 40 and on the sides. The sealing material 23 is fixed to the support substrate 25. The portion where the light sources 22 and the wiring 28 are electrically connected may also be covered with the sealing material 23. As the material for the sealing material 23, for example, thermosetting resins such as silicone resins and epoxy resins, or thermoplastic resins such as olefin resins can be used.

[0099] In the example shown in Figure 2, the diffusion member 40 is placed on the sealing material 23. That is, the diffusion member 40 is supported by the sealing material 23 and is spaced apart from the light source 22 and the support substrate 25 in the stacking direction D3. The sealing material 23 may be joined to the diffusion member 40 by adhesion, bonding, welding, etc. The distance DX shown in Figure 2 is the distance between the light source 22 and the diffusion member 40 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 22 facing the diffusion member 40 and the light-receiving side surface 40a of the diffusion member 40.

[0100] Next, the diffusion member 40 will be described. The diffusion member 40 has a light diffusion portion 50 and a light reflection portion 70 in that order. The light diffusion portion 50 is located on the incoming side of the light to be diffused by the diffusion member 40, with respect to the light reflection portion 70. The light reflection portion 70 is located on the outgoing side of the light to be diffused by the diffusion member 40, with respect to the light diffusion portion 50. In the example shown in Figure 2, the diffusion member 40 is in the form of a sheet. The diffusion member 40 extends in a first direction D1 and a second direction D2 perpendicular to the stacking direction D3. The light diffusion portion 50 forms the incoming side 40a of the diffusion member 40. The light reflection portion 70 forms the outgoing side 40b of the diffusion member 40. Note that the light diffusion portion 50 and the light reflection portion 70 may be joined to each other, or they may simply be in contact and not joined, or they may be spaced apart from each other.

[0101] First, the light-diffusing section 50 will be described. The light-diffusing section 50 has light-transmitting and light-diffusing properties with respect to light emitted from the light source 22 or light used for emission in the surface light source device 20. The light-diffusing section 50 has light-transmitting and light-diffusing properties with respect to visible light. The light-diffusing section 50 may include an optical sheet 55 that is simply superimposed on other members or joined to other members by adhesive or bonding, or it may be the optical sheet 55, or a part of the optical sheet 55, members and structures, or it may even be a surface of the optical sheet, members and structures, etc.

[0102] The light transmittance of the light diffusing section 50 is preferably 50% or more, more preferably 70% or more, and even more preferably 90% or more. By setting the total light transmittance of the light diffusing section 50 within the above range, the utilization efficiency of light from the light source 22 is improved. In addition, when the light diffusing section 50 is applied to the surface light source device 20, the in-plane distribution of illuminance on the light-emitting side surface 40b of the diffusion member 40 can be effectively made uniform. Therefore, the light diffusing section 50 is made of a material that has high transmittance to light emitted from the light source 22 or to light used for emission in the surface light source device 20. The total light transmittance is the value measured by the method in accordance with JIS K7361-1:1997 with an incident angle of 0 degrees. The total light transmittance is the value measured using a UV-Vis-Near-Infrared Spectrophotometer V-7200 manufactured by JASCO Corporation.

[0103] The light diffusion properties of the light diffusion section 50 may be isotropic or anisotropic. The light diffusion section 50 may diffuse light in a direction within a specific angular range. This specific angular range may be one or multiple, spaced apart from each other. Furthermore, the diffusion by the light diffusion section 50 is not limited to diffusing transmitted light, but may also be diffusing reflected light.

[0104] Regarding the light diffusing properties of the light diffusing section 50, the diffusion angle α of the light incident on the light diffusing section 50 is preferably 10° or more, more preferably 15° or more, and even more preferably 20° or more. Furthermore, the diffusion angle of the light incident on the light diffusing section 50 is preferably 85° or less, more preferably 60° or less, and even more preferably 50° or less. By setting the diffusion angle of the light diffusing section 50 within this range, when the diffusion member 40 is applied to the surface light source device 20, the in-plane distribution of illuminance on the light-emitting side surface 40b of the diffusion member 40 can be effectively made uniform.

[0105] The diffusion angle α is the full width at half maximum (FWHM) in the angular distribution of radiant intensity (watts / steradians) obtained when light is incident on the incoming side of the light diffusion section 50 at an incident angle of 0°. Figure 4 is a graph showing the angular distribution of radiant intensity on the outgoing side of the light diffusion section 50 when a parallel beam of light is incident on the incoming side of the light diffusion section 50 at an incident angle of 0°. In the graph of Figure 4, the vertical axis is the value of radiant intensity, and the horizontal axis is the exit angle. The full width at half maximum in the angular distribution of radiant intensity corresponding to each diffusion angle α is the maximum transmitted light intensity I in the angular distribution of radiant intensity. max This refers to the range (°) of emission angles over which half the radiation intensity can be obtained.

[0106] The angular distribution of radiant intensity can be measured using a bending-angle photometer or a bending-angle spectrophotometer. For measuring the diffusion angle α, for example, a bending-angle photometer (goniophotometer) such as the GP-200 manufactured by Murakami Color Technology Laboratory Co., Ltd. can be used.

[0107] The angle of incidence refers to the angle (°) that the direction of propagation of incident light makes with respect to the normal direction of a sheet-like or other material from which light is incident. The angle of exit refers to the angle (°) that the direction of propagation of exiting light makes with respect to the normal direction of a sheet-like or other material from which light is exiting.

[0108] Furthermore, Figure 5 is a perspective view illustrating a different light diffusion property from Figure 4, and another preferred light diffusion property of the light diffusion section 50. In Figure 5, a light ray L51 is incident on the light diffusion section 50 at an incident angle of 0°. That is, the light ray L51 is incident perpendicularly on the light diffusion section 50. The light ray L51 is diffused by optical effects such as refraction, reflection, and diffraction in the light diffusion section 50. According to the light diffusion section 50 shown in Figure 5, the light ray L51 mainly travels along an optical path from the apex of a cone whose apex is located on the light diffusion section 50 and whose base is arranged parallel to the light diffusion section 50, toward each position on the circumference of the base. In this example, when a light ray is incident on the light diffusion section 50 at an incident angle of 0°, the radiation intensity on the side of the light diffusion section 50 facing the light reflection section 70 has a peak at emission angles other than 0°. More preferably, when a light ray is incident on the light diffusion section 50 at an incident angle of 0°, the radiant intensity on the side of the light diffusion section 50 facing the light reflection section 70 has a peak at an exit angle other than 0° in the angular distribution within any plane including the exit direction where the exit angle is 0°. The absolute value of the exit angle having the peak of radiant intensity may be 30° or more and 60° or less, more preferably 30° or more and 50° or less, and even more preferably 30° or more and 45° or less. Also, the absolute value of the exit angle of 90% or more of the light incident on the light diffusion section 50 at an incident angle of 0° may be 30° or more and 60° or less. The absolute value of the exit angle of 95% or more of the light incident on the light diffusion section 50 at an incident angle of 0° may be 30° or more and 60° or less. The absolute value of the exit angle of 98% or more of the light incident on the light diffusion section 50 at an incident angle of 0° may be 30° or more and 60° or less.

[0109] By imparting the light-diffusing properties described with reference to Figure 5 to the light-diffusing section 50, the diffusion member 40 can suppress excessive illuminance in the region directly above the light source 22 and increase the illuminance in the region spaced away from the light source 22 in a direction perpendicular to the stacking direction D3. This effectively homogenizes the in-plane distribution of illuminance. In particular, from the viewpoint of homogenizing the in-plane distribution of illuminance, the reflectance of light incident on the light-reflecting section 70 described later at an incident angle of 0° or more and less than or equal to the peak angle in absolute value is preferably 80% or more. More preferably 85% or more, and even more preferably 90% or more. Here, the peak angle means the absolute value of the emission angle having the peak of the radiant intensity.

[0110] The solid line in Figure 6 is a graph showing the angular distribution of radiant intensity on the light-emitting side of the light-diffusing section 50 shown in Figure 5, when the incident angle of the incident light is 0°.

[0111] The light diffusion section 50 is not particularly limited and can employ various configurations having both light transmission and light diffusion properties. The light diffusion section 50 may include at least one of a transmissive diffractive optical element 60 and a microlens 65.

[0112] The diffractive optical element 60 is an element that exerts a diffracting effect on incident light. The diffractive optical element 60 may also be a holographic element. A diffractive optical element having diffraction characteristics to achieve the desired light diffusion can be designed relatively easily. For example, the diffractive optical element 60 may have the diffusion characteristics shown in Figure 6.

[0113] Figure 7 shows a diffractive optical element 60 configured as a phase-modulated hologram. A phase-modulated hologram has an uneven surface 52 on which phase information is recorded. The uneven surface 52 shown in Figure 7 records multi-level phase information as the height of the bottom surface. A phase-modulated hologram utilizes the diffraction phenomenon based on the difference in optical path length of the medium. This diffractive optical element 60 has a plurality of unit pixels 61 arranged along a first direction D1 and a second direction D2 perpendicular to the stacking direction D3. A unit pixel 61 is the smallest unit that adjusts the amount of modulation applied to the incident light. According to the illustrated phase-modulated diffractive optical element 60, the phase of the incident light can be modulated by a different amount for each unit pixel 61. Phase modulation can be applied to light traveling in both directions along the stacking direction D3. Therefore, the diffractive optical element 60 can diffract light incident from the light source 22 side and bend its direction of propagation, and can also diffract light incident from the light reflection section 70 side and bend its direction of propagation.

[0114] In the diffractive optical element 60 shown in Figure 7, the unit pixel 61 is set to one of eight height levels along the third direction d3. In the illustrated diffractive optical element 60, the amount of phase modulation applied to the incident light can be controlled in eight steps. However, the number of steps for the unit pixel 61 is not particularly limited. From the viewpoint of ensuring diffraction characteristics to achieve desired light diffusion, the length of one side of the unit pixel 61 is preferably 10 nm or more and 10 μm or less, more preferably 50 nm or more and 5 μm or less, and even more preferably 100 nm or more and 2 μm or less.

[0115] The diffractive optical element 60 can, for example, be fabricated as a computer-generated hologram (CGH). A computer-generated hologram is fabricated by calculating a diffraction structure on a computer that achieves arbitrary diffraction characteristics. By using a computer-generated hologram as a diffractive optical element, the generation of object light and reference light using a light source and optical system, and the recording of interference fringes on the hologram recording material by exposure become unnecessary. For example, a surface 52 with diffraction characteristics that achieve the desired light diffusion can be identified by computer calculations. By forming the identified structure, for example, by resin molding, a diffractive optical element as a computer-generated hologram can be fabricated at low cost using a simple procedure.

[0116] As shown in Figure 8, a single diffractive optical element 60 may include multiple elemental diffractive optical elements 62. In the example shown in Figure 8, the multiple elemental diffractive optical elements 62 are joined together. The multiple elemental diffractive optical elements 62 may have the same diffraction characteristics or may have different diffraction characteristics.

[0117] Furthermore, the diffractive optical element forming the light diffusion section 50 is not limited to a phase-modulated hologram, but may also be an amplitude-modulated hologram. Also, the diffractive optical element forming the light diffusion section 50 is not limited to a computer-generated hologram, but may also be a volume hologram, for example. In addition, although the example shown in Figure 7 shows the uneven surface 52 of the diffractive optical element 60 facing away from the light-reflecting section 70 in the stacking direction D3, the example is not limited to this, and the uneven surface 52 may face the light-reflecting section 70 side in the stacking direction D3. Even if the uneven surface 52 is in contact with the light-reflecting section 70, the unevenness of the uneven surface 52 allows it to form an interface between the light diffusion section 50 and the air gap V, significantly bending the incident light.

[0118] The microlens 65 has multiple unit optical elements 66. As shown in Figures 9 to 12, the unit optical elements 66 are elements that change the direction of light propagation by refraction, reflection, etc. The unit optical elements 66 are a concept that includes elements called unit shape elements, unit prisms, and unit lenses. The unit optical elements 66 are configured as convex portions 68 or concave portions 69. In the example shown in Figures 9 to 12, the light diffusion portion 50 has a main body portion 58, and the unit optical elements 66 as convex portions 68 are formed on the main body portion 58. However, as will be described later, the light diffusion portion 50 may have a main body portion 58 and unit optical elements 66 as concave portions 69 provided on the main body portion 58. The main body portion 58 is sheet-like. The main body portion 58 extends in a first direction D1 and a second direction D2 perpendicular to the stacking direction D3. In the example shown in Figure 2, the main body portion 58 is joined to the light reflection portion 70.

[0119] As shown in Figures 9 to 12, the unit optical element 66 has an element surface 67 that is inclined with respect to the stacking direction D3. The unit optical element 66 is defined by the element surface 67. The microlens 65 has an uneven surface 52 formed by the element surface 67 of the unit optical element 66. The microlens 65 can bend the direction of propagation of incident light by this uneven surface 52.

[0120] The uneven surface 52 may face either direction in the stacking direction D3. In Figures 9 and 10, the uneven surface 52 faces the light source 22 side in the stacking direction D3. In Figures 11 and 12, the uneven surface 52 faces the light reflecting portion 70 side in the stacking direction D3. The uneven surface 52 can bend the direction of propagation of light L91, L101, L111, L121 incident from the light source 22 side, and can also bend the direction of propagation of light L92, L102, L112, L122 incident from the light reflecting portion 70 side. In particular, as shown in Figures 9 to 12, the microlens 65 can bend the direction of propagation of light incident from a direction with a small inclination angle with respect to the stacking direction D3, and can increase the inclination angle with respect to the stacking direction D3 compared to the incident light. In other words, the inclination angle of the direction of propagation of light emitted from the light diffusion section 50 with respect to the stacking direction D3 can be made larger than the inclination angle of the direction of propagation of light incident on the light diffusion section 50 with respect to the stacking direction D3.

[0121] In the examples shown in Figures 9 and 11, the direction of propagation of light L91, L92, L111, and L112 changes due to refraction at the element surface 67. In the examples shown in Figures 10 and 12, the direction of propagation of light L102 and L121 changes due to reflection at the element surface 67, preferably by total internal reflection. The change in direction of propagation due to reflection shown in Figures 10 and 12 tends to be larger than the change in direction of propagation due to refraction shown in Figures 9 and 11. The greater the inclination of the normal direction ND of the element surface 67 with respect to the stacking direction D3, in other words, the more the element surface 67 rises relative to the stacking direction D3, the easier it is for light to be reflected at the element surface 67. More specifically, when the inclination angle θa of the normal direction ND of the element surface 67 is greater than 45° with respect to the stacking direction D3, light that is not significantly inclined with respect to the stacking direction D3 tends to be reflected at the element surface 67, causing the direction of propagation of the light to be significantly inclined with respect to the stacking direction D3.

[0122] From this perspective, as shown in Figures 10 and 12, the unit optical element 66 may include an element surface 67 having a normal direction ND that is inclined at an inclination angle θa greater than 45° with respect to the stacking direction D3. Since this element surface 67 rises in the stacking direction D3, it is more likely to cause reflection, preferably total internal reflection. That is, with a unit optical element 66 including this element surface 67, the optical path of light passing through the microlens 65 can be greatly bent by reflection, preferably total internal reflection. By greatly adjusting the direction of light propagation, the in-plane distribution of illuminance can be more effectively made uniform.

