JP5593639B2 - Surface light source device and display device - Google Patents

Description

  The present invention relates to a surface light source device, an optical member, an optical sheet, and a display device that can ensure excellent front direction luminance and in-plane uniformity of front direction luminance, and in particular, can improve the utilization efficiency of light source light. Also, in accordance with this, the present invention relates to a surface light source device, an optical member, an optical sheet, and a display device that can smoothly change the angular distribution of luminance.

  A direct type surface light source device used for a transmissive display device includes a light source and a plurality of optical sheets (optical films) for changing the traveling direction of light from the light source. As a light source, a light source in which a plurality of light emitting units (typically, cold cathode tubes extending in a linear shape) are arranged in parallel is widely used. Among the optical sheets, a light diffusing sheet that diffuses light from the light source and hides the image of the light source (makes it inconspicuous), and a light collection that narrows the light traveling direction to the front direction and improves the brightness in the front direction Sheet.

  As the condensing sheet, an optical sheet formed by arranging unit-shaped elements (unit optical elements) extending linearly in a direction orthogonal to the longitudinal direction (so-called linear array) is widely used (for example, Patent Document 1). ). In particular, as a unit shape element that is generally used, there is known a unit lens whose shape in a cross section (main cut surface) perpendicular to the longitudinal direction thereof is a circular part or an elliptic part. This optical sheet can adjust the angular distribution of luminance by changing the traveling direction of light mainly in a plane along the arrangement direction of the unit shape elements. Therefore, as disclosed in Patent Document 1, two optical sheets may be incorporated in the surface light source device such that the arrangement directions of the unit shape elements are orthogonal to each other. In this example, the angular distribution of luminance can be adjusted in two different directions.

In a surface light source device using a light source in which a plurality of light emitting units are arranged in parallel, the luminance in the front direction tends to decrease at an intermediate position between two adjacent light emitting units. The optical sheet used in the surface light source device also has a light diffusing function that alleviates such surface variations in luminance in the front direction. The optical sheet used in the surface light source device is designed so as to prevent this inconvenience and make the in-plane variation in brightness (also referred to as tube unevenness) inconspicuous. For example, in Patent Document 1, light directly incident from a light emitting unit to a portion facing an intermediate position between two adjacent light emitting units in an optical sheet is refracted at an end of a unit shape element disposed at the position. Further, it is preferable that total reflection can be performed so that the traveling direction can be changed beyond at least the front direction (the normal direction of the optical sheet).
WO2007 / 094426A1

  However, in the surface light source device disclosed in Patent Document 1, it is possible to improve the luminance in the front direction and make the in-plane variation of the luminance uniform, while the angle distribution of the luminance of the surface light source device sharply increases. May change. That is, when observing a display device in which the surface light source device is incorporated, when the observation direction is slightly changed, a sudden change (cutoff) in the brightness of the image may occur. Such a phenomenon (occurrence of cut-off) is very undesirable in a display device, particularly in a display device that is enlarged and observed by a large number of observers from various directions.

  In recent years, with the social trend in which environmental issues are regarded as important, it is also important to improve the light source light utilization efficiency for transmissive display devices (typically liquid crystal display devices). It has been. And it would be very convenient if the angular distribution of luminance could be changed gently while maintaining excellent frontal luminance and in-plane uniformity of frontal luminance by improving the light source light utilization efficiency. .

  The present invention has been made in consideration of such points, and can improve the light source light utilization efficiency while maintaining excellent front direction luminance and in-plane uniformity of front direction luminance. Accordingly, an object of the present invention is to provide a surface light source device, an optical member, an optical sheet, and a display device that can smoothly change the angular distribution of luminance.

  As a result of repeating various experiments, the present inventors have adjusted the light collection efficiency of the first optical sheet disposed on the light incident side of the two optical sheets, thereby improving the light source light utilization efficiency. It can be improved, and by improving the light source light utilization efficiency, it becomes possible to change the angular distribution of luminance smoothly while maintaining in-plane uniformity of front direction luminance and front direction luminance. , Found. Specifically, by reducing the light condensing function of the first optical sheet on the light incident side, the light that has been totally reflected and returned to the light source side can be transmitted through the first optical sheet, and The light condensing function of the first optical sheet can be effectively reduced from the second optical sheet on the light output side with respect to the light transmitted through the first optical sheet by reducing the condensing function of the first optical sheet. Thus, it was found that the angular distribution of luminance can be changed gently while maintaining the front direction luminance and the in-plane uniformity of the front direction luminance. The present invention is based on such knowledge of the present inventors.

  A surface light source device according to the present invention includes a light source including a plurality of light emitting units arranged side by side, and a sheet-like optical member that receives light from the light source, wherein the optical member includes a first optical sheet and a first optical sheet. A second optical sheet disposed on the light output side of the optical sheet, wherein the first optical sheet includes a sheet-shaped first main body portion and a plurality of first optical elements arranged side by side on the first main body portion. The second optical sheet has a sheet-like second main body part, and a plurality of second unit shape elements arranged side by side on the second main body part, and Each of the first unit shape elements extends linearly in a direction that intersects with the arrangement direction of the first unit shape elements and also intersects with the arrangement direction of the light emitting units, and each of the second unit shape elements Extends linearly in a direction intersecting the arrangement direction of the second unit shape elements, The arrangement direction of the first unit shape elements intersects with the arrangement direction of the second unit shape elements, and is parallel to both the normal direction of the first main body and the arrangement direction of the first unit shape elements. In the main cutting plane of the first optical sheet, the angle formed by the tangent to the outer contour of the first unit shape element with respect to the sheet surface of the first main body portion is the angle of the tangent to the first unit shape element. A contact point from the top on the outer contour of the first unit shape element furthest away from the first body portion to the end on the outer contour of the first unit shape element closest to the first body portion. As it goes, it becomes larger and light emitted from one light emitting unit and traveling in a direction parallel to the main cutting surface of the first optical sheet travels in a straight line from the one light emitting unit to the first optical sheet. Incident on the first optical sheet, and then the one Assuming that the light is incident on the end of the first unit-shaped element disposed at a position facing the intermediate position between the light emitting unit and the other light emitting unit adjacent to the one light emitting unit, the light And the light traveling direction changes within a range not exceeding the normal direction of the first main body portion on the main cutting surface of the first optical sheet, and the light traveling direction and the first main body are changed. The first unit shape element is configured such that the angle formed by the normal direction of the portion is small.

In the surface light source device according to the present invention, the distance d in the main cutting surface of the first optical sheet between the one light emitting unit and the other light emitting unit, the first optical sheet from the light emitting unit to the first optical sheet. And the angle θaa formed by the tangent to the end of the unit-shaped element and the sheet surface of the main body portion on the main cutting surface of the first optical sheet is expressed by the following equation: (1) may be satisfied.
θaa <Arcsin (n × sin ((θaa) -Arcsin (sin (Arctan (d / (h × 2) )) / n))) (1)

  In the surface light source device according to the present invention, the tangent to the outer contour of the first unit shape element is 45 ° or more with respect to the sheet surface of the first main body portion on the main cutting surface of the first optical sheet. This is because the position of the contact point of the tangent to the outer contour of the first unit shape element is in the direction parallel to the sheet surface of the first main body portion. In the main occupying surface of the first optical sheet, the tangent to the outer contour of the first unit shape element is the sheet surface of the first main body portion. With respect to the outer contour of the first unit-shaped element in a direction parallel to the sheet surface of the first main body portion. 5% or more of the total width of the first unit shape element You may make it be a case in the area to occupy.

  Further, in the surface light source device according to the present invention, the second optical parallel to both the normal direction of the second main body portion of the second optical sheet and the arrangement direction of the second unit shape elements of the second optical sheet. In the main cutting plane of the sheet, the width of the second unit shape element of the second optical sheet parallel to the sheet surface of the second main body portion is the second optical along the normal direction of the second main body portion. You may make it be 1.5 to 2.5 times the height of the said 2nd unit shape element of a sheet | seat.

  An optical member according to the present invention is a sheet-like optical member used in a direct-type surface light source device including a plurality of light emitting units arranged side by side, and includes a sheet-like first main body portion and the first main body portion. A first optical sheet having a plurality of first unit shape elements arranged side by side, a second optical sheet disposed on the light output side of the first optical sheet, and a sheet-like second main body portion; A second optical sheet having a plurality of second unit shape elements arranged side by side on the first main body portion, each of the first unit shape elements being an array of the first unit shape elements The second unit shape elements intersect with the arrangement direction of the second unit shape elements in a direction that intersects the direction and also intersects with the arrangement direction of the light emitting units. The first unit shape element array extends linearly in the direction of The direction intersects with the arrangement direction of the second unit shape elements, and the main cutting of the first optical sheet is parallel to both the normal direction of the first main body portion and the arrangement direction of the first unit shape elements In the plane, the angle formed by the tangent to the outer contour of the first unit shape element with respect to the sheet surface of the first body portion is such that the contact point of the tangent to the first unit shape element is the first body. As it goes from the top on the outer contour of the first unit shape element farthest from the portion toward the end on the outer contour of the first unit shape element closest to the first main body, the size increases. The light emitted from one light emitting unit and traveling in a direction parallel to the main cutting surface of the first optical sheet travels straight from the one light emitting unit to the first optical sheet and enters the first optical sheet. Then, the one light emitting unit and the one light emitting unit Assuming that the light is incident on the end of the first unit shape element disposed at a position facing an intermediate position between the light emitting unit and another light emitting unit adjacent thereto, the light is refracted at the end, The traveling direction of light changes in a range not exceeding the normal direction of the first main body portion on the main cut surface of the first optical sheet, and depends on the traveling direction of the light and the normal direction of the first main body portion. The first unit shape element is configured so that the angle formed is small.

