Optical sheet, surface light source device, and display device

Abstract

This invention provides an optical sheet comprising a substrate layer and an optical functional layer deposited on one side of the substrate layer. The optical sheet, when viewed from above, has a rectangular shape with a pair of first sides extending along a first direction and a pair of second sides extending along a second direction. The optical functional layer comprises: a plurality of light-transmitting portions, each having a specific cross-section and extending along a direction; and light-absorbing portions formed between adjacent light-transmitting portions. The specific cross-section of each light-transmitting portion is trapezoidal, with the shorter upper base designated as the light-incident side. When the transmittance of light in a third direction orthogonal to the first and second directions is set to 100%, the ratio of the transmittance of light in a direction inclined ±30° towards the first direction relative to the third direction, i.e., the relative transmittance, is 1% or less. The extending direction of each light-transmitting portion has an angle of 5° or more and 20° or less relative to the second direction.

Description

Optical Sheet, Surface Light Source Device, and Display Device The present invention relates to an optical sheet, a surface light source device, and a display device. Display devices such as the screens of televisions and personal computers (monitors) are equipped with an image source that emits the image to be displayed, and are also equipped with an optical sheet that improves the quality of the image light and supplies it to the observer side (for example, Patent Documents 1 to 3). The emission direction of the image light is mostly set to the front and viewing angles at specific angles from the front to the up, down, left, and right. Thereby, not only can the image projected on the screen be visually recognized from the front, but also the image projected on the screen can be visually recognized from a position at a certain degree of angle. On the other hand, depending on the need, such as preventing peeping, etc., the front direction is set as the main emission direction to limit the viewing angle. For example, an optical sheet for this purpose is disclosed in Patent Document 4. [Prior Art Documents] [Patent Documents] [Patent Document 1] Japanese Unexamined Patent Application Publication No. 2009-080198 [Patent Document 2] Japanese Unexamined Patent Application Publication No. 2015-014681 [Patent Document 3] Japanese Unexamined Patent Application Publication No. 2017-215440 [Patent Document 4] Japanese Unexamined Patent Application Publication No. 2006-171701 [Problems to be Solved by the Invention] In recent years, for the purpose of entertaining a person sitting in the passenger seat, etc., there is a situation where a display device is arranged in front of the passenger seat of a vehicle such as a car. For such a display device for the passenger seat, it is required to control the emission of the image light toward the driver side in a manner that does not interfere with the driver's driving. However, when the conventional optical sheet is mounted on the display device for the passenger seat, when the transmittance (%) of the light from the front is set to 100%, for example, the ratio of the transmittance (%) of the light in the direction inclined ±30° from the front to the left and right directions, that is, the relative transmittance becomes about 10%, and the ratio of the transmittance (%) of the light in the direction inclined ±20° from the front to the left and right directions, that is, the relative transmittance becomes about 55%, and the emitted light is visually recognized on the driver side. Furthermore, in the case of a right-hand drive vehicle, the display device for the passenger seat is generally arranged in a direction inclined at least 20° to 30° to the left from the front direction of the driver. Similarly, in the case of a left-hand drive vehicle, the display device for the passenger seat is generally arranged in a direction inclined at least 20° to 30° to the right from the front direction of the driver. Fig. 11(a) shows a schematic perspective view of a conventional optical sheet. The optical sheet 90 shown in Fig. 11(a) has, for example, a layer (optical function layer 32) formed by alternately arranging in parallel a light-penetrating portion (light penetration portion 33) that extends along one side direction of the sheet material (the second direction D2 in Fig. 11(a)) and a light-absorbing portion (light absorption portion 34) that absorbs light, along the sheet surface. Such an optical sheet can only control the viewing angle in a direction (the first direction D1 in Fig. 11(a)) orthogonal to the extending direction of the light penetration portion 33 and the light absorption portion 34 (the second direction D2 in Fig. 11(a)), and it is difficult to control the viewing angle in the parallel direction (the second direction D2 in Fig. 11(a)). Therefore, as shown in Fig. 11(b), when the optical sheet 90 is used in the display device 100 for the passenger seat, there is a case where the image light enters the passenger seat side of the vehicle windshield. Therefore, it is also required to control the entry (in the up and down direction) into the windshield in front of the passenger seat. Furthermore, in Fig. 11(b), components other than the optical sheet of the display device 100 are omitted. The present invention has been completed in view of the above circumstances, and an object thereof is to provide an optical sheet for a display device that can obtain image light emission capable of controlling the up and down directions and the left and right directions. Specifically, an object is to provide an optical sheet that, when used as an optical sheet for a display device disposed in front of the passenger seat of a vehicle, can obtain a display device capable of controlling the emission of image light toward the driver side and capable of controlling the entry of image light into the windshield in front of the passenger seat. [Technical Means for Solving the Problem] An embodiment of the present invention is an optical sheet including a base material layer and an optical function layer laminated on one surface of the base material layer, and the optical sheet has a rectangular shape in a plan view, the rectangular shape having a pair of first sides extending along a first direction and a pair of second sides extending along a second direction. The optical function layer has: a plurality of light penetration portions having a specific cross-section and extending along one direction; and light absorption portions formed between adjacent ones of the light penetration portions. The specific cross-section of the light penetration portion is trapezoidal, with the shorter upper base being set as the light incident side. When the light transmittance in a third direction orthogonal to the first direction and the second direction is set to 100%, the ratio of the light transmittance in a direction inclined by ±30° toward the first direction side with respect to the third direction, that is, the relative transmittance, is 1% or less. The extending direction of the light penetration portion has an angle of 5° or more and 20° or less with respect to the second direction. Another embodiment of the present invention is an optical sheet, which includes a base material layer and an optical functional layer laminated on one surface of the base material layer, and the optical sheet has a rectangular shape when viewed from above. The rectangular shape has a pair of first sides extending along a first direction and a pair of second sides extending along a second direction. The optical functional layer has: a plurality of light penetration portions, which have a specific cross-section and extend along one direction; and light absorption portions, which are formed between adjacent ones of the light penetration portions. The specific cross-section of the light penetration portion is trapezoidal, and the shorter upper base is set as the light incident side. The optical sheet is an optical sheet for a display device disposed in front of the passenger seat of a vehicle, and the extending direction of the light penetration portion has an angle of 5° or more and 20° or less with respect to the second direction. Another embodiment of the present invention is an optical sheet, which includes a base material layer and an optical functional layer laminated on one surface of the base material layer, and the optical sheet has a rectangular shape when viewed from above. The rectangular shape has a pair of first sides extending along a first direction and a pair of second sides extending along a second direction. The optical functional layer has: a plurality of light penetration portions, which have a specific cross-section and extend along one direction; and light absorption portions, which are formed between adjacent ones of the light penetration portions. The specific cross-section of the light penetration portion is trapezoidal, and the shorter upper base is set as the light incident side. When the light transmittance in the third direction orthogonal to the first direction and the second direction is set to 100%, the ratio of the light transmittance in the direction inclined ±30° toward the first direction side with respect to the third direction, that is, the relative transmittance is 1% or less. The extending direction of the light penetration portion has an angle of 1.5° or more and 20° or less with respect to the second direction. Another embodiment of the present invention is an optical sheet, which includes a base material layer and an optical functional layer laminated on one surface of the base material layer, and the optical sheet has a rectangular shape when viewed from above. The rectangular shape has a pair of first sides extending along a first direction and a pair of second sides extending along a second direction. The optical functional layer has: a plurality of light penetration portions, which have a specific cross-section and extend along one direction; and light absorption portions, which are formed between adjacent ones of the light penetration portions. The specific cross-section of the light penetration portion is trapezoidal, and the shorter upper base is set as the light incident side. The optical sheet is an optical sheet for a display device disposed in front of the passenger seat of a vehicle, and the extending direction of the light penetration portion has an angle of 1.5° or more and 20° or less with respect to the second direction. Another embodiment of the present invention is an optical sheet, which includes a substrate layer and an optical functional layer laminated on one surface of the substrate layer. The optical sheet has a rectangular shape when viewed from above. The rectangular shape has a pair of first sides extending along a first direction and a pair of second sides extending along a second direction. The optical functional layer has: a plurality of light penetration portions, which have a specific cross-section and extend along one direction; and light absorption portions, which are formed between adjacent light penetration portions. The specific cross-section of the light penetration portion is trapezoidal, and the shorter upper base is set as the light incident side. When the light transmittance in the third direction orthogonal to the first direction and the second direction is 100%, the ratio of the light transmittance in the direction inclined by ±20° toward the first direction side with respect to the third direction, that is, the relative transmittance, is 10% or less. The extending direction of the light penetration portion has an angle of 1.5° or more and 20° or less with respect to the second direction. Another embodiment of the present invention is an optical sheet, which includes a substrate layer and an optical functional layer laminated on one surface of the substrate layer. The substrate layer is a resin substrate. The optical sheet has a rectangular shape when viewed from above. The rectangular shape has a pair of first sides extending along a first direction and a pair of second sides extending along a second direction. The optical functional layer has: a plurality of light penetration portions, which have a specific cross-section and extend along one direction; and light absorption portions, which are formed between adjacent light penetration portions. The specific cross-section of the light penetration portion is trapezoidal, and the shorter upper base is set as the light incident side. The optical sheet is an optical sheet for a display device disposed in front of the passenger seat of a vehicle. The extending direction of the light penetration portion has an angle of 1.5° or more and 20° or less with respect to the second direction. Another embodiment of the present invention is a surface light source device, which includes: the above optical sheet; and a light source, which emits light incident on the optical sheet. Another embodiment of the present invention is a display device, which includes: the above surface light source device; and a display panel, which is laminated on the surface light source device. Another embodiment of the present invention is a display device, which includes a surface light source device including an optical sheet and a display panel laminated on the surface light source device. The optical sheet includes a substrate layer and an optical functional layer laminated on one surface of the substrate layer. The optical functional layer has: a plurality of light penetration portions, which have a specific cross-section and extend along a direction; and a light absorption portion formed between adjacent light penetration portions. The specific cross-section of the light penetration portion is trapezoidal, and the shorter upper base is set as the light incident side. When the display device is provided, in the optical sheet, when the light transmittance in the normal direction of the main surface of the optical sheet is set to 100%, the ratio of the light transmittance in the direction inclined by ±30° from the normal direction to the left and right directions, that is, the relative transmittance, is 1% or less. The extension direction of the light penetration portion observed from the normal direction has an angle of 5° or more and 20° or less with respect to the vertical direction. Another embodiment of the present invention is a display device, which includes a surface light source device including an optical sheet and a display panel laminated on the surface light source device, and is disposed in front of the passenger seat of a vehicle. The optical sheet includes a substrate layer and an optical functional layer laminated on one surface of the substrate layer. The optical functional layer has: a plurality of light penetration portions, which have a specific cross-section and extend along a direction; and a light absorption portion formed between adjacent light penetration portions. The specific cross-section of the light penetration portion is trapezoidal, and the shorter upper base is set as the light incident side. When the display device is provided in front of the passenger seat of the vehicle, in the optical sheet, the extension direction of the light penetration portion observed from the normal direction of the main surface of the optical sheet has an angle of 5° or more and 20° or less with respect to the vertical direction. Another embodiment of the present invention is a display device, which includes an optical sheet and a display panel. The optical sheet includes a substrate layer and an optical functional layer laminated on one surface of the substrate layer. The optical functional layer has: a plurality of light penetration portions, which have a specific cross-section and extend along a direction; and a light absorption portion formed between adjacent light penetration portions. The specific cross-section of the light penetration portion is trapezoidal, and the shorter upper base is set as the light incident side. When the display device is provided, in the optical sheet, when the light transmittance in the normal direction of the main surface of the optical sheet is set to 100%, the ratio of the light transmittance in the direction inclined by ±30° from the normal direction to the left and right directions, that is, the relative transmittance, is 1% or less. The extension direction of the light penetration portion observed from the normal direction has an angle of 1.5° or more and 20° or less with respect to the vertical direction. Another embodiment of the present invention is a display device, which includes an optical sheet and a display panel, is disposed in front of the passenger seat of a vehicle, and the above-mentioned optical sheet includes a substrate layer and an optical functional layer laminated on one surface of the above-mentioned substrate layer. The above-mentioned optical functional layer has: a plurality of light penetration portions, which have a specific cross-section and extend along a direction; and a light absorption portion, which is formed between adjacent above-mentioned light penetration portions. The above-mentioned specific cross-section of the above-mentioned light penetration portion is trapezoidal, and the shorter upper base is set as the light incident side. When the above-mentioned display device is disposed in front of the passenger seat of the vehicle, in the above-mentioned optical sheet, the extension direction of the above-mentioned light penetration portion observed from the normal direction of the main surface of the above-mentioned optical sheet has an angle of 1.5° or more and 20° or less with respect to the vertical direction. Another embodiment of the present invention is a display device, which includes an optical sheet and a display panel, and the above-mentioned optical sheet includes a substrate layer and an optical functional layer laminated on one surface of the above-mentioned substrate layer. The above-mentioned optical functional layer has: a plurality of light penetration portions, which have a specific cross-section and extend along a direction; and a light absorption portion, which is formed between adjacent above-mentioned light penetration portions. The above-mentioned specific cross-section of the above-mentioned light penetration portion is trapezoidal, and the shorter upper base is set as the light incident side. When the above-mentioned display device is disposed, in the above-mentioned optical sheet, when the light transmittance in the normal direction of the main surface of the above-mentioned optical sheet is set to 100%, the ratio of the light transmittance in the direction inclined ±20° from the above-mentioned normal direction to the left and right directions, that is, the relative transmittance is 10% or less. The extension direction of the above-mentioned light penetration portion observed from the above-mentioned normal direction has an angle of 1.5° or more and 20° or less with respect to the vertical direction. Another embodiment of the present invention is a display device, which includes an optical sheet and a display panel, is disposed in front of the passenger seat of a vehicle, and the above-mentioned optical sheet includes a substrate layer and an optical functional layer laminated on one surface of the above-mentioned substrate layer. The above-mentioned substrate layer is a resin substrate. The above-mentioned optical functional layer has: a plurality of light penetration portions, which have a specific cross-section and extend along a direction; and a light absorption portion, which is formed between adjacent above-mentioned light penetration portions. The above-mentioned specific cross-section of the above-mentioned light penetration portion is trapezoidal, and the shorter upper base is set as the light incident side. When the above-mentioned display device is disposed in front of the passenger seat of the vehicle, in the above-mentioned optical sheet, the extension direction of the above-mentioned light penetration portion observed from the normal direction of the main surface of the above-mentioned optical sheet has an angle of 1.5° or more and 20° or less with respect to the vertical direction. [Effects of the Invention] In the present invention, an optical sheet of a display device capable of controlling the emission of image light in the up and down directions and the left and right directions can be provided. Furthermore, in the present invention, an optical sheet can be provided, which, when used as an optical sheet for a display device disposed in front of the passenger seat of a vehicle, can obtain a display device capable of controlling the emission of image light toward the driver side and capable of controlling the image light from entering the windshield in front of the passenger seat. Hereinafter, embodiments of the present invention will be described with reference to the drawings and the like. However, the present invention can be implemented in many different forms and is not limited to the description of the embodiments illustrated below. Also, to make the description clearer, there are cases where the drawings schematically show the widths, thicknesses, shapes, etc. of each part compared to the actual form, but this is only an example and does not limit the interpretation of the present invention. Also, in this specification and each drawing, the same reference numerals are assigned to elements that are the same as those in the previously described drawings, and detailed descriptions are appropriately omitted. In this specification, when expressing the aspect of arranging other components on a certain component, when simply described as "on..." or "under...", unless otherwise specified, it includes the following two cases: arranging other components directly above or below a certain component in contact with it; and arranging other components above or below a certain component with other components intervening. Also, in this specification, when expressing the aspect of arranging other components on the surface of a certain component, when simply described as "on the... side" or "on the... surface", unless otherwise specified, it includes the following two cases: arranging other components directly above or below a certain component in contact with it; and arranging other components above or below a certain component with other components intervening. Hereinafter, the optical sheet, surface light source device, and display device of the present invention will be described in detail. A-1. Optical Sheet (First Embodiment) The optical sheet of this embodiment includes a substrate layer and an optical functional layer laminated on one surface of the substrate layer, and the optical sheet has a rectangular shape in plan view. The rectangular shape has a pair of first sides extending along a first direction and a pair of second sides extending along a second direction. The optical functional layer has: a plurality of light-penetrating portions having a specific cross-section and extending along one direction; and light-absorbing portions formed between adjacent ones of the light-penetrating portions. The specific cross-section of the light-penetrating portion is trapezoidal, with the shorter upper base being set as the light-incident side. When the light transmittance in the third direction orthogonal to the first direction and the second direction is set to 100%, the ratio of the light transmittance in the direction inclined ±30° toward the first direction side with respect to the third direction, that is, the relative transmittance, is 1% or less; the extending direction of the light-penetrating portion has an angle of 1.5° or more and 20° or less with respect to the second direction. The optical sheet of the present embodiment will be described with reference to the drawings. FIG. 1 is a schematic perspective view showing an example of the optical sheet of the present embodiment. Further, FIG. 2 shows a cross-sectional view of the optical sheet cut along the line I-I in FIG. 1. FIG. 3 is a plan view of the optical sheet shown in FIG. 1 as viewed in the direction (-D3 direction) from the base material layer 1 toward the optical functional layer 2. FIG. 4 is an enlarged cross-sectional view of the optical sheet shown in FIG. 2. Furthermore, in the third direction D3, the direction from the optical functional layer 2 toward the base material layer 1 is defined as the +D3 direction, and the direction from the base material layer 1 toward the optical functional layer 2 is defined as the -D3 direction. In FIGS. 1 to 3, the directions (vertical direction and horizontal