JP7658191B2 - Surface light source device and display device - Google Patents

Description

This disclosure relates to a surface light source device and a display device.

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

JP2014-199831A

Conventional technology has not been able to sufficiently uniform the in-plane distribution of brightness while thinning the surface light source device. The present invention has been made in consideration of this point. The object of the present invention is to sufficiently uniform the in-plane distribution of brightness while thinning the surface light source device.

A surface light source device according to an embodiment of the present disclosure includes:
A wavelength selective reflective layer;
a light source substrate including a light source facing the wavelength selective reflection layer and a support substrate supporting the light source;
a wavelength conversion agent located between the wavelength selective reflective layer and the light source substrate,
the light source substrate includes a reflective layer facing the wavelength-selective reflective layer;
The wavelength conversion agent absorbs primary light from the light source and emits secondary light having a wavelength different from that of the primary light;
The reflectance of the secondary light at the wavelength-selective reflective layer is smaller than the reflectance of the primary light at the wavelength-selective reflective layer.

In a surface light source device according to one embodiment of the present disclosure, the reflectance of the secondary light at the wavelength-selective reflective layer may be 50% or less.

In a surface light source device according to one embodiment of the present disclosure, the reflectance of the primary light at the wavelength-selective reflective layer may be 90% or more.

In a surface light source device according to an embodiment of the present disclosure,
A region between the wavelength selective reflecting layer and the light source substrate, which overlaps an area having a certain area of the wavelength selective reflecting layer and the wavelength selective reflecting layer in a direction in which the wavelength selective reflecting layer and the light source substrate face each other, is defined as a reference volume region,
The volume of the wavelength conversion agent contained in one reference volume region may be larger than the volume of the wavelength conversion agent contained in another reference volume region located between the one reference volume region and a light source closest to the one reference volume region.

In a surface light source device according to one embodiment of the present disclosure, the volume of the wavelength conversion agent contained in any one reference volume region may be equal to or greater than the volume of the wavelength conversion agent contained in any other reference volume region located between the one reference volume region and the one light source.

In a surface light source device according to an embodiment of the present disclosure,
A conversion agent-containing portion containing the wavelength conversion agent may be provided between the wavelength selective reflection layer and the light source substrate,
One or more of the thickness of the conversion agent-containing portion, the proportion of the area in which the conversion agent-containing portion is arranged, and the content of the wavelength conversion agent contained in the conversion agent-containing portion may vary depending on the distance from the light source.

In a surface light source device according to one embodiment of the present disclosure, a conversion agent-containing portion containing the wavelength conversion agent may be provided between the wavelength selective reflection layer and the light source substrate.

The conversion agent-containing portion is provided on at least one of the wavelength-selective reflecting layer and the reflecting layer.

In a surface light source device according to one embodiment of the present disclosure, the conversion agent-containing portion may be provided away from both the wavelength-selective reflection layer and the reflection layer.

In a surface light source device according to one embodiment of the present disclosure, one or more of the thickness of the conversion agent-containing portion, the proportion of the area in which the conversion agent-containing portion is disposed, and the content of the wavelength conversion agent contained in the conversion agent-containing portion may vary depending on the distance from the light source.

In a surface light source device according to an embodiment of the present disclosure,
a conversion agent-containing portion containing the wavelength conversion agent is provided between the wavelength selective reflection layer and the light source substrate,
The conversion agent-containing portion may constitute a part or the whole of an intermediate layer that maintains a constant distance between the wavelength selective reflection layer and the light source substrate.

In a surface light source device according to one embodiment of the present disclosure, the intermediate layer may include a first portion that contains the wavelength conversion agent, and a second portion that contains the wavelength conversion agent at a content rate lower than that of the first portion or does not contain the wavelength conversion agent.

In a surface light source device according to one embodiment of the present disclosure, the intermediate layer may contain a light diffusing component.

In a surface light source device according to an embodiment of the present disclosure,
the second portion comprises a light diffusing component;
The second portion may be located at least partially between the first portion and the wavelength-selective reflective layer.

In a surface light source device according to one embodiment of the present disclosure, the intermediate layer may be bonded to at least one of the wavelength selective reflection layer and the light source substrate.

In a surface light source device according to one embodiment of the present disclosure, the intermediate layer may be in contact with a portion of the light source from which the primary light is emitted.

In a surface light source device according to one embodiment of the present disclosure, the light source may emit light with a wavelength of less than 380 nm.

In a surface light source device according to one embodiment of the present disclosure, the shortest wavelength of the secondary light may be 1.31 times or more the wavelength of the primary light.

A surface light source device according to an embodiment of the present disclosure includes:
The optical sheet may further include an optical sheet having a light-entering side surface facing the wavelength-selective reflecting layer and a light-exiting side surface as an uneven surface facing the light-entering side surface,
The wavelength-selective reflective layer may be located between the optical sheet and the light source substrate.

A display device according to an embodiment of the present disclosure includes:
Any one of the surface light source devices according to an embodiment of the present disclosure;
The surface light source device includes a display panel overlapped with the surface light source device.

The objective of the present invention is to achieve a thin surface light source device while achieving a sufficiently uniform in-plane distribution of brightness.

FIG. 1 is a diagram for explaining an embodiment of the present invention, and is a perspective view showing a display device and a surface light source device. FIG. 2 is a vertical cross-sectional view of the surface light source device of FIG. FIG. 3 is a plan view showing a light source substrate that can be included in the surface light source device of FIG. 2, and shows an example of an arrangement of a plurality of light sources. FIG. 4 is a cross-sectional view showing a light source substrate that can be included in the surface light source device of FIG. 2, and shows an example of the configuration of the light source substrate. FIG. 5 is an enlarged cross-sectional view showing a converter-containing portion that may be included in the surface light source device of FIG. FIG. 6A is a cross-sectional view corresponding to FIG. 2 and is a view for explaining another example of the conversion agent-containing portion. FIG. 6B is a cross-sectional view corresponding to FIG. 2 and is a view for explaining still another example of the conversion-agent-containing portion. FIG. 7A is a cross-sectional view corresponding to FIG. 2 and is a view for explaining still another example of the conversion-agent-containing portion. FIG. 7B is a cross-sectional view corresponding to FIG. 2 and is a view for explaining still another example of the conversion-agent-containing portion. FIG. 8 is a plan view illustrating still another example of the conversion-agent-containing portion. FIG. 9 is a cross-sectional view corresponding to FIG. 2, showing a surface light source device having the conversion agent-containing portion of FIG. FIG. 10A is a cross-sectional view corresponding to FIG. 2 and is a view for explaining still another example of the conversion agent-containing portion. FIG. 10B is a cross-sectional view corresponding to FIG. 2 and is a view for explaining still another example of the conversion agent-containing portion. FIG. 11A is a cross-sectional view corresponding to FIG. 2 and is a view for explaining still another example of the conversion-agent-containing portion. FIG. 11B is a cross-sectional view corresponding to FIG. 2 and is a view for explaining still another example of the conversion-agent-containing portion. FIG. 12A is a cross-sectional view corresponding to FIG. 2 and is a view for explaining still another example of the conversion-agent-containing portion. FIG. 12B is a cross-sectional view corresponding to FIG. 2 and is a view for explaining still another example of the conversion agent-containing portion. FIG. 13 is a graph showing an example of optical characteristics of a wavelength selective reflection layer that can be included in the surface light source device of FIG. 2, and is a graph illustrating the wavelength dependency of reflectance and transmittance. 14A is a cross-sectional view showing an example of an optical sheet that can be included in the surface light source device of FIG. 2. FIG. 14B is a cross-sectional view showing another example of an optical sheet that can be included in the surface light source device of FIG. 2. FIG. FIG. 15A is a plan view showing an example of a specific configuration of an optical sheet that can be included in the surface light source device of FIG. 2. FIG. 15B is a perspective view showing a unit optical element of the optical sheet of FIG. 15A. FIG. 15C is a plan view showing another example of a specific configuration of an optical sheet that can be included in the surface light source device of FIG. FIG. 15D is a perspective view showing still another example of a specific configuration of an optical sheet that can be included in the surface light source device of FIG. FIG. 16 is a vertical cross-sectional view showing the surface light source device, and is a diagram illustrating the operation of the surface light source device. FIG. 17 is a vertical cross-sectional view showing an optical sheet, illustrating the function of the optical sheet. FIG. 18 is a partially enlarged cross-sectional view showing the surface light source device.

An embodiment of the present disclosure will be described below with reference to the drawings. Note that in the drawings attached to this specification, the scale and aspect ratios have been appropriately altered and exaggerated from those of the actual objects for the convenience of illustration and ease of understanding. Also, configurations shown in some drawings may be omitted in other drawings.

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

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

In addition, in this specification, the normal direction of a sheet-like (sheet-like, plate-like) member refers to the normal direction to the sheet surface of the target sheet-like (film-like, plate-like) member. Also, the "sheet surface (film surface, plate surface)" refers to the surface that coincides with the planar direction of the target sheet-like (film-like, plate-like) member when the target sheet-like (film-like, plate-like) member is viewed overall and globally.

To clarify the directional relationships between the drawings, some drawings show the first direction D1, the second direction D2, and the third direction D3 as common directions using arrows with common symbols. The tip of the arrow is one side of each direction. An arrow pointing into the paper in a direction perpendicular to the paper surface of the drawing is shown by a symbol with an x in a circle, as shown in Figure 2, for example. An arrow pointing out from the paper in a direction perpendicular to the paper surface of the drawing is shown by a symbol with a dot in a circle, as shown in Figure 3, for example.

