Lighting fixture and display device

Abstract

To regulate a light emission angle without using a louver.SOLUTION: A lighting fixture 12 includes: a light source 13; a light guide plate 15 where at least a part of an outer peripheral end plane is defined as a first end plane 15A; one main plane is defined as a first main plane 15B; and the other main plane is defined as a second main plane 15C; and a first prism sheet 16 where one main plane is defined as a third main plane 16A1 disposed facing the second main plane 15C, and the other main plane is defined as a fourth main plane 16A2. The second main plane 15C of the guide plate 15 is provided with a first inclined plane 22A having a rising inclination toward the side of the light source 13 from a side opposite to the side of the light source 13 with respect to a first direction. The fourth main plane 16A2 of the first prism sheet 16 is provided with a plurality of first prisms 16B extending along the first direction and aligned along a second direction. The first prism 16B includes: a first bottom side 16B1 parallel to the second direction; and a pair of first inclined sides 16B2, 16B3 rising from both ends of the first bottom side 16B1.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The technology disclosed in this specification relates to a lighting device and a display device. [Background technology]

[0002] Conventionally, an example of an illumination device is known, as described in the following Patent Document 1. Patent Document 1 describes an illumination device used in a vehicle instrument. The vehicle instrument described in Patent Document 1 is arranged under the windshield, and a front cover covers the front of a dial plate on which a display unit indicated by a pointer is formed, and indirectly illuminates the display unit and the indication unit of the pointer by turning on a light source. This vehicle instrument has an anti-reflection film formed on the surface of the front cover to omit a hood above the front cover, and louvers are formed on the upper surface of the indication unit of the pointer and on a white diffusion layer facing an indication slit formed in a black opaque layer in accordance with the indication unit of the dial, respectively, to regulate the emission angle so that the emitted light does not head toward the windshield. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 3755778 Summary of the Invention [Problem to be solved by the invention]

[0004] In the vehicle instrument described in Patent Document 1, louvers are used to prevent the phenomenon of external light from outside the vehicle being reflected toward the driver and the occurrence of light-emitting displays being reflected on the windshield. However, such louvers are expensive parts, so there has been a demand for a method of regulating the light emission angle and preventing the occurrence of reflections on the windshield without using louvers.

[0005] The technology described in this specification was developed based on the above circumstances, and has an object to regulate the light emission angle without using a louver. [Means for solving the problem]

[0006] (1) A lighting device related to the technology described in this specification includes a light source; a light guide plate having at least a part of an outer peripheral end face that faces the light source and is a first end face through which light is incident, one main surface being a first main surface and the other main surface being a second main surface; and a first prism sheet having one main surface being a third main surface arranged facing the second main surface and the other main surface being a fourth main surface, wherein the second main surface of the light guide plate is provided with a first inclined surface that rises from a side opposite the light source toward the light source in a first direction that includes a direction from the light source to the light guide plate, and the fourth main surface of the first prism sheet is provided with a plurality of first prisms that extend along the first direction and are aligned along a second direction that intersects with the first direction and is along the fourth main surface, and each of the first prisms has a first base that is parallel to the second direction and a pair of first oblique sides that rise from both ends of the first base.

[0007] (2) In addition to the above (1), the lighting device may further include a light absorbing sheet having a fifth principal surface with one principal surface facing the fourth principal surface and having higher light absorbency than both the light guide plate and the first prism sheet.

[0008] (3) In addition to the above (1), the lighting device may further include a light reflecting sheet having a sixth principal surface with one principal surface facing the fourth principal surface and having higher light reflectivity than both the light guide plate and the first prism sheet.

[0009] (4) In addition to any one of (1) to (3), the above lighting device may further include a second prism sheet having one principal surface defined as a seventh principal surface and the other principal surface defined as an eighth principal surface facing the first principal surface, and a third prism sheet having one principal surface defined as a ninth principal surface and the other principal surface defined as a tenth principal surface facing the seventh principal surface, wherein the seventh principal surface of the second prism sheet is provided with a plurality of second prisms extending along the second direction and arranged in a row along the first direction, and the ninth principal surface of the third prism sheet is provided with a plurality of third prisms extending along the second direction and arranged in a row along the first direction.

[0010] (5) In addition to the above-mentioned (4), the second prism may have a second base parallel to the first direction and a pair of second hypotenuses rising from both ends of the second base, and of the pair of second hypotenuses, the second hypotenuse on the light source side in the first direction may form a larger angle with respect to the second base than the second hypotenuse on the opposite side to the light source side in the first direction.

[0011] (6) In addition to (4) or (5) above, the lighting device may further include a third prism having a third base parallel to the first direction and a pair of third oblique sides rising from both ends of the third base, the pair of third oblique sides forming equal angles with respect to the third base.

[0012] (7) In addition to any one of (1) to (6) above, the lighting device may be configured such that a plurality of the first inclined surfaces are arranged side by side along the first direction, and the areas of the plurality of first inclined surfaces increase as they are disposed farther away from the light source.

[0013] (8) A display device related to the technology described in this specification includes an illumination device described in any one of (1) to (7) above, and a display panel that performs display using light from the illumination device. Effect of the Invention

[0014] According to the technology described in this specification, it is possible to regulate the light emission angle without using a louver. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is an exploded perspective view of a liquid crystal display device according to a first embodiment. [Diagram 2] FIG. 1 is a cross-sectional view of a backlight device constituting a liquid crystal display device according to a first embodiment, taken along the Y-axis direction. [Diagram 3] FIG. 1 is a cross-sectional view of a backlight device according to a first embodiment taken along the X-axis direction. [Figure 4] FIG. 3 is a perspective view of a light guide plate constituting the backlight device according to the first embodiment, viewed from the second main surface side. [Diagram 5] FIG. 4 is a bottom view showing the configuration of the second main surface of the light guide plate according to the first embodiment. [Figure 6] FIG. 1 is a schematic diagram showing a state in which a liquid crystal display device according to a first embodiment is mounted on a passenger vehicle; [Figure 7] FIG. 2 is a cross-sectional view of a backlight device of Type B according to the first embodiment taken along the Y-axis direction. [Figure 8] Graph showing light distribution in the Y-axis direction in Comparative Experiment 1 according to Embodiment 1. [Figure 9] Table showing the experimental results of Comparative Experiment 2 according to the first embodiment [Figure 10] FIG. 11 is a cross-sectional view of the backlight device according to the second embodiment taken along the Y-axis direction. [Figure 11] Graph showing light distribution in the Y-axis direction in Comparative Experiment 3 according to the second embodiment. [Figure 12] Table showing the experimental results of Comparative Experiment 4 according to the second embodiment [Figure 13] Graph showing light distribution in the Y-axis direction in Comparative Experiment 5 according to the second embodiment. [Figure 14] FIG. 11 is a cross-sectional view of the backlight device according to the third embodiment taken along the Y-axis direction. [Figure 15] Graph showing light distribution in the Y-axis direction in Comparative Experiment 6 according to the third embodiment. [Figure 16]Table showing the experimental results of Comparative Experiment 7 according to the third embodiment DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] <Embodiment 1> A first embodiment will be described with reference to Fig. 1 to Fig. 9. In this embodiment, a liquid crystal display device (display device) 10 is illustrated. Note that the X-axis, Y-axis, and Z-axis are shown in a part of each drawing, and each axis direction is drawn to be the direction shown in each drawing. Also, the up-down direction is based on Fig. 2, Fig. 3, and Fig. 7, and the upper side of each drawing is the front side and the lower side of each drawing is the back side.

[0017] 1, the liquid crystal display device 10 includes a liquid crystal panel (display panel) 11 that displays an image, and a backlight device (illumination device) 12 that is disposed on the rear side of the liquid crystal panel 11 and irradiates light used for display toward the liquid crystal panel 11. In this embodiment, an in-vehicle liquid crystal display device 10 is illustrated. The in-vehicle liquid crystal display device 10 is mounted, for example, in a car navigation system that displays maps and the like as images, a multifunction display that displays the operating status of devices such as an air conditioner in addition to maps and the like as images, an instrument panel that displays gauges and warnings as images, and an infotainment system that displays television images and audio information in addition to maps and the like as images.

[0018] The liquid crystal panel 11 is in the shape of a horizontally long rectangular plate as a whole. The long side direction of the liquid crystal panel 11 coincides with the X-axis direction, the short side direction with the Y-axis direction, and the plate thickness direction (the normal direction of the main surface) with the Z-axis direction. The central part of the main surface of the liquid crystal panel 11 is a display area AA capable of displaying an image, and the frame-like peripheral end part surrounding the display area AA is a non-display area NAA. The liquid crystal panel 11 has a pair of substrates and a liquid crystal layer sealed between the pair of substrates. Of the pair of substrates constituting the liquid crystal panel 11, the one disposed on the front side is a CF substrate (opposing substrate), and the one disposed on the back side is an array substrate (TFT substrate). The CF substrate is provided with color filters exhibiting R (red), G (green), B (blue), etc., and a light-shielding portion (black matrix) that separates adjacent color filters. The array substrate (TFT substrate) is provided with at least gate wiring and source wiring that are perpendicular to each other, switching elements (e.g., TFTs) connected to the gate wiring and source wiring, and pixel electrodes that are connected to the switching elements and form pixels. An alignment film is provided on each inner surface of the array substrate and the CF substrate that form the liquid crystal panel 11. A polarizing plate is attached to each outer surface of the array substrate and the CF substrate that form the liquid crystal panel 11.

[0019] Next, the backlight device 12 will be described. As shown in Fig. 1, the backlight device 12 includes at least LEDs 13 as light sources, an LED board (light source board) 14 on which the LEDs 13 are mounted, a light guide plate 15 for guiding light from the LEDs 13, a first prism sheet 16 arranged on the back side (opposite the light output side) of the light guide plate 15, a light absorbing sheet 17 arranged on the back side of the first prism sheet 16, a second prism sheet 18 arranged on the front side (light output side) of the light guide plate 15, and a third prism sheet 19 arranged on the front side of the second prism sheet 18. Of these, the first prism sheet 16 and the light absorbing sheet 17 will be described later, and the other components (LEDs 13, LED board 14, second prism sheet 18, and third prism sheet 19) will be described in order. The backlight device 12 according to this embodiment is of a one-side light-entry edge light type in which light from the LEDs 13 enters the light guide plate 15 only from one side.

[0020] As shown in FIG. 1, the LED 13 is configured by sealing an LED chip on a substrate fixed to the LED substrate 14 with a sealing material. The LED chip of the LED 13 emits a single color, for example, blue light, and a phosphor is dispersed and mixed in the sealing material to emit white light as a whole. The phosphor includes a yellow phosphor, a green phosphor, a red phosphor, and the like. The LED 13 is a so-called side emission type in which the side surface adjacent to the mounting surface for the LED substrate 14 becomes the light emitting surface 13A. The LED substrate 14 is installed with its main surface parallel to the main surface of the light guide plate 15, and the front main surface becomes the mounting surface for the LED 13. On the mounting surface of the LED substrate 14, a plurality of LEDs 13 are arranged side by side at approximately equal intervals along the X-axis direction. The arrangement direction of the plurality of LEDs 13 coincides with the X-axis direction.

