JP7492141B2 - Surface Light Source - Google Patents

Description

This disclosure relates to a surface light source.

The following patent documents 1 to 3 disclose surface-emitting devices having a light guide plate and multiple light sources arranged on a substrate.

JP 2011-210674 A JP 2007-329114 A JP 2009-063684 A

Provide a surface light source that can reduce brightness unevenness.

The surface light source according to an embodiment of the present disclosure includes a light guide plate having an upper surface and a lower surface opposite to the upper surface, and a through hole penetrating from the upper surface to the lower surface, a wiring board located on the lower surface side of the light guide plate and including a wiring layer, a light source including a light emitting element electrically connected to the wiring layer of the wiring board and disposed inside the through hole, and a light reflective member located above the light source, the through hole including a first portion having a first side surface inclined with respect to the upper surface of the light guide plate, and a second portion having a second side surface located between the upper surface of the light guide plate and the first side surface of the first portion, and the light reflective member is located in the first portion of the through hole.

According to an embodiment of the present disclosure, a surface light source capable of reducing brightness unevenness is provided.

1 is a schematic perspective view showing an exemplary configuration of a surface light source according to an embodiment of the present disclosure. 2 is a diagram showing a schematic cross section of an example of a light emitting region of the surface light source shown in FIG. 1 and an exemplary external appearance of a light guide plate as viewed from the upper surface side; FIG. 3 is a schematic cross-sectional view showing an enlarged view of a light source and its periphery in the cross section shown in FIG. 2. 10A and 10B are schematic enlarged cross-sectional views showing other examples of the shape of the through hole provided in the light guide plate. 13 is a schematic enlarged cross-sectional view showing still another example of the shape of the through hole provided in the light guide plate. FIG. 10A to 10C are schematic top views showing other examples of the shape of a light reflective member disposed in a first portion of a through hole. 3 is a schematic cross-sectional view showing a light source and a wiring board in the light-emitting region shown in FIG. 2 . FIG. 11 is a schematic top view showing another example of a surface light source. 13 is a diagram showing a schematic cross section of another example of a light-emitting region and an exemplary external appearance of a light guide plate as viewed from the upper surface side. FIG. 13A and 13B are schematic top views showing still other examples of the shape of the through holes provided in the light guide plate. 5A to 5C are schematic cross-sectional views showing exemplary configurations of light-emitting regions of a surface light source according to another embodiment of the present disclosure. 11 is a schematic cross-sectional view showing an exemplary configuration of a light-emitting region of a surface light source according to still another embodiment of the present disclosure. 11 is a schematic cross-sectional view showing another example of a light emitting device that can be applied to a light source of a surface light source according to an embodiment of the present disclosure. FIG. 11 is a schematic cross-sectional view showing yet another example of a light emitting device that can be applied to a light source of a surface light source according to an embodiment of the present disclosure. FIG. 11 is a schematic cross-sectional view showing yet another example of a light emitting device that can be applied to a light source of a surface light source according to an embodiment of the present disclosure. FIG. 11 is a schematic cross-sectional view showing yet another example of a light emitting device that can be applied to a light source of a surface light source according to an embodiment of the present disclosure. FIG.

Below, the embodiments of the present disclosure will be described in detail with reference to the drawings. The following embodiments are merely examples, and the surface light source according to the present disclosure is not limited to the following embodiments. For example, the numerical values, shapes, materials, steps, and the order of the steps shown in the following embodiments are merely examples, and various modifications are possible as long as no technical contradictions arise. Each embodiment described below is merely an example, and various combinations are possible as long as no technical contradictions arise.

The dimensions, shapes, etc. of components shown in the drawings may be exaggerated for clarity and may not reflect the dimensions, shape, and size relationships between components in an actual surface light source. Also, some elements may be omitted from the illustration to avoid overly complicating the drawings.

In the following description, components having substantially the same functions are indicated by common reference symbols, and descriptions may be omitted. In the following description, terms indicating a specific direction or position (for example, "up", "down", "right", "left", and other terms including these terms) may be used. However, these terms are merely used for the sake of clarity of the relative direction or position in the referenced drawings. As long as the relationship of the relative direction or position by terms such as "up" and "down" in the referenced drawings is the same, the arrangement in drawings other than this disclosure, actual products, manufacturing equipment, etc. may not be the same as in the referenced drawings. In this disclosure, "parallel" includes cases where two straight lines, sides, faces, etc. are in the range of about 0° to ±5°, unless otherwise specified. In addition, in this disclosure, "perpendicular" or "orthogonal" includes cases where two straight lines, sides, faces, etc. are in the range of about 90° to ±5°, unless otherwise specified.

(Embodiment 1)
FIG. 1 illustrates an exemplary configuration of a surface light source according to an embodiment of the present disclosure. The surface light source 200 illustrated in FIG. 1 includes a light guide plate 210 having an upper surface 210a, a wiring board 240 located below the light guide plate 210, and a plurality of light sources 50. As described below, each light source 50 includes a light emitting element such as an LED. For convenience of explanation, FIG. 1 also illustrates arrows indicating the mutually orthogonal X-direction, Y-direction, and Z-direction. Arrows indicating these directions may also be illustrated in other drawings of the present disclosure.

The surface light source 200 is generally plate-shaped. The upper surface 210a of the light guide plate 210, which constitutes the light-emitting surface of the surface light source 200, typically has a rectangular shape. Here, the above-mentioned X direction and Y direction respectively coincide with one and the other of two mutually perpendicular sides of the rectangular shape of the light guide plate 210. The length of one side of the rectangular shape of the upper surface 210a is, for example, in the range of 20 mm to 40 mm.

In the configuration illustrated in FIG. 1, the surface light source 200 includes a plurality of light-emitting regions 100, each of which includes at least one light source 50. In the example illustrated in FIG. 1, the surface light source 200 includes a total of 16 light-emitting regions 100 arranged two-dimensionally in four rows and four columns. The number and arrangement of the light-emitting regions 100 included in the surface light source 200 are arbitrary and are not limited to the configuration illustrated in FIG. 1. For example, the surface light source 200 may be configured with a one-dimensional array of two or more light-emitting regions 100. The surface light source 200 may be configured with a single light-emitting region 100.

As shown in FIG. 1, each light-emitting region 100 has a through-hole 10 that includes an opening located on the upper surface 210a of the light guide plate 210. The light source 50 of each light-emitting region 100 is located inside the through-hole 10. Each light-emitting region 100 further has a light-reflective member 31 in the through-hole 10. As described below, the light-reflective member 31 of each light-emitting region 100 is located above the light source 50 and covers the light source 50 in a planar view.

In the example shown in FIG. 1, the light sources 50 are arranged in four rows and four columns on the wiring board 240 along the X direction and the Y direction, corresponding to the light emitting region 100 being arranged in four rows and four columns. The arrangement pitch of the light sources 50 can be, for example, about 7.5 mm to 10.0 mm, and may be in the range of about 8.0 mm to 9.5 mm. Here, the arrangement pitch of the light sources 50 means the distance between the optical axes of the light sources 50. The optical axis of the light source 50 refers to an axis that is perpendicular to the upper surface of the light source 50 and passes through the center of the upper surface of the light source 50 in a planar view. Alternatively, it refers to an axis that is perpendicular to the upper surface of the light emitting element included in the light source 50 and passes through the center of the upper surface of the light emitting element in a planar view. The light sources 50 may be arranged at equal intervals on the wiring board 240, or may be arranged at unequal intervals. When the light sources 50 are arranged at equal intervals, the arrangement pitch may be the same or different between two different directions.

Figure 2 shows a schematic cross-section of light-emitting region 100A, which is an example of light-emitting region 100 shown in Figure 1, and its appearance as seen from the upper surface 210a side of light guide plate 210 in one diagram. Light-emitting region 100A includes light guide plate 110A, light source 50, light-reflective member 31, and wiring board 140. Figure 2 shows an example of a configuration in which light-emitting element 120 is used as light source 50.