Figures 1 to 18 are diagrams for explaining one embodiment. Of these, Figure 1 is a perspective view that shows a display device 10 as an example of an application of a surface light source device 20. The display device 10 may display, for example, moving images, still images, text information, or images composed of a combination of these. The display device 10 may be used for various purposes, such as advertising, presentations, television images, and display of various information, indoors or outdoors. The display device 10 may be used, for example, as an in-vehicle liquid crystal display device. The display device 10 shown in Figure 1 has a surface light source device 20 having a light-emitting surface 20a, and a display panel 15 facing the light-emitting surface 20a.

Figure 2 is a vertical cross-sectional view showing the surface light source device 20. The surface light source device 20 has a light source substrate 22, an optical member 30, and a wavelength conversion agent 38 as main components. The light source substrate 22 includes a light source 23. The optical member 30 includes a wavelength selective reflection layer 40. The light source substrate 22 and the optical member 30 face each other in the third direction D3. The wavelength conversion agent 38 is located between the light source substrate 22 and the wavelength selective reflection layer 40 in the third direction D3. The light source substrate 22, the optical member 30, and the wavelength selective reflection layer 40 are sheet-shaped. The light source substrate 22, the optical member 30, and the wavelength selective reflection layer 40 extend in the first direction D1 and the second direction D2. The first direction D1, the second direction D2, and the third direction D3 are perpendicular to each other. The surface light source device 20 and the display panel 15 are stacked in the third direction D3.

In the illustrated example, the optical member 30 includes multiple sheet-like members. The illustrated optical member 30 has an optical sheet 50 and a reflective polarizing plate 60 superimposed on the wavelength-selective reflecting layer 40 in the third direction D3. In the illustrated example, the reflective polarizing plate 60 forms the light-emitting surface 20a.

The surface light source device 20 described in this embodiment is designed to sufficiently uniform the in-plane distribution of brightness while making the surface light source device 20 thinner. More specifically, the device is designed to eliminate unevenness in brightness caused by the presence of the light source 23. As a result, the illuminance at each position on the light-emitting surface 20a of the surface light source device 20, or the illuminance at each position on a virtual light-receiving surface parallel to the light-emitting surface 20a located near the light-emitting surface 20a, is uniformed. Note that the "illuminance of the light-emitting surface 20a" used in the following description means "illuminance on the light-emitting surface 20a" or "illuminance on a virtual light-receiving surface parallel to the light-emitting surface 20a located near the light-emitting surface 20a".

The display device 10 and surface light source device 20 in one embodiment will be described below with reference to the illustrated specific example.

First, the display panel 15 of the display device 10 will be described. The display panel 15 has a display surface 15a on which an image is displayed. The display surface 15a faces the opposite side to the surface light source device 20 in the third direction D3, i.e., toward the observer. In the illustrated example, the display panel 15 has a rectangular shape when observed from the third direction D3.

In the illustrated example, the third direction D3 is parallel to the normal direction of the display surface 15a, the normal direction of the light-emitting surface 20a, the normal direction of the light source substrate 22, the normal direction of the wavelength-selective reflecting layer 40, the normal direction of the optical sheet 50, and the normal direction of the reflective polarizing plate 60. The third direction D3 is also referred to as the front direction.

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

As an example of such a display panel 15, a liquid crystal display panel having a pair of polarizing plates and a liquid crystal cell (liquid crystal layer) arranged between the pair of polarizing plates may be used. The polarizing plates separate the incident light into two orthogonal polarized components, transmit the polarized component in one direction, and absorb the polarized component in the other direction orthogonal to the one direction. The liquid crystal cell has a pair of support plates and liquid crystal arranged between the pair of support plates. The liquid crystal cell is designed so that an electric field can be applied to each region that forms one pixel. The orientation of the liquid crystal changes when an electric field is applied. As an example, a polarized component in a specific direction rotates its polarization direction by 90 degrees when passing through a liquid crystal cell to which an electric field is not applied. The polarized component in a specific direction maintains its polarization direction when passing through a liquid crystal cell to which an electric field is applied. This makes it possible to control the transmission and light blocking of a pair of polarizing plates arranged on both sides of the liquid crystal cell depending on whether or not an electric field is applied to the liquid crystal cell.

Next, the surface light source device 20 will be described. The surface light source device 20 has a light-emitting surface 20a that emits planar light. The surface light source device 20 includes a light source board 22 having a light source 23, and an optical member 30 that is overlapped with the light source board 22 in the third direction D3. The light source 23 of the light source board 22 is provided in an area that overlaps with the light-emitting surface 20a when projected in the third direction D3. The surface light source device 20 is configured as a so-called direct-type backlight.

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

The light source 23 has a light-emitting element that emits light. As the light-emitting element, a light-emitting diode, abbreviated as LED, may be used. The dimensions of the light-emitting diode are not particularly limited. From the viewpoint of making the image of the light source 23 less noticeable, a small light-emitting diode, for example, a mini LED or a micro LED, may be used. Specifically, the length WL1, WL2 of one side of the light source 23 having a rectangular shape when observed from the third direction D3 shown in FIG. 3 may be 0.5 mm or less, or 0.2 mm or less.

The emission wavelength of the light source 23 may be appropriately selected depending on the application of the surface light source device 20. The light emitted by the light source 23 is absorbed by the wavelength conversion agent 38 as primary light. Therefore, the emission wavelength of the light source 23 may be appropriately selected depending on the optical characteristics of the wavelength conversion agent 38. In the illustrated example, the light source 23 may emit invisible light. Invisible light is light other than visible light. Visible light is light having a wavelength of 380 nm or more and 780 nm or less. The light source 23 may emit ultraviolet light. The wavelength of the light from the light source 23 may be less than 380 nm, 360 nm or less, 350 nm or less, or 340 nm or less.

As an example, the light source 23 may be composed of only a light-emitting element. As another example, the light source 23 may include, in addition to the light-emitting element, optical elements such as a cover or a lens that adjust the light distribution from the light-emitting element.

The light distribution characteristic of the light source 23 is not particularly limited. A Lambertian light distribution can typically be adopted as the light distribution characteristic of the light source 23. On the other hand, in the emission luminous intensity distribution of the light source 23 whose optical axis is aligned with the third direction D3, a peak luminous intensity may be obtained in a direction other than the third direction D3. For example, the bud wing light distribution disclosed in Patent Document 1 (JP6299811B) may be used as the light distribution characteristic of the light source 23.

As in the illustrated surface light source device 20, the light source substrate 22 may include a plurality of light sources 23. The number of light sources 23 is appropriately selected depending on the application of the surface light source device 20, the area of the light-emitting surface 20a, etc. From the viewpoint of eliminating unevenness in brightness caused by the arrangement of the light sources 23, the plurality of light sources 23 included in the surface light source device 20 may be regularly arranged on a surface perpendicular to the third direction D3. As an example of a regular arrangement of the light sources 23, a honeycomb arrangement or a square arrangement may be adopted. In a honeycomb arrangement, the light sources 23 may be arranged at a constant pitch in each of three directions inclined at 60° from each other. In a square arrangement, the light sources 23 may be arranged at a constant pitch in each of two directions perpendicular to each other.

In the example shown in FIG. 3, the light sources 23 are arranged at a constant pitch in each of the mutually orthogonal first and second directions D1 and D2. In the example shown in the figure, the arrangement pitch PL1 in the first direction D1 and the arrangement pitch PL2 of the light sources 23 in the second direction D2 are the same. In the example shown in FIG. 2, the arrangement pitch PL1 and the arrangement pitch PL2 may be different. In the example shown in the figure, the first direction D1 and the second direction D2 are parallel to the side edges of the rectangular surface light source device 20 and the optical member 30, respectively. The arrangement pitch PL1 and the arrangement pitch PL2 may each be 0.2 mm or more and 10 mm or less.

Next, the support substrate 25 that 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 side opposite the optical member 30 in the third direction D3. The support substrate 25 is sheet-shaped. The support substrate 25 includes a circuit that supplies power to the light sources 23. The support substrate 25 has optical reflectivity that reflects light toward the optical member 30.

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

The reflective layer 27 is laminated on the substrate body 26 from the side of the wavelength-selective reflective layer 40 in the third direction D3. The reflective layer 27 covers the area on the substrate body 26 where the light source 23 is not arranged. The reflective layer 27 is reflective to light of a specific wavelength emitted by the light source 23 or to light used for emission in the surface light source device 20. The reflectivity of the reflective layer 27 may be regular reflection, also called specular reflection, diffuse reflection, or anisotropic diffuse reflection. By forming the reflective layer 27 from a white reflective layer containing white particles such as silicon dioxide, the reflective layer 27 can be given diffuse reflectivity. From the viewpoint of uniforming the in-plane distribution of the illuminance of the light-emitting surface 20a in combination with other configurations of the surface light source device 20, it is preferable that the gloss of the reflective surface of the reflective layer 27 is 70 or more. Here, the gloss is a value measured using a gloss meter VG7000 manufactured by Nippon Denshoku Kogyo Co., Ltd. at an incident angle of 20° in accordance with JIS Z8741. The reflective layer 27 may be a metal layer laminated on the substrate body 26, or may be a reflective diffractive optical element.

The wavelength conversion agent 38 absorbs the primary light LA and emits secondary light LB having a wavelength different from the wavelength of the primary light LA. The light source 23 emits at least the primary light LA. The reflectance of the primary light LA at the wavelength-selective reflecting layer 40 described below is higher than the reflectance of the secondary light LB at the wavelength-selective reflecting layer 40. Quantum dots or phosphors may be used as the wavelength conversion agent 38.

