JP2017037829A - Surface light source apparatus and display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface light source apparatus capable of generating a luminance peak in a direction other than a front direction, with a simple configuration.SOLUTION: A surface light source apparatus 20 comprises: a light guide plate 30; a light source 24; and an optical sheet 60. A rear surface 32 of the light guide plate includes a plurality of inclined surfaces 37 arranged in a first direction d. The optical sheet includes: a body part 65; and a plurality of unit prisms 65 provided on a light guide plate-side of the body part. Each unit prism includes: a first prism surface that acts as an incidence surface of light emitted from a light emission surface of the light guide plate; and a second prism surface that totally reflects the light passing through the first prism surface and incident in the unit prism. In a luminance angle distribution on an opposite surface of the optical sheet to the light guide plate in each direction in a plane parallel to the first direction and parallel to a normal direction of the optical sheet, a direction in which a luminance peak is obtained is inclined with respect to the normal direction of the optical sheet.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an edge light type surface light source device, and more particularly to a surface light source device having a luminance peak in a direction other than the front direction. The present invention also relates to a display device including the surface light source device.

  2. Description of the Related Art A surface light source device having a light emitting surface that emits light in a planar shape is widely used as a backlight that is incorporated in, for example, a liquid crystal display device and illuminates a liquid crystal display panel from the back side (for example, Patent Document 1). Surface light source devices for liquid crystal display devices can be broadly classified into a direct type in which a light source is arranged directly under an optical member and an edge light type in which a light source is arranged on a side of the optical member (also referred to as a side light type). being classified. The edge light type surface light source device is superior to the direct type surface light source device in that the thickness can be reduced.

  In the edge light type surface light source device disclosed in Patent Document 1, the light guide plate, the light deflecting element disposed to face the light output surface of the light guide plate, and the one side surface of the light guide plate are disposed. And a light source. The light guide plate distributes light from the light source so that the amount of light along the light guide direction is uniform. The incident side surface facing the light guide plate side of the light deflection element has a plurality of inclined surfaces arranged in a direction parallel to the light guide direction of the light guide plate, and is opposite to the light guide plate side of the light deflection element; The outgoing side surface has a plurality of lens surfaces arranged in a direction parallel to the light guide direction of the light guide plate. In this light deflection element, the light emission direction is controlled by a combination of refraction at the incident side and refraction at the emission side.

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Nowadays, the edge light side liquid crystal display device has been applied to various devices. In many applications, it is ideal that the liquid crystal display device has a luminance peak in the normal direction of the display surface. However, depending on the application, it may be preferable that a luminance peak occurs in a direction inclined from the normal direction of the display surface. For example, a liquid crystal display device applied to an automobile center console is observed from an oblique upper side by an automobile driver.
Therefore, in this liquid crystal display device, it is preferable that the luminance peak appears obliquely upward rather than in the front direction.

  According to the liquid crystal display device disclosed in Patent Literature 1, a luminance peak can be generated in a direction other than the front direction by the configuration of the incident side surface and the output side surface of the light deflection element. However, in Patent Document 1, the light emission direction is controlled by a combination of refraction at the incident side surface of the light deflection element and refraction at the emission side surface of the light deflection element. This complicates the configuration of the optical deflection element and increases the design burden.

  The present invention has been made in consideration of the above points, and an object of the present invention is to provide a surface light source device capable of generating a luminance peak in a direction other than the front direction with a simple configuration.

A first surface light source device according to the present invention includes:
A light exit surface; a back surface disposed opposite the light exit surface; and a side surface located between the light exit surface and the back surface, and a portion located on one side in the first direction of the side surfaces. A light guide plate forming a light incident surface;
A light source disposed facing the light incident surface;
An optical sheet disposed to face the light exit surface of the light guide plate,
The back surface of the light guide plate includes a plurality of inclined surfaces arranged in the first direction,
Each inclined surface is inclined with respect to the normal direction of the light guide plate and the first direction so as to approach the light exit surface as it goes from one side to the other side in the first direction,
The optical sheet has a sheet-like main body, and a plurality of unit prisms provided on the light guide plate side of the main body,
The plurality of unit prisms are arranged in a third direction, and each unit prism extends linearly in a direction non-parallel to the third direction,
Each unit prism faces one side in the third direction and faces the other side in the third direction and the first prism surface that forms the incident surface of the light emitted from the light exit surface of the light guide plate A second prism surface that totally reflects light incident on the unit prism through the first prism surface;
In the angular distribution of luminance on the surface opposite to the light guide plate side of the optical sheet in each direction in a plane parallel to the first direction and parallel to the normal direction of the optical sheet, The direction in which the luminance peak is obtained is inclined with respect to the normal direction of the optical sheet.

A second surface light source device according to the present invention comprises:
A light exit surface; a back surface disposed opposite the light exit surface; and a side surface located between the light exit surface and the back surface, and a portion located on one side in the first direction of the side surfaces. A light guide plate forming a light incident surface;
A light source disposed facing the light incident surface;
An optical sheet disposed to face the light exit surface of the light guide plate,
In the angular distribution of luminance on the light exit surface of the light guide plate in each direction within a plane parallel to both the normal direction of the light guide plate and the first direction, the direction in which a luminance peak is obtained is the direction of the light guide plate. The angle θ _aImax1 inclined from the normal direction to the other side along the first direction, and half the luminance peak positioned between the normal direction of the light guide plate and the direction in which the luminance peak is obtained The angle θ _{aIα1 in} which the direction from which the luminance peak is obtained is inclined to the one side along the first direction from the direction in which the luminance peak is obtained _satisfies the following two conditions (1) and (2):
60 ° ≦ θ _aImax1 ≦ 80 ° (1)
5 ° ≦ θ _aIα1 ≦ 25 ° (2)
The optical sheet has a sheet-like main body, and a plurality of unit prisms provided on the light guide plate side of the main body,
The plurality of unit prisms are arranged in a third direction, and each unit prism extends linearly in a direction non-parallel to the third direction,
Each unit prism faces one side in the third direction and faces the other side in the third direction and the first prism surface that forms the incident surface of the light emitted from the light exit surface of the light guide plate A second prism surface that totally reflects light incident on the unit prism through the first prism surface;
In the angular distribution of luminance on the surface opposite to the light guide plate side of the optical sheet in each direction in a plane parallel to the first direction and parallel to the normal direction of the optical sheet, The direction in which the luminance peak is obtained is inclined with respect to the normal direction of the optical sheet.

In the second surface light source device according to the present invention, in the angular distribution of luminance on the light exit surface of the light guide plate in each direction in a plane parallel to the normal direction of the light guide plate and perpendicular to the first direction. The angle θ _aImax2 that the direction in which the luminance peak is obtained is made with respect to the normal direction of the light guide plate, and the luminance that is half of the luminance peak is obtained on both sides of the direction in which the luminance peak is obtained. The average value θ _aIα2 of the angles whose directions are inclined from the direction in which the luminance peak is obtained may _satisfy the following conditions (3) and (4).
θ _aImax2 ≦ 3 ° (3)
12 ° ≦ θ _aIα2 ≦ 27 ° (4)

  1st or 2nd surface light source device by this invention WHEREIN: With the said light guide plate side of the said optical sheet to each direction in the surface parallel to the said 1st direction and parallel to the normal line direction of the said optical sheet In the luminance angular distribution on the opposite surface, the direction in which the luminance peak is obtained may be inclined by 10 ° or more with respect to the normal direction of the optical sheet.

In the first or second surface light source device according to the present invention,
The third direction is inclined upward by 15 ° with respect to the first direction,
In an angular distribution of luminance on a surface opposite to the light guide plate side of the optical sheet in each direction in a plane orthogonal to the first direction and parallel to the normal direction of the optical sheet The direction in which the luminance peak is obtained may be inclined with respect to the normal direction of the optical sheet.

  In the first or second surface light source device according to the present invention, the light guide plate side of the optical sheet in each direction in a plane orthogonal to the first direction and parallel to the normal direction of the optical sheet; In the angular distribution of the luminance on the opposite surface, the direction in which the luminance peak is obtained may be inclined by 10 ° or more with respect to the normal direction of the optical sheet.

  In the first or second surface light source device according to the present invention, a light diffusion layer may be formed on a surface of the optical sheet that is opposite to the light guide plate.

A display device according to the present invention comprises:
One of the first and second surface light source devices according to the present invention described above;
A display panel disposed to face the surface light source device.

  According to the present invention, a luminance peak can be generated in a direction other than the front direction by a surface light source device having a simple configuration.

FIG. 1 is a cross-sectional view illustrating a schematic configuration of a display device and a surface light source device for explaining an embodiment according to the present invention. FIG. 2 is a diagram for explaining the operation of the surface light source device of FIG. FIG. 3 is a top view showing the surface light source device of FIG. 1 from the light emitting surface side. FIG. 4 is a perspective view showing the light guide plate incorporated in the surface light source device of FIG. 1 from the light exit surface side. FIG. 5 is a perspective view showing the light guide plate incorporated in the surface light source device of FIG. 1 from the back side. FIG. 6 is a diagram for explaining the operation of the light guide plate, and is a view showing the light guide plate in a cross section taken along the line VI-VI in FIG. 4. FIG. 7 is a perspective view showing an optical sheet incorporated in the surface light source device of FIG. FIG. 8 is a partial cross-sectional view showing the optical sheet of FIG. 7 in its main cut surface (cross section taken along line VIII-VIII in FIG. 7). FIG. 9 is a diagram for explaining the operation of the optical sheet, and is a partial cross-sectional view showing the surface light source device in the same cross section as FIG. FIG. 10 is a diagram corresponding to FIG. 9 and showing a modification of the optical sheet. FIG. 11 is a graph showing the angular distribution of luminance on the light exit surface of the light guide plate in a plane parallel to both the front direction and the first direction. FIG. 12 is a graph showing the angular distribution of luminance on the light exit surface of the light guide plate in a plane parallel to both the front direction and the second direction. FIG. 13 is a graph showing the angular distribution of luminance on the light exit surface of the optical sheet in a plane parallel to both the front direction and the first direction. FIG. 14 is a diagram illustrating the angular distribution of luminance on the light exit surface of the optical sheet when the bias angle of the optical sheet is 0 °. FIG. 15 is a diagram showing the angular distribution of luminance on the light exit surface of the optical sheet when the bias angle of the optical sheet is 10 °. FIG. 16 is a diagram illustrating the angular distribution of luminance on the light exit surface of the optical sheet when the bias angle of the optical sheet is 20 °. FIG. 17 is a diagram showing the angular distribution of luminance on the light exit surface of the optical sheet when the bias angle of the optical sheet is 30 °. FIG. 18 is a diagram illustrating the angular distribution of luminance on the light exit surface of the optical sheet when the bias angle of the optical sheet is 40 °. FIG. 19 is a cross-sectional view showing a modification of the optical sheet at the main cutting plane.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the drawings attached to the present specification, for the sake of illustration and ease of understanding, the scale, the vertical / horizontal dimension ratio, and the like are appropriately changed and exaggerated from those of the actual product.

