Illumination device and display device

Abstract

The light emission angle can be limited without using a shutter. An illumination device (12) is provided with: a light source (13); a light guide plate (15) in which at least a part of the outer peripheral end surface is a first end surface (15A), one main surface is a first main surface (15B), and the other main surface is a second main surface (15C); and a first prism sheet (16), one principal surface of which is a third principal surface (16A1) disposed toward the second principal surface (15C) and the other principal surface of which is a fourth principal surface (16A2), the second principal surface (15C) of the light guide plate (15) being provided with a first inclined surface (22A) that is inclined so as to rise in the first direction from the opposite side of the light source (13) toward the light source (13) side, and a second inclined surface (22B) that is inclined so as to rise in the second direction from the opposite side of the light source (13) toward the light source (13). A plurality of first prisms (16B) extending in the first direction and arranged in the second direction are provided on a fourth principal surface (16A2) of the first prism sheet (16). Each first prism (16B) has: a first bottom side (16B1) parallel to the second direction; and a pair of first bevel edges (16B2, 16B3) raised from both ends of the first bottom edge (16B1).

Description

Technical Field

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

[0002] In the past, as an example of a lighting device, there is a device described in the following patent document 1. Patent document 1 describes a lighting device used for a vehicle instrument. The vehicle instrument described in patent document 1 is arranged below the windshield, and the front of the dial on which a display portion indicated by a pointer is formed is covered by a front cover, and the display portion and the pointer indicating portion are indirectly illuminated by lighting a light source. The vehicle instrument forms an anti-reflection film on the surface of the front cover and omits the cover above the front cover, and forms a louver on the upper surface of the indicating portion of the pointer and a white diffusion layer, respectively. The white diffusion layer matches the display portion of the dial and faces the display slit formed on the black non-transparent layer. The louver limits the emission angle in a manner that the emitted light does not go toward the windshield side. Prior art literature Patent Literature

[0003] Patent Document 1: Japanese Patent No. 3755778 Summary of the invention Technical Problems to be Solved by the Invention

[0004] In the vehicle instrument described in Patent Document 1, a louver is used to prevent the phenomenon that the external light from outside the vehicle is reflected to the driver's side and the occurrence of the reflection of the light display on the windshield. However, since such louver components are expensive, it is desired to limit the light emission angle and prevent the occurrence of the reflection on the windshield without using a louver.

[0005] The technology described in this specification is a technology completed based on the above situation, and its purpose is to limit the emission angle of light without using a blind. Technical solutions for solving technical problems

[0006] (1) The technical related lighting device described in this specification comprises: a light source; a light guide plate, at least a portion of its outer peripheral end surface is opposite to the light source and is a first end surface for incident light, one principal surface is a first principal surface, and the other principal surface is a second principal surface; and a first prism sheet, one principal surface of which is a third principal surface arranged toward the second principal surface, and the other principal surface is a fourth principal surface, an inclined first inclined surface is provided on the second principal surface of the light guide plate, the first inclined surface rises from the opposite side of the light source toward the light source side in a first direction including a direction from the light source toward the light guide plate, a plurality of first prisms are provided on the fourth principal surface of the first prism sheet, the plurality of first prisms extend along the first direction and are arranged in a second direction intersecting the first direction and along the fourth principal surface, the first prism comprising: a first base parallel to the second direction; and a pair of first oblique sides rising from both ends of the first base.

[0007] (2) In addition, the above-mentioned lighting device can also be constructed based on the above-mentioned (1), that is, the lighting device includes a light absorbing sheet, and the main surface of one side of the light absorbing sheet is a fifth main surface arranged toward the fourth main surface, and has a higher light absorption than either the light guide plate or the first prism sheet.

[0008] (3) In addition, the above-mentioned lighting device can also be constructed based on the above-mentioned (1), that is, the lighting device includes a light reflecting sheet, and the main surface of one side of the light reflecting sheet is a sixth main surface arranged toward the fourth main surface, and has a higher light reflectivity than either the light guide plate or the first prism sheet.

[0009] (4) In addition, the above-mentioned lighting device can also be constructed based on any one of the above-mentioned (1) to (3), that is, the lighting device includes: a second prism sheet, one principal surface of which is the seventh principal surface, and the other principal surface of which is the eighth principal surface arranged toward the first principal surface; and a third prism sheet, one principal surface of which is the ninth principal surface, and the other principal surface of which is the tenth principal surface arranged toward the seventh principal surface, wherein a plurality of second prisms are arranged on the seventh principal surface of the second prism sheet, and the plurality of second prisms extend along the second direction and are arranged along the first direction, and a plurality of third prisms are arranged on the ninth principal surface of the third prism sheet, and the plurality of third prisms extend along the second direction and are arranged along the first direction.

[0010] (5) In addition, based on the above (4), the above-mentioned lighting device can also be constructed as follows: the second prism includes: a second base parallel to the first direction; and a pair of second hypotenuses rising from both ends of the second base, and among the pair of second hypotenuses, the second hypotenuse on the light source side in the first direction forms a larger angle with the second base than the second hypotenuse on the opposite side of the light source side in the first direction.

