Optical components, surface light source devices, and display devices

Abstract

To improve the luminosity of a light emitting face.SOLUTION: A surface light source device 20 includes a first sheet 40 and a second sheet 50 in this order. The first sheet 40 includes a wavelength conversion agent for absorbing primary light, and radiating secondary light. The second sheet 50 includes a first layer and a second layer in this order. The first layer is located between the first sheet and the second layer. A permeation rate of the first layer with respect to light having a specified wavelength which is incident to the second sheet at an incident angle of 0° is lower than a permeation rate of the first layer with respect to light having a specified wavelength which is incident to the second sheet at an incident angle of 30°. The permeation rate of the first layer with respect to the light having the specified wavelength which is incident to the second sheet at the angle of 30° is lower than a permeation rate of the first layer with respect to light having a specified wavelength which is incident to the second sheet at an angle of 60°. The second layer includes at least either of a diffractive optical element and an optical element part including a plurality of unit optical elements. The optical element part constitutes an irregular face of the second sheet by the plurality of unit optical elements.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] This disclosure relates to optical components, surface light source devices, and display devices. [Background technology]

[0002] Patent Document 1 discloses a surface light source device having a light-emitting surface. The surface light source device of Patent Document 1 is a direct-below type device. The surface light source device of Patent Document 1 includes a plurality of light sources and optical components. The optical components face the plurality of light sources in a direction perpendicular to the light-emitting surface. The optical components include a dielectric multilayer film and a wavelength conversion sheet, in order from the light source side. The light sources emit blue light. The transmittance of blue light in the dielectric multilayer film increases as the angle of incidence increases. The wavelength conversion sheet has a wavelength conversion function. The wavelength conversion sheet absorbs the light source light and emits light of a different wavelength than the light source light. In the surface light source device described in Patent Document 1, the in-plane distribution of brightness is made uniform by a dielectric multilayer film having an angle-dependent transmission characteristic. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-022964 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] However, conventional surface light source devices have the drawback of insufficient brightness of the light-emitting surface. This disclosure aims to improve the brightness of the light-emitting surface. [Means for solving the problem]

[0005] A first optical member according to one embodiment of the present disclosure is The first sheet and the second sheet are provided in this order. The aforementioned first sheet contains a wavelength conversion agent that absorbs primary light and emits secondary light. The second sheet includes the first layer and the second layer in this order. The first layer is located between the first sheet and the second layer. The transmittance of the first layer for light of a specific wavelength incident on the second sheet at an incident angle of 0° is smaller than the transmittance of the first layer for light of the specific wavelength incident on the second sheet at an incident angle of 30°. The transmittance of the first layer for light of a specific wavelength incident on the second sheet at an incident angle of 30° is smaller than the transmittance of the first layer for light of a specific wavelength incident on the second sheet at an incident angle of 60°. The second layer includes at least one of a diffractive optical element and an optical element portion including a plurality of unit optical elements. The optical element portion is formed by the plurality of unit optical elements, which constitute the uneven surface of the second sheet.

[0006] A second optical member according to one embodiment of the present disclosure is The first sheet and the second sheet are provided in this order. The aforementioned first sheet contains a wavelength conversion agent that absorbs primary light and emits secondary light. The second sheet includes the first layer and the second layer in this order. The first layer is located between the first sheet and the second layer. The transmittance of the second sheet is greater for light of a specific wavelength incident on the second sheet at an incident angle of 30° than for light of a specific wavelength incident on the second sheet at an incident angle of 0°. The transmittance of the second sheet is greater for light of a specific wavelength incident on the second sheet at an incident angle of 60° than for light of a specific wavelength incident on the second sheet at an incident angle of 30°. The second layer includes at least one of a diffractive optical element and an optical element portion including a plurality of unit optical elements. The optical element portion is formed by the plurality of unit optical elements, which constitute the uneven surface of the second sheet.

[0007] A surface light source device according to one embodiment of the present disclosure is Either the first or second optical member according to an embodiment of the present disclosure, and a light source facing the optical member.

[0008] A display device according to an embodiment of the present disclosure comprises: any one of the surface light source devices according to an embodiment of the present disclosure, and a display panel stacked over the surface light source device. Effects of the Invention

[0009] According to the present disclosure, the light emitting surface can be made brighter. Brief Description of the Drawings

[0010] [Figure 1] Figure 1 is a diagram for describing an embodiment, and is a perspective view showing a display device and a surface light source device. [Figure 2] Figure 2 is a vertical cross-sectional view of the surface light source device shown in Figure 1, showing an optical member and a light source substrate that may be included in the surface light source device. [Figure 3] Figure 3 is a plan view showing the light source substrate shown in Figure 2, and shows an example of the arrangement of a plurality of light sources. [Figure 4] Figure 4 is a cross-sectional view showing the light source substrate shown in Figure 2, and shows an example of the configuration of the light source substrate. [Figure 5] Figure 5 is a cross-sectional view showing an example of a first sheet that may be included in the optical member shown in Figure 2. [Figure 6A] Figure 6A is a cross-sectional view showing an example of a second sheet that may be included in the optical member shown in Figure 2. [Figure 6B] Figure 6B is a cross-sectional view showing another example of the second sheet that may be included in the optical member shown in Figure 2. [Figure 7] Figure 7 is a graph showing an example of the optical characteristics of a first layer that may be included in the second sheet shown in Figure 6A and Figure 6B. [Figure 8A]Figure 8A is a plan view showing an example of an optical element section that may be included in the second or third layer of the second sheet shown in Figures 6A and 6B, and shows the arrangement of unit optical elements that may be included in the optical element section. [Figure 8B] Figure 8B is a perspective view showing a specific example of the unit optical element shown in Figure 8A. [Figure 8C] Figure 8C is a diagram corresponding to Figure 8A, showing another example of the arrangement of unit optical elements. [Figure 9A] Figure 9A is a plan view showing another example of an optical element section that may be included in the second or third layer of the second sheet shown in Figures 6A and 6B, and shows the arrangement of unit optical elements that may be included in the optical element section. [Figure 9B] Figure 9B is a perspective view showing a specific example of the unit optical element shown in Figure 9A. [Figure 9C] Figure 9C is a diagram corresponding to Figure 9A and shows another example of the arrangement of unit optical elements. [Figure 10] Figure 10 is a perspective view showing an example of an optical sheet that may be included in the surface light source device shown in Figure 2. [Figure 11] Figure 11 is a cross-sectional view showing one modified example of an optical component. [Figure 12] Figure 12 is a cross-sectional view showing a modified example of the second sheet of the optical component. [Figure 13] Figure 13 is a cross-sectional view showing another variation of the second sheet of the optical component. [Figure 14] Figure 14 is a graph showing the transmission spectrum of the second sheet according to Example 1. [Figure 15] Figure 15 is a graph showing the transmission spectrum of the second sheet according to Example 2. [Figure 16] Figure 16 is a graph showing the transmission spectrum of the second sheet according to Example 3. [Figure 17] Figure 17 is a graph showing the transmission spectrum of the second sheet according to Comparative Example 1. [Figure 18] Figure 18 is a graph showing the transmission spectrum of the second sheet according to Comparative Example 2. [Figure 19] Figure 19 is a table showing the evaluation results for the examples and comparative examples. [Modes for carrying out the invention]

[0011] One embodiment of the present disclosure relates to the following [1] to

[13] .

[0012] [1] The first sheet and the second sheet are provided in this order, The aforementioned first sheet contains a wavelength conversion agent that absorbs primary light and emits secondary light. The second sheet includes the first layer and the second layer in this order. The first layer is located between the first sheet and the second layer. The transmittance of the first layer for light of a specific wavelength incident on the second sheet at an incident angle of 0° is smaller than the transmittance of the first layer for light of the specific wavelength incident on the second sheet at an incident angle of 30°. The transmittance of the first layer for light of a specific wavelength incident on the second sheet at an incident angle of 30° is smaller than the transmittance of the first layer for light of a specific wavelength incident on the second sheet at an incident angle of 60°. The second layer includes at least one of a diffractive optical element and an optical element portion including a plurality of unit optical elements. The optical element portion is an optical member in which the plurality of unit optical elements constitute the uneven surface of the second sheet.

[0013] [2] The first sheet and the second sheet are provided in this order: The aforementioned first sheet contains a wavelength conversion agent that absorbs primary light and emits secondary light. The second sheet includes the first layer and the second layer in this order. The first layer is located between the first sheet and the second layer. The transmittance of the second sheet for light of a specific wavelength incident on the second sheet at an incident angle of 0° is smaller than the transmittance of the second sheet for light of the same wavelength incident on the second sheet at an incident angle of 30°. The transmittance of the second sheet for light of a specific wavelength incident on the second sheet at an incident angle of 30° is smaller than the transmittance of the second sheet for light of a specific wavelength incident on the second sheet at an incident angle of 60°. The second layer includes at least one of a diffractive optical element and an optical element portion including a plurality of unit optical elements. The optical element portion is an optical member in which the plurality of unit optical elements constitute the uneven surface of the second sheet.

[0014] [3] The second sheet includes a third layer located between the first sheet and the first layer, The third layer includes at least one of a diffractive optical element and a second optical element portion including a plurality of second unit optical elements. The second optical element portion is an optical member [1] or [2] in which the plurality of second unit optical elements constitute the uneven surface of the second sheet.

[0015] [4] Any optical member from [1] to [3], wherein the transmittance of the second sheet for light of a wavelength of 550 nm incident on the second sheet at an incident angle of 60° is 50% or more.

[0016] [5] Any optical member from [1] to [4], wherein the transmittance of the second sheet for light with a wavelength of 650 nm incident on the second sheet at an incident angle of 60° is 50% or more.

[0017] [6] The transmittance of the second sheet for light with a wavelength of 550 nm incident on the second sheet at an incident angle of 0° is less than the transmittance of the second sheet for light with a wavelength of 550 nm incident on the second sheet at an incident angle of 30°. An optical member of any of [1] to [5] wherein the transmittance of the second sheet for light with a wavelength of 550 nm incident on the second sheet at an incident angle of 30° is smaller than the transmittance of the second sheet for light with a wavelength of 550 nm incident on the second sheet at an incident angle of 60°.

[0018] [7] The transmittance of the second sheet for light with a wavelength of 650 nm incident on the second sheet at an incident angle of 0° is less than the transmittance of the second sheet for light with a wavelength of 5650 nm incident on the second sheet at an incident angle of 30°. An optical member of any of [1] to [6] wherein the transmittance of the second sheet for light with a wavelength of 650 nm incident on the second sheet at an incident angle of 30° is smaller than the transmittance of the second sheet for light with a wavelength of 650 nm incident on the second sheet at an incident angle of 60°.

[0019] [8] The unit optical element is an optical member of any of [1] to [7], which is a cone-shaped convex or concave portion.

[0020] [9] The optical component of any of [1] to [8], wherein the specific wavelength is 430 nm or more and 500 nm or less.

[0021]

[10] One of the optical components from [1] to [9], A surface light source device comprising a light source facing the aforementioned optical member.

[0022]

[11] Further comprising a reflective polarizing plate superimposed on the optical element, The optical element is a surface light source device

[10] located between the light source and the reflective polarizing plate.

[0023]

[12] Further comprising an optical sheet superimposed on the optical member, The optical member is a surface light source device

[10] or

[11] located between the light source and the optical sheet.

[0024]

[13] A surface light source device of any of

[10] to

[12] , A display device comprising a display panel superimposed on the aforementioned surface light source device.

[0025] An embodiment of the present invention will be described below 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. Some components shown in some drawings may be omitted in others.

[0026] In this specification, terms such as "parallel," "orthogonal," and "identical," as well as values ​​of length and angle, which specify shapes, geometric conditions, and their degrees, shall not be limited to their strict meanings, but shall be interpreted to include a range that can be expected to function similarly.

[0027] In this specification, terms such as "sheet," "film," and "plate" are not distinguished from each other solely on the basis of differences in name. For example, an "optical sheet" cannot be distinguished from components such as optical films or optical plates solely on the basis of differences in name.

[0028] In this specification, the normal direction of a sheet-like (sheet-like, plate-like) member refers to the direction parallel to the normal or perpendicular to the sheet surface of the sheet-like (film-like, plate-like) member in question. 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 viewed as a whole and in a broad sense.