[0123] The diffusion characteristics of the microlens 65 are affected by the inclination angle θa of the element surface 67 of the unit optical element 66. Therefore, the cross-sectional shape of the microlens 65 can be appropriately adjusted based on the optical characteristics required for the surface light source device 20 and the diffusion member 40. For example, the inclination angles θa of the multiple element surfaces 67 included in a single unit optical element 66 may be different from each other or the same. The multiple unit optical elements 66 included in the microlens 65 may differ from each other in terms of shape, orientation, size, and other configurations. The multiple unit optical elements 66 included in the microlens 65 may have the same configuration as each other.

[0124] Furthermore, from the viewpoint of uniformizing illuminance through combination with the reflection characteristics of the light-reflecting portion 70, it may be preferable to increase the inclination angle θa, or it may be preferable to decrease the inclination angle θa, depending on the arrangement of the unit optical elements 66 and the optical characteristics of other parts. For example, when used in combination with the optical element portion 110, as in the second specific example described later, the inclination angle θa is preferably 25° or less, more preferably 20° or less, and even more preferably 15° or less.

[0125] Furthermore, as shown by the dashed lines in Figures 9 to 12, the element surface 67 may be somewhat curved. The unit optical element 66 may have an external shape that is part of a sphere, such as a hemisphere, or an external shape that is part of a spheroid. When the unit optical element 66 includes a curved element surface 67, the optical path of light passing through the microlens 65 is bent in various directions due to reflection and refraction. This makes it possible to more effectively homogenize the in-plane distribution of illuminance. It also makes it possible to effectively smooth changes in the angular distribution of radiant intensity.

[0126] For essentially the same reasons as for the curved element surface 67, the unit optical element 66 may include an element surface 67 formed as a matte surface. The element surface 67 as a matte surface scatters light in various directions. This allows for a more effective homogenization of the in-plane distribution of illuminance. It also allows for a more effective smoothing of changes in the angular distribution of radiant intensity.

[0127] The multiple unit optical elements 66 contained in the microlens 65 are arranged in a two-dimensional array. Therefore, the element faces 67 of the unit optical elements 66 contained in the microlens 65 face in various directions. As a result, the microlens 65 can guide light in various directions by the two-dimensionally arranged unit optical elements 66. The multiple unit optical elements 66 may be arranged irregularly or regularly. By arranging the multiple unit optical elements 66 regularly, the design of the microlens 65 becomes easier, and it becomes easier to tile the unit optical elements 66 without gaps.

[0128] Here, several specific examples of the microlens 65 will be described with reference to Figures 13A to 16B. In particular, the microlenses 65 shown in these figures were the subject of the simulation described later.

[0129] First, in the examples shown in Figures 13A and 13B, the arrangement of the multiple unit optical elements 66 is a square arrangement. The multiple unit optical elements 66 are arranged at a constant pitch in the first direction D1. The multiple unit optical elements 66 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 illustrated example, the arrangement pitch in the first direction D1 and the arrangement pitch in the second direction D2 are the same, at 0.1 mm. As shown in Figure 13B, each unit optical element 66 has a shape in which the base of a cone is cut off from all four sides. The cones are arranged at an arrangement pitch shorter than the diameter of the cone base shown by the dotted line in Figure 13A, and the portion where adjacent cones overlap in the first direction D1 and the second direction D2 is cut off to produce a microlens 65. As a result, as shown in the examples in Figures 13A and 13B, multiple unit optical elements 66 are arranged without gaps. The height of each unit optical element 66 in the stacking direction D3 is, for example, 0.09 mm. The illustrated unit optical element 66 has an element surface 67 corresponding to the side surface of a cone. Each unit optical element 66 can diffuse light radially when observed from the stacking direction D3.

[0130] Next, in the example shown in Figures 14A and 14B, the arrangement of the multiple unit optical elements 66 is a square arrangement. The multiple unit optical elements 66 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 66 in the two directions is the same, at 0.1 mm. As shown in Figures 14A and 14B, the unit optical elements 66 have a square pyramidal shape with a square base. The height of each unit optical element 66 in the stacking direction D3 is, for example, 0.07 mm.

[0131] In the example shown in Figures 15A and 15B, the microlens 65 has two types of unit optical elements 66. Each type of unit optical element 66 is arranged at a constant pitch in the second direction D2 and in two directions tilted ±60° with respect to the second direction. That is, the two types of unit optical elements 66 are each arranged at a constant pitch in each of the three directions tilted 60° relative to each other. The illustrated arrangement of unit optical elements 66 is also called a honeycomb arrangement. The arrangement pitch in each direction may be the same or different. In the illustrated example, the arrangement pitch of the unit optical elements 66 in the three directions is the same. The shape of the base of the two types of unit optical elements 66 is the same. The shape of the base is an equilateral triangle. The orientation of the base of the two types of unit optical elements 66 is different. When one unit optical element 66 is rotated by 60°, the orientation of the base of one unit optical element 66 coincides with the orientation of the base of the other unit optical element 66. In the examples shown in Figures 15A and 15B, the unit optical element 66 has the shape of a triangular pyramid with an equilateral triangle as its base. In the illustrated examples, the height of the base of the unit optical element 66 is, for example, 0.1 mm. Also, the height of the unit optical element 66 is, for example, 0.08 mm. Each unit optical element 66 may also have the shape of a regular triangular pyramid.

[0132] Next, in the example shown in Figures 16A and 16B, unit optical elements 66 with identical base shapes are arranged in four directions. As a result, multiple unit optical elements 66 with identical base shapes and orientations are arranged at a constant pitch in each of the first direction D1 and the second direction D2. The arrangement pitch in the two directions may be the same or different. In the illustrated example, the arrangement pitch in each of the two directions is the same. The unit optical element 66 has a triangular pyramidal shape with a right-angled isosceles triangle base. In the illustrated example, the length of the equal sides of the right-angled isosceles triangle forming the base is, for example, 0.1 mm. The height of the unit optical element 66 is, for example, 0.01 mm.

[0133] In the four specific examples shown in Figures 13A to 16B, the perpendicular from the vertex of the cone forming the unit optical element 66 to the base may pass through the centroid of the base. In the four specific examples shown in Figures 13A to 16B, the unit optical element 66 protrudes toward the light source 22 in the stacking direction D3. That is, the unit optical element 66 is a convex portion 68 that protrudes from the main body portion 58. However, as already mentioned above, the unit optical element 66 may also be a recess 69 formed in the main body portion 58.

[0134] Incidentally, if the dimensions of the unit optical element 66 are large when observed from the stacking direction D3, unevenness in brightness caused by the shape of the unit optical element 66 becomes visible. From the viewpoint of preventing this problem, the maximum length of the unit optical element 66 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.

[0135] Furthermore, if the dimensions of the unit optical element 66 become larger when observed from the stacking direction D3, it becomes necessary to position the unit optical element 66 relative to the light source 22. Specifically, it becomes necessary to position the relative positions of the light source 22 and the unit optical element 66 in directions perpendicular to the stacking direction D3, for example, the first direction D1 and the second direction D2. Such positioning work is complicated and becomes a burden in manufacturing. From the viewpoint of eliminating the need for this positioning, it is preferable that, when observed from the stacking direction D3, one unit optical element 66 has dimensions smaller than three times the dimensions of the light source 22 in each of two mutually perpendicular directions. As described above, the side lengths WL1 and WL2 of the light source 22, which has a rectangular shape when observed from the stacking direction D3 as shown in Figure 3, are preferably 0.5 mm or less, and more preferably 0.2 mm or less. From this point of view, when observed from the stacking direction D3, the unit optical element 66 preferably has dimensions smaller than a 1.5 mm square, and more preferably smaller than a 0.6 mm square. Here, one dimension being smaller than the other means that the outer contour of one is located on or inside the outer contour of the other in at least one orientation. More preferably, when observed from the stacking direction D3, the dimension of the unit optical element 66 along any direction may be three times or less the dimension of the light source 22 along that direction. The light emitted from the diffuser member 40 using these unit optical elements 66 will have a constant light distribution characteristic, regardless of the relative position of the diffuser member 40 and the light source 22 along directions D1 and D2 perpendicular to the stacking direction D3. In other words, the surface light source device 20 can be assembled without positioning the diffuser member 40 and the light source 22 along directions D1 and D2 perpendicular to the stacking direction D3. That is, the diffuser member 40 can be placed on the light source 22 without alignment.

[0136] The arrangement pitch of the unit optical elements 66 having such dimensions may be 0.01 mm or more and 1.5 mm or less. From the viewpoint of effectively homogenizing the in-plane distribution of illuminance on the light-emitting side surface 40b of the diffusion member 40 when applied to the surface light source device 20, the arrangement pitch of the unit optical elements 66 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.

[0137] Furthermore, as can be understood from Figures 9 to 12 and demonstrated in particular by the results of Sample 3 of the simulation described later, the microlens 65 diffuses light in the normal direction ND to the element surface 67 when observed from the stacking direction D3. In other words, the microlens 65 guides light in the normal direction ND to the element surface 67 observed from the stacking direction D3. On the other hand, as can be understood from Figure 2, the spacing between the multiple light sources 22 becomes shorter along the direction of arrangement of the light sources 22, but longer in the direction nonparallel to the direction of arrangement of the light sources 22. Therefore, from the viewpoint of homogenizing the in-plane distribution of illuminance, preferably, the unit optical element 66 includes an element surface 67 having a normal direction ND that is nonparallel to the direction of arrangement of the multiple light sources 22 when observed from the stacking direction D3. More preferably, the unit optical element 66 includes an element surface 67 having a normal direction ND that is inclined at an angle of 35° to 55° with respect to the direction of arrangement of the multiple light sources 22 when observed from the stacking direction D3. With this arrangement, light can be effectively diffused in a direction non-parallel to the arrangement direction of the multiple light sources 22 through reflection and refraction at the unit optical element 66. This allows for a more effective uniformization of the in-plane distribution of illuminance.

[0138] For example, in the example shown in Figures 14A and 14B, the unit optical element 66 has four element faces 67. When observed from the stacking direction D3, the normal direction ND of the four element faces 67 is inclined at 45° with respect to the first direction D1 and the second direction D2, which are the arrangement directions of the light sources 22. As shown in Figure 3, when the light sources 22 are arranged in a square, the position CP (see Figure 3), which is the center of four adjacent light sources 22, tends to be the darkest. The four light sources 22 include two light sources 22A adjacent to each other in one arrangement direction D1, and two other light sources 22B adjacent to each of these two light sources 22A from one side in the other arrangement direction D2. In the example shown in Figures 14A and 14B, light can be efficiently directed toward this position CP, which tends to be the darkest, thereby effectively homogenizing the in-plane distribution of illuminance.

[0139] As described above, by adjusting the dimensions of the unit optical element 66 and the light source 22, it is possible to eliminate the need to position the light source 22 and the microlens 65 in a direction perpendicular to the stacking direction D3. On the other hand, as explained just before, it is effective to position the normal direction ND to the element surface 67 included in the unit optical element 66 so that it is non-parallel to the arrangement direction of the light source 22. From this point of view, a mark 42 (see Figure 1) indicating the direction in which the diffusion member 40 should be positioned may be provided on the diffusion member 40. The mark 42 functions as a so-called alignment mark. The mark 42 provided on the diffusion member 40 may indicate the direction of the normal direction ND of the element surface 67. Alternatively, the mark 42 may indicate a preferred direction in which the diffusion member 40 should be positioned relative to the light source 22 or the support substrate 25. Alternatively, as shown in Figure 1, the mark 42 may indicate a preferred arrangement direction of the light source 22 relative to the diffusion member 40. Furthermore, a display related to the arrangement direction of the light sources 22 may be provided on the support substrate 25, and the diffusion member 40 may be positioned in an appropriate orientation with respect to the arrangement of the light sources 22 based on the display on the support substrate 25 and the display 42 on the diffusion member 40.

[0140] Furthermore, the light diffusion section 50 may include a microlens 65 having a plurality of unit optical elements 66 arranged in a direction nonparallel to the arrangement direction of the plurality of light sources 22. That is, the arrangement direction of the plurality of unit optical elements 66 may be nonparallel to the arrangement direction of the plurality of light sources 22. With such an arrangement, moiré patterns caused by the superposition of the arrangement of the unit optical elements 66 and the arrangement of the light sources 22 can be effectively made less noticeable.

[0141] The above describes diffractive optical elements 60 and microlenses 65 that can be used in the light diffusion section 50. However, the diffractive optical elements 60 and microlenses 65 are merely examples, and other elements having both light transmission and light diffusion properties may be used as the light diffusion section 50. In particular, elements having the specific light transmission and light diffusion properties described above may be suitably used as the light diffusion section 50. As an example of another light diffusion section 50, an optical sheet having a light-transmitting base material and light-diffusing particles dispersed in the base material may be used as the light diffusion section 50.

[0142] Next, the light-reflecting portion 70 will be described. The light-reflecting portion 70 is located on the opposite side of the light-diffusing portion 50 from the light source 22 in the stacking direction D3. The light-reflecting portion 70 has light reflectivity that reflects visible light. The reflectance and transmittance of the light-reflecting portion 70 change depending on the angle of incidence.

[0143] The transmittance of light of a specific wavelength incident at an incident angle of 0° at the light reflecting part 70 is smaller than the transmittance of light of a specific wavelength incident at an incident angle greater than 0° at the light reflecting part 70. That is, the transmittance of light of a specific wavelength incident perpendicularly at the light reflecting part 70 is smaller than the transmittance of light of a specific wavelength incident from at least one oblique direction at the light reflecting part 70. The reflectance of light of a specific wavelength incident at an incident angle of 0° at the light reflecting part 70 is larger than the reflectance of light of a specific wavelength incident at an incident angle greater than 0° at the light reflecting part 70. That is, the reflectance of light of a specific wavelength incident perpendicularly at the light reflecting part 70 is larger than the reflectance of light of a specific wavelength incident from at least one oblique direction at the light reflecting part 70. The light reflecting part 70 can also be described as a selective light reflecting part, a light transmitting part, or a selective light transmitting part.

[0144] For example, the light reflecting section 70 reflects light of a specific wavelength incident at an incident angle of 0° with a reflectivity of 80% or more. The light reflecting section 70 transmits light of a specific wavelength incident at an incident angle of 0° with a transmittance of less than 20%. In addition, the light reflecting section 70 reflects at least some light of a specific wavelength incident at an incident angle greater than 45° in absolute value with a reflectivity of less than 50%. The light reflecting section 70 transmits at least some light of a specific wavelength incident at an incident angle greater than 45° in absolute value with a transmittance of 50% or more. The light reflecting section 70 has an incident angle dependence of reflectivity. In addition, the light reflecting section 70 has an incident angle dependence of transmittance.

[0145] Figure 17 is a graph showing an example of the reflection and transmission characteristics of the light reflecting section 70 according to the angle of incidence. In the characteristics of the light reflecting section 70 shown in Figure 17, the reflectance of light of a specific wavelength at the light reflecting section 70 increases as the absolute value of the angle of incidence to the light reflecting section 70 decreases. The reflectance of light of a specific wavelength at the light reflecting section 70 with an angle of incidence of 70° or more and less than 90° in absolute value may be less than 70%, less than 60%, or less than 50%. The reflectance of light of a specific wavelength at the light reflecting section 70 with an angle of incidence of 60° or less in absolute value may be 50% or more and less than 100%, 80% or more and less than 100%, or 90% or more and less than 100%. The reflectance of light of a specific wavelength at an angle of incidence of 0° may be 80% or more and less than 100%, 90% or more and less than 100%, or 95% or more and less than 100%.

