Lighting device

Abstract

The present invention reduces luminance unevenness. This lighting device comprises: a light guide body that has a cavity provided therein; a light source that emits light toward an end surface of the light guide body; and a light diffusion member that is disposed between the end surface and the light source, and that diffuses and transmits the light from the light source. In the light diffusion member, a half-value angle in at least one cross-section of a bidirectional transmittance distribution function, measured using light incident at an incident angle of 0°, is 50° or more.

Description

lighting equipment

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

[0002] For example, Patent Document 1 discloses a lighting device having a first prism pattern and a second prism pattern that intersect at a right angle between a light source and a light guide plate, and Patent Document 2 discloses a lighting device having a moth-eye pattern and protrusions on the light incident surface of a light guide plate that receives light from a light source.

[0003] Patent No. 4691543 Patent No. 6068747

[0004] An object of the present invention is to reduce brightness unevenness.

[0005] An illumination device according to one aspect of the present invention includes a light guide having a cavity formed therein, a light source that emits light toward an end face of the light guide, and a light diffusing member that is disposed between the end face and the light source and diffuses and transmits the light from the light source, wherein the light diffusing member has a half-value angle of 50° or greater in at least one cross section of a bidirectional transmittance distribution function measured by incident light at an incident angle of 0°.

[0006] According to the present invention, it is possible to reduce brightness unevenness.

[0007] 1 is a schematic plan view showing a first example of an illumination device according to an embodiment. FIG. 2 is a schematic cross-sectional view taken along line II-II in FIG. 1. FIG. 3 is a view showing light diffused by a light diffusing member included in an illumination device according to an embodiment. FIG. 4 is a view showing a method for measuring a bidirectional transmittance distribution function of light diffused by a light diffusing member included in an illumination device according to an embodiment. FIG. 5 is a view explaining a half-value angle of a bidirectional transmittance distribution function of light diffused by a light diffusing member included in an illumination device according to an embodiment. FIG. 6 is a schematic cross-sectional view of a cavity included in an illumination device according to an embodiment. FIG. 7 is a schematic plan view showing a first example of a cavity included in an illumination device according to an embodiment. FIG. 8 is a schematic plan view showing a second example of a cavity included in an illumination device according to an embodiment. FIG. 9 is a view explaining a method for evaluating luminance unevenness in illumination devices according to examples and comparative examples. FIG. 10 is a view showing luminance unevenness evaluation regions of illumination devices according to examples and comparative examples. FIG. 11 is a view showing an example of measurement results of luminance distribution. FIG. 12 is a view showing an image of emitted light in an illumination device according to comparative example 4. FIG. 13 is a view showing an image of emitted light in an illumination device according to example 4. FIG. 14 is a schematic cross-sectional view showing a second example of an illumination device according to an embodiment.

[0008] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same components are given the same reference numerals, and duplicated descriptions will be omitted as appropriate.

[0009] The embodiments shown below are examples of lighting devices that embody the technical concepts of the present invention, and the present invention is not limited to the embodiments shown below. The dimensions, materials, shapes, relative positions, etc. of the components described below are intended to be illustrative and not to limit the scope of the present invention, unless otherwise specified to limit it to a specific embodiment. Furthermore, the sizes and positional relationships of components shown in the drawings may be exaggerated for clarity of explanation.

[0010] In the drawings shown below, directions are expressed using a Cartesian coordinate system having an X-axis, a Y-axis, and a Z-axis. The X-axis, the Y-axis, and the Z-axis are substantially perpendicular to one another. The direction of the arrow representing the X-axis is referred to as the +X direction or +X side, and the direction opposite to the +X direction is referred to as the -X direction or -X side. The direction of the arrow representing the Y-axis is referred to as the +Y direction or +Y side, and the direction opposite to the +Y direction is referred to as the -Y direction or -Y side. The direction of the arrow representing the Z-axis is referred to as the +Z direction or +Z side, and the direction opposite to the +Z direction is referred to as the -Z direction or -Z side. The X direction corresponds to the "parallel direction" in which multiple light sources provided in the lighting device according to the embodiment are arranged, and also corresponds to the "longitudinal direction" of the end face of the light guide provided in the lighting device according to the embodiment.

[0011] The Z direction along the Z axis indicates the direction along the normal to the light output surface of the lighting device according to the embodiment. In this specification, "planar view" refers to viewing an 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 the purpose of explanation and do not limit the directions in the embodiment.

[0012] In this specification and claims, "substantially parallel" means that the absolute value of the angular deviation from the parallel state is between 0 and 10 degrees. Furthermore, "substantially perpendicular" means that the absolute value of the angular deviation from the perpendicular state is between 0 and 10 degrees. "Arranged" does not necessarily mean direct contact, but also includes indirect arrangement, for example, via another member. Furthermore, in this specification, "thickness" refers to the length of the object in the Z direction. Furthermore, in this specification, cross-sectional views may be shown as end views showing only the cross section.

