planar light source

Abstract

To provide a planar light source with minimal brightness unevenness. [Solution] A planar light source comprising a plurality of light-emitting units, each of which is disposed on the lower side of the light guide member and includes a light guide member having an upper surface that serves as a light extraction surface and a lower surface opposite to the upper surface; a light source disposed within the light guide member; and a light-reflecting member having a base material and a light-reflecting substance contained in the base material that is capable of diffuse reflection, wherein in each of the light-emitting units, the light guide member has a first portion with refractive index n1 disposed in contact with the periphery of the light source, a second portion with refractive index n2 disposed in contact with the periphery of the first portion and having refractive index n2, a third portion with refractive index n3 disposed in contact with the periphery of the second portion and having refractive index n3, and a fourth portion with refractive index n4 that is in contact with the first portion, the second portion and the third portion and constitutes the lower surface of the light guide member.

Description

Technical Field

[0001] The present disclosure relates to a planar light source.

Background Art

[0002] A planar light source using a plurality of light sources is known.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] An object is to provide a planar light source with less luminance unevenness.

Means for Solving the Problems

[0005] The present disclosure includes the following configurations. A light guide member including an upper surface serving as a light extraction surface and a lower surface opposite to the upper surface, A light source disposed within the light guide member, A light reflecting member disposed on the lower surface side of the light guide member, including a base material and a light reflecting substance contained in the base material and capable of diffuse reflection, A planar light source including a plurality of light emitting portions, In each of the light emitting portions, the light guide member has a first portion with a refractive index n1 disposed in contact with the periphery of the light source, a second portion with a refractive index n2 disposed in contact with the periphery of the first portion, a third portion with a refractive index n3 disposed in contact with the periphery of the second portion, and a fourth portion with a refractive index n4 in contact with the first portion, the second portion, and the third portion and constituting the lower surface of the light guide member. The refractive index n2 of the second part is greater than the refractive index n4 of the fourth part, the refractive index n4 of the fourth part is greater than the refractive index n1 of the first part, and the refractive index of the first part is the same as or greater than the refractive index n3 of the third part. A planar light source wherein the refractive index n30 of the base material of the light-reflecting member is greater than the refractive index n4 of the fourth portion. [Effects of the Invention]

[0006] This makes it possible to realize a planar light source with minimal brightness unevenness. [Brief explanation of the drawing]

[0007] [Figure 1A] This is a schematic enlarged top view showing an example of a planar light source according to the first embodiment. [Figure 1B] Figure 1A is a cross-sectional view showing the cross-section along the IB-IB line. [Figure 1C] This is a schematic enlarged cross-sectional view showing an example of a planar light source according to Modification 1-1 of the first embodiment. [Figure 2A] This is a schematic enlarged top view showing an example of a planar light source of Modification 1-2 according to the first embodiment. [Figure 2B] Figure 1A is a cross-sectional view showing the cross-section along the IB-IB line. [Figure 3] This is a schematic enlarged cross-sectional view showing an example of a planar light source according to the second embodiment. [Figure 4] This is a schematic enlarged cross-sectional view showing another example of a planar light source according to the second embodiment. [Figure 5] This is a schematic enlarged cross-sectional view showing another example of a planar light source according to the second embodiment. [Figure 6] This is a schematic enlarged top view showing a modified example of the planar light source according to the embodiment. [Figure 7] This is a schematic enlarged top view showing another modification of the planar light source according to the embodiment. [Figure 8] This is a schematic cross-sectional view showing an example of a light source used in the planar light source according to the embodiment. [Figure 9] This figure shows the light emission state of Example 1. [Figure 10] It is a diagram showing the light emission state of Example 2. [Figure 11] It is a diagram showing the light emission state of Example 3. [Figure 12] It is a diagram showing the light emission state of the reference example. [Figure 13] It is a graph showing the cross-sectional illuminance distribution of the light-emitting parts of Example 1 and the reference example.

Modes for Carrying Out the Invention

[0008] While referring to the drawings, embodiments of the present invention will be described in detail. The following embodiments are illustrative, and the planar light source according to the embodiments of the present invention is not limited to the following embodiments. For example, the numerical values, shapes, materials, processes, the order of those processes, etc. shown in the following embodiments are merely examples, and various modifications are possible as long as there is no technical contradiction. Each of the embodiments described below can be combined in various ways as long as there is no technical contradiction.

[0009] The dimensions, shapes, etc. of the components shown in the drawings may be exaggerated for ease of understanding, and may not reflect the actual dimensions, shapes, and size relationships between the components. Also, in order to avoid making the drawings overly complex, schematic diagrams with some elements omitted may be used, or end views showing only the cut surfaces as cross-sectional views may be used.

[0010] The planar light source includes a plurality of light-emitting parts. Each light-emitting part includes a light guide member, a light source, and a light reflection member. The light guide member includes an upper surface that serves as a light extraction surface and a lower surface opposite to the upper surface. The light source is disposed within the light guide member. The light reflection member is disposed on the lower surface side of the light guide member.

[0011] The light guide member is a translucent member that, when viewed from above, spreads light from the light source located at the center of the light guide member of each light-emitting section in the lateral direction. In each light-emitting section, the light guide member comprises at least two parts. Specifically, the light guide member comprises a first part that is centered on the light source and positioned in contact with its periphery when viewed from above, a second part positioned in contact with the periphery of the first part, and a third part positioned in contact with the periphery of the second part. Furthermore, it comprises a fourth part positioned in contact with the lower surface of the first part, the lower surface of the second part, and the lower surface of the third part.

[0012] The third part may be integrated with or separate from the first part. If the third part and the first part are integrated, they are connected on the upper surface of the second part. That is, the third part (or the first part) is positioned to cover the upper surface of the second part and the sides of the light source, starting from the part located outside the second part. In such a case, the third part (or the first part) may cover the upper surface of the light source, or it may be positioned so that the upper surface of the light source is exposed. In any case, if the third part and the first part are integrated, the upper surface of the light guide member may be composed only of the third part (or the first part), and the lower surface of the light guide member may be composed only of the fourth part.

[0013] Furthermore, if the third part and the first part are separate, the third part may extend onto the upper surface of the second part, or it may extend onto the upper surfaces of both the second and first parts. In such cases, the upper surface of the light guide member may be composed only of the third part (or only of the first part), and the lower surface of the light guide member may be composed only of the fourth part.

[0014] Furthermore, if the third part and the first part are separate components, the upper surfaces of the first part and the second part may be exposed from the third part. In other words, the upper surface of the light guide member can be composed of the first part, the second part and the third part, while the lower surface of the light guide member can be composed of only the fourth part.

[0015] In the first embodiment, the light guide member does not contain scattering particles. In the second embodiment, the light guide member contains scattering particles. There is a difference in the relative magnitudes of the refractive indices of the parts constituting the light guide member between the case where scattering particles are not included and the case where scattering particles are included.

[0016] Furthermore, regarding the names of the parts constituting the light guide member, the refractive index n of each part constituting the light guide member shall be followed by "a" in the first embodiment and by "b" in the second embodiment.

[0017] The following describes each embodiment in detail with reference to the drawings.

[0018] Figures 1A to 2B illustrate planar light source 100 (100A to 100C) according to the first embodiment. Figures 3 to 5 illustrate planar light source 100 (100D to 100F) according to the second embodiment. The planar light source 100 comprises a plurality of light-emitting units E. In the planar light source 100 shown in Figure 1A, four light-emitting units E are shown in an enlarged view. Each light-emitting unit E comprises a light guide member 10, a light source 20, and a light-reflecting member 30. The light guide member 10 comprises an upper surface 10U which serves as the light extraction surface, and a lower surface 10L opposite to the upper surface 10U. The light source 20 is arranged inside the light guide member 10. The light-reflecting member 30 capable of diffuse reflection is arranged on the lower surface 10L side of the light guide member 10. Light emitted from the light source 20 enters the light guide member 10, is diffusely reflected by the light-reflecting member 30, and then is emitted to the outside from the upper surface 10U of the light guide member 10.

[0019] In each light-emitting section E of each embodiment, the light guide member 10 can have a rectangular shape when viewed from above, as shown in Figure 1A. However, it is not limited to this, and the light guide member 10 can have a triangular shape when viewed from above, as in the planar light source 100G shown in Figure 6. Alternatively, the light guide member 10 can have a hexagonal shape when viewed from above, as in the planar light source 100H shown in Figure 7. When the light guide member 10 has multiple light-emitting sections E, it is preferable that their top-view shapes are the same. Note that the planar light source 100 shown in Figures 6 and 7 shows examples in which the light adjustment member is not shown. Even in such a planar light source 100, a light adjustment member can be provided.

