Planar lighting device

Abstract

A planar illumination device (1) according to an embodiment comprises a substrate (3), a reflector (5), and a condenser lens (6). A plurality of light sources (4) are two-dimensionally arranged on the substrate (3). The reflector (5) is disposed on the substrate (3) and has an inclined reflective surface (5a) that surrounds the emission side of each of the light sources (4). The condenser lens (6) is disposed on the emission side of the light sources (4) and the reflector (5), and condenses emitted light from the light sources (4). The full width at half maximum of the emitted light from the light source (4) is set to a value such that, at least in a predetermined direction, the emitted light within the full width at half maximum does not directly hit the reflector (5).

Description

[Technical Field]

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

[0002] A so-called direct-type planar lighting device is known, which has a substrate on which multiple light sources are arranged two-dimensionally, and a reflector arranged on the substrate and having a reflective surface that surrounds the emission side of each light source (see, for example, Patent Documents 1 to 3, etc.).

[0003] Generally, LEDs (Light Emitting Diodes) with an ideal diffuse Lambertian light distribution (full width at half maximum 120°) are used as light sources. The light emitted from the light source at a low angle hits the reflecting surface of the reflector. In theory, total reflection in the forward direction can be achieved by making the reflecting surface of the reflector mirror-like and setting an appropriate inclination angle relative to the light source. However, since the reflector has a reflective surface surrounding thousands of light sources, it is difficult to create a highly accurate mirror surface for them. Furthermore, due to constraints on the pitch of the light source arrangement and the thickness of the planar lighting device, it is difficult to give the reflector the shape required for ideal total reflection.

[0004] Therefore, most of the light that is emitted from the light source at a low angle and hits the reflecting surface of the reflector does not exit in the forward direction, and is not condensed in a controlled manner by the condenser lens at the subsequent stage, so most of it is lost. Therefore, the function of the reflector is not to reflect all of the light emitted from the light source in the forward direction without any leakage, but to scatter the light evenly to prevent stray light from causing problems. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2022 / 004036 [Patent Document 2] International Publication No. 2011 / 158555 [Patent Document 3] Japanese Patent Application Laid-Open No. 2012-174370 Summary of the Invention [Problem to be solved by the invention]

[0006] As described above, conventionally, there has been a problem in that there is a large loss of light emitted from the light source, and as a result, the light efficiency cannot be improved.

[0007] The present invention has been made in view of the above, and a first object of the present invention is to provide a planar lighting device that can improve light efficiency. [Means for solving the problem]

[0008] In order to solve the above-mentioned problems and achieve the object, a planar lighting device according to one aspect of the present invention includes a substrate, a reflector, and a condenser lens. Distributed The reflector is disposed on the substrate and has a wall portion including an inclined reflecting surface surrounding the emission side of each of the light sources. The condenser lens is disposed on the emission side of the light source and the reflector and condenses the light emitted from the light source. The reflector has a light source and a second reflector whose wall portion extends in a second direction perpendicular to the first direction corresponding to the boundary between the light source and an adjacent light source. The condenser lens is ,before The second reflector has linear Fresnel lenses that extend in the second direction, condense the light emitted from the light source in the first direction, and are periodically formed in accordance with the intervals between the light sources arranged directly below. The second reflector has a height such that the top of the wall portion located at the boundary does not contact the incident surface of the condenser lens. The linear Fresnel lenses are The path of light incident on the linear Fresnel lens from the light source includes: The light incident on the adjacent light source side in the vicinity of the boundary with the adjacent light source without being blocked by the wall portion of the second reflector is totally reflected. Routes included It is structured as follows.

[0009] A surface lighting device according to one aspect of the present invention can improve light efficiency. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is an end view showing an example of the configuration of a planar illumination device according to an embodiment, illustrating the state within the thickness thereof. [Figure 2] FIG. 2 is a diagram showing an example of luminous intensity versus light distribution angle of a top-hat type light source. [Figure 3] FIG. 3 is a cross-sectional view showing an example of the configuration of a top-hat type light source. [Figure 4] FIG. 4 is an end view showing an example of the configuration of the prism of the first lens. [Figure 5] FIG. 5 is an enlarged view of the top-hat type light source and its vicinity in the planar illumination device of FIG. [Figure 6] FIG. 6 is an end view showing the state within the thickness of the surface illumination device of the comparative example. [Figure 7] FIG. 7 is a diagram showing an example of the difference in luminous intensity with respect to the light distribution angle between a top-hat light source and a general Lambertian light source. [Figure 8A] FIG. 8A is a diagram showing an example of a luminance distribution caused by a Lambertian light source. [Figure 8B] FIG. 8B is a diagram showing an example of relative luminance versus position of a Lambertian light source. [Figure 9A] FIG. 9A is a diagram showing an example of a luminance distribution caused by a top-hat type light source. [Figure 9B] FIG. 9B is a diagram showing an example of relative luminance with respect to the position of a top-hat light source. [Figure 10] FIG. 10 is a diagram showing an example of the configuration of a surface illumination device according to the first modification. [Figure 11A] FIG. 11A is a diagram showing an example of an emission path from a light source. [Figure 11B] FIG. 11B is a diagram showing an example of an emission path from a light source. [Figure 12] FIG. 12 is an enlarged view of the light source and reflector. [Figure 13A] FIG. 13A is an angular luminance distribution diagram showing the light distribution characteristics of the entire light emitted from the surface illumination device. [Figure 13B]FIG. 13B is an angular luminance cross-sectional view at a specific position in FIG. 13A. [Figure 13C] FIG. 13C is a luminance distribution diagram of the surface illumination device 1 as viewed from viewpoint P in FIG. 13A. [Figure 13D] FIG. 13D is a luminance cross-sectional view at a specific position in FIG. 13C. [Figure 14A] FIG. 14A is an angular luminance distribution diagram showing the light distribution characteristics of the entire light emitted from the surface illumination device. [Figure 14B] FIG. 14B is an angular luminance cross-sectional view at a particular position in FIG. 14A. [Figure 14C] FIG. 14C is a luminance distribution diagram of the surface illumination device as viewed from viewpoint P in FIG. 14A. [Figure 14D] FIG. 14D is a luminance cross-sectional view at a specific position in FIG. 14C. [Figure 15] FIG. 15 is a diagram showing an example of the configuration of a surface illumination device 1 according to the second modification. [Figure 16] FIG. 16 is a diagram showing a modified example of a surface illumination device of a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, a surface lighting device according to an embodiment will be described with reference to the drawings. Note that the present invention is not limited to these embodiments. Furthermore, the dimensional relationships and ratios of elements in the drawings may differ from reality. The dimensional relationships and ratios may differ between the drawings. Furthermore, the content described in one embodiment or modification is, in principle, applicable to other embodiments or modifications as well.