[0011] (6) In addition, the above-mentioned lighting device can also be constructed based on any one of the above-mentioned (4) or (5), wherein the third prism includes: a third base parallel to the first direction; and a pair of third hypotenuses rising from both ends of the third base, and the angles formed by the pair of third hypotenuses and the third base are equal.

[0012] (7) In addition, the lighting device described above, based on any one of the above (1) to (6), may be configured such that a plurality of first inclined surfaces are arranged along the first direction, and the plurality of first inclined surfaces are configured such that the farther away from the light source, the larger the area.

[0013] (8) A display device related to the technology described in this specification includes: the lighting device described in any one of (1) to (7) above; and a display panel that uses light from the lighting device to perform display. Beneficial Effects

[0014] According to the technology described in this specification, it is possible to limit the emission angle of light without using a blind. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is an exploded perspective view of the liquid crystal display device according to the first embodiment. Figure 2 This is a cross-sectional view of the backlight device constituting the liquid crystal display device according to the first embodiment cut along the Y-axis direction. Figure 3 This is a cross-sectional view of the backlight device according to the first embodiment cut along the X-axis direction. Figure 4 This is a perspective view of the light guide plate constituting the backlight device according to the first embodiment, as viewed from the second main surface side. Figure 5 It is a bottom view showing the structure of the second main surface of the light guide plate according to the first embodiment. Figure 6 This is a schematic diagram showing a state where the liquid crystal display device according to the first embodiment is mounted on a passenger car. Figure 7 This is a cross-sectional view of the backlight device of type B according to the first embodiment cut along the Y-axis direction. Figure 8This is a graph showing the light distribution in the Y-axis direction in Comparative Experiment 1 of the first embodiment. Fig. 9 This is a table showing the experimental results of Comparative Experiment 2 of the first embodiment. Fig.10 This is a cross-sectional view of the backlight device according to the second embodiment cut along the Y-axis direction. Fig.11 This is a graph showing the light distribution in the Y-axis direction in Comparative Experiment 3 of the second embodiment. Fig.12 This is a table showing the experimental results of Comparative Experiment 4 of the second embodiment. Fig.13 This is a graph showing the light distribution in the Y-axis direction in Comparative Experiment 5 of the second embodiment. Fig.14 This is a cross-sectional view of the backlight device according to the third embodiment cut along the Y-axis direction. Fig.15 This is a graph showing the light distribution in the Y-axis direction in Comparative Experiment 6 of the third embodiment. Fig.16 This is a table showing the experimental results of Comparative Experiment 7 of the third embodiment. DETAILED DESCRIPTION

[0016] <First Embodiment> pass Figures 1 to 9 The first embodiment is described. In this embodiment, a liquid crystal display device (display device) 10 is exemplified. In addition, the X-axis, Y-axis, and Z-axis are shown in a part of each drawing, and the directions of each axis are described in a manner that is shown in each drawing. In addition, the up and down directions are shown in Figure 2 , Figure 3 and Figure 7 as a reference, and the upper side of these figures is set as the front side, and the lower side of these figures is set as the back side.

[0017] like Figure 1 As shown, 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 arranged on the back side of the liquid crystal panel 11 and irradiates light for display to the liquid crystal panel 11. In this embodiment, a vehicle-mounted liquid crystal display device 10 is exemplified. The vehicle-mounted liquid crystal display device 10 is mounted on, for example, a car navigation system that displays a map or the like as an image, a multi-function display that displays the operating status of equipment such as an air conditioner in addition to a map or the like as an image, an instrument panel that displays instruments, warnings, etc. as an image, and an infotainment system that displays a TV image, audio information, etc. in addition to a map or the like as an image.

[0018] The liquid crystal panel 11 is in the shape of a horizontally long square plate as a whole. The long side direction of the liquid crystal panel 11 is consistent with the X-axis direction, the short side direction is consistent with the Y-axis direction, and the plate thickness direction (the normal direction of the main surface) is consistent with the Z-axis direction. The central side portion of the main surface of the liquid crystal panel 11 becomes a display area AA that can display images, and the frame-shaped peripheral end side portion 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. The substrate arranged on the front side of the pair of substrates constituting the liquid crystal panel 11 is a CF substrate (opposite substrate), and the substrate arranged on the back side is an array substrate (TFT substrate). Color filters such as R (red), G (green), and B (blue) or a light shielding portion (black matrix) separating adjacent color filters are provided on the CF substrate. The array substrate (TFT substrate) is provided with at least mutually orthogonal gate wiring and source wiring, a switching element (such as TFT) connected to the gate wiring and the source wiring, and a pixel electrode connected to the switching element and constituting a pixel. In addition, alignment films are provided on the inner surfaces of the array substrate and the CF substrate constituting the liquid crystal panel 11. In addition, polarizing plates are provided on the outer surfaces of the array substrate and the CF substrate constituting the liquid crystal panel 11.