[0020] In each embodiment, the planar light source 100 may include, for example, 1 to 20,000 light-emitting units E. In each light-emitting unit E, the light guide members 10 may be separated from each other as shown in Figure 1B, or they may be partially or entirely continuous as shown in Figure 1C. In the example shown in Figure 1C, only the fourth portion 14 of the light guide member 10 is continuous with the adjacent light-emitting unit E, while the third portion 13 is separated. However, both the third portion 13 and the fourth portion 14 may be continuous with the adjacent light-emitting unit E or separated. When the third portions 13 of adjacent light-emitting units E are continuous, it is preferable to provide grooves on the upper surface 10U or the lower surface 10L. This reduces the propagation of unwanted light to adjacent light-emitting units E and allows light to be extracted from the necessary light-emitting units E.

[0021] In each embodiment, the light guide member 10 comprises a plurality of parts with different refractive indices in each light-emitting part E. The light guide member 10 includes a first part 11 with refractive index n1 that is arranged around the light source 20. The first part 11 is in contact with the side surface of the light source 20. A second part 12 with refractive index n2 is arranged around the first part 11. The second part 12 is arranged in contact with the periphery of the first part 11. In other words, the second part 12 is in contact with the side surface of the first part 11. A third part 13 with refractive index n3 is arranged around the second part 12. The third part 13 is in contact with the periphery of the second part 12. In other words, the third part 13 is in contact with the side surface of the second part 12.

[0022] In each embodiment, the planar light source 100 further includes a fourth portion 14 with refractive index n4 that is in contact with the lower surfaces of the first portion 11, the second portion 12, and the third portion 13, and constitutes the lower surface 10L of the light guide member 10. In other words, the lower surfaces of the first portion 11, the second portion 12, and the third portion 13 are in contact with the upper surface of the fourth portion 14. The light reflecting member 30 is also in contact with the fourth portion 14. The entire lower surface of the fourth portion 14 is in contact with the light reflecting member 30. That is, the first portion 11, the second portion 12, and the third portion 13 are not in contact with the light reflecting member 30. The upper surface 10U of the light guide member 10 is preferably flush with each light-emitting portion E. Furthermore, the light guide member 10 is preferably the same thickness with respect to each light-emitting portion E, and it is preferable that multiple light-emitting portions E have the same thickness.

[0023] (First Embodiment) In the first embodiment, the refractive index n2a of the second portion 12A of the light guide member 10A is greater than the refractive index n4a of the fourth portion 14A (n2a>n4a), the refractive index n4a of the fourth portion 14A is greater than the refractive index n1a of the first portion 11A (n4a>n1a), and the refractive index n1a of the first portion 11A is the same as or greater than the refractive index n3a of the third portion 13A (n1a≧n3a). In other words, within the light guide member 10, the relationship n2a>n4a>n1a≧n3a (relationship 1) holds for refractive indices. In other words, in the second and third parts that occupy a large portion of the light guide member 10, the refractive index n2a of the second part 12, which is closer to the light source 20, is greater than the refractive index n4a of the fourth part 14 located below it, while the refractive index n3a of the third part 13, which is further from the light source 20 than the second part 12, is smaller than the refractive index n4a of the fourth part 14 located below it. That is, the refractive index in the vertical direction is reversed on the side closer to the light source 20 and the side further away from it. By using this configuration, it is possible to reduce the third part 13 from becoming too dark or too bright, and to create a planar light source with less brightness unevenness.

[0024] Furthermore, the light-reflecting member 30 comprises a translucent base material and a light-reflecting substance contained within the base material. In the relationship between the light-guiding member 10 and the light-reflecting member 30, the refractive index n30 of the base material of the light-reflecting member 30 is greater than the refractive index n4a of the fourth part 14A of the light-guiding member 10. In other words, in the relationship between the light-guiding member 10 and the light-reflecting member 30, the refractive index relationship n30 > n4a (relationship 2) holds. With both relation 1 and relation 2 of refractive index holding, light can be efficiently propagated to the third part 13A, which is located far from the light source 20, and light can be extracted from the third part 13A to the outside.

[0025] In the planar light source 100A shown in Figure 1B, the third portion 13A of the light guide member 10A extends over the second portion 12A and is integral with the first portion 11A. That is, the inner surface, outer surface, and top of the second portion 12A are in contact with the third portion 13A (first portion 11A). In this case, one of relation 1, n2a>n4a>n1a (=n3a), holds, and relation 2 (n30>n4a) also holds.

[0026] The propagation of light emitted from the light source 20 will be explained in detail. In the planar light source 100A shown in Figure 1B, the light emitted from the light source 20 first enters the first portion 11A (third portion 13A) of the light guide member 10A that is in contact with the light source 20. Then, some of the light from the first portion 11A (third portion 13A) enters the fourth portion 14A. Since the refractive index of the fourth portion 14A is greater than that of the first portion 11A (n4a > n1a), light enters the fourth portion 14A efficiently. Then, the light diffusely reflected by the light-reflective material in the light-reflecting member 30 enters the fourth portion 14A and returns to the first portion 11A. Since the refractive index n4a of the fourth portion 14A is greater than the refractive index n1a of the first portion 11A and less than the refractive index n30 of the base material of the light-reflecting member 30, total internal reflection on the upper and lower surfaces of the fourth portion 14A is reduced, and light is efficiently incident on the light-reflecting member 30. As a result, light near the light source 20, which has a high light density, is efficiently diffusely reflected, and the excessive brightness near the light source 20 can be reduced.

[0027] Furthermore, some of the light incident on the first part 11A, which is in contact with the light source 20, is incident on the second part 12A. Since the refractive index of the second part 12A is greater than that of the first part 11A (n2a > n1a), light is incident on the second part 12A efficiently. In other words, light can be propagated efficiently in the lateral direction.

[0028] In a top view, the portion where the second portion 12A is located constitutes a laminated structure in cross-sectional view, where the fourth portion 14A of the light guide member 10A is located on the light reflecting member 30, the second portion 12A of the light guide member 10A is located on top of that, and the first portion 11A (third portion 13A) is located on top of that. In this laminated structure, the refractive index n1a (n3a) of the first portion 11A (third portion 13A) is smaller than the refractive index n2a of the second portion 12A (n2a>n1a=n3a), the refractive index n2a of the second portion 12A is larger than the refractive index n4a of the fourth portion 14A (n2a>n4a), and the refractive index n30 of the base material of the light reflecting member 30 is also larger than the refractive index n4a of the fourth portion 14A (n30>n4a). In other words, both the second portion 12A and the base material of the light reflecting member 30 have a higher refractive index than the fourth portion 14A. The refractive index n2a of the second part 12A only needs to be greater than the refractive index n4a of the fourth part 14A, and may be greater than, less than, or the same as the refractive index n30 of the base material of the light-reflecting member 30.

[0029] Light incident on the second part 12A from the first part 11A, which is positioned between the light source 20 and the second part 12A, is refracted at the interface between the first part 11A and the second part 12A and travels in a straight line. Some of the light is then incident on the first part 11A (third part 13A) positioned above the second part 12A from its upper surface.

[0030] Furthermore, some of the light incident on the second part 12A is incident on the fourth part 14A. In particular, in the part of the second part 12A closest to the light source 20, the light does not undergo total internal reflection on the lower surface of the second part 12A, but is efficiently incident on the fourth part 14A. The refractive index n30 of the base material of the light-reflecting member 30 located below the fourth part 14A is greater than the refractive index of the fourth part 14A (n30 > n4a). Therefore, light from the fourth part 14A is efficiently incident on the light-reflecting member 30. The light diffusely reflected by the light-reflecting material in the light-reflecting member 30 is then incident on the fourth part 14A and returns to the second part 12A. As a result, the light is efficiently extracted to the outside from the first part 11A (third part 13A) located on the upper surface of the second part 12A.

