Planar lighting device

Abstract

The present disclosure provides a planar lighting device capable of suppressing color unevenness in an exit surface without high-precision alignment of a light source and a light guide plate. A planar lighting device according to an embodiment includes: a light guide plate that emits light incident from a light incident side surface from one of two main surfaces; and a plurality of light sources arranged along the longitudinal direction of the light incident side surface and emitting light to be incident on the light incident side surface. The light source includes: a light emitting element that emits first light; and a wavelength conversion material that emits second light having a wavelength longer than that of the first light by the light emitted by the light emitting element. On the light incident side surface, a plurality of rows of first recesses and projections extending in the width direction of the light guide plate and diffusing incident light in the thickness direction are formed in a local range in the thickness direction of the light guide plate and in a range facing the light emitting elements.

Description

Technical Field

[0001] The invention relates to a planar lighting device. Background Art

[0002] As a planar lighting device used as a backlight of a liquid crystal panel, an edge-light type planar lighting device is known, in which a light source emitting white light is arranged along a side surface (light incident side surface) of a light guide plate, and light incident on the light incident side surface is emitted from one main surface (exit surface) of the light guide plate. A technology for suppressing color unevenness within the exit surface in such a planar lighting device is known.

[0003] As a light source emitting white light, a structure is known in which a red light emitting LED (Light Emitting Diode), a green light emitting LED, and a blue light emitting LED are simultaneously turned on to mix red light, green light, and blue light to obtain white light. For example, Patent Document 1 discloses a backlight, which, in order to suppress color unevenness caused by insufficient color mixing, is formed with a semi-cylindrical first light scattering unit and a second light scattering unit extending in the width direction and the thickness direction, respectively, on the entire surface of the light incident side. In this backlight, the red light, green light, and blue light incident from the light incident side are widely scattered in the thickness direction and the width direction and mixed near the light incident side, so that uniform white light can be emitted in the emission surface.

[0004] In addition, as a light source that emits white light, a structure is known in which white light is obtained by configuring a yellow phosphor around a blue LED chip. It is known that in a light source of this structure, the longer the distance that the blue light passes through the phosphor, the stronger the yellow light will be emitted, so the yellow color of the emitted light will become stronger on the exit surface near the light entrance side of the light guide plate. For example, Patent Document 2 discloses a backlight, which has an incident surface protrusion extending in the thickness direction formed on the light entrance side opposite to the area with more blue spectrum in the light emitting surface of the light source. In this backlight, the light with a strong blue color will be scattered in the width direction due to the incident surface protrusion, so the yellow color of the exit surface near the light entrance side can be suppressed.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Publication No. 2008-10291

[0008] Patent Document 2: Japanese Patent Application Publication No. 2016-85329

[0009] However, in the above-mentioned patent document 2, it is necessary to align the position of the blue LED chip in the light source with the position of the protrusion on the incident surface with high precision. In addition, in a light source in which a phosphor is arranged around the blue LED chip, the chromaticity of the light in the thickness direction will also change according to the distance that the blue light passes through in the phosphor. Even if the technology of patent document 1 that makes the incident light diffuse uniformly in both the width direction and the thickness direction is applied to a backlight using such a light source, it is difficult to control the chromaticity in the exit surface. Thus, in the above-mentioned prior art, there is room for further improvement in suppressing color unevenness in the exit surface. Summary of the invention

[0010] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a planar lighting device capable of suppressing color unevenness within an emission surface without requiring high-precision alignment of a light source and a light guide plate.

[0011] In order to solve the above problems and achieve the purpose, a planar lighting device of one embodiment of the present invention comprises: a light guide plate, which allows light incident from the light incident side surface to be emitted from one of the two main surfaces; and a plurality of light sources, which are arranged along the long dimension direction of the light incident side surface and emit light to be incident on the light incident side surface. The light source includes: a light emitting element, which emits a first light; and a wavelength conversion material, which emits a second light with a wavelength longer than the first light by the light emitted by the light emitting element. On the light incident side surface, in a local range in the thickness direction of the light guide plate and in a range opposite to the light emitting element, a plurality of rows of first concave-convex portions extending along the width direction of the light guide plate and diffusing the incident light in the thickness direction are formed.