[0019] Next, the backlight device 12 will be described. Figure 1 As shown, the backlight device 12 at least includes: LED 13 as a light source; LED substrate (light source substrate) 14 on which LED 13 is mounted; light guide plate 15 for guiding light from LED 13; first prism sheet 16 arranged on the back side (opposite to the light emitting side) of light guide plate 15; light absorption sheet 17 arranged on the back side of first prism sheet 16; second prism sheet 18 arranged on the front side (light emitting side) of light guide plate 15; and third prism sheet 19 arranged on the front side of second prism sheet 18. The first prism sheet 16 and light absorption sheet 17 will be described again later, and the other components (LED 13, LED substrate 14, second prism sheet 18 and third prism sheet 19) will be described in sequence. The backlight device 12 of this embodiment is set as a single-side incident light type edge light type in which light from LED 13 is incident on light guide plate 15 only from one side.

[0020] like Figure 1As shown, LED13 is configured such that an LED chip is sealed with a sealing material on a substrate portion fixed to an LED substrate 14. The LED chip of LED13 emits, for example, monochromatic blue light, and emits white light as a whole by dispersing and matching phosphors in the sealing material. Phosphors include yellow phosphors, green phosphors, red phosphors, and the like. LED13 is configured as a so-called side-emitting type in which the side surface adjacent to the mounting surface of the LED substrate 14 becomes the light-emitting surface 13A. The LED substrate 14 is set in a posture in which its main surface is parallel to the main surface of the light guide plate 15, and the main surface on the front side serves as the mounting surface of the LED 13. On the mounting surface of the LED substrate 14, a plurality of LEDs 13 are arranged at approximately equal intervals along the X-axis direction. The arrangement direction of the plurality of LEDs 13 is consistent with the X-axis direction.

[0021] The light guide plate 15 is made of a synthetic resin material that has a refractive index that is substantially higher than that of air and is substantially transparent. Specifically, the light guide plate 15 uses an acrylic resin such as PMMA as a synthetic resin material, and its refractive index is, for example, about 1.49. Figure 1 As shown, the light guide plate 15 is in the shape of a plate, and its main surface is parallel to the main surface of the liquid crystal panel 11. In addition, the long side direction of the main surface of the light guide plate 15 is consistent with the X-axis direction (second direction), the short side direction is consistent with the Y-axis direction (first direction), and the plate thickness direction as the normal direction of the main surface is consistent with the Z-axis direction (third direction). The light guide plate 15 is arranged directly below the liquid crystal panel 11. The end surface on the long side of one of the outer peripheral end surfaces of the light guide plate 15 is opposite to the light emitting surface 13A of the LED 13, and is a light incident end surface (first end surface) 15A for direct incidence of light from the light emitting surface 13A. The long side direction of the light incident end surface 15A is consistent with the X-axis direction, and the short side direction is consistent with the Z-axis direction. Among the pair of main surfaces of the light guide plate 15, the main surface on the front side facing the liquid crystal panel 11 becomes the first main surface 15B for emitting light guided inside, and the main surface on the back side facing the light absorbing sheet 17 becomes the second main surface 15C. Furthermore, the light guide plate 15 has the following functions: light emitted from the LED 13 toward the light guide plate 15 is introduced from the light incident end surface 15A, and after the light is propagated inside, it is emitted from the first main surface 15B toward the front side (light exit side). The detailed structure of the light guide plate 15 will be described again later. In addition, the normal direction of the light incident end surface 15A is consistent with the Y-axis direction (first direction) including the direction from the LED 13 toward the light guide plate 15.

[0022] like Figure 1As shown, the second prism sheet 18 and the third prism sheet 19 are in sheet form, and their respective main surfaces are parallel to the main surfaces of the liquid crystal panel 11 and the light guide plate 15. In addition, the main surfaces of the second prism sheet 18 and the third prism sheet 19 are parallel to the X-axis direction and the Y-axis direction, and the normal direction (thickness direction) of the main surface is consistent with the Z-axis direction. The second prism sheet 18 and the third prism sheet 19 are stacked on the surface side of the light guide plate 15, and have the function of giving a predetermined optical effect to the light emitted from the first main surface 15B of the light guide plate 15 and making it emit.

[0023] like Figure 1 and Figure 2 As shown, the second prism sheet 18 has a sheet-shaped second substrate 18A and a second prism 18B provided on the second substrate 18A. A pair of principal surfaces in the second substrate 18A include a second light emitting principal surface (seventh principal surface) 18A1 and a second light incident principal surface (eighth principal surface) 18A2. The second light emitting principal surface 18A1 is a principal surface on the front side (light emitting side) of the second substrate 18A opposite to the third prism sheet 19, and emits light to the third prism sheet 19. The second light incident principal surface 18A2 is a principal surface on the back side (opposite side to the light emitting side) of the second substrate 18A opposite to the first principal surface 15B of the light guide plate 15, and is incident with light emitted from the first principal surface 15B.