[0146] In the characteristics of the light reflecting section 70 shown in Figure 17, the transmittance of light of a specific wavelength in the light reflecting section 70 decreases as the absolute value of the angle of incidence to the light reflecting section 70 decreases. The transmittance of light of a specific wavelength at an angle of incidence of 70° or more and less than 90° in absolute value in the light reflecting section 70 may be 30% or more, 40% or more, or 50% or more. The transmittance of light of a specific wavelength at an angle of incidence of 60° or less in absolute value in the light reflecting section 70 may be 0% or more and less than 50%, 0% or more and less than 20%, or 0% or more and less than 10%. The transmittance of light of a specific wavelength at an angle of incidence of 0° at the light reflecting section 70 may be 0% or more and less than 20%, 0% or more and less than 10%, or 0% or more and less than 5%.

[0147] The specific wavelength of light can be appropriately set according to the application of the surface light source device 20 and the diffusion member 40. Typically, the light emitted from the light source 22 or the light used for emission in the surface light source device 20 may be considered the specific wavelength of light. The specific wavelength of light may also be visible light. "Visible light" means light with a wavelength of 380 nm or more and a wavelength of 780 nm or less. The reflectance of the light-reflecting part shall be the value measured using a GP-200 bend-angle photometer (goniophotometer) manufactured by Murakami Color Technology Laboratory Co., Ltd. The transmittance of the light-reflecting part is the total light transmittance measured in accordance with JIS K7361-1:1997. The transmittance of the light-reflecting part shall be the value measured using a GP-200 bend-angle photometer (goniophotometer) manufactured by Murakami Color Technology Laboratory Co., Ltd.

[0148] Figure 18 is a graph showing another example of the optical properties of a light-reflecting surface. The light-reflecting surface with the optical properties shown in Figure 18 differs from the light-reflecting surface with the optical properties shown in Figure 17. Figure 18 is a graph showing the reflection and transmission properties of the light-reflecting surface for light with a wavelength of 450 nm, which is blue light.

[0149] As shown in 18, the reflectance of light at the light reflection section 70 for light of a specific wavelength with an incident angle of 0° or more and 30° or less in absolute value may be 80% or more, 90% or more, or 95% or more. The reflectance of light at the light reflection section 70 for light of a specific wavelength with an incident angle of 0° or more and 45° or less in absolute value may be 80% or more, 85% or more, or 90% or more. With such reflection characteristics, in combination with the light diffusion section 50, it is possible to effectively prevent the illuminance in the region directly above the light source 22 from becoming too high and to effectively equalize the in-plane distribution of illuminance.

[0150] As shown in Figure 18, the transmittance of light at the light reflection section 70 for specific wavelengths of light with an incident angle of 0° to 30° in absolute value may be less than 20%, less than 10%, or less than 5%. The transmittance of light at the light reflection section 70 for specific wavelengths of light with an incident angle of 0° to 45° in absolute value may be less than 20%, less than 15%, or less than 10%. With such transmission characteristics, in combination with the light diffusion section 50, it is possible to effectively prevent the illuminance in the region directly above the light source 22 from becoming too high, and to effectively equalize the in-plane distribution of illuminance.

[0151] As shown in Figure 18, the reflectance at the light reflection section 70 for light of a specific wavelength incident at a certain incident angle that is between 45° and 75° in absolute value may be 50%. The reflectance at the light reflection section 70 for light of a specific wavelength incident at a certain incident angle that is between 50° and 60° in absolute value may also be 50%. As the absolute value of the incident angle increases within the range of 50° to 60°, the reflectance at the light reflection section for light of a specific wavelength may decrease. In a region spaced away from the light source 22 in a direction perpendicular to the stacking direction D3, there is a relatively large amount of light traveling in a direction inclined with respect to the stacking direction D3. Therefore, with these reflection characteristics, in combination with the diffusion characteristics of the light diffusion section 50, the illuminance in the region spaced away from the light source 22 can be increased, and the in-plane distribution of illuminance can be effectively made uniform.

[0152] As shown in Figure 18, the transmittance at the light reflection section 70 for light of a specific wavelength incident at a certain incident angle that is between 45° and 75° in absolute value may be 50%. The transmittance at the light reflection section 70 for light of a specific wavelength incident at a certain incident angle that is between 50° and 60° in absolute value may also be 50%. As the absolute value of the incident angle increases within the range of 50° to 60°, the transmittance at the light reflection section for light of a specific wavelength may increase. In the region spaced away from the light source 22 in a direction perpendicular to the stacking direction D3, there is a relatively large amount of light traveling in a direction inclined with respect to the stacking direction D3. Therefore, with these transmission characteristics, in combination with the diffusion characteristics of the light diffusion section 50, the illuminance in the region spaced away from the light source 22 can be increased, and the in-plane distribution of illuminance can be effectively made uniform.

[0153] Figures 19 and 20 are graphs showing yet another example of the optical properties of the light-reflecting portion. The light-reflecting portion with the optical properties shown in Figures 19 and 20 differs from the light-reflecting portion with the optical properties shown in Figure 18, and also differs from the light-reflecting portion with the optical properties shown in Figure 18. Figures 19 and 20 are graphs showing the transmission characteristics of the light-reflecting portion for light with a wavelength of 450 nm, which is blue light.

[0154] As shown in Figures 19 and 20, the transmittance of light of a specific wavelength with an incident angle of 0° to 30° in absolute value at the light reflection section 70 may be less than 15%, less than 8%, or less than 3%. The transmittance of light of a specific wavelength with an incident angle of 0° to 45° in absolute value at the light reflection section 70 may be less than 50%, less than 40%, or less than 30%. With such transmission characteristics, in combination with the diffusion characteristics of the light diffusion section 50, it is possible to effectively prevent the illuminance in the region directly above the light source 22 from becoming too high, and to effectively equalize the in-plane distribution of illuminance.

[0155] The reflectance of light at the light reflection section 70 for light of a specific wavelength with an incident angle of 0° or more and 30° or less in absolute value may be 85% or more, 92% or more, or 97% or more. The reflectance of light at the light reflection section 70 for light of a specific wavelength with an incident angle of 0° or more and 45° or less in absolute value may be 50% or more, 60% or more, or 70% or more. With such reflection characteristics, in combination with the diffusion characteristics of the light diffusion section 50, it is possible to effectively prevent the illuminance in the region directly above the light source 22 from becoming too high and to effectively equalize the in-plane distribution of illuminance.

[0156] As shown in Figures 19 and 20, the transmittance at the light-reflecting section 70 for light of a specific wavelength incident at a certain incident angle that is between 40° and 60° in absolute value may be 50%. The transmittance at the light-reflecting section 70 for light of a specific wavelength incident at a certain incident angle that is between 45° and 55° in absolute value may also be 50%. The transmittance at the light-reflecting section for light of a specific wavelength may increase as the absolute value of the incident angle increases within the range of 30° to 60°. The transmittance at the light-reflecting section for light of a specific wavelength may increase as the absolute value of the incident angle increases within the range of 50° or less. In a region spaced away from the light source 22 in a direction perpendicular to the stacking direction D3, there is a relatively large amount of light traveling in a direction inclined with respect to the stacking direction D3. Therefore, the reflection characteristics of the light-reflecting section 70 having such reflection characteristics, in combination with the diffusion characteristics of the light-diffusing section 50, can increase the illuminance in the region spaced away from the light source 22 and effectively homogenize the in-plane distribution of illuminance.

[0157] The reflectance of light at the light-reflecting part 70 for light of a specific wavelength incident at a certain incident angle that is between 40° and 60° in absolute value may be 50%. The reflectance of light at the light-reflecting part 70 for light of a specific wavelength incident at a certain incident angle that is between 45° and 55° in absolute value may be 50%. As the absolute value of the incident angle increases in the range between 30° and 60°, the reflectance of light at the light-reflecting part for light of a specific wavelength may decrease. As the absolute value of the incident angle increases in the range of 50° or less, the reflectance of light at the light-reflecting part for light of a specific wavelength may decrease. In a region spaced away from the light source 22 in a direction perpendicular to the stacking direction D3, there is a relatively large amount of light traveling in a direction inclined with respect to the stacking direction D3. Therefore, according to the reflection characteristics of the light-reflecting part 70 having such reflection characteristics, in combination with the diffusion characteristics of the light-diffusing part 50, the illuminance in the region spaced away from the light source 22 can be increased, and the in-plane distribution of illuminance can be effectively made uniform.

[0158] The light-reflecting portion 70 is stacked with the light-diffusing portion 50 in the stacking direction D3. If the light-reflecting portion 70 and the light-diffusing portion 50 are not joined by adhesive or other means, for example, if the light-reflecting portion 70 and the light-diffusing portion 50 are simply stacked on top of each other, the light-reflecting portion 70 may have a matte surface facing the light-diffusing portion 50. That is, the light-receiving side of the light-reflecting portion 70 may be a matte surface. By providing a matte surface to the light-reflecting portion 70, it is possible to suppress the light-reflecting portion 70 and the light-diffusing portion 50 from sticking together. In addition, the light-scattering properties of the matte surface can effectively smooth out changes in the angular distribution of radiant intensity.

[0159] The light-reflecting portion 70 is not particularly limited as long as it has an incident angle dependence of reflectance and an incident angle dependence of transmittance. A reflective volume hologram, a cholesteric liquid crystal structure layer, a retroreflective film, and a reflective diffractive optical element can be used as the light-reflecting portion 70. In particular, a dielectric multilayer film, which offers a relatively high degree of design freedom for its reflective and transmittance characteristics, is suitable as the light-reflecting portion 70. Furthermore, a reflective structure that is structurally given an incident angle dependence of reflectance and transmittance due to its low wavelength dependence is also suitable as the light-reflecting portion 70.

[0160] As the dielectric multilayer film forming the light-reflecting portion 70, a multilayer film of an inorganic compound in which inorganic layers with different refractive indices are alternately stacked may be used. Alternatively, as the dielectric multilayer film forming the light-reflecting portion 70, a multilayer film of resin in which resin layers with different refractive indices are alternately stacked may be used.

[0161] Dielectric multilayer films, as multilayer films of inorganic compounds, can be obtained by alternately stacking high-refractive-index inorganic layers and low-refractive-index inorganic layers, for example, by CVD, sputtering, vacuum deposition, or wet coating. The thickness of the multilayer film of inorganic compounds may 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 may be 1.7 or more and 2.5 or less. As the inorganic compound contained in the high-refractive-index inorganic layer, titanium dioxide, zirconium oxide, tantalum pentoxide, niobium pentoxide, lanthanum oxide, yttrium oxide, zinc oxide, zinc sulfide, and indium oxide may be the main components. As the inorganic compound contained in the high-refractive-index inorganic layer, small amounts of titanium dioxide, tin oxide, cerium oxide, etc. may be included in addition to the main components. The refractive index of the inorganic compound contained in the low-refractive-index inorganic layer may be 1.2 or more and 1.6 or less. Examples of inorganic compounds contained in the low-refractive-index inorganic layer include silica, alumina, lanthanum fluoride, magnesium fluoride, and sodium aluminum hexafluoride.

[0162] A dielectric multilayer film, as a resin multilayer film, contains, for example, many layers of thermoplastic resin or thermosetting resin. Thermoplastic resin is preferred because of its excellent moldability. Various additives, such as antioxidants, antistatic agents, nucleating agents, inorganic particles, organic particles, viscosity reducers, heat stabilizers, lubricants, infrared absorbers, ultraviolet absorbers, and doping agents for refractive index adjustment, may be added to the resin layer.

[0163] Among the resin layers with different refractive indices, the difference in the average in-plane 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. A large difference in the average in-plane refractive index allows for easy achievement of desired reflectance and transmittance.

[0164] The difference between the in-plane average refractive index and the refractive index in the thickness direction of the high refractive index resin layer may preferably be 0.03 or more. The difference between the in-plane average refractive index and the refractive index in the thickness direction of the low refractive index resin layer may preferably be 0.03 or less. In this example, even if the angle of incidence is large, a decrease in the reflectance of the reflection peak is less likely to occur.

[0165] The number of layers of high-refractive-index resin layers and low-refractive-index resin layers is adjusted according to the required reflective and transmittance characteristics of the light-reflecting portion 70. For example, the high-refractive-index resin layers and low-refractive-index resin layers may be layered alternately in quantities of 30 or more, or alternately in quantities of 200 or more. The total number of layers of high-refractive-index resin layers and low-refractive-index resin layers may be, for example, 600 or more. If the number of layers is too small, sufficient reflectance may not be obtained. Furthermore, by keeping the number of layers within the above range, the desired reflectance and transmittance can be easily obtained.

[0166] The multilayer film of the resin constituting the dielectric multilayer film may have a surface layer containing polyethylene terephthalate or polyethylene naphthalate with a thickness of 3 μm or more on one or both sides. The thickness of the surface layer may be 5 μm or more. The surface layer can protect the surface of the resin multilayer film.

[0167] As a method for manufacturing the multilayer film of the resin constituting the dielectric multilayer film, co-extrusion or the like may be employed. Specifically, the method for manufacturing a laminated film described in Japanese Patent Application Publication No. 2008-200861 may be employed.

[0168] Commercially available laminated films can be used as the resin multilayer film constituting the dielectric multilayer film, such as Picasus® manufactured by Toray Industries, Inc. and ESR manufactured by 3M Corporation.

[0169] Next, the reflective structure 71 forming the light-reflecting portion 70 will be described with reference to Figures 21 to 24. Figures 21 and 22 are longitudinal cross-sectional views or plan views showing a first example of the reflective structure 71, respectively. Figures 23 and 24 are longitudinal cross-sectional views or plan views showing a second example of the reflective structure 71, respectively. In the following descriptions of the first and second examples of the reflective structure 71, the same reference numerals will be used for parts that can be configured identically, and redundant explanations will be omitted.

[0170] The reflective structure 71 shown in Figures 21 and 22 comprises a transparent substrate 72, a first reflective layer 73 provided on the light-receiving side of the transparent substrate 72, and a second reflective layer 74 provided on the light-emitting side of the transparent substrate 72. The transparent substrate 72 is light-transmitting to at least light of a specific wavelength, for example, light emitted from a light source 22 or light used for emission in a surface light source device 20. Preferably, the transparent substrate 72 is visible light-transmitting. The transparent substrate 72 is formed, for example, from a resin film. The first reflective layer 73 and the second reflective layer 74 are light-reflecting to at least light of a specific wavelength, for example, light emitted from a light source 22 or light used for emission in a surface light source device 20. Preferably, the first reflective layer 73 and the second reflective layer 74 are visible light-reflecting. The first reflective layer 73 and the second reflective layer 74 include, for example, a thin metal film formed on the transparent substrate 72. The reflection in the first reflective layer 73 and the second reflective layer 74 may be specular reflection, diffuse reflection, or anisotropic diffuse reflection. The first reflective layer 73 is provided with a plurality of first apertures 73a. Similarly, the second reflective layer 74 is provided with a plurality of second apertures 74a. The first apertures 73a and the second apertures 74a are arranged at a sufficiently small and short pitch to prevent unevenness in brightness.

[0171] As shown in Figures 21 and 22, the first opening 73a and the second opening 74a are positioned so as not to overlap when viewed from the stacking direction D3. In the illustrated example, the first opening 73a and the second opening 74a are positioned at different locations in a direction perpendicular to the stacking direction D3. More specifically, the first opening 73a and the second opening 74a are arranged in a square with the same pitch to each other, but are positioned offset by half a pitch in the first direction D1 and the second direction D2.

