Planar luminaire

Abstract

To improve contrast and luminance uniformity.SOLUTION: A planar luminaire comprises a plurality of light sources, a condenser lens and a field lens. The light sources are arranged two-dimensionally on a substrate and have light emission controlled individually. The condenser lens is arranged on a light emission side of the light sources in parallel with the substrate, and converges light emitted from the light sources into substantially parallel light. The field lens is arranged on a light emission side of the condenser lens obliquely to at least one of orthogonal directions in a plane parallel to the substrate, and diverges the light made incident from the condenser lens outward and also has a uniform optical distance secured with an external liquid crystal panel.SELECTED DRAWING: Figure 6

Description

[Technical field]

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

[0002] Head-up displays (HUDs) that use the windshield of an automobile are known (see, for example, Patent Documents 1 and 2). Since the light source unit of such a head-up display is installed near the windshield that is exposed to sunlight, measures against heat and stray light caused by sunlight are often taken.

[0003] For example, a surface lighting device used as a backlight for a head-up display has a liquid crystal panel on its emission surface side, and one or more mirrors are provided behind it to project light onto the windshield. Therefore, the heat from sunlight entering from outside the vehicle through the windshield and mirrors can deteriorate the liquid crystal panel and surface lighting device, and stray light can adversely affect the display.

[0004] As a countermeasure, the liquid crystal panel is often arranged so that it is tilted in the same direction as the first mirror with respect to the main optical axis from the surface lighting device to the first mirror. By arranging the liquid crystal panel in an inclined state, sunlight that enters in the opposite direction to the projection is easily reflected by the surface of the liquid crystal panel, and by preventing sunlight from entering the liquid crystal panel and the surface lighting device, problems caused by heat and stray light are reduced. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2018-83593 A [Patent Document 2] JP 2019-61128 A Summary of the Invention [Problem to be solved by the invention]

[0006] The tilt of the liquid crystal panel described above does not pose any particular problem for planar lighting devices that do not support local dimming, but for planar lighting devices that support local dimming, it causes new problems that reduce contrast and brightness uniformity. Local dimming is a technology that significantly increases the contrast ratio of different areas on the same screen by controlling the light intensity of each light source in a direct-type planar lighting device that arranges light sources such as LEDs (Light Emitting Diodes) in two dimensions.

[0007] That is, in this type of planar lighting device, the light distribution characteristic is often given to the outside so that the visibility of the periphery does not decrease even if the light is converged by a concave mirror used as a part of the mirror in the subsequent stage. Therefore, by arranging the liquid crystal panel at an angle with respect to the main optical axis of the planar lighting device, a difference in optical distance occurs between the field lens for giving the light distribution characteristic to the outside and the liquid crystal panel. This difference in optical distance causes light to be generated that goes beyond the local dimming zone area (dimming zone), reducing contrast and brightness uniformity.

[0008] The present invention has been made in view of the above, and an object of the present invention is to provide a surface illumination device capable of improving contrast and luminance uniformity. [Means for solving the problem]

[0009] In order to solve the above-mentioned problems and achieve the object, a surface illumination device according to one aspect of the present invention includes a plurality of light sources, a condenser lens, and a field lens. The plurality of light sources are two-dimensionally arranged on a substrate, and light emission is controlled individually. The condenser lens is arranged on the emission side of the light sources and parallel to the substrate, and converges the light emitted from the light sources into approximately parallel light. The field lens is arranged on the emission side of the condenser lens and inclined in at least one direction perpendicular to the plane parallel to the substrate, and spreads the light incident from the condenser lens outward, ensuring a uniform optical distance between the condenser lens and an externally attached liquid crystal panel.