The light guide plate 110A has an upper surface 110a and a lower surface 110b opposite to the upper surface 110a, and has a through hole 10A penetrating from the upper surface 110a to the lower surface 110b. The through hole 10A includes an opening 10b (first opening) located on the lower surface 110b of the light guide plate 110, and an opening 10a (second opening) located on the upper surface 110a of the light guide plate 110. The shape of the through hole 10A is determined by the openings 10a and 10b and the inner wall surface of the light guide plate 110A between them. In the example shown in FIG. 2, each of the openings 10a and 10b has a perfect circle shape in a plan view, and the diameter of the opening 10a is larger than the diameter of the opening 10b.

In this embodiment, the through hole 10A has a first portion 11A and a second portion 12A including an opening 10a. As shown in FIG. 2, the first portion 11A is located closer to the light source 50 (the light-emitting element 120 in the example shown in FIG. 2) than the second portion 12A.

The portion of the inner wall surface of the light guide plate 110A that defines the first portion 11A of the through hole 10A includes a first side surface 11c that is inclined with respect to the upper surface 110a of the light guide plate 110A. The portion of the inner wall surface of the light guide plate 110A that defines the second portion 12A of the through hole 10A includes a second side surface 12c that is located between the opening 10a located on the upper surface 110a of the light guide plate 110A and the first side surface 11c of the first portion 11A. In a typical embodiment of the present disclosure, the second side surface 12c is also inclined with respect to the upper surface 110a of the light guide plate 110A, similar to the first side surface 11c of the first portion 11A.

In the configuration illustrated in FIG. 2, the inclination angle of the light guide plate 110A with respect to the upper surface 110a is different between the first side surface 11c and the second side surface 12c. In detail, the angle between the second side surface 12c and the upper surface 110a is larger than the angle between the first side surface 11c and the upper surface 110a. However, this is not limited thereto, and the angle between the second side surface 12c and the upper surface 110a may be smaller than the angle between the first side surface 11c and the upper surface 110a.

In the example shown in FIG. 2, the through hole 10A further has a third portion 13A located between the first portion 11A and the bottom surface 110b of the light guide plate 110A. The third portion 13A is a cylindrical portion defined by an opening 10b located on the bottom surface 110b of the light guide plate 110A and a third side surface 13c, which is an inner wall surface perpendicular to the bottom surface 110b.

The light emitting element 120 serving as the light source 50 is disposed inside the third portion 13A of the through hole 10A. The first translucent member 30 is disposed in the space inside the third portion 13A of the through hole 10A except for the light emitting element 120. In other words, the light emitting element 120 is covered by the first translucent member 30.

In the embodiment of the present disclosure, the light reflective member 31 is selectively disposed in the first portion 11A of the through hole 10A. The light reflective member 31 is a member that reflects at least a part of the light from the light source 50, and is disposed so as to be located approximately directly above the light source 50 in the through hole 10A. This makes it possible to prevent the brightness directly above the light source 50 on the upper surface 110a of the light guide plate 110A from being extremely high compared to other regions. In the example shown in FIG. 2, the light reflective member 31 is selectively disposed inside the first portion 11A of the through hole 10A, so that it is possible to avoid the brightness directly above the light source 50 from being lowered more than necessary. In this way, according to the embodiment of the present disclosure, a planar light source with reduced brightness unevenness can be provided. Furthermore, in this embodiment, the first side surface 11c of the first portion 11A is inclined with respect to the upper surface 110a of the light guide plate 110A, so that the light emitted from the light emitting element 120 can be diffused more efficiently within the surface of the light guide plate 110A.

The second side surface 12c of the second portion 12A of the through hole 10A functions as a reflective surface. In the example shown in FIG. 2, the second side surface 12c is an inclined surface. Therefore, by utilizing reflection at the second side surface 12c, light traveling toward the second side surface 12c inside the light guide plate 110A can be returned to the surface of the light guide plate 110A. A member with a lower refractive index than the material of the light reflective member 31, or air, is placed inside the second portion 12A.

The wiring board 140 shown in FIG. 2 is a part of the wiring board 240 shown in FIG. 1 and is located on the lower surface 110b side of the light guide plate 110A. The wiring board 140 includes a wiring layer 141 and an insulating part 144 such as a resin. The wiring board 140 has an upper surface 140a and a lower surface 140b located opposite to the upper surface 140a. The upper surface 140a of the wiring board 140 and the lower surface 110b of the light guide plate 110A are bonded to each other by an adhesive sheet 150. As described later, other functional layers such as a light-reflective resin sheet may be disposed between the adhesive sheet 150 and the wiring board 140. The light source 50 is electrically connected to the wiring layer 141 of the wiring board 140. The light source 50 may be bonded to the adhesive sheet 150.

According to an embodiment of the present disclosure, light from the light emitting element 120 can be efficiently diffused within the surface of the light guide plate 110A by utilizing reflection from the first side surface 11c and/or the second side surface 12c, thereby reducing brightness unevenness. Furthermore, it is possible to reduce the thickness of the light guide plate 110A and, in turn, the entire surface light source 200. The overall thickness of the surface light source, including the wiring board 140, can be, for example, in the range of 0.8 mm to 0.9 mm. By making the surface light source thinner, it is possible to further miniaturize the device including the backlight.

Below, we will explain the details of each component that makes up the surface light source using light-emitting area 100A as an example.

[Light guide plate 110A]
The light guide plate 110A has a function of propagating light from the light emitting elements 120 inside the light guide plate 110A and emitting the light from the upper surface 110a. The upper surface 110a of the light guide plate 110A typically has a rectangular shape similar to the upper surface 210a of the light guide plate 210. In this embodiment, a collection of the upper surfaces 110a of the multiple light guide plates 110A constitutes the light emitting surface of the surface light source 200.

The light guide plate 110A is a generally plate-shaped member made of a thermoplastic resin such as acrylic, polycarbonate, cyclic polyolefin, polyethylene terephthalate, or polyester, or a thermosetting resin such as epoxy or silicone, and has light-transmitting properties. Of these materials, polycarbonate is particularly preferable because it is inexpensive and has a high transmittance. Note that the term "light-transmitting properties" in this specification is not limited to "transparent" and also includes transmitting 50% or more of the incident light. The light guide plate 110A may have a light-diffusing function, for example, by containing a material having a refractive index different from that of the base material.

The thickness of the light guide plate 110A, i.e., the distance from the lower surface 110b to the upper surface 110a, is typically about 200 μm or more and 800 μm or less. According to an embodiment of the present disclosure, the thickness of the light guide plate 110A can also be in the range of about 400 μm or more and 600 μm or less.

In the configuration illustrated in FIG. 3, the inclination of the first side surface 11c relative to the upper surface 110a of the light guide plate 110A is smaller than the inclination of the second side surface 12c. With this shape of the through hole 10A, the area of the first side surface 11c can be increased while avoiding an increase in the combined depth of the first portion 11A and the second portion 12A. Therefore, the light incident on the first side surface 11c can be more effectively diffused within the surface of the light guide plate 110A while avoiding an increase in the thickness of the light guide plate 110A.

The inclination of the second side surface 12c relative to the upper surface 110a of the light guide plate 110A may be smaller than the inclination of the first side surface 11c. With this configuration, the volume of the second portion 12A can be expanded while avoiding an increase in the thickness of the light guide plate 110A. By expanding the volume of the second portion 12A, for example, the air layer located inside the second portion 12A can be expanded to a wider area. Therefore, more light is incident on the second side surface 12c, and the light can be more effectively diffused within the surface of the light guide plate 110A.

The magnitude of the inclination of the first side surface 11c can be calculated as the angle between a line segment connecting the lower end and upper end of the first side surface 11c and a straight line parallel to the upper surface 110a of the light guide plate 110A in a cross-sectional view. Similarly, the inclination of the second side surface 12c can be calculated as the angle between a line segment connecting the lower end and upper end of the second side surface 12c and a straight line parallel to the upper surface 110a of the light guide plate 110A in a cross-sectional view.