[0172] As shown in Figure 21, in the first example of the reflective structure 71, light L211 and L212 incident at a large angle of incidence and incident on the first aperture 73a of the first reflective layer 73 can be transmitted through the reflective structure 71 by either directly heading towards the second aperture 74a of the second reflective layer 74, or by being reflected by the first reflective layer 73 and the second reflective layer 74 and heading towards the second aperture 74a of the second reflective layer 74. On the other hand, light L213 incident on the reflective structure 71 at a small angle of incidence, even if it proceeds to the first aperture 73a of the first reflective layer 73, is reflected by the second reflective layer 74 facing the first aperture 73a, reverses direction in the stacking direction D3, and proceeds out of the reflective structure 71 towards the light diffusion section 50. Also, light L214 incident on the first reflective layer 73 regardless of the angle of incidence is reflected by the first aperture 73a and again proceeds towards the light diffusion section 50 in the stacking direction D3.

[0173] Next, the reflective structure 71 shown in Figures 23 and 24 has a light-transmitting substrate 72, similar to the first example. Protruding elements 75 are dispersed on the light-diffusing portion 50 side of the translucent substrate 72. The protruding elements 75 protrude from the translucent substrate 72 toward the light-diffusing portion 50 side in the stacking direction D3. The protruding elements 75 have a tip surface 75a covered by the first reflective layer 73, and a side surface 75b adjacent to the tip surface 75a that extends to the light-receiving side of the translucent substrate 72. In addition, a second reflective layer 74 is provided in the region of the light-receiving side of the translucent substrate 72 where the protruding elements 75 are not provided. The first reflective layer 73 and the second reflective layer 74 have reflective properties, similar to the first example. In the examples shown in Figures 23 and 24, the side surface 75b of the protruding element 75 is cut in the stacking direction D3 and is exposed in the first direction D1 and the second direction D2 between the first reflective layer 73 and the second reflective layer 74.

[0174] As shown in Figure 23, in the first example of the reflective structure 71, light L231 incident on the side surface 75b of the protruding element 75 can pass through the reflective structure 71. Since the side surface 75b is sharply cut in the stacking direction D3, the angle of incidence of light incident on the side surface 75b is large. On the other hand, regardless of the angle of incidence, light L232 and L233 incident on the first reflective layer 73 and the second reflective layer 74 other than the side surface 75b are reflected and again proceed toward the light diffusion portion 50 in the stacking direction D3.

[0175] According to the reflective structure 71 forming the light-reflecting section 70 shown in Figures 21 to 24, only light with a large incident angle can be transmitted. In particular, since the first reflective layer 73 and the second reflective layer 74, which are made using inexpensive and widely available materials such as aluminum, have visible light reflectivity, it is possible to achieve reflection characteristics that are dependent on the incident angle over the entire visible light spectrum.

[0176] Next, the operation of generating planar light with the surface light source device 20 using the diffusion member 40 having the above configuration will be explained, mainly with reference to Figures 25 to 28. In Figures 25 to 28, the amount of light traveling in the direction of the arrow is indicated by the thickness of the arrow.

[0177] As shown in Figure 25, first, light LP1 is emitted from the light source 22. In the examples shown in Figures 25 to 28, the light source 22 emits light LP1 with a wavelength of 450 nm, which is blue light, and the light reflecting section 70 has the reflection characteristics described above for the light emitted from the light source 22. When a typical light source 22 is used, a large amount of light LP1 is emitted in the stacking direction D3. This light LP1 is incident on the light diffusing section 50 of the diffusing member 40. The light diffusing section 50 has light transmittance and light diffusing properties. The light LP1 is transmitted through the light diffusing section 50 and diffused.

[0178] Furthermore, if the light diffusion section 50 has the diffusion characteristics shown in Figures 5 and 6, most of the light LP1 traveling in the stacking direction D3 will travel in a direction inclined with respect to the stacking direction D3.

[0179] Next, as shown in Figure 26, the light LP2 and LP3 diffused by the light diffusion section 50 are directed toward the light reflection section 70 of the light diffusion section 50. For example, the light reflection section 70 can reflect light incident at an incident angle of 0° with a reflectivity of 80% or more. On the other hand, the light reflection section 70 can reflect at least some of the light incident at an incident angle greater than 45° in absolute value with a reflectivity of 50%. In other words, the light reflection section 70 transmits only the light LP3 that is tilted very sharply with respect to the stacking direction D3, and reflects the other light LP2. In the region including the position directly facing the light source 22 and its surroundings, that is, the region directly above the light source 22, a large amount of light tends to travel in a direction that is not tilted sharply with respect to the stacking direction D3. This reflection characteristic of the light reflection section 70 makes it possible to suppress the transmission of a large amount of light with a small incident angle through the light reflection section 70.

[0180] In particular, when the light reflector 70 reflects the light LP2 incident on it at the peak angle where the radiant intensity peak of the light diffused by the light diffusing section 50 appears, with a reflectivity of 80% or more, it is possible to suppress the brightening directly above the light source 22, that is, to suppress the perception of an image of the light source 22. For example, when using the light diffusing section 50 having the diffusion characteristics shown in Figure 6, a large amount of light travels in the direction where the emission angle is 20° to 50°. The light reflector 70, having the reflection characteristics shown in Figures 17 and 18, reflects the light emitted from the light diffusing section 50 in the direction where the emission angle is 20° to 50° with a reflectivity of 90% or more. In other words, much of the light LP1 emitted from the light source 22 and traveling to the diffusion member 40 is reflected at least once by the light reflector 70. Therefore, it is possible to very effectively suppress the brightening of the area directly above the light source 22.

[0181] Next, as shown in Figure 27, the light LP2 reflected by the light reflecting section 70 diffuses and passes through the light diffusing section 50 again, and proceeds in a direction that is even more inclined with respect to the stacking direction D3. That is, the light LP2 reflected by the light reflecting section 70 diffuses and passes through the light diffusing section 50 twice, and proceeds in a direction that is much more inclined with respect to the stacking direction D3. As a result, the light LP4 that has diffused and passed through the light diffusing section 50 twice proceeds in a direction perpendicular to the stacking direction D3. In the illustrated example, the light LP4 proceeds to move away from the light source 22 in the first direction D1. Then, as shown in Figure 27, the light LP4 that has diffused and passed through the light diffusing section 50 twice is reflected by the support substrate 25 that supports the light source 22. Next, the light LP5 proceeds to move further away from the light source 22 in a direction perpendicular to the stacking direction D3, and proceeds towards the diffusion member 40 again in the stacking direction D3.

[0182] As shown in Figure 28, the light LP5 that then heads back towards the diffusion member 40 is diffused by being transmitted through the light diffusion section 50. Much of the light LP6 diffused by the light diffusion section 50 then heads towards the light reflection section 70. Of this light LP6, light with a large angle of incidence to the light reflection section 70 is transmitted through the light reflection section 70. On the other hand, light with a small angle of incidence to the light reflection section 70 is reflected again by the light reflection section 70.

[0183] As described above, the combination of the light diffusion transmittance of the light diffusion section 50 and the light reflectivity of the light reflection section 70 allows the light emitted from the light source 22 to be effectively spread in a direction perpendicular to the stacking direction D3 without being significantly constrained by the light distribution characteristics of the light source 22. This effectively eliminates brightness unevenness caused by the presence of the light source 22, that is, it effectively makes the image of the light source 22 less conspicuous. Due to the light diffusion properties of the diffusion member 40, it is also possible to significantly reduce the thickness of the surface light source device 20. As a result, while reducing the thickness of the surface light source device 20, the illuminance at each position on the surface of the light reflection section 70 that emits light can be effectively made uniform, that is, the in-plane distribution of illuminance can be effectively made uniform.

[0184] Here, we will explain the simulation results performed by the inventors of this case. The simulation was performed on the surface light source devices related to Samples 1 to 7. The simulation was conducted using ray tracing simulation with LightTools from Synopsys.

[0185] For samples 1 to 5, the surface light source device 20 shown in Figures 25 to 28 was used. The surface light source device 20 for samples 1 to 5 includes a light source 22, a support substrate 25 that supports the light source 22, and a diffusion member 40 that is positioned facing the light source 22 and the support substrate 25 in the stacking direction D3. The light source 22 consists of one light-emitting diode placed on the support substrate 25. The reflection at the surface of the support substrate 25 is diffuse reflection with a reflectance of 95%.

[0186] In the surface light source devices 20 of Samples 1 to 5, the diffusion member 40 has a light diffusion section 50 and a light reflection section 70 in that order from the light source side. Common to all surface light source devices 20 of Samples 1 to 5, the light reflection section 70 is a dielectric multilayer film having the reflection and transmission characteristics shown in Figure 17. In the surface light source device 20 of Sample 1, the light diffusion section 50 is a diffractive optical element 60 having the diffusion characteristics shown in Figure 6. In the surface light source device 20 of Sample 2, the light diffusion section 50 is a microlens 65 having the shape, dimensions, arrangement, etc. described with reference to Figures 13A and 13B. In the surface light source device 20 of Sample 3, the light diffusion section 50 is a microlens 65 having the shape, dimensions, arrangement, etc. described with reference to Figures 14A and 14B. In the surface light source device 20 of Sample 4, the light diffusion section 50 is a microlens 65 having the shape, dimensions, arrangement, etc. described with reference to Figures 15A and 15B. In the surface light source device 20 of Sample 5, the light diffusion section 50 is a microlens 65 having the shape, dimensions, arrangement, etc., as described with reference to Figures 16A and 16B.

[0187] In the surface light source devices 20 for samples 1 to 5, the thickness of the diffusion member 40 along the stacking direction D3 was set to 200 μm. In addition, in the surface light source devices 20 for samples 1 to 5, the distance DX (see Figure 2) along the stacking direction D3 from the surface of the light source 22 facing the diffusion member 40 to the light-receiving side of the diffusion member 40 facing the light source 22 was set to 0.5 mm.

[0188] Sample 6 was the same as Samples 1-5, except that the diffusion member 40 was replaced with a light diffusion sheet "Orupas B910" manufactured by Keiwa Co., Ltd. In the surface light source device of Sample 6, the distance along the lamination direction from the surface of the light source facing the diffusion member to the light-receiving side of the light diffusion sheet facing the light source was set to 0.5 mm. The thickness of the light diffusion sheet was set to 100 μm.

[0189] Sample 7 was the same as Samples 1 to 5, except that the diffusion member 40 was omitted. In other words, the surface light source device for Sample 7 consisted only of a support substrate 25 and a light source 22 supported on the support substrate 25.

[0190] For samples 1 to 5, with the light source 22 emitting 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 support substrate 25 facing the diffusion member 40, and the illuminance at each position on this light-receiving surface was simulated. The illuminance calculation was performed using a region on the light-receiving surface with a length of 6 mm in the first direction D1 and 6 mm in the second direction D2, with the light source 22 at its center. In other words, in projection onto the stacking direction D3, the light source 22 was positioned at the center of a light-receiving surface with an area of ​​6 mm × 6 mm. The in-plane distribution of illuminance on the light-receiving surface calculated for the surface light source device 20 for samples 1 to 5 is shown in Figures 29A to 29E, respectively.

[0191] Under similar conditions, the same light-receiving surfaces as those used for samples 1-5 were set for the surface light source devices related to samples 6 and 7, and the in-plane distribution of illuminance on the light-receiving surfaces was calculated. The calculated in-plane distributions of illuminance on the light-receiving surfaces for the surface light source devices related to samples 6 and 7 are shown in Figures 29F and 29G, respectively.

[0192] Figures 29A to 29G show the in-plane distribution of illuminance on a light-receiving surface with an area of ​​6 mm x 6 mm, along with graphs showing the illuminance at each position along the straight line of the first direction D1 that passes through the position facing the light source 22 in the third direction D3 on the light-receiving surface. In the in-plane distribution diagram, the illuminance at each position on the light-receiving surface is represented by color, with lighter colors indicating higher illuminance. The results shown in Figures 29A to 29G show the relative illuminance at each position within each sample, and do not compare illuminance between different samples.

[0193] According to the simulation results, in samples 1 to 5, even though the gap between the light source 22 and the diffusion member 40 was set to 0.5 mm, which is extremely short compared to approximately 2.5 mm in Patent Document 1 (JP6299811B), it was possible to uniformly distribute the illuminance in the region 3 mm away from the light source in the first direction D1 and the second direction D2, respectively. From this, it was confirmed that when the diffusion member 40 according to this embodiment is used in the surface light source device 20, the surface light source device 20 can be made significantly thinner while sufficiently uniformizing the in-plane distribution of illuminance. Furthermore, in the surface light source device 20 according to samples 2 to 5 using the microlens 65, it was confirmed that light can be effectively guided in the direction along the normal direction ND of the element surface 67 in the observation direction from the stacking direction D3.

[0194] In the embodiment described above, the diffusion member 40 has a light diffusion section 50 and a light reflection section 70 in that order. When the diffusion member according to this embodiment is applied to a surface light source device, the combination of the light transmittance and light diffusion properties of the light diffusion section 50 and the reflection properties of the light reflection section 70 makes it possible to effectively spread the light emitted from the light source 22 in a direction perpendicular to the stacking direction D3. As a result, while making the surface light source device thinner, it is possible to effectively eliminate brightness unevenness caused by the presence of the light source 22, that is, to effectively make the image of the light source 22 less conspicuous. As a result, while making the surface light source device 20 thinner, it is possible to effectively equalize the illuminance at each position on the light-emitting side surface 40b of the diffusion member 40 that is on the light-emitting side, that is, to effectively equalize the in-plane distribution of illuminance.

[0195] In the first specific example of the embodiment described above, when a light ray is incident on the light diffusion section 50 at an incident angle of 0°, the radiant intensity on the light-emitting side of the light diffusion section 50 facing the light-reflecting section 70 has a radiant intensity peak at a peak angle other than 0° for the emission angle. Furthermore, the reflectance of light of a specific wavelength incident on the light-reflecting section 70 at an incident angle that is between 0° and the peak angle in absolute value is 50% or more, more preferably 80% or more. According to this example, much of the light that is incident on the light diffusion section 50 at an incident angle of 0° and diffused by the light diffusion section 50 is reflected by the light-reflecting section 70 without passing through it. That is, much of the light emitted from the light source 22 is reflected once or more by the light-reflecting section 70 and its direction of propagation in the stacking direction D3 is reversed. This promotes the light emitted from the light source 22 to travel in a direction perpendicular to the stacking direction D3. By promoting reflection at the light-reflecting portion 70 in this way, the distance DX between the light source 22 and the diffusion member 40 along the stacking direction D3 can be shortened while making the in-plane distribution of illuminance uniform. In other words, while making the surface light source device 20 thinner, the unevenness of brightness caused by the presence of the light source 22 can be effectively eliminated, and the in-plane portion of the illuminance can be effectively made uniform.

[0196] As a specific example of the embodiment described above, the specific wavelength can be set to 450 nm. In this example, a light-emitting diode that emits high-output blue light can be used as the light source 22. It is also possible to emit white light by using a phosphor or the like.

[0197] The first specific example of one embodiment has been described above. Next, a second specific example of one embodiment will be described with reference to Figures 30 to 37. The second specific example differs from the first specific example in that the diffusion member 40 has an optical element portion 110. The second specific example may adopt the same configuration as the first specific example described above in configurations other than the optical element portion 110. In the following description, the optical element portion 110 will be described mainly. In the following description of the second specific example and in the drawings used in the following description, parts that can be configured in the same way as the first specific example described above will be given the same reference numerals as those used for the corresponding parts in the above specific example, and redundant explanations will be omitted.

[0198] As shown in Figure 30, the optical element portion 110 is located on the light-emitting side of the light that is to be diffused by the diffusion member 40, with respect to the light-reflecting portion 70. The optical element portion 110 forms the light-emitting side surface 40b of the diffusion member 40. The light-reflecting portion 70 and the optical element portion 110 may be joined to each other, or they may simply be in contact without being joined, or they may be spaced apart from each other.