[0010] A surface illumination device according to an aspect of the present invention can improve contrast and luminance uniformity. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram showing an example of the configuration of a head-up display system. [Diagram 2] FIG. 2 is a plan view of a surface illumination device equipped with a liquid crystal panel. [Diagram 3] FIG. 3 is a cross-sectional view taken along line AA of FIG. [Figure 4] FIG. 4 is a cross-sectional view taken along line BB of FIG. [Diagram 5] FIG. 5 is a diagram showing an example of light distribution in the horizontal direction (X-axis direction). [Figure 6] FIG. 6 is a diagram showing an example of light distribution in the vertical direction (Y-axis direction). [Figure 7] FIG. 7 is a diagram showing an example of the configuration of a surface illumination device and a liquid crystal panel of Comparative Example #1, and an example of light distribution in the vertical direction (Y-axis direction). [Figure 8] FIG. 8 is a diagram showing an example of the configuration of a surface illumination device and a liquid crystal panel of Comparative Example #2, and an example of light distribution in the vertical direction (Y-axis direction). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, a planar lighting device according to an embodiment will be described with reference to the drawings. Note that the present invention is not limited to this embodiment. In addition, the dimensional relationship of each element in the drawings, the ratio of each element, etc. may differ from reality. The drawings may also include parts with different dimensional relationships and ratios. In principle, the contents described in one embodiment or modified example are similarly applied to other embodiments or modified examples.

[0013] Fig. 1 is a diagram showing an example of the configuration of a head-up display system 100. In Fig. 1, in the case of the head-up display system 100 mounted on an automobile, the traveling direction of the automobile is the left direction in the figure (the positive direction of the Y axis).

[0014] 1, light emitted from the surface illumination device 1 passes through a liquid crystal panel 101 (L1), is reflected by a mirror 102 (L2), and is guided to a concave mirror 103. The light reflected from the concave mirror 103 (L3) is irradiated onto a windshield 104 of a vehicle, and the reflected light (L4) enters an eye box (field of vision) EB of a driver or the like, and the image displayed on the liquid crystal panel 101 is recognized as a virtual image. Note that "H (horizontal direction)" written alongside the X-axis and "V (vertical direction)" written alongside the Y-axis indicate the horizontal and vertical directions of the virtual image as seen from the eye box EB.

[0015] Furthermore, the liquid crystal panel 101 is arranged so as to be inclined in the same direction as the mirror 102 with respect to the main optical axis (L1) from the surface lighting device 1 toward the first mirror 102. By arranging the liquid crystal panel 101 in an inclined state, when sunlight irradiated from above the windshield 104 enters the liquid crystal panel 101 through the windshield 104, the concave mirror 103, and the mirror 102, the sunlight is more likely to be reflected by the surface of the liquid crystal panel 101. This prevents sunlight from entering the liquid crystal panel 101 and the surface lighting device 1, thereby reducing problems caused by heat and stray light.

[0016] Note that the components and arrangement of the head-up display system 100 in FIG. 1 are merely an example, and the optical axis of the surface illumination device 1 may be set horizontally, and the configuration of the mirrors, including the number of mirrors, may be different.

[0017] 2 is a plan view of the surface lighting device 1 equipped with a liquid crystal panel 101. For convenience, the bottom surface of the surface lighting device 1 is in the XY plane, and the thickness direction of the surface lighting device 1 is the Z direction. In addition, in a usage state in which the light is reflected by the windshield 104 and seen by the user, the X-axis direction corresponds to the horizontal direction (H) and the Y-axis direction corresponds to the vertical direction (V), as already shown in FIG. 1. In the following, the horizontal direction and the vertical direction in a usage state in which the light is reflected by the windshield 104 and seen by the user may be simply referred to as the "horizontal direction" and the "vertical direction".

[0018] 2, the surface illumination device 1 has a substantially rectangular outer shape in plan view, and has a liquid crystal panel 101 disposed on its light exit surface. The liquid crystal panel 101 is surrounded by a frame portion 101b, and the inside of this is a display area 101a.