[0012] (Embodiment) FIG. 1 is an end view showing an example of the configuration of a surface lighting device 1 according to one embodiment, illustrating the state within the thickness. For convenience, the light-emitting surface of the surface lighting device 1 is in the XY plane, and the thickness direction of the surface lighting device 1 is defined as the Z direction. Furthermore, when the surface lighting device 1 is used, for example, as a backlight for a head-up display (HUD) of an automobile, and is reflected by the windshield and visible to the user, the X-axis direction corresponds to the horizontal direction (H) and the Y-axis direction corresponds to the vertical direction (V). While FIG. 1 shows an example of the configuration of the surface lighting device 1 in the V direction (YZ cross section), the H direction (XZ cross section) is basically the same. However, if the required light distribution is anisotropic, the presence or absence and shape of optical elements formed on each lens (described later) will differ depending on the direction. Details will be described later. The V direction will also be referred to as the "first direction," and the H direction will also be referred to as the "second direction." Furthermore, the surface lighting device can be used not only for HUDs but also as a backlight for ordinary displays.

[0013] In FIG. 1, a substrate 3 is provided at the bottom of a bottom frame 2 that is substantially box-shaped and has a bottom. The substrate 3 has light sources 4, such as LEDs (Light Emitting Diodes), arranged two-dimensionally (e.g., in a grid pattern). The light sources 4 have a light distribution pattern known as a top-hat pattern. The top-hat pattern light sources 4 will be described later. A reflector 5 is provided on the side of the substrate 3 where the light sources 4 are arranged. The reflector 5 has four inclined reflective surfaces 5a that surround the emission sides of the individual light sources 4 in a rectangular shape. The reflector 5 has walls connected in a grid pattern, and the side surfaces of the walls form the reflective surfaces 5a. The reflective surfaces 5a of the reflector 5 are inclined to distribute light evenly and maintain uniformity. The tapered shape is also suitable for injection molding and facilitates manufacturing. The area (space) surrounded by the reflective surfaces 5a is called a segment.

[0014] Furthermore, a substantially plate-shaped first lens 6 is provided on the side of the reflector 5 opposite the substrate 3. In the illustrated example, the first lens 6 is a linear Fresnel lens that serves as a condensing lens for condensing light. Linear Fresnel lenses with concave and convex grooves extending in mutually perpendicular directions are formed on the incident and exit sides of the first lens 6. That is, the first lens 6 is formed with linear Fresnel lenses with concave and convex grooves extending in a first direction in the plane of the incident side and in a second direction in the plane of the exit side that is perpendicular to the first direction. The optical axis of the linear Fresnel lens is aligned with the position of the light source 4. Instead of two orthogonal linear Fresnel lenses, a concentric Fresnel lens formed on one side may be used. Alternatively, a normal convex lens may be used. Furthermore, a cylindrical lens may be used instead of the linear Fresnel lens.

[0015] Furthermore, a substantially plate-shaped second lens 7 is provided adjacent to the first lens 6 on the side opposite the substrate 3. In the illustrated example, the second lens 7 is a lenticular lens that diffuses light, and lenticular lenses with concave and convex grooves extending in mutually perpendicular directions are formed on the incident side and the exit side of the second lens 7. That is, the second lens 7 is formed with lenticular lenses with concave and convex grooves extending in a first direction in the plane of the incident side and in a second direction in the plane of the exit side. Compared to diffusion using diffusing particles, etc., diffusion using a lenticular lens allows the diffusion range to be controlled to a required range, thereby preventing a decrease in light efficiency.

[0016] A substantially plate-shaped third lens 8 is provided at a slight distance from the second lens 7 on the side opposite the substrate 3. In the illustrated example, the third lens 8 is a peak shift lens that tilts light. The tilt of light is performed for purposes such as controlling the field of view. When the light is tilted in one direction, a peak-shifting microprism with concave and convex grooves extending in one direction is formed on either the incident or exit side of the third lens 8. That is, the third lens 8 has a peak shift lens with concave and convex grooves extending in a first direction or a second direction perpendicular to the first direction on either the incident or exit side. In the embodiment shown in FIG. 1, a peak shift lens with concave and convex grooves extending in a second direction (X-axis direction, perpendicular to the paper surface) is formed on the incident side surface, and the light emitted from the third lens is tilted in a first direction (negative Y-axis direction).

[0017] A reflective polarizing film 9, such as a substantially plate-shaped DBEF (Dual Brightness Enhancement Films), is provided on the side of the third lens 8 opposite the substrate 3. The reflective polarizing film 9 polarizes light in accordance with a liquid crystal panel (not shown) provided downstream, thereby improving brightness. The side of the reflective polarizing film 9 opposite the substrate 3 (the exit surface of the planar lighting device 1) is covered by a top frame 10 that fits into the side wall of the bottom frame 2. The top frame 10 is provided with an exit opening 10a.