[0029] In this specification, if multiple upper limit candidates and multiple lower limit candidates are given for a certain parameter, the numerical range of that parameter may be constructed by combining any one upper limit candidate and any one lower limit candidate. As an example, consider the statement, "Parameter B may be A1 or greater, A2 or greater, A3 or greater. Parameter B may be A4 or less, A5 or less, A6 or less." In this example, the numerical range of parameter B may be A1 or greater and A4 or less, A1 or greater and A5 or less, A1 or greater and A6 or less, A2 or greater and A4 or less, A2 or greater and A5 or less, A2 or greater and A6 or less, A3 or greater and A4 or less, A3 or greater and A5 or less, and A3 or greater and A6 or less.

[0030] To clarify directional relationships between drawings, some drawings use arrows with common symbols to indicate the first direction D1, the second direction D2, and the third direction D3 as common directions. The tip of the arrow is the first side of each direction. The opposite side of the arrow is the second side of each direction. For example, as shown in Figure 2, the symbol with an "x" inside a circle indicates an arrow pointing towards the back of the drawing along a direction perpendicular to the plane of the drawing. For example, as shown in Figure 3, the symbol with a dot inside a circle indicates an arrow pointing towards the front of the drawing along a direction perpendicular to the plane of the drawing.

[0031] "Suppression" means to prevent or hinder the realization or occurrence of something. "Suppression" means not only completely preventing the realization or occurrence of something, but also reducing the possibility of it happening or making it less likely to occur.

[0032] Figures 1 to 16 are diagrams illustrating one embodiment. Figure 1 is a schematic perspective view showing a surface light source device 20 and a display device 10 as an example of an application of the optical member 30. The display device 10 may display, for example, moving images, still images, text information, or images composed of a combination thereof. The display device 10 may be used indoors or outdoors for various purposes such as advertising, presentations, television images, and displaying various types of information. The display device 10 may be used, for example, as an in-vehicle liquid crystal display device. The display device 10 shown in Figure 1 includes a surface light source device 20 including a light-emitting surface 20a and a display panel 15 facing the light-emitting surface 20a.

[0033] Figure 2 is a longitudinal cross-sectional view showing a specific example of a surface light source device 20. As shown in Figure 2, the surface light source device 20 includes, as its main components, a light source 23 and an optical member 30 that adjusts the optical path of the light emitted from the light source 23. The optical member 30 faces the light source 23 directly. The optical member 30 is sheet-shaped. The optical member 30 faces the light source 23 in the direction normal to it. The optical member 30 is a diffuser that diffuses the light emitted from the light source 23. The optical member 30 can effectively suppress in-plane variations in illuminance caused by the arrangement of the light source 23. Diffusion by the optical member 30 can effectively equalize the illuminance at each position on the second surface 30b, which is the light-emitting surface of the optical member 30, or the illuminance at each position on a virtual light-receiving surface parallel to the second surface 30b and located near the second surface 30b.

[0034] The following description will explain the display device 10, the surface light source device 20, and the optical member 30 in one embodiment, with reference to the illustrated specific examples.

[0035] As shown in Figure 1, the display panel 15 is superimposed on the area light source device 20 in the third direction D3. The display panel 15 is positioned facing the light-emitting surface 20a of the area light source device 20. The display panel 15 includes a display surface 15a on which an image is displayed, which faces the side opposite to the area light source device 20 in the third direction D3, i.e., the first side. In the illustrated example, the display panel 15 is flat. The display panel 15 extends in the first direction D1 and the second direction D2, which are perpendicular to the third direction D3. When viewed from the third direction D3, the display panel 15 has a rectangular shape. The first direction D1 and the second direction D2 are perpendicular.

[0036] 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.

[0037] The surface light source device 20 includes a light-emitting surface 20a. Light is emitted from the light-emitting surface 20a. The surface light source device 20 may also be a direct-lit backlight. The surface light source device 20 includes a light source 23 and an optical member 30. In projection in the third direction D3, the light source 23 is provided within the region that overlaps with the optical member 30.

[0038] The surface light source device 20 shown in Figure 2 includes a light source substrate 22 and an optical control member 18. The light source substrate 22 includes a light source 23. The optical control member 18 includes an optical member 30. The optical control member 18 controls the optical path of light from the light source 23. The optical control member 18 includes a first surface 18a and a second surface 18b. The first surface 18a faces the second side in the third direction D3. The second surface faces the first side in the third direction D3. In the illustrated example, the surface light source device 20 includes a light source substrate 22 including the light source 23, an optical member 30, a first optical sheet 81, a second optical sheet 82, and a reflective polarizer 85. In the illustrated example, the optical control member 18 includes the optical member 30, the first optical sheet 81, the second optical sheet 82, and the reflective polarizer 85 in the order from the first surface 18a to the second surface 18b. The light source substrate 22, optical member 30, first optical sheet 81, second optical sheet 82, and reflective polarizer 85 are in sheet form. The light source substrate 22, optical member 30, first optical sheet 81, second optical sheet 82, and reflective polarizer 85 extend in the first direction D1 and the second direction D2. The light source substrate 22, optical member 30, first optical sheet 81, second optical sheet 82, and reflective polarizer 85 have a normal direction parallel to the third direction.

[0039] The light source substrate 22 includes a light source 23 and a support substrate 25. In the illustrated example, the light source substrate 22 has a rectangular shape when viewed from a third direction D3.

[0040] The light source 23 has a light-emitting element that emits light. The light-emitting element may be a light-emitting diode, denoted as an LED. The dimensions of the light-emitting diode are not particularly limited. From the viewpoint of making the image of the light source 23 inconspicuous, the light source 23 may be a small light-emitting diode, such as a mini-LED or micro-LED. The lengths of the sides WL1 and WL2 of the light source 23, which has a rectangular shape when observed from the third direction D3 shown in Figure 3, may be 0.5 mm or less, or 0.2 mm or less.

[0041] The emission wavelength of the light source 23 can be appropriately selected depending on the application of the surface light source device 20. The light emitted from the light source 23 is absorbed by the wavelength conversion agent 47, described later, as primary light LA. Therefore, the emission wavelength of the light source 23 can be appropriately selected depending on the optical properties of the wavelength conversion agent 47. In the illustrated example, the light source 23 emits blue light. The wavelength of the light emitted from the light source 23 may be between 430 nm and 500 nm.

[0042] The light distribution characteristics of the light source 23 are not particularly limited. The light distribution characteristics of the light source 23 may be Lambertsian. In the luminous intensity distribution of the light source 23 whose optical axis is aligned with the third direction D3, the peak luminous intensity may be obtained in directions other than the third direction D3. For example, the light source 23 may have the batwing light distribution disclosed in JP6299811B. As an example, the light source 23 may consist only of light-emitting elements. In addition to light-emitting elements, the light source 23 may include optical elements such as covers and lenses that adjust the light distribution from the light-emitting elements.

[0043] As shown in the illustrated surface light source device 20, the light source substrate 22 may include multiple light sources 23. The number of light sources 23 is appropriately selected according to the application of the surface light source device 20 and the area of ​​the light-emitting surface 20a. The multiple light sources 23 may be arranged in a two-dimensional array on a plane perpendicular to the third direction D3. A two-dimensional array means that objects such as light sources 23 are arranged in two or more non-parallel directions. From the viewpoint of suppressing brightness unevenness caused by the arrangement of light sources 23, the multiple light sources 23 may be arranged regularly. As an example of a regular arrangement of light sources 23, a honeycomb array or a square array may be adopted. In a honeycomb array, light sources 23 can be arranged at a constant pitch in each of three directions that are tilted at 60° from each other. In a square array, light sources 23 can be arranged at a constant pitch in each of two directions that are orthogonal to each other.

[0044] As shown in Figure 3, the multiple light sources 23 may be arranged at a constant pitch in each of the mutually orthogonal first direction D1 and second direction D2. The arrangement pitch PL1 of the light sources 23 in the first direction D1 and the arrangement pitch PL2 of the light sources 23 in the second direction D2 may be the same. The arrangement pitches PL1 and PL2 may be different. The first direction D1 and the second direction D2 may be parallel to the side edges of the rectangular surface light source device 20 and optical member 30, respectively. The arrangement pitches PL1 and PL2 may each be between 0.2 mm and 10 mm.

[0045] Next, the support substrate 25, which constitutes the light source substrate 22 together with the multiple light sources 23, will be described. The support substrate 25 supports the multiple light sources 23 from the second side in the third direction D3. The support substrate 25 is in the form of a sheet. The support substrate 25 may include a circuit that supplies power to the light sources 23. The support substrate 25 may have light reflectivity that reflects light and directs it toward the optical member 30.

[0046] The support substrate 25 shown in Figure 4 includes a sheet-like substrate body 26, a reflective layer 27 and wiring 29 provided on the substrate body 26. The substrate body 26 extends in a first direction D1 and a second direction D2. The substrate body 26 may be insulating. The substrate body 26 may be a resin film, for example, a polyethylene terephthalate film. The wiring 29 is electrically connected to the light source 23. The wiring 29 is electrically connected to terminals of the light source 23 (not shown) via solder or the like. If the substrate body 26 and the reflective layer 27 are insulating, the wiring 29 may be located between the substrate body 26 and the reflective layer 27, as shown in Figure 4.

[0047] The reflective layer 27 is laminated on the substrate body 26. The reflective layer 27 faces the optical element 30. The reflective layer 27 covers the area on the substrate body 26 where the light source 23 is not located. The reflective layer 27 is reflective to light of a specific wavelength emitted by the light source 23 or to light used for emission by the surface light source device 20. The reflection at the reflective layer 27 may be specular reflection, diffuse reflection, or anisotropic diffuse reflection. The reflective layer 27 having diffuse reflectivity may include a white reflective layer containing white particles such as silicon dioxide. The reflective layer 27 may be a metal layer laminated on the substrate body 26, or it may be a reflective diffractive optical element.

[0048] As shown in Figure 2, the optical member 30 includes a first surface 30a and a second surface 30b. The first surface 30a and the second surface 30b face the third direction D3. The first surface 30a faces the second side in the third direction D3. The first surface 30a may constitute the first surface 18a, which is the light-receiving surface of the light control member 18. The second surface 30b faces the first side in the third direction D3. The optical member 30 includes a first sheet 40 and a second sheet 50, in the order from the first surface 30a to the second surface 30b. The first sheet 40 and the second sheet 50 are superimposed in the third direction D3. In the illustrated example, both the first sheet 40 and the second sheet 50 extend in the first direction D1 and the second direction D2. In the illustrated example, the first sheet 40 constitutes the first surface 30a of the optical member 30. In the illustrated example, the second sheet 50 constitutes the second surface 30b of the optical element 30.

[0049] The first sheet 40 and the second sheet 50 may be joined to each other. The first sheet 40 and the second sheet 50 may simply be in contact with each other and not be joined. The first sheet 40 and the second sheet 50 may be separated from each other.

[0050] As shown in Figures 2 and 5, the first sheet 40 includes a first surface 40a and a second surface 40b. The first surface 40a and the second surface 40b face the third direction D3. The first surface 40a faces the second side in the third direction D3. The second surface 40b faces the first side in the third direction D3. In the illustrated example, the first surface 40a constitutes the first surface 30a which is the light-receiving surface of the optical member 30. The first sheet 40 contains a wavelength conversion agent 47. The wavelength conversion agent 47 absorbs the primary light LA ​​and emits secondary light LB with a different wavelength from the primary light LA. The wavelength of the secondary light LB may be longer than the wavelength of the primary light LA. The wavelength of the primary light LA ​​may be between 430 nm and 500 nm. The wavelength of the secondary light LB may be longer than 500 nm and 780 nm or less.

[0051] In the example shown in Figure 5, the first sheet 40 includes a first barrier layer 41, a wavelength conversion layer 45, and a second barrier layer 42, in the order from the first surface 40a to the second surface 40b. The first barrier layer 41, the wavelength conversion layer 45, and the second barrier layer 42 are stacked in this order in the third direction D3. The first barrier layer 41, the wavelength conversion layer 45, and the second barrier layer 42 are arranged in this order from the first side to the second side in the third direction D3. The first barrier layer 41, the wavelength conversion layer 45, and the second barrier layer 42 are in the form of sheets. The first barrier layer 41, the wavelength conversion layer 45, and the second barrier layer 42 extend in the first direction D1 and the second direction D2.

