JP2013161743A - Planar light source device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an edge light type planar light source device capable of attaining a balanced light emission distribution and raising use efficiency of light of a primary light source in a wide angle range in the vicinity of a normal direction of a light-emitting surface and raising display performance of a display device.SOLUTION: In a planar light source device, a primary light source 1 are arranged to be respectively opposite to two light-incident end faces 31 made by two opposite side end faces of a light guide 3. A light polarizing element 4 is formed by making a plurality of prism rows, wherein a cross section is formed by symmetrical prism surfaces on a light-incident surface, arranged in parallel with each other. An 80% full width on a luminance distribution of light emitted from a light-emitting surface of the light polarizing element 4 is 20° or more. A difference between a 20% full width and the 80% full width on the luminance distribution of light emitted from the light-emitting surface of the light polarizing element 4 is smaller than 24°.

Description

  The present invention relates to an edge light type surface light source device that constitutes a liquid crystal display device used as a display unit in a monitor, a television, or the like.

  2. Description of the Related Art In recent years, color liquid crystal display devices have been widely used in various fields as display units for mobile phones, personal digital assistants, monitors for notebook computers and personal computers, and televisions. In particular, monitors and televisions are rapidly spreading as display devices replacing conventional cathode ray tubes.

  The liquid crystal display device basically includes a backlight unit and a liquid crystal display element unit. As the backlight unit, that is, the surface light source device, there are a direct light type device in which a light source is disposed directly under a liquid crystal display element unit, and an edge light type device in which a light source is disposed so as to face a side end surface of a light guide. From the viewpoint of making the display device compact, the edge light system is preferable. In the edge light type surface light source device, the primary light source is disposed adjacent to the side end surface of the plate-shaped light guide, and the light deflection element is disposed on the light emitting surface which is one main surface of the plate-shaped light guide. The light emitted from the light guide light exit surface enters the light incident surface that is one main surface of the light deflection element and exits from the light exit surface that is the other main surface.

  Japanese Laid-Open Patent Publication No. 2003-59321 (Patent Document 1) discloses a surface light source device using a prism sheet having a microprism with an apex angle of 65 to 75 ° as a light deflection element. In this surface light source device, light incident from one side end face of the light guide is emitted from the light exit face and directed in the normal direction by the light deflection element, and primary light sources are disposed on both end faces of the light guide. Is not particularly considered.

  By the way, in a liquid crystal display device used for a relatively large device such as a monitor or a television, in order to secure a light amount, in the edge light type surface light source device, a primary light source is disposed adjacent to both left and right end surfaces of the light guide. There is.

  Japanese Patent No. 4544517 (Patent Document 2) discloses a surface light source device in which a primary light source is disposed adjacent to both left and right end faces of a light guide.

JP 2003-59321 A Japanese Patent No. 4544517

  In a surface light source device in which a primary light source is disposed adjacent to left and right side end surfaces on opposite sides of a light guide, when only the primary light source adjacent to one side end surface of the light guide is turned on, a light deflection element is not necessarily provided. It is not necessary that the luminance distribution peak in the normal direction of the light exit surface. When primary light source light is incident only from one end face of the light guide, the primary light source light is incident from both end faces even if the luminance distribution peak angle of the light emitted from the light deflection element is deviated from the normal direction of the light exit surface. It is sufficient that the light emitted from the light deflection element is balanced when the light is deflected. Here, the fact that the light is balanced means that in the outgoing light luminance distribution, there is a substantially peak angle in the direction of the light exit surface normal, and the widest possible angular range in the vicinity of the direction of the light exit surface normal. It means high brightness.

  The surface light source device described in Patent Document 2 is for a liquid crystal display device suitable for observing from two or more directions, and the emitted light luminance distribution from the light deflection element peaks in two or more directions. have.

  Accordingly, an object of the present invention is to obtain a balanced distribution of emitted light in an edge light type surface light source device that is incident on both end faces of a light guide, and thereby primary in a wide angular range in the vicinity of the light exit surface normal direction. An object of the present invention is to provide a surface light source device that makes it possible to increase the utilization efficiency of light source light and enhance the display performance of the display device.

