Planar luminaire

Abstract

To provide a planar luminaire capable of achieving high luminance.SOLUTION: A planar luminaire includes: a plurality of light sources arranged on a substrate; a first optical sheet arranged on the emission side of the light sources; a second optical sheet arranged on the emission side of the first optical sheet; and a third optical sheet arranged on the emission side of the second optical sheet. The first optical sheet includes a plurality of first optical elements protruding in a first direction approaching the light sources. The second optical sheet includes a plurality of second optical elements protruding in a second direction opposite from the first direction. The third optical sheet includes a plurality of third optical elements protruding in the second direction.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] An embodiment of the present invention relates to a surface illumination device. [Background technology]

[0002] Planar lighting devices used as backlights for displays and the like are required to have performance and functions such as high brightness, high contrast, high brightness uniformity, low power consumption, thinness, and support for local dimming. In order to realize these performance and functions in direct-type backlights, various technologies have been proposed. As one example, an optical sheet (brightness enhancement sheet) having triangular prisms protruding in the emission direction is used to improve brightness (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2023-17428 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, particularly for backlights for virtual reality (VR), there is a demand for even higher brightness due to, for example, higher resolution of liquid crystals and reduced transmittance of eyepiece lenses.

[0005] The present invention has been made in view of the above, and an object of the present invention is to provide a surface illumination device capable of achieving high brightness. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems and achieve the object, a surface lighting device according to one embodiment of the present invention comprises a plurality of light sources arranged on a substrate, a first optical sheet arranged on the exit side of the light sources, a second optical sheet arranged on the exit side of the first optical sheet, and a third optical sheet arranged on the exit side of the second optical sheet, wherein the first optical sheet has a plurality of first optical elements protruding in a first direction approaching the light source, the second optical sheet has a plurality of second optical elements protruding in a second direction opposite to the first direction, and the third optical sheet has a plurality of third optical elements protruding in the second direction.

[0007] A surface illumination device according to an aspect of the present invention can achieve high brightness. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a front view of a surface illumination device according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a cross-sectional view of the surface illumination device according to the embodiment taken along line AA in FIG. [Diagram 3] FIG. 3 is a cross-sectional view of the surface illumination device according to the embodiment taken along line BB in FIG. [Figure 4] FIG. 4 is a perspective view of a part of the internal structure of the surface illumination device. [Diagram 5] FIG. 5 is a cross-sectional view of the surface illumination device taken along line AA in FIG. [Figure 6] FIG. 6 is a cross-sectional view of the surface illumination device taken along line BB in FIG. [Figure 7] FIG. 7 shows the results of an optical simulation of the relative luminance for the comparative example. [Figure 8A] FIG. 8A is a diagram showing the luminance distribution in a surface illumination device. [Figure 8B] FIG. 8B is a diagram showing the luminance distribution in the surface illumination device. [Figure 8C] FIG. 8C is a diagram showing the luminance distribution in the surface illumination device. [Figure 9A] FIG. 9A is a diagram showing the luminance distribution in a surface illumination device. [Figure 9B] FIG. 9B is a diagram showing the luminance distribution in the surface illumination device. [Figure 9C] FIG. 9C is a diagram showing the luminance distribution in the surface illumination device. [Figure 10] FIG. 10 is a diagram for explaining the function of the light distribution conversion sheet according to the embodiment. [Figure 11] FIG. 11 is a cross-sectional view of the surface illumination device taken along line AA in FIG. [Figure 12] FIG. 12 is a cross-sectional view of the surface illumination device taken along line BB in FIG. [Figure 13] FIG. 13 is a perspective view of a part of the internal structure of the surface illumination device. [Figure 14A] FIG. 14A is a diagram showing a luminance distribution in a surface illumination device according to Modification 1. FIG. [Figure 14B] FIG. 14B is a diagram showing the luminance distribution in the surface illumination device according to the first modification. [Figure 14C] FIG. 14C is a diagram showing a luminance distribution in the surface illumination device according to the first modification. [Figure 15] FIG. 15 is a cross-sectional view of the surface illumination device taken along line AA in FIG. [Figure 16] FIG. 16 is a cross-sectional view of the surface illumination device taken along line BB in FIG. [Figure 17A] FIG. 17A is a diagram showing a luminance distribution in a surface illumination device according to Modification 2. FIG. [Figure 17B] FIG. 17B is a diagram showing the luminance distribution in the surface illumination device according to the second modification. [Figure 17C] FIG. 17C is a diagram showing the luminance distribution in the surface illumination device according to the second modification. [Figure 18] FIG. 18 shows the results of an optical simulation of the relative luminance for a comparative example of a modified example in which quadrangular pyramidal prisms are used in the light distribution conversion sheet. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, a planar lighting device according to an embodiment will be described with reference to the drawings. Note that the present invention is not limited to this embodiment. In addition, the dimensional relationship of each element in the drawings, the ratio of each element, etc. may differ from reality. The drawings may also include parts with different dimensional relationships and ratios. In principle, the contents described in one embodiment or modified example are similarly applied to other embodiments or modified examples.

[0010] (Embodiment) 1 is a front view of a surface lighting device 10 according to an embodiment. For ease of explanation, the light emitting surface of the surface lighting device 1 corresponds to the XY plane, and the thickness direction of the surface lighting device 1 corresponds to the Z direction.