When the shape of the first side surface 11c and the shape of the second side surface 12c in a cross-sectional view are curved, the line segment connecting the lower end 11a, which is the part of the first portion 11A that is the smallest distance from the lower surface 110b of the light guide plate 110A, to the upper end 12a of the first portion 11A is defined as C1 (see FIG. 3). The angle θ1 between this line segment C1 and a line parallel to the upper surface 110a of the light guide plate 110A is defined as the magnitude of the inclination of the first side surface 11c. Similarly, the angle θ2 between the line segment C2 connecting the upper end 12a of the first portion 11A and the opening 10a of the second portion 12A and a line parallel to the upper surface 110a of the light guide plate 110A can be defined as the magnitude of the inclination of the second side surface 12c.

In the configuration illustrated in FIG. 3, the cross-sectional shapes of the first side 11c and the second side 12c are both curved. However, the cross-sectional shapes of the first side 11c and the second side 12c are not limited to curved, and may be bent and/or stepped, or may be linear. The cross-sectional shapes of the first side 11c and the second side 12c may be the same as each other, or may be different. If the cross-sectional shapes of the first side 11c and/or the second side 12c are curved as illustrated in FIG. 3, particularly convex curved shapes that bulge toward the inside of the through hole 10A, it is easy to diffuse light to positions away from the center of the light guide plate 110A, and the brightness unevenness on the upper surface 110a side can be effectively reduced.

In the example shown in FIG. 3, the first portion 11A has a lower end 11a located at the portion where the first portion 11A and the third portion 13A are connected. The lower end 11a of the first portion 11A has a circular shape with the same diameter as the opening 10b of the third portion 13A. The first portion 11A also has an upper end 12a located at the boundary between the first portion 11A and the second portion 12A. The upper end 12a coincides with the lower end of the second portion 12A, and here has a perfect circle shape with a larger diameter than the lower end 11a.

Figure 4 shows another example of the shape of the through-hole provided in the light guide plate of the light-emitting region. The light-emitting region 100B shown in Figure 4 includes a light guide plate 110B provided with a through-hole 10B.

Similar to the through hole 10A described with reference to FIG. 3, the through hole 10B includes a first portion 11B having a first side surface 11c, a second portion 12A having a second side surface 12c, and a third portion 13A having a third side surface 13c. Of these, the first portion 11B located between the second portion 12A and the third portion 13A further has an inner wall surface 11w located between the upper end portion 12a and the first side surface 11c.

In the configuration illustrated in FIG. 4, the inner wall surface 11w is generally perpendicular to the upper surface 110a of the light guide plate 110B. The inner wall surface 11w of the first portion 11B has a height of, for example, about 50 μm along the Z direction in the figure.

As described above, the light-reflecting member 31 is disposed in a portion of the through-hole of the light guide plate. In the example shown in FIG. 4, the light-reflecting member 31 is disposed in the space from the lower end 11a to the upper end 12a of the first portion 11B of the through-hole 10B, and has a shape that combines a generally cylindrical portion with a generally inverted truncated cone portion.

By providing an inner wall surface 11w between the first side surface 11c and the upper end portion 12a of the first portion 11B, it is possible to prevent the material of the light-reflective member 31 from spreading beyond the position of the upper end portion 12a onto the second side surface 12c of the second portion 12A when the light-reflective member 31 is formed. Therefore, it is possible to avoid the occurrence of uneven brightness caused by a part of the material of the light-reflective member 31 remaining irregularly on the second side surface 12c of the second portion 12A. Note that the inner wall surface 11w may be inclined within a range of about 5° with respect to the normal to the upper surface 110a of the light guide plate 110B so that the first portion 11B has a shape that spreads from the lower surface 110b side toward the upper surface 110a of the light guide plate 110B.

The first and second parts of the through hole provided in the light guide plate may have a polygonal truncated pyramid shape or the like. The depth of the first part of the through hole may be, for example, in the range of 100 μm to 200 μm. The diameter of the upper end 12a located at the boundary between the first and second parts may be, for example, about 2.0 mm, and the diameter of the opening 10a of the second part 12A may be, for example, about 3.0 mm.

Here, the third portion of the through hole has a cylindrical shape. The size (or diameter) of the opening 10b is, for example, about 1.0 mm. The width (diameter) of the opening 10b of the third portion and the lower end 11a of the first portion are determined appropriately according to the shape of the light source 50 located in the through hole. The shape of the third portion is not limited to a cylindrical shape, and may be, for example, a prismatic shape.

In the configuration illustrated in FIG. 4, the shape of the third side surface 13c of the third portion in a cross-sectional view is generally linear. However, the shape of the third side surface 13c in a cross-sectional view is not limited to a linear shape, and may be a shape that includes bends and/or steps, or may be a curved shape, etc.

Figure 5 shows yet another example of the shape of the through-hole provided in the light guide plate of the light-emitting region. The light-emitting region 100C shown in Figure 5 includes a light guide plate 110C provided with a through-hole 10C.

The light guide plate 110C has a through hole 10C including a first portion 11B, a second portion 12A, and a third portion 13C. In the example shown in FIG. 5, a part of the third side surface 13c of the third portion 13C has a shape that is inclined so as to widen toward the upper surface 110a of the light guide plate 110C. In this manner, at least a part of the third side surface 13c may have a shape that is inclined with respect to the upper surface 110a of the light guide plate. The shape of the third portion of the through hole may be a truncated cone shape or an inverted truncated cone shape, or a truncated polygonal pyramid shape or an inverted truncated polygonal pyramid shape, etc.

The light guide plates 110A-110C may be a single layer, or may have a laminated structure including multiple light-transmitting layers. When multiple light-transmitting layers are laminated, a layer with a different refractive index from the others, such as an air layer, may be interposed between any of the layers.

[Light reflective member 31]
The material of the light reflective member 31 is, for example, a resin material containing a light reflective filler. Here, in this specification, "light reflectivity" refers to a reflectance of 60% or more at the emission peak wavelength of the light emitting element 120. It is more beneficial for the light reflective member 31 to have a reflectance of 70% or more at the emission peak wavelength of the light emitting element 120, and even more beneficial for the reflectance of 80% or more.

The base material of the light-reflective member 31 may be a resin material such as silicone resin, phenolic resin, epoxy resin, BT resin, or polyphthalamide (PPA). The light-reflective filler may be metal particles, or particles of an inorganic or organic material having a higher refractive index than the base material. Examples of light-reflective fillers include particles of titanium dioxide, silicon oxide, zirconium dioxide, potassium titanate, aluminum oxide, aluminum nitride, boron nitride, mullite, niobium oxide, barium sulfate, or particles of various rare earth oxides such as yttrium oxide and gadolinium oxide. It is beneficial for the light-reflective member 31 to have a white color.

The light-reflective filler contained in the light-reflective member 31 may be dispersed throughout the light-reflective member 31, or may be unevenly distributed or have a gradient in distribution within the light-reflective member 31. For example, in the process of forming the light-reflective member 31, the filler is allowed to settle before the base material hardens, thereby creating a bias in the distribution of the light-reflective filler in the light-reflective member 31. If the number density of the filler, defined as the number of fillers per unit area in a plan view, is relatively high near the center of the light-reflective member 31 compared to near the outer edge, the brightness of the area directly above the light-emitting element 120 is likely to be reduced. The reflectance of the light-reflective member 31 may be, for example, about 10% to 95%.

