Planar lighting device

Abstract

The planar illuminating device (1) of the embodiment includes a substrate (2), a first linear Fresnel lens (5, 5a), and a second linear Fresnel lens (5, 5b). The substrate (2) is provided with a plurality of light sources (3) in a grid-like two-dimensional arrangement. The first linear Fresnel lens (5, 5a) is arranged on the emission side of the plurality of light sources (3), and grooves (5c) of the concave-convex surface of the lens of the first linear Fresnel lens (5, 5a) extend in one direction. The second linear Fresnel lens (5, 5b) is arranged on the emission side of the first linear Fresnel lens (5, 5a), and grooves (5d) of the concave-convex surface of the lens of the second linear Fresnel lens (5, 5b) extend in a direction orthogonal to the one direction.

Description

Technical Field

[0001] This invention relates to a planar lighting device. Background Technology

[0002] Planar lighting devices used as backlights for head-up displays (HUDs) and similar devices require performance and functionality such as high brightness, high contrast, high brightness uniformity, low power consumption, thinness, and local dimming processing. In particular, compared to displays such as clusters and CIDs (Center Information Displays) where users directly view the displayed image, head-up displays require backlights that are approximately 100 times brighter, making the achievement of high brightness crucial.

[0003] On the other hand, some documents disclose direct-lit backlights for head-up displays (e.g., see Patent Documents 1 to 5, etc.).

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2009-169399

[0007] Patent Document 2: Japanese Patent Application Publication No. 2019-20704

[0008] Patent Document 3: Japanese Patent Application Publication No. 2007-87792

[0009] Patent Document 4: Japanese Patent Application Publication No. 2012-203176

[0010] Patent Document 5: Japanese Patent Application Publication No. 2016-218391 Summary of the Invention

[0011] The problem that the invention aims to solve

[0012] However, it is difficult to simultaneously meet several of the aforementioned performance and functional requirements, such as high brightness, high contrast, high brightness uniformity, low power consumption, thinness, and local dimming processing.

[0013] The present invention was made in view of the above, and its purpose is to provide a planar lighting device that can simultaneously satisfy several of the following performance and functions: high brightness, high contrast, high brightness uniformity, low power consumption, thinness, and local dimming processing.

[0014] Solution for solving the problem

[0015] To solve the aforementioned technical problems and achieve the objective, one aspect of the present invention provides a planar illumination device comprising a substrate, a first linear Fresnel lens, and a second linear Fresnel lens. The substrate has a plurality of light sources arranged in a grid-like two-dimensional configuration. The first linear Fresnel lens is disposed on the emission side of the plurality of light sources, and the grooves on the concave and convex surfaces constituting the lens of the first linear Fresnel lens extend in one direction. The second linear Fresnel lens is disposed on the emission side of the first linear Fresnel lens, and the grooves on the concave and convex surfaces constituting the lens of the second linear Fresnel lens extend in a direction orthogonal to the stated direction. The first linear Fresnel lens is arranged to correspond to one of the rows or columns of the plurality of light sources arranged in a grid-like two-dimensional configuration, and each segment of the corresponding row or column of light sources has a prism structure with a cylindrical convex lens serving as the Fresnel lens. The second linear Fresnel lens is arranged to correspond to the other row or column, and each segment of the corresponding row or column of light sources has a prism structure with a cylindrical convex lens serving as the Fresnel lens.

[0016] One aspect of the planar lighting device of the present invention can simultaneously satisfy several of the following performance and functional requirements: high brightness, high contrast, high brightness uniformity, low power consumption, thinness, and local dimming processing. Attached Figure Description

[0017] Figure 1 This is a diagram illustrating an example of the structure of a head-up display system.

[0018] Figure 2 This is a front view of the planar lighting device 1 according to the first embodiment.

[0019] Figure 3 It is a planar lighting device Figure 2 Sectional view A-A in the diagram.

[0020] Figure 4 It is a schematic diagram of the grooves applied to both sides of the condenser lens.

[0021] Figure 5 This is a diagram showing an example of the cross-sectional structure of the incident side of a condenser lens.

[0022] Figure 6 This is a cross-sectional view A-A showing other structural examples of a planar lighting device.

[0023] Figure 7 It is a schematic diagram of the grooves provided on one side of each condenser lens.

[0024] Figure 8A This is a diagram illustrating the refraction of horizontal light rays by a condenser lens.

[0025] Figure 8BThis is a diagram illustrating an example of the directional characteristics of luminance in the horizontal direction.

[0026] Figure 9A This diagram illustrates the refraction of light rays in the vertical direction achieved by a condenser lens.

[0027] Figure 9B This is a diagram illustrating the directional characteristics of light intensity in the vertical direction.

[0028] Figure 10 This is a diagram showing an example of the cross-sectional structure of the incident side of a field lens.

[0029] Figure 11 This diagram illustrates the refraction of horizontal light rays achieved by a field lens.

[0030] Figure 12 It is an enlarged view used to show the spot on the other side of the field lens.

[0031] Figure 13 This is a diagram showing an example of the surface structure on the exit side of a field lens.

[0032] Figure 14 This is a cross-sectional view of the planar lighting device according to the second embodiment.

[0033] Figure 15 This is a schematic diagram of the grooves applied to both sides of the first field lens.

[0034] Figure 16 This is a diagram showing an example of the cross-sectional structure of the incident side of the first field lens.

[0035] Figure 17 This is a diagram illustrating an example of the directional characteristics of light intensity in the horizontal and vertical directions after passing through the first field lens.

[0036] Figure 18 This is a diagram illustrating an example of the directional characteristics of light intensity in the horizontal and vertical directions after passing through a second field lens.

[0037] Figure 19 This is a cross-sectional view of the planar lighting device according to the third embodiment.

[0038] Figure 20 This is a diagram showing the construction of the incident side of a field lens.

[0039] Figure 21 This is a diagram showing the structure of the exit side of the field lens.

[0040] Figure 22 This is a diagram showing other examples of field lenses.

[0041] Figure 23This is a cross-sectional view of the planar lighting device according to the fourth embodiment along the X-axis direction (horizontal direction).

[0042] Figure 24 This is a cross-sectional view of the planar lighting device according to the fourth embodiment along the Y-axis direction (vertical direction).

[0043] Figure 25 This diagram illustrates the refraction of light rays in the vertical direction achieved by the exiting side of the condenser lens.

[0044] Figure 26 This diagram illustrates the refraction of horizontal light rays achieved by a field lens.

[0045] Figure 27 This is an enlarged cross-sectional view of a cylindrical lens on the incident side of a field lens.