[0013] [Embodiment] <Overall Configuration of Illumination Device According to Embodiment> The overall configuration of an illumination device according to an embodiment will be described with reference to FIGS. 1 to 4. FIG. 1 is a schematic plan view showing a first example of an illumination device 100 according to an embodiment. FIG. 2 is a schematic cross-sectional view taken along line II-II in FIG. 1. FIG. 3A is a diagram showing an example of light Lc diffused by a light diffusing member 20 included in the illumination device 100 according to an embodiment. FIG. 3B is a diagram showing an example of a method for measuring the bidirectional transmittance distribution function (hereinafter referred to as BTDF) of light Lc diffused by the light diffusing member 20 included in the illumination device 100 according to an embodiment. FIG. 4 is a diagram explaining the half-value angle θ0 of the BTDF of light Lc diffused by the light diffusing member 20 included in the illumination device 100 according to an embodiment. Note that the BTDF is a six-dimensional function whose variables are the position, incident direction, and transmission direction of an object surface, and represents the characteristics of an object surface regarding transmission.

[0014] The lighting device 100 includes a laminate 80 with a light guide layer having a cavity 64 formed therein, a light source LS that emits light Lr toward an end surface 81 of the laminate 80 with a light guide layer, and a light diffusion member 20 that is disposed between the end surface 81 and the light source LS and diffuses and transmits the light Lr from the light source LS. In the example shown in Fig. 2, a portion of the light Lr emitted from the light source LS and a portion of the light Lc diffused by the light diffusion member 20 are indicated by dashed arrows. In the example shown in Fig. 1, the light source LS includes a plurality of light sources LS that are arranged at predetermined intervals in a parallel direction corresponding to the X direction.

[0015] The laminate 80 with a light guide layer shown in FIG. 2 includes a light guide layer 10, a laminate 70, and a first adhesive layer 52. The first adhesive layer 52 is disposed between the light guide layer 10 and the laminate 70 and serves to bond the light guide layer 10 and the laminate 70 together. The laminate 70 includes a substrate 30 and a direction changing layer 60. The direction changing layer 60 includes a shaped film 62 and a second adhesive layer 54. The second adhesive layer 54 is disposed between the shaped film 62 and the substrate 30 and serves to bond the shaped film 62 and the substrate 30 together. The substrate 30 is disposed opposite the main surface 621 of the shaped film 62. The light guide layer 10 is disposed opposite the shaped film 62. The shaped film 62 is a film manufactured without cutting the material. In the description of this embodiment, the light guide is exemplified as a laminate 80 with a light guide layer, but the light guide does not need to be a laminate with a light guide layer as long as the light guide has a cavity 64 inside. The light guide may be composed of only a laminate 80 having a cavity 64 inside, and the light guide does not need to be a laminate.

[0016] As shown in FIG. 2 , multiple cavities 64 are provided inside the direction-changing layer 60. Each of the multiple cavities 64 has a first inclined surface ISa and a second inclined surface ISb arranged on the opposite side of the first inclined surface ISa in the Y direction. For example, air is present inside the cavities 64. A plurality of recesses 622 are provided on the main surface 621 of the shaped film 62. The open portions of each of the multiple recesses 622 are blocked by the substrate 30 arranged on the main surface 621 via the second adhesive layer 54, thereby forming the cavities 64. The cavities 64 may also be referred to as internal spaces or air cavities.

[0017] The lighting device 100 is used, for example, with the light guide layer-equipped laminate 80 disposed on an adherend such as glass, a window, a wall, a floor, or a ceiling. Light Lr emitted from the light source LS of the lighting device 100 is diffused and transmitted through the light diffusing member 20. Diffused light Lc diffused by the light diffusing member 20 passes through an end face 81 of the light guide layer-equipped laminate 80, enters the inside of the light guide layer-equipped laminate 80, and is guided inside the light guide layer-equipped laminate 80. A portion of the diffused light Lc guided inside the light guide layer-equipped laminate 80 is reflected toward the −Z side by either the first inclined surface ISa or the second inclined surface ISb of the cavity 64, and passes through an exit surface 82 of the light guide layer-equipped laminate 80 that intersects with the end face 81, and is emitted in the −Z direction that intersects with the main surface 621 of the shaping film 62. The lighting device 100 can illuminate an indoor space or the like in which the laminate with a light guide layer 80 is placed, by using diffused light Lc emitted from almost the entire exit surface 82 of the laminate with a light guide layer 80 .

