JP2012164511A - Light guide plate and planar light source device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light guide plate with high brightness and capable of reducing unevenness of incident light in the vicinity of a light source.SOLUTION: The light guide plate is provided with a base body 4 including a first and a second main surfaces 12, 14 facing each other, and a plurality of side surfaces surrounding the first and the second main surfaces 12, 14, with at least one of the side surfaces to be as a light-incident surface 10, a plurality of first optical elements 16 arranged on the first main surface 12 and extended in a direction orthogonal to the light-incident surface 10, a plurality of second optical elements 18 arranged on the second main surface 14 and extended in a direction parallel to the incident surface 10, and a plurality of third optical elements 20 arranged on a light-incident surface 10 side of the second main surface 14 and extended in a direction orthogonal to the light-incident surface 10.

Description

  The present invention relates to a light guide plate and a surface light source device for irradiating a liquid crystal display element or the like from the back.

  The liquid crystal display element does not emit light by itself. Therefore, in order to display an image, a surface light source device that emits illumination light to the back surface of the liquid crystal display element is required. The surface light source device includes a light guide plate that guides light incident from a light source and emits the light from a light exit surface.

  The surface light source device is required to have high luminance and high efficiency without display unevenness. In the currently most popular surface light source device, two upward prism sheets are arranged on the light exit surface of the light guide plate in order to prevent display unevenness. On the other hand, as a method for realizing a surface light source device with higher luminance and higher efficiency, it has been proposed to use a downward prism sheet on the light exit surface of the light guide plate (see Patent Documents 1 and 2).

  A conventional surface light source device using a downward prism includes a light source, a light guide plate, a reflecting member, a downward prism sheet, and a diffusion sheet. The light guide plate is disposed to face the light emitting surface of the light source. The reflection member is disposed on the lower surface of the light guide plate. The downward prism sheet is disposed on the upper surface of the light guide plate. The diffusion sheet is disposed on the downward prism sheet.

  A plurality of point light sources such as light emitting diodes (LEDs) are used as the light source. In the light guide plate, one side surface facing the light source is a light incident surface, one main surface orthogonal to the light incident surface is a light output surface, and the other main surface is a reflection surface. An optical element extending in a direction parallel to the light incident surface is provided on the reflection surface. In order to make the illumination light uniform, a plurality of fine optical elements extending in a direction orthogonal to the light incident surface may be arranged on the light exit surface.

  Light emitted from the light source is introduced into the light guide plate from the light incident surface. The light is repeatedly reflected by the optical element on the reflection surface within the light guide plate, and is emitted to the outside of the light guide plate through the light output surface when the angle exceeds the critical angle. The light emitted to the outside of the light guide plate is deflected in the normal direction of the light output surface by the downward prism sheet, and further radiated through the diffusion sheet. The diffusion sheet is disposed in order to prevent moiré with the liquid crystal display element. If there is no moiré, no diffusion sheet may be provided.

  In a surface light source device using a downward prism sheet, high luminance and high efficiency are realized by emitting light having strong directivity from a light guide plate. For this reason, the diffusion of light in the light guide plate is weak, and in the vicinity of the light incident surface, a bright part in each of the light incident parts facing a plurality of light sources, a dark part between the light incident parts, and a strong bright line in the vicinity of the light incident part Uneven light incidence occurs.

  In order to improve unevenness of incident light, a method has been proposed in which light is emitted from the lower surface of the light guide plate and reflected again to the light guide plate by an optical element formed on the reflection surface of the reflecting member (see Patent Document 3). The optical element provided on the reflecting member has a shape that diffuses light in a region corresponding to the vicinity of the light incident surface of the light guide plate.

  Further, in order to improve the unevenness of incident light, a method is adopted in which light is diffused on the light incident surface of the light guide plate so that the light is uniformly incident on the light guide plate. Alternatively, light may be diffused on the light exit surface of the light guide plate so that the light is uniformly emitted from the light exit surface. In this case, a rough surface pattern or a lens pattern processed by blasting or the like is disposed on the light incident surface or the light exit surface. Irradiation unevenness can be improved to some extent by a method of diffusing light on the light incident surface. However, compared with the appearance of a conventional surface light source device that uses two upwardly facing prism sheets, the unevenness in incident light is not sufficiently improved.