[0021] The light guide plate 15 is made of a synthetic resin material that has a refractive index sufficiently higher than that of air and is almost transparent. Specifically, the light guide plate 15 is made of a synthetic resin material such as an acrylic resin such as PMMA, and the refractive index is, for example, about 1.49. As shown in FIG. 1, the light guide plate 15 is plate-shaped, and its main surface is parallel to the main surface of the liquid crystal panel 11. The light guide plate 15 has a long side direction on its main surface that coincides with the X-axis direction (second direction), a short side direction that coincides with the Y-axis direction (first direction), and a plate thickness direction that is a normal direction to the main surface that coincides with the Z-axis direction (third direction). The light guide plate 15 is disposed directly below the liquid crystal panel 11. One of the long side end faces of the outer peripheral end faces of the light guide plate 15 faces the light emitting surface 13A of the LED 13 and is a light incident end face (first end face) 15A into which light from the light emitting surface 13A is directly incident. The light-entering end surface 15A has a long side aligned with the X-axis direction and a short side aligned with the Z-axis direction. Of the pair of main surfaces of the light guide plate 15, the front main surface facing the liquid crystal panel 11 is the first main surface 15B that outputs light guided inside, and the back main surface facing the light absorbing sheet 17 is the second main surface 15C. The light guide plate 15 has a function of introducing light emitted from the LEDs 13 toward the light guide plate 15 from the light-entering end surface 15A, propagating the light inside, and then outputting the light from the first main surface 15B toward the front side (light output side). The detailed structure of the light guide plate 15 will be described later. The normal direction of the light-entering end surface 15A is aligned with the Y-axis direction (first direction) including the direction from the LEDs 13 toward the light guide plate 15.

[0022] 1, the second prism sheet 18 and the third prism sheet 19 are in the form of sheets, and their respective main surfaces are parallel to the respective main surfaces of the liquid crystal panel 11 and the light guide plate 15. The second prism sheet 18 and the third prism sheet 19 have their main surfaces parallel to the X-axis direction and the Y-axis direction, and the normal direction (thickness direction) of the main surfaces coincides with the Z-axis direction. The second prism sheet 18 and the third prism sheet 19 are laminated on the front side of the light guide plate 15, and have the function of imparting a predetermined optical effect to the light emitted from the first main surface 15B of the light guide plate 15 and emitting it.

[0023] As shown in Fig. 1 and Fig. 2, the second prism sheet 18 has a sheet-like second base material 18A and a second prism 18B provided on the second base material 18A. The pair of main surfaces of the second base material 18A includes a second light-emitting main surface (seventh main surface) 18A1 and a second light-entering main surface (eighth main surface) 18A2. The second light-emitting main surface 18A1 is a main surface on the front side (light-emitting side) of the second base material 18A facing the third prism sheet 19, and emits light toward the third prism sheet 19. The second light-entering main surface 18A2 is a main surface on the back side (opposite to the light-emitting side) of the second base material 18A facing the first main surface 15B of the light guide plate 15, and receives the light emitted from the first main surface 15B.

[0024] The second base material 18A is made of a nearly transparent synthetic resin, specifically, a crystalline transparent resin material such as PET (polyethyleneterephthalate). In manufacturing the second base material 18A, a crystalline transparent resin material is stretched in a biaxial stretching process to form a sheet, which is suitable for reducing manufacturing costs. The second prism 18B is made of a nearly transparent ultraviolet curable resin material, which is a type of photocurable resin material. In manufacturing the second prism sheet 18, for example, an uncured ultraviolet curable resin material is filled in a mold for molding, and the second base material 18A is placed on the open end of the mold so that the uncured ultraviolet curable resin material is arranged in contact with the main surface on the front side. In this state, when ultraviolet light is irradiated onto the ultraviolet curable resin material through the second base material 18A, the ultraviolet curable resin material is cured, and the second prism 18B is provided integrally with the second base material 18A. The ultraviolet curable resin material constituting the second prism 18B is, for example, an acrylic resin such as PMMA. The refractive index of the ultraviolet curable resin material constituting the second prism 18B is preferably in the range of 1.49 to 1.52, and is most preferably 1.49.

[0025] As shown in FIG. 2, the second prism 18B is provided on the second light-emitting main surface 18A1 on the front side of the second base material 18A. More specifically, the second prism 18B is provided in a shape that protrudes from the second light-emitting main surface 18A1 of the second base material 18A toward the front side (the side opposite to the light guide plate 15) along the Z-axis direction. The second prism 18B has a cross-sectional shape cut along the Y-axis direction that is substantially triangular (substantially mountain-shaped) and extends linearly along the X-axis direction (second direction), and a plurality of the second prisms 18B are arranged side by side along the Y-axis direction (first direction) on the second light-emitting main surface 18A1 of the second base material 18A. The plurality of second prisms 18B are arranged continuously with almost no intervals along the Y-axis direction. The second prism 18B has a second base 18B1 parallel to the Y-axis direction and a pair of second oblique sides 18B2, 18B3 rising from both ends of the second base 18B1. Of the pair of second oblique sides 18B2, 18B3 in the second prism 18B, the one on the LED 13 side in the Y-axis direction (left side in FIG. 2) is referred to as the second LED side oblique side (one second oblique side) 18B2, and the one on the opposite side to the LED 13 side in the Y-axis direction (right side in FIG. 2) is referred to as the second LED opposite oblique side (the other second oblique side) 18B3. Of the light incident on the second prism 18B, the second LED opposite oblique side 18B3 is hit and refracted by the light that mainly travels in the direction away from the LED 13 in the Y-axis direction (right side in FIG. 2). On the other hand, the second LED side oblique side 18B2 is hit and refracted by the light that mainly travels in the direction toward the LED 13 in the Y-axis direction (left side in FIG. 2) among the light incident on the second prism 18B. In any case, most of the light refracted by the pair of second oblique sides 18B2, 18B3 of the second prism 18B is selectively raised in the Y-axis direction and condensed.

[0026] As shown in FIG. 2, the second prism 18B has a larger inclination angle (third base angle) θ1 of the second LED side oblique side 18B2 with respect to the second base 18B1 than the inclination angle (fourth base angle) θ2 of the second LED opposite oblique side 18B3 with respect to the second base 18B1. That is, the second prism 18B has an asymmetrical cross-sectional shape in the form of a scalene triangle. Specifically, the inclination angle θ1 of the second LED side oblique side 18B2 with respect to the second base 18B1 in the second prism 18B is preferably in the range of 50° to 60°, and is most preferably 55°. On the other hand, the inclination angle θ2 of the second LED opposite oblique side 18B3 with respect to the second base 18B1 in the second prism 18B is preferably in the range of 35° to 50°, and is most preferably 45°. Moreover, the angle (second apex angle) θ3 formed by the pair of second oblique sides 18B2, 18B3 of the second prism 18B is preferably in the range of 70° to 95°, and most preferably 80°. The multiple second prisms 18B aligned along the X-axis direction are all substantially identical in height, width of second base 18B1, and inclination angle of each of second oblique sides 18B2, 18B3 relative to second base 18B1, and the arrangement interval between adjacent second prisms 18B is also substantially constant and equally spaced.

[0027] As shown in Fig. 1 and Fig. 2, the third prism sheet 19 has a sheet-like third base material 19A and a third prism 19B provided on the third base material 19A. The pair of main surfaces of the third base material 19A includes a third light-emitting main surface (ninth main surface) 19A1 and a third light-entering main surface (tenth main surface) 19A2. The third light-emitting main surface 19A1 is the main surface on the front side of the third base material 19A, and emits light to the outside. The third light-entering main surface 19A2 is the main surface on the back side of the third base material 19A that faces the second prism sheet 18, and receives the light emitted from the second prism sheet 18.

[0028] The third base material 19A is made of a nearly transparent synthetic resin, and specifically, for example, the same crystalline transparent resin material as the second base material 18A, such as PET. The third prism 19B is made of a nearly transparent ultraviolet-curable resin material, which is a type of photocurable resin material. The manufacturing method of the third prism sheet 19 is the same as the manufacturing method of the second prism sheet 18 described above. The ultraviolet-curable resin material constituting the third prism 19B is, for example, an acrylic resin such as PMMA, and its refractive index is set higher than the refractive index of the material of the second prism 18B, for example, about 1.61.

[0029] As shown in FIG. 2, the third prism 19B is provided on the third light-emitting main surface 19A1 on the front side of the third base material 19A. More specifically, the third prism 19B is provided in a shape that protrudes from the third light-emitting main surface 19A1 of the third base material 19A toward the front side (the side opposite to the second prism sheet 18) along the Z-axis direction. The third prism 19B has a cross-sectional shape cut along the Y-axis direction that is substantially triangular (substantially mountain-shaped) and extends linearly along the X-axis direction (second direction), and a plurality of the third prisms 19B are arranged side by side along the Y-axis direction (first direction) on the third light-emitting main surface 19A1 of the third base material 19A. The plurality of third prisms 19B are arranged continuously with almost no intervals along the Y-axis direction. The third prism 19B has a third base 19B1 parallel to the Y-axis direction and a pair of third oblique sides 19B2, 19B3 rising from both ends of the third base 19B1. Of the pair of third oblique sides 19B2, 19B3 in the third prism 19B, the one on the LED 13 side in the Y-axis direction (left side in FIG. 2) is referred to as the third LED side oblique side (one third oblique side) 19B2, and the one on the opposite side to the LED 13 side in the Y-axis direction (right side in FIG. 2) is referred to as the third LED opposite oblique side (the other third oblique side) 19B3. Of the light incident on the third prism 19B, the third LED opposite oblique side 19B3 is hit and refracted by the light that mainly travels in the direction away from the LED 13 in the Y-axis direction (right side in FIG. 2). On the other hand, the third LED side oblique side 19B2 is hit and refracted by the light that mainly travels in the direction toward the LED 13 in the Y-axis direction (left side in FIG. 2) among the light incident on the third prism 19B. In any case, most of the light refracted by the pair of third oblique sides 19B2, 19B3 of the third prism 19B is selectively raised in the Y-axis direction and condensed.

[0030] 2, the third prism 19B has the same inclination angle (fifth base angle) θ4 of the third LED side oblique side 19B2 with respect to the third base 19B1 and the same inclination angle (sixth base angle) θ5 of the third LED opposite oblique side 19B3 with respect to the third base 19B1. That is, the third prism 19B has a symmetrical cross-sectional shape of an isosceles triangle. In addition, the inclination angle θ4 of the third LED side oblique side 19B2 with respect to the third base 19B1 in the third prism 19B is smaller than the inclination angle θ1 of the second LED side oblique side 18B2 with respect to the second base 18B1 in the second prism 18B provided in the second prism sheet 18. Specifically, the inclination angles θ4, θ5 of the pair of third oblique sides 19B2, 19B3 with respect to the third base 19B1 of the third prism 19B are preferably in the range of 40° to 50°, and are most preferably 45°. On the other hand, the angle (third apex angle) θ6 of the pair of third oblique sides 19B2, 19B3 of the third prism 19B is preferably in the range of 80° to 100°, and are most preferably 90°, i.e., a right angle. The height dimension, width dimension of the third base 19B1, and inclination angle of each of the third oblique sides 19B2, 19B3 with respect to the third base 19B1 of the multiple third prisms 19B aligned along the X-axis direction are all substantially the same, and the arrangement intervals between adjacent third prisms 19B are also substantially constant and equally spaced. Moreover, it is preferable that the height dimension and arrangement interval of the third prisms 19B are different from the height dimension and arrangement interval of the second prisms 18B, respectively, in order to suppress the occurrence of interference fringes called moire.