[0018] In a lighting device having a laminate with a light guide layer provided therein, when the laminate with a light guide layer is viewed in plan, brightness unevenness including a band-shaped dark area or the like extending in the longitudinal direction of the end face (e.g., the X direction) may occur near the end face of the laminate with a light guide layer, where light is incident from the light source. Such brightness unevenness including a band-shaped dark area or the like is thought to occur because there is an area inside the laminate with a light guide layer near the end face where light that has entered the laminate with a light guide layer does not reach, or because the high directivity of light reflected by the cavity results in an area inside the laminate with a light guide layer where the light does not pass. Such brightness unevenness including a band-shaped dark area or the like reduces the quality of the lighting device.

[0019] In the lighting device 100 according to this embodiment, the light diffusing member 20 has a half-value angle of 50° or greater in at least one cross section of the BTDF measured by incident light at an incident angle of 0°. Note that "at least one cross section (profile cross section) of the BTDF" refers to the BTDF in a cross section including the central axis 20C of the light diffusing member 20, among the BTDF data that is three-dimensional data. Here, FIG. 3A shows how xenon light Lx emitted from the xenon light source Xe is incident on the light diffusing member 20 at an incident angle of 0° and is diffused by and transmitted through the light diffusing member 20. The incident angle of 0° is an angle corresponding to a direction parallel to the normal NL of the light diffusing member 20.

[0020] A goniophotometer (GP-4) manufactured by Nikka Densoku Co., Ltd. can be used to measure the BTDF. The xenon light Lx can be light with a wavelength of 555 nm extracted from a xenon light source Xe using a bandpass filter. As shown in FIG. 3B , in measuring the BTDF, the xenon light Lx is incident on the light diffusing member 20 at an incident angle of 0°. Then, on the exit side (+Y side) of the light diffusing member 20, the photodetector of the Nikka Densoku Co., Ltd. goniophotometer is moved along the hemispherical trajectory f(θ,φ) to perform measurements, thereby obtaining the BTDF corresponding to the hemispherical trajectory f(θ,φ). θ is the elevation angle (diffusion angle), and φ is the azimuth angle. The diffused light Lc is diffused by the light diffusing member 20 and passes through it in accordance with the BTDF of the light diffusing member 20.

[0021] FIG. 4 shows an example of the relationship between θ (elevation angle (diffusion angle)) and light intensity value of the BTDF of the profile cross section when φ is set to 0° and θ is moved from -90° to +90° in a hemispherical orbit f(θ,φ). The light intensity value was measured for θ in increments of 10°. The vertical axis of FIG. 4 represents the light intensity value normalized with the maximum intensity value set to 1. The half-value angle θ0 means the BTDF of the diffused light Lc when the normalized light intensity value is 0.5.

[0022] In the lighting device 100 according to this embodiment, by using a light diffusing member 20 in which the half-value angle in at least one profile cross section of the BTDF measured by incident light at an incident angle of 0° is 50° or greater, it is possible to reduce the directivity of the diffused light Lc that is emitted from the light diffusing member 20 and enters the inside of the light guide layer-equipped laminate 80. By reducing the directivity of the diffused light Lc, there are fewer areas within the light guide layer-equipped laminate 80 where the diffused light Lc that enters the inside of the light guide layer-equipped laminate 80 does not reach. As a result, in this embodiment, it is possible to reduce brightness unevenness, including band-like dark areas. Furthermore, by reducing brightness unevenness, it is possible to improve the quality of the lighting device 100.

[0023] 3A and 3B , at least one profile cross section of the BTDF is a YZ cross section that includes the central axis 20C of the light diffusing member 20 and is perpendicular to the X direction. The central axis 20C of the light diffusing member 20 passes through the center 20P of the light diffusing member 20 and is parallel to the normal NL of the light diffusing member 20. By using the YZ cross section as the "at least one profile cross section of the BTDF," it is possible to reduce the directivity of the diffused light Lc that is emitted from the light diffusing member 20 and enters the light-guiding layer-equipped laminate 80, compared to, for example, a case in which the "at least one profile cross section of the BTDF" is a cross section that includes the central axis 20C of the light diffusing member 20 and is other than the YZ cross section.

[0024] In the lighting device 100, in the hemispherical orbit f(θ,φ), φ is set to 0°, and φ=0° is set to be along the normal direction of the light exit surface 82 that intersects with the end face 81. This allows light to be diffused particularly in the normal direction of the light exit surface 82 where light diffusion is desired, making it easier to reduce brightness unevenness. However, the direction of φ=0° does not necessarily have to be along the normal direction of the light exit surface 82. The light diffusing member 20 may be configured so that the BTDF is isotropic or anisotropic.

[0025] 2 , the light guide layer-equipped laminate 80 includes an exit surface 82 intersecting with the end surface 81, and guides diffused light Lc that has entered the light guide layer-equipped laminate 80 through the end surface 81. The cavity 64 reflects a portion of the diffused light Lc that has been guided through the light guide layer-equipped laminate 80 toward the exit surface 82. The diffused light Lc reflected by the cavity 64 exits the light guide layer-equipped laminate 80 through the exit surface 82. As a result, this embodiment can provide a surface-illumination type lighting device 100 that can emit light that has entered the light guide layer-equipped laminate 80 through the end surface 81 from almost the entire exit surface 82.