JP 2005-142078 A JP 2008-218418 A International Publication No. 2005/061957

  It is an object of the present invention to provide a light guide plate and a surface light source device that have high brightness and can reduce unevenness in incident light in the vicinity of the light source.

  In order to achieve the above object, according to a first aspect of the present invention, there are provided first and second main surfaces facing each other, a plurality of side surfaces surrounding the first and second main surfaces, and at least one side surface is incident. A substrate as a surface, a plurality of first optical elements disposed on the first main surface and extending in a direction orthogonal to the light incident surface, and disposed on the second main surface and extending in a direction parallel to the light incident surface. The gist of the present invention is a light guide plate including a plurality of second optical elements and a plurality of third optical elements arranged on the light incident surface side of the second main surface and extending in a direction orthogonal to the light incident surface.

  A second aspect of the present invention is a surface light source device that irradiates a liquid crystal display element, the light guide plate according to the first aspect of the present invention, a light source disposed to face the light incident surface, and a plurality of prisms. The gist of the invention is a surface light source device including a prism sheet arranged so that a main surface on which rows are formed faces the first main surface and a reflecting member arranged to face the second main surface. .

  According to a third aspect of the present invention, there is provided a surface light source device for irradiating a liquid crystal display element, the light guide plate according to the first aspect of the present invention, a light source disposed facing the light incident surface, and a first main light source. The gist of the present invention is a surface light source device including a reflecting member disposed facing a surface and a prism sheet disposed such that a principal surface on which a plurality of prism rows are formed faces a second principal surface. .

  ADVANTAGE OF THE INVENTION According to this invention, it is high-intensity and can provide the light-guide plate and surface light source device which can reduce the light incident nonuniformity of the light source vicinity.

1 is a schematic side view showing an example of a surface light source device according to an embodiment of the present invention. It is a top view which shows an example of the light-guide plate which concerns on embodiment of this invention. It is a figure which shows an example of the AA cross section of the light-guide plate shown in FIG. It is a figure which shows the other example of the AA cross section of the light-guide plate shown in FIG. FIG. 3 is a bottom view of the light guide plate shown in FIG. 2. It is a figure which shows an example of the BB cross section of the light-guide plate shown in FIG. It is a figure which shows an example of CC cross section of the light-guide plate shown in FIG. It is a figure which shows the other example of CC cross section of the light-guide plate shown in FIG. It is a figure which shows the other example of CC cross section of the light-guide plate shown in FIG. It is a figure which shows the other example of CC cross section of the light-guide plate shown in FIG. It is the side surface schematic diagram which shows the other example of the surface light source device which concerns on embodiment of this invention.

  Next, embodiments of the present invention will be described with reference to the drawings. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. However, it should be noted that the drawings are schematic, and the relationship between the thickness and the planar dimensions, the ratio of the thickness of each layer, and the like are different from the actual ones. Therefore, specific thicknesses and dimensions should be determined in consideration of the following description. Moreover, it is a matter of course that portions having different dimensional relationships and ratios are included between the drawings.

  Further, the following embodiments exemplify apparatuses and methods for embodying the technical idea of the present invention, and the technical idea of the present invention is the material, shape, structure, The layout is not specified as follows. The technical idea of the present invention can be variously modified within the scope of the claims.

  An example of a surface light source device according to an embodiment of the present invention is shown in FIG. A light source 1, a light guide plate 3, a prism sheet 5, a diffusion sheet 9, and a reflection member 7 are provided. The light guide plate 3 includes a base body 4, a plurality of first optical elements 16 provided on the first main surface 12 of the base body 4, and a plurality of second optical elements provided on a second main surface 14 facing the first main surface. 18 and a plurality of third optical elements 20. A region having a width L from the light incident surface 10 to an end portion on the light incident surface 10 side of the display area 30 of the liquid crystal display element irradiated by the surface light source device is defined as a light incident area 32.

  The light source 1 is disposed so as to face the light incident surface 10 of the light guide plate 3. The prism sheet 5 is disposed so that the main surface on which the plurality of prism rows 26 are formed faces the first main surface 12 that is the light output surface of the light guide plate 3. The diffusion sheet 9 is disposed so as to face the light guide plate 3 with the prism sheet 5 interposed therebetween. The reflecting member 7 is disposed so as to face the second main surface 14 that is the reflecting surface of the light guide plate 3.