That is, the surface light source device of the present invention is
A primary light source, a light guide that allows light emitted from the primary light source to enter from a light incident end surface, guides the incident light, and emits the light from a light exit surface, and is disposed adjacent to the light exit surface of the light guide A surface light source device comprising:
The primary light source is disposed so as to face the two light incident end faces composed of two side end faces facing each other of the light guide,
The light deflection element includes a plurality of prism surfaces whose cross-sectional shapes orthogonal to both the light incident end surface and the light exit surface are symmetric to a light incident surface on which light emitted from the light guide is incident. Are arranged in parallel with each other,
The 80% full width, which is an angular range having a luminance value of 80% or more with respect to the peak luminance value in the luminance distribution of light emitted from the light exiting surface located on the opposite side of the light guide of the light deflection element, is 20 degrees or more. ,
The difference between the 20% full width, which is an angle range having a luminance value of 20% or more with respect to the peak luminance value in the luminance distribution of the light emitted from the light exit surface of the light deflection element, and the 80% full width is smaller than 24 degrees. Features.

  In one aspect of the present invention, when only one of the primary light sources is turned on, a direction indicating a peak luminance in a luminance distribution of light emitted from the light exit surface of the light deflection element is the light deflection element. Is inclined 5 to 10 degrees with respect to the normal direction of the light exit surface. In one aspect of the present invention, when the height of the prism row of the light deflection element is h and the pitch of the prism row is P, h / P is in the range of 0.89 to 0.95.

  According to the present invention, the light emitted from the primary light source disposed opposite to the two light incident end faces of the light guide is incident on the light incident end face, and the light emitted from the light deflecting element is the light exit surface of the light deflecting element. Since there is a substantial luminance peak in the normal direction of the light source and high brightness is maintained in a wide angular range in the vicinity of the normal direction, and the luminance is drastically reduced at angles beyond the angular range, the light exit surface normal direction It is possible to increase the use efficiency of the primary light source light in a wide angle range in the vicinity of and to improve the display performance of the display device.

It is a typical perspective view which shows embodiment of the surface light source device by this invention. It is explanatory drawing of the cross-sectional shape of the prism row | line | column in embodiment of the optical deflection | deviation element of the surface light source device by this invention. It is a figure which shows the outgoing light luminous intensity distribution of the light guide in the embodiment of the surface light source device by this invention depending on the outgoing angle. It is a figure which shows the cross-sectional shape of the prism row | line | column of the light deflection | deviation element in Example 1 of this invention. It is a figure which shows the cross-sectional shape of the prism row | line | column of the optical deflection | deviation element in Example 3 of this invention. It is a figure which shows the cross-sectional shape of the prism row | line | column of the light deflection | deviation element in the comparative example 1 of this invention. It is a figure which shows the cross-sectional shape of the prism row | line | column of the light deflection | deviation element in the comparative example 2 of this invention. It is a figure which shows the cross-sectional shape of the prism row | line | column of the optical deflection | deviation element in Example 3 of this invention. It is a figure which shows the cross-sectional shape of the light guide in embodiment of the surface light source device by this invention. It is a figure which shows 80% full width, full width at half maximum, and 20% full width in an emitted light distribution. It is a figure which shows the emitted light distribution at the time of the primary light source light incidence to the one side end surface of the light guide in the Example and comparative example of this invention. It is a figure which shows the emitted light distribution at the time of the primary light source light incidence to the both-sides end surface of the light guide in the Example and comparative example of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic perspective view showing one embodiment of a surface light source device according to the present invention. The light guide 3 is arranged in parallel with the XY plane and has a rectangular plate shape as a whole. The light guide 3 has four side end faces, and a pair of side end faces parallel to the YZ plane is a light incident end face 31. The primary light source 1 is disposed so as to face the light incident end face 31, and light emitted from the primary light source 1 enters the light incident end face 31 and is introduced into the light guide 3. In FIG. 1, only one of the light incident end faces 31 formed of a pair of side end faces parallel to the YZ plane appears, and the other light incident end face does not appear. Similarly, the primary light source arranged facing the other light incident end face does not appear.