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

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

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

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

The surface light source device 20 may include a plurality of quantum dots with different emission wavelengths as the wavelength conversion agent 38. By adjusting the content of each quantum dot, the color of the light emitted from the surface light source device 20 can be adjusted. In the example shown in FIG. 5, the wavelength conversion agent 38 includes a first wavelength conversion agent 38A, a second wavelength conversion agent 38B, and a third wavelength conversion agent 38C. The first wavelength conversion agent 38A, the second wavelength conversion agent 38B, and the third wavelength conversion agent 38C have sizes different from each other. The first wavelength conversion agent 38A, the second wavelength conversion agent 38B, and the third wavelength conversion agent 38C emit light of different wavelengths from each other.

The first wavelength conversion agent 38A may absorb the primary light LA from the light source 23 and emit blue light having a wavelength of 430 nm or more and 500 nm or less. The second wavelength conversion agent 38B may absorb the primary light LA from the light source 23 and emit green light having a wavelength of 500 nm or more and 600 nm or less. The third wavelength conversion agent 38C may absorb the primary light LA from the light source 23 and emit red light having a wavelength of 600 nm or more and 750 nm or less. According to this example, the surface light source device 20 can emit white light by adjusting the contents of the first wavelength conversion agent 38A, the second wavelength conversion agent 38B, and the third wavelength conversion agent 38C.

The wavelength conversion agent 38 may be installed in the surface light source device 20 while being contained in the conversion agent-containing portion 35. The conversion agent-containing portion 35 shown in FIG. 5 has a wavelength conversion agent 38 and a base material portion 36 that holds the wavelength conversion agent 38. The conversion agent-containing portion 35 allows the wavelength conversion agent 38 to be stably held at a predetermined position in the surface light source device 20. The wavelength conversion agent 38 is surrounded by the base material portion 36, so that deterioration of the wavelength conversion agent 38 can be prevented. A resin may be used as the base material portion 36. Examples of resins that constitute the base material portion 36 include thermoplastic resins, cured products of thermosetting resin compositions, and cured products of ionizing radiation curable resin compositions. The conversion agent-containing portion 35 may have various configurations.

As an example, the conversion agent-containing portion 35 shown in FIG. 2 is located between the support substrate 25 and the wavelength-selective reflecting layer 40 in the third direction D3. The conversion agent-containing portion 35 shown in FIG. 2 is sheet-shaped. The conversion agent-containing portion 35 shown in FIG. 2 extends in both the first direction D1 and the second direction D2. In the example shown in FIG. 2, the conversion agent-containing portion 35 is separated from the wavelength-selective reflecting layer 40 and the support substrate 25. The conversion agent-containing portion 35 shown in FIG. 2 can be produced, for example, by applying a resin composition having flowability including the wavelength conversion agent 38 to form a coating film and drying the coating film.

6A and 6B are located between the support substrate 25 and the wavelength selective reflecting layer 40 in the third direction D3. The conversion agent-containing portion 35 shown in FIG. 6A and 6B is sheet-shaped. The conversion agent-containing portion 35 shown in FIG. 6A and 6B extends in both the first direction D1 and the second direction D2. In the example shown in FIG. 6A, the conversion agent-containing portion 35 is in contact with the wavelength selective reflecting layer 40. The conversion agent-containing portion 35 shown in FIG. 6A may be bonded to the wavelength selective reflecting layer 40. In the example shown in FIG. 6B, the conversion agent-containing portion 35 is in contact with the reflecting layer 27 of the support substrate 25. The conversion agent-containing portion 35 shown in FIG. 6B may be bonded to the reflecting layer 27. By bonding the wavelength selective reflecting layer 40 to another member, the arrangement of the wavelength selective reflecting layer 40 is stabilized. In the example shown in Figures 6A and 6B, the conversion agent-containing portion 35 can be fabricated on the wavelength-selective reflecting layer 40 or on the reflecting layer 27, for example by printing.

In the example shown in Figures 7A and 7B, the surface light source device 20 has an intermediate layer 32 in contact with both the wavelength selective reflecting layer 40 and the third direction D3 of the support substrate 25. The intermediate layer 32 may be bonded to both or either of the wavelength selective reflecting layer 40 and the support substrate 25. According to this example, the relative positions of the support substrate 25 and the wavelength selective reflecting layer 40 can be stably aligned, and further, the support substrate 25 and the wavelength selective reflecting layer 40 can be maintained in an appropriate relative position.

7A, the intermediate layer 32 is a single layer composed of the conversion agent-containing portion 35. On the other hand, in the example shown in FIG. 7B, the intermediate layer 32 has a first portion 33A and a second portion 33B. The first portion 33A and the second portion 33B are overlapped in the third direction D3. In the example shown in FIG. 7B, the first portion 33A is disposed between two second portions 33B in the third direction D3. In the example shown in FIG. 7B, the first portion 33A is composed of the conversion agent-containing portion 35. In the example shown in FIG. 7B, the second portion 33B may not contain the wavelength conversion agent 38. The second portion 33B that does not contain the wavelength conversion agent 38 may be composed as a transparent resin layer. The second portion 33B may contain a light diffusing component. Examples of light diffusing components include metal compounds, porous substances containing gas, resin beads that hold metal compounds around them, white fine particles, and even simple air bubbles.

As used herein, "transparent" means that the visible light transmittance is 50% or more, and preferably 80% or more. The visible light transmittance is determined as the average value of the total light transmittance at each wavelength when measured at an incident angle of 0° every 1 nm in the measurement wavelength range of 380 nm to 780 nm using a spectrophotometer (Shimadzu Corporation's "UV-3100PC", compliant with JIS K 0115).

In the example shown in FIG. 7B, the second portion 33B may contain the wavelength conversion agent 38 at a content ratio different from that of the first portion 33A. The second portion 33B may contain the wavelength conversion agent 38 of a different size than that of the first portion 33A. The first portion 33A may be disposed adjacent to the wavelength selective reflecting layer 40. The first portion 33A may be disposed adjacent to the reflecting layer 27.

As will be described in detail later, in this embodiment, the illuminance of the light-emitting surface 20a is high near the area where a large amount of wavelength conversion agent 38 is present in combination with the wavelength-selective reflection layer 40. The illuminance of the light-emitting surface 20a is low near the area where only a small amount of wavelength conversion agent 38 is present or where no wavelength conversion agent 38 is present. On the other hand, the general tendency of the direct-type surface light source device 20 is that the illuminance of the light-emitting surface 20a is high directly above the light source 23 and low above the middle between two adjacent light sources 23. In consideration of this tendency, the arrangement of the wavelength conversion agent 38 may be adjusted to make the illuminance distribution of the light-emitting surface 20a uniform. An example of providing a distribution in the arrangement of the wavelength conversion agent 38 will be described with reference to the specific examples shown in Figures 8 to 11B.

Figure 8 shows a portion of the support substrate 25 and the optical member 30. The portion shown in Figure 8 is the portion closest to a certain light source 23. Within this portion, the volume of the wavelength conversion agent 38 contained in a certain region may be larger than the volume of the wavelength conversion agent 38 contained in another region closer to the certain light source 23 than the certain region. The region that overlaps the area 35A having a certain area of the wavelength selective reflection layer 40 in the third direction D3 is defined as a reference volume region 35V. The volume of the wavelength conversion agent 38 contained in one reference volume region 35V may be larger than the volume of the wavelength conversion agent 38 contained in another reference volume region 35V located between the one reference volume region 35V and one light source 23 closest to the one reference volume region 35V.

Furthermore, within the portion shown in FIG. 8, the volume of the wavelength conversion agent 38 contained in the reference volume region 35V may increase with increasing distance from one of the light sources 23. The volume of the wavelength conversion agent 38 contained in any one of the reference volume regions 35V may be equal to or greater than the volume of the wavelength conversion agent 38 contained in any other reference volume region 35V located between the one of the reference volume regions 35V and one of the light sources 23.

When the surface light source device 20 includes multiple types of wavelength conversion agents 38, it is preferable that each type of wavelength conversion agent 38 satisfies the above conditions. In the example shown in FIG. 5, which includes first to third wavelength conversion agents 38A to 38C, each of the first to third wavelength conversion agents 38A to 38C may be distributed as described above.

That is, the volume of the first wavelength conversion agent 38A contained in one reference volume region 35V may be larger than the volume of the first wavelength conversion agent 38A contained in another reference volume region 35V located between the one reference volume region 35V and one light source 23 closest to the one reference volume region 35V. The volume of the first wavelength conversion agent 38A contained in any one reference volume region 35V may be larger than the volume of the first wavelength conversion agent 38A contained in any other reference volume region 35V located between the one reference volume region 35V and one light source 23.

The volume of the second wavelength conversion agent 38B contained in one reference volume region 35V may be larger than the volume of the second wavelength conversion agent 38B contained in another reference volume region 35V located between the one reference volume region 35V and one light source 23 closest to the one reference volume region 35V. The volume of the second wavelength conversion agent 38B contained in any one reference volume region 35V may be larger than the volume of the second wavelength conversion agent 38B contained in any other reference volume region 35V located between the one reference volume region 35V and one light source 23.

The volume of the third wavelength conversion agent 38C contained in one reference volume region 35V may be larger than the volume of the third wavelength conversion agent 38C contained in another reference volume region 35V located between the one reference volume region 35V and one light source 23 closest to the one reference volume region 35V. The volume of the third wavelength conversion agent 38C contained in any one reference volume region 35V may be larger than the volume of the third wavelength conversion agent 38C contained in any other reference volume region 35V located between the one reference volume region 35V and one light source 23.

