Light guide body and lighting device

Abstract

The present invention improves diffusibility of light incident on a light guide body. This light guide body, into which light from a light source enters, has a cavity provided inside, and includes an end surface and an emission surface which is continuous with the end surface and which intersects with the end surface. The light guide body reflects a part of light guided inside the light guide body with the cavity, and emits the light reflected by the cavity from the emission surface. The cavity has a convex shape in a first cross section intersecting with each of the end surface and the emission surface, and includes a flat part at a top part of the convex shape.

Description

Light guide, and lighting device

[0001] The present invention relates to a light guide and a lighting device.

[0002] For example, Patent Document 1 discloses a lighting device including a first prism pattern and a second prism pattern that intersect perpendicularly between a light source and a light guide plate. Further, Patent Document 2 discloses a lighting device having a moth-eye pattern and protrusions on an incident surface of a light guide plate for incident light from a light source.

[0003] Japanese Patent No. 4691543 Japanese Patent No. 6068747

[0004] An object of the present invention is to improve the diffusibility of light incident on a light guide.

[0005] A light guide according to an aspect of the present invention is a light guide provided with a cavity inside, into which light from a light source is incident, and includes an end face and an emission face that is continuous with the end face and intersects the end face. The light guide reflects a part of the light guided inside the light guide by the cavity, emits the light reflected by the cavity from the emission face, the cavity has a convex shape in a first cross section intersecting each of the end face and the emission face, and includes a flat portion at the top of the convex shape.

[0006] According to the present invention, the diffusibility of light incident on the light guide can be improved.

[0007] It is a schematic plan view showing a lighting device including a light guide according to an embodiment. It is a schematic cross-sectional view taken along line II-II in FIG. 1. It is a schematic cross-sectional view showing the shape in a first cross section of a cavity included in the light guide according to the embodiment. It is a schematic perspective view showing a cavity included in the light guide according to the embodiment. It is a view showing the shape in a second cross section of a cavity included in the light guide according to the embodiment. It is a schematic perspective view showing a state of manufacturing a mold for manufacturing a concave portion of a cavity included in the light guide according to the embodiment. It is a view showing the relationship between the viewing angle and the normalized luminance of the light taken out from the emission face side for each cavity shape. It is a view showing the relationship between the viewing angle and the normalized luminance of the light taken out from the side opposite to the emission face for each cavity shape.

[0008] Embodiments of the present invention will be described in detail below with reference to the drawings. In each drawing, the same reference numerals are used for the same components, and redundant explanations are omitted as appropriate.

[0009] The embodiments shown below illustrate light guides and lighting devices that embody the technical concept of the present invention, and the present invention is not limited to the embodiments shown below. The size and positional relationships of the components shown in the drawings may be exaggerated for clarity of explanation.

[0010] In the diagrams shown below, a Cartesian coordinate system with X, Y, and Z axes is used to represent direction. The X, Y, and Z axes are approximately orthogonal to each other. The direction in which the arrow representing the X axis points is denoted as the +X side, and the opposite direction is denoted as the -X side. The direction in which the arrow representing the Y axis points is denoted as the +Y side, and the opposite direction is denoted as the -Y side. The direction in which the arrow representing the Z axis points is denoted as the +Z side, and the opposite direction is denoted as the -Z side.

[0011] The Z-direction along the Z-axis corresponds to the direction along the normal to the emission surface of the light guide according to the embodiment. The Y-direction along the Y-axis corresponds to the direction along the normal to the end face of the light guide according to the embodiment. In this specification, "plan view" means viewing the object from the +Z direction. The +Z direction is referred to as "up," and the -Z direction is referred to as "down." However, the above directional expressions merely represent relative positional relationships for explanatory purposes and do not limit the directions of the embodiments.

[0012] In this specification and in the claims, "parallel" means that the angular deviation from the parallel state is ±10 degrees or less. "Orthogonal" means that the angular deviation from the orthogonal state is ±10 degrees or less. "To be positioned" is not limited to direct contact, but also includes indirect positions, such as those arranged via other members. Furthermore, in this specification, "thickness" or "height" refers to the length in the Z direction.