[0199] As described above, the reflection and transmission characteristics of the light-reflecting section 70 are dependent on the angle of incidence. The light-reflecting section 70 reflects light at low angles of incidence and folds the direction of propagation of the light back in the stacking direction D3. The direction of propagation of light transmitted through the light-reflecting section 70 is mainly within an angular range that is greatly inclined with respect to the stacking direction D3, due to the reflection and transmission characteristics of the light-reflecting section 70. The optical element section 110 reinforces the reflection and transmission characteristics of the light-reflecting section 70. The optical element section 110 reflects a portion of the incident light from the light-reflecting section 70. Through the cooperation of the light-reflecting section 70 and the optical element section 110, the in-plane distribution of illuminance can be made more uniform.

[0200] As a specific configuration, as shown in Figure 30, the optical element portion 110 has an uneven surface 112. The uneven surface 112 faces away from the light-reflecting portion 70 in the stacking direction D3. In other words, the uneven surface 112 faces the light-emitting side in the stacking direction D3. Light can change its direction of travel through refraction and reflection at the uneven surface 112. The optical element portion 110 may include an optical sheet 115 that is simply stacked with other members or bonded to other members by adhesive or bonding, or it may be the optical sheet 115, or a part of the optical sheet 115, members and structures, or even a surface of the optical sheet 115, members and structures, etc. In the example shown in Figure 30, the optical element portion 110 is bonded to the light-reflecting portion 70. In the example shown in Figure 30, the light-diffusing portion 50, the light-reflecting portion 70 and the optical element portion 110 are bonded together and can be handled as a single unit.

[0201] In order to distinguish it from the uneven surface 52 of the light diffusion section 50 described above, the uneven surface of the light diffusion section 50 is sometimes called the first uneven surface 52, and the uneven surface of the optical element section 110 is sometimes called the second uneven surface 112. The light reflection section 70 and the optical element section 110 also contain parts and elements with the same names other than the uneven surfaces. For these parts and elements, the parts and elements of the light diffusion section 50 may be designated as "first," and the parts and elements of the optical element section 110 may be designated as "second."

[0202] The optical element 110 has light transmittance. The light transmittance of the optical element 110 is preferably 50% or more, more preferably 70% or more, and even more preferably 90% or more. By setting the total light transmittance of the optical element 110 within the above range, the utilization efficiency of light from the light source 22 is improved. In addition, when the optical element 110 is applied to the surface light source device 20, the in-plane distribution of illuminance on the light-emitting side surface 40b of the diffusion member 40 can be effectively made uniform. Therefore, the optical element 110 is made of a material that has high transmittance to light emitted from the light source 22 or to light used for emission in the surface light source device 20. The total light transmittance is a value measured according to the method in accordance with JIS K7361-1:1997.

[0203] The optical element portion 110 is not particularly limited and can employ various configurations having an uneven surface 112. As shown in Figures 31A and 31B, the optical element portion 110 may include a microlens 125. In this example, the microlens 125 forms the uneven surface 112. The unit optical element 126 is a concept that includes elements called unit shape elements, unit prisms, and unit lenses. The unit optical element 126 may be configured as a convex portion 128 as shown in Figure 31A. The unit optical element 126 may be configured as a concave portion 129 as shown in Figure 31B.

[0204] In the examples shown in Figures 31A and 31B, the optical element portion 110 has a base portion 118. The base portion 118 is sheet-like. The base portion 118 extends in a first direction D1 and a second direction D2 perpendicular to the stacking direction D3. In the examples shown in Figures 31A and 31B, the base portion 118 is bonded to the light-reflecting portion 70. In the example shown in Figure 31A, a unit optical element 126 as a convex portion 128 is provided on the base portion 118. In the example shown in Figure 31B, a unit optical element 126 as a concave portion 129 is formed on the base portion 118.

[0205] As shown in Figures 31A and 31B, the unit optical element 126 has an element surface 127 that is inclined with respect to the stacking direction D3. The unit optical element 126 is defined by the element surface 127. The microlens 125 has an uneven surface 112 formed by the element surface 127 of the unit optical element 126. The microlens 125 can bend the direction of propagation of incident light by this uneven surface 112.

[0206] The optical properties of the uneven surface 112 are affected by the inclination angle θb of the element surface 127 of the unit optical element 126. Therefore, the cross-sectional shape of the unit optical element 126 can be appropriately adjusted based on the optical properties required for the surface light source device 20 and the optical element section 110. For example, the inclination angles θb of the multiple element surfaces 127 included in a single unit optical element 126 may be different from each other or the same. Multiple unit optical elements 126 included in a microlens 125 may differ from each other in terms of shape, orientation, size, and other configurations. Multiple unit optical elements 126 included in a microlens 125 may have the same configuration as each other.

[0207] As described above, the direction of light transmitted through the light-reflecting section 70 is mainly within an angular range that is significantly inclined with respect to the stacking direction D3, due to the reflection and transmission characteristics of the light-reflecting section 70. The optical element section 110 reinforces the reflection and transmission characteristics of the light-reflecting section 70. The optical element section 110 reflects a portion of the incident light from the light-reflecting section 70. Through the cooperation of the light-reflecting section 70 and the optical element section 110, the in-plane distribution of illuminance can be made more uniform. From the viewpoint of making the above-mentioned functions of the optical element section 110 more effective, the inclination angle θb of the normal direction NDA of the element surface 127 with respect to the stacking direction D3 may be 25° or less, 20° or less, or 15° or less. The inclination angle θb may also be greater than 0°. From the viewpoint of ensuring the above-mentioned functions of the optical element section 110, the inclination angle θb may be 3° or more, 5° or more, or 8° or more.

[0208] It should be noted that each element surface 127 may not be flat. The inclination angle θb of the element surface 127 is determined at the central position of the element surface 127 in the stacking direction D3. For the element surface 127 as a convex portion 128, the inclination angle θb is determined at the central position in the stacking direction D3 between the base end of the element surface 127 that connects to the base portion 118 and the tip portion that is furthest from the base portion 118 in the stacking direction D3. For the element surface 127 as a concave portion 129, the inclination angle θb is determined at the central position in the stacking direction D3 between the base end (deepest part) of the element surface 127 that is closest to the light-reflecting portion 70 in the stacking direction D3 and the tip portion that is furthest from the light-reflecting portion 70 in the stacking direction D3.

[0209] Furthermore, as shown by the dashed lines in Figures 31A and 31B, the element surface 127 may be somewhat curved. The unit optical element 126 may have an external shape that is part of a sphere, such as a hemisphere, or an external shape that is part of a spheroid. When the unit optical element 126 includes a curved element surface 127, the optical path of light passing through the microlens 125 is bent in various directions due to reflection and refraction. This allows for more effective uniformization of the in-plane distribution of illuminance. It also allows for more effective smoothing of changes in the angular distribution of radiant intensity.

[0210] For essentially the same reasons as for the curved element surface 127, the unit optical element 126 may include an element surface 127 formed as a matte surface. The element surface 127 as a matte surface scatters light in various directions. This allows for a more effective homogenization of the in-plane distribution of illuminance. It also allows for a more effective smoothing of changes in the angular distribution of radiant intensity.

[0211] Multiple unit optical elements 126 may be arranged in a two-dimensional array. That is, multiple unit optical elements 126 may be arranged in two or more directions that are not parallel to each other. Therefore, the element faces 127 of the unit optical elements 126 face in various directions. As a result, the two-dimensionally arranged unit optical elements 126 can guide light in various directions. Multiple unit optical elements 126 may be arranged irregularly or regularly. By arranging multiple unit optical elements 126 regularly, the design of the microlens 125 becomes easier, and it becomes easier to tile the unit optical elements 126 without gaps.

[0212] As for the arrangement, shape, and other configuration of the second unit optical element 126 of the optical element section 110, the arrangement, shape, and other configuration of the first unit optical element 66 included in the light diffusion section 50 may be adopted, as shown in Figures 13A to 16B which have already been described in detail. For example, as the configuration of the unit optical element 126, the configuration shown in Figures 13A to 16B which have already been described may be adopted. In the four specific examples shown in Figures 13A to 16B, the perpendicular line from the vertex of the cone forming the unit optical element 126 to the base may pass through the centroid of the base. In the four specific examples shown in Figures 13A to 16B, the unit optical element 126 is a recess 129 formed in the base 118. However, in the four specific examples shown in Figures 13A to 16B, the unit optical element 126 may be a convex portion 128 that protrudes from the base 118 on the opposite side from the light source 22 in the stacking direction D3.

[0213] If the size of the unit optical element 126 in the observation from the stacking direction D3 is large, unevenness in brightness due to the shape of the unit optical element 126 will become visible. From the viewpoint of preventing this problem, the maximum length of the unit optical element 126 in the direction perpendicular to the stacking direction D3 is preferably 1.5 mm or less, more preferably 1 mm or less, and still more preferably 0.5 mm or less.

[0214] When the size of the unit optical element 126 in the observation from the stacking direction D3 becomes large, it may be necessary to position the unit optical element 126 with respect to the light source 22. This point is the same as the necessity of positioning the unit optical element 66 of the light diffusing portion 50 with respect to the light source 22 described above. Therefore, similarly to the unit optical element 66 of the light diffusing portion 50, it is preferable to configure the unit optical element 126 of the optical element portion 110. That is, when observed from the stacking direction D3, it is preferable that in each of two mutually perpendicular directions, one unit optical element 126 has a size smaller than three times the size of the light source 22. For example, in the observation from the stacking direction D3, the unit optical element 126 preferably has a size smaller than a square of 1.5 mm on each side, and more preferably a size smaller than a square of 0.6 mm on each side. Still more preferably, in the observation from the stacking direction D3, the dimension along any direction of the unit optical element 126 may be three times or less the dimension along the corresponding direction of the light source 22.

[0215] The array pitch of the unit optical element 126 having such a size may be 0.01 mm or more and 1.5 mm or less. From the viewpoint of effectively equalizing the in-plane distribution of the illuminance on the light-emitting side surface 40b of the diffusion member 40 when applied to the surface light source device 20, the array pitch of the unit optical element 126 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.

[0216] The uneven surface 112 of the optical element portion 110 guides light in the normal direction NDA to the element surface 127 when observed from the stacking direction D3. Therefore, from the viewpoint of homogenizing the in-plane distribution of illuminance, preferably, the uneven surface 112 includes an element surface 127 having a normal direction NDA that is non-parallel to the arrangement direction of the multiple light sources 22 when observed from the stacking direction D3. More preferably, the unit optical element 126 includes an element surface 127 having a normal direction ND that is inclined at an angle of 35° to 55° with respect to the arrangement direction of the multiple light sources 22 when observed from the stacking direction D3. With such an arrangement, light can be guided in a direction non-parallel to the arrangement direction of the multiple light sources 22 by reflection and refraction at the unit optical element 126. This makes it possible to more effectively homogenize the in-plane distribution of illuminance. For example, with the arrangement of the unit optical element 126 shown in Figures 14A and 14B, the in-plane distribution of illuminance can be effectively homogenized when combined with the arrangement of light sources 22 shown in Figure 3. The display 42 described above may also display the direction of the normal direction NDA of the element surface 127.

[0217] Furthermore, the optical element section 110 may have a plurality of unit optical elements 126 arranged in a direction nonparallel to the arrangement direction of the plurality of light sources 22. That is, the arrangement direction of the plurality of unit optical elements 126 may be nonparallel to the arrangement direction of the plurality of light sources 22. With such an arrangement, moiré patterns caused by the superposition of the arrangement of the unit optical elements 126 and the arrangement of the light sources 22 can be effectively made less noticeable.

[0218] Furthermore, as shown in FIG. 32, the plurality of unit optical elements 126 may be arranged in a one-dimensional array. In this example, the plurality of unit optical elements are arranged in one direction, and each unit optical element 126 may linearly extend in another direction non-parallel to the one direction. For example, as shown in FIG. 32, each unit optical element 126 may linearly extend in another direction perpendicular to the one direction. Each unit optical element 126 may linearly extend in the other direction. The arrangement direction of the unit optical elements 126 may be the first direction D1, may be the second direction D2, or may be a direction non-parallel to both the first direction D1 and the second direction D2. For example, the arrangement direction of the unit optical elements 126 may be inclined at 25° or more and 65° or less with respect to both the first direction D1 and the second direction D2, or may be inclined at 35° or more and 55° or less with respect to both the first direction D1 and the second direction D2.

[0219] The cross-sectional shape in a cross-section orthogonal to the longitudinal direction of the linear unit optical element 126 is not particularly limited, and may be a polygonal shape such as a triangular shape or a pentagonal shape, or may be a shape with chamfers on one or more corners of the polygonal shape. The arrangement pitch of the linear unit optical elements 126 may be set as already described above. Specifically, it may be 0.01 mm or more and 1.5 mm or less, may be 0.05 mm or more and 1 mm or less, and more preferably may be 0.1 mm or more and 0.5 mm or less. Other configurations of the linear unit optical element 126 may adopt the configurations of the unit optical elements 126 constituting the above-described microlens 125. For example, the element surface 127 and the tilt angle θb of the linear unit optical element 126 may be 25° or less, may be 20° or less, or may be 15° or less. The tilt angle θb may be greater than 0°. The tilt angle θb may be 3° or more, may be 5° or more, or may be 8° or more. The element surface 127 of the linear unit optical element 126 may be a curved surface. The element surface 127 of the linear unit optical element 126 may be a matte surface. The unit optical element 126 may include the element surface 127 having a normal direction ND inclined at an angle of 35° or more and 55° or less with respect to the arrangement direction of the plurality of light sources 22 in an observation from the stacking direction D3.

[0220] Next, the operation of generating planar light with the planar light source device 20 using the diffusion member 40 having the above configuration will be explained, mainly with reference to Figures 33 to 37. In Figures 33 to 36, the amount of light traveling in the direction of the arrow is indicated by the thickness of the arrow. In the example shown in Figures 33 to 37, the light source 22 emits blue light LP1 with a wavelength of 450 nm. The light reflecting part 70 has the characteristics shown in Figures 19 and 20 with respect to the light emitted from the light source 22.

[0221] As shown in Figure 33, first, light LP1 is emitted from the light source 22. Light LP1 is transmitted through the light diffusion section 50 and diffused. Next, as shown in Figure 34, the light LP2 and LP3 diffused by the light diffusion section 50 are directed toward the light reflection section 70 of the diffusion member 40. The light reflection section 70 tends to transmit light LP3 that is significantly inclined with respect to the stacking direction D3, and reflect the other light LP2. In the region including the position directly facing the light source 22 and its surroundings, that is, the region directly above the light source 22, a large amount of light tends to travel in a direction that is not significantly inclined with respect to the stacking direction D3. However, the light reflection section 70 can effectively suppress the transmission of a large amount of light with a small incident angle through the light reflection section 70.

[0222] As shown in Figure 35, the light LP2 reflected by the light reflecting section 70 diffuses and passes through the light diffusing section 50 again, and proceeds in a direction that is even more inclined with respect to the stacking direction D3. The light LP4 that has diffused and passed through the light diffusing section 50 twice proceeds in a direction perpendicular to the stacking direction D3 and moves away from the light source 22. Subsequently, the light LP4 is reflected by the support substrate 25 that supports the light source 22. The light LP5 reflected by the support substrate 25 proceeds to move even further away from the light source 22 in a direction perpendicular to the stacking direction D3, and then proceeds towards the diffusion member 40 again in the stacking direction D3.