[0019] Fig. 3 is a cross-sectional view taken along line AA in Fig. 2. Fig. 4 is a cross-sectional view taken along line BB in Fig. 2. In Figs. 3 and 4, the surface lighting device 1 has a box-shaped frame 2 with a bottom. A substrate 3 made of aluminum or the like having excellent heat dissipation properties is disposed on the bottom of the frame 2. On the substrate 3, which has been appropriately insulated, a plurality of light sources 4 made of LEDs (Light Emitting Diodes) or the like are disposed two-dimensionally in a lattice pattern. Each light source 4 is driven individually and its light emission is controlled individually, corresponding to so-called local dimming.

[0020] A reflector 5 having four reflective surfaces 5a, 5b surrounding each of the light sources 4 is disposed on the emission side of the substrate 3 where the light sources 4 are disposed. The reflector 5 is made of resin or the like. The reflector 5 may be disposed in a state where it is floating above the light sources 4. The reflector 5 may be omitted.

[0021] A condenser lens 6 for collecting light is arranged parallel to the substrate 3 on the exit side of the reflector 5. As shown in FIG. 3, a linear Fresnel lens 6a is formed on the lower entrance side surface of the condenser lens 6, in which grooves constituting the concave-convex surface of the lens extend in one direction (depth direction (Y-axis direction) in the figure). As shown in FIG. 4, a linear Fresnel lens 6b is formed on the upper exit side surface of the condenser lens 6, in which grooves constituting the concave-convex surface of the lens extend in a direction perpendicular to the one direction of the lower surface (left-right direction (X-axis direction) in the figure). Each of the linear Fresnel lenses 6a and 6b has a prism structure in which a cylindrical convex lens is used as the Fresnel lens, and grooves are formed periodically in accordance with the pitch of the light source 4 arranged directly below, and the angle of the prism is inverted at the segment boundary between adjacent segments. It is easier to manufacture than an annular Fresnel lens.

[0022] A field lens 7 for widening the light distribution is disposed on the exit side of the condenser lens 6. As shown in FIG. 3, a lenticular lens 7a is formed on the lower surface of the field lens 7, in which grooves constituting the concave-convex surface of the lens extend in one direction (depth direction (Y-axis direction) in the figure). As shown in FIG. 4, a lenticular lens 7b is formed on the upper surface of the field lens 7, in which grooves constituting the concave-convex surface of the lens extend in a direction perpendicular to the one direction of the lower surface (left-right direction (X-axis direction) in the figure). The lenticular lenses 7a and 7b have a prism shape with a semi-cylindrical cross section, and widen the incident light. A diffusion plate spreads light in all directions, which leads to a decrease in efficiency, but the lenticular lenses 7a and 7b are advantageous because the spread of the light distribution can be adjusted within a required range by the cross-sectional shape, and there is no decrease in light efficiency.

[0023] A field lens 8 for spreading the light distribution outward is disposed on the exit side of the field lens 7. The reason for spreading the light distribution is to provide an outwardly open light distribution characteristic so that peripheral visibility is not reduced even if the light is converged by the concave mirror 103 included in the head-up display system 100 (FIG. 1). As shown in FIG. 3, the field lens 8 is not inclined in the X-axis direction (horizontal direction) and is disposed parallel to the substrate 3, the condenser lens 6, and the field lens 7. Also, as shown in FIG. 4, the field lens 8 is inclined in the Y-axis direction (vertical direction) relative to the substrate 3, the condenser lens 6, and the field lens 7.

[0024] As shown in FIG. 3, the lower surface of the field lens 8 has a linear prism 8a in which grooves constituting the concave-convex surface of the lens extend in one direction (depth direction in the figure (Y-axis direction)). As shown in FIG. 4, the upper surface of the field lens 8 has a linear prism 8b in which grooves constituting the concave-convex surface of the lens extend in a direction perpendicular to the one direction of the lower surface (left-right direction in the figure (X-axis direction)). The linear prisms 8a and 8b direct light passing through the center part of the full width in a straight line in the Z-axis direction, and orient the optical axis of each location outward as it moves outward. The light passing through the center part of the full width may also be inclined from the Z-axis direction.