  One surface substantially orthogonal to the light incident end face 31 of the light guide 3 is used as a light exit surface 33, the light deflection element 4 and the light diffusion element 6 are disposed on the light exit surface 33 of the light guide 3, and the light guide The light reflecting element 5 is disposed opposite to the back surface 34 on the side opposite to the light emitting surface 33 of FIG.

  Two main surfaces that are substantially orthogonal to the light incident end surface 31 of the light guide 3 are respectively positioned substantially parallel to the XY plane, and one of the surfaces (the upper surface in the drawing) serves as the light emitting surface 33. At least one of the light emitting surface 33 and the back surface 34 located on the opposite side thereof has a directional light emitting function portion formed of a rough surface, a prism array, a lenticular lens array, a V-shaped groove, and the like. By providing a directional light emitting function unit composed of lens surfaces in which lens rows are formed in parallel, the light incident on the light incident end surface 31 is guided through the light guide 3 while the light incident end surface 31 is exposed to the light incident end surface. In the outgoing light distribution in the plane (XZ plane) orthogonal to both 31 and the light emitting surface 33, light having directivity is emitted. If the angle formed by the direction of the peak of the emitted light distribution in the XZ plane and the light emitting surface 33 is a, this angle a is preferably 10 to 40 degrees.

  In the present invention, light diffusing fine particles are mixed and dispersed in the light guide instead of or in combination with the light emitting surface 33 or the back surface 34 as described above. What provided the directional light emission function may be used. Further, the light guide 3 is not limited to a substantially parallel plate shape (that is, the XZ cross-sectional shape is rectangular) as shown in FIG. 1, but has various XZ cross-sectional shapes such as a ship shape. Can be used.

  The light guide 3 of the present invention can be composed of a synthetic resin having a high light transmittance. Examples of such synthetic resins include methacrylic resins, acrylic resins, polycarbonate resins, polyester resins, and vinyl chloride resins. In particular, methacrylic resins are optimal because of their high light transmittance, heat resistance, mechanical properties, and molding processability. Such a methacrylic resin is a resin mainly composed of methyl methacrylate, and preferably has a methyl methacrylate content of 80% by weight or more. When the surface structure of the rough surface of the light guide 3 is formed, the transparent synthetic resin plate may be formed by hot pressing using a mold member having a desired surface structure, screen printing, extrusion molding, You may form by injection molding etc. The structural surface can also be formed using heat or a photocurable resin. Furthermore, on a transparent substrate such as a polyester film, acrylic resin, polycarbonate resin, vinyl chloride resin, polymethacrylamide resin, or other transparent substrate or rough surface structure made of an active energy ray curable resin. May be formed on the surface, or such a sheet may be bonded and integrated on a separate transparent substrate by a method such as adhesion or fusion. As the active energy ray-curable resin, polyfunctional (meth) acrylic compounds, vinyl compounds, (meth) acrylic acid esters, allyl compounds, (meth) acrylic acid metal salts, and the like can be used.

  FIG. 2 is an explanatory diagram of the cross-sectional shape of the prism row in the light deflection element 4. FIG. 2 corresponds to the XZ section in FIG. The light deflection element 4 has one of the main surfaces as a light incident surface 41 and the other as a light output surface 42. A large number of prism rows extending in a direction perpendicular to the paper surface of FIG. 2 (Y direction) are arranged in parallel on the light incident surface 41, and each prism row is composed of a first prism surface 44 and a second prism surface 45. It consists of two prism surfaces. The second prism surface 45 is obtained by inverting the first prism surface 44 with a line in the normal direction (Z direction: vertical direction in FIG. 2) of the light exit surface 42 as a symmetric line. It has a shape. In a monitor or television, a primary light source may be disposed adjacent to the left and right end faces of the light guide to secure the amount of light. In this case, in order to efficiently emit light from the surface light source device and thus the liquid crystal display device, it is preferable that the light deflection element has a symmetrical prism array. The first prism surface 44 and the second prism surface 45 are substantially symmetric. Here, the term “substantially symmetrical” includes not only the case of being completely left-right symmetric but also the case of being considered substantially left-right symmetric. Here, “substantially left-right symmetric” means within a range where only a change in light emission that can be regarded as equivalent to that in actual use occurs even when the left-right inversion is used.