[0046] Figure 28 This diagram illustrates the refraction of light rays in the horizontal direction according to the fifth embodiment.

[0047] Figure 29 This is a diagram illustrating an example of the relationship between the diffusion angle of the emitted light from light source 3 and the prism spacing and prism height. Detailed Implementation

[0048] Hereinafter, the planar lighting device according to the embodiments will be described with reference to the accompanying drawings. It should be noted that the present invention is not limited to this embodiment. Furthermore, the dimensional relationships and proportions of the elements in the drawings may sometimes differ from reality. Sometimes the drawings may also include parts with different dimensional relationships or proportions. Moreover, the content described in one embodiment or modification is generally applicable to other embodiments and modifications as well.

[0049] (System Architecture)

[0050] Figure 1 This is a diagram illustrating a structural example of a head-up display system 100. Figure 1 In the case of the head-up display system 100 installed in the car, the direction of the car's movement is to the left (positive Y-axis direction) as shown in the figure.

[0051] Figure 1In this process, the light emitted from the planar illumination device 1, after passing through the liquid crystal panel 101 (L1), is reflected (L2) by the reflector 102 and directed to the concave mirror 103. The light (L3) reflected by the concave mirror 103 illuminates the screen 104 of a car, such as the windshield, and its reflected light (L4) enters the eye movement range (viewpoint) EB of the driver, etc., and the image displayed on the liquid crystal panel 101 is recognized as a virtual image. It should be noted that "H (horizontal direction)" is written along with the X-axis direction and "V (vertical direction)" is written along with the Y-axis direction to indicate the correspondence between the horizontal and vertical directions of the virtual image observed from the eye movement range EB and the direction of the emission surface of the planar illumination device 1, as will be described later.

[0052] (First Implementation)

[0053] Figure 2 This is a front view of the planar illumination device 1 according to the first embodiment. For convenience, the light-emitting surface of the planar illumination device 1 is located in the X-Y plane, and the thickness direction of the planar illumination device 1 is set as the Z direction. Furthermore, in the usage state where the illumination for a head-up display is reflected by a screen or the like and can be seen by the user, such as when the illumination for a head-up display is already reflected by a screen or the like... Figure 1 As shown, the X-axis corresponds to the horizontal direction (H), and the Y-axis corresponds to the vertical direction (V). It should be noted that, in the following, the horizontal direction that can be seen by the user when reflected by the screen or other objects will sometimes be simply referred to as the "horizontal direction", and the vertical direction that can be seen by the user when reflected by the screen or other objects will sometimes be simply referred to as the "vertical direction".

[0054] Figure 2 In the diagram, the planar lighting device 1 has a generally rectangular, plate-like shape, and light is emitted from the inside of the opening 7a in the frame 7. The dimensions of the opening 7a are, for example, 42 mm in the X-axis direction and 21 mm in the Y-axis direction. It should be noted that the shape of the planar lighting device 1 is not limited to the shape shown in the diagram. Furthermore, the frame 7 may sometimes be omitted.

[0055] Figure 3 It is a planar lighting device 1 Figure 2 Sectional view A-A in the diagram. Figure 3 In this design, on a substrate 2 made of aluminum or similar material with excellent heat dissipation, multiple light sources 3 formed of LEDs (Light Emitting Diodes) are arranged in a two-dimensional grid pattern, with appropriate insulation provided. Each light source 3 is driven independently, enabling local dimming.

[0056] A reflector 4 is disposed on the emission side of the substrate 2 where the light source 3 is located. The reflector 4 has four reflective surfaces 4a surrounding each of the plurality of light sources 3. The periphery of the reflector 4 is frame-shaped and thicker than the height of the reflective surfaces 4a, and a space is provided at the top of the reflective surfaces 4a. It should be noted that, alternatively, no space may be provided at the top of the reflective surfaces 4a, and the reflective surfaces 4a may extend to connect with the condensing lens 5 described later. The reflector 4 is formed of resin or the like. It should be noted that the reflector 4 may sometimes be omitted.

[0057] A condenser lens 5 is disposed on the exit side of the reflector 4. A first linear Fresnel lens is formed on the lower entrance side surface 5a of the condenser lens 5 in the figure. The grooves of the concave and convex surfaces constituting the first linear Fresnel lens extend along one direction (the depth direction (Y-axis direction) in this embodiment). Furthermore, a second linear Fresnel lens is formed on the upper exit side surface 5b of the condenser lens 5 in the figure. The grooves of the concave and convex surfaces constituting the second linear Fresnel lens extend along a direction orthogonal to one direction of surface 5a (the left-right direction (X-axis direction) in this embodiment) in the figure.

[0058] A field lens 6 is disposed on the exit side of the condenser lens 5. This field lens 6 alters the light distribution and diffuses the light. The field lens 6 is assumed to alter the horizontal light distribution and is formed by a prism formed on the lower surface 6a of the field lens 6 in the diagram. The groove of this prism extends along the depth direction (Y-axis direction) of the diagram. On the upper surface 6b of the field lens 6 in the diagram, tiny spots that diffuse the light are formed throughout the entire surface. Figure 3 In the middle, the opening 7a of frame 7 can be seen. Figure 2 The end of the lens is not visible, and its cross-section is not visible. The periphery of either the condenser lens 5 or the field lens 6 is a thick frame, and a gap is provided between the condenser lens 5 and the field lens 6 outside the periphery. Alternatively, in addition to the condenser lens 5 or the field lens 6, a frame-shaped spacer is also provided between the condenser lens 5 and the field lens 6.

[0059] Figure 4 This is a schematic diagram of the grooves 5c and 5d provided on both sides of the condenser lens 5. A groove 5c, extending along the Y-axis, constituting a first linear Fresnel lens, is formed on the lower (incident) surface 5a of the condenser lens 5. A groove 5d, extending along the X-axis, constituting a second linear Fresnel lens, is formed on the upper (emission) surface 5b of the condenser lens 5. Figure 5 This is a diagram showing an example of the cross-sectional structure of the incident side of the condenser lens 5. The incident side surface 5a of the condenser lens 5 intersects with the light source 3 ( Figure 3Each segment has a prism structure with a cylindrical convex lens serving as a Fresnel lens, and a groove extending along the depth direction (Y-axis direction) of the figure. At the segment boundary BL between adjacent segments, the angle of the prism is reversed. On the exit side of the condenser lens 5, although the extension direction of the groove is orthogonal, the same prism structure is also provided.