In the example shown in Figures 3 to 5, the upper surface 31a of the light-reflective member 31 is a generally flat surface. However, the shape of the upper surface 31a of the light-reflective member 31 is not limited to this example, and may be a convex shape that protrudes on the side opposite the light-emitting element 120, or a concave shape that is recessed toward the light-emitting element 120. In particular, when the upper surface 31a of the light-reflective member 31 is a convex shape that protrudes on the side opposite the light-emitting element 120, the thickness near the center of the light-reflective member 31 becomes relatively large when the position of the upper end 12a of the first portion 11A is used as a reference, and as a result, the brightness of the area directly above the light-emitting element 120 can be more effectively reduced.

In a typical embodiment of the present disclosure, the light reflective member 31 has a shape that blocks the through hole. For example, in the example shown in FIG. 3, the light reflective member 31 is disposed between the lower end 11a and the upper end 12a of the first portion 11A. The light reflective member 31 may have a shape that covers the entire inner area of the upper end 12a of the first portion 11A in a plan view. On the other hand, in the example shown in FIG. 6, the light reflective member 31 is disposed in the through hole 10A so as to extend larger than the upper end 12a of the first portion 11A in a plan view. In other words, the light reflective member 31 may include a portion that is located above the upper end 12a of the first portion 11A and inside the second portion 12A. Note that if the inclination of the second side surface 12c is steeper than the inclination of the first side surface 11c, even if a portion of the light reflective member 31 reaches the inside of the second portion 12A, the area of the light reflective member 31 that occupies the through hole 10A in a plan view is easily reduced. In other words, it becomes easier to avoid the brightness near the through hole 10A becoming unnecessarily low.

The light-reflective member 31 may occupy at least a portion of the first portion 11A. For example, the light-reflective member 31 may occupy 50% or more of the volume of the first portion 11A. Within the first portion 11A, the light-reflective member 31 may have a single-layer structure or a multilayer structure.

[Light-emitting element 120]
2 illustrates a light emitting element 120 as an example of the light source 50. As illustrated in Fig. 7, the light emitting element 120 has a semiconductor laminate 125 and a pair of positive and negative electrodes 124. In the illustrated example, the electrodes 124 are located on the side opposite to the upper surface 120a of the light emitting element 120.

The semiconductor laminate 125 includes, for example, a device substrate such as sapphire or gallium nitride, and one or more semiconductor layers on the device substrate. The semiconductor layers include an n-type semiconductor layer, a p-type semiconductor layer, and a light emitting layer sandwiched between them. The semiconductor layers may include a nitride semiconductor (In _x Al _y Ga _1-xy N, 0≦x, 0≦y, x+y≦1) capable of emitting light in the ultraviolet to visible range.

The light source 50 of each light-emitting region 100 (e.g., light-emitting region 100A) in the surface light source 200 includes one or more light-emitting elements 120. The light-emitting element 120 may be an element that emits blue light, or an element that emits light in a wavelength range other than blue. The light-emitting layer in the semiconductor laminate 125 may have a structure such as a double heterojunction or a single quantum well (SQW), or may have a multiple quantum well (MQW) structure.

The semiconductor laminate 125 may also include multiple light-emitting layers. For example, the semiconductor laminate may have a structure including multiple light-emitting layers between an n-type semiconductor layer and a p-type semiconductor layer, or may have a structure in which a structure including an n-type semiconductor layer, a light-emitting layer, and a p-type semiconductor layer in sequence is repeated multiple times. The color of light (emission color) emitted from the light-emitting layer may be different between these multiple light-emitting layers, or may be the same between these light-emitting layers. Here, "same emission color" also includes cases where the peak wavelength varies by about several nm. The combination of emission colors of the multiple light-emitting layers can be appropriately selected. For example, when the semiconductor laminate includes two light-emitting layers, the combination of emission colors from these light-emitting layers may be blue and blue, green and green, red and red, blue and green, blue and red, or green and red. The semiconductor laminate 125 may include a light-emitting layer that emits ultraviolet light. In the case of ultraviolet light, the above-mentioned "emission color" can be read as "peak wavelength".

In the following, a light-emitting element that emits blue light is exemplified as the light-emitting element 120. As shown in FIG. 7, the light-emitting element 120 in each light-emitting region 100A is electrically connected to the wiring layer 141 by the conductive member 40.

The shape of the light-emitting element 120 in a plan view is typically rectangular. The length of one side of the rectangle of the light-emitting element 120 is, for example, 1000 μm or less. The vertical and horizontal dimensions of the rectangle of the light-emitting element 120 may be 500 μm or less. Light-emitting elements with vertical and horizontal dimensions of 500 μm or less are easy to procure at low cost. Alternatively, the vertical and horizontal dimensions of the rectangle of the light-emitting element 120 may be 200 μm or less. If the length of one side of the rectangle of the light-emitting element 120 is small, it is advantageous for expressing high-definition images, local dimming operation, etc., when applied to a backlight unit of a liquid crystal display device. In particular, a light-emitting element with both vertical and horizontal dimensions of 250 μm or less has a small area of the top surface, so that the amount of light emitted from the side of the light-emitting element is relatively large. Therefore, it is easy to obtain a batwing-type light distribution characteristic. Here, the batwing-type light distribution characteristic refers, in a broad sense, to a light distribution characteristic that is defined by an emission intensity distribution in which the emission intensity is high at angles where the absolute value of the light distribution angle is greater than 0°, with the optical axis perpendicular to the top surface of the light-emitting element being 0°.

[Wiring Board 140 (Wiring Board 240)]
An example of the wiring board 240 is a flexible printed circuit board (FPC). The wiring board 240 may be a double-sided printed circuit board or a single-sided printed circuit board.

In the example shown in FIG. 7, the wiring layer 141 includes a first wiring layer 141a located on the upper surface 140a side of the wiring board 140 and a second wiring layer 141b located on the lower surface 140b side of the wiring board 140. A typical example of the material of the first wiring layer 141a and the second wiring layer 141b is a metal such as copper, and the first wiring layer 141a and the second wiring layer 141b are electrically connected to each other inside the wiring layer 141 by a conductive member such as a via (not shown in FIG. 7).

In the example shown in FIG. 7, a portion of the second wiring layer 141b is exposed from the insulating portion 144 at a terminal portion 248 located at an end of the wiring board 240. The terminal portion 248 functions as a connection terminal for connecting the surface light source 200 to a driver or the like. As shown in FIG. 7, the terminal portion 248 may have a plate-shaped reinforcing member 246 made of polyimide or the like.

The first wiring layer 141a and the second wiring layer 141b can have various wiring patterns. For example, the wiring pattern can be such that the multiple light sources 50 in the surface light source 200 are connected in series or parallel, and the multiple light sources 50 are turned on and off simultaneously. Alternatively, the wiring pattern can be such that the multiple light sources 50 are divided into multiple groups, and the light sources 50 can be individually controlled to be turned on and off for each group. The portion of the conductive member 40 that appears on the lower surface 140b side of the wiring board 140 can be covered with an insulating protective member 145 such as resin, as shown in FIG. 7.

The insulating section 144 includes a sheet-like insulating base material 144s that supports the first wiring layer 141a and the second wiring layer 141b, a first covering layer 144t that covers the first wiring layer 141a on the upper surface 140a side of the wiring board 140, a second covering layer 144u that covers the second wiring layer 141b on the lower surface 140b side of the wiring board 140, and the above-mentioned protective member 145. An adhesive layer of a resin material such as epoxy, acrylic, or olefin may be disposed between the first covering layer 144t and the insulating base material 144s and/or between the insulating base material 144s and the second covering layer 144u.

The insulating base material 144s of the insulating section 144 is formed from a resin such as polyimide (PI), polyethylene naphthalate (PEN), or polyethylene terephthalate (PET). The material of the insulating base material 144s may be, for example, FR4 as specified by the National Electrical Manufacturers Association (NEMA). If electrical insulation from the first wiring layer 141a and the second wiring layer 141b is ensured, a metal substrate may be used for the insulating base material 144s. The material of the first coating layer 144t and the second coating layer 144u is, for example, a resin such as PI, PEN, PET, or epoxy.