[0011] 1, the surface lighting device 10 has a substantially rectangular plate-like outer shape, and includes a liquid crystal panel 20 inside an opening 21a of a frame 21. The outer shape of the surface lighting device 10 is not limited to that shown in the figure.

[0012] The cross-sectional configuration of the planar lighting device 10 will be described with reference to Figures 2 and 3. Figure 2 is a cross-sectional view of the planar lighting device 10 according to the embodiment taken along line AA in Figure 1. Figure 3 is a cross-sectional view of the planar lighting device 10 according to the embodiment taken along line BB in Figure 1. Note that, hereinafter, the positive Z-axis direction in Figures 2 and 3 may simply be referred to as the "upward direction" or "upward", and the negative Z-axis direction in Figures 2 and 3 may simply be referred to as the "downward direction" or "downward".

[0013] 2 and 3, the surface illumination device 10 includes a substrate 11, a light source 12, a reflector 13, a dichroic sheet 14, a wavelength conversion sheet 15, a diffusion sheet 16, a light distribution conversion sheet 17, a brightness enhancement sheet 18, a brightness enhancement sheet 19, a liquid crystal panel 20, and a frame 21. Note that in Figs. 2 and 3, the frame 21 is not shown in cross section, but rather, only the end of an opening 21a (Fig. 1) is visible.

[0014] The substrate 11 is made of, for example, aluminum or the like having excellent heat dissipation properties. A plurality of light sources 12 are two-dimensionally arranged in a lattice pattern on the substrate 11, with appropriate insulation being provided thereon. In addition, a reflector 13 is arranged on the emission side of the substrate 11 where the light sources 12 are arranged.

[0015] The light source 12 is, for example, an LED (Light Emitting Diode) that emits blue light. Each light source 12 is driven individually and can support so-called local dimming. The size of the light source 12 is, for example, 450 μm×260 μm, and the pitch of each light source 12 is, for example, 1.5 mm×1.2 mm.

[0016] The reflector 13 has four reflective surfaces 13a surrounding each of the multiple light sources 12. The periphery of the reflector 13 is in the shape of a frame that is higher (thicker) than the height of the reflective surfaces 13a, and a space is provided on the tip side of the reflective surfaces 13a. Note that the reflective surfaces 13a may be configured to extend until they contact the dichroic sheet 14 described below without providing a space on the tip side of the reflective surfaces 13a. The reflector 13 is made of resin or the like. Note that the reflector 13 may be omitted in some cases.

[0017] The dichroic sheet 14 is an optical sheet disposed on the exit side of the reflector 13 and has a bandpass filter function. For example, the dichroic sheet 14 has a filter function of transmitting blue light generated from the light source 12 and reflecting yellow light (a mixture of green light and red light) from the wavelength conversion sheet 15 described later.

[0018] The wavelength conversion sheet 15 is an optical sheet disposed on the exit side of the dichroic sheet 14, and converts the wavelength of the light (primary light) emitted from the light source 12 into light of a longer wavelength (secondary light). For example, the wavelength conversion sheet 15 transmits a part of the blue light from the light source 12 and absorbs the other part of the blue light to emit yellow light (a mixture of green light and red light).

[0019] For example, the wavelength conversion sheet 15 is a mixture of quantum dot phosphors dispersed in a highly transparent resin (e.g., polyester resin, acrylic resin). In this embodiment, the quantum dot phosphor is a mixture of a green quantum dot phosphor that absorbs and is excited by blue light from the light source 12 to emit green light in a wavelength range of about 500 nm to about 570 nm and a red quantum dot phosphor that emits red light in a wavelength range of about 600 nm to about 780 nm, in a predetermined ratio. Note that the wavelength conversion material is not limited to the quantum dot phosphor as long as it is a material that can convert the wavelength of primary light included in a predetermined wavelength range into secondary light included in a different wavelength range. For example, inorganic phosphors, organic phosphors, etc. can be used as other wavelength conversion materials.

[0020] The diffusion sheet 16 is an optical sheet that is disposed on the emission side of the wavelength conversion sheet 15 and diffuses the light emitted from the wavelength conversion sheet 15 to improve the in-plane uniformity.

[0021] The light distribution conversion sheet 17 is disposed on the emission side of the diffusion sheet 16, and is an optical sheet having a plurality of triangular prisms protruding in a direction approaching the light source 12 (i.e., the negative direction of the Z axis). For example, the triangular prisms of the light distribution conversion sheet 17 have a linear ridge line along the Y axis direction, and a plurality of them are disposed along the X axis direction. The cross-sectional shape of each of these triangular prisms in the XZ plane (a plane substantially perpendicular to the Y axis direction) shown in FIG. 2 is an isosceles triangle with the ridge line as the apex. The apex angle of this isosceles triangle is preferably about 80 degrees, as described later. The pitch of each of the triangular prisms is, for example, 100 μm. The triangular prisms are an example of an optical element.

[0022] The brightness enhancing sheet 18 is an optical sheet disposed on the emission side of the light distribution conversion sheet 17 and having a plurality of triangular prisms protruding in a direction away from the light source 12 (i.e., the Z-axis direction). For example, the triangular prisms of the brightness enhancing sheet 18 have linear ridgelines along the X-axis direction, and a plurality of them are disposed along the Y-axis direction. The cross-sectional shape of each of these triangular prisms in the YZ plane (a plane substantially perpendicular to the X-axis direction) shown in FIG. 3 is an isosceles triangle with the ridgeline as a vertex. The apex angle of this isosceles triangle is approximately 90 degrees. The pitch of each of the triangular prisms is, for example, 25 μm.