[0052] In the example shown in Figure 5, the wavelength conversion layer 45 includes a first surface 45a and a second surface 45b. The first surface 45a faces the second side in the third direction D3. The second surface 45b faces the first side in the third direction D3. The wavelength conversion layer 45 is bonded to the first barrier layer 41 at the first surface 45a. The wavelength conversion layer 45 is bonded to the second barrier layer 42 at the second surface 45b.

[0053] The wavelength conversion layer 45 may include a base material portion 46 that holds the wavelength conversion agent 47. The base material portion 46 may be a resin. Examples of resins constituting the base material portion 46 include thermoplastic resins, cured products of thermosetting resin compositions, and cured products of ionizing radiation-curable resin compositions. Examples of ionizing radiation-curable resin compositions include electron beam-curable resin compositions and ultraviolet-curable resin compositions.

[0054] The wavelength converter 47 absorbs primary light LA ​​of a certain wavelength and emits secondary light LB having a different wavelength from the primary light LA. Quantum dots or phosphors may be used as the wavelength converter 47. The wavelength of primary light LA ​​may also be the wavelength of light emitted from the light source 23. That is, the light emitted from the light source 23 may contain primary light LA ​​of a certain wavelength.

[0055] A quantum dot is a nanometer-sized semiconductor particle. A quantum dot may contain one semiconductor compound. A quantum dot may contain two or more semiconductor compounds. A quantum dot may have a core-shell structure. The core-shell structure may include a core made of a semiconductor compound and a shell made of a different semiconductor compound.

[0056] Examples of materials for quantum dot cores include group II-VI semiconductor compounds such as MgS, MgSe, MgTe, CaS, CaSe, CaTe, SrS, SrSe, SrTe, BaS, BaSe, BaTe, ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, HgS, HgSe, and HgTe. Examples of materials for quantum dot cores include group III-V semiconductor compounds such as AlN, AlP, AlAs, AlSb, GaAs, GaP, GaN, GaSb, InN, InAs, InP, InSb, TiN, TiP, TiAs, and TiSb. Examples of materials for quantum dot cores include semiconductor compounds such as group IV semiconductors such as Si, Ge, and Pb, or semiconductor crystals containing semiconductors.

[0057] When using a core-shell type quantum dot, the semiconductor material constituting the shell may have a higher band gap than the semiconductor compound forming the core. In this case, excitons are confined to the core, improving the luminescence efficiency of the quantum dot. Examples of core-shell structures (core / shell) with such band gap relationships include CdSe / ZnS, CdSe / ZnSe, CdSe / CdS, CdTe / CdS, InP / ZnS, Gap / ZnS, Si / ZnS, InN / GaN, InP / CdSSe, InP / ZnSeTe, InGaP / ZnSe, InGaP / ZnS, Si / AlP, InP / ZnSTe, InGaP / ZnSTe, and InGaP / ZnSSe.

[0058] The size of the quantum dots is adjusted considering the desired wavelength of secondary light band gap (LB). As the particle size of the quantum dots decreases, the energy band gap increases. As the crystal size decreases, the emission of quantum dots shifts towards the blue side, i.e., to the higher energy side. By changing the size of the quantum dots, the wavelength of secondary light band gap can be adjusted. The average particle size of the quantum dots may be less than 20 nm, between 0.5 nm and 20 nm, or between 1 nm and 10 nm. The shape and dispersion state of the quantum dots are determined by transmission electron microscopy (TEM). The crystal structure and particle size of the quantum dots are determined by X-ray crystal diffraction (XRD).

[0059] The wavelength conversion layer 45 may contain multiple quantum dots with different emission wavelengths as the wavelength conversion agent 47. By adjusting the content of each quantum dot, the color of the light emitted from the surface light source device 20 can be adjusted. In the example shown in Figure 5, the wavelength conversion agent 47 includes a first converter 47A and a second converter 47B. The first converter 47A and the second converter 47B have different sizes. The first converter 47A and the second converter 47B emit light of different wavelengths.

[0060] As a specific example, the light source 23 may emit blue light having a wavelength of 430 nm to 500 nm or more. The first conversion agent 47A may absorb the primary light LA ​​from the light source 23 and emit green light having a wavelength of 500 nm to 600 nm or more as the first secondary light LB1. The second conversion agent 47B may absorb the primary light LA ​​from the light source 23 and emit red light having a wavelength of 600 nm to 750 nm or more as the second secondary light LB2. According to this example, the light-emitting surface 20a of the surface light source device 20 can reproduce various colors by additive color mixing of the first secondary light LB1, the second secondary light LB2, and the primary light LA ​​that was not wavelength-converted by the wavelength conversion layer 45. By adjusting the content of the first conversion agent 47A and the second conversion agent 47B, the surface light source device 20 can emit white light.

[0061] The wavelength conversion layer 45 may contain a light-diffusing component that diffuses transmitted light. The light-diffusing component may be dispersed within the base material 46. Examples of light-diffusing components include metal compounds, porous materials containing gas, resin beads with metal compounds surrounding them, white fine particles, and simple bubbles.

[0062] The first barrier layer 41 is bonded to the first surface 45a of the wavelength conversion layer 45. The first barrier layer 41 constitutes the first surface 40a. The second barrier layer 42 is bonded to the second surface 45b of the wavelength conversion layer 45. The second barrier layer 42 constitutes the second surface 40b. The first barrier layer 41 and the second barrier layer 42 have the function of protecting the wavelength conversion agent 47 from oxygen and moisture.

[0063] The first barrier layer 41 and the second barrier layer 42 may have oxygen barrier properties. In this example, the oxygen permeability of the first barrier layer 41 and the second barrier layer 42 is 1.0 × 10⁻¹⁰ at 23°C and 90% relative humidity. -1 cc / m 2 It can also be / day / atm or below, 1.0 × 10 -2 cc / m 2 A value of less than / day / atm is also acceptable. Oxygen permeability can be measured using an oxygen gas permeability meter (MOCON, OX-TRAN 2 / 21).

[0064] The first barrier layer 41 and the second barrier layer 42 may have water vapor barrier properties. In this example, the water vapor transmission rate of the first barrier layer 41 and the second barrier layer 42 under the conditions of 40°C and a relative humidity of 90% is 1.0×10 -1 g / m 2 / day or less, and may be 1.0×10 -2 g / m 2 / day or less. The water vapor transmission rate can be measured using a water vapor transmission rate measurement apparatus (DELTAPERM, manufactured by Technolox).

[0065] The first barrier layer 41 and the second barrier layer 42 can be produced using a material capable of exhibiting barrier properties, by a physical vapor deposition (PVD) method such as a sputtering method or an ion plating method, a vapor deposition method such as a chemical vapor deposition (CVD) method, or a coating method such as roll coating or spin coating. As the material, inorganic oxide, metal, sol-gel material or the like may be used. Examples of the inorganic oxide include silicon oxide (SiO x ), aluminum oxide (Al n O m ), titanium oxide (TiO2), yttrium oxide, boron oxide (B2O3), calcium oxide (CaO), silicon oxycarbonitride (SiO x N y C z ) and the like. Examples of the metal include Ti, Al, Mg, Zr and the like. Examples of the sol-gel material include siloxane-based sol-gel materials.

[0066] As shown in Figure 2, Figure 6A and Figure 6B, the second sheet 50 includes a first surface 50a and a second surface 50b. The first surface 50a and the second surface 50b face each other in the third direction D3. The first surface 50a faces the second side in the third direction D3. The second surface 50b faces the first side in the third direction D3. In the illustrated example, the second surface 50b constitutes the second surface 50b of the second sheet 50. In the illustrated example, the second surface 50b constitutes the second surface 30b that serves as the light exit surface of the optical member 30.

[0067] The second sheet 50 includes a first layer 55 and a second layer 60, in the order from the first surface 50a to the second surface 50b. The first layer 55 and the second layer 60 are stacked in the third direction D3. In the illustrated example, both the first layer 55 and the second layer 60 extend in the first direction D1 and the second direction D2.

[0068] The first layer 55 includes a first surface 55a and a second surface 55b. The first surface 55a and the second surface 55b face the third direction D3. The first surface 55a constitutes the first surface 50a. The first layer 55 is joined to the second layer 60 at the second surface 50b.

[0069] The transmission and reflection properties of the first layer 55 are dependent on the angle of incidence. The transmittance and reflectance of the first layer 55 change depending on the angle of incidence. The first layer 55 can also be described as a selective transmission layer or a selective reflection layer. 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.

[0070] The transmittance of the first layer 55 for light of a specific wavelength incident on the second sheet 50 at an incident angle of 0° may be less than the transmittance of the first layer 55 for light of a specific wavelength incident on the second sheet 50 at an incident angle greater than 0°. The transmittance of the first layer 55 may be greater for light of a specific wavelength incident on the second sheet 50 at an incident angle greater than 0° than for light of a specific wavelength incident on the second sheet 50 at an incident angle of 0°. That is, the transmittance of the first layer 55 for light of a specific wavelength incident on the second sheet 50 perpendicularly may be less than the transmittance of the first layer 55 for light of a specific wavelength incident on the second sheet 50 from at least one oblique direction. The reflectance of the first layer 55 for light of a specific wavelength incident on the second sheet 50 at an incident angle of 0° may be greater than the reflectance of the first layer 55 for light of a specific wavelength incident on the second sheet 50 at an incident angle greater than 0°. The reflectivity of the first layer 55 may be lower for light of a specific wavelength incident on the second sheet 50 at an incident angle greater than 0° than for light of a specific wavelength incident on the second sheet 50 at an incident angle of 0°. In other words, the reflectivity of the first layer 55 for light of a specific wavelength incident perpendicularly on the second sheet 50 may be higher than the reflectivity of the first layer 55 for light of a specific wavelength incident on the second sheet 50 from at least one oblique direction.

[0071] The transmittance of the first layer 55 for light of a specific wavelength incident on the second sheet 50 at an incident angle of 0°, the transmittance of the first layer 55 for light of a specific wavelength incident on the second sheet 50 at an incident angle of 30°, and the transmittance of the first layer 55 for light of a specific wavelength incident on the second sheet 50 at an incident angle of 60° may increase in this order. The transmittance of the first layer 55 for light of a specific wavelength incident on the second sheet 50 at incident angles of 0°, 10°, 20°, 30°, 40°, 50°, and 60° may gradually increase with increasing incident angle. The reflectance of the first layer 55 for light of a specific wavelength incident on the second sheet 50 at an incident angle of 0°, the reflectance of the first layer 55 for light of a specific wavelength incident on the second sheet 50 at an incident angle of 30°, and the reflectance of the first layer 55 for light of a specific wavelength incident on the second sheet 50 at an incident angle of 60° may decrease in this order. The reflectance of the first layer 55 for light of a specific wavelength incident on the second sheet 50 at incident angles of 0°, 10°, 20°, 30°, 40°, 50°, and 60° may gradually decrease as the incident angle increases.

[0072] The first layer 55 may have various transmission and reflection properties.

[0073] Figure 7 is a graph showing an example of the optical properties of the first layer 55. As shown in Figure 7, the transmittance in the first layer 55 for light of a specific wavelength with an incident angle to the second sheet 50 of 0° or more and 30° or less in absolute value may be less than 15%, less than 8%, or less than 3%. The transmittance in the first layer 55 for light of a specific wavelength with an incident angle to the second sheet 50 of 0° or more and 50° or less in absolute value may be less than 15%, less than 10%, or less than 5%.

[0074] The reflectance of light of a specific wavelength at the first layer 55, where the angle of incidence to the second sheet 50 is between 0° and 30° in absolute value, may be 85% or higher, 92% or higher, or 97% or higher. The reflectance of light of a specific wavelength at the first layer 55, where the angle of incidence to the second sheet 50 is between 0° and 50° in absolute value, may be 85% or higher, 90% or higher, or 95% or higher.

[0075] As shown in Figure 7, the transmittance in the first layer 55 of light of a specific wavelength incident on the second sheet 50 at a certain incident angle that is between 60° and 70° in absolute value may be 50%. The transmittance in the first layer 55 of light of a specific wavelength may increase as the absolute value of the incident angle on the second sheet 50 increases within the range of 0° to 65°. The transmittance in the first layer 55 of light of a specific wavelength may increase as the absolute value of the incident angle on the second sheet 50 increases.