  As shown in FIGS. 2 and 5, a substantially rectangular base 4 is used for the light guide plate 3. Of the four side surfaces surrounding the first and second main surfaces 12 and 14 of the substrate 4, one side surface is defined as a light incident surface 10. A plurality of, for example, three light sources 1 are arranged facing the light incident surface 10. In the following description, a rectangular base 4 is used for explanation, but the shape of the base 4 is not limited. For example, the base 4 may be a quadrilateral or more polygon. Further, a plurality of polygonal side surfaces used for the substrate 4 may be used as the light incident surface.

  As the substrate 4, a transparent thermoplastic such as polymethyl methacrylate (PMMA), polycarbonate (PC), cycloolefin polymer (COP), cycloolefin copolymer (COC) is used. The first to third optical elements 16, 18, and 20 of the light guide plate 3 are formed on the base 4 by an injection molding method or the like.

  The light incident surface 10 of the light guide plate 3 is provided with an anisotropic diffusion optical pattern that spreads the light emitted from the light source 1 in a direction substantially orthogonal to the traveling direction. The anisotropic diffusion optical pattern is provided so that, for example, a wave shape, an arc shape, a V shape, or the like extends in the thickness direction of the light guide plate 3. In particular, the wavy pattern is preferable because it has strong diffusibility and can suppress generation of bright lines.

  As shown in FIG. 2, a plurality of first optical elements 16 extending in a direction orthogonal to the light incident surface 10 are provided on the first main surface 12 of the substrate 4. The plurality of first optical elements 16 are provided on the entire first main surface 12. As shown in FIG. 3, each first optical element 16 is preferably a protrusion whose cross-sectional shape cut parallel to the light incident surface 10 is an isosceles triangle having an apex angle θ. The apex angle θ is preferably in the range of greater than 90 degrees and less than 140 degrees. The plurality of first optical elements 16 preferably include isosceles triangles having a plurality of different apex angles θ of 2 or more, preferably 3 or more within a range of greater than 90 degrees and less than 140 degrees. In addition, as shown in FIG. 4, even when a groove shape is used as the first optical element, the same effect can be obtained.

  The first optical element 16 causes light propagating through the light guide plate 3 and tilted in a direction parallel to the light incident surface 10 to be emitted from the light guide plate 3 close to the front direction (normal direction of the light exit surface). , It has a function to increase the amount of light in the front direction. By setting the apex angle θ to a range greater than 90 degrees and less than 140 degrees, the amount of light in the front direction can be increased efficiently, and a high-intensity light guide plate can be realized. In addition, by using an isosceles triangle having a plurality of different apex angles θ in which the apex angle θ is greater than 90 degrees and less than 140 degrees, the amount of light in the front direction can be adjusted, and directivity can be improved. It is possible to weaken or strengthen the light emission characteristic.

  Moreover, the height of the plurality of first optical elements 16 is 5 μm or more, more preferably 6 μm or more. If the height of the first optical element 16 is less than 5 μm, the first optical element 16 is likely to be in close contact with the prism sheet 5 disposed facing the first main surface 12 and display defects are likely to occur.

  As shown in FIG. 5, the second main surface 14 of the substrate 4 has a plurality of second optical elements 18 extending in a direction parallel to the light incident surface 10 and a plurality of members extending in a direction orthogonal to the light incident surface 10. The third optical element 20 is provided. The plurality of second optical elements 18 are provided on the entire second main surface. As shown in FIG. 1 and FIG. 5, the plurality of third optical elements 20 are from the light incident surface 10 to the position beyond the boundary between the light incident area 32 and the display area 30 and the width DL on the display area 30 side. Provided in the region.

  As shown in FIG. 6, each of the plurality of second optical elements 18 preferably has a protrusion shape having a first inclined surface 22 and a second inclined surface 24 in a cross section cut perpendicularly to the light incident surface 10. The slope where the normal line toward the inside of the light guide plate 3 intersects the plane parallel to the light incident surface 10 is the first slope 22, and the slope which does not intersect the plane parallel to the light incident surface 10 is the second slope 24. The width of the first slope 22 in the direction perpendicular to the light incident surface 10 is preferably in the range of 60 μm to hundreds of tens of μm. The angle α formed by the first inclined surface 22 and the normal line of the light incident surface 10 is greater than 0.5 degrees and less than 5 degrees, preferably greater than 0.5 degrees and less than 3 degrees. The angle β formed by the second inclined surface 24 and the normal line of the light incident surface 10 is greater than 50 degrees and less than 80 degrees, preferably greater than 70 degrees and less than 80 degrees.