[0023] The brightness enhancing sheet 19 is an optical sheet disposed on the emission side of the brightness enhancing sheet 18 and having a plurality of triangular prisms protruding in a direction away from the light source 12 (i.e., the Z-axis direction). For example, the triangular prisms of the brightness enhancing sheet 19 have linear ridgelines along the Y-axis direction, and are disposed along the X-axis direction. The cross-sectional shape of each triangular prism in the XZ plane (a plane substantially perpendicular to the Y-axis direction) shown in FIG. 2 is an isosceles triangle with the ridgeline as the apex. The apex angle of this isosceles triangle is approximately 90 degrees. The pitch of each triangular prism is, for example, 25 μm. That is, the brightness enhancing sheet 19 is a prism sheet having a similar configuration to the brightness enhancing sheet 18, disposed so that the direction in which the ridgelines of the prisms extend is perpendicular to the brightness enhancing sheet 18.

[0024] The multiple triangular prisms formed on the light distribution conversion sheet 17, the brightness enhancement sheet 18, and the brightness enhancement sheet 19 are arranged continuously so that no flat (parallel to the XY plane) portion is formed between the triangular prisms.

[0025] The liquid crystal panel 20 is a display panel that displays images. The liquid crystal panel 20 has a plurality of liquid crystal elements arranged two-dimensionally along the XY plane, and displays an image by controlling the light passing through each liquid crystal element according to the pattern of the image to be displayed.

[0026] Fig. 4 is a perspective view of a part of the internal structure of the surface lighting device 10. In Fig. 4, a diffusion sheet 16, a light distribution conversion sheet 17, a luminance enhancing sheet 18, and a luminance enhancing sheet 19 are placed in a stacked manner in this order.

[0027] Unlike the luminance enhancing sheets 18 and 19, which have upward-facing triangular prisms, the light distribution conversion sheet 17 according to the embodiment has downward-facing triangular prisms. Furthermore, the light distribution conversion sheet 17 is arranged so that the ridgeline of the downward-facing triangular prism is parallel to the ridgeline of the triangular prism of the luminance enhancing sheet 19 (the luminance enhancing sheet arranged on the exit side of the pair of luminance enhancing sheets). As a result, the planar lighting device 10 according to the embodiment can achieve high luminance.

[0028] Here, the luminance improvement effect of the planar lighting device 10 according to the embodiment will be described in comparison with a planar lighting device 30 according to a comparative example. The configuration of the planar lighting device 30 is similar to that of the planar lighting device 10, except that a diffusion sheet 22 is provided instead of the light distribution conversion sheet 17. In other words, the front view of the planar lighting device 30 is similar to the front view of the planar lighting device 10 shown in Fig. 1, and therefore a description thereof will be omitted.

[0029] The cross-sectional configuration of the surface lighting device 30 will be described with reference to Fig. 5 and Fig. 6. Fig. 5 is a cross-sectional view of the surface lighting device 30 taken along line AA in Fig. 1. Fig. 6 is a cross-sectional view of the surface lighting device 30 taken along line BB in Fig. 1. In Figs. 5 and 6, the same components as those shown in Figs. 2 and 3 are designated by the same reference numerals, and their description will be omitted.

[0030] 5 and 6, the surface illumination device 30 includes a substrate 11, a light source 12, a reflector 13, a dichroic sheet 14, a wavelength conversion sheet 15, a diffusion sheet 16, a diffusion sheet 22, a brightness enhancement sheet 18, a brightness enhancement sheet 19, a liquid crystal panel 20, and a frame 21. Here, the configuration of the diffusion sheet 22 is similar to that of the diffusion sheet 16.

[0031] FIG. 7 shows the optical simulation results of the relative luminance for the comparative example. In FIG. 7, the "relative luminance" on the vertical axis indicates the ratio of the BL luminance of the planar lighting device 10 to the backlight (BL) luminance of the planar lighting device 30. The "apex angle" on the horizontal axis indicates the magnitude of the apex angle of the triangular prism of the light distribution conversion sheet 17. "PC" indicates the case where the light distribution conversion sheet 17 is made of polycarbonate resin. "PMMA" indicates the case where the light distribution conversion sheet 17 is made of polymethyl methacrylate resin. "Top" indicates the case where the light distribution conversion sheet 17 has an upward-facing triangular prism. "Bottom" indicates the case where the light distribution conversion sheet 17 has a downward-facing triangular prism. "0" indicates the case where the angle difference in the XY plane between the ridge line of the triangular prism of the light distribution conversion sheet 17 and the ridge line of the triangular prism of the luminance improvement sheet 19 is 0 degrees. "90" indicates that the angular difference in the XY plane between the ridgeline of the triangular prism of the light distribution conversion sheet 17 and the ridgeline of the triangular prism of the luminance improving sheet 19 is 90 degrees.

[0032] As shown in Fig. 7, when the apex angle of the triangular prism of the light distribution conversion sheet 17 of "PMMA_down 0" and "PC_down 0" was 78 degrees to 83 degrees, a good relative luminance value was obtained. Furthermore, when the apex angle was about 80 degrees, a particularly good relative luminance value was obtained.