[0012] A planar lighting device according to one aspect of the present invention can suppress color unevenness within an emission surface. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a plan view schematically showing the structure of the planar lighting device according to the embodiment.

[0014] Figure 2 It is a side view schematically showing the structure of the planar lighting device according to the embodiment.

[0015] Figure 3 It is used for Figure 2 A diagram illustrating the emitted light of the light source shown.

[0016] Figure 4 This is a side view schematically showing the structure of a planar lighting device in a mode different from that of the embodiment.

[0017] Figure 5 It is a diagram for explaining the range in which the first concavoconvexity is formed.

[0018] Figure 6 This is a diagram for explaining Example 1.

[0019] Fig. 7A FIG. (1) is a diagram for explaining the light incident side surface of Example 1.

[0020] Figure 7B FIG. (2) is a diagram for explaining the light incident side surface of Example 1.

[0021] Figure 7C FIG. (3) is a diagram for explaining the light incident side surface of Example 1.

[0022] Fig.7D FIG. (4) is a diagram for explaining the light incident side surface of Example 1.

[0023] Figure 8 This is a diagram showing the color gradient of the emission surface of Example 1.

[0024] Fig. 9 This is a diagram for explaining Example 2.

[0025] Fig.10 This is a diagram for explaining Example 3.

[0026] Fig.11 FIG. (1) is a diagram for explaining a modification example.

[0027] Fig.12 FIG. (2) is a diagram for explaining a modification example.

[0028] Fig.13 FIG. (3) is a diagram for explaining a modification example.

[0029] Description of Reference Numerals

[0030] 1, 1', 1A: planar lighting device; 10, 10', 10A: light guide plate; 11, 11', 11A: light incident side; 11a: first concave-convex; 11b: second concave-convex; 12, 12', 12A: exit surface; 13, 13', 13A: terminal surface; 14: opposite surface; 20: light source; 21: blue light emitting diode chip (blue LED chip); 22: sealing body; 23: packaging component. DETAILED DESCRIPTION

[0031] Hereinafter, the planar lighting device of the embodiment will be described with reference to the accompanying drawings. It should be noted that the present invention is not limited to the present embodiment. In addition, the dimensional relationship of each element in the drawings, the proportion of each element, etc. may sometimes be different from the actual one. Sometimes the drawings may include parts with different dimensional relationships and proportions. In addition, the contents described in one embodiment or variant example are also applicable to other embodiments or variant examples in principle.

[0032] (Implementation Method)

[0033] Figure 1 is a plan view schematically showing the structure of a planar lighting device 1 according to an embodiment. Figure 2 1 is a side view schematically showing the structure of the planar lighting device 1 according to the embodiment. Figure 1 and Figure 2 As shown, the planar lighting device 1 includes a light guide plate 10 and a plurality of light sources 20 .

[0034] The light guide plate 10 is a flat plate member formed in a rectangular shape in a plan view, and is made of a transparent material such as polycarbonate resin. The light guide plate 10 has a light incident side surface 11 , an emission surface 12 , a terminal surface 13 , and an opposite surface 14 .

[0035] The light incident side surface 11 is opposite to the light emitting surface of the light source 20, and is the side surface on which the light from the light source 20 is to be incident. The terminal surface 13 is the side surface located on the opposite side of the light incident side surface 11. The exit surface 12 is the main surface on the positive direction side of the Z axis, which is the exit direction of the light, of the two main surfaces of the light guide plate 10. The opposite surface 14 is the main surface on the negative direction side of the Z axis, which is the opposite side to the exit surface 12, of the two main surfaces of the light guide plate 10. For example, a light path change pattern consisting of a plurality of dots is formed on the opposite surface 14.

[0036] The light incident from the light incident side surface 11 travels along the positive direction of the Y axis as the light guiding direction, and is emitted from the emission surface 12 through the light path change pattern formed on the opposite surface 14. That is, the planar lighting device 1 of the embodiment is an edge-light type lighting device. It should be noted that the first concavoconvex 11a for diffusing the incident light in the thickness direction of the light guide plate 10 is formed on the light incident side surface 11 of the light guide plate 10. The first concavoconvex 11a will be described later.