[0025] On the exit side of the field lens 8, an optical sheet 9 adapted to the characteristics of the attached liquid crystal panel 101 is arranged parallel to the field lens 8. A polarizing reflective sheet or a diffusion sheet is used as the optical sheet 9. The thickness of the optical sheet 9 is, for example, about 0.4 mm.

[0026] On the exit side of the optical sheet 9, a liquid crystal panel 101 for forming an image to be projected is arranged parallel to the optical sheet 9 and the field lens 8. What is important here is that a uniform optical distance is ensured between the field lens 8 and the liquid crystal panel 101. It is also important that the field lens 8 and the liquid crystal panel 101 are close to each other. The smaller the distance between the field lens 8 and the liquid crystal panel 101, the less light that spreads to the adjacent dimming zone, the less light loss, and the improved contrast. The distance between the field lens 8 and the liquid crystal panel 101 may be zero (closeness with substantially no gap), but considering the optical characteristics, the thickness of the optical sheet 9 if provided, the thickness of the positioning mechanism for each optical member, etc., it is preferable that the distance is 3 mm or less, and more preferably 2 mm or less. Note that as long as the distance between the field lens 8 and the liquid crystal panel 101 is 3 mm or less, the field lens 8 and the liquid crystal panel 101 do not necessarily have to be arranged parallel to each other.

[0027] Fig. 5 is a diagram showing an example of light distribution in the horizontal direction (X-axis direction). In Fig. 5, light L11 emitted from the light source 4 is converged by the condenser lens 6 (linear Fresnel lens 6a on the lower surface) into approximately parallel light to become light L12. The light distribution of light L12 is expanded by the field lens 7 (lenticular lens 7a on the lower surface) while keeping the optical axis unchanged, to become light L13. The optical axis of light L13 is tilted outward at each location by the field lens 8 (linear prism 8a on the lower surface), the light distribution is expanded outward, and the light becomes light L14 passing through the optical sheet 9 and the liquid crystal panel 101.

[0028] Fig. 6 is a diagram showing an example of light distribution in the vertical direction (Y-axis direction). In Fig. 6, light L21 emitted from the light source 4 is converged by the condenser lens 6 (linear Fresnel lens 6b on the upper surface) into approximately parallel light to become light L22. The light distribution of the light L22 is expanded by the field lens 7 (lenticular lens 7b on the upper surface) while keeping the optical axis unchanged, to become light L23. The optical axis of the light L23 is tilted outward at each location by the field lens 8 (linear prism 8b on the upper surface), the light distribution is expanded outward, and the light becomes light L24 passing through the optical sheet 9 and the liquid crystal panel 101.

[0029] FIG. 7 is a diagram showing an example of the configuration of a surface illumination device 1' and a liquid crystal panel 101' of Comparative Example #1 and an example of light distribution in the vertical direction (Y-axis direction). In FIG. 7, the surface illumination device 1' of Comparative Example #1 does not support local dimming. That is, the frame 2' has a substrate 3', a light source 4', a reflector 5', a condenser lens 6', a field lens 8', an optical sheet 9', and a liquid crystal panel 101' arranged in this order from the bottom side, but the whole is covered by a small number of light sources 4'. Therefore, there is no concept of a zone area in local dimming, and even if the optical distance between the field lens 8' and the liquid crystal panel 101' is not uniform, there is no problem with the dimming zone. However, at the end side where the optical distance is the longest (the left end of FIG. 7), light rays enter the frame 2', causing a loss of light.

[0030] FIG. 8 is a diagram showing an example of the configuration of a surface lighting device 1" and liquid crystal panel 101" of comparative example #2 and an example of light distribution in the vertical direction (Y-axis direction). In FIG. 8, the surface lighting device 1" of comparative example #2 supports local dimming. On the frame 2", from the bottom side, a substrate 3", a light source 4", a reflector 5", a condenser lens 6", a field lens 7", a field lens 8", an optical sheet 9" and a liquid crystal panel 101" are arranged in this order. However, the field lens 8" is arranged parallel to the substrate 3", the condenser lens 6" and the field lens 7".

