Planar illuminating device

Abstract

A planar illuminating device (1) according to an embodiment comprises a plurality of light sources (4), a first optical element (6) that is disposed on the emission side of the light sources (4) and that condenses light emitted from the plurality of light sources (4), and a fourth optical element (73) that is disposed on the emission side of the first optical element (6) and that is obtained by combining a second optical element (71) that tilts the light distribution of the light condensed by the first optical element (6) in one direction and a third optical element (72) that spreads the light condensed by the first optical element (6) in the one direction, wherein the fourth optical element (73) has a contact angle that differs in accordance with the position within a segment defined by each light source (4).

Description

Planar lighting device

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

[0002] A so-called direct-type planar lighting device is known, which includes a substrate on which multiple light sources are arranged two-dimensionally and a reflector arranged on the substrate and having a reflective surface surrounding the emission sides of each light source. In such a direct-type planar lighting device, light from the light sources is focused by a linear Fresnel lens with concave and convex grooves extending in one direction (e.g., the horizontal direction when the user directly or indirectly views the emission surface), and a peak-shift prism with concave and convex grooves extending in the same direction as the linear Fresnel lens to tilt the optical axis and achieve a narrow light distribution in a direction perpendicular to the grooves (e.g., the vertical direction). Direct-type planar lighting devices equipped with a linear Fresnel lens and a peak-shift prism are used, for example, in head-up displays (HUDs), which require high brightness.

[0003] JP 2023-127243 A

[0004] Generally, display devices including HUDs are expected to be viewed from two directions, such as the front direction (H=0°) and an oblique direction (e.g., H=30°), and a backlight (planar lighting device) that illuminates a liquid crystal display panel serving as a display device is required to improve the non-uniformity of luminance in each direction while maintaining a good appearance from both directions. For this reason, various improvement methods have been proposed for planar lighting devices, but further improvements are desired.

[0005] The problem to be solved by the present invention is to provide a surface lighting device that can improve the non-uniformity of luminance in each direction while maintaining a good appearance from two directions.

[0006] In order to solve the above-mentioned problems and achieve the object, one aspect of the present invention provides a surface lighting device comprising: a plurality of light sources; a first optical element arranged on the emission side of the light sources and collecting light emitted from the plurality of light sources; a second optical element arranged on the emission side of the first optical element and tilting the distribution of light collected by the first optical element in one direction; and a fourth optical element which is a combination of a third optical element and spreading the light collected by the first optical element in the one direction, wherein the fourth optical element has a contact angle which differs depending on its position within a segment defined by each light source.

[0007] FIG. 1 is a diagram illustrating an example of the configuration of a surface lighting device according to an embodiment. FIG. 2 is a diagram for explaining an example of the configuration of a light distributing lens according to an embodiment. FIG. 3A is a diagram illustrating an example of a luminance distribution using a composite prism according to a comparative example. FIG. 3B is a diagram illustrating an example of a luminance distribution using a composite prism according to a comparative example. FIG. 4A is a diagram illustrating an example of a relative luminance using a composite prism according to a comparative example. FIG. 4B is a diagram illustrating an example of a relative luminance using a composite prism according to a comparative example. FIG. 5 is a diagram for explaining a decrease in luminance in a partial region S1 on the upper side in the front direction. FIG. 6 is a diagram for explaining a continuous change in contact angle depending on the position of a composite prism according to an embodiment. FIG. 7A is a diagram illustrating an example of a luminance distribution using a composite prism according to an embodiment. FIG. 7B is a diagram illustrating an example of a luminance distribution using a composite prism according to an embodiment. FIG. 8A is a diagram illustrating an example of a relative luminance using a composite prism according to an embodiment. FIG. 8B is a diagram illustrating an example of a relative luminance using a composite prism according to an embodiment. FIG. 9A is a diagram for explaining an effect of the surface lighting device according to an embodiment. FIG. 9B is a diagram for explaining an effect of the surface lighting device according to an embodiment.

[0008] 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.