  When the angle α is 5 degrees or more, a lot of light is emitted on the light incident surface 10 side. When the angle α is 0.5 degrees or less, a large amount of light tends to be emitted on the side surface facing the light incident surface. For this reason, in order for the surface light source device to emit light uniformly within the surface, it is preferable to set the angle α in the range of more than 0.5 degrees and less than 5 degrees.

  When the angle β is 50 degrees or less, the light reflected by the side surface facing the light incident surface 10 is reflected by the second inclined surface 24 and is emitted out of the light guide plate 3 in a direction inclined from a specified angle. For this reason, when the surface light source device is viewed from an oblique direction, a display defect occurs in which a bright portion is partially generated. When the angle β is 80 degrees or more, the corner portion of the second optical element 18 is taken by the mold during injection molding, and molding defects such as chipping tend to occur.

  The height of the plurality of second optical elements 18 is 5 μm or more, more preferably 6 μm or more. If the height of the second optical element 18 is less than 5 μm, the second optical element 18 is likely to be in close contact with the reflecting member 7 disposed facing the second main surface 14, and display defects are likely to occur.

  As shown in FIGS. 5 and 7, each of the plurality of third optical elements 20 preferably has a protrusion shape in which a cross-sectional shape cut in parallel to the light incident surface 10 is an isosceles triangle having a base angle η. The base angle η is preferably greater than 20 degrees and less than 45 degrees. Similar to the first optical element 16, the third optical element 20 causes light propagating through the light guide plate 3 to be inclined in a direction parallel to the light incident surface 10 in the front direction (normal direction of the light exit surface). It has a function of increasing the amount of light in the front direction by allowing the light to be emitted from the light guide plate 3 closer. By setting the base angle η of the third optical element 20 to a range greater than 20 degrees and less than 45 degrees, the amount of light in the front direction can be efficiently increased.

  Further, as shown in FIG. 1, the plurality of third optical elements 20 travel from the light incident surface 10 into the display area 30 beyond the position corresponding to the end of the display area 30 on the light incident surface 10 side. It arrange | positions to the area | region to the position of width DL within 4 mm in a direction. That is, since the width L of the light incident area 32 of the normal liquid crystal display device is 4 mm, the width (L + DL) from the light incident surface 10 of the region where the third optical element 20 is disposed is orthogonal to the light incident surface 10. It is the range within 4 mm or more and 8 mm or less in the direction to do. When the width DL exceeds 4 mm, the boundary between the region where the third optical element 20 is disposed and the region where the third optical element 20 is not disposed is visually recognized, and a display defect is likely to occur.

  Further, the height of the plurality of third optical elements 20 is 10 μm to 15 μm at the end of the light incident surface 10, gradually decreases toward the display area 30, and becomes substantially zero in width (L + DL). The reason why the height of the third optical element 20 is set to 10 μm to 15 μm at the end of the light incident surface 10 is to balance the slope ratio of the first and third optical elements 16 and 20 described later and the third optical element 20. Is placed within the width (L + DL). By increasing the height of the third optical element 20 in the vicinity of the light incident surface 10, display unevenness in the vicinity of the light incident surface 10 can be reduced.

  The third optical element 20 has been described using a protrusion shape. However, as shown in FIG. 8, even if the cross section cut parallel to the light incident surface 10 is an isosceles triangular groove having a base angle η, An effect equivalent to that of the case can be obtained. Further, as shown in FIG. 9 or FIG. 10, even if the cross-sectional shape cut parallel to the light incident surface 10 is an isosceles trapezoidal protrusion or groove having a base angle η, an isosceles triangular protrusion or groove is used. It is possible to achieve the same effect as if there were.

  In the light guide plate 3 according to the embodiment, the light emitted from the light source 1 is introduced into the light guide plate 3 through the light incident surface 10. The light guided in the light guide plate 3 is repeatedly reflected on the first inclined surface 22 of the second optical element 18 on the second main surface 14. The light having a critical angle or more on the first main surface 12 is emitted from the light guide plate 3 toward the prism sheet 5. The light having a critical angle or more on the second main surface 14 is emitted from the light guide plate 3 toward the reflecting member 7, reflected by the reflecting member 7, and again introduced into the light guide plate 3 through the second main surface 14. Is done.