  FIGS. 1-19 is a figure for demonstrating one Embodiment by this invention. Among these, FIG. 1 is a cross-sectional view showing a schematic configuration of a liquid crystal display device and a surface light source device, FIG. 2 is a cross-sectional view for explaining the operation of the surface light source device, and FIG. 3 shows the surface light source device. It is a top view. 4 and 5 are perspective views showing the light guide plate included in the surface light source device, and FIG. 6 is a cross-sectional view showing the light guide plate in the main cut surface of the light guide plate. FIG. 7 is a perspective view showing an optical sheet included in the surface light source device, FIG. 8 is a cross-sectional view showing the optical sheet on the main cutting surface of the optical sheet, and FIGS. 9 and 10 show the action of the optical sheet. It is a figure for demonstrating. Moreover, FIGS. 11-18 is a figure which shows an example of the angle distribution of the brightness | luminance on the light emission surface of the light-guide plate of a surface light source device, or the light emission surface of an optical sheet.

  As shown in FIG. 1, the display device 10 includes a liquid crystal display panel 15 and a surface light source device 20 that is disposed on the back side of the liquid crystal display panel 15 and illuminates the liquid crystal display panel 15 in a planar shape from the back side. . The display device 10 has a display surface 11 for displaying an image. The liquid crystal display panel 15 functions as a shutter that controls transmission or blocking of light from the surface light source device 20 for each pixel, and is configured to display an image on the display surface 11.

  The illustrated liquid crystal display panel 15 is disposed between the upper polarizing plate 13 disposed on the light output side, the lower polarizing plate 14 disposed on the light incident side, and the upper polarizing plate 13 and the lower polarizing plate 14. And a liquid crystal layer 12. The polarizing plates 14 and 13 decompose the incident light into two orthogonally polarized components (P wave and S wave) and oscillate in one direction (direction parallel to the transmission axis) (for example, P wave). ) And absorbs a linearly polarized light component (for example, S wave) that vibrates in the other direction (direction parallel to the absorption axis) perpendicular to the one direction.

  An electric field can be applied to the liquid crystal layer 12 for each region where one pixel is formed. Then, the alignment direction of the liquid crystal molecules in the liquid crystal layer 12 changes depending on whether or not an electric field is applied. As an example, the polarization component in a specific direction transmitted through the lower polarizing plate 14 disposed on the light incident side rotates the polarization direction by 90 ° when passing through the liquid crystal layer 12 to which no electric field is applied, The polarization direction is maintained when passing through the liquid crystal layer 12 to which an electric field is applied. In this case, depending on whether or not an electric field is applied to the liquid crystal layer 12, does the polarized light component that vibrates in a specific direction transmitted through the lower polarizing plate 14 further pass through the upper polarizing plate 13 disposed on the light output side of the lower polarizing plate 14? Alternatively, it is possible to control whether the light is absorbed and blocked by the upper polarizing plate 13.

  In this manner, the liquid crystal panel (liquid crystal display unit) 15 can control transmission or blocking of light from the surface light source device 20 for each pixel. The details of the liquid crystal display panel 15 are described in various publicly known documents (for example, “Flat Panel Display Dictionary (supervised by Tatsuo Uchida, Hiraki Uchiike)” published in 2001 by the Industrial Research Council). The detailed description above is omitted.

  Next, the surface light source device 20 will be described. The surface light source device 20 has a light emitting surface 21 that emits light in a planar shape, and is used as a device that illuminates the liquid crystal display panel 15 from the back side in the present embodiment.

  As shown in FIG. 1, the surface light source device 20 is configured as an edge light type surface light source device, and is disposed on the side of the light guide plate 30 and one side (left side in FIG. 1) of the light guide plate 30. And the optical sheet (prism sheet) 60 and the reflection sheet 28 disposed so as to face the light guide plate 30, respectively. In the illustrated example, the optical sheet 60 is disposed facing the liquid crystal display panel 15. The light emitting surface 21 of the surface light source device 20 is defined by the light exit surface 61 of the optical sheet 60.

  In the illustrated example, the light exit surface 31 of the light guide plate 30 has a planar view shape (in FIG. 3, looking down from above), like the display surface 11 of the liquid crystal display device 10 and the light emitting surface 21 of the surface light source device 20. (Viewed shape) is formed in a square shape. As a result, the light guide plate 30 is generally configured as a rectangular parallelepiped member having a pair of main surfaces (the light exit surface 31 and the back surface 32) in which the sides in the thickness direction are smaller than the other sides. A side surface defined between the pair of main surfaces includes four surfaces. Similarly, the optical sheet 60 and the reflection sheet 28 are generally configured as rectangular parallelepiped members having relatively thin sides in the thickness direction than other sides.

The light guide plate 30 includes a light output surface 31 constituted by one main surface on the liquid crystal display panel 15 side, a back surface 32 formed of the other main surface facing the light output surface 31, and a space between the light output surface 31 and the back surface 32. And a side surface extending. One of the two surfaces facing the first direction d ₁ of the side surfaces forms the light incident surface 33. As shown in FIGS. 1 and 3, a light source 24 is provided facing the light incident surface 33. As shown in FIG. 2, the light that has entered the light guide plate 30 from the light incident surface 33 is directed substantially toward the opposite surface 34 that faces the light incident surface 33 along the first direction (light guide direction) d ₁ . comes to be guided in one direction (light guide direction) light guide plate 30 along the d _1. As shown in FIGS. 1 and 2, the optical sheet 60 is disposed so as to face the light exit surface 31 of the light guide plate 30, and the reflection sheet 28 is disposed so as to face the back surface 32 of the light guide plate 30. ing.

  The light source may be configured in various modes such as a fluorescent lamp such as a linear cold cathode tube, a point LED (light emitting diode), an incandescent lamp, and the like. As shown in FIG. 3, the light source 24 in the present embodiment includes a large number of point-like light emitters 25 arranged side by side along the longitudinal direction of the light incident surface 33, specifically, a large number of light emitting diodes (LEDs). ). 4 and 5 show the arrangement positions of a large number of point-like light emitters 25 forming the light source 24. FIG.

  The reflection sheet 28 is a member for reflecting the light leaking from the back surface 32 of the light guide plate 30 so as to enter the light guide plate 30 again. The reflection sheet 28 is composed of a white scattering reflection sheet, a sheet made of a material having a high reflectance such as metal, a sheet containing a thin film (for example, a metal thin film) made of a material having a high reflectance as a surface layer, and the like. obtain. The reflection on the reflection sheet 28 may be regular reflection (specular reflection) or diffuse reflection. When the reflection on the reflection sheet 28 is diffuse reflection, the diffuse reflection may be isotropic diffuse reflection or anisotropic diffuse reflection.

  By the way, in this specification, the “light-emitting side” means that the light source 24, the light guide plate 30, the optical sheet 60, the liquid crystal display panel 15, and the components of the display device 10 are advanced without going back to each other. It is the downstream side (observer side, for example, the upper side of the paper surface in FIG. 1) in the traveling direction of the light emitted and directed to the observer, and the “light incident side” is the light source 24, the light guide plate 30, and the optical sheet 60. It is the upstream side in the traveling direction of the light that proceeds from the liquid crystal display panel 15 and the components of the display device 10 without reversing and exits from the display device 10 toward the observer.

  Further, in the present specification, terms such as “sheet”, “film”, and “plate” are not distinguished from each other only based on the difference in names. Therefore, for example, a “sheet” is a concept including a member that can also be called a film or a plate.

Further, in this specification, the “sheet surface (plate surface, film surface)” corresponds to the planar direction of the target sheet-like member when the target sheet-like member is viewed as a whole and globally. Refers to the surface. In this embodiment, the plate surface of the light guide plate 30, the sheet surface (plate surface) of the base 40 (to be described later) of the light guide plate 30, the sheet surface of the optical sheet 60, the sheet surface of the reflective sheet 28, and the panel of the liquid crystal display panel The surface, the display surface 11 of the display device 10, and the light emitting surface 21 of the surface light source device 20 are parallel to each other. Furthermore, in this specification, the normal line direction of a sheet-like member refers to the normal line direction to the sheet | seat surface of the sheet-like member used as object.
Further, in the present specification, the “front direction” is a normal direction to the light emitting surface 21 of the surface light source device 20, and in this embodiment, the normal to the light emitting surface 21 of the surface light source device 20. The normal direction to the plate surface of the light guide plate 30, the normal direction to the sheet surface of the optical sheet 60, the normal direction to the display surface 11 of the display device 10, and the like (see, for example, FIG. 2). .

  Next, the light guide plate 30 will be described in more detail with reference mainly to FIGS. As shown in FIGS. 2 to 6, the light guide plate 30 is formed on a base portion 40 formed in a plate shape and a surface (surface facing the observer side, light-emitting side surface) 41 on one side of the base portion 40. A plurality of unit optical elements 50 formed. The base 40 is configured as a flat member having a pair of parallel main surfaces. The back surface 32 of the light guide plate 30 is configured by the surface 42 on the other side of the base 40 located on the side facing the reflection sheet 28.

  The “unit prism”, “unit shape element”, “unit optical element”, and “unit lens” in the present specification refer to the optical action such as refraction and reflection on the light, and indicate the traveling direction of the light. It refers to an element having a function to be changed, and is not distinguished from each other based only on a difference in designation.