[0033] Table 1 shows the results of actual evaluation of the luminance characteristics of the surface illumination device 10 and the surface illumination device 30.

[0034] [Table 1]

[0035] In Table 1, BL luminance indicates the luminance (center luminance) of the light emitted from the backlight. Optical efficiency indicates how efficiently the light from the light source is used as light emitted from the backlight. Light distribution angle indicates the half-width of the luminance distribution of the light emitted from the backlight. LCD luminance indicates the luminance of the light emitted from the liquid crystal panel.

[0036] The results in Table 1 suggest that the planar lighting device 10 has higher optical efficiency than the planar lighting device 30 and is able to properly concentrate light from the light source, thereby improving the BL luminance and LCD luminance.

[0037] 8A, 8B, and 8C are diagrams showing the (relative) luminance distribution in the planar lighting device 30 (maximum value is 100). FIG. 8A is a diagram showing the luminance distribution of light emitted from the diffusion sheet 22 of the planar lighting device 30. FIG. 8B is a diagram showing the luminance distribution of light emitted from the luminance improving sheet 18 of the planar lighting device 30. FIG. 8C is a diagram showing the luminance distribution of light emitted from the luminance improving sheet 19 of the planar lighting device 30. Note that the circular graph of the luminance distribution shows the luminance measured at the normal direction (elevation angle 0 degrees) of the light emitting surface of the light source 12 at its center, and the luminance measured at a larger elevation angle is shown as it moves away from the center of the circular graph. Note that the minimum elevation angle is 0 degrees, and the maximum elevation angle is 90 degrees. The direction connecting 0L and 180L in the circular graph corresponds to the X-axis direction, the direction connecting 90L and 270L in the circular graph corresponds to the Y-axis direction, and the normal direction of the circular graph corresponds to the Z-axis direction.

[0038] 8A, a unimodal luminance distribution was measured that was uniformly distributed in both the X-axis and Y-axis directions, which indicates that the diffusion sheet 22 provided an isotropic diffusion effect on the light from the diffusion sheet 16.

[0039] In Fig. 8B, a unimodal luminance distribution focused in the Y-axis direction was measured, as compared with the luminance distribution in Fig. 8A. This indicates that the triangular prisms of the luminance enhancing sheet 18, which have ridges along the X-axis direction, provided a focusing effect in the Y-axis direction to the light from the diffusion sheet 22.

[0040] In Fig. 8C, a unimodal luminance distribution focused in the X-axis direction was measured, as compared with the luminance distribution in Fig. 8B. This indicates that the triangular prisms of the luminance enhancing sheet 19, which have ridges along the Y-axis direction, provided a focusing effect in the X-axis direction to the light from the luminance enhancing sheet 18.

[0041] 9A, 9B, and 9C are diagrams showing luminance distribution (relative to the maximum value being 100) in the planar lighting device 10. FIG. 9A is a diagram showing the luminance distribution of light emitted from the light distribution conversion sheet 17 of the planar lighting device 10. FIG. 9B is a diagram showing the luminance distribution of light emitted from the luminance improving sheet 18 of the planar lighting device 10. FIG. 9C is a diagram showing the luminance distribution of light emitted from the luminance improving sheet 19 of the planar lighting device 10. The method of depicting the circular graphs of the luminance distribution is the same as in FIGS. 8A to 8C.

[0042] In Fig. 9A, a bimodal luminance distribution distributed in the X-axis direction was measured. This shows that the triangular prisms of light distribution conversion sheet 17, which have downward ridges along the Y-axis direction, impart a light distribution effect in the X-axis direction to the unimodal light from diffusion sheet 16. In other words, this shows that light distribution conversion sheet 17 converts the unimodal luminance distribution of the incident light into a bimodal luminance distribution in the X-axis direction.

[0043] In Fig. 9B, a bimodal luminance distribution focused in the Y-axis direction was measured, as compared with the luminance distribution in Fig. 9A. This indicates that the triangular prisms of the luminance enhancing sheet 18, which have upward ridges along the X-axis direction, provided a focusing effect in the Y-axis direction to the light from the light distribution conversion sheet 17.

[0044] In Fig. 9C, a unimodal luminance distribution focused in the X-axis direction was measured, as compared with the luminance distribution in Fig. 9B. This indicates that the triangular prisms of the luminance enhancing sheet 19, which have upward ridges along the Y-axis direction, provided a focusing effect in the X-axis direction to the light from the luminance enhancing sheet 18.

[0045] Here, the luminance distribution in Fig. 9C has a narrower half-width and a higher luminance peak than the luminance distribution in Fig. 8C (see Table 1). This result suggests that the planar illumination device 10 was able to properly collect light from the light source compared to the planar illumination device 30, thereby increasing the luminance.

[0046] Fig. 10 is a diagram for explaining the function of the light distribution conversion sheet 17 according to the embodiment. Fig. 10 shows the state of light refraction in the brightness enhancing sheet 18. Note that the brightness enhancing sheet 19 is similar to the brightness enhancing sheet 18 except for the arrangement direction of the triangular prisms, and therefore a description thereof will be omitted.