[0009] FIG. 1 is a diagram showing an example of the configuration of a surface lighting device 1 according to an embodiment, and is an end view showing the state within the thickness. For convenience, the light-emitting surface of the surface lighting device 1 is in the X-Y plane, and the thickness direction of the surface lighting device 1 is defined as the Z direction. Furthermore, in a usage state in which light emitted from the surface lighting device 1 is incident on a liquid crystal panel (not shown) or the like attached to the surface lighting device 1 and is visible to a user, the X-axis direction corresponds to the horizontal direction (H) and the Y-axis direction corresponds to the vertical direction (V). Specifically, in a usage state of the surface lighting device 1, the positive direction of the Y-axis corresponds to the "upper side" and the negative direction of the Y-axis corresponds to the "lower side." Note that the usage state of the surface lighting device 1 is not limited to the above-mentioned direction and can be used in any direction.

[0010] In this embodiment, the surface lighting device 1 is assumed to be viewed from two directions, namely, the front direction (H=0°) and the diagonal direction (H=30°), and the case where the optical axis of the emitted light is tilted (peak shifted) in the V=-12° direction is described, but the present invention is not limited to this.

[0011] As shown in FIG. 1, the surface lighting device 1 includes a bottom frame 2 , a substrate 3 , a light source 4 , a reflector 5 , a condenser lens 6 , a light distribution lens 7 , and a reflective polarizing film 8 .

[0012] The bottom frame 2 is a substantially box-shaped member with a bottom that houses the substrate 3 (described later) and other components. The bottom frame 2 is fitted with a top frame (not shown) that has an opening for emitting light, thereby forming the exterior of the surface illumination device 1. Although not described in detail, the bottom frame 2 is appropriately provided with structures (projections, holes, etc.) for housing the substrate 3 and other components, connectors for electrical connection, etc.

[0013] The substrate 3 is a member provided at the bottom of the bottom frame 2 and equipped with electronic components such as a light source 4, which will be described later.

[0014] The light sources 4 are configured with LEDs (Light Emitting Diodes) or the like, and a plurality of them are arranged two-dimensionally (for example, in a grid pattern) on the substrate 3. The light sources 4 are preferably those having a light distribution pattern known as a top hat type. Each of the plurality of light sources 4 is driven individually, and can support so-called local dimming drive.

[0015] The reflector 5 is disposed on the side of the substrate 3 where the light sources 4 are disposed, and includes a reflective wall 51 extending along the Y-axis direction and a reflective wall 52 extending along the X-axis direction. The reflective walls 51 and 52 of the reflector 5 are disposed at equal intervals between each of the plurality of light sources 4, thereby forming a reflective surface that rectangularly surrounds the emission side of each of the light sources 4. This improves contrast when the plurality of light sources 4 are driven using local dimming. Note that the unit area into which the individual light sources 4 are separated by the reflector 5 is referred to as a "segment (or zone)." The height of the reflector 5 can be set arbitrarily, but it is preferable that the reflective wall 52 be higher than the reflective wall 51, as shown in the figure, to reduce stray light.

[0016] The condenser lens 6 is an optical element disposed on the exit side of the reflector 5 and condenses light from the light source 4 in the Y-axis direction. For example, the condenser lens 6 is an optical element having a lenticular lens with concave and convex grooves extending along the Y-axis direction in the incident surface, and a linear Fresnel lens (corresponding to the first optical element) with concave and convex grooves extending along the X-axis direction in the exit surface. The linear Fresnel lens has grooves formed periodically in accordance with the spacing (pitch) between the multiple light sources 4.

[0017] The light distributing lens 7 is an optical element disposed on the exit side of the condensing lens 6 and tilts the light distribution of the light condensed by the condensing lens 6 in the Y-axis direction. For example, the light distributing lens 7 has a compound prism that combines, in the incident surface, a linear prism with concave and convex grooves extending along the X-axis direction and a lenticular lens with concave and convex grooves extending along the X-axis direction. With this configuration, the compound prism can simultaneously function as a linear prism that tilts the light (peak shift in the V=-12° direction) and as a lenticular lens that widens the light. The light distributing lens 7 also has a lenticular lens with concave and convex grooves extending along the Y-axis direction in the exit surface.