[0076] The reflectivity of the first layer 55 for light of a specific wavelength incident on the second sheet 50 at a certain incident angle that is between 60° and 70° in absolute value may be 50%. The reflectivity of the first layer 55 for light of a specific wavelength may decrease as the absolute value of the incident angle on the second sheet 50 increases within the range of 0° to 65°. The reflectivity of the first layer 55 for light of a specific wavelength may decrease as the absolute value of the incident angle on the second sheet 50 increases.

[0077] The optical properties of the first layer 55 described here assume that the first surface 55a of the first layer 55 is perpendicular to the third direction D3, and that the first surface 55a and the second surface 55b are adjacent to the air layer.

[0078] The specific wavelength of light can be appropriately set according to the application of the surface light source device 20 and the optical component 30. The light emitted from the light source 23 may be the specific wavelength of light. The specific wavelength of light may be visible light. "Visible light" means light with a wavelength of 380 nm or more and a wavelength of 780 nm or less.

[0079] The reflectance (%) of the first layer 55 and the second sheet 50, and the transmittance (%) of the first layer 55 and the second sheet 50, shall be values ​​measured in accordance with JIS Z 8722:2009. For the measurement of reflectance, method b using a single-path spectrophotometer as specified in JIS Z 8722:2009 shall be adopted. The geometric conditions for illumination and reception when measuring reflectance at a specific angle of incidence shall be geometric conditions d as specified in JIS Z8722:2009, except for the selection of the angle of incidence. The geometric conditions for illumination and reception when measuring transmittance at a specific angle of incidence shall be geometric conditions f as specified in JIS Z8722:2009, except for the selection of the angle of incidence.

[0080] The first layer 55 is not particularly limited as long as it has an incident angle dependence of reflectivity and an incident angle dependence of transmittance. The first layer 55 may include a dielectric multilayer film 56, a reflective volume hologram, a cholesteric liquid crystal structure layer, a retroreflective film, or a reflective diffractive optical element. Dielectric multilayer films are superior in that they offer a relatively high degree of design freedom for their reflective and transmittance properties. The optical properties shown in Figure 7 are an example of the optical properties of the dielectric multilayer film 56.

[0081] The dielectric multilayer film 56 constituting the first layer 55 may include alternatingly stacked low-refractive-index layers and high-refractive-index layers with different refractive indices. The low-refractive-index layers and high-refractive-index layers may be layers of inorganic compounds or resin layers. The multilayer film constituting the dielectric multilayer film 56 may have a protective film on one or both sides. The material of the protective film may be polyethylene terephthalate or polyethylene naphthalate. The thickness of the protective film may be 5 μm or more. Co-extrusion or the like may be used as the manufacturing method for the dielectric multilayer film. Specifically, the manufacturing method for laminated films described in JP2008-200861A may be used. A commercially available laminated film may be used as the dielectric multilayer film. Examples of commercially available dielectric multilayer films include Picassus (registered trademark) from Toray Industries, Inc. and ESR from 3M Ltd.

[0082] As shown in Figures 6A and 6B, the second layer 60 includes a first surface 60a and a second surface 60b. The first surface 60a and the second surface 60b face the third direction D3. The first surface 60a faces the second side in the third direction D3. The second surface 60b faces the first side in the third direction D3. The second layer 60 is bonded to the first layer 55 at the first surface 60a. In the illustrated example, the second surface 60b constitutes the second surface 50b, which is the light-emitting surface of the second sheet 50. In the illustrated example, the second surface 60b constitutes the second surface 30b, which is the light-emitting surface of the optical member 30. The second surface 60b includes an uneven surface 61.

[0083] The second layer 60 may include an optical element section 60X. The optical element section 60X includes a plurality of unit optical elements 65, each formed as a convex portion 63 or a concave portion 64. In the example shown in Figures 6A and 6B, the second layer 60 is composed of the optical element section 60X. The unit optical element 65 is an element that changes the direction of light propagation by refraction, reflection, etc. The unit optical element 65 is a concept that includes elements called unit shape elements, unit prisms, and unit lenses. The unit optical element 65 constitutes the second surface 60b. The unit optical element 65 constitutes the concave-convex surface 61. The unit optical element 65 may be a polygonal pyramidal shape such as a triangular pyramid, a square pyramid, or a hexagonal pyramid, or it may be a cone shape or an elliptical cone shape.

[0084] The optical element 60X shown in Figure 6A includes a sheet-like main body 62 and a plurality of protrusions 63 provided on the main body 62. In the example shown in Figure 6A, the plurality of protrusions 63 may be provided adjacent to each other without any gaps. The optical element 60X shown in Figure 6B includes a main body 62 provided with a plurality of recesses 64. In the example shown in Figure 6B, the plurality of recesses 64 may be provided adjacent to each other without any gaps.

[0085] As shown in Figures 6A and 6B, the unit optical element 65 includes an element surface 66. The element surface 66 is inclined with respect to a third direction D3. This element surface 66 defines the unit optical element 65. The uneven surface 61 is formed by the element surface 66 of the unit optical element 65.

[0086] To distinguish it from the configuration of the third layer 70 described later, the optical element section, uneven surface, main body section, unit optical element, and element surface of the second layer 60 are sometimes referred to as the first optical element section, first uneven surface, first main body section, first unit optical element, and first element surface, respectively.

[0087] The optical properties of the first uneven surface 61 are affected by the inclination angle of the first element surface 66 of the first unit optical element 65. Therefore, the cross-sectional shape of the first unit optical element 65 can be appropriately adjusted based on the optical properties required for the surface light source device 20 and the optical member 30. The inclination angles of the multiple first element surfaces 66 included in a single first unit optical element 65 may be different from each other or the same. The first optical element section 60X may include first unit optical elements 65 that differ in at least one of their shape and orientation, or it may include only first unit optical elements 65 that are identical to each other.

[0088] As will be described later, the upper and lower limits of the inclination angle θ66 of the first element surface 66 may be determined from the viewpoint of suppressing reflection of light, particularly secondary light LB, at the second surface 50b. In this example, the inclination angle θ66 of the first element surface 66 may be 5° or more, 10° or more, or 15° or more. The inclination angle θ66 of the first element surface 66 may be 75° or less, 60° or less, or 50° or less. As shown in Figures 6A and 6B, the inclination angle θ66 of the first element surface 66 is the angle (°) between the normal direction ND of the first element surface 66 and the third direction D3, and is a value between 0° and less than 90°.

[0089] Unlike the examples shown in Figures 6A and 6B, the first element surface 66 may be somewhat curved. The first unit optical element 65 may have an external shape that is part of a sphere, such as a hemisphere, or it may have an external shape that is part of a spheroid.

[0090] Multiple first unit optical elements 65 may be arranged in a two-dimensional array. A two-dimensional array means that objects such as the first unit optical elements 65 are arranged in two or more non-parallel directions. Therefore, the first unit optical elements 65 may be dispersed in two or more directions. In this example, the first element surfaces 66 of the first unit optical elements 65 included in the first optical element section 60X face various directions. As a result, the first optical element section 60X can guide light in various directions by the two-dimensionally arranged first unit optical elements 65. In other words, light can be guided in multiple non-parallel directions, and the in-plane distribution of illuminance can be effectively made uniform. Each first unit optical element 65 may be configured with rotational symmetry about an axis parallel to the third direction D3. For example, each first unit optical element 65 may be configured with 3-fold rotational symmetry, 4-fold symmetry, or 6-fold symmetry about an axis parallel to the third direction D3.

[0091] The multiple first unit optical elements 65 may be arranged irregularly or regularly. By arranging the multiple first unit optical elements 65 regularly, the design of the first optical element section 60X can be simplified. By arranging the multiple first unit optical elements 65 regularly, it becomes easier to tile the first unit optical elements 65 without any gaps.

[0092] When observed from the third direction D3, if the dimensions of the first unit optical element 65 are large, unevenness in brightness caused by the shape of the first unit optical element 65 becomes more easily visible. From the viewpoint of preventing such problems, the maximum length of the first unit optical element 65 in the direction perpendicular to the stacking direction D3 may be 1.5 mm or less, 1 mm or less, or 0.5 mm or less. The arrangement pitch of the first unit optical element 65 may be 0.001 mm or more and 1.5 mm or less. Furthermore, from the viewpoint of effectively homogenizing the in-plane distribution of illuminance on the second surface 30b of the optical member 30 when applied to the surface light source device 20, the arrangement pitch of the first unit optical element 65 may be 0.005 mm or more and 1 mm or less, or 0.01 mm or more and 0.5 mm or less. The height or depth of the first unit optical element 65 in the third direction D3 may be 0.005 mm or more and 0.5 mm or less, or 0.01 mm or more and 0.25 mm or less.

[0093] Figures 8A and 8B show a specific example of a first unit optical element 65 included in the first optical element section 60X. In the example shown in Figures 8A and 8B, the arrangement of the multiple first unit optical elements 65 is a square arrangement. The multiple first unit optical elements 65 are arranged at a constant pitch in the first direction D1. The multiple first unit optical elements 65 are also arranged at a constant pitch in the second direction D2. The arrangement pitch in the first direction D1 and the arrangement pitch in the second direction D2 may be the same or different. In the example shown in Figures 8A and 8B, the multiple first unit optical elements 65 are tiled without any gaps. In the illustrated example, the arrangement pitch in the first direction D1 and the arrangement pitch in the second direction D2 are the same.

[0094] The first unit optical elements 65 may be arranged in directions inclined to the first direction D1 and the second direction D2. For example, in the example shown in Figure 8C, a plurality of first unit optical elements 65 are arranged at a constant pitch in two directions inclined ±45° with respect to the first direction D1. The arrangement in Figure 8C can be applied to the first unit optical elements 65 shown in Figure 8B. In this example, the first element surface 66 faces in two directions inclined ±45° with respect to the first direction D1, and light can be spread in these two directions.

[0095] Figures 9A and 9B show other specific examples of the first unit optical element 65 included in the first optical element section 60X. In the first optical element section 60X shown in Figures 9A and 9B, the first unit optical elements 65, each having the same bottom shape, are arranged in four orientations. As a result, multiple first unit optical elements 65 with the same bottom shape and orientation are arranged at a constant pitch in each of the first direction D1 and the second direction D2. The arrangement pitches in the two directions may be the same or different.

[0096] In the illustrated example, the arrangement pitch in each of the two directions is the same. The first unit optical element 65 has a triangular pyramidal shape with a right-angled isosceles triangle base. Two first unit optical elements 65 are arranged so that the bases of their isosceles triangles face each other. Pairs of two first unit optical elements 65 with facing bases are arranged in the first direction D1 and the second direction D2. Each first unit optical element 65 is arranged such that the equal sides of its right-angled isosceles triangle extend in the first direction D1 and the second direction D2. In the illustrated example, the orientation of the bases of one pair of first unit optical elements 65 is different from the orientation of the bases of another pair of first unit optical elements 65 adjacent to that pair in the first direction D1. The orientation of the bases of one pair of first unit optical elements 65 is different from the orientation of the bases of another pair of first unit optical elements 65 adjacent to the said pair of first unit optical elements 65 in the second direction D2.

[0097] The first unit optical elements 65 shown in Figure 9B may be arranged in a different arrangement than that shown in Figure 9A. For example, as shown in Figure 9C, multiple first unit optical elements 65 may be arranged in two directions inclined at ±45° with respect to the first direction D1. In this example, the equal sides of the right-angled isosceles triangle shape forming the base of the first unit optical element 65 may extend in two directions inclined at ±45° with respect to the first direction D1. The base of the right-angled isosceles triangle shape forming the base of the first unit optical element 65 may extend in the first direction D1 or the second direction D2.

[0098] Similar to the first layer 55, the transmission and reflection properties of the second sheet 50 may be dependent on the angle of incidence. The reflectance and transmittance of the second sheet 50 may change depending on the angle of incidence.

[0099] The transmittance of the second sheet 50 for light of a specific wavelength incident on the second sheet 50 at an incident angle of 0° may be less than the transmittance of the second sheet 50 for light of a specific wavelength incident on the second sheet 50 at an incident angle greater than 0°. The reflectance of the second sheet 50 for light of a specific wavelength incident on the second sheet 50 at an incident angle of 0° may be greater than the reflectance of the second sheet 50 for light of a specific wavelength incident on the second sheet 50 at an incident angle greater than 0°.