  As well shown in FIG. 5, the other side surface 42 of the base 40 that forms the back surface 32 of the light guide plate 30 is formed as an uneven surface. As a specific configuration, the back surface 32 has an inclined surface 37, a step surface 38 extending in the normal direction nd of the light guide plate 30, and a connection extending in the plate surface direction of the light guide plate 30 due to the unevenness of the other side surface 42 of the base 40. And a surface 39. The light guide in the light guide plate 30 is based on the total reflection action on the pair of main surfaces 31 and 32 of the light guide plate 30. On the other hand, the inclined surface 37 is inclined with respect to the plate surface of the light guide plate 30 so as to approach the light exit surface 31 from the light incident surface 33 side toward the opposite surface 34 side. Therefore, the incident angle when the light reflected by the inclined surface 37 enters the pair of main surfaces 31 and 32 becomes small. When the incident angle on the pair of main surfaces 31 and 32 is less than the total reflection critical angle by reflecting on the inclined surface 37, the light is emitted from the light guide plate 30. That is, the inclined surface 37 functions as an element for extracting light from the light guide plate 30.

The distribution of the inclined surface 37 along the first direction d ₁ is a light guiding direction by adjusting in the back surface 32, to adjust the first distribution along the direction d ₁ of the amount of light emitted from the light guide plate 30 it can. In the example shown in FIGS. 2 to 6, the proportion of the inclined surface 37 in the back surface 32 increases as the light incident surface 33 approaches the opposite surface 34 along the light guide direction. According to such a configuration, the emission of light from the light guide plate 30 in the region separated from the light incident surface 33 along the light guide direction is promoted, and the amount of emitted light decreases as the distance from the light incident surface 33 increases. Can be effectively prevented.

Note that in one example shown, the arrangement pitch Ps of the inclined surface 37 in the first direction d ₁ (see FIG. 3) is constant. Further, the inclination angles of the inclined surfaces 39 are the same among the plurality of connection surfaces 39. On the other hand, the length of one connection surface 39 in the first direction d ₁ is different among the plurality of connection surfaces 39. Length in the first direction d ₁ of the connection surface 39, as position of the connecting surface 39 toward the other side from one side in the first direction d _1, gradually becomes longer. Note that "gradually longer", not always necessary to continue to change as long, the length in the first direction d ₁ of the two connecting surfaces 39 adjacent in the first direction d ₁ is made identical to each other It may be. In other words, “slowly longer” means that the length of the plurality of connection surfaces 39 in the first direction d ₁ is not constant, and the length of one connection surface 39 in the first direction d ₁ is than the length in the first direction d ₁ of the other connecting surface 39 located on one side in the first direction d ₁ than the connecting surface 39, not be shorter, which means that.

Next, the unit optical element 50 provided on the surface 41 on one side of the base 40 will be described. As seen in FIG. 4, a plurality of unit optical elements 50, is at the first direction d ₁ and intersect and one side face 41 parallel to the array direction of the base 40 (Fig. 4 left-right direction ) And arranged on the surface 41 on one side of the base 40. Each unit optical element 50 extends linearly on the surface 41 on one side of the base 40 in a direction intersecting with the arrangement direction.

In particular, in the present embodiment, as shown in FIG. 4, the plurality of unit optical elements 50 are arranged on the surface 41 on one side of the base 40 in the second direction (arrangement direction) d ₂ orthogonal to the first direction d _1. Are arranged side by side without any gaps. Therefore, the light exit surface 31 of the light guide plate 30 is configured as inclined surfaces 35 and 36 formed by the surface of the unit optical element 50. Each unit optical element 50 extends linearly along a first direction d ₁ orthogonal to the arrangement direction. Further, each unit optical element 50 is formed in a column shape and has the same cross-sectional shape along the longitudinal direction thereof. In the present embodiment, the plurality of unit optical elements 50 are configured identically. As a result, the light guide plate 30 in the present embodiment, at each position along the first direction d _1, which is to have a constant cross-sectional shape.

Then, cross-section shown in FIG. 6, ie, in both the normal direction nd of the arrangement direction of the unit optical elements one side 41 of the (second direction) d ₂ and the base 40 (the plate surface of the light guide plate 30) A cross-sectional shape of each unit optical element 50 in a parallel cross section (hereinafter, also simply referred to as a main cut surface of the light guide plate) will be described. As shown in FIG. 6, in the illustrated example, the cross-sectional shape of each unit optical element 50 on the main cut surface of the light guide plate is a shape that tapers toward the light output side. That is, in the main cut surface of the light guide plate, the width of the unit optical element 50 parallel to the plate surface of the light guide plate 30 decreases as the distance from the base 40 increases along the normal direction nd of the light guide plate 30.

Further, in the present embodiment, the outer contour (corresponding to the light emitting side surface 31) 51 on the main cut surface of the unit optical element 50 is a light emitting surface angle that is an angle formed by the outer contour with respect to the one side surface 41 of the base 40. theta _a is, to be larger toward the base portion 40 to the farthest unit optical from the tip portion 52a of the outer contour 51 of the element 50 on the outer contour 51 of the unit optical elements 50 closest to the base portion 40 of the base end portion 52b Is changing. About this light emission surface angle (theta) _a , it can set as disclosed by Unexamined-Japanese-Patent No. 2013-51149, for example.

Here, the light exit surface angle θ _a is an angle formed by the light exit side surface (outer contour) 51 of the unit optical element 50 with respect to the one side surface 41 of the base 40 in the main cut surface of the light guide plate as described above. It is. As in the example shown in FIG. 6, when the outer contour (light-emitting side surface) 51 in the main cut surface of the unit optical element 50 is formed in a polygonal line shape, one side surface of each linear part and the base part 40 constituting the polygonal line. (strictly, the smaller the angle of the ones of the two angles formed (angle of minor angle)) the angle formed between the 41 becomes the light exit surface an angle theta _a. On the other hand, when the outer contour (light-emitting side surface) 51 on the main cutting surface of the unit optical element 50 is configured by a curved surface, an angle formed between the tangent to the outer contour and one side surface 41 of the base 40 ( strictly speaking, the smaller the angle of the ones of the two angles formed (angle of minor angle)), and be identified as the light exit surface an angle theta _a.

  The unit optical element 50 as one specific example shown in FIG. 6 has one side located on one side 41 of the base 40 on the main cut surface of the light guide plate 30 and the front end 52a on the outer contour 51 and each base. It is a pentagonal shape in which two sides are located between the end 52b or a shape formed by chamfering one or more corners of this pentagonal shape. In the example shown in the drawing, the cross-sectional shape of the main cutting surface of the unit optical element 50 is symmetric with respect to the front direction nd. That is, as well shown in FIG. 6, the light exit side surface 51 of each unit optical element 50 is configured by a pair of bent surfaces 35 and 36 that are configured symmetrically about the front direction. The pair of bent surfaces 35 and 36 are connected to each other to define a tip portion 52a. Each folding surface 35, 36 has a first surface 35a, 36a that defines a tip 52a, and a second surface 35b, 36b that connects to the first surface 35a, 36a from the base 40 side. . The pair of first inclined surfaces 35a and 36a have a symmetric configuration with respect to the front direction nd, and the pair of second inclined surfaces 35b and 36b also have a symmetric configuration with the front direction nd as the center.

As an overall configuration of the unit optical element 50, the width from the base cutting surface of the light guide plate 30 to the width W _{a in} the arrangement direction of the unit optical elements 50 on the main cutting surface of the light guide plate 30 from the base 40 of the unit optical element 50. the ratio of protrusion height _{H a} along the front direction _(H a / _{W a)} are preferably has a 0.3 to 0.45. According to such a unit optical element 50, an excellent light condensing function is exhibited with respect to light components along the arrangement direction (second direction) of the unit optical elements 50 due to refraction and reflection at the light exit side surface 51. And generation of side lobes can be effectively suppressed.

  In addition, the “pentagonal shape” in the present specification includes not only a pentagonal shape in a strict sense but also a substantially pentagonal shape including limitations in manufacturing technology, errors in molding, and the like. Similarly, terms used in the present specification to specify other shapes and geometric conditions, for example, terms such as “parallel”, “orthogonal”, and “symmetric” are not limited to strict meanings. Interpretation will be made including such an error that a similar optical function can be expected.

Here, the dimension of the light guide plate 30 may be set as follows as an example. First, as a specific example of the unit optical element 50, the width W _a (see FIG. 6) can be set to 10 μm or more and 500 μm or less. On the other hand, the thickness of the base 40 can be 0.2 mm to 6 mm.

  The light guide plate 30 having the above-described configuration can be produced by molding the unit optical element 50 on a base material or by extrusion molding. Various materials can be used as the material forming the base portion 40 and the unit optical element 50 of the light guide plate 30. In particular, it is widely used as a material for an optical sheet incorporated in a display device, and has excellent mechanical properties, optical properties, stability, workability, etc., and can be obtained at low cost, such as acrylic resin, polystyrene, polycarbonate, etc. Transparent resins mainly composed of one or more of polyethylene terephthalate, polyacrylonitrile, etc., and epoxy acrylate and urethane acrylate-based reactive resins (ionizing radiation curable resins, etc.) can be suitably used. If necessary, a diffusive component having a function of diffusing light can be added into the light guide plate 30. As an example, the diffusion component uses particles made of a transparent material such as silica (silicon dioxide), alumina (aluminum oxide), acrylic resin, polycarbonate resin, silicone resin and the like having an average particle size of about 0.5 to 100 μm. Can do.

  When the light guide plate 30 is produced by curing the ionizing radiation curable resin on the base material, the sheet-shaped land portion that is positioned between the unit optical element 50 and the base material is provided together with the unit optical element 50. It may be formed on a substrate. In this case, the base 40 is composed of a base material and a land portion formed of an ionizing radiation curable resin. Moreover, the board | plate material which consists of a resin material extrusion-molded with the light-diffusion particle as a base material can be used. On the other hand, in the light guide plate 30 manufactured by extrusion molding, the base 40 and the plurality of unit optical elements 50 on one side surface 41 of the base 40 can be integrally formed.

  Next, the optical sheet (prism sheet) 60 will be described in further detail with reference mainly to FIGS. 2, 3, and 7 to 10. The optical sheet 60 is a member having a function of changing the traveling direction of transmitted light.

  As shown in FIG. 7, the optical sheet 60 includes a main body portion 65 formed in a plate shape and a plurality of unit prisms (unit shape elements, unit units) formed on the light incident side surface 67 of the main body portion 65. Optical element, unit lens) 70. The main body portion 65 is configured as a flat plate-like member having a pair of parallel main surfaces. The light exit surface 61 of the optical sheet 60 is configured by the light exit side surface 66 of the main body 65 located on the side not facing the light guide plate 30.