[0031] The operation and effect of the second prism sheet 18 and the third prism sheet 19 configured as above will be described. The light emitted from the LEDs 13 and incident on the light-entering end surface 15A of the light guide plate 15 propagates within the light guide plate 15, and is emitted from the first main surface 15B to be incident on the second prism sheet 18. Most of the light incident on the second prism sheet 18 is refracted by the second LED-opposite oblique side 18B3, which is the oblique side opposite the LED 13 side in the Y-axis direction, of the pair of second oblique sides 18B2, 18B3 of the second prism 18B, and is emitted while being raised, or is directed toward the second LED-side oblique side 18B2, which is the oblique side on the LED 13 side in the Y-axis direction. As described above, the second prism 18B has an inclination angle θ1 that the second LED side oblique side 18B2, which is the oblique side on the LED 13 side in the Y-axis direction, makes with respect to the second base 18B1, which is larger than the inclination angle θ2 that the second LED opposite oblique side 18B3, which is the oblique side opposite to the LED 13 side in the Y-axis direction, makes with respect to the second base 18B1. Therefore, compared to the case where the inclination angles θ1 and θ2 are the same angle or the case where the inclination angle θ2 is larger than the inclination angle θ1, the light incident on the second prism sheet 18 is less likely to hit the second LED side oblique side 18B2, which is the oblique side on the LED 13 side of the second prism 18B. Here, when the incident light on the second prism sheet 18 hits the second LED side oblique side 18B2, which is the oblique side on the LED 13 side of the second prism 18B, when it is emitted from the second prism 18B, it tends to be emitted as a side lobe light without being raised when it is emitted from the second prism 18B. Therefore, if it becomes difficult for the incident light of the second prism sheet 18 to directly strike the second LED side oblique side 18B2, which is the oblique side of the second prism 18B facing the LED 13, the generation of side lobe light is suppressed, resulting in improved light utilization efficiency.

[0032] Most of the light that exits the second prism sheet 18 and enters the third prism sheet 19 is refracted by the third LED-opposite hypotenuse 19B3, which is the hypotenuse opposite to the LED 13 side in the Y-axis direction, of the pair of third hypotenuses 19B2, 19B3 of the third prism 19B, and exits while being raised, or proceeds toward the third LED-side hypotenuse 19B2, which is the hypotenuse on the LED 13 side in the Y-axis direction. As described above, in the third prism 19B, the inclination angles θ4, θ5 that the pair of third hypotenuses 19B2, 19B3 make with respect to the third base 19B1 are equal. Therefore, compared to the case where the inclination angles θ4 and θ5 are different, the light refracted by the third LED opposite oblique side 19B3, which is the oblique side opposite to the LED 13 side in the Y-axis direction, and proceeding toward the third LED side oblique side 19B2, which is the oblique side on the LED 13 side in the Y-axis direction, is more likely to be returned to the second prism sheet 18 side by the third LED side oblique side 19B2, which is the oblique side on the LED 13 side in the Y-axis direction. As a result, the amount of light returned from the third prism sheet 19 to the second prism sheet 18 side (hereinafter referred to as "returned light") increases. This returned light reaches the third prism sheet 19 again by being reflected within the backlight device 12, and is emitted while being raised by one of the pair of third oblique sides 19B2, 19B3 of the third prism 19B, thereby improving the light utilization efficiency.

[0033] Here, a detailed description will be given of the structure of light guide plate 15. Light guide plate 15 is provided with a first light guide plate lens 20, a second light guide plate lens 21, and a third light guide plate lens (first lens) 22, as shown in Figs.

[0034] As shown in FIG. 3, the first light guide plate lens 20 is provided on the first main surface 15B of the light guide plate 15. The first light guide plate lens 20 extends along the Y-axis direction (first direction) and is arranged in a line along the X-axis direction (second direction). The first light guide plate lenses 20 are arranged continuously along the X-axis direction with almost no space between them. In this embodiment, the first light guide plate lens 20 is a so-called cylindrical lens. The first light guide plate lens 20 is a convex shape that protrudes from the first main surface 15B to the front side. In detail, the first light guide plate lens 20 has a semicircular cross section cut along the X-axis direction and a kamaboko shape that extends linearly along the Y-axis direction, and its surface is an arc-shaped surface 20A. When the angle that the tangent at the base end of the arc-shaped surface 20A makes with respect to the X-axis direction is defined as the "contact angle," the contact angle of the first light guide plate lens 20 is, for example, about 51°. The arrangement interval of the first light guide plate lenses 20 (the interval between the central positions along the X-axis direction) is, for example, about 0.041 mm. The first light guide plate lenses 20 arranged along the X-axis direction are all substantially the same in contact angle, width, arrangement interval, and height. To provide the first light guide plate lenses 20 configured as described above integrally with the light guide plate 15, for example, the light guide plate 15 may be manufactured by injection molding, and a transfer shape for transferring the first light guide plate lenses 20 may be formed in advance on a molding surface of the molding die for molding the first main surface 15B.

[0035] As shown in FIG. 3, the second light guide plate lens 21 is provided on the second main surface 15C of the light guide plate 15. The second light guide plate lens 21 extends along the Y-axis direction, and a plurality of second light guide plate lenses 21 are arranged side by side along the X-axis direction. In this embodiment, the second light guide plate lens 21 is a convex prism protruding from the second main surface 15C to the rear side. In detail, the second light guide plate lens 21 has a cross-sectional shape cut along the X-axis direction that is substantially triangular (substantially mountain-shaped) and extends linearly along the Y-axis direction. The width dimension (dimension along the X-axis direction) of the second light guide plate lens 21 is constant over the entire length along the Y-axis direction. The cross-sectional shape of the second light guide plate lens 21 is substantially an isosceles triangle, and the second light guide plate lens 21 has a pair of fourth inclined surfaces 21A. The apex angle of the second light guide plate lenses 21 (the angle formed by the pair of fourth inclined surfaces 21A) is preferably an obtuse angle (an angle exceeding 90°), specifically in the range of 100° to 150°, and most preferably 140°. The apex angle, width dimension, arrangement interval, and height dimension of the multiple second light guide plate lenses 21 aligned along the X-axis direction are all substantially the same. In this embodiment, the arrangement interval of the second light guide plate lenses 21 is greater than the arrangement interval of the first light guide plate lenses 20. In order to integrally provide the second light guide plate lenses 21 with such a configuration with the light guide plate 15, for example, the light guide plate 15 may be manufactured by injection molding, and a transfer shape for transferring the second light guide plate lenses 21 may be formed in advance on a molding surface of the molding die for molding the second main surface 15C.

[0036] According to the light guide plate 15 having such a configuration, the light propagating in the light guide plate 15 hits the arcuate surface 20A of each first light guide plate lens 20 on the first main surface 15B side along the Z axis direction, and is repeatedly totally reflected, and proceeds in a zigzag manner along the X axis direction. The light propagating in the light guide plate 15 hits the pair of fourth inclined surfaces 21A of each second light guide plate lens 21 on the second main surface 15C side along the Z axis direction, and is repeatedly totally reflected, and proceeds in a zigzag manner along the Y axis direction. As a result, the spread of the light propagating in the light guide plate 15 in the X axis direction is limited, and unevenness in brightness is unlikely to occur between the vicinity of the LED 13 and its surroundings in the X axis direction. On the other hand, the light that is not totally reflected by the arcuate surface 20A of the first light guide plate lens 20 on the first main surface 15B is refracted by the arcuate surface 20A, and is encouraged to exit from the first main surface 15B.

[0037] As shown in Fig. 2, the third light guide plate lenses 22 are provided on the second main surface 15C of the light guide plate 15. A plurality of the third light guide plate lenses 22 are arranged side by side along the Y-axis direction. The third light guide plate lenses 22 protrude from the second main surface 15C toward the rear side along the Z-axis direction. The third light guide plate lenses 22 have a first inclined surface 22A arranged on the opposite side to the LED 13 side in the Y-axis direction (the right side in Fig. 2), a second inclined surface 22B arranged on the LED 13 side in the Y-axis direction (the left side in Fig. 2), and a third inclined surface 22C located between the first inclined surface 22A and the second inclined surface 22B in the Y-axis direction. The first inclined surface 22A has a slope that rises from the side opposite to the LED 13 side (right side in FIG. 2) toward the LED 13 side (left side in FIG. 2) toward the back side (first prism sheet 16 side, protruding direction of the third light guide plate lens 22 from the second main surface 15C) along the Y axis direction of the light guide plate 15. The second inclined surface 22B has a slope that rises from the LED 13 side (left side in FIG. 2) toward the opposite side (right side in FIG. 2) along the Y axis direction of the light guide plate 15. The third inclined surface 22C has a slope that rises from the side opposite to the LED 13 side (right side in FIG. 2) toward the LED 13 side (left side in FIG. 2) along the Y axis direction of the light guide plate 15 toward the back side.

[0038] As shown in FIG. 2, the first inclined surface 22A and the second inclined surface 22B can reflect the light propagating in the light guide plate 15 and raise it toward the front side at an angle close to the Z-axis direction, thereby promoting emission from the first main surface 15B. In detail, the first inclined surface 22A mainly functions to reflect and raise the light traveling away from the LED 13 in the Y-axis direction. On the other hand, the second inclined surface 22B mainly functions to reflect and raise the light traveling toward the LED 13 in the Y-axis direction. The first inclined surface 22A has a gradient such that the distance from the first main surface 15B (a portion where the third light guide plate lens 22 is not installed) decreases as it moves away from the LED 13 in the Y-axis direction. The inclination angle (first angle) θ7 of the first inclined surface 22A with respect to the Y-axis direction is, for example, about 8°. The second inclined surface 22B has a gradient in which the distance from the first main surface 15B increases the farther away from the LED 13 in the Y-axis direction, that is, a gradient opposite to that of the first inclined surface 22A. The second inclined surface 22B has a gradient angle (second angle) θ8 with respect to the Y-axis direction that is steep and close to vertical, for example, about 80°, and is larger than the gradient angle θ7 of the first inclined surface 22A.

[0039] 2, 4, and 5, the third light guide plate lenses 22 arranged along the Y-axis direction are designed so that their height (dimension along the Z-axis direction) and length (dimension along the Y-axis direction) increase as they move away from the LED 13 in the Y-axis direction. More specifically, when comparing a third light guide plate lens 22 close to the LED 13 in the Y-axis direction with a third light guide plate lens 22 far from the LED 13 in the Y-axis direction, the areas of the first and second inclined surfaces 22A and 22B of the latter are larger than those of the former. In other words, the first and second inclined surfaces 22A and 22B of the multiple first and second inclined surfaces 22A and 22B arranged at intervals in the Y-axis direction on the second main surface 15C are configured so that their areas increase as they move away from the LED 13 in the Y-axis direction. As a result, on the side closer to LED 13 in the Y-axis direction, light is less likely to strike first inclined surface 22A and second inclined surface 22B of third light guide plate lens 22, suppressing light output, but on the side farther from LED 13 in the Y-axis direction, light is more likely to strike first inclined surface 22A and second inclined surface 22B of third light guide plate lens 22, promoting light output. As a result, the amount of light output from first main surface 15B is uniform between the LED 13 side and the opposite side in the Y-axis direction.