[0024] The second substrate 18A is formed of a substantially transparent synthetic resin, specifically, a crystalline transparent resin material such as PET (polyethylene terephthalate). When manufacturing the second substrate 18A, it is preferable to form the crystalline transparent resin material as the raw material into a sheet by stretching it using a biaxial stretching process in order to reduce the manufacturing cost. The second prism 18B is composed of a substantially transparent ultraviolet curing resin material, which is a type of photocurable resin material. When manufacturing the second prism sheet 18, for example, uncured ultraviolet curing resin material is filled into a molding mold, and the uncured ultraviolet curing resin material is arranged in contact with the main surface of the front side by placing the second substrate 18A against the open end of the mold. When the ultraviolet curing resin material is irradiated with ultraviolet rays through the second substrate 18A in this state, the ultraviolet curing resin material is cured, and the second prism 18B is integrally provided with the second substrate 18A. The ultraviolet curing 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 most preferably 1.49.

[0025] like Figure 2As shown, the second prism 18B is arranged on the second light emitting main surface 18A1 on the surface side of the second substrate 18A. In detail, the second prism 18B is arranged in the form of protruding from the second light emitting main surface 18A1 of the second substrate 18A along the Z-axis direction toward the surface side (the opposite side of the light guide plate 15 side). The cross-sectional shape of the second prism 18B cut along the Y-axis direction is roughly triangular (roughly mountain-shaped), and extends in a straight line along the X-axis direction (second direction), and a plurality of second prisms 18B are arranged along the Y-axis direction (first direction) in the second light emitting main surface 18A1 of the second substrate 18A. The plurality of second prisms 18B are arranged continuously along the Y-axis direction basically without any interval. The second prism 18B has a second base 18B1 parallel to the Y-axis direction and a pair of second oblique sides 18B2 and 18B3 rising from both ends of the second base 18B1. Of the pair of second oblique sides 18B2 and 18B3 in the second prism 18B, the side of the LED 13 in the Y-axis direction ( Figure 2 The left side of the LED 13 in the Y-axis direction is the second LED side oblique side (the second oblique side on one side) 18B2, and the opposite side ( Figure 2 The portion on the right side of the prism 18B is used as the oblique side on the opposite side of the second LED (the second oblique side on the other side) 18B3. Among them, the light incident on the second prism 18B mainly moves in the direction away from the LED 13 in the Y-axis direction ( Figure 2 The light incident on the second prism 18B is mainly refracted in the direction close to LED 13 (on the right side) along the Y axis. Figure 2 The light traveling on the left side of the prism 18B is refracted by the second LED side oblique edge 18B2. In any case, the light refracted by the pair of second oblique edges 18B2 and 18B3 in the second prism 18B is mostly selectively raised and focused in the Y-axis direction.

[0026] Moreover, if Figure 2As shown, when the inclination angle (third base angle) θ1 of the second LED side hypotenuse 18B2 relative to the second base 18B1 is compared with the inclination angle (fourth base angle) θ2 of the second LED opposite side hypotenuse 18B3 relative to the second base 18B1, the former is larger than the latter. That is, the cross-sectional shape of the second prism 18B is an asymmetric shape, forming an unequal-sided triangle. Specifically, in the second prism 18B, the inclination angle θ1 of the second LED side hypotenuse 18B2 relative to the second base 18B1 is preferably in the range of 50° to 60°, with 55° being the most preferred. In contrast, in the second prism 18B, the inclination angle θ2 of the second LED opposite side hypotenuse 18B3 relative to the second base 18B1 is preferably in the range of 35° to 50°, with 45° being the most preferred. In addition, the angle (second vertex angle) θ3 formed by a pair of second oblique sides 18B2 and 18B3 in the second prism 18B is preferably in the range of 70° to 95°, and is most preferably 80°. In addition, the height dimension of the plurality of second prisms 18B arranged along the X-axis direction, the width dimension of the second base 18B1, the inclination angle of each second oblique side 18B2 and 18B3 relative to the second base 18B1, etc. are all substantially the same, and the arrangement intervals between adjacent second prisms 18B are also substantially constant and arranged at equal intervals.

[0027] like Figure 1 and Figure 2 As shown, the third prism sheet 19 has a sheet-shaped third substrate 19A and a third prism 19B arranged on the third substrate 19A. A pair of principal surfaces in the third substrate 19A include a third light-emitting principal surface (ninth principal surface) 19A1 and a third light-entering principal surface (tenth principal surface) 19A2. The third light-emitting principal surface 19A1 is a principal surface on the front side of the third substrate 19A, and emits light toward the outside. The third light-entering principal surface 19A2 is a principal surface on the back side of the third substrate 19A opposite to the second prism sheet 18, and is incident with light emitted from the second prism sheet 18.

[0028] The third substrate 19A is made of a substantially transparent synthetic resin, and specifically, is made of a crystalline transparent resin material such as PET, which is the same as the second substrate 18A. The third prism 19B is made of a substantially transparent ultraviolet curing 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. The ultraviolet curing resin material constituting the third prism 19B is, for example, an acrylic resin such as PMMA, and its refractive index is higher than that of the material of the second prism 18B, for example, about 1.61.