[0018] Here, the composite prisms according to the embodiment have a pitch smaller than the pitch of the light sources 4 (i.e., multiple composite prisms exist within one segment), and have different contact angles depending on the position in the Y-axis direction within the segment S defined by each light source 4. Note that configuration examples and contact angles of the light distributing lens 7 will be described in detail later.

[0019] The reflective polarizing film 8 is an optical component disposed on the output side of the light distributing lens 7, and enhances the brightness of the output light. The reflective polarizing film 8 is formed, for example, from a substantially plate-shaped DBEF (Dual Brightness Enhancement Films) or the like, and has polarization that matches the liquid crystal panel provided on the output side of the planar lighting device 1.

[0020] Fig. 2 is a diagram for explaining an example of the configuration of a light distributing lens 7 according to an embodiment. The right side of Fig. 2 illustrates an example of a light distributing lens 7 according to an embodiment. The left side of Fig. 2 illustrates an example of a light distributing lens 7' according to a comparative example. Note that the "upper side" on the paper surface of Fig. 2 corresponds to the "upper side" when the planar lighting device 1 is in use, and the "lower side" on the paper surface of Fig. 2 corresponds to the "lower side" when the planar lighting device 1 is in use.

[0021] 2, when the linear prism 71a and the linear prism 71b are referred to collectively without distinction, they are referred to as "linear prism 71." When the lenticular lens 72a and the lenticular lens 72b are referred to collectively without distinction, they are referred to as "lenticular lens 72." When the composite prism 73a and the composite prism 73b are referred to collectively without distinction, they are referred to as "composite prism 73."

[0022] As shown in FIG. 2 , the light distributing lens 7 includes a composite prism 73 (corresponding to a fourth optical element) that combines a linear prism 71 (corresponding to a second optical element) with a triangular cross section that tilts the light distribution of light collected by the collecting lens 6 in the Y-axis direction (for example, tilting in the V=−12° direction) and a lenticular lens 72 (corresponding to a third optical element) with an arc-shaped cross section that spreads the light collected by the collecting lens 6 in the Y-axis direction. Specifically, the composite prism 73 is an optical element in which a lenticular lens 72 extending along the X-axis direction is formed on the main surface of the linear prism 71 that extends along the X-axis direction, and multiple composite prisms 73 are arranged in the Y-axis direction. Note that the main surface of the linear prism 71 is the inclined surface with the smaller inclination angle of a pair of inclined surfaces. In this embodiment, the lenticular lens 72 is formed as a curved surface (arc-shaped cross section) with a constant curvature R that is convex outward, starting from the vertex side of the main surface of the linear prism 71. In addition, although a boundary line is shown between the linear prism 71 and the lenticular lens 72 in FIG. 2, in reality, the two are molded as a single unit, so there is no boundary line.

[0023] The light distributing lens 7' also has a composite prism 73' that combines a linear prism 71' and a lenticular lens 72'. Here, the basic configurations of the linear prism 71', the lenticular lens 72', and the composite prism 73' are similar to the configurations of the linear prism 71, the lenticular lens 72, and the composite prism 73, so a description thereof will be omitted.

[0024] Here, the height H and pitch length L of all composite prisms 73′ included in the light distributing lens 7′ according to the comparative example are constant at any position within the segment S. For this reason, the contact angle, which is the angle between the curved surface of the lenticular lens 72′ in the composite prism 73′ and the plane of the base portion (X-Y plane) of the light distributing lens 7′, is uniform regardless of the composite prism 73′.

[0025] On the other hand, the light distributing lens 7 according to this embodiment has different contact angles depending on the position within the segment S. In the example of Fig. 2, the contact angle θa of the composite prism 73a is larger than the contact angle θb of the composite prism 73b. The larger the contact angle, the greater the degree of diffusion of light passing through the curved surface, and therefore the degree of diffusion of light exiting the composite prism 73a is greater than the degree of diffusion of light exiting the composite prism 73b.