[0031] A portion of the light incident on the second part 12A is incident on the third part 13A (first part 11A), which is located outside the second part 12A in a top view. Since the refractive index n3a (n1a) of the third part 13A (first part 11A) is smaller than the refractive index n2a of the second part 12A, it can refract the light toward the fourth part 14A. In other words, the amount of light totally reflected in the third part 13A is reduced, and light can be extracted from the top surface of the third part 13A. In addition, a portion of the light incident on the second part 12A is reflected at the interface with the inside of the first part 11A (third part 13A) located on the top surface of the second part 12A, and some of that light is also incident on the third part 13A. Furthermore, a portion of the light incident on the fourth part 14A and diffusely reflected by the light reflecting member 30 also passes through the second part 12A and is incident on the third part 13A.

[0032] The distance from the light source 20 to the outer periphery of the second portion 12A, that is, the distance from the light source 20 to the interface between the second portion 12A and the third portion 13A (first portion 11A) located outside thereof, is preferably set to a distance at which light from the light source 20 is not totally reflected at the fourth portion 14A. That is, if the distance from the light source 20 to the outer periphery of the second portion 12A is too long, total reflection will occur at the upper surface of the fourth portion 14A (lower surface of the second portion 12A), making it difficult to extract the light to the outside from the upper surface of the second portion 12A. As a result, a part of the second portion 12A becomes dark in top view, which is likely to cause luminance unevenness. Further, by setting the distance from the light source 20 to the outer periphery of the second portion 12A to a distance at which total reflection is unlikely to occur at the interface between the second portion 12A and the fourth portion 14A, light that is not extracted to the outside from the upper surface can enter the third portion 13A at an angle that reduces such light.

[0033] In top view, the portion where the third portion 13A (first portion 11A) located outside the second portion 12A is arranged forms a laminated structure in cross-sectional view where the fourth portion 14A of the light guide member 10A is arranged on the light reflection member 30, and the third portion 13A (first portion 11A) of the light guide member 10A is arranged thereon. In this laminated structure, the refractive index n3a of the third portion 13A is smaller than the refractive index n4a of the fourth portion 14A (n3a < n4a), and the refractive index n30 of the base material of the light reflection member 30 is larger than the refractive index n4a of the fourth portion 14A (n30 > n4a). That is, the relationship n3a < n4a < n30 holds.

[0034] A portion of the light incident on the third portion 13A (first portion 11A), which is located outside the second portion 12A, is emitted to the outside from the upper surface of the third portion 13A. Also, a portion of the light incident on the third portion 13A is incident on the fourth portion 14A. Since the refractive index of the fourth portion 14A is greater than that of the third portion 13A (n4a > n3a), light is incident on the fourth portion 14A efficiently. The refractive index n30 of the base material of the light-reflecting member 30 located below the fourth portion 14A is greater than that of the fourth portion 14A (n30 > n4a). Therefore, light from the fourth portion 14A is incident on the light-reflecting member 30 efficiently. The light diffusely reflected by the light-reflecting material in the light-reflecting member 30 is then incident on the fourth portion 14A and returns to the third portion 13A. Since the refractive index n4a of the fourth part 14A is greater than the refractive index n3a of the third part 13A, and less than the refractive index n30 of the base material of the light-reflecting member 30, the amount of light that is totally reflected can be reduced. As a result, light is efficiently emitted to the outside from the upper surface of the third part 13A.

[0035] As described above, in the light-emitting device according to the embodiment, in each light-emitting section E, light that reaches the lower surface of the third section 13A, which is located away from the light source 20 near the outer periphery of the light-emitting section E, is not totally reflected but is incident on the fourth section 14A. The light that passes through the fourth section 14A and is diffusely reflected by the light-reflective material in the light-reflecting member 30 then passes through the fourth section 14A and the third section 13A and is emitted to the outside from the upper surface of the third section 13A. This makes it possible to reduce the problem of the third section 13A, which is located outside the second section 12A, becoming too dark.

[0036] Furthermore, the integration of the first part 11A and the third part 13A facilitates the formation of the light guide member 10. For example, a translucent sheet is placed on the light reflecting member 30 as the fourth part 14A, and then the second part 12A and the light source 20 are placed on the fourth part 14A. The second part 12A may be a pre-molded piece, or an uncured resin material may be placed and then cured to form the second part 12A. The light source 20 can be placed before or after the second part 12A is placed. Then, the uncured resin material can be placed so as to cover the second part 12A and the light source 20, and cured to form the first part 11A (third part 13A). This shortens the process compared to forming the first part 11A and the third part 13A separately.

[0037] In the modified example 1-1 shown in Figure 1C, the planar light source 100B has a first part 11A and a third part 13A that are separate. In modified example 1-1, the third part 13A of the light guide member 10A extends over the first part 11A and the second part 12A. Furthermore, the third part 13A also extends over the light source 20. In other words, the entire upper surface of the light guide member 10A is composed of the third part 13A. The other configurations are the same as the planar light source 100A, so we will mainly explain the differences. In this modified example 1-1 as well, relations 1 and 2 hold for each part of the light guide member 10A. That is, among n2a>n4a>n1a≧n3a, 2a>n4a>n1a>n3a and n30>n4a.

[0038] In modified example 1-1, a third portion 13A, which has a lower refractive index than the first portion 11A, is placed on top of the first portion 11A. When the light source 20 has a structure as shown in Figure 8, that is, comprising a light-emitting element 21 and a light-transmitting first sealing member 221, if the refractive index n221 of the first sealing member is greater than the refractive index n1a of the first portion 11A, the amount of light extracted from the light source 20 can be increased.

[0039] In the modified example 1-2 of the planar light source 100C shown in Figures 2A and 2B, the first part 11A and the third part 13A are separate components. Furthermore, it differs from modified example 1-1 in that the upper surfaces of the first part 11A and the second part 12A are exposed, that is, they constitute part of the upper surface of the light guide member 10. In a top view, the portion where the first part 11A is located constitutes a laminated structure in a cross-sectional view, where the upper part of the fourth part 14A of the light guide member 10 is located on the light reflecting member 30, and the first part 11A is located on top of that. In a top view, the portion where the second part 12A is located constitutes a laminated structure in a cross-sectional view, where the fourth part 14A of the light guide member 10 is located on the light reflecting member 30, and the second part 12A is located on top of that. In this modified example 1-2 as well, relationships 1 and 2 hold true for each part of the light guide member 10A. That is, n2a > n4a > n1a ≥ n3a, and n30 > n4a.

[0040] In the planar light source 100C, the light emitted from the light source 20 first enters the first portion 11A. Subsequently, some of the light is emitted to the outside from the upper surface of the first portion 11A. Some of the light that enters the second portion 12A is also emitted to the outside from the upper surface of the second portion 12A. Then, the light that enters the third portion 13A is refracted towards the fourth portion 14A at the interface with the second portion 12A, efficiently entering the fourth portion 14A, being diffusely reflected by the light reflecting member 30, and emitted to the outside from the upper surface of the third portion 13A. In this way, the arrangement of the second portion 12A makes it easier for light to be emitted to the outside from the third portion 13A, and reduces the problem of the third portion 13A becoming too dark.

[0041] (Second Embodiment) Figures 3 to 5 show the planar light source 100 (100D to 100F) according to the second embodiment. The planar light source 100D has basically the same structure (shape) as the planar light source 100A of the first embodiment. The planar light source 100E has basically the same structure (shape) as the planar light source 100B of the first embodiment. The planar light source 100F has basically the same structure (shape) as the planar light source 100C of the first embodiment. The second embodiment differs from the first embodiment in that the first part 11B is composed of a base material 11BB with a refractive index n1b and scattering particles S with a refractive index nS contained in the base material 11BB, and the third part 13B is composed of a base material 13BB with a refractive index n3b and scattering particles S with a refractive index nS contained in the base material 13BB.

[0042] In the second embodiment, the refractive index n2b of the second portion 12B of the light guide member 10B is greater than the refractive index n1b of the first portion 11B (n2b>n1b), the refractive index n1b of the first portion 11B is the same as or greater than the refractive index n3b of the third portion 13B (n1b≧n3b), and the refractive index n3b of the third portion 13B is greater than the refractive index n4b of the fourth portion 14B (n3b>n4b). Also, the refractive index nS of the scattering particle S is different from the refractive index n1b of the first portion 11B and the refractive index n3b of the third portion 13B (n1≠nS, n3≠nS). In other words, in the second embodiment, within the light guide member 10B, the relationships n2b>n1b≧n3b>n4b (relationship 3) and n1b≧n3b>nS (relationship 4) partially hold.