direction) in which the display device is arranged when the optical sheet is used in the display device are shown together, but the arrangement is not limited thereto. For example, when the optical sheet is used in the display device, as shown in FIG. 1, the display device is preferably arranged such that the first direction D1 is the horizontal direction and the second direction D2 is the vertical direction, but the arrangement is not limited to this. Hereinafter, each component will be described. As shown in FIGS. 1 to 4, the optical sheet 10A of the present embodiment includes a sheet-shaped base material layer 1 and an optical functional layer 2 provided on one surface of the base material layer 1. The base material layer 1 and the optical functional layer 2 are laminated along the third direction D3. Further, as shown in FIG. 3, the optical sheet 10A of the present embodiment has a rectangular shape in plan view, and the rectangular shape has a pair of first sides L1 extending along the first direction D1 and a pair of second sides L2 extending along the second direction D2. The optical functional layer 2 has: a plurality of light transmission portions 3, which have a specific cross-section and extend along one direction; and a light absorption portion 4 formed between adjacent light transmission portions 3. As shown in FIG. 2, the cross-section of the light transmission portion 3 cut along the D1-D3 plane is trapezoidal, and the shorter upper base is set as the light incident side (light source side). In the present embodiment, as shown in FIG. 2, when the light transmittance in the third direction D3 is 100%, the ratio of the light transmittance in the direction inclined ±30° from the third direction D3 toward the first direction D1, that is, the relative transmittance, is 1% or less. Further, as shown in FIG. 3, the extending direction of the light transmission portion 3 has an angle θ of 1.5° or more and 20° or less with respect to the second direction D2. With the optical sheet 10A of the present embodiment, when the light transmittance in the third direction D3 is set to 100%, since the ratio of the light transmittance in the direction inclined by ±30° from the third direction D3 toward the first direction side, that is, the relative transmittance, is below a specific value, the light emission angle in the first direction D1 can be controlled. Further, in a state where the light emission angle in the first direction D1 is controlled, the extending direction of the light transmission portion 3 has an angle θ of 1.5° or more and 20° or less with respect to the second direction D2, whereby the light emission angle in the second direction D2 can be controlled. The reason is that the viewing angle in the first direction D1 has a very narrow characteristic, and when this state is maintained and the angle θ is 1.5° or more and 20° or less, the light transmittance of the light in the second direction D2 decreases rapidly. Therefore, when the optical sheet of the present embodiment is used in a display device, the light emission angles in the left - right direction and the up - down direction of the display device can be controlled. More specifically, when used as an optical sheet for a display device disposed in front of the passenger seat of a vehicle, the emission of image light toward the driver side can be controlled, and the entry of image light into the windshield in front of the passenger seat can be controlled. For example, it is considered that by overlapping two conventional optical sheets 90 shown in FIG. 11 in directions orthogonal to each other, the light emission angle in the first direction D1 can be controlled, and at the same time, the light emission angle in the second direction D2 can be controlled. However, in this method, the light transmittance decreases, and the brightness of the display device decreases. In contrast, with the optical sheet 10A of the present embodiment, since the light emission angle in the first direction D1 can be controlled by one sheet, and at the same time, the light emission angle in the second direction D2 can be controlled, a decrease in the light transmittance can be suppressed. 1. Optical functional layer The optical sheet in the present embodiment includes a substrate layer and an optical functional layer laminated on one surface of the substrate layer. When the optical sheet is used in a display device, it is arranged such that the optical functional layer is on the light source side and the substrate layer is on the observer side. As shown in FIG. 1, the optical functional layer 2 is a layer laminated on one surface of the substrate layer 1, and along the layer surface, the light transmission portions 3 and the light absorption portions 4 are alternately arranged in the first direction D1. In the cross - section shown in FIG. 2, the optical functional layer 2 includes: a light transmission portion 3 having a substantially trapezoidal shape; and a light absorption portion 4 formed between two adjacent light transmission portions 3 and having a substantially trapezoidal cross - section. The light entering the optical sheet 10A enters the optical functional layer 2 from the incident surface Pin, and except for a part of it, the other light is emitted from the exit surface Pout. FIG. 4 is an enlarged view of the cross-sectional view shown in FIG. 2. As shown in FIG. 4, the light La of "the part that enters the light-penetrating part 3 of the optical functional layer 2 vertically at an incident angle of 0°" travels straight inside the light-penetrating part 3 and is emitted from the light-emitting surface Pout. Furthermore, although not shown, the light of "the part that enters the light-absorbing part 4 of the optical functional layer 2 vertically at an incident angle of 0°" is absorbed by the light-absorbing part 4 and blocked by the optical functional layer 2. Among the light of "the part that enters the light-penetrating part 3 of the optical functional layer 2 obliquely at an incident angle greater than 0°", the light Lb that enters near the boundary between the light-penetrating part 3 and the light-absorbing part 4 travels obliquely inside the light-penetrating part 3, is not blocked by the light-absorbing part 4 adjacent to the light-penetrating part 3, and is emitted from the light-emitting surface Pout. Therefore, the light that enters the light-penetrating part 3 at an angle greater than the incident angle of the light Lb is blocked by the light-absorbing part 4, and as a result, all the light that enters the optical functional layer 2 is controlled. Among the light of "the part that enters the light-penetrating part 3 of the optical functional layer 2 obliquely at an incident angle greater than 0°", at least a part of the light Lc of "traveling obliquely inside the light-penetrating part 3 and reaching the side surface of the light-absorbing part 4" is reflected on the side surface of the light-absorbing part 4, the traveling direction changes to the front direction side and converges, and passes through the light-penetrating part 3. At this time, if the refractive index of the light-absorbing part 4 is set to be smaller than the refractive index of the light-penetrating part 3, the light Lc that reaches the side surface of the light-absorbing part 4 at an incident angle greater than the critical angle will be totally reflected and will not be absorbed by the light-absorbing part 4. Therefore, by the total reflection effect, the light transmittance is increased. Among the light of "the part that enters the light-penetrating part 3 of the optical functional layer 2 obliquely at an incident angle greater than 0°", only a part of the light Ld of "traveling obliquely inside the light-penetrating part 3 and reaching the side surface at an incident angle smaller than that of the light Lc with respect to the side surface of the light-absorbing part 4" is reflected on the side surface of the light-absorbing part 4, and the remaining part is absorbed by the light-absorbing part 4. The light-penetrating part 3 is a part mainly for light penetration. As shown in FIG. 2, it is an element having a substantially trapezoidal cross-sectional shape in cross-section. The substantially trapezoid has a longer lower base on the side of the base material layer 1 and a shorter upper base on the opposite side. The light-penetrating part 3 maintains this cross-section along the plane of the base material layer 1, extends along one direction (a direction forming an angle θ with respect to the second direction D2), and is arranged at a specific interval in a direction different from the extending direction (the first direction D1). In the optical sheet of this embodiment, when the light transmittance in the third direction is set to 100%, the ratio of the light transmittance in the direction inclined ±30° from the third direction toward the first direction side, that is, the relative transmittance, is 1% or less. The relative transmittance of the above light is preferably 0.6% or less, and more preferably 0.4% or less. Furthermore, the average value of the relative transmittance of the light in the -30° inclined direction and the relative transmittance of the light in the +30° inclined direction is defined as "the relative transmittance of the light in the ±30° inclined direction". When the light transmittance in the third direction is set to 100%, the ratio of the light transmittance in the direction inclined ±30° from the third direction toward the first direction side, that is, the relative transmittance, can be obtained by the following method. (Measurement method) First, without disposing the optical sheet, measure the brightness of the light in the third direction D3 of the surface light source unit by the viewing angle characteristic measuring device. As the surface light source, an edge light type surface light source using an LED as the light source is used. Subsequently, dispose the surface light source on the back side (optical functional layer side) of the optical sheet, and measure the brightness of the light in the third direction D3 that penetrates the optical sheet and the brightness of the light in the direction inclined ±30° from the third direction D3 toward the first direction D1 on the surface side (base material layer side) of the optical sheet by the viewing angle characteristic measuring device. Then, calculate the ratio of the brightness of the light in the third direction D3 that penetrates the optical sheet to the brightness of the light in the third direction D3 of the surface light source unit, and use it as the light transmittance in the third direction D3 of the optical sheet. Similarly, calculate the ratio of the brightness of the light in the direction inclined ±30° from the third direction D3 toward the first direction D1 that penetrates to the brightness of the light in the third direction D3 of the surface light source unit, and use it as the light transmittance in the direction inclined ±30° from the third direction toward the first direction side. Finally, calculate the ratio of the light transmittance in the direction inclined ±30° from the third direction D3 toward the first direction D1 when the light transmittance in the third direction D3 of the optical sheet is set to 100%, that is, the relative transmittance. ・The light transmittance T of the light in the third direction D3 of the optical sheet 0 (%) = {(brightness of the light emitted from the optical sheet in the third direction D3) / (brightness of the light in the third direction D3 of the surface light source)} × 100 (%) ・The light transmittance T of the light in the direction inclined ±30° from the third direction D3 toward the first direction D1 30 (%) = {(brightness of the light emitted from the optical sheet in the direction inclined ±30° from the third direction D3 toward the first direction D1) / (brightness of the light in the third direction D3 of the surface light source)} × 100 (%) ・Relative transmittance (%) = (T 30 / T 0 ) × 100 (%) The optical sheet having such optical characteristics can be obtained by adjusting any one or more of the cross-sectional shapes of the light absorption portion and the light penetration portion, the refractive indices of the light absorption portion and the light penetration portion, the incident side aperture ratio, the height of the light absorption portion, the OD value of the light absorption portion, etc. In the optical sheet of the present embodiment, when the light transmittance in the third direction is set to 100%, the ratio of the light transmittance in the direction inclined by ±20° from the third direction toward the first direction side, that is, the relative transmittance, is preferably 10% or less, more preferably 5% or less. Furthermore, the average value of the relative transmittance of the light in the direction inclined by -20° and the relative transmittance of the light in the direction inclined by +20° is defined as the "relative transmittance of the light in the direction inclined by ±20°". When the light transmittance in the third direction is set to 100%, the ratio of the light transmittance in the direction inclined by ±20° from the third direction toward the first direction side, that is, the relative transmittance, is obtained by the following method, that is: the same method as the relative transmittance which is the ratio of the light transmittance in the direction inclined by ±30° from the third direction toward the first direction side when the light transmittance in the third direction is set to 100%. Also, in the optical sheet of the present embodiment, when the light transmittance in the third direction is set to 100%, the ratio of the light transmittance in the direction inclined by ±30° from the third direction toward the second direction side, that is, the relative transmittance, can be 32% or less, can also be 30% or less, and can also be 25% or less. When the light transmittance in the third direction is set to 100%, the ratio of the light transmittance in the direction inclined by ±30° from the third direction toward the second direction side, that is, the relative transmittance, is obtained by the following method, that is: the same method as the relative transmittance which is the ratio of the light transmittance in the direction inclined by ±30° from the third direction toward the first direction side when the light transmittance in the third direction is set to 100%. In the present embodiment, in a plan view, the extending direction of the light penetration portion 3 has an angle θ of 1.5° or more and 20° or less with respect to the second direction D2. The above angle θ is 1.5° or more, can also be 5° or more, and can also be 10° or more. On the other hand, the above angle θ is 20° or less, can also be 15° or less. That is, the above angle θ is 1.5° or more and 20° or less, can also be 5° or more and 20° or less, and can also be 10° or more and 15° or less. By making the above angle θ within the above range, the light emission angle in the second direction can be controlled. Furthermore, when the display device is arranged as shown in FIG. 1, the right side observed from the observer is set as the +D1 direction, and the left side is set as the -D1 direction. In FIGS. 1 and 3, the light penetration portion 3 has an angle θ on the right side (+D1 side) with respect to the second direction D2. In this case, it is preferable that the left side (-D1 side) becomes the driver's seat side. On the other hand, the light penetration portion 3 can also have an angle θ on the left side (-D1 side) with respect to the second direction D2. In this case, it is preferable that the right side (+D1 side) becomes the driver's seat side. The above-mentioned angle θ can be obtained by the following method. First, as illustrated in FIG. 3, the optical sheet 10 is placed such that the extending direction of the light-penetrating portion 3 is longitudinal. At this time, the optical sheet may be longitudinally long or horizontally long. Then, the smaller one of the angles formed by the longitudinal side (L2) of the optical sheet 10 and the boundary line BL between the light-penetrating portion 3 and the light-absorbing portion 4 is measured. When measuring the above-mentioned angle, the boundary line BL between the light-penetrating portion 3 and the light-absorbing portion 4 of the shorter upper base of the light-penetrating portion 3 of the optical functional layer 2 and the longer lower base surface of the light-absorbing portion 4 is used. Also, as illustrated in FIG. 3, the above-mentioned angles at two positions are respectively measured for each of the two longitudinal sides (L2a, L2b) of the optical sheet 10, and the arithmetic mean of the four measured values is set as the above-mentioned angle θ. An interval (groove) having a substantially trapezoidal cross-section is formed between adjacent light-penetrating portions 3. Therefore, this interval (groove) has a trapezoidal cross-section having a longer lower base on the upper base side of the light-penetrating portion 3 (opposite to the substrate layer 1 side) and a shorter upper base on the lower base side of the light-penetrating portion 3 (substrate layer 1 side), and the light-absorbing portion 4 is formed by filling the following required material. Furthermore, in FIGS. 1 to 4, adjacent light-penetrating portions 3 are connected by a sheet-like connecting portion 2a on the longer lower base side. The refractive index of the light-penetrating portion 3 is set to Nt. Such a light-penetrating portion 3 can be formed by hardening the composition constituting the light-penetrating portion. Details will be described below. The value of the refractive index Nt is not particularly limited. For example, it is 1.50 or more, preferably 1.54 or more. On the other hand, the value of the refractive index Nt is, for example, 1.65 or less, preferably 1.60 or less. Specifically, the value of the refractive index Nt is 1.50 or more and 1.65 or less, preferably 1.54 or more and 1.60 or less. The purpose is to easily obtain the refractive index difference from the following light-absorbing portion. The light-absorbing portion 4 functions as an "intermediate portion in the above-mentioned interval (groove) formed between adjacent light-penetrating portions 3" and has a cross-sectional shape the same as the cross-sectional shape of the interval. Therefore, the shorter upper base faces the substrate layer 1 side, and the longer lower base is on the side opposite to the substrate layer 1. By setting the shorter upper base as the light-emitting surface Pout side, the light-absorbing portion can reflect a part of the light that travels inside the light-penetrating portion and reaches the side surface of the light-absorbing portion, specifically, the interface between the light-absorbing portion and the light-penetrating portion, and gather it in the front direction, thereby improving the light transmittance. Regarding the light absorption part 4, its refractive index is set to Nr and it is configured to be able to absorb light. Specifically, light absorption particles are dispersed in a transparent resin with a refractive index of Nr. The refractive index Nr is preferably less than the refractive index Nt of the light transmission part 3. Thus, by making the refractive index of the light absorption part 4 less than the refractive index of the light transmission part 3, light incident on the light transmission part 3 can be appropriately totally reflected at the interface with the light absorption part 4 under specific conditions. Also, even when the total reflection condition is not satisfied, a part of the light is reflected at this interface. The value of the refractive index Nr is not particularly limited. For example, it is 1.47 or more, preferably 1.51 or more. On the other hand, the value of the refractive index Nr is, for example, 1.65 or less, preferably 1.57 or less. Specifically, the value of the refractive index Nr is 1.47 or more and 1.65 or less, preferably 1.51 or more and 1.57 or less. The purpose is to easily obtain the following refractive index difference from the light transmission part. The difference Nt - Nr between the refractive index Nt of the light transmission part 3 and the refractive index Nr of the light absorption part 4 is not particularly limited, preferably 0.05 or less, more preferably 0.03 or less. The refractive index difference Nt - Nr is, for example, 0 or more. By reducing the refractive index difference, total reflection can be moderately suppressed and the viewing angle in the first direction (in the case of an optical sheet used as a display device disposed in front of the passenger seat of a vehicle, it is the left - right direction) can be controlled. FIG. 4 shows the angle θ formed by the interface between the light transmission part 3 and the light absorption part 4 with respect to the normal line of the plane of the optical function layer 2. 11 、θ 12 。The angle θ 11 is the angle formed by the interface 4a in the interface between the light transmission part 3 and the light absorption part 4 and the normal line of the plane of the optical function layer 2. When the optical sheet 10 is arranged with the substrate layer 1 side as the observer side, the interface 4a becomes the right side of the light absorption part 4. The angle θ 12 is the angle formed by the interface 4b (which becomes the left side of the light absorption part 4 in the interface between the light transmission part 3 and the light absorption part 4) and the normal line of the plane of the optical function layer 2 under the same arrangement. The angle θ 11 and the angle θ 12 (that is, the inclination angle of the hypotenuse of the trapezoidal cross - section) is not particularly limited. For example, it is 4.0° or more, preferably 4.5° or more. By making θ 11 and θ 12Within the above range, it becomes easy to control the viewing angle in the first direction (in the case of an optical sheet used as a display device disposed in front of the passenger seat of a vehicle, it is the left-right direction). On the other hand, the angle θ 11 and the angle θ 12 are, for example, 6.5° or less, preferably 5.5° or less. That is, the angle θ 11 and the angle θ 12 are, for example, 4.0° or more and 6.5° or less, preferably 4.5° or more and 5.5° or less. In the present embodiment, the light incident side aperture ratio is, for example, 40% or less, preferably 35% or less. By making the light incident side aperture ratio within the above range, it becomes easy to control the viewing angle in the first direction (in the case of an optical sheet used as a display device disposed in front of the passenger seat of a vehicle, it is the left-right direction). On the other hand, the light incident side aperture ratio is, for example, 25% or more, preferably 30% or more. By making the light incident side aperture ratio within the above range, a reduction in the brightness of the display device can be suppressed. That is, the light incident side aperture ratio is, for example, 25% or more and 40% or less, preferably 25% or more and 35% or less, more preferably 30% or more and 35% or less. The above light incident side aperture ratio means, as shown in FIG. 4, the ratio (Wa / Pa) of the width Wa of the light penetration portion 3 existing between the light absorption portions 4 on the surface opposite to the substrate layer 1 side to the distance Pa between the centers of the adjacent light absorption portions 4. The height Da of the light absorption portion is not particularly limited, and is, for example, 110 μm or more, preferably 120 μm or more. By making the height Da of the light absorption portion within the above range, it becomes easy to control the viewing angle in the first direction (in the case of an optical sheet used as a display device disposed in front of the passenger seat of a vehicle, it is the left-right direction). On the other hand, the height Da of the light absorption portion is equal to or less than the thickness of the optical functional layer, for example, 140 μm or less. The OD value (optical density value) of the light absorption portion is not particularly limited, and is, for example, 3.5 or more, preferably 4.0 or more. On the other hand, the OD value of the light absorption portion is, for example, 5.0 or less, preferably 4.5 or less. Specifically, the OD value of the light absorption portion is, for example, 3.5 or more and 5.0 or less, preferably 4.0 or more and 4.5 or less. The method for measuring the OD value of the above-mentioned light absorption part is as described below. First, the composition constituting the light absorption part is coated on an easily adherable PET film with a thickness of 60 μm, laminated with an untreated PET film, and UV-cured on one side. Thereafter, it is also UV-cured from the other side to produce a sample for measurement. The transmittance of the light absorption layer is measured by a penetration densitometer, and the OD value is calculated. In FIGS. 1 to 4, an example is shown in which the interface between the light penetration part 3 and the light absorption part 4 is linear in cross section, but it is not limited thereto. The interface may also be a folded line shape, a convex curved surface shape, a concave curved surface shape, etc. Also, among the plurality of light penetration parts 3 and light absorption parts 4, they may have the same cross-sectional shape or may have specific regularity and different cross-sectional shapes. 