[0029] like Figure 2As shown, the third prism 19B is arranged on the third light-emitting main surface 19A1 on the surface side of the third substrate 19A. In detail, the third prism 19B is arranged in the form of protruding from the third light-emitting main surface 19A1 of the third substrate 19A along the Z-axis direction toward the surface side (the opposite side of the second prism sheet 18). The cross-sectional shape of the third prism 19B after being cut along the Y-axis direction is roughly triangular (roughly mountain-shaped), and extends in a straight line along the X-axis direction (second direction), and a plurality of third prisms 19B are arranged along the Y-axis direction (first direction) in the third light-emitting main surface 19A1 of the third substrate 19A. A plurality of third prisms 19B are arranged continuously along the Y-axis direction substantially without intervals. The third prism 19B has a third base 19B1 parallel to the Y-axis direction and a pair of third hypotenuses 19B2 and 19B3 rising from both ends of the third base 19B1. Of the pair of third oblique sides 19B2 and 19B3 in the third prism 19B, the LED 13 side in the Y-axis direction ( Figure 2 The left side of the LED 13 in the Y-axis direction is the third LED side oblique side (the third oblique side on one side) 19B2, and the opposite side ( Figure 2 The portion on the right side of the prism 19B is used as the oblique side on the opposite side of the third LED (the other third oblique side) 19B3. Among them, the light incident on the third prism 19B mainly moves in the direction away from the LED 13 in the Y-axis direction ( Figure 2 The light incident on the third prism 19B is mainly refracted in the direction close to LED 13 (on the right side) along the Y axis. Figure 2 The light traveling on the left side of the third prism 19B is refracted by the third LED side oblique edge 19B2. In any case, the light refracted by the pair of third oblique edges 19B2 and 19B3 in the third prism 19B is mostly selectively raised in the Y-axis direction and focused.

[0030] Moreover, if Figure 2As shown, the inclination angle θ4 (fifth base angle) of the third LED side hypotenuse 19B2 of the third prism 19B relative to the third base 19B1 is the same as the inclination angle (sixth base angle) θ5 of the third LED opposite side hypotenuse 19B3 relative to the third base 19B1. That is, the cross-sectional shape of the third prism 19B is a symmetrical shape, forming an isosceles triangle. Moreover, in the third prism 19B, the inclination angle θ4 of the third LED side hypotenuse 19B2 relative to the third base 19B1 is smaller than the inclination angle θ1 of the second LED side hypotenuse 18B2 of the second prism 18B of the second prism sheet 18 relative to the second base 18B1. Specifically, the inclination angles θ4 and θ5 of the pair of third hypotenuses 19B2 and 19B3 in the third prism 19B relative to the third base 19B1 are preferably in the range of 40° to 50°, among which 45° is most preferred. In contrast, the angle (third vertex angle) θ6 formed by a pair of third hypotenuses 19B2 and 19B3 in the third prism 19B is preferably in the range of 80° to 100°, with 90°, i.e., a right angle, being the most preferred. In addition, the height dimensions of the plurality of third prisms 19B arranged along the X-axis direction, the width dimensions of the third base 19B1, the inclination angles of the third hypotenuses 19B2 and 19B3 relative to the third base 19B1, etc. are all substantially the same, and the arrangement intervals between adjacent third prisms 19B are also substantially constant and arranged at equal intervals. In addition, the height dimension and arrangement interval of the third prism 19B are different from the height dimension and arrangement interval of the second prism 18B, respectively, which is preferred from the perspective of suppressing the generation of interference fringes known as moiré fringes.

[0031] The functions and effects of the second prism sheet 18 and the third prism sheet 19 constructed as described above are described. The light emitted from the LED 13 and incident on the light-entering end surface 15A of the light guide plate 15 propagates in the light guide plate 15, and is emitted from the first main surface 15B and is incident on the second prism sheet 18. Most of the light incident on the second prism sheet 18 is irradiated on the oblique side on the opposite side of the LED 13 side in the Y-axis direction, that is, the second LED opposite side oblique side 18B3, of a pair of second oblique sides 18B2 and 18B3 in the second prism 18B, and refracted, and is emitted while rising, or is directed toward the oblique side on the LED 13 side, that is, the second LED side oblique side 18B2, in the Y-axis direction. Furthermore, as described above, the angle of inclination θ1 formed by the second LED side bevel 18B2 on the LED 13 side in the Y-axis direction of the second prism 18B with respect to the second base 18B1 is greater than the angle of inclination θ2 formed by the second LED opposite side bevel 18B3 on the opposite side of the LED 13 side in the Y-axis direction with respect to the second base 18B1. Therefore, compared with the case where the inclination angles θ1 and θ2 are equal or the case where the inclination angle θ2 is greater than the inclination angle θ1, it is difficult for the light incident on the second prism sheet 18 to be irradiated with the second LED side bevel 18B2 on the LED 13 side of the second prism 18B. Here, if the incident light of the second prism sheet 18 is irradiated with the second LED side bevel 18B2 on the LED 13 side of the second prism 18B, there is a tendency that the light will not rise when exiting the second prism 18B and will become side lobe light and will be easily emitted. Therefore, if the incident light of the second prism sheet 18 is less likely to directly hit the second LED side bevel 18B2 which is the bevel on the LED 13 side of the second prism 18B, the generation of side lobe light can be suppressed, resulting in improved light utilization efficiency.