The change in the volume of the wavelength conversion agent 38 contained in the reference volume region 35V according to the distance from the light source 23 may change stepwise, as in the examples shown in Figures 8 and 9. The change in the amount of the wavelength conversion agent 38 according to the distance from the light source 23 may change continuously, as in the example shown in Figure 10B, which will be described in detail later.

The region 35A of a certain area used to specify the reference volume region 35V may be assumed to be a square of 5 mm on each side, and the area of the region 35A may be set to 25 ^mm2 . When the emission wavelengths of the wavelength conversion agents 38 are uniform, the particle sizes of the wavelength conversion agents 38 are also roughly uniform. In this case, the comparison of the volumes of the wavelength conversion agents 38 contained in the reference volume region 35V may be confirmed by comparing the quantities of the wavelength conversion agents 38 contained in the reference volume region 35V. The quantity of the wavelength conversion agents 38 can be measured using a transmission electron microscope.

The change in the volume of the wavelength conversion agent 38 contained in the reference volume region 35V can be adjusted by the thickness of the conversion agent-containing portion 35, the proportion of the area in which the conversion agent-containing portion 35 is arranged, and the content of the wavelength conversion agent 38 contained in the conversion agent-containing portion 35, etc.

The ratio of the area where the converter-containing portion 35 is disposed means the ratio of the area where the converter-containing portion 35 is disposed in a region having a certain area of the surface where the converter-containing portion 35 is disposed. In other words, it is the ratio of the area ( ^mm2 ) where the converter-containing portion 35 is disposed to the certain area ( ^mm2 ). Here, the region of the certain area ( ^mm2 ) is assumed to be a square with 5 mm sides, and the certain area may be set to 25 ^mm2 .

The content ratio is the ratio (%) of the volume ( ^mm3 ) of the wavelength conversion agent 38 contained in a certain volume ( ^mm3 ) of the conversion agent-containing portion 35. The volume of the wavelength conversion agent 38 contained in the conversion agent-containing portion 35 is obtained by multiplying the volume of one wavelength conversion agent 38 by the quantity measured with a transmission electron microscope. The volume of one wavelength conversion agent 38 is determined using the particle size measured by the above-mentioned method, assuming that the wavelength conversion agent 38 has a spherical shape.

8 and 9, the surface light source device 20 has an intermediate layer 32 in contact with the support substrate 25 and the wavelength selective reflection layer 40. The intermediate layer 32 is divided into a plurality of parts according to the distance from the nearest light source 23 along the direction perpendicular to the third direction D3. The intermediate layer 32 includes a first part 33A, a second part 33B, and a third part 33C. The first part 33A is the furthest from the light source 23. The third part 33C is the closest to the light source 23. When observed from the third direction D3 shown in FIG. 8, the third part 33C surrounds the light source 23. When observed from the third direction D3 shown in FIG. 8, the second part 33B surrounds the third part 33C. The second part 33B is located between the first part 33A and the third part 33C in the direction perpendicular to the third direction D3.

8 and 9, the content (%) of the wavelength conversion agent 38 in the first portion 33A is greater than the content (%) of the wavelength conversion agent 38 in the second portion 33B. The content (%) of the wavelength conversion agent 38 in the second portion 33B is greater than the content (%) of the wavelength conversion agent 38 in the third portion 33C. In this example, the first portion 33A and the second portion 33B are composed of the conversion agent-containing portion 35. The third portion 33C may be composed of the conversion agent-containing portion 35 or may be composed of a transparent resin that does not contain the wavelength conversion agent 38. The third portion 33C may contain a light diffusing component. Examples of light diffusing components include metal compounds, porous substances containing gas, resin beads that hold metal compounds around them, white fine particles, and even simple air bubbles.

10A and 10B, the percentage of the area where the conversion agent-containing portion 35 is disposed varies depending on the distance from the light source 23. In the examples shown in FIG. 10A and FIG. 10B, the content ratio of the wavelength conversion agent 38 in the conversion agent-containing portion 35 is constant. In each example shown in FIG. 10A and FIG. 10B, the thickness of the conversion agent-containing portion 35 in the third direction D3 is constant. In the example shown in FIG. 10A, the conversion agent-containing portion 35 is provided on the surface of the wavelength selective reflection layer 40 facing the support substrate 25. That is, it is provided on the light incident side surface 40a of the wavelength selective reflection layer 40. The percentage of the area where the conversion agent-containing portion 35 is provided in a region having a certain area of the light incident side surface 40a increases as it moves away from the nearest light source 23. In the example shown in FIG. 10B, the conversion agent-containing portion 35 is provided on the reflective layer 27 of the support substrate 25. The ratio of the area where the conversion agent-containing portion 35 is provided in a region of a certain area of the reflective layer 27 increases as it moves away from the light source 23. In the example shown in FIG. 10A and FIG. 10B, the conversion agent-containing portion 35 may be in the form of dots. The dot-shaped conversion agent-containing portion 35 may be formed on the wavelength-selective reflection layer 40 or the reflective layer 27 by printing. The change in the ratio (%) of the area where the conversion agent-containing portion 35 is provided may be continuous or stepwise.

11A and 11B, the thickness T (mm) of the conversion agent-containing portion 35 in the third direction D3 changes depending on the distance from the light source 23. In the examples shown in FIG. 11A and 11B, the content ratio of the wavelength conversion agent 38 in the conversion agent-containing portion 35 is constant. In the example shown in FIG. 11A, the conversion agent-containing portion 35 is provided on the light-entering side surface 40a of the wavelength-selective reflecting layer 40. In this example, the conversion agent-containing portion 35 is provided in the area of the light-entering side surface 40a excluding the area directly above the light source 23 and the area surrounding the light source 23. In the example shown in FIG. 11B, the conversion agent-containing portion 35 is provided on the reflective layer 27. In this example, the conversion agent-containing portion 35 is provided in the area of the reflective layer 27 excluding the area surrounding the light source 23. In the example shown in FIG. 11A and FIG. 11B, the thickness T (mm) of the conversion agent-containing portion 35 in the third direction D3 increases as it moves away from the nearest light source 23. The change in the thickness T (mm) of the conversion agent-containing portion 35 in the third direction D3 may be continuous as in the illustrated example, or may be stepwise.

In the examples shown in Figs. 10A to 11B, an intermediate layer 32 may be provided in contact with the support substrate 25 and the wavelength selective reflection layer 40. Fig. 12A shows an example in which an intermediate layer 32 is provided in the surface light source device 20 of Fig. 11A. Fig. 12B shows an example in which an intermediate layer 32 is provided in the surface light source device 20 of Fig. 11B. In such a modified example, the intermediate layer 32 may include a first portion 33A and a second portion 33B, and the first portion 33A may be constituted by the conversion agent-containing portion 35 shown in Figs. 10A to 11B. The second portion 33B may contain a wavelength conversion agent 38 at a lower content rate than the first portion 33A, or may not contain the wavelength conversion agent 38. In these examples, as in the examples shown in Figs. 10A to 11B, the volume of the wavelength conversion agent 38 in the reference volume region 35V increases with increasing distance from the nearest light source 23.

The optical member 30 shown in FIG. 2 includes, in this order from the support substrate 25 side in the third direction D3, a wavelength-selective reflecting layer 40, an optical sheet 50, and a reflective polarizing plate 60. The wavelength-selective reflecting layer 40, the optical sheet 50, and the reflective polarizing plate 60 may be bonded to each other, may simply be in contact with each other and not bonded, or may even be spaced apart from each other.

The wavelength-selective reflective layer 40 is a reflective layer having wavelength selectivity. The reflectance of the wavelength-selective reflective layer 40 changes depending on the wavelength of the incident light. The transmittance (%) of the wavelength-selective reflective layer 40 changes depending on the wavelength of the incident light. The wavelength-selective reflective layer 40 in this embodiment is used together with the wavelength conversion agent 38 described above. The wavelength conversion agent 38 absorbs the primary light LA from the light source 23 and emits secondary light LB of a different wavelength. The reflectance of the secondary light LB at the wavelength-selective reflective layer 40 is smaller than the reflectance of the primary light LA at the wavelength-selective reflective layer 40. The transmittance of the secondary light LB at the wavelength-selective reflective layer 40 is larger than the transmittance of the primary light LA at the wavelength-selective reflective layer 40.

The reflectance and transmittance of the wavelength-selective reflective layer 40 are values measured using a spectrophotometer (Shimadzu Corporation's UV-3100PC, compliant with JIS K 0115).

Figure 13 is a graph showing an example of the reflection and transmission characteristics of the wavelength-selective reflective layer 40 according to the wavelength. In the graph shown in Figure 13, the vertical axis indicates reflectance (%) and transmittance (%). In the graph shown in Figure 13, the horizontal axis indicates the wavelength (nm) of the incident light. In the example shown in Figure 13, the reflectance of visible light in the wavelength-selective reflective layer 40 may be smaller than the reflectance of invisible light in the wavelength-selective reflective layer 40.

The reflection and transmission characteristics shown in the graph of FIG. 13 are characteristics for light that travels in the normal direction of the wavelength-selective reflecting layer 40 and enters the wavelength-selective reflecting layer 40. Furthermore, in this specification, unless there is an explanation of the direction of incidence of the incident light, the reflectance and transmittance of the wavelength-selective reflecting layer 40 refer to the characteristics for light that travels in the normal direction of the wavelength-selective reflecting layer 40 and enters the wavelength-selective reflecting layer 40.