  The arrangement pitch P of the prism rows is not particularly limited, but is preferably about 10 to 100 μm. However, a value that can avoid moiré with the liquid crystal panel (liquid crystal display element) may be selected.

  In the embodiment shown in FIG. 2, each of the first prism surface 44 and the second prism surface 45 has an XZ cross-sectional shape formed by one arc. However, in the present invention, each of the two prism surfaces of each prism row need not be the only arc shape in the XZ cross-sectional shape, and may be, for example, a linear shape or a curved shape other than the arc. The shape which connected 2 or more of the straight line or the curve may be sufficient.

  An angle range having a luminance value of 80% or more with respect to the peak luminance value in the luminance distribution of light emitted from the light exit surface 42 (80% full width: see FIG. 10: the unit of angle is “degree” in FIG. 10) is 20 degrees. The difference between the angular range (20% full width: see FIG. 10) having a luminance value of 20% or more with respect to the peak luminance value in the luminance distribution of the light emitted from the light exit surface 42 is 24 degrees or less. Thus, the brightness can be rapidly reduced at an angle away from the normal direction without causing a sharp brightness change in the direction of the normal line of the light exit surface 42 and in a wide angle range in the vicinity thereof. Thereby, the utilization efficiency of the primary light source light is enhanced in the normal direction of the light exit surface and in the wide angular range in the vicinity thereof, and a display device having excellent contrast in the wide angular range when an image is observed through the liquid crystal panel can be provided.

  In order to set the 80% full width of the luminance distribution of the light emitted from the light exit surface 42 to 20 degrees or more and the difference between the 20% full width and the 80% full width to 24 degrees or less, When only the primary light source 1 is turned on, it is preferable that the direction indicating the peak luminance in the luminance distribution of the light emitted from the light exit surface 42 is inclined (shifted) by 5 degrees to 10 degrees with respect to the normal direction. If the deviation from the normal direction of the peak luminance direction of the light emitted from the light exit surface 42 is less than 5 degrees, the light tends to be concentrated too much in the normal direction, and the luminance change in the vicinity of the normal direction tends to increase. The 80% full width tends to be smaller than 20 degrees. Conversely, if the deviation from the normal direction of the emitted light peak luminance direction is larger than 10 degrees, the luminance in the vicinity of the normal direction tends to be lower than the luminance in the direction far away from the normal direction. The brightness tends to be lower than the surrounding area.

  Further, when only one of the primary light sources 1 is turned on in the light deflection element 4, the direction showing the peak luminance in the luminance distribution of the light emitted from the light exit surface 42 is inclined 5 to 10 degrees with respect to the normal direction. The ratio h / P of the prism row height h to the prism row arrangement pitch P of the light deflection element 4 is preferably in the range of 0.89 to 0.95. When the ratio h / P is smaller than 0.89, the deviation from the normal direction of the peak luminance direction in the luminance distribution of the light emitted from the light emitting surface 42 when only one of the primary light sources 1 is turned on is smaller than 5 degrees. It tends to become. Conversely, if the ratio h / P is greater than 0.95, the deviation of the peak luminance direction from the normal direction in the luminance distribution of the light emitted from the light emitting surface 42 when only one of the primary light sources 1 is turned on is 10%. It tends to be larger than the degree.

  As the primary light source 1, for example, a point light source such as an LED light source, a halogen lamp, or a metal halide lamp, or a linear light source extending in the Y direction such as a fluorescent lamp or a cold cathode tube can be used. A plurality of point light sources may be arranged in the Y direction. If necessary, a light source reflector may be installed so as to surround the primary light source. This reflects light that cannot enter the light guide 3 out of the light emitted from the primary light source toward the light guide. As a material, for example, a plastic film having a metal-deposited reflective layer on the surface can be used. A reflection member similar to such a light source reflector may be attached to a side end face other than the side end face 31 that is the light incident end face of the light guide 3.