[0013] <Configuration of the lighting device equipped with a light guide according to the embodiment> The configuration of the lighting device equipped with a light guide according to the embodiment will be described with reference to Figures 1 and 2. Figure 1 is a schematic plan view showing a lighting device 100 equipped with a light guide 80 according to the embodiment. Figure 2 is a schematic cross-sectional view taken along line II-II in Figure 1. In the example shown in Figure 2, a portion of the light Lt emitted from the light source LS is indicated by a dashed arrow.

[0014] The lighting device 100 includes a light guide 80 and a light source LS. The light guide 80 has a cavity 64 inside and is a light guide into which light Lt from the light source LS is incident. The light guide 80 includes an end face 81 and an exit face 82 that is continuous with and intersects the end face 81.

[0015] In the example shown in Figure 2, the light guide 80 is a laminate with a light guide layer, which includes a light guide layer 10, a laminate 70, and a first adhesive layer 52. The first adhesive layer 52 is placed between the light guide layer 10 and the laminate 70 and is a layer that adheres the light guide layer 10 and the laminate 70. The laminate 70 includes a base material 30 and a direction changing layer 60. The direction changing layer 60 includes a shaping film 62 and a second adhesive layer 54.

[0016] The second adhesive layer 54 is placed between the shaping film 62 and the substrate 30, and is a layer that adheres the shaping film 62 and the substrate 30. The substrate 30 is positioned opposite the first main surface 621 of the shaping film 62 via the second adhesive layer 54. The light guide layer 10 is positioned opposite the second main surface 622 of the shaping film 62 via the second adhesive layer 54. The shaping film 62 is a film manufactured without cutting the material. In the example shown in Figures 1 and 2, a light guide 80 which is a laminate with a light guide layer is described as an example of a light guide according to the embodiment, but the light guide according to the embodiment does not necessarily have to be a laminate with a light guide layer as long as there is a cavity 64 inside the light guide. The light guide according to the embodiment may consist only of a laminate having a cavity 64 inside, or it may not even be a laminate.

[0017] As shown in Figure 2, a plurality of cavities 64 are provided inside the direction changing layer 60. Each of the plurality of cavities 64 has a first inclined surface ISa and a second inclined surface ISb located on the opposite side of the first inclined surface ISa in the Y direction. Inside the cavity 64, for example, air is present. A plurality of recesses are provided on the first main surface 621 of the shaping film 62. The cavities 64 are formed when the open portions of each of the plurality of recesses are closed by the substrate 30, which is placed on the first main surface 621 via the second adhesive layer 54. The cavities 64 can also be referred to as internal spaces.

[0018] The lighting device 100 is used, for example, when the light guide 80 is placed on a substrate such as glass, a window, a wall, a floor, or a ceiling. The lighting device 100 causes light Lt emitted from the light source LS to enter the interior of the light guide 80 through the end face 81. Light Lt enters the light guide 80 from the end face 81. The light guide 80 reflects a portion of the light Lt guided through its interior by the cavity 64, and emits the light Lt reflected by the cavity 64 from the emission surface 82. In other words, the light guide 80 can extract the light Lt reflected by the cavity 64 from the emission surface 82. The lighting device 100 can illuminate the room or other space on which the light guide 80 is placed by the light Lt emitted from almost the entire emission surface 82 of the light guide 80. The reflection by the cavity 64 includes at least one of specular reflection and diffuse reflection.

[0019] The lighting device 100 has a light distribution control structure having a plurality of cavities 64. The first inclined surface ISa in each of the plurality of cavities 64 directs a portion of the light Lt guided through the light guide 80 toward the emission surface 82 by total internal reflection (TIR). The light Lt may be refracted as it passes through the interface, depending on the refractive index of the material constituting the interface.

[0020] The light guide 80 is configured to emit light Lt having a desired light distribution from the emission surface 82 by a light distribution control structure. The light distribution can be controlled, for example, by adjusting the cross-sectional shape, planar shape, size, arrangement density, distribution, etc., of the cavity 64.

[0021] The light guide 80 has a visible light transmittance of 60% or more and a haze value of less than 30%. Preferably, the visible light transmittance is 70% or more, and more preferably 80% or more. Preferably, the haze value is less than 10%, and more preferably 5% or less. Because the light guide 80 has a high visible light transmittance and a low haze value, objects or displays can be seen through the light guide 80. Visible light is light with a wavelength of 380 nm to 780 nm. The visible light transmittance and haze value can be measured using a haze meter (manufactured by Murakami Color Technology Laboratory: product name HM-150), etc.