2. Substrate layer The substrate layer in this embodiment is a flat sheet-like member that supports the optical functional layer. As the substrate layer, a resin substrate can be used. As the material of the substrate layer, various materials can be used. For example, the following can be used, that is, a material that is widely used as a material for an optical sheet assembled into a display device, has excellent mechanical properties, optical properties, stability, processability, etc., and can be obtained at a low price. As such a material, for example, polyesters such as polyethylene terephthalate (PET), triacetyl cellulose (TAC), acrylic resin, methacrylic resin, polycarbonate, cycloolefin polymer can be cited. As described below, when the optical sheet of this embodiment is used in a liquid crystal display device, considering the combination of the surface light source device and the lower polarizing plate, it is preferable that the birefringence (retardation) of the substrate layer is small. As a material with small birefringence, TAC, methacrylic resin, and polycarbonate are suitably used. Furthermore, in applications that require high heat resistance such as in-vehicle use, polycarbonate with a higher glass transition point is more preferable. Specifically, the glass transition point of polycarbonate is 143 °C, which is suitable for in-vehicle use that generally requires durability at 105 °C. On the other hand, from the viewpoint of suppressing rainbow spots, it is preferable that the birefringence (retardation) of the substrate layer is large. As a material with large birefringence, polyester is suitably used. Polyester is also advantageous in terms of cost and mechanical strength. From the viewpoint of suppressing rainbow spots, the retardation of the substrate layer is preferably 3000 nm or more. The upper limit of the retardation of the substrate layer is not particularly limited, and is preferably about 30000 nm. If the retardation of the substrate layer is too large, there is a risk that the substrate layer will become quite thick. From the viewpoint of thinning the substrate layer, the retardation of the substrate layer is more preferably 5000 nm or more and 25000 nm or less, and even more preferably 7000 nm or more and 20000 nm or less. The retardation Re of the base material layer is represented by the following formula using the refractive index nx in the direction of the maximum in-plane refractive index (slow axis direction) of the base material layer, the refractive index ny in the direction orthogonal to the slow axis direction (fast axis direction), and the thickness d of the base material layer. Re = (nx - ny) × d The above retardation is measured using a retardation measurement device. As the retardation measurement device, for example, the retardation measurement device "KOBRA-WR" manufactured by Oji Scientific Instruments Co., Ltd. is used. The measurement angle is set to 0° and the measurement wavelength is set to 589.3 nm. The above nx - ny (hereinafter referred to as Δn) is preferably 0.05 or more. If the above Δn is too small, the thickness required to obtain the above retardation becomes thick. On the other hand, the above Δn is preferably 0.25 or less. If the above Δn is too large, since the base material layer needs to be stretched excessively, the base material layer is likely to break or be damaged, and the practicality as an industrial material is significantly reduced. Therefore, the above Δn is more preferably 0.07 or more and 0.15 or less. Furthermore, if the above Δn exceeds 0.15, the durability of the base material layer in the damp heat resistance test deteriorates. From the viewpoint of excellent durability in the damp heat resistance test, the above Δn is further preferably 0.12 or less. The above nx is preferably 1.66 or more and 1.78 or less, and more preferably 1.68 or more and 1.73 or less. Also, the above ny is preferably 1.55 or more and 1.65 or less, and more preferably 1.57 or more and 1.62 or less. By making the above nx and ny within the above ranges and satisfying the relationship of the above Δn, better antireflection performance and improvement in brightness contrast can be achieved. As the polyester, as long as the above retardation is satisfied, there is no particular limitation. For example, linear saturated polyesters synthesized from aromatic dicarboxylic acids or their ester-forming derivatives and diols or their ester-forming derivatives can be mentioned. Specific examples include polyethylene terephthalate, poly(ethylene isophthalate), polybutylene terephthalate, poly(1,4-cyclohexylene dimethylene terephthalate), and polyethylene 2,6-naphthalate. Also, the polyester may be a copolymer of these polyesters. Further, a mixture of a polyester mainly composed of a polyester and other types of resins can also be used. In the above mixture, the content of the polyester is, for example, 80 mol% or more. Among them, from the viewpoint of better balance of mechanical properties and optical properties, etc., polyethylene terephthalate and polyethylene 2,6-naphthalate are preferred. Particularly preferred is polyethylene terephthalate (PET). The reason is that PET has high versatility and is easily available. Furthermore, PET has excellent transparency, thermal properties, and mechanical properties, and the retardation can be controlled by stretching processing. Even if the intrinsic birefringence is large and the thickness is thin, a relatively large retardation can be obtained relatively easily. In the case where the base material layer is a polyester base material, as a method for producing the polyester base material, as long as it satisfies the above-mentioned retardation method rules, there is no particular limitation. For example, the following methods can be cited: melting the polyester and extruding it into a sheet to obtain an unoriented polyester, and then using a tenter or the like at a temperature above the glass transition temperature to laterally orient it, and then performing heat treatment on it. The lateral orientation temperature is preferably 80 °C or higher and 130 °C or lower, more preferably 90 °C or higher and 120 °C or lower. Also, the lateral orientation ratio is preferably 2.5 times or more and 6.0 times or less, more preferably 3.0 times or more and 5.5 times or less. If the lateral orientation ratio is too large, the transparency of the obtained polyester base material may easily decrease. Also, if the lateral orientation ratio is too small, the stretching tension will become small, so the birefringence of the obtained polyester base material may become small and the above-mentioned retardation may not be satisfied. Also, in the method for producing the polyester base material, a biaxial orientation test device can also be used. After laterally orienting the above-mentioned unoriented polyester under the above conditions, it is oriented along the flow direction relative to the lateral orientation (hereinafter, also referred to as longitudinal orientation). In this case, the longitudinal orientation ratio is preferably 2 times or less. If the longitudinal orientation ratio is too large, the above-mentioned Δn may not satisfy the above-mentioned preferred range. Also, the heat treatment temperature is 100 °C or higher and 250 °C or lower, preferably 180 °C or higher and 245 °C or lower. As a method for controlling the retardation of the polyester base material produced by the above method within the above range, examples include: a method of appropriately setting the orientation ratio, the orientation temperature, or the thickness of the produced polyester base material. Specifically, the higher the orientation ratio, the easier it is to obtain a higher retardation, and the lower the orientation ratio, the easier it is to obtain a lower retardation. The lower the orientation temperature, the easier it is to obtain a higher retardation, and the higher the orientation temperature, the easier it is to obtain a lower retardation. The thicker the thickness, the easier it is to obtain a higher retardation, and the thinner the thickness, the easier it is to obtain a lower retardation. The thickness of the polyester base material is preferably 20 μm or more and 500 μm or less, more preferably 50 μm or more and 300 μm or less, and even more preferably 50 μm or more and 150 μm or less. If the thickness of the polyester base material is too thin, the retardation of the polyester base material may not satisfy the above range. Also, if the thickness of the polyester base material is too thin, the anisotropy of the mechanical properties will become obvious, and it will easily break, crack, etc., and there is a case where the practicality as an industrial material is significantly reduced. On the other hand, if the thickness of the polyester base material is too thick, the polyester base material is very rigid, and the softness peculiar to the polymer film is reduced, and there is still a case where the practicality as an industrial material is reduced. The total light transmittance of the base material layer is preferably 80% or more, more preferably 84% or more. The total light transmittance is measured according to JIS K7361-1:1997. 3. Other Layers The optical sheet of this embodiment may have other layers in addition to the above-mentioned substrate layer and optical functional layer. As the other layer, for example, a hard coat layer with a rough surface can be cited. The hard coat layer with such a rough surface is, for example, a hard coating whose surface presents a rough surface with an arithmetic mean roughness Ra of 0.1 μm or more according to JIS B0601:1994. In this embodiment, the arithmetic mean roughness Ra of the hard coat layer is preferably 0.2 μm or more, and more preferably 0.4 μm or less. Due to the rough surface of the hard coat layer, when the optical sheet is assembled into a display device, it is not easily scratched due to contact with other adjacent optical members. Also, due to the rough surface of the hard coat layer, light contact can be suppressed, thereby suppressing the generation of interference fringes caused by light contact and making it difficult for the optical performance to deteriorate. The hard coat layer with a rough surface can be disposed on the surface of the substrate layer on the side opposite to the optical functional layer side (light-emitting side), or can also be disposed on the surface of the optical functional layer on the side opposite to the substrate layer side (light-incident side). 4. Manufacturing Method The optical sheet of this embodiment can be manufactured, for example, as described below. First, a light-penetrating portion is formed on the substrate layer. That is, a substrate sheet that becomes the substrate layer is inserted between a mold roll and a nip roll, the surface of the mold roll has a shape capable of transferring the light-penetrating portion, and the nip roll is disposed opposite to the mold roll. At this time, a composition constituting the light-penetrating portion is supplied between the substrate sheet and the mold roll, and at the same time, the mold roll and the nip roll are rotated. Thereby, the composition constituting the light-penetrating portion is filled into the grooves corresponding to the light-penetrating portion formed on the surface of the mold roll (a shape obtained by inverting the shape of the light-penetrating portion), and the composition becomes one that follows the surface shape of the mold roll. As the composition constituting the light-penetrating portion, for example, free-radical radiation-curable resins such as epoxy acrylate-based, urethane acrylate-based, polyether acrylate-based, polyester acrylate-based, and polythiol-based resins can be cited. The composition constituting the light-penetrating portion sandwiched between the mold roll and the substrate sheet and filled therein is irradiated with light for hardening by a light irradiation device from the substrate sheet side. Thereby, the composition can be hardened and its shape can be fixed. Then, the substrate layer and the formed light-penetrating portion are demolded from the mold roll by a demolding roll. Subsequently, a light-absorbing portion is formed. In order to form the light-absorbing portion, first, a composition constituting the light-absorbing portion is filled in the interval between the above-mentioned light-penetrating portions. Thereafter, the excess of the above-mentioned composition is scraped off by a doctor blade or the like. Then, the remaining composition is hardened from the light-penetrating portion side, and a light-absorbing portion can be formed. As the hardening method, for example, hardening by ultraviolet irradiation, hardening by heating, etc. can be cited. The composition constituting the light absorption part is not particularly limited. For example, a composition in which light absorption particles that have been colored are dispersed in a photocurable resin such as urethane (meth)acrylate, polyester (meth)acrylate, epoxy (meth)acrylate, and butadiene (meth)acrylate can be cited. Further, a composition in which light absorption particles that have been colored are dispersed in a thermosetting resin can also be used. Further, instead of dispersing light absorption particles, a pigment or a dye can be used to color the entire light absorption part. As the light absorption particles, light-absorbing colored particles such as carbon black are preferably used. The light absorption particles are not limited to these, and colored particles that selectively absorb a specific wavelength according to the characteristics of the image light can also be used. Specifically, examples include carbon black, graphite, metal salts such as black iron oxide, organic fine particles colored with a dye or a pigment, or glass beads. From the viewpoints of cost, quality, availability, etc., colored organic fine particles are particularly preferably used. The average particle diameter of the colored particles is preferably 1.0 μm or more and 20 μm or less, more preferably 1.0 μm or more and 10 μm or less, and even more preferably 1.0 μm or more and 4.0 μm or less. Here, the "average particle diameter" refers to the diameter obtained by observing 100 light absorption particles with an electron microscope, measuring their diameters, and calculating the arithmetic average. 5. Optical sheet The optical sheet of this embodiment has a rectangular shape in a plan view, and the rectangular shape has a pair of first sides L1 extending in the first direction and a pair of second sides L2 extending in the second direction. The first side L1 may be longer than the second side L2, may be shorter, or may be the same. The first direction, the second direction, and the third direction are usually orthogonal to each other. In FIG. 1, the first side L1 is longer than the second side L2. The use of the optical sheet of this embodiment is not particularly limited. For example, it can be used in a display device. Among them, the optical sheet of this embodiment is preferably used in an in-vehicle display device, and more preferably used in a display device disposed in front of the passenger seat of a vehicle. The optical sheet can be disposed on the observer side of the display panel in the display device, or can be included in the surface light source device of the display device. B-1. Surface light source device (first embodiment) The surface light source device of this embodiment includes the optical sheet of the above first embodiment and a light source that emits light incident on the optical sheet. The surface light source device is usually used in a display device. FIG. 5 is an exploded perspective view of a display device including the surface light source device of this embodiment. Further, FIG. 6 shows a part of an exploded cross-sectional view of the display device cut along the line II-II in FIG. 5, and FIG. 7 shows a part of an exploded cross-sectional view of the display device cut along the line III-III in FIG. 5. The display device shown in FIGS. 5 to 7 is an example of a liquid crystal display device. As shown in FIGS. 5 to 7, the display device 50A including the surface light source device 20 of the present embodiment includes a liquid crystal panel 15, a surface light source device 20, and a functional film 40. The direction in which the display device is disposed is also shown in FIGS. 5 to 7, but the setting is not limited thereto. For example, as shown in FIG. 5, the display device is preferably arranged such that the first direction D1 in FIGS. 1 to 4 is the horizontal direction and the second direction D2 is the vertical direction, but the arrangement is not limited to this. Hereinafter, each component will be described. The surface light source device 20 in FIGS. 5 to 7 is an illumination device that "has the above-described optical sheet 10A, is disposed at a position on the side opposite to the observer side of the liquid crystal panel 15, and emits planar light to the liquid crystal panel 15". Further, the surface light source device 20 in FIGS. 5 to 7 is configured as an edge illumination type surface light source device, and includes a light guide plate 21, a light source 25, a light diffusion plate 26, a prism layer 27, a reflective polarizing plate 28, an optical sheet 10A, and a reflective sheet 29. As shown in FIGS. 5 to 7, in the surface light source device 20, the optical sheet 10A is arranged such that the base material layer 1 is on the observer side with respect to the optical functional layer 2. As shown in FIGS. 5 to 7, the light guide plate 21 has a base portion 22 and a backside optical element 23. The light guide plate 21 is a member having a plate shape as a whole formed of a light-transmissive material. As shown in FIGS. 5 to 7, one plate surface side of the light guide plate 21 on the observer side is set as a smooth surface, and the other plate surface side on the opposite side is set as the backside, and a plurality of backside optical elements 23 are arranged on the backside. Various materials can be used as the materials for the base portion 22 and the backside optical element 23. For example, materials that are widely used as materials for optical sheets assembled into display devices, have excellent mechanical properties, optical properties, stability, processability, etc., and can be obtained at low cost can be used. As such materials, for example, polymer resins having an alicyclic structure, methacrylic resins, polycarbonates, polystyrenes, acrylonitrile-styrene copolymers, methyl methacrylate-styrene copolymers, ABS resins, polyether sulfone and other thermoplastic resins, or epoxy acrylate, urethane acrylate-based reactive resins (such as free radiation curing type resins) can be cited. The base portion 22 is "a portion that guides light inside thereof and serves as a base for the backside optical element 23, and has a plate shape with a specific thickness". The back optical element 23 is a protruding element formed on the back side of the base 22, and is in the shape of a triangular prism in FIGS. 5 to 7. The back optical element 23 is columnar with the ridge line at the protruding top extending in the horizontal direction, and a plurality of back optical elements 23 are arranged at a specific interval in the direction (vertical direction) orthogonal to the extending direction. The cross-section of the back optical element 23 in FIGS. 5 to 7 is triangular, but is not limited thereto, and may also be a cross-section of any shape such as a polygon, a hemispherical shape, a part of a sphere, a lens shape, etc. The arrangement direction of the plurality of back optical elements 23 is preferably the light guiding direction. That is, they are arranged in the direction away from the light source 25, and the ridge line of each back optical element 23 extends along the arrangement direction of the light source 25, or if it is a single long light source, it extends parallel to the extending direction of the light source. Furthermore, the "triangular shape" in this specification does not refer only to the strictly defined triangular shape, but also includes a substantially triangular shape, and the above-mentioned substantially triangular shape includes the limits in manufacturing technology or errors during molding, etc. Also, similarly, the terms of specific other shapes or geometric conditions used in this specification, such as terms like "parallel", "orthogonal", "ellipse", "circle", etc. are not limited to the strict meaning, but should be interpreted including the errors to the extent that the same optical function can be expected. The light guide plate 21 having such a configuration can be manufactured by extrusion molding or by shaping the back optical element 23 on the base 22. Furthermore, in the light guide plate 21 manufactured by extrusion molding, the base 22 and the back optical element 23 can be formed integrally. Also, in the case of manufacturing the light guide plate 21 by shaping, the back optical element 23 can be the same resin material as the base 22 or a different material. The light source 25 is disposed on "the side surface (end surface) of the side of the arrangement direction of the back optical element 23 in the side surface (end surface) that the base 22 of the light guide plate 21 has". The light source is not particularly limited and can be composed of various forms such as a fluorescent lamp such as a linear cold cathode tube, a dot-shaped LED (light emitting diode), or an incandescent bulb. In FIGS. 5 to 7, the light source 25 is composed of a plurality of LEDs, and is configured such that the lighting and extinguishing of each LED and / or the brightness of each LED when lit can be independently adjusted by a control device (not shown). Furthermore, FIGS. 5 to 7 illustrate an example where the light source 25 is disposed on one side surface (end surface) as described above, and it is also possible to have a configuration where a light source is further disposed on the side surface (end surface) opposite to the side surface (end surface). Also, in this case, the shape of the back optical element is also formed by following a known example. Next, the light diffusion plate 26 will be described. The light diffusion plate 26 is disposed on the light-emitting side of the light guide plate 21 and is a member having a function of diffusing the incident light and emitting it. Thereby, the uniformity of the light emitted from the light guide plate 21 can be further improved, and the scratches present in the light guide plate 21 can be made less obvious. Regarding the specific form of the light diffusion plate, a known light diffusion plate can be used. For example, a form in which a light diffusing agent is dispersed in a base material can be cited. The light diffusion plate 26 can be used as a support plate for the prism layer 27 as shown in FIGS. 5 to 7. Also, when the light-emitting surface of the light guide plate 21 is smooth, the light diffusion plate 26 can be bonded to the light guide plate 21 to form an integral body. As can be seen from FIGS. 5 to 7, the prism layer 27 is provided at a position closer to the liquid crystal panel 15 side than the light diffusion plate 26 and is a layer having unit prisms 27a protruding toward the liquid crystal panel 15 side. In FIGS. 5 to 7, the unit prisms 27a are in a form having a specific cross section and extending along the light guiding direction of the light guide plate 21 (the vertical direction in this embodiment). Further, a plurality of unit prisms 27a are arranged in a direction different from the light guiding direction (the direction orthogonal to the light guiding direction in plan view in this embodiment, the horizontal direction). The cross-sectional shape of the unit prism of such a prism layer can be a known shape according to the required function. With this shape, the light can be further diffused and the light can also be focused. Also, the extending direction and the arranging direction of the unit prisms are not limited to the above form and can be other forms. For example, the unit prism can also be in the form of "having a specific cross section and extending along a direction orthogonal to the light guiding direction of the light guide plate 21, and a plurality of unit prisms are arranged in the light guiding direction". The reflective polarizing plate 28 has the following function: decomposing the incident light into two orthogonal polarization components (P wave and S wave), allowing the polarization component in one direction (the direction parallel to the transmission axis) (for example, the P wave) to pass through, and reflecting the polarization component in the other direction (the direction parallel to the reflection axis) orthogonal to the one direction (for example, the S wave). The structure of such a reflective polarizing plate can be a known one. The reflective sheet 29 of the surface light source device 20 will be described. The reflective sheet 29 is a member for reflecting the light emitted from the back surface of the light guide plate 21 and causing the light to be incident again into the light guide plate 21. The reflective sheet 29 is preferably applicable to "a sheet formed of a material having a high reflectivity such as metal, a sheet including a thin film formed of a material having a high reflectivity (for example, a metal thin film) as a surface layer", etc., which can perform so-called specular reflection. C-1. Display Device (First Embodiment) The display device of this embodiment includes the optical sheet of the first embodiment described above and a display panel. The display device is, for example, a device that displays an image composed of a moving image, a still image, text information, or a combination thereof on the display panel. With the display device of this embodiment, it becomes possible to control the emission of image light in the vertical and horizontal directions. In particular, in the case of a display device disposed in front of the passenger seat of a vehicle, it is possible to control the emission of image light toward the driver side and to control the incidence of image light on the windshield in front of the passenger seat. The display device of this embodiment further has two embodiments. The display device of this embodiment includes a surface light source device, and the surface light source device may also include the above optical sheet. Also, in the display device of this embodiment, the above optical sheet may be disposed on the observer side of the display panel. C-1-1. Display Device (First Example of the First Embodiment) The display device of this embodiment includes a surface light source device including the optical sheet of the first embodiment described above and a display panel laminated on the surface light source device. Figs. 5 to 7 are schematic top views and cross-sectional views showing an example of the display device of this embodiment. Furthermore, regarding Figs. 5 to 7, since they have been described in the section of "B-1. Surface Light Source Device (First Embodiment)" above, the description here is omitted. 