[0018] The lens configuration of the surface illumination device 1 is not limited to that shown in Fig. 1, but various other configurations are possible. Modified examples will be described later.

[0019] Fig. 2 is a diagram showing an example of luminous intensity versus light distribution angle of a top-hat light source 4. The top-hat light source 4 emits light whose luminous intensity is steep in the region near the boundary of the full width at half maximum θ of the light distribution angle (110° between -55° and 55° in Fig. 2) and whose luminous intensity is gentle in other regions. In particular, the luminous intensity is gentle near the peak.

[0020] Fig. 3 is a cross-sectional view showing an example of the configuration of a top-hat type light source 4. In Fig. 3, a light-emitting chip 4b is disposed on an element substrate 4a, and its exterior is covered with a lens 4c that is roughly shaped like the depression of an apple. In other words, the lens 4c protrudes in the emission direction of the light-emitting chip 4b and has a recessed center. A power supply electrode 4d is provided on the back side of the element substrate 4a.

[0021] Fig. 4 is an end view showing an example of the configuration of prism 6a of first lens 6. In Fig. 4, the light emitted from top-hat light source 4 is not particularly strong in the optical axis direction and is generally highly uniform, so it is desirable that the shape of prism 6a in the part of first lens 6 directly above light source 4 and the surrounding part be such that it directs light in the optical axis direction, similar to a normal Fresnel lens.

[0022] Fig. 5 is an enlarged view of the vicinity of the top-hat light source 4 of the surface lighting device 1 of Fig. 1. In Fig. 5, the top-hat light source 4 emits uniform light, and the full width at half maximum is approximately θ [°].

[0023] The height h of the reflecting surface of the reflector 5 is set to a value such that the emitted light within the full width at half maximum θ of the emitted light from the light source 4 does not directly hit the reflecting surface 5a of the reflector 5. That is, when the height of the reflector 5 is h, the full width at half maximum of the light source 4 is θ [°], the height from the substrate 3 to the top surface of the light source 4 is D, the distance from the center of the light source 4 to the center of the reflector 5 is a, and the height from the top surface of the light source 4 of the point where the light emitted from the light source 4, whose emission angle corresponds to 1 / 2 of the full width at half maximum θ (half width at half maximum), intersects with a perpendicular line passing through the center between adjacent light sources (a virtual line passing through the center of the reflector 5 or the boundary between adjacent segments of the first lens 6), the following formula (1) is satisfied. Note that b corresponds to the height (height from the top surface of the light source 4) reached by the light from the light source 4, whose emission angle corresponds to half width at half maximum, on the perpendicular line passing through the center between adjacent light sources.

[0024] h ≦ D+b ≦ D+a·tan(90-θ / 2) (b=a·tan(90-θ / 2) ···(1)

[0025] The full width at half maximum θ of the light emitted from the light source 4 is preferably, for example, 110° or less, and in this case, the height h of the reflector 5 preferably satisfies the following formula (2).

[0026] h ≦ D+a·tan35° (2)

[0027] As a result, most of the light emitted from the light source 4 does not hit the reflector 5, but is instead controlled and emitted through the first lens 6, the second lens 7, the third lens 8 and the reflective polarizing film 9, thereby reducing unnecessary light loss and increasing light efficiency.

[0028] Fig. 6 is an end view showing the state within the thickness of a surface lighting device 1' of a comparative example. In Fig. 6, a bottom frame 2', a substrate 3', a light source 4', a reflector 5' (reflective surface 5a'), a first lens 6', a second lens 7', a third lens 8', a reflective polarizing film 9', and a top frame 10' (opening 10a') correspond to the bottom frame 2, the substrate 3, the light source 4, the reflector 5, the first lens 6, the second lens 7, the third lens 8, the reflective polarizing film 9, and the top frame 10 of the surface lighting device 1 in Fig. 1.

[0029] The surface lighting device 1' in Figure 6 differs from the surface lighting device 1 in Figure 1 in that the full width at half maximum θ' of the light emitted from the light source 4' is large (θ' = 120°), and the light emitted from the light source 4' at a low angle hits the reflecting surface 5a' of the reflector 5', resulting in loss.

[0030] FIG. 7 is a diagram showing an example of the difference in luminous intensity versus luminous intensity distribution angle between a top-hat light source 4 and a general Lambertian light source 4', comparing the luminous intensity when the same total luminous flux (e.g., 6.3 lm) is input. For the Lambertian light source 4' indicated by the dashed line, the luminous intensity changes gradually overall, and the full width at half maximum θ' of the luminous intensity distribution angle is 120°, from -60° to 60°. In contrast, for the top-hat light source 4 indicated by the solid line, as described above, the luminous intensity increases sharply in the region near the boundary of the full width at half maximum θ of the luminous intensity distribution angle (110°, from -55° to 55°), and decreases gradually in other regions. In particular, high luminous intensity continues gradually near the luminous intensity peak. Therefore, when the reflector 5 is provided so as not to reflect light within the full width at half maximum θ=110°, the light between the full width at half maximum θ'=120° and the full width at half maximum θ=110° is lost due to reflection in the Lambertian light source 4', but this is not lost in the top-hat light source 4. This improves the luminance efficiency (light efficiency). Note that the improvement in luminance efficiency is not limited to the top-hat type, but is an effect of the emitted light within the full width at half maximum not directly hitting the reflector 5.

[0031] Furthermore, as mentioned above, in the top-hat type light source 4, high luminous intensity continues gradually near the peak of luminous intensity, and as a result of combining light with light from adjacent light sources 4, brightness uniformity is improved.