In the optical member according to the present invention, a distance d in the main cutting surface of the first optical sheet between the one light emitting unit and the other light emitting unit, and the first optical sheet from the light emitting unit to the first optical sheet. The separation distance h in the main cutting plane and the angle θaa formed by the tangent to the end of the unit-shaped element and the sheet plane of the main body in the main cutting plane of the first optical sheet are expressed by the following formula ( 2) may be satisfied.
θaa <Arcsin (n × sin ((θaa) -Arcsin (sin (Arctan (d / (h × 2) )) / n))) (2)

  In the optical member according to the present invention, the tangent to the outer contour of the first unit-shaped element is 45 ° or more with respect to the sheet surface of the first main body portion on the main cutting surface of the first optical sheet. An angle is formed because the position of the contact point of the tangent to the outer contour of the first unit shape element is in the direction parallel to the sheet surface of the first main body portion, and the entire width of the first unit shape element. Of the first optical sheet, the tangent to the outer contour of the first unit shape element is on the sheet surface of the first main body portion. The angle of 10 ° or less with respect to the first unit-shaped element is that the position of the contact point of the tangent to the outer contour of the first unit-shaped element is in the direction parallel to the sheet surface of the first main body portion. Occupies 5% or more of the full width of one unit shape element It may be the case where it is in the area to be checked.

  Furthermore, in the optical member according to the present invention, the second optical sheet parallel to both the normal direction of the second main body portion of the second optical sheet and the arrangement direction of the second unit shape elements of the second optical sheet. The width of the second unit shape element of the second optical sheet parallel to the sheet surface of the second main body section is the second optical sheet along the normal direction of the second main body section. The height of the second unit shape element may be 1.5 times or more and 2.5 times or less.

  An optical sheet according to the present invention is an optical sheet used in a direct type surface light source device including a plurality of light emitting units arranged side by side, and includes a sheet-like main body unit and a plurality of side by side arranged on the main body unit. Each of the unit shape elements extends linearly in a direction that intersects with the arrangement direction of the unit shape elements and also intersects with the arrangement direction of the light emitting units. In the main cutting surface of the optical sheet parallel to both the normal direction of the main body portion and the arrangement direction of the unit shape elements, the tangent to the outer contour of the unit shape elements is relative to the sheet surface of the main body portion. The contact angle of the tangent line to the unit shape element is such that the outside of the unit shape element closest to the main body portion from the top on the outer contour of the unit shape element furthest away from the main body portion. To the edge on the contour As the light increases, the light emitted from one light-emitting unit and traveling in a direction parallel to the main cutting surface travels in a straight line from the one light-emitting unit to the optical sheet and enters the optical sheet. Then, assuming that the light is incident on the end portion of the unit-shaped element disposed at a position facing the intermediate position between the one light-emitting portion and the other light-emitting portion adjacent to the one light-emitting portion. Is refracted at the end portion, so that the traveling direction of the light changes in a range not exceeding the normal direction of the main body at the main cutting plane, and the traveling direction of the light and the normal direction of the main body The unit shape element is configured so that the angle formed by and becomes smaller.

In the optical sheet according to the present invention, a distance d in the main cutting surface between the one light emitting unit and the other light emitting unit, the main cutting surface from the light emitting unit to the optical sheet in the normal direction of the main body unit. And the angle θaa formed by the tangent to the end portion of the unit-shaped element and the sheet surface of the main body portion in the main cut surface satisfy the following expression (3). Good.
θaa <Arcsin (n × sin ((θaa) -Arcsin (sin (Arctan (d / (h × 2) )) / n))) Equation (3)

  Further, in the optical sheet according to the present invention, the tangent to the outer contour of the unit-shaped element is at an angle of 45 ° or more with respect to the sheet surface of the main body part in the main cutting surface. The position of the contact point of the tangent to the outer contour of the unit shape element is in a region occupying 85% or less of the total width of the unit shape element in a direction parallel to the sheet surface of the main body part, In the main cutting plane, the tangent to the outer contour of the unit-shaped element makes an angle of 10 ° or less with respect to the sheet surface of the main body part to the outer contour of the unit-shaped element. The position of the contact point of the tangent line may be in a region occupying 5% or more of the total width of the unit shape element in the direction parallel to the sheet surface of the main body portion.

  A display device according to the present invention includes any one of the surface light source devices according to the present invention described above and a transmissive display unit disposed on a light output side of the surface light source device.

  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.

  1 to 12 are diagrams for explaining an embodiment according to the present invention. Among these, FIG. 1 is a perspective view showing a schematic configuration of a transmissive display device and a surface light source device. 2 and 3 are cross-sectional views of the main cut surface showing the first optical sheet. 4 to 8 are diagrams for explaining refraction of light that travels in a direction intersecting both the arrangement direction of the first unit shape elements and the longitudinal direction of each first unit shape element and is emitted from the first optical sheet. It is. 9-11 is a figure for demonstrating the in-plane distribution of the brightness | luminance in the light emission surface of a 1st optical sheet. FIG. 12 is a graph showing the angular distribution of luminance.

  The transmissive display device 10 shown in FIG. 1 includes a transmissive display unit 15, a surface light source device 20 that is disposed on the back side of the transmissive display unit 15 and illuminates the transmissive display unit 15 in a planar shape from the back side, It has. The transmissive display unit 15 functions as a shutter that controls transmission or blocking of light from the surface light source device 20 for each pixel and forms an image.

  In the present embodiment, the transmissive display unit 15 includes a liquid crystal panel (liquid crystal cell). That is, the transmissive display device 10 functions as a liquid crystal display device. The liquid crystal panel (transmissive display unit) 15 has a pair of polarizing plates 16 and 17 and a liquid crystal layer 18 disposed between the pair of polarizing plates. The polarizing plates 16 and 17 have a function of decomposing incident light into two orthogonal polarization components, transmitting the polarization component in one direction, and absorbing the polarization component in the other direction orthogonal to the one direction. doing.

  An electric field can be applied to the liquid crystal layer 18 for each region where one pixel is formed. Then, the orientation of the liquid crystal layer 18 applied with an electric field changes. The polarized light in a specific direction transmitted through the lower polarizing plate 16 disposed on the light incident side rotates the polarization direction by 90 ° when passing through the liquid crystal layer 18 to which an electric field is applied. Maintains its polarization direction as it passes. For this reason, depending on whether or not an electric field is applied to the liquid crystal layer 18, polarized light in a specific direction transmitted through the lower polarizing plate 16 is further transmitted through the upper polarizing plate 17 disposed on the light output side of the lower polarizing plate 16, or Whether the light is absorbed and blocked by the upper polarizing plate 17 can be controlled.

  In this way, the liquid crystal panel (transmission type display unit) 15 can control transmission or blocking of light from the surface light source device 20 for each pixel. The configuration of the liquid crystal panel (liquid crystal cell) can be configured in the same manner as a device (member) incorporated in a conventional liquid crystal display device, and detailed description thereof is omitted here.

  By the way, in this specification, the “light-emitting side” means the downstream side (observer side, FIG. 2 and FIG. 2) in the traveling direction of light traveling from the light source 25 to the observer through the transmissive display unit 15 without folding the traveling direction. In FIG. 3, the upper side of the paper surface is the “incident side”, and the upstream side in the traveling direction of the light traveling from the light source 25 to the observer through the transmissive display unit 15 without being folded back. That is.

  Next, the surface light source device 20 will be described. As illustrated in FIG. 1, the surface light source device 20 includes a light source 25 and a sheet-like optical member 28 that transmits light from the light source 25. The optical member 28 is disposed on the most light emitting side of the surface light source device 20 and constitutes a light emitting surface (light emitting surface). The optical member 28 is adjacent to the lower polarizing plate 16 of the transmissive display unit 15. Moreover, in the example shown in FIG. 1, the light-diffusion sheet which diffuses light is not provided.

  The surface light source device 20 is configured as a direct type backlight unit. Therefore, the light source 25 is disposed so as to face the optical member 28 on the light incident side of the optical sheet 40. The light source 25 is covered from the back side by the reflection plate 22. The reflection plate 22 is formed in a box shape having an opening (window) on the optical sheet 40 side.

  In the present embodiment, the light source 25 has a plurality of light emitting portions 25a extending linearly. The plurality of light emitting portions 25a extending linearly are arranged side by side so that their longitudinal directions are parallel to each other. That is, the plurality of light emitting portions 25a extending linearly are arranged in parallel on a certain virtual plane. The light emitting unit 25a can be configured by a fluorescent lamp such as a linear cold cathode tube, for example. However, the light source 25 is not limited to this example, and the light source 25 may include various types of light emitting units such as a point LED (light emitting diode), an incandescent light bulb, and a planar EL (electroluminescent).

  As shown in FIG. 1, the reflection plate 22 is a member for directing light from the light source 25 toward the optical member 28. At least the inner surface of the reflecting plate 22 is made of a material having a high reflectance such as metal.

  Next, the optical member 28 will be described. In the present embodiment, the optical member 28 is configured as a sheet-like member having the first optical sheet 30 and the second optical sheet 40 disposed on the light output side of the first optical sheet 30. The optical member 28 is disposed so that its sheet surface is parallel to a virtual plane on which the light emitting portions 25a of the light sources 25 are arranged, and faces the light emitting portions 25a of the light sources 25.