  The light that has guided through the light guide plate 3 and reached the first main surface 12 is emitted out of the light guide plate 3 by refraction at the slope of the first optical element 16 compared to the flat portion of the first main surface 12. There are many opportunities. Similarly, the light that has reached the second main surface 14 is emitted out of the light guide plate 3 by refraction at the inclined surface of the third optical element 20 as compared with the first inclined surface 22 of the second optical element 18 of the second main surface. There are many opportunities. For example, in the light incident area 32, if the ratio of the slopes of the first and third optical elements 16 and 20 is small, the light incident area 32 becomes dark. On the other hand, in the light incident area 32, if the ratio of the slopes of the first and third optical elements 16 and 20 is large, the light incident area 32 becomes brighter. That is, in order to suppress display unevenness in the light incident area 32, it is necessary to appropriately set the ratio of the slopes of the first and third optical elements 16 and 20.

  In a general surface light source device, the distance from the light incident surface to the display area, that is, the width of the light incident area is about 4 mm. In consideration of tolerances and the like, it is necessary to prevent display unevenness in an area exceeding 3 mm from the light incident surface. Moreover, the interval between the plurality of light sources is usually in the range of 6 mm to 15 mm. From this, the interval of the plurality of light sources 1 was set to 6 mm to 15 mm, and the slope ratio capable of suppressing display unevenness was calculated by optical simulation in a region up to a position 3 mm away from the light incident surface 10. As a result, it was confirmed that display unevenness can be suppressed when the slope ratio is in the range of 10% to 60%. Here, the “slope ratio” is the target when the first and second main surfaces 12 and 14 are projected onto a plane orthogonal to the light incident surface 10 in the target region up to a position 3 mm away from the light incident surface 10. It is defined as an arithmetic mean value of the percentage of the projected area of the plurality of first optical elements 16 with respect to the projected area of the area and the percentage of the projected area of the plurality of third optical elements 20 with respect to the projected area of the target area.

  As described above, in the light guide plate 3 according to the embodiment, the third optical element 20 extending in the direction orthogonal to the light incident surface 10 is disposed on the light incident surface 10 side of the second main surface 14. The third optical element 20 is a region from the light incident surface 10 to a position in a range of 4 mm or more and within 8 mm in a direction orthogonal to the light incident surface 10, that is, the light incident surface of the display area 30 from the light incident surface 10. The display unevenness can be suppressed by disposing it in the region up to the position within 4 mm toward the display area 30 beyond the position corresponding to the end portion on the 10 side. In addition, in the target region up to a position 3 mm away from the light incident surface 10, the display unevenness is suppressed by setting the slope ratio of the first and third optical elements 16 and 20 to a range of 10% to 60%. be able to.

  Further, in the surface light source device according to the embodiment, the prism sheet 5 is arranged between the diffusion sheet 9 and the light guide plate 3 with the main surface on which the plurality of prism rows 26 are formed facing the light guide plate 3. As a result, a surface light source device with high brightness and high efficiency can be realized.

  In the above description, as shown in FIG. 1, the first main surface 12 of the light guide plate 3 is the light exit surface, and the second main surface 14 is the reflection surface. However, as shown in FIG. 11, the same effect can be obtained even if the second main surface 14 is used as the light exit surface so as to face the prism sheet 5. In this case, the light emitted from the first main surface 12 is reflected by the reflecting member 7 facing the first main surface 12 and introduced again into the light guide plate 3.

(Other embodiments)
As mentioned above, although this invention was described by embodiment of this invention, it should not be understood that the statement and drawing which make a part of this indication limit this invention. From this disclosure, various alternative embodiments, examples and operational techniques will be apparent to those skilled in the art. Accordingly, the technical scope of the present invention is defined only by the invention specifying matters according to the scope of claims reasonable from the above description.

  The light guide plate and surface light source device of the present invention can be used for liquid crystal display devices such as mobile phones, game machines, electronic notebooks, car navigation systems, notebook PCs, and TVs.