[0060] The first linear Fresnel lens and the second linear Fresnel lens are positioned with the light source 3 located directly below. Figure 3 The condenser lens 5 is periodically formed with a spacing (the first linear Fresnel lens has a spacing in the X-axis direction, and the second linear Fresnel lens has a spacing in the Y-axis direction) matching. Furthermore, during assembly, the condenser lens 5 is positioned such that the center of the lens is directly above the light source 3 in both the Y-axis and X-axis directions. While it is difficult to form a ring-shaped Fresnel lens that matches the number of light sources in relation to their positions, it is relatively easy to form linear linear Fresnel lenses in columns or rows to match multiple light sources arranged in a straight line. By forming linear Fresnel lenses orthogonally on both sides of the transparent substrate material, the intersection of the center of one linear Fresnel lens and the center of the other linear Fresnel lens acts as a Fresnel lens corresponding to the center of the light source.

[0061] Figure 6 This is a cross-sectional view A-A showing another structural example of the planar lighting device 1. Figure 6 In, with Figure 3 Compared to the previous structure, the difference lies in the fact that the condenser lens 5 is composed of two condenser lenses 51 and 52; otherwise, the structure is the same. It should be noted that several variations can be achieved by combining different options for placing the Fresnel lens groove on either the lower surface 51a or the upper surface 51b of the condenser lens 51, and on either the lower surface 52a or the upper surface 52b of the condenser lens 52. One of the condenser lenses 51 and 52 has a thick frame-like periphery, and a gap is provided between the condenser lenses 51 and 52 outside the periphery. Alternatively, in addition to the condenser lenses 51 and 52, a frame-like spacer may also be provided between the condenser lenses 51 and 52.

[0062] according to Figure 6 This structure, with a linear Fresnel lens placed on one side of the transparent substrate material, makes manufacturing easier. Furthermore, since the spacing along the X-axis and Y-axis of the light source is the same, it is only necessary to manufacture a larger linear Fresnel lens and cut it for use by changing its orientation, thus further simplifying manufacturing.

[0063] Figure 7 It is a schematic diagram of the grooves 51c and 52c on one side of each condenser lens 51 and 52. Figure 7In the middle, the lower surface 51a of the lower condenser lens 51 is provided with a groove 51c extending along the Y-axis direction, and the upper surface 52b of the upper condenser lens 52 is provided with a groove 52c of a Fresnel lens extending along the X-axis direction.

[0064] Figure 8A This diagram illustrates the refraction of horizontal light rays by the condenser lens 5. That is, Figure 8A The traces of light within a cross section along the horizontal direction (X, H) and the normal direction (Z) of the exit surface are shown. Illustrations of field lens 6 are omitted. Figure 8A In this process, the light emitted from the light source 3, represented by the dashed line, is refracted into approximately parallel light in the X-Z plane by a first linear Fresnel lens with a groove extending along the Y-axis on the lower surface 5a of the condenser lens 5. It should be noted that although parallel light along the normal direction of the emission surface is used, parallel light with a predetermined tilt relative to the normal direction of the emission surface can also be used. The second linear Fresnel lens, with a groove extending along the X-axis on the upper surface 5b of the condenser lens 5, does not function in the horizontal direction, so the approximately parallel light is emitted directly. Figure 8B This is a diagram illustrating the directional characteristics of light intensity in the horizontal direction, with the angle range (1 / 2 beam angle) maintaining about half the peak intensity being approximately 10°.

[0065] Figure 9A This diagram illustrates the refraction of light rays in the perpendicular direction achieved by the condenser lens 5. That is, Figure 9A The traces of light within a cross section along the vertical direction (Y, V) and the normal direction (Z) of the exit surface are shown. Illustrations of field lens 6 are omitted. Figure 9A In this light source, the light emitted from the light source 3, indicated by the dashed line, is not strongly refracted by the first linear Fresnel lens located on the lower surface 5a of the condenser lens 5, but instead enters the interior of the condenser lens 5 almost directly. Then, it is refracted in the Y-Z plane by a second linear Fresnel lens located on the upper surface 5b of the condenser lens 5, forming a concave-convex surface with a groove extending along the X-axis, and emitted as approximately parallel light. It should be noted that although parallel light along the normal direction of the emission surface is used, parallel light with a predetermined tilt relative to the normal direction of the emission surface can also be used. Figure 9B This is a diagram illustrating the directional characteristics of light intensity in the vertical direction, with the angle range (1 / 2 beam angle) maintaining about half the peak intensity being approximately 10°.

[0066] then, Figure 10 This is a diagram showing an example of the cross-sectional structure of the incident side of the field lens 6. Figure 10In the field lens 6, one cross-section of the incident side surface 6a has a prism structure equivalent to that of a Fresnel lens constructed with a concave annular lens. It is a linear prism with a groove extending along the depth direction (Y-axis direction) of the figure. The tilt angle of the prism becomes steeper with increasing distance from the center.

[0067] Figure 11 This diagram illustrates the refraction of horizontal light rays achieved by field lens 6. That is, Figure 11 The trace of light is shown in a cross-section along the horizontal direction (X, H) and the normal direction (Z) of the emission surface during use. Figure 1 In the case of a head-up display, light emitted from the planar illumination device 1, which serves as the backlight of the liquid crystal panel 101, is reflected on the screen 104 after passing through the reflector 102 and the concave mirror 103, and then enters the user's eyes. The optical axis of the light reflected by the concave mirror 103 tilts inwards. Therefore, to ensure the required angular range of the optical axis of the emitted light from the concave mirror 103, light needs to be supplied from the planar illumination device 1 such that the outer optical axis is tilted outwards relative to the center. It should be noted that the optical axis is the axis of highest intensity in light emitted from a light source, a small part (whether parallel or scattered light). Therefore, the optical axis is tilted outwards in the horizontal direction based on the horizontal distance from the center of the planar illumination device 1. This ensures the required angular range of the optical axis of the emitted light from the concave mirror 103, preventing the end of the virtual image from being invisible.

[0068] It should be noted that, in the vertical direction, the outer optical axis also needs to be tilted outward according to the curvature of the concave mirror 103. However, generally speaking, the tilt of the optical axis in the vertical direction is smaller than that in the horizontal direction, so it is set to be approximately parallel light in this embodiment. If the optical axis in the vertical direction also needs to be tilted, then the optical axis in the vertical direction is also tilted. An example of tilting the optical axis in the vertical direction will be described later. It should be noted that, regarding the tilt of the optical axis, it is also possible that the center is not approximately parallel light but tilted in a predetermined direction, while the two sides of the center only need to be tilted outward relative to the tilt of the center.