  This sheet-like optical member 28 has a function (condensing function) that changes the traveling direction of light incident from the light incident side and emits the light from the light output side, and intensively improves the luminance in the front direction nd and the vicinity thereof. )have. Further, the sheet-like optical member 28 alleviates luminance unevenness (also referred to as tube unevenness) due to the configuration of the light source 25, more specifically, due to the arrangement of the light emitting portions 25a, thereby improving the luminance in-plane. It also has a function (light diffusion function) for making the distribution uniform and making the image of the light emitting portion 25a of the light source 25 inconspicuous.

  In the present specification, the terms “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 (film surface, plate surface)” corresponds to the planar direction of the target sheet-like member when the target sheet-like member is viewed globally and globally. Refers to the surface. In the present embodiment, the sheet surface of the first optical sheet 30, the sheet surface of the first main body portion 32 described later of the first optical sheet 30, the sheet surface of the second optical sheet 40, and the second optical sheet 40. A sheet surface of the second main body 42, which will be described later, a light emitting surface of the surface light source device 20, a display surface of the transmissive display device 10, and the like are parallel to each other.

  Further, in the present specification, the “front direction” is a direction nd of the normal to the sheet surface of the optical member 28 (see, for example, FIG. 2), the normal direction to the sheet surface of the first optical sheet 30, the second direction. This also coincides with the normal direction to the sheet surface of the optical sheet, the normal direction of the light emitting surface of the surface light source device 20, and the like.

  First, the first optical sheet 30 disposed on the light incident side will be described. The 1st optical sheet 30 comes to exhibit both the condensing function and light-diffusion function which were mentioned above. However, the first optical sheet 30 exhibits a light collecting function mainly on a plane parallel to the arrangement direction of the first unit shape elements 35. In other words, the light condensing function of the first optical sheet 30 can mainly affect the angular distribution of luminance in a plane parallel to the arrangement direction of the first unit shape elements 35.

  As shown in FIG. 1, the first optical sheet 30 includes a sheet-like first main body portion 32 and a first lens portion 34 positioned on the light output side of the first main body portion 32. The first lens unit 34 includes a large number of first unit shape elements (unit optical elements, unit lenses) 35 arranged side by side on the light exit side surface 32 a of the sheet-like first main body unit 32. In the present embodiment, the first unit shape element 35 is disposed on the light exit side surface 32 a of the first main body portion 32 without a gap. As a result, the light exit surface 30 a of the first optical sheet 30 is constituted only by the light exit surface 35 a of the first unit shape element 35.

  In this specification, the term “lens” refers to a so-called narrow-sense lens composed of a curved surface such as a spherical surface, a so-called narrow-sense prism composed of a plane, and an optical element composed of a curved surface and a plane. It is used in a broad sense that includes

  2 and 3 are cross sections parallel to both the normal direction nd of the sheet surface of the first main body portion 32 of the first optical sheet 30 and the arrangement direction of the first unit shape elements 35 (“the main optical sheet main surface”). The first optical sheet 30 is shown in FIG. 2 and 3 also correspond to the cross section taken along the line II-II in FIG.

  As shown in FIGS. 2 and 3, the first main body 32 functions as a sheet-like member that supports the first unit shape element 35. As shown in FIGS. 2 and 3, in the present embodiment, the first unit-shaped elements 35 are arranged side by side on the light output side surface 32 a of the first main body portion 32 without leaving a gap. A first lens portion 34 is formed on the first. On the other hand, as shown in FIGS. 2 and 3, in the present embodiment, the first main body 32 has a light incident surface 30 b of the first optical sheet 30 as a light incident side surface 32 b that faces the light output side surface 32 a. It has a flat (flat) and smooth surface.

  As used herein, “smoothing” means smoothing in an optical sense. That is, here, a certain proportion of visible light is refracted while satisfying Snell's law on the light incident surface 30b of the first optical sheet 30 (light incident side surface 32b of the first main body portion 32). Means. Therefore, for example, the ten-point average roughness Rz (JISB0601) of the light incident side surface 32b of the first main body 32 (light incident surface 30b of the first optical sheet 30) is equal to or shorter than the shortest visible light wavelength (0.38 μm). If so, it is sufficiently smooth.

  Next, the first unit shape element 35 will be described in detail. As shown in FIG. 1, the first unit shape element 35 extends linearly in a direction intersecting with the arrangement direction of the first unit shape elements 35. In the present embodiment, the first unit shape element 35 extends linearly. Further, the longitudinal direction of the first unit shape elements 35 is orthogonal to the arrangement direction of the first unit shape elements 35 on a plane parallel to the sheet surface of the first main body portion 32. As shown in FIG. 1, the arrangement direction of the first unit shape elements 35 intersects the longitudinal direction of the light emitting part 25 a of the light source 25. In the present embodiment, the arrangement direction of the first unit shape elements 35 is orthogonal to the longitudinal direction of the light emitting portion 25a of the light source 25, and the longitudinal direction of each first unit shape element 35 is the longitudinal direction of each light emitting portion 25a. It is parallel to.

  As shown in FIG. 1, in the present embodiment, the cross-sectional shape of each first unit shape element 35 on the main cut surface of the first optical sheet extends in the longitudinal direction (linearly) of the first unit shape element 35. Direction). The plurality of first unit shape elements 35 forming the first lens portion 34 of the first optical sheet 30 are all configured in the same manner. Hereinafter, the cross-sectional shape of the first unit shape element 35 included in the first optical sheet 30 at the main cutting surface will be described in more detail.

  As shown in FIGS. 2 and 3, in the present embodiment, the cross-sectional shape of each first unit shape element 35 on the main cut surface of the first optical sheet is a shape that tapers toward the light output side. Yes. That is, the width of the first unit shape element 35 parallel to the sheet surface of the first main body portion 32 on the main cutting surface of the first optical sheet is the first main body portion along the normal direction nd of the first main body portion 32. It becomes smaller as it moves away from 32.

  Further, as shown in FIG. 3, in the main cutting plane of the first optical sheet, the outer contour of the first unit-shaped element 35 is composed of three or more arcs (arc or elliptical arc) joined together. It consists of three elliptical arcs A1, A2 and A3. Two adjacent arcs connected to each other (arc A1 and arc A2, and arc A2 and arc A3) have a common tangent CTL at the connecting portion. That is, two adjacent arcs are connected continuously. Thereby, the angular distribution of the luminance on the light exit surface 30a of the first optical sheet 30 can be changed gently, and the brightness changes abruptly when the observation direction is changed (cutoff occurs). Can be prevented.

  In the present embodiment, the outer contour of the first unit shape element 35 on the main cut surface of the first optical sheet is line-symmetric with respect to an axis parallel to the normal direction nd of the first main body 32. It has become. Thereby, the angular distribution of the luminance on the light exit surface 30a of the first optical sheet 30 is symmetric about the front direction on a plane parallel to the arrangement direction of the first unit shape elements 35.

  Furthermore, as shown in FIG. 3, the tangent TL to the outer contour of the first unit shape element 35 is the sheet surface of the first main body 32 on the main cut surface (in this embodiment, the light output of the first main body 32). The angle (also referred to as “light-emitting surface angle”) θa formed with respect to the side surface 32 a) is the first body part in the normal direction nd of the first body part 32 when the contact TP of the tangent TL to the first unit shape element 35 is The first unit shape element 35 adjacent to the first main body portion 32 in the normal direction nd of the first main body portion 32 from the top 35b1 on the outer contour (light-emitting surface) 35a of the first unit shape element 35 farthest from the second main body 32. Increases toward both ends 35b2 on the outer contour (light exit surface) 35a. Here, the light exit surface angle θa “becomes larger” only means that the light exit surface angle θa constantly changes greatly (the mode in the present embodiment shown in FIGS. 2 and 3). Instead, the concept includes a case where the light exit surface angle θa does not change in at least a part of the region. That is, here, the light exit surface angle θa is “increased” when the contact point TP travels from the top portion 35b1 on the outer contour (light exit surface) 35a to the end portion 35b2 on the outer contour (light exit surface) 35a. Further, it means that the light exit surface angle θa is “not reduced”.

Moreover, in this Embodiment, the 1st unit shape element 35 is comprised so that following Formula (4) may be satisfy | filled. When the first unit shape element 35 is configured so as to satisfy Expression (4), as shown in FIG. 2, the light is emitted by one light emitting portion 25a1 and proceeds in a direction parallel to the main cutting surface of the first optical sheet. The light L21 travels in a straight line from one light emitting unit 25a1 to the first optical sheet 30 and enters the first optical sheet 30, and then one light emitting unit 25a1 and another adjacent to the one light emitting unit 25a1. The light L31 is refracted at the end 35b2 of the first unit shape element 35 when incident on the end 35b2 of the first unit shape element 35 disposed at a position facing the intermediate position CP with the light emitting unit 25a2. As a result, the traveling direction of the light L31 changes within a range not exceeding the normal direction nd of the first main body portion 32 on the main cut surface of the first optical sheet, and the traveling direction of the light L31 and the first main body portion 32 Normal direction nd and Thus the angle made becomes smaller. That is, due to refraction at the end portion 35b2 of the first unit shape element 35, the traveling direction of the light L31 changes so that the inclination angle with respect to the normal direction of the first optical sheet 30 becomes small, but the traveling direction of the light L31 is The side inclined with respect to the normal direction of the first optical sheet 30 (for example, the light L31 shown in FIG. 2 is directed toward the light output side, the right side of the drawing surface in the arrangement direction of the unit shape elements 35) does not change. It has become. As a result, as described in detail later, it is possible to improve the light source light utilization efficiency while maintaining excellent frontal luminance and in-plane uniformity of frontal luminance, and accordingly, the luminance angle It becomes possible to change the distribution gently.
θaa <Arcsin (n × sin ((θaa) -Arcsin (sin (Arctan (d / (h × 2) )) / n))) (4)

  In the formula (4), d is a separation distance on the main cutting surface of the first optical sheet along the sheet surface of the first main body portion 32 between two adjacent light emitting units 25a included in the light source 25. is there. More precisely, as shown in FIG. 2 and FIG. 3, d is a separation distance between the centers of two adjacent light emitting portions 25a. 2 and 3, h is a main cut surface of the first optical sheet along the normal direction nd of the first main body portion 32 from the light emitting portion 25 of the light source 25 to the first optical sheet 30. Is a separation distance. More precisely, as shown in FIGS. 2 and 3, h is a separation distance between the center of the light emitting part 25 a of the light source 25 and the light incident surface 30 b of the first optical sheet 30. As shown in FIG. 3, θaa is an angle formed by a tangent TL to the end 35b2 of the first unit shape element 35 and the sheet surface of the first main body 32 on the main cut surface of the first optical sheet (hereinafter, referred to as “theta”). , Also referred to as the base angle of the light exit surface).