[0223] As shown in Figure 36, the light LP5 that returns to the diffusion member 40 is diffused and transmitted through the light diffusion section 50. Much of the light LP6 diffused in the light diffusion section 50 then returns to the light reflection section 70. Light LP6 with a large angle of incidence to the light reflection section 70 is transmitted through the light reflection section 70. On the other hand, light with a small angle of incidence to the light reflection section 70 is reflected again by the light reflection section 70.

[0224] The optical process up to the point of transmission through the light-reflecting section 70, as described above, is the same as the optical process described in the first specific example above with reference to Figures 25 to 28. That is, the combination of the light-diffusing transmittance of the light-diffusing section 50 and the light-reflectance of the light-reflecting section 70 allows the light emitted from the light source 22 to be effectively spread in directions D1 and D2 perpendicular to the stacking direction D3 without being greatly constrained by the light distribution characteristics of the light source 22. This effectively eliminates brightness unevenness caused by the presence of the light source 22, that is, it effectively makes the image of the light source 22 less conspicuous. Due to the light-diffusing properties of the diffusion member 40, it is also possible to significantly reduce the thickness of the surface light source device 20. As a result, while reducing the thickness of the surface light source device 20, it is possible to effectively equalize the illuminance at each position on the surface on the light-emitting side of the light-reflecting section 70, that is, to effectively equalize the in-plane distribution of illuminance.

[0225] Next, the light LP3 and LP6 that have passed through the light-reflecting portion 70 are incident on the optical element portion 110 of the diffusion member 40. As shown in Figure 37, the optical element portion 110 has an uneven surface 112 on the light-emitting side that is spaced away from the light source 22 in the stacking direction D3. A portion L371 of the incident light L371 on the optical element portion 110 is reflected by the uneven surface 112. The reflected light L371 from the uneven surface 112 folds back in the direction of travel in the stacking direction D3 and heads towards the light source 22 in the stacking direction D3. This reflected light L371 passes through the light-reflecting portion 70 and diffuses through the light-diffusing portion 50 and is reflected by the support substrate 25. The reflected light from the support substrate 25 can be re-incident to the diffusion member 40 at a position spaced away from the light source 22 in a direction perpendicular to the stacking direction D3, similar to the reflected light LP2 described above. Therefore, reflection at the optical element 110 effectively spreads the light emitted from the light source 22 in a direction perpendicular to the stacking direction D3. This ensures sufficient brightness in areas far from the light source 22, where brightness tends to be insufficient. In other words, reflection at the optical element 110 reinforces the reflection characteristics of the light reflecting section 70, further promoting the uniformity of the in-plane distribution of illuminance.

[0226] Another portion L372 of the light incident on the optical element 110 passes through the uneven surface 112. The light L372 is emitted from the light-emitting side surface 40b of the diffusion member 40 formed by the uneven surface 112 of the optical element 110.

[0227] As described above, the unevenness in brightness caused by the presence of the light source 22 can be effectively eliminated, and the illuminance on the light-emitting surface 20a can be effectively made uniform. In particular, by reinforcing the reflection characteristics of the light-reflecting part 70 with the optical element part 110, the surface light source device 20 can be made thinner while guiding light in a direction perpendicular to the stacking direction D3. As a result, the illuminance at each position on the light-emitting side surface 40b of the diffusion member 40 can be effectively made uniform, that is, the in-plane distribution of illuminance can be effectively made uniform, while the surface light source device 20 can be made thinner.

[0228] Here, with reference to Figure 37, the optical function of the optical element 110 will be described in more detail. As shown in Figure 37, the optical element 110 according to this embodiment has an uneven surface 112 on the side opposite to the light reflecting portion 70. As shown in Figure 37, the light L371 and L372 traveling through the optical element 110 travel in a direction that is significantly inclined with respect to the stacking direction D3, due to the optical properties of the light reflecting portion 70. In the cross-section of the optical element 110 along the stacking direction D3, the uneven surface 112 includes an element surface 127A that is inclined on the same side as the direction of light propagation with respect to the stacking direction D3, and an element surface 127B that is inclined on the opposite side as to the direction of light propagation with respect to the stacking direction D3. As shown in Figure 37, the incident angle θx of the light L371 incident on this element surface 127A is greater than the incident angle θy of the light L371 incident on a flat surface perpendicular to the stacking direction D3. Therefore, light L371 is more easily reflected on the same-side element surface 127A. In this way, because the optical element portion 110 has an uneven surface 112 on the side opposite to the light-reflecting portion 70 in the stacking direction D3, it can reflect a portion of the light that has passed through the light-reflecting portion 70, thereby reinforcing the optical properties of the light-reflecting portion 70. This effectively equalizes the illuminance at each position on the light-emitting side surface 40b of the diffusion member 40, that is, it effectively equalizes the in-plane distribution of illuminance.

[0229] Furthermore, from the viewpoint of promoting uniformity of the in-plane distribution of illuminance, it is preferable that the reflection at the uneven surface 112 is total internal reflection. Considering the refractive index of transparent resin materials widely used in optical applications, total internal reflection is more likely to occur when the incident angle of light L371 on the element surface 127 becomes as large as approximately 40°. Taking into account the reflection and transmission characteristics of the light reflection portion 70, the inclination angle θb of the normal direction NDA of the element surface 127 with respect to the stacking direction D3 is preferably 25° or less, more preferably 20° or less, and even more preferably 15° or less. By adjusting the inclination angle θb of the element surface 127 to this range, the illuminance at each position on the light-emitting side surface 40b of the diffusion member 40 can be made more uniform.

[0230] Furthermore, as the inclination angle θb increases, it becomes more difficult for light to enter the ipsilateral element surface 127A that causes reflection. From this point of view, the inclination angle θb that the normal direction NDA of the element surface 127 makes with respect to the stacking direction D3 is preferably 25° or less, more preferably 20° or less, and even more preferably 15° or less. By adjusting the inclination angle θb of the element surface 127 to this range, the illuminance at each position on the light-emitting side surface 40b of the diffusion member 40 can be made more uniform.

[0231] In the example shown in Figure 37, the unit optical element 126 is a convex portion 128. In the unit optical element 126 as a convex portion 128, most of the area of ​​the element surface 127 is located on the light-reflecting portion 70 side in the stacking direction D3. Therefore, light traveling through the optical element portion 110 is more likely to be incident not only on the opposite side element surface 127B as described above, but also on the same side element surface 127A as described above. As a result, with the optical element portion 110 having the unit optical element 126 as a convex portion 128, reflection in the optical element portion 110 is promoted, and the illuminance at each position on the light-emitting side surface 40b of the diffusion member 40 can be made even more uniform.

[0232] By setting a lower limit for the inclination angle θb, it becomes difficult for light traveling within the optical element section 110 that travels in a direction significantly inclined with respect to the stacking direction D3 to be incident on the aforementioned ipsilateral element surface 127A. Therefore, by setting a lower limit for the inclination angle θb, the uneven surface 112 exhibits selective reflection characteristics, selectively reflecting light traveling within the optical element section 110 that travels in a direction with a relatively small inclination angle with respect to the stacking direction D3. As a result, the reflection by the optical element section 110 can reinforce the reflection and transmission characteristics of the light reflecting section 70. That is, light incident on the optical element section 110 travels in a direction significantly inclined with respect to the stacking direction D3 due to the optical characteristics of the light reflecting section 70. The optical element section 110 then selectively reflects light traveling within the light reflecting section 70 that travels in a direction with a relatively small inclination angle with respect to the stacking direction D3. Conversely, the optical element section 110 selectively transmits light traveling within the light reflecting section 70 that travels in a direction with a relatively large inclination angle with respect to the stacking direction D3. This makes it possible to further uniformize the illuminance at each position on the light-emitting side surface 40b of the diffusion member 40. From this viewpoint, the inclination angle θb that the normal direction NDA of the element surface 127 makes with respect to the stacking direction D3 is preferably 3° or more, more preferably 5° or more, and even more preferably 8° or more.

[0233] In a combination with an optical element section 110 that includes a second uneven surface 112 having an inclination angle θb having the upper limit described above, the first uneven surface 52 of the light diffusion section 50 may include a first element surface 67 having a normal direction ND inclined at an inclination angle θa of 25° or less with respect to the stacking direction D3. Through diligent experiments conducted by the Discloser, it has been found that the inclination angle θa of the normal direction ND of the first element surface 67 with respect to the stacking direction D3 is preferably 25° or less, more preferably 20° or less, and even more preferably 15° or less. Furthermore, this inclination angle θa is preferably 3° or more, more preferably 5° or more, and even more preferably 8° or more. By combining a light diffusion section 50 having such a first element surface 67 with a light diffusion section 50 having a second element surface 127 with an inclination angle θb of 25° or less described above, the illuminance at each position on the light-emitting side surface 40b of the diffusion member 40 can be made even more uniform.

[0234] As shown in Figure 37, when light L372 passes through the opposite element surface 127B described above, it is refracted at the opposite element surface 127B. The emission angle θz of this light L372 is smaller than the emission angle θw of light L372X assuming that it is emitted by passing through a flat surface perpendicular to the stacking direction D3. In other words, the uneven surface 112 of the optical element part 110 exhibits a light-gathering function for emitted light. The light-gathering function of the optical element part 110 reduces the burden of optical path correction for light transmitted through the diffusion member 40. As a result, the utilization efficiency of light transmitted through the diffusion member 40 can be improved. In addition, the number and thickness of components incorporated into the surface light source device 20 can be reduced, which can contribute to making the surface light source device 20 thinner.

[0235] In the second specific example of the embodiment described above, the diffusion member 40 comprises, in this order, a light diffusion section 50 having light transmittance and light diffusion properties, a light reflection section 70 whose transmittance for light of a specific wavelength incident at an incident angle of 0° is lower than the transmittance for light of a specific wavelength incident at a certain incident angle greater than 0°, and an optical element section 110 having an uneven surface 112 on the opposite side from the light reflection section 70. When the diffusion member 40 according to this embodiment is applied to a surface light source device, the combination of the light transmittance and light diffusion properties of the light diffusion section 50 and the reflection properties of the light reflection section 70 effectively spreads the light emitted from the light source 22 in a direction perpendicular to the stacking direction D3. In addition, the uneven surface 112 of the optical element section 110 reinforces the reflection properties of the light reflection section 70, thereby effectively spreading the light in a direction perpendicular to the stacking direction D3. As a result, while making the surface light source device thinner, it is possible to effectively eliminate brightness unevenness caused by the presence of the light source 22, that is, to effectively make the image of the light source 22 less conspicuous. As a result, while making the surface light source device 20 thinner, the illuminance at each position on the light-emitting side surface 40b of the diffusion member 40, which is the light-emitting side, can be effectively made uniform, that is, the in-plane distribution of illuminance can be effectively made uniform.

[0236] In the above, one embodiment has been described with reference to specific examples, but these examples do not limit the embodiment. The above-described embodiment may be implemented in various other examples, and various omissions, substitutions, modifications, and additions can be made without departing from its essence.

[0237] An example of modification will be described below with reference to the drawings. In the following description and the drawings used therein, parts that can be configured in the same way as in the specific example described above will be given the same reference numerals as those used for the corresponding parts in the specific example described above, and redundant explanations will be omitted.

[0238] As shown by the dashed line in Figure 2, the surface light source device 20 may have other components in addition to the light source 22, support substrate 25, and diffusion member 40. Examples of other components added to the surface light source device 20 include a wavelength conversion sheet 76, a light diffusion sheet 77, and a reflective polarizer 78. The wavelength conversion sheet 76, for example, has a phosphor and absorbs light from the light source 22, emitting light with a different wavelength than the absorbed light. For example, the light source 22 may emit blue light, and the wavelength conversion sheet 76 may convert a portion of the blue light into red and green light. In this example, the reflection characteristics of the light reflection section 70 only need to be adjusted for light in a limited wavelength range. Therefore, the surface light source device 20 can generate white planar light while providing the light reflection section 70 with ideal reflection characteristics corresponding to the diffusion transmission characteristics of the light diffusion section 50. The light diffusion sheet 77 can smoothly change the angular distribution of radiant intensity on the light-emitting surface 20a of the surface light source device 20. The reflective polarizer 78 transmits only linearly polarized light usable by the display panel 15 and reflects linearly polarized light unusable by the display panel 15. The polarization component of the light reflected by the reflective polarizer can be changed to a polarization component usable by the display panel 15 through reflection in the subsequent optical path.

[0239] Further, as shown in FIG. 38, the diffusion member 40 may further have a thermoplastic resin layer 80 located on the side opposite to the light reflection portion 70 of the light diffusion portion 50 in the stacking direction D3. By providing the thermoplastic resin layer 80, the relative positions of the support substrate 25 that supports the light source 22 and the diffusion member 40 in the stacking direction D3 can be positioned. The thermoplastic resin layer 80 functions as a spacer. Also, the thermoplastic resin layer 80 may be joined to at least one of the support substrate 25 and the diffusion member 40. In this case, the thermoplastic resin layer 80 can function as a sealing material that covers and protects the light source 22, and can effectively stabilize the relative positional relationship between the support substrate 25 and the diffusion member 40 in the stacking direction D3.

[0240] As the material of the thermoplastic resin layer 80, for example, a thermoplastic resin such as an olefin-based resin having light transmissivity may be used for production. Further, the thermoplastic resin layer 80 may include a base material made of a thermoplastic resin and diffusion particles dispersed in the base material. In this example, the diffusion member 40 also has light diffusing properties in the thermoplastic resin layer 80. Furthermore, when the thermoplastic resin layer 80 has diffusing properties and functions as the light diffusion portion 50, the diffusion member 40 may have this thermoplastic resin layer 80, the light reflection portion 70, and the optical element portion 110.

[0241] Furthermore, as shown in FIG. 39, the thermoplastic resin layer 80 may be provided with a concave portion 80a on the side facing the support substrate 25. According to the example shown in FIG. 39, the light L291 emitted from the light source 22 is refracted at the interface between the gap V located between the thermoplastic resin layer 80 and the light source 22 and the thermoplastic resin layer 80. Thereby, the light L281 from the light source 22 can be effectively diffused, and the in-plane distribution of the illuminance can be effectively made more uniform. By adjusting the shape of the concave portion 80a, it is also possible to more effectively diffuse the light from the light source 22.

[0242] Furthermore, as shown in Figure 40, the thermoplastic resin layer 80 may include a resin main portion 83 made of thermoplastic resin and low refractive index particles 84 having a refractive index lower than that of the material constituting the light diffusion portion 50. In this example, the light diffusion portion 50 is in contact with the low refractive index particles 84 protruding from the resin main portion 83 and is supported in the lamination direction D3 by the low refractive index particles 84. According to this specific example, the refractive index of the thermoplastic resin layer 80 can be sufficiently reduced to that of the light diffusion portion 50. As described above, the light diffusion portion 50 may exhibit light diffusion properties through the uneven surface 52 formed on its surface. Such a light diffusion portion 50 can exhibit sufficient light diffusion properties by utilizing reflection and refraction at the interface with the thermoplastic resin layer 80 by being adjacent to an air gap V or a thermoplastic resin layer 80 having a sufficiently low refractive index. In this example, the resin main portion 83 may be made using a thermoplastic resin such as an olefin resin. Also, as the low refractive index particles 84, particles such as silica, alumina, lanthanum fluoride, magnesium fluoride, and sodium aluminum hexafluoride may be used.