  Next, the unit prism 70 provided on the light incident side surface of the main body 65 will be described. As well shown in FIGS. 2 and 7, the plurality of unit prisms 70 are arranged side by side on the light incident side surface 67 of the main body 65. Each unit prism 70 is formed in a columnar shape and extends in a direction intersecting with the arrangement direction.

In the present embodiment, each unit prism 70 extends linearly. Each unit prism 70 is formed in a columnar shape and has the same cross-sectional shape along the longitudinal direction. Further, the plurality of unit prisms 70 are arranged on the light incident side surface 67 of the main body 65 with no gap along the direction orthogonal to the longitudinal direction. Therefore, the light incident surface 62 of the optical sheet 60 is formed by the surfaces (prism surfaces) 71 and 72 of the unit prisms 70 arranged on the main body portion 65 without a gap. As shown in FIGS. 2 and 7, a plurality of unit prisms 70 are arranged in the third direction d _3. Each unit prism 70 extends linearly in the fourth direction d ₄ perpendicular to the third direction d ₃ which is the arrangement direction.

As described above, the optical sheet 60 is disposed so as to overlap the light guide plate 30, and the unit prism 70 of the optical sheet 60 faces the light exit surface 31 of the light guide plate 30. As shown in FIG. 3, in the optical sheet 60, the longitudinal direction (fourth direction d ₄ ) of the unit prism 70 is guided in the light guide direction by the light guide plate 30 (the light incident surface 33 of the light guide plate 30 and the light incident surface). such that the first direction) d ₁ connecting the opposite surface 34 which faces and non-parallel, are positioned with respect to the light guide plate 30. The third direction d ₃ is the arrangement direction of the unit prisms 70 is arranged to be parallel or inclined with respect to the first direction d ₁ is a light guiding direction. In the example shown in FIG. 3, the third direction d ₃ is inclined with respect to the first direction d ₁ . As will be described later, when the optical sheet 60 of the present embodiment is used, the direction in which the luminance peak occurs is controlled in various directions by inclining the third direction d ₃ with respect to the first direction d ₁ . be able to. In particular, when the third direction d ₃ is inclined by 15 ° or more with respect to the first direction d ₁ , the direction in which the luminance peak occurs is within a range that could not be realized by a surface light source device having a simple configuration. Can be controlled.

As seen in FIG. 8, each unit prism 70, the arrangement direction of the unit prisms 70, i.e. along a third direction d _3, the first prism surface 71 and a second prism arranged to face each other A surface 72 is provided. The first prism surface 71 of each unit prism 70 is located on one side in the third direction d ₃ (left side in the plane of FIG. 8), and the second prism surface 72 is on the other side in the third direction d ₃ ( It is located on the right side in FIG. 1, 2, in the cross section of the surface light source device along the main cut surface of the light guide plate shown in FIGS. 9 and 10, one side of the third direction d ₃ is a side in the first direction d ₁ next, the other side in the third direction d ₃ becomes the other side in the first direction d _1.

Accordingly, in the surface light source device 20, the first prism surface 71 of each unit prism 70 faces the one side in the first direction d ₁ positioned on the side of the light source 24 in the third direction d _3. The second prism surface 72 of each unit prism 70 is located on the side away from the light source 24 in a third direction d _3, facing the other side in the first direction d _1. As will be described later, the first prism surface 71 mainly travels from the light source 24 arranged on one side in the first direction d ₁ into the light guide plate 30, and then the light emitted from the light guide plate 30 is converted into the optical sheet 60. It functions as an incident surface when entering the lens. On the other hand, the second prism surface 72 has a function of reflecting light incident on the optical sheet 60 and correcting the optical path of the light.

  As well shown in FIG. 8, the first prism surface 71 and the second prism surface 72 extend from the main body portion 65 and are connected to each other. A base end portion 75b of the unit prism 70 is defined at a position where the first prism surface 71 and the second prism surface 72 are connected to the main body portion 65, respectively. In addition, at a position where the first prism surface 71 and the second prism surface 72 are connected to each other, a tip portion (a top portion) 75a of the unit prism 70 that protrudes most from the main body portion 65 to the light incident side is defined.

As shown in FIG. 8, the normal direction nd to the sheet surface of the main body 65 (the light incident side surface 67 of the main body 65, the sheet surface of the optical sheet 60) and the third direction d ₃ that is the arrangement direction of the unit prisms 70. The cross-sectional shape of each unit prism 70 in a cross section parallel to both (hereinafter, also simply referred to as a main cutting surface of the optical sheet) is along the longitudinal direction (direction extending linearly) of the unit prism 70. It is constant.

  Hereinafter, the cross-sectional shape of the unit prism 70 on the main cutting surface of the optical sheet will be described in more detail. In addition, in FIG. 8, the cross section of the optical sheet along the VIII-VIII line | wire of FIG. 7 equivalent to the main cut surface of an optical sheet is shown. On the other hand, in FIG.9 and FIG.10, the surface light source device 20 is shown in the cross section parallel to the main cut surface of a light-guide plate. As shown in FIG. 8, in the present embodiment, the cross-sectional shape of each unit prism 70 on the main cut surface of the optical sheet is a shape that tapers toward the light incident side (light guide plate side). Yes. That is, on the main cutting surface of the optical sheet, the width of the unit prism 70 parallel to the sheet surface of the main body 65 decreases as the distance from the main body 65 increases along the normal direction nd of the main body 65.

In the illustrated example, the second prism surface 72 that forms part of the outer contour of the unit prism 70 on the main cutting surface of the optical sheet 60 (the second prism surface 72 that forms part of the light incident side surface) is in the third direction. When the angle with respect to d ₃ and the inclination angle theta _t, the inclination angle theta _t of at least one of the unit prisms 70 is not in the constant in the second prism surface 72. As shown in FIG. 8, the inclination angle θ _t is the base end of the unit prism 60 closest to the main body 65 from the tip 75 a of the unit prism farthest from the main body 65 in the second prism surface 72. It changes so that it may become large toward the part 75b. As shown in FIGS. 9 and 10, in the region of the second prism surface 72 on the base end portion 75b side, the relatively rising lights L91 and L101 proceeding in a direction in which the inclination angle with respect to the front direction nd becomes relatively small. Becomes easy to enter. In addition, the light L92 and L102 which are relatively sleeping and traveling in a direction in which the inclination angle with respect to the front direction nd becomes very large are likely to enter the region of the second prism surface 72 on the tip end portion 75a side. By changing the inclination angle θ _t within the second prism surface 72, the optical sheet 60 can more effectively exhibit the light condensing function with respect to the light of the light guide plate 30. That is, the light traveling from one unit prism 70 travels in a direction within a narrower angle range.

As a specific configuration, the inclination angle θ _t with respect to the third direction d ₃ gradually increases from the distal end portion 75a side to the proximal end portion 65b side of the unit prism 70 on the main cut surface of the optical sheet. In this way, n element surfaces 73 (n is a natural number of 2 or more), that is, a plurality of element surfaces are included. In the illustrated embodiment, the contour of the second prism surface 72 of the unit prism 70 is formed by joining the straight portions on the main cut surface of the optical sheet, or joining the straight portions and chamfering the joint. The shape is In other words, the outer contour of the second prism surface 72 of the unit prism 70 is formed in a polygonal line shape or a shape formed by chamfering the corners of the polygonal line. In particular, in the illustrated example, the second prism surface 72 includes a first element surface 73a that defines the distal end portion 75a, and a second element surface 73b that is adjacent to the first element surface 73a from the main body 65 side. Have. As shown in FIG. 8, the inclination angle θ ₁ of the first element surface 73a is smaller than the inclination angle θ ₂ of the second element surface 73b. However, the present invention is not limited to this example, and the second prism surface 72 may have three or more element surfaces 73, may be a curved surface, or may be a flat single surface (single element). Surface).

Note that, as described above, the inclination angles θ _t , θ ₁ , and θ ₂ are such that the light incident side surface (second prism surface 72) of the unit prism 60 is in the third direction d ₃ on the main cut surface of the optical sheet 60. It is the angle to make. More specifically, an angle formed between each element surface 73 that forms a polygonal line on the main cutting surface of the optical sheet 60 and the third direction d ₃ (strictly speaking, two formed angles) The smaller one of them (the angle of the inferior angle) becomes the inclination angles θ _t , θ ₁ , θ ₂ .

In the optical sheet 60 having the above-described configuration, in the main cutting surface of the optical sheet, the width W _b (see FIG. 8) of the unit prisms 70 along the arrangement direction of the unit prisms 70 in the main cutting surface of the optical sheet. The ratio of the unit prism 70 to the height H _b along the normal direction nd of the main body 65, that is, the aspect ratio (W _b / H _b ) of the second prism surface 72, and the second prism surface 72 the inclination angle theta _t of each element surface 73 Nasu, condensing of the optical sheet 60, and further influences the direction the direction to be focused, in other words the intensity peak occurs. As shown in FIG. 9, the traveling direction of the outgoing light L91, L92 which come forward in a direction inclined to the first direction d ₁ is a light guiding direction from the front direction nd of the light exit surface 31 of the light guide plate 30, back to front direction nd In order to cause the luminance peak to occur in a direction inclined with respect to the first direction d ₁ without being interrupted, the aspect ratio (W _b / H _b ) of the unit prism 70 is set to 1.15 or more and 1.5 or less. further, it is preferable that the inclination angle theta ₁ of the first element surface 73a city 38 ° or 53 ° or less, the inclination angle theta ₂ to 43 ° or more 57 ° or less of the second component surface 73b. On the other hand, as shown in FIG. 10, the traveling direction of the emitted light L101, L102 to come forward in a direction inclined to the first direction _{d 1} is a light guiding direction from the front direction nd of the light exit surface 31 of the light guide plate 30, the front direction nd The aspect ratio (W _b / H _b ) of the unit prism 70 is 1.1 or more and 1.50 in order to generate the luminance peak in the direction inclined with respect to the first direction d ₁ . city below, further, it is preferable that the inclination angle theta ₁ of the first element surface 73a city 53 ° or 68 ° or less, the inclination angle theta ₂ to 59 ° or more 72 ° or less of the second component surface 73b.