[0069] Figure 11 The lower side and Figure 3 Similarly, the cross-sectional structure of the planar illumination device 1 is shown. The two light sources 3 near the center of the planar illumination device 1 have an inclination angle of 0°, the light source next to the center has an inclination angle of 2°, and the light source further to the center has an inclination angle of 4°. The values ​​of the inclination angles shown are for illustrative purposes only. It should be noted that the inclination angles are determined by the shape of the prism constituting the field lens 6.

[0070] Figure 11In region R1, near the center, the tilt angle is 0°, as shown in the magnified view at the top of the figure. Light is emitted along the frontal direction (normal direction) of the field lens 6. In region R2, located to the left of the center, the tilt angle is 6°, as shown in the magnified view at the top of the figure. Light is emitted tilted to the left relative to the frontal direction of the field lens 6. In region R3, located to the right of the center, the tilt angle is 6°, as shown in the magnified view at the top of the figure. Light is emitted tilted to the right relative to the frontal direction of the field lens 6. It should be noted that... Figure 11 In this case, the tilt angle can be changed according to each light source 3, but it can also be changed according to each region containing multiple light sources 3.

[0071] then, Figure 12 This is an enlarged view used to show the spot 6c on another surface 6b of the field lens 6. Figure 11 (Enlarged view of region R in the image). Figure 13 This is a diagram showing an example of the surface structure on the exit side of the field lens 6. Figure 12 and Figure 13 In the image of the field lens 6, tiny spots 6c are formed on the upper surface 6b. These tiny spots 6c are formed by a mold or the like through laser processing. Light passing through the tiny spots 6c is diffused, improving brightness uniformity.

[0072] Regarding spot 6c, simulations were performed for cases where a hexagonal arrangement was used, the spot size was set to 35 μm, and the spot contact angles were set to 5°, 10°, 15°, and 20°. It should be noted that the spot heights were 0.8 μm, 1.5 μm, 2.3 μm, and 3.1 μm when the spot contact angles were set to 5°, 10°, 15°, and 20°, respectively.

[0073] The simulation results show that a larger spot contact angle (e.g., a spot contact angle of 15° compared to 10°) results in higher brightness uniformity and a wider light distribution angle. Furthermore, it was confirmed that for the same power consumption of the light source 3, a smaller spot contact angle (e.g., a spot contact angle of 10° compared to 15°) results in higher average brightness. The field lens 6 can also be replaced by a common diffuser separate from the field lens 6, instead of the spot on the other surface 6b.

[0074] (Second Implementation)

[0075] exist Figure 3In the first embodiment shown, for light that is set to be almost parallel after passing through the condenser lens 5, the light distribution is adjusted in the horizontal direction by the field lens 6. However, if the light distribution of the emitted light from the condenser lens 5 is too narrow, the brightness uniformity may sometimes deteriorate. That is, the brightness of the peripheral portion may sometimes decrease excessively compared to the central portion. Therefore, in the second embodiment, the light distribution in both the horizontal and vertical directions of the emitted light from the condenser lens 5 is widened.

[0076] Figure 14 This is a cross-sectional view of the planar lighting device 1 according to the second embodiment. Figure 14 middle, Figure 3 The field lens 6 directly becomes the second field lens 62, and the first field lens 61 is disposed between the condenser lens 5 and the second field lens 62. A first cylindrical lens is formed on the lower incident-side surface 61a of the first field lens 61, and the grooves of the concave and convex surfaces constituting the lens of the first cylindrical lens extend along one direction (in this embodiment, the depth direction (Y-axis direction)). Furthermore, a second cylindrical lens is formed on the upper exit-side surface 61b of the field lens 61, and the grooves of the concave and convex surfaces constituting the lens of the second cylindrical lens extend along a direction orthogonal to one direction of surface 61a (in this embodiment, the left-right direction (X-axis direction)). The cylindrical lens is a linear lens with a semi-cylindrical cross-section. For the second field lens 62, the incident-side surface 62a has a prism structure that changes the light distribution, and the exit-side surface 62b has spots formed, which is related to… Figure 3 The field lens 6 is the same. Furthermore, it can also be used with... Figure 6 Similarly, the condenser lens 5 is configured as a dual structure of condenser lenses 51 and 52.

[0077] Figure 15 This is a schematic diagram of the grooves 61c and 61d on both sides of the first field lens 61. A groove 61c extending along the Y-axis, constituting the first cylindrical lens, is formed on the lower (incident) surface 61a of the field lens 61. A groove 61d extending along the X-axis, constituting the second cylindrical lens, is formed on the upper (emission) surface 61b of the field lens 61. Figure 16 This diagram shows an example of the cross-sectional structure of the entrance side of the first field lens 61. The entrance side surface 61a of the first field lens 61 has a linear first cylindrical lens with a semi-cylindrical (arc-shaped) cross-section. On the exit side of the first field lens 61, although the extension direction of the groove is orthogonal, a second cylindrical lens with the same structure is also provided.

[0078] Figure 17This diagram illustrates an example of the directional characteristics of light intensity in the horizontal and vertical directions after passing through the first field lens 61. The first cylindrical lens on the entrance side of the first field lens 61 functions in the horizontal direction (H), while the second cylindrical lens on the exit side functions in the vertical direction (V). The cylindrical lenses are an assembly of linear convex lenses, where nearly parallel light entering from the condenser lens 5 is focused and intersected, resulting in diffused light. According to... Figure 17 The horizontal beam angle of the light emitted from the condenser lens 5 is 10°. Figure 8B The beam angle is widened to 30°, and the half-beam angle of the vertical light is 10°. Figure 9B (Expanded to 13°)

[0079] Next, for the light that has passed through the first field lens 61, its distribution in the horizontal direction is adjusted by the second field lens 62. Figure 18 This is a diagram illustrating an example of the directional characteristics of light intensity in the horizontal and vertical directions after passing through the second field lens 62. According to... Figure 18 The half beam angle of the horizontal light emitted from the first field lens 61 is 30°. Figure 17 The beam angle is slightly widened to 31°. The half beam angle of the vertical light remains unchanged at 13.0°.

[0080] (Third Implementation)

[0081] The third embodiment is an improved version of the second embodiment, which uses a field lens 63 to achieve the second embodiment. Figure 14 The main function of field lenses 61 and 62 in the ) is to easily reduce the number of main components.