[0037] The plurality of light sources 20 are arranged along the X-axis direction to emit light to be incident on the light incident side surface 11. Here, the X-axis direction is the width direction of the light guide plate 10, and the Z-axis direction is the thickness direction of the light guide plate 10. In addition, the X-axis direction is also the long dimension direction of the light incident side surface 11, and the Z-axis direction is also the short dimension direction of the light incident side surface 11.

[0038] The light source 20 includes: a light emitting element that emits blue light (first light); and a phosphor (yellow phosphor) as a wavelength conversion material that emits yellow light (second light having a longer wavelength than the first light) through the light emitted by the light emitting element. Figure 2As shown, the light source 20 has a blue light emitting diode (LED) chip 21 (hereinafter referred to as the blue LED chip 21), a sealing body 22 and a package 23. The blue LED chip 21 is arranged at the approximate center of the bottom of a rectangular recess provided in the package 23. The sealing body 22 is composed of a resin that seals the blue LED chip 21, and a yellow phosphor is dispersed in the resin, and the sealing body 22 is filled in the recess of the package 23. By mixing the blue light emitted by the blue LED chip 21 with the yellow light emitted by the yellow phosphor that absorbs the blue light, the light source 20 emits approximately white light. The multiple light sources 20 are respectively mounted (electrically connected) on an FPC (Flexible Printed Circuit) not shown in the figure via electrodes not shown formed on the outer surface of the package 23. It should be noted that, although not shown in the figure, the planar lighting device 1 includes, in addition to the FPC, various optical sheets stacked on the emission surface 12 side of the light guide plate 10, a reflective sheet arranged on the opposite surface 14 side of the light guide plate 10, a frame for accommodating the light guide plate 10 and the light source 20, etc. In addition, the phosphor as a wavelength conversion material is not limited to a single yellow phosphor, and may be, for example, a phosphor obtained by combining a red phosphor and a green phosphor.

[0039] Here, use Figure 3 and Figure 4 , the generation of color unevenness caused by the structure of the light source 20 is described. Figure 3 It is used for Figure 2 FIG. 2 is a diagram for explaining the emitted light of the light source 20 shown in FIG. Figure 4 It is a side view schematically showing the structure of a planar lighting device 1 ′ in a mode different from that of the embodiment.

[0040] Figure 3 The light L1 shown is light emitted in the optical axis direction (Y-axis direction) of the light source 20. Figure 3 The light L2 shown is light emitted in a direction with a large angle with the optical axis of the light source 20. Compared with the light L1 that goes straight from the blue LED chip 21, the light L2 that goes obliquely from the blue LED chip 21 passes a longer distance in the sealing body 22, so the light L2 is white light with a stronger yellow tint than the light L1. In other words, compared with the light L2, the light L1 passes a shorter distance in the sealing body 22, so the light L1 is white light with a stronger blue tint than the light L2.

[0041] Figure 4 The planar lighting device 1' shown is Figure 3 The light guide plate 10 of the planar lighting device 1 shown in the figure is replaced by a light guide plate 10'. The first concavoconvex 11a described later is not formed on the light incident side surface 11' of the light guide plate 10'. Figure 4 As shown in FIG. 1 , the light L2 traveling obliquely is emitted from the emission surface 12' near the light incident side surface 11'. Therefore, the emission surface 12' near the light incident side surface 11' has a yellowish feel (more yellow components). Figure 4 As shown, the light L1 has a tendency to propagate in the light guide plate 10' and be emitted from the exit surface 12' on the side of the terminal surface 13' relative to the center. Therefore, the position of the exit surface 12' on the side of the terminal surface 13' relative to the center has a blue feeling (more blue components). As a result, a color gradient is generated on the exit surface 12'.

[0042] On the other hand, Figure 2 As shown, on the light incident side surface 11 of the light guide plate 10 of the embodiment, a plurality of first concave-convex portions 11a ( Figure 2 The range in the thickness direction where the first concavoconvex 11a is formed is the range opposite to the blue LED chip 21. Figure 2 Although not shown in the figure, the first concavo-convex 11 a is formed on the light incident side surface 11 from one end to the other end in the width direction.