[0243] Furthermore, in the example shown in Figure 40, the thermoplastic resin layer 80 may include a first layer 81 spaced apart from the light-diffusing portion 50 in the lamination direction D3, and a second layer 82 located between the first layer 81 and the light-diffusing portion 50 in the lamination direction D3. The low refractive index particles 84 may be included only in the second layer 82 of the two layers 82. According to this example, the refractive index can be reduced only in the second layer 82 of the thermoplastic resin layer 80 that forms an interface with the light-diffusing portion 50. Therefore, the amount of low refractive index particles 84 used can be reduced, making it easier to manufacture the diffusion member 40 and lowering manufacturing costs. In particular, in the example shown in Figure 40, the thickness DR2 of the second layer 82 is thinner than the thickness DR1 of the first layer 81. According to this example, the amount of low refractive index particles 84 used can be effectively reduced, making it easier to manufacture the diffusion member 40 and further lowering manufacturing costs.

[0244] Furthermore, as shown in Figure 41, the surface light source device 20 may also have beads 37 positioned between the support substrate 25 and the diffusion member 40, and a binder 38 that fixes the beads 37 to the support substrate 25. In this example, the light diffusion portion 50 is in contact with the beads 37 and is supported by the beads 37 in the stacking direction D3. In the example shown in Figure 41, the light diffusion portion 50 of the diffusion member 40 can form an interface with the air layer V. As a result, due to the large refractive index difference between the light diffusion portion 50 and the air layer V, the light diffusion portion 50 can fully exhibit light diffusion properties due to reflection and refraction.

[0245] Furthermore, as shown in Figure 42, the surface light source device 20 may have a void-forming layer 36 located between the support substrate 25 and the light diffusion section 50. The void-forming layer 36 has a plurality of voids V. The void-forming layer 36 may be a resin film patterned in a mesh pattern, or a three-dimensional mesh-like member formed from fibrous resin. In this example, it is preferable that the void-forming layer 36 has light transmittance. Alternatively, a porous material with a high porosity may be used as the void-forming layer 36. In this example, the light diffusion section 50 is in contact with the void-forming layer 36 and is supported by the void-forming layer 36 in the stacking direction D3. According to the example shown in Figure 42, the light diffusion section 50 of the diffusion member 40 can form an interface with the voids V of the void-forming layer 36. As a result, due to the large refractive index difference between the light diffusion section 50 and the voids V, the light diffusion section 50 can fully exhibit light diffusion properties due to reflection and refraction.

[0246] The light-diffusing portion 50 of the diffusion member 40 described above may have an uneven surface 52 in order to exhibit light-diffusing properties. The light-diffusing portion 50 may be manufactured, for example, by molding using an ionizing radiation-curable resin, as shown in Figure 43. An example of a method for manufacturing the light-diffusing portion 50 will be described below.

[0247] As shown in Figure 43, the wound substrate 90 is unwound and transported by the guide roll 101 to a position facing the mold 100. Then, the resin composition 91 is supplied between the mold 100 and the substrate 90. The resin composition 91 contains an uncured ionizing radiation-curable resin. Next, using the exposure apparatus 102, the resin composition 91 located between the mold 100 and the substrate 90 is irradiated with ionizing radiation, such as ultraviolet light or an electron beam, to cure the resin composition 91. After that, guided by the guide roll 101, the light-diffusing portion 50, which is made of the cured resin composition 91 and laminated with the substrate 90, is peeled off from the mold 100. In this way, as shown in Figure 43, an optical sheet 55 having a substrate 90 and a light-diffusing portion 50 formed on the substrate 90 is obtained. According to this manufacturing method, a diffractive optical element 60 or a microlens 65 having the above-mentioned uneven surface 52 can be manufactured as the light-diffusing portion 50.

[0248] In the manufacturing method shown in Figure 43, the light-diffusing sections 50 are continuously produced by roll-to-roll molding. However, the method is not limited to this example, and the light-diffusing sections 50 may also be produced by molding a single sheet.

[0249] The optical element portion 110 of the diffusion member 40 has a second uneven surface 112. The optical element portion 110 having the second uneven surface 112 may be manufactured in the same manner as the light diffusion portion 50 having the first uneven surface 52. Referring to Figure 43, by forming the optical element portion 110 made of a cured resin composition 91 on the substrate 90 using the above-described manufacturing method, an optical sheet 115 having the substrate 90 and the optical element portion 110 formed on the substrate 90 is obtained. According to this manufacturing method, a microlens 125 having a second uneven surface 112 formed by the element surface 127 of the unit optical element 126 described above can be manufactured as the optical element portion 110.

[0250] The diffusion member 40 may be made using the optical sheet 55 shown in Figure 43. The base material 90 used for the optical sheet 55 is not particularly limited, and a wide range of sheet-like materials may be used. From the viewpoint of adhesion with the light diffusion part 50, a resin film may be used as the base material 90. If the base material 90 is used as is as part of the diffusion member 40, a material with light transmittance may be used for the base material 90.

[0251] Furthermore, as the base material 90, a light-reflecting portion 70, such as a dielectric multilayer film, can be used. Preferably, the dielectric multilayer film is a relatively flexible multilayer film of resin layers. In this case, as shown in Figure 44, the light-diffusing portion 50 included in the diffusion member 40 has an uneven surface 52 facing the opposite direction from the light-reflecting portion 70 in the lamination direction D3 and is joined to the light-reflecting portion 70. Since the light-diffusing portion 50 and the light-reflecting portion 70 are joined in this diffusion member 40, the handling of the diffusion member 40 is improved. Therefore, assembly of the diffusion member 40 to the surface light source device 20 can be facilitated. Also, since the light-diffusing portion 50 and the light-reflecting portion 70 are joined, the surface light source device 20 can be stably installed.

[0252] Similarly, the light-reflecting portion 70, for example, a dielectric multilayer film, may be used as the substrate 90, and the optical element portion 110 may be fabricated on this substrate 90. In this case, as shown in Figures 31A to 32, the optical element portion 110 included in the diffusion member 40 has an uneven surface 112 facing the opposite direction from the light-reflecting portion 70 in the stacking direction D3, and is joined to the light-reflecting portion 70. In this diffusion member 40, the light-reflecting portion 70 and the optical element portion 110 are joined, improving the handling of the diffusion member 40. Therefore, assembly of the diffusion member 40 to the surface light source device 20 can be facilitated. In addition, since the light-reflecting portion 70 and the optical element portion 110 are joined, the surface light source device 20 can be stably installed.

[0253] Furthermore, the light-reflecting portion 70 may be used as the base material 90, and a light-diffusing portion 50 may be formed on one side of the base material 90 by the manufacturing method described with reference to Figure 43, and an optical element portion 110 may be formed on the other side of the base material 90 by the manufacturing method described with reference to Figure 43. The light-diffusing portion 50 and the optical element portion 110 may be manufactured in any order. According to this example, as shown in Figure 30, a diffusion member 40 is obtained in which the light-diffusing portion 50, the light-reflecting portion 70 and the optical element portion 110 are stacked in this order in the stacking direction D3 and joined to each other. In this diffusion member 40, since the light-diffusing portion 50, the light-reflecting portion 70 and the optical element portion 110 are joined, the handling of the diffusion member 40 is improved. Therefore, assembly of the diffusion member 40 to the surface light source device 20 can be made easier. In addition, since the light-diffusing portion 50, the light-reflecting portion 70 and the optical element portion 110 are joined, the surface light source device 20 can be stably installed.

[0254] As shown in Figure 45, the light-diffusing portion 50 can be manufactured by embossing. In the manufacturing method shown in Figure 45, first, a substrate 90 including at least a thermoplastic resin layer as a molded surface is placed on a support base 106. Next, a heated mold 105 is pressed onto the substrate 90 to transfer the irregularities of the mold 105 to the substrate 90. Then, by separating the mold 105 from the molded substrate 90, an optical sheet 55 as a light-diffusing portion 50 is obtained, consisting of the substrate 90 onto which the shape of the mold 105 has been transferred. Similarly, by using embossing, an optical element portion 110 consisting of the substrate 90 onto which the shape of the mold 105 has been transferred may be manufactured as an optical sheet 115.

[0255] Furthermore, when the light diffusion portion 50 and the optical element portion 110 are manufactured by the embossing process shown in Figure 45, a dielectric multilayer film having a thermoplastic resin layer as the outermost layer can also be used as the base material 90. For example, as shown in Figure 46, the light diffusion portion 50 included in the diffusion member 40 may be formed as the uneven surface 52 that forms the surface of the light reflection portion 70. Similarly, as shown in Figures 31A to 32, the optical element portion 110 included in the diffusion member 40 may be formed as the uneven surface 112 that forms the surface of the light reflection portion 70. Moreover, the light reflection portion 70 may be used as the base material 90, the light diffusion portion 50 may be formed on one side of the base material 90 by the embossing process shown in Figure 45, and the optical element portion 110 may be formed on the other side of the base material 90 by the embossing process shown in Figure 45. The light diffusion portion 50 and the optical element portion 110 may be manufactured in any order. As a result, a light-diffusing portion 50 is formed on one surface of the light-reflecting portion 70, and an optical element portion 110 is formed on the other surface of the light-reflecting portion 70. In the diffusion member 40 obtained in this way, the outermost layer of the light-reflecting portion 70 and at least one of the light-diffusing portion 50 and the optical element portion 110 are integrally molded. With such a diffusion member 40, the diffusion member 40 and the surface light source device 20 can be made thinner. With this diffusion member 40, the light-reflecting portion 70 and at least one of the light-diffusing portion 50 and the optical element portion 110 can be integrally molded without seams. As a result, the surface light source device 20 can be stably installed.

[0256] According to the manufacturing method described with reference to Figures 43 and 45, the light-diffusing portion 50 can also be manufactured as a separate optical sheet 55 from the light-reflecting portion 70. Furthermore, by performing the manufacturing method described with reference to Figures 43 and 45 twice, an optical sheet 55 can be manufactured in which uneven surfaces 52 are formed on both sides of a pair of main surfaces. The resulting optical sheet 55 can then be used to manufacture the diffusion member 40 shown in Figures 47 to 49. In the example shown in Figure 47, the light-diffusing portion 50 includes an optical sheet 55 having an uneven surface 52 with light-diffusing properties on the side of the light-reflecting portion 70 in the stacking direction D3. In the example shown in Figure 48, the light-diffusing portion 50 includes an optical sheet 55 having an uneven surface 52 with light-diffusing properties on the side opposite to the light-reflecting portion 70 in the stacking direction D3. In the example shown in Figure 49, the light-diffusing portion 50 includes an optical sheet 55 having an uneven surface 52 with light-diffusing properties on both sides in the stacking direction D3. Furthermore, the light diffusion section 50 may include a plurality of optical sheets 55. The plurality of optical sheets 55 may have different configurations or may have the same configuration. According to these specific examples, by appropriately adjusting the combination of the optical sheets 55 constituting the light diffusion section 50 and the light reflection section 70, the in-plane distribution of illuminance can be effectively made uniform while making the surface light source device 20 thinner.

[0257] Similarly, the optical element portion 110 can be manufactured as an optical sheet 115 separate from the light-reflecting portion 70. Similar to the optical sheet 55 described with reference to Figures 47 to 49, by appropriately combining the optical sheet 115 constituting the optical element portion 110 with the light-reflecting portion 70, the in-plane distribution of illuminance can be effectively made uniform while thinning the surface light source device 20. As an example, as shown in Figure 50, the optical element portion 110 may include an optical sheet 115 having an uneven surface 112 on the side opposite to the light-reflecting portion 70 in the stacking direction D3.

[0258] Furthermore, the diffusion member 40 having the layered structure shown in Figures 44, 46 to 49 may also include a thermoplastic resin layer 80, as indicated by the dashed line. This thermoplastic resin layer 80 may be bonded to the light diffusion portion 50, may be in contact with the light diffusion portion 50 without being bonded to it, or may be spaced apart from the light diffusion portion 50 in the lamination direction D3.

[0259] Furthermore, when the light diffusion section 50 is manufactured by embossing as shown in Figure 45, a substrate having a thermoplastic resin layer as the outermost layer can also be used as the base material. In this case, as shown in Figure 51, the light diffusion section 50 includes a thermoplastic resin layer 80 having a light-diffusing uneven surface 52 on the light-reflecting section 70 side in the stacking direction D3. In this example as well, by appropriately adjusting the combination of the optical sheet 55 and the light-reflecting section 70 that constitute the light diffusion section 50, taking into consideration the arrangement of the light source 22 and the positional relationship between the light source 22 and the diffusion member 40, the in-plane distribution of illuminance can be effectively made uniform while making the surface light source device 20 thinner. In addition, the thermoplastic resin layer 80 can be bonded to the support substrate 25 that supports the light source 22. This allows the light source 22 to be protected using the thermoplastic resin layer 80, which also functions as the light diffusion section 50. Furthermore, the relative positional relationship between the support substrate 25 and the uneven surface 52 and light-reflecting section 70 of the light diffusion section 50 of the diffusion member 40 can be effectively stabilized in the stacking direction D3.

[0260] In the diffusion member 40 shown in Figures 47 to 49 and Figure 51, the light-reflecting portion 70 and the light-diffusing portion 50 may be joined by adhesive or other means, or they may simply be in contact and not joined. Furthermore, the light-reflecting portion 70 and the light-diffusing portion 50 may be held by a housing or the like so that a gap is formed between them.

[0261] Similarly, in the diffusion member 40 shown in Figure 50, the light-reflecting portion 70 and the optical element portion 110 may be joined by adhesive or other means, or they may simply be in contact and not joined. Furthermore, the relative positions of the light-reflecting portion 70 and the optical element portion 110 may be maintained by being held by a housing or the like.

[0262] Gaps may be provided on both sides of the light diffusion portion 50 in the stacking direction D3. In this example, total internal reflection at the surface of the optical sheet 55 forming the light diffusion portion 50 makes it possible to guide light within the light diffusion portion 50 in directions perpendicular to the stacking direction D3, for example, the first direction D1 or the second direction D2. That is, light can be guided in directions perpendicular to the stacking direction D3 by total internal reflection without reflection loss. As a result, the in-plane distribution of illuminance can be effectively made uniform while using the light from the light source 22 with high utilization efficiency.

[0263] Furthermore, when forming a light-diffusing section 50 having a highly detailed uneven surface 52, it can be difficult to enlarge the molds 100 and 105. In this case, as shown in Figure 52, the light-diffusing section 50 may have a plurality of elemental diffusers 51 arranged in a direction perpendicular to the stacking direction D3. That is, the light-diffusing section 50 may be formed by a plurality of elemental diffusers 51 arranged on a surface. In this example, each elemental diffuser 51 may be an optical sheet 55 obtained by the molding shown in Figures 43 and 45. As shown in Figure 53, the side end faces 51a of the elemental diffusers 51 may be colored with a dark color such as black or brown. In this example, the light-diffusing section 50 can be made larger in area by arranging the elemental diffusers 51 on a surface. Also, since the side end faces 51a of the elemental diffusers 51 are colored with a dark color, the boundary B between two adjacent elemental diffusers 51 can be effectively made less noticeable.

[0264] Furthermore, as another example, as shown in Figure 54, at least a portion of the boundary B between two adjacent element diffusion sections 51 may include a curve when observed from the stacking direction D3. In such an example, by making at least a portion of the boundary B between two adjacent element diffusion sections 51 a non-linear curve when observed from the stacking direction D3, the boundary B can be made less conspicuous. In particular, in the example shown in Figure 54, the entire length of the boundary B between two adjacent element diffusion sections 51 is curved. That is, while enabling the light diffusion section 50 to be made larger in area by tiling the element diffusion sections 51, the boundary B of the element diffusion sections 51 can be effectively made less conspicuous.