DESCRIPTION OF SYMBOLS 1 ... Light source 3 ... Light guide plate 4 ... Base | substrate 5 ... Prism sheet 7 ... Reflection member 9 ... Diffusion sheet 10 ... Light-incidence surface 12 ... 1st main surface 14 ... 2nd main surface 16 ... 1st optical element 18 ... 2nd optics Element 20 ... Third optical element 22 ... First slope 24 ... Second slope 26 ... Prism array 30 ... Display area 32 ... Light incident area

Claims (14)

A first and second main surfaces facing each other, a plurality of side surfaces surrounding the first and second main surfaces, and a base body having at least one side surface as a light incident surface;
A plurality of first optical elements disposed on the first main surface and extending in a direction perpendicular to the light incident surface;
A plurality of second optical elements disposed on the second main surface and extending in a direction parallel to the light incident surface;
A light guide plate comprising: a plurality of third optical elements arranged on the light incident surface side of the second main surface and extending in a direction orthogonal to the light incident surface.   Each of the plurality of third optical elements is an isosceles triangle having a cross-sectional shape cut parallel to the light incident surface and having a base angle in the range of greater than 30 degrees and less than 50 degrees. Item 4. The light guide plate according to Item 1.   Each of the plurality of third optical elements is an isosceles trapezoid whose cross-sectional shape cut parallel to the light incident surface has a base angle in the range of greater than 20 degrees and less than 45 degrees. Item 4. The light guide plate according to Item 1.   4. The light guide plate according to claim 1, wherein each of the plurality of third optical elements is a protrusion or a groove.   The plurality of third optical elements extend from the light incident surface to a position within a range of 4 mm or more and 8 mm or less in a direction orthogonal to the light incident surface. The light guide plate according to item.   When the first and second main surfaces are projected onto a plane orthogonal to the light incident surface in a target region up to a position 3 mm away from the light incident surface, the plurality of first regions relative to the projected area of the target region. The arithmetic average value of the percentage of the projected area of the optical element and the percentage of the projected area of the plurality of third optical elements with respect to the projected area of the target region is in the range of 10% to 60%. The light guide plate according to claim 5.   Each of the plurality of second optical elements has a cross section cut perpendicularly to the light incident surface, and a first inclined surface that intersects the light incident surface with a normal line toward the inside of the base, and a first surface that faces the first inclined surface. The angle formed by the first inclined surface and the normal line of the light incident surface is greater than 0.5 degrees and less than 5 degrees, and the second inclined surface is formed by the normal line of the light incident surface. The light guide plate according to any one of claims 1 to 6, characterized in that the range is greater than 50 degrees and less than 80 degrees.   Each of the plurality of first optical elements is an isosceles triangle having a cross-sectional shape cut parallel to the light incident surface and having an apex angle in the range of greater than 90 degrees and less than 140 degrees. Item 8. The light guide plate according to any one of Items 1 to 7.   The plurality of first optical elements include a plurality of isosceles triangles having cross-sectional shapes cut parallel to the light incident surface and having different apex angles in a range of greater than 90 degrees and less than 140 degrees. The light guide plate according to claim 1.   The light guide plate according to claim 1, wherein each of the plurality of first optical elements is a protrusion or a groove. A surface light source device for irradiating a liquid crystal display element,
The light guide plate according to any one of claims 1 to 10,
A light source disposed opposite the light incident surface;
A prism sheet arranged such that a principal surface on which a plurality of prism rows are formed faces the first principal surface;
A surface light source device comprising: a reflecting member disposed to face the second main surface. A surface light source device for irradiating a liquid crystal display element,
The light guide plate according to any one of claims 1 to 10,
A light source disposed opposite the light incident surface;
A reflective member disposed to face the first main surface;
A surface light source device, comprising: a prism sheet arranged such that a main surface on which a plurality of prism rows are formed faces the second main surface.   The plurality of third optical elements extend from the light incident surface to a position within 4 mm in a direction toward the display area beyond a position corresponding to the end of the display area of the liquid crystal display element on the light incident surface side. The surface light source device according to claim 11, wherein the surface light source device is disposed in a region of the surface light source.   When the first and second main surfaces are projected onto a plane orthogonal to the light incident surface in a target region up to a position 3 mm away from the light incident surface, the plurality of first regions relative to the projected area of the target region. The arithmetic average value of the percentage of the projected area of the optical element and the percentage of the projected area of the plurality of third optical elements with respect to the projected area of the target region is in the range of 10% to 60%. The surface light source device according to claim 13.

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