[0032] Most of the light emitted from the second prism sheet 18 and incident on the third prism sheet 19 is incident on the oblique side on the opposite side of the LED 13 side in the Y-axis direction, that is, the third LED opposite side oblique side 19B3, of the pair of third oblique sides 19B2 and 19B3 in the third prism 19B and refracted, and is emitted while rising, or is directed toward the oblique side on the LED 13 side, that is, the third LED side oblique side 19B2 in the Y-axis direction. In addition, as described above, in the third prism 19B, the inclination angles θ4 and θ5 formed by the pair of third oblique sides 19B2 and 19B3 and the third base 19B1 are equal. Therefore, compared with the case where the inclination angles θ4 and θ5 are different, light that is refracted in the Y-axis direction by the oblique side on the opposite side of the LED 13 side, that is, the third LED opposite side oblique side 19B3, and is directed toward the oblique side on the LED 13 side, that is, the third LED side oblique side 19B2, is easily returned to the second prism sheet 18 side through the oblique side on the LED 13 side, that is, the third LED side oblique side 19B2, in the Y-axis direction. As a result, the amount of light (hereinafter referred to as return light) that returns from the third prism sheet 19 to the second prism sheet 18 side increases. The return light reaches the third prism sheet 19 again by being reflected in the backlight device 12, and is raised and emitted by any one of the pair of third oblique sides 19B2 and 19B3 in the third prism 19B, thereby improving the efficiency of light utilization.

[0033] Here, the detailed structure of the light guide plate 15 is described. Figure 2 and Figure 3 As shown, a first light guide plate lens 20 , a second light guide plate lens 21 , and a third light guide plate lens (first lens) 22 are provided on the light guide plate 15 .

[0034] like Figure 3Indicates that the first light guide plate lens 20 is arranged on the first principal surface 15B of the light guide plate 15. The first light guide plate lens 20 extends along the Y-axis direction (first direction), and a plurality of the first light guide plate lenses 20 are arranged in a row along the X-axis direction (second direction). A plurality of first light guide plate lenses 20 are arranged continuously along the X-axis direction substantially without spacing. In the present 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 protruding from the first principal surface 15B to the front side. Specifically, the cross-sectional shape of the first light guide plate lens 20 cut along the X-axis direction is a semicircular shape and an ellipse extending linearly along the Y-axis direction, and its surface is an arc-shaped surface 20A. When the angle formed by the tangent of the base end of the arc-shaped surface 20A relative to the X-axis direction is set as the "contact angle", the contact angle of the first light guide plate lens 20 is, for example, about 51°. The arrangement interval (the interval between the central positions along the X-axis direction) of the first light guide plate lens 20 is, for example, about 0.041 mm. The contact angles, width dimensions, arrangement intervals, and height dimensions of the plurality of first light guide plate lenses 20 arranged along the X-axis direction are all substantially the same. In order to integrally set the first light guide plate lenses 20 configured in this manner with the light guide plate 15, for example, the light guide plate 15 can be manufactured by injection molding, and a transfer shape for transferring the first light guide plate lenses 20 can be preliminarily formed on the molding surface for molding the first main surface 15B in the molding mold.

[0035] like Figure 3 Indicates that the second light guide plate lens 21 is arranged on the second main surface 15C of the light guide plate 15. The second light guide plate lens 21 extends in the Y-axis direction, and a plurality of them are arranged in the X-axis direction. In the present embodiment, the second light guide plate lens 21 is a convex prism protruding from the second main surface 15C to the back side. Specifically, the cross-sectional shape of the second light guide plate lens 21 cut along the X-axis direction is roughly triangular (roughly mountain-shaped), and extends in a straight line 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 roughly an isosceles triangle, and has a pair of fourth inclined surfaces 21A. The vertex angle of the second light guide plate lens 21 (the angle formed by a pair of fourth inclined surfaces 21A) is preferably an obtuse angle (an angle exceeding 90°), specifically preferably in the range of 100° to 150°, and most preferably 140°. The vertex angles, width dimensions, arrangement intervals, and height dimensions of the plurality of second light guide plate lenses 21 arranged along the X-axis direction are all roughly the same. In this embodiment, the arrangement interval of the second light guide plate lenses 21 is larger than the arrangement interval of the first light guide plate lenses 20. In order to integrally provide the second light guide plate lenses 21 configured in this way with the light guide plate 15, for example, the light guide plate 15 can be manufactured by injection molding, and a transfer shape for transferring the second light guide plate lenses 21 can be preliminarily formed on the molding surface for molding the second main surface 15C in the molding mold.

