Planar lighting device

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). Because the light source unit of such a head-up display is installed near the windshield, which is exposed to sunlight, measures are often taken to protect against heat and stray light from sunlight.

[0003] For example, a surface lighting device used as a backlight for a head-up display has a liquid crystal panel on its output side, followed by one or more mirrors for projecting light onto the windshield. As a result, 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] To address this issue, the LCD panel is often positioned so that it is tilted in the same direction as the first mirror with respect to the main optical axis that runs from the surface lighting device to the first mirror. By positioning the LCD panel in an inclined position, sunlight that enters in the opposite direction to that of projection is more likely to be reflected by the surface of the LCD panel, preventing sunlight from entering the LCD panel or the surface lighting device, thereby reducing problems caused by heat and stray light. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2018-83593 [Patent Document 2] Japanese Patent Application Publication No. 2019-61128 Summary of the Invention [Problem to be solved by the invention]

[0006] The tilt of the LCD panel described above did not pose any particular problems for planar lighting devices that do not support local dimming, but it causes new problems in planar lighting devices that support local dimming, reducing contrast and brightness uniformity.Local dimming is a technology that significantly improves 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, an outward-opening light distribution characteristic is often provided so that peripheral visibility is not reduced even when light is converged by a concave mirror used as a part of the mirror in the subsequent stage. Therefore, when the liquid crystal panel is positioned 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 that provides the outward-opening light distribution characteristic and the liquid crystal panel. This difference in optical distance causes light to be generated outside 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 has as its object to provide a surface illumination device that can improve contrast and brightness 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 comprises: A surface illumination device that illuminates a liquid crystal panel that is arranged at an angle with respect to an optical axis, Multiple light sources; A reflector; The light sources are arranged two-dimensionally on a substrate, and each light is emitted from a corresponding one of the light sources. individually Controlled Local dimming is possible . The reflector is disposed on the output side of the substrate and has a reflective surface surrounding each of the plurality of light sources. The condenser lens is disposed on the output side of the light source. Placed , the light emitted from the light source Concentrate lightThe field lens is disposed on the output side of the condenser lens. ,before The light coming in from the condenser lens is diffused outward. Grow . The field lens is disposed along the externally attached liquid crystal panel.

[0010] A surface illumination device according to one aspect of the present invention can improve contrast and brightness uniformity. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram showing an example of the configuration of a head-up display system. [Figure 2] FIG. 2 is a plan view of a surface illumination device equipped with a liquid crystal panel. [Figure 3] FIG. 3 is a cross-sectional view taken along line AA in FIG. [Figure 4] FIG. 4 is a cross-sectional view taken along line BB in FIG. [Figure 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 the surface illumination device and 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 INVENTION

[0012] 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.

[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 to the left in the figure (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 directed to a concave mirror 103. The light (L3) reflected from the concave mirror 103 is irradiated onto a windshield 104 of an automobile, and the reflected light (L4) enters the eyebox (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 refer to the horizontal and vertical directions of the virtual image as seen from the eyebox 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) that runs 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 interior of the surface lighting device 1, thereby reducing problems caused by heat and stray light.

[0016] 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 lighting 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 defined as the Z direction. In addition, in the usage state where 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. Note that, hereinafter, the horizontal direction and the vertical direction in the usage state where 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 planar shape, and has a liquid crystal panel 101 disposed on its light-emitting surface. The liquid crystal panel 101 is surrounded by a frame 101b, and the area inside 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 other material with excellent heat dissipation properties is disposed on the bottom of the frame 2. On the substrate 3, which is appropriately insulated, a plurality of light sources 4 such as LEDs (Light Emitting Diodes) are arranged two-dimensionally in a grid pattern. Each light source 4 is driven individually and its light emission is controlled individually, enabling 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 output 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 also be omitted.

[0021] A condenser lens 6 for focusing light is disposed parallel to the substrate 3 on the output side of the reflector 5. As shown in FIG. 3, a linear Fresnel lens 6a is formed on the lower input surface of the condenser lens 6. The grooves that make up the concave-convex surface of the lens extend in one direction (the depth direction in the figure, or the Y-axis direction) as shown in FIG. 3. Furthermore, a linear Fresnel lens 6b is formed on the upper output surface of the condenser lens 6. The grooves that make up the concave-convex surface of the lens extend in a direction perpendicular to the direction of the lower surface (the left-right direction in the figure, or the X-axis direction) as shown in FIG. 4. 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. The grooves are periodically formed according to the pitch of the light sources 4 disposed directly below, and the angle of the prism is reversed at the boundary between adjacent segments. This makes it easier to manufacture than a circular Fresnel lens.