[0047] As shown in FIG. 10, the brightness enhancing sheet 18 is known to improve brightness by doubly reflecting (retroreflecting) light incident in an upward direction on the brightness enhancing sheet 18 downward, while refracting light incident in an oblique direction from a triangular prism and emitting it in an upward direction. The light distribution conversion sheet 17 according to the embodiment distributes light to a brightness distribution in which there is more light incident in an oblique direction than light incident in a vertical direction (upward direction) on the brightness enhancing sheet 18 (or the light distribution conversion sheet 17 refracts light incident in a vertical direction (upward direction) into a pair of oblique directions by a pair of inclined surfaces constituting a triangular prism). As a result, the planar lighting device 10 according to the embodiment is considered to improve brightness by increasing the amount of light refracted and emitted in an upward direction compared to the light doubly reflected downward by the brightness enhancing sheet 18. For example, the planar lighting device 10 can realize high brightness of a backlight for VR.

[0048] The surface illumination device 10 according to the embodiment can be widely applied to backlights for various purposes other than VR backlights.

[0049] (Variation 1) In the above embodiment, the light distribution conversion sheet 17 has triangular prisms protruding downward, but the present invention is not limited to this. The planar lighting device 40 according to the first modification includes a light distribution conversion sheet 23 having quadrangular pyramidal prisms protruding downward, instead of the light distribution conversion sheet 17.

[0050] The configuration of the planar lighting device 40 is similar to that of the planar lighting device 10, except that a light distribution conversion sheet 23 is provided instead of the light distribution conversion sheet 17. That is, the front view of the planar lighting device 40 is similar to the front view of the planar lighting device 10 shown in FIG. 1, and therefore a description thereof will be omitted.

[0051] The cross-sectional configuration of the surface lighting device 40 will be described with reference to Fig. 11 and Fig. 12. Fig. 11 is a cross-sectional view of the surface lighting device 40 taken along line AA in Fig. 1. Fig. 12 is a cross-sectional view of the surface lighting device 40 taken along line BB in Fig. 1. In Figs. 11 and 12, the same components as those shown in Figs. 2 and 3 are designated by the same reference numerals, and their description will be omitted.

[0052] 11 and 12, the surface lighting device 40 includes a substrate 11, a light source 12, a reflector 13, a dichroic sheet 14, a wavelength conversion sheet 15, a diffusion sheet 16, a light distribution conversion sheet 23, a brightness enhancement sheet 18, a brightness enhancement sheet 19, a liquid crystal panel 20, and a frame 21.

[0053] The light distribution conversion sheet 23 is an optical sheet disposed on the emission side of the diffusion sheet 16 and having a plurality of quadrangular pyramidal prisms protruding in a direction approaching the light source 12 (i.e., the negative direction of the Z axis). For example, the quadrangular pyramidal prism of the light distribution conversion sheet 23 has a bottom surface including a base along the X-axis direction and a base along the Y-axis direction. A plurality of such quadrangular pyramidal prisms are disposed in the X-axis direction and the Y-axis direction. Of the four side surfaces constituting the quadrangular pyramidal prism, the angle formed by two side surfaces facing each other across the apex is 78 degrees to 83 degrees, more preferably about 80 degrees. A suitable protruding direction and angle of the quadrangular pyramidal prism of the light distribution conversion sheet 23 will be described later using data on which the protrusions are based. The pitch of each quadrangular pyramidal prism is, for example, 100 μm×100 μm. The quadrangular pyramidal prism is an example of an optical element.

[0054] Fig. 13 is a perspective view of a partial internal structure of the planar lighting device 40. In Fig. 13, the diffusion sheet 16, the light distribution conversion sheet 23, the luminance improving sheet 18, and the luminance improving sheet 19 are placed in a stacked manner in this order. That is, the light distribution conversion sheet 23 according to the first modification has downward-facing quadrangular pyramid prisms. As a result, the planar lighting device 10 according to the first modification can achieve high luminance.

[0055] 14A, 14B, and 14C are diagrams showing luminance distributions (relative to the maximum value being 100) in the planar lighting device 40 according to the first modification. FIG. 14A is a diagram showing the luminance distribution of light emitted from the light distribution conversion sheet 23 of the planar lighting device 40. FIG. 14B is a diagram showing the luminance distribution of light emitted from the luminance improving sheet 18 of the planar lighting device 40. FIG. 14C is a diagram showing the luminance distribution of light emitted from the luminance improving sheet 19 of the planar lighting device 40. The method of depicting the circular graphs of the luminance distributions is the same as in FIGS. 8A to 8C.

[0056] 14A, a quadrimodal luminance distribution in the X-axis direction was measured. This shows that the square pyramidal prisms of light distribution conversion sheet 23 aligned along the X-axis and Y-axis directions impart a light distribution effect in the X-axis and Y-axis directions to the unimodal light from diffusion sheet 16. In other words, light distribution conversion sheet 23 converts the unimodal luminance distribution of the incident light into a quadrimodal (bimodal in the X-axis and Y-axis directions, respectively) luminance distribution.

[0057] In Fig. 14B, a bimodal luminance distribution focused in the Y-axis direction was measured, as compared with the luminance distribution in Fig. 14A. This indicates that the triangular prisms of the luminance enhancing sheet 18, which have ridgelines along the X-axis direction, provided a focusing effect in the Y-axis direction to the light from the light distribution conversion sheet 23.