[0040] As shown in Fig. 2, the end of the third inclined surface 22C on the opposite side to the LED 13 side along the Y axis direction (the right side in Fig. 2) is connected to the first inclined surface 22A, and the end of the third inclined surface 22C on the LED 13 side along the Y axis direction (the left side in Fig. 2) is connected to the second inclined surface 22B. The third inclined surface 22C has a gradient such that the distance from the first main surface 15B (the portion where the third light guide plate lens 22 is not installed) increases as it moves away from the LED 13 in the Y axis direction. In other words, the third inclined surface 22C has a gradient similar to that of the second inclined surface 22B. The third inclined surface 22C has an inclination angle (third angle) θ9 with respect to the Y axis direction of, for example, about 1.4°, which is smaller than each of the inclination angles θ7 and θ8 of the first inclined surface 22A and the second inclined surface 22B. The third inclined surface 22C having such a configuration reflects the light traveling in the light guide plate 15 away from the LED 13, and directs the light toward the first main surface 15B, but the angle of incidence of the light with respect to the first main surface 15B does not exceed the critical angle. Therefore, the light is totally reflected by the first main surface 15B and guided away from the LED 13. This makes it difficult for the light emitted from the first main surface 15B to be biased toward the LED 13 in the Y-axis direction. As described above, in the second main surface 15C of the light guide plate 15, the inclination angle θ9 of the third inclined surface 22C with respect to the Y-axis direction is the smallest, the inclination angle θ7 of the first inclined surface 22A with respect to the Y-axis direction is larger than the inclination angle θ9, and the inclination angle θ8 of the second inclined surface 22B with respect to the Y-axis direction is the largest. In addition, the multiple third inclined surfaces 22C arranged along the Y-axis direction are designed so that the length dimension becomes smaller as it moves away from the LED 13 in the Y-axis direction. This is because the length dimension of third light guide plate lens 22 increases as it moves away from LED 13 in the Y-axis direction, and the range occupied by third light guide plate lens 22 increases.

[0041] 3 to 5, the third light guide plate lens 22 configured as above is disposed between two adjacent second light guide plate lenses 21 in the X-axis direction. Therefore, the third light guide plate lenses 22 are disposed so as to be alternately arranged with the second light guide plate lenses 21 in the X-axis direction. The maximum value of the protruding dimension (height dimension) of the third light guide plate lenses 22 from the second main surface 15C is smaller than the same protruding dimension of the second light guide plate lenses 21. Therefore, even the third light guide plate lens 22 located farthest from the LED 13 in the Y-axis direction does not protrude further back than the second light guide plate lens 21.

[0042] Incidentally, the in-vehicle liquid crystal display device 10 according to the present embodiment is installed in a position in which the X-axis direction and the Z-axis direction are approximately coincident with the horizontal direction, and the Y-axis direction is parallel to the vertical direction (perpendicular direction), as shown in FIG. 6. The "position in which the Y-axis direction is parallel to the vertical direction" referred to here may be a position in which the Y-axis direction is coincident with the vertical direction, or a position in which the Y-axis direction includes the vertical direction as a vector component, that is, a position in which the Y-axis direction is slightly tilted with respect to the vertical direction. The Z-axis direction coincides with the front direction of the in-vehicle liquid crystal display device 10. A driver (user) DR is present on the front side (right side in FIG. 6) of the in-vehicle liquid crystal display device 10. The in-vehicle liquid crystal display device 10 is installed so that the line of sight of the driver DR is tilted upward with respect to the front direction (Z-axis direction). The angle (peak angle) at which the peak luminance in the light distribution related to the light emitted from the in-vehicle liquid crystal display device 10 is peak luminance coincides with the angle θvp of the line of sight of the driver DR with respect to the front direction of the in-vehicle liquid crystal display device 10. That is, the in-vehicle liquid crystal display device 10 is installed so that the displayed image is visually recognized by the driver DR in the brightest state.

[0043] As shown in FIG. 6, the windshield FG of the passenger vehicle is located above the in-vehicle liquid crystal display device 10 in the Y-axis direction. The LED 13 is located near the lower end of the liquid crystal display device 10 in FIG. 6 in the Y-axis direction, and is disposed in a position in which the light-emitting surface 13A faces the upper side of FIG. 6 in the Y-axis direction. Of the light emitted from the in-vehicle liquid crystal display device 10, a part of the light heading toward the windshield FG is reflected by the windshield FG and heads toward the driver DR. Such reflected light can be visually recognized by the driver DR as a "reflection" that is an image reflected on the windshield FG. Here, the front direction of the in-vehicle liquid crystal display device 10 is 0° (reference), and an angle toward the upper side of FIG. 6 (the side going away from the LED 13) in the Y-axis direction with respect to the front direction is "+ (plus)", and an angle toward the lower side of FIG. 6 (the side approaching the LED 13) in the Y-axis direction with respect to the front direction is "- (minus)". The light causing the above-mentioned "glare" is light emitted in the range of "+50° to +80°" from the light emitted from the liquid crystal display device 10 for vehicle mounting. In this embodiment, the light in the emission angle range (+50° to +80°) causing the "glare" is defined as "side lobe light". In order to suppress such side lobe light, a louver has been used in the past, but since the component price of the louver is high, it has been desired to suppress the side lobe light by regulating the emission angle of light at low cost without using a louver and prevent the reflection on the windshield FG. In this embodiment, the above-mentioned angle θvp (peak angle) is set to, for example, "+6°".

[0044] Therefore, the backlight device 12 according to the present embodiment includes a first prism sheet 16 and a light absorbing sheet 17, as shown in FIG. 1 and FIG. 3. First, the first prism sheet 16 will be described in detail. The first prism sheet 16 is arranged so as to overlap the back side of the light guide plate 15. The first prism sheet 16 has a sheet-like first base material 16A and a first prism 16B provided on the first base material 16A. The pair of main surfaces of the first base material 16A includes a third main surface 16A1 and a fourth main surface 16A2. The third main surface 16A1 is a front main surface of the first base material 16A that faces the light guide plate 15, and emits light toward the light guide plate 15. The fourth main surface 16A2 is a rear main surface of the first base material 16A that faces the light absorbing sheet 17.

[0045] The first base material 16A is made of a substantially transparent synthetic resin, and specifically, for example, the same crystalline transparent resin material as the second base material 18A, such as PET. The first prism 16B is made of a substantially transparent ultraviolet curable resin material, which is a type of photocurable resin material. The manufacturing method of the first prism sheet 16 is the same as the manufacturing method of the second prism sheet 18 described above. The ultraviolet curable resin material constituting the first prism 16B is, for example, a crystalline transparent resin material such as PET, and its refractive index is, for example, about 1.65.

[0046] As shown in FIG. 3, the first prism 16B is provided on the fourth main surface 16A2 on the back side of the first base material 16A. More specifically, the first prism 16B is provided in a shape that protrudes from the fourth main surface 16A2 of the first base material 16A toward the back side (light absorbing sheet 17 side) along the Z-axis direction. The first prism 16B has a cross-sectional shape cut along the X-axis direction that is substantially triangular (substantially mountain-shaped) and extends linearly along the Y-axis direction (first direction), and a plurality of first prisms 16B are arranged side by side along the X-axis direction (second direction) on the fourth main surface 16A2 of the first base material 16A. The plurality of first prisms 16B are arranged continuously with almost no intervals along the X-axis direction. The first prism 16B has a first base 16B1 parallel to the X-axis direction and a pair of first oblique sides 16B2, 16B3 rising from both ends of the first base 16B1. Of the pair of first hypotenuses 16B2, 16B3 in the first prism 16B, the one on one side in the X-axis direction (left side in Figure 3) is referred to as one first hypotenuse 16B2, and the one on the other side in the X-axis direction (right side in Figure 3) is referred to as the other first hypotenuse 16B3.

[0047] As shown in FIG. 3, the first prism 16B has an inclination angle (first base angle) θ10 of one first oblique side 16B2 with respect to the first base 16B1 and an inclination angle (second base angle) θ11 of the other first oblique side 16B3 with respect to the first base 16B1 that are the same. That is, the first prism 16B has a symmetrical cross-sectional shape that is an isosceles triangle. Specifically, the inclination angles θ10 and θ11 of the pair of first oblique sides 16B2 and 16B3 with respect to the first base 16B1 in the first prism 16B are preferably in the range of 40° to 50°, and most preferably 45°. On the other hand, the angle (third apex angle) θ12 formed by the pair of first oblique sides 16B2 and 16B3 in the first prism 16B is preferably in the range of 80° to 100°, and most preferably 90°, i.e., a right angle. The multiple first prisms 16B lined up along the X-axis direction all have approximately the same height dimensions, width dimensions of the first base sides 16B1, and inclination angles of each of the first oblique sides 16B2, 16B3 relative to the first base side 16B1, and the arrangement spacing between adjacent first prisms 16B is also approximately constant and equally spaced.

[0048] According to this configuration, when the light emitted from the LEDs 13 and incident on the light-entering end surface 15A of the light guide plate 15 reaches the first inclined surface 22A having an inclination rising from the side opposite the LEDs 13 toward the LEDs 13 in the Y-axis direction on the second main surface 15C in the process of propagating through the light guide plate 15, as shown in Fig. 2, most of the light is reflected by the first inclined surface 22A, but the remaining light is refracted and emitted from the first inclined surface 22A toward the back side. Of this, the light reflected by the first inclined surface 22A heads toward the first main surface 15B, and is reflected again or emitted from the first main surface 15B. On the other hand, the light emitted from the first inclined surface 22A heads toward the first prism sheet 16. The light traveling from first inclined surface 22A toward first prism sheet 16 is reflected by third main surface 16A1 (the interface between first substrate 16A and the air layer) of first prism sheet 16, or enters first prism sheet 16. When the light reflected by third main surface 16A1 of first prism sheet 16 enters second main surface 15C of light guide plate 15, it is either emitted directly from first main surface 15B, or propagates within light guide plate 15 and then emitted from first main surface 15B.

[0049] As shown in FIG. 3, light incident on the first prism sheet 16 is reflected by the first base 16B1 of the first prism 16B (the interface between the first substrate 16A and the first prism 16B) or by a pair of first hypotenuses 16B2, 16B3 of the first prism 16B, and thereby exits the first prism sheet 16 and proceeds toward the second main surface 15C of the light guide plate 15. Specifically, the light incident on the third main surface 16A1 of the first base material 16A is totally reflected at the interface between the first base material 16A and the first prism 16B, or the light incident on the first prism 16B is reflected by one of the first hypotenuses 16B2 and travels toward the other first hypotenuse 16B3 and is reflected by the other first hypotenuse 16B3, or the light is reflected by the other first hypotenuse 16B3 and travels toward the one first hypotenuse 16B2 and is reflected by the one first hypotenuse 16B2, and is emitted from the third main surface 16A1 toward the front side (the light guide plate 15 side). When the light emitted from the first prism sheet 16 to the front side is incident on the second main surface 15C of the light guide plate 15, it is emitted directly from the first main surface 15B, or is emitted from the first main surface 15B after propagating through the light guide plate 15.

[0050] Incidentally, the light that reaches the second main surface 15C while propagating through the light guide plate 15 and is refracted by the first inclined surface 22A is angled according to the refractive index of the light guide plate 15 and the inclination angle θ7 of the first inclined surface 22A with respect to the Y-axis direction. Specifically, in this embodiment, the light emitted from the second main surface 15C of the light guide plate 15 contains the most light that forms an angle of about 10° (80° with respect to the Z-axis direction) toward the first prism sheet 16 side (the lower side of FIG. 2) with respect to the Y-axis direction. In other words, the light emitted from the second main surface 15C of the light guide plate 15 has such high directivity that the light that forms an angle of about 10° with respect to the Y-axis direction with the first prism sheet 16 side has a peak brightness, and contains almost no diffused light. As a result, the light emitted from the second main surface 15C of the light guide plate 15 is specularly reflected with high efficiency (specifically, the average reflectance of P waves and S waves is about 40%) by the third main surface 16A1 of the first prism sheet 16 and the first base side 16B1 of the first prism 16B, and is efficiently totally reflected by the pair of first oblique sides 16B2, 16B3 of the first prism 16B, and any of the reflected lights contains almost no diffuse light. As a result, the light emitted from the backlight device 12 is unlikely to contain light emitted in the range of "+50° to +80°", that is, side lobe light. As described above, it is possible to regulate the light emission angle without using a conventional louver, and to reduce side lobe light.