The reflectance of the wavelength-selective reflecting layer 40 for light with a wavelength of less than 360 nm, or the reflectance of the wavelength-selective reflecting layer 40 for light with a wavelength of 300 nm or more and less than 360 nm, may be 30% or more, 50% or more, 80% or more, or 90% or more. The reflectance of the wavelength-selective reflecting layer 40 for light with a wavelength of less than 340 nm, or the reflectance of the wavelength-selective reflecting layer 40 for light with a wavelength of 300 nm or more and less than 340 nm, may be 50% or more, 80% or more, 90% or more, or 95% or more. The reflectance of the wavelength-selective reflecting layer 40 for light with a central wavelength of the primary light LA emitted by the light source 23 may be 90% or more, 93% or more, 95% or more, or 98% or more.

The reflectance of the wavelength selective reflective layer 40 for light with a wavelength of 380 nm or more and 780 nm or less may be less than 70%, less than 50%, less than 20%, or less than 10%. The reflectance of the wavelength selective reflective layer 40 for light with a wavelength of 420 nm or more and 700 nm or less may be less than 50%, less than 20%, less than 10%, or less than 5%. The reflectance of the wavelength selective reflective layer 40 for light with the central wavelength of the secondary light LB emitted from the wavelength conversion agent 38 may be 50% or less, 20% or less, 10% or less, or 5% or less.

When multiple types of wavelength conversion agents 38 are provided in the surface light source device 20, the reflectance of the wavelength selective reflection layer 40 for the light of the central wavelength of the secondary light LB emitted from each type of wavelength conversion agent 38 may be 50% or less, 20% or less, 10% or less, or 5% or less. In the example shown in FIG. 5, the reflectance of the wavelength selective reflection layer 40 for the light of the central wavelength of the first secondary light LB1 emitted from the first wavelength conversion agent 38A may be 50% or less, 20% or less, 10% or less, or 5% or less. The reflectance of the wavelength selective reflection layer 40 for the light of the central wavelength of the second secondary light LB2 emitted from the second wavelength conversion agent 38B may be 50% or less, 20% or less, 10% or less, or 5% or less. The reflectance of the wavelength selective reflection layer 40 for the light of the central wavelength of the third secondary light LB3 emitted from the third wavelength conversion agent 38C may be 50% or less, 20% or less, 10% or less, or 5% or less.

The transmittance of the wavelength-selective reflecting layer 40 for light with a wavelength of less than 360 nm, or the transmittance of the wavelength-selective reflecting layer 40 for light with a wavelength of 300 nm or more and less than 360 nm, may be less than 70%, less than 50%, less than 20%, or less than 10%. The transmittance of the wavelength-selective reflecting layer 40 for light with a wavelength of less than 340 nm, or the transmittance of the wavelength-selective reflecting layer 40 for light with a wavelength of 300 nm or more and less than 340 nm, may be less than 50%, less than 20%, less than 10%, or less than 5%. The transmittance of the wavelength-selective reflecting layer 40 for light with the central wavelength of the primary light LA emitted by the light source 23 may be less than 10%, less than 8%, less than 5%, or less than 2%.

The transmittance of the wavelength selective reflecting layer 40 for light with a wavelength of 380 nm or more and 780 nm or less may be greater than 30%, greater than 50%, greater than 80%, or greater than 90%. The transmittance of the wavelength selective reflecting layer 40 for light with a wavelength of 420 nm or more and 700 nm or less may be greater than 50%, greater than 80%, greater than 90%, or greater than 95%. The transmittance of the wavelength selective reflecting layer 40 for light with the central wavelength of the secondary light LB emitted from the wavelength conversion agent 38 may be greater than 50%, greater than 80%, greater than 90%, or greater than 95%.

When multiple types of wavelength conversion agents 38 are provided in the surface light source device 20, the transmittance of the wavelength selective reflection layer 40 for the light of the central wavelength of the secondary light LB emitted from each type of wavelength conversion agent 38 may be greater than 50%, greater than 80%, greater than 90%, or greater than 95%. In the example shown in FIG. 5, the transmittance of the wavelength selective reflection layer 40 for the light of the central wavelength of the first secondary light LB1 emitted from the first wavelength conversion agent 38A may be greater than 50%, greater than 80%, greater than 90%, or greater than 95%. The transmittance of the wavelength selective reflection layer 40 for the light of the central wavelength of the second secondary light LB2 emitted from the second wavelength conversion agent 38B may be greater than 50%, greater than 80%, greater than 90%, or greater than 95%. The transmittance in the wavelength selective reflecting layer 40 for the light of the central wavelength of the third secondary light LB3 emitted from the third wavelength conversion agent 38C may be greater than 50%, greater than 80%, greater than 90%, or greater than 95%.

The wavelength-selective reflective layer 40 is not particularly limited as long as it has wavelength-dependent reflectance and transmittance. As a specific example, a dielectric multilayer film that has high design freedom in reflectance and transmittance characteristics may be used as the wavelength-selective reflective layer 40.

A multilayer film of an inorganic compound in which inorganic layers with different refractive indices are alternately stacked may be used as the dielectric multilayer film constituting the wavelength-selective reflecting layer 40. As another example, a resin multilayer film in which resin layers with different refractive indices are alternately stacked may be used as the wavelength-selective reflecting layer 40.

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

The dielectric multilayer film, which is a resin multilayer film, contains many layers of, for example, thermoplastic resin or thermosetting resin. The resin layers may contain various additives, such as antioxidants, antistatic agents, crystal nucleating agents, inorganic particles, organic particles, viscosity reducers, heat stabilizers, lubricants, infrared absorbers, ultraviolet absorbers, and doping agents for adjusting the refractive index.

Among the resin layers with different refractive indices, the difference in the in-plane average refractive index between the high refractive index resin layer and the low refractive index resin layer may be 0.03 or more, 0.05 or more, or 0.1 or more.

The number of high-refractive index resin layers and low-refractive index resin layers stacked is adjusted according to the reflection and transmission characteristics required for the wavelength-selective reflection layer 40. For example, 30 or more high-refractive index resin layers and 200 or more high-refractive index resin layers may be stacked alternately. The total number of high-refractive index resin layers and low-refractive index resin layers stacked may be, for example, 600 or more. If the number of layers is too small, sufficient reflectance may not be obtained. Furthermore, by having the number of layers in the above range, the desired reflectance can be easily obtained.

The resin multilayer film constituting the dielectric multilayer film may have a surface layer containing polyethylene terephthalate or polyethylene naphthalate with a thickness of 3 μm or more on at least one side. The resin multilayer film constituting the dielectric multilayer film may have the above surface layer on both sides. The thickness of the surface layer may be 5 μm or more.

Examples of methods for producing the resin multilayer film that constitutes the dielectric multilayer film include co-extrusion methods. For specific examples, see the method for producing a laminated film described in JP 2008-200861 A.

The optical sheet 50 is laminated on the wavelength selective reflecting layer 40 from the side opposite the light source 23 in the third direction D3. The optical sheet 50 is installed to achieve various functions. The optical sheet 50 shown in FIG. 14A and FIG. 14B adjusts the optical path of light transmitted through the wavelength selective reflecting layer 40. The illustrated optical sheet 50 can adjust the luminance angle distribution on the light emitting surface 20a of the surface light source device 20.

14A and 14B, the optical sheet 50 has a light-entering side 50a and a light-exiting side 50b. The light-entering side 50a is a flat surface. The light-exiting side 50b is an uneven surface 51. The main body 52 faces the wavelength-selective reflecting layer 40. The main body 52 may be in contact with the wavelength-selective reflecting layer 40. The main body 52 may be bonded to the wavelength-selective reflecting layer 40. The optical sheet 50 includes a sheet-like main body 52 and a plurality of unit optical elements 55 each formed as a convex portion 53 or a concave portion 54. The unit optical element 55 is an element that changes the traveling direction of light by refraction, reflection, etc. The unit optical element 55 is a concept that includes elements called unit shaped elements, unit prisms, and unit lenses. The unit optical elements 55 are provided on the main body 52. The uneven surface 51 is formed by the plurality of unit optical elements 55.

The optical sheet 50 shown in FIG. 14A has a plurality of convex portions 53 provided on the surface of the main body 52 facing the reflective polarizing plate 60. In the example shown in FIG. 14A, the plurality of convex portions 53 are provided adjacent to each other with no gaps. The optical sheet 50 shown in FIG. 14B has a plurality of concave portions 54 provided on the surface of the main body 52 facing the reflective polarizing plate 60. In the example shown in FIG. 14B, the plurality of concave portions 54 are provided adjacent to each other with no gaps.

As shown in Figures 14A and 14B, the unit optical element 55 has an element surface 56 that is inclined with respect to the third direction D3. The unit optical element 55 is defined by this element surface 56. The uneven surface 51 of the optical sheet 50 is formed by the element surface 56 of the unit optical element 55.

The optical characteristics of the optical sheet 50 are affected by the inclination angle of the element surface 56 of the unit optical element 55. Therefore, the cross-sectional shape of the unit optical element 55 can be appropriately adjusted based on the optical characteristics required for the surface light source device 20 and the optical member 30. For example, the inclination angles of the element surfaces 56 included in one unit optical element 55 may be different from each other or may be the same. The optical sheet 50 may include unit optical elements 55 that are different in at least one of the shape and orientation, or may include only unit optical elements 55 that are identical to each other. Unlike the examples of Figures 14A and 14B, the light-entering side surface 50a of the optical sheet 50 may be an uneven surface 51 formed by the element surfaces 56 of the unit optical elements 55. In this example, the light-exiting side surface 50b of the optical sheet 50 may be a flat surface or an uneven surface 51.