[0026] Furthermore, the lighting device 100 does not include a component such as a diffusion plate or a prism array that further diffuses the diffused light Lc emitted from the exit surface 82 of the light-guiding layer-equipped laminate 80. This simplifies the configuration of the lighting device 100.

[0027] <Details of the Configuration of the Illumination Device 100> The following describes the details of the configuration of the illumination device 100. The illumination 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 diffused light Lc guided within the light-guiding layer-equipped laminate 80 toward the exit surface 82 by total internal reflection (TIR). Note that when the diffused light Lc passes through an interface, it may be refracted according to the refractive index of the material that constitutes the interface.

[0028] The light-guiding layer-equipped laminate 80 is configured, by the light distribution control structure, to emit diffused light Lc having a desired light distribution from the exit surface 82. The light distribution can be controlled by adjusting, for example, the cross-sectional shape, planar shape, size, arrangement density, distribution, etc. of the cavities 64.

[0029] The laminate 80 with a light guide layer has a visible light transmittance of 60% or more and a haze value of less than 30%. The visible light transmittance is preferably 70% or more, and more preferably 80% or more. The haze value is preferably less than 10%, and more preferably 5% or less. Since the laminate 80 with a light guide layer has a high visible light transmittance and a low haze value, objects (displays) can be seen through the laminate 80 with a light guide layer. Visible light is light with a wavelength of 380 nm or more and 780 nm or less. The visible light transmittance and haze value can be measured using a haze meter (manufactured by Murakami Color Research Laboratory: product name HM-150) or the like.

[0030] The ratio of the area of ​​the plurality of cavities 64 to the area of ​​the light guide layer 10 (occupancy rate) is preferably 1% or more and 80% or less when the light guide layer 10 is viewed from the normal direction of the light exit surface 82. The upper limit of the occupation rate is more preferably 50% or less, and even more preferably 45% or less, and in order to obtain at least one of high transmittance and low haze value, it is preferably 30% or less, more preferably 10% or less, and even more preferably 5% or less.

[0031] For example, when the cavity occupancy rate is 50%, a haze value of 30% can be obtained. The cavity occupancy rate may be uniform, or may increase with increasing distance from the light source LS so that brightness does not decrease even when the distance from the light source LS increases. For mass production using a roll-to-roll method or a roll-to-sheet method, it is preferable that the cavity occupancy rate be uniform.

[0032] In the laminate 80 with a light guide layer, the light guide layer 10 and the shaped film 62 are bonded together by a first adhesive layer 52. The substrate 30 and the shaped film 62 are bonded together by a second adhesive layer 54 that constitutes the shaped film 62 and the direction changing layer 60. The light guide layer 10 and the substrate 30 may be transparent substrates or films.

[0033] 1, the cavities 64 are discretely arranged in the X and Y directions of the light guide layer 10. However, the discrete arrangement of the cavities 64 may be appropriately set depending on the shape of the light guide layer 10, the desired light distribution, etc.

[0034] 1, a plurality of cavities 64 having substantially the same shape and curved surfaces convex in the same direction are discretely and periodically arranged over the entire region in the X and Y directions. 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 FIG. 1, the laminate 80 with a light guide layer further includes cavities 64 that are shifted by half the pitch Px in the X direction and by half the pitch Py in the Y direction.

[0035] The light source LS is, for example, an LED (Light Emitting Diode) device. A plurality of LED devices are arranged in a line in the X direction. There are no particular limitations on the number and arrangement of the LEDs. Note that the light source LS is not limited to an LED device and may be a halogen lamp or the like.

[0036] The detailed configuration of the cavity 64 will be described with reference to Figures 5 to 7. Figure 5 is a schematic cross-sectional view showing an example of the cavity 64. Figure 6 is a schematic plan view showing a first example of the cavity 64. Figure 7 is a schematic plan view showing a second example of the cavity 64.

[0037] The cross-sectional shape of the cavity 64 shown in Fig. 5 is substantially triangular. However, the cross-sectional shape of the cavity 64 is not limited to a substantially triangular shape and may be a substantially trapezoid, etc. In the example shown in Fig. 5, the inclination angle θa of the first inclined surface ISa is larger than the inclination angle θb of the second inclined surface ISb.

[0038] The inclination angle θa of the first inclined surface ISa on the light source LS side is, for example, 10° or more and 70° or less. If the inclination angle θa is smaller than 10°, the controllability of the light distribution may decrease and the light extraction efficiency may also decrease. On the other hand, if the inclination angle θa exceeds 70°, it may become difficult to process the shaped film 62. By setting the inclination angle θa to 10° or more and 70° or less, the light extraction efficiency can be increased and the processing of the shaped film 62 can be made easier.