[0036] According to the light guide plate 15 of such a configuration, light propagating in the light guide plate 15 is as follows: Figure 3 As shown, along the Z-axis direction, on the first main surface 15B side, the light is repeatedly totally reflected by being irradiated by the arc-shaped surface 20A of each first light guide plate lens 20, and moves roughly in a zigzag shape along the X-axis direction. The light propagating in the light guide plate 15 is repeatedly totally reflected by being irradiated by the fourth inclined surface 21A of each pair of second light guide plate lenses 21 on the second main surface 15C side along the Z-axis direction, and moves roughly in a zigzag shape along the Y-axis direction. As a result, the expansion of the light propagating in the light guide plate 15 in the X-axis direction is limited, so it is difficult to produce uneven brightness between the vicinity of LED 13 and its surroundings in the X-axis direction. On the other hand, in the first main surface 15B, the light that is not totally reflected by the arc-shaped surface 20A of the first light guide plate lens 20 is refracted by the arc-shaped surface 20A, which promotes the emission from the first main surface 15B.

[0037] like Figure 2 As shown, the third light guide plate lens 22 is disposed on the second main surface 15C of the light guide plate 15. A plurality of third light guide plate lenses 22 are arranged in a row along the Y-axis direction. The third light guide plate lens 22 protrudes from the second main surface 15C toward the back side along the Z-axis direction. The third light guide plate lens 22 has: a first inclined surface 22A, which is disposed on the opposite side of the LED 13 side in the Y-axis direction ( Figure 2 The second inclined surface 22B is arranged on the LED13 side in the Y-axis direction ( Figure 2 and a third inclined surface 22C, which is located between the first inclined surface 22A and the second inclined surface 22B in the Y-axis direction. The first inclined surface 22A has an opposite side ( Figure 2 right side) toward LED13 side ( Figure 2 The second inclined surface 22B has a slope that rises from the LED 13 side (the left side of the light guide plate 15) to the back side (the first prism sheet 16 side, the protruding direction from the second main surface 15C to the third light guide plate lens 22). Figure 2 ) to the opposite side ( Figure 2 The third inclined surface 22C has a slope that rises from the opposite side of the LED 13 side (the right side of the LED 13) along the Y-axis direction of the light guide plate 15. Figure 2 right side) toward LED13 side ( Figure 2 The left side of the device is inclined to rise toward the back side.

[0038] like Figure 2As shown, the first inclined surface 22A and the second inclined surface 22B reflect the light propagating in the light guide plate 15, and rise toward the front side in a manner close to the Z-axis direction, thereby promoting emission from the first main surface 15B. In detail, the first inclined surface 22A mainly plays the role of reflecting and raising the light traveling in a manner away from the LED 13 in the Y-axis direction. On the other hand, the second inclined surface 22B mainly plays the role of reflecting and raising the light traveling in a manner close to the LED 13 in the Y-axis direction. The first inclined surface 22A has a gradient in which the distance from the first main surface 15B (the portion where the third light guide plate lens 22 is not provided) becomes smaller 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 relative 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 becomes larger as it moves away from the LED 13 in the Y-axis direction, that is, a gradient opposite to that of the first inclined surface 22A. The inclination angle (second angle) θ8 of the second slope 22B with respect to the Y-axis direction is set to be a steep slope close to vertical at, for example, about 80°, and is larger than the inclination angle θ7 of the first slope 22A.

[0039] In addition, if Figure 2 , Figure 4 and Figure 5 As shown, the plurality of third light guide plate lenses 22 arranged along the Y-axis direction are designed in such a way that the height dimension (dimension along the Z-axis direction) and the length dimension (dimension along the Y-axis direction) increase as they are farther away from the LED 13 in the Y-axis direction. In more detail, when comparing the third light guide plate lens 22 close to the LED 13 in the Y-axis direction and the third light guide plate lens 22 far away from the LED 13 in the Y-axis direction, the latter has a larger area of ​​the first inclined surface 22A and the second inclined surface 22B than the former. That is, in the second main surface 15C, the plurality of first inclined surfaces 22A and the plurality of second inclined surfaces 22B arranged at intervals in the Y-axis direction are configured so that the farther away from the LED 13 in the Y-axis direction, the larger the area of ​​each is. Thus, although the light is difficult to be irradiated to the first inclined surface 22A and the second inclined surface 22B of the third light guide plate lens 22 on the side close to the LED 13 in the Y-axis direction, thereby suppressing the light emission, the light is easily irradiated to the first inclined surface 22A and the second inclined surface 22B of the third light guide plate lens 22 on the side far from the LED 13 in the Y-axis direction, thereby promoting the light emission. As a result, the amount of light emitted from the first main surface 15B is uniformed on the LED 13 side and the opposite side in the Y-axis direction.

