JP7615500B2 - Optical member, surface light source device, display device and wavelength conversion sheet - Google Patents

Description

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

As disclosed in Patent Document 1, a surface light source device having a monochromatic light source is known. The surface light source device of Patent Document 1 includes a fluorescent layer containing a wavelength conversion agent. When light from the light source collides with the wavelength conversion agent, the wavelength conversion agent absorbs the light from the light source and emits light of a different wavelength. By including a sufficient amount of wavelength conversion agent in the fluorescent layer, the emitted color can be adjusted. However, wavelength conversion agents are easily degraded by oxygen and moisture.

JP 2013-519232 A

The present disclosure aims to reduce the amount of wavelength conversion agent.

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

In an optical element according to one embodiment of the present disclosure, the transmittance of the selective transmission portion for light of the specific wavelength incident on the selective transmission portion at an incident angle of 0° may be 5% or less.

In an optical element according to one embodiment of the present disclosure, the transmittance of the selective transmission portion for the light of the specific wavelength that is emitted from the selective transmission sheet at an emission angle of 0° may be 5% or less.

In an optical element according to one embodiment of the present disclosure, the transmittance of the selective transmission section for light of the specific wavelength that is emitted from the selective transmission sheet at an emission angle of 0° or more and 35° or less in absolute value may be less than half the maximum transmittance of the selective transmission section.

In an optical member according to an embodiment of the present disclosure,
The inclination angle θp (°) of the element surfaces constituting the concave-convex surface and the refractive index np of the portion constituting the element surfaces of the wavelength conversion sheet satisfy the following formula:
sin ^-1 (1/np)≦90-θp
The inclination angle θp (°) may be an angle between a plane perpendicular to a stacking direction of the selective transmission sheet and the wavelength conversion sheet and the element surface.

In an optical member according to an embodiment of the present disclosure,
The inclination angle θp (°) of the element surfaces constituting the concave-convex surface, the refractive index np of the portion constituting the element surfaces of the wavelength conversion sheet, and the angle θx (°) with respect to the incident direction on the wavelength conversion sheet satisfy the following formula:
sin ^-1 (1/np)≦sin ^-1 (sin(θx-θp)/np)+θp
the inclination angle θp (°) is an angle between a plane perpendicular to the stacking direction of the selective transmission sheet and the wavelength conversion sheet and the element surface,
The angle θx (°) may be the angle between the peak emission direction from the selective transmission sheet of light that is incident on the selective transmission section at an incident angle at which the transmittance of light of the specific wavelength in the selective transmission section is 1/2 of its maximum value, and the stacking direction.

In an optical member according to an embodiment of the present disclosure,
The inclination angle θp (°) of the element surfaces constituting the concave-convex surface, the refractive index np of the portion constituting the element surfaces of the wavelength conversion sheet, and the angle θx (°) with respect to the incident direction on the wavelength conversion sheet satisfy the following formula:
sin ^-1 (sin(θx-θp)/np)+θp≦90-θp
the inclination angle θp (°) is an angle between a plane perpendicular to the stacking direction of the selective transmission sheet and the wavelength conversion sheet and the element surface,
The angle θx (°) may be the angle between the peak emission direction from the selective transmission sheet of light that is incident on the selective transmission section at an incident angle at which the transmittance of light of the specific wavelength in the selective transmission section is 1/10 of the maximum value, and the stacking direction.

In an optical member according to an embodiment of the present disclosure,
the wavelength conversion sheet includes an optical element portion including the uneven surface,
The optical element section may include a plurality of unit optical elements including the element surface.

In an optical member according to an embodiment of the present disclosure,
The wavelength conversion agent includes a first conversion agent that absorbs the primary light and emits a first secondary light, and a second conversion agent that absorbs the primary light and emits a second secondary light,
the wavelength of the second secondary light is longer than the wavelength of the first secondary light;
the wavelength of the first secondary light is longer than the wavelength of the primary light;
A conversion efficiency of the second conversion agent in the wavelength conversion sheet may be greater than a conversion efficiency of the first conversion agent in the wavelength conversion sheet.

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

The optical member according to one embodiment of the present disclosure includes:
The wavelength conversion sheet further includes a reflective polarizing plate overlapped with the wavelength conversion sheet,
The wavelength conversion sheet may be located between the selective transmission sheet and the reflective polarizing plate.

The optical member according to one embodiment of the present disclosure includes:
Further comprising an optical sheet overlapping the wavelength conversion sheet,
The wavelength conversion sheet may be located between the selective transmission sheet and the optical sheet.

A surface light source device according to an embodiment of the present disclosure includes:
Any one of the optical members according to an embodiment of the present disclosure;
and a light source facing the optical member.

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

In a surface light source device according to one embodiment of the present disclosure, a portion of the optical member closest to the light source substrate may be joined to the light source substrate.

In a surface light source device according to an embodiment of the present disclosure, the selectively transmitting sheet and the light source substrate may be joined. The selectively transmitting portion or the light diffusing portion of the selectively transmitting sheet may be joined to the light source substrate.

In a surface light source device according to an embodiment of the present disclosure,
The inclination angle θp (°) of the element surfaces constituting the concave-convex surface, the refractive index np of the portion constituting the element surfaces of the wavelength conversion sheet, and the angle θx (°) with respect to the incident direction on the wavelength conversion sheet satisfy the following formula:
sin ^-1 (1/np)≦sin ^-1 (sin(θx-θp)/np)+θp
the inclination angle θp (°) is an angle between a plane perpendicular to the stacking direction of the selective transmission sheet and the wavelength conversion sheet and the element surface,
The angle θx (°) may be the angle between the stacking direction and a direction in which a luminance that is half the peak luminance in the luminance angular distribution on a surface of the selective transmission sheet facing the wavelength conversion sheet, obtained in a state in which components closer to the wavelength conversion sheet than the selective transmission sheet are removed, is obtained.

In a surface light source device according to an embodiment of the present disclosure,
The inclination angle θp (°) of the element surfaces constituting the concave-convex surface, the refractive index np of the portion constituting the element surfaces of the wavelength conversion sheet, and the angle θx (°) with respect to the incident direction on the wavelength conversion sheet satisfy the following formula:
sin ⁻¹ (sin(θx−θp)/np)+θp≦90−θp
the inclination angle θp (°) is an angle between a plane perpendicular to the stacking direction of the selective transmission sheet and the wavelength conversion sheet and the element surface,
The angle θx (°) may be the angle between the stacking direction and a direction in which a luminance that is 1/10 of the peak luminance in the luminance angular distribution on a surface of the selective transmission sheet facing the wavelength conversion sheet, obtained in a state in which components closer to the wavelength conversion sheet than the selective transmission sheet are removed, is obtained.

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.

A first wavelength conversion sheet according to an embodiment of the present disclosure includes:
The first page and
a second surface opposite to the first surface;
a wavelength converting agent located between the first surface and the second surface,
an optical element portion that configures the first surface and the second surface is provided;
The optical element portion includes a plurality of unit optical elements,
at least one of the first surface and the second surface includes an uneven surface formed by a plurality of unit optical elements,
The wavelength conversion agent absorbs the primary light of the specific wavelength and emits the secondary light,
The secondary light has a wavelength different from the particular wavelength.

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

In the first and second wavelength conversion sheets according to the embodiment of the present disclosure,
The first surface faces a light source;
The first surface may include a textured surface.

According to this disclosure, the amount of wavelength conversion agent can be reduced.

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 shown in FIG. 1, showing an optical member and a light source substrate that can be included in the surface light source device. FIG. 3 is a plan view showing the light source substrate shown in FIG. 2, illustrating an example of an arrangement of a plurality of light sources. FIG. 4 is a cross-sectional view showing the light source substrate shown in FIG. 2, and shows an example of the configuration of the light source substrate. FIG. 5 is a vertical cross-sectional view showing a specific example of a selective transmission sheet that can be included in the optical member shown in FIG. FIG. 6 is a graph showing a first specific example and a second specific example of the optical characteristics of the selective transmission portion that can be included in the selective transmission sheet shown in FIG. FIG. 7 is a cross-sectional view showing an example of a wavelength conversion sheet that can be included in the optical member shown in FIG. FIG. 8 is a cross-sectional view showing another example of a wavelength conversion sheet that can be included in the optical member shown in FIG. FIG. 9 is a vertical sectional view showing an example of a wavelength converting portion that can be included in the wavelength conversion sheet shown in FIGS. FIG. 10A is a plan view showing an example of an optical element section that can be included in the wavelength conversion sheet shown in FIGS. 7 and 8, and shows the arrangement of unit optical elements that can be included in the optical element section. FIG. 10B is a perspective view showing a specific example of the unit optical element shown in FIG. 10A. FIG. 10C is a diagram corresponding to FIG. 10A and shows another example of the arrangement of unit optical elements. FIG. 11 is a perspective view showing an example of an optical sheet that can be included in the optical member shown in FIG. FIG. 12 is a diagram illustrating the function of a wavelength conversion sheet that can be included in the optical member shown in FIG. FIG. 13 is a graph showing an example of the luminance angular distribution on the second surface of the selective transmission sheet that can be included in the optical member shown in FIG.