[0051] Next, the light absorbing sheet 17 will be described in detail. As shown in Figs. 1 to 3, the light absorbing sheet 17 is arranged so that its main surface is parallel to each main surface of the light guide plate 15 and the first prism sheet 16 and covers the fourth main surface 16A2 of the first prism sheet 16. The light absorbing sheet 17 is arranged so as to overlap with the fourth main surface 16A2 of the first prism sheet 16 over almost the entire area. The light absorbing sheet 17 is made of, for example, PET having a black surface, and has higher light absorption than both the light guide plate 15 and the first prism sheet 16. The light absorbing sheet 17 has a pair of main surfaces, and the front main surface is arranged facing the fourth main surface 16A2 of the first prism sheet 16 and serves as a light absorbing main surface (fifth main surface) 17A that absorbs light.

[0052] According to this configuration, the light emitted from the fourth main surface 16A2 of the first prism sheet 16 toward the back side travels toward the light absorbing sheet 17 and is efficiently absorbed by the light absorbing main surface 17A. Since the light emitted from the fourth main surface 16A2 of the first prism sheet 16 often has characteristics similar to diffuse light, the light is absorbed by the light absorbing sheet 17, so that the emission angle of the light emitted from the backlight device 12 can be more effectively regulated. This allows the side lobe light to be further reduced. Note that the amount of light emitted from the fourth main surface 16A2 of the first prism sheet 16 is small, so even if the light is absorbed by the light absorbing sheet 17, the effect on the brightness of the light emitted from the backlight device 12 is only slight.

[0053] Next, in order to verify the superiority of the backlight device 12 and the liquid crystal display device 10 according to the present embodiment, the following comparative experiments 1 and 2 were performed. First, comparative experiment 1 will be described. Comparative experiment 1 obtained the light distribution related to the emitted light of each backlight device of Example 1 and Comparative Examples 1 to 4 below. Example 1 is a backlight device 12 having the same configuration as that described before Comparative experiment 1. Comparative Examples 1 to 4 are backlight devices having a different configuration from Example 1. Specifically, the backlight devices of Comparative Examples 1, 2, and 4 include at least a light guide plate 1, a light reflecting sheet 2 laminated on the back side of the light guide plate 1, a light diffusion sheet 3 laminated on the front side of the light guide plate 1, and a prism sheet 4 laminated on the front side of the light diffusion sheet 3, as shown in FIG. 7, in addition to the LEDs serving as light sources. The light guide plate 1 provided in the backlight devices of Comparative Examples 1, 2, and 4 has a light reflecting portion 5 on the main surface 1B on the back side that diffuses and reflects light to raise it toward the front side. The light reflecting portion 5 is a rough surface (fine irregularities) selectively provided on the rear principal surface 1B of the light guide plate 1. A part of the light diffusely reflected by the light reflecting portion 5 is emitted from the front principal surface 1A of the light guide plate 1. The light reflecting sheet 2 has a white surface and has high light reflectivity. The light reflecting sheet 2 can diffusely reflect the light emitted from the rear principal surface 1B of the light guide plate 1 so that it re-enters the light guide plate 1. The light diffusion sheet 3 contains a diffusing agent that diffuses and reflects light. The prism sheet 4 has a structure similar to that of the third prism sheet 19 (see FIG. 3) described before Comparative Experiment 1, and therefore a detailed description of the structure of the prism sheet 4 will be omitted here.

[0054] The backlight device of Comparative Example 1 includes a louver similar to that of the conventional device in addition to the configuration shown in FIG. 7. The louver is laminated on the front side of the prism sheet 4 in the backlight device of Comparative Example 1. The louver is configured such that light-shielding portions and light-transmitting portions are alternately arranged along the Y-axis direction, and the emission angle of light passing through the light-transmitting portions is regulated by the two light-shielding portions sandwiching the light-transmitting portions. Meanwhile, the backlight device of Comparative Example 2 is configured as shown in FIG. 7. The backlight device of Comparative Example 4 includes a first prism sheet 16 (see FIGS. 2 and 3) in addition to the configuration shown in FIG. 7. In the backlight device of Comparative Example 4, the first prism sheet 16 is disposed between the light guide plate 1 and the light reflecting sheet 2 (see FIG. 7). Meanwhile, the backlight device of Comparative Example 3 is configured such that the first prism sheet 16 is removed from the backlight device 12 of Example 1 (see FIGS. 2 and 3) and the light reflecting sheet 2 (see FIG. 7) is provided instead of the light absorbing sheet 17. Hereinafter, the type of backlight device including the light guide plate 15, the second prism sheet 18, and the third prism sheet 19 shown in FIG. 2 and FIG. 3 in addition to the LED 13, as in Example 1 and Comparative Example 3, is referred to as "Type A". Also, the type of backlight device including the light guide plate 1, the light reflecting sheet 2, the light diffusion sheet 3, the prism sheet 4, and the light reflecting portion 5 shown in FIG. 7 in addition to the LED, as in Comparative Examples 1, 2, and 4, is referred to as "Type B". Therefore, Example 1 and Comparative Example 3 are classified as Type A, and Comparative Examples 1, 2, and 4 are classified as Type B. It can be said that Example 1 is a type A configuration including the first prism sheet 16 and the light absorbing sheet 17. It can be said that Comparative Example 3 is a type A configuration including the light reflecting sheet 2 without the first prism sheet 16.

[0055] In Comparative Experiment 1, the backlight devices of Example 1 and Comparative Examples 1 to 4 were used to measure the luminance of the emitted light with the LEDs turned on, and a graph of the light distribution (luminance angle distribution) in the Y-axis direction was created. The experimental results of the light distribution in Comparative Experiment 1 are shown in FIG. 8. In the light distribution graph shown in FIG. 8, the horizontal axis represents the angle (unit: "°") in the Y-axis direction with respect to the front direction (Z-axis direction), and the vertical axis represents the relative luminance (unit: "%") with the peak luminance as the reference (100%). Among the positive and negative symbols attached to the angle on the horizontal axis in FIG. 8, "- (minus)" means the lower side (opposite side to the windshield FG side) of FIG. 6 in the Y-axis direction (vertical direction) with respect to the reference value of 0° (front direction) when the backlight device 12 is viewed from the front, and "+ (plus)" means the upper side (windshield FG side) of FIG. 6 in the Y-axis direction with respect to the reference value of 0° (front direction) when the backlight device 12 is viewed from the front. In FIG. 8, the graph for Example 1 is shown by a solid line, the graph for Comparative Example 1 is shown by a dashed line, the graph for Comparative Example 2 is shown by a dotted line, the graph for Comparative Example 3 is shown by a thick double-dot chain line, and the graph for Comparative Example 4 is shown by a thin double-dot chain line.

[0056] The experimental results of Comparative Experiment 1 will be described. According to FIG. 8, the light distributions of Comparative Examples 1, 2, and 4 have a peak angle at which the peak luminance is reached, which is "+3°", and a half-width wider than that of the light distribution of Example 1. The reason why the half-width of the light distributions of Comparative Examples 1, 2, and 4 is wider than that of Example 1 is presumably because light is diffusely reflected by the light reflecting sheet 2, the light diffusing sheet 3, and the light reflecting section 5 provided in the backlight device of Type B. On the other hand, the light distribution of Example 1 has a peak angle at which the peak luminance is reached, which is "+6°". The light distribution of Comparative Example 3 has a peak angle at which the peak luminance is reached, which is "+8°". The light distributions of Example 1 and Comparative Example 3 have a half-width narrower than that of Comparative Examples 1, 2, and 4. The reason why the half-widths of the light distributions of Example 1 and Comparative Example 3 are narrower than those of Comparative Examples 1, 2, and 4 is presumably because the two prism sheets 18, 19 provided in the backlight device of Type A provide a high light-collecting effect in the Y-axis direction, and in addition, there is almost no diffuse reflection in either the light guide plate 15 or the prism sheets 18, 19. The reason why the peak angle of the light distribution of Comparative Example 3 is larger than that of Example 1 is presumably because there is no reflected light by the first prism sheet 16 because the first prism sheet 16 is not provided, and in addition, the light is diffusely reflected by the light reflecting sheet 2.

[0057] According to the light distribution of Comparative Example 1, the side lobe light, which is light emitted in the range of "+50° to +80°", is suppressed sufficiently low. The reason is presumed to be because the louver satisfactorily restricts the light emission angle range in the Y-axis direction even if the light is diffusely reflected by each of the light reflecting sheet 2, the light diffusion sheet 3, and the light reflecting section 5 included in the backlight device of Type B. According to each light distribution of Comparative Examples 2 and 4, the side lobe light has a relative luminance of approximately 20% or more, and reflections caused by the side lobe light are easily visible. The reason is presumed to be because Comparative Example 2 does not include a configuration for restricting the emission angle range of the light diffusely reflected by each of the light reflecting sheet 2, the light diffusion sheet 3, and the light reflecting section 5 included in the backlight device of Type B. In the light distribution of Example 1, the side lobe light, which is light emitted in the range of "+50° to +80°", is suppressed sufficiently low to a degree close to the light distribution of Comparative Example 1. The reason is presumed to be that diffuse reflection hardly occurs in either the light guide plate 15 or each prism sheet 18, 19 provided in the type A backlight device, and in particular, the light emitted from the first inclined surface 22A toward the back side is appropriately angled, so that the light can be efficiently specularly reflected or totally reflected by the first prism sheet 16. Furthermore, it is presumed that the absorption of diffuse light emitted from the first prism sheet 16 by the light absorbing sheet 17 also contributes to suppression of side lobe light. In the light distribution distribution of Comparative Example 3, the side lobe light is suppressed compared to the light distribution distributions of Comparative Examples 2 and 4, but the side lobe light is slightly more than the light distribution distributions of Example 1 and Comparative Example 1. The reason is presumed to be that, since Comparative Example 3 is a type A backlight device, the light emission angle range is restricted, but in addition to the absence of reflected light by the first prism sheet 16, the light is diffusely reflected by the light reflecting sheet 2.

[0058] Next, Comparative Experiment 2 will be described. In Comparative Experiment 2, the ratio of side lobe light was extracted from the light distribution obtained using each of the backlight devices of Example 1 and Comparative Examples 1 to 4 described in Comparative Experiment 1. In Comparative Experiment 2, the luminance of the emitted light was measured with the LED turned on using each of the backlight devices of Example 1 and Comparative Examples 1 to 4, and the light distribution in the Y-axis direction was obtained. Then, the relative luminance (unit: "%) at each angle of +50°, +60°, +70°, and +80° was extracted from the orientation distribution in the Y-axis direction. The relative luminance at each angle of +50°, +60°, +70°, and +80° is based on the peak luminance at the peak angle (100%). Here, the significance of extracting the relative luminance at each angle of +50°, +60°, +70°, and +80° is to provide an index regarding whether or not "reflection" caused by side lobe light (light emitted in the range of +50° to +80°) is easily visible. That is, in order to make the "reflection" less visible, it is preferable that the relative luminance at each of the angles of +50°, +60°, +70°, and +80° is 3% or less.