[0039] The inclination angle θb of the second inclined surface ISb is, for example, 50° or more and 100° or less. If the inclination angle θb is less than 50°, stray light may be generated in an unintended direction. On the other hand, if the inclination angle θb exceeds 100°, it may become difficult to process the shaping film 62. By setting the inclination angle θba to 50° or more and 100° or less, the light extraction efficiency can be increased and the shaping film 62 can be easily processed.

[0040] 6 is a curved surface convex toward the light source LS in a plan view. Here, light emitted from each of the plurality of LED devices constituting the light source LS has a spread in the Y direction. Therefore, the first inclined surface ISa acts uniformly on the light when the first inclined surface ISa has a curved surface convex toward the light source LS. Note that if a coupling optical system is provided between the light source LS and the end surface 81 of the laminate 80 with a light guide layer to allow highly parallel light (light with a small spread in the Y direction) to be incident, the first inclined surface ISa may be parallel to the X direction.

[0041] As shown in Figures 6 and 7, the length L of the cavity 64 is preferably 10 µm or more and 500 µm or less, and the width W is preferably 1 µm or more and 100 µm or less. The length L is preferably, for example, at least twice the width W. The height H is preferably 1 µm or more and 100 µm or less. Depending on the processing accuracy when forming the shaped film 62 including the recess 622 having the shape shown in Figure 6 in plan view, the recess 622 may have the shape shown in Figure 7 in plan view. Even in such a case, the shape of the cavity 64 in plan view can be specified by the length L and the width W.

[0042] The shaped film 62 can be produced according to the method described in JP-A-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 on the film surface containing the lacquer, and then the lacquer is cured to produce the desired shaped film 62. The total thickness of the shaped film 62 is, for example, 130 μm.

[0043] The light guide layer 10 is formed of a known material with high transmittance to visible light. The light guide layer 10 is formed, for example, of 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. The thickness of the light guide layer 10 is, for example, 0.05 mm or more and 50 mm or less.

[0044] The thickness of the substrate 30 is, for example, 1 μm to 1000 μm, preferably 10 μm to 100 μm, and more preferably 20 μm to 80 μm. The refractive index of the substrate 30 is independently preferably 1.40 to 1.70, and more preferably 1.43 to 1.65.

[0045] The thicknesses of the first adhesive layer 52 and the second adhesive layer 54 are each independently, for example, from 0.1 μm to 100 μm, preferably from 0.3 μm to 100 μm, and more preferably from 0.5 μm to 50 μm. The refractive indexes of the first adhesive layer 52 and the second adhesive layer 54 are each independently preferably from 1.42 to 1.60, and more preferably from 1.47 to 1.58. The refractive indexes of the first adhesive layer 52 and the second adhesive layer 54 are preferably close to the refractive index of the light guide layer 10 or the shaping film 62 to which they are in contact, and the absolute value of the difference in refractive index is preferably 0.2 or less.

[0046] The second adhesive layer 54 can preferably be bonded without filling the recesses 622 of the shaped film 62. Suitable adhesives for forming the second adhesive layer 54 include those described in International Application PCT / JP2021 / 006452, International Application PCT / JP2021 / 006453, or Japanese Patent Application No. 2021-025496 filed by the present applicant. The entire 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.

[0047] <Method for Evaluating Brightness Unevenness> Next, a method for evaluating brightness unevenness in the lighting device 100 will be described with reference to Figs. 8 to 10. Fig. 8 is a diagram for explaining an example of a method for evaluating brightness unevenness in lighting devices according to examples and comparative examples. Fig. 9 is a diagram showing an example of a brightness unevenness evaluation region P for lighting devices according to examples and comparative examples. Fig. 10 is a diagram showing an example of measurement results of brightness distribution.

[0048] 8, the luminance unevenness was evaluated by measuring the luminance of light emitted from a light source LS, diffused and transmitted through the light diffusing member 20, guided through the inside of the laminate 80 with a light guide layer, and emitted from almost the entire exit surface 82 using a two-dimensional spectroradiometer 600. An SR-5000 manufactured by Topcon Corporation was used as the two-dimensional spectroradiometer 600. The distance Tz from the exit surface 82 to the two-dimensional spectroradiometer 600 was set to 0.7 m.

[0049] In the image obtained by the two-dimensional spectroradiometer 600, a linear image region corresponding to the luminance unevenness evaluation region P shown in Fig. 9 was extracted, and the luminance distribution in the linear image region was evaluated. The distance Δ in Fig. 9 means the distance between the light-emitting surface LS0 of the light source LS and the surface of the light diffusing member 20 on the light source LS side.