[0032] Furthermore, improved brightness uniformity makes it possible to reduce the distance between the light source 4 and lenses, etc. (first lens 6, second lens 7, third lens 8, reflective polarizing film 9), enabling the planar lighting device 1 to be made thinner. In other words, in a direct-type planar lighting device 1, the light from the light source 4 tends to be strong directly above, impairing brightness uniformity, so to suppress this, it is necessary to install lenses, etc. with a diffusion function, away from the light source. However, brightness uniformity is improved by the light distribution of the light source 4 itself, making it possible to reduce the distance from the lenses, etc.

[0033] Fig. 8A is a diagram showing an example of the luminance distribution by a Lambertian light source 4'. Fig. 8B is a diagram showing an example of the relative luminance with respect to the position of the Lambertian light source 4'. Note that the surface lighting device 1' in which the light source 4' is provided is not the one shown in Fig. 6, but a modified surface lighting device 1' described later in Fig. 12. As can be seen from Fig. 8B, the change in relative luminance in the horizontal direction (Horizontal) indicated by the solid line is small, but the change in relative luminance in the vertical direction (Vertical) indicated by the dashed line is large, resulting in horizontal line-like uneven portions as shown in Fig. 8A.

[0034] FIG. 9A is a diagram showing an example of the luminance distribution caused by a top-hat type light source 4. FIG. 9B is a diagram showing an example of the relative luminance with respect to the position of the top-hat type light source 4. Note that the surface lighting device 1 in which the light source 4 is provided is not the one shown in FIG. 1, but a modified surface lighting device 1 described later in FIG. 10. As can be seen from FIG. 9B, the change in relative luminance in the horizontal direction (Horizontal) indicated by the solid line is small, as in FIG. 8B. However, the change in relative luminance in the vertical direction (Vertical) indicated by the dashed line is also small, so the uneven horizontal lines shown in FIG. 9A disappear, and the luminance uniformity is improved.

[0035] In the above embodiment, the full width at half maximum of the light emitted from the light source 4 is set to a value in the H direction and the V direction such that the emitted light within the full width at half maximum does not directly strike the reflector 5. However, the present invention is not limited to this. For example, the height of the reflector 5 in the H direction and the height of the reflector 5 in the V direction may be different from each other. In this case, the reflector 5 in either the H direction or the V direction may be set to a height at which the emitted light within the full width at half maximum of the light source 4 directly strikes the reflector 5. In other words, it is preferable that the full width at half maximum of the light emitted from the light source 4 is set to a value such that the emitted light within the full width at half maximum does not directly strike the reflector, at least in a predetermined direction.

[0036] (Variation 1) 10 is a diagram showing an example of the configuration of a surface lighting device 1 according to Modification 1. The diagram also shows a liquid crystal panel 11 attached to the surface lighting device 1. The surface lighting device 1 in FIG. 10 has the same configuration as that in FIG. 1 in terms of the bottom frame 2, substrate 3, light source 4, and top frame 10, except for the configuration of lenses, etc. Furthermore, the reflective polarizing film 9 such as DBEF on the exit side is also the same as that in FIG. 1.

[0037] 10, the surface lighting device 1 includes, as reflectors 5, reflector 51 extending in the V direction and reflector 52 extending in the H direction. Reflector 51 and reflector 52 have different heights. In the example of FIG. 10, reflector 52 is higher than reflector 51. For convenience of explanation, FIG. 10 shows a cross-sectional view of the surface lighting device 1, and reflector 51 is illustrated behind the light source 4.

[0038] The surface illumination device 1 also includes a first lens 6 and a second lens 7 disposed on the emission side of the light source 4 and the reflector 5 (reflectors 51 and 52). The first lens 6 includes a lenticular lens 6g having concave and convex grooves extending in a first direction (Y-axis direction) in the plane on the incidence side, and a linear Fresnel lens 6h having concave and convex grooves extending in a second direction (X-axis direction) perpendicular to the first direction in the plane on the emission side. The linear Fresnel lens 6h focuses light from the light source 4 in the first direction (Y-axis direction). (Note that, in the first modification, there is no linear Fresnel lens having concave and convex grooves extending in the first direction, and therefore light is not focused in the second direction (X-axis direction).)

[0039] The first lens 6 has grooves formed periodically to match the spacing (pitch) of the light sources 4 arranged directly below it. The second lens 7 has a peak shift prism 7g with concave and convex grooves extending in a second direction (X-axis direction) in its plane on the incident side, and a lenticular lens 7h with concave and convex grooves extending in a first direction (Y-axis direction) in its plane on the output side. Note that instead of the linear Fresnel lens 6h, for example, a cylindrical lens extending in the second direction (X-axis direction) may be used.

[0040] As a result, the planar lighting device 1 according to Modification 1 can obtain a desired light distribution. In the example shown in Fig. 10, the first lens 6 and the second lens 7 of the planar lighting device 1 collect the light emitted from the light source 4 in the negative Y-axis direction.

[0041] Here, the reason why the reflector 52 is higher than the reflector 51 is to reduce stray light that occurs when obtaining a desired light distribution in the Y-axis direction.

[0042] 11A and 11B are diagrams showing an example of an emission path from a light source 4. FIG. 11A illustrates a typical light path when light emitted from a specific light source 4 is focused in the Y-axis direction in an end view of the surface illumination device 1 according to Modification 1. FIG. 11B illustrates an enlarged view of the area surrounded by the dashed rectangle in FIG. 11A. In FIGS. 11A and 11B, arrows indicate the light path. In addition, in FIG. 11A, light source 41 and light source 42 are illustrated to distinguish between the individual light sources 4.

[0043] 11A, most of the light emitted from light source 41 is distributed in the negative direction of the Y axis through the first lens 6 and the second lens 7 corresponding to range r1 (segment). Similarly, most of the light emitted from light source 42 is distributed in the negative direction of the Y axis through the first lens 6 and the second lens 7 corresponding to range r2 (segment adjacent to range r1).