  Further, the tangent TL to the outer contour 35a of the first unit shape element 35 forms an angle of 45 ° or more (90 ° or less) with respect to the sheet surface of the first main body portion 32 on the main cutting surface of the first optical sheet. This is because the position of the contact point TP of the tangent line TL to the outer contour 35a of the first unit shape element 35 is the full width of the first unit shape element 35 in the direction parallel to the sheet surface of the first main body portion 32. It is preferable to be in a region that occupies 85% or less of them. That is, in the first unit shape element 35 in which the light exit surface angle θa becomes smaller from the end 35b2 to the top 35b1 of the light exit surface 35a, the first unit shape element 35 of the first optical sheet is cut in the main cut surface. The light exit surface angle θa at a position displaced by 42.5% of the width of the first unit shape element 35 in the direction parallel to the sheet surface of the first main body 32 from the end 35b2 (0 ° or more) It is preferable that it is 45 degrees or less. In addition, on the main cut surface of the first optical sheet, the tangent TL to the outer contour 35a of the first unit shape element 35 has an angle of 10 ° or less (0 ° or more) with respect to the sheet surface of the first main body portion 32. What is formed is that the position of the contact point TP of the tangent line TL to the outer contour 35a of the first unit shape element 35 is the full width of the first unit shape element 35 in the direction parallel to the sheet surface of the first main body portion 32. Of these, it is preferable to be in a region occupying at least 5%. That is, in the first unit shape element 35 in which the light exit surface angle θa increases from the top portion 35b1 to the end portion 35b2 of the light exit surface 35a, the first unit shape element 35 on the main cut surface of the first optical sheet. The light exit surface angle θa at a position shifted from the top 35b1 by a length of 2.5% of the width of the first unit shape element 35 in the direction parallel to the sheet surface of the first main body 32 is 10 (0 ° or more). It is preferable that it is below.

  When the present inventors have repeated experiments, according to the first optical sheet 30 designed as described above, a direction (for example, 60 ° to 80 °) that is largely inclined from the front direction to the arrangement direction of the first unit shape elements 35. It was confirmed that it was possible to prevent an unnecessary peak in luminance from being formed in the (inclined direction). That is, it was possible to prevent the formation of singular points in the angular distribution of luminance in the arrangement direction of the first unit shape elements 35, thereby preventing the occurrence of side lobes.

  Moreover, when the present inventors repeated experiments, according to the optical member 28 including the first optical sheet 30 designed as described above, the surface light source device 20 or the display device 10 is viewed from the direction inclined from the front direction. It was confirmed that the in-plane variation in brightness when observed could be made sufficiently inconspicuous. That is, according to the optical member 28 including the first optical sheet 30 designed as described above, the in-plane distribution of luminance in the direction inclined from the front direction can be sufficiently uniformed.

  On the other hand, on the main cutting surface of the first optical sheet, the tangent TL to the outer contour 35a of the first unit shape element 35 is an angle of 45 ° or more (0 ° or more) with respect to the sheet surface of the first main body portion 32. The position of the contact point TP of the tangent TL to the outer contour 35a of the first unit shape element 35 is in the direction parallel to the sheet surface of the first main body portion 32. It is preferable to be in a region of at least 75% of the total width. That is, in the first unit shape element 35 in which the light exit surface angle θa becomes smaller from the end 35b2 to the top 35b1 of the light exit surface 35a, the first unit shape element 35 of the first optical sheet is cut in the main cut surface. The light exit surface angle θa at a position shifted by 37.5% of the width of the first unit shape element 35 in the direction parallel to the sheet surface of the first main body 32 from the end 35b2 is 45 ° or more (90 It is preferable that it is (degrees or less). In addition, on the main cut surface of the first optical sheet, the tangent TL to the outer contour 35a of the first unit shape element 35 has an angle of 10 ° or less (0 ° or more) with respect to the sheet surface of the first main body portion 32. What is formed is that the position of the contact point TP of the tangent line TL to the outer contour 35a of the first unit shape element 35 is the full width of the first unit shape element 35 in the direction parallel to the sheet surface of the first main body portion 32. Of these, it is preferable to be in a region occupying 15% or less. That is, in the first unit shape element 35 in which the light exit surface angle θa increases from the top portion 35b1 to the end portion 35b2 of the light exit surface 35a, the first unit shape element 35 on the main cut surface of the first optical sheet. The light exit surface angle θa at a position shifted by 7.5% of the width of the first unit shape element 35 in the direction parallel to the sheet surface of the first main body portion 32 from the top portion 35b1 is 10 ° or more (90 ° The following is preferable. As a result of repeated experiments by the present inventors, it has been confirmed that according to the optical member 28 including the first optical sheet 30 designed as described above, sufficiently excellent front direction luminance can be ensured.

  As a specific example of the first unit shape element 35 configured as described above, the width W (see FIG. 3) of the first unit shape element 35 can be set to 1 μm to 200 μm. Further, the protrusion height H (see FIG. 3) of the first unit shape element 35 from the light exit side surface 32a of the first main body 32 along the normal direction nd to the sheet surface of the first optical sheet 30 is 0.25 μm. It can be set to ˜50 μm.

  And such a 1st optical sheet 30 can be produced very easily by extrusion process or by shape | molding the 1st unit shape element 35 on a base material. Various materials can be used as the material forming the first optical sheet 30. However, it is widely used as a material for an optical sheet (condensing sheet) incorporated in a display device, and has excellent mechanical characteristics, optical characteristics, stability, workability and the like, and can be obtained at a low price, for example, Transparent resins mainly composed of one or more of acrylic, styrene, polycarbonate, polyethylene terephthalate, acrylonitrile and the like, and epoxy acrylate and urethane acrylate-based reactive resins (ionizing radiation curable resins and the like) can be suitably used. When a material widely used as a material for an optical sheet (light collecting sheet) incorporated in such a display device is used, the refractive index of the first unit shape element 35 of the manufactured first optical sheet 30 is 1. Within the range of .45 to 1.60.

  Next, the second optical sheet 40 of the optical member 28 will be described. The second optical sheet 40 intensively improves the brightness in the front direction (normal direction) nd by changing the traveling direction of the light incident from the light incident side and emitting the light from the light output side by changing the traveling direction of the light. It is a sheet-like member having a function of However, the second optical sheet 40 exhibits a light collecting function mainly in a direction intersecting with the arrangement direction of the first unit shape elements 35 of the first optical sheet 30. That is, the light condensing function of the second optical sheet 40 can mainly influence the angular distribution of luminance in the plane intersecting the arrangement direction of the first unit shape elements 35 of the first optical sheet 30. The 2nd optical sheet 40 may be comprised as various sheet-like members which can exhibit the above condensing functions. The second optical sheet 40 in the present embodiment shown in FIG. 1 is an example, and has substantially the same configuration as the first optical sheet 30 described above.

  As shown in FIG. 1, the second optical sheet 40 in the present embodiment has a sheet-like second main body portion 42 and a second lens portion 44 located on the light output side of the second main body portion 42. ing. The second lens portion 44 has a large number of second unit shape elements (unit optical elements, unit lenses) 45 arranged side by side on the light exit side surface 42a of the sheet-like second main body portion 42. In the present embodiment, the second unit shape element 45 is disposed on the second light exit side surface 42 a of the second main body portion 42 without a gap. As a result, the light exit surface of the second optical sheet 40 is constituted only by the light exit surface of the second unit shape element 45.

  The second unit shape elements 45 are arranged side by side on the light exit side surface 42 a of the second main body portion 42. As shown in FIG. 1, the second unit shape element 45 extends linearly in a direction intersecting with the arrangement direction of the second unit shape elements 45. In the present embodiment, the second unit shape element 45 extends linearly. The longitudinal direction of the second unit shape elements 45 is orthogonal to the arrangement direction of the second unit shape elements 45 on a plane parallel to the sheet surface of the second main body portion 42.

  As shown in FIG. 1, the arrangement direction of the second unit shape elements 45 of the second optical sheet 40 intersects the arrangement direction of the first unit shape elements 35 of the first optical sheet 30. In the present embodiment, the arrangement direction of the second unit shape elements 45 of the second optical sheet 40 is orthogonal to the arrangement direction of the first unit shape elements 35 of the first optical sheet 30. In the present embodiment, the arrangement direction of the second unit shape elements 45 of the second optical sheet 40 extends parallel to the longitudinal direction of the light emitting portion 25a of the light source 25, and the second unit shape elements of the second optical sheet 40 The longitudinal direction of 45 is orthogonal to the longitudinal direction of each light emitting portion 25a.