[0026] In this embodiment, the contact angle of the composite prism 73 can be arbitrarily changed (designed) by varying the height to the apex of each prism, since the curvature of the curved surface is constant. For example, in manufacturing a mold for molding the light distributing lens 7 by injection molding or the like, the height of each composite prism 73 can be varied by varying the depth of the tool (bite) used to cut the uneven surface of each composite prism 73. In this case, since the same cutting tool is used, the contact angle varies depending on the height (depth of the mold groove), and the higher the height (deeper the mold groove), the larger the contact angle. In the example of FIG. 2, by making the height Ha of the composite prism 73 higher than the height Hb of the composite prism 73b, the contact angle θa can be designed to be larger than the contact angle θb. Note that the contact angle is calculated using, for example, the θ / 2 method, but any known calculation method can be applied as appropriate.

[0027] Since the height Hb of the composite prism 73b is smaller than the height Ha by Δh, the pitch length Lb of the composite prism 73b is also shorter than the length La by Δl. For this reason, it is preferable to arrange the composite prisms 73a and 73b closely together so that no flat portion (a portion where the composite prism 73 is not arranged) is created between them.

[0028] 3A and 3B are diagrams showing an example of the luminance distribution by the composite prism 73' according to the comparative example. FIGS. 4A and 4B are diagrams showing an example of the relative luminance by the composite prism 73' according to the comparative example. FIG. 3A illustrates the luminance distribution in the front direction (H=0°), and FIG. 3B illustrates the luminance distribution in the oblique direction (H=30°). In FIGS. 3A and 3B, "S" indicates a segment, "S1" indicates a partial region above segment S, and "S2" indicates a partial region below segment S. FIGS. 4A and 4B illustrate the relative luminance for each position in the H and V directions.

[0029] As shown in Figures 3A and 4A, in the front direction, it was found that the upper partial region S1 had the lowest brightness among the segments S. It was also found that the lower partial region S2 had the second lowest brightness after the partial region S1. Furthermore, as shown in Figures 3B and 4B, it was found that in the oblique direction, both ends of the segment S (partial regions S1 and S2) had low brightness.

[0030] 5 is a diagram illustrating the decrease in luminance in the upper partial region S1 in the front direction. As shown in Fig. 5, the light distribution lens 7' is required to tilt its optical axis downward (toward the negative Y-axis, V = -12 deg), but the preceding condenser lens 6 is designed to be symmetrical above and below the optical axis and to somewhat broaden (defocus) the light beam. Therefore, in the upper partial region S1, light is emitted mainly in an upward direction, and in the lower partial region S2, light is emitted mainly in a downward direction.

[0031] Here, in the partial region S1, upward-directed light may be incident on the rising surface 7'-2 rather than the main surface 7'-1 of the light distributing lens 7' (composite prism 73'), preventing the light distribution performance of the light distributing lens 7' from being properly demonstrated. Furthermore, even if the light is incident on the main surface 7'-1, it is difficult to tilt it in the desired direction (V = -12 deg direction), so it is thought that brightness is likely to decrease in the upper partial region S1. Note that in the partial region S2, more light is directed downward, so it is more likely to be incident on the main surface 7'-1 than in the partial region S1, but it is difficult to tilt it in the desired direction unless the incident light is approximately parallel.

[0032] Therefore, the composite prism 73 according to this embodiment is configured to have different contact angles and different heights (vertex positions) depending on the position within the segment S in order to compensate for the light distribution performance of the composite prism 73'.

[0033] 6 is a diagram for explaining the continuous change in the contact angle depending on the position of the composite prism 73 according to the embodiment, and illustrates a graph showing the magnitude of the contact angle relative to the vertex position of the composite prism 73 in the Y-axis direction.

[0034] 6, the contact angle of the composite prism 73 in the partial region S1 is configured to be smaller than that in the other regions. For example, the minimum contact angle in the partial region S1 is 15.2 degrees. This reduces the degree of diffusion in the partial region S1, which is expected to improve brightness and eliminate the dark lines that occurred in the composite prism 73'.