Figure 8 shows another example of a surface light source. The light emitting regions 100 of the surface light source 300 shown in Figure 8 are arranged in 25 rows and 40 columns. The number and arrangement of the light emitting regions 100 in the surface light source 300 are not limited to this example and may be any number and arrangement. By arranging surface light sources 300, each having a plurality of light sources 50 as exemplified in Figure 8, in two or one dimensions, a surface light source device having a larger light emitting surface can be obtained.

[First light-transmissive member 30]
The first light-transmissive member 30 is located in a through hole of a light guide plate (for example, the through hole 10A of the light guide plate 110A) and covers the light source 50 (for example, the light-emitting element 120). A resin material containing a transparent resin as a base material can be used as the material of the first light-transmissive member 30. Examples of the base material of the first light-transmissive member 30 include epoxy resin, silicone resin, silicone-modified resin, phenol resin, polycarbonate resin, acrylic resin, polymethylpentene resin, polynorbornene resin, polyethylene terephthalate, or polyester, or a material containing two or more of these.

The first light-transmissive member 30 may be composed of a single layer, or may include multiple layers. Some or all of the multiple layers may contain, for example, a material having a refractive index different from that of the base material and/or a phosphor.

The first light-transmissive member 30 has a transmittance of, for example, 60% or more for light having the emission peak wavelength of the light-emitting element 120. From the viewpoint of effective use of light, it is beneficial if the transmittance of the first light-transmissive member 30 at the emission peak wavelength of the light-emitting element 120 is 70% or more, and more beneficial if it is 80% or more. From the viewpoint of efficiently introducing light from the light-emitting element 120 into the light guide plate, it is advantageous if the first light-transmissive member 30 has a refractive index equal to or higher than that of the material of the light guide plate.

The upper surface 30a of the first translucent member 30 can be a flat surface. Alternatively, the upper surface 30a of the first translucent member 30 can be a shape that protrudes upward or a shape that is recessed downward based on the position of the lower end 11a of the first portion 11A.

[Adhesive sheet 150]
A known resin sheet having an adhesive layer can be used as the adhesive sheet 150. For example, a sheet-shaped optically clear adhesive (OCA) can be applied to the adhesive sheet 150.

The adhesive sheet 150 may be optically reflective. By making the adhesive sheet 150 optically reflective, light introduced from the light source 50 into the light guide plate and directed toward the lower surface 110b of the light guide plate can be reflected by the adhesive sheet 150 toward the upper surface 110a of the light guide plate, improving the light utilization efficiency. It is beneficial if the reflectance of the adhesive sheet 150 at the emission peak wavelength of the light emitting element 120 is 70% or more, and it is even more beneficial if it is 80% or more.

[Light-reflecting sheet 160]
7, the surface light source can further include a light reflecting sheet 160. The light reflecting sheet 160 is disposed, for example, between the adhesive sheet 150 and an adhesive sheet 170 located on the wiring board 140.

The light reflecting sheet 160 improves the light utilization efficiency by reflecting the light traveling toward the wiring board 140 inside the light guide plate toward the upper surface 110a of the light guide plate. As with the material of the light reflecting member 31 described above, a resin material containing a light reflective filler in the resin can be used as the material of the light reflecting sheet 160. The light reflecting sheet 160 is, for example, a resin sheet containing polyethylene terephthalate as a base material. As the light diffusing material contained in the light reflecting sheet 160, for example, titanium oxide particles can be used. Instead of containing a light diffusing material in the base material, a white polyethylene terephthalate sheet containing a large number of air bubbles may be used as the light reflecting sheet 160.

It is beneficial for the light reflecting sheet 160 to have a portion located directly below the light source 50. In other words, it is preferable that a portion of the light reflecting sheet is located within the through-hole of the light guide plate. By positioning a portion of the adhesive sheet 150 within the through-hole of the light guide plate, it becomes possible to bond the light source 50 to the light reflecting sheet 160 by the adhesive sheet 150. By providing a hole through which the electrode of the light source 50 can pass in the portion of the light reflecting sheet 160 and the adhesive sheet 170 located within the through-hole of the light guide plate, it becomes possible to electrically connect the electrode of the light source 50 to the wiring layer 141 of the wiring board 140 via the conductive member 40.

The thickness of the light-reflective sheet 160 is, for example, preferably 35 μm to 350 μm, more preferably 50 μm to 100 μm. The light-reflective sheet 160 may be a resin sheet manufactured by Toray Industries, Inc., commercially available under the name Lumirror (registered trademark) (#38-E20, #50-E20, #75-E20, #100-E20, #188-E6SR, etc.), or a light-reflective sheet manufactured by 3M (ESR series). The surface of the light-reflective sheet 160 may be a specular reflection surface or a diffuse reflection surface.

[Adhesive sheet 170]
The adhesive sheet 170 is disposed between the wiring board 140 and the light reflecting sheet 160, and fixes the light reflecting sheet 160 to the upper surface 140a of the wiring board 140. The adhesive sheet 170 is an adhesive layer formed of a resin material such as acrylic. A known resin sheet having an adhesive layer, such as a bonding sheet, may be used as the adhesive sheet 170. Like the adhesive sheet 150 described above, the adhesive sheet 170 may have light reflectivity.

Figure 9 shows light-emitting region 100D, which is yet another example of light-emitting region 100. Light-emitting region 100D shown in Figure 9 includes a light guide plate 110D having a through-hole 10D. As shown in Figure 9, through-hole 10D has second portion 12A, first portion 11D, and third portion 13A from upper surface 110a to lower surface 110b of light guide plate 110D.

The upper end 12a of the first portion 11A of the through hole 10A shown in FIG. 2 is circular in plan view. In contrast, the upper end 12a of the first portion 11D of the through hole 10D shown in FIG. 9 is oval. Here, the oval shape of the upper end 12a of the first portion 11D is longer in the Y direction than in the X direction.

In this specification, the term "oval shape" refers to a closed curve having two mutually perpendicular axes of symmetry, and broadly includes ellipses, ovals, rounded rectangles, and shapes that are combinations of these. For example, in the case of an ellipse, the two mutually perpendicular axes of symmetry are the major and minor axes of the ellipse. In the following explanation, an ellipse is used as an example of an oval shape.

In the configuration illustrated in FIG. 9, the shape of the upper end 12a of the first portion 11D is an ellipse defined by a first major axis LA as the first axis and a first minor axis SA as the second axis perpendicular to the first major axis. Here, the first major axis of the ellipse of the upper end 12a is parallel to the Y direction in the figure, and the first minor axis is shorter than the first major axis and parallel to the X direction in the figure. The first major axis and the first minor axis intersect approximately at the center of the light guide plate 110D in a plan view, and the light emitting element 120 is disposed inside the third portion 13A of the through hole 10D so that its optical axis passes through the intersection of these axes.

When the surface light source 200 is used as a backlight for a liquid crystal display device or the like, the upper surface 210a of the light guide plate 210 constituting the light emitting surface of the surface light source 200 is typically rectangular. In this case, the shape of each upper surface 110a of one or more light guide plates 110D constituting the surface light source 200 can be a rectangle similar to the rectangle of the surface light source 200. In that case, the first major axis defining the ellipse of the upper end portion 12a is parallel to the short side of the rectangle of the light guide plate 110D, and the first minor axis is parallel to the long side of the rectangle of the light guide plate 110D. This can have the effect of reducing luminance unevenness on the upper surface of the light guide plate.

When the upper surface of the light guide plate has a rectangular shape, the shape of the upper end 12a of the first portion 11D in a plan view can be a shape having a first axis parallel to the short side of the rectangular shape of the light guide plate and a second axis parallel to the long side of the rectangular shape and shorter than the first axis. For example, the shape of the upper end 12a of the first portion 11D in a plan view can be an oval shape elongated in the direction of the short side of the rectangular shape of the light guide plate 110D, as shown in FIG. 9.