  In addition, each second unit shape element on a cut surface (also referred to as “main cut surface of the second optical sheet”) parallel to both the normal direction nd of the second main body portion 42 and the arrangement direction of the second unit shape elements 45. The cross-sectional shape of 45 may be configured similarly to the first unit shape element 35 shown in FIGS. 2 and 3. As can be understood from FIG. 1, in the present embodiment, the cross-sectional shape of the second unit shape element 45 in the main cutting surface of the second optical sheet has a shape corresponding to a part of an ellipse or a part of a circle. ing. Further, the cross-sectional shape of the second unit shape element 45 on the main cutting surface of the second optical sheet is constant along the longitudinal direction of the second unit shape element 45 (direction extending linearly). Further, the plurality of second unit shape elements 45 forming the second lens portion 44 are all configured similarly. However, the configuration is not limited to the illustrated example, and the configuration of the second unit shape element 45 may be appropriately changed according to the configuration of the surface light source device 20 other than the second optical sheet 40, for example, the configuration of the light source 25.

  As a specific example of the second unit shape element 45 configured as described above, the width of the second unit shape element 45 can be set to 1 μm to 200 μm. The projecting height of the second unit shape element 45 from the light exit side surface 42a of the second main body 42 along the normal direction nd to the sheet surface of the second optical sheet 40 may be 0.25 μm to 50 μm. it can. Such a second optical sheet 40 can be formed by the same method as the first optical sheet 30 described above and using the same material as the first optical sheet 30 described above.

  When the inventors repeated experiments, the second unit shape element 45 of the second optical sheet 40 along the direction parallel to the sheet surface of the second main body portion 42 at the main cutting surface of the second optical sheet. The width W of the second main body 42 may be 1.5 to 2.5 times the height H of the second unit shape element 45 from the second main body 42 along the normal direction nd of the second main body 42. It has been found that this is preferable in combination with the first optical sheet 30 described above. When the width W of the second unit shape element 45 and the height H of the second unit shape element 45 are set within this range, the front direction luminance is effectively increased as compared with the case where the width is set outside this range. Because it can.

  Next, operations of the first optical sheet 30, the optical member 28, the surface light source device 20, and the transmissive display device 10 as described above will be described.

  First, the overall operation of the transmissive display device 10 and the surface light source device 20 will be described.

  The light emitted from the light emitting unit 25a of the light source 25 travels to the viewer side directly or after being reflected by the reflecting plate 22. The light that has traveled to the viewer side enters the first optical sheet 30 of the optical member 28.

  As shown in FIG. 2, light L21 to L28 emitted from the first unit shape element 35 of the first optical sheet 30 is refracted on the light exit surface (lens surface) of the first unit shape element (unit lens) 35. Due to this refraction, the traveling direction (outgoing direction) of the lights L21 to L28 traveling in the direction inclined from the front direction nd is mainly compared with the traveling direction of the light just before entering the first optical sheet 30. The sheet 30 is bent so that the angle with respect to the normal direction nd to the sheet surface becomes small. By such an action of the first optical sheet 30, the first unit shape element 35 can narrow the traveling direction of the transmitted light to the front direction nd side. That is, the first unit shape element 35 has a light collecting effect on the transmitted light.

  The angle change amount in the traveling direction of the light before entering the first optical sheet 30 and after exiting from the first optical sheet 30 is significantly inclined from the front direction nd and enters the first optical sheet 30. (For example, the light L21 and L25 in FIG. 2) becomes larger. That is, the light condensing action of the first unit shape element 35 is more effectively exerted on the light traveling with a large inclination from the front direction nd.

  Here, as shown in FIG. 2, when the light reflected by the reflecting plate 22 and incident on the first optical sheet 30 is excluded, that is, the first optical sheet 30 directly from the light emitting portion 25a of the light source 25. As for the light L21 to L28 incident on the first optical sheet 30 as the incident position of the light on the first optical sheet 30 moves away from the light emitting unit 25a of the light source 25 in a direction parallel to the sheet surface of the first optical sheet 30. Incident angle θ1 to the sheet 30 increases. That is, with respect to the light source light (hereinafter also referred to as “direct incident light”) that is linearly incident directly on the first optical sheet 30, the method of the first optical sheet 30 is performed as the incident position moves away from the light emitting unit 25a. The inclination angle with respect to the line direction nd increases. As a result, the light condensing action can be effectively exerted on the light incident on the region of the light source 25 away from the light emitting portion 25a.

  On the other hand, as shown in FIG. 2, the light L24 having a small inclination angle in the traveling direction with respect to the front direction nd repeats total reflection on the light exit surface (lens surface) of the unit-shaped element 35, and the traveling direction is changed to the incident side It may change to (light source side). For this reason, it is possible to prevent the luminance from becoming too high at a position immediately above the light emitting portion 25a of the light source 25 where the light from the light source 25 is directly incident at a small incident angle θ1.

  As described above, the optical action mainly exerted from the first unit shape element 35 on the transmitted light is different depending on the separation distance of the light source 25 from the light emitting portion 25a. Thereby, the luminance unevenness (tube unevenness) generated according to the arrangement of the light emitting portions 25a of the light source 25 can be effectively reduced, and the light source image (light image) can be made inconspicuous. In other words, the first optical sheet 30 also has a light diffusing function that makes the in-plane variation in luminance uniform. Such a light diffusion function is such that the arrangement direction of the first unit shape elements 35 of the first optical sheet 30 and the longitudinal direction of the light emitting portion 25a of the light source 25 intersect with each other with respect to the light source 25. By arranging 30, it comes to be demonstrated. In particular, as shown in FIG. 1, such a light diffusion function is performed so that the arrangement direction of the first unit shape elements 35 of the first optical sheet 30 and the longitudinal direction of the light emitting portion 25a of the light source 25 are orthogonal to each other. That is, by arranging the first optical sheet 30 with respect to the light source 25 so that the arrangement direction of the unit shape elements 35 of the first optical sheet 30 and the arrangement direction of the arc tube 25a of the light source 25 are parallel to each other, It will come out more effectively.

  As described above, the emission angle of the light emitted from the first optical sheet 30 is within a narrow angle range centered on the front direction on a plane parallel to the arrangement direction of the unit shape elements 35 of the first optical sheet 30. It is narrowed down.

  The light emitted from the first optical sheet 30 of the optical member 28 then enters the second optical sheet 40 of the optical member 28. The second optical sheet 40 is refracted at the light exit surface of the second unit shape element 45 in the same manner as the action of the first optical sheet 30 (for example, the same as the action of the light L26 to L28 in FIG. 2). Then, it has a condensing effect on the transmitted light. That is, in the second optical sheet 40, the light condensing action is further exerted on the light condensed by the first optical sheet 30.

  However, the light whose traveling direction is largely changed by the second optical sheet 40 is a component that travels in parallel with the main cutting surface of the second optical sheet, and the component condensed by the first optical sheet 30. Is different. That is, the second optical sheet 40 narrows the traveling direction of light within a narrow angle range centered on the front direction in a direction parallel to the arrangement direction of the second unit shape elements 45, while The one optical sheet 30 narrows the traveling direction of light within a narrow angle range centering on the front direction in a direction parallel to the arrangement direction of the first unit shape elements 35. Accordingly, the front direction luminance can be further increased without harming the front direction luminance raised by the first optical sheet 30 due to the optical action of the second optical sheet 40.

  The light emitted from the optical member 28 composed of the first optical sheet 30 and the second optical sheet 40 enters the lower polarizing plate 16 of the transmissive display unit 15. The lower polarizing plate 16 transmits one polarization component of incident light and absorbs the other polarization component. The light transmitted through the lower polarizing plate 16 selectively passes through the upper polarizing plate 17 according to the state of electric field application to each pixel. In this manner, the light from the surface light source device 20 is selectively transmitted for each pixel by the transmissive display unit 15 so that the observer of the transmissive display device 10 can observe the image. Become.

  Here, the action exerted by the optical member 28 including the first optical sheet 30 and the second optical sheet 40 will be described in more detail.

  First, referring mainly to FIG. 2 and FIG. 3, the effect exerted on the light that travels parallel to the main cutting surface of the first optical sheet and directly enters the first optical sheet 30 from the light emitting portion 25 a of the light source 25. Will be described.

  In general, the arrangement interval of the unit-shaped elements 35 of the first optical sheet 30 used as the light collecting sheet is much smaller than the arrangement interval of the light emitting units 25a of the light source 25. Accordingly, when light that directly proceeds from the light emitting unit 25a to the first optical sheet 30 and is directly incident on the first optical sheet 30 (direct incident light on the first optical sheet 30) is examined, as illustrated in FIG. Furthermore, the incident angles of the light L31 to L35 incident on each part of the light exit surface 35a of one first unit shape element 35 (see FIG. 2 and FIG. 3: the traveling direction of the light in the first optical sheet 30 is the first optical sheet. 30) (the angle formed with respect to the normal line direction nd) θ2 can be regarded as substantially constant regardless of the incident position on the first unit shape element 35. In addition, as described above, in the present embodiment, the light exit surface angle θa increases from the top 35b1 toward the end 35b2. The condensing function of the first unit shape element 35 with respect to the incident light gradually becomes stronger from the top 35b1 to the end 35b2 of the light exit surface 35.