[0043] Through the first concavoconvex 11a, part of the light L1, which is white light with a strong blue feel, is diffused in the thickness direction. Figure 2 As shown, the light is emitted from the exit surface 12 near the light incident side surface 11. As a result, Figure 4 In contrast, the light incident side surface 11 of the emission surface 12 has a blue tint (increased blue component). Figure 2 As shown, the blue component of the light propagating in the light guide plate 10 is reduced, so Figure 4 In comparison, the light has a yellowish feel. As a result, compared with the comparative example, the blue sense of the exit surface 12 on the side close to the terminal surface 13 relative to the center is reduced (the blue component is reduced). As a result, the color balance of the light emitted from the light guide plate can be achieved, and the color gradient of the exit surface 12 becomes smaller. In this way, by forming the first concavo-convex 11a on the light incident side surface 11, the color unevenness in the exit surface 12 can be suppressed.

[0044] Figure 5 The figure is used to explain the range of forming the first concavo-convex 11a. The "range facing the blue LED chip 21" where the first concavo-convex 11a is formed on the light incident side surface 11 is not limited to the range of forming the first concavo-convex 11a. Figure 5As shown, the range R is obtained by parallel projecting the blue LED chip 21 along the Y-axis direction. For example, the range in which the first concave-convex 11a is formed may be a range partially overlapping with the range R, or a range included in the range R but smaller than the range R. In addition, the range in which the first concave-convex 11a is formed may be a range that includes the range R but is larger than the range R, so as to absorb the positional displacement in the thickness direction of the plurality of blue LED chips 21 arranged along the width direction. Alternatively, the range in which the first concave-convex 11a is formed may be defined as, for example, a range in which light with a blue sense having a v' value below a specified value in the CIE (International Commission on Illumination) chromaticity diagram is incident. That is, the range in which the first concave-convex 11a is formed may be any range as long as it can suppress the color unevenness in the exit surface 12 to the extent required by the design specifications.

[0045] It should be noted that in the planar lighting device 1, a plurality of light sources 20 are arranged at intervals, so sometimes light and dark are generated in the width direction of the exit surface 12. Therefore, in the embodiment, it is preferred that the light emitted from the light source 20 is diffused in the width direction at the light incident side surface 11. A plurality of rows of second concave-convex 11b extending in the thickness direction and diffusing the incident light in the width direction as described below may also be formed on the light incident side surface 11 of the light guide plate 10 of the embodiment.

[0046] [Example]

[0047] Hereinafter, the above-mentioned embodiment will be described in more detail based on examples, but the embodiment is not limited to these examples.

[0048] [Example 1]

[0049] Figure 6 is a diagram for explaining Example 1. Fig. 7A , Figure 7B , Figure 7C , Fig.7D is a diagram for explaining the light incident side surface 11 of Example 1. Figure 8 This is a diagram showing the color gradient of the light exit surface 12 of Example 1.

[0050] Figure 6 In the figure, for the light incident side surface 11 of the light guide plate 10 of Example 1, a "schematic diagram of the shape observed from the positive direction of the Z axis (a top view in the figure)", a "schematic diagram of the shape observed from the negative direction of the Y axis (a side view in the figure)" are shown. Figure 1 )" and "Schematic diagram of the shape observed from the positive direction of the X-axis (the figure is a side view Figure 2 )".like Figure 6 Top and side views Figure 1As shown, a plurality of rows of semi-cylindrical second concavoconvexo lenses 11b extending in the thickness direction (Z-axis direction) are formed on the entire surface of the light incident side surface 11. In this embodiment, the second concavoconvexo lenses 11b are biconvex lenses.

[0051] And, if Figure 6 Side view Figure 1 and side view Figure 2 As shown, in Example 1, twelve rows of first concavoconvexo ... Figure 6 Side view Figure 2 As shown, the thickness of the light guide plate 10 is 0.52 mm, and the range of the first concavoconvex 11a formed in the light incident side surface 11 is 0.166 mm. In Example 1, the center of the 0.166 mm range is the center in the thickness direction of the light guide plate 10, which is 0.26 mm away from the exit surface 12 in the negative direction of the Z axis. Twelve columns of first concavoconvex 11a are formed in this range at intervals of 12.8 μm. The maximum height difference of the first concavoconvex 11a is 9 μm.