  The light reflecting element 5 is disposed so as to face the back surface 34 on the side opposite to the light emitting surface 33 of the light guide 3. As the light reflecting element 5, for example, a plastic sheet having a metal vapor deposition reflecting layer on the surface can be used. In the present invention, it is also possible to use a light reflecting layer or the like formed on the back surface 34 of the light guide 3 by metal vapor deposition or the like, instead of the reflecting sheet, as the light reflecting element 5. As a result, the light leaking from the light guide 3 can be returned again into the light guide, and the amount of light emitted from the primary light source can be used effectively.

  The light diffusing element 6 may be integrated with the light deflecting element 4 on the light exiting surface side of the light deflecting element 4, or the light diffusing element 6 may be individually placed on the light exiting surface of the light deflecting element 4. good. When the light diffusing element 6 is individually mounted, the surface adjacent to the light deflecting element 4 of the light diffusing element 6, that is, the incident surface is provided with an uneven structure to prevent sticking with the light deflecting element 4. It is preferable to give. Similarly, it is necessary to consider sticking between the light diffusing element 6 and the liquid crystal display element disposed thereon, and it is preferable to provide a concavo-convex structure on the light emitting surface. When this uneven structure is provided only for the purpose of preventing sticking, the average inclination angle according to ISO 4287 / 1-1984 described in paragraphs [0019] to [0021] of the specification of Japanese Patent Application Laid-Open No. 2010-192433. However, it is preferable to set it as a structure which becomes 0.7 degree | times or more, More preferably, it is 1 degree | times or more, More preferably, it is 1.5 degree | times or more. The light diffusing element 6 may be omitted.

  A liquid crystal display device is configured by disposing a liquid crystal display element on the light emitting surface of the surface light source device as described above. The liquid crystal display device is observed by an observer through the liquid crystal display element from above in FIG.

  Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples.

  In addition, the preparation method of the light guide used in the following examples and comparative examples and the measurement method of each physical property are shown below.

[Production of light guide]
A lens array 331 as shown in FIG. 9 is formed on the processed surface of a NiP plating block (molding die material) having an effective portion of 285 mm (Y-direction dimension) × 480 mm (X-direction dimension) and a thickness of 3 mm. Cutting was performed so as to form a transfer surface for transfer forming. The lens array 331 has a width of 50 μm (dimension in the X direction), a height of 18.4 μm (dimension in the Z direction), a radius of curvature R of the tip portion of 16 μm, and an apex angle in the XZ cross section perpendicular to the extending direction of the lens array 331. It was a 90 degree triangular shape. The transfer area of the block has a corresponding inverted shape.

  As described above, a first transfer surface forming mold (molding mold member) was obtained.

  The effective surface 285 mm (Y direction dimension) x 480 mm (X direction dimension) and 3 mm thickness of another NiP plating block (molding die material) with a mirror-finished machining surface is projected as shown in FIG. Cutting was performed using a triangular diamond tool having an XZ cross-sectional shape with a radius of curvature R16 μm at the tip portion and an apex angle of 100 degrees so that a transfer region for transferring and forming the structure 341 was formed. The convex structure 341 has a height of 8.2 μm, a length (dimension in the Y direction) of 170 μm, an XZ cross-sectional shape having a radius of curvature R of 16 μm at the tip, and a vertex angle of 100 degrees, and a width (dimension in the X direction). Was 21 μm, and the height gradually increased along the Y direction, and then the height gradually decreased. The average inclination angle of the region where the height gradually increases and the region where the height gradually decreases is 4.57 degrees. The arrangement interval of the convex structures 341 was 170 μm in the Y direction and 40 μm in the X direction. In addition, the area occupancy of the convex structure 45 on the light exit surface was set to 39%. Next, a transfer surface for transferring and forming the lens array was formed in the same manner as the transfer surface for transferring and forming the lens array 331 of the first transfer surface forming mold. The transfer area of the block has a corresponding inverted shape.