[0035] The composite prism 73 is also configured so that the contact angle near the center is larger than that in other regions. For example, the maximum contact angle near the center is 15.9 degrees. This increases the degree of diffusion near the center, which is expected to reduce the brightness near the center and improve brightness uniformity in the segment S.

[0036] Furthermore, the contact angle of the composite prism 73 below the optical axis is configured to be larger overall compared to the above the optical axis. This is because the brightness below the optical axis tends to be higher than the above. In other words, this configuration increases the degree of diffusion below the optical axis, which is expected to suppress the brightness below the optical axis and improve the brightness uniformity in the segment S.

[0037] The contact angle of the composite prism 73 in the partial region S2 is smaller than that near the center, but larger than that in the other regions. This increases the degree of diffusion in the partial region S2, which is expected to suppress the brightness of the partial region S2 and improve the bright lines that occurred in the composite prism 73'.

[0038] 7A and 7B are diagrams illustrating an example of a luminance distribution by the composite prism 73 according to the embodiment. 8A and 8B are diagrams illustrating an example of a relative luminance by the composite prism 73 according to the embodiment. Fig. 7A illustrates a luminance distribution in the front direction (H = 0°), and Fig. 7B illustrates a luminance distribution in an oblique direction (H = 30°). Figs. 8A and 8B illustrate relative luminance for each position in the H direction and V direction.

[0039] As shown in Figures 7A to 8B, the brightness fluctuation range is small in both the front direction and the oblique direction, and it was found that the bright lines and dark lines that occurred in the comparative example (composite prism 73') were improved.

[0040] 9A and 9B are diagrams for explaining the effects of the surface illumination device 1 according to the embodiment. Fig. 9A and 9B illustrate the results of a comparison of the relative luminance of the composite prism 73 (the surface illumination device 1) and the relative luminance of the composite prism 73' (comparison example) with respect to the V-section.

[0041] 9A and 9B, in the front direction (H=0°), the application of the composite prism 73 improved the relative luminance by approximately 2% at most. Furthermore, in the oblique direction (H=30°), the application of the composite prism 73 improved the relative luminance by approximately 4% at most. Furthermore, it was found that the improvement in appearance achieved by the composite prism 73 can be obtained regardless of the light distribution characteristics of the light source 4.

[0042] 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.

[0043] As described above, the planar lighting device according to the embodiment includes a plurality of light sources, a first optical element disposed on the light output sides of the light sources and configured to collect light emitted from the plurality of light sources, a second optical element disposed on the light output side of the first optical element and configured to tilt the light distribution of the light collected by the first optical element in one direction, and a third optical element disposed on the light output side of the first optical element and configured to expand the light collected by the first optical element in the one direction, the fourth optical element being a combination of these elements, wherein the fourth optical element has different contact angles depending on the position within the segment defined by each light source. This allows the planar lighting device to achieve a good appearance from two directions while precisely improving non-uniformity of luminance in each direction without using any additional components.

[0044] The one direction is a first direction (e.g., a Y-axis direction), and the fourth optical element is an optical element in which the second optical element has a triangular cross section extending along a second direction (e.g., an X-axis direction) orthogonal to the optical axis of the light and the first direction, and the third optical element has an arc-shaped cross section extending along the second direction, formed on one surface of the second optical element. This makes it possible for the planar illumination device to improve non-uniformity in luminance in, for example, the Y-axis direction.

[0045] In addition, the fourth optical elements are arranged in a plurality in the one direction, and the plurality of fourth optical elements have different contact angles due to the fact that the curvature of the curved surface of the third optical element is constant and the height to the apex of each fourth optical element varies depending on the position in the one direction within the segment. This makes it possible for the surface illumination device to improve non-uniformity of luminance, particularly in the one direction.