[0022] A field lens 7 for expanding the light distribution is disposed on the output 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. The grooves constituting the concave-convex surface of the lens extend in one direction (the depth direction in the figure (Y-axis direction)). As shown in FIG. 4, a lenticular lens 7b is formed on the upper surface of the field lens 7. The grooves constituting the concave-convex surface of the lens extend in a direction perpendicular to the one direction on the lower surface (the left-right direction in the figure (X-axis direction)). The lenticular lenses 7a and 7b have a prism shape with a semi-cylindrical cross section, which expands the incident light. While a diffuser spreads light in all directions, resulting in reduced efficiency, the lenticular lenses 7a and 7b are advantageous because the spread of the light distribution can be adjusted within a desired range by changing their cross-sectional shape, preventing a decrease in light efficiency.

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

[0024] As shown in FIG. 3, a linear prism 8a is formed on the lower surface of field lens 8 in the figure, with grooves that form the concave-convex surface of the lens extending in one direction (the depth direction in the figure (Y-axis direction)). As shown in FIG. 4, a linear prism 8b is formed on the upper surface of field lens 8 in the figure, with grooves that form the concave-convex surface of the lens extending in a direction perpendicular to the one direction of the lower surface (the left-right direction in the figure (X-axis direction)). Linear prisms 8a and 8b direct light that passes through the center portion of their entire width in a straight line in the Z-axis direction, and orient the optical axis of each location outward as it moves outward. Note that light that passes through the center portion of their entire width may also be tilted from the Z-axis direction.

[0025] On the exit side of field lens 8, optical sheet 9 adapted to the characteristics of liquid crystal panel 101 to be attached is arranged parallel to field lens 8. A polarizing reflective sheet or a diffusion sheet is used as optical sheet 9. The thickness of 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 the projected image is arranged parallel to the optical sheet 9 and the field lens 8. It is important to ensure a uniform optical distance 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 located close to each other. The shorter the distance between the field lens 8 and the liquid crystal panel 101, the less light spreads to adjacent dimming zones, resulting in less light loss and improved contrast. The distance between the field lens 8 and the liquid crystal panel 101 can be zero (close enough to eliminate any gap), but considering the optical characteristics, the thickness of the optical sheet 9 (if provided), and the thickness of the positioning mechanisms for each optical component, a distance of 3 mm or less is preferable, and 2 mm or less is more preferable. Note that the field lens 8 and the liquid crystal panel 101 do not necessarily need to be arranged parallel to each other as long as the distance between them is 3 mm or less.

[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 light source 4 is converged into approximately parallel light by condenser lens 6 (linear Fresnel lens 6a on the bottom surface) to become light L12. The light distribution of light L12 is expanded by field lens 7 (lenticular lens 7a on the bottom surface) while keeping the optical axis unchanged, to become light L13. The optical axis of light L13 is tilted outward at each location by field lens 8 (linear prism 8a on the bottom surface), expanding the light distribution outward, and becoming light L14 which passes through optical sheet 9 and 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 light source 4 is converged into approximately parallel light by condenser lens 6 (linear Fresnel lens 6b on the upper surface) to become light L22. The light distribution of light L22 is expanded by field lens 7 (lenticular lens 7b on the upper surface) while keeping the optical axis unchanged, to become light L23. The optical axis of light L23 is tilted outward at each location by field lens 8 (linear prism 8b on the upper surface), expanding the light distribution outward, and becoming light L24 which passes through optical sheet 9 and liquid crystal panel 101.

[0029] FIG. 7 shows an example of the configuration of a surface illumination device 1′ and a liquid crystal panel 101′ of Comparative Example #1, as well as 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′ is arranged, from the bottom, with a substrate 3′, light source 4′, reflector 5′, condenser lens 6′, field lens 8′, optical sheet 9′, and liquid crystal panel 101′, in that order, but the entire area 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 where the optical distance is longest (the left end of FIG. 7), light rays enter the frame 2′, resulting in light loss.