The multiple unit optical elements 55 included in the optical sheet 50 may be arranged two-dimensionally. According to this example, the element surfaces 56 of the unit optical elements 55 included in the optical sheet 50 face various directions. As a result, the optical sheet 50 is able to guide light in various directions by the two-dimensionally arranged unit optical elements 55. In other words, it is possible to guide light in multiple non-parallel directions, and to homogenize the in-plane distribution of illuminance. Each unit optical element 55 may be configured with rotational symmetry around the third direction D3. For example, each unit optical element 55 may be configured with three-fold rotational symmetry, four-fold symmetry, or six-fold symmetry around the third direction D3.

15A and 15B show specific examples of unit optical elements 55 in the optical sheet 50. In the example shown in FIG. 15A and FIG. 15B, the arrangement of the unit optical elements 55 is a square arrangement. The unit optical elements 55 are arranged at a constant pitch in the first direction D1. The unit optical elements 55 are also arranged at a constant pitch in the second direction D2. The arrangement pitch in the first direction D1 and the arrangement pitch in the second direction D2 may be the same or different. In the example shown in FIG. 15A and FIG. 15B, the unit optical elements 55 are arranged without 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. The arrangement pitch in the first direction D1 and the arrangement pitch in the second direction D2 may be 0.05 mm or more and 1 mm or less, or 0.1 mm or more and 0.5 mm or less. In the example shown in Figures 15A and 15B, the unit optical elements 55 are configured as quadrangular pyramid-shaped convex portions 53 or concave portions 54 with a square base. The height or depth of each unit optical element 55 in the third direction D3 may be 0.025 mm or more and 0.5 mm or less, or 0.05 mm or more and 0.25 mm or less.

The unit optical elements 55 may be arranged in directions inclined in the first direction D1 and the second direction D2. For example, in the example shown in FIG. 15C, a plurality of unit optical elements 55 are arranged at a constant pitch in two directions inclined at ±45° with respect to the first direction D1. The arrangement in FIG. 15C can be applied to the unit optical elements 55 shown in FIG. 15B. According to this example, the element surface 56 faces two directions inclined at ±45° with respect to the first direction D1, and light can be spread in these two directions.

As shown in FIG. 15D, the multiple unit optical elements 55 included in the optical sheet 50 may be arranged one-dimensionally. That is, the multiple unit optical elements 55 may be arranged in the arrangement direction, and each unit optical element 55 may extend linearly in a direction non-parallel to the arrangement direction. In the example shown in FIG. 15D, each unit optical element 55 extends linearly in a direction perpendicular to the arrangement direction. The unit optical elements 55 may be arranged in the first direction D1. The unit optical elements 55 may extend linearly in the second direction D2. The arrangement direction of the unit optical elements 55 may be the second direction D2. The arrangement direction of the unit optical elements 55 may be a direction inclined to both the first direction D1 and the second direction D2. The arrangement direction of the unit optical elements 55 may be a direction inclined at 45° with respect to the first direction D1 and the second direction D2.

The multiple unit optical elements 55 may be arranged irregularly or regularly. By arranging the multiple unit optical elements 55 regularly, the design of the optical sheet 50 can be simplified. Furthermore, by arranging the multiple unit optical elements 55 regularly, it becomes easier to arrange the unit optical elements 55 closely together without gaps.

The reflective polarizing plate 60 is overlapped with the optical sheet 50 in the third direction D3. The optical sheet 50 is located between the reflective polarizing plate 60 and the wavelength selective reflection layer 40 in the third direction D3. The reflective polarizing plate 60 transmits one linearly polarized component and reflects the other linearly polarized component. The reflective polarizing plate 60 can selectively transmit linearly polarized light that can pass through the polarizing plate located on the surface light source device 20 side of the display panel 15. The light reflected by the reflective polarizing plate 60 can change its polarization state by subsequent reflection or the like and re-enter the reflective polarizing plate 60. The reflective polarizing plate 60 may be "DBEF" (registered trademark) available from 3M, USA. The reflective polarizing plate 60 may be a high-brightness polarizing sheet "WRPS" available from Shinwa Intertek, Korea, a wire grid polarizer, or the like.

Next, the operation of generating planar light using the surface light source device 20 having the above configuration will be described mainly with reference to Figures 16 and 17.

As shown in FIG. 16, the light source 23 emits primary light LA. As an example, the primary light LA is ultraviolet light. The wavelength of this primary light LA is less than 380 nm. The primary light LA emitted by the light source 23 travels toward the conversion agent-containing portion 35 containing the wavelength conversion agent 38. As shown in FIG. 5, a portion of the primary light LA is incident on the wavelength conversion agent 38 and absorbed. The wavelength conversion agent 38 that absorbs the primary light LA emits secondary light LB. Regardless of the incidence path of the primary light LA to the wavelength conversion agent 38, the secondary light LB is emitted from the wavelength conversion agent 38 as diffuse light. The remaining primary light LA that is incident on the conversion agent-containing portion 35 does not collide with the wavelength conversion agent 38 and passes through the conversion agent-containing portion 35.

The primary light LA and secondary light LB that have passed through the conversion agent-containing portion 35 are incident on the wavelength-selective reflection layer 40. The wavelength-selective reflection layer 40 has the optical characteristics shown in FIG. 13, for example. That is, the reflectance of the secondary light LB at the wavelength-selective reflection layer 40 is smaller than the reflectance of the primary light LA at the wavelength-selective reflection layer 40. For example, the reflectance of the secondary light LB at the wavelength-selective reflection layer 40 is 50% or less. The reflectance of the primary light LA at the wavelength-selective reflection layer 40 is 90% or more. Therefore, most of the primary light LA can be reflected by the wavelength-selective reflection layer 40. Most of the secondary light LB can be transmitted through the wavelength-selective reflection layer 40. As a result, only the secondary light LB emitted from the wavelength conversion agent 38 is emitted in the area directly above the light source 23. This makes it possible to prevent the area directly above the light source 23 from becoming too bright.

The surface light source device 20 shown in FIG. 16 is the same as the surface light source device 20 shown in FIG. 2, and has a sheet-shaped conversion agent-containing portion 35. In this example, the content (%) of the wavelength conversion agent 38 in the conversion agent-containing portion 35 can be reduced to reduce the illuminance in the area directly above the light source 23.

As shown in FIG. 16, the light L161 and light L162 as the primary light LA reflected by the wavelength-selective reflecting layer 40 are reflected by the reflecting layer 27 and the wavelength-selective reflecting layer 40 until they are wavelength-converted by the wavelength conversion agent 38. These lights L161 and L162 proceed in the first direction D1 and the second direction D2 perpendicular to the third direction D3. The light L161 and light L162 move away from the light source 23, and are absorbed by the wavelength conversion agent 38 with a certain probability when passing through the conversion agent-containing portion 35. These lights L161 and L162 pass through the wavelength-selective reflecting layer 40 in the area away from the light source 23. This makes it possible to prevent the area away from the light source 23 from becoming too dark.

The surface light source device 20 shown in FIG. 16 has a sheet-shaped conversion agent-containing portion 35. In this example, by reducing the content (%) of the wavelength conversion agent 38 in the conversion agent-containing portion 35, the movement of the primary light LA in the first direction D1 and the second direction D2 perpendicular to the third direction D3 is promoted. Therefore, by reducing the content (%) of the wavelength conversion agent 38 in the conversion agent-containing portion 35, the area away from the light source 23 can be brightened.

As described above, the wavelength conversion agent 38 and the wavelength-selective reflecting layer 40 work together to effectively eliminate uneven brightness depending on the distance from the light source 23, and the illuminance distribution on the light-emitting side surface 40b of the wavelength-selective reflecting layer 40 is sufficiently uniform.

From the viewpoint of uniform illuminance, the wavelength conversion agent 38 may be arranged in consideration of the arrangement of the light source 23, as shown in Figs. 8 to 12A. Specifically, the volume of the wavelength conversion agent 38 contained in one reference volume region 35V may be made larger than the volume of the wavelength conversion agent 38 contained in another reference volume region 35V located between the reference volume region 35V and one light source 23 closest to the reference volume region 35V. Furthermore, the volume of the wavelength conversion agent 38 contained in any one reference volume region 35V may be made larger than the volume of the wavelength conversion agent 38 contained in any other reference volume region 35V located between the reference volume region 35V and one light source 23.

According to these specific examples, in the area directly above the light source 23, the primary light LA can be prevented from being converted to secondary light LB by the wavelength conversion agent 38. Therefore, the area directly above the light source 23 can be more effectively prevented from becoming too bright. On the other hand, in areas away from the light source 23 in the first direction D1 or the second direction D2, the primary light LA can be promoted from being converted to secondary light LB by the wavelength conversion agent 38. Therefore, the area away from the light source 23 can be prevented from becoming too dark. This allows the surface light source device 20 to be sufficiently thin while the in-plane distribution of brightness can be sufficiently uniformed.

In addition, in the area between two adjacent light sources 23, the primary light LA can be promoted to be converted into secondary light LB by the wavelength conversion agent 38. Therefore, it is possible to prevent the light emitted from one light source 23 from moving to the vicinity of another light source 23. In other words, it is possible to reduce the number of reflections of the primary light LA. This makes it possible to suppress reflection losses and improve the utilization efficiency of the light sources 23.

Local dimming is known as a control method for controlling the turning on and off of the light source 23 of the surface light source device 20 in accordance with the image displayed by the display device 10. In local dimming, the light source 23 facing the dark part of the image is turned off, and the light source 23 facing the bright part of the image is turned on. By using local dimming, the contrast of the image can be improved. Local dimming is considered to be an effective control, especially in a liquid crystal display device in which oblique light leaks from the display panel 15. By setting a distribution in the arrangement of the wavelength conversion agent 38 as shown in Figures 8 to 12A, the conversion of the primary light LA to secondary light LB by the wavelength conversion agent 38 is promoted in the area between two adjacent light sources 23. This makes it possible to prevent the primary light LA emitted from one light source 23 from reaching the vicinity of the other light source 23. Therefore, the primary light LA emitted from one light source 23 is easily converted into secondary light LB while moving to the midpoint between the one light source 23 and the adjacent other light source 23. This makes it possible to effectively utilize local dimming.