[0100] The transmittance of the second sheet 50 for light of a specific wavelength incident on the second sheet 50 at an incident angle of 0°, the transmittance of the second sheet 50 for light of a specific wavelength incident on the second sheet 50 at an incident angle of 30°, and the transmittance of the second sheet 50 for light of a specific wavelength incident on the second sheet 50 at an incident angle of 60° may increase in this order. The transmittance of the second sheet 50 for light of a specific wavelength incident on the second sheet 50 at incident angles of 0°, 10°, 20°, 30°, 40°, 50°, and 60° may gradually increase with increasing incident angle. The transmittance of the second sheet 50 for light of a specific wavelength incident on the second sheet 50 may gradually increase with increasing incident angle.

[0101] The reflectance of the second sheet 50 for light of a specific wavelength incident on the second sheet 50 at an incident angle of 0°, the reflectance of the second sheet 50 for light of a specific wavelength incident on the second sheet 50 at an incident angle of 30°, and the reflectance of the second sheet 50 for light of a specific wavelength incident on the second sheet 50 at an incident angle of 60° may decrease in this order. The reflectance of the second sheet 50 for light of a specific wavelength incident on the second sheet 50 at incident angles of 0°, 10°, 20°, 30°, 40°, 50°, and 60° may gradually decrease with increasing incident angle. The reflectance of the second sheet 50 for light of a specific wavelength incident on the second sheet 50 may gradually decrease with increasing incident angle.

[0102] The reflection and transmission characteristics of the second sheet 50 described above are the same as those of light from the light source 23, with the first surface 50a as the incident surface and the second surface 50b as the exit surface.

[0103] As shown in Figure 2, the surface light source device 20 includes a first optical sheet 81, a second optical sheet 82, and a reflective polarizer 85 superimposed on the optical member 30.

[0104] The first optical sheet 81 and the second optical sheet 82 exert optical effects such as reflection, refraction, and diffraction on incident light. The first optical sheet 81 and the second optical sheet 82 may have functions appropriate for the applications of the optical component 30 and the surface light source device 20.

[0105] Figure 10 shows a specific example of the first optical sheet 81 and the second optical sheet 82. The first optical sheet 81 and the second optical sheet 82 shown in Figure 10 are prism sheets that include a plurality of linearly extending unit prisms 84. The prism sheet includes a sheet-like main body portion 83 and a plurality of unit prisms 84 provided on the main body portion 83. The unit prisms 84 may extend linearly in a direction perpendicular to the arrangement direction of the plurality of unit prisms 84. That is, the first optical sheet 81 and the second optical sheet 82 are prism sheets in which the unit prisms 84 are linearly arranged.

[0106] The linearly arranged unit prisms 84 shown in Figure 10 primarily adjust the luminance angle distribution in a plane parallel to both the arrangement direction of the unit prisms 84 and the third direction D3. Therefore, the first optical sheet 81 and the second optical sheet 82 may be incorporated into the optical member 30 such that the arrangement directions of the unit prisms 84 are non-parallel. For example, the arrangement direction of the unit prisms 84 of the first optical sheet 81 may be orthogonal to the arrangement direction of the unit prisms 84 of the second optical sheet 82. The prism sheets shown in Figure 10 may also be "BEF" (registered trademark) available from 3M Corporation in the United States.

[0107] The reflective polarizer 85 transmits one linearly polarized component and reflects the other linearly polarized component. The reflective polarizer 85 allows for the selective transmission of linearly polarized light that can pass through the polarizer located on the surface light source device 20 side of the display panel 15. The light reflected by the reflective polarizer 85 can change its polarization state through subsequent reflections and may be re-entered into the reflective polarizer 85. This improves the utilization efficiency of the light emitted from the light source 23. The reflective polarizer 85 may be "DBEF" (registered trademark) available from 3M Corporation in the United States. The reflective polarizer 85 may also be "WRPS" high-brightness polarizing sheet available from Shinwa Intertek Corporation in South Korea, or a wire grid polarizer, etc.

[0108] Next, we will explain the operation of the surface light source device 20 having the above configuration when generating surface light.

[0109] As shown in Figure 2, the light source 23 emits primary light LA. Primary light LA ​​is, for example, blue light. The wavelength of the blue primary light LA ​​may be between 430 nm and 500 nm. The light L21 emitted from the light source 23 is directed toward the optical member 30. As shown in Figure 5, the primary light LA ​​from the light source 23 is incident on the first sheet 40 of the optical member 30.

[0110] As shown in Figure 5, the first sheet 40 includes a first barrier layer 41, a wavelength conversion layer 45, and a second barrier layer 42, starting from the second side in the third direction D3. Light incident on the first sheet 40 passes through the first barrier layer 41 and proceeds to the wavelength conversion layer 45.

[0111] As shown in Figure 5, the wavelength conversion layer 45 contains a wavelength conversion agent 47. Some of the light traveling through the wavelength conversion layer 45 collides with the wavelength conversion agent 47. The wavelength conversion agent 47 absorbs the primary light LA ​​emitted from the light source 23 and emits secondary light LB of a different wavelength. In the illustrated example, the wavelength conversion layer 45 contains a first converter 47A and a second converter 47B. The first converter 47A absorbs some of the blue primary light LA ​​L51 and emits green first secondary light LB1. The second converter 47B absorbs some of the blue primary light LA ​​L52 and emits red second secondary light LB2. As shown in Figure 5, some of the primary light LA ​​L53 does not enter the wavelength conversion agent 47 but reaches the second surface 60b.

[0112] The light that has passed through the wavelength conversion layer 45 then passes through the second barrier layer 42 and is emitted from the first sheet 40.

[0113] Light transmitted through the first sheet 40 is directed toward the second sheet 50. The second sheet 50 includes a first layer 55 and a second layer 60, starting from the second side in the third direction D3. Primary light LA ​​from the light source 23 is incident on the first layer 55 of the second sheet 50. The transmittance of the first layer 55 depends on the angle of incidence to the second sheet 50. As an example, the second sheet 50 may have the reflective and transmitting properties described below.

[0114] The reflectance of the first layer 55 for primary light LA ​​incident on the second sheet 50 at a certain incident angle greater than 0° is less than the reflectance of the first layer 55 for primary light LA ​​incident on the second sheet 50 at a 0° incident angle. The reflectance of the first layer 55 is less for primary light LA ​​incident on the second sheet 50 at a certain incident angle greater than 0° than for primary light LA ​​incident on the second sheet 50 at a 0° incident angle. The transmittance of the first layer 55 for primary light LA ​​incident on the second sheet 50 at a certain incident angle greater than 0° is greater than the transmittance of the first layer 55 for primary light LA ​​incident on the second sheet 50 at a 0° incident angle. The transmittance of the first layer 55 is greater for primary light LA ​​incident on the second sheet 50 at a certain incident angle greater than 0° than for primary light LA ​​incident on the second sheet 50 at a 0° incident angle.

[0115] The reflectance of the first layer 55 for light of a specific wavelength incident on the second sheet 50 at an incident angle of 0°, the reflectance of the first layer 55 for light of a specific wavelength incident on the second sheet 50 at an incident angle of 30°, and the reflectance of the first layer 55 for light of a specific wavelength incident on the second sheet 50 at an incident angle of 60° may decrease in this order. The reflectance of the first layer 55 for light of a specific wavelength incident on the second sheet 50 at incident angles of 0°, 10°, 20°, 30°, 40°, 50°, and 60° may gradually decrease as the incident angle increases. The transmittance of the first layer 55 for light of a specific wavelength incident on the second sheet 50 at an incident angle of 0°, the transmittance of the first layer 55 for light of a specific wavelength incident on the second sheet 50 at an incident angle of 30°, and the transmittance of the first layer 55 for light of a specific wavelength incident on the second sheet 50 at an incident angle of 60° may increase in this order. The transmittance of the first layer 55 for light of a specific wavelength incident on the second sheet 50 at incident angles of 0°, 10°, 20°, 30°, 40°, 50°, and 60° may gradually increase with increasing incident angle.

[0116] The region facing the light source 23 in the third direction D3, and the surrounding region in the vicinity of this region, are defined as the direct overhead region. A large amount of primary light LA ​​is directly incident on this direct overhead region from the light source 23. The angle of incidence of the primary light LA ​​on the direct overhead region is relatively small. The light of a specific wavelength that affects the optical properties of the first layer 55 may include primary light LA. The light L21 and L22, which are primary light LA ​​emitted from the light source 23 and have traveled to the first layer 55, are reflected with high reflectivity in the direct overhead region. In the direct overhead region, the light L21 and L22 are transmitted through the first layer 55 with low transmittance. This prevents the light-emitting surface 20a from becoming too bright in the direct overhead region.

[0117] As shown in Figure 2, the primary light LA, L21 and L22, reflected by the first layer 55, pass through the first sheet 40 and head towards the light source substrate 22. This light L21 and L22 are reflected back in the direction of propagation in the third direction D3 by, for example, the reflective layer 27 of the light source substrate 22. The light L21 and L22 pass through the first sheet 40 and head towards the second sheet 50 again. Such light L21 may travel in a direction that is significantly inclined with respect to the third direction D3 due to the diffusion component within the first sheet 40. Similarly, such light L22 may travel in a direction that is significantly inclined with respect to the third direction D3 due to diffuse reflection by the reflective layer 27. As shown in Figure 2, the re-incident light L21 and L22 to the first layer 55 re-incident to the optical member 30 at a position away from the light source 23 in the first direction D1 and the second direction D2 which are perpendicular to the third direction D3. As a result, the re-incident light L21 and L22 on the second sheet 50 can pass through the first layer 55 in the separated region away from the light source 23 in a direction perpendicular to the third direction D3. This prevents the light-emitting surface 20a from becoming too dark in the separated region.

[0118] As described above, the selective transmittance of the first layer 55 according to the incident angle suppresses in-plane variations in brightness according to the arrangement of the light source 23. This effectively equalizes the illuminance at each position on the second surface 55b of the first layer 55.

[0119] The selective reflectivity and selective transmittance of the first layer 55 are affected by light of a specific wavelength. In many first layers 55 made of dielectric multilayer films 56 or diffractive optical elements, the optical properties affected by light of a specific wavelength differ from those affected by light of other wavelengths. The first layer 55 made of dielectric multilayer films 56, etc., does not easily exhibit selective reflectivity or selective transmittance for light of wavelengths longer than the specific wavelength. Therefore, in the illustrated example, the first layer 55 made of dielectric multilayer films 56, etc., does not exhibit selective reflectivity or selective transmittance for red light or green light. With respect to red light and green light, the variation in transmittance and reflectivity of the first layer 55 depending on the angle of incidence to the second sheet 50 may be small. Taking this into consideration, in the above example, the amount of wavelength conversion agent 47 contained in the wavelength conversion layer 45 may be reduced. By reducing the content of the wavelength conversion agent 47, the in-plane brightness distribution caused by the primary light LA ​​can be sufficiently homogenized before the wavelength conversion of the primary light LA ​​to the secondary light LB can be performed. While reducing the content of the wavelength conversion agent 47, it is possible to suppress in-plane variations in brightness caused by primary light LA ​​and secondary light LB, as well as in-plane variations in color caused by primary light LA ​​and secondary light LB.

[0120] As a result, the brightness on the second surface 55b can be made sufficiently uniform, and the color on the second surface 55b can be made sufficiently uniform. In addition, since the thickness of the second layer 60 can be reduced, the thickness of the optical component 30 and the surface light source device 20 can be kept sufficiently thin.

[0121] Furthermore, the angle between the direction of propagation of the primary light LA ​​and the third direction D3 tends to be small in the region directly above the light source 23. The angle between the direction of propagation of the primary light LA ​​and the third direction D3 tends to be large in the separated region, which is perpendicular to the third direction D3 from the light source 23. Due to this tendency, the optical path length of the primary light LA ​​within the first sheet 40 becomes shorter in the region directly above. Therefore, the probability that the primary light LA ​​is wavelength-converted by the wavelength-converting agent 47 in the region directly above becomes low. In the separated region, the optical path length of the primary light LA ​​within the first sheet 40 becomes longer. Therefore, the probability that the primary light LA ​​is wavelength-converted by the wavelength-converting agent 47 in the separated region becomes high. This suppresses in-plane color variation.