[0043] Furthermore, the light-reflecting member 30 comprises a translucent base material and scattering particles S contained within the base material. In the relationship between the light-guiding member 10 and the light-reflecting member 30, the refractive index n30 of the base material of the light-reflecting member 30 is greater than the refractive index n4a of the fourth portion 14A of the light-guiding member 10. In other words, the relationship n30 > n4b (relationship 5) holds in the relationship between the light-guiding member 10 and the light-reflecting member 30. Relationship 2 in the first embodiment and relation 5 in the second embodiment are the same. In the second embodiment, which includes scattering particles S, all of the refractive index relationships 3, 4, and 5 hold, allowing light to be efficiently propagated to the third portion 13B, which is located far from the light source 20, and allowing light to be extracted to the outside from the third portion 13A.

[0044] In the planar light source 100D shown in Figure 3, the third portion 13B of the light guide member 10B extends over the second portion 12B and is integral with the first portion 11B. That is, the inner surface, outer surface, and top surface of the second portion 12B are in contact with the third portion 13B (first portion 11B). In this case, one of relation 3, n2b>n1b=n3b>n4b, and one of relation 4, n3b ⇒ n1b=n3b>nS and n30>n4b (relation 5), hold.

[0045] In a top view, the portion where the first portion 11B in contact with the light source 20 is located constitutes a laminated structure in a cross-sectional view, where the fourth portion 14B of the light guide member 10 is located on the light reflecting member 30, and the first portion 11B (third portion 13B) is located on top of that. In this laminated structure, the refractive index n1b of the base material 1BB of the first portion 11B is greater than the refractive index n4b of the fourth portion 14B (n1b>n4b). In this respect, it is the opposite of the relationship between the refractive indices of the first portion 11A and the fourth portion 14A in the first embodiment. Furthermore, the refractive index n1b of the base material 11BB of the first portion 11B is greater than the refractive index nS of the scattering particles S contained in the base material 11BB (n1b>nS). In addition, the refractive index n30 of the base material of the light reflecting member 30 is greater than the refractive index n4b of the fourth portion 14A (n30>n4a).

[0046] The propagation of light emitted from the light source 20 will be explained in detail. The light emitted from the light source 20 first enters the base material 11BB of the first part 11B that is in contact with the light source 20, and is irradiated by scattering particles S contained in the base material 11BB, where it is scattered. Subsequently, some of the light is emitted to the outside from the upper surface of the first part 11B. In addition, some of the light enters the fourth part 14B.

[0047] In a top view, the portion where the second portion 12B is positioned constitutes a laminated structure in a cross-sectional view, where the fourth portion 14B of the light guide member 10 is positioned on the light reflecting member 30, the second portion 12B of the light guide member 10 is positioned on top of that, and the first portion 11B is positioned on top of that. In this laminated structure, the refractive index n2b of the second portion 12B is greater than the refractive index n4b of the fourth portion 14B (n2a>n4a), and the refractive index n30 of the base material of the light reflecting member 30 is also greater than the refractive index n4b of the fourth portion 14B (n30>n4b). In other words, both the second portion 12B and the base material of the light reflecting member 30 have a greater refractive index than the fourth portion 14B. The refractive index n2a of the second portion 12A may be greater than, less than, or the same as the refractive index n30 of the base material of the light reflecting member 30.

[0048] In the second embodiment, since the first portion 11B in contact with the light source 20 contains scattering particles S, the angle of light incident from the first portion 11B to the second portion 12B is different from that of the first embodiment. That is, light scattered by the scattering particles S of the first portion 11B in contact with the light source 20 and propagating in various directions is incident on the second portion 12B.

[0049] Furthermore, some of the light incident on the second part 12B is incident on the fourth part 14B. In particular, in the part of the second part 12A closest to the light source 20, the light does not undergo total internal reflection on the lower surface of the second part 12A, but is efficiently incident on the fourth part 14A. The refractive index n30 of the base material of the light-reflecting member 30 located below the fourth part 14B is greater than the refractive index of the fourth part 14B (n30 > n4b). Therefore, light from the fourth part 14B is efficiently incident on the light-reflecting member 30. The light diffusely reflected by the light-reflecting material in the light-reflecting member 30 is then incident on the fourth part 14B and returns to the second part 12B. As a result, the light is efficiently extracted to the outside from the first part 11A (third part 13A) located on the upper surface of the second part 12A.

[0050] A portion of the light incident on the second portion 12B is incident on the third portion 13B, which is located outside the second portion 12B. Also, a portion of the light reflected at the interface between the upper surface of the second portion 12B and the first portion 11B (third portion 13B) located above it is incident on the third portion 13B, which is located outside the second portion 12B. No light from the first portion 11B, which is in contact with the light source 20, propagates through the first portion 11B located on the upper surface of the second portion 12B, and reaches the third portion 13B, which is located outside the second portion 12B. Furthermore, a portion of the light incident on the fourth portion 14B and diffusely reflected by the light reflecting member 30 is incident on the second portion 12B and then incident on the third portion 13B.

[0051] The distance from the light source 20 to the outer periphery of the second portion 12B, that is, the distance from the light source 20 to the interface between the second portion 12B and the third portion 13BA, is preferably such that the light from the light source 20 does not undergo total internal reflection by the fourth portion 14B. This is because if the interface between the second portion 12B and the third portion 13B is far from the light source 20, the light will undergo total internal reflection between the second portion 12B and the fourth portion 14B in the region of the second portion 12B that is far from the light source 20, resulting in less light being extracted from the upper surface of the second portion 12B. The second portion 12B is incident on light scattered by the scattering particle S in the first portion 11B, and therefore differs from the first embodiment in that light incident at different angles of incidence is incident from random positions within the second portion 12B.

[0052] The refractive index n3b of the base material 13BB of the third portion 13B located outside the second portion 12B is smaller than the refractive index n2b of the second portion 12B (n3b < n2b). Therefore, the light traveling on the outer side surface of the third portion 13B can be refracted in the direction of the fourth portion 14B. Also, the refractive index nS of the scattering particles S contained in the base material 13BB of the third portion 13B is smaller than the refractive index n3b of the base material 13BB (nS < n3b). Therefore, light is scattered at the interface between the base material 13BB and the scattering particles S, and a part of it is emitted to the outside from the upper surface of the third portion 13B located outside the second portion 12B. Also, a part of the light incident on the third portion 13B located outside the second portion 12B is incident on the fourth portion 14B. The length from the outer periphery of the second portion 12B, that is, from the interface between the second portion 12B and the third portion 13B to the light source 20 is preferably a distance at which the light from the light source 20 is not totally reflected at the fourth portion 14A.

[0053] In a top view, the portion where the third portion 13B located outside the second portion 12B is arranged forms a laminated structure in a cross-sectional view where the upper part of the fourth portion 14B of the light guide member 10 is arranged on the light reflecting member 30, and the third portion 13B of the light guide member 10 is arranged thereon. In this laminated structure, the refractive index n3b of the third portion 13B is larger than the refractive index n4b of the fourth portion 14B (n3b > n4b), and the refractive index n30 of the base material of the light reflecting member 30 is larger than the refractive index n4b of the fourth portion 14B (n30 > n4b). The refractive index n3b of the third portion 13B may be the same as, smaller than, or larger than the refractive index n30 of the base material of the light reflecting member 30.

[0054] A part of the light incident on the third portion 13B located outside the second portion 12B is emitted to the outside from the upper surface of the third portion 13B. Also, a part of the light incident on the third portion 13B located outside the second portion 12B is incident on the fourth portion 14B. Since the refractive index of the fourth portion 14B is smaller than that of the base material of the third portion 13B (n4b < n3b), light is totally reflected at these interfaces. Since a part of the totally reflected light is not taken out from the upper surface of the third portion 13B, it is possible to reduce the situation where the third portion 13B located outside the second portion 12B becomes too bright.

[0055] As described above, in the light-emitting device according to the second embodiment, in each light-emitting section E, the light that reaches the third section 13B located outside the second section 12B, which is located away from the light source 20, that is, the light that passes through the second section 12B and is refracted at the interface of the third section 13B, exceeds the critical angle when it is incident on the interface between the lower surface of the third section 13B and the upper surface of the fourth section 14B. Then, the light that is totally reflected at the interface between the third section 13B and the fourth section 14B, which is located outside the second section 12B, is scattered by scattering particles S within the third section 13B and is emitted to the outside from the upper surface of the third section 13B, which is located outside the second section 12B. This makes it possible to reduce the problem of the third section 13B, which is located outside the second section 12B, becoming too dark.