In the embodiment of the present disclosure, a light reflective member 31 is disposed in the first portion 11D of the through hole 10D, and the reflection of light inside the light guide plate 110D at the position of the first side surface 11c of the first portion 11D is dominated by diffuse reflection. Therefore, by making the planar shape of the upper end portion 12a of the first portion 11D an oval shape extended in the direction of the extension of the rectangular short side of the light guide plate 110D, it is possible to reduce the light that reaches the side surface on the rectangular long side of the light guide plate 110D. This can reduce the brightness, particularly near the center, of the rectangular long side of the light guide plate 110D when viewed from the top surface 110a side. In other words, it is possible to reduce brightness unevenness.

Regarding the oval shape of the upper end 12a of the first portion 11D, the ratio of the lengths along the two symmetrical axes can be determined based on the ratio (aspect ratio) between the long side length and the short side length of the rectangular shape of the light guide plate. For example, when the aspect ratio of the rectangular shape of the light guide plate 210 of the surface light source 200 is 16:10 and the surface light source 200 includes an arrangement of 16 light-emitting regions 100D in 4 rows and 4 columns, the upper surface 110a of the light guide plate 110D of each light-emitting region 100D can also be rectangular with the same aspect ratio as the light guide plate 210. In this case, the ratio between the length along the first symmetrical axis (e.g., the first long axis) of the upper end 12a of the first portion 11D and the length along the second symmetrical axis (e.g., the first short axis) can be 16:10 according to the aspect ratio of the rectangular shape of the light guide plate 110D. The ratio of the length of the upper end 12a along the first axis of symmetry to the length of the upper end 12a along the second axis of symmetry is, for example, in the range of (6.0/5.5) to (2/1). The size of the upper end 12a of the first portion 11D along the long or short side of the rectangular shape of the light guide plate 110D is, for example, in the range of about 2 mm to 2.5 mm.

Figure 10 shows light-emitting region 100E, which is yet another example of light-emitting region 100. Light-emitting region 100E shown in Figure 9 includes light guide plate 110E having through-hole 10E. Through-hole 10E has first portion 11D including lower end 11a and upper end 12a, and second portion 12E including opening 10a.

In the example shown in FIG. 10, both the upper end 12a of the first portion 11D of the through hole 10E and the opening 10a of the second portion 12E are elliptical. The long axis of the ellipse of the upper end 12a and the long axis of the ellipse of the opening 10a are perpendicular to each other. The third axis of the opening 10a of the second portion 12E, which are perpendicular to each other, and the fourth axis, which is shorter than the third axis, are parallel to the long and short sides of the rectangular shape of the light guide plate 110D, respectively.

In this example, the opening 10a of the second portion 12E is oval-shaped and elongated in the direction of the long side of the rectangular light guide plate 110E. By reducing the distance between the side of the light guide plate 110E extending in the Y direction and the second side 12c of the second portion 12E, light is more likely to propagate in the X direction inside the light guide plate 110E. On the other hand, when looking at the Y direction, the distance between the side of the light guide plate 110E extending in the X direction and the second side 12c of the second portion 12E is expanded. This balances the reflection by the second side 12c of the second portion 12E between the X direction and the Y direction, making it possible to effectively reduce brightness unevenness.

The ratio between the length of the opening 10a in the second portion 12E along the first axis of symmetry and the length of the opening 10a along the second axis of symmetry can be determined according to the aspect ratio of the rectangular shape of the light guide plate 110D. For example, the ratio between the length of the third axis and the fourth axis of the opening 10a may be 16:10. The size of the opening 10a in the second portion 12A along the long or short side of the rectangular shape of the light guide plate 110D can be in the range of, for example, about 3 mm to 4 mm.

(Embodiment 2)
Fig. 11 is a schematic cross-sectional view of one of the light-emitting regions constituting a surface light source according to another embodiment of the present disclosure. The light-emitting region 100F shown in Fig. 11 has a light-emitting device 50F instead of the light-emitting element 120 as the light source 50 inside the third portion 13C.

[Light-emitting device 50F]
The light emitting device 50F includes a light emitting element 120, a second light-transmissive member 52, and a covering member 54. The shape of the light emitting device 50F in a plan view is typically rectangular. The length of one side of the upper surface of the light emitting device 50F is, for example, about 500 μm to 1000 μm. Inside the through hole 10B, the light emitting device 50F can be arranged so that one side of the rectangular shape of its upper surface is approximately parallel to one side of the rectangular shape of the light guide plate 110C, or so that it is inclined with respect to one side of the rectangular shape of the light guide plate 110C.

It is preferable that the center of the light-emitting region, the center of the through hole of the light guide plate, and the optical axis of the light source generally coincide. However, the positional relationship between these may be adjusted depending on the position of the light-emitting region 100F in the surface light source 200. In other words, depending on whether the light-emitting region 100F in question is located near the center of the surface light source 200 or near the periphery, the position of the other two may be adjusted when one of the center of the light-emitting region, the center of the through hole of the light guide plate, and the optical axis of the light source is used as a reference. This is also true in embodiment 1 in which the light-emitting element 120 is applied to the light source 50.

[Second light-transmissive member 52]
The second light-transmitting member 52 has light-transmitting properties similar to the first light-transmitting member 30, and covers the upper surface 120a and/or the side surface of the light-emitting element 120. As the material of the second light-transmitting member 52, silicone resin, modified silicone resin, epoxy resin, modified epoxy resin, urea resin, phenol resin, polycarbonate resin, trimethylpentene resin, polynorbornene resin, acrylic resin, urethane resin, or fluororesin, or a resin containing two or more of these resins can be used. From the viewpoint of efficiently introducing light into the first light-transmitting member 30, it is beneficial for the material of the second light-transmitting member 52 to have a lower refractive index than the material of the first light-transmitting member 30. By making the material of the second light-transmitting member 52 contain a material having a refractive index different from that of the base material, the second light-transmitting member 52 can be given a light diffusion function. For example, the base material of the second light-transmitting member 52 may contain particles of titanium dioxide, silicon oxide, or the like.

The second translucent member 52 may contain phosphor particles or the like. The phosphor in the second translucent member 52 absorbs at least a portion of the light emitted from the light-emitting element 120 and emits light of a wavelength different from the wavelength of the light from the light-emitting element 120. In this case, the second translucent member 52 can convert the wavelength of a portion of the blue light from the light-emitting element 120 to emit, for example, yellow light. With this configuration, white light is obtained by mixing the blue light that has passed through the second translucent member 52 and the yellow light emitted from the phosphor contained in the second translucent member 52.

In the configuration illustrated in FIG. 11, the light emitted from the light-emitting element 120 is basically introduced into the light guide plate 110C via the second light-transmissive member 52. Therefore, the mixed light is diffused inside the light guide plate 110C, and it is possible to extract, for example, white light with reduced luminance unevenness from the upper surface 110a of the light guide plate 110C.

Known materials can be used for the phosphor contained in the second light-transmissive member 52. Examples of the phosphor include yttrium aluminum garnet phosphors (e.g., _Y3 (Al,Ga) _5O12 :Ce), lutetium aluminum garnet phosphors (e.g., _Lu3 (Al,Ga) _5O12 :Ce), terbium aluminum garnet phosphors (e.g., _Tb3 (Al,Ga) _5O12 :Ce), β-sialon phosphors (e.g., ( _Si ,Al) ₃ (O,N) ₄ :Eu), α-sialon phosphors (e.g., Ca(Si,Al) ₁₂ ( _{O,N)16 : Eu} ), nitride phosphors, and fluoride phosphors. As the nitride phosphor, a CASN phosphor (e.g., _CaAlSiN3 :Eu) or a SCASN phosphor (e.g., (Sr,Ca) _AlSiN3 :Eu) can be used. As the fluoride phosphor, a KSF phosphor (e.g., _K2SiF6 :Mn), _{a KSAF phosphor (e.g., K2 (} Si,Al) _F6 :Mn), or a MGF phosphor (e.g., _{3.5MgO.0.5MgF2.GeO2} : _Mn ) can be used.