[0059] The experimental results of Comparative Experiment 2 are as shown in the table of FIG. 9. The table of FIG. 9 shows information on the configurations of Example 1 and Comparative Examples 1 to 4 (peak angle, backlight type, presence or absence of louver, presence or absence of first prism sheet 16, presence or absence of light absorbing sheet 17, presence or absence of light reflecting sheet 2) and the experimental results of relative brightness at each angle of +50°, +60°, +70°, and +80°. The peak angle is "+6°" in Example 1, "+3°" in Comparative Examples 1, 2, and 4, and "+8°" in Comparative Example 3. The backlight type is the type of backlight device, and is either Type A or Type B as described above. Only Comparative Example 1 has a louver. Example 1 and Comparative Example 4 have a first prism sheet 16. Only Example 1 has a light absorbing sheet 17. Comparative Examples 1 to 4 have a light reflecting sheet 2.

[0060] The results of the comparative experiment 2 will be described. According to FIG. 9, in the comparative examples 2 to 4, the relative luminance exceeds 3% at all angles of +50°, +60°, +70°, and +80°, so it can be said that the reflection caused by the side lobe light is easily visible. Among them, the relative luminance exceeds 20% at each angle of +50°, +60°, and +70° in the comparative examples 2 and 4, so it can be said that the reflection is particularly likely to be visible. In the comparative example 3, although the relative luminance at each angle exceeds the reference value of 3%, it is suppressed to 5% or less, and the reflection is suppressed compared to the comparative examples 2 and 4. The reason for this is presumably that the directivity of the emitted light is high because the comparative example 3 is type A, although it does not include the first prism sheet 16. In the comparative example 4, the side lobe light is generated most frequently, although the first prism sheet 16 is included. This suggests that it is difficult to restrict the light emission angle range even when the first prism sheet 16 is used in combination with the backlight device of type B because a lot of diffuse reflection light occurs. On the other hand, in Example 1 and Comparative Example 1, the relative luminance is 3% or less at any angle of +50°, +60°, +70°, and +80°, and it can be said that the reflection caused by the side lobe light is not sufficiently visible. In Comparative Example 1, the side lobe light is most suppressed. This is presumed to be because the louver effectively restricts the light emission angle range. In contrast, in Example 1, the side lobe light is suppressed to a level similar to that of Comparative Example 1, even though the louver is not used. This is presumed to be because the first prism sheet 16 and the light absorbing sheet 17 are used in the backlight device of type A, and the light emission angle range can be restricted while suppressing the occurrence of diffuse reflection light. In this way, the first embodiment can sufficiently suppress glare caused by side lobe light at low cost without using a louver.

[0061] As described above, the backlight device (illumination device) 12 of the present embodiment includes the LEDs (light source) 13, the light guide plate 15 having at least a part of an outer peripheral end face that faces the LEDs 13 and serves as a light incident end face (first end face) 15A into which light is incident, one main face being a first main face 15B and the other main face being a second main face 15C, and the first prism sheet 16 having one main face that faces the second main face 15C and serves as a third main face 16A1 and is disposed to face the second main face 15C, and the other main face being a fourth main face 16A2. A first inclined surface 22A is provided which rises from the side opposite to LED 13 toward LED 13 in a first direction which includes the direction from the first side to light guide plate 15, and a plurality of first prisms 16B are provided on fourth main surface 16A2 of first prism sheet 16 extending along the first direction and aligned along a second direction which intersects with the first direction and is along fourth main surface 16A2, and first prism 16B has a first base 16B1 which is parallel to the second direction, and a pair of first oblique sides 16B2, 16B3 which rise from both ends of first base 16B1.

[0062] The light emitted from the LED 13 is incident on the light-entering end surface 15A of the light guide plate 15 and propagates through the light guide plate 15. When the light propagating through the light guide plate 15 reaches the first inclined surface 22A having an inclination rising from the side opposite the LED 13 toward the LED 13 side in the first direction on the second main surface 15C, most of the light is reflected by the first inclined surface 22A, and the remaining light is refracted and emitted from the first inclined surface 22A. The light reflected by the first inclined surface 22A travels toward the first main surface 15B, and is reflected again or emitted from the first main surface 15B. The light emitted from the first inclined surface 22A travels toward the first prism sheet 16. The light traveling toward the first prism sheet 16 is reflected by the third main surface 16A1 of the first prism sheet 16, or enters the first prism sheet 16. When the light reflected by the third main surface 16A1 of the first prism sheet 16 enters the second main surface 15C of the light guide plate 15, it is either directly emitted from the first main surface 15B or is emitted from the first main surface 15B after propagating inside the light guide plate 15. The light incident on the first prism sheet 16 is reflected by the first base 16B1 of the first prism 16B or is reflected by a pair of first oblique sides 16B2, 16B3 of the first prism 16B, and is emitted from the first prism sheet 16 toward the second main surface 15C of the light guide plate 15. When the light emitted from the first prism sheet 16 toward the light guide plate 15 enters the second main surface 15C of the light guide plate 15, it is either directly emitted from the first main surface 15B or is emitted from the first main surface 15B after propagating inside the light guide plate 15.

[0063] Incidentally, the light that reaches the second main surface 15C during the process of propagating through the light guide plate 15 and is refracted by the first inclined surface 22A is angled according to the refractive index of the light guide plate 15 and the inclination angle of the first inclined surface 22A with respect to the first direction. That is, the light emitted from the second main surface 15C of the light guide plate 15 contains almost no diffused light. Therefore, the light reflected by the third main surface 16A1 of the first prism sheet 16, the light reflected by the first base side 16B1 of the first prism 16B, and the light reflected by the pair of first inclined sides 16B2 and 16B3 of the first prism 16B also contain almost no diffused light, so that the light emitted from the backlight device 12 is unlikely to contain side lobe light that is emitted at an angle close to the first direction. This makes it possible to regulate the light emission angle without using a louver as in the past, and to reduce side lobe light.

[0064] The backlight device 12 further includes a light absorbing sheet 17 having a light absorbing property higher than both the light guide plate 15 and the first prism sheet 16, the light absorbing sheet 17 having one of its main surfaces being a light absorbing main surface (fifth main surface) 17A facing the fourth main surface 16A2. The light emitted from the fourth main surface 16A2 of the first prism sheet 16 travels toward the light absorbing sheet 17. Since the light absorbing sheet 17 has a light absorbing property higher than both the light guide plate 15 and the first prism sheet 16, the light emitted from the fourth main surface 16A2 can be efficiently absorbed by the light absorbing main surface 17A. Since the light emitted from the fourth main surface 16A2 of the first prism sheet 16 often has characteristics similar to diffused light, the light is absorbed by the light absorbing sheet 17, so that the emission angle of the light emitted from the backlight device 12 can be more effectively regulated, and the side lobe light can be further reduced. Incidentally, since the amount of light emitted from the fourth main surface 16A2 of the first prism sheet 16 is small, even if it is absorbed by the light absorbing sheet 17, the effect on the brightness of the light emitted from the backlight device 12 is only slight.

[0065] The optical element further includes a second prism sheet 18 having one main surface which is a second light-emitting main surface (seventh main surface) 18A1 and the other main surface which is a second light-entering main surface (eighth main surface) 18A2 facing the first main surface 15B, and a third prism sheet 19 having one main surface which is a third light-emitting main surface (ninth main surface) 19A1 and the other main surface which is a third light-entering main surface (tenth main surface) 19A2 facing the second light-emitting main surface 18A1. The second light-emitting main surface 18A1 of the second prism sheet 18 is provided with a plurality of second prisms 18B extending along the second direction and arranged side by side along the first direction, and the third light-emitting main surface 19A1 of the third prism sheet 19 is provided with a plurality of third prisms 19B extending along the second direction and arranged side by side along the first direction. When the light emitted from the first main surface 15B of the light guide plate 15 enters the second light-input main surface 18A2 of the second prism sheet 18, the light is selectively given a light-collecting effect in the first direction by the multiple second prisms 18B extending along the second direction on the second light-output main surface 18A1, and is then emitted from the second light-output main surface 18A1. When the light emitted from the second light-output main surface 18A1 of the second prism sheet 18 enters the third light-input main surface 19A2 of the third prism sheet 19, the light is selectively given a light-collecting effect in the first direction by the multiple third prisms 19B extending along the second direction on the third light-output main surface 19A1, and is then emitted from the third light-output main surface 19A1. In this way, the light emitted from the light guide plate 15 is selectively focused in the first direction by the second prism 18B and the third prism 19B, so that the light emission angle can be better regulated and the side lobe light can be further reduced.

[0066] The second prism 18B has a second base 18B1 parallel to the first direction and a pair of second oblique sides 18B2, 18B3 rising from both ends of the second base 18B1, and of the pair of second oblique sides 18B2, 18B3, the second LED side oblique side 18B2 which is the second oblique side on the LED 13 side in the first direction forms a larger angle with the second base 18B1 than the second LED opposite oblique side 18B3 which is the second oblique side opposite the LED 13 side in the first direction. In this way, the light incident on the second light entrance main surface 18A2 of the second prism sheet 18 is less likely to hit the second LED side oblique side 18B2 which is the second oblique side on the LED 13 side in the first direction than the second LED opposite oblique side 18B3 which is the second oblique side opposite the LED 13 side in the first direction among the pair of second oblique sides 18B2, 18B3 of the second prism 18B. Here, when the incident light of the second prism sheet 18 hits the second LED side oblique side 18B2, which is the second oblique side on the LED 13 side, it tends to be emitted as a side lobe light without being raised when it is emitted from the second prism 18B. Therefore, if the incident light of the second prism sheet 18 is less likely to hit the second LED side oblique side 18B2, which is the second oblique side on the LED 13 side, directly, it is possible to suppress the generation of side lobe light. Note that most of the incident light of the second prism sheet 18 is refracted by the second LED opposite oblique side 18B3, which is the second oblique side on the opposite side to the LED 13 side, and is emitted, entering the third prism sheet 19, and is likely to be effectively used.

[0067] The third prism 19B has a third base 19B1 parallel to the first direction and a pair of third oblique sides 19B2, 19B3 rising from both ends of the third base 19B1, and the pair of third oblique sides 19B2, 19B3 form equal angles with the third base 19B1. Of the light incident on the third light-entering main surface 19A2 of the third prism sheet 19, the light that strikes the third LED-opposite oblique side 19B3, which is the third oblique side opposite the LED 13 side in the first direction, of the pair of third oblique sides 19B2, 19B3 of the third prism 19B, is refracted there and emitted, or is reflected there and directed toward the third LED-side oblique side 19B2, which is the third oblique side on the LED 13 side. Here, the pair of third oblique sides 19B2, 19B3 form the same angle with respect to the third base 19B1, so when the light reflected by the third LED opposite oblique side 19B3, which is the third oblique side opposite to the LED 13 side, hits the third LED side oblique side 19B2, which is the third oblique side on the LED 13 side, it is reflected there and is likely to be returned to the second prism sheet 18 side. The light returned to the second prism sheet 18 side (returned light) reaches the third prism sheet 19 again by being reflected within the backlight device 12, and is emitted while being raised by one of the pair of third oblique sides 19B2, 19B3 of the third prism 19B. This can improve the light utilization efficiency.

[0068] Further, the first inclined surfaces 22A are arranged in a row along the first direction, and the first inclined surfaces 22A are configured to have an area that increases with increasing distance from the LED 13. Most of the light that reaches the second main surface 15C during the process of propagating through the light guide plate 15 is reflected by the first inclined surfaces 22A. Since the first inclined surfaces 22A arranged along the first direction are configured to have an area that increases with increasing distance from the LED 13, the amount of light reflected by the first inclined surfaces 22A tends to increase with increasing distance from the LED 13. This makes the amount of light emitted from the first main surface 15B of the light guide plate 15 uniform in the first direction, which is suitable for suppressing uneven brightness.