Other dimensions of the optical sheet 60 can be set as follows as an example. First, as a specific example of the unit prism 70 configured as described above, the arrangement pitch of the unit prisms 70 (corresponding to the width W _b of the unit prism 70 in the illustrated example) can be set to 10 μm or more and 200 μm or less. . However, in recent years, the arrangement of the unit prisms 70 has been rapidly refined, and the arrangement pitch of the unit prisms 70 is preferably set to 10 μm or more and 35 μm or less. Similarly, the width W _b2 of the second prism surface 72 of the unit prism 70 can be set to 5 μm or more and 100 μm or less, and can be set to 5 μm or more and 20 μm or less considering recent trends. Further, the protruding height _Hb of the unit prism 70 from the main body 65 along the normal direction nd to the sheet surface of the optical sheet 60 can be set to 5.5 μm or more and 180 μm or less.

The optical sheet 60 having the above-described configuration can be produced by molding the optical sheet 60 on a base material or by extrusion molding. Various materials can be used as the material forming the main body 65 and the unit prism 70 of the optical sheet 60.
In particular, it is widely used as a material for an optical sheet incorporated in a display device, and has excellent mechanical properties, optical properties, stability, workability, etc., and can be obtained at low cost, such as acrylic resin, polystyrene, polycarbonate, etc. Transparent resins mainly composed of one or more of polyethylene terephthalate, polyacrylonitrile, etc., and epoxy acrylate and urethane acrylate-based reactive resins (ionizing radiation curable resins, etc.) can be suitably used.

  When the optical sheet 60 is produced by curing the ionizing radiation curable resin on the base material, the sheet-like land portion that is positioned between the unit prism 70 and the base material is used together with the unit prism 70. You may make it form on a material. In this case, the main body portion 65 is composed of a base material and a land portion formed of an ionizing radiation curable resin. On the other hand, in the optical sheet 60 produced by extrusion molding, the main body portion 65 and the plurality of unit prisms 70 on the light incident side surface 67 of the main body portion 65 can be integrally formed.

  Next, the operation of the display device 10 having the above configuration will be described.

First, as shown in FIGS. 1 and 2, the light emitted from the light emitter 25 constituting the light source 24 enters the light guide plate 30 via the light incident surface 33. As shown in FIG. 2, the light L21 and L22 incident on the light guide plate 30 is reflected on the light output surface 31 and the back surface 32 of the light guide plate 30, particularly due to a difference in refractive index between the material forming the light guide plate 30 and air. The total reflection is repeated, and the light advances to the first direction (light guide direction) d ₁ connecting the light incident surface 33 and the opposite surface 34 of the light guide plate 30.

  The back surface 32 of the light guide plate 30 has an inclined surface 37 that is inclined so as to approach the light exit surface 31 from the light incident surface 33 toward the opposite surface 34. The inclined surface 37 is connected via a step surface 38 and a connection surface 39. Among these, the step surface 38 extends in the normal direction nd of the plate surface of the light guide plate 30. Therefore, most of the light traveling in the light guide plate 30 from the light incident surface 33 side to the opposite surface 34 side does not enter the step surface 38 of the back surface 32, and is incident on the inclined surface 37 or the connection surface 39. Reflected. Then, when reflected by the inclined surface 37 of the back surface 32, the traveling direction of the light in the cross section shown in FIG. 2 increases the inclination angle with respect to the plate surface of the light guide plate 30. That is, when the light is reflected by the inclined surface 37 of the back surface 32, the incident angle of the light on the light output surface 31 and the back surface 32 in the following becomes small. Therefore, the incident angle of the light traveling in the light guide plate 30 to the light exit surface 31 and the back surface 32 is gradually reduced by one or more reflections on the inclined surface 37 of the back surface 32, and is less than the total reflection critical angle. Become. In this case, the light can be emitted from the light exit surface 31 and the back surface 32 of the light guide plate 30. The light L21 and L22 emitted from the light exit surface 31 travels to the optical sheet 60 disposed on the light exit side of the light guide plate 30. On the other hand, the light emitted from the back surface 32 is reflected by the reflection sheet 28 disposed on the back surface of the light guide plate 30, enters the light guide plate 30 again, and travels through the light guide plate 30.

In particular, in the illustrated example, the proportion of the inclined surface 37 in the back surface 32 increases as the light incident surface 33 approaches the opposite surface 34 along the first direction d ₁ that is the light guide direction. . More specifically, the inclined surface 37 has been arranged at a predetermined pitch Ps in the first direction d _1, the length along the first direction d ₁ of the inclined surfaces 37, in the first direction d ₁ The length gradually increases from one side to the other. This ensures a sufficient amount of light emitted from the light exit surface 31 of the light guide plate 30 in a region separated from the light incident surface 33 where the amount of emitted light tends to decrease, and the amount of emitted light uniform along the light guide direction. Can be achieved.

  By the way, the light exit surface 31 of the illustrated light guide plate 30 is constituted by a plurality of unit optical elements 50, and the cross-sectional shape of the main cut surface of each unit optical element 50 is a pentagonal shape arranged symmetrically about the front direction or The shape is formed by chamfering one or more corners of the pentagonal shape. More specifically, as described above, the light exit surface 31 of the light guide plate 30 is configured as a bent surface inclined with respect to the back surface 32 of the light guide plate 30 (see FIG. 6). The bent surfaces are inclined surfaces 35 and 36 inclined to opposite sides with respect to the normal direction nd to the light output side surface 41 of the base 40. The light that is totally reflected by the inclined surfaces 35 and 36 and travels through the light guide plate 30 and the light that passes through the inclined surfaces 35 and 36 and is emitted from the light guide plate 30 are transmitted from the inclined surfaces 35 and 36 to the following. It comes to have an effect to explain. First, the effect exerted on the light traveling through the light guide plate 30 after being totally reflected by the inclined surfaces 35 and 36 will be described.

In FIG. 6, the optical paths of the lights L61 and L62 that travel through the light guide plate 30 while repeating total reflection on the light exit surface 31 and the back surface 32 are shown in the main cut surface of the light guide plate. As described above, the inclined surfaces 35 and 36 forming the light exit surface 31 of the light guide plate 30 include two types of surfaces inclined opposite to each other across the normal direction nd to the light exit side surface 41 of the base 40. . Further, the two types of inclined surfaces 35 and 36 inclined in opposite sides to each other, along the second direction d _2, are arranged alternately. As shown in FIG. 6, the light L61 and L62 that travel in the light guide plate 30 toward the light exit surface 31 and enter the light exit surface 31 are often guided out of the two types of inclined surfaces 35 and 36. The light enters the inclined surface inclined to the opposite side of the traveling direction of the light with reference to the normal direction nd to the light exit side surface 41 of the base 40 on the main cut surface of the optical plate.

As a result, as shown in FIG. 6, the light L61, L62 traveling in the light guide plate 30 are often totally reflected by the inclined surfaces 35 and 36 of the light exit surface 31, reduces the component along the second direction _{d 2} Further, the traveling direction of the main cut surface is directed to the opposite side with respect to the front direction nd. In this way, the inclined surfaces 35, 36 forming the exit surface 31 of the light guide plate 30, light emitted radially emitting point there is, it is restricted to continue spreading it in the second direction d _2. That is, light emitted from the light emitter 25 of the light source 24 in a direction greatly inclined with respect to the first direction d ₁ and entering the light guide plate 30 is also mainly controlled in the first direction while being restricted from moving in the second direction d ₂ . so advance in the direction _{d 1.} Thus, the light intensity distribution along the second direction d ₂ of the light emitted from the light exit surface 31 of the light guide plate 30, the configuration of a light source 24 (e.g., the sequence of emitters 25) and, by the output of the light emitter 25, adjusted It becomes possible to do.

Next, the effect exerted on the light that passes through the light exit surface 31 and exits from the light guide plate 30 will be described. As shown in FIG. 6, the lights L <b> 61 and L <b> 62 emitted from the light guide plate 30 through the light output surface 31 are refracted on the light output side surface of the unit optical element 50 that forms the light output surface 31 of the light guide plate 30.
Due to this refraction, the traveling direction (outgoing direction) of the light L61 and L62 traveling in the direction inclined from the front direction nd on the main cut surface is mainly compared with the traveling direction of the light when passing through the light guide plate 30. Thus, it is bent so that the angle formed with respect to the front direction nd is small. Such action unit optical element 50, the component of light along the second direction d ₂ perpendicular to the light guiding direction, the traveling direction of the transmitted light can be narrowed down in the front direction nd side. In other words, the unit optical element 50, the component of light along the second direction d ₂ perpendicular to the light guiding direction, so exert a light condensing effect. In this way, the emission angle of the light emitted from the light guide plate 30 is narrowed down to a narrow angle range centering on the front direction in a plane parallel to the arrangement direction of the unit optical elements 50 of the light guide plate 30.

As described above, the emission angle of the light emitted from the light guide plate 30 is narrowed down to a narrow angle range centering on the front direction nd on the plane parallel to the arrangement direction of the unit optical elements 50 of the light guide plate 30. On the other hand, the emission angle of the light emitted from the light guide plate 30 has so far progressed mainly in the first direction d ₁ in the light guide plate 30 until the first direction as shown in FIG. in (light guiding direction) d ₁ parallel to the plane, a relatively large emission angle theta _k was relatively large inclination from the front direction nd. That is, the outgoing angle of the first direction component d ₁ of the light emitted from the light guide plate 30 (the angle θ _k formed by the first direction component of the outgoing light and the normal direction nd to the plate surface of the light guide plate 30 (see FIG. 2). )) Is a relatively large angle. In particular, in the present embodiment, the back surface 32 of the light guide plate 30 includes a plurality of inclined surfaces 37 arranged in the first direction d ₁ , and each inclined surface 37 is from one side in the first direction d ₁ . The light guide plate 30 is inclined with respect to the normal direction nd and the first direction d ₁ so as to approach the light exit surface 31 as it goes to the other side. As a result, as shown in FIG. 2, in a first direction (light guide direction) d ₁ parallel to the plane, the emission direction from the light guide plate 30, relatively large emission angle which is relatively large inclination from the front direction nd There is a tendency to be biased within a narrow angle range of θ _k .