Below, an embodiment of the present invention will be described 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. 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, a "wavelength conversion sheet" cannot be distinguished solely from a component called a wavelength conversion film or a wavelength conversion plate. A "selectively transmitting sheet" cannot be distinguished solely from a component called a selectively transmitting film or a selectively transmitting plate.

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

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 the first side of each direction. The side opposite the tip of the arrow is the second side of each direction. For example, as shown in Figure 2, a symbol with an x in a circle indicates an arrow pointing into the paper in a direction perpendicular to the paper surface of the drawing. For example, as shown in Figure 3, a symbol with a dot in a circle indicates an arrow pointing out from the paper surface in a direction perpendicular to the paper surface of the drawing.

Figures 1 to 13 are diagrams for explaining one embodiment. Figure 1 is a perspective view that shows a surface light source device 20 and a display device 10 as an application example of an optical member 30. The display device 10 may display, for example, moving images, still images, text information, or 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 includes 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 a specific example of the surface light source device 20. As shown in Figure 2, the surface light source device 20 includes, as main components, a light source 23 and an optical member 30 that adjusts the optical path of the light emitted from the light source 23. The optical member 30 faces the light source 23. The optical member 30 is a sheet-like member. The optical member 30 faces the light source 23 in its normal direction. The optical member 30 is a diffusion member that diffuses the light emitted from the light source 23. The optical member 30 can effectively suppress the in-plane variation in illuminance caused by the arrangement of the light source 23. The diffusion by the optical member 30 can effectively uniform the illuminance at each position on the light-emitting side surface 30b of the optical member 30, or the illuminance at each position on a virtual light-receiving surface parallel to the light-emitting side surface 30b located in the vicinity of the light-emitting side surface 30b.

The display device 10, surface light source device 20, and optical member 30 in one embodiment will be described below with reference to the illustrated specific examples.

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

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

The surface light source device 20 includes a light-emitting surface 20a that emits light in a planar manner. The surface light source device 20 is configured as a direct-type backlight. The surface light source device 20 includes a light source 23 and an optical member 30. The light source 23 is provided in a region that overlaps with the optical member 30 when projected in the third direction D3.

The surface light source device 20 shown in FIG. 2 includes a light source substrate 22 including a light source 23. The light source substrate 22 and the optical member 30 are stacked in this order in the third direction D3. The light source substrate 22 and the optical member 30 are sheet-shaped. The light source substrate 22 and the optical member 30 extend in the first direction D1 and the second direction D2.

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 can be appropriately selected depending on the application of the surface light source device 20. The light emitted from the light source 23 is absorbed by the wavelength conversion agent 67 described below as primary light LA. Therefore, the emission wavelength of the light source 23 can be appropriately selected depending on the optical characteristics of the wavelength conversion agent 67. In the illustrated example, the light source 23 emits blue light. The light source 23 may have an emission wavelength of 430 nm or more and 500 nm or less.

The light distribution characteristic of the light source 23 is not particularly limited. The light distribution characteristic of the light source 23 may be a Lambertian light distribution. On the other hand, 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 light source 23 may have a bud wing light distribution disclosed in JP6299811B. As an example, the light source 23 may be composed only of light-emitting elements. As another example, the light source 23 may include optical elements such as a cover and a lens that adjust the light distribution from the light-emitting elements in addition to the light-emitting elements.

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 suppressing unevenness in brightness due to the arrangement of the light sources 23, the plurality of light sources 23 included in the surface light source device 20 may be regularly arranged on a 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 multiple light sources 23 are arranged at a constant pitch in each of the mutually orthogonal first direction D1 and second direction D2. In the illustrated example, the arrangement pitch PL1 of the light sources 23 in the first direction D1 and the arrangement pitch PL2 of the light sources 23 in the second direction D2 are the same. The arrangement pitch PL1 and the arrangement pitch PL2 may be different. In the illustrated example, the first direction D1 and the second direction D2 are parallel to the side edges of the rectangular surface light source device 20 and the 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 second side in the third direction D3. The support substrate 25 is sheet-shaped. The support substrate 25 may include a circuit that supplies power to the light sources 23. The support substrate 25 may have optical reflectivity that reflects light toward the optical member 30.

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

The reflective layer 27 is laminated on the substrate body 26 from the optical member 30 side. 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 the light of a specific wavelength emitted by the light source 23 or to the light used for emission in the surface light source device 20. The reflection in the reflective layer 27 may be regular reflection, also called specular reflection, diffuse reflection, or anisotropic diffuse reflection. The reflective layer 27 may be formed of a white reflective layer containing white particles such as silicon dioxide, thereby imparting diffuse reflectivity to the reflective layer 27. The reflective layer 27 may be a metal layer laminated on the substrate body 26, or may be a reflective diffractive optical element.

The optical member 30 includes a selective transmission sheet 40 and a wavelength conversion sheet 60 in this order. The selective transmission sheet 40 and the wavelength conversion sheet 60 are stacked in the third direction D3. That is, the third direction D3 is the stacking direction of the selective transmission sheet 40 and the wavelength conversion sheet 60. The selective transmission sheet 40 is located on the second side in the third direction D3 from the wavelength conversion sheet 60. The wavelength conversion sheet 60 is located on the first side in the third direction D3 from the selective transmission sheet 40. In the illustrated example, the selective transmission sheet 40 and the wavelength conversion sheet 60 are both sheet-like members extending in the first direction D1 and the second direction D2. In the illustrated example, the selective transmission sheet 40 forms the light-entering side surface 30a of the optical member 30. The selective transmission sheet 40 and the wavelength conversion sheet 60 may be joined to each other, may simply be in contact with each other and not joined, or may be separated from each other.

The selective transmission sheet 40 includes a selective transmission section 45. The reflectance and transmittance of the selective transmission section 45 change depending on the angle of incidence.

In the example shown in FIG. 5, the selectively transparent sheet 40 is composed only of the selectively transparent portion 45. The illustrated selectively transparent portion 45 is in sheet form.

The illustrated selective transmission sheet 40 includes a first surface 40a and a second surface 40b. The first surface 40a faces the second side, which is the light source side in the third direction D3, and the second surface 40b faces the first side, which is the observer side in the third direction D3. The selective transmission portion 45 includes a first surface 45a and a second surface 45b. The first surface 45a faces the second side in the third direction D3. The second surface 45b faces the first side in the third direction D3. The first surface 45a of the selective transmission portion 45 constitutes the first surface 40a of the selective transmission sheet 40. The second surface 45b of the selective transmission portion 45 constitutes the second surface 40b of the selective transmission sheet 40. The first surface 40a and the second surface 40b are parallel flat surfaces.

The transmission and reflection characteristics of the selective transmission section 45 depend on the angle of incidence. The angle of incidence means the angle (°) that the direction of propagation of the incident light makes with respect to the normal direction of the sheet-like member on which the light is incident.

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

The selective transmission section 45 may have various transmission and reflection characteristics.

The transmittance of the selective transmission section 45 for light of a specific wavelength incident at an incident angle of 0° may be less than 5%, less than 3%, or less than 1%. The reflectance of the selective transmission section 45 for light of a specific wavelength incident at an incident angle of 0° may be 95% or more, 97% or more, or 99% or more.

The transmittance of the selective transmission portion 45 for light of a specific wavelength that is incident on the selective transmission portion 45 at an angle of incidence of 0° or more and 35° or less in absolute value may be half or less of the maximum transmittance of the selective transmission portion 45, may be 1/5 or less of the maximum transmittance of the selective transmission portion 45, or may be 1/10 or less of the maximum transmittance of the selective transmission portion 45. The transmittance of the selective transmission portion 45 for light of a specific wavelength that is incident on the selective transmission portion 45 at an angle of incidence of 0° or more and 45° or less in absolute value may be half or less of the maximum transmittance of the selective transmission portion 45, may be 1/5 or less of the maximum transmittance of the selective transmission portion 45, or may be 1/10 or less of the maximum transmittance of the selective transmission portion 45. The transmittance of the selective transmission section 45 for light of a specific wavelength that is incident on the selective transmission section 45 at an incident angle of 0° or more and 55° or less in absolute value may be less than half the maximum transmittance of the selective transmission section 45, may be less than 1/5 the maximum transmittance of the selective transmission section 45, or may be less than 1/10 the maximum transmittance of the selective transmission section 45.