[0069] Moreover, the liquid crystal display device (display device) 10 according to this embodiment includes the above-described backlight device 12 and a liquid crystal panel (display panel) 11 that performs display using light from the backlight device 12. The liquid crystal display device 10 configured in this manner can regulate the light emission angle without using a conventional louver, thereby achieving a display with excellent display quality.

[0070] <Embodiment 2> A second embodiment will be described with reference to Fig. 10 to Fig. 13. In this second embodiment, a light reflecting sheet 23 is used instead of the light absorbing sheet 17. Note that a duplicated description of the structure, action, and effects similar to those of the first embodiment will be omitted.

[0071] As shown in FIG. 10, the backlight device 112 according to this embodiment includes a light reflecting sheet 23 instead of the light absorbing sheet 17 (see FIG. 2 and FIG. 3) described in the above-mentioned embodiment 1. The light reflecting sheet 23 is arranged so as to overlap the back side (the side opposite to the light guide plate 115 side) of the first prism sheet 116. The light reflecting sheet 23 is arranged so that its main surface is parallel to each main surface of the light guide plate 115 and the first prism sheet 116 and covers the fourth main surface 116A2 of the first prism sheet 116. The light reflecting sheet 23 is arranged so as to overlap the fourth main surface 116A2 of the first prism sheet 116 over almost the entire area. The light reflecting sheet 23 is made of, for example, PET having a white surface, and has higher light reflectivity than both the light guide plate 115 and the first prism sheet 116. Of the pair of main surfaces of the light reflecting sheet 23, the front main surface is disposed facing the fourth main surface 116A2 of the first prism sheet 116 and serves as a light reflecting main surface (sixth main surface) 23A that reflects light.

[0072] According to this configuration, the light emitted from the fourth main surface 116A2 of the first prism sheet 116 toward the rear side travels toward the light reflecting sheet 23 and is efficiently reflected by the light reflecting main surface 23A. Although the amount of light emitted from the fourth main surface 116A2 of the first prism sheet 116 is small, by reflecting the light by the light reflecting sheet 23, it is possible to improve the brightness of the light emitted from the backlight device 112.

[0073] Next, the following comparative experiments 3 to 5 were performed. First, comparative experiment 3 will be described. In comparative experiment 3, a light distribution related to the emitted light of the backlight device of Example 2 was obtained. Example 2 is a backlight device 112 having the same configuration as that described before this paragraph. That is, Example 2 is a type A backlight device, and is different from Example 1 described in Comparative Experiments 1 and 2 in that it has a light reflecting sheet 23 instead of the light absorbing sheet 17. In comparative experiment 3, similarly to comparative experiment 1, the backlight device of Example 2 was used to measure the luminance related to the emitted light with the LED turned on, and a graph related to the light distribution (luminance angle distribution) in the Y-axis direction was created. The experimental results related to the light distribution in comparative experiment 3 are as shown in FIG. 11. The graph related to the light distribution shown in FIG. 11 is the same as FIG. 8. In FIG. 11, in addition to the graph of Example 2, the graphs of Example 1 and Comparative Example 3, which are the experimental results of Comparative Experiment 1, are also shown for reference. In FIG. 11, the graph of Example 2 is shown by a solid line, the graph of Example 1 is shown by a dashed line, and the graph of Comparative Example 3 is shown by a dashed double-dashed line.

[0074] The experimental results of Comparative Experiment 3 will be described. According to FIG. 11, the light distribution of Example 2 has a peak angle, which is the angle at which the peak luminance is reached, of "+9°", and a half-width that is slightly wider than that of the light distribution of Example 1 and is equivalent to that of Comparative Example 3. The reason why the half-width of the light distribution of Example 2 is slightly wider than that of Example 1 is presumably because the light is diffusely reflected by the light reflecting sheet 23 of Example 2, and the light emission angle range is slightly wider. The peak angle of the light distribution of Example 2 is larger than both the peak angle (+6°) of the light distribution of Example 1 and the peak angle (+8°) of the light distribution of Comparative Example 3. In the light distribution of Example 2, the side lobe light, which is light emitted in the range of "+50° to +80°", is suppressed sufficiently low to approximate the light distribution of Example 1.

[0075] Next, Comparative Experiment 4 will be described. In Comparative Experiment 4, the ratio of side lobe light was extracted from the light distribution obtained using the backlight device of Example 2. In Comparative Experiment 4, similarly to Comparative Experiment 2, the backlight device of Example 2 was used to measure the luminance of the emitted light with the LED turned on, and the light distribution in the Y-axis direction was obtained, and then the relative luminance (unit: "%) at each angle of +50°, +60°, +70°, and +80° of the orientation distribution in the Y-axis direction was extracted. As explained in Comparative Experiment 2, in order to make the "reflection" less visible, it is preferable that the relative luminance at each angle of +50°, +60°, +70°, and +80° is 3% or less.

[0076] The experimental results of Comparative Experiment 4 are as shown in the table of Fig. 12. In addition to the experimental results of Example 2, the table of Fig. 12 also lists the experimental results of Example 1 and Comparative Example 3, which are the experimental results of Comparative Experiment 2, for reference. As with the table of Fig. 9, the table of Fig. 12 shows information regarding the configurations of Examples 1 and 2 and Comparative Example 3 (peak angle, backlight type, presence or absence of louver, presence or absence of first prism sheet 16, presence or absence of light absorbing sheet 17, presence or absence of light reflecting sheet 2) and the experimental results of relative luminance at angles of +50°, +60°, +70°, and +80°.

[0077] The experimental results of Comparative Experiment 4 will be described. According to FIG. 12, in Example 2, the reflection exceeds the reference value of 3% at +60° and +70°, but is suppressed to 3% or less at +50° and +80°. That is, in Example 2, the reflection is more easily visible than in Example 1, which is 3% or less at all angles, but is suppressed compared to Comparative Example 3, which exceeds 3% at all angles. The reason for this result is that Example 2 is common to Example 1 in that it is a type A backlight device and includes the first prism sheet 116, and therefore, even if light is diffusely reflected by the light reflecting sheet 23, the light emission angle range can be restricted to a certain degree. In this way, Example 2 can achieve low cost without using a louver, and can suppress reflection caused by side lobe light to a certain degree while obtaining the luminance improvement effect by the light reflecting sheet 23.

[0078] Next, comparative experiment 5 will be described. In comparative experiment 5, the light distribution of the emitted light of each of the backlight devices of Examples 1 and 2 was obtained in the same manner as in comparative experiment 3 described above, and the vertical axis of the light distribution graph was set to the absolute value of "brightness." In comparative experiment 5, similar to comparative experiment 1, the backlight devices of Examples 1 and 2 were used to measure the brightness of the emitted light with the LEDs turned on, and a graph of the light distribution in the Y-axis direction was created. The experimental results of the light distribution in comparative experiment 5 are as shown in FIG. 13. In the light distribution graph shown in FIG. 13, the horizontal axis represents the angle (unit: "°") in the Y-axis direction with respect to the front direction (Z-axis direction), and the vertical axis represents brightness (unit: "cd / m 2 In FIG. 3, the graph of Example 2 is shown by a solid line, and the graph of Example 1 is shown by a dashed line.

[0079] The experimental results of Comparative Experiment 5 will be described. According to FIG. 13, the peak luminance of the light distribution of Example 1 is 2000 cd / m 2 , whereas the peak luminance of the light distribution in Example 2 is 2300 cd / m 2That is, the peak luminance of the light distribution in Example 2 is higher than that of the light distribution in Example 1. The reason for this is presumably that in Example 1, the light emitted from the first prism sheet 16 to the rear side is absorbed by the light absorbing sheet 17 and is not used as emitted light, whereas in Example 2, the light emitted from the first prism sheet 16 to the rear side is reflected by the light reflecting sheet 23 and used as emitted light. Thus, according to Example 2, the effect of improving the peak luminance of the emitted light can be obtained.

[0080] As described above, according to the present embodiment, the backlight device 112 includes a light reflecting sheet 23 having a light reflecting main surface (sixth main surface) 23A, one of the main surfaces of which is arranged facing the fourth main surface 116A2, and has higher light reflectivity than both the light guide plate 115 and the first prism sheet 116. The light emitted from the fourth main surface 116A2 of the first prism sheet 116 travels toward the light reflecting sheet 23. Since the light reflecting sheet 23 has a higher light reflectivity than both the light guide plate 115 and the first prism sheet 116, the light emitted from the fourth main surface 116A2 can be efficiently reflected by the light reflecting main surface 23A. Although the amount of light emitted from the fourth main surface 116A2 of the first prism sheet 116 is small, the light is reflected by the light reflecting sheet 23, thereby improving the brightness of the light emitted from the backlight device 112.

[0081] <Embodiment 3> A third embodiment will be described with reference to Fig. 14 to Fig. 16. In this third embodiment, a modified configuration of a light guide plate 215 is shown. Note that a duplicated description of the structure, action, and effects similar to those of the first embodiment will be omitted.

[0082] In the backlight device 212 according to this embodiment, as shown in FIG. 14, the material and the refractive index of the light guide plate 215 are changed from those in the first embodiment. The light guide plate 215 according to this embodiment is made of a material having a higher refractive index than the light guide plate 15 (see FIGS. 2 and 3) described in the first embodiment. Specifically, in this embodiment, the light guide plate 215 is made of a synthetic resin material such as PC (polycarbonate), and the refractive index is set to, for example, about 1.52. In this way, the angle given when the light enters the light guide plate 215 or when the light exits the light guide plate 215 is different from that in the first embodiment. In addition, the critical angle in the light guide plate 215 is also different from that in the first embodiment. As a result, in this embodiment, the angle (peak angle) at which the peak luminance in the light distribution related to the exiting light in the backlight device 212 becomes "+4°".

[0083] Next, Comparative Experiments 6 and 7 were carried out similarly to Comparative Experiments 1 and 2 described in the first embodiment. In Comparative Experiment 6, the light distribution of the emitted light of each backlight device of the following Example 3 was obtained. Example 3 is a backlight device 212 having the same configuration as that described before this paragraph. That is, Example 3 is a type A backlight device, and the material and refractive index of the light guide plate 215 are different from those of Example 1 described in Comparative Experiment 1. In Comparative Experiment 6, similarly to Comparative Experiment 1, the backlight device of Example 3 was used to measure the luminance of the emitted light in a state where the LED was turned on, and a graph of the light distribution (luminance angle distribution) in the Y-axis direction was created. The experimental results of the light distribution in Comparative Experiment 6 are as shown in FIG. 15. The graph of the light distribution shown in FIG. 15 is the same as FIG. 8. In FIG. 15, in addition to the graph of Example 3, the graphs of Example 1 and Comparative Example 1, which are the experimental results of Comparative Experiment 1, are also shown for reference. In FIG. 15, the graph of Example 3 is shown by a solid line, the graph of Example 1 is shown by a dashed line, and the graph of Comparative Example 1 is shown by a broken line.