Yttrium aluminum garnet phosphor (YAG phosphor) is an example of a wavelength conversion material that converts blue light to yellow light. β-sialon phosphor is an example of a wavelength conversion material that converts blue light to green light. CASN phosphor and SCASN phosphor are examples of wavelength conversion materials that convert blue light to red light, and KSF phosphor, KSAF phosphor, and MGF phosphor are also examples of wavelength conversion materials that convert blue light to red light. The phosphor may be a phosphor with a perovskite structure (e.g., CsPb(F,Cl,Br,I) ₃ ), or a quantum dot phosphor (e.g., CdSe, InP, _AgInS2 , or _AgInSe2 ), etc.

[Covering member 54]
The covering member 54 is a member that covers at least a part of the lower surface 120b opposite to the upper surface 120a of the light-emitting element 120. For example, in the example shown in Fig. 11, the covering member 54 also covers the surface of the second light-transmissive member 52 that is located opposite to the upper surface 52a. Note that the lower surface of the electrode 124 of the light-emitting element 120 is exposed from the covering member 54 and is connected to the wiring layer 141 of the wiring board 140 by the conductive member 40.

The covering member 54 typically has light reflectivity. As with the above-described light-reflective member 31, the material of the covering member 54 may be, for example, a white resin material containing a light-reflective filler. The material of the covering member 54 may be the same as the material of the light-reflective member 31, or may be different.

By covering the lower surface 120b of the light emitting element 120 with the covering member 54, except for the lower surface of the electrode 124, the light emitted from the semiconductor laminate 125 of the light emitting element 120 toward the lower surface 120b of the light emitting element 120 can be reflected by the covering member 54 toward, for example, the upper surface 110a of the light guide plate 110C. In other words, by providing the covering member 54 to the light emitting device 50F, the light utilization efficiency can be improved.

FIG. 12 shows an exemplary configuration of a surface light source according to yet another embodiment of the present disclosure. The light-emitting region 100G shown in FIG. 12 further includes a diffusion sheet 220 arranged above the upper surface 110a of the light guide plate 110C. Here, a first prism sheet 221 and a second prism sheet 222 are further arranged above the upper surface 220a of the diffusion sheet 220. The light-emitting region 100G also includes a light-emitting device 50G instead of the light-emitting device 50F. The light-emitting device 50G includes a second light-reflective member 56 that covers the entire upper surface 52a of the second light-transmissive member 52.

[Light reflective member 56]
12, a second light-reflecting member 56 may be disposed on the upper surface 52a of the second light-transmitting member 52. An example of the material of the light-reflecting member 56 is the same material as the light-reflecting member 31 or the covering member 54, for example, a resin material containing titanium dioxide particles. By disposing the light-reflecting member 56, for example, in the form of a layer, above the light-emitting element 120, it is possible to effectively reduce luminance unevenness on the light-emitting surface of the light-emitting region 100G. The reflectance of the light-reflecting member 56 with respect to the light emitted from the light-emitting element 120 can be about 10% to 95%, similar to the light-reflecting member 31.

In this embodiment, a light-reflective member 31 is further positioned on the first light-transmissive member 30 that covers the light-emitting device 50G. This makes it possible to more effectively reduce the luminance difference between the region directly above the light-emitting element 120 on the light-emitting surface of the light-emitting region 100G and a position away from the light-emitting element 120. From the perspective of reducing the luminance difference between the region directly above the light-emitting element 120 on the light-emitting surface of the light-emitting region 100G and a position away from the light-emitting element 120, it is beneficial for the light-reflective member 31 to have a shape that covers at least the entire first portion of the through-hole in a plan view.

[Diffusion sheet 220]
12, a diffusion sheet 220 is disposed above an upper surface 110a of the light guide plate 110C. A lower surface 220b of the diffusion sheet 220, which faces the upper surface 110a of the light guide plate 110C, may be in contact with at least a part of the upper surface 110a of the light guide plate 110C, or may be separated from the upper surface 110a of the light guide plate 110C.

The diffusion sheet 220 is made of a material that has low light absorption for visible light, such as polycarbonate, polystyrene, acrylic, or polyethylene. The structure that diffuses light is provided in the diffusion sheet 220 by providing irregularities on the surface of the diffusion sheet 220 or by incorporating a material having a refractive index different from that of the base material in the diffusion sheet 220. As the diffusion sheet 220, optical sheets that are commercially available under names such as light diffusion sheet or diffuser film can be used. The thickness of the diffusion sheet 220 is, for example, about 0.443 mm.

[First prism sheet 221, second prism sheet 222]
The first prism sheet 221 has a surface on which a plurality of prisms are formed, each extending in a predetermined direction. Similarly, the second prism sheet 222 has a surface on which a plurality of prisms are formed, each extending in a predetermined direction. For example, in Fig. 12, the first prism sheet 221 has a plurality of prisms that extend in the X direction, and the second prism sheet 222 has a plurality of prisms that extend in the Y direction.

As the first prism sheet 221 and the second prism sheet 222, a wide variety of commercially available optical members for backlights can be used. The thicknesses of the first prism sheet 221 and the second prism sheet 222 are, for example, approximately 0.07 mm and 0.09 mm, respectively. The diffusion sheet 220, the first prism sheet 221, and the second prism sheet 222 may be in contact with each other, or may be fixed to a frame or the like arranged on the wiring board 240 and arranged above the light guide plate 110C at intervals. Instead of optical sheets such as the diffusion sheet 220, the first prism sheet 221, and the second prism sheet 222, or together with one or more of these, a phosphor sheet containing phosphor particles or the like may be arranged above the light guide plate 110C.

(Modifications of the Light Source)
13 to 16 show examples of light emitting devices applicable to the light source 50 of the surface light source according to the embodiment of the present disclosure. A light emitting device 50A shown in Fig. 13 includes a light emitting element 120, a second light-transmissive member 52A, a covering member 54A, and a light reflective member 56A.

In the light-emitting device 50A, the second light-transmissive member 52A is plate-shaped and covers the upper surface 120a of the light-emitting element 120 and the upper surface 54a of the covering member 54A. The second light-transmissive member 52A may be made of silicate glass, borosilicate glass, quartz glass, or an inorganic material such as sapphire. The light-reflective member 56A is typically a resin layer having light reflectivity, and is disposed on the upper surface 52a of the second light-transmissive member 52A.

In this example, the covering member 54A covers the entire side surface 120c of the light-emitting element 120 and the area of the underside 120b other than the area where the electrode 124 is arranged. The underside 124b of the electrode 124 is exposed from the covering member 54A.

The covering member 54A is typically white and light reflective. Since the covering member 54A covers the entire side surface 120c of the light emitting element 120, the light from the light emitting element 120 is mainly extracted from the upper surface 120a of the light emitting element 120. Furthermore, since the light reflective member 56A is located on the upper surface 52a of the second translucent member 52A, most of the light emitted from the light emitting element 120 is emitted to the outside of the light emitting device 50A from the side surface 52c of the second translucent member 52A. Such a configuration of the light emitting device makes it easy to diffuse light within the surface of the light guide plate, and can advantageously reduce uneven brightness.

In the structure illustrated in FIG. 13, the light-emitting element 120 is joined to the second light-transmissive member 52A by a light-transmissive adhesive. In this case, a portion of the light-transmissive adhesive may be located on the side surface 120c of the light-emitting element 120. The covering member 54A also covers the portion of the light-transmissive adhesive that is located on the side surface 120c of the light-emitting element 120.

The light-emitting device 50B shown in FIG. 14 has a second translucent member 52B and a covering member 54B instead of the second translucent member 52A and covering member 54A of the light-emitting device 50A shown in FIG. 13. The covering member 54B covers not only the side surface 120c of the light-emitting element 120 but also the side surface 52c of the second translucent member 52B. The light-emitting device 50B does not have a light-reflective structure that covers the upper surface 52a of the second translucent member 52B, and the upper surface 52a of the second translucent member 52B is exposed from the covering member 54B. With this configuration, it is easy to extract light toward the upper side of the light-emitting element 120.