The transmittance of the selective transmission section 45 for light of a specific wavelength incident on the selective transmission section 45 at an absolute angle of incidence of 0° to 35° may be less than 10%, less than 5%, or less than 1%. The transmittance of the selective transmission section 45 for light of a specific wavelength incident on the selective transmission section 45 at an absolute angle of incidence of 0° to 40° may be less than 10%, less than 5%, or less than 1%. The transmittance of the selective transmission section 45 for light of a specific wavelength incident on the selective transmission section 45 at an absolute angle of incidence of 0° to 45° may be less than 15%, less than 10%, or less than 5%. The transmittance of the selective transmission section 45 for light of a specific wavelength incident on the selective transmission section 45 at an absolute angle of incidence of 0° to 50° may be less than 15%, less than 10%, or less than 5%.

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

Figure 6 shows a first and second specific example of the transmission characteristics of the selective transmission portion 45. The incident angle (°) on the horizontal axis in the graph of Figure 6 indicates the incident angle when the selective transmission portion 45 forms an interface with the air layer. In the first and second specific examples shown in Figure 6, the transmittance of the selective transmission portion 45 reaches its maximum value when the incident angle is in the range of 65° to 70° in absolute value. As the incident angle increases from 0° to the incident angle at which the maximum value is reached, the transmittance of the selective transmission portion 45 increases. The maximum transmittance of the selective transmission portion 45 is 40% to 50%.

The optical characteristics of the selective transmission section 45 described here assume that the first surface 45a and the second surface 45b of the selective transmission section 45 are parallel and that the first surface 45a and the second surface 45b are adjacent to an air layer.

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

The reflectance of the selectively transmitting portion 45 is a value measured using a variable angle photometer (goniophotometer) GP-200 manufactured by Murakami Color Research Laboratory Co., Ltd. The transmittance of the selectively transmitting portion 45 is a total light transmittance measured in accordance with JIS K7361-1:1997. The transmittance of the selectively transmitting portion 45 is a value measured using a variable angle photometer (goniophotometer) GP-200 manufactured by Murakami Color Research Laboratory Co., Ltd.

The selective transmission section 45 is not particularly limited as long as it has a reflectance and a transmittance that depend on the angle of incidence. The selective transmission section 45 may include a dielectric multilayer film, a reflective volume hologram, a cholesteric liquid crystal structure layer, a retroreflective film, or a reflective diffractive optical element. The dielectric multilayer film is superior in that it has a relatively high degree of freedom in designing the reflection and transmission characteristics. The transmission characteristics shown in FIG. 6 are an example of the transmission characteristics of a dielectric multilayer film. The selective transmission section 45 may include a reflection structure that is structurally given a reflectance and a transmittance that depend on the angle of incidence. The reflection structure is superior in that it has a low wavelength dependency.

The dielectric multilayer film constituting the selective transmission section 45 may include low-refractive index layers and high-refractive index layers having different refractive indices, which are alternately stacked. The low-refractive index layers and high-refractive index layers may be layers of inorganic compounds or resin layers. The multilayer film constituting the dielectric multilayer film may have a protective layer on one side or both sides. The material of the protective layer may be polyethylene terephthalate or polyethylene naphthalate. The thickness of the protective layer may be 5 μm or more. The dielectric multilayer film may be manufactured by a co-extrusion method or the like. Specifically, the manufacturing method of the laminated film described in JP2008-200861A may be adopted. A commercially available laminated film may be used as the dielectric multilayer film. Examples of commercially available dielectric multilayer films include Picasus (registered trademark) manufactured by Toray Industries, Inc. and ESR manufactured by 3M.

7 and 8, the wavelength conversion sheet 60 includes a first surface 60a and a second surface 60b. The first surface 60a faces a second side that is the light source side in the third direction D3. The second surface 60b faces a first side that is the observer side in the third direction D3. The first surface 60a includes an uneven surface 61. The illustrated first surface 60a is the uneven surface 61 over the entire surface. The second surface 60b includes a flat surface. The illustrated second surface 60b is a flat surface over the entire surface. The second surface 60b may be a surface perpendicular to the third direction D3. The wavelength conversion sheet 60 includes a wavelength conversion agent 67. The wavelength conversion agent 67 absorbs primary light and emits secondary light having a wavelength different from that of the primary light.

In the example shown in Figs. 7 and 8, the wavelength conversion sheet 60 includes an optical element section 70, a first barrier layer 63, a wavelength conversion section 65, and a second barrier layer 64 in this order. The optical element section 70, the first barrier layer 63, the wavelength conversion section 65, and the second barrier layer 64 are stacked in this order in the third direction D3. The optical element section 70, the first barrier layer 63, the wavelength conversion section 65, and the second barrier layer 64 are arranged in this order from the first side to the second side in the third direction D3. The optical element section 70, the first barrier layer 63, the wavelength conversion section 65, and the second barrier layer 64 are sheet-shaped. The optical element section 70, the first barrier layer 63, the wavelength conversion section 65, and the second barrier layer 64 extend in the first direction D1 and the second direction D2.

7 and 8, the wavelength conversion section 65 includes a first surface 65a and a second surface 65b. The first surface 65a faces the second side in the third direction D3. The second surface 65b faces the first side in the third direction D3. The wavelength conversion section 65 may include a base material section 66 that holds a wavelength conversion agent 67. A resin may be used as the base material section 66. Examples of resins that constitute the base material section 66 include a thermoplastic resin, a cured product of a thermosetting resin composition, and a cured product of an ionizing radiation curable resin composition.

The wavelength conversion agent 67 absorbs primary light LA of a certain wavelength and emits secondary light LB having a wavelength different from the wavelength of the primary light LA. Quantum dots or phosphors may be used as the wavelength conversion agent 67. The wavelength of the primary light LA may be the wavelength of the light emitted from the light source 23. In other words, the light emitted from the light source 23 may include primary light LA of a certain wavelength.

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 wavelength conversion section 65 may include a plurality of quantum dots with different emission wavelengths as the wavelength conversion agent 67. 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. 9, the wavelength conversion agent 67 includes a first conversion agent 67A and a second conversion agent 67B. The first conversion agent 67A and the second conversion agent 67B have different sizes. The first conversion agent 67A and the second conversion agent 67B emit light of different wavelengths.

As a specific example, the light source 23 may emit blue light having a wavelength of 430 nm or more and 500 nm or more. The first conversion agent 67A may absorb the primary light LA from the light source 23 and emit green light having a wavelength of 500 nm or more and 600 nm or more as the first secondary light LB1. The second conversion agent 67B may absorb the primary light LA from the light source 23 and emit red light having a wavelength of 600 nm or more and 750 nm or more as the second secondary light LB2. According to this example, the surface light source device 20 can emit light of various colors by additive color mixing of the first secondary light LB1, the second secondary light LB2, and the primary light LA that has not been wavelength converted by the wavelength conversion unit 65. By adjusting the content of the first conversion agent 67A and the second conversion agent 67B, the surface light source device 20 can emit white light.

The wavelength conversion section 65 may contain a light diffusing component that diffuses the transmitted light. The light diffusing component may be dispersed within the base material section 66. Examples of light diffusing components include metal compounds, porous substances containing gas, resin beads surrounding metal compounds, white fine particles, and simple air bubbles.

In the illustrated example, the wavelength conversion agent 67 includes a first conversion agent 67A that absorbs the primary light LA and emits a first secondary light LB1, and a second conversion agent 67B that absorbs the primary light LA and emits a second secondary light LB2. In this example, the wavelength of the second secondary light LB2 is longer than the wavelength of the first secondary light LB1. The wavelength of the first secondary light LB1 is longer than the wavelength of the primary light LA. The conversion efficiency by the second conversion agent 67B in the wavelength conversion section 65 may be greater than the conversion efficiency by the first conversion agent 67A.

The conversion efficiency of the wavelength conversion agent is evaluated as the ratio (%) of the amount of secondary light LB (W) emitted from the second surface 60b, 65b of the wavelength conversion sheet 60 or the wavelength conversion unit 65 to the amount of primary light LA (W) incident on the first surface 60a, 65a of the wavelength conversion sheet 60 or the wavelength conversion unit 65. This evaluation is performed with the first surface 60a, 65a and the second surface 60b, 65b of the wavelength conversion sheet 60 or the wavelength conversion unit 65 as flat surfaces perpendicular to the third direction D3. It can be said that the higher the ratio of secondary light LB, the higher the conversion efficiency. In measuring the conversion efficiency, the angle of incidence of the primary light LA on the first surface 60a, 65a of the wavelength conversion sheet 60 or the wavelength conversion unit 65 is 0°. The first secondary light LB1 and the second secondary light LB2 emitted from the second surface 60b, 65b of the wavelength conversion sheet 60 or the wavelength conversion unit 65 are collected in an integrating sphere, and the light amount (W) of the first secondary light LB1 and the light amount (W) of the second secondary light LB are measured. This makes it possible to determine the conversion efficiency.