As shown in FIG. 17, the light transmitted through the wavelength selective reflecting layer 40 travels toward the optical sheet 50. As shown in FIG. 17, the light exit side 50b of the optical sheet 50 facing the wavelength selective reflecting layer 40 is an uneven surface 51. The light L171, L172 emitted from the wavelength selective reflecting layer 40 travels in a direction greatly inclined with respect to the third direction D3. These light beams L171, L172 pass through the element surface 56 inclined in the opposite direction from the traveling direction and the third direction D3 as the center, and are emitted from the optical sheet 50. The light beams L171, L172 are refracted at the element surface 56 and bend their traveling direction. At this time, the traveling direction of the light beams L171, L172 bends so that the angle with respect to the third direction D3 becomes smaller. That is, the angle that the traveling direction of the light L171, L172 makes with respect to the third direction D3 is reduced by the refraction of the light L171, L172 at the element surface 56. That is, the optical sheet 50 exerts the function of concentrating the light emitted from the surface light source device 20 in the third direction D3.

The light that exits the optical sheet 50 enters the reflective polarizing plate 60. The reflective polarizing plate 60 transmits the linearly polarized light component that can enter the display panel 15 and reflects the linearly polarized light component that cannot enter the display panel 15. The reflected light can be reflected repeatedly and re-enter the reflective polarizing plate 60 as a linearly polarized light component that can enter the display panel 15. The polarization separation function of the reflective polarizing plate 60 can greatly improve the utilization efficiency of the light source 23.

In this manner, the light-emitting surface 20a emits light, illuminating, for example, the display panel 15.

As described above, the light source 23 may emit light with a wavelength of less than 380 nm. In this specific example, the primary light LA emitted from the light source 23 is invisible light. Therefore, even if the primary light LA passes through the wavelength-selective reflecting layer 40 with a non-uniform in-plane distribution of the amount of light, it is possible to suppress the occurrence of color unevenness perceived by the observer on the light-emitting surface 20a of the surface light source device 20. In this specific example, a layer containing an ultraviolet absorber may be provided between the wavelength-selective reflecting layer 40 and the display surface 15a in the third direction D3. For example, the optical sheet 50 or the reflective polarizing plate 60 may include a layer containing an ultraviolet absorber.

For example, the wavelength-selective reflecting layer 40 made of a dielectric multilayer film can exert an optical effect on light of wavelength λx (nm) traveling in a direction inclined by θ (°) with respect to the third direction D3 similar to the optical effect on light of wavelength λ = λ / cos θ traveling in the third direction D3. That is, the optical effect of the wavelength-selective reflecting layer 40 on light of wavelength λx (nm) traveling in a direction inclined by θ (°) with respect to the third direction D3 can be similar to the optical effect of the wavelength-selective reflecting layer 40 on light of wavelength λ = λ / cos θ traveling in the third direction D3. Therefore, an optical effect similar to the optical effect on primary light LA traveling in the third direction D3 can also be exerted on secondary light LB traveling in an oblique direction.

From this point of view, in the above-mentioned specific example, the shortest wavelength (nm) of the secondary light LB obtained by conversion with the wavelength conversion agent 38 may be 1.31 (=1/cos40°) times or more the wavelength λ1 (nm) of the primary light. The shortest wavelength (nm) of the secondary light LB means the central wavelength of the light emitted by the type of wavelength conversion agent 38 that emits the shortest wavelength of light when multiple types of wavelength conversion agents 38 are included in the surface light source device 20. In the example shown in FIG. 5, the central wavelength (nm) of the first secondary light LB1 emitted from the first wavelength conversion agent 38A is the shortest wavelength (nm) of the secondary light LB obtained by conversion with the wavelength conversion agent 38.

According to this example, the secondary light LB traveling in a direction that forms an angle of less than 40° with the third direction D3 in the wavelength-selective reflecting layer 40 can be prevented from being reflected by the wavelength-selective reflecting layer 40 to the same extent as the primary light LA. The reflectance of the secondary light LB traveling in a direction that forms an angle of less than 40° with the third direction D3 in the wavelength-selective reflecting layer 40 in the wavelength-selective reflecting layer 40 can be reduced to be lower than the reflectance of the primary light LA in the wavelength-selective reflecting layer 40. Therefore, the transmittance of the secondary light LB in the wavelength-selective reflecting layer 40 can be sufficiently improved. This makes it possible to avoid unnecessary reflections and improve the utilization efficiency of the light source 23.

The wavelength-selective reflective layer 40 can be made using a resin with a refractive index of 1.4 or more and 1.6 or less. The critical angle of total reflection at the interface between such a wavelength-selective reflective layer 40 and the air layer is 38.7° or more and 45.6° or less. That is, light traveling in the wavelength-selective reflective layer 40 in a direction that forms an angle of more than 40° with respect to the third direction D3 is likely to be totally reflected at the light-emitting side surface 40b of the wavelength-selective reflective layer 40. Therefore, according to an example in which the shortest wavelength (nm) of the secondary light LB obtained by conversion with the wavelength conversion agent 38 is 1.31 (=1/cos40°) times or more the wavelength λ1 of the primary light LA, color unevenness can be suppressed in the surface light source device 20 in which multiple secondary lights LB of different wavelengths pass through the wavelength-selective reflective layer 40.

In the embodiment described above, the surface light source device 20 has a wavelength selective reflective layer 40, a light source substrate 22, and a wavelength conversion agent 38 located between the wavelength selective reflective layer 40 and the light source substrate 22. The light source substrate 22 includes a light source 23 facing the wavelength selective reflective layer 40 and a support substrate 25 supporting the light source 23. The support substrate 25 includes a reflective layer 27 facing the wavelength selective reflective layer 40. The wavelength conversion agent 38 absorbs the primary light LA from the light source 23 and emits secondary light LB (secondary light) having a wavelength different from that of the primary light LA. The reflectance of the secondary light LB at the wavelength selective reflective layer 40 is smaller than the reflectance of the primary light LA at the wavelength selective reflective layer 40.

In this embodiment, the reflectance of the wavelength-selective reflective layer 40 depends on the wavelength of the light. Therefore, the primary light LA emitted from the light source 23 can be repeatedly reflected by the wavelength-selective reflective layer 40 and the reflective layer 27 until it is absorbed by the wavelength conversion agent 38 and converted into secondary light LB of a different wavelength. That is, the primary light LA emitted from the light source 23 can proceed in the first direction D1 and the second direction D2 perpendicular to the third direction D3 until it collides with the wavelength conversion agent 38. This makes it possible to prevent the illuminance in the area directly above the light source 23 from becoming too high. The illuminance in the area away from the light source 23 can be increased. As a result, the brightness distribution caused by the light source 23 is eliminated, and the in-plane distribution of illuminance can be effectively uniformed. In addition, the primary light LA emitted from the light source 23 is suppressed from passing through the wavelength-selective reflective layer 40 until it is converted into secondary light LB by the wavelength conversion agent 38. Therefore, even if the distance from the light source substrate 22 to the wavelength-selective reflecting layer 40 is shortened, the primary light LA can be sufficiently diffused between the wavelength-selective reflecting layer 40 and the light source substrate 22. As a result, the surface light source device 20 can be made sufficiently thin while the in-plane distribution of brightness can be sufficiently uniform.

In addition, in a conventional direct-type surface light source device such as that in Patent Document 1 (JP2014-199831A), the thickness of the layer containing the wavelength conversion agent was made thick to ensure a collision opportunity between the primary light and the wavelength conversion agent. However, in this embodiment, the primary light LA can be repeatedly reflected by the wavelength-selective reflection layer 40 and the reflection layer 27 until it collides with the wavelength conversion agent 38. Therefore, even if the thickness of the conversion agent-containing portion 35 containing the wavelength conversion agent 38 is made thin, the primary light LA can be sufficiently converted into secondary light LB by the wavelength conversion agent 38. By making the conversion agent-containing portion 35 containing the wavelength conversion agent 38 thinner, the surface light source device 20 can be made thinner. In addition, the amount of wavelength conversion agent 38 used can be reduced, so the manufacturing cost of the surface light source device 20 can be reduced.

In the specific example of the embodiment described above, a conversion agent-containing portion 35 containing a wavelength conversion agent 38 is provided between the wavelength selective reflection layer 40 and the light source substrate 22. One or more of the thickness (mm) of the conversion agent-containing portion 35, the ratio (%) of the area in which the conversion agent-containing portion 35 is disposed, and the content (%) of the wavelength conversion agent 38 contained in the conversion agent-containing portion 35 change depending on the distance from the light source 23. In such an example, the conversion agent-containing portion 35 can be produced by a simple method such as printing or molding. This conversion agent-containing portion 35 allows the distribution of the wavelength conversion agent 38 to be adjusted with a high degree of freedom. This allows the surface light source device 20 to be sufficiently thin while sufficiently uniforming the in-plane distribution of brightness.