[0044] However, some of the light emitted from the light source 41 may exit from the linear Fresnel lens 6h corresponding to the light source 42 adjacent to the light source 41. For example, light emitted from the light source 41 along path L1 enters the first lens 6 through the lenticular lens 6g in the range r2 corresponding to the adjacent light source 42 and exits from the linear Fresnel lens 6h. The light emitted from the linear Fresnel lens 6h passes through the second lens 7 and is distributed in the positive direction of the Y-axis before being emitted. This light is "stray light" that is distributed in the opposite direction to the direction in which most of the light is distributed (the negative direction of the Y-axis). Stray light occurs periodically in accordance with the spacing between the light sources 4, causing periodic unevenness in the luminance distribution of the light emitted from the surface illumination device 1 (liquid crystal panel).

[0045] However, it has been found that even if light emitted from light source 41 enters lenticular lens 6g in range r2 corresponding to light source 42, not all of the incident light becomes stray light. For example, as shown in FIGS. 11A and 11B, light emitted from light source 41 along path L2 (light incident near the boundary between adjacent lenticular lenses 6g) enters first lens 6 from lenticular lens 6g in range r2 but is totally reflected by linear Fresnel lens 6h (exit surface). As a result, the light along path L2 does not exit linear Fresnel lens 6h and does not become stray light. (In other words, light rays that are inclined toward range r2 with respect to an imaginary line connecting light source 41 and the boundary between ranges r1 and r2 in linear Fresnel lens 6h generate stray light.)

[0046] 12 is an enlarged view of the light source 4 and the reflector 52. In FIG. 12, the tilt angle of the light source 4 in the Y-axis direction (corresponding to the angle of the stray light relative to the optical axis) is φ [°], the height of the reflector 52 is h, the height from the substrate 3 to the top surface of the light source 4 is D, the distance from the center of the light source 4 to the center of the reflector 52 is a, and the height from the top surface of the light source 4 of the point where light emitted from the light source 4 with an emission angle φ intersects with a perpendicular line passing through the center between adjacent light sources (a virtual line passing through the center of the reflector 52 or the boundary between adjacent segments of the lens 6) is b. In order to suppress the generation of stray light due to the lens, the following formula (3) must be satisfied. Note that b corresponds to the height (height from the top surface of the light source 4) at which light with an emission angle φ from the light source 4 reaches on the perpendicular line passing through the center between the adjacent light sources.

[0047] h ≧ D+b ≧ D+a·tan(90-φ) (b=a·tan(90-φ) ···(3)

[0048] This value of h is greater than the value of h calculated by the above-mentioned formulas (1) and (2).

[0049] Specifically, as a result of detailed investigations using a realistic model, the inclination angle φ is desirably set to, for example, 40° or less as the angle at which light emitted from one light source is emitted from the linear Fresnel lens corresponding to the light source adjacent to that light source. In this case, it is desirably that the height h of the reflector 52 satisfies the following formula (4) with φ set to 40°.

[0050] h ≧ D+a tan50° (4)

[0051] As a result, the surface lighting device 1 according to Modification 1 can reduce stray light that occurs when obtaining a desired light distribution. As described above, stray light is generated by light rays that are inclined toward the range r2 side with respect to the imaginary line connecting the boundary between the ranges r1 and r2 of the linear Fresnel lens 6h and the light source 41. Therefore, the height of the reflector 52 can be set to a height that does not cause it to come into contact with the first lens 6, in other words, a height that is lower than the height of the incident surface side of the first lens 6. If the top of the reflector 52 were to come into contact with the first lens 6, shadows (dark areas) would likely occur in the emitted light, which could impair brightness uniformity. Therefore, based on the mechanism by which stray light occurs, it is preferable from the perspective of brightness uniformity and improved brightness to set the height of the reflector 52 lower than the height of the incident surface side of the first lens 6.

[0052] Since reflector 51 acts on light traveling in a direction not affected by a linear Fresnel lens (a direction in which no linear Fresnel lens is included (see paragraph 0038) and no stray light is generated), it is preferable to set the full width at half maximum of the light emitted from light source 4 to a value in the X-axis direction such that the emitted light within the full width at half maximum does not directly strike reflector 51. This makes it possible to increase the optical efficiency of the light emitted from light source 4 in the X-axis direction while reducing stray light in the Y-axis direction when obtaining a desired light distribution in the Y-axis direction. In this case, from the viewpoint of optical efficiency and brightness uniformity in the X-axis direction, light emitted from light source 4 with an emission angle corresponding to the half width at half maximum (half the full width at half maximum θ) in the X-axis direction (second direction) may be configured not to directly strike reflector 51 but to enter a region of first lens 6 corresponding to an adjacent segment. Note that an adjacent segment is a segment adjacent to a segment including each light source.

[0053] Here, we will explain the stray light reduction effect depending on the height of the reflector 52. For ease of explanation, the height h of the reflector 52 will be described as "high" when it satisfies the formula when the tilt angle φ is 40°, and will be described as "low" when it does not.

[0054] 13A, 13B, 13C, and 13D show simulation results when the reflector 52 is high. FIG. 13A is an angular luminance distribution diagram showing the light distribution characteristic (Viewing Angle) of the entire light emitted from the surface lighting device 1. In FIG. 13A, the horizontal axis corresponds to the angle value (°) in the H direction, and the vertical axis corresponds to the angle value (°) in the V direction. FIG. 13B is an angular luminance cross-sectional diagram at a specific position in FIG. 13A. In FIG. 13B, the horizontal axis corresponds to the angle (°) and the vertical axis corresponds to the luminance (% standard value). The solid line graph shows the luminance in the V direction at an angle value of 0° in the H direction, and the dashed line graph shows the luminance in the H direction at an angle value of -10° in the V direction. FIG. 13C is a luminance distribution diagram of the surface lighting device 1 viewed from viewpoint P in FIG. 13A. In FIG. 13C, the horizontal axis corresponds to the position (mm) in the V direction, and the vertical axis corresponds to the position (mm) in the H direction. Fig. 13D is a luminance cross-sectional view at a specific position in Fig. 13C. In Fig. 13D, the horizontal axis corresponds to position (mm) and the vertical axis corresponds to luminance (% of normalized value).