[0056] In the modified example 2-1 shown in Figure 4, the planar light source 100E has a first part 11B and a third part 13B that are separate. Modified example 2-1 differs from modified example 1-1 in that the first part 11B and the third part 13B are equipped with scattering particles S, but the positional relationships of each part are the same. In modified example 2-1, the third part 13B of the light guide member 10B extends over the first part 11B and the second part 12A. Furthermore, the third part 13B also extends over the light source 20. In other words, the entire upper surface of the light guide member 10B is composed of the third part 13B. Since the other configurations are the same as the planar light source 100B, we will mainly explain the differences. Even in this modified example 2-1, relations 3, 4, and 5 hold true for each part of the light guide member 10B. In other words, the following relationships hold: n2b>n1b≧n3b>n4b (relation 3), n1b≧n3b>nS (relation 4), and n30>n4b (relation 5).

[0057] In modified example 2-1, a third part 13B is placed on the first part 11B, the third part 13B having a base material 13BB with a refractive index smaller than or the same as that of the first part 11B. When the light source 20 has a structure as shown in Figure 8, that is, a light-emitting element 21 and a light-transmitting first sealing member 221, if the refractive index n221 of the first sealing member is greater than the refractive index n1b of the first part 11B, the amount of light extracted from the light source 20 can be increased.

[0058] In the modified example 2-2 shown in Figure 5, the planar light source 100F has a first part 11B and a third part 13B that are separate. Furthermore, it is the same as modified example 1-2 in that the first part 11B and the second part 12B constitute a part of the upper surface of the light guide member 10, but it differs from modified example 1-2 in that the first part 11B and the third part 13B are equipped with scattering particles S. In this modified example 2-2 as well, relations 3, 4, and 5 hold true for each part of the light guide member 10B. That is, the relationships n2b>n1b≧n3b>n4b (relationship 3), n1b≧n3b>nS (relationship 4), and n30>n4b (relationship 5) hold true.

[0059] In the planar light source 100F, a portion of the light emitted from the light source 20 is emitted directly from the top surface of the first section 11B. Furthermore, the light scattered by the scattering particles S within the first section 11B is also emitted from the top surface of the first section 11B. A portion of the light incident on the second section 12B is also emitted from the top surface of the second section 12B. And the light incident on the third section 13B is scattered by the scattering particles S within the third section 13B and is therefore emitted from the top surface of the third section 13B. In this way, by adding scattering particles S within the third section 13B, it is possible to reduce the problem of the third section 13B becoming too dark.

[0060] In both the first and second embodiments, it is possible to reduce the problem of the third portion 13 becoming too dark.

[0061] The following describes in detail the components common to each embodiment.

[0062] In each embodiment, in each light-emitting section E, the first portion 11 of the light guide member 10 is arranged around the light source 20 located at the center of the light guide member 10 in a top view. The first portion 11 is in contact with the side surface of the light source 20. The first portion 11 constitutes a part of the top surface 10U of the light guide member 10. The first portion 11 can be arranged so as to expose the top surface of the light source 20. In other words, the first portion 11 can have the same thickness as the height of the light source 20, or a thickness less than the height of the light source 20. Alternatively, the first portion 11 may be arranged in contact with the light source 20. In other words, the thickness of the first portion 11 can be greater than the height of the light source 20. In a top view, the outer circumference of the first portion 11 is circular, as shown in Figure 1A. In a top view, the area of ​​the portion enclosed by the outer circumference of the first portion 11 can be, for example, 2.1 times or more and 6.8 times or less the area of ​​the light source 20. The interface between the first part 11 and the second part 12 may be a plane perpendicular to the upper surface 10U or lower surface 10D of the light guide member 10, or it may be inclined, as shown in Figure 1B in cross-sectional view.

[0063] In the first embodiment, the refractive index n1a of the first part 11A can be between 1.40 and 1.59. The refractive index n1a of the first part 11A is smaller than the refractive index n2a of the second part 12A. The difference in refractive index between the first part 11A and the second part 12A can be, for example, between 0.04 and 0.17. This reduces the problem of the area near the light source 20 becoming too bright.

[0064] In the first embodiment, the first part 11A and the third part 13A are either a single unit or separate. The refractive index n1a of the first part 11A is the same as or greater than the refractive index n3a of the third part 13A.

[0065] In the first embodiment, the refractive index n1a of the first portion 11A is smaller than the refractive index n4a of the fourth portion 14A. The difference in refractive index between the first portion 11A and the fourth portion 14A can be, for example, between 0.01 and 0.06. This reduces total internal reflection of light on the upper surface of the fourth portion 14A, thereby reducing excessive brightness near the light source 20.

[0066] In the second embodiment, the refractive index n1b of the base material 11BB of the first portion 11B can be between 1.50 and 1.59. The refractive index n1b of the base material 11BB of the first portion 11B is smaller than the refractive index n2b of the second portion 12B. The difference in refractive index between the base material 11BB of the first portion 11B and the second portion 12BA can be, for example, between 0.04 and 0.17. This reduces the problem of the area near the light source 20 becoming too bright.

[0067] In the second embodiment, the first portion 11A and the third portion 13A are either a single unit or separate. The refractive index n1a of the first portion 11A is the same as or greater than the refractive index n3a of the base material 13BB of the third portion 13A.

[0068] In the second embodiment, the refractive index n1b of the base material 11BB of the first portion 11B is greater than the refractive index n4a of the fourth portion 14A. The difference in refractive index between the base material 11BB of the first portion 11A and the fourth portion 14A can be, for example, 0.01 or more and 0.05 or less.

[0069] The second part 12 can be an annular shape with a rectangular outer perimeter in a top view, as shown in Figures 1A and 2A. In the example shown in Figures 1A and 2A, the corners of the second part 12 are positioned at the center of each side of the rectangular light-emitting part E in a top view. In other words, the second part 12, which has a rectangular outer perimeter in a top view, is positioned so as to be rotated 45 degrees relative to the rectangular light-emitting part E in a top view. This makes it easier to position the third part 13 in a region that is far from the light source 20 and prone to total internal reflection.

[0070] As shown in Figure 6, when the light-emitting portion E of the light guide member 10 is triangular in a top view, the second portion 12 can be hexagonal. This makes it easier to position the third portion 13 near each corner of the triangle that is far from the light source 20. Here, each light-emitting portion E is an equilateral triangle, and the second portion 12 is a hexagon with three short sides and three long sides. Each short side is sandwiched between two long sides. The lengths of each short side and each long side are the same.

[0071] As shown in Figure 7, when the light-emitting portion E of the light guide member 10 is hexagonal in a top view, the second portion 12 can also be hexagonal. In the example shown in Figure 7, the corners of the second portion 12 are positioned at the center of each side of the light-emitting portion E, which has a hexagonal shape in a top view. In other words, the second portion 12, whose outer circumference is hexagonal in a top view, is positioned so as to be rotated 30 degrees relative to the light-emitting portion E, which is hexagonal in a top view. This makes it easier to position the third portion 13 at the corner of the light-emitting portion E, which is located away from the light source 20.

[0072] The interface between the second part 12 and the third part 13 may be a plane perpendicular to the upper surface 10U or lower surface 10D of the light guide member 10 in a cross-sectional view, as shown in Figure 1B, or it may be inclined. Furthermore, when the first part 11 (third part 13) is located above the second part 12, the interface between the second part 12 and the first part 11 (third part 13) located above it, i.e., the upper surface of the second part 12, may be a plane parallel to the upper surface 10U or lower surface 10L of the light guide member 10 in a cross-sectional view, or it may be an inclined surface. In addition, the second part 12 as a whole or its upper surface may be a curved surface such as an arc in a cross-sectional view.

[0073] The area of ​​the portion enclosed by the perimeter of the second portion 12 can be, for example, 20% to 50% of the area of ​​the portion enclosed by the perimeter of the first portion 11.