  As a result, when considering the directly incident lights L32 to L35 incident on one first unit shape element 35, as shown in FIG. 3, after the light incident position is separated from the top 35b1 of the unit shape element 35, the end portion is reached. As it approaches 35b2, the light emission direction approaches the front direction, and further approaches the outer contour 35a of the unit-shaped element 35 that has been bent and transmitted beyond the front direction (for example, FIG. 3). Light L33). When the directly incident light enters the vicinity of the end 35b2 of the unit shape element 35, it may be totally reflected by the light exit surface 35a and return to the light incident side (for example, the light L32 in FIG. 3). Therefore, the directly incident light incident on the end portion 35b2 having the strongest condensing function among the light exit surfaces 35a of the first unit shape element 35 is bent beyond the front direction by refraction at the end portion 35b2. 2 (for example, the light L23 in FIG. 2), that is, the emission direction of the directly incident light is closer to the first unit shape element 35 through which the light is transmitted than the normal direction nd of the first optical sheet 30. When it is inclined, high front direction luminance can be expected on the light exit surface 30 a of the first optical sheet 30. This is because such direct incident light emitted from the first unit shape element 35 always includes light emitted in the front direction (for example, the light L34 in FIG. 3).

  Incidentally, the emission direction of the direct incident light L23 emitted from the end portion 35b2 of the first unit shape element 35 arranged at a position not far from the light emitting portion 25a, that is, the incident angle θ1 to the first optical sheet 30 is compared. The outgoing direction of the directly incident light L23 that becomes smaller from the first unit shape element 35 can be bent beyond the normal direction nd by refraction at the end 35b2. On the other hand, as described above, in the present embodiment, the traveling directions of the directly incident lights L21, L25, L31 that have traveled to the portion facing the intermediate position CP of the two light emitting sections 25a are arranged at the positions. Due to the refraction at the end 35b2 of the first unit shape element 35, the first unit shape element 35 can be bent in a range not exceeding the front direction. Therefore, in the present embodiment, the directly incident lights L21 and L31 that are emitted from the first optical sheet 30 from the intermediate position CP of the two light emitting portions 25a and the region in the vicinity thereof are emitted in directions other than the front direction. . Therefore, when the light exit surface 30a of the first optical sheet 30 is observed from the front direction, as shown in FIGS. 9 (a), 9 (b), and 9 (c), two adjacent light emitting portions 25a The brightness in the area Zb in between becomes darker than the brightness in the other areas Za.

In addition, about the direct incident light L31 which injects into the edge part 35b2 of the 1st unit shape element 35 which faces the intermediate position CP of the light emission part 25a of two adjacent light sources 25, the following formula | equation (5)-Formula (9) Holds. Here, the angles θaa, θ1, θ2, θ3, θ4, and θ5 in the equations (5) to (9) are as shown in FIG. That is, θ1 is relative to the incident angle to the first optical sheet 30 (the normal direction of the incident surface to the first optical sheet 30 (in the present embodiment, the normal direction of the sheet surface of the first main body portion 32)). (Tilt angle of light). θ2 is an inclination angle when passing through the first main body portion 32. θ3 is an incident angle of the first unit shape element 35 with respect to the light exit surface 35a (an inclination angle of the light incident direction with respect to the normal direction of the light exit surface 35a of the first unit shape element 35). θ4 is an emission angle of the first unit shape element 35 with respect to the light output surface 35a (an inclination angle of the light emission direction with respect to the normal direction of the light output surface 35a of the first unit shape element 35). θ5 is an angle formed by the emission direction with respect to the normal direction of the first optical sheet 30, that is, the emission angle. Further, n in the formula is the value of the refractive index of the material forming the first optical sheet 30 (the first unit shape element 35 and the first main body portion 32). Further, d and h in the formula (5) are the same as those used in the above formula (4).
tan (θ1) = d / 2 / h = d / (h × 2) ... Formula (5)
sin (θ1) = n × sin (θ2) (6)
θ3 = θaa-θ2 (7)
sin (θ4) = n × sin (θ3) (8)
θ5 = θaa-θ4 (9)
Here, as shown in FIG. 3, the emission direction of the direct incident light L31 emitted from the end portion 35b2 of the first unit shape element 35 has passed through the normal direction nd passing through the end portion 35b2. In order to be on the side opposite to the one-unit shape element 35, the angle θ5 in the equation (9) must be larger than 0 ° as in the following equation (10). And if Formula (10) is rewritten using Formula (5)-Formula (8), the conditions of Formula (4) mentioned above will be obtained.
θ5 = θa-θ4> 0 (Equation 10)
θaa <Arcsin (n × sin ((θaa) -Arcsin (sin (Arctan (d / (h × 2) )) / n))) (4)

  The description so far regarding refraction at the light exit surface 35 a of the first unit shape element 35 is for light that travels parallel to the main cutting surface of the first optical sheet and passes through the first optical sheet 30. Next, with reference to FIGS. 4 to 8, the light is applied to light that is inclined with respect to the main cutting surface of the first optical sheet and is directly incident on the first optical sheet 30 from the light emitting unit 25 a of the light source 25. The operation will be described.

  FIG. 4 is a perspective view showing the first unit shape element 35 of the first optical sheet 30 disposed at a position facing the intermediate position CP between the two adjacent light emitting sections 25a. At the end 35b2 of the light exit surface 35a of the first unit shape element 35 shown in FIG. 4, the direct incident light that has entered the first optical sheet 30 in a direction inclined with respect to the main cutting surface of the first optical sheet. L41 and the direct incident light L42 that has entered the first optical sheet 30 in parallel with the main cutting surface of the first optical sheet are refracted. FIGS. 6 to 8 are views showing the first optical sheet 30 (first unit shape element 35) shown in FIG. 4 from the light output side, the front side, and the side, respectively.

  The direct incident lights L41 and L42 shown in FIG. 4 are incident on the first optical sheet 30 at the position A. Thereafter, the light L41 that is inclined with respect to the main cutting surface of the first optical sheet is emitted from the first optical sheet 30 via the position B located at the end 35b2 of the first unit shape element 35. On the other hand, the light L42 traveling parallel to the main cutting surface of the first optical sheet enters the first unit shape element 35 via the position A, and then moves to the position Ba positioned at the end 35b2 of the first unit shape element 35. Through the first optical sheet 30.

  The direct incident light L42 that travels parallel to the main cut surface of the first optical sheet and enters the first optical sheet 30 is light that takes the same optical path as the light L21 in FIG. 2 and the light L31 in FIG. And about this light L42, refraction should just be examined based on Snell's law in the main section of the 1st optical sheet.

  On the other hand, the direct incident light L41 that is inclined with respect to the main cutting surface of the first optical sheet is a surface Pa that is orthogonal to the contact surface TS to the light exit surface 35a at the exit position B, and the direct incident light L41. Refraction based on Snell's law must be considered on the plane Pa parallel to the entry direction to the emission position B (that is, the traveling direction of the directly incident light L41 in the first optical sheet 30). In this example, in the surface Pa defined by the position A, the position B, and the position C (perpendicular to the perpendicular) with respect to the contact surface TS from the position A, the direct incident light L41 Refraction must be considered. FIG. 5 shows a plane Pa that passes through position A, position B, and position C. Further, on this plane Pa, the interface when the directly incident light L41 is emitted from the first unit shape element 35 is represented by a straight line connecting the position B and the position C. Then, by specifying the straight line BC that forms the output interface, the incident angle θ3a (see FIG. 5) of the direct incident light L41 on the light exit surface 35a of the first unit shape element 35 is specified, and Snell's law is followed. Further, the emission direction of the direct incident light L41 is specified.

  By the way, as can be understood from the front view shown in FIG. 7 (corresponding also to the main cutting surface of the first optical sheet) and the perspective view shown in FIG. 4, the first unit-shaped element 35 is observed from the longitudinal direction. When the two lights L41 and L42 traveling in the same direction in the first unit shape element 35 are compared, the light exiting surface 35a of the light L41 traveling inclined with respect to the main cutting surface of the first optical sheet is obtained. Is larger than the incident angle θ3 (see FIG. 7) of the light L42 that travels parallel to the main cutting surface of the first optical sheet on the light exit surface 35a. Therefore, when the incident angle θ3 of the light L42 traveling parallel to the main cut surface of the first optical sheet on the light exit surface 35a exceeds the total reflection critical angle, the light L42 is inclined with respect to the main cut surface of the first optical sheet. The incident angle θ3a of the light L41 traveling on the light exit surface 35a also exceeds the total reflection critical angle. That is, in other words, when the light L42 traveling parallel to the main cutting surface of the first optical sheet is totally reflected by the light exit surface 35a of the first unit shape element 35, it is inclined to the main cutting surface of the first optical sheet. The light L41 that travels in this way is also totally reflected.

  On the other hand, when the light L42 that travels in parallel with the main cutting surface of the first optical sheet is not totally reflected by the light exit surface 35a of the first unit shape element 35, the light of the first optical sheet There is also a possibility that the light L41 that is inclined toward the main cutting plane is emitted without being totally reflected. In particular, as shown in the figure, the light L42 traveling parallel to the main cutting surface of the first optical sheet is refracted by the light exit surface 35a of the first unit-shaped element 35 such that the traveling direction does not exceed the front direction. The emission direction of the light L41 that is inclined toward the main cutting surface of the first optical sheet is inclined from the front direction in the field of view from the arrangement direction of the first unit shape elements 35 (FIG. 8). In the field of view from the longitudinal direction of the unit-shaped element 35 (FIG. 7), it can be parallel to the front direction.