[0082] Figure 19 This is a cross-sectional view of the planar lighting device 1 according to the third embodiment. Figure 19 In, with Figure 14 The difference lies in the replacement of field lenses 61 and 62 with field lens 63 and diffuser plate 64. Specifically, the emission side of field lens 61 is concave, covering almost the entire emission surface of the planar illumination device 1, thus eliminating the need for a prism structure on the injection side of field lens 62. Furthermore, the diffuser spots on the emission side of field lens 62 are replaced by diffuser plate 64. It should be noted that diffuser plate 64 can also be moved outwards from the frame 7, and can be omitted if diffusion is not required.

[0083] Figure 20 This is a diagram showing the construction of the incident side of the field lens 63. Figure 21 This is a diagram showing the structure of the emission side of the field lens 63. Figure 20 and Figure 21In the field lens 63, a cylindrical lens with a semi-cylindrical cross-section is provided on the flat surface 63a of the incident side, extending along the Y-axis. Furthermore, the incident side surface 63b of the field lens 63 is concave in the X-Z plane, and a cylindrical lens with a semi-cylindrical cross-section is provided on this surface 63b, extending along the X-axis. It should be noted that although the case where the incident side surface of the field lens 63 is concave has been described, it is also possible for the incident side surface to be concave (while the incident side surface is flat). Moreover, it is also possible for both the incident and incident side surfaces of the field lens 63 to be concave. Figure 22 The diagram shows another example of the field lens 63, where the incident side surface 63a is concave in the Y-Z plane and the exit side surface 63b is concave in the X-Z plane.

[0084] (Fourth Implementation)

[0085] In the fourth embodiment, the first condenser lens 5, through its incident surface 5a, focuses the light horizontally towards approximately parallel light; through its exit surface 5b, it focuses the light vertically and tilts the optical axis; the second field lens 6, through its incident surface 6a, diffuses the light horizontally; and through its exit surface 6b, tilts the optical axis horizontally. Figure 1 In the head-up display system 100, although the horizontal optical axis tilt is larger compared to the vertical direction, the optical axis can be easily tilted in two stages in the horizontal direction, allowing for the supply of appropriately controlled light to the concave mirror of the head-up display system utilizing planar illumination. That is, although it is structurally difficult to achieve focusing and a large tilt of the optical axis for each light source 3 such as an LED using a linear Fresnel lens with a single surface, it becomes easier to achieve this by tilting the optical axis using a linear prism after temporarily focusing the light to approximately parallel light. Furthermore, although light diffusion occurs in the horizontal direction, there are many cases where the required light distribution diffusion angle in the vertical direction is small and diffusion is unnecessary; therefore, a structure that does not diffuse in the vertical direction is adopted.

[0086] Figure 23 This is a cross-sectional view of the planar lighting device 1 according to the fourth embodiment along the X-axis direction (horizontal direction). Figure 24 This is a cross-sectional view of the planar lighting device 1 according to the fourth embodiment along the Y-axis direction (vertical direction). Figure 23 and Figure 24 In the middle, substrate 2, light source 3, reflector 4, condenser lens 5, field lens 6 and Figure 3 (First Embodiment) Same. In this embodiment, the point shown in the full-frame illustration, the point where the frame 7 is not shown, and the point where a diffuser 8 is provided on the emission side of the field lens 6 and is configured to be tilted relative to the optical axis in the Y-Z plane are the same as those shown in the first embodiment. Figure 3They are different. The diffuser 8 is configured to be tilted relative to the optical axis in order to reduce the influence of external light (mainly sunlight).

[0087] Figure 23 and Figure 24 In the middle, a first linear Fresnel lens is used in the horizontal direction on the surface 5a of the incident side of the condenser lens 5 and... Figure 4 and Figure 5 The same applies. That is, a linear Fresnel lens is provided on the incident surface 5a of the condenser lens 5 to focus light in the horizontal direction for each LED or other light source 3. The refraction of light in the horizontal direction achieved by the condenser lens 5 is the same as... Figure 8A same.

[0088] Figure 23 and Figure 24 In the middle, the orientation of the groove of the second linear Fresnel lens, which is located perpendicular to the surface 5b on the emission side of the condenser lens 5, is the same as... Figure 4 and Figure 5 Similar to the previous example, this second linear Fresnel lens not only focuses light into approximately parallel beams for each LED or other light source 3, but its lens angle is also adjusted to allow the optical axis to vary outwards in the vertical direction of use, depending on the distance from the center. That is, the center of the emission surface remains approximately parallel, and the optical axis tilts further outwards from the center. It should be noted that, as mentioned above, regarding the tilt of the optical axis, the center may not be approximately parallel but tilted in a predetermined direction, while the two sides of the center only need to tilt outwards relative to the tilt of the center. Figure 25 This diagram illustrates the refraction of light rays in the perpendicular direction achieved by the exit surface 5b of the condenser lens 5. That is, Figure 25 The trace of light is shown in a cross section along the vertical direction (Y, V) and the normal direction (Z) of the emission surface. Figure 25 In the diagram, the center of the planar illumination device 1 is focused into approximately parallel light, and on both sides, the optical axis is further tilted outward. It should be noted that the field lens 6 is not shown in the diagram.

[0089] Figure 23 and Figure 24 In the field lens 6, the incident surface 6a is provided with a cylindrical lens for horizontal direction with a groove extending along the Y-axis, which is configured to diffuse light in the horizontal direction. The exit surface 6b of the field lens 6 is provided with a linear prism for horizontal direction with a groove extending along the Y-axis, which is configured to tilt the optical axis in the horizontal direction. Figure 26 This diagram illustrates the refraction of horizontal light rays achieved by field lens 6. That is, Figure 26 The trace of light is shown in a cross section along the horizontal direction (X, H) and the normal direction (Z) of the emission surface during use. Figure 26In the middle, the linear prism on the emission side surface 6b does not tilt the optical axis at the center, but the tilt of the optical axis increases as it moves outward.

[0090] Furthermore, in the cylindrical lens of the incident side surface 6a, the diffusion angle of the light on the outer side is larger than that of the light generated by diffused light at the center. This is to improve the brightness uniformity of the virtual image in the outer portion where the optical axis is tilted. That is, when a highly directional light (light with a narrow diffusion angle) is emitted towards the user, the brightness changes drastically when the user moves their gaze left or right, resulting in decreased visibility. This is particularly noticeable at the end where the optical axis is tilted. Therefore, the diffusion angle of the light on the outer side is set to be larger than that of the light generated by diffused light at the center. As a result, even if the user moves their gaze left or right, the brightness does not change drastically, and the gaze is drawn into the eye movement range where the displayed image appears, thus improving visibility and enhancing safety even when used while driving a car.