[0050] Fig. 10 shows an example of the measurement results of the luminance distribution in the luminance unevenness evaluation area P. The horizontal axis in Fig. 10 represents the position on the luminance unevenness evaluation area P shown in Fig. 9. The position 0 mm is the position closest to the light source LS in the luminance unevenness evaluation area P. The larger the position value, the farther it is from the light source LS.

[0051] In the example shown in Figure 10, the highest luminance value Q1 is at a position near 10 mm, and the lowest luminance value Q2 is at a position near 20 mm. At positions farther away than 20 mm, the change in luminance becomes smaller. The low luminance value Q2 is a luminance value obtained at a position where luminance is minimal, farther away from the position where the highest luminance value Q1 is obtained, in the luminance unevenness evaluation region P. The smaller the luminance ratio obtained by dividing the low luminance value Q2 by the highest luminance value Q1, the greater the luminance unevenness, including band-like dark areas. In evaluating luminance unevenness, this luminance ratio was used as one of the evaluation indexes.

[0052] <Evaluation Results of Luminance Unevenness> Table 1 shows the main specifications and evaluation results of the lighting devices according to Comparative Examples 1 to 8 and Examples 1 to 5.

[0053]

[0054] In Table 1, "End surface processing of laminate with light guide layer" indicates information on whether or not the end surface of the laminate with light guide layer, onto which light from the light source is incident, was processed, and indicates the type of processed shape if processed. In Comparative Example 2, a plurality of grooves extending in the horizontal direction, i.e., the X direction in FIG. 9, were processed on the end surface of the laminate with light guide layer. In Comparative Example 3, a plurality of grooves extending in the vertical direction, i.e., the Z direction in FIG. 9, were processed on the end surface of the laminate with light guide layer. In Comparative Example 4, a plurality of lattice-shaped grooves extending both vertically and horizontally were processed on the end surface of the laminate with light guide layer. In Comparative Example 1 and Examples 1 to 5, the end surface of the laminate with light guide layer was not processed.

[0055] "Presence or absence of light diffusing member" indicates information on whether or not a light diffusing member was disposed between the light source and the end face of the laminate with a light guide layer. In Comparative Examples 1 to 6, a light diffusing member was not disposed. In Comparative Examples 7 and 8 and Examples 1 to 5, a light diffusing member was disposed. Note that the light diffusing member was disposed so that the surface of the light diffusing member facing the end face of the laminate with a light guide layer was in contact with the end face of the laminate with a light guide layer. In other words, the distance between the light diffusing member and the end face of the laminate with a light guide layer was set to approximately 0 mm.

[0056] The "diffused light half-value angle (°)" indicates the half-value angle of the BTDF of the diffused light emitted from the light diffusing member. In Comparative Examples 1 to 6, a light diffusing member was not provided, and thus a "-" is displayed. In Comparative Examples 7 and 8, the diffused light half-value angle was less than 50°. In Examples 1 to 5, the diffused light half-value angle was 50° or greater. The diffused light half-value angle is preferably 60° or greater, 65° or greater, 70° or greater, 80° or greater, or 90° or greater. The upper limit is not particularly limited, but is preferably 150° or less or 120° or less. Examples of materials that can be used for the light diffusing member include polycarbonate, polystyrene, polyester, silicone, and PMMA. For example, particles such as silica or titanium oxide can be added to these materials and the amount added can be adjusted to achieve the desired half-value angle. Fine irregularities may be formed on the surface of the substrate. Holographic technology can also be used to create films with specific diffusion characteristics. In this example, a milky white polycarbonate cover attached to an LED aluminum frame (product name LPJ1707) was used as the light diffusing member 20. This light diffusing member 20 has isotropy. The half-value angle was measured by the above-mentioned measurement method.

[0057] "Distance Δ (mm)" indicates the distance between the light-emitting surface LS0 of the light source LS shown in Fig. 9 and the surface of the light diffusing member 20 on the light source LS side. In Comparative Examples 1 to 5, a light diffusing member was not provided, and therefore "0 mm" is displayed. Note that only "5 mm" in Comparative Example 6 represents the distance between the light source and the end face of the laminate with a light guide layer.

[0058] "Half-value angle of light source distribution angle (°)" indicates the half-value angle of the light distribution angle of light emitted from the light source. In all of Comparative Examples 1 to 6 and Examples 1 to 5, the half-value angle of the light source distribution angle was set to 120°.

[0059] "Brightness ratio (%)" is the brightness ratio obtained by dividing the lowest brightness value Q2 shown in FIG. 10 by the highest brightness value Q1, and is expressed as a percentage.

[0060] "Luminance unevenness evaluation" shows the results of visual evaluation of the image obtained by the two-dimensional spectroradiometer 600. The symbols have the following meanings. "◎", "◯", and "△" are pass marks, and "×" is fail marks. ◎: No luminance unevenness was visible at all. ◯: Almost no luminance unevenness was visible. △: Luminance unevenness was visible but not noticeable. ×: Luminance unevenness was clearly visible.