[0055] 14A, 14B, 14C, and 14D show simulation results when the reflector 52 is low. FIG. 14A is an angular luminance distribution diagram showing the light distribution characteristic (Viewing Angle) of the entire light emitted from the surface lighting device 1. FIG. 14B is an angular luminance cross-sectional view at a specific position in FIG. 14A. FIG. 14C is a luminance distribution diagram of the surface lighting device 1 viewed from viewpoint P in FIG. 14A. FIG. 14D is a luminance cross-sectional view at a specific position in FIG. 14C. Note that the ways of viewing FIGS. 14A to 14D are the same as those of FIGS. 13A to 13D, and therefore description thereof will be omitted.

[0056] As shown in Fig. 13A, the surface lighting device 1 according to the first modification emits light distributed at a light distribution angle of approximately -10° in the V direction. When the reflector 52 is low, a small peak is detected in region R of the luminous intensity profile near a light distribution angle of 0° in the H direction (Fig. 14B). This small peak is stray light generated as a result of the light distribution in the V direction. This stray light is not detected when the reflector 52 is high (Fig. 13B), confirming the stray light reducing effect of the reflector 52.

[0057] Furthermore, when the reflector 52 was low, periodic unevenness was observed in the luminance distribution (FIG. 14C), and the luminance distribution profile in the V direction was also disturbed (clear peaks appeared) (FIG. 14D), confirming the occurrence of stray light. Such periodic unevenness and disturbance in the luminance distribution profile were not detected when the reflector 52 was high (FIGS. 13C and 13D), confirming the stray light reduction effect of the reflector 52.

[0058] (Variation 2) FIG. 15 is a diagram showing an example of the configuration of a surface lighting device 1 according to Modification 2, in which the peak shift function is omitted. The liquid crystal panel 11 attached to the surface lighting device 1 is also shown. The surface lighting device 1 in FIG. 15 has the same configuration as that in FIG. 1, except for the configuration of lenses, etc., including the bottom frame 2, substrate 3, light source 4, reflector 5, and top frame 10. The reflective polarizing film 9 such as DBEF on the exit side is also the same as that in FIG. 1. As such, even if a lens with a peak shift function is not provided and the positions of the various lenses are different, the effects of improving light efficiency and brightness uniformity can be observed.

[0059] 15, the surface lighting device 1 includes a light source 4 and a first lens 6 disposed on the light-emitting side of a reflector 5. The first lens 6 includes a linear Fresnel lens 6i having concave and convex grooves extending in a first direction (X-axis direction) in the plane on the incident side, and a lenticular lens 6j having concave and convex grooves extending in a second direction (Y-axis direction) orthogonal to the first direction in the plane on the exit side.

[0060] Fig. 16 is a diagram showing a modified example of a surface lighting device 1' of a comparative example. The diagram also shows a liquid crystal panel 11' attached to the surface lighting device 1'. In Fig. 16, the surface lighting device 1' has the same configuration as the lenses and the like in Fig. 10, except that the light source 4' has a Lambertian light distribution.

[0061] Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and various modifications are possible without departing from the spirit of the present invention. For example, the peak shift function may be omitted from the planar lighting device 1 according to the above embodiment. Furthermore, the heights of the four reflective surfaces 5a (reflectors 5) may all be low, prioritizing brightness, or the heights of the four reflective surfaces 5a may all be high, prioritizing suppression of stray light.

[0062] As described above, the planar lighting device according to the embodiment includes a substrate on which a plurality of light sources are arranged two-dimensionally, a reflector arranged on the substrate and having an inclined reflective surface surrounding the emission side of each of the light sources, and a condenser lens arranged on the emission side of the light sources and the reflector to condense the light emitted from the light sources, wherein the full width at half maximum of the light emitted from the light sources is set to a value such that the emitted light within the full width at half maximum does not directly strike the reflector, at least in a predetermined direction. This increases the light efficiency. As a result, ultra-high brightness and ultra-high efficiency are possible.

[0063] Furthermore, in the planar lighting device, when the full width at half maximum of the light source is approximately θ [°], the height of the reflector is h, the height from the substrate to the top surface of the light source is D, the distance from the center of the light source to the center of the reflector is a, and the height from the top surface of the light source 4 of a point at which light emitted from the light source and whose emission angle corresponds to half the full width at half maximum θ (half width at half maximum) intersects with a perpendicular line passing through the center between adjacent light sources (a virtual line passing through the center of the reflector 5 or the boundary between adjacent segments of the first lens 6), h ≦ D + b ≦ D + a tan(90 − θ / 2) (b = a tan(90 − θ / 2) is satisfied. This clarifies the relationship between the full width at half maximum of the light source and the height of the reflector, etc. Note that b corresponds to the height (height from the top surface of the light source 4) reached by light from the light source 4 whose emission angle corresponds to half width at half maximum on a perpendicular line passing through the center between adjacent light sources.

[0064] Furthermore, in the planar lighting device, the full width at half maximum of the light source is 110° or less, the height of the reflector is h, the height from the substrate to the upper surface of the light source is D, and the distance from the center of the light source to the center of the reflector is a, and the relationship h≦D+a tan(35°) has been confirmed to be highly effective.