The first barrier layer 63 is bonded to the first surface 65a of the wavelength conversion section 65. The second barrier layer 64 is bonded to the second surface 65b of the wavelength conversion section 65. The first barrier layer 63 and the second barrier layer 64 have the function of protecting the wavelength conversion agent 67 from oxygen and moisture.

The first barrier layer 63 and the second barrier layer 64 may have oxygen barrier properties. In this example, the oxygen permeability of the first barrier layer 63 and the second barrier layer 64 may be 1.0×10 ⁻¹ cc/m ² /day/atm or less, or 1.0×10 ⁻² cc/m ² /day/atm or less, under conditions of 23° C. and relative humidity 90%. The oxygen permeability can be measured using an oxygen gas permeability measuring device (OX-TRAN 2/21, manufactured by MOCON).

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

The first barrier layer 63 and the second barrier layer 64 can be produced by a physical vapor deposition (PVD) method such as sputtering or ion plating, a deposition method such as chemical vapor deposition (CVD), or a coating method such as roll coating or spin coating using a material capable of exhibiting barrier properties. Inorganic oxides, metals, sol-gel materials, and the like may be used as the material. Examples of inorganic oxides include silicon oxide (SiO _x ), aluminum oxide (Al _n O _m ), titanium oxide (TiO ₂ ), yttrium oxide, boron oxide (B ₂ O ₃ ), calcium oxide (CaO), and silicon oxynitride carbide (SiO _x N _y C _z ). Examples of metals include Ti, Al, Mg, and Zr. Examples of sol-gel materials include siloxane-based sol-gel materials.

The optical element unit 70 includes a second surface 70b facing a first side that is the viewer side in the third direction D3. The optical element unit 70 is bonded to the first barrier layer 63 at the second surface 70b. The optical element unit 70 includes a first surface 70a facing a first side that is the light source side in the third direction D3. The first surface 70a of the optical element unit 70 constitutes the first surface 60a of the wavelength conversion sheet 60. The first surface 70a includes an uneven surface 61.

In the example shown in Figures 7 and 8, the optical element section 70 includes a number of unit optical elements 75, each formed as a convex portion 73 or a concave portion 74. The unit optical elements 75 are elements that change the traveling direction of light by refraction, reflection, or the like. The unit optical elements 75 are a concept that includes elements called unit shape elements, unit prisms, and unit lenses. The unit optical elements 75 directly face the selective transmission sheet 40. The unit optical elements 75 form the uneven surface 61.

The optical element unit 70 shown in FIG. 7 includes a sheet-like main body unit 72 and a plurality of convex portions 73 provided on the main body unit 72. In the example shown in FIG. 7, the plurality of convex portions 73 may be provided adjacent to each other with no gaps. The optical element unit 70 shown in FIG. 8 includes a main body unit 72 provided with a plurality of concave portions 74 on the surface facing the selectively transparent sheet 40 in the third direction D3. In the example shown in FIG. 8, the plurality of concave portions 74 may be provided adjacent to each other with no gaps.

As shown in Figures 7 and 8, the unit optical element 75 has an element surface 76 that is inclined with respect to the third direction D3. The unit optical element 75 is defined by this element surface 76. The uneven surface 61 of the wavelength conversion sheet 60 is formed by the element surface 76 of the unit optical element 75.

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

Unlike the examples shown in Figures 7 and 8, the element surface 76 may be somewhat curved. The unit optical element 75 may have an outer shape of a portion of a sphere, such as a hemisphere, or may have an outer shape of a portion of a spheroid.

The multiple unit diffusion elements 55 may be arranged two-dimensionally. According to this example, the element surfaces 76 of the unit optical elements 75 included in the optical element section 70 face various directions. As a result, the optical element section 70 can guide light in various directions by the two-dimensionally arranged unit optical elements 75. In other words, it is possible to guide light in multiple non-parallel directions, and the in-plane distribution of illuminance can be effectively uniformed. Each unit optical element 75 may be configured with rotational symmetry about an axis parallel to the third direction D3. For example, each unit optical element 75 may be configured with three-fold rotational symmetry, four-fold symmetry, or six-fold symmetry about an axis parallel to the third direction D3.

The multiple unit optical elements 75 may be arranged irregularly or regularly. By arranging the multiple unit optical elements 75 in a regular pattern, the design of the optical element section 70 can be simplified. By arranging the multiple unit optical elements 75 in a regular pattern, it becomes easier to arrange the unit optical elements 75 tightly without gaps.

If the dimensions of the unit optical elements 75 are large when observed from the third direction D3, unevenness in brightness due to the shape of the unit optical elements 75 is easily visible. From the viewpoint of preventing such defects, the maximum length of the unit optical elements 75 in the direction perpendicular to the third direction D3 may be 1.5 mm or less, 1 mm or less, or 0.5 mm or less. The arrangement pitch of the unit optical elements 75 may be 0.01 mm or more and 1.5 mm or less. Furthermore, from the viewpoint of effectively uniforming the in-plane distribution of illuminance on the light-emitting side surface 30b of the optical member 30 when applied to the surface light source device 20, the arrangement pitch of the unit optical elements 75 may be 0.05 mm or more and 1 mm or less, or 0.1 mm or more and 0.5 mm or less. The height or depth of the unit optical elements 75 in the third direction D3 may be 0.025 mm or more and 0.5 mm or less, or 0.05 mm or more and 0.25 mm or less.

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

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

The optical element section 70 shown in Figures 7 to 10C can be produced by embossing or resin molding. The optical element section 70 including the unit optical elements 75 may be bonded to the first barrier layer 63 via a bonding layer including a pressure-sensitive adhesive or adhesive. The optical element section 70 including the unit optical elements 75 may be produced on the first barrier layer 63.

The optical element section 70 may include a diffractive optical element.

2, the optical member 30 may include further components in addition to the selective transmission sheet 40 and the wavelength conversion sheet 60. The optical member 30 shown in FIG. 2 includes a first optical sheet 81, a second optical sheet 82, and a reflective polarizing plate 85 that are superimposed on the selective transmission sheet 40 and the wavelength conversion sheet 60 in the third direction D3. The first optical sheet 81, the second optical sheet 82, and the reflective polarizing plate 85 are located on the first side in the third direction D3 from the wavelength conversion sheet 60. The first optical sheet 81, the second optical sheet 82, and the reflective polarizing plate 85 are superimposed in this order in the third direction D3. The first optical sheet 81, the second optical sheet 82, and the reflective polarizing plate 85 may be sheet-like members that extend in the first direction D1 and the second direction D2.

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

11 shows a specific example of the first optical sheet 81 and the second optical sheet 82. The first optical sheet 81 and the second optical sheet 82 shown in FIG. 11 are prism sheets including a plurality of linearly extending unit prisms 84. The prism sheet includes a sheet-like main body 83 and a plurality of unit prisms 84 provided on the main body 83. The unit prisms 84 may extend linearly in a direction perpendicular to the arrangement direction of the plurality of unit prisms 84. That is, the first optical sheet 81 and the second optical sheet 82 are prism sheets in which the unit prisms 84 are linearly arranged. The linearly arranged unit prisms 84 shown in FIG. 11 mainly adjust the luminance angle distribution in a plane parallel to both the arrangement direction of the unit prisms 84 and the third direction D3. Therefore, the first optical sheet 81 and the second optical sheet 82 may be incorporated into the optical member 30 such that the arrangement direction of the unit prisms 84 is non-parallel. For example, the arrangement direction of the unit prisms 84 of the first optical sheet 81 may be perpendicular to the arrangement direction of the unit prisms 84 of the second optical sheet 82. The prism sheet shown in FIG. 11 may be "BEF" (registered trademark) available from 3M Corporation of the United States.

The reflective polarizing plate 85 transmits one linearly polarized component and reflects the other linearly polarized component. The reflective polarizing plate 85 can selectively transmit linearly polarized light that can pass through a polarizing plate located on the surface light source device 20 side of the display panel 15. The light reflected by the reflective polarizing plate 85 can change its polarization state by subsequent reflection or the like and enter the reflective polarizing plate 85 again. This can improve the utilization efficiency of the light emitted from the light source 23. The reflective polarizing plate 85 may be "DBEF" (registered trademark) available from 3M in the United States. The reflective polarizing plate 85 may be a high-brightness polarizing sheet "WRPS" available from Shinwa Intertek in Korea, a wire grid polarizer, or the like.

Next, we will explain the action of the surface light source device 20 having the above configuration when generating surface light.

As shown in FIG. 2, the light source 23 emits primary light LA. As an example, the primary light LA is blue light. The wavelength of the blue primary light LA may be 430 nm or more and 500 nm or less. The light L21 emitted from the light source 23 travels toward the optical element 30. As shown in FIG. 5, the primary light LA from the light source 23 is incident on the selective transmission sheet 40 of the optical element 30. As shown in FIG. 5, the selective transmission sheet 40 includes a selective transmission portion 45.