[0052] Fig. 7A yes Figure 6 The side view schematically shown in Figure 1 Photos, Figure 7B yes Fig. 7A The enlarged photograph of the area P shown in Figure 7C It was taken using a laser microscope Fig. 7A The surface shape of the area P is shown. Fig.7D Yes Figure 7B and Figure 7C The AA section is a diagram that depicts the surface position of the light incident side surface 11 in the AA cross-sectional view of FIG. The AA section is a section obtained by cutting the light guide plate 10 at the YZ section passing through the boundary between two adjacent second concavo-convex 11 b.

[0053] like Figure 7B and Figure 7C As shown, the semi-cylindrical biconvex lens (second concavoconvex 11b) extending in the Z-axis direction is continuously arranged on the light-entering side along the X-axis direction. In addition, the prism (first concavoconvex 11a) extending in the X-axis direction in a manner of crossing the biconvex lens is continuously arranged in the Z-axis direction in the central part in the thickness direction. In addition, in this embodiment, the second concavoconvex 11b (biconvex lens) and the first concavoconvex 11a (prism) are at the same height.

[0054] For manufacturing Figure 6 , FIG. 7A to FIG. 7DA mold in the shape of the light-entering side surface 11 of the shown embodiment 1 can be made in the following manner: for a mold for forming a plurality of rows of double convex lenses extending along the thickness direction, the position of the tool for the prism is offset in the thickness direction at intervals of 12.8 μm, while the tool is repeatedly moved in the width direction to perform cutting operations.

[0055] Figure 8 This is a graph plotting the chromaticity v' value measured at a line along the Y-axis direction of the light exit surface 12 in Example 1 (the dotted line B in the figure). Figure 8 In FIG. 1 , the horizontal axis represents the position from the light incident side surface 11 to the terminal surface 13 in the light guiding direction (positive direction of the Y axis), and the vertical axis represents the v' value. Figure 8 In FIG. 1 , a graph is shown by a dotted line to depict the v' value measured in the light guide plate of Comparative Example 1 in which the first concavoconvexity 11a is not formed and only the second concavoconvexity 11b is formed. Figure 8 In FIG. 1 , a solid line shows a graph plotting the v' value measured in the light guide plate of Example 1. It should be noted that a larger v' value indicates a stronger yellow color, and a smaller v' value indicates a stronger blue color.

[0056] like Figure 8 As shown, in Comparative Example 1, the difference between the maximum and minimum v' values, Δv', is 0.0049, while in Example 1, Δv' is reduced to 0.0028, which shows that the color unevenness of the irradiation surface 12 is reduced by forming the first concavoconvexity 11 a.

[0057] [Example 2]

[0058] Fig. 9 FIG. 2 is a diagram for explaining Example 2. Fig. 9 As shown in the above figure, the first concavoconvex 11a of Example 2 is formed in the same shape and at the same pitch (12.8 μm) as Example 1, but the number of columns is eight columns, which is different from Example 1. That is, the range for forming the first concavoconvex 11a is 0.166 mm in Example 1, while it is narrowed to 0.115 μm in Example 2.

[0059] exist Fig. 9 In the figure below, Figure 8 Similarly, the horizontal axis represents the position from the light incident side surface 11 to the terminal surface 13 in the light guiding direction (Y-axis direction), and the vertical axis represents the v' value. Fig. 9 In FIG. 1 , a graph of Comparative Example 1 is shown by a dotted line, and a graph plotting the v′ values ​​measured in the light guide plate 10 of Example 2 is shown by a solid line.

[0060] like Fig. 9As shown, in Comparative Example 1, Δv' is 0.0049, whereas in Example 2, Δv' is reduced to 0.0032, and it can be seen that the color unevenness of the exit surface 12 is reduced. However, the value of Δv' is larger than that of Example 1. It can be considered that this is because the range for forming the first concavoconvex 11a is smaller than that of Example 1, so the diffusion amount of light with a strong blue component is less than that of Example 1.

[0061] [Example 3]

[0062] Fig.10 3 is a diagram for explaining Example 3. Fig.10 As shown in the above figure, the first concavoconvexities 11a of Example 3 are different from those of Examples 1 and 2, and are formed in thirty-two rows at a pitch of 3.2 μm.

[0063] exist Fig.10 In the figure below, Figure 8 , Fig. 9 Similarly, the horizontal axis represents the position from the light incident side surface 11 to the terminal surface 13 in the light guiding direction (Y-axis direction), and the vertical axis represents the v' value. Fig.10 In FIG. 1 , a graph of Comparative Example 1 is shown by a dotted line, and a graph plotting the v′ values ​​measured in the light guide plate 10 of Example 3 is shown by a solid line.