[0022] The ratio of the area of ​​the multiple cavities 64 to the area of ​​the light guide layer 10, i.e., the occupied area ratio, is preferably 1% to 80% when the light guide layer 10 is viewed from the direction normal to the emission surface 82. The upper limit of the occupied area ratio is more preferably 50% or less, and even more preferably 45% or less. To obtain at least one of high transmittance and low haze value, it is preferably 30% or less, even more preferably 10% or less, and even more preferably 5% or less.

[0023] For example, when the cavity occupancy rate is 50%, a haze value of 30% can be obtained. The cavity occupancy rate of 64 may be uniform, and the occupancy rate may increase with increasing distance so that the brightness does not decrease even when the distance from the light source LS increases. For mass production using the roll-to-roll method or the roll-to-sheet method, it is preferable that the cavity occupancy rate of 64 be uniform.

[0024] In the light guide 80, the light guide layer 10 and the shaping film 62 are bonded together by a first adhesive layer 52. Furthermore, the shaping film 62 and the substrate 30 are bonded together by a second adhesive layer 54 that constitutes the direction changing layer 60. The light guide layer 10 and the substrate 30 may be transparent substrates or films.

[0025] In the example shown in Figure 1, the multiple cavities 64 are spaced apart in the X and Y directions of the light guide layer 10. However, the spacing of the cavities 64 may be appropriately set according to the shape of the light guide layer 10 or the desired light distribution.

[0026] In the example shown in Figure 1, a plurality of cavities 64 having substantially the same shape and a curved surface convex in the same direction are arranged throughout the entire region, periodically spaced apart in the X and Y directions. In this case, the pitch Px is preferably, for example, 10 μm or more and 500 μm or less, and the pitch Py is preferably, for example, 10 μm or more and 500 μm or less. In the example shown in Figure 1, the light guide 80 further has cavities 64 arranged offset by half the pitch Px in the X direction and half the pitch Py in the Y direction.

[0027] The light source LS is, for example, an LED (Light Emitting Diode) device. Multiple LED devices are arranged in a line in the X direction. There are no particular restrictions on the number or arrangement of LEDs. Note that the light source LS is not limited to LED devices, but may also be a halogen lamp or the like.

[0028] The shaping film 62 can be manufactured according to the method described in Japanese Patent Publication No. 2013-524288. Specifically, the surface of a polymethyl methacrylate (PMMA) film is coated with lacquer (FineCure RM-64, manufactured by Sanyo Chemical Industries, Ltd.), an optical pattern is embossed onto the film surface containing the lacquer, and then the lacquer is cured to produce the desired shaping film 62. The total thickness of the shaping film 62 is, for example, 130 μm.

[0029] The light guide layer 10 is formed from a known material with high transmittance to visible light. For example, the light guide layer 10 is formed from an acrylic resin such as polymethyl methacrylate (PMMA), a polycarbonate (PC) resin, a cycloolefin resin, or glass (quartz glass, alkali-free glass, borosilicate glass, etc.). The refractive index nGP of the light guide layer 10 is, for example, 1.40 or more and 1.80 or less. Unless otherwise specified, the refractive index refers to the refractive index measured with an ellipsometer at a wavelength of 550 nm. The thickness of the light guide layer 10 can be appropriately set depending on the application. For example, the thickness of the light guide layer 10 is 0.05 mm or more and 50 mm or less.

[0030] The thickness of the substrate 30 is, for example, 1 μm or more and 1000 μm or less, preferably 10 μm or more and 100 μm or less, and more preferably 20 μm or more and 80 μm or less. The refractive index of the substrate 30 is preferably 1.40 or more and 1.70 or less, and more preferably 1.43 or more and 1.65 or less, independently of each other.

[0031] The thickness of the first adhesive layer 52 and the second adhesive layer 54 is, independently of each other, for example, 0.1 μm to 100 μm, preferably 0.3 μm to 100 μm, and more preferably 0.5 μm to 50 μm. The refractive index of the first adhesive layer 52 and the second adhesive layer 54 is, independently of each other, preferably 1.42 to 1.60, and more preferably 1.47 to 1.58. Furthermore, the refractive index of the first adhesive layer 52 and the second adhesive layer 54 is preferably close to the refractive index of the light guide layer 10 or shaping film 62 in contact with them, and the absolute value of the difference in refractive index is preferably 0.2 or less.