The primary light LA from the light source 23 is incident on the selective transmission section 45. The transmittance of the selective transmission section 45 depends on the angle of incidence. The transmittance of the selective transmission section 45 for the primary light LA incident at an angle of incidence greater than 0° is greater than the transmittance of the selective transmission section 45 for the primary light LA incident at an angle of incidence of 0°. In the optical characteristics shown in FIG. 6, the transmittance of the selective transmission section 45 for the light incident on the selective transmission section 45 at an angle of incidence of 0° is 5% or less. In addition, the transmittance of the selective transmission section 45 for the light exiting the selective transmission sheet 40 at an exit angle of 0° or more and 35° or less in absolute value is less than half the maximum value of the transmittance of the selective transmission section 45. Furthermore, as the exit angle increases within a wide range of 0° or more and 65° or less in absolute value, the transmittance of the selective transmission section 45 increases. When the exit angle is in the range of 0° or more and 50° or less in absolute value, the transmittance is 10% or less. That is, light inclined with respect to the third direction D3 can pass through the selective transmission section 45 with a higher transmittance than light traveling in the third direction D3. The exit angle refers to the angle (°) that the traveling direction of the exiting light makes with respect to the normal direction of the sheet-like member from which the light exits.

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

Most of the light L22 reflected by the selective transmission section 45 travels toward the light source substrate 22. As shown in FIG. 2, the light L22 is reflected by the reflective layer 27 of the light source substrate 22. Due to this reflection, the light L23 reflected by the reflective layer 27 travels toward the optical element 30 in the third direction D3. The reflection by the reflective layer 27 may be diffuse reflection. Due to the diffuse reflection, the angle that the traveling direction of the reflected light L23 makes with the third direction D3 becomes large. As shown in FIG. 2, the light L23 re-enters the optical element 30 at a position away from the light source 23 in the first direction D1 or the second direction D2 perpendicular to the third direction D3.

The light L23 may re-enter the selectively transparent sheet 40 in a spaced region away from the light source 23 in a direction perpendicular to the third direction D3. If the reflected light L23 travels in a direction significantly inclined relative to the third direction D3, the light L23 may transmit through the selectively transparent sheet 40. This prevents the light-emitting surface 20a from becoming too dark in the spaced region.

The selective transmission function of the selective transmission section 45 as described above can suppress in-plane variations in brightness according to the arrangement of the light sources 23. This can effectively uniformize the illuminance at each position on the second surface 40b of the selective transmission sheet 40.

As shown in FIG. 7, light L71 emitted from the selective transmission sheet 40 travels toward the wavelength conversion sheet 60. The wavelength conversion sheet 60 includes, from the second side, which is the light source side in the third direction D3, an optical element section 70, a first barrier layer 63, a wavelength conversion section 65, and a second barrier layer 64. The optical element section 70 provides an uneven surface 61 on the first surface 60a of the wavelength conversion sheet 60. As shown in FIG. 7, the light L71 changes its traveling direction when it enters the optical element section 70. The light L71 passes through the first barrier layer 63 and travels toward the wavelength conversion section 65.

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

Most of the light L24 (see FIG. 2) traveling through the wavelength conversion sheet 60 travels in a direction that is greatly inclined with respect to the third direction D3 due to the transmission characteristics of the selective transmission section 45. Therefore, even if the thickness of the wavelength conversion section 65 is reduced, the optical path length of the light L24 within the wavelength conversion section 65 becomes longer. This makes it easier for the light L24 to enter the wavelength conversion agent 67 within the wavelength conversion sheet 60. In this way, the wavelength conversion agent 67 can be used efficiently, and the amount of the wavelength conversion agent 67 contained in the selective transmission section 45 can be reduced.

The traveling direction of the secondary light LB emitted from the wavelength conversion agent 67 does not depend on the traveling direction of the primary light LA before being absorbed by the wavelength conversion agent 67. As shown in FIG. 9, the secondary light LB is emitted from the wavelength conversion agent 67 over a wide angular range. The angular distribution of the luminance caused by the secondary light LB is uniformized to a certain extent on the second surface 60b of the wavelength conversion sheet 60. Most of the secondary light LB emitted from the wavelength conversion agent 67 passes through the flat second surface 60b and exits from the wavelength conversion sheet 60.

As shown in FIG. 9, a portion L93 of the primary light LA is not incident on the wavelength conversion agent 67, but is incident on the second surface 60b. A portion of this light L93 also passes through the flat second surface 60b and exits from the wavelength conversion sheet 60.

In this manner, light L25 (see FIG. 2), such as the primary light LA, the first secondary light LB1, and the second secondary light LB2, is emitted from the wavelength conversion sheet 60 to the first side in the third direction D3. The light L25 passes through the first optical sheet 81, the second optical sheet 82, and the reflective polarizing plate 85, and is emitted from the light-emitting side surface 30b of the optical member 30. In this manner, the light-emitting side surface 30b of the optical member 30 emits light.

2 and 12, the light L26, L121 incident on the second surface 60b of the wavelength conversion sheet 60 may be reflected by the second surface 60b. The light L26, L121 reflected by the second surface 60b travels toward the second side in the third direction D3. Such light may be reflected by any interface, for example, the surface of the reflective layer 27, to turn back its traveling direction in the third direction D3 and enter the wavelength conversion sheet 60 again. When such light is incident on the second surface 60b, it travels in a direction greatly inclined with respect to the third direction D3 due to the optical characteristics of the selective transmission section 45. Therefore, the light L26, L121 is reflected by the second surface 60b with a relatively high reflectance. In addition, the light L26, L121 reflected by the wavelength conversion sheet 60 travels in the first direction D1 or the second direction D2 perpendicular to the third direction D3 and moves away from the light source 23. Therefore, by utilizing the reflection at the second surface 60b, it is possible to effectively suppress the in-plane variation in brightness caused by the arrangement of the light source 23. In other words, the wavelength conversion sheet 60 reinforces or complements the optical characteristics of the selective transmission portion 45 that have the incidence angle dependency, and can sufficiently uniformize the in-plane distribution of illuminance.

12, the thickness of the wavelength conversion sheet 60 is shown thin to facilitate understanding of the optical action related to the optical path in the wavelength conversion sheet 60. Also, in FIG. 12, the wavelength conversion agent 67 is omitted from the illustration. In reality, the wavelength conversion agent 67 is provided between the first surface 60a and the second surface 60b of the wavelength conversion sheet 60. By utilizing the reflection at the second surface 60b of the wavelength conversion sheet 60, the wavelength conversion agent 67 is located in the circulating optical path of the light emitted from the light source 23. In particular, the wavelength conversion agent 67 is dispersed inside the wavelength conversion sheet 60 that turns back the traveling direction in the third direction D3 in the circulating optical path. Therefore, in the wavelength conversion sheet 60 containing the wavelength conversion agent 67, the light travels in a direction inclined with respect to the third direction D3. The optical path length in the wavelength conversion sheet 60 becomes very long. This can significantly improve the utilization efficiency of the wavelength conversion agent 67, and can significantly reduce the content of the wavelength conversion agent 67 in the wavelength conversion portion 65. For example, the thickness of the wavelength conversion section 65 can be reduced, and the thickness of the optical member 30 and the surface light source device 20 in the third direction D3 can be reduced. The density of the wavelength conversion agent 67 in the wavelength conversion section 65 can be reduced.

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

Here, the transmittance of the selective transmission portion 45, which is a dielectric multilayer film, changes with different wavelengths. The transmittance of the selective transmission portion 45, which is a dielectric multilayer film, tends to be large for light with a wavelength longer than the specific wavelength. In other words, the selective transmission property that depends on the incident angle of the selective transmission portion 45 is weak for light with a wavelength longer than the specific wavelength. Therefore, the selective transmission portion 45 cannot effectively exhibit selective transmission property that depends on the incident angle for secondary light LB having a wavelength longer than the specific wavelength. In other words, the selective transmission portion 45 cannot reflect the secondary light LB, just like the primary light LA.

Therefore, from the viewpoint of sufficiently uniforming the in-plane distribution of illuminance, it is preferable to circulate the primary light LA sufficiently between the optical member 30 and the light source substrate 22 to uniformize the in-plane distribution of illuminance, and then convert the primary light LA into secondary light LB. In other words, from the viewpoint of suppressing the in-plane variation in brightness, it is preferable to reduce the content of the wavelength conversion agent 67 in the selective transmission section 45, which is in the circulating light path.