[0030] FIG. 8 is a diagram showing an example of the configuration of a surface illumination device 1" and a 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 illumination device 1" of comparative example #2 supports local dimming. On a 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 extends 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" and L2" in FIG. 8 are light that extends beyond the local dimming zone area. Such light reduces contrast and brightness uniformity. In other words, light that extends into an adjacent zone area will provide unnecessary light when that adjacent zone area is off (zero light amount), and will also cause an insufficient amount of light in the original zone area that extends beyond it, resulting in overall reduction in contrast and brightness uniformity.

[0032] In this regard, in the above-described embodiment, as shown in FIG. 6, a uniform optical distance is ensured between the field lens 8 and the liquid crystal panel 101, thereby suppressing the generation of light that exceeds the local dimming zone area, preventing a decrease in contrast and brightness uniformity, and improving contrast and brightness uniformity. Furthermore, the proximity of the field lens 8 and the liquid crystal panel 101 makes these effects more effective. This embodiment can also be applied to a normal backlight that does not support local dimming and provides a certain level of effectiveness. In other words, in the case of the surface illumination device 1′ in FIG. 7 that does not support local dimming, light rays enter the frame 2′ at the end with the longest optical distance (the left end in FIG. 7), resulting in light loss. However, by applying the configuration of this embodiment, light loss at the end can be prevented.

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

[0034] As described above, the planar illumination device according to the embodiment includes a plurality of light sources arranged two-dimensionally on a substrate, each light source having its light emission controlled individually; a condenser lens arranged parallel to the substrate on the light source output side and converging the light emitted from the light source into approximately parallel light; and a field lens arranged on the condenser lens output side and tilted in at least one direction perpendicular to the substrate in a plane parallel to the substrate, spreading the light incident from the condenser lens outward and ensuring a uniform optical distance between the field lens and an externally attached liquid crystal panel. This improves contrast and brightness uniformity. In other words, even when the field lens spreads the light incident from the condenser lens outward, a uniform optical distance is maintained between the field lens and the liquid crystal panel, thereby suppressing the generation of light that exceeds the local dimming zone area and preventing a decrease in contrast and brightness uniformity. Note that this embodiment can also be applied to ordinary backlights that do not support local dimming and provides certain benefits.

[0035] The field lens is also placed close to the LCD panel, which reduces the amount of light that spreads to adjacent dimming zones, reducing light loss and improving contrast.

[0036] The condenser lens is a linear Fresnel lens with grooves on the incident and exit sides that are orthogonal to each other, and the field lens is a linear prism with grooves on the incident and exit sides that are orthogonal to each other, making it easy to create a 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 with a lenticular lens in which the grooves forming the unevenness on the incident side and the exit side are oriented perpendicular to each other. This makes it possible to improve brightness uniformity without incurring a decrease in light efficiency, as occurs with a diffuser plate.

[0038] The light source is also provided with a reflector that is disposed on the light output side of the substrate and has a reflective surface that surrounds the light source, thereby preventing light leaking from the light source to the substrate side from being wasted and increasing light efficiency.

[0039] The projector also includes an optical sheet, such as a polarizing reflective sheet or a diffusion sheet, placed on the exit side of the tilted field lens, which makes it easy to achieve optical characteristics suited to the externally attached liquid crystal panel.

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

[0042] In addition, the field lens is positioned close to the LCD panel, with the distance between the lens and the LCD panel being 3 mm or less, which is expected to produce effective results.

[0043] 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]

[0044] 1 planar lighting device, 2 frame, 3 substrate, 4 light source, 5 reflector, 5a, 5b reflective 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 windshield, 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 arranged two-dimensionally on a substrate, each of which has its light emission 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 the output 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 externally attached 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 the central part of the entire width of the light incident from the condenser lens in the direction of the optical axis, and to spread light incident outside the central part outward based on the central part.

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 located 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 as 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 has a linear Fresnel lens formed on the incident side and the exit side, in which the directions of grooves forming concaves and convexes are perpendicular to each other, The field lens has a linear prism formed on the incident side and the exit side, in which the directions of grooves forming the concave and convex portions 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 output side of the field lens.

4. The spread illuminating device according to claim 1.

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