[0061] As shown in Table 1, in Comparative Examples 1 to 8, the luminance ratio was 47% or less. Furthermore, in Comparative Examples 1 to 8, the "luminance unevenness judgment" was "×". Here, FIG. 11 is a diagram showing an example of an image of emitted light from the lighting device according to Comparative Example 4. As shown in FIG. 11, in Comparative Example 4, luminance unevenness including band-shaped dark portions S was visually recognized. Similarly, in Comparative Examples 1 to 3 and Comparative Examples 5 to 7, luminance unevenness including band-shaped dark portions S was visually recognized. From the above, it was found that the lighting devices according to Comparative Examples 1 to 8 had large luminance unevenness and were therefore unacceptable.

[0062] On the other hand, in Examples 1 to 5, the luminance ratio was 70% or more. Furthermore, in Examples 1 to 5, the "luminance unevenness judgment" was either "△", "◯", or "◎". Here, FIG. 12 is a diagram showing an example of an image of emitted light from the lighting device according to Example 4. As shown in FIG. 12, in Example 4, no luminance unevenness was visible. Similarly, in Example 5, no luminance unevenness was visible. In Examples 1 and 2, luminance unevenness was visible but not noticeable. In Example 3, luminance unevenness was hardly visible. From the above, it was found that the lighting devices according to Examples 1 to 5 had reduced luminance unevenness. It was also found that the lighting devices according to Examples 1 to 5 passed the test.

[0063] In Table 1, in Examples 2 to 5 in which the half-value angle of the BTDF of the light Lc diffused by the light diffusing member 20 was 70° or more, the "brightness ratio" was 81% or more. Therefore, from the viewpoint of increasing the "brightness ratio" and reducing brightness unevenness, it was found that it is preferable that the half-value angle of the angle at which the light Lc diffused by the light diffusing member 20 is diffused be 70° or more.

[0064] In Table 1, in Examples 3 to 5 in which the distance from the light source LS to the light diffusing member 20 was 1 mm or more, the "brightness ratio" was 87% or more, and the "brightness unevenness assessment" was "◯" or "◎". Therefore, from the viewpoint of increasing the "brightness ratio" and reducing brightness unevenness, it was found that it is more preferable that the half-value angle of the BTDF of the light Lc diffused by the light diffusing member 20 is 70° or more, and that the distance from the light source LS to the light diffusing member 20 is 1 mm or more.

[0065] In Table 1, in Examples 4 and 5 in which the distance from the light source LS to the light diffusing member 20 was 5 mm or more, the "brightness ratio" was 92% or more and the "brightness unevenness evaluation" was "◎". Therefore, from the viewpoint of increasing the "brightness ratio" and reducing brightness unevenness, it was found that it is particularly preferable that the half-value angle of the BTDF of the light Lc diffused by the light diffusing member 20 is 70° or more and the distance from the light source LS to the light diffusing member 20 is 5 mm or more.

[0066] The upper limit of the distance from the light source LS to the light diffusing member 20 is, for example, 20 mm or less, 15 mm or less, or 10 mm or less.

[0067] [Other Preferred Modifications] Fig. 13 is a schematic cross-sectional view showing a second example of the lighting device 100 including the shaped film according to the embodiment. Fig. 13 shows a part of the cross section corresponding to the line II-II in Fig. 1 in the second example of the lighting device 100.

[0068] In the second example of the lighting device 100 shown in Fig. 13, the light guide layer 10 is disposed opposite the substrate 30. Light incident from the light source LS into the laminate 80 with a light guide layer is emitted from an exit surface 82 located on the opposite side to the light guide layer 10. The second example of the lighting device 100 is mainly different from the first example of the lighting device 100 shown in Fig. 2 in these respects.

[0069] 13 also provides the same effects as those of the embodiment. The light exit surface from which light exits the light-guiding layer-equipped laminate 80 may be at least one of the upper surface (the surface on the +Z side) and the lower surface (the surface on the −Z side) of the light-guiding layer-equipped laminate 80.

[0070] The laminate 80 with a light guide layer may have a low refractive index layer disposed on one side of the laminate 80 with a light guide layer and having a refractive index lower than that of the light guide layer 10 or the shaping film 62. The laminate 80 with a light guide layer may also have a low refractive index layer between the shaping film 62 and the substrate 30. The low refractive index layer preferably has a refractive index of 1.30 or less. The laminate 80 with a light guide layer may also have a hard coat layer or an anti-reflection layer.

[0071] The adherend on which the laminate 80 with a light guide layer is placed is not limited to glass, but may also be an electronic substrate such as a liquid crystal cell, or a non-light-transmitting member such as a ceiling, wall, or floor. The shaping film 62 is not limited to extracting light to the side opposite to the side on which the adherend is located, but may extract light to the side on which the adherend is located. In this case, if the adherend has high light transmittance, the extracted light may pass through the adherend, and if the adherend has low light transmittance, the adherend may reflect the light.