  For this reason, as shown in FIGS. 9, 10 and 11, when the observation angle θv of the light exit surface 30a of the first optical sheet 30 is inclined from the front direction to the longitudinal direction of the first unit shape element 35, The width of the dark part of the brightness existing between the two adjacent light emitting parts 25a gradually becomes narrower, and finally the bright parts of the light stick to each other. On the contrary, when observed from the direction inclined in the longitudinal direction of the first unit shape element 35 from the front direction in this way, a region that is dark when observed from the front (region facing between two adjacent light emitting portions 25a) Zb tends to be brighter than the area Za (the area immediately above the light emitting portion 25a and the surrounding area) Za bright when observed from the front. On the light exit surface 35a of the first unit shape element 35 arranged in the bright area Za when observed from the front, the directly incident light traveling parallel to the main cut surface of the first optical sheet is refracted in the front direction. This is because the direct incident light that is inclined with respect to the main cut surface of the first optical sheet is likely to be totally reflected when entering the light exit surface 35a.

  The light incident on the first optical sheet 30 is not only the direct incident light that is directly incident on the first optical sheet in a straight line from the light emitting unit 25a of the light source 25, but also the diffused light that is reflected by the reflecting plate 22 and incident. Is also present. However, the in-plane distribution of luminance at the light exit surface 35a of the first optical sheet 30 is mainly governed by the transmission distribution of the direct incident light, and the diffused light from the reflector 22 exhibits the in-plane distribution of luminance due to the direct incident light. It only relaxes.

  From the above, regarding the in-plane distribution of luminance on the light exit surface 35 of the first optical sheet 30, with respect to the luminance in the front direction, the position facing the intermediate position CP of the light emitting portions 25a of the two adjacent light sources 25 and the vicinity thereof. It becomes dark in the region (region Zb in FIG. 9A). On the other hand, the in-plane distribution of luminance in the direction inclined from the front direction to the longitudinal direction of the first unit shape element 35 depends on the observation angle θv, but conversely, the light emitting portions 25a of the two light sources 25 adjacent to each other. There is a tendency to become brighter at a position facing the intermediate position CP and an area in the vicinity thereof (area Zb in FIG. 9A).

  Thereafter, the light emitted from the first optical sheet 30 of the optical member 28 enters the second optical sheet 40. As described above, the second optical sheet 40 has the light traveling direction in the plane along the arrangement direction of the second unit shape elements 45, in other words, in the plane along the longitudinal direction of the first unit shape elements 35. It functions to concentrate on a narrow angle range centering on the front direction and the front direction. Therefore, the light L101 and L111 emitted from the light exit surface 35a of the first optical sheet 35 in the direction inclined in the longitudinal direction of the first unit shape element 35 from the front direction is the light exit surface (first surface) of the second optical sheet 40. Due to refraction at the light exit surface) of the 2 unit shape element 45, the exit direction can be directed to the front direction. That is, the lights L101 and L111 emitted from the light exit surface 35a of the first optical sheet 35 in the direction inclined from the front direction to the longitudinal direction of the first unit shape element 35 are collected by the second optical sheet 40. Due to the light action, the light contributes to an increase in front direction luminance on the light exit surface of the optical member 28.

  As described above, in the region Zb including the position facing the intermediate position CP of the two adjacent light emitting portions 25a in the light exit surface 30a of the first optical sheet 30, a large amount of light L101, L111 is transmitted from the front direction. The light is emitted in a direction inclined in the longitudinal direction of the one unit shape element 35. That is, on the light exit surface 30a of the first optical sheet 30, the luminance in the front direction is low in the region Zb including the position facing the intermediate position CP between the two adjacent light emitting sections 25a, and in-plane variation in luminance occurs. On the other hand, on the light exit surface of the second optical sheet 40, the luminance in the front direction in the region Zb including the position facing the intermediate position CP of the two adjacent light emitting units 25 a due to the light condensing action on the second optical sheet 40. Can be effectively increased.

  By the way, in Patent Document 1, the emission direction of the light incident on the end portion of the unit shape element facing the intermediate position CP between the two adjacent light emitting portions 25a is a collection that passes through the end portion due to refraction at the end portion. It is considered preferable to be directed to a range between the normal direction nd of the light sheet and the outer contour of the unit shape element through which light has been transmitted. That is, it has been preferred that the angle θ5 in FIG. 3 is 0 ° or less. Certainly, according to such a condensing sheet, direct incident light emitted in the front direction can be secured in all unit shape elements. Thereby, the outstanding front direction brightness | luminance and the uniformity of the outstanding front direction brightness | luminance can be anticipated.

  On the other hand, in the present embodiment, in the light exit surface 30a of the first optical sheet 30, the front luminance in a part of the region Zb is lowered, and accordingly, in-plane uniformity of sufficient front luminance is ensured. It may not be possible. However, as described above, the second optical sheet 40 disposed on the light output side of the first optical sheet 30 and having a light collecting function in a direction different from the first optical sheet 30 is combined with the first optical sheet 30. Thus, it is possible to intensively increase the luminance in the front direction in a part of the region Zb.

  As a result, the in-plane variation of the luminance in the front direction is eliminated on the light exit surface of the second optical sheet 40 (in this embodiment, the light exit surface of the optical member 28 and further the light emission surface of the surface light source device 20). It is possible to ensure excellent front direction luminance and excellent in-plane uniformity of front direction luminance. As a result of repeated experiments by the present inventors, it is required for a commercially available liquid crystal display device (liquid crystal television) without providing a diffusion plate between the light source 25 and the optical member 28 as in the illustrated embodiment. It was confirmed that in-plane uniformity of brightness can be ensured.

  In addition, light L101, L111 that contributes to the increase in frontal luminance in the region Zb including the position facing the intermediate position CP of the two adjacent light emitting portions 25a of the light exit surface 30a of the first optical sheet 30 (FIG. 10 and FIG. 10). As described above, FIG. 11) is the direct incident light that travels inclined with respect to the main cut surface of the first optical sheet. The reason why such light can be used is that the light condensing property of the first unit shape element 35 of the first optical sheet 30 is weakened.

  On the other hand, in the concentrating sheet disclosed in Patent Document 1 that has been regarded as preferable in the past, the unit-shaped element disposed at a position facing the intermediate position CP between the two adjacent light emitting portions 25a is also sufficiently strong. have. Therefore, the direct incident lights L101 and L111 that are inclined with respect to the main cut surface of the first optical sheet are likely to be totally reflected when entering the unit shape element. Will be returned to. The light returned to the light source 25 can be reused by repeating the reflection, but a loss occurs every time the reflection is repeated. Therefore, when a large amount of light is returned to the light source side by reflection, the light use efficiency is lowered.

  That is, in the present embodiment, light that has not been used can be used in a light collecting sheet that has been considered preferable in the past. And while improving the utilization efficiency of light source light in this way, it is possible to maintain excellent frontal luminance and excellent in-plane uniformity of frontal luminance. As a result, as shown in FIG. 12, the luminance in a wide angle region can be improved, and as a result, the viewing angle can be expanded and the luminance angular distribution can be changed gently.

  FIG. 12 shows the angular distribution of luminance measured in one of many experiments conducted by the inventors changing various conditions. The solid line in FIG. 12 is the measurement result for the surface light source device having the same configuration as the surface light source device in the present embodiment described above. On the other hand, the dotted line in FIG. 12 is a measurement result for the surface light source device configured by replacing the first optical sheet of the surface light source device used in the solid line experiment with another light collecting sheet. The condensing sheet of the surface light source device used for the dotted line experiment was configured such that θ5 shown in FIG. 3 was 0 °, similarly to the condensing sheet disclosed in Patent Document 1.

  According to the present embodiment as described above, the light L101 and L111 that have been totally reflected and returned to the light source 25 side by adjusting the light collecting function of the first optical sheet 30 on the light incident side. Can pass through the first optical sheet 30. That is, the light utilization efficiency can be improved by adjusting the light collecting function of the first optical sheet 30. Further, by adjusting the light collecting function of the first optical sheet 30, the light collecting action from the second optical sheet 40 on the light output side is effectively applied to the light L101 and L111 that are transmitted through the first optical sheet 30. Can be affected. As a result, it is possible to smoothly change the angular distribution of luminance while maintaining in-plane uniformity of excellent front direction luminance and excellent front direction luminance.

  Various modifications can be made to the above embodiment. Hereinafter, an example of modification will be described.

  For example, in the above-described embodiment, the example in which the first unit shape elements 35 of the first optical sheet 30 are disposed adjacent to each other has been described, but the present invention is not limited thereto. For example, as shown in FIG. 13, a flat portion 38 may be formed between two adjacent first unit shape elements 35, or as shown in FIG. 14, two adjacent first unit shape elements 35. A recess 39 may be formed therebetween.

  In FIGS. 13 and 14 for explaining the modification, the same reference numerals are given to the parts that can be configured in the same manner as the above-described embodiment shown in FIGS.

  In the above-described embodiment, the example in which all the first unit shape elements 35 of the first optical sheet 30 have the same configuration has been described, but the present invention is not limited thereto. As an example, unit-shaped elements having different shapes may be included in one first optical sheet 30.

  Furthermore, in the above-described embodiment, an example of the second optical sheet 40 has been described. However, the above-described second optical sheet 40 is merely an example, and various changes can be made. For example, although the cross-sectional shape of the 2nd unit shape element 45 of the 2nd optical sheet 40 showed the example which consists of a part of circular shape or a part of elliptical shape in the main cut surface, it is not restricted to this. The cross-sectional shape of the second unit shape element 45 may be a polygonal shape such as a triangle, for example. In addition, the 2nd optical sheet 40 can be comprised from the various member which can exhibit a condensing function in the direction which cross | intersects the sequence direction of the 1st unit shape element 35 of the 1st optical sheet 30. FIG.