[0032] Preferably, the second adhesive layer 54 can be bonded to the shaping film 62 without filling in any recesses. Suitable adhesives for forming the second adhesive layer 54 include those described in the present applicant's international applications PCT / JP2021 / 006452, PCT / JP2021 / 006453, or Japanese Patent Application No. 2021-025496. All disclosures of these applications are incorporated herein by reference. In particular, the polyester-based adhesive described in Japanese Patent Application No. 2021-025496 is preferred.

[0033] <Configuration of Cavity 64> The configuration of the cavity 64 provided in the light guide 80 will be described in detail with reference to Figures 3 and 4. Figure 3 is a schematic cross-sectional view showing the shape of the cavity 64 in its first cross-section. Figure 4 is a schematic perspective view showing the cavity 64.

[0034] In this embodiment, as shown in Figure 3, the cavity 64 has a convex shape in a first cross-section that intersects with the end face 81 and the ejection surface 82 shown in Figure 2, and includes a flat portion 640 at the top of the convex shape.

[0035] In the examples shown in Figures 3 and 4, the first cross-section is a cross-section parallel to the YZ plane. In the example shown in Figure 3, the cavity 64 has an arc-shaped convex form in the first cross-section that is convex on the side where the ejection surface 82 is located, for example, on the +Z side, and includes a flat portion 640 parallel to the ejection surface 82. The convex shape is mirror-symmetric with respect to the central axis 64C of the cavity 64 that extends in the direction normal to the ejection surface 82. However, the convex shape of the cavity 64 may be any shape as long as it is convex on the +Z side and includes a flat portion 640 at its apex. For example, the convex shape in the first cross-section of the cavity 64 may be a substantially trapezoidal shape with the flat portion 640 as the upper base and the opposite side of the flat portion 640 as the lower base, or it may be a substantially circular arc shape with a flat apex. Furthermore, the convex shape may have a shape that is not mirror-symmetric with respect to the central axis 64C of the cavity 64. Furthermore, the flat portion 640 does not necessarily have to be parallel to the ejection surface 82.

[0036] In the cavity 64, the first inclination angle θa of the first inclined surface ISa is, for example, 10° or more and 70° or less. If the first inclination angle θa is less than 10°, the controllability of light distribution may be insufficient, and the light extraction efficiency from the light guide 80 may be insufficient. On the other hand, if the first inclination angle θa exceeds 70°, for example, processing the shaping film 62 may become difficult. The second inclination angle θb of the second inclined surface ISb is, for example, 50° or more and 100° or less. If the second inclination angle θb is less than 50°, stray light may be generated in an unintended direction. If the second inclination angle θb exceeds 100°, for example, processing the shaping film 62 that constitutes the light extraction layer 11 may become difficult. The length L of the cavity 64 in the X direction is preferably 10 μm or more and 500 μm or less. The width W of the cavity 64 in the Y direction is preferably 1 μm or more and 100 μm or less. The length L is, for example, twice or more the width W. The height H corresponding to the length of the cavity 64 in the Z direction is preferably 1 μm or more and 100 μm or less.

[0037] In this embodiment, in a first cross-section parallel to the YZ plane, the flat width Wt in the direction along the exit surface 82 of the flat portion 640 is preferably 5 μm or less, and more preferably 3 μm or less.

[0038] Furthermore, in this embodiment, the cavity 64 may have a free curve shape in a second cross-section parallel to the end face 81. The second cross-section is a cross-section parallel to the XZ plane in Figures 3 and 4. However, the cavity 64 is not limited to a free curve shape in the second cross-section; it may also have an arc shape, a circular arc shape, or a cosine shape following a cosine function.

[0039] Here, Figure 5 shows the shape of the cavity 64 in a second cross-section. In Figure 5, graph 50 shows an example of a cosine shape of the cavity 64 in the second cross-section that follows the cosine function. Graph 51 shows an example of an arc shape of the cavity 64 in the second cross-section.