[0064] like Fig.10 As shown in FIG. 1 , Δv' is 0.0049 in Comparative Example 1, whereas Δv' is reduced to 0.0034 in Example 3, which shows that the color unevenness of the exit surface 12 is reduced. However, the value of Δv' is larger than that of Example 1 and Example 2. In addition, compared with Example 1 and Example 2, the blue sense is stronger on the side of the light incident side 11, and the yellow sense is stronger on the side of the terminal surface 13. It can be considered that this is because the straight light with a strong blue sense ( Figure 2 The degree of diffusion of light L1) shown in the figure is greater in Example 3 than in Examples 1 and 2.

[0065] In other words, in this embodiment, the range of forming the first concavoconvex 11a, the number of columns of the first concavoconvex 11a, and the spacing can be appropriately adjusted to produce a light guide plate 10 that reduces color unevenness in the exit surface 12 and satisfies the chromaticity characteristics required by the backlight. It should be noted that the shape of the first concavoconvex 11a is also one of the design parameters of the first concavoconvex 11a. In Examples 1 to 3, the shape of the first concavoconvex 11a is a prism shape of an isosceles triangle with an obtuse vertex angle, but the shape of the first concavoconvex 11a can also be any shape as long as the chromaticity characteristics required by the backlight can be achieved.

[0066] As described above, the planar lighting device 1 of the embodiment includes the light guide plate 10 and the plurality of light sources 20. The light guide plate 10 emits light incident from the light incident side surface 11 from the emission surface 12. The plurality of light sources 20 are arranged along the long dimension direction (X-axis direction) of the light incident side surface 11, and emit light to be incident on the light incident side surface 11. The light source 20 includes: a blue LED chip 21 (an example of a light emitting element that emits first light) that emits blue light; and a sealing body 22 formed of a resin in which a phosphor (an example of a wavelength conversion material that emits second light having a longer wavelength than the first light by light emitted by the light emitting element) that emits yellow light by light emitted by the blue LED chip 21 is dispersed. In addition, on the light incident side surface 11, in a local range in the thickness direction (Z-axis direction) of the light guide plate 10 and in a range opposite to the blue LED chip 21, a plurality of rows of first concave-convex 11a extending along the width direction (X-axis direction) of the light guide plate 10 and diffusing the incident light in the thickness direction (Z-axis direction) are formed. Therefore, the present embodiment can suppress color unevenness in the emission surface 12 .

[0067] That is, in this embodiment, a plurality of first concavoconvexities 11a are formed only in the range opposite to the blue LED chip 21 to diffuse the incident light in the thickness direction (Z-axis direction), so that the light with a strong blue component and the light with a strong yellow component can be mixed and emitted from the exit surface 12 near the light incident side surface 11. In addition, in this embodiment, the first concavoconvexities 11a can reduce the light with a strong blue component advancing in the light guide plate 10, and can reduce the blue sense at the position of the exit surface 12 on the side of the terminal surface 3 relative to the center. It should be noted that this effect is difficult to achieve when the first concavoconvexities 11a are formed on the entire surface of the light incident side surface 11.

[0068] In addition, in the present embodiment, a plurality of rows of second concavoconvexities 11b extending in the thickness direction (Z-axis direction) and diffusing the incident light in the width direction (X-axis direction) are formed on substantially the entire surface of the light incident side surface 11. The light emitted from the light source 20 is diffused in the width direction at the light incident side surface 11 through the second concavoconvexities 11b. As a result, the brightness difference in the width direction of the emission surface 12 caused by the light source 20 being arranged at intervals can be suppressed.

[0069] It should be noted that it is considered that when the second concavoconvex 11b is formed only in the range opposite to the blue LED chip 21, light and dark will be generated in the width direction of the emission surface 12. In addition, when comparing the case where the second concavoconvex 11b is formed only in the range opposite to the blue LED chip 21 and the case where the first concavoconvex 11a is formed only in the range opposite to the blue LED chip 21 as in the embodiment, the embodiment makes it easier to align the light source 20 with the light incident side surface 11. That is, in this embodiment, the color unevenness in the emission surface 12 can be suppressed without high-precision alignment of the light source 20 and the light guide plate 10.