  Further, in the above-described embodiment, the light emitting unit 25a of the light source 25 of the surface light source device 20 is formed of a cold cathode tube extending linearly, but is not limited thereto. As the light source 25, a light emitting unit composed of a dot-like LED (light emitting diode), a planar EL (electroluminescent body), or the like may be provided.

  Furthermore, in the above-described embodiment, an example of the entire configuration of the optical member 28 in which the first optical sheet 30 is incorporated, the surface light source device 20, and the transmissive display device 10 has been described. can do. For example, an optical sheet (for example, a light diffusion sheet) having various functions may be further incorporated in the optical member 28, the surface light source device 20, and the transmissive display device 10.

  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.

FIG. 1 is a diagram for explaining an embodiment according to the present invention, and is a perspective view showing a schematic configuration of a transmissive display device and a surface light source device. FIG. 2 is a cross-sectional view taken along the line II-II in FIG. 1 and shows the first optical sheet incorporated in the surface light source device of FIG. FIG. 3 is an enlarged view showing the optical sheet of FIG. 2 in the same cross section as FIG. FIG. 4 shows the first of the light traveling in parallel with the main cutting surface of the first optical sheet and the light traveling in the direction intersecting both the arrangement direction of the first unit shape elements and the longitudinal direction of each first unit shape element. It is a perspective view for demonstrating the refraction | bending in the light emission surface of a unit shape element. FIG. 5 is a view orthogonal to the contact surface on the light exit surface of the first unit shape element and going in a direction intersecting both the arrangement direction of the first unit shape elements and the longitudinal direction of each first unit shape element. FIG. 6 is a diagram for explaining the refracting action of light on a plane parallel to the light traveling direction shown in FIG. FIG. 6 is a view showing the first optical sheet of FIG. 4 from the light exit side (above). FIG. 7 is a diagram illustrating the first optical sheet of FIG. 4 from a direction (front side) parallel to the longitudinal direction of the first unit shape element. FIG. 7 is a plane orthogonal to the contact surface on the light exit surface of the first unit shape element and parallel to the main cutting plane of the first optical sheet and parallel to the light traveling direction shown in FIG. FIG. 3 is a diagram for explaining the refraction action of the light. FIG. 8 is a diagram showing the first optical sheet of FIG. 4 from a direction (side) parallel to the arrangement direction of the first unit shape elements. FIG. 9 is a diagram for explaining the in-plane distribution of luminance in the front direction on the light exit surface of the first optical sheet. Among these, Fig.9 (a) is a figure which shows a 1st optical sheet from the light emission side (above). FIG. 9B is a diagram illustrating the first optical sheet from a direction (side) parallel to the arrangement direction of the first unit shape elements. FIG. 9C is a cross-sectional view taken along the line cc in FIG. 9B. FIG. 10 is a diagram for explaining in-plane distribution of luminance on the light exit surface of the first optical sheet in a direction inclined in the longitudinal direction of the first unit shape element from the front direction. Among these, Fig.10 (a) is a figure which shows a 1st optical sheet from the light emission side (above). FIG.10 (b) is a figure which shows a 1st optical sheet from the direction (side) parallel to the arrangement direction of a 1st unit shape element. FIG.10 (c) is sectional drawing along the cc line of FIG.10 (b). FIG. 11 is a diagram for explaining the in-plane distribution of luminance on the light exit surface of the first optical sheet in a direction inclined from the front direction to the longitudinal direction of the first unit shape element at a larger inclination angle than FIG. 10. . Among these, Fig.11 (a) is a figure which shows a 1st optical sheet from the light emission side (above). FIG.11 (b) is a figure which shows a 1st optical sheet from the direction (side) parallel to the sequence direction of a 1st unit shape element. FIG.11 (c) is sectional drawing along the cc line | wire of FIG.11 (b). FIG. 12 is a graph showing the angular distribution of luminance on the light exit surface of the surface light source device. FIG. 13 is a view for explaining a modification of the first optical sheet in the same cross section as FIG. FIG. 14 is a diagram for explaining another modification of the first optical sheet in the same cross section as FIG.

DESCRIPTION OF SYMBOLS 10 Transmission type display apparatus 15 Transmission type display part 16 Lower polarizing plate 17 Upper polarizing plate 18 Liquid crystal layer 20 Surface light source device 25 Light source 25a Light emission part 28 Optical member 30 1st optical sheet 30a Light emission surface 30b Light incident surface 32 1st main-body part 32a Light exit side surface 32b Light entrance side surface 34 First lens portion 35 First unit shape element 35a Light exit surface 35b1 Top portion 35b2 End portion 40 Second optical sheet 42 Second body portion 42a Light exit side surface 44 Second lens portion 45 Second unit shape element

Claims (6)

A light source including a plurality of light emitting units arranged side by side;
A sheet-like optical member that receives light from the light source,
The optical member includes a first optical sheet, and a second optical sheet disposed on the light output side of the first optical sheet,
The first optical sheet has a sheet-like first main body part and a plurality of first unit shape elements arranged side by side on the first main body part,
The second optical sheet has a sheet-like second main body part, and a plurality of second unit shape elements arranged side by side on the second main body part,
Each of the first unit shape elements extends linearly in a direction that intersects with the arrangement direction of the first unit shape elements and also intersects with the arrangement direction of the light emitting units,
Each of the second unit shape elements extends linearly in a direction intersecting with the arrangement direction of the second unit shape elements,
The arrangement direction of the first unit shape elements intersects with the arrangement direction of the second unit shape elements,
In the main cutting surface of the first optical sheet parallel to both the normal direction of the first main body and the arrangement direction of the first unit shape elements, the tangent to the outer contour of the first unit shape elements is the The angle formed with respect to the seat surface of the first main body is such that the contact point of the tangent to the first unit shape element is the top of the outer contour of the first unit shape element farthest from the first main body portion. From the end of the first unit shape element closest to the first body portion toward the end on the outer contour,
Light emitted from one light emitting unit and traveling in a direction parallel to the main cutting surface of the first optical sheet travels straight from the one light emitting unit to the first optical sheet and enters the first optical sheet. Then, on the assumption that the light is incident on the end of the first unit-shaped element disposed at a position facing an intermediate position between the one light-emitting part and the other light-emitting part adjacent to the one light-emitting part, When the light is refracted at the end, the traveling direction of the light changes in a range not exceeding the normal direction of the first main body at the main cut surface of the first optical sheet, and the traveling of the light The surface light source device, wherein the first unit shape element is configured so that an angle formed by a direction and a normal direction of the first main body is small. The refractive index value n of the material constituting the first optical sheet, the distance d between the one light emitting part and the other light emitting part on the main cutting surface of the first optical sheet, the first optical from the light emitting part A separation distance h at the main cutting surface of the first optical sheet to the sheet, and a tangent to the end of the unit-shaped element and the sheet surface of the main body at the main cutting surface of the first optical sheet. The surface light source device according to claim 1, wherein the angle θaa satisfies the following expression (1).
θaa <Arcsin (n × sin ((θaa) -Arcsin (sin (Arctan (d / (h × 2) )) / n))) (1) In the main cutting surface of the first optical sheet, the tangent to the outer contour of the first unit shape element is at an angle of 45 ° or more with respect to the sheet surface of the first main body part. A region in which the position of a contact point of a tangent to the outer contour of the first unit shape element occupies 85% or less of the total width of the first unit shape element in a direction parallel to the sheet surface of the first main body. In the case of
In the main cutting surface of the first optical sheet, the tangent to the outer contour of the first unit-shaped element comes to form an angle of 10 ° or less with respect to the sheet surface of the first main body part. A region in which the position of the contact point of the tangent to the outer contour of the first unit shape element occupies 5% or more of the total width of the first unit shape element in a direction parallel to the sheet surface of the first main body. The surface light source device according to claim 1, wherein the surface light source device is a surface light source device. In the main cutting surface of the second optical sheet parallel to both the normal direction of the second main body portion of the second optical sheet and the arrangement direction of the second unit shape elements of the second optical sheet, the second The width of the second unit shape element of the second optical sheet parallel to the sheet surface of the main body portion is a height of the second unit shape element of the second optical sheet along the normal direction of the second main body portion. The surface light source device according to any one of claims 1 to 3, wherein the surface light source device is 1.5 times or more and 2.5 times or less. A plurality of light emitting units arranged side by side ;
An optical sheet that receives light from the light emission , and
The optical sheet includes a sheet-like main body portion, and a plurality of unit shaped elements arranged side by side on the main body portion,
Each of the unit shape elements extends linearly in a direction that intersects with the arrangement direction of the unit shape elements and also intersects with the arrangement direction of the light emitting units,
In the main cutting surface of the optical sheet parallel to both the normal direction of the main body portion and the arrangement direction of the unit shape elements, a tangent to the outer contour of the unit shape elements is relative to the sheet surface of the main body portion. The angle formed is such that the contact point of the tangent to the unit shape element is the outer contour of the unit shape element closest to the main body from the top on the outer contour of the unit shape element farthest from the main body. As you go to the top edge,
Light emitted from one light emitting unit and traveling in a direction parallel to the main cutting surface travels straight from the one light emitting unit to the optical sheet and enters the optical sheet, and then the one light emitting unit. And the light is refracted at the end, assuming that the light enters the end of the unit-shaped element arranged at a position facing an intermediate position between the one light-emitting unit and another adjacent light-emitting unit. As a result, the traveling direction of the light changes in a range not exceeding the normal direction of the main body at the main cutting plane, and the angle formed by the traveling direction of the light and the normal direction of the main body is reduced. As described above, a direct-type surface light source device in which the unit shape element is configured. The surface light source device according to any one of claims 1 to 5 ,
And a transmissive display unit disposed on the light output side of the surface light source device.

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