[0058] In Fig. 14C, a unimodal luminance distribution focused in the X-axis direction was measured, as compared with the luminance distribution in Fig. 14B. This indicates that the triangular prisms of the luminance enhancing sheet 19, which have ridges along the Y-axis direction, provided a focusing effect in the X-axis direction to the light from the luminance enhancing sheet 18.

[0059] Here, the luminance distribution in Fig. 14C has a narrower half-width and a higher luminance peak than the luminance distribution in Fig. 8C. This result suggests that the planar illumination device 40 has increased luminance by more appropriately concentrating light from the light source than the planar illumination device 30. Specific data regarding the half-width and luminance peak of the luminance distribution in Fig. 14C and the luminance distribution in Fig. 8C will be described later.

[0060] (Variation 2) In the above modification 1, the light distribution conversion sheet 23 has a quadrangular pyramidal prism protruding downward, but this is not limited to the above. The planar lighting device 50 according to modification 2 includes a light distribution conversion sheet 24 having upwardly protruding quadrangular pyramidal prisms instead of the light distribution conversion sheet 23.

[0061] The configuration of the planar lighting device 50 is similar to that of the planar lighting device 40, except that a light distribution conversion sheet 24 is provided instead of the light distribution conversion sheet 23. That is, the front view of the planar lighting device 50 is similar to the front view of the planar lighting device 10 shown in FIG. 1, and therefore a description thereof will be omitted.

[0062] The cross-sectional configuration of the surface lighting device 50 will be described with reference to Fig. 15 and Fig. 16. Fig. 15 is a cross-sectional view of the surface lighting device 50 taken along line AA in Fig. 1. Fig. 16 is a cross-sectional view of the surface lighting device 50 taken along line BB in Fig. 1. In Fig. 15 and Fig. 16, the same components as those shown in Fig. 2 and Fig. 3 are denoted by the same reference numerals, and their description will be omitted.

[0063] 15 and 16, a surface lighting device 50 includes a substrate 11, a light source 12, a reflector 13, a dichroic sheet 14, a wavelength conversion sheet 15, a diffusion sheet 16, a light distribution conversion sheet 24, a brightness enhancement sheet 18, a brightness enhancement sheet 19, a liquid crystal panel 20, and a frame 21.

[0064] The light distribution conversion sheet 24 is an optical sheet disposed on the emission side of the diffusion sheet 16 and having a plurality of quadrangular pyramidal prisms protruding in a direction away from the light source 12 (i.e., the Z-axis direction). For example, the quadrangular pyramidal prism of the light distribution conversion sheet 24 has a bottom surface including a base along the X-axis direction and a base along the Y-axis direction. A plurality of such quadrangular pyramidal prisms are disposed in the X-axis direction and the Y-axis direction. Of the four side surfaces constituting the quadrangular pyramidal prism, the angle formed by two side surfaces facing each other across the apex is 144 to 157 degrees, more preferably about 147 degrees. A suitable protruding direction and angle of the quadrangular pyramidal prism of the light distribution conversion sheet 24 will be described later using data on which the protrusions are based. The pitch of each quadrangular pyramidal prism is, for example, 100 μm×100 μm. The quadrangular pyramidal prism is an example of an optical element.

[0065] That is, in the planar lighting device 50 according to the second modification, the diffusion sheet 16, the light distribution conversion sheet 24, the brightness enhancing sheet 18, and the brightness enhancing sheet 19 are placed in a stacked manner in this order. The light distribution conversion sheet 24 according to the second modification has upward-facing quadrangular pyramid prisms. As a result, the planar lighting device 50 according to the second modification can achieve high brightness.

[0066] 17A, 17B, and 17C are diagrams showing luminance distributions (relative to the maximum value being 100) in a planar lighting device 50 according to Modification 2. FIG. 17A is a diagram showing the luminance distribution of light emitted from the light distribution conversion sheet 24 of the planar lighting device 50. FIG. 17B is a diagram showing the luminance distribution of light emitted from the luminance improving sheet 18 of the planar lighting device 50. FIG. 17C is a diagram showing the luminance distribution of light emitted from the luminance improving sheet 19 of the planar lighting device 50. The method of depicting the circular graphs of the luminance distributions is the same as in FIGS. 8A to 8C.

[0067] In Fig. 17A, a unimodal luminance distribution focused in each of the X-axis and Y-axis directions was measured. This shows that the pyramidal prisms of the light distribution conversion sheet 24 aligned along the X-axis and Y-axis directions provided a focusing effect in the X-axis and Y-axis directions to the unimodal light from the diffusion sheet 16. In other words, this shows that the light distribution conversion sheet 24 distributes light so as to bring the direction of light incident on the luminance improving sheet 18 closer to the vertical direction. This also shows that the light distribution conversion sheet 24 distributes light so as to narrow the half-width of the luminance distribution of the incident light.

[0068] In Fig. 17B, a unimodal luminance distribution focused in the Y-axis direction was measured, as compared with the luminance distribution in Fig. 17A. This indicates that the triangular prisms of the luminance enhancing sheet 18, which have ridgelines along the X-axis direction, provided a focusing effect in the Y-axis direction to the light from the light distribution conversion sheet 24.

[0069] In Fig. 17C, a unimodal luminance distribution focused in the X-axis direction was measured, as compared with the luminance distribution in Fig. 17B. This indicates that the triangular prisms of the luminance enhancing sheet 19, which have ridges along the Y-axis direction, provided a focusing effect in the X-axis direction to the light from the luminance enhancing sheet 18.