[0031] As a result, light is generated that goes beyond the local dimming zone area surrounded by the vertically extending two-dot chain line corresponding to each light source 4". For example, light L1", L2" in FIG. 8 is light that goes beyond the local dimming zone area. Such light reduces contrast and brightness uniformity. In other words, light that goes beyond an adjacent zone area will provide unnecessary light when the adjacent zone area is off (zero light amount), and the amount of light in the original zone area that goes beyond will be insufficient, resulting in an overall reduction in contrast and brightness uniformity.

[0032] In this respect, in the above embodiment, as shown in FIG. 6, a uniform optical distance is ensured between the field lens 8 and the liquid crystal panel 101, so that the generation of light that goes beyond the local dimming zone area is suppressed, and the deterioration of contrast and brightness uniformity is prevented, and the contrast and brightness uniformity can be improved. In addition, since the field lens 8 and the liquid crystal panel 101 are close to each other, these effects are more effectively exhibited. Note that this embodiment can also be applied to a normal backlight that does not support local dimming, and exerts a certain effect. That is, in the case of the surface illumination device 1' that does not support local dimming in FIG. 7, at the end side where the optical distance is the largest (the left end in FIG. 7), the light rays enter the frame 2', causing a loss of light, but by applying the configuration of this embodiment, the loss of light at the end can be prevented.

[0033] Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications are possible without departing from the spirit of the present invention.

[0034] As described above, the surface illumination device according to the embodiment includes a plurality of light sources arranged two-dimensionally on a substrate, each of which has its light emission controlled individually; a condenser lens arranged on the emission side of the light source, parallel to the substrate, for converging the light emitted from the light source into substantially parallel light; and a field lens arranged on the emission side of the condenser lens, inclined in at least one direction perpendicular to the substrate in a plane parallel to the substrate, for spreading the light incident from the condenser lens outward, and for ensuring a uniform optical distance between the field lens and the liquid crystal panel attached externally. This can improve contrast and brightness uniformity. That is, even if the field lens spreads the light incident from the condenser lens outward, a uniform optical distance is ensured between the field lens and the liquid crystal panel, so that the generation of light that goes beyond the zone area of ​​the local dimming can be suppressed, and a decrease in contrast and brightness uniformity can be prevented. Note that this embodiment can also be applied to a normal backlight that is not compatible with local dimming, and a certain effect is achieved.

[0035] In addition, the field lens is provided close to the liquid crystal panel, which reduces the amount of light that spreads to the adjacent dimming zone by the field lens, reducing light loss and improving contrast.

[0036] In addition, the condenser lens is formed as a linear Fresnel lens in which the grooves forming the unevenness on the incident side and the exit side are orthogonal in direction, and the field lens is formed as a linear prism in which the grooves forming the unevenness on the incident side and the exit side are orthogonal in direction. This makes it easy to realize the condenser lens.

[0037] In addition, another field lens is provided between the condenser lens and the field lens, and is arranged parallel to the substrate, and the other field lens is formed as a lenticular lens in which the grooves forming the unevenness on the entrance side and the exit side are orthogonal in direction, which makes it possible to improve the luminance uniformity without causing a decrease in light efficiency as occurs with a diffusion plate.

[0038] The light emitting device further includes a reflector disposed on the light output side of the substrate and having a reflective surface surrounding the light source, thereby preventing light leaking from the light source to the substrate side from being wasted and improving light efficiency.

[0039] In addition, an optical sheet made of a polarizing reflective sheet or a diffusion sheet is provided on the exit side of the tilted field lens, which makes it easy to achieve optical characteristics according to the externally attached liquid crystal panel.