[0074] In the first embodiment, the refractive index n2a of the second portion 12A can be between 1.40 and 1.60. The refractive index n2a of the second portion 12A is greater than the refractive index n3a of the third portion 13A. The difference in refractive index between the second portion 12A and the third portion 13A can be, for example, between 0.10 and 0.17. This allows light traveling toward the outer side surface of the third portion 13A to be refracted toward the fourth portion 14A, and light can be efficiently extracted from the upper surface of the third portion 13A.

[0075] In the first embodiment, the refractive index n2a of the second portion 12A is greater than the refractive index n4a of the fourth portion 14A. The difference in refractive index between the second portion 12A and the fourth portion 14A can be, for example, 0.01 or more and 0.1 or less. As a result, some of the light that passes through the second portion 12A is totally reflected and incident on the third portion 13A, which reduces the second portion 12A from becoming excessively bright.

[0076] In the second embodiment, the refractive index n2b of the second portion 12B can be between 1.40 and 1.60. The refractive index n2b of the second portion 12B is greater than the refractive index n3b of the base material of the third portion 13B. The difference in refractive index between the second portion 12A and the third portion 13A can be, for example, between 0.05 and 0.10.

[0077] In the second embodiment, the refractive index n2b of the second portion 12B is greater than the refractive index n4b of the fourth portion 14B. The difference in refractive index between the second portion 12B and the fourth portion 14B can be, for example, 0.01 or more and 0.1 or less. This reduces the problem of the second portion 12B becoming excessively bright because some of the light that passes through the second portion 12B is totally reflected and incident on the third portion 13B.

[0078] The third portion 13 of the light guide member 10 is positioned around the second portion 12 in a top view. The third portion 13 is in contact with the outer surface of the second portion 12. The third portion 13 constitutes a part of the top surface 10U of the light guide member 10. The outer circumference of the third portion 13 is also the outer circumference of each light-emitting portion E. In a top view, the shape of the third portion 13 can be a rectangle on its outer circumference, as shown in Figure 1A. However, as shown in Figure 5 or Figure 6, the outer shape of the third portion 13 can be a polygon such as a hexagon or a triangle. The thickness of the third portion 13 can be about the same as the thickness of the first portion 11.

[0079] In the first embodiment, the refractive index n3a of the third portion 13A is smaller than the refractive index n4a of the fourth portion 14A. The difference in refractive index between the third portion 13A and the fourth portion 14A can be, for example, between 0.01 and 0.07. This reduces the amount of light totally reflected at the lower surface of the third portion 13A, and allows light to be efficiently emitted to the outside from the upper surface of the third portion 13A.

[0080] In the second embodiment, the refractive index n3b of the base material 13BB of the third portion 13B is greater than the refractive index n4b of the fourth portion 14B. The difference in refractive index between the base material 13BB of the third portion 13B and the fourth portion 14B can be, for example, 0.01 or more and 0.04 or less. This reduces the total internal reflection of light incident on the lower surface of the third portion 13B, which can cause the third portion 13B to become excessively bright.

[0081] The fourth portion 14 of the light guide member 10 constitutes the lower surface 10L of the light guide member 10. That is, the fourth portion 14 is in contact with the lower surfaces of the first portion 11, the second portion 12, and the third portion 13. The fourth portion 14 may be positioned below the light source 20. In that case, it may be in contact with the light source 20 or it may be separated from it.

[0082] The refractive index n4a of the fourth part 14A is between 1.42 and 1.65.

[0083] As the material for the light guide member 10, a thermoplastic resin such as acrylic, polycarbonate, cyclic polyolefin, polyethylene terephthalate, or polyester, or a resin material such as epoxy or silicone, or an optically transparent material such as glass can be used. Silicone resin is preferred as the material for the first part 11. Polycarbonate is preferred as the material for the second part 12. Silicone resin is preferred as the material for the third part 13. Acrylic is preferred as the material for the fourth part 14.

[0084] As the material for the scattering particles S, at least one selected from, for example, titanium oxide, zirconium oxide, aluminum oxide, silicon oxide, acrylic, etc., can be used. The median particle size of the scattering particles S can be, for example, 1 μm or more and 30 μm or less. The median particle size of the scattering particles S can be measured, for example, by a particle size measuring device (model number Mastersizer 3000+) manufactured by Malvern Panalytical. The content of the scattering particles S in the third part 13B can be 2% by mass or more and 25% by mass or less, and can be appropriately adjusted depending on the shape or size of the light-emitting part E.

[0085] (light source) The light source 20 is positioned at the center of each light-emitting portion E of the planar light source 100 when viewed from above. The light source 20 can emit light in the upward and lateral directions. The light emitted from the light source 20 mainly enters the first portion 11 of the light guide member 10.

[0086] The light source 20 includes a light-emitting element 21. The light source 20 may consist only of the light-emitting element 21, or, as shown in Figure 8, it may include the light-emitting element 21 and a sealing member 22 that seals the light-emitting element 21.

[0087] The light-emitting element 21 includes a semiconductor stack 211 and a pair of positive and negative electrodes 212. The semiconductor stack 211 has an upper surface and a lower surface opposite the upper surface. The electrodes 212 are located on the lower surface of the semiconductor stack 211.

[0088] The light-emitting element 21 can utilize known semiconductor light-emitting elements such as light-emitting diodes. The composition, emission peak wavelength, size, and number of elements of the semiconductor laminate 211 of the light-emitting element 21 can be appropriately selected according to the purpose. The light-emitting element 21 can be selected to emit light of any wavelength from ultraviolet to visible light. For example, as a light-emitting element 21 that emits ultraviolet, blue, and green light, the semiconductor laminate 211 can be made of nitride semiconductor (In x Al y Ga 1-x-y A light-emitting element 21 using N (0 ≤ X, 0 ≤ Y, X + Y ≤ 1) can be used. Examples of light-emitting elements 21 that emit red light include GaAs, GaP, and InP. Various emission wavelengths can be selected depending on the material of the semiconductor laminate 211 and its mixed crystallinity. The shape of the semiconductor laminate 211 can be a quadrilateral such as a square or rectangle, or a polygon such as a triangle or hexagon when viewed from above. The size of the semiconductor laminate 211 when viewed from above can be, for example, a side length of 500 μm or more and 3000 μm or less. The thickness of the semiconductor laminate 211 can be, for example, 25 μm or more and 40 μm or less. For the electrodes 212 of the light-emitting element 21, for example, copper, gold, nickel, etc. can be used. The thickness of the electrodes 212 can be, for example, 10 μm or more and 50 μm or less.

[0089] The light source 20 shown in Figure 8 includes a sealing member 22 that seals the light-emitting element 21 so that at least the electrodes 212 of the light-emitting element 21 are exposed. The sealing member 22 may include resin or glass. Examples of resins include epoxy, silicone, polyethylene terephthalate, and the like.

[0090] The light source 20 may include a light-transmitting member and a light-reflective member as the sealing member 22.

[0091] As shown in Figure 8, the light source 20 may include a translucent first sealing member 221 that is positioned in contact with the side and top surfaces of the semiconductor laminate 211 of the light-emitting element 21. The first sealing member 221 constitutes a part of the side surface of the light source 20, and the light emitted from the light-emitting element 21 is mainly emitted to the outside through the first sealing member 221.

[0092] The first sealing member 221 is translucent, allowing at least light from the light-emitting element 21 to pass through, transmitting 60% or more of the light emitted from the light-emitting element 21, preferably 90% or more. As the resin material, thermosetting resin materials such as epoxy and silicone can be used. The first sealing member 221 can be made solely from these translucent resin materials. Alternatively, a translucent resin material can be used as the base material, and a phosphor can be included as a wavelength conversion material.

[0093] It is preferable that the refractive index n221 of the base material of the first sealing member 221 is smaller than the refractive index n1 of the first portion 11 of the light guide member 10. This allows light from the light-emitting element 21 to be efficiently incident into the first portion 11A.

[0094] Examples of phosphors that can be used include yttrium-aluminum-garnet phosphors, lutetium-aluminum-garnet phosphors, terbium-aluminum-garnet phosphors, CCA phosphors, SAE phosphors, chlorosilicate phosphors, silicate phosphors, oxynitride phosphors such as β-sialon phosphors or α-sialon phosphors, LSN phosphors, BSESN phosphors, SLA phosphors, CASN phosphors or SCASN phosphors, fluoride phosphors such as KSF phosphors, KSAF phosphors or MGF phosphors, quantum dots having a perovskite structure, group II-VI quantum dots, group III-V quantum dots, or quantum dots having a chalcopyrite structure.