[0122] The first sheet 40, containing the wavelength conversion agent 47, is located in the third direction D3 between the light source substrate 22 and the second sheet 50, which has a selective reflection function. That is, the first sheet 40 is located within the circulating optical path of the primary light LA ​​for homogenizing the in-plane brightness distribution. Therefore, the content of the wavelength conversion agent 47 in the first sheet 40 can be reduced.

[0123] Light transmitted through the first layer 55 enters the second layer 60. The second layer 60 contains a plurality of first unit optical elements 65. The second layer 60 provides a first uneven surface 61 to the second surface 50b of the second sheet 50 and the second surface 30b of the optical member 30. The first uneven surface 61 is composed of the first element surface 66 of the first unit optical element 65. As shown in Figure 6A, light L61 exits the first layer 55 and the optical member 30 by passing through the first uneven surface 61. The light L61 bends in its direction of propagation due to refraction at the first uneven surface 61.

[0124] As described above, the light L21 and L22 (see Figure 2), including the primary light LA, the first secondary light LB1, and the second secondary light LB2, can be emitted from the optical member 30 towards the first side in the third direction D3. The light L21 and L22 emitted from the optical member 30 passes through the first optical sheet 81, the second optical sheet 82, and the reflective polarizer 85, and is emitted from the light-emitting surface 20a of the surface light source device 20. In this way, the light-emitting surface 20a of the surface light source device 20 emits light.

[0125] Incidentally, conventional surface light source devices have suffered from problems such as the light-emitting surface becoming dim. Conventional surface light source devices include a light source and optical components. The optical components include, in order from the light source side, a second sheet having transmission and reflection characteristics dependent on the angle of incidence, and a first sheet containing a wavelength conversion agent. The inventors of this invention first tried swapping the arrangement of the first and second sheets in the optical components. That is, the inventors of this invention investigated a surface light source device that includes a first sheet containing a wavelength conversion agent and a second sheet having transmission and reflection characteristics dependent on the angle of incidence, in this order from the light source side. In the surface light source device in which the arrangement of the first and second sheets was swapped, in order to eliminate in-plane brightness variations caused by the light source, an uneven surface made of a unit optical element was provided on the surface of the second sheet facing the first sheet. This uneven surface on the light-receiving side was able to suppress in-plane brightness variations. The brightness of the light-emitting surface was improved to some extent by swapping the arrangement of the first and second sheets. However, when applied to display devices and the like, the light-emitting surface did not achieve sufficient brightness.

[0126] In the surface light source device 20 according to this embodiment, the second sheet 50 further includes a second layer 60 in addition to a first layer 55 having transmission and reflection characteristics dependent on the angle of incidence. The first layer 55 is located between the first sheet 40 and the second layer 60 in a third direction D3. The second layer 60 includes a first optical element section 60X which includes a plurality of first unit optical elements 65. The first optical element section 60X, with the plurality of first unit optical elements 65, constitutes a first uneven surface 61 of the second sheet 50. The first uneven surface 61 constitutes the so-called light-emitting surface of the optical member 30.

[0127] As demonstrated in the later embodiment, the surface light source device 20 according to this embodiment allows for sufficient brightness reduction while adequately suppressing in-plane variations in brightness, resulting in sufficiently bright illumination of the second surface 30b of the optical element 30 and the light-emitting surface 20a of the surface light source device 20. The inventors confirmed that the reason for the effect of brightening the light-emitting surface 20a is that the transmittance of the second sheet 50 for secondary light LB is sufficiently high. If the transmittance of the second sheet 50 for secondary light LB is low, the secondary light LB is reflected or absorbed by the second sheet 50. Absorption results in a loss of light from the light source. When secondary light LB is reflected, a portion of the secondary light LB is also lost. When a first layer 55 made of a dielectric multilayer film 56 or the like is used, the transmittance and reflectance for secondary light LB, which has a longer wavelength than primary light LA, do not vary significantly depending on the angle of incidence to the second sheet 50. In other words, selective reflection of secondary light LB by the first layer 55 for the purpose of suppressing in-plane variations in illuminance is not anticipated. Under these assumptions, it is not necessary to set the reflectivity of the second sheet 50 for the secondary light LB above a certain level. The transmittance of the second sheet 50 for the secondary light LB may be high. By making the transmittance of the second sheet 50 for the secondary light LB sufficiently high, the utilization efficiency of the secondary light LB can be improved. Consequently, the utilization efficiency of the light from the light source 23 is improved, and the light-emitting surface 20a can be made sufficiently bright.

[0128] In terms of specific configuration, in the optical member 30 according to this embodiment, the second layer 60 includes a first optical element section 60X that constitutes the second surface 60b. The first optical element section 60X includes a plurality of first unit optical elements 65. The first optical element section 60X, with its first element surfaces 66 of the plurality of first unit optical elements 65, constitutes the first uneven surface 61 of the second sheet 50. As shown in Figure 6A, this first uneven surface 61 makes it possible to reduce the angle of incidence of secondary light LB, which travels in a direction inclined with respect to the third direction D3, onto the first element surface 66. This makes it possible to suppress reflection of secondary light LB at the first element surface 66. In particular, it makes it possible to suppress total internal reflection of secondary light LB at the first element surface 66. The first uneven surface 61, which is composed of a plurality of first unit optical elements 65, makes it possible to increase the transmittance for secondary light LB. By improving the utilization efficiency of secondary light LB, the light-emitting surface 20a can be made brighter.

[0129] On the other hand, if the second layer 60 is not provided, as shown by the dashed line in Figure 6A, the light L62 is easily reflected by the flat second surface of the second sheet, and may even undergo total internal reflection. In other words, when a second sheet without the second layer 60 is used, it is presumed that the reflectance of the second sheet with respect to the secondary light LB increases, and consequently the transmittance of the second sheet with respect to the secondary light LB decreases. Due to the reflection loss of the secondary light LB, the utilization efficiency of the secondary light LB decreases, and the light-emitting surface becomes darker.

[0130] To suppress in-plane variations in brightness and color, the transmission characteristics for green and red light as secondary light LB may be the same as those for blue light as primary light LA. Specifically, the second sheet 50 may have the following optical characteristics for green light. Here, green light may be light with a wavelength of 550 nm.

[0131] The transmittance of the second sheet 50 for green light incident on the second sheet 50 at an incident angle of 60° may be 50% or more. The reflectance of the second sheet 50 for green light incident on the second sheet 50 at an incident angle of 60° may be less than 50%. The transmittance of the second sheet 50 for green light incident on the second sheet 50 at an incident angle of 0° may be less than the transmittance of the second sheet 50 for light of a specific wavelength incident on the second sheet 50 at a certain incident angle greater than 0°. The reflectance of the second sheet 50 for green light incident on the second sheet 50 at an incident angle of 0° may be greater than the reflectance of the second sheet 50 for green light incident on the second sheet 50 at an incident angle greater than 0°. The transmittance of the second sheet 50 for green light incident on the second sheet 50 at an incident angle of 0° may be smaller than the transmittance of the second sheet 50 for green light incident on the second sheet 50 at an incident angle of 30°, and the transmittance of the second sheet 50 for green light incident on the second sheet 50 at an incident angle of 30° may be smaller than the transmittance of the second sheet 50 for green light incident on the second sheet 50 at an incident angle of 60°. In other words, the transmittance of the second sheet 50 may be larger for green light incident on the second sheet 50 at an incident angle of 30° than for green light incident on the second sheet 50 at an incident angle of 0°, and the transmittance of the second sheet 50 may be larger for green light incident on the second sheet 50 at an incident angle of 60° than for green light incident on the second sheet 50 at an incident angle of 30°. The transmittance of the second sheet 50 for green light incident on the second sheet 50 at incident angles of 0°, 10°, 20°, 30°, 40°, 50°, and 60° may gradually increase with increasing incident angle. The transmittance of the second sheet 50 with respect to green light incident on the second sheet 50 may gradually increase with increasing angle of incidence. The reflectance of the second sheet 50 for green light incident on the second sheet 50 at an incident angle of 0° may be greater than the reflectance of the second sheet 50 for green light incident on the second sheet 50 at an incident angle of 30°, and the reflectance of the second sheet 50 for green light incident on the second sheet 50 at an incident angle of 30° may be greater than the reflectance of the second sheet 50 for green light incident on the second sheet 50 at an incident angle of 60°. In other words, the reflectance of the second sheet 50 may be smaller for green light incident on the second sheet 50 at an incident angle of 30° than for green light incident on the second sheet 50 at an incident angle of 0°, and the reflectance of the second sheet 50 may be smaller for green light incident on the second sheet 50 at an incident angle of 60° than for green light incident on the second sheet 50 at an incident angle of 30°. The reflectance of the second sheet 50 for green light incident on the second sheet 50 at incident angles of 0°, 10°, 20°, 30°, 40°, 50°, and 60° may gradually decrease as the incident angle increases. The reflectance of the second sheet 50 with respect to green light incident on the second sheet 50 may gradually decrease as the angle of incidence increases.

[0132] When the wavelength conversion agent 47 is uniformly dispersed in the wavelength conversion layer 45, the amount of secondary light LB generated tends to be greater in the region directly above where the amount of primary light LA ​​is high than in the region between the primary and secondary light LA. That is, the brightness caused by green light as secondary light LB tends to be brighter in the region directly above than in the region between the primary and secondary light LA. Also, although the direction in which secondary light LB is emitted from the wavelength conversion agent 47 does not coincide with the direction in which primary light LA ​​is incident on the wavelength conversion agent 47, it is dispersed within a range centered on the incident direction of primary light LA. That is, the direction of propagation of secondary light LB tends to form a relatively small angle with respect to the third direction D3 in the region directly above, similar to the direction of propagation of primary light LA. The direction of propagation of secondary light LB tends to form a relatively large angle with respect to the third direction D3 in the region between the primary and secondary light LA, similar to the direction of propagation of primary light LA. Therefore, according to the transmission and reflection characteristics of the second sheet 50 for green light described above, in-plane variations in brightness caused by green light can be suppressed. As a result, in-plane variations in color can also be suppressed.

[0133] The second sheet 50 may have the following optical properties with respect to red light. Here, red light may be light with a wavelength of 650 nm.

[0134] The transmittance of the second sheet 50 for red light incident on the second sheet 50 at an incident angle of 60° may be 50% or more. The reflectance of the second sheet 50 for red light incident on the second sheet 50 at an incident angle of 60° may be less than 50%. The transmittance of the second sheet 50 for red light incident on the second sheet 50 at an incident angle of 0° may be less than the transmittance of the second sheet 50 for light of a specific wavelength incident on the second sheet 50 at an incident angle greater than 0°. The reflectance of the second sheet 50 for red light incident on the second sheet 50 at an incident angle of 0° may be greater than the reflectance of the second sheet 50 for red light incident on the second sheet 50 at an incident angle greater than 0°. The transmittance of the second sheet 50 for red light incident on the second sheet 50 at an incident angle of 0° may be smaller than the transmittance of the second sheet 50 for red light incident on the second sheet 50 at an incident angle of 30°, and the transmittance of the second sheet 50 for red light incident on the second sheet 50 at an incident angle of 30° may be smaller than the transmittance of the second sheet 50 for red light incident on the second sheet 50 at an incident angle of 60°. In other words, the transmittance of the second sheet 50 may be larger for red light incident on the second sheet 50 at an incident angle of 30° than for red light incident on the second sheet 50 at an incident angle of 0°, and the transmittance of the second sheet 50 may be larger for red light incident on the second sheet 50 at an incident angle of 60° than for red light incident on the second sheet 50 at an incident angle of 30°. The transmittance of the second sheet 50 for red light incident on the second sheet 50 at incident angles of 0°, 10°, 20°, 30°, 40°, 50°, and 60° may gradually increase with increasing incident angle. The transmittance of the second sheet 50 with respect to red light incident on the second sheet 50 may gradually increase with increasing angle of incidence. The reflectance of the second sheet 50 for red light incident on the second sheet 50 at an incident angle of 0° may be greater than the reflectance of the second sheet 50 for red light incident on the second sheet 50 at an incident angle of 30°, and the reflectance of the second sheet 50 for red light incident on the second sheet 50 at an incident angle of 30° may be greater than the reflectance of the second sheet 50 for red light incident on the second sheet 50 at an incident angle of 60°. In other words, the reflectance of the second sheet 50 may be smaller for red light incident on the second sheet 50 at an incident angle of 30° than for red light incident on the second sheet 50 at an incident angle of 0°, and the reflectance of the second sheet 50 may be smaller for red light incident on the second sheet 50 at an incident angle of 60° than for red light incident on the second sheet 50 at an incident angle of 30°. The reflectance of the second sheet 50 for red light incident on the second sheet 50 at incident angles of 0°, 10°, 20°, 30°, 40°, 50°, and 60° may gradually decrease as the incident angle increases. The reflectance of the second sheet 50 with respect to red light incident on the second sheet 50 may gradually decrease as the angle of incidence increases.