In the illustrated example, the first surface 60a of the wavelength conversion sheet 60 is composed of an optical element section 70. The optical element section 70 includes a plurality of unit optical elements 75. The unit optical elements 75 as the convex portions 73 or the concave portions 74 include a plurality of element faces 76. The first surface 60a is composed of the plurality of element faces 76. According to this example, as shown in FIG. 12, the light L121 incident on the wavelength conversion sheet 60 is likely to be incident on the element faces 76 that are inclined toward the opposite side of the traveling direction with respect to the third direction D3, among the element faces 76 that constitute the uneven surface 61. In this case, even after the light L121 is incident on the unit optical elements 75, the light L121 maintains the traveling direction that is greatly inclined toward the third direction D3. As a result, the angle of incidence θy on the flat second surface 60b of the wavelength conversion sheet 60 becomes large, and the reflectance at the second surface 60b becomes high. By promoting the reflection at the second surface 60b, the in-plane variation in brightness can be effectively uniformed.

From the viewpoint of sufficiently uniforming the in-plane distribution of illuminance, the reflection on the second surface 60b of the wavelength conversion sheet 60 may be total reflection. That is, the formula (A) using the angle of incidence θy (°) on the second surface 60b may be established.
np×Sinθy≧1...Formula (A)
In formula (A), "np" is the refractive index of the portion constituting the element surface 76 of the wavelength conversion sheet 60. Therefore, "np" may be the refractive index of the portion constituting the unit optical element 75. Strictly speaking, "np" should be the refractive index of the portion constituting the second surface 60b. As shown in FIG. 7 and FIG. 8, the second surface 70b of the optical element unit 70, the first surface 65a and the second surface 65b of the wavelength conversion unit 65, and the second surface 60b of the wavelength conversion sheet 60 are usually parallel to each other and are approximately perpendicular to the third direction D3. Therefore, "np" in formula (A) may be the refractive index of the portion constituting the element surface 76 of the wavelength conversion sheet 60.

In order not to impede the progression of light toward the second surface 60b at an incident angle that satisfies formula (A), the inclination angle θp of the element surface 76 may be determined as follows.
sin ^-1 (1/np)≦90-θp...(X)
In formula (X), θp (°) is the angle (°) between a plane perpendicular to the third direction D3 and the element surface 76. When formula (X) is satisfied, light traveling in a direction inclined at an angle equal to or greater than the total reflection critical angle (°) with respect to the third direction D3 can be promoted to be incident on the second surface 60b without being incident on the element surface 76. This setting promotes light circulation between the wavelength conversion sheet 60 and the light source substrate 22, and effectively uniforms the in-plane distribution of illuminance.

As shown in FIG. 12, the following equation is established regarding the optical path of light L121 incident on the element surface 76 of the unit optical element 75.
θ1=θx-θp...Formula (B)
Sinθ1=np×Sinθ2...Formula (C)
θy=θp+θ2...Formula (D)
θx (°) in formula (B) is the angle (°) between the traveling direction of the light L121 toward the wavelength conversion sheet 60 and the third direction D3. θp (°) in formula (B) is the angle (°) between a plane perpendicular to the third direction D3 and the element surface 76 on which the light L121 is incident. θ1 (°) in formula (C) is the angle of incidence (°) of the light L121 with respect to the element surface 76 on which the light L121 is incident. θ2 (°) in formula (C) is the refraction angle (°) of the light L121 at the element surface 76 through which the light L121 passes. That is, θ2 (°) is the angle between the normal direction to the element surface 76 and the traveling direction of the light after refraction at the element surface 76.

By rewriting equation (A) using equations (B) to (D), the following conditional equation (E) is obtained.
sin ^-1 (1/np)≦sin ^-1 (sin(θx-θp)/np)+θp
Formula (E)
When formula (E) is satisfied, light traveling in a direction inclined by θx (°) with respect to the third direction D3 passes through the element surface 76, enters the wavelength conversion sheet 60, and is then totally reflected at the second surface 60b. The refractive index np of the portion constituting the element surface 76 and the inclination angle θp (°) of the element surface 76 may be set so that formula (E) is satisfied for at least a part of the light incident on the wavelength conversion sheet 60. Such a setting can promote light circulation between the wavelength conversion sheet 60 and the light source substrate 22, and effectively uniform the in-plane distribution of illuminance.

Here, the light travel angle θx (°) used in formula (E) may be a first specific angle θx1 (°), which is the angle (°) between the peak emission direction from the selective transmission sheet 40 of light incident on the selective transmission section 45 at an incident angle at which the transmittance of light of a specific wavelength in the selective transmission section 45 is 1/2 of the maximum value, and the third direction D3. The incident angle at which the transmittance is 1/2 of the maximum value is set to an angle smaller than the incident angle at which the transmittance is maximum. In an actual surface light source device, the travel direction of most of the light that is emitted from the selective transmission sheet 40 and heads toward the wavelength conversion sheet 60 is a direction inclined by the first specific angle θx1 with respect to the third direction D3. Therefore, when the following formula (F) using the first specific angle θx1 is satisfied, most of the light that heads from the selective transmission sheet 40 toward the wavelength conversion sheet 60 is totally reflected by the wavelength conversion sheet 60. As a result, when formula (F) is satisfied, light circulation between the wavelength conversion sheet 60 and the light source substrate 22 can be promoted, and the in-plane distribution of illuminance can be effectively uniformed.
sin ^-1 (1/np)≦sin ^-1 (sin(θx1-θp)/np)+θp
Formula (F)

When the optical element 70 is formed from a resin material that is typically used for optical sheets in combination with the selective transmission section 45 having the transmission characteristics of the first specific example shown in FIG. 6, according to formula (F), the inclination angle θp of the element surface 76 is preferably 16° or more.

As another example, the light travel angle θx (°) used in formula (E) may be a second specific angle θx2 (°), which is the angle (°) between the peak emission direction from the selective transmission sheet 40 of light incident on the selective transmission section 45 at an incident angle at which the transmittance of light of a specific wavelength in the selective transmission section 45 is 1/10 of the maximum value, and the third direction D3. The incident angle at which the transmittance is 1/10 of the maximum value is an angle smaller than the incident angle at which the transmittance is maximum. The light traveling at the second specific angle θx2 is light with a very small incident angle among the incident lights on the wavelength conversion sheet 60. When this light with a small incident angle satisfies the total reflection condition on the second surface 60b, most of the light incident on the wavelength conversion sheet 60 can satisfy the total reflection condition on the wavelength conversion sheet 60. Therefore, when the following formula (G) using the second specific angle θx2 is satisfied, the light circulation between the wavelength conversion sheet 60 and the light source substrate 22 can be further promoted, and the in-plane distribution of illuminance can be very effectively uniformed.
sin ^-1 (1/np)≦sin ^-1 (sin(θx2-θp)/np)+θp
... Formula (G)

When the optical element 70 is formed from a resin material that is typically used for optical sheets in combination with the selective transmission section 45 having the transmission characteristics of the first specific example shown in FIG. 6, according to formula (G), the inclination angle θp of the element surface 76 is preferably 30° or more.

As yet another example, the light travel angle θx (°) used in formula (E) may be a third specific angle θx3, which is a half-value angle (°) in the luminance angle distribution on the second surface 40b of the selective transmission sheet 40. According to this example, in the surface light source device 20 actually used, light having a relatively small incident angle among the light incident on the wavelength conversion sheet 60 satisfies the total reflection condition on the second surface 60b. Therefore, when the following formula (H) using the third specific angle θx3 is satisfied, the light circulation between the wavelength conversion sheet 60 and the light source substrate 22 can be promoted, and the in-plane distribution of illuminance can be effectively uniformed.
sin ^-1 (1/np)≦sin ^-1 (sin(θx3-θp)/np)+θp
Formula (H)
The third specific angle θx3 is specified from the luminance angle distribution on the second surface 40b of the selective transmission sheet 40. This luminance angle distribution is a distribution of luminance in each direction measured on the second surface 40b when light is emitted from the light source 23 in a state in which the components on the first side, which is closer to the observer in the third direction D3 than the selective transmission sheet 40, are removed from the surface light source device 20. An example of this luminance angle distribution is shown in Fig. 13. The half-value angle in the luminance angle distribution is the minimum value of the magnitude (absolute value) of the angle between the direction in which a luminance half the peak luminance in the luminance angle distribution is obtained and the third direction D3.

Note that formulas (F), (G), and (H) do not need to be satisfied for the inclination angle θp over the entire region of the element surface 76. If this condition is satisfied over 50% or more of the region of the element surface 76, the in-plane distribution of illuminance can be advantageously made uniform. Formulas (F), (G), and (H) are preferably satisfied for the inclination angle θp over 70% or more of the region of the element surface 76, and more preferably for the inclination angle θp over 80% or more of the region of the element surface 76.

The total reflection conditions described above are the conditions for the light L121 shown in FIG. 12. This light L121 passes through one element surface 76 and travels through the wavelength conversion sheet 60. This light L121 is incident on the second surface 60b without being incident on another element surface 76. On the other hand, it is also assumed that the light L122 that has passed through one element surface 76 is incident on another element surface 76 facing the one element surface 76. This light L122 is totally reflected by the other element surface 76 and can be incident on the second surface 60b at a small angle of incidence. The reflectance of this light L122 on the second surface 60b becomes small.