[0095] Examples of light scattering agents that can be used include titanium dioxide, silicon dioxide, aluminum oxide, zinc oxide, magnesium oxide, zirconium oxide, yttrium oxide, calcium fluoride, magnesium fluoride, niobium pentoxide, barium titanate, tantalum pentoxide, barium sulfate, or particles of glass, etc.

[0096] Furthermore, the light source 20 may include a second sealing member 222 positioned to be in contact with the electrode 212 of the light-emitting element 21. The second sealing member 222 is in contact with the lower surface of the first sealing member 221 and is positioned so that the lower surface of the electrode 212 is exposed. The second sealing member 222 constitutes a part of the lower surface of the light source 20. The second sealing member 222 constitutes a part of the side surface of the light source 20. The second sealing member 222 is light-reflective and reflects at least a portion of the light emitted from the light-emitting element 21.

[0097] Furthermore, the light source 20 may include a third sealing member 223 positioned in contact with the upper surface of the first sealing member 221. The third sealing member 223 constitutes the upper surface of the light source 20. The third sealing member 223 constitutes a part of the side surface of the light source 20. The third sealing member 223 is light-reflective and reflects at least a portion of the light emitted from the light-emitting element 21. Note that the third sealing member 223 can be omitted. That is, the upper surface of the light source 20 can be made up of the first sealing member 221.

[0098] The second sealing member 222 and the third sealing member 223 have a reflectance of 60% or more, preferably 90% or more, with respect to light emitted from the light-emitting element 21. The material of the second sealing member 22 can be, for example, metal, a white resin member, a white inorganic member, a DBR film, etc. A white resin member is particularly preferred for the material of the second sealing member 22. As a white resin member, for example, epoxy, silicone, polyethylene terephthalate, etc. can be used as the base material, and particles such as titanium dioxide, silicon dioxide, aluminum oxide, zinc oxide, magnesium oxide, zirconium oxide, yttrium oxide, calcium fluoride, magnesium fluoride, niobium pentoxide, barium titanate, tantalum pentoxide, barium sulfate, or glass can be used as scattering particles on these base materials. The reflectance of the second sealing member 222 and the third sealing member 223 may be the same or different.

[0099] The light source 20 shown in Figure 8 is an example in which the sealing member 22 comprises a first sealing member 221, a second sealing member 222, and a third sealing member 223. However, the light source 20 is not limited to this, and may comprise only one or two of these members. Furthermore, the light source 20 shown in Figure 8 is an example in which the sealing member 22 is arranged so that only the lower surface of the electrode 212 is exposed. However, the light source 20 is not limited to this, and may comprise the sealing member 22 such that at least a portion of the semiconductor laminate 211 of the light-emitting element 21 is exposed.

[0100] The planar light source 100 includes a light reflecting member 30 positioned on the lower surface 10L side of the light guide member 10. The light reflecting member 30 is positioned in contact with the fourth portion 14 that constitutes the lower surface 10L of the light guide member 10.

[0101] The light-reflecting member 30 has a reflectance of 70% to 98% with respect to light emitted from the light source 20, preferably 90% to 95%. The material of the light-reflecting member 30 can be, for example, a white resin material. Examples of white resin materials include those containing a light-reflecting substance in the base material. Examples of light-reflecting substances include resin materials containing titanium oxide, aluminum oxide, silicon oxide, zinc oxide, gas, etc. As the base material, translucent thermosetting resin materials such as epoxy, silicone, and polyethylene terephthalate can be used. The light-reflecting member 30 may be provided with through holes that expose the electrodes of the light source 20. This allows power to be supplied to the light source 20 from the wiring of the substrate placed beneath the light-reflecting member 30.

[0102] The refractive index n30 of the base material of the light-reflecting member 30 can be 1.60 or more and 1.70 or less.

[0103] (Light adjustment component) The light-adjusting member 40 has reflectivity and light transmission properties to the light emitted from the light source 20. A portion of the light emitted from the light source 20 is reflected by the light-adjusting member 40, and another portion is transmitted through the light-adjusting member 40. The transmittance of the light-adjusting member 40 with respect to the peak wavelength of the light source 20 is preferably 1% to 50%, and more preferably 3% to 30%. The light-adjusting member 40 may be composed of a single layer or a laminate of multiple layers.

[0104] The light adjustment member 40 is positioned above the light source 20. By positioning the light adjustment member 40 above the light source 20, it is possible to reduce the excessive brightness in the area directly above the light source 20.

[0105] The light adjustment member 40 is also located above the light guide member 10. In the example shown in Figure 1A, the light adjustment member 40 is located above the first portion 11 of the light guide member 10 and above a portion of the second portion 12. In the example shown in Figure 2A, the light adjustment member 40 is located above the first portion of the light guide member 10 and above a portion of the second portion 12. By positioning the light adjustment member 40 above a portion of the light guide member 10 that is located close to the light source 20, it is possible to reduce the excessive brightness in the area directly above the light guide member 10 located near the light source 20.

[0106] The top view shape of the light adjustment member 40 can be circular, polygonal, or the like. The outer edge of the light adjustment member 40 can be a straight line, a curve, or a combination of these. In the example shown in Figure 1A, a light adjustment member 40 is shown that has a straight portion and an inwardly recessed semi-circular portion, and is generally rectangular in shape. Also in the example shown in Figure 1A, a light adjustment member 40 is shown that is rotated 45 degrees relative to the light guide member 10, which has a rectangular outer shape when viewed from above. This makes it possible to improve the brightness in parts that are far from the light source 20 and tend to have low brightness (for example, the corners of the light guide member, which has a rectangular top view). In addition, the four sides of the second portion 12, which has a rectangular outer shape when viewed from above, are parallel to the straight portion of the outer periphery of the light adjustment member 40.

[0107] The light adjustment member 40 preferably has at least one through-hole 41. Having a through-hole 41 in the light adjustment member 40 makes it easier to adjust the brightness in the region directly above the light adjustment member 40. For example, by changing the size and position of the through-hole 41, the light from the light source 20 that is blocked by the light adjustment member 40 can be adjusted. This makes it easier to adjust the brightness in the region directly above the light adjustment member 40, thus making it easier to reduce brightness unevenness in the planar light source 100. In a top view, the through-hole 41 can be located away from the outer edge of the light adjustment member 40.

[0108] The through-hole 41 of the light adjustment member 40 is preferably located away from the light source 20 when viewed from above. This reduces the likelihood of the area directly above the light source 20 becoming excessively bright.

[0109] The shape of the through-hole 41 in a top view is not particularly limited. In the example shown in Figure 1A, the shape of the through-hole 41 in a top view is circular. The shape of the through-hole 41 in a top view may be elliptical, or a polygon such as a triangle, square, hexagon, or octagon. The shape of the through-hole 41 in a top view may include linear portions. For example, the shape of the through-hole 41 in a top view may include V-shaped or L-shaped portions extending in two directions.

[0110] As the light-adjusting member 40, for example, a resin member containing a gas such as nitrogen and / or oxygen, or a resin member containing scattering particles can be used. As the resin member of the light-adjusting member 40, for example, a thermoplastic resin such as acrylic, polycarbonate, cyclic polyolefin, polyethylene terephthalate or polyester, or a thermosetting resin such as epoxy or silicone can be used. As scattering particles for the light-adjusting member 40, for example, particles such as titanium dioxide, silicon dioxide, aluminum oxide, zinc oxide, magnesium oxide, zirconium oxide, yttrium oxide, calcium fluoride, magnesium fluoride, niobium pentoxide, barium titanate, tantalum pentoxide, barium sulfate, or glass can be used. The light-adjusting member 40 contains both gas and scattering particles. That's good too.