[0040] <Effects of the Light Guide 80> Next, the effects of the light guide 80 will be explained. First, before explaining the effects of the light guide 80, the manufacturing method of the shaping film that constitutes the cavity in the light guide 80 and other light guides will be explained.

[0041] In the method for manufacturing a shaped film, for example, a mold is manufactured and used that has mold recesses that are approximately the same shape as the recesses that constitute the cavity. Here, Figure 6 is a schematic perspective view showing the manufacturing process of a mold for manufacturing the recesses of the cavity of a light guide. As shown in Figure 6, the mold recesses 64a are formed by cutting the base material of the mold 300 with a cutting tool 200 that moves at least in the X direction. Using a mold 300 in which multiple such mold recesses 64a are formed, an intermediate transfer body having multiple convex portions that are the inverse shape of the mold recesses 64a is manufactured. By transferring the inverse shape of the convex portions to the shaped film using this intermediate transfer body, recesses that constitute the cavity are formed in the shaped film.

[0042] In the above-described method for manufacturing the shaped film, the inverted shape of the cutting tool 200 is indirectly transferred to the recess of the cavity in the Y direction. The thinness of the tip of the cutting tool 200 in the Y direction is determined by the width of the cavity in the Y direction. Therefore, if the width of the cavity corresponding to the Y direction, for example the width W of cavity 64 in Figure 3, becomes narrower, the tip of the cutting tool 200 becomes thinner and may be prone to chipping. If the tip of the cutting tool 200 chips, the mold 300 cannot be manufactured. As a result, it becomes impossible to manufacture the shaped film that constitutes the cavity using the mold 300.

[0043] On the other hand, if the width of the cavity corresponding to the Y direction, for example the width W of cavity 64 in Figure 3, is wide, the light diffusion due to the cavity may decrease. When the light diffusion due to the cavity decreases, brightness unevenness occurs in the light extracted from the light guide, and it becomes difficult to obtain the desired light distribution.

[0044] In the present embodiment, as shown in FIGS. 3 and 4, the cavity 64 has a convex shape in a first cross-section parallel to the YZ plane, and includes a flat portion 640 at the top of the convex shape. This convex shape is an inverted shape of the tip portion of the insert 200 corresponding to the shape of the tip portion of the insert 200. By including the flat portion 640 at the top of the convex-shaped cavity 64, it is possible to avoid the tip portion of the insert 200 from becoming extremely thin. As a result, it is possible to avoid the tip portion of the insert 200 from being easily chipped, and the width W of the cavity 64 in FIG. 3 can be narrowed. As a result, in the present embodiment, the diffusibility of the light Lt incident on the light guide 80 can be improved. By improving the diffusibility of the light Lt incident on the light guide 80, the luminance unevenness of the light Lt extracted from the light guide 80 is reduced, and a desired light distribution pattern can be easily obtained. The lighting device 100 having the light guide 80 can illuminate the light Lt with reduced luminance unevenness, or the light Lt having a desired light distribution pattern. From the viewpoint of preferably reducing the luminance unevenness of the light Lt extracted from the light guide 80 or preferably obtaining a desired light distribution pattern, in the first cross-section parallel to the YZ plane, the convex shape is preferably convex toward the side where the emission surface 82 is located, and in the first cross-section, the flat portion 640 is more preferably parallel to the emission surface 82.

[0045] FIG. 7 is a diagram showing the relationship between the viewing angle and the normalized luminance of the light extracted from the emission surface 82 side for each shape of the cavity 64. FIG. 8 is a diagram showing the relationship between the viewing angle and the normalized luminance of the light extracted from the side opposite to the emission surface 82 for each shape of the cavity 64.

[0046] In FIGS. 7 and 8, the graph 71 shown by the solid line shows the relationship between the viewing angle and the normalized luminance of the light Lt extracted from the light guide 80 having the cavity 64 including the flat portion 640 with a flat width Wt of 3 μm. The graph 72 shown by the broken line shows the relationship between the viewing angle and the normalized luminance of the light Lt extracted from the light guide 80 having the cavity 64 including the flat portion 640 with a flat width Wt of 5 μm. The first inclination angle θa and the second inclination angle θb of the cavity 64 in the graphs 71 and 72 are both 73 degrees.