1. Surface Light Source Device The surface light source device has been described in the section of "B-1. Surface Light Source Device (First Embodiment)" above, so the description here is omitted. 2. Display Panel The display panel is, for example, a liquid crystal panel. The liquid crystal panel 15 shown in Figs. 5 to 7 has an upper polarizing plate 13 disposed on the observer side, a lower polarizing plate 14 disposed on the side of the surface light source device 20, and a liquid crystal layer 12 disposed between the upper polarizing plate 13 and the lower polarizing plate 14. The upper polarizing plate 13 and the lower polarizing plate 14 have the following functions: decomposing incident light into two orthogonal polarization components (P wave and S wave), allowing the polarization component in one direction (the direction parallel to the transmission axis) (for example, P wave) to pass through, and absorbing the polarization component in the other direction orthogonal to this one direction (the direction parallel to the absorption axis) (for example, S wave). The liquid crystal layer 12 has a plurality of pixels arranged longitudinally and transversely in the direction along the layer plane, and an electric field can be applied to each region forming a pixel. Subsequently, the alignment of the pixels to which the electric field is applied changes. Thereby, the polarization component (e.g., P wave) that penetrates the lower polarizing plate 14 on the side of the surface light source device 20 (i.e., the light incident side) and is parallel to the transmission axis rotates its polarization direction by 90° when passing through the pixels to which the electric field is applied. On the other hand, when passing through the pixels to which no electric field is applied, its polarization direction remains unchanged. Therefore, it is possible to control whether the polarization component (e.g., P wave) that penetrates the lower polarizing plate 14 further penetrates the upper polarizing plate 13 arranged on the light output side or is absorbed by the upper polarizing plate 13 and blocked, depending on whether an electric field is applied to the pixels. In this way, the liquid crystal panel 15 has a structure that controls the transmission or blocking of light from the surface light source device 20 in each pixel to display an image. There are several types of liquid crystal panels, but their types are not particularly limited, and known types of liquid crystal panels can be used. Specifically, examples include: TN, STN, VA, MVA, IPS, OCB, etc. 3. Other components As shown in FIGS. 5 to 7, the display device of the present embodiment may have a functional film 40 arranged on the light output side of the liquid crystal panel 15. The functional film 40 is a component having a function of improving the quality of image light or protecting the display device 50A. Examples of the functional film include: an antireflection film, an antiglare film, a hard coat film, a color tone correction film, a light diffusion film, etc., and these can be used alone or in combination of plural types. 4. Operation Subsequently, regarding the operation of the display device 50A having the above configuration, an optical path example is shown and explained. However, this optical path example is a concept for explanation and does not strictly show the degree of reflection and refraction. First, as shown in FIG. 7, the light emitted from the light source 25 enters the light guide plate 21 from the light incident surface which is the side surface (end surface) of the light guide plate 21. As an example, the optical path examples of the light L21 and L22 incident from the light source 25 to the light guide plate 21 are shown in FIG. 7. As shown in FIG. 7, the light L21 and L22 incident on the light guide plate 21 are repeatedly totally reflected on the light output side surface and the back surface on the opposite side of the light guide plate 21 due to the refractive index difference with air, and travel in the light guiding direction (the downward direction of the paper surface in FIG. 7). Among them, a back optical element 23 is arranged on the back surface of the light guide plate 21. Therefore, as shown in FIG. 7, the light L21 and L22 traveling in the light guide plate 21 may change their traveling directions due to the back optical element 23 and enter the light output surface and the back surface at an incident angle that does not reach the total reflection critical angle. In this case, the light may be emitted from the light output surface of the light guide plate 21 and the back surface on the opposite side. The light L21 and L22 emitted from the light-emitting surface are directed towards the light diffusion plate 26 disposed on the light-emitting side of the light guide plate 21. On the other hand, the light emitted from the back surface is reflected on the reflection sheet 29 disposed on the back surface of the light guide plate 21, and then re-enters the light guide plate 21 and enters the light guide plate 21. In each region along the light guide direction within the light guide plate 21, there is light traveling within the light guide plate 21 and light that has its direction changed by the back optical element 23 and reaches the light-emitting surface at an incident angle less than the total reflection critical angle. Therefore, the light traveling within the light guide plate 21 gradually exits from the light-emitting surface. Thereby, the light quantity distribution along the light guide direction of the light emitted from the light-emitting surface of the light guide plate 21 can be made uniform. After that, the light emitted from the light guide plate 21 reaches the light diffusion plate 26, and the uniformity is improved. Then, it is diffused or aggregated by the prism layer 27 as needed, and the light emitted from the prism layer 27 reaches the reflective polarizing plate 28. Here, the light polarized in the direction along the transmission axis of the reflective polarizing plate 28 passes through the reflective polarizing plate 28 and is directed towards the optical sheet 10A. On the other hand, the light polarized in the direction along the reflection axis of the reflective polarizing plate 28 is reflected as shown by the dashed arrow in FIG. 7 and returns to the side of the light guide plate 21. The returned light is reflected on the light guide plate 21, the back optical element 23, or the reflection sheet 29 and travels towards the reflective polarizing plate 28 again. During this reflection, the polarization direction of a part of the light changes, and a part of it passes through the reflective polarizing plate 28. The other light returns to the light guide plate side again. Thus, the light reflected by the reflective polarizing plate 28 can also pass through the reflective polarizing plate 28 by repeated reflection. Thereby, the utilization rate of the light from the light source 25 is increased. Here, the light emitted from the reflective polarizing plate 28 becomes polarized light whose polarization direction is along the transmission axis of the lower polarizing plate 14 and passes through the lower polarizing plate 14. The light emitted from the reflective polarizing plate 28 reaches the optical sheet 10A. The light incident on the optical sheet 10A travels along the above optical path. The light emitted from the optical sheet 10A is incident on the lower polarizing plate 14 of the liquid crystal panel 15. The lower polarizing plate 14 allows a part of the polarization component of the incident light to pass through and absorbs the other polarization components. The light passing through the lower polarizing plate 14 selectively passes through the upper polarizing plate 13 according to the state of the electric field applied to each pixel. In this way, through the liquid crystal panel 15, the light from the surface light source device 20 selectively passes through each pixel, and thereby the observer of the liquid crystal display device can observe the image. At this time, the image light is provided to the observer through the functional film 40, and the quality of the image is improved. 5. Use The display device of the present embodiment is preferably used for applications that require controlling the emission of image light in the up-down direction and the left-right direction. The display device of the present embodiment is preferably used as, for example, an in-vehicle display device, and more preferably as a display device for a front passenger seat disposed in front of the front passenger seat of a vehicle. As shown in FIGS. 5 to 7, in the display device 50A of the present embodiment, the base material layer 1 of the optical sheet 10A is disposed so as to be on the observer side with respect to the optical functional layer 2. FIG. 8(a) is a schematic view of the front inside of a vehicle in which the display device 50A of the present embodiment is disposed in front of the front passenger seat of the vehicle. FIG. 8(b) is a plan view for explaining the state of the optical sheet of the display device in FIG. 8(a). In FIGS. 8(a) and 8(b), the first direction D1 of the optical sheet is arranged to be the horizontal direction (the left-right direction of the vehicle), the second direction D2 is arranged to be the vertical direction, and the third direction D3 is arranged to be the horizontal direction (the front-rear direction of the vehicle). On the other hand, the setting and arrangement of the display device are not limited to this. When the display device of the present embodiment is used as a display device for a front passenger seat disposed in front of the front passenger seat of a vehicle, the emission of image light toward the driver side can be controlled. Further, the image light incident on the windshield in front of the front passenger seat can be controlled, and the driver's visual recognition of the image light incident on the windshield can be suppressed. Further, the display device of the present embodiment can be used for a rear seat display device disposed on the ceiling or headrest of a vehicle. When rear seat display devices are respectively provided in the rear seats, the emission of image light in the left-right direction can be suppressed, and the reduction in visibility caused by the image light of an adjacent rear seat display device incident on the observer's rear seat display device can be suppressed. In particular, in the case where the observer is observing a low-brightness image on the rear seat display device, when a high-brightness image is projected on an adjacent rear seat display device, the reduction in visibility can be further suppressed. Further, the emission of image light in the upward direction can be suppressed. In particular, the image light incident on the ceiling of the rear seat at night can be controlled, and the driver's visual recognition of the image light incident on the ceiling can be suppressed. Further, the display device of the present embodiment can be used for a display device disposed on the seats of a bus, a train, an airplane, etc. In this case, the emission of image light in the left-right direction can be suppressed, and privacy can be protected. Further, the emission of image light in the upward direction can be suppressed. In particular, the image light incident on the ceiling of the seat at night can be controlled, and the non-observer's visual recognition of the image light incident on the ceiling can be suppressed. The display device of the present embodiment can be used for the following various purposes, namely: displaying advertisements, presentations, television images, various information, etc. indoors or outdoors. C-1-2. Display Device (Second Example of the First Embodiment) The display device of the present embodiment includes a display panel and the optical sheet of the first embodiment disposed on the observer side of the display panel. FIG. 9 is an exploded cross-sectional view of the display device of the present embodiment. As shown in FIG. 9, the display device 50E of the present embodiment includes a display panel 30 and an optical sheet 10A disposed on the observer side of the display panel 30. As shown in FIG. 9, in the display device 50E, the optical sheet 10A is disposed such that the substrate layer 1 is on the observer side with respect to the optical functional layer 2. The direction in which the display device is installed is also shown in FIG. 9, but the installation is not limited thereto. For example, as shown in FIG. 9, the display device is preferably arranged such that the first direction D1 in FIGS. 1 to 4 is the horizontal direction and the second direction D2 is the vertical direction, but the arrangement is not limited to this. 1. Optical sheet The optical sheet has been described in the above item "A-1. Optical sheet (First Embodiment)", so the description here is omitted. 2. Display panel Examples of the display panel include, for example, a liquid crystal panel and an organic electroluminescence panel. The liquid crystal panel is the same as the liquid crystal panel described in the above item "C-1-1. Display device (First example of the First Embodiment)". A publicly known organic electroluminescence panel can be used as the organic electroluminescence panel. 3. Other components As shown in FIG. 9, the display device of the present embodiment may have a functional film 40 disposed on the light-emitting side of the optical sheet 10A. The functional film is the same as the functional film described in the above item "C-1-1. Display device (First example of the First Embodiment)". When the display panel is a liquid crystal panel, the display device of the present embodiment generally has a surface light source device on the surface of the liquid crystal panel opposite to the optical sheet side. A publicly known surface light source device can be used as the surface light source device. On the other hand, when the display panel is an organic electroluminescence panel, the organic electroluminescence panel is a self-luminous type. 4. Use The use of the display device of the present embodiment is the same as that described in the above item "C-1-1. Display device (First example of the First Embodiment)", so the description here is omitted. A-2. Optical Sheet (Second Embodiment) For example, as shown in FIGS. 1 to 4, the optical sheet 10B of the present embodiment includes a base material layer 1 and an optical functional layer 2 laminated on one surface of the base material layer 1. The optical sheet 10B of the present embodiment has a rectangular shape in a plan view, and the rectangular shape has a pair of first sides L1 extending along the first direction and a pair of second sides L2 extending along the second direction. The optical functional layer 2 has: a plurality of light transmission portions 3, which have a specific cross-section and extend along one direction; and a light absorption portion 4 formed between adjacent light transmission portions 3; the specific cross-section of the light transmission portion 3 is trapezoidal, and the shorter upper base is set as the light incident side. The optical sheet 10B is an optical sheet for a display device disposed in front of the passenger seat of a vehicle, and the extending direction of the light transmission portion 3 has an angle of 1.5° or more and 20° or less with respect to the second direction D2. Details of FIGS. 1 to 4 have been described in the above item "A-1. Optical Sheet (First Embodiment)", so the description here is omitted. The optical sheet of the present embodiment includes an optical functional layer having a light transmission portion and a light absorption portion, and the light transmission portion extends along a specific direction and has a specific cross-section; thereby, the light transmittance in the direction inclined by ±30° from the third direction toward the first direction side can be reduced. Specifically, when the light transmittance in the third direction is set to 100%, the ratio of the light transmittance in the direction inclined by ±30° from the third direction toward the first direction side, that is, the relative transmittance, can be made 1% or less. Furthermore, in a state where the light emission angle in the first direction D1 is controlled, the extending direction of the light transmission portion 3 has an angle θ of 1.5° or more and 20° or less with respect to the second direction, whereby the light emission angle in the second direction D2 can be controlled. Therefore, when the optical sheet of the present embodiment is used in a display device, the light emission angles in the left-right direction and the up-down direction of the display device can be controlled. More specifically, when used as an optical sheet for a display device disposed in front of the passenger seat of a vehicle, the emission of image light toward the driver side can be controlled, and the entry of image light into the windshield in front of the passenger seat can be controlled. The optical sheet of the present embodiment is an optical sheet for a display device disposed in front of the passenger seat of a vehicle. Since other features of the optical sheet of the present embodiment are the same as those of the above "A-1. Optical Sheet (First Embodiment)", the description here is omitted. B-2. Surface Light Source Device (Second Embodiment) For example, as shown in FIGS. 5 to 7, the surface light source device 20 of the present embodiment includes the optical sheet 10B of the second embodiment described above and a light source 25 that emits light incident on the optical sheet 10B. The surface light source device of the present embodiment is used in a display device for a passenger seat. Details regarding FIGS. 5 to 7 have been described in the above item "B-1. Surface Light Source Device (First Embodiment)", and thus the description thereof is omitted here. Regarding the light source and other components of the surface light source device, they have been described in the above item "B-1. Surface Light Source Device (First Embodiment)", and thus the description thereof is omitted here. C-2. Display Device (Second Embodiment) The display device of this embodiment includes the optical sheet of the above-described second embodiment and a display panel. With the display device of this embodiment, when used as a display device disposed in front of the passenger seat of a vehicle, the emission of image light toward the driver side can be controlled, and the entry of image light into the windshield in front of the passenger seat can be controlled. The display device of this embodiment further has two embodiments. The display device of this embodiment includes a surface light source device, and the surface light source device may also include the above optical sheet. Also, in the display device of this embodiment, the above optical sheet may be disposed on the observer side of the display panel. C-2-1. Display Device (First Example of the Second Embodiment) The display device of this embodiment includes a surface light source device including the above optical sheet and a display panel laminated on the above surface light source device. FIGS. 5 to 7 are schematic top views and cross-sectional views showing an example of the display device of this embodiment. Regarding FIGS. 5 to 7, they have been described in the above item "B-1. Surface Light Source Device (First Embodiment)", and thus the description thereof is omitted here. As shown in FIGS. 5 to 7, the display device 50B in this embodiment is disposed such that the base material layer 1 in the optical sheet 10B is on the observer (passenger seat) side with respect to the optical functional layer 2. 1. Surface Light Source Device Regarding the surface light source device, it has been described in the above item "B-2. Surface Light Source Device (Second Embodiment)", and thus the description thereof is omitted here. 2. Display Panel and Other Components Regarding the display panel and other components, they have been described in the above item "C-1-1. Display Device (First Example of the First Embodiment)", and thus the description thereof is omitted here. 3. Use The display device of this embodiment is used as a display device disposed in front of the passenger seat of a vehicle. FIG. 8(a) is a schematic diagram of the front inside of a vehicle when the display device 50B of this embodiment is disposed in front of the passenger seat of the vehicle. FIG. 8(b) is a top view illustrating the state of the optical sheet of the display device 50B in FIG. 8(a). In FIGS. 8(a) and 8(b), the first direction D1 of the optical sheet is arranged to be the horizontal direction (the left-right direction of the vehicle), the second direction D2 is arranged to be the vertical direction, and the third direction D3 is arranged to be the horizontal direction (the front-rear direction of the vehicle). On the other hand, the installation arrangement of the display device is not limited to this. C-2-2. Display Device (Second Example of the Second Embodiment) The display device of this embodiment includes a display panel and the optical sheet of the second embodiment disposed on the observer side of the above display panel. FIG. 9 is an exploded cross-sectional view illustrating the display device 50F of this embodiment. Regarding FIG. 9, it has been described in the above item of "C-1-2. Display Device (Second Example of the First Embodiment)", so the description here is omitted. As shown in FIG. 9, in the display device 50F of this embodiment, the base material layer 1 in the optical sheet 10B is arranged such that it faces the observer (passenger seat) side with respect to the optical functional layer 2. 1. Optical Sheet Regarding the optical sheet, it has been described in the above item of "A-2. Optical Sheet (Second Embodiment)", so the description here is omitted. 