[0135] When the wavelength conversion agent 47 is uniformly dispersed in the wavelength conversion layer 45, the amount of secondary light LB generated tends to be greater in the region directly above where the amount of primary light LA ​​is high than in the region between the primary and secondary light LA. That is, the brightness caused by red light as secondary light LB tends to be brighter in the region directly above than in the region between the primary and secondary light LA. Also, although the direction in which secondary light LB is emitted from the wavelength conversion agent 47 does not coincide with the direction in which primary light LA ​​is incident on the wavelength conversion agent 47, it is dispersed within a range centered on the incident direction of primary light LA. That is, the direction of propagation of secondary light LB tends to form a relatively small angle with respect to the third direction D3 in the region directly above, similar to the direction of propagation of primary light LA. The direction of propagation of secondary light LB tends to form a relatively large angle with respect to the third direction D3 in the region between the primary and secondary light LA, similar to the direction of propagation of primary light LA. Therefore, according to the transmission and reflection characteristics of the second sheet 50 for red light described above, in-plane variations in brightness caused by red light can be suppressed. As a result, in-plane variations in color can also be suppressed.

[0136] In the embodiment described above, the surface light source device 20 includes a first sheet 40 and a second sheet 50 in that order. The first sheet 40 includes a wavelength conversion agent 47 that absorbs primary light LA ​​and emits secondary light LB. The second sheet 50 includes a first layer 55 and a second layer 60 in that order. The first layer 55 is located between the first sheet 40 and the second layer 60. The second layer 60 includes a first optical element section 60X which includes a plurality of first unit optical elements 65. The first optical element section 60X, with the plurality of first unit optical elements 65, constitutes the uneven second surface 50b of the second sheet 50. The transmittance of the first layer 55 for light of a specific wavelength incident on the second sheet 50 at an incident angle of 0°, the transmittance of the first layer 55 for light of a specific wavelength incident on the second sheet 50 at an incident angle of 30°, and the transmittance of the first layer 55 for light of a specific wavelength incident on the second sheet 50 at an incident angle of 60° may increase in this order. The transmittance of the second sheet 50 for light of a specific wavelength incident on the second sheet 50 at an incident angle of 0°, the transmittance of the second sheet 50 for light of a specific wavelength incident on the second sheet 50 at an incident angle of 30°, and the transmittance of the second sheet 50 for light of a specific wavelength incident on the second sheet 50 at an incident angle of 60° may increase in this order. According to this embodiment, the brightness of the light-emitting surface 20a can be made sufficiently bright while suppressing in-plane brightness variations caused by the arrangement of the light source 23. Furthermore, since the thickness of the second layer 60 can be reduced, the thickness of the surface light source device 20 can be kept sufficiently thin.

[0137] While one embodiment has been described with reference to specific examples, the above-mentioned example does not limit this embodiment. The above-described embodiment can be implemented in various other examples, and various omissions, substitutions, modifications, and additions can be made without departing from its essence.

[0138] An example of modification will be described below with reference to the drawings. In the following explanation 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.

[0139] As shown in Figure 11, the first sheet 40 and the second sheet 50 may be joined together. In the example shown in Figure 11, the first sheet 40 and the second sheet 50 are joined via a bonding layer 32. The bonding layer 32 is located between the first sheet 40 and the second sheet 50 in the third direction D3. The bonding layer 32 is bonded to both the first sheet 40 and the second sheet 50. By using the bonding layer 32, the second surface 40b of the first sheet 40 does not adjoin the air layer. By using the bonding layer 32, the first surface 50a of the second sheet 50 does not adjoin the air layer. Therefore, the refractive index difference at the interface formed between the adjacent portions of the second surface 40b and the first surface 50a can be reduced. This suppresses unintended reflections on the second surface 40b and the first surface 50a. This improves the light utilization efficiency and makes the light-emitting surface 20a brighter. The bonding layer 32 can be formed using various adhesives and tacks such as acrylic resin, epoxy resin, and polyester resin. The thickness of the bonding layer 32 along the third direction D3 may be, for example, 1 μm or more and 50 μm or less.

[0140] The optical member 30 is not limited to the specific examples described above. As shown in Figure 12, the second sheet 50 may include a third layer 70 located between the first sheet 40 and the first layer 55. The third layer 70 has a diffusion function that diffuses light. Diffusion by the third layer 70 can suppress in-plane brightness variations caused by the position of the light source 23. The third layer 70 includes a first surface 70a and a second surface 70b. The first surface 70a and the second surface 70b face the third direction D3. The first surface 70a faces the second side in the third direction D3. The second surface 70b faces the first side in the third direction D3. The third layer 70 is bonded to the first layer 55 at the second surface 70b. In the illustrated example, the first surface 70a may constitute the first surface 50a of the second sheet 50 and the first surface 40a of the first sheet 40, which is the light-receiving surface. The first surface 70a includes the second uneven surface 71.

[0141] The third layer 70 may include a second optical element section 70X. The second optical element section 70X includes a plurality of second unit optical elements 75, each formed as a convex portion 73 or a concave portion 74. In the example shown in Figure 12, the third layer 70 is composed of the second optical element section 70X. The second unit optical element 75 is an element that changes the direction of light propagation by refraction, reflection, etc. The second unit optical element 75 is a concept that includes elements called unit shape elements, unit prisms, and unit lenses. The second unit optical element 75 constitutes the first surface 70a. The second concave-convex surface 71 is composed of the second unit optical element 75.

[0142] The second optical element 70X shown in Figure 12 includes a sheet-like second main body 72 and a plurality of protrusions 73 provided on the second main body 72. In the example shown in Figure 12, the plurality of protrusions 73 may be provided adjacent to each other without gaps. The second optical element 70X may also include a second main body 72 provided with a plurality of recesses. The plurality of recesses may be provided adjacent to each other without gaps.

[0143] As shown in Figure 12, the second unit optical element 75 includes a second element surface 76. The second element surface 76 is inclined with respect to the third direction D3. The second unit optical element 75 is defined by this second element surface 76. The second uneven surface 71 is formed by the second element surface 76 of the second unit optical element 75.

[0144] The optical properties of the second uneven surface 71 are affected by the inclination angle of the second element surface 76 of the second unit optical element 75. Therefore, the cross-sectional shape of the second unit optical element 75 can be appropriately adjusted based on the optical properties required for the surface light source device 20 and the optical member 30. The inclination angles of the multiple second element surfaces 76 included in a single second unit optical element 75 may be different from each other or the same. The second optical element section 70X may include second unit optical elements 75 that differ in at least one of their shape and orientation, or it may include only second unit optical elements 75 that are identical to each other.

[0145] From the viewpoint of suppressing in-plane brightness variations caused by the arrangement of the light source 23, upper and lower limits may be determined for the inclination angle θ76 of the second element surface 76. In this example, the inclination angle θ76 of the second element surface 76 may be 5° or more, 10° or more, or 15° or more. The inclination angle θ76 of the second element surface 76 may be 75° or less, 60° or less, or 50° or less. As shown in Figure 12, the inclination angle θ76 of the second element surface 76 is the angle (°) between the normal direction ND2 of the second element surface 76 and the third direction D3, and is a value between 0° and less than 90°.

[0146] The second optical element section 70X may have a configuration similar to that of the first optical element section 60X described above. For example, the arrangement method, arrangement pitch, shape, dimensions, material, etc. of the second unit optical element 75 may be the same as the arrangement method, arrangement pitch, shape, dimensions, material, etc. already described for the first unit optical element 65. The second optical element section 70X may have the configuration shown in Figures 8A, 8B, 8C, 9A, 9B, and 9C, except that it is located on the second side of the third direction D3 of the first layer 55 rather than the first side of the third direction D3 of the first layer 55. Furthermore, the second sheet 50 including the third layer 70 may have the transmission and reflection characteristics of the second sheet 50 described above.

[0147] As another modification, the second layer 60 may include a diffractive optical element 60Y in place of or in addition to the first optical element 60X. Similarly, the third layer 70 may include a diffractive optical element 70Y in place of or in addition to the second optical element 70X. As shown in Figure 13, the second layer 60 may consist of a diffractive optical element 60Y. The third layer 70 may consist of a diffractive optical element 70Y. The diffractive optical elements 60Y, 70Y are elements that exert a diffractive effect on incident light. The diffractive optical elements 60Y, 70Y may also be holographic elements. Diffractive optical elements 60Y, 70Y having diffraction characteristics to achieve desired optical properties can be designed relatively easily.

[0148] The diffractive optical elements 60Y and 70Y may also be computer-generated holograms (CGH). Computer-generated holograms are fabricated by calculating a diffraction structure on a computer that achieves arbitrary diffraction characteristics. By using computer-generated holograms as the diffractive optical elements 60Y and 70Y, 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, uneven surfaces 61 and 71 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, the diffractive optical elements 60Y and 70Y as computer-generated holograms can be fabricated at low cost using a simple procedure.

[0149] The diffractive optical elements 60Y and 70Y may be phase-modulated holograms. The diffractive optical elements 60Y and 70Y may be amplitude-modulated holograms. The diffractive optical elements 60Y and 70Y are not limited to computer-generated holograms. The diffractive optical elements 60Y and 70Y may be, for example, volume holograms.

[0150] The second layer 60 and the third layer 70 may be formed on the first layer 55. The second layer 60 and the third layer 70 may be joined to the first layer 55 using a bonding layer consisting of an adhesive layer or a tack layer.

[0151] One or more of the first optical sheet 81, the second optical sheet 82, and the reflective polarizer 85 may be omitted from the optical control member 18 of the surface light source device 20. The optical control member 18 may further include members that are expected to perform some function. [Examples]

[0152] The above-described embodiment will be explained in more detail below using examples, but the above-described embodiment is not limited to the following examples.

[0153] The surface light source devices for Examples 1-3 and Comparative Examples 1 and 2 were manufactured as follows.

[0154] <Example 1> The surface light source device of Example 1 had the configuration shown in Figures 2 to 6A. The surface light source device included a light source substrate containing a light source, an optical component, a first optical sheet, a second optical 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 PL1 of the light sources in the first direction was 6 mm. The arrangement pitch PL2 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 so that their sides aligned with the first and second directions. The distance along the third direction D3 from the surface of the light source facing the optical component to the light-receiving side of the optical component was 0.5 mm.

[0155] In the surface light source device of Example 1, the optical components included a first sheet and a second sheet in the order shown in Figure 2, from the second side to the first side in the third direction D3. The first sheet was QF-6000, available from Showa Denko Materials. The first sheet contained a first converter and a second converter. The first converter absorbed light with a wavelength of 450 nm and emitted green light. The second converter absorbed light with a wavelength of 450 nm and emitted red light.

[0156] As shown in Figure 6A, the second sheet 50 contained the first and second layers in this order from the second side to the first side in the third direction D3. The first layer was a dielectric multilayer film. The transmission and reflection characteristics of the dielectric multilayer film constituting the first layer had the same trend as the transmission and reflection characteristics shown in Figure 7. The second layer was the first optical element. The first optical element was molded by supplying an uncured ultraviolet-curable resin composition between the mold and the first layer and curing it between the mold and the first layer.