From the viewpoint of suppressing the generation of such light L122 and promoting reflection at the second surface 60b, the angle between the traveling direction of the light traveling within the unit optical element 75 and the third direction D3 may be equal to or smaller than the angle between the element surface 76 and the third direction D3. Specifically, the following formula (I) may be satisfied. Formula (J), which is obtained by rewriting formula (I) in consideration of the above-mentioned formulas (B) to (D), may be satisfied. The angles and refractive indices used in formulas (I) and (J) are as described above.
θp+θ2≦90-θp...Formula (I)
sin ⁻¹ (sin(θx−θp)/np)+θp≦90−θp
... Formula (J)
Here, the light travel angle θx (°) used in formula (J) may be the above-mentioned first specific angle θx1 (°).

Here, the light travel angle θx (°) used in formula (J) may be the above-mentioned second specific angle θx2 (°). When the following formula (L) using the second specific angle θx2 is satisfied, at least a part of the light incident on the unit optical element 75 from one element surface 76 can be incident on the second surface 60b without being incident on another element surface 76 facing the one element surface 76. Therefore, when formula (L) is satisfied, light circulation between the wavelength conversion sheet 60 and the light source substrate 22 can be expected, and the in-plane variation in illuminance can be suppressed.
sin ^-1 (sin(θx2-θp)/np)+θp≦90-θp
Formula (L)

When the optical element 70 is formed from a resin material that is typically used for optical sheets in combination with the selective transmission section 45 having the transmission characteristics of the first specific example shown in FIG. 6, according to formula (L), the inclination angle θp of the element surface 76 is preferably 45° or less.

As another example, the light travel angle θx (°) used in formula (J) may be a third specific angle θx4, which is the angle (°) between the direction in which a luminance of 1/10 of the peak luminance in the luminance angle distribution on the second surface 40b of the selective transmission sheet 40 is obtained and the third direction D3. According to this example, in the surface light source device 20 actually used, at least a part of the light incident on the unit optical element 75 from one element surface 76 can be incident on the second surface 60b without being incident on another element surface 76 facing the one element surface 76. Therefore, when the following formula (M) using the third specific angle θx4 is satisfied, light circulation between the wavelength conversion sheet 60 and the light source substrate 22 can be expected, and the in-plane variation in illuminance can be suppressed.
sin ^-1 (sin(θx4-θp)/np)+θp≦90-θp
Formula (M)
The fourth specific angle θx4 is specified from the luminance angle distribution on the second surface 40b of the selective transmission sheet 40. This luminance angle distribution is a distribution of luminance in each direction measured on the second surface 40b when light is emitted from the light source 23 in a state in which the components on the first side, which is closer to the observer in the third direction D3 than the selective transmission sheet 40, are removed from the surface light source device 20. An example of this luminance angle distribution is shown in FIG. 13. The angle between the direction in which a luminance of 1/10 of the peak luminance in the luminance angle distribution is obtained and the third direction D3 is the minimum value of the magnitude (absolute value) of the angle between the direction in which a luminance of 1/10 of the peak luminance in the luminance angle distribution is obtained and the third direction D3.

Note that formulas (K), (L), and (M) do not need to be satisfied for the inclination angle θp over the entire area of the element surface 76. If this condition is satisfied over 50% or more of the area of the element surface 76, the in-plane distribution of illuminance can be advantageously made uniform. Formulas (K), (L), and (M) are preferably satisfied for the inclination angle θp over 70% or more of the area of the element surface 76, and more preferably for the inclination angle θp over 80% or more of the area of the element surface 76.

In order to satisfy both the above-mentioned formula (E) and formula (J), it is preferable that the specific angle θx is 35° or more. By setting the specific angle θx to 35° or more, the inclination angle θp has an appropriate range when the refractive index np of the portion constituting the element surface 76 is in the range of 1.50 to 1.60. From this point of view, the angle that the traveling direction of the light from the selective transmission sheet 40 toward the wavelength conversion sheet 60 makes with respect to the third direction D3 may be 35° or more, 40° or more, or 45° or more. In addition, the transmittance of the selective transmission portion 45 for the light of a specific wavelength that is emitted from the selective transmission sheet 40 at an emission angle of 0° to 35° in absolute value may be half or less of the maximum transmittance of the selective transmission portion 45, or may be 1/10 or less of the maximum transmittance of the selective transmission portion 45.

In the embodiment described above, the optical member 30 includes a selective transmission sheet 40 including a selective transmission portion 45, and a wavelength conversion sheet 60 including a first surface 40a on the selective transmission sheet 40 side and a second surface 40b facing the first surface 40a. The transmittance of the selective transmission portion 45 for light of a specific wavelength that is incident on the selective transmission portion 45 at an incident angle greater than 0° is greater than the transmittance of the selective transmission portion 45 for light of the selective transmission portion 45 that is incident on the selective transmission portion 45 at an incident angle of 0°. The first surface 40a of the selective transmission sheet 40 includes an uneven surface.

According to the optical member 30 of this embodiment, the primary light LA from the light source 23 can be reflected by the second surface 60b of the wavelength conversion sheet 60. That is, the second surface 60b of the wavelength conversion sheet 60 can reflect light toward the first side, which is the observer side in the third direction D3. That is, a circulation light path in which the primary light LA circulates can be formed between the second surface 60b of the wavelength conversion sheet 60 and the light source substrate 22, etc. According to this embodiment, the wavelength conversion agent 67 is included in the wavelength conversion sheet 60 that turns back the traveling direction in the third direction D3. The primary light LA advances in the wavelength conversion sheet 60 in a direction inclined with respect to the third direction D3. Therefore, the content of the wavelength conversion agent 67 in the wavelength conversion sheet 60 can be significantly reduced. Rather, by reducing the content of the wavelength conversion agent 67 that emits the secondary light LB in various directions, the circulation of the primary light LA using the reflection on the second surface 60b can be promoted. In other words, by circulating the primary light LA, the content of the wavelength conversion agent 67 can be significantly reduced while suppressing the in-plane variation in brightness caused by the arrangement of the light source 23 and suppressing the in-plane variation in illuminance.

Here, we will explain the results of a simulation carried out by the inventors. The simulation was a ray tracing simulation using LightTools manufactured by Synopsys.

The subject of the simulation was the surface light source device shown in Figures 2 to 6, 7, 9, 10A, and 10B. That is, the surface light source device included a light source substrate and an optical member. The optical member included a selective transmission sheet, a wavelength conversion sheet, a first optical sheet, a second optical sheet, and a reflective polarizing plate. The light source substrate had blue micro light-emitting diodes arranged at a pitch of 6 mm in both the first and second directions. The distance along the third direction D3 from the surface of the light source facing the optical member 30 to the light-entering side surface of the optical member was set to 0.5 mm. The selective transmission sheet included only a selective transmission portion. The first and second surfaces of the selective transmission portion were parallel to each other. The first and second surfaces were perpendicular to the third direction D3. The wavelength conversion sheet included an optical element portion, a first barrier layer, a wavelength conversion portion, and a second barrier layer. The first and second optical sheets were "BEF" (registered trademark) available from 3M Company, USA. The reflective polarizing plate used was "DBEF" (registered trademark) available from 3M Corporation, USA.

The inclination angle θp of the element surface included in the optical element unit described above was changed as shown in Tables 1 and 2. For each simulation target with an inclination angle θp, the content of the wavelength conversion agent was changed to investigate the content of the wavelength conversion agent that would result in a white light emission color and a uniform in-plane distribution of illuminance. For each simulation target, the wavelength conversion agent included a first conversion agent that absorbs blue light from the light source and emits green light, and a second conversion agent that absorbs blue light from the light source and emits red light. The conversion efficiency of the first conversion agent and the conversion efficiency of the second conversion agent were set to 11:20. By making the conversion efficiency of the second conversion agent 67B in the wavelength conversion unit 65 greater than the conversion efficiency of the first conversion agent 67A, the color balance could be improved.

The results of the simulation are shown in Tables 1 and 2. Table 1 shows the results of a simulation using the selective transmission section 45 having the transmission characteristics of the first specific example shown in FIG. 6. Table 2 shows the results of a simulation using the selective transmission section 45 having the transmission characteristics of the second specific example shown in FIG. 6. The "Conversion Efficiency" column in Tables 1 and 2 shows the relative conversion efficiency that best suppressed the in-plane variation in illuminance for each simulation target. The "Overall Evaluation" column in Tables 1 and 2 shows the evaluation based on the lowest optimal conversion efficiency and the uniformity of the in-plane distribution of illuminance. The sample with "x" in the "Overall Evaluation" column is the sample with the lowest evaluation. The sample with "○" in the "Overall Evaluation" column is the sample with the highest evaluation. In the "Overall Evaluation" column, more "○"s are entered for samples with high evaluations.