For example, in the light guide plate 30 having the above-described exemplary shape and size, on the light exit surface 31 of the light guide plate 30 in each direction in a plane parallel to both the normal direction nd and the first direction d ₁ of the light guide plate 30. The angle θ _aImax1 in which the direction in which the luminance peak is obtained is inclined from the normal direction nd of the light guide plate 30 along the first direction d ₁ to the other side (opposite surface 34 side), and The direction in which half the luminance peak located between the normal direction nd of the light guide plate 30 and the direction in which the luminance peak is obtained is one side along the first direction d ₁ from the direction in which the luminance peak is obtained ( The angle θ _aIα1 inclined to the light incident surface 33 side can be set to a range that satisfies the following conditions (1) and (2), more preferably the conditions (1 ′) and (2 ′).
60 ° ≦ θ _aImax1 ≦ 80 ° (1)
5 ° ≦ θ _aIα1 ≦ 25 ° (2)
70 ° ≦ θ _aImax1 ≦ 80 ° (1 ′)
5 ° ≦ θ _aIα1 ≦ 15 ° (2 ′)

Moreover, in the light guide plate 30 having the above-described exemplary shape and size, a luminance peak is obtained in the angular distribution of the luminance on the light output surface 31 of the light guide plate 30 in each direction within the main cut surface of the light guide plate 30. The direction of the angle θ _aImax2 that the direction forms with respect to the normal direction nd of the light guide plate 30 and the direction in which the luminance peak is obtained and half the luminance peak is obtained are the luminance peaks. The average value θ _aIα2 (= (θ _aIα2x + θ _aIα2y ) / 2) of the angle inclined from the obtained direction can be set in the following range.
0 ° ≦ θ _aImax2 ≦ 3 ° (3)
12 ° ≦ θ _aIα2 ≦ 27 ° (4)

11 and 12 show an example of the angular distribution of luminance actually measured on the light exit surface 31 of the light guide plate 30 having the configuration shown in FIGS. 4 to 6. Indicated luminance distribution in Figure 11 is the result of actually examined the luminance distribution in each direction in the plane parallel to both the first direction d ₁ and the front direction nd. In the graph shown in FIG. 11, and the angle value which is inclined to the other side along the first direction d ₁ from the front direction is positive. On the other hand, it indicated luminance distribution in FIG. 12 shows the result of actually examined the luminance distribution in each direction in the plane parallel to both the second direction d ₂ and the front direction nd.

The light emitted from the light guide plate 30 then enters the optical sheet 60. As described above, the optical sheet 60 includes the unit prism 70 with the tip end portion 75a protruding toward the light guide plate 30 side. As seen in FIG. 3, the unit prisms 70 extend in the direction the fourth direction d ₄ crossing by the light guide plate 30 guiding light direction (first direction) d _1. In FIG. 3, the inclined surface 37 of the light guide plate 30 is indicated by a dotted line, and the unit prism 70 of the optical sheet 60 is indicated by a one-dot chain line.

The result, light L21, L22 toward the optical sheet 60 through the light guide plate 30 is emitted by a light source 24 disposed (the left side in the plane of FIG. 2) the first one side in the direction d ₁ is connected to one another The light enters the unit prism 70 via the first prism surface 71 located on one side of the first prism surface 71 and the second prism surface 72 which is the light source 24 side in the first direction d ₁ . As shown in FIG. 2, the light L21, L22 is then the first light source in the direction d ₁ is totally reflected by the second prism surface 72 located on the other side of the opposite side (right side in the plane of FIG. 2) Change its direction of travel.

Then, by total reflection at the second prism surface 72 of the unit prisms 70, the main cross in FIG. 9 or the indicated light guide plate in FIG. 10 (first direction (light guide direction) d ₁ and both the front direction nd Light L91, L92, L101, L102 traveling in a direction inclined from the front direction nd in a cross section parallel to the front direction nd is bent so that the angle formed by the traveling direction with respect to the front direction nd is small. However, in the present embodiment, the unit prism 70 transmits light components along the first direction (light guide direction) d ₁ by adjusting the inclination angle θ _t of the second prism surface 72 and the like. The traveling direction of light can be narrowed down to a direction inclined from the front direction nd. That is, the optical sheet 60, the component of light along the first direction d _1, will exert a light condensing effect toward the direction inclined from the front direction nd.

In the present embodiment, each unit prism 70 has a first prism surface 71 that faces one side in the third direction d ₃ and forms an incident surface for light emitted from the light exit surface 31 of the light guide plate 30, and the third direction. and it faces the other side of d ₃ through the first prism surface 71 has a second prism surface 72 for totally reflecting the light incident on the unit prisms 75, a. The light collecting function by the unit prism 70 is based on the total reflection function on the second prism surface 72. For this reason, the optical sheet 60 can change the traveling direction of light greatly, and can adjust the condensing direction with a high degree of freedom. In the example shown in FIG. 9, the traveling direction of the outgoing light L91, L92 which come forward in a direction inclined to the first direction d ₁ is a light guiding direction from the front direction nd of the light exit surface 31 of the light guide plate 30, the front direction nd The luminance peak is generated in a direction inclined with respect to the first direction d ₁ so as not to return to the maximum. On the other hand, in the example shown in FIG. 10, the traveling direction of the outgoing light L91, L92 which come forward in a direction inclined to the first direction d ₁ is a light guiding direction from the front direction nd of the light exit surface 31 of the light guide plate 30, a front The luminance peak is generated in a direction inclined with respect to the first direction d ₁ so as to change beyond the direction nd. According to the surface light source device 20 having such an optical sheet 60, a luminance peak on the light emitting surface 21 can be generated in a direction other than the front direction with a simple configuration.

Here, FIG. 13 shows an example of the angular distribution of luminance measured on the light exit surface 61 of the optical sheet 60. Figure 13 shows the luminance distribution is the result of actually investigated luminance in each direction in both directions parallel surfaces of the first direction d ₁ and the front direction nd. In the graph shown in FIG. 13, and the angle value which is inclined to the other side along the first direction d ₁ from the front direction is positive. In the example shown in FIG. 13, the optical sheet 60 having the configuration shown in FIGS. 7 and 8 is arranged on the light output side of the light guide plate 30 showing the luminance characteristics shown in FIGS. 11 and 12. Thus, the luminance distribution actually measured. However, unlike the illustrated example, the angular distribution of the brightness shown in FIG. 13 is such that the third direction d ₃ is parallel to the first direction d _1, and the optical sheet 60 is moved with respect to the light guide plate 30. It is a measurement result about the positioned surface light source device 20. In the luminance angle distribution shown in FIG. 13, the direction in which the luminance peak is obtained is inclined by 12.0 ° with respect to the normal direction nd of the optical sheet 60. When this inventor repeated experiment, the brightness | luminance equivalent to the brightness | luminance peak when a brightness | luminance peak appears in a front direction, More specifically, 100% or more of the brightness | luminance peaks when a brightness | luminance peak appears in a front direction While securing the luminance peak, the angle at which the direction in which the luminance peak is obtained is inclined with respect to the normal direction nd of the optical sheet 60 can be set to 10 ° or more. At this time, the direction in which the luminance peak appears is the front direction. It could be clearly detected visually that it deviates from nd.

In addition, each dimension (refer FIG. 8) of the optical sheet 60 used for the measurement of luminance distribution is as follows.
Width W _b along the third direction d ₃ of the unit prism 70: 18 μm
Height H _b along the front direction nd of the unit prism 70: 14 μm
Width W _b2 along the third direction d ₃ of the second prism surface 72: 7.5 μm
Inclination angle θ ₁ of first element surface 73a of second prism surface 72: 51.0 °
Inclination angle θ ₂ of second element surface 73b of second prism surface 72: 53.5 °

Further, FIGS. 14 to 18 show the results of measuring the luminance in all directions on the light exit surface 61 of the optical sheet 60. 14 to 18 show the results of actual measurement of the surface light source device 20 (the light guide plate 30 and the optical sheet 60) used for the measurement of the luminance angle distribution shown in FIGS. However, in FIGS. 14 to 18, the angles formed by the third direction d ₃ and the first direction d ₁ (bias angle of the optical sheet) in the surface light source device 20 are 0 °, 10 °, 20 °, and 30 °, respectively. And 40 °. In this measurement, the third direction d ₃ to the first direction d _1, went shifted in the direction shown in FIG. 14 to 0 and the angular distribution of brightness in the direction connecting the 180 in the circular graph shown in Figure 18, it was measured in each direction in the front direction and a plane parallel to the second direction d ₂ luminance The angle distribution is shown.

Similarly, the distribution of brightness in the direction connecting the 90 and 270 in the circular graph shown in FIGS. 14 to 18 is measured in each direction in a plane parallel to and the first direction d ₁ front direction The angular distribution of brightness is shown. In addition, the center of the circular graph represents the luminance measured in the front direction, and the larger the measurement angle (the angle formed by the direction in which the luminance is measured with respect to the front direction) as the distance from the center of the circular graph increases in the radial direction. ) Shows the brightness value measured. In the direction connecting 0 and 180 in the circular graph, the 180 side shows the luminance in the direction inclined leftward from the front direction nd in FIG. 3, and the 0 side inclined from the front direction nd to the right side in FIG. The luminance in the direction is shown. In the direction connecting 90 and 270 in the circular graph, the 90 side indicates luminance in a direction inclined from the front direction nd to one side in the first direction d ₁ , and the 270 side indicates the first direction from the front direction nd. The luminance in the direction inclined to the other side at d ₁ is shown.

  Therefore, the angular distribution of luminance in the direction connecting 270 and 90 in FIG. 14 coincides with the angular distribution of luminance shown in FIG. Further, the luminance angular distributions shown in FIGS. 14 to 18 show the luminance distribution in a relative ratio to the luminance value at the luminance peak shown in FIG.

As shown in the results of FIGS. 14 to 18, by inclining the third direction d ₃ to the first direction d _1, the normal direction of the orthogonal and the optical sheet 60 in the first direction d ₁ In the angular distribution of luminance on the light exit surface 61 of the optical sheet 60 in each direction in a plane parallel to nd, the direction in which the luminance peak is obtained can be inclined with respect to the normal direction nd of the optical sheet 60. It was. That is, with a simple configuration, the direction in which the luminance peak appears on the light emitting surface 21 can be inclined from the front direction nd not only in the first direction d ₁ but also in the second direction d ₂ .