[0070] Here, the luminance distribution in Fig. 17C has a narrower half-width and a higher luminance peak than the luminance distribution in Fig. 8C. This result suggests that the planar illumination device 50 according to the second modification is able to appropriately collect light from the light source, thereby increasing the luminance, compared to the planar illumination device 30. Specific data regarding the half-width and luminance peak of the luminance distribution in Fig. 17C and the luminance distribution in Fig. 8C will be described later.

[0071] First, the preferred protruding direction and angle of the pyramidal prism will be described with reference to FIG. 18. FIG. 18 shows the result of an optical simulation of the relative luminance of the comparative example of the modified example using the pyramidal prism in the light distribution conversion sheet. In FIG. 18, the "relative luminance" on the vertical axis indicates the ratio of the backlight (BL) luminance of the modified planar lighting device using the pyramidal prism in the light distribution conversion sheet to the backlight (BL) luminance of the planar lighting device 30, which is the comparative example. The "apex angle" on the horizontal axis indicates the angle between two side surfaces facing each other across the apex, among the four side surfaces constituting the pyramidal prism. "PC" indicates the case where the light distribution conversion sheet is made of polycarbonate resin. "PMMA" indicates the case where the light distribution conversion sheet is made of polymethyl methacrylate resin. "Top" indicates the case where the light distribution conversion sheet has a pyramidal prism facing upward. "Bottom" indicates the case where the light distribution conversion sheet has a pyramidal prism facing downward. "0" indicates that the base of the quadrangular pyramidal prism of the light distribution conversion sheet is formed with a base along the X-axis direction and a base along the Y-axis direction. "45" indicates that the base of the quadrangular pyramidal prism of the light distribution conversion sheet is arranged in such a way that the base in the case of "0" is rotated 45 degrees on the XY plane.

[0072] As shown in Fig. 18, good relative luminance values ​​were obtained when, of the four side surfaces constituting the quadrangular pyramidal prisms of the "PMMA_down0" and "PC_down0" light distribution conversion sheets, the angle formed by two side surfaces opposing each other across the apex was 78 degrees to 83 degrees. Furthermore, particularly good relative luminance values ​​were obtained when this angle was approximately 80 degrees. The "PMMA_down0" or "PC_down0" light distribution conversion sheet having quadrangular pyramidal prisms with an angle of approximately 80 degrees corresponds to the light distribution conversion sheet 23 of the planar lighting device 40 of the above-mentioned modification 1.

[0073] Also, as shown in Fig. 18, good relative luminance values ​​were obtained when the angle between two of the four side surfaces that constitute the pyramidal prisms of the light distribution conversion sheets "PMMA_up 0", "PMMA_up 45", "PC_up 0", and "PC_up 45" that face each other across the apex was 144 degrees to 157 degrees. Also, when this angle was about 147 degrees, a particularly good relative luminance value was obtained. That is, in the light distribution conversion sheet having upward-facing pyramidal prisms with angles of 144 degrees to 157 degrees, an improvement in luminance was confirmed whether the rotation angle of the pyramid was 0 degrees or 45 degrees.

[0074] A light distribution conversion sheet having pyramidal prisms with an angle of approximately 147 degrees in "PMMA_up 0" or "PC_up 0" corresponds to the light distribution conversion sheet 24 of the planar lighting device 50 of the above-mentioned modified example 2. However, a light distribution conversion sheet having pyramidal prisms with an angle of approximately 147 degrees in "PMMA_up 45" or "PC_up 45" can also be applied as the light distribution conversion sheet 24 of the planar lighting device 50 of modified example 2.

[0075] Here, light distribution conversion sheet 24 of modification 2 will be described in more detail. As shown in Fig. 18, PMMA has a slightly higher luminance improvement effect than PC. For PMMA, the angle range where the relative luminance is 110% or more is 144 degrees to 153 degrees. For PC, the angle range where the relative luminance is 108% or more is 147 degrees to 157 degrees.

[0076] Next, the half-widths and luminance peaks of the luminance distributions of Modified Example 1 and Modified Example 2 compared to the comparative example will be described with reference to Table 2. Table 2 also shows the luminance distributions of the embodiment. Table 2 shows the evaluation results obtained by evaluating the luminance characteristics of the planar lighting device 30 (comparative example), the planar lighting device 10 (embodiment), the planar lighting device 40 (Modified Example 1), and the planar lighting device 50 (Modified Example 2) by simulation. Note that for the embodiment, Table 1 shows the results of actual measurements, while Table 2 shows the results of simulations, so there are slight differences in the values.

[0077] [Table 2]

[0078] In Table 2, the relative luminance indicates the relative value of the luminance (center luminance) of the light emitted from the backlight of the comparative example, relative to the luminance (center luminance) of the light emitted from the backlight of the embodiment, the modification 1, and the modification 2. The light distribution angle indicates the half-width of the luminance distribution of the light emitted from the backlight.

[0079] From Table 2, it can be seen that the luminance distribution of the embodiment, the luminance distribution of the modification 1, and the luminance distribution of the modification 2 all have narrower half-widths and higher luminance peaks than the luminance distribution of the comparative example.