As shown in Tables 1 and 2, when the tilt angle θp of the unit optical elements included in the optical element section is in the range of 10° to 50°, the in-plane distribution of illuminance can be made uniform while reducing the conversion efficiency. When the tilt angle θp of the unit optical elements included in the optical element section is in the range of 30° to 45°, the in-plane distribution of illuminance can be made more uniform while further reducing the conversion efficiency.

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.

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

For example, in the specific example described above, one or more of the first optical sheet 81, the second optical sheet 82, and the reflective polarizing plate 85 may be omitted from the optical member 30.

In the illustrated specific example, an example is shown in which the first surface 60a of the wavelength-converting sheet 60 includes an uneven surface. Instead of the first surface 60a of the wavelength-converting sheet 60 including an uneven surface, the second surface 60b of the wavelength-converting sheet 60 may include an uneven surface. In addition to the first surface 60a of the wavelength-converting sheet 60 including an uneven surface, the second surface 60b of the wavelength-converting sheet 60 may include an uneven surface. By having at least one of the first surface 60a and the second surface 60b include an uneven surface, it is possible to cause total reflection at the second surface 60b.

10: display device, 15: display panel, 15a: display surface, 20: surface light source device, 20a: light emitting surface, 22: light source substrate, 23: light source, 25: support substrate, 26: substrate body, 27: reflective layer, 29: wiring, 30: optical member, 30a: light incident side, 30b: light emitting side, 40: selective transmission sheet, 40a: first surface, 40b: second surface, 45: selective transmission section, 45a: first surface, 45b: second surface, 46: dielectric multilayer film, 60: wavelength conversion sheet, 60a: first surface, 60b: second surface, 61: uneven surface, 63: first barrier layer, 64: second barrier layer, 65: wavelength conversion section, 65a: first surface, 65b: second surface, 66: base material section, 67: wavelength conversion agent, 67A: first conversion agent, 67B: second conversion agent, 70: optical element section, 70a: first surface, 70b: second surface, 72: main body section, 73: convex section, 74: concave section, 75: unit optical element, 76: element surface, 81: first optical sheet, 82: second optical sheet, 83: main body section, 84: unit prism, 85: reflective polarizing plate, D1: first direction, D2: second direction, D3: third direction, LA: primary light, LB: secondary light, LB1: first secondary light, LB2: second secondary light

Claims (17)

A selectively permeable sheet including a selectively permeable portion;
a wavelength conversion sheet including a first surface on the selective transmission sheet side and a second surface opposite to the first surface,
the transmittance of the selective transmission part for light of a specific wavelength incident on the selective transmission part at an incident angle greater than 0° is greater than the transmittance of the selective transmission part for light of the specific wavelength incident on the selective transmission part at an incident angle of 0°;
the first surface includes an uneven surface;
the wavelength conversion sheet includes a wavelength conversion agent that absorbs primary light and emits secondary light,
The secondary light has a wavelength different from a wavelength of the primary light. The optical member according to claim 1, wherein the transmittance of the selective transmission section for light of the specific wavelength incident on the selective transmission section at an incident angle of 0° is 5% or less. The optical member according to claim 1 or 2, wherein the transmittance of the selective transmission portion for the light of the specific wavelength that is emitted from the selective transmission sheet at an emission angle of 0° or more and 35° or less in absolute value is less than half the maximum transmittance of the selective transmission portion. The inclination angle θp (°) of the element surfaces constituting the concave-convex surface and the refractive index np of the portion constituting the element surfaces of the wavelength conversion sheet satisfy the following formula:
sin ^-1 (1/np)≦90-θp
4. The optical member according to claim 1, wherein the inclination angle θp (°) is an angle between the element surface and a plane perpendicular to a stacking direction of the selective transmission sheet and the wavelength conversion sheet. The inclination angle θp (°) of the element surfaces constituting the concave-convex surface, the refractive index np of the portion constituting the element surfaces of the wavelength conversion sheet, and the angle θx (°) with respect to the incident direction on the wavelength conversion sheet satisfy the following formula:
sin ^-1 (1/np)≦sin ^-1 (sin(θx-θp)/np)+θp
the inclination angle θp (°) is an angle between a plane perpendicular to the stacking direction of the selective transmission sheet and the wavelength conversion sheet and the element surface,
The angle θx (°) is an angle between the peak emission direction from the selective transmission sheet of light incident on the selective transmission section at an incident angle at which the transmittance of light of the specific wavelength in the selective transmission section is 1/2 of its maximum value, and the stacking direction. The optical member according to any one of claims 1 to 4. The inclination angle θp (°) of the element surfaces constituting the concave-convex surface, the refractive index np of the portion constituting the element surfaces of the wavelength conversion sheet, and the angle θx (°) with respect to the incident direction on the wavelength conversion sheet satisfy the following formula:
sin ^-1 (sin(θx-θp)/np)+θp≦90-θp
the inclination angle θp (°) is an angle between a plane perpendicular to the stacking direction of the selective transmission sheet and the wavelength conversion sheet and the element surface,
The angle θx (°) is an angle between the peak emission direction from the selective transmission sheet of light incident on the selective transmission section at an incident angle at which the transmittance of light of the specific wavelength in the selective transmission section is 1/10 of the maximum value, and the stacking direction. The optical member according to any one of claims 1 to 5. the wavelength conversion sheet includes an optical element portion including the uneven surface,
7. The optical member according to claim 4, wherein the optical element section includes a plurality of unit optical elements each including the element surface. the wavelength conversion sheet includes a wavelength converting portion including the wavelength converting agent, a first barrier layer and a second barrier layer overlapped with the wavelength converting portion, and an optical element portion overlapped with the first barrier layer and including the uneven surface,
the wavelength converting portion is located between the first barrier layer and the second barrier layer,
The optical member according to any one of claims 1 to 7, wherein the first barrier layer is located between the wavelength converting portion and the optical element portion. The wavelength conversion sheet further includes a reflective polarizing plate overlapped with the wavelength conversion sheet,
9. The optical member according to claim 1, wherein the wavelength conversion sheet is located between the selective transmission sheet and the reflective polarizing plate. Further comprising an optical sheet overlapping the wavelength conversion sheet,
The optical member according to any one of claims 1 to 9, wherein the wavelength conversion sheet is located between the selective transmission sheet and the optical sheet. An optical member according to any one of claims 1 to 10;
a light source facing the optical member. An optical member according to any one of claims 1 to 10;
A surface light source device comprising: a light source substrate having a reflective layer facing the optical member; and a light source that emits light incident on the optical member. The inclination angle θp (°) of the element surfaces constituting the concave-convex surface, the refractive index np of the portion constituting the element surfaces of the wavelength conversion sheet, and the angle θx (°) with respect to the incident direction on the wavelength conversion sheet satisfy the following formula:
sin ^-1 (1/np)≦sin ^-1 (sin(θx-θp)/np)+θp
the inclination angle θp (°) is an angle between a plane perpendicular to the stacking direction of the selective transmission sheet and the wavelength conversion sheet and the element surface,
13. The surface light source device according to claim 11 or 12, wherein the angle θx (°) is the angle between the stacking direction and a direction in which a brightness that is half the peak brightness in a brightness angular distribution on a surface of the selective transmission sheet facing the wavelength conversion sheet, obtained in a state in which components on the wavelength conversion sheet side of the selective transmission sheet are removed, is obtained. The inclination angle θp (°) of the element surfaces constituting the concave-convex surface, the refractive index np of the portion constituting the element surfaces of the wavelength conversion sheet, and the angle θx (°) with respect to the incident direction on the wavelength conversion sheet satisfy the following formula:
sin ^-1 (sin(θx-θp)/np)+θp≦90-θp
the inclination angle θp (°) is an angle between a plane perpendicular to the stacking direction of the selective transmission sheet and the wavelength conversion sheet and the element surface,
The surface light source device according to any one of claims 11 to 13, wherein the angle θx (°) is an angle between the stacking direction and a direction in which a luminance of 1/10 of the peak luminance in a luminance angular distribution on a surface of the selective transmission sheet facing the wavelength conversion sheet, obtained in a state in which components on the wavelength conversion sheet side of the selective transmission sheet are removed, is obtained. A surface light source device according to any one of claims 11 to 14,
A display device comprising the surface light source device and a display panel overlapped therewith. The first page and
a second surface opposite to the first surface;
a wavelength converting agent located between the first surface and the second surface,
an optical element portion constituting at least one of the first surface and the second surface is provided;
the optical element portion includes a plurality of unit optical elements,
at least one of the first surface and the second surface includes an uneven surface formed by a plurality of unit optical elements,
The wavelength conversion agent absorbs primary light of a specific wavelength and emits secondary light,
The secondary light has a wavelength different from the specific wavelength. The first surface faces a light source;
The wavelength conversion sheet according to claim 16 , wherein the first surface includes a concave-convex surface.

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