2. Display Panel and Other Components Regarding the display panel and other components, it has been described in the above item of "C-1-2. Display Device (Second Example of the First Embodiment)", so the description here is omitted. 4. Use The display device of this embodiment is used as a display device disposed in front of the passenger seat of a vehicle. The use of the display device of this embodiment is the same as that described in the above item of "C-1-2. Display Device (Second Example of the First Embodiment)", so the description here is omitted. C-3. Display Device (Third Embodiment) The display device of this embodiment includes an optical sheet and a display panel, and the above optical sheet includes a base material layer and an optical functional layer laminated on one surface of the above base material layer. The above optical functional layer has: a plurality of light penetration portions, which have a specific cross-section and extend along one direction; and a light absorption portion formed between adjacent above light penetration portions. The above specific cross-section of the above light penetration portion is trapezoidal, and the shorter upper base is set as the light incident side. When the display device is provided, in the above optical sheet, when the light transmittance in the normal direction of the main surface of the above optical sheet is set to 100%, the ratio of the light transmittance in the direction inclined ±30° from the above normal direction to the left and right directions, that is, the relative transmittance, is 1% or less; the extension direction of the above light penetration portion observed from the above normal direction has an angle of 1.5° or more and 20° or less with respect to the vertical direction. The display device of this embodiment further has two embodiments. The display device of this embodiment includes a surface light source device, and the surface light source device may also include the above optical sheet. Also, in the display device of this embodiment, the above optical sheet may be disposed on the observer side of the display panel. C-3-1. Display Device (First Example of the Third Embodiment) FIGS. 5 to 7 are schematic top views and cross-sectional views showing an example of the display device of the present embodiment. Further, FIGS. 1 to 4 are schematic perspective views, cross-sectional views, and top views showing an example of the optical sheet in the display device of the present embodiment. As shown in FIGS. 5 to 7, the display device 50C of the present embodiment includes a surface light source device 20 including an optical sheet 10C, and a liquid crystal panel 15 laminated on the surface light source device 20. As shown in FIGS. 1 to 4, the optical sheet 10C in the present embodiment includes a base material layer 1 and an optical functional layer 2 laminated on one surface of the base material layer 1, and the optical functional layer 2 has: a plurality of light penetration portions 3 having a specific cross-section and extending in one direction; and a light absorption portion 4 formed between adjacent light penetration portions 3. The specific cross-section of the light penetration portion 3 is trapezoidal, and the shorter upper base is set as the light incident side. As shown in FIG. 2, when the display device 50C is provided, in the optical sheet 10C, when the light transmittance in the normal direction N of the main surface S of the optical sheet (the third direction D3 in FIGS. 1 to 4) is set to 100%, the ratio of the light transmittance in the direction inclined ±30° from the normal direction N to the left and right directions, that is, the relative transmittance, is 1% or less. Further, as shown in FIG. 3, when the display device 50C is provided, in the optical sheet 10C, the extending direction of the light penetration portion 3 observed from the normal direction N has an angle of 1.5° or more and 20° or less with respect to the vertical direction. Details of FIGS. 1 to 4 have been described in the above item "A-1. Optical Sheet (First Embodiment)", so the description here is omitted. Further, regarding FIGS. 5 to 7, they have been described in the above item "B-1. Surface Light Source Device (First Embodiment)", so the description here is omitted. The display device 50C of the present embodiment has a specific optical sheet 10C. When the display device is provided, in the optical sheet 10C of the present embodiment, since the ratio of the light transmittance in the direction inclined ±30° from the normal direction to the left and right directions, that is, the relative transmittance, is a specific value or less, the light emission angle of the display device in the left and right directions can be controlled. Further, in a state where the light emission angle in the left and right directions is controlled, the extending direction of the light penetration portion observed from the normal direction has an angle θ in a specific range with respect to the vertical direction, whereby the light emission angle of the display device in the up and down directions can be controlled. Therefore, it becomes a display device capable of controlling the light emission angles in the left and right directions and the up and down directions. More specifically, when it is arranged in front of the passenger seat of a vehicle, the emission of image light toward the driver side can be controlled, and the entry of image light into the windshield in front of the passenger seat can be controlled. 1. Surface light source device The surface light source device includes a specific optical sheet. As shown in FIGS. 1 to 4, when a display device is provided, in the optical sheet 10C of the present embodiment, when the light transmittance in the normal direction N (the third direction D3 in FIGS. 1 to 4) of the main surface of the optical sheet is set to 100%, the ratio of the light transmittance in the direction inclined ±30° from the normal direction N to the left and right directions, that is, the relative transmittance, is 1% or less. The relative transmittance of the above light is preferably 0.6% or less, and more preferably 0.4% or less. In the optical sheet of the present embodiment, when the light transmittance in the normal direction is set to 100%, the ratio of the light transmittance in the direction inclined ±20° from the normal direction to the left and right directions, that is, the relative transmittance, is preferably 10% or less, and more preferably 5% or less. Furthermore, when a display device is provided, in the optical sheet of the present embodiment, the extending direction of the light penetration portion observed from the normal direction has an angle of 1.5° or more and 20° or less with respect to the vertical direction. The above angle θ is 1.5° or more, and may also be 5° or more, or may also be 10° or more. On the other hand, the above angle θ is 20° or less, and may also be 15° or less. That is, the above angle θ is 1.5° or more and 20° or less, may also be 5° or more and 20° or less, or may also be 10° or more and 15° or less. By making the above angle θ within the above range, it becomes possible to control the light emission angle in the left and right directions. Furthermore, in FIGS. 1 and 3, the light penetration portion 3 has an angle θ with respect to the vertical direction on the right side (+D1 side). In this case, it is preferable that the left side (-D1 side) is the driver's seat side. On the other hand, the light penetration portion 3 may also have an angle θ with respect to the second direction D2 on the left side (-D1 side). In this case, it is preferable that the right side (+D1 side) is the driver's seat side. The above-mentioned angle θ can be obtained by the following method. First, as illustrated in FIGS. 8(a) and 8(b), it is assumed that the display device 50 has been set up. At this time, the optical sheet of the display device 50 can be vertically long or horizontally long. Then, the angle is measured, which is the smaller of the angles formed by the vertical line (the straight line in the direction of gravity) and the boundary line BL between the light transmissive portion 3 and the light absorbing portion 4 when observed from the normal direction of the main surface of the optical sheet (the third direction D3 in FIG. 8(b)), that is, when the observer (e.g., the co-pilot seat) observes the display device 50 from the front. When measuring the above-mentioned angle, the boundary line BL between the light transmissive portion 3 and the light absorbing portion 4 on the surface of the shorter upper base of the light transmissive portion 3 and the longer lower base of the light absorbing portion 4 of the optical functional layer 2 is used. Also, as illustrated in FIG. 8(b), the above-mentioned angle is measured for two positions on each of the left and right sides of the display device 50, and the arithmetic mean of the four measured values is set as the above-mentioned angle θ. The above two positions are set as: the position at 1 / 3 of the vertical length K of the display device 50 from the upper side of the display device 50; and the position at 1 / 3 of the vertical length K of the display device 50 from the lower side of the display device 50. Since the features and other features of the optical sheet having the above-mentioned optical characteristics in this embodiment are the same as those of the above-mentioned "A-1. Optical Sheet (First Embodiment)", the description here is omitted. As for the other components of the surface light source device, they are already described in the above item "B-1. Surface Light Source Device (First Embodiment)", so the description here is omitted. 2. Display Panel and Other Components Regarding the display panel and other components, they are already described in the above item "C-1-1. Display Device (First Example of the First Embodiment)", so the description here is omitted. 3. Use Since the use of the display device in this embodiment is the same as that of the above-mentioned "C-1-1. Display Device (First Example of the First Embodiment)", the description here is omitted. C-3-2. Display Device (Second Example of the Third Embodiment) Fig. 9 is a schematic top view and a cross-sectional view showing an example of the display device of this embodiment. Also, Figs. 1 to 4 are schematic perspective views, cross-sectional views, and top views showing an example of the optical sheet in the display device of this embodiment. As shown in Fig. 9, the display device 50G of this embodiment includes a display panel 30 and an optical sheet 10C disposed on the observer side of the display panel 30. As shown in Figs. 1 to 4, the optical sheet 10C in this embodiment includes a substrate layer 1 and an optical functional layer 2 laminated on one surface of the substrate layer 1, and the optical functional layer 2 has: a plurality of light-penetrating portions 3, which have a specific cross-section and extend along one direction; and a light-absorbing portion 4, which is formed between adjacent light-penetrating portions 3. The specific cross-section of the light-penetrating portion 3 is trapezoidal, and the shorter upper base is set as the light-incident side. As shown in Fig. 2, when the display device 50G is provided, in the optical sheet 10C, when the light transmittance in the normal direction N of the main surface S of the optical sheet (the third direction D3 in Figs. 1 to 4) is set to 100%, the ratio of the light transmittance in the direction inclined ±30° from the normal direction N to the left and right directions, that is, the relative transmittance, is 1% or less. Also, as shown in Fig. 3, when the display device 50G is provided, in the optical sheet 10C, the extension direction of the light-penetrating portion 3 observed from the normal direction N has an angle of 1.5° or more and 20° or less with respect to the vertical direction. Details regarding Figs. 1 to 4 have been described in the above item "A-1. Optical Sheet (First Embodiment)", so the description here is omitted. Also, regarding Fig. 9, it has been described in the above item "C-1-2. Display Device (Second Example of the First Embodiment)", so the description here is omitted. 1. Optical Sheet Regarding the optical sheet, it is the same as the optical sheet described in the above item "C-3-1. Display Device (First Example of the Third Embodiment)", so the description here is omitted. 2. Display Panel and Other Components Regarding the display panel and other components, they have been described in the above item "C-1-2. Display Device (Second Example of the First Embodiment)", so the description here is omitted. 3. Use Since the use of the display device of this embodiment is the same as that of the above item "C-1-1. Display Device (First Example of the First Embodiment)", the description here is omitted. C-4. Display Device (Fourth Embodiment) The display device of this embodiment includes an optical sheet and a display panel, and is disposed in front of the passenger seat of a vehicle. The optical sheet includes a substrate layer and an optical functional layer laminated on one surface of the substrate layer. The optical functional layer has: a plurality of light penetration portions having a specific cross-section and extending in one direction; and a light absorption portion formed between adjacent light penetration portions. The specific cross-section of the light penetration portion is trapezoidal, and the shorter upper base is set as the light incident side. When the display device is disposed in front of the passenger seat of a vehicle, in the optical sheet, the extension direction of the light penetration portion observed from the normal direction of the main surface of the optical sheet with respect to the vertical direction has an angle of 1.5° or more and 20° or less. The display device in this embodiment further has two embodiments. The display device of this embodiment includes a surface light source device, and the surface light source device may also include the optical sheet. Also, in the display device of this embodiment, the optical sheet may be disposed on the observer side of the display panel. C-4-1. Display Device (First Example of the Fourth Embodiment) FIGS. 5 to 7 are schematic top views and cross-sectional views showing an example of the display device of this embodiment. Also, FIGS. 1 to 4 are schematic perspective views, cross-sectional views, and top views showing an example of the optical sheet in the display device of this embodiment. As shown in FIGS. 5 to 7, the display device 50D in this embodiment includes a surface light source device 20 including an optical sheet 10D and a liquid crystal panel 15 laminated on the surface light source device 20, and is a display device disposed in front of the passenger seat of a vehicle. As shown in FIGS. 1 to 4, the optical sheet 10D in this embodiment includes a substrate layer 1 and an optical functional layer 2 laminated on one surface of the substrate layer 1, and the optical functional layer 2 has: a plurality of light penetration portions 3 having a specific cross-section and extending in one direction; and a light absorption portion 4 formed between adjacent light penetration portions 3. The specific cross-section of the light penetration portion 3 is trapezoidal, and the shorter upper base is set as the light incident side. When the display device is disposed in front of the passenger seat of a vehicle, in the optical sheet 10D, the extension direction of the light penetration portion 3 observed from the normal direction N (the third direction D3 in FIGS. 1 to 4) of the main surface of the optical sheet 10D with respect to the vertical direction has an angle of 1.5° or more and 20° or less. The display device 50D in this embodiment has a specific optical sheet 10D. The optical sheet 10D in this embodiment includes an optical functional layer having a light penetration portion and a light absorption portion. The light penetration portion extends along a specific direction and has a specific cross-section. Thereby, when the display device is disposed in front of the passenger seat of the vehicle, the light transmittance in the direction inclined by ±30° in the left-right direction with respect to the normal direction can be reduced. Specifically, when the light transmittance in the normal direction is set to 100%, the ratio of the light transmittance in the direction inclined by ±30° in the left-right direction with respect to the normal direction, that is, the relative transmittance, can be made 1% or less. Therefore, the light emission angle of the display device in the left-right direction can be controlled. Furthermore, in a state where the light emission angle in the left-right direction is controlled, the extending direction of the light penetration portion observed from the normal direction has an angle θ within a specific range with respect to the vertical direction, whereby the light emission angle of the display device in the up-down direction can be controlled. Therefore, the display device of this embodiment can control the emission of image light toward the driver side and can control the image light from entering the windshield in front of the passenger seat. 1. Surface light source device The surface light source device includes a specific optical sheet. The optical sheet 10D in this embodiment includes an optical functional layer having a light penetration portion and a light absorption portion. The light penetration portion extends along a specific direction and has a specific cross-section. Thereby, when the display device 50D having the specific optical sheet 10D is disposed in front of the passenger seat of the vehicle, the ratio of the light transmittance in the direction inclined by ±30° in the left-right direction from the normal direction N (the third direction D3 in FIGS. 1 to 4), that is, the relative transmittance, can be made 1% or less when the light transmittance in the normal direction of the main surface of the optical sheet 10D is set to 100%. The relative transmittance of the above light is preferably 0.6% or less, more preferably 0.4% or less. In the optical sheet of this embodiment, when the light transmittance in the normal direction is set to 100%, the ratio of the light transmittance in the direction inclined by ±20° in the left-right direction with respect to the normal direction, that is, the relative transmittance, is preferably 10% or less, more preferably 5% or less. Furthermore, when a display device is provided in front of the front passenger seat of a vehicle, in the optical sheet of the present embodiment, the extending direction of the light-penetrating portion observed from the normal direction has an angle of 1.5° or more and 20° or less with respect to the vertical direction. The above angle θ is 1.5° or more, may be 5° or more, or may be 10° or more. On the other hand, the above angle θ is 20° or less, may be 15° or less. That is, the above angle θ is 1.5° or more and 20° or less, may be 5° or more and 20° or less, or may be 10° or more and 15° or less. By making the above angle θ within the above range, it becomes possible to control the light-emitting angle in the left-right direction. Furthermore, in FIGS. 1 and 3, the light-penetrating portion 3 has an angle θ with respect to the vertical direction on the right side (+D1 side). In this case, it is preferable that the left side (-D1 side) is the driver's seat side. On the other hand, the light-penetrating portion 3 may have an angle θ with respect to the vertical direction on the left side (-D1 side). In this case, it is preferable that the right side (+D1 side) is the driver's seat side. Since the other features of the optical sheet in the present embodiment are the same as those of the above "A-1. Optical Sheet (First Embodiment)", the description here is omitted. The other components of the surface light source device are described in the above item "B-1. Surface Light Source Device (First Embodiment)", so the description here is omitted. 2. Display Panel and Other Components Regarding the display panel and other components, they are described in the above item "C-1-1. Display Device (First Example of the First Embodiment)", so the description here is omitted. 3. Use The display device in the present embodiment is arranged in front of the front passenger seat of a vehicle. FIG. 8(a) is a schematic view of the front inside of the vehicle when the display device 50D in the present embodiment is arranged in front of the front passenger seat of the vehicle. FIG. 8(b) is a plan view showing the state of the optical sheet of the display device in FIG. 8(a). In FIGS. 8(a) and 8(b), the left-right direction of the optical sheet is the horizontal direction (left-right direction of the vehicle), the up-down direction is the vertical direction, and the thickness direction is the horizontal direction (front-rear direction of the vehicle). On the other hand, the installation and arrangement of the display device are not limited to this. C-4-2. Display Device (Second Example of the Fourth Embodiment) Fig. 9 is a schematic top view and a sectional view showing an example of the display device of the present embodiment. Figs. 1 to 4 are schematic perspective views, sectional views, and top views showing an example of the optical sheet in the display device of the present embodiment. As shown in Fig. 9, the display device 50H of the present embodiment includes a display panel 30 and an optical sheet 10D disposed on the observer side of the display panel 30, and is a display device disposed in front of the passenger seat of a vehicle. As shown in Figs. 1 to 4, the optical sheet 10D of the present embodiment includes a base material layer 1 and an optical functional layer 2 laminated on one surface of the base material layer 1, and the optical functional layer 2 has: a plurality of light penetration portions 3, which have a specific cross-section and extend along one direction; and a light absorption portion 4, which is formed between adjacent light penetration portions 3. The specific cross-section of the light penetration portion 3 is trapezoidal, and the shorter upper base is set as the light incident side. When a display device is provided in front of the passenger seat of a vehicle, in the optical sheet 10D, the extension direction of the light penetration portion 3 observed from the normal direction N of the main surface of the optical sheet 10D (the third direction D3 in Figs. 1 to 4) with respect to the vertical direction has an angle of 1.5° or more and 20° or less. The display device 50D in the present embodiment has a specific optical sheet 10D. The optical sheet 10D in the present embodiment includes an optical functional layer having a light penetration portion and a light absorption portion, and the light penetration portion extends along a specific direction and has a specific cross-section; thereby, when a display device is provided in front of the passenger seat of a vehicle, the light transmittance in the direction inclined by ±30° with respect to the normal direction to the left and right directions can be reduced. Specifically, the "ratio of the light transmittance in the direction inclined by ±30° with respect to the normal direction to the left and right directions when the light transmittance in the normal direction is set to 100%, that is, the relative transmittance" can be made 1% or less. Therefore, it becomes possible to control the light emission angle of the display device in the left and right directions. Furthermore, in a state where the light emission angle in the left and right directions is controlled, the extension direction of the light penetration portion observed from the normal direction has an angle θ within a specific range with respect to the vertical direction, whereby the light emission angle of the display device in the up and down directions can be controlled. Therefore, the display device of the present embodiment can control the emission of image light toward the driver side and can control the image light from entering the windshield in front of the passenger seat. 1. Optical Sheet Regarding the optical sheet, it is the same as the optical sheet described in the item of "C-4-2. Display Device (Second Example of the Fourth Embodiment)" above. 2. Display Panel and Other Components Regarding the display panel and other components, they have been described in the item of "C-1-1. Display Device (First Example of the First Embodiment)" above, so the description here is omitted. 