[0072] Although the preferred embodiments have been described in detail above, the present invention is not limited to the above-described embodiments, and various modifications and substitutions can be made to the above-described embodiments without departing from the scope of the claims.

[0073] The ordinal numbers, quantities, and other figures used in the description of the embodiments are all provided as examples to specifically explain the technology of the present invention, and the present invention is not limited to the illustrated figures. Furthermore, the connection relationships between the components are provided as examples to specifically explain the technology of the present invention, and do not limit the connection relationships that realize the functions of the present invention.

[0074] The lighting device according to the embodiment can reduce brightness unevenness, and by being placed on building components such as glass, windows, walls, floors, and ceilings, it can illuminate the interior or exterior space of a building with reduced brightness unevenness.

[0075] Furthermore, the lighting device according to the embodiment can be used as a partition to suitably partition a room or conceal a desired space. Furthermore, by disposing the shape-imparting film, laminate, and laminate with a light guide layer provided in the lighting device according to the embodiment on a glass substrate of a display device such as a liquid crystal panel or an organic EL (Electro Luminescence) display panel, it is possible to brighten backlight illumination in the display device. In addition, the lighting device according to the embodiment can provide new uses other than those described above.

[0076] The present invention provides, for example, the following aspects. <1> An illumination device including a light guide having a cavity therein, a light source that emits light toward an end face of the light guide, and a light diffusing member disposed between the end face and the light source and diffusing and transmitting the light from the light source, wherein the light diffusing member has a half-value angle of 50° or greater in at least one cross section of a bidirectional transmittance distribution function measured when light is incident at an incident angle of 0°. <2> The illumination device according to <1>, wherein the light source includes a plurality of light sources arranged in a predetermined parallel direction, and at least one cross section of the bidirectional transmittance distribution function includes a central axis of the light diffusing member and is perpendicular to the parallel direction, the central axis of the light diffusing member being an axis that passes through the center of the light diffusing member and is parallel to a normal to the light diffusing member. <3> The illumination device according to <1> or <2>, wherein the light diffusing member has a half-value angle of 70° or greater in at least one cross section of a bidirectional transmittance distribution function measured when light is incident at an incident angle of 0°. <4> The lighting device according to <3>, wherein a distance from the light source to the light diffusing member is 1 mm or more. <5> The lighting device according to <3> or <4>, wherein a distance from the light source to the light diffusing member is 5 mm or more. <6> The lighting device according to any one of <1> to <5>, wherein the light guide includes a shaped film and a light guide layer.

[0077] This application claims priority based on Japanese Patent Application No. 2024-055660 filed with the Japan Patent Office on March 29, 2024, and includes the entire contents of this Japanese patent application.

[0078] 10 Light guide layer 20 Light diffusion member 20C Central axis 20P Center 30 Substrate 52 First adhesive layer 54 Second adhesive layer 60 Direction conversion layer 62 Shaped film 621 Main surface 622 Recess 64 Cavity 70 Laminate 80 Laminate with light guide layer 81 End surface 82 Emission surface 100 Lighting device 600 Two-dimensional spectroradiometer H Height ISa First inclined surface ISb Second inclined surface L Length Lc Diffused light Lr Light LS Light source NL Normal to light diffusion member P Luminance unevenness evaluation area Px, Py Pitch Q1 Maximum luminance value Q2 Lowest luminance value S Dark area Tz Distance W Width θa, θb Inclination angle θ0 Half-value angle Δ Spacing

Claims

1. A lighting device comprising: a light guide having an internal cavity; a light source that emits light toward an end face of said light guide; and a light diffusing member that is disposed between said end face and the light source and diffuses and transmits the light from said light source, wherein the light diffusing member has a half-value angle of 50° or greater in at least one cross section of a bidirectional transmittance distribution function measured by incident light at an incident angle of 0°.

2. The lighting device according to claim 1, wherein the light source includes a plurality of light sources arranged in a predetermined parallel direction, at least one cross section of the bidirectional transmittance distribution function includes the central axis of the light diffusing member and is a cross section perpendicular to the parallel direction, and the central axis of the light diffusing member is an axis that passes through the center of the light diffusing member and is parallel to the normal to the light diffusing member.

3. The lighting device according to claim 1, wherein the light diffusing member has a half-value angle of 70° or more in at least one cross section of a bidirectional transmittance distribution function measured by irradiating light at an incident angle of 0°.

4. The lighting device according to claim 3, wherein the distance from the light source to the light diffusing member is 1 mm or more.

5. The lighting device according to claim 4, wherein the distance from the light source to the light diffusing member is 5 mm or more.

6. The lighting device of claim 1, wherein the light guide comprises a shaped film and a light guide layer.

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