  As described above, a second transfer surface forming mold (molding mold member) was obtained.

  The first and second transfer surface forming molds were incorporated into a molding apparatus, and press molding was performed to obtain a light guide 3. As the molding material, an acrylic resin (manufactured by Mitsubishi Rayon Co., Ltd., L001) was used.

  A total of 108 LEDs (E1S62-YWOS7-07 manufactured by Toyoda Gosei Co., Ltd.) were arranged on both sides of the light guide so as to face the light incident end face 31 at equal intervals along the long side. . Further, a light scattering reflection sheet (E6SP manufactured by Toray Industries, Inc.) was disposed as a light reflecting element so as to face the back surface 34 of the light guide. The result of measuring the light intensity distribution of the light guide is shown in FIG. 3 (the unit of the angle is “degree”, and the light intensity is indicated by a relative value. Note that the angle 0 is a method of the light emitting surface 33 of the light guide. Line direction).

[Measurement of luminous intensity distribution of light emitted from light guide]
In the configuration in which the light deflecting element 4 and the light diffusing element 6 are removed from the configuration shown in FIG. 1, the primary light source 1 is turned on, and black paper having a 3 mmφ pinhole is pinned on the light emitting surface 33 of the light guide 3. The hole was fixed so as to be located at the center of the light guide. The luminous intensity distribution of the emitted light was measured with a luminance meter while the normal direction of the light emitting surface 33, that is, the Z direction was set to 0 °, and the XZ plane was tilted at 1 ° intervals within a range of + 85 ° to −85 °.

[Measurement of luminance distribution of light emitted from surface light source device, and specification of peak luminance, angle indicating peak luminance, full width at half maximum, full width at 80% and full width at 20%]
In the configuration shown in FIG. 1, all the primary light sources 1 on both sides were turned on, the viewing angle of the luminance meter was set to 1 degree, and the measurement position was adjusted to the center of the surface light source device. The luminance distribution of the emitted light was measured with a luminance meter while tilting at an interval of 1 ° within the range of + 45 ° to −45 °, with the normal direction of the light exit surface 42 of the light deflection element 4, that is, the Z direction being 0 degree. Based on this, the peak luminance, the full width at half maximum of the luminance distribution (the spread angle of the distribution of luminance values greater than or equal to 1/2 of the peak luminance value), the full width of 80% of the luminance distribution (the distribution of luminance values greater than 80% of the peak luminance value) (Broadening angle) and 20% full width of the luminance distribution (broadening angle of the luminance value distribution of 20% or more of the peak luminance value). Similarly, the luminance distribution of the emitted light when only the primary light source on one side was turned on was measured, and based on this, the angle (peak angle) indicating the peak luminance was obtained.

Example 1:
A surface light source device (however, no light diffusing element is used) belonging to the embodiment of FIG. 1 was produced as follows.

  First, the emitted light luminous intensity distribution shown in FIG. 3 (the unit of the angle is “degree”, and the luminous intensity is represented by a relative value. Note that the angle 0 is the normal direction of the light emitting surface 33 of the light guide). The light guide 3 having On the light emitting surface 33 of the light guide, the light deflection element 4 manufactured using an acrylic ultraviolet curable resin having a refractive index of 1.506 was placed. The light deflection element 4 is a prism sheet in which a large number of prism rows are formed on the light incident surface. A prism row was formed on a surface of a polyester film having a thickness of 125 μm in which fine irregularities having a center line average roughness Ra = 0.4 were previously formed on one surface, and no fine irregularities were formed, to prepare a prism sheet. The cross-sectional shape of each prism row is a part of an arc having a radius of curvature r = 300 μm with the coordinates of the center point being (x, z) = (− 248.78, 167.66) when the coordinates of the prism apex are the origin. And a part of an arc having a radius of curvature r = 300 μm with the coordinates of the center point being (x, z) = (248.78, 167.66), and an array of prism rows The pitch P is 50 μm, and the height of the prism row is 45 μm (see FIG. 4: the unit of the numerical value of the length in FIG. 4 is “μm”). This prism sheet was placed so that the light incident surface 41 formed of the prism row forming surface faces the light emitting surface 33 of the light guide 3. Furthermore, the primary light source 1 and the light reflecting element 5 were arranged to obtain a surface light source device.