[0157] The first optical element section included a first main body and first unit optical elements as convex portions arranged on the first main body. The first optical element section included first unit optical elements having the shape, arrangement, and other configurations described with reference to Figures 9A and 9B. As shown in Figure 9B, the first unit optical element was a convex portion in the shape of a triangular pyramid. The first unit optical element included three first element faces. The base of the triangular pyramid was a right-angled isosceles triangle. As shown in Figure 9A, first unit optical elements of the same shape were laid out without gaps on the surface of the first main body, with the orientation of the base faces varied in four ways. The element faces of the first unit optical element included equilateral element faces extending from the equilateral sides of the right-angled isosceles triangle that forms the base, and base element faces extending from the base of the right-angled isosceles triangle that forms the base. The lengths of the two equal sides of the right-angled isosceles triangle forming the base were each 0.1 mm. The inclination angle θ66 of each equal-angled element face was 45°. The inclination angle θ66 of the base element face was also 45°. As shown in Figure 6A, the inclination angle θ66 of the element face is the angle between the normal direction to the element face and a third direction, and is a value between 0° and less than 90°. The equal-angled element faces and the base element face formed the first uneven surface that becomes the light-emitting surface of the optical member.

[0158] Two BEF® luminance-enhancing films, available from 3M, were used as the first and second optical sheets. For the first optical sheet, the longitudinal direction of the prism extended in the second direction. For the second optical sheet, the longitudinal direction of the prism extended in the first direction. A DBEF® luminance-enhancing film, also available from 3M, was used as the reflective polarizer.

[0159] <Example 2> Example 2 differed from Example 1 described above in that the second sheet of the optical member included a third layer. Example 2 had the same configuration as Example 1 described above, except for the third layer. In Example 2, as shown in Figure 12, the optical member included the third layer, the first layer, and the second layer in this order from the second side to the first side in the third direction D3. The third layer served as the second optical element. The second optical element was molded by supplying an uncured UV-curable resin composition between the mold and the first layer and curing it between the mold and the first layer.

[0160] The second optical element section included a second main body and second unit optical elements as convex portions arranged on the second main body. The second optical element section included second unit optical elements having the shape, arrangement, and other configurations described with reference to Figures 9A and 9B. As shown in Figure 9B, the second unit optical element was a convex portion in the shape of a triangular pyramid. The second unit optical element included three element faces. The base of the triangular pyramid was a right-angled isosceles triangle. As shown in Figure 9A, second unit optical elements of the same shape were laid out without gaps on the second main body with the orientation of the base changed in four different ways. The element faces of the second unit optical element included equilateral element faces extending from the equilateral sides of the right-angled isosceles triangle that forms the base, and base element faces extending from the base of the right-angled isosceles triangle that forms the base. 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 θ76 of each equal-sided element face was 16.5°. The inclination angle θ76 of the base element face was 16.5°. As shown in Figure 12, the inclination angle of an element face is the angle between the normal direction to the element face and a third direction, and is a value between 0° and less than 90°. The equal-sided element faces and the base element faces formed the second uneven surface which became the light-receiving surface of the second sheet.

[0161] <Example 3> Example 3 differed from Example 2 in the second layer of the second sheet included in the optical member. Example 3 had the same configuration as Example 2 except for the second layer. In Example 3, as shown in Figure 12, the second sheet contained the third layer, the first layer, and the second layer in this order from the second side to the first side in the third direction D3.

[0162] The first optical element section included a first main body and first unit optical elements as convex portions arranged on the first main body. The first optical element section included first unit optical elements having the shape, arrangement, and other configurations described with reference to Figures 8B and 8C. As shown in Figure 8B, the first unit optical element was a convex portion in the shape of a regular square pyramid. The first unit optical element included four first element faces. As shown in Figure 8C, first unit optical elements of the same shape were arranged at a constant pitch in two directions inclined ±45° in the first direction. The first unit optical elements were laid out without gaps on the second main body. The length of one side of the square forming the base was 0.05 mm. The inclination angle θ66 of each first element face was 45°. The first element faces formed a first concave-convex surface which became the light-emitting surface of the optical member.

[0163] <Comparative Example 1> Comparative Example 1 differed from Example 1 in that the second layer was omitted from the second sheet of the optical component. Comparative Example 1 had the same configuration as Example 1 except for the second layer. In Comparative Example 1, the second sheet contained only the first layer, which was a dielectric multilayer film.

[0164] <Comparative Example 2> Comparative Example 2 differed from Example 2 described above in that the second layer was omitted from the second sheet of the optical element. Comparative Example 2 had the same configuration as Example 2 described above, except for the second layer. In Comparative Example 2, the second sheet contained the third layer and the first layer in this order from the second side to the first side in the third direction D3.

[0165] <Rating 1> The transmittance of the second sheet was adjusted. The transmittance was measured using a V-670 ultraviolet-visible-near-infrared spectrophotometer manufactured by JASCO Corporation. The incident angles for measuring transmittance were 0°, 30°, and 60°. The wavelength used for measuring transmittance was varied in 1 nm increments within the wavelength range including the visible light range from 380 nm to 780 nm. The transmittance characteristics of the second sheet in Example 1 are shown in Figure 14. The transmittance characteristics of the second sheet in Example 2 are shown in Figure 15. The transmittance characteristics of the second sheet in Example 3 are shown in Figure 16. The transmittance characteristics of the second sheet in Comparative Example 1 are shown in Figure 17. The transmittance characteristics of the second sheet in Comparative Example 2 are shown in Figure 18. The transmittance of the second sheet for light at a wavelength of 450 nm, the transmittance of the second sheet for light at a wavelength of 550 nm, and the transmittance of the second sheet for light at a wavelength of 650 nm are shown in Table 1 of Figure 19.

[0166] The transmission characteristics shown in Figure 17 represent the transmission characteristics of the dielectric multilayer film that constituted the second sheet of Comparative Example 1 and was included in the second sheet of Examples 1 to 3 and Comparative Example 2. In Examples 1 to 3 shown in Figures 14 to 16, the transmittance of the second sheet for light with a wavelength of 550 nm incident at an incident angle of 60° was 50% or more. In Examples 1 to 3 shown in Figures 14 to 16, the reflectance of the second sheet for light with a wavelength of 650 nm incident at an incident angle of 60° was less than 50%. In Example 3 shown in Figure 14, the transmittance of the second sheet for light with a wavelength of 550 nm incident at an incident angle of 0°, the transmittance of the second sheet for light with a wavelength of 550 nm incident at an incident angle of 30°, and the transmittance of the second sheet for light with a wavelength of 550 nm incident at an incident angle of 60° gradually increased in this order. In Example 3 shown in Figure 14, the transmittance of the second sheet for 650 nm light incident on the second sheet at an incident angle of 0°, the transmittance of the second sheet for 650 nm light incident on the second sheet at an incident angle of 30°, and the transmittance of the second sheet for 650 nm light incident on the second sheet at an incident angle of 60° increased in this order.

[0167] <Rating 2> For the surface light source devices of Examples 1-3 and Comparative Examples 1 and 2, the brightness of the light-emitting surface of the surface light source device and the in-plane variation of brightness on the light-emitting surface were evaluated while the light source was emitting light. The evaluation criteria for brightness and the evaluation criteria for in-plane variation of brightness were as follows. The evaluation results for brightness on the light-emitting surface are shown in "Evaluation 1" in Table 1 of Figure 19. The evaluation results for in-plane variation of brightness on the light-emitting surface are shown in "Evaluation 2" in Table 1 of Figure 19. (Rating 1: Brightness) B: It was too dark to pass the actual product inspection. A: It was bright enough to pass the test in the actual product. AA: This level of brightness was acceptable for the actual product, and was brighter than an A rating. (Evaluation 2: Intra-plane variation in brightness) B: The product exhibited in-plane brightness variations to a degree that would result in failure, and the position of the light source was visible. A: The in-plane variation in brightness was suppressed to a level that would pass the actual product inspection. AA: The product meets the requirements for an actual product, and the in-plane brightness distribution was more uniform than that of a grade A. [Explanation of Symbols]

[0168] D1: First direction, D2: Second direction, D3: Third direction, LA: Primary light, LB: Secondary light, θ66: Tilt angle θ66, θ76: Tilt angle θ76, 10: Display device, 15: Display panel panel, 15a: display surface, 20: surface light source device, 20a: light emitting surface, 22: light source board, 23: light source, 25: support board, 26: board body, 27: reflective layer, 29: wiring, 18: Optical control member 18, 18a: first surface 18a, 18b: second surface 18b, 30: optical member, 30a: first surface, 30b: second surface, 32: bonding layer, 40: first sheet, 40a: first surface, 40b: second surface, 41: first barrier layer, 42: second barrier layer, 45: wavelength conversion layer, 45a: first surface, 45b: second surface, 46: base material part, 47: wavelength conversion agent, 47 A: First conversion agent, 47B: Second conversion agent, 50: Second sheet, 50a: First surface, 50b: Second surface, 55: First layer, 55a: First surface, 55b: Second surface, 56: Dielectric multilayer film, 60: Second layer, 60X: First optical element part, 60Y: Diffractive optical element, 60a: First surface, 60b: Second surface, 61: First uneven surface, 62: First main body part, 63: Protrusion, 64 : recess, 65: first unit optical element, 66: first element surface, 70: third layer, 70X: second optical element part, 70Y: diffractive optical element, 70a: first surface, 70b: second surface, 71: second concave / convex surface, 72: second main body part, 73: convex part, 74: recess, 75: second unit optical element, 76: second element surface, 81: optical sheet, 82: optical sheet, 85: reflective polarizer

Claims

1. The first sheet and the second sheet are provided in this order. The first sheet contains a wavelength conversion agent that absorbs primary light and emits secondary light. The second sheet has a first surface facing the first sheet and a second surface facing the first surface and away from the first sheet. The second sheet includes the third layer, the first layer, and the second layer in this order from the first surface to the second surface. The third layer is located between the first sheet and the first layer. The transmittance of the second sheet is greater for light of a specific wavelength incident on the second sheet at an incident angle of 30° than for light of a specific wavelength incident on the second sheet at an incident angle of 0°. The transmittance of the second sheet is greater for light of a specific wavelength incident on the second sheet at an incident angle of 60° than for light of a specific wavelength incident on the second sheet at an incident angle of 30°. The second layer includes at least one of a diffractive optical element and an optical element portion including a plurality of unit optical elements. The third layer includes at least one of a diffractive optical element and a second optical element portion including a plurality of second unit optical elements. The optical element portion is formed by the plurality of unit optical elements, which constitute the uneven second surface of the second sheet. The second optical element portion is an optical member in which the plurality of second unit optical elements constitute the uneven first surface of the second sheet.

2. The optical member according to claim 1, wherein the transmittance of the second sheet with respect to light of a wavelength of 550 nm incident on the second sheet at an incident angle of 60° is 50% or more.

3. The optical member according to claim 1, wherein the transmittance of the second sheet with respect to light of a wavelength of 650 nm incident on the second sheet at an incident angle of 60° is 50% or more.

4. The transmittance of the second sheet for light with a wavelength of 550 nm incident on the second sheet at an incident angle of 0° is smaller than the transmittance of the second sheet for light with a wavelength of 550 nm incident on the second sheet at an incident angle of 30°. The optical member according to claim 1, wherein the transmittance of the second sheet with respect to light of a wavelength of 550 nm incident on the second sheet at an incident angle of 30° is less than the transmittance of the second sheet with respect to light of a wavelength of 550 nm incident on the second sheet at an incident angle of 60°.

5. The transmittance of the second sheet for light with a wavelength of 650 nm incident on the second sheet at an incident angle of 0° is smaller than the transmittance of the second sheet for light with a wavelength of 650 nm incident on the second sheet at an incident angle of 30°. The optical member according to claim 1, wherein the transmittance of the second sheet with respect to light of a wavelength of 650 nm incident on the second sheet at an incident angle of 30° is smaller than the transmittance of the second sheet with respect to light of a wavelength of 650 nm incident on the second sheet at an incident angle of 60°.

6. The optical member according to claim 1, wherein the unit optical element is a cone-shaped convex or concave portion.

7. The optical member according to claim 1, wherein the specified wavelength is 430 nm or more and 500 nm or less.

8. An optical member as described in any one of claims 1 to 7, A surface light source device comprising a light source facing the aforementioned optical member.

9. The optical element further comprises a reflective polarizing plate superimposed on the aforementioned optical element, The surface light source device according to claim 8, wherein the optical member is located between the light source and the reflective polarizing plate.

10. The optical sheet further comprises the optical member superimposed on the optical member, The surface light source device according to claim 8, wherein the optical member is located between the light source and the optical sheet.

11. A surface light source device according to claim 8, A display device comprising a display panel superimposed on the aforementioned surface light source device.

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