[0065] Furthermore, the light source is a top-hat type, and emits light whose luminous intensity is steep in the region near the boundary of the full width at half maximum of the light distribution angle and whose luminous intensity is gentle in other regions. This further increases the light efficiency and alleviates the problem of high luminance directly above the light source, which is a problem with direct-type planar lighting devices, resulting in poor luminance uniformity, thereby improving luminance uniformity. It also enables the planar lighting device to be made thinner.

[0066] Furthermore, the Fresnel lens has a prism shape in the area directly above the light source and in the area around the light source that directs light in the direction of the optical axis. This allows the use of a Fresnel lens with a general prism shape to improve brightness uniformity even in a top-hat type light source.

[0067] The planar lighting device includes the light source and a first lens, a second lens, and a third lens arranged on the exit side of the reflector, wherein the first lens has a linear Fresnel lens as the condenser lens, with concave and convex grooves extending in a first direction in the plane of the incident side and a second direction in the plane of the exit side perpendicular to the first direction, the second lens has a lenticular lens, with concave and convex grooves extending in the first direction in the plane of the incident side and the second direction in the plane of the exit side, and the third lens has a peak shift lens, with concave and convex grooves extending in the first direction or the second direction in either the plane of the incident side or the plane of the exit side, thereby achieving a desired light distribution.

[0068] The planar lighting device also has a condenser lens that extends in a second direction perpendicular to the first direction in the plane on the exit side as the condenser lens, and a peak shift prism with concave and convex grooves that extend in the second direction in the plane on the entrance side, thereby achieving a desired light distribution.

[0069] The reflector includes a first reflector extending in the first direction and a second reflector extending in the second direction, the condensing lens condenses the light emitted from the light source in the first direction, the full width at half maximum of the light emitted from the light source is set to a value such that the emitted light within the full width at half maximum in the second direction does not directly hit the first reflector, and the second reflector is higher than the first reflector, thereby reducing stray light that occurs when obtaining a desired light distribution.

[0070] The condenser lens is formed to match the interval (pitch) of the light sources arranged directly below it, and satisfies h ≧ D + b ≧ D + a tan(90 − φ) (b = a tan(90 − φ), where φ is the tilt angle from the optical axis of the light source in the first direction, h is the height of the second reflector, D is the height from the substrate to the top surface of the light source, a is the distance from the center of the light source to the center of the second reflector, and b is the height from the top surface of the light source 4 at which light emitted from the light source 4 at an emission angle φ intersects with a perpendicular line passing through the center between adjacent light sources (a virtual line passing through the center of the reflector 52 or the boundary between adjacent segments of the lens 6). This makes it possible to clarify the relationship between the tilt angle from the optical axis of the light source in the first direction and the height of the reflector, etc. Note that b corresponds to the height (height from the top surface of the light source 4) at which light from the light source 4 at an emission angle φ reaches on the perpendicular line passing through the center between adjacent light sources.

[0071] The tilt angle is set to an angle at which light emitted from one light source is emitted from the condenser lens corresponding to the light source adjacent to the light source, thereby effectively reducing stray light.

[0072] When the tilt angle from the optical axis of the light source to the first direction is 40° or less, the height of the second reflector is h, the height from the substrate to the upper surface of the light source is D, and the distance from the center of the light source to the center of the second reflector is a, the relationship h ≧ D+a tan(50°) is satisfied. This has been confirmed to be highly effective.

[0073] When the full width at half maximum of the light source is approximately θ [°], the height of the first reflector is h, the height from the substrate to the upper surface of the light source is D, the distance from the center of the light source to the center of the first reflector is a, and the height from the upper surface of the light source to the first reflector is b, the following relationship is satisfied: h ≦ D + b ≦ D + a tan(90−θ / 2) (b=a tan(90−θ / 2)). As a result, when obtaining a desired light distribution in a first direction, it is possible to reduce stray light in the first direction while increasing the optical efficiency of the light emitted from the light source in the second direction.

[0074] The condenser lens is a linear Fresnel lens with concave and convex grooves extending in one direction, which allows a desired light distribution to be obtained.

[0075] The planar lighting device also includes a first lens disposed on the light source and the light exit side of the reflector, the first lens having a linear Fresnel lens with concave and convex grooves extending in a second direction perpendicular to the first direction within the plane of the incident side, and a lenticular lens with concave and convex grooves extending in the first direction within the plane of the exit side, thereby achieving a desired light distribution.

[0076] Furthermore, light emitted from the light source at an emission angle corresponding to the half-width at half maximum (half the full-width at half maximum) in the predetermined direction (X-axis direction) is configured to be incident on an area of ​​the condenser lens corresponding to an adjacent segment without entering the reflector. This makes it possible to improve light efficiency and brightness uniformity in the second direction in which no stray light is generated. Note that the above-mentioned "predetermined direction" corresponds to the direction in which no stray light is generated, the direction in which the linear Fresnel lens extends (the direction perpendicular to the condensing direction).

[0077] Furthermore, the present invention is not limited to the above-described embodiments. Configurations in which the above-described components are appropriately combined are also included in the present invention. Furthermore, 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-described embodiments, and various modifications are possible. [Explanation of symbols]

[0078] 1 Planar lighting device, 2 Bottom frame, 3 Substrate, 4 Light source, 4a Element substrate, 4b Light-emitting chip, 4c Lens, 4d Electrode, 5 Reflector, 5a Reflecting surface, 6 First lens, 6a Prism, 7 Second lens, 8 Third lens, 9 Reflective polarizing film, 10 Top frame, 10a Opening, 11 Liquid crystal panel, θ Full width at half maximum

Claims

1. a substrate on which a plurality of light sources are arranged; a reflector disposed on the substrate and having a wall portion including an inclined reflecting surface surrounding an emission side of each of the light sources; a condenser lens disposed on an output side of the light source and the reflector, and configured to condense light emitted from the light source; the reflector includes a second reflector, the wall of which extends in a second direction perpendicular to the first direction in correspondence with a boundary between the light source and an adjacent light source; the condensing lens includes a linear Fresnel lens that extends in the second direction, condenses the light emitted from the light source in the first direction, and is periodically formed in accordance with the intervals between the light sources disposed directly below the linear Fresnel lens; the second reflector has a height such that a top of the wall portion located at the boundary does not contact an incident surface of the condenser lens, The linear Fresnel lens is configured such that a path of light incident on the linear Fresnel lens from the light source includes a path that totally reflects light that is not blocked by a wall portion of the second reflector and that is incident on the side of the adjacent light source in the vicinity of the boundary with the adjacent light source. Surface lighting device.