[0046] Furthermore, the plurality of fourth optical elements have a large contact angle near the center in the one direction within the segment, which increases the degree of diffusion near the center, thereby suppressing the brightness near the center and improving the brightness uniformity in the segment S.

[0047] Furthermore, the plurality of fourth optical elements have a small contact angle near the end (partial region S1) of the segment on the side opposite to the tilt direction (e.g., the lower side / negative Y-axis direction) of the second optical element, thereby suppressing the degree of diffusion near the end, thereby improving brightness and eliminating the dark lines that occurred in the comparative example.

[0048] In addition, the contact angles of the fourth optical elements on the side in the tilt direction of the second optical element within the segment are larger than the contact angles on the side opposite to the tilt direction (upper side), thereby increasing the degree of diffusion below the optical axis, thereby suppressing the brightness below the optical axis and improving the brightness uniformity in the segment.

[0049] Furthermore, the plurality of fourth optical elements have a large contact angle near the end portion (partial region S2) of the segment that is closer to the tilt direction of the second optical element, thereby increasing the degree of diffusion in the partial region S2, thereby suppressing the brightness of the partial region S2 and improving the bright lines that occurred in the comparative example.

[0050] The plurality of light sources are arranged in a grid pattern, which makes it easy to support local dimming drive and allows the fourth optical elements, which are arranged according to the positions of the light sources, to be regularly arranged, thereby efficiently improving bright lines and dark lines.

[0051] Furthermore, each of the plurality of light sources is surrounded by a reflective surface of a reflector in a rectangular shape to define the segment, thereby improving contrast when the plurality of light sources are driven with local dimming, and also enabling the fourth optical element, which is disposed according to the position of each light source, to be appropriately disposed for each segment, thereby effectively reducing bright lines and dark lines.

[0052] 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.

[0053] REFERENCE SIGNS LIST 1 Planar lighting device, 2 Bottom frame, 3 Substrate, 4 Light source, 5 Reflector, 51, 52 Reflecting wall, 6 Condenser lens, 7 Light distribution lens, 71 Linear prism, 72 Lenticular lens, 73 Compound prism, 8 Reflective polarizing film

Claims

1. A surface lighting device comprising: a plurality of light sources; a first optical element arranged on the emission side of the light sources and concentrating light emitted from the plurality of light sources; a fourth optical element arranged on the emission side of the first optical element and combining a second optical element that tilts the distribution of light concentrated by the first optical element in one direction; and a third optical element that spreads the light concentrated by the first optical element in the one direction; wherein the fourth optical element has a contact angle that varies depending on its position within a segment defined by each light source.

2. The surface illumination device of claim 1, wherein the one direction is a first direction, and the fourth optical element is an optical element in which the third optical element having an arc-shaped cross section extending along the second direction is formed on one surface of the second optical element having a triangular cross section extending along the second direction perpendicular to the optical axis of the light and the first direction.

3. A surface illumination device as described in claim 1 or 2, wherein the fourth optical elements are arranged in multiple in the one direction, and the multiple fourth optical elements have different contact angles from each other because the curvature of the curved surface of the third optical element is constant and the height to the apex of each fourth optical element varies depending on the position in the one direction within the segment.

4. The surface illumination device according to claim 3, wherein the plurality of fourth optical elements have a large contact angle near the center in the one direction within the segment.

5. A surface illumination device according to claim 3, wherein the plurality of fourth optical elements have a small contact angle near the end of the segment opposite to the tilt direction side of the second optical element.

6. A surface illumination device according to claim 3, wherein the contact angle of the plurality of fourth optical elements on the side in the tilt direction of the second optical element within the segment is larger than the contact angle on the side opposite to the tilt direction.

7. The surface illumination device according to claim 3, wherein the plurality of fourth optical elements have a large contact angle near the end of the segment on the side in the tilt direction of the second optical element.

8. The planar lighting device according to claim 1, wherein the plurality of light sources are arranged in a grid pattern.

9. The spread illuminating device according to claim 1, wherein each of said plurality of light sources is surrounded by a reflective surface of a reflector in a rectangular shape to define said segment.

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