[0111] (substrate) The planar light source 100 may have a substrate below the light-reflecting member 30. The substrate comprises an insulating base material and wiring. The wiring on the substrate and the electrodes of the light source 20 are electrically connected by a conductive material such as solder. The substrate may be a rigid substrate or a flexible substrate. For example, ceramics or resin can be used as the base material. Specific materials for ceramics include silicon nitride and aluminum oxide. Examples of resins include composite materials such as phenol, epoxy, polyimide, BT resin, polyphthalamide, polyethylene terephthalate, unsaturated polyester, and glass epoxy. These can be used in single layers or by laminating multiple layers. When multiple layers are used, they can be laminated with an adhesive between them. Examples of wiring include metal plates, metal foils, etc., electroplated or electroless plated substrates, or conductive paste placed and cured. Specific materials for wiring include materials mainly composed of metals such as copper, silver, and aluminum. [Examples]

[0112] Assuming a light source comprising a light-emitting element 21 and a sealing member 22 as shown in Figure 8, the following structures were simulated. Examples 1 and 2 adopted the structure of planar light sources 100A and 100B, respectively, which include a light guide member 10 comprising a first part 11A to a fourth part 14A, as shown in Figures 1B and 1C. Example 3 adopted the structure of planar light source 100D, which includes a light guide member 10 comprising a first part 11B to a fourth part 14B, as shown in Figure 3. In Example 3, the first part 11B and the third part 13B contain scattering particles S. In the reference example, a planar light source is used that employs a light guide member in which the second and third parts are integrated, as shown in Figure 1A, etc.

[0113] The light source 20 measures 0.85 mm × 0.85 mm in a top view and has a height of 0.25 mm. Each light-emitting part E of the light guide member 10 measures 7.27 mm × 7.27 mm in a top view and has a thickness of 0.275 mm. The first part 11 has a circular outer circumference with a diameter of 2.5 mm in a top view. The second part 12 has a square outer circumference with a side length of 5.0 mm in a top view. The thickness of the second part 12 is 0.2 mm. The light adjusting member 40, which is placed on top of the light source 20, has a thickness of 0.075 mm. The refractive indices are shown in Table 1.

[0114] [Table 1]

[0115] The simulation results are shown in Figures 9 to 12. Each figure shows a top view of a single light-emitting unit E viewed from above. Figure 9 shows the results for Example 1. Figure 10 shows the results for Example 2. Figure 11 shows the results for Example 3. Figure 12 shows the results for the Reference Example. These graphs show a single light-emitting unit E as shown in Figure 1A, and each light-emitting unit E is shown rotated 45 degrees relative to the rectangle of the entire image (Figure 1A rotated 45 degrees). Compared to each example, the Reference Example shows that the part corresponding to the third portion of the light-emitting unit E in Examples 1 to 3 is dark, and the outer edge is bright.

[0116] Furthermore, Figure 13 is a graph showing the illuminance distribution cross-section at the light-emitting section E in both Example 1 and the Reference Example. According to this, in Example 1, the third portion of the light-emitting section E is brighter and the outer edge is darker compared to the Reference Example, resulting in an improved abrupt change. This indicates a reduction in brightness unevenness. [Industrial applicability]

[0117] The planar light source described herein can be used, for example, as a backlight for a liquid crystal display device.

[0118] Examples of the present invention are as follows:

[0119] [Section 1] A light guide member comprising an upper surface that serves as a light extraction surface and a lower surface opposite to the upper surface, A light source arranged within the light guide member, A light-reflecting member is disposed on the lower side of the light-guiding member and comprises a base material and a light-reflecting substance contained in the base material, and is capable of diffuse reflection. A planar light source comprising a plurality of light-emitting units, In each of the light-emitting sections, the light guide member has a first portion with refractive index n1 that is positioned in contact with the periphery of the light source, a second portion with refractive index n2 that is positioned in contact with the periphery of the first portion, a third portion with refractive index n3 that is positioned in contact with the periphery of the second portion, and a fourth portion with refractive index n4 that is in contact with the first portion, the second portion and the third portion and constitutes the lower surface of the light guide member. The refractive index n2 of the second part is greater than the refractive index n4 of the fourth part, the refractive index n4 of the fourth part is greater than the refractive index n1 of the first part, and the refractive index of the first part is the same as or greater than the refractive index n3 of the third part. A planar light source wherein the refractive index n30 of the base material of the light-reflecting member is greater than the refractive index n4 of the fourth portion. [Section 2] The planar light source according to item 1, wherein the first and third parts are integral and connected on the upper surface of the second part. [Section 3] The planar light source according to item 1 or 2, wherein the refractive index n1 of the first part is greater than the refractive index n3 of the third part. [Section 4] A light guide member comprising an upper surface that serves as a light extraction surface and a lower surface opposite to the upper surface, A light source arranged within the light guide member, A light reflective member disposed on the lower side of the light guide member, Equipped with, The light guide member has a first portion with refractive index n1 that is positioned in contact with the light source, a second portion with refractive index n2 that is positioned in contact with the first portion, a third portion that is positioned in contact with the second portion and contains scattering particles with refractive index nS in a matrix material with refractive index n3, and a fourth portion with refractive index n4 that is in contact with the first portion, the second portion and the third portion and constitutes the lower surface of the light guide member. A planar light source wherein the refractive index n2 of the second part is greater than the refractive index n4 of the fourth part, the refractive index n3 of the base material of the third part is greater than the refractive index n4 of the fourth part, and the refractive index nS of the scattering particles is different from the refractive index n3 of the base material of the third part. [Section 5] The planar light source according to item 4, wherein the first and third parts are integral and connected on the upper surface of the second part. [Section 6] The planar light source according to item 4 or 5, wherein the refractive index n1 of the first part is greater than the refractive index n3 of the third part. [Explanation of Symbols]

[0120] 100...Surface light source E...light-emitting part 10...Light guiding member (10U...top surface, 10L...bottom surface) 10A...Light guide member (11A...First part, 12A...Second part, 13A...Third part, 14A...Fourth part) 10B...Light guide member (11B...First part, 11BB...Base material for the first part, 12B...Second part, 13B...Third part, 13BB...Base material for the third part, 14B...Fourth part, S...Scattering particle (nS...Refractive index of the scattering particle) 20…Light source 21…Light-emitting element 211… Semiconductor stack 212...Electrode 22...Sealing member (221...First sealing member, n221...Refractive index of the first sealing member, 222...Second sealing member, 223...Third sealing member) 30...Light-reflecting material (n30...Refractive index of the base material of the light-reflecting material) 40...Light adjustment member (41...Through hole)

Claims

1. A light guide member comprising an upper surface that serves as a light extraction surface and a lower surface opposite to the upper surface, A light source arranged within the light guide member, A light-reflecting member is disposed on the lower side of the light-guiding member and comprises a base material and a light-reflecting substance contained in the base material, and is capable of diffuse reflection. A planar light source comprising a plurality of light-emitting units, In each of the light-emitting sections, the light guide member has a first portion with refractive index n1 that is positioned in contact with the periphery of the light source, a second portion with refractive index n2 that is positioned in contact with the periphery of the first portion, a third portion with refractive index n3 that is positioned in contact with the periphery of the second portion, and a fourth portion with refractive index n4 that is in contact with the first portion, the second portion and the third portion and constitutes the lower surface of the light guide member. The refractive index n2 of the second part is greater than the refractive index n4 of the fourth part, the refractive index n4 of the fourth part is greater than the refractive index n1 of the first part, and the refractive index of the first part is the same as or greater than the refractive index n3 of the third part. A planar light source wherein the refractive index n30 of the base material of the light-reflecting member is greater than the refractive index n4 of the fourth portion.

2. The planar light source according to claim 1, wherein the first part and the third part are integral and connected on the upper surface of the second part.

3. The planar light source according to claim 1, wherein the refractive index n1 of the first portion is greater than the refractive index n3 of the third portion.

4. A light guide member comprising an upper surface that serves as a light extraction surface and a lower surface opposite to the upper surface, A light source arranged within the light guide member, A light reflective member disposed on the lower side of the light guide member, Equipped with, The light guide member has a first portion with refractive index n1 that is positioned in contact with the periphery of the light source, a second portion with refractive index n2 that is positioned in contact with the periphery of the first portion, a third portion that is positioned in contact with the periphery of the second portion and contains scattering particles with refractive index nS in a base material with refractive index n3, and a fourth portion with refractive index n4 that is in contact with the first portion, the second portion and the third portion and constitutes the lower surface of the light guide member. A planar light source wherein the refractive index n2 of the second part is greater than the refractive index n4 of the fourth part, the refractive index n3 of the base material of the third part is greater than the refractive index n4 of the fourth part, and the refractive index nS of the scattering particles is different from the refractive index n3 of the base material of the third part.

5. The planar light source according to claim 4, wherein the first part and the third part are integral and connected on the upper surface of the second part.

6. The planar light source according to claim 4, wherein the refractive index n1 of the first portion is greater than the refractive index n3 of the third portion.

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