[0080] In the above embodiments and variations, "approximately perpendicular" is not limited to a state in which the sheets intersect at an exact angle, but is a concept that includes a state in which the sheets intersect at an angle that is shifted within a range in which the functionality of each sheet is not lost.

[0081] Furthermore, in the above embodiment and modified examples, a case has been described in which a diffusion sheet is provided, but as long as the required luminance characteristics are satisfied, a diffusion sheet may not be provided.

[0082] The present invention is not limited to the above-mentioned embodiment. The present invention also includes a configuration in which the above-mentioned components are appropriately combined. Further effects and modifications can be easily derived by those skilled in the art. Therefore, the broader aspects of the present invention are not limited to the above-mentioned embodiment, and various modifications are possible. [Explanation of symbols]

[0083] 10, 30, 40, 50 surface lighting device, 11 substrate, 12 light source, 13 reflector, 14 dichroic sheet, 15 wavelength conversion sheet, 16, 22 diffusion sheet, 17, 23, 24 light distribution conversion sheet, 18, 19 brightness enhancement sheet, 20 liquid crystal panel, 21 frame

Claims

1. A plurality of light sources disposed on a substrate; A first optical sheet disposed on an exit side of the light source; a second optical sheet disposed on the exit side of the first optical sheet; a third optical sheet disposed on the exit side of the second optical sheet; Equipped with the first optical sheet includes a plurality of first optical elements protruding in a first direction toward the light source, the second optical sheet includes a plurality of second optical elements protruding in a second direction opposite to the first direction; the third optical sheet includes a plurality of third optical elements protruding in the second direction; Surface lighting device.

2. the second optical element is a triangular prism having a linear ridge line along a third direction in a plane substantially perpendicular to the first direction, the third optical element is a triangular prism having a linear ridgeline along a fourth direction substantially perpendicular to the third direction in a plane substantially perpendicular to the first direction, 2. The spread illuminating device according to claim 1.

3. the first optical element is a triangular prism having a linear ridge line along the fourth direction; 3. The spread illuminating device according to claim 2.

4. The first optical element is arranged in a plurality of parts along the third direction, The second optical element is arranged in a plurality of parts along the fourth direction, The third optical element is arranged in a plurality of parts along the third direction.

4. The spread illuminating device according to claim 3.

5. the first optical element has a cross-sectional shape substantially perpendicular to the fourth direction that is an isosceles triangle having a ridge line of the first optical element as a vertex; 4. The spread illuminating device according to claim 3.

6. The first optical element has an isosceles triangle with an apex angle of 78 to 83 degrees.

6. The spread illuminating device according to claim 5.

7. The first optical element is a quadrangular pyramid prism.

3. The spread illuminating device according to claim 2.

8. the first optical element is a quadrangular pyramid prism having a base surface including a first base along the third direction and a second base along the fourth direction; 8. The spread illuminating device according to claim 7.

9. The first optical element is arranged in a plurality of directions in the third direction and the fourth direction, The second optical element is arranged in a plurality of parts along the fourth direction, The third optical element is arranged in a plurality of parts along the third direction.

8. The spread illuminating device according to claim 7.

10. The first optical element has four side surfaces constituting the quadrangular pyramidal prism, and an angle between two side surfaces facing each other across an apex of the first optical element is 78 to 83 degrees.

8. The spread illuminating device according to claim 7.

11. the first optical sheet distributes light to a luminance distribution in which light incident in an oblique direction on the second optical sheet is greater than light incident in a perpendicular direction on the second optical sheet; 2. The spread illuminating device according to claim 1.

12. The first optical sheet converts a unimodal luminance distribution of the incident light into a bimodal luminance distribution.

2. The spread illuminating device according to claim 1.

13. The first optical sheet converts a unimodal luminance distribution of the incident light into a four-modal luminance distribution.

2. The spread illuminating device according to claim 1.

14. A plurality of light sources disposed on a substrate; A first optical sheet disposed on an exit side of the light source; a second optical sheet disposed on the exit side of the first optical sheet; a third optical sheet disposed on the exit side of the second optical sheet; Equipped with the first optical sheet includes a plurality of first optical elements each of which is a quadrangular pyramidal prism protruding in a first direction away from the light source; the second optical sheet includes a plurality of second optical elements protruding in the first direction, the third optical sheet includes a plurality of third optical elements protruding in the first direction; Surface lighting device.

15. the first optical element is a quadrangular pyramid-shaped prism having a base including a first base along a second direction in a plane substantially perpendicular to the first direction, and a second base along a third direction substantially perpendicular to the second direction in a plane substantially perpendicular to the first direction, the second optical element is a triangular prism having a linear ridge line along the second direction, the third optical element is a triangular prism having a linear ridge line along the third direction; The spread illuminating device according to claim 14.

16. The first optical element is arranged in a plurality of directions in the second direction and the third direction, The second optical element is arranged in a plurality of parts along the third direction, The third optical element is arranged in a plurality of parts along the second direction.

16. The spread illuminating device according to claim 15.

17. The first optical element has four side surfaces constituting the quadrangular pyramidal prism, and an angle between two side surfaces facing each other across an apex of the first optical element is 144 to 157 degrees. The spread illuminating device according to claim 14.

18. The first optical sheet distributes light so as to narrow the half-value width of the luminance distribution of the incident light. The spread illuminating device according to claim 14.

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