The light-emitting device 50C shown in FIG. 15 is an example in which the light-reflective member 56A is omitted from the light-emitting device 50A shown in FIG. 13. A configuration in which the covering member 54 is further omitted from the light-emitting device 50F shown in FIG. 11 can also be applied to a light source disposed inside a through-hole of a light guide plate. In other words, a configuration in which the covering member 54 is not positioned on the side surface of the electrode 124 of the light-emitting element 120 can also be applied to the light source 50 in the surface light source 200, 300 of the embodiment of the present disclosure.

As shown in FIG. 16, a single light emitting device may have multiple light emitting elements. The light emitting device 50D shown in FIG. 16 includes a first light emitting element 121, a second light emitting element 122, and a third light emitting element 123. The light emitting device 50D further includes a second translucent member 52D, a joining member 58, a first covering member 54D, and a second covering member 55D.

In the example shown in FIG. 16, the first light-emitting element 121, the second light-emitting element 122, and the third light-emitting element 123 are arranged in a linear row. However, the arrangement of the light-emitting elements in the light-emitting device 50D is not limited to this example. The number of light-emitting elements and the combination of emission peak wavelengths included in the light-emitting device 50D can also be changed appropriately depending on the application of the surface light source. The first light-emitting element 121, the second light-emitting element 122, and the third light-emitting element 123 may be a set of light-emitting elements having different emission peak wavelengths, or may be a set of light-emitting elements having the same emission peak wavelength.

In the configuration illustrated in FIG. 16, the second translucent member 52D is located above the first light-emitting element 121, the second light-emitting element 122, and the third light-emitting element 123, and collectively covers the upper surfaces 120a of these light-emitting elements. In this example, the first light-emitting element 121, the second light-emitting element 122, and the third light-emitting element 123 are fixed to the lower surface 52b of the second translucent member 52D by a bonding member 58. The bonding member 58 is, for example, a translucent adhesive.

When the light emitting device 50D includes multiple light emitting elements with different peak wavelengths, the light with different peak wavelengths is mixed inside the second translucent member 52D. It is beneficial to impart a light diffusion function to the second translucent member 52D by including a light diffusing material (e.g., particles of titanium dioxide, silicon oxide, etc.) in the second translucent member 52D. The second translucent member 52D may or may not include phosphor particles.

The first covering member 54D is a light-reflective member that covers the light-emitting elements and the bonding member 58, except for the lower surface 124b of the electrode 124 of each light-emitting element. The second covering member 55D is located on the upper surface 54a of the first covering member 54D and covers the side surface 52c of the second translucent member 52D so as to surround the second translucent member 52D. The second covering member 55D has light reflectivity similar to the first covering member 54D, and light from the first light-emitting element 121, the second light-emitting element 122, and the third light-emitting element 123 is extracted to the outside of the light-emitting device 50D from the upper surface 52a of the second translucent member 52D. In this example, the side surface 55c of the second covering member 55D is aligned with the side surface 54c of the first covering member 54D.

These light-emitting devices 50A-50D, 50F may be combined with any of the light-emitting areas 100A-100E described with reference to Figures 2-10, as well as with light-emitting area 100F or 100G.

Embodiments of the present disclosure are useful for various lighting light sources, in-vehicle light sources, display light sources, and the like. In particular, they can be advantageously applied to backlight units intended for liquid crystal display devices. Planar light sources according to embodiments of the present disclosure can be suitably used for backlights for display devices of mobile devices that have strict requirements for reducing thickness, planar light-emitting devices capable of local dimming control, and the like.

10, 10A to 10E Through hole of light guide plate 11A, 11B, 11D, 11E First portion of through hole 11c First side surface of first portion of through hole 11w Inner wall surface 12A, 12E Second portion of through hole 12c Second side surface of second portion of through hole 13A, 13C Third portion of through hole 13c Third side surface of third portion of through hole 30 First light-transmissive member 31 Light-reflecting member 50 Light source 50A to 50D, 50F, 50G Light-emitting device 52, 52A, 52B, 52D Second light-transmissive member 54, 54A, 54B, 54D, 55D Covering member 56, 56A Second light-reflecting member 100, 100A to 100G Light-emitting region 110, 110A to 110E Light guide plate 120 to 123 Light emitting element 140 Wiring board in light emitting region 141 Wiring layer of wiring board 150, 170 Adhesive sheet 160 Light reflecting sheet 200, 300 Planar light source 210 Light guide plate 220 Diffusion sheet 240 Wiring board

Claims (15)

a light guide plate having an upper surface and a lower surface located opposite to the upper surface, the light guide plate having a through hole extending from the upper surface to the lower surface;
a wiring board located on the lower surface side of the light guide plate and including a wiring layer;
a light source including a light emitting element electrically connected to the wiring layer of the wiring board and disposed inside the through hole;
a light reflective member located above the light source,
The through hole is
a first portion having a first side surface inclined with respect to the top surface of the light guide plate;
a second portion having a second side surface located between the top surface of the light guide plate and the first side surface of the first portion,
the light reflective member is located in the first portion of the through hole ,
The through hole is
a first opening located on the lower surface of the light guide plate;
a third side located between the first opening and the first side of the first portion; and
and further comprising a third portion having
the light source is disposed in the third portion;
a first light-transmitting member that covers the light source inside the through hole;
The first light-transmissive member is located in the third portion of the through hole . the second side surface of the second portion is inclined with respect to the upper surface,
The surface light source according to claim 1 , wherein an inclination of the first side surface relative to the upper surface is smaller than an inclination of the second side surface relative to the upper surface. The surface light source according to claim 2, wherein the shape of the second side surface in a cross section perpendicular to the upper surface of the light guide plate is curved. The surface light source according to claim 1 , wherein at least a part of the third side surface is inclined with respect to the upper surface of the light guide plate. The surface light source according to claim 1 , wherein the light reflective member closes the through hole. The first portion of the through hole has an upper end located at a boundary with the second portion,
The surface light source according to claim 5 , wherein the light reflective member covers an entire area inside the upper end portion in a plan view. The surface light source according to claim 6 , wherein the first portion of the through hole further has an inner wall surface located between the upper end and the first side surface. The light guide plate has a rectangular shape in a plan view,
The shape of the upper end portion in a plan view has a first axis parallel to a short side of the rectangular shape of the light guide plate and a second axis parallel to a long side of the rectangular shape and shorter than the first axis.
8. The surface light source according to claim 6 or 7 . The surface light source according to claim 8 , wherein the shape of the upper end portion in a plan view is an oval shape having a first major axis parallel to a short side of the rectangular shape of the light guide plate and a first minor axis parallel to the long side of the rectangular shape. the second portion of the through hole has a second opening located on the top surface of the light guide plate;
the second side of the second portion is located between the second opening and the top end of the first portion;
10. The surface light source according to claim 8, wherein the shape of the second opening in a planar view has a third axis parallel to a long side of the rectangular shape of the light guide plate and a fourth axis parallel to a short side of the rectangular shape and shorter than the third axis. The surface light source according to claim 10 , wherein a shape of the second opening in a plan view is an oval shape having the third axis and the fourth axis. The surface light source according to claim 1 , wherein a refractive index inside the second portion of the through hole is lower than a refractive index of the light reflective member. the light emitting element has a top surface;
The surface light source according to claim 1 , wherein the light source includes a second light-transmitting member that covers at least the upper surface of the light-emitting element. The surface light source according to claim 13 , wherein the light source includes a cover member that covers at least a part of a lower surface of the light emitting element opposite to the upper surface. The surface light source according to claim 1 , further comprising a diffusion sheet located on or above the upper surface of the light guide plate.

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