3. Use The use of the display device in the present embodiment is the same as that in the item of "C-1-1. Display Device (First Example of the First Embodiment)" above. A-3. Optical Sheet (5th Embodiment) FIG. 1 is a schematic perspective view showing an example of the optical sheet of the present embodiment. Further, FIG. 10 shows a cross-sectional view of the optical sheet cut along the line I-I shown in FIG. 1. FIG. 3 is a top view of the optical sheet shown in FIG. 1 as viewed in the direction (-D3 direction) from the base material layer 1 toward the optical functional layer 2. FIG. 4 is an enlarged cross-sectional view of the optical sheet shown in FIG. 10. As shown in FIGS. 1, 3, 4, and 10, the optical sheet 10E of the present embodiment includes a base material layer 1 and an optical functional layer 2 laminated on one surface of the base material layer 1. The optical sheet 10E of the present embodiment has a rectangular shape in a top view, and the rectangular shape has a pair of first sides L1 extending along the first direction D1 and a pair of second sides L2 extending along the second direction D2. The optical functional layer 2 has: a plurality of light-penetrating portions 3, which have a specific cross-section and extend along one direction; and a light-absorbing portion 4 formed between adjacent light-penetrating portions 3. As shown in FIG. 10, the cross-section of the light-penetrating portion 3 is trapezoidal, and the shorter upper base is set as the light-incident side (light source side). In the present embodiment, as shown in FIG. 10, when the light transmittance in the third direction D3 is set to 100%, the ratio of the light transmittance in the direction inclined by ±20° from the third direction D3 toward the first direction D1 side, that is, the relative transmittance, is 10% or less. Further, as shown in FIG. 3, the extending direction of the light-penetrating portion 3 has an angle θ of 1.5° or more and 20° or less with respect to the second direction D2. With the optical sheet 10E of the present embodiment, when the light transmittance in the third direction D3 is set to 100%, the ratio of the light transmittance in the direction inclined by ±20° from the third direction D3 toward the first direction side, that is, the relative transmittance, is a specific value or less, so that the light-emitting angle in the first direction D1 can be controlled. Further, in a state where the light-emitting angle in the first direction D1 is controlled, the extending direction of the light-penetrating portion 3 has an angle θ of 1.5° or more and 20° or less with respect to the second direction D2, whereby the light-emitting angle in the second direction D2 can be controlled. The reason is that the viewing angle in the first direction D1 has a very narrow characteristic, and when this state is maintained and the angle θ is 1.5° or more and 20° or less, the light transmittance in the second direction D2 will急剧 decrease. Therefore, when the optical sheet of the present embodiment is used in a display device, the light-emitting angles in the left-right direction and the up-down direction of the display device can be controlled. More specifically, when used as an optical sheet for a display device disposed in front of the passenger seat of a vehicle, the emission of image light toward the driver side can be controlled, and the entry of image light into the windshield can be controlled. Since the other features of the optical sheet in the present embodiment are the same as those of the above-mentioned "A-1. Optical Sheet (1st Embodiment)", the description here is omitted. B-3. Surface Light Source Device (5th Embodiment) For example, as shown in FIGS. 5 to 7, the surface light source device 20 of this embodiment includes the optical sheet 10E of the above 5th embodiment and a light source 25 that emits light incident on the optical sheet 10E. Details of FIGS. 5 to 7 have been described in the above item "B-1. Surface Light Source Device (1st Embodiment)", so the description here is omitted. Regarding the light source and other components of the surface light source device, they have been described in the above item "B-1. Surface Light Source Device (1st Embodiment)", so the description here is omitted. C-5. Display Device (5th Embodiment) The display device of this embodiment includes the optical sheet of the above 5th embodiment and a display panel. The display device in this embodiment further has two embodiments. The display device of this embodiment includes a surface light source device, and the surface light source device may also include the above optical sheet. Also, in the display device of this embodiment, the above optical sheet may be disposed on the observer side of the display panel. C-5-1. Display Device (1st Example of 5th Embodiment) The display device of this embodiment includes a surface light source device including the optical sheet of the above 5th embodiment and a display panel laminated on the above surface light source device. FIGS. 5 to 7 are schematic top views and cross-sectional views showing an example of the display device 50I of this embodiment. Details of FIGS. 5 to 7 have been described in the above item "B-1. Surface Light Source Device (1st Embodiment)", so the description here is omitted. 1. Surface Light Source Device Regarding the surface light source device, it has been described in the above item "B-3. Surface Light Source Device (5th Embodiment)", so the description here is omitted. 2. Display Panel and Other Components Regarding the display panel and other components, they have been described in the above item "C-1-1. Display Device (1st Example of 1st Embodiment)", so the description here is omitted. 3. Use The use of the display device in this embodiment is the same as that described in the above item "C-1-1. Display Device (1st Example of 1st Embodiment)", so the description here is omitted. C-5-2. Display Device (2nd Example of 5th Embodiment) The display device of this embodiment includes a display panel and the optical sheet of the above 5th embodiment disposed on the observer side of the above display panel. FIG. 9 is a schematic top view and a cross-sectional view showing an example of the display device 50J of the present embodiment. Regarding FIG. 9, it has been described in the above item "C-1-2. Display device (the second example of the first embodiment)", so the description here is omitted. As shown in FIG. 9, in the display device 50J of the present embodiment, the base material layer 1 in the optical sheet 10E is arranged with respect to the optical functional layer 2 so as to be on the side of the observer (the passenger seat). 1. Optical sheet Regarding the optical sheet, it has been described in the above item "A-3. Optical sheet (the fifth embodiment)", so the description here is omitted. 2. Display panel and other components Regarding the display panel and other components, it has been described in the above item "C-1-2. Display device (the second example of the first embodiment)", so the description here is omitted. 3. Use The use of the display device in the present embodiment is the same as that described in the above item "C-1-1. Display device (the first example of the first embodiment)", so the description here is omitted. A-4. Optical sheet (the sixth embodiment) For example, as shown in FIGS. 1, 3, 4, and 10, the optical sheet 10F of the present embodiment includes a base material layer 1 and an optical functional layer 2 laminated on one surface of the base material layer 1. The optical sheet 10F of the present embodiment has a rectangular shape when viewed from above, and the rectangular shape has a pair of first sides L1 extending along the first direction and a pair of second sides L2 extending along the second direction. The optical functional layer 2 has: a plurality of light penetration portions 3, which have a specific cross-section and extend along one direction; and a light absorption portion 4 formed between adjacent light penetration portions 3. The specific cross-section of the light penetration portion 3 is trapezoidal, and the shorter upper base is set as the light incident side. The optical sheet 10F is an optical sheet for a display device arranged in front of the passenger seat of a vehicle, and the extending direction of the light penetration portion 3 has an angle of 1.5° or more and 20° or less with respect to the second direction D2. Details of FIGS. 1, 3, and 4 have been described in the above item "A-1. Optical sheet (the first embodiment)", so the description here is omitted. Also, regarding FIG. 10, it has been described in the above item "A-3. Optical sheet (the fifth embodiment)", so the description here is omitted. The optical sheet in the present embodiment includes an optical functional layer having a light penetration portion and a light absorption portion, and the light penetration portion extends along a specific direction and has a specific cross-section; thereby, the light transmittance in the direction inclined by ±20° with respect to the third direction toward the first direction side can be reduced. Specifically, when the light transmittance in the third direction is set to 100%, the ratio of the light transmittance in the direction inclined by ±20° with respect to the third direction toward the first direction side, that is, the relative transmittance, can be made 10% or less. Furthermore, in a state where the emission angle in the first direction D1 is controlled, the extending direction of the light transmission part 3 has an angle θ of 1.5° or more and 20° or less with respect to the second direction D2, whereby the emission angle in the second direction D2 can be controlled. Therefore, when the optical sheet of the present embodiment is used in a display device, the emission angles in the left-right direction and the up-down direction of the display device can be controlled. More specifically, when it is used as an optical sheet for a display device disposed in front of the passenger seat of a vehicle, the emission of image light toward the driver side can be controlled, and the entry of image light into the windshield in front of the passenger seat can be controlled. The optical sheet in the present embodiment is an optical sheet for a display device disposed in front of the passenger seat of a vehicle. Since other features of the optical sheet of the present embodiment are the same as those of the above-mentioned "A-1. Optical Sheet (First Embodiment)", the description thereof is omitted here. B-4. Surface Light Source Device (Sixth Embodiment) For example, as shown in FIGS. 5 to 7, the surface light source device 20 of the present embodiment includes the optical sheet 10F of the above-mentioned sixth embodiment and a light source 25 that emits light incident on the optical sheet 10F. The surface light source device of the present embodiment is used in a display device for a passenger seat. Details of FIGS. 5 to 7 have been described in the above item "B-1. Surface Light Source Device (First Embodiment)", and thus the description thereof is omitted here. Regarding other components of the light source and the surface light source device, they have been described in the above item "B-1. Surface Light Source Device (First Embodiment)", and thus the description thereof is omitted here. C-6. Display Device (Sixth Embodiment) The display device of the present embodiment includes the optical sheet of the above-mentioned sixth embodiment and a display panel. The display device in the present embodiment further has two embodiments. The display device of the present embodiment includes a surface light source device, and the surface light source device may also include the above-mentioned optical sheet. Also, in the display device of the present embodiment, the above-mentioned optical sheet may be disposed on the observer side of the display panel. C-6-1. Display Device (First Example of Sixth Embodiment) The display device of the present embodiment includes a surface light source device including the optical sheet of the above-mentioned sixth embodiment and a display panel laminated on the surface light source device. FIGS. 5 to 7 are schematic top views and cross-sectional views showing an example of the display device 50K of the present embodiment. Regarding FIGS. 5 to 7, they have been described in the above item "B-1. Surface Light Source Device (First Embodiment)", and thus the description thereof is omitted here. 1. Surface Light Source Device Regarding the surface light source device, it has been described in the above item "B-4. Surface Light Source Device (Sixth Embodiment)", and thus the description thereof is omitted here. 2. Display Panel and Other Components Regarding the display panel and other components, they have been described in the above item "C-1-1. Display Device (First Example of the First Embodiment)", so the description here is omitted. 3. Use The use of the display device in this embodiment is the same as that described in the above item "C-1-1. Display Device (First Example of the First Embodiment)", so the description here is omitted. C-6-2. Display Device (Second Example of the Sixth Embodiment) The display device of this embodiment includes a display panel and the optical sheet of the above sixth embodiment disposed on the observer side of the above display panel. FIG. 9 is a schematic top view and a cross-sectional view showing an example of the display device 50L of this embodiment. Regarding FIG. 9, it has been described in the above item "C-1-2. Display Device (Second Example of the First Embodiment)", so the description here is omitted. 1. Optical Sheet The optical sheet is the same as the optical sheet described in the above item "C-6-1. Display Device (First Example of the Sixth Embodiment)", so the description here is omitted. 2. Display Panel and Other Components Regarding the display panel and other components, they have been described in the above item "C-1-2. Display Device (Second Example of the First Embodiment)", so the description here is omitted. 3. Use The use of the display device in this embodiment is the same as that described in the above item "C-1-1. Display Device (First Example of the First Embodiment)", so the description here is omitted. C-7. Display Device (Seventh Embodiment) The display device of this embodiment includes an optical sheet and a display panel, and the above optical sheet includes a substrate layer and an optical functional layer laminated on one surface of the above substrate layer. The above optical functional layer has: a plurality of light penetration portions having a specific cross-section and extending along a direction; and a light absorption portion formed between adjacent above light penetration portions. The above specific cross-section of the above light penetration portion is trapezoidal, and the shorter upper base is set as the light incident side; when the display device is provided, in the above optical sheet, when the light transmittance in the normal direction of the main surface of the above optical sheet is set to 100%, the ratio of the light transmittance in the direction inclined ±20° from the above normal direction to the left and right directions, that is, the relative transmittance is 10% or less; the extending direction of the above light penetration portion observed from the above normal direction has an angle of 1.5° or more and 20° or less with respect to the vertical direction. The display device in this embodiment further has two embodiments. The display device of this embodiment includes a surface light source device, and the surface light source device may also include the above optical sheet. Also, in the display device of this embodiment, the above optical sheet may be disposed on the observer side of the display panel. C-7-1. Display Device (First Example of the Seventh Embodiment) FIGS. 5 to 7 are schematic top views and cross-sectional views showing an example of the display device of the present embodiment. Further, FIGS. 1, 3, 4, and 10 are schematic perspective views, cross-sectional views, and top views showing an example of the optical sheet in the display device of the present embodiment. As shown in FIGS. 5 to 7, the display device 50M of the present embodiment includes a surface light source device 20 including an optical sheet 10G, and a liquid crystal panel 15 laminated on the surface light source device 20. As shown in FIGS. 1, 3, 4, and 10, the optical sheet 10G of the present embodiment includes a base material layer 1 and an optical functional layer 2 laminated on one surface of the base material layer 1, and the optical functional layer 2 has: a plurality of light penetration portions 3 having a specific cross-section and extending in one direction; and a light absorption portion 4 formed between adjacent light penetration portions 3. The specific cross-section of the light penetration portion 3 is trapezoidal, and the shorter upper base is set as the light incident side. As shown in FIG. 10, when the display device 50M is provided, in the optical sheet 10G, when the light transmittance in the normal direction N of the main surface S of the optical sheet (the third direction D3 in FIGS. 1, 3, 4, and 10) is set to 100%, the ratio of the light transmittance in the direction inclined ±20° from the normal direction N to the left and right directions, that is, the relative transmittance is 10% or less. Further, as shown in FIG. 3, when the display device 50M is provided, in the optical sheet 10G, the extending direction of the light penetration portion 3 observed from the normal direction N has an angle of 1.5° or more and 20° or less with respect to the vertical direction. Details of FIGS. 1, 3, and 4 have been described in the above item "A-1. Optical Sheet (First Embodiment)", so the description here is omitted. Details of FIG. 10 have been described in the above item "A-3. Optical Sheet (Fifth Embodiment)", so the description here is omitted. Further, details of FIGS. 5 to 7 have been described in the above item "B-1. Surface Light Source Device (First Embodiment)", so the description here is omitted. The display device 50M of the present embodiment has a specific optical sheet 10G. When the display device is provided, in the optical sheet 10G of the present embodiment, since the ratio of the light transmittance in the direction inclined ±20° from the normal direction to the left and right directions, that is, the relative transmittance is a specific value or less, it becomes possible to control the light emission angle of the display device in the left and right directions. Further, in a state where the light emission angle in the left and right directions is controlled, the extending direction of the light penetration portion observed from the normal direction has an angle θ in a specific range with respect to the vertical direction, whereby it becomes possible to control the light emission angle of the display device in the up and down directions. Therefore, it becomes a display device capable of controlling the light emission angles in the left and right directions and the up and down directions. More specifically, when it is arranged in front of the passenger seat of a vehicle, it is possible to control the emission of image light toward the driver side, and it becomes possible to control the image light from entering the windshield in front of the passenger seat. 1. Surface light source device The surface light source device includes a specific optical sheet. As shown in FIGS. 1, 3, 4, and 10, when a display device is provided, in the optical sheet 10G of this embodiment, when the light transmittance in the normal direction N of the main surface of the optical sheet (the third direction D3 in FIGS. 1, 3, 4, and 10) is set to 100%, the ratio of the light transmittance in the direction inclined ±20° from the normal direction N to the left and right directions, that is, the relative transmittance, is 10% or less. The relative transmittance of the above light is preferably 5% or less. Furthermore, when a display device is provided, in the optical sheet of this embodiment, the extending direction of the light penetration portion observed from the normal direction has an angle of 1.5° or more and 20° or less with respect to the vertical direction. The above angle θ is 1.5° or more, and can also be 5° or more, or 10° or more. On the other hand, the above angle θ is 20° or less, and can also be 15° or less. That is, the above angle θ is 1.5° or more and 20° or less, can also be 5° or more and 20° or less, or can also be 10° or more and 15° or less. By making the above angle θ within the above range, it becomes possible to control the light emission angle in the left and right directions. Furthermore, in FIGS. 1 and 3, the light penetration portion 3 has an angle θ with respect to the vertical direction on the right side (+D1 side). In this case, it is preferable that the left side (-D1 side) is the driver's seat side. On the other hand, the light penetration portion 3 can also have an angle θ with respect to the second direction D2 on the left side (-D1 side). In this case, it is preferable that the right side (+D1 side) is the driver's seat side. Since the features of the optical sheet having the above optical characteristics and other features in this embodiment are the same as those of the above "A-1. Optical sheet (first embodiment)", the description here is omitted. As for the other components of the surface light source device, they are described in the above item "B-1. Surface light source device (first embodiment)", so the description here is omitted. 2. Display panel and other components Regarding the display panel and other components, they are described in the above item "C-1-1. Display device (first example of the first embodiment)", so the description here is omitted. 3. Use Since the use of the display device in this embodiment is the same as that of the above "C-1-1. Display device (first example of the first embodiment)", the description here is omitted. C-7-2. Display Device (Second Example of the Seventh Embodiment) FIG. 9 is a schematic plan view and a sectional view showing an example of the display device of the present embodiment. FIGS. 1, 3, 4, and 10 are schematic perspective views, sectional views, and plan views showing an example of the optical sheet in the display device of the present embodiment. As shown in FIG. 9, the display device 50N of the present embodiment includes a display panel 30 and an optical sheet 10G disposed on the observer side of the display panel 30. As shown in FIGS. 1, 3, 4, and 10, the optical sheet 10G in the present embodiment includes a base material layer 1 and an optical functional layer 2 laminated on one surface of the base material layer 1, and the optical functional layer 2 has: a plurality of light penetration portions 3, which have a specific cross-section and extend along one direction; and a light absorption portion 4, which is formed between adjacent light penetration portions 3. The specific cross-section of the light penetration portion 3 is trapezoidal, and the shorter upper base is set as the light incident side. As shown in FIG. 10, when the display device 50N is provided, in the optical sheet 10G, when the light transmittance in the normal direction N of the main surface S of the optical sheet (the third direction D3 in FIGS. 1 to 4) is set to 100%, the ratio of the light transmittance in the direction inclined ±20° from the normal direction N to the left and right directions, that is, the relative transmittance, is 10% or less. Also, as shown in FIG. 3, when the display device 50N is provided, in the optical sheet 10G, the extending direction of the light penetration portion 3 observed from the normal direction N has an angle of 1.5° or more and 20° or less with respect to the vertical direction. Details of FIGS. 1, 3, and 4 have been described in the above item "A-1. Optical Sheet (First Embodiment)", so the description here is omitted. Details of FIG. 10 have been described in the above item "A-3. Optical Sheet (Fifth Embodiment)", so the description here is omitted. Also, details of FIG. 9 have been described in the above item "C-1-2. Display Device (Second Example of the First Embodiment)", so the description here is omitted. 1. Optical Sheet Regarding the optical sheet, it is the same as the optical sheet described in the above item "C-7-1. Display Device (First Example of the Seventh Embodiment)", so the description here is omitted. 2. Display Panel and Other Components Regarding the display panel and other components, they have been described in the above item "C-1-2. Display Device (Second Example of the First Embodiment)", so the description here is omitted. 