In the example shown in FIG. 14 (an example in which the angle formed by the third direction d ₃ and the first direction d ₁ (the bias angle of the optical sheet 60) is 0 °), the luminance peak is from the front direction nd. It appeared in a direction inclined by 12 ° in the first direction d ₁ and 0 ° in the second direction d ₂ from the front direction nd.
In the example shown in FIG. 15 (third example in which the direction d ₃ and the first direction d ₁ and the angle formed is a 10 °), the luminance peak, 13 ° inclined from the front direction in the first direction d ₁ And appeared in a direction inclined 9.5 ° in the second direction d ₂ from the front direction. In the example shown in FIG. 16 (example third direction _{d 3} and the first direction _{d 1} and the angle formed is a 20 °), the luminance peaks, the first direction _{d 1} from the front direction 18.7 ° emerged from inclined and the front direction in the second direction d ₂ to 16.8 ° tilted directions. In the example shown in FIG. 17 (an example in which the angle formed by the third direction d ₃ and the first direction d ₁ is 30 °), the luminance peak is 25.3 in the first direction d ₁ from the front direction. ° emerged from inclined and the front direction in the second direction d ₂ to 22.3 ° tilted directions. In the example shown in FIG. 18 (an example in which the angle formed by the third direction d ₃ and the first direction d ₁ is 40 °), the luminance peak is 37.8 from the front direction to the first direction d ₁ . ° emerged from inclined and the front direction in the second direction d ₂ to 24.8 ° tilted directions.

Further, when the present inventors have repeated intensive experiments, by tilting the third direction d ₃ first direction d ₁ with respect to more than 15 °, perpendicular to and laws of the optical sheet 60 in the first direction d ₁ In the angular distribution of luminance on the light exit surface 61 of the optical sheet 60 in each direction within a plane parallel to the line direction nd, the direction in which the luminance peak is obtained is 10 ° or more with respect to the normal direction nd of the optical sheet 60. It was possible to incline, and by this, it was clearly possible to visually detect that the direction in which the luminance peak appears deviated from the front direction nd. Further, when the present inventors have repeated experiments, when the angle of inclination with respect to the first direction d ₁ of the third direction d ₃ and 40 ° or less, 88% peak luminance when the luminance peak appears in the front direction nd The above luminance peak can be ensured, and the direction in which the luminance peak appears on the light emitting surface 21 appears not only in the first direction d ₁ but also in the second direction d ₂ without visually detecting a decrease in luminance. It was also possible to incline from the front direction nd.

  The light of one polarization component emitted from the optical sheet 60 forming the light emitting surface 21 of the surface light source device 20 is then incident on the liquid crystal display panel 15 and is transmitted through the lower polarizing plate 14. The light transmitted through the lower polarizing plate 14 selectively passes through the upper polarizing plate 13 according to the state of electric field application to each pixel. In this manner, the liquid crystal display panel 15 selectively transmits light from the surface light source device 20 for each pixel, so that an observer of the liquid crystal display device 10 can observe an image.

In the present embodiment as described above, the surface light source device 20 includes the light guide plate 30, the light source 24, and the optical sheet 60. The back surface 32 of the light guide plate 30 includes a plurality of inclined surfaces 37 arranged in the first direction d ₁ , and each inclined surface 37 approaches the light exit surface 31 as it goes from one side to the other side in the first direction d ₁ . as to inclined with respect to the normal direction nd and the first direction d ₁ of the light guide plate 30. The optical sheet 60 includes a sheet-like main body 65 and a plurality of unit prisms 70 provided on the light guide plate side of the main body 65. The plurality of unit prisms 70 are arranged in the third direction d ₃ , and each unit prism 70 extends linearly in a direction non-parallel to the third direction d ₃ . Each unit prism 70 has a first prism surface 71 which forms a third direction d one light incident surface 33 of the light emitted from the light exit surface 31 of the side orientation and the light guide plate 30 of _3, the other in the third direction d ₃ And a second prism surface 72 that totally reflects light incident on the unit prism 70 after passing through the first prism surface 71. According to such a surface light source device 20, the light exit surface 61 of the optical sheet 60 in each direction in a plane parallel to the first direction d ₁ and parallel to the normal direction nd of the optical sheet 60 with a simple configuration. In the luminance angular distribution above, the direction in which the luminance peak is obtained can be inclined with respect to the normal direction nd of the optical sheet 60.

In the present embodiment, the surface light source device 20 includes a light guide plate 30, a light source 24, and an optical sheet 60. In the angular distribution of luminance on the light exit surface 31 of the light guide plate 30 in each direction in a plane parallel to both the normal direction nd and the first direction d ₁ of the light guide plate 30, the direction in which the luminance peak is obtained is derived. The angle θ _aImax1 inclined from the normal direction nd of the light plate 30 to the other side along the first direction d ₁ and the luminance peak located between the normal direction nd of the light guide plate 30 and the direction in which the luminance peak is obtained. The angle θ _{aIα1 in} which the direction in which half the luminance is obtained is inclined to the one side along the first direction d ₁ from the direction in which the luminance peak is obtained _satisfies the following two conditions (1) and (2).
60 ° ≦ θ _aImax1 ≦ 80 ° (1)
5 ° ≦ θ _aIα1 ≦ 25 ° (2)
The optical sheet 60 includes a sheet-like main body 65 and a plurality of unit prisms 70 provided on the light guide plate side of the main body 65. The plurality of unit prisms 70 are arranged in the third direction d ₃ , and each unit prism 70 extends linearly in a direction non-parallel to the third direction d ₃ . Each unit prism 70 has a first prism surface 71 which forms a third direction d one light incident surface 33 of the light emitted from the light exit surface 31 of the side orientation and the light guide plate 30 of _3, the other in the third direction d ₃ And a second prism surface 72 that totally reflects light incident on the unit prism 70 after passing through the first prism surface 71. According to such a surface light source device 20, the light exit surface 61 of the optical sheet 60 in each direction in a plane parallel to the first direction d ₁ and parallel to the normal direction nd of the optical sheet 60 with a simple configuration. In the luminance angular distribution above, the direction in which the luminance peak is obtained can be inclined with respect to the normal direction nd of the optical sheet 60.

  The display device 10 and the surface light source device 20 according to the present embodiment can be used for various applications, and is particularly suitable for an in-vehicle display device. A passenger on the vehicle observes the in-vehicle display device from a substantially fixed direction. Usually, the observation direction of the in-vehicle display device by the occupant is directed to the display surface of the display device due to space restrictions in the vehicle. The direction is inclined with respect to the normal direction. Therefore, the display device 10 and the surface light source device 20 of the present embodiment that can set the direction in which the luminance peak occurs with a simple configuration to a direction other than the front direction are an in-vehicle display device, more specifically, a display device. It is particularly suitable for an in-vehicle center console using a display, an in-vehicle rearview mirror using a display device, an in-vehicle side mirror using a display device, and the like.

  Note that various modifications can be made to the above-described embodiment. Hereinafter, an example of modification will be described with reference to the drawings. In the following description and the drawings used in the following description, the same reference numerals as those used for the corresponding parts in the above-described embodiment are used for parts that can be configured in the same manner as in the above-described embodiment, and overlapping Description to be omitted is omitted.

  First, in the above-described embodiment, an example of the unit prism 70 of the optical sheet 60 has been described. However, the present invention is not limited to this example, and various modifications can be made. For example, the plurality of unit prisms 70 may have different configurations. Moreover, although the 2nd prism surface 72 showed the example containing two element surfaces 73, it is not restricted to this, The 2nd prism surface 72 may contain the 3 or more element surfaces 73. Furthermore, the cross-sectional shape of the main cutting surface of the unit prism 70 is not limited to the specific example shown in FIG. 8, and may be, for example, a pentagonal shape or a hexagonal shape.

  As shown in FIG. 19, a light diffusion layer 65 a may be formed on the light exit surface 61 that is opposite to the surface formed by the unit prism 70 of the optical sheet 60. In the example shown in FIG. 19, the light diffusion layer 65 a has a binder resin 69 and light diffusion particles 68 dispersed in the binder resin 69. The diffusing power of the light diffusion layer 65a is set so that the angle range in which half the peak luminance can be obtained when the parallel light beam enters the light diffusion layer 65a is 0.8 ° or more. Is preferred. In this case, it is possible to conceal the defects generated in the optical sheet 60 and the light guide plate 30 by making diffusion in the light diffusion layer 65a inconspicuous. For example, even if a bright spot or a defect occurs due to scratches or dents produced during the manufacture of the optical sheet 60 or the light guide plate 30, the defect is made invisible by the diffusing ability of the light diffusion layer (mat layer) 65a. Can do. By such a light diffusion function in the light diffusion layer 65a, it is possible to expand the tolerance for defects in the unit prism 70, the reflection sheet 28, the light guide plate 30 or the light diffusion layer 65a of the optical sheet 60, and as a result, The yield of the optical sheet 60, the reflective sheet 28, the light guide plate 30, or the light diffusion layer 65a can be improved. Moreover, the diffusion function in the light diffusion layer 65a can smooth the angular distribution of the luminance measured on the light emitting surface 21 of the surface light source device 20, and is large when the observer changes the observation angle. It is possible to provide an angle category (viewing angle) capable of effectively avoiding a change in brightness and observing an appropriate image.

  However, if the diffusing ability of the light diffusion layer 65a is too strong, the peak value of the peak luminance is lowered. From this point, the diffusing power of the light diffusion layer 65a is set so that the angle range in which half the peak luminance can be obtained when the parallel light beam enters the light diffusion layer 65a is 2.6 ° or less. It is preferable.

  Furthermore, in the above-described embodiment, an example of the unit optical element 50 of the light guide plate 30 has been described. However, the present invention is not limited to this example, and various modifications can be made. For example, the plurality of unit optical elements 50 included in the light guide plate 30 may have different configurations. Further, the cross-sectional shape of the unit optical element 50 at the main cut surface is not limited to the specific example shown in FIG. 6 and may be, for example, a triangular shape or a semicircular shape.

In the illustrated example, the outer contour 51 (corresponding to the light-emitting side surface 31) 51 on the main cutting surface of the unit optical element 50 is a light-emitting surface angle θ that is an angle formed by the outer contour with respect to the one side surface 41 of the base 40. _a increases from the tip 52a on the outer contour 51 of the unit optical element 50 furthest away from the base 40 toward the base end 52b on the outer contour 51 of the unit optical element 50 closest to the base 40. It was changing. However, the light exit surface an angle theta _a is, toward the front end portion 52a on the outer contour 51 to the base end portion 52 b, it may vary so as to become smaller. Moreover, although the example in which the unit optical element 50 is formed as a convex portion protruding from the base portion 40 is shown, the present invention is not limited to this example, and the unit optical element 50 may be formed as a concave concave portion.