[0040] Also, a surface illumination device for illuminating a liquid crystal panel arranged at an angle with respect to an optical axis includes a plurality of light sources arranged two-dimensionally on a substrate, each of which has its light emission controlled, a condenser lens arranged on the emission side of the light source to converge the light emitted from the light source into a substantially parallel light, and a field lens arranged on the emission side of the condenser lens to spread the light incident from the condenser lens outward, the field lens being arranged parallel to and close to the externally attached liquid crystal panel, thereby improving contrast and brightness uniformity.

[0041] Also, a surface illumination device for illuminating a liquid crystal panel arranged at an angle with respect to an optical axis includes a plurality of light sources arranged two-dimensionally on a substrate, each of which has its light emission controlled, a condenser lens arranged on the exit side of the light source to converge the light emitted from the light source into a substantially parallel light, and a field lens arranged on the exit side of the condenser lens to spread the light incident from the condenser lens outward, the field lens being arranged close to an externally attached liquid crystal panel, thereby improving contrast and brightness uniformity.

[0042] In addition, the field lens is located close to the LCD panel with a distance of 3 mm or less, which is expected to produce effective results.

[0043] Furthermore, the present invention is not limited to the above-mentioned embodiment. The present invention also includes a configuration in which the above-mentioned components are appropriately combined. Further effects and modifications can be easily derived by those skilled in the art. Therefore, the broader aspects of the present invention are not limited to the above-mentioned embodiment, and various modifications are possible. [Explanation of symbols]

[0044] REFERENCE SIGNS LIST 1 Planar lighting device, 2 Frame, 3 Substrate, 4 Light source, 5 Reflector, 5a, 5b Reflecting surface, 6 Condenser lens, 6a, 6b Linear Fresnel lens, 7 Field lens, 7a, 7b Lenticular lens, 8 Field lens, 8a, 8b Linear prism, 9 Optical sheet, 100 Head-up display system, 101 Liquid crystal panel, 101a Display area, 101b Frame portion, 102 Mirror, 103 Concave mirror, 104 Window shield, EB Eye box

Claims

1. A surface illumination device that illuminates a liquid crystal panel that is arranged at an angle with respect to an optical axis, A plurality of light sources are arranged two-dimensionally on a substrate, and light emission is individually controlled to enable local dimming; a reflector disposed on the output side of the substrate and having a reflective surface surrounding each of the plurality of light sources; a condenser lens disposed on an emission side of the light source and configured to condense light emitted from the light source; a field lens disposed on an exit side of the condenser lens and configured to spread outward the light incident from the condenser lens; Equipped with The field lens is disposed along the external liquid crystal panel. Surface lighting device.

2. The substrate is arranged perpendicular to the optical axis.

2. The spread illuminating device according to claim 1.

3. The field lens is configured to emit light incident on a central portion of the entire width of the light incident from the condenser lens in the direction of the optical axis, and to spread light incident on the outside of the central portion outward based on the central portion.

2. The spread illuminating device according to claim 1.

4. The field lens is adjacent to the liquid crystal panel.

4. The spread illuminating device according to claim 1.

5. The field lens is close to the liquid crystal panel with a distance of 3 mm or less.

5. The spread illuminating device according to claim 4.

6. The field lens is arranged parallel to the liquid crystal panel.

4. The spread illuminating device according to claim 1.

7. The field lens is formed of a linear prism.

4. The spread illuminating device according to claim 1.

8. The condenser lens is formed as a linear Fresnel lens.

4. The spread illuminating device according to claim 1.

9. The condenser lens is formed with a linear Fresnel lens in which the directions of grooves forming unevenness on the incident side and the exit side are perpendicular to each other, The field lens is formed with a linear prism in which the directions of grooves forming unevenness on the incident side and the exit side are perpendicular to each other.

4. The spread illuminating device according to claim 1.

10. a field lens provided between the condenser lens and the field lens and parallel to the substrate; The other field lens is formed as a lenticular lens.

4. The spread illuminating device according to claim 1.

11. An optical sheet such as a polarizing reflective sheet or a diffusion sheet is provided on the exit side of the field lens.

4. The spread illuminating device according to claim 1.

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