3. Use Since the use of the display device in the present embodiment is the same as that in the above item "C-1-1. Display Device (First Example of the First Embodiment)", the description here is omitted. C-8. Display Device (Eighth Embodiment) The display device of this embodiment includes an optical sheet and a display panel, and is disposed in front of the passenger seat of a vehicle. The optical sheet includes a base material layer and an optical functional layer laminated on one surface of the base material layer. The base material layer is a resin base material, and the optical functional layer has: a plurality of light penetration portions having a specific cross-section and extending in one direction; and a light absorption portion formed between adjacent light penetration portions. The specific cross-section of the light penetration portion is trapezoidal, and the shorter upper base is set as the light incident side. When the display device is disposed in front of the passenger seat of a vehicle, in the optical sheet, the extension direction of the light penetration portion observed from the normal direction of the main surface of the optical sheet with respect to the vertical direction has an angle of 1.5° or more and 20° or less. The display device in this embodiment further has two embodiments. The display device of this embodiment includes a surface light source device, and the surface light source device may also include the optical sheet. Also, in the display device of this embodiment, the optical sheet may be disposed on the observer side of the display panel. C-8-1. Display Device (First Example of the Eighth Embodiment) FIGS. 5 to 7 are schematic top views and cross-sectional views showing an example of the display device of this embodiment. Also, FIGS. 1, 3, 4, and 10 are schematic perspective views, cross-sectional views, and top views showing an example of the optical sheet in the display device of this embodiment. As shown in FIGS. 5 to 7, the display device 50O in this embodiment includes a surface light source device 20 including an optical sheet 10H and a liquid crystal panel 15 laminated on the surface light source device 20, and is a display device disposed in front of the passenger seat of a vehicle. As shown in FIGS. 1, 3, 4, and 10, the optical sheet 10H in this embodiment includes a base material layer 1 and an optical functional layer 2 laminated on one surface of the base material layer 1. The base material layer 1 is a resin base material, and the optical functional layer 2 has: a plurality of light penetration portions 3 having a specific cross-section and extending in one direction; and a light absorption portion 4 formed between adjacent light penetration portions 3. The specific cross-section of the light penetration portion 3 is trapezoidal, and the shorter upper base is set as the light incident side. When the display device is disposed in front of the passenger seat of a vehicle, in the optical sheet 10H, the extension direction of the light penetration portion 3 observed from the normal direction N (the third direction D3 in FIGS. 1 to 4) of the main surface of the optical sheet 10H with respect to the vertical direction has an angle of 1.5° or more and 20° or less. The display device 50O in the present embodiment has a specific optical sheet 10H. The optical sheet 10H in the present embodiment includes an optical functional layer having a light penetration portion and a light absorption portion. The light penetration portion extends along a specific direction and has a specific cross-section. Thereby, when the display device is disposed in front of the passenger seat of the vehicle, the light transmittance in the direction inclined by ±20° in the left and right directions with respect to the normal direction can be reduced. Specifically, when the light transmittance in the normal direction is set to 100%, the ratio of the light transmittance in the direction inclined by ±20° in the left and right directions with respect to the normal direction, that is, the relative transmittance, can be made 10% or less. Therefore, it becomes possible to control the light emission angle of the display device in the left and right directions. Furthermore, in a state where the light emission angle in the left and right directions is controlled, the extending direction of the light penetration portion observed from the normal direction has an angle θ within a specific range with respect to the vertical direction, whereby it becomes possible to control the light emission angle of the display device in the up and down directions. Therefore, the display device of the present embodiment can control the emission of image light toward the driver side and can control the image light from entering the windshield in front of the passenger seat. 1. Surface light source device The surface light source device includes a specific optical sheet. The optical sheet 10H in the present embodiment includes an optical functional layer having a light penetration portion and a light absorption portion. The light penetration portion extends along a specific direction and has a specific cross-section. Thereby, when the display device 50O having the specific optical sheet 10H is disposed in front of the passenger seat of the vehicle, the ratio of the light transmittance in the direction inclined by ±20° in the left and right directions from the normal direction N (the third direction D3 in FIGS. 1, 3, 4, and 10) of the main surface of the optical sheet 10H, that is, the relative transmittance, can be made 10% or less when the light transmittance in the normal direction N is set to 100%. The relative transmittance of the above light is preferably 5% or less. Furthermore, when the display device is disposed in front of the passenger seat of the vehicle, in the optical sheet of the present embodiment, the extending direction of the light penetration portion observed from the normal direction has an angle of 1.5° or more and 20° or less with respect to the vertical direction. The above angle θ is 1.5° or more, and may also be 5° or more, or may also be 10° or more. On the other hand, the above angle θ is 20° or less, and may also be 15° or less. That is, the above angle θ is 1.5° or more and 20° or less, may also be 5° or more and 20° or less, or may also be 10° or more and 15° or less. By making the above angle θ within the above range, it becomes possible to control the light emission angle in the left and right directions. Furthermore, in FIGS. 1 and 3, the light penetration portion 3 has an angle θ with respect to the vertical direction on the right side (+D1 side). In this case, it is preferable that the left side (-D1 side) is the driver seat side. On the other hand, the light penetration portion 3 may have an angle θ with respect to the vertical direction on the left side (-D1 side). In this case, it is preferable that the right side (+D1 side) is the driver seat side. Since the other features of the optical sheet in this embodiment are the same as those of the "A-1. Optical Sheet (First Embodiment)" described above, the description here is omitted. Regarding the other components of the surface light source device, they are already described in the above "B-1. Surface Light Source Device (First Embodiment)", so the description here is omitted. 2. Display Panel and Other Components Regarding the display panel and other components, they are already described in the above "C-1-1. Display Device (First Example of the First Embodiment)", so the description here is omitted. 3. Use The display device in this embodiment is arranged in front of the co-pilot's seat of the vehicle. Fig. 8(a) is a schematic front view inside the vehicle when the display device 50O of this embodiment is arranged in front of the co-pilot's seat. Fig. 8(b) is a top view showing the state of the optical sheet of the display device in Fig. 8(a). In Fig. 8(a) and Fig. 8(b), the optical sheet is arranged such that the left-right direction is the horizontal direction (the left-right direction of the vehicle), the up-down direction is the vertical direction, and the thickness direction is the horizontal direction (the front-rear direction of the vehicle). On the other hand, the setting and arrangement of the display device are not limited to this. C-8-2. Display Device (Second Example of the Eighth Embodiment) Fig. 9 is a schematic top view and a cross-sectional view showing an example of the display device of this embodiment. Also, Fig. 1, Fig. 3, Fig. 4, and Fig. 10 are schematic perspective views, cross-sectional views, and top views showing an example of the optical sheet in the display device of this embodiment. As shown in Fig. 9, the display device 50P of this embodiment includes a display panel 30 and an optical sheet 10H disposed on the observer side of the display panel 30. As shown in Fig. 1, Fig. 3, Fig. 4, and Fig. 10, the optical sheet 10H of this embodiment includes a substrate layer 1 and an optical functional layer 2 laminated on one surface of the substrate layer 1, and the optical functional layer 2 has: a plurality of light penetration portions 3, which have a specific cross-section and extend along one direction; and a light absorption portion 4 formed between adjacent light penetration portions 3. The specific cross-section of the light penetration portion 3 is trapezoidal, and the shorter upper base is set as the light incident side. As shown in Fig. 3, when the display device 50P is provided, in the optical sheet 10H, the extension direction of the light penetration portion 3 observed from the normal direction N has an angle of 1.5° or more and 20° or less with respect to the vertical direction. Details of Fig. 1, Fig. 3, and Fig. 4 are already described in the above "A-1. Optical Sheet (First Embodiment)", so the description here is omitted. Regarding Fig. 10, it is already described in the above "A-3. Optical Sheet (Fifth Embodiment)", so the description here is omitted. Also, regarding Fig. 9, it is already described in the above "C-1-2. Display Device (Second Example of the First Embodiment)", so the description here is omitted. 1. Optical sheet Regarding the optical sheet, it is the same as the optical sheet described in the above item "C-8-1. Display device (the first example of the eighth embodiment)", so the description here is omitted. 2. Display panel and other components Regarding the display panel and other components, they have been described in the above item "C-1-2. Display device (the second example of the first embodiment)", so the description here is omitted. 3. Use Since the use of the display device in this embodiment is the same as that in the above item "C-8-1. Display device (the first example of the eighth embodiment)", the description here is omitted. Furthermore, the present invention is not limited to the above embodiments. The above embodiments are merely illustrative, and all those having a configuration substantially the same as the technical idea described in the claims of the present invention and exhibiting the same effects are included in the technical scope of the present invention. [Examples] Examples and comparative examples are shown below to explain the present invention in more detail. [Examples 1 to 18 and Comparative Examples 1 to 14] Optical sheets having a substrate layer and an optical functional layer as shown in FIGS. 1 to 4 were manufactured. At this time, as shown in Tables 1 and 2, the angle of the light penetration portion with respect to the second direction (deviation angle θ), the inclined angle θ of the hypotenuse of the trapezoidal cross-section 11 and θ 12 , the light incident side aperture ratio, the height Da of the light absorption portion, the OD value of the light absorption portion, and the refractive index difference Nt - Nr between the light penetration portion and the light absorption portion were changed. Furthermore, in Sample Groups 1 to 3, the refractive index Nt of the light penetration portion was 1.57, and the refractive index difference Nr of the light absorption portion was 1.54. For the obtained optical sheets, the brightness of light was measured as described below, and the transmittance and relative transmittance were calculated. (Measurement method) First, without disposing the optical sheet, the brightness of the light in the third direction D3 of the surface light source (an edge-illuminated surface light source using an LED as the light source) alone is measured by a viewing angle characteristic measuring device (EZ Contrast XL80 manufactured by ELDIM). Subsequently, the surface light source (an edge-illuminated surface light source using an LED as the light source) is disposed on the back side (optical functional layer side) of the optical sheet, and the brightness of the light passing through the optical sheet in the third direction D3 and the brightness of the light passing through the direction inclined ±30° from the third direction D3 to the first direction D1 side are measured by a viewing angle characteristic measuring device (EZ Contrast XL80 manufactured by ELDIM) on the surface side (base material layer side). Then, the ratio of the brightness of the light passing through the optical sheet in the third direction D3 to the brightness of the light in the third direction D3 of the surface light source alone is calculated, and this is taken as the light transmittance of the optical sheet in the third direction D3. Similarly, the ratio of the brightness of the light passing through the direction inclined ±30° from the third direction to the first direction D1 side to the brightness of the light in the third direction D3 of the surface light source alone is calculated, and this is taken as the light transmittance of the light passing through the direction inclined ±30° from the third direction D3 to the first direction D1 side. Finally, the ratio of the light transmittance of the light passing through the direction inclined ±30° from the third direction D3 to the first direction D1 side when the light transmittance of the optical sheet in the third direction D3 is set to 100% is calculated, that is, the relative transmittance. The results are shown in Tables 1 and 2. Also, in the same manner as described above, the ratio of the light transmittance of the light passing through the direction inclined ±20° from the third direction D3 to the first direction D1 side when the light transmittance of the optical sheet in the third direction D3 is set to 100% is calculated, that is, the relative transmittance. The results of the relative transmittances of the optical sheets of Measurement Example 4 and Comparative Example 8 are shown in FIGS. 12(a) and 13(a). In FIG. 12(a), the horizontal axis represents the viewing angle in the left-right direction (first direction D1), and the vertical axis represents the ratio (relative transmittance) of the light transmittance at each viewing angle in the left-right direction when the light transmittance at a viewing angle of 0° is set to 100%. The optical sheet of Measurement Example 4 obtained a relative transmittance of 0.5% at a viewing angle of ±30° in the first direction D1 and a relative transmittance of 5.0% at a viewing angle of ±20° in the first direction D1. On the other hand, the optical sheet of Comparative Example 8 had a relative transmittance of 17.8% at a viewing angle of ±30° in the first direction D1 and a relative transmittance of 57.8% at a viewing angle of ±20° in the first direction D1. In Fig. 13(a), the horizontal axis represents the viewing angle in the up-down direction (second direction D2), and the vertical axis represents the ratio of the light transmittance at each viewing angle in the up-down direction (relative transmittance) when the light transmittance at a viewing angle of 0° is set to 100%. The optical sheet of Example 4 obtained a relative transmittance of 18% at a viewing angle of ±30° in the second direction D2. On the other hand, the optical sheet of Comparative Example 8 obtained a relative transmittance of 31.1% at a viewing angle of ±30° in the second direction D2. [Table 1] [Table 2] [Table 3] [Table 4] The optical sheets of Example 4 and Comparative Example 8 were used in a display device, and the display device was observed from the front and obliquely from a position where the viewing angle in the left-right direction was approximately 30°. Fig. 12(b) shows the situation of observing the display device. It can be confirmed that in Comparative Example 8, image light was visually recognized from a position where the viewing angle in the left-right direction was approximately 30°, whereas in Example 4, image light was not visually recognized from a position where the viewing angle in the left-right direction was approximately 30°. Assume a case where the optical sheets of Examples 1 to 18 and Comparative Examples 1 to 14 are used in a display device for the passenger seat, and observe whether image light is incident on the windshield in front of the passenger seat. It can be confirmed that in Comparative Example 8, image light incident on the windshield was observed, but the incidence in Example 4 was suppressed (Fig. 13(b)). Also, Tables 1 and 2 show whether there is incidence on the windshield when using the optical sheets of other examples and comparative examples. It can be confirmed from Tables 1 and 2 that when the light transmittance in the third direction is set to 100%, the incidence on the windshield is suppressed when the ratio of the light transmittance in the direction inclined ±30° from the third direction toward the second direction side, that is, the relative transmittance, is 32% or less. That is, in the present invention, the following inventions can be provided. [1] An optical sheet including a base material layer and an optical functional layer laminated on one surface of the base material layer, wherein the optical sheet has a rectangular shape in plan view, the rectangular shape has a pair of first sides extending along a first direction and a pair of second sides extending along a second direction, the optical functional layer has: a plurality of light penetration portions having a specific cross-section and extending along one direction; and light absorption portions formed between adjacent ones of the light penetration portions, the specific cross-section of the light penetration portions is trapezoidal, and the shorter upper base is set as the light incident side, when the light transmittance in a third direction orthogonal to the first direction and the second direction is set to 100%, the ratio of the light transmittance in a direction inclined by ±30° toward the first direction side with respect to the third direction, that is, the relative transmittance is 1% or less, the extending direction of the light penetration portions has an angle of 5° or more and 20° or less with respect to the second direction. [2] An optical sheet including a base material layer and an optical functional layer laminated on one surface of the base material layer, wherein the optical sheet has a rectangular shape in plan view, the rectangular shape has a pair of first sides extending along a first direction and a pair of second sides extending along a second direction, the optical functional layer has: a plurality of light penetration portions having a specific cross-section and extending along one direction; and light absorption portions formed between adjacent ones of the light penetration portions, the specific cross-section of the light penetration portions is trapezoidal, and the shorter upper base is set as the light incident side, the optical sheet is an optical sheet for a display device disposed in front of the passenger seat of a vehicle, the extending direction of the light penetration portions has an angle of 5° or more and 20° or less with respect to the second direction. [3] The optical sheet according to [2], wherein when the light transmittance in a third direction orthogonal to the first direction and the second direction is set to 100%, the ratio of the light transmittance in a direction inclined by ±30° toward the first direction side with respect to the third direction, that is, the relative transmittance is 1% or less. [4] An optical sheet including a base material layer and an optical functional layer laminated on one surface of the base material layer, wherein the optical sheet has a rectangular shape in plan view, the rectangular shape has a pair of first sides extending along a first direction and a pair of second sides extending along a second direction, the optical functional layer has: a plurality of light penetration portions having a specific cross-section and extending along one direction; and light absorption portions formed between adjacent ones of the light penetration portions, the specific cross-section of the light penetration portions is trapezoidal, and the shorter upper base is set as the light incident side, when the light transmittance in a third direction orthogonal to the first direction and the second direction is set to 100%, the ratio of the light transmittance in a direction inclined by ±30° toward the first direction side with respect to the third direction, that is, the relative transmittance is 1% or less, the extending direction of the light penetration portions has an angle of 1.5° or more and 20° or less with respect to the second direction.[5] An optical sheet includes a base material layer and an optical functional layer laminated on one surface of the base material layer. The optical sheet has a rectangular shape in a plan view. The rectangular shape has a pair of first sides extending in a first direction and a pair of second sides extending in a second direction. The optical functional layer has: a plurality of light penetration portions having a specific cross-section and extending in one direction; and light absorption portions formed between adjacent light penetration portions. The specific cross-section of the light penetration portions is trapezoidal, and the shorter upper base is set as the light incident side. The optical sheet is an optical sheet for a display device disposed in front of the passenger seat of a vehicle. The extending direction of the light penetration portions has an angle of 1.5° or more and 20° or less with respect to the second direction. [6] The optical sheet according to [5], wherein when the light transmittance in a third direction orthogonal to the first direction and the second direction is set to 100%, the ratio of the light transmittance in a direction inclined by ±30° toward the first direction side with respect to the third direction, that is, the relative transmittance is 1% or less. [7] An optical sheet includes a base material layer and an optical functional layer laminated on one surface of the base material layer. The optical sheet has a rectangular shape in a plan view. The rectangular shape has a pair of first sides extending in a first direction and a pair of second sides extending in a second direction. The optical functional layer has: a plurality of light penetration portions having a specific cross-section and extending in one direction; and light absorption portions formed between adjacent light penetration portions. The specific cross-section of the light penetration portions is trapezoidal, and the shorter upper base is set as the light incident side. When the light transmittance in a third direction orthogonal to the first direction and the second direction is set to 100%, the ratio of the light transmittance in a direction inclined by ±20° toward the first direction side with respect to the third direction, that is, the relative transmittance is 10% or less. The extending direction of the light penetration portions has an angle of 1.5° or more and 20° or less with respect to the second direction. [8] An optical sheet includes a base material layer and an optical functional layer laminated on one surface of the base material layer. The base material layer is a resin base material. The optical sheet has a rectangular shape in a plan view. The rectangular shape has a pair of first sides extending in a first direction and a pair of second sides extending in a second direction. The optical functional layer has: a plurality of light penetration portions having a specific cross-section and extending in one direction; and light absorption portions formed between adjacent light penetration portions. The specific cross-section of the light penetration portions is trapezoidal, and the shorter upper base is set as the light incident side. The optical sheet is an optical sheet for a display device disposed in front of the passenger seat of a vehicle. The extending direction of the light penetration portions has an angle of 1.5° or more and 20° or less with respect to the second direction.[9] The optical sheet as described in [8], wherein when the transmittance of light in the third direction orthogonal to the above-mentioned first direction and the above-mentioned second direction is set to 100%, the ratio of the transmittance of light in the direction inclined by ±20° toward the above-mentioned first direction with respect to the above-mentioned third direction, that is, the relative transmittance is 10% or less.