  The luminance distribution of emitted light when all the primary light sources on both sides of the surface light source device are turned on is measured, and based on the measured luminance distribution, the peak luminance ratio, the full width at half maximum of the luminance distribution, and the luminance based on Comparative Example 1 described later are used. An 80% full width of the distribution and a 20% full width of the luminance distribution were obtained. Moreover, the luminance distribution of the emitted light when only the primary light source on one side was turned on was measured, and the peak angle was obtained based on this. The results are shown in FIG. 11 and FIG. 12 (in FIG. 11 and FIG. 12, the unit of the numerical value of the angle is “degree”) and Table 1.

Example 2:
The cross-sectional shape of each prism row is a part of an arc having a radius of curvature r = 300 μm where the coordinates of the center point are (x, z) = (− 251.32, 163.83) when the coordinates of the prism apex are the origin. And a part of an arc having a radius of curvature r = 300 μm where the coordinates of the center point are (x, z) = (251.32, 163.83), and the height of the prism row A surface light source device was obtained in the same manner as in Example 1 except that a prism sheet having a thickness of 47 μm was used.

  In the same manner as in Example 1, the emitted light luminance distribution when all the primary light sources on both sides of the surface light source device are turned on is measured, and based on this, the peak luminance ratio when Comparative Example 1 described later is used as a reference The full width at half maximum of the luminance distribution, the full width of 80% of the luminance distribution, and the full width of 20% of the luminance distribution were obtained. Moreover, the luminance distribution of the emitted light when only the primary light source on one side was turned on was measured, and the peak angle was obtained based on this. The results are shown in FIGS. 11 and 12 and Table 1.

Example 3:
The cross-sectional shape of each prism row is 32.56 degrees with respect to the normal direction of the light emitting surface 42 up to 8 μm in the pitch direction when the coordinate of the prism apex is the origin as shown in FIG. In the direction from 8 μm to 16 μm, the angle formed with the normal direction of the light output surface 42 is 29.59 degrees, and in the pitch direction from 16 μm to 25 μm, the angle formed with the normal direction of the light output surface 42 is 26.09 degrees. A surface light source device was obtained in the same manner as in Example 1 except that the left and right symmetrical shapes were used. In FIG. 5, the unit of the numerical value of the length is “μm”, and the unit of the numerical value of the angle is “degree”.

  In the same manner as in Example 1, the emitted light luminance distribution when all the primary light sources on both sides of the surface light source device are turned on is measured, and based on this, the peak luminance ratio when Comparative Example 1 described later is used as a reference The full width at half maximum of the luminance distribution, the full width of 80% of the luminance distribution, and the full width of 20% of the luminance distribution were obtained. Moreover, the luminance distribution of the emitted light when only the primary light source on one side was turned on was measured, and the peak angle was obtained based on this. The results are shown in FIGS. 11 and 12 and Table 1.

Comparative Example 1:
Example 1 except that the cross-sectional shape of each prism row is a symmetrical shape in which the angle formed with the normal direction of the light exit surface 42 is a straight line of 32.7 degrees as shown in FIG. In the same manner, a surface light source device was obtained. In FIG. 6, the unit of the numerical value of the length is “μm”, and the unit of the numerical value of the angle is “degree”.

  In the same manner as in Example 1, the emitted light luminance distribution when all the primary light sources on both sides of the surface light source device are turned on is measured. Based on the measured luminance distribution, the obtained peak luminance is set to 1.000. The full width at half maximum, 80% full width of the luminance distribution, and 20% full width of the luminance distribution were obtained. Moreover, the luminance distribution of the emitted light when only the primary light source on one side was turned on was measured, and the peak angle was obtained based on this. The results are shown in FIGS. 11 and 12 and Table 1.