2. a full width at half maximum of the light emitted from the light source is set to a value such that the light emitted within the full width at half maximum does not directly strike the reflector at least in a predetermined direction; 2. The spread illuminating device according to claim 1.

3. When the full width at half maximum of the light source is approximately θ [°], the height of the reflector is h, the height from the substrate to the top surface of the light source is D, the distance from the center of the light source to the center of the reflector is a, and the height from the top surface of the light source of a point at which light emitted from the light source and having an emission angle corresponding to the half width at half maximum intersects with a perpendicular line passing through the center between adjacent light sources is b, h≦D+b ≦ D+a・tan(90−θ / 2) (b=a・tan(90−θ / 2) Satisfy the 3. The spread illuminating device according to claim 2.

4. When the full width at half maximum of the light source is 110° or less, the height of the reflector is h, the height from the substrate to the upper surface of the light source is D, and the distance from the center of the light source to the center of the reflector is a, h ≦ D+a・tan (35°) Let's say, 3. The spread illuminating device according to claim 2.

5. The light source is a top hat type, and emits light whose luminous intensity becomes steep in a region near the boundary of the full width at half maximum of the light distribution angle and whose luminous intensity becomes gentle in other regions.

2. The spread illuminating device according to claim 1.

6. The condenser lens has a prism shape in a portion directly above the light source and a peripheral portion thereof that directs light in the optical axis direction.

6. The spread illuminating device according to claim 5.

7. a first lens, a second lens, and a third lens disposed on the light source and the output side of the reflector; the first lens has a linear Fresnel lens as the condenser lens, in which concave and convex grooves extend in the first direction in a plane on an incident side and in the second direction in a plane on an exit side, the second lens has a lenticular lens having concave and convex grooves extending in the first direction in a plane on an incident side and in the second direction in a plane on an exit side, the third lens has a peak shift lens having concave and convex grooves extending in the first direction or the second direction on either the incident side or the exit side of the third lens; 2. The spread illuminating device according to claim 1.

8. a condenser lens extending in the second direction in a plane on the exit side as the condenser lens; a peak shift prism having concave and convex grooves extending in the second direction in the incident side surface, 2. The spread illuminating device according to claim 1.

9. the reflector includes a first reflector having a wall portion extending in the first direction; the condenser lens condenses the light emitted from the light source in the first direction; a full width at half maximum of the emitted light from the light source is set to a value such that the emitted light within the full width at half maximum does not directly strike the first reflector in the second direction; the second reflector is higher than the first reflector; 9. The spread illuminating device according to claim 8.

10. The condenser lenses are formed to match the intervals between the light sources arranged directly below them, When the tilt angle from the optical axis of the light source to the first direction is φ [°], the height of the second reflector is h, the height from the substrate to the top surface of the light source is D, the distance from the center of the light source to the center of the second reflector is a, and the height from the top surface of the light source 4 of a point where light emitted from the light source at an emission angle φ intersects with a perpendicular line passing through the center between adjacent light sources is b, h≧D+b ≧ D+a・tan(90−φ) (b=a・tan(90−φ) Satisfy the 10. The spread illuminating device according to claim 9.

11. the tilt angle is set to an angle at which light emitted from one light source is emitted from the condenser lens corresponding to the light source adjacent to the light source; The spread illuminating device according to claim 10.

12. When the tilt angle from the optical axis of the light source to the first direction is 40° or less, the height of the second reflector is h, the height from the substrate to the upper surface of the light source is D, and the distance from the center of the light source to the center of the second reflector is a, h ≧ D+a・tan (50°) Let's say, The spread illuminating device according to claim 9 .

13. When the full width at half maximum of the light source is approximately θ [°], the height of the first reflector is h, the height from the substrate to the top surface of the light source is D, the distance from the center of the light source to the center of the first reflector is a, and the height from the top surface of the light source 4 of a point at which light emitted from the light source and having an emission angle corresponding to the half width at half maximum intersects with a perpendicular line passing through the center between adjacent light sources is b, h≦D+b ≦ D+a・tan(90−θ / 2) (b=a・tan(90−θ / 2) Satisfy the The spread illuminating device according to claim 9 .

14. The condenser lens is a linear Fresnel lens having concave and convex grooves extending in one direction.

8. The spread illuminating device according to claim 7.

15. a first lens disposed on an output side of the light source and the reflector; the first lens has a linear Fresnel lens having concave and convex grooves extending in the second direction in a surface on the light-emitting side, and a lenticular lens having concave and convex grooves extending in the first direction in a surface on the light-incident side, 2. The spread illuminating device according to claim 1.

16. a light source configured to emit light having an emission angle corresponding to a half width at half maximum in the predetermined direction, the light source not being incident on the reflector but being incident on a region of the condenser lens corresponding to an adjacent segment; 3. The spread illuminating device according to claim 2.

17. The plurality of light sources are arranged in a grid pattern.

2. The spread illuminating device according to claim 1.

18. The linear Fresnel lens is formed on the output side surface of the condenser lens.

2. The spread illuminating device according to claim 1.

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