  Although not shown, in the surface light source device 20, between the light exit surface of the optical sheet 60 (the light emitting surface 21 of the surface light source device in FIG. 1) and the lower polarizing plate 14 of the liquid crystal display panel 15. A known reflective polarizer (also referred to as a polarization separation film) may be disposed. In such a configuration, only the specific polarization component of the light emitted from the optical sheet 60 is transmitted, and the polarization component orthogonal to the specific polarization component is reflected without being absorbed. The polarized light component reflected from the reflective polarizer is reflected by the reflective sheet 28 and the like to depolarize (including both the specific polarized light component and the polarized light component orthogonal to the specific polarized light component), and then reflected again. Is incident on the polarizer. Therefore, the polarization component that has been converted into the specific polarization component in the light incident again passes through the reflective polarizer, and the polarization component orthogonal to the specific polarization component is reflected again. Hereinafter, by repeating the above process, about 70 to 80% of the light emitted from the optical sheet 60 is emitted as the light source light that has become the specific polarization component. Accordingly, by positioning the polarization direction of the specific polarization component (transmission axis component) of the reflective polarizer and the transmission axis direction of the lower polarizing plate 14 of the liquid crystal display panel 15, all the light emitted from the surface light source device 20 is emitted. The liquid crystal display panel 15 can be used for image formation. Therefore, even when the light energy input from the light source 24 is the same, it is possible to form an image with higher brightness than in the case where the reflective polarizer is not arranged, and the light source 24 (and more The energy utilization efficiency (of the power source) is also improved.

  Furthermore, although illustration is omitted, the surface light source device 20 may include a light diffusing sheet for isotropically or anisotropically diffusing light. As an example, the light diffusion sheet may be disposed on the most light-emitting side of the surface light source device to form the light emitting surface 21.

  In addition, although the some modification with respect to embodiment mentioned above was demonstrated above, naturally, it is also possible to apply combining several modifications suitably.

Industrial application fields

The surface light source device 20 or the display device 10 described above can be applied to the following uses as an example.
-Application of automatic teller machine (ATM) to display device and surface light source device of display device During operation of ATM, peeping from the side can be prevented.
・ Application to in-vehicle display device By controlling the direction of image light emission, it is possible to brighten the image for viewers such as drivers while preventing the image from being reflected on the windshield etc. .
・ Application to digital signage Optics suitable for the location of digital signage (also called electronic signage, electronic billboards, electronic bulletin boards, etc.) and the position of viewers by changing the direction of the unit prism of the optical sheet Characteristics can be obtained. Such suitable optical characteristics include, for example, the distribution of the estimated viewers by matching the luminance peak direction of the emitted light with the direction toward the viewer assumed from the display surface of the digital signage, and assuming the angular distribution of luminance. For example, the range may be included.
Since, trains applied viewer into the vehicle display device will be observed the display device from below, it is preferable to display an image toward the (downward than the installation position) the viewer. In addition, when applied to the position of a hanging advertisement, the train is long and narrow, and it is not necessary to widen the viewing angle in the horizontal direction. Therefore, an image can be efficiently displayed for the viewer.
-Application to a display device such as a security room Each of a large number of display devices can have a light emission characteristic that matches the viewer (guard) located in the center.
-Application to table display The viewer is always located at the same relative position to the desk with built-in display. Therefore, it is possible to set the light output characteristics according to the position of the viewer.
-Application to amusement facilities For example, display devices of game machines installed at game centers, etc. When the positional relationship between the installation position and the user is usually constant, a specific user (observer) from the display surface It is possible to achieve an optical characteristic that matches the direction of the luminance peak of the emitted light in the direction toward.
· Applying indirect lighting and desk lights, etc. to the illumination, the light emission characteristic based on the lighting application and lighting setting position can be set appropriately.
・ Automatic ticket gate display device and application of the display device to a surface light source device Since the position of the line of sight of the ticket gate passer is limited, the light emission that matches the luminance peak direction of the emitted light to that position (or the direction of the line of sight) It is desirable to have characteristics.
-Application to a display device for a wristwatch It is necessary to twist an arm in order to view it from the front, and it is often observed from an oblique downward direction of the wristwatch. Therefore, the luminance peak direction of the emitted light and the luminance angle distribution are set so as to include a range in a direction connecting the position of the wristwatch and the position of the eyes of the observer that are normally used. Moreover, since it is often observed under sunlight, it is desirable to have high luminance.
Other examples include display devices behind the seats of airplanes, display devices used to explain safety equipment such as airplanes, display devices near the ceiling such as sightseeing buses, display devices for operation guidance such as airports and stations, multiple screens (e.g., screen within the screen and the vertical plane in a horizontal plane) of at least one of the display device of the game machine having, applied to the liquid crystal operation panel (keyboard, etc.) and the like are also possible.

DESCRIPTION OF SYMBOLS 10 Display apparatus 11 Display surface 12 Liquid crystal layer 13 Upper polarizing plate 14 Lower polarizing plate 15 Liquid crystal display panel 20 Surface light source device 21 Light emission surface 24 Light source 25 Light emitter 28 Reflective sheet 30 Light guide plate 31 Light emission surface 32 Back surface 33 Light incident surface 34 Opposite Surface 35 inclined surface 35a first surface 35b second surface 36 inclined surface 36a first surface 36b second surface 37 inclined surface 38 step surface 39 connecting surface 40 base 41 one side 42 other side 50 unit optical element 51 outer contour 52a tip 52b Base end portion 60 Optical sheet 61 Light exit surface 65 Main body portion 65a Light diffusion layer 66 Light exit side surface 67 Light entrance side surface 68 Light diffusion particle 69 Binder resin 70 Unit prism 71 First prism surface 72 Second prism surface 73 Element surface 73a First Element surface 73b Second element surface 75a Tip portion 75b Base end portion

Claims (8)

A light exit surface; a back surface disposed opposite the light exit surface; and a side surface located between the light exit surface and the back surface, and a portion located on one side in the first direction of the side surfaces. A light guide plate forming a light incident surface;
A light source disposed facing the light incident surface;
An optical sheet disposed to face the light exit surface of the light guide plate,
The back surface of the light guide plate includes a plurality of inclined surfaces arranged in the first direction,
Each inclined surface is inclined with respect to the normal direction of the light guide plate and the first direction so as to approach the light exit surface as it goes from one side to the other side in the first direction,
The optical sheet has a sheet-like main body, and a plurality of unit prisms provided on the light guide plate side of the main body,
The plurality of unit prisms are arranged in a third direction, and each unit prism extends linearly in a direction non-parallel to the third direction,
Each unit prism faces one side in the third direction and faces the other side in the third direction and the first prism surface that forms the incident surface of the light emitted from the light exit surface of the light guide plate A second prism surface that totally reflects light incident on the unit prism through the first prism surface;
In the angular distribution of luminance on the surface opposite to the light guide plate side of the optical sheet in each direction in a plane parallel to the first direction and parallel to the normal direction of the optical sheet, A surface light source device in which a direction in which a luminance peak is obtained is inclined with respect to the normal direction of the optical sheet. A light exit surface; a back surface disposed opposite the light exit surface; and a side surface located between the light exit surface and the back surface, and a portion located on one side in the first direction of the side surfaces. A light guide plate forming a light incident surface;
A light source disposed facing the light incident surface;
An optical sheet disposed to face the light exit surface of the light guide plate,
In the angular distribution of luminance on the light exit surface of the light guide plate in each direction within a plane parallel to both the normal direction of the light guide plate and the first direction, the direction in which a luminance peak is obtained is the direction of the light guide plate. The angle θ _aImax1 inclined from the normal direction to the other side along the first direction, and half the luminance peak positioned between the normal direction of the light guide plate and the direction in which the luminance peak is obtained The angle θ _{aIα1 in} which the direction from which the luminance peak is obtained is inclined to the one side along the first direction from the direction in which the luminance peak is obtained _satisfies the following two conditions (1) and (2):
60 ° ≦ θ _aImax1 ≦ 80 ° (1)
5 ° ≦ θ _aIα1 ≦ 25 ° (2)
The optical sheet has a sheet-like main body, and a plurality of unit prisms provided on the light guide plate side of the main body,
The plurality of unit prisms are arranged in a third direction, and each unit prism extends linearly in a direction non-parallel to the third direction,
Each unit prism faces one side in the third direction and faces the other side in the third direction and the first prism surface that forms the incident surface of the light emitted from the light exit surface of the light guide plate A second prism surface that totally reflects light incident on the unit prism through the first prism surface;
In the angular distribution of luminance on the surface opposite to the light guide plate side of the optical sheet in each direction in a plane parallel to the first direction and parallel to the normal direction of the optical sheet, A surface light source device in which a direction in which a luminance peak is obtained is inclined with respect to the normal direction of the optical sheet. In the angular distribution of luminance on the light exit surface of the light guide plate in each direction in a plane parallel to the normal direction of the light guide plate and orthogonal to the first direction, the direction in which a luminance peak is obtained is the light guide plate. The angle θ _{aImax2 made with} respect to the normal line direction and the direction where the luminance peak is obtained by being located on both sides of the luminance peak are respectively from the direction where the luminance peak is obtained. The surface light source device according to claim 2, wherein the average value θ _{aIα2 of the} tilted angle _satisfies the following conditions (3) and (4).
θ _aImax2 ≦ 3 ° (3)
12 ° ≦ θ _aIα2 ≦ 27 ° (4)   In the angular distribution of the luminance on the surface opposite to the light guide plate side of the optical sheet in each direction in a plane parallel to the first direction and parallel to the normal direction of the optical sheet The surface light source device according to claim 1, wherein a direction in which the luminance peak is obtained is inclined by 10 ° or more with respect to the normal direction of the optical sheet. The third direction is inclined by 15 ° or more with respect to the first direction,
In an angular distribution of luminance on a surface opposite to the light guide plate side of the optical sheet in each direction in a plane orthogonal to the first direction and parallel to the normal direction of the optical sheet The surface light source device according to any one of claims 1 to 4, wherein a direction in which a luminance peak is obtained is inclined with respect to the normal direction of the optical sheet.   Angular distribution of the brightness on a surface opposite to the light guide plate side of the optical sheet in each direction in a plane orthogonal to the first direction and parallel to the normal direction of the optical sheet The surface light source device according to claim 5, wherein a direction in which the luminance peak is obtained is inclined by 10 ° or more with respect to the normal direction of the optical sheet.   The surface light source device as described in any one of Claims 1-6 in which the light-diffusion layer is formed in the surface on the opposite side to the said light-guide plate side of the said optical sheet. A surface light source device according to any one of claims 1 to 7,
A display panel disposed to face the surface light source device.

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