[0084] The experimental results of Comparative Experiment 6 will be described. According to FIG. 15, the light distribution of Example 3 has a peak angle, which is the angle at which the peak luminance is reached, of "+4°", and the half-width is slightly wider than that of the light distribution of Example 1. The reason why the half-width of the light distribution of Example 3 is slightly wider than that of Example 1 is presumably because the refractive index of the light guide plate 215 of Example 3 is made higher than that of the light guide plate 15 of Example 1, and the light emission angle range is slightly wider. The peak angle of the light distribution of Example 3 is larger than the peak angle (+3°) of the light distribution of Comparative Example 1, but smaller than the peak angle (+6°) of the light distribution of Example 1. In the light distribution of Example 3, the side lobe light, which is light emitted in the range of "+50° to +80°", is suppressed sufficiently low to approximate the light distribution of Example 1.

[0085] Next, Comparative Experiment 7 will be described. In Comparative Experiment 7, the ratio of side lobe light was extracted from the light distribution obtained using the backlight device of Example 3 described in Comparative Experiment 6. In Comparative Experiment 7, similarly to Comparative Experiments 2 and 4, the backlight device of Example 3 was used to measure the luminance of the emitted light with the LED turned on, and the light distribution in the Y-axis direction was obtained, and then the relative luminance (unit: "%) at each angle of +50°, +60°, +70°, and +80° of the orientation distribution in the Y-axis direction was extracted. As described in Comparative Experiment 2, in order to make the "reflection" less visible, it is preferable that the relative luminance at each angle of +50°, +60°, +70°, and +80° is 3% or less.

[0086] The experimental results of Comparative Experiment 7 are as shown in the table of Fig. 16. In the table of Fig. 16, in addition to the experimental results of Example 5, the experimental results of Examples 1 and 2 and Comparative Example 1, which are the experimental results of Comparative Experiments 2 and 4, are also shown for reference. As with the table of Fig. 9, the table of Fig. 16 shows information on the configurations of Examples 1 to 3 and Comparative Example 1 (peak angle, backlight type, presence or absence of louver, presence or absence of first prism sheet 16, presence or absence of light absorbing sheet 17, presence or absence of light reflecting sheet 2) and the experimental results of relative luminance at angles of +50°, +60°, +70°, and +80°.

[0087] The experimental results of Comparative Experiment 7 will be described. According to FIG. 16, in Example 3, the relative luminance is suppressed to 3% or less at all angles of +50°, +60°, +70°, and +80°. In detail, in Example 3, the side lobe light is suppressed more than in Example 2, although the side lobe light is slightly more than in Example 1 at all angles. The peak angle of the light distribution in Example 3 is closer to the peak angle of the light distribution in Comparative Example 1 than in Examples 1 and 2. Thus, in Example 3, the peak angle of the light distribution is approximately similar to that of Comparative Example 1, and the side lobe light is suppressed to an approximately similar level to that of Example 1.

[0088] <Other embodiments> The technology disclosed in this specification is not limited to the embodiments described above and illustrated in the drawings, and the following embodiments, for example, are also included in the technical scope.

[0089] (1) In the third embodiment, the material and refractive index of the light guide plate 215 are changed from those in the first embodiment, but it is also possible to adjust the peak angle related to the light distribution of the emitted light by, for example, changing the material and refractive index of the second prism sheet 18 from those in the first embodiment, or changing the inclination angles θ1 and θ2 of the second oblique sides 18B2 and 18B3 relative to the second base 18B1 or the angle θ3 formed by the pair of second oblique sides 18B2 and 18B3 from those in the first embodiment. Note that in the configurations described in each embodiment, the specific value of the peak angle (θvp) related to the light distribution of the emitted light can be appropriately changed to values ​​other than those mentioned above.

[0090] (2) In the first prism sheets 16 and 116, the specific values ​​of the inclination angles θ10 and θ11 that the first oblique sides 16B2 and 16B3 make with respect to the first base side 16B1 and the angle θ12 that the pair of first oblique sides 16B2 and 16B3 make can be changed as appropriate.

[0091] (3) In the second prism sheet 18, the specific values ​​of the inclination angles θ1, θ2 that the second oblique sides 18B2, 18B3 make with respect to the second base side 18B1 and the angle θ3 that the pair of second oblique sides 18B2, 18B3 make can be changed as appropriate.

[0092] (4) In the third prism sheet 19, the specific values ​​of the inclination angles θ4, θ5 that the third oblique sides 19B2, 19B3 make with respect to the third base side 19B1 and the angle θ6 that the pair of third oblique sides 19B2, 19B3 make can be changed as appropriate.

[0093] (5) The values ​​of the inclination angles θ7 to θ9 that the first inclined surface 22A, the second inclined surface 22B, and the third inclined surface 22C of the third light guide plate lens 22 make with respect to the Y-axis direction can be changed as appropriate.

[0094] (6) In the configurations described in the first and third embodiments, the light absorbing sheet 17 may have a color other than black (for example, gray, etc.).

[0095] (7) In the configuration described in the second embodiment, the light reflecting sheet 23 may have a color other than white (for example, silver, etc.).

[0096] (8) The numbers of LEDs 13 and 113, the intervals between first light guide lens 20, the contact angles of first light guide lens 20, and the apex angles of second light guide lens 21 can be changed as appropriate.

[0097] (9) The materials and refractive indices of the first prism sheets 16, 116, second prism sheet 18, and third prism sheet 19 may be changed as appropriate to those other than those mentioned above.

[0098] (10) The materials and refractive indexes of the light guide plates 15, 115, and 215 may be changed appropriately to those other than those mentioned above.

[0099] (11) It is possible to appropriately change the specific cross-sectional shape of first light guide plate lens 20. For example, first light guide plate lens 20 may have a triangular cross-sectional shape.

[0100] (12) It is possible to appropriately change the specific cross-sectional shape of the second light guide plate lenses 21. For example, the cross-sectional shape of the second light guide plate lenses 21 may be a semicircle (cylindrical lens) or the like.

[0101] (13) The specific cross-sectional shape of the third light guide plate lens 22 can be changed as appropriate.

[0102] (14) The light guide plates 15, 115, and 215 may have a constant thickness over the entire length, or may have a thickness that decreases with increasing distance from the LEDs 13 and an opposite main surface that is inclined.

[0103] (15) The planar shape of the light guide plate 15, 115, 215 may be a trapezoid, an inverted trapezoid, a bow, a semicircle, a semi-ellipse, a trapezoid with an arc-shaped upper base, etc. By changing the planar shape of the light guide plate 15, 115, 215, the planar shapes of the backlight device 12, 112, 212 and the liquid crystal display device 10 can also be changed.

[0104] (16) The LED 13 may be a top-emitting type instead of a side-emitting type.

[0105] (17) Instead of the LED 13, a light source such as an organic EL (Electro Luminescence) may be used.

[0106] (18) A reflective polarizing sheet may be attached to the rear (outer) main surface of the array substrate constituting the liquid crystal panel 11 instead of the polarizing plate. The reflective polarizing sheet has a polarizing layer having a specific polarization axis (transmission axis), a multilayer film in which layers having different refractive indexes are alternately stacked, a protective layer, and the like. The polarizing layer has a polarization axis and an absorption axis perpendicular to the polarization axis, and can selectively transmit linearly polarized light parallel to the polarization axis and can convert circularly polarized light into linearly polarized light along the polarization axis. The polarization axis of this polarizing layer is perpendicular to the polarization axis of the polarizing plate attached to the outer main surface of the CF substrate. The multilayer film has a multilayer structure and has a reflection characteristic in which the reflectance for s waves contained in light is generally higher than the reflectance for p waves. By providing the multilayer film, the reflective polarizing sheet can reuse the s waves that would otherwise be absorbed by the polarizing layer by reflecting them to the rear side, thereby improving the light utilization efficiency (and therefore the brightness).

[0107] (19) The in-vehicle liquid crystal display device 10 may be installed in a position other than in front of the driver's seat of a passenger vehicle. For example, it may be installed in a position in front of the passenger seat or between the passenger seat and the driver's seat.

[0108] (20) The liquid crystal display device 10 may be used for purposes other than in-vehicle use.

[0109] (21) The lighting device may be used in a type of display device other than the liquid crystal display device 10. [Explanation of symbols]

[0110] 10... liquid crystal display device (display device), 11... liquid crystal panel (display panel), 12, 112, 212... backlight device (illumination device), 13... LED (light source), 15, 115, 215... light guide plate, 15A... light incident end surface (first end surface), 15B... first main surface, 15C... second main surface, 16, 116... first prism sheet, 16A1... third main surface, 16A2, 116A2... fourth main surface, 16B... first prism, 16B1... first base, 16B2, 16B3... first hypotenuse, 17... light absorbing sheet, 17A... light absorption Main surface (5th main surface), 18... 2nd prism sheet, 18A1... 2nd light exiting main surface (7th main surface), 18A2... 2nd light entering main surface (8th main surface), 18B... 2nd prism, 18B1... 2nd base, 18B2, 18B3... 2nd oblique side, 19... 3rd prism sheet, 19A1... 3rd light exiting main surface (9th main surface), 19A2... 3rd light entering main surface (10th main surface), 19B... 3rd prism, 19B1... 3rd base, 19B2, 19B3... 3rd oblique side, 22A... 1st oblique surface, 23... light reflecting sheet, 23A... light reflecting main surface (6th main surface)

Claims

1. A light source; a light guide plate having at least a part of an outer peripheral end surface serving as a first end surface facing the light source and receiving light therethrough, one main surface serving as a first main surface, and the other main surface serving as a second main surface; a first prism sheet having one main surface serving as a third main surface facing the second main surface and the other main surface serving as a fourth main surface, a first inclined surface that is inclined from a side opposite to the light source toward the light source in a first direction including a direction from the light source toward the light guide plate is provided on the second main surface of the light guide plate, a plurality of first prisms are provided on the fourth main surface of the first prism sheet, the first prisms extending along the first direction and aligned along a second direction intersecting the first direction and along the fourth main surface; The first prism has a first base that is parallel to the second direction, and a pair of first oblique sides that rise from both ends of the first base.

2. 2. The lighting device according to claim 1, further comprising a light absorbing sheet having a fifth main surface facing the fourth main surface and having higher light absorbency than both the light guide plate and the first prism sheet.

3. 2. The lighting device according to claim 1, further comprising a light reflecting sheet having a sixth main surface, one of the main surfaces of which faces the fourth main surface, and which has higher light reflectivity than both the light guide plate and the first prism sheet.

4. a second prism sheet having one principal surface serving as a seventh principal surface and the other principal surface serving as an eighth principal surface facing the first principal surface; a third prism sheet having one principal surface serving as a ninth principal surface and the other principal surface serving as a tenth principal surface facing the seventh principal surface, a plurality of second prisms extending along the second direction and arranged side by side along the first direction are provided on the seventh main surface of the second prism sheet; 4. The lighting device according to claim 1, wherein a plurality of third prisms extending along the second direction and arranged side by side along the first direction are provided on the ninth main surface of the third prism sheet.

5. the second prism has a second base parallel to the first direction and a pair of second oblique sides rising from both ends of the second base, The lighting device according to claim 4 , wherein of the pair of second oblique sides, the second oblique side on the light source side in the first direction forms a larger angle with respect to the second base side than the second oblique side opposite the light source side in the first direction.

6. the third prism has a third base parallel to the first direction and a pair of third oblique sides rising from both ends of the third base, The lighting device according to claim 4 , wherein the pair of third oblique sides form equal angles with the third base side.

7. The first inclined surface is arranged in a plurality of layers along the first direction, The lighting device according to claim 1 , wherein the first inclined surfaces are configured to have areas that increase with increasing distance from the light source.

8. The lighting device according to any one of claims 1 to 3, a display panel that performs display using light from the illumination device.

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