[0070] It should be noted that, if the chromaticity characteristics required for the backlight can be achieved, the second concavo-convex 11 b may not be formed on the light incident side surface 11 and only the first concavo-convex 11 a may be formed.

[0071] (Variation Example)

[0072] The shape of the light guide plate 10 in the above embodiment is rectangular when viewed from above, but in recent years, from the perspective of appearance design, a light guide plate with a chamfered corner (for example, a rounded corner) is sometimes used. Fig.11 , Fig.12 as well as Fig.13 A formation pattern of the first concavo-convex 11 a applied when using this light guide plate will be described. Fig.11 , Fig.12 as well as Fig.13 It is a diagram for explaining a modification example.

[0073] Fig.11 The planar lighting device 1A of the modified example shown in FIG. 1 includes a light guide plate 10A and a plurality of light sources 20. Fig.10 As shown, the light guide plate 10A has a rectangular shape with chamfered corners when viewed from above. Specifically, the rectangular corners of the light guide plate 10A are arc-shaped when viewed from above. When using a light guide plate 10A of such a shape, it is impossible to configure the light source 20 at both ends of the light incident side surface 11A (refer to area C in the figure).

[0074] The light guide plate 10A has a light incident side surface 11A disposed opposite to the plurality of light sources 20 and a terminal surface 13A, which is a side surface opposite to the light incident side surface 11A. As in the first embodiment, the light incident side surface 11A is formed with twelve rows of first concavoconvexo ...

[0075] Fig.12 The upper right figure is a line along the Y-axis direction of the light guide plate 10A's emission surface 12A ( Fig.12 A graph depicting the chromaticity v' value measured at the dotted line D) in the upper left figure. Fig.12 In the upper right figure of FIG. 1 , the horizontal axis represents the position from the light incident side surface 11A to the terminal surface 13A in the light guiding direction (positive direction of the Y axis), and the vertical axis represents the v' value. Fig.12 In the upper right figure of FIG. 1 , a graph is shown by a dotted line to depict the v' value measured in the light guide plate of Comparative Example 2 in which the first concavoconvexity 11a is not formed and only the second concavoconvexity 11b is formed. Fig.12 In the upper right figure of FIG. 1 , a graph plotting the v′ value measured in the light guide plate 10A is shown by a solid line. Fig.12 The upper right graph of Figure 8 The graphs of have the same shape, indicating that the color unevenness of the emission surface 12A is reduced in the light guiding direction.

[0076] However, in the light guide plate 10A in which the light source 20 cannot be arranged at the corner, the color gradient in the width direction (X-axis direction) becomes large. Fig.12 The lower right figure shows the position of the light guide plate 10A at a line along the X-axis direction and 10 mm away from the light incident side surface 11A in the positive direction of the Y-axis ( Fig.12 A graph depicting the chromaticity v' value measured at the dotted line E) in the upper left figure. Fig.12 The lower left figure is a diagram of the light guide plate of Comparative Example 2. That is, Fig.12 The lower left figure is a diagram of a light guide plate without the first concavoconvex 11a. Fig.12 The lower right figure of is a graph having the first concavoconvexity 11a.

[0077] like Fig.12 As shown in the lower right figure of , at the 10 mm position, the blue component increases within the range where the light source 20 is arranged, and the v' value is smaller than that of Comparative Example 2, while the v' value is large at both ends in the width direction of the light guide plate 10A, which is the same as the v' value of Comparative Example 2. That is, when the first concavoconvex 11a is formed in the same pattern as that of Example 1, in the light guide plate 10A, although the yellow component decreases and the blue component increases in the center in the width direction, the light with a strong blue component diffused by the first concavoconvex 11a cannot reach the both ends in the width direction corresponding to the area C, and the yellow component is dominant, and the color gradient in the width direction becomes large.

[0078] As a countermeasure, in a modified example, the number of rows of the first concavoconvexities 11a is reduced from the center in the longitudinal direction of the light incident side surface 11A toward the end. Fig.13 The formation pattern of the first concavo-convex 11a shown in (1) is changed to Fig.13 The pattern is formed as shown in (2). Fig.13 (1) is a schematic diagram showing that twelve rows of first projections and recesses 11a are formed on the entire surface of the light incident side surface 11A. Fig.13(1) also shows the above Fig.12 The chart in the lower right figure.