[0091] Figure 27 This is an enlarged cross-sectional view of the cylindrical lens on the incident side surface 6a of the field lens 6. By increasing the contact angle α of the cylindrical lens (the angle formed by the principal surface of the field lens 6 and the tangent at the arc-shaped end), the light diffusion angle can be increased. That is, compared to the contact angle α at the center of the exit surface, the contact angle α increases as it moves outward.

[0092] The structures and functions of the incident and exiting sides of the field lens 6 can also be interchanged, or the structures and functions of the incident and exiting sides of the condenser lens 5 can be interchanged. That is, the incident surface 5a of the first condenser lens 5 can be used to focus light in a horizontal direction towards approximately parallel light, the exiting surface 5b can be used to focus light in a vertical direction and tilt the optical axis, the incident surface 6a of the second field lens 6 can be used to tilt the optical axis in a horizontal direction, and the exiting surface 6b can be used to diffuse light in a horizontal direction. Alternatively, the incident surface 5a of the first condenser lens 5 can be used to focus light in a vertical direction and tilt the optical axis, the exiting surface 5b can be used to focus light in a horizontal direction towards approximately parallel light, the incident surface 6a of the second field lens 6 can be used to diffuse light in a horizontal direction, and the exiting surface 6b can be used to tilt the optical axis in a horizontal direction. Alternatively, the light can be focused and the optical axis tilted in the vertical direction through the incident surface 5a of the first condenser lens 5, focused in the horizontal direction towards approximately parallel light through the exit surface 5b, and the optical axis tilted in the horizontal direction through the incident surface 6a of the second field lens 6, and the light diffused in the horizontal direction through the exit surface 6b.

[0093] (Fifth Implementation)

[0094] In the fifth embodiment, the first condenser lens 5 uses its entrance-side surface 5a to focus light and tilt the optical axis in the horizontal direction, and its exit-side surface 5b to focus light and tilt the optical axis in the vertical direction. The second field lens 6 uses its entrance-side surface 6a to diffuse light in the horizontal direction, and its exit-side surface 6b to diffuse light in the vertical direction. Therefore, the tilting of the optical axis can be completed at the stage of the condenser lens 5 before entering the field lens 6, and the function of the field lens 6 can be simplified to only diffuse light, thus simplifying the structure.

[0095] Overview of the overall structure and Figure 23 and Figure 24 While similar, the condenser lens 5 and field lens 6 differ slightly in structure and function. The first linear Fresnel lens, located on the incident side surface 5a of the condenser lens 5, not only focuses light into approximately parallel beams for each LED or other light source 3, but its angle is also adjusted to allow the optical axis to shift outwards in the horizontal direction depending on its distance from the center of the light source during use. That is, the center of the exit surface remains approximately parallel, and the optical axis tilts further outwards from the center. When the tilt of the optical axis in the horizontal direction is not too large, focusing and tilting of the optical axis can be achieved solely through the first linear Fresnel lens. Figure 28 This diagram illustrates the refraction of light rays in the horizontal direction according to the fifth embodiment. That is, Figure 28 The trace of light is shown in a cross section along the horizontal direction (X, H) and the normal direction (Z) of the emission surface during use. Figure 28 In the text, the diagram for field lens 6 is omitted. Figure 28 In the center of the planar lighting device 1, the light is focused into approximately parallel light, and on both sides, the light axis is further tilted outward.

[0096] Similar to the fourth embodiment, the second linear Fresnel lens, located perpendicular to the emission side surface 5b of the condenser lens 5, not only focuses the light into approximately parallel beams for each LED or other light source 3, but its angle is also adjusted so that the light axis varies outward in the vertical direction of use depending on the distance from the center of the vertical direction during use. The refraction of light is similar to... Figure 25 The same applies. That is, the center of the emission surface remains approximately parallel to the light, and the optical axis tilts further outward from the center. It should be noted that, as mentioned above, the tilt of the optical axis can also mean that the center is not approximately parallel to the light but tilted in a predetermined direction, while the two sides of the center only need to tilt outward relative to the tilt of the center.

[0097] Similar to the fourth embodiment, the field lens 6 has a cylindrical lens on its incident side surface 6a, with a groove extending along the Y-axis, which diffuses light in the horizontal direction. The field lens 6 also has a cylindrical lens on its exit side surface 6b, with a groove extending along the X-axis, which diffuses light in the vertical direction.

[0098] The structures and functions of the entrance and exit sides of the field lens 6 can also be interchanged, or the structures and functions of the entrance and exit sides of the condenser lens 5 can be interchanged. That is, the entrance surface 5a of the first condenser lens 5 can be used for horizontal focusing and optical axis tilting, the exit surface 5b for vertical focusing and optical axis tilting, the entrance surface 6a of the second field lens 6 for vertical light diffusion, and the exit surface 6b for horizontal light diffusion. Alternatively, the entrance surface 5a of the first condenser lens 5 can be used for vertical focusing and optical axis tilting, the exit surface 5b for horizontal focusing and optical axis tilting, the entrance surface 6a of the second field lens 6 for horizontal light diffusion, and the exit surface 6b for vertical light diffusion. Alternatively, the light can be focused and the optical axis tilted in the vertical direction through the incident surface 5a of the first condenser lens 5, focused and the optical axis tilted in the horizontal direction through the exit surface 5b, and the light diffused in the vertical direction through the incident surface 6a of the second field lens 6, and diffused in the horizontal direction through the exit surface 6b.

[0099] (Sixth Implementation Method)

[0100] Next, the design of relatively reducing the prism height relative to the prism spacing of the linear Fresnel lens used in the above embodiments will be described. Figure 29 This is a diagram illustrating an example of the relationship between the diffusion angle of the emitted light from light source 3 and the prism spacing and prism height. Figure 29 The diagram illustrates the following scenario: light is emitted from a light source 3 disposed on substrate 2, diffused at a predetermined angle, and enters a segmented region of a linear Fresnel lens formed on surface 5a of a condenser lens 5. Furthermore, a portion of the prisms of the linear Fresnel lens is shown magnified, with a prism spacing of a and a prism height of b.

[0101] Here, in the linear Fresnel lens corresponding to the convex lens that performs focusing (conversion of light parallel to the normal direction), the prism height b relative to the prism spacing a is relatively small at the center of the segment, while it is relatively large at the ends of the segment. Furthermore, when maintaining the same linear Fresnel lens configuration and the diffusion angle of the incident light emitted from the light source 3 increases, the portion further away from the center is used within a segment, thus the prism height b at the ends of the segment becomes larger. When the prism height b increases, the linear Fresnel lens becomes thicker, or the angle at which light must be refracted increases, resulting in decreased light efficiency, which is undesirable.