[10] The optical sheet as described in any one of [1] to [9], wherein the angle formed by the interface between the above-mentioned light-transmitting portion and the above-mentioned light-absorbing portion with respect to the normal line of the plane of the above-mentioned optical functional layer is 4.5° or more.

[11] The optical sheet as described in any one of [1] to

[10] , wherein the light-incident-side aperture ratio of the above-mentioned optical functional layer is 35% or less.

[12] The optical sheet as described in any one of [1] to

[11] , wherein the height of the above-mentioned light-absorbing portion is 120 μm or more.

[13] The optical sheet as described in any one of [1] to

[12] , wherein the OD value of the above-mentioned light-absorbing portion is 3.5 or more.

[14] The optical sheet as described in any one of [1] to

[13] , wherein the difference Nt - Nr between the refractive index Nt of the above-mentioned light-transmitting portion and the refractive index Nr of the above-mentioned light-absorbing portion is 0.05 or less.

[15] The optical sheet as described in [1], wherein the above-mentioned optical sheet is an optical sheet for a display device disposed in front of the passenger seat of a vehicle.

[16] The optical sheet as described in any one of [1] to

[15] , wherein the retardation of the above-mentioned substrate layer is 3000 nm or more.

[17] A surface light source device, comprising: an optical sheet as described in any one of [1] to

[16] ; and a light source that emits light incident on the above optical sheet.

[18] A display device, comprising: a surface light source device as described in

[17] ; and a display panel laminated on the above surface light source device.

[19] A display device, comprising a surface light source device including an optical sheet and a display panel laminated on the above surface light source device, and the above optical sheet includes a base material layer and an optical functional layer laminated on one surface of the above base material layer, the above optical functional layer having: a plurality of light penetration portions having a specific cross-section and extending in one direction; and a light absorption portion formed between adjacent ones of the above light penetration portions, the above specific cross-section of the above light penetration portion being trapezoidal, with the shorter upper base being set as the light incident side, when the above display device is provided, in the above optical sheet, when the light transmittance in the normal direction of the main surface of the above optical sheet is set to 100%, the ratio of the light transmittance in the direction inclined ±30° from the above normal direction to the left and right directions, that is, the relative transmittance, is 1% or less, and the extending direction of the above light penetration portion observed from the above normal direction of the main surface of the above optical sheet has an angle of 5° or more and 20° or less with respect to the vertical direction.

[20] A display device, comprising a surface light source device including an optical sheet and a display panel laminated on the above surface light source device, and being disposed in front of the passenger seat of a vehicle, and the above optical sheet includes a base material layer and an optical functional layer laminated on one surface of the above base material layer, the above optical functional layer having: a plurality of light penetration portions having a specific cross-section and extending in one direction; and a light absorption portion formed between adjacent ones of the above light penetration portions, the above specific cross-section of the above light penetration portion being trapezoidal, with the shorter upper base being set as the light incident side, when the above display device is provided in front of the passenger seat of a vehicle, in the above optical sheet, the extending direction of the above light penetration portion observed from the normal direction of the main surface of the above optical sheet has an angle of 5° or more and 20° or less with respect to the vertical direction.

[21] The display device as described in

[20] , wherein when the above display device is provided in front of the passenger seat of a vehicle, in the above optical sheet, when the light transmittance in the normal direction of the main surface of the above optical sheet is set to 100%, the ratio of the light transmittance in the direction inclined ±30° from the above normal direction to the left and right directions, that is, the relative transmittance, is 1% or less.

[22] A display device includes an optical sheet and a display panel. The optical sheet includes a substrate layer and an optical functional layer laminated on one surface of the substrate layer. The optical functional layer has: a plurality of light penetration portions having a specific cross-section and extending in one direction; and light absorption portions formed between adjacent ones of the light penetration portions. The specific cross-section of the light penetration portions is trapezoidal, and the shorter upper base is set as the light incident side. When the display device is provided, in the optical sheet, when the light transmittance in the normal direction of the main surface of the optical sheet is set to 100%, the ratio of the light transmittance in the direction inclined ±30° from the normal direction to the left and right directions, that is, the relative transmittance, is 1% or less. The extending direction of the light penetration portions observed from the normal direction has an angle of 1.5° or more and 20° or less with respect to the vertical direction.

[23] A display device includes an optical sheet and a display panel, and is disposed in front of the passenger seat of a vehicle. The optical sheet includes a substrate layer and an optical functional layer laminated on one surface of the substrate layer. The optical functional layer has: a plurality of light penetration portions having a specific cross-section and extending in one direction; and light absorption portions formed between adjacent ones of the light penetration portions. The specific cross-section of the light penetration portions is trapezoidal, and the shorter upper base is set as the light incident side. When the display device is provided in front of the passenger seat of the vehicle, in the optical sheet, the extending direction of the light penetration portions observed from the normal direction of the main surface of the optical sheet has an angle of 1.5° or more and 20° or less with respect to the vertical direction.

[24] The display device according to

[23] , wherein when the display device is provided in front of the passenger seat of the vehicle, in the optical sheet, when the light transmittance in the normal direction of the main surface of the optical sheet is set to 100%, the ratio of the light transmittance in the direction inclined ±30° from the normal direction to the left and right directions, that is, the relative transmittance, is 1% or less.

[25] A display device includes an optical sheet and a display panel. The optical sheet includes a substrate layer and an optical functional layer laminated on one surface of the substrate layer. The optical functional layer has: a plurality of light penetration portions having a specific cross-section and extending in one direction; and light absorption portions formed between adjacent ones of the light penetration portions. The specific cross-section of the light penetration portions is trapezoidal, and the shorter upper base is set as the light incident side. When the display device is provided, in the optical sheet, when the light transmittance in the normal direction of the main surface of the optical sheet is set to 100%, the ratio of the light transmittance in the direction inclined ±20° from the normal direction to the left and right directions, that is, the relative transmittance, is 10% or less. The extending direction of the light penetration portions observed from the normal direction has an angle of 1.5° or more and 20° or less with respect to the vertical direction.

[26] A display device includes an optical sheet and a display panel, and is disposed in front of the co-pilot seat of a vehicle. The optical sheet includes a substrate layer and an optical functional layer laminated on one surface of the substrate layer. The substrate layer is a resin substrate. The optical functional layer has: a plurality of light penetration portions having a specific cross-section and extending in one direction; and a light absorption portion formed between adjacent light penetration portions. The specific cross-section of the light penetration portion is trapezoidal, and the shorter upper base is set as the light incident side. When the display device is disposed in front of the co-pilot seat of the vehicle, in the optical sheet, the extension direction of the light penetration portion observed from the normal direction of the main surface of the optical sheet has an angle of 1.5° or more and 20° or less with respect to the vertical direction.

[27] The display device according to

[26] , wherein when the display device is disposed in front of the co-pilot seat of the vehicle, in the optical sheet, when the light transmittance in the normal direction of the main surface of the optical sheet is set to 100%, the ratio of the light transmittance in the direction inclined ±20° from the normal direction to the left and right directions, that is, the relative transmittance is 10% or less.

[28] The display device according to any one of

[22] to

[27] , wherein the display device includes a surface light source device, and the surface light source device includes the optical sheet.

[29] The display device according to any one of

[22] to

[27] , wherein the optical sheet is disposed on the observer side of the display panel.

[30] The display device according to

[29] , which is an organic electroluminescent display device.

[31] The display device according to any one of

[19] to

[29] , which is a liquid crystal display device. 1: Substrate layer 2: Optical functional layer 3: Light penetration portion 4: Light absorption portion 10, 10A~10H: Optical sheet 15: Liquid crystal panel 20: Surface light source device 21: Light guide plate 25: Light source 26: Light diffusion plate 27: Prism layer 28: Reflective polarizing plate 50: Display device L1: First side L2: Second side D1: First direction D2: Second direction D3: Third direction I~III: Cutting direction [Fig. 1] is a schematic perspective view illustrating the optical sheet of the present invention. [Fig. 2] is a schematic cross-sectional view illustrating the optical sheet of the present invention. [Fig. 3] is a schematic top view illustrating the optical sheet of the present invention. [Fig. 4] is a schematic cross-sectional view illustrating the optical sheet of the present invention. [Fig. 5] is an exploded perspective view illustrating the display device of the present invention. [Fig. 6] is a partial exploded cross-sectional view illustrating the display device of the present invention. [Fig. 7] is a partial exploded cross-sectional view illustrating the display device of the present invention. [Fig. 8] is a schematic view of the front inside of a vehicle in which the display device of the present invention is arranged as a display device for a passenger seat, and a front view of the display device. [Fig. 9] is a partial exploded cross-sectional view illustrating the display device of the present invention. [Fig. 10] is a schematic cross-sectional view illustrating the optical sheet of the present invention. [Fig. 11] is a schematic perspective view of a conventional optical sheet and a schematic view of the front inside of a vehicle in which the conventional optical sheet is arranged as a display device for a passenger seat. [Fig. 12] is a result of measuring the relative transmittance (in the left-right direction) of the optical sheets of Example 4 and Comparative Example 8, and an observation view of the display devices including the optical sheets of Example 4 and Comparative Example 8. [Fig. 13] is a result of measuring the relative transmittance (in the up-down direction) of the optical sheets of Example 4 and Comparative Example 8, and an observation view of the display devices including the optical sheets of Example 4 and Comparative Example 8. 1: Substrate layer 2: Optical functional layer 3: Light transmission part 4: Light absorption part 10, 10A~10H: Optical sheet D1: First direction D2: Second direction D3: Third direction L1: First side L2: Second side

Claims

1. An optical sheet comprising a substrate layer and an optical functional layer deposited on one side of the substrate layer, wherein the optical sheet has a rectangular shape when viewed from above, the rectangular shape having a pair of first sides extending along a first direction and a pair of second sides extending along a second direction, the optical functional layer having: a plurality of light-transmitting portions having a specific cross-section and extending along a direction; and light-absorbing portions formed between adjacent light-transmitting portions, wherein the specific cross-section of the light-transmitting portions is trapezoidal, the shorter upper bottom being designated as the light-incident side, and when the transmittance of light in a third direction orthogonal to the first and second directions is set to 100%, the ratio of the transmittance of light in a direction inclined ±20° toward the first direction relative to the third direction, i.e., the relative transmittance, is 10% or less, the extending direction of the light-transmitting portions having an angle of 1.5° or more and 20° or less relative to the second direction, and the height of the light-absorbing portions being 120 μm or more.

2. An optical sheet comprising a substrate layer and an optical functional layer deposited on one side of the substrate layer, wherein the substrate layer is a resin substrate, the optical sheet having a rectangular shape when viewed from above, the rectangular shape having a pair of first sides extending along a first direction and a pair of second sides extending along a second direction, the optical functional layer having: a plurality of light-transmitting portions having specific cross-sections and extending along a direction; and light-absorbing portions formed between adjacent light-transmitting portions, the specific cross-sections of the light-transmitting portions being trapezoidal, the shorter upper bottom being designated as the light-incident side, the optical sheet being an optical sheet for a display device disposed in front of the passenger seat of a vehicle, the extending direction of the light-transmitting portions having an angle of 1.5° or more and 20° or less relative to the second direction, and the height of the light-absorbing portions being 120 μm or more.

3. The optical sheet as described in claim 2, wherein, When the transmittance of light in the third direction, which is orthogonal to the first and second directions, is set to 100%, the ratio of the transmittance of light in the direction inclined at ±20° towards the first direction from the third direction, i.e., the relative transmittance, is 10% or less.

4. The optical sheet as requested in item 1 or 2, wherein, The angle formed by the interface between the light-transmitting portion and the light-absorbing portion relative to the normal of the optical functional layer is 4.5° or more.

5. The optical sheet as requested in item 1 or 2, wherein, The light-incident aperture ratio of the aforementioned optical functional layer is less than 35%.

6. The optical sheet as requested in item 1 or 2, wherein, The OD value of the aforementioned light-absorbing part is 3.5 or higher.

7. The optical sheet as requested in item 1 or 2, wherein, The difference between the refractive index Nt of the light-transmitting part and the refractive index Nr of the light-absorbing part, Nt-Nr, is less than 0.

05.

8. The optical sheet as requested in item 1 or 2, wherein, The retardation of the aforementioned substrate layer is 3000 nm or more.

9. A surface light source apparatus comprising: an optical sheet according to any one of claims 1 to 8; and a light source emitting light incident on the optical sheet.

10. A display device comprising: a surface light source device of claim 9; and a display panel laminated on the surface light source device.

Images