[0079] In contrast, Fig.13 In the formation pattern of (2), the number of rows of the first concavoconvex 11a decreases toward the end of the light incident side surface 11A, and the first concavoconvex 11a is not formed on the front surface of the light source 20 located at the end. Fig.13 In the formation pattern of (2), twelve columns of first concave-convex 11a are formed from the center to X1, eight columns of first concave-convex 11a are formed from X1 to X2, four columns of first concave-convex 11a are formed from X2 to X3, and no first concave-convex 11a is formed from X3 to the end. Fig.13 (1) Fig.13 In the schematic diagram shown in (2), the second concavo-convex 11b is not shown.

[0080] Fig.13 (2) shows a graph depicting the chromaticity v' value measured at a position 10 mm away from the light incident side surface 11A in the positive direction of the Y axis under such a formation pattern of the first concavo-convex 11a. Fig.13 (1) and Fig.13 When compared with the graph in (2), at both ends in the width direction, Fig.13 The chromaticity of (2) changes more gradually, and it can be seen that the color gradient in the width direction is relaxed. It can be considered that this is because Fig.13 In the formation pattern of (2), the amount of light with a strong blue component diffused gradually decreases from the center toward the end in the width direction.

[0081] It should be noted that in Fig.13 In (2), a pattern is shown in which the number of columns of the first concavoconvex 11a gradually decreases from the center in the thickness direction toward both ends within the range in the thickness direction where the first concavoconvex 11a is formed, but the present invention is not limited thereto. For example, a pattern in which the number of columns of the first concavoconvex 11a gradually decreases from both ends in the thickness direction toward the center, or a pattern in which the number of columns of the first concavoconvex 11a gradually decreases from one end in the thickness direction toward the other end may also be used.

[0082] As described above, the modified example planar lighting device 1A has a light guide plate 10A in a shape in which the corners of a rectangle are chamfered when viewed from above. When using a light guide plate 10A in a shape in which the light source 20 cannot be arranged at the corners, the diffusion effect of the blue component achieved by the first concave-convex 11a cannot be obtained at the corners, and the color gradient in the width direction on the exit surface 12A becomes larger. Therefore, in the modified example, the number of columns of the first concave-convex 11a is reduced from the center of the long dimension direction (X-axis direction) of the light incident side surface 11A toward the end. As a result, the amount of light diffusion with a strong blue component can be gradually reduced from the center of the width direction toward the end to suppress the color gradient in the width direction.

[0083] It should be noted that the present invention is not limited to the above-mentioned embodiments. The schemes formed by appropriately combining the above-mentioned components are also included in the present invention. In addition, those skilled in the art can derive further effects and variations. Therefore, the more extensive schemes of the present invention are not limited to the above-mentioned embodiments, and various changes can be made.

Claims

1. A planar lighting device, comprising: A light guide plate that allows light incident from the light incident side to be emitted from one of the two main surfaces; as well as A plurality of light sources are arranged along the long dimension of the light incident side surface, emitting light to be incident on the light incident side surface, The light source comprises: A light emitting element that emits a first light; and a wavelength conversion material for emitting second light having a wavelength longer than the first light by the light emitted by the light emitting element, On the light incident side surface, a plurality of rows of first projections and depressions extending along the width direction of the light guide plate and diffusing incident light in the thickness direction are formed in a local range in the thickness direction of the light guide plate and in a range opposite to the light emitting element.

2. The planar lighting device according to claim 1, wherein: A plurality of rows of second concavo-convexodies extending in the thickness direction and diffusing incident light in the width direction are formed on the light incident side surface.

3. The planar lighting device according to claim 2, wherein: The first concavoconvex is in the shape of a triangular prism, The second concavoconvex is a biconvex lens.

4. The planar lighting device according to claim 1 or 2, wherein: The light guide plate has a rectangular shape with chamfered corners when viewed from above. The number of rows of the first concavo-convex portions decreases from the center in the longitudinal direction of the light incident side surface toward the end portion.

5. The planar lighting device according to claim 1 or 2, wherein: The first light is blue light, The second light is yellow light.

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