Comparative Example 2:
The cross-sectional shape of each prism row is a part of an arc having a radius of curvature r = 300 μm with the coordinates of the center point being (x, z) = (− 247.41, 169.67) when the coordinates of the prism vertex are the origin. And the coordinate of the center point is (x, z) = (247.41, 169.67), and has a symmetrical shape composed of a part of an arc having a radius of curvature r = 300 μm, and the height of the prism row Was 44 μm (see FIG. 7: the unit of the numerical value of length in FIG. 7 is “μm”), a surface light source device was obtained in the same manner as in Example 1.

  In the same manner as in Example 1, the luminance distribution of emitted light when all the primary light sources on both sides of the surface light source device were turned on was measured, and based on this, the peak luminance ratio and luminance when Comparative Example 1 was used as a reference The full width at half maximum of the distribution, the full width of 80% of the luminance distribution, and the full width of 20% of the luminance distribution were obtained. Moreover, the luminance distribution of the emitted light when only the primary light source on one side was turned on was measured, and the peak angle was obtained based on this. The results are shown in FIGS. 11 and 12 and Table 1.

Comparative Example 3:
The cross-sectional shape of each prism row is a part of an arc having a radius of curvature r = 300 μm with the coordinates of the center point being (x, z) = (− 254.66, 158.58) when the coordinates of the prism apex are the origin. And a part of an arc having a radius of curvature r = 300 μm where the coordinates of the center point are (x, z) = (254.66, 158.58), and the height of the prism row A surface light source device was obtained in the same manner as in Example 1 except that a prism sheet having a thickness of 50 μm (see FIG. 8: the unit of the numerical value of length in FIG. 8 is “μm”) was used.

  In the same manner as in Example 1, the luminance distribution of emitted light when all the primary light sources on both sides of the surface light source device were turned on was measured, and based on this, the peak luminance ratio and luminance when Comparative Example 1 was used as a reference The full width at half maximum of the distribution, the full width of 80% of the luminance distribution, and the full width of 20% of the luminance distribution were obtained. Moreover, the luminance distribution of the emitted light when only the primary light source on one side was turned on was measured, and the peak angle was obtained based on this. The results are shown in FIGS. 11 and 12 and Table 1.

DESCRIPTION OF SYMBOLS 1 Primary light source 3 Light guide 4 Light deflection element 5 Light reflection element 6 Light diffusion element 31 Light incident end surface
33 Light exit surface 331 Lens array 34 Back surface 341 Convex structure 41 Light incident surface 42 Light exit surface 44 First prism surface 45 Second prism surface

Claims (3)

A primary light source, a light guide that allows light emitted from the primary light source to enter from a light incident end surface, guides the incident light, and emits the light from a light exit surface, and is disposed adjacent to the light exit surface of the light guide A surface light source device comprising:
The primary light source is disposed so as to face the two light incident end faces composed of two side end faces facing each other of the light guide,
The light deflection element includes a plurality of prism surfaces whose cross-sectional shapes orthogonal to both the light incident end surface and the light exit surface are symmetric to a light incident surface on which light emitted from the light guide is incident. Are arranged in parallel with each other,
The 80% full width, which is an angular range having a luminance value of 80% or more with respect to the peak luminance value in the luminance distribution of light emitted from the light exiting surface located on the opposite side of the light guide of the light deflection element, is 20 degrees or more. ,
The difference between the 20% full width, which is an angle range having a luminance value of 20% or more with respect to the peak luminance value in the luminance distribution of the light emitted from the light exit surface of the light deflection element, and the 80% full width is smaller than 24 degrees. A characteristic surface light source device. The surface light source device according to claim 1,
When only one of the primary light sources is turned on, the direction indicating the peak luminance in the luminance distribution of light emitted from the light exit surface of the light deflection element is the normal direction of the light exit surface of the light deflection element A surface light source device that is inclined by 5 to 10 degrees with respect to the surface.   2. The height of the prism row of the light deflection element is h, and the pitch of the prism row is P, h / P is in the range of 0.89 to 0.95. Or the surface light source device of 2.