[0102] Therefore, the diffusion angle of the emitted light from the light source 3 is set to approximately 90° or less (approximately -45° to +45° or less relative to the normal direction), and the prism height b at the end of the segment relative to the prism spacing a is relatively reduced, set to a > b. That is, only the central portion satisfying a > b is used as a segment.

[0103] As mentioned above, the backlight of a head-up display is required to be approximately 100 times brighter than that of a regular display backlight; therefore, the light source 3, such as an LED, also requires high brightness. In this regard, high-brightness LEDs are predominantly those with a narrow light distribution angle and an emitted light diffusion angle of less than 90°. This allows for a reduction in the diffusion angle of the emitted light from the light source 3 while minimizing the aforementioned prism height b. Therefore, by setting the diffusion angle of the emitted light from the light source 3 to approximately 90° or less and ensuring that the prism spacing a and prism height b satisfy a > b, it is possible to achieve thinner linear Fresnel lenses, improve light efficiency, and ultimately achieve higher brightness.

[0104] It should be noted that, although for the surface 5a formed on the condenser lens 5 ( Figure 3 The linear Fresnel lens of 5 was described, but the same principle applies to the surface 5b of the condenser lens 5. Figure 3 ), condenser lens 51 surface 51a, condenser lens 52 surface 52b Figure 6 , Figure 7 Linear Fresnel lenses, and other embodiments of linear Fresnel lenses shown.

[0105] The embodiments of the present invention have been described above, but the present invention is not limited to the above embodiments. Various modifications can be made as long as they do not depart from the spirit of the invention.

[0106] As described above, the planar lighting device of the embodiment includes: a substrate having a plurality of light sources arranged in a grid-like two-dimensional configuration; a first linear Fresnel lens disposed on the emission side of the plurality of light sources, wherein the grooves of the concave and convex surfaces constituting the first linear Fresnel lens extend along one direction; and a second linear Fresnel lens disposed on the emission side of the first linear Fresnel lens, wherein the grooves of the concave and convex surfaces constituting the second linear Fresnel lens extend along a direction orthogonal to one direction. Thus, several of the performance and functionalities such as high brightness, high contrast, high brightness uniformity, low power consumption, thinness, and local dimming processing can be simultaneously satisfied.

[0107] In other words, by using two orthogonal linear Fresnel lenses, light that is approximately parallel and whose optical axis can be arbitrarily tilted is efficiently collimated, thus achieving high brightness and high brightness uniformity. Furthermore, by using multiple light sources arranged in a two-dimensional grid, local dimming can be handled, achieving high contrast. Moreover, due to the high brightness achieved, low power consumption can be achieved for the same level of brightness as before. Additionally, the use of linear Fresnel lenses enables a thin profile.

[0108] Furthermore, the first linear Fresnel lens is configured to correspond to one of the rows or columns of multiple light sources arranged in a two-dimensional grid, and the second linear Fresnel lens is configured to correspond to the other row or column. Therefore, compared to forming a ring-shaped Fresnel lens for each light source, forming a linear Fresnel lens in columns or rows in coordination with multiple light sources arranged in a straight line can be easily manufactured, achieving low cost.

[0109] Furthermore, it includes a condenser lens with a first linear Fresnel lens on one side and a second linear Fresnel lens on the other side. Thus, the first and second linear Fresnel lenses can be implemented using a single condenser lens, simplifying the construction.

[0110] Furthermore, it includes: a first condenser lens with a first linear Fresnel lens on one side; and a second condenser lens with a second linear Fresnel lens on the other side. This makes manufacturing easier.

[0111] Furthermore, either the first or second linear Fresnel lens focuses the light into approximately parallel beams in a cross-section along the horizontal direction during use and the normal direction of the exit surface, while the other lens focuses the light into approximately parallel beams in a cross-section along the vertical direction during use and the normal direction of the exit surface. This allows for efficient focusing of parallel light.

[0112] Furthermore, it includes a field lens positioned on the exit side of the second linear Fresnel lens to alter the light distribution. This allows for the achievement of an appropriate light distribution.

[0113] Furthermore, one of the first or second linear Fresnel lenses focuses the light into approximately parallel beams within a cross-section along the horizontal direction of use and the normal direction of the exit surface. The other of the first or second linear Fresnel lenses tilts the light axis outwards in the vertical direction of use based on the distance from the center of the vertical direction of use. One of the field lenses, on the entrance or exit side, diffuses the light within a cross-section along the horizontal direction of use and the normal direction of the exit surface using a cylindrical lens. The other of the field lenses, on the entrance or exit side, tilts the light axis outwards in the horizontal direction of use based on the distance from the center of the horizontal direction of use using a linear prism. Thus, even when the tilt of the optical axis in the horizontal direction of use is large, the optical axis can be easily tilted in two stages, allowing for the supply of appropriately controlled light to the concave mirror of the head-up display system utilizing the light from the planar illumination device. Furthermore, it can diffuse the light in the horizontal direction of use, where the brightness uniformity of the virtual image becomes a problem due to line-of-sight movement, thereby improving the brightness uniformity of the virtual image.

[0114] Furthermore, the contact angle of the arc-shaped end of the cylindrical lens increases as it moves outward from the center in the horizontal direction during use. This allows for easier diffusion of light in the horizontal direction compared to the center, improving the uniformity of virtual image brightness as the line of sight moves.

[0115] Furthermore, either the first or second linear Fresnel lens tilts the optical axis outward in the horizontal direction of use based on its distance from the center in the horizontal direction of use, while the other tilts the optical axis outward in the vertical direction of use based on its distance from the center in the vertical direction of use. This allows the optical axis to be tilted before entering the field lens, simplifying the function of the field lens.

[0116] Furthermore, it includes a second field lens disposed on the emission side of the second linear Fresnel lens, with a first cylindrical lens on one side and a second cylindrical lens on the other side. The grooves of the concave and convex surfaces constituting the first cylindrical lens extend in one direction, and the grooves of the concave and convex surfaces constituting the second cylindrical lens extend in a direction orthogonal to the first direction. This broadens the horizontal and vertical light distribution of the emitted light, improving the uniformity of brightness.

[0117] Furthermore, it includes a third field lens disposed on the emission side of the second linear Fresnel lens, with a first cylindrical lens on one side and a second cylindrical lens on the other side. The grooves of the concave and convex surfaces constituting the first cylindrical lens extend in one direction, and the grooves of the concave and convex surfaces constituting the second cylindrical lens extend in a direction orthogonal to the first direction. One or both surfaces of the third field lens are concave. This allows for a reduction in the number of main components.