[0047] In FIGS. 7 and 8, a graph 73 indicated by a dashed line shows the relationship between the viewing angle and the normalized luminance of the light Lt extracted from the light guide 80 having the cavity 64 that does not include the flat portion 640. The first inclination angle θa and the second inclination angle θb of the cavity 64 in the graph 73 are both 63 degrees. A graph 74 indicated by a chain double-dashed line shows the relationship between the viewing angle and the normalized luminance of the light Lt extracted from the light guide 80 having the cavity 64 that does not include the flat portion 640. The first inclination angle θa and the second inclination angle θb of the cavity 64 in the graph 74 are both 73 degrees. Note that each graph shown in FIGS. 7 and 8 is an experimental result.

[0048] As shown in FIG. 7, the change in the normalized luminance according to the viewing angle of the light Lt extracted from the light-emitting surface 82 side of the light guide 80 was smaller in the graphs 71 and 72 compared to the graphs 73 and 74. In particular, in the range where the viewing angle was ±40 degrees or less, the change in the normalized luminance according to the viewing angle in the graphs 71 and 72 was smaller compared to the graphs 73 and 74. That is, it was found that in the light guide 80 in which the cavity 64 includes the flat portion 640, the change in the normalized luminance according to the viewing angle of the light Lt extracted from the light-emitting surface 82 side is smaller compared to the light guide in which the cavity 64 does not include the flat portion 640. Therefore, in the light guide 80 in which the cavity 64 includes the flat portion 640, it is possible to extract the light Lt with reduced luminance unevenness.

[0049] The change in normalized brightness of the light Lt extracted from the emission surface 82 side of the light guide 80 with respect to the viewing angle was smaller in Graph 71 than in Graph 72. In particular, in the range of viewing angles of ±40 degrees or less, the change in normalized brightness with respect to the viewing angle in Graphs 71 and 72 was smaller compared to Graphs 73 and 74. In other words, it was found that in the light guide 80 including a flat portion 640 with a flat width Wt of 3 μm, the change in normalized brightness of the light Lt extracted from the emission surface 82 side with respect to the viewing angle was smaller compared to the light guide 80 including a flat portion 640 with a flat width Wt of 5 μm. Therefore, in the light guide 80 having a cavity 64 including a flat portion 640 with a flat width Wt of 3 μm, it is possible to extract light Lt with reduced brightness unevenness compared to the light guide 80 having a cavity 64 including a flat portion 640 with a flat width Wt of 5 μm.

[0050] On the other hand, the relationship between the normalized luminance and viewing angle of the light Lt extracted from the side opposite to the output surface 82 shown in Figure 8 did not show as much difference between graphs 71, 72, 73, and 74 as it did in Figure 7. In other words, the relationship between the normalized luminance and viewing angle of the light Lt extracted from the side opposite to the output surface 82 does not differ significantly depending on the shape of the cavity 64. Furthermore, in the viewing angle range of ±40 degrees or less, the normalized luminance of the light Lt was almost zero in all of graphs 71, 72, 73, and 74. In other words, regardless of the shape of the cavity 64, it was found that almost no light Lt is extracted from the side opposite to the output surface 82 in the viewing angle range of ±40 degrees or less.

[0051] In this embodiment, the cavity 64 can have a free curve shape in a second cross-section parallel to the end face 81. By having a free curve shape, the free curve shape in the second cross-section of the cavity 64 can be determined according to the intended use of the light guide 80, thereby optimizing the diffusion and light distribution of the light Lt.

[0052] In this embodiment, the cavity 64 may have an arc shape in the second cross-section. Having an arc shape in the cavity 64 allows for optimization of the light diffusion and light distribution of the light guide 80 according to its intended use. Furthermore, having an arc shape in the cavity 64 makes it easier to design and manufacture compared to the case where the cavity 64 has a free curve shape.

[0053] In this embodiment, the cavity 64 may have an arc shape or a cosine shape that follows a cosine function. Having an arc shape or a cosine shape makes it easier to design and manufacture the cavity 64 compared to having a free curve shape or an arc shape.

[0054] The ordinal numbers, quantities, and other figures used in the description of the embodiments are all illustrative to specifically illustrate the technology of the present invention, and the present invention is not limited to these illustrative figures. Furthermore, the connection relationships between the components are illustrative to specifically illustrate the technology of the present invention, and do not limit the connection relationships that realize the functions of the present invention.