In the specific example of the embodiment described above, a conversion agent-containing portion 35 containing a wavelength conversion agent 38 is provided between the wavelength selective reflection layer 40 and the light source substrate 22. The conversion agent-containing portion 35 constitutes a part or all of the intermediate layer 32 that maintains a constant distance between the wavelength selective reflection layer 40 and the light source substrate 22. For example, as disclosed in Patent No. 6299811, in order to achieve uniform brightness, light is usually diffused by refraction or total reflection at the refractive index interface. On the other hand, in this embodiment, the light emitted from the light source 23 is diffused by the wavelength conversion agent 38 of the wavelength selective reflection layer 40. Therefore, since an interface with a large refractive index difference does not need to be used, the intermediate layer 32 can be disposed between the wavelength selective reflection layer 40 and the light source substrate 22. Furthermore, the intermediate layer 32 may be filled between the wavelength selective reflection layer 40 and the light source substrate 22. In the specific example described above, the conversion agent-containing portion 35 containing the wavelength conversion agent 38 is provided between the wavelength selective reflection layer 40 and the light source substrate 22, and the conversion agent-containing portion 35 constitutes part or all of the intermediate layer 32. The intermediate layer 32 allows the wavelength selective reflection layer 40 to be aligned to an appropriate position relative to the light source 23. Also, the wavelength conversion agent 38 can be aligned to an appropriate position relative to the light source 23. This makes it possible to stably ensure uniformity of the in-plane distribution of brightness.

In the specific example of the embodiment described above, the intermediate layer 32 includes a first portion 33A containing a wavelength conversion agent 38, and a second portion 33B containing a lower content (%) of the wavelength conversion agent 38 than the first portion 33A or not containing the wavelength conversion agent 38. In this specific example, the first portion 33A and the second portion 33B can be produced by a simple method such as printing or molding. The intermediate layer 32 including the first portion 33A and the second portion 33B allows the distribution of the wavelength conversion agent 38 to be adjusted with a high degree of freedom. This allows the surface light source device 20 to be sufficiently thin while the in-plane distribution of brightness to be sufficiently uniform.

In the specific example of the embodiment described above, the intermediate layer 32 is bonded to at least one of the wavelength selective reflecting layer 40 and the light source substrate 22. According to this specific example, the intermediate layer 32 can maintain the wavelength selective reflecting layer 40 in an appropriate position relative to the light source 23. Also, the wavelength conversion agent 38 can be maintained in an appropriate position relative to the light source 23. This allows the in-plane distribution of brightness to be stably and uniformly achieved while the surface light source device 20 is in use.

In the specific example of the embodiment described above, the optical sheet 50 has a light-entering side 50a facing the wavelength-selective reflecting layer 40 and a light-exiting side 50b facing the light-entering side 50a, and the light-exiting side 50b is an uneven surface 51. The wavelength-selective reflecting layer 40 is located between the optical sheet 50 and the light source substrate 22 in the third direction D3. As shown in FIG. 17, in this specific example, the light L171 and L172 traveling from the wavelength-selective reflecting layer 40 to the optical sheet 50 travels in a direction that forms a large angle with the third direction D3. The optical sheet 50 can bend the traveling direction of the light L171 and L172 by refraction. That is, the optical sheet 50 can adjust the traveling direction of the light L171 and L172 so that the angle that the traveling direction of the light L171 and L172 emitted from the wavelength-selective reflecting layer 40 forms with the third direction D3 is significantly reduced. This effectively improves the front-direction brightness of the surface light source device 20.

Although one embodiment has been described with reference to specific examples, the above-mentioned specific examples do not limit the embodiment. The above-mentioned one embodiment can be implemented with various other specific examples, and various omissions, substitutions, modifications, additions, etc. can be made within the scope of the gist of the embodiment.

Below, an example of a modification will be described with reference to the drawings. In the following description and the drawings used in the following description, parts that can be configured similarly to the specific example described above will be designated by the same reference numerals as those used for the corresponding parts in the specific example described above, and duplicate descriptions will be omitted.

12B, the intermediate layer 32 may contain a light diffusing component 39. Examples of the light diffusing component 39 include metal compounds, porous substances containing gas, resin beads with metal compounds around them, white fine particles, and even simple air bubbles. By including the light diffusing component 39, the in-plane distribution of brightness can be made more uniform. In addition, the distribution of the wavelength conversion agent 38 can be made sufficiently inconspicuous. In the example shown in FIG. 12B, the second portion 33B contains the light diffusing component 39. The second portion 33B contains the wavelength conversion agent 38 at a lower content rate (%) than the first portion 33A, or does not contain the wavelength conversion agent 38. The second portion 33B is at least partially located between the first portion 33A and the wavelength selective reflection layer 40. According to the configuration shown in FIG. 12B, the distribution of the first portion 33A, in which the wavelength conversion agent 38 is dispersed at a high concentration, can be made more effectively inconspicuous by diffusion by the light diffusing component 39.

As shown in FIG. 18, the intermediate layer 32 may be in contact with the portion of the light source 23 from which the primary light LA is emitted. That is, the intermediate layer 32 may be in contact with the emission surface 23S of the light source 23. According to this example, the emission surface 23S of the light source 23 is in optical contact with the intermediate layer 32. As shown in FIG. 18, the edge of the emission surface 23S is usually curved. At this curved portion, total reflection of the light L182 generated by the light source 23 may occur. By covering this curved portion with the intermediate layer 32, the refractive index difference is reduced, suppressing total reflection. This improves the utilization efficiency of the light source 23. In the first place, the light L181 that can be used is light that travels in an oblique direction, which can contribute to uniform brightness. In addition, the intermediate layer 32 can protect the emission surface 23S of the light source 23.

The optical member 30 may further include a second optical sheet superimposed on the optical sheet 50 in the third direction D3. In this example, the optical sheet 50 and the second optical sheet may both be the optical sheets shown in FIG. 15D. The arrangement direction of the unit optical elements 55 in the optical sheet 50 and the arrangement direction of the unit optical elements 55 in the second optical sheet may be non-parallel or perpendicular to each other.

D1: first direction, D2: second direction, D3: third direction, LA: primary light, LB: secondary light, LB1: first secondary light, LB2: second secondary light, LB3: third secondary light, 10: display device, 15: display panel, 15a: display surface, 20: surface light source device, 20a: light emitting surface, 22: light source substrate, 23: light source, 23S: emission surface, 25: support substrate, 26: substrate body, 27: reflective layer, 29: wiring, 30: optical member, 32: intermediate layer, 33A: first part, 33B: second part, 35 : conversion agent-containing portion, 35A: area, 35V: reference volume region, 36: base material portion, 38: wavelength conversion agent, 38A: first wavelength conversion agent, 38B: second wavelength conversion agent, 38C: third wavelength conversion agent, 39: light diffusion component, 40: wavelength selective reflection layer, 40a: light entrance side, 40b: light exit side, 50: optical sheet, 50a: light entrance side, 50b: light exit side, 51: uneven surface, 52: main body portion, 53: convex portion, 54: concave portion, 55: unit optical element, 56: element surface, 60: reflective polarizing plate

Claims (12)

A wavelength selective reflective layer;
a light source substrate including a light source facing the wavelength selective reflection layer and a support substrate supporting the light source;
a wavelength conversion agent located between the wavelength selective reflective layer and the light source substrate,
the light source substrate includes a reflective layer facing the wavelength-selective reflective layer;
The wavelength conversion agent absorbs primary light from the light source and emits secondary light having a wavelength different from that of the primary light;
the reflectance of the secondary light at the wavelength-selective reflective layer is smaller than the reflectance of the primary light at the wavelength-selective reflective layer,
If an area having a certain area of the wavelength selective reflecting layer and an area between the wavelength selective reflecting layer and the light source substrate that overlaps in a direction in which the wavelength selective reflecting layer and the light source substrate face each other are defined as a reference volume area,
A surface light source device, wherein the volume of the wavelength conversion agent contained in one reference volume region is larger than the volume of the wavelength conversion agent contained in another reference volume region located between the one reference volume region and a light source closest to the one reference volume region . 2. The surface light source device of claim 1, wherein the volume of the wavelength conversion agent contained in any one of the reference volume regions is greater than or equal to the volume of the wavelength conversion agent contained in any other reference volume region located between the one of the reference volume regions and the one of the light sources. a conversion agent-containing portion containing the wavelength conversion agent is provided between the wavelength selective reflection layer and the light source substrate,
3. The surface light source device of claim 1, wherein one or more of the thickness of the conversion agent-containing portion, the proportion of the area in which the conversion agent-containing portion is arranged, and the content of the wavelength conversion agent contained in the conversion agent-containing portion change depending on the distance from the light source. a conversion agent-containing portion containing the wavelength conversion agent is provided between the wavelength selective reflection layer and the light source substrate,
3 . The surface light source device according to claim 1 , wherein the conversion agent-containing portion constitutes a part or the whole of an intermediate layer that maintains a constant distance between the wavelength selective reflection layer and the light source substrate. The surface light source device according to claim 4 , wherein the intermediate layer includes a first portion containing the wavelength conversion agent and a second portion containing the wavelength conversion agent at a content rate lower than that of the first portion or not containing the wavelength conversion agent. The surface light source device according to claim 4 , wherein the intermediate layer contains a light diffusing component. the second portion comprises a light diffusing component;
The surface light source device according to claim 5 , wherein the second portion is at least partially located between the first portion and the wavelength-selective reflecting layer. 8. The surface light source device according to claim 4 , wherein the intermediate layer is bonded to at least one of the wavelength selective reflection layer and the light source substrate. 9. The surface light source device according to claim 4 , wherein the intermediate layer is in contact with a portion of the light source from which the primary light is emitted. The surface light source device according to claim 1 , wherein the light source emits light having a wavelength of less than 380 nm. 11. The surface light source device according to claim 1, wherein the shortest wavelength of the secondary light is 1.31 times or more as long as the wavelength of the primary light. A surface light source device according to any one of claims 1 to 11 ,
A display device comprising the surface light source device and a display panel overlapped therewith.

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