[0265] Furthermore, the configuration of the light diffusion section 50 described with reference to Figures 52 to 54 may also be applied to the optical element section 110. That is, the optical element section 110 may have a plurality of elemental optical sections 111 arranged in a direction perpendicular to the stacking direction D3. The optical element section 110 may be formed by a plurality of elemental optical sections 111 arranged on a grid. In this example, each elemental optical section 111 may be an optical sheet 115 obtained by molding as shown in Figures 43 and 45. As shown in Figure 53, the side end faces 111a of the elemental optical sections 111 may be colored with a dark color such as black or brown. In such an example, the optical element section 110 can be made larger in area by arranging the elemental optical sections 111 on a grid. Also, as shown in Figure 53, since the side end faces 111a of the elemental optical sections 111 are colored with a dark color, the boundary BX between two adjacent elemental optical sections 111 can be effectively made less noticeable.

[0266] As shown in Figure 54, at least a portion of the boundary BX between two adjacent optical element sections 111 may include a curve when observed from the stacking direction D3. In such an example, by making at least a portion of the boundary BX between two adjacent optical element sections 111 a non-linear curve when observed from the stacking direction D3, the boundary BX can be made less conspicuous. In particular, in the example shown in Figure 54, the entire length of the boundary BX between two adjacent optical element sections 111 is curved. That is, while enabling the optical element section 110 to be made larger in area by tiling the optical element sections 111, the boundary BX of the optical element sections 111 can be effectively made less conspicuous.

[0267] As shown in Figure 55, the light diffusion portion 50 may have a diffusion body portion 53 including an uneven surface 53a, and a reflective coating portion 54 that covers the uneven surface 53a while maintaining the unevenness of the uneven surface 53a and forms a reflective surface. The reflective coating portion 54 extends thinly along the uneven surface 53a of the diffusion body portion 53. In the illustrated example, the surface of the reflective coating portion 54 forms the uneven surface 52 of the light diffusion portion 50. The reflective coating portion 54 is, for example, a thin film of metal, and like a half mirror, transmits some of the incident light L551 (light L552) and reflects some of the incident light L551 (light L553). According to this specific example, the in-plane distribution of illuminance can be made more effectively uniform by the diffusion caused by the configuration of the diffusion body portion 53 and the diffusion caused by the reflection on the reflective surface formed by the reflective coating portion 54.

[0268] Furthermore, referring to Figure 32, an example is shown in which the optical element section 110 includes linear unit optical elements 126 arranged in one direction. The light diffusion section 50 may also include linear unit optical elements 66 arranged in one direction. The one-dimensionally arranged plurality of unit optical elements 66 of the light diffusion section 50 can be configured in the same way as the one-dimensionally arranged plurality of unit optical elements 126 of the optical element section 110 described above. In addition, the arrangement direction of the plurality of unit optical elements 66 included in the light diffusion section 50 may be parallel, non-parallel, inclined, or perpendicular to the arrangement direction of the plurality of unit optical elements 126 included in the optical element section 110. [Examples]

[0269] The above-described embodiment will be explained in more detail below using examples, but the above-described embodiment is not limited to this embodiment.

[0270] The surface light source devices of Examples 1 to 6 and Comparative Example 1 were manufactured as follows.

[0271] <Example 1> The surface light source device of Example 1 had the configuration shown in Figure 2. In addition to the light source, support substrate, and diffusion member, the surface light source device of Example 1 also had a wavelength conversion sheet, a light diffusion sheet, and a reflective polarizer. The support substrate had a white reflective layer containing titanium oxide. The reflection at the reflective layer of the support substrate was diffuse reflection with a reflectance of 95%. The light sources were arranged in a square arrangement on the support substrate as shown in Figure 3. The arrangement pitch of the light sources in the first direction was 6 mm. The arrangement pitch of the light sources in the second direction perpendicular to the first direction was 6 mm. As each light source, a light-emitting diode emitting blue light with a central wavelength of 450 nm was used. The planar shape of this light-emitting diode was a rectangle of 0.2 mm × 0.4 mm. The light-emitting diodes were placed on the support substrate 25 so that their sides were aligned with the first and second directions.

[0272] In the surface light source device of Example 1, the diffusion member, as shown in Figure 2, had a light diffusion section, a light reflection section, and an optical element section in this order from the light source side in the stacking direction D3. A dielectric multilayer film obtained from Toray Industries, Inc. was used as the light reflection section. This light reflection section had the transmission characteristics shown in Figures 19 and 20 for 450 nm light. The optical element section was molded on one surface of this light reflection section. Subsequently, the light diffusion section was molded on the other surface of the light reflection section. The optical element section and the light diffusion section were molded by supplying an uncured UV-curable resin composition between the mold and the light reflection section and curing it between the mold and the light reflection section, as explained with reference to Figure 43. As a result, a diffusion member was obtained in which the light diffusion section, the light reflection section, and the optical element section were joined in this order in the stacking direction. Note that the manufacturing of the diffusion member of Example 1 differed from the roll-to-roll manufacturing method shown in Figure 43, and was manufactured in a single-sheet form.

[0273] The optical element portion of the diffusing member was located on the opposite side of the light source from the light reflecting portion. The optical element portion had a sheet-like base portion joined to the light reflecting portion and second unit optical elements as convex portions arranged on the base portion. The optical element portion had second unit optical elements having the shape and arrangement described with reference to Figures 16A and 16B. As shown in Figure 16A, second unit optical elements of the same shape were arranged without gaps on the surface of the base portion, with the orientation of the base surface varied in four ways. Each second unit optical element had a triangular pyramidal shape and three second element surfaces. A second microlens was formed as a collection of the second element surfaces of the second unit optical elements. The base surface of the second unit optical element was a right-angled isosceles triangle shape. The element surfaces of the second unit optical element include equilateral element surfaces extending from the equilateral sides of the right-angled isosceles triangle shape forming the base surface, and base element surfaces extending from the base of the right-angled isosceles triangle shape forming the base surface. The lengths of the two equal sides of the right-angled isosceles triangle forming the base were set to 0.1 mm each. The inclination angle θb of the normal direction NDA to each equal-side element face with respect to the stacking direction D3 was set to 16.5°. The inclination angle θb of the normal direction NDA to the base element face with respect to the stacking direction D3 was set to 16.5°.

[0274] The light-diffusing portion of the diffusing member was located on the light source side of the light-reflecting portion. The light-diffusing portion had a sheet-like main body portion joined to the light-reflecting portion and first unit optical elements as recesses arranged on the main body portion. The light-diffusing portion had first unit optical elements having the shape and arrangement described with reference to Figures 16A and 16B. As shown in Figure 16A, first unit optical elements of the same shape were arranged without gaps on the surface of the main body portion, with the orientation of the base surface varied in four ways. Each first unit optical element had a triangular pyramidal shape and three first element surfaces. A first microlens was formed as a collection of the first element surfaces of the first unit optical elements. The base surface of the first unit optical element was a right-angled isosceles triangle shape. The element surfaces of the second unit optical element included equilateral element surfaces extending from the equilateral sides of the right-angled isosceles triangle shape forming the base surface, and base element surfaces extending from the base of the right-angled isosceles triangle shape forming the base surface. The lengths of the two equal sides of the right-angled isosceles triangle forming the base were set to 0.1 mm each. The inclination angle θb of the normal direction ND to each equal-side element surface with respect to the stacking direction D3 was set to 16.5°. The inclination angle θb of the normal direction ND to the base element surface with respect to the stacking direction D3 was also set to 16.5°. As a result, the first uneven surface of the light diffusion section was constructed identically to the second uneven surface of the optical element section, except that the unevenness was reversed.

[0275] As a wavelength conversion sheet, QF-6000, available from Showa Denko Materials, was used. As light diffusion sheets, two BEF® luminance-enhancing films, available from 3M, were used. For one BEF film, the longitudinal direction of the prism extended in the first direction. For the other BEF film, the longitudinal direction of the prism extended in the second direction. As a reflective polarizer, DBEF® luminance-enhancing film, available from 3M, was used.

[0276] In the surface light source device of Example 1, the thickness of the diffusion member along the stacking direction was 70 μm. Also, in the surface light source device of Example 1, the distance DX (see Figure 2) along the stacking direction from the surface of the light source facing the diffusion member to the light-receiving side of the diffusion member facing the light source was 0.5 mm.

[0277] <Example 2> The surface light source device of Example 2 differed from the surface light source device of Example 1 in the inclination angle θa of the first element surface, but otherwise had the same configuration. The inclination angle θa of the normal direction ND to each equilateral element surface included in the first element surface of the light diffusion section with respect to the stacking direction D3 was set to 30°. The inclination angle θa of the normal direction ND to the base element surface included in the first element surface with respect to the stacking direction D3 was set to 40°. <Example 3> The surface light source device of Example 3 differed from the surface light source device of Example 1 in the inclination angle θa of the first element surface, but otherwise had the same configuration. The inclination angle θa of the normal direction ND to each equilateral element surface included in the first element surface of the light diffusion section with respect to the stacking direction D3 was set to 40°. The inclination angle θa of the normal direction ND to the base element surface included in the first element surface with respect to the stacking direction D3 was set to 45°.

[0278] <Example 4> The surface light source device of Example 4 differed from the surface light source device of Example 1 in the inclination angle θb of the second element surface, but otherwise had the same configuration. The inclination angle θb of the normal direction ND to each equilateral element surface included in the second element surface of the optical element part with respect to the stacking direction D3 was set to 30°. The inclination angle θb of the normal direction NDA to the base element surface included in the second element surface with respect to the stacking direction D3 was set to 40°.

[0279] <Example 5> The surface light source device of Example 5 differed from the surface light source device of Example 1 in the inclination angle θb of the second element surface, but otherwise had the same configuration. The inclination angle θb of the normal direction ND to each equilateral element surface included in the second element surface of the optical element part with respect to the stacking direction D3 was set to 40°. The inclination angle θb of the normal direction NDA to the base element surface included in the second element surface with respect to the stacking direction D3 was set to 45°.

[0280] <Example 6> The surface light source device of Example 6 differed from the surface light source device of Example 1 in its diffusion member, but otherwise had the same configuration. The diffusion member of Example 6 consisted of a light diffusion section and a light reflection section. The diffusion member of Example 6 did not have an optical element section. The light reflection section of Example 6 was the same as the light reflection section of Example 1. In the surface light source device of Comparative Example 1, the thickness of the diffusion member along the lamination direction was 55 μm.

[0281] <Example 7> The surface light source device of Example 7 differed from the surface light source device of Example 1 in the inclination angle θb of the second element surface, but otherwise had the same configuration. The inclination angle θb of the normal direction ND to each equilateral element surface included in the first element surface of the light diffusion section with respect to the stacking direction D3 was set to 5.5°. The inclination angle θb of the normal direction ND to the base element surface included in the first element surface with respect to the stacking direction D3 was set to 5.5°.

[0282] <Comparative Example 1> The surface light source device of Comparative Example 1 was the same as the surface light source device of Example 1, except that the diffusion member was replaced with a light diffusion plate HBS222 manufactured by Keiwa Co., Ltd. The light diffusion plate was located on the light source side of the wavelength conversion sheet. In the surface light source device of Comparative Example 3, the light source and the support substrate faced the light diffusion plate in the stacking direction. In the surface light source device of Comparative Example 1, the distance along the stacking direction from the surface of the light source facing the light diffusion plate to the light-receiving side of the light diffusion plate facing the light source was 0.5 mm.

[0283] <Rating> For the surface light source devices of Examples 1-7 and Comparative Example 1, the distribution of radiant intensity on the light-emitting surface of the surface light source device was measured while the light source was emitting light. The measurement range for radiant intensity was defined as a square evaluation area with a length of 18 mm in the first direction and 18 mm in the second direction on the light-emitting surface of the surface light source device. The evaluation area was set up so that one light source was located at the center of the evaluation area when observed from a third direction. The in-plane distribution of radiant intensity on the light-emitting surface of the surface light source devices of Examples 1-6 and Comparative Example 1 is shown in Figures 56-62, respectively. Figures 56-62 are plan views showing the evaluation area with an area of ​​18 mm × 18 mm. Figures 56-62 show the magnitude of radiant intensity at each position within the evaluation area by the intensity of the color at that position. Positions with low radiant intensity are shown with darker colors.

[0284] In the area light source device of Comparative Example 1 shown in Figure 62, there was unevenness in the radiant intensity distribution according to the arrangement of the light sources, making it possible to clearly see the position of the light sources. The in-plane distribution of radiant intensity for the area light source devices of Examples 1 to 7 was sufficiently uniform compared to the in-plane distribution of radiant intensity for the area light source device of Comparative Example 1. In particular, for Examples 1 and 7, the brightness distribution was uniform, making it difficult to determine the position of the light sources. The ratio of the minimum value of radiant intensity to the maximum value of radiant intensity within the evaluation area of ​​each area light source device 20 (= minimum radiant intensity / maximum radiant intensity) was 97% for Example 1, 95% for Example 2, 94% for Example 3, 93% for Example 4, 92% for Example 5, 90% for Example 6, 96% for Example 7, and 50% for Comparative Example 1. [Explanation of symbols]

[0285] 10: Display device, 20: Surface light source device, 22: Light source, 40: Diffuser, 42: Display, 50: Light diffusion part, 52: Uneven surface, 53: Diffuser body part, 53a: Uneven surface, 54: Reflective coating part, 58: Body part, 65: Microlens, 66: Unit optical element, 67: Element surface, 68: Convex part, 69: Recess, 70: Light reflecting part, 110: Optical element part, 112: Uneven surface, 115: Optical sheet, 118: Base, 125: Microlens, 126: Unit optical element, 127: Element surface, 128: Convex part, 129: Recess

Claims

1. Multiple light sources that emit light of a specific wavelength and are arranged in a two-dimensional array, A diffusion member facing directly towards the aforementioned multiple light sources, The light-diffusing sheet laminated with the aforementioned diffusion member, A direct-below surface light source device comprising a wavelength conversion sheet positioned between the diffusion member and the light diffusion sheet, The aforementioned diffusion member is A light-diffusing section having light-transmitting and light-diffusing properties, It includes a light-reflecting portion whose transmittance of light of a specific wavelength incident at an incident angle of 0° is lower than the transmittance of light of the same wavelength incident at an incident angle greater than 0°, When a light ray is incident on the light diffusion portion at an incident angle of 0°, the radiation intensity on the side of the light diffusion portion facing the light reflection portion has a peak at an exit angle other than 0°. In the stacking direction in which the diffusion member, the wavelength conversion sheet, and the light diffusion sheet are stacked, the diffusion member is located between the light source and the light diffusion sheet. The light-reflecting portion is located between the light-diffusing portion and the wavelength-converting sheet in the stacking direction. The wavelength conversion sheet is a surface light source device that absorbs light from the light source and emits light with a different wavelength from the wavelength of the absorbed light.

2. A support substrate that supports the plurality of light sources from the opposite side of the diffusion member, The system comprises a thermoplastic resin layer located between the diffusion member and the support substrate, The surface light source device according to claim 1, wherein the thermoplastic resin layer covers the plurality of light sources and is bonded to the support substrate.

3. The surface light source device according to claim 2, wherein the thermoplastic resin layer is in contact with the diffusion member.

4. The surface light source device according to claim 2 or 3, wherein the thermoplastic resin layer is bonded to the diffusion member.

5. A display device comprising a surface light source device according to any one of claims 1 to 4.

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