[0055] The light guide and lighting device according to this embodiment can improve the diffusion of light incident on the light guide, and by being placed on building components such as glass, windows, walls, floors, and ceilings, they can illuminate the interior or exterior space of a building with reduced brightness unevenness.

[0056] Furthermore, the light guide and lighting device according to the embodiment can be used as a partition to suitably partition a room or to conceal a desired space. In addition, by placing the light guide and lighting device according to the embodiment on the glass substrate of a display device such as a liquid crystal panel or an organic EL (Electroluminescence) display panel, the backlight illumination of the display device can be made brighter. Moreover, the light guide and lighting device according to the embodiment can provide new applications other than those mentioned above.

[0057] Aspects of the present invention are, for example, as follows: <1> A light guide having a cavity inside into which light from a light source is incident, comprising an end face and an exit surface continuous with and intersecting the end face, wherein the light guide reflects a portion of the light guided inside the light guide by the cavity and causes the light reflected by the cavity to exit from the exit surface, and the cavity has a convex shape in a first cross section intersecting the end face and the exit surface, and includes a flat portion at the top of the convex shape. <2> The light guide according to <1>, wherein in the first cross section, the convex shape is convex toward the side where the exit surface is located. <3> The light guide according to <1> or <2>, wherein in the first cross section, the flat portion is parallel to the exit surface. <4> The cavity is a light guide according to any one of <1> to <3>, having a free curve shape in a second cross section parallel to the end face. <5> The cavity is a light guide according to any one of <1> to <3>, having an arc shape in a second cross section parallel to the end face. <6> The cavity is a light guide according to any one of <1> to <3>, having a circular arc shape or a cosine shape following a cosine function in a second cross section parallel to the end face. <7> The light guide according to any one of <1> to <6>, having a flat width of the flat portion in the direction along the exit surface in the first cross section of the flat portion. <8> The light guide according to any one of <1> to <6>, having a flat width of the flat portion in the direction along the exit surface in the first cross section of the flat portion. <9> An illumination device having a light guide described in any one of <1> to <8> above, and the light source.

[0058] This application claims priority based on Japanese Patent Application No. 2024-160721, filed with the Japan Patent Office on 18 September 2024, and includes the entire contents of that Japanese Patent Application.

[0059] 10 Light guide layer 30 Substrate 50, 51 Graph 52 First adhesive layer 54 Second adhesive layer 60 Direction change layer 62 Shaping film 621 First main surface 622 Second main surface 64 Cavity 64a Mold recess 64C Central axis 70 Laminate 71, 72, 73, 74 Graph 80 Light guide 81 End face 82 Emission surface 100 Lighting device 200 Bite 300 Mold 640 Flat section H Height ISa First inclined surface ISb Second inclined surface Lt Light LS Light source Px, Py Pitch W Width Wt Flat width θa First inclination angle θb Second inclination angle

Claims

1. A light guide having a cavity inside into which light from a light source is incident, comprising an end face and an exit surface continuous with and intersecting the end face, wherein the light guide reflects a portion of the light guided inside the light guide by the cavity and causes the light reflected by the cavity to exit from the exit surface, and the cavity has a convex shape in a first cross section intersecting the end face and the exit surface, and includes a flat portion at the top of the convex shape.

2. The light guide according to claim 1, wherein in the first cross-section, the convex shape is convex on the side where the emission surface is located.

3. The light guide according to claim 1, wherein in the first cross-section, the flat portion is parallel to the emission surface.

4. The light guide according to claim 1, wherein the cavity has a free curve shape in a second cross-section parallel to the end face.

5. The light guide according to claim 1, wherein the cavity includes an arc shape in a second cross-section parallel to the end face.

6. The light guide according to claim 1, wherein the cavity has an arc shape or a cosine shape following a cosine function in a second cross-section parallel to the end face.

7. The light guide according to claim 1, wherein in the first cross-section, the width of the flat portion in the direction along the emission surface is 5 μm or less.

8. The light guide according to claim 1, wherein in the first cross-section, the width of the flat portion in the direction along the emission surface is 3 μm or less.

9. An illumination device comprising a light guide according to any one of claims 1 to 8, and the light source.

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