[0118] Furthermore, the field lens tilts the optical axis outward in the horizontal direction of use, based on its distance from the center of the planar illumination device during use. This allows for the supply of appropriately controlled optical axis light to the concave mirror of the head-up display system utilizing the light from the planar illumination device. Moreover, even when the user moves their gaze left or right, the brightness does not change drastically, improving visibility.

[0119] Furthermore, it features tiny spots positioned on the exit side of the field lens to diffuse the emitted light. This improves the uniformity of brightness.

[0120] Furthermore, it includes a reflector disposed between the substrate and the first linear Fresnel lens, having a reflective surface surrounding each of the plurality of light sources. This reduces light loss from the light sources, enabling even higher brightness.

[0121] Furthermore, the diffusion angle of the emitted light from the light source is set to approximately 90° or less, and the prism spacing 'a' and prism height 'b' of the linear Fresnel lens are set to a > b. This allows for the thinning of the linear Fresnel lens and the improvement of its light efficiency, thereby achieving higher brightness.

[0122] Furthermore, the present invention is not limited to the embodiments described above. Solutions constructed by appropriately combining the above-described components are also included in the present invention. Moreover, those skilled in the art can readily derive further effects and modifications. Therefore, the present invention is not limited to the embodiments described above, and various modifications can be made.

[0123] Explanation of reference numerals in the attached figures

[0124] 1: Planar lighting device; 2: Substrate; 3: Light source; 4: Reflector; 4a: Reflecting surface; 5, 51, 52: Condensing lens; 6, 61, 62, 63: Field lens; 7: Frame.

Claims

1. A planar lighting device, comprising: A first linear Fresnel lens, disposed on the emission side of a plurality of light sources arranged in a grid-like two-dimensional configuration, includes a plurality of first segments, each of which is formed by a plurality of grooves constituting the concave and convex surfaces of the lens, the plurality of grooves extending in one direction; and A second linear Fresnel lens, disposed on the emission side of the first linear Fresnel lens, includes multiple second segments, each of which is formed by multiple grooves constituting the concave and convex surfaces of the lens, the multiple grooves extending along a direction orthogonal to the first direction. The first segment is arranged in a manner corresponding to one of the rows or columns of the plurality of light sources configured in a two-dimensional grid, and has a prism structure with a cylindrical convex lens serving as a Fresnel lens. The second segment is arranged in a manner corresponding to the other side of the row or column, and has a prism structure with a cylindrical convex lens serving as a Fresnel lens. The plurality of light sources are configured to correspond to the points where the center of any one of the plurality of first segments intersects with the center of any one of the plurality of second segments.

2. The planar lighting device according to claim 1, wherein, have: A condenser lens has a first linear Fresnel lens on one side and a second linear Fresnel lens on the other side.

3. The planar lighting device according to claim 1, wherein, have: A first condenser lens, having a first linear Fresnel lens disposed on one of its surfaces; and The second condenser lens has a second linear Fresnel lens on either side of it.

4. The planar lighting device according to any one of claims 1 to 3, wherein, One of the first linear Fresnel lens or the second linear Fresnel lens focuses the light into approximately parallel beams within a cross-section along the horizontal direction of use and the normal direction of the exit surface. The first linear Fresnel lens or the other of the second linear Fresnel lenses focuses the light into approximately parallel beams within a cross section along the direction perpendicular to the direction of use and the normal direction of the exit surface.

5. The planar lighting device according to any one of claims 1 to 3, wherein, It is equipped with a field lens, which is disposed on the emission side of the second linear Fresnel lens to change the light distribution.

6. The planar lighting device according to claim 5, wherein, One of the first linear Fresnel lens or the second linear Fresnel lens focuses the light into approximately parallel beams within a cross-section along the horizontal direction of use and the normal direction of the exit surface. The first linear Fresnel lens or the other of the second linear Fresnel lens tilts the optical axis outward from the vertical direction of use, depending on the distance from the center of the vertical direction of use. The field lens diffuses light within a cross-section along the horizontal direction of use and the normal direction of the exit surface through a cylindrical lens, either on the entrance or exit side. The other side of the field lens, either the entrance or exit side, is tilted outward in the horizontal direction of use by a linear prism, depending on the distance from the center of the horizontal direction of use.

7. The planar lighting device according to claim 6, wherein, The contact angle of the arc-shaped end of the cylindrical lens increases as it moves outward from the center in the horizontal direction during use.

8. The planar lighting device according to any one of claims 1 to 3, wherein, The first linear Fresnel lens or the second linear Fresnel lens tilts the optical axis outward in the horizontal direction of use, based on its distance from the center in the horizontal direction of use. The first linear Fresnel lens or the other of the second linear Fresnel lens tilts the optical axis outward in the vertical direction of use, depending on the distance from the center in the vertical direction of use.

9. The planar lighting device according to any one of claims 1 to 3, wherein, The lens is equipped with a second field lens, which is disposed on the emission side of the second linear Fresnel lens. A first cylindrical lens is provided on one side of the second field lens, and a second cylindrical lens is provided on the other side. The grooves of the concave and convex surfaces of the first cylindrical lens extend in one direction, and the grooves of the concave and convex surfaces of the second cylindrical lens extend in a direction orthogonal to the first direction.

10. The planar lighting device according to any one of claims 1 to 3, wherein, The third field lens is disposed on the emission side of the second linear Fresnel lens. A first cylindrical lens is provided on one side of the third field lens, and a second cylindrical lens is provided on the other side. The grooves of the concave and convex surfaces of the first cylindrical lens extend in one direction, and the grooves of the concave and convex surfaces of the second cylindrical lens extend in a direction orthogonal to the first direction. One or both surfaces of the third field lens are concave.

11. The planar lighting device according to claim 5, wherein, The field lens tilts the optical axis outward in the horizontal direction of use, depending on the distance from the center of the planar illumination device during use.

12. The planar lighting device according to claim 5, wherein, It has tiny spots, which are located on the emission side of the field lens to diffuse the emitted light.

13. The planar lighting device according to any one of claims 1 to 3, wherein, have: A substrate, wherein the plurality of light sources are disposed; and A reflector, disposed between the substrate and the first linear Fresnel lens, has a reflective surface surrounding each of the plurality of light sources.

14. The planar lighting device according to any one of claims 1 to 3, wherein, The diffusion angle of the emitted light from the light source is set to approximately 90° or less, and the prism spacing a and prism height b of the first linear Fresnel lens and / or the second linear Fresnel lens are set to a > b.

Images