[0040] like Figure 2 As shown, the side of the third inclined surface 22C opposite to the LED 13 side along the Y-axis direction ( Figure 2 The end portion of the LED 13 side (on the right side) is connected to the first inclined surface 22A, and the LED 13 side (on the right side) along the Y-axis direction Figure 2The third inclined surface 22C has a gradient in which the distance from the first main surface 15B (the portion where the third light guide plate lens 22 is not provided) increases the further away from the LED 13 in the Y-axis direction. That is, the third inclined surface 22C has the same slope as the second inclined surface 22B. The inclination angle (third angle) θ9 of the third inclined surface 22C relative to the Y-axis direction is, for example, about 1.4°, which is smaller than the inclination angles θ7 and θ8 of the first inclined surface 22A and the second inclined surface 22B. The third inclined surface 22C constructed in this way reflects the light traveling in the light guide plate 15 in a manner away from the LED 13, thereby directing the light toward the first main surface 15B side, but the incident angle of the light relative 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 is guided further away from the LED 13. As a result, it is difficult for the outgoing light from the first main surface 15B to deviate toward the LED 13 side 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 relative to the Y-axis direction is the smallest, the inclination angle θ7 of the first inclined surface 22A relative to the Y-axis direction is greater than the inclination angle θ9, and the inclination angle θ8 of the second inclined surface 22B relative to the Y-axis direction is the largest. In addition, the plurality of third inclined surfaces 22C arranged along the Y-axis direction are designed to have a smaller length dimension the farther away from the LED 13 in the Y-axis direction. This is because the length dimension of the third light guide plate lens 22 is larger the farther away from the LED 13 in the Y-axis direction, and the larger the occupied range of the third light guide plate lens 22.

[0041] like Figures 3 to 5 As shown, the third light guide plate lens 22 of the above-mentioned structure is arranged between two second light guide plate lenses 21 adjacent in the X-axis direction. Therefore, the third light guide plate lens 22 is arranged in a manner of alternating and repeating 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 lens 22 protruding from the second main surface 15C is smaller than the protruding dimension of the second light guide plate lens 21. Therefore, even in the third light guide plate lens 22 located on the side farthest from the LED 13 in the Y-axis direction, it does not protrude further to the back side than the second light guide plate lens 21.

[0042] In addition, if Figure 6 As shown, the vehicle-mounted liquid crystal display device 10 of the present embodiment is arranged in a posture in which the X-axis direction and the Z-axis direction are roughly consistent with the horizontal direction, and the Y-axis direction is parallel to the vertical direction (perpendicular direction). The "posture in which the Y-axis direction is parallel to the vertical direction" mentioned here can be a posture in which the Y-axis direction is consistent with the vertical direction, or a posture in which the Y-axis direction includes the vertical direction as a vector component, that is, a posture in which the Y-axis direction is slightly inclined relative to the vertical direction. In addition, the Z-axis direction is consistent with the front direction of the vehicle-mounted liquid crystal display device 10. With respect to the vehicle-mounted liquid crystal display device 10 on the front side ( Figure 6The vehicle-mounted liquid crystal display device 10 is arranged so that the line of sight of the driver DR is inclined upward relative to the front direction (Z-axis direction). The angle (peak angle) of the peak brightness in the light distribution of the outgoing light from the vehicle-mounted liquid crystal display device 10 is consistent with the angle θvp formed by the line of sight of the driver DR relative to the front direction of the vehicle-mounted liquid crystal display device 10. That is, the vehicle-mounted liquid crystal display device 10 is arranged in a manner that the driver DR can visually recognize the image in the brightest state.

[0043] like Figure 6 As shown in FIG. 1 , the windshield FG of the passenger car is located above the vehicle-mounted liquid crystal display device 10 in the Y-axis direction. Figure 6 Near the lower end of the light emitting surface 13A, the light emitting surface 13A is oriented in the Y-axis direction. Figure 6 Here, a portion of the light emitted from the vehicle-mounted liquid crystal display device 10 that is directed toward the windshield FG is reflected by the windshield FG and directed toward the driver DR. Such reflected light can be visually recognized by the driver DR as an image reflected on the windshield FG, that is, "reflected". Here, the front direction of the vehicle-mounted liquid crystal display device 10 is set to 0° (reference), and the Y-axis direction relative to the front direction is set to Figure 6 The angle of the upper side (the side away from LED13) is set to "+ (positive)", and the angle in the Y-axis direction relative to the front direction is set to "+ (positive)". Figure 6 The angle on the lower side (the side close to LED 13) is set to "- (negative)". The above-mentioned "reflected" light is light emitted from the range of "+50° to +80°" in the emitted light emitted from the vehicle-mounted liquid crystal display device 10. In the present embodiment, the light in the emission angle range (+50° to +80°) that will be "reflected" is defined as "side lobe light". In order to suppress such side lobe light, blinds have been used in the past, but the components of blinds are expensive. Therefore, it is desired to limit the emission angle of light at a low cost without using blinds to suppress side lobe light and prevent reflection on the windshield FG. In addition, in the present embodiment, the above-mentioned angle θvp (peak angle) is, for example, "+6°".

[0044] Therefore, if Figure 1 as well as Figure 3As shown, the backlight device 12 of the present embodiment includes a first prism sheet 16 and a light absorbing sheet 17. First, the first prism sheet 16 is described in detail. The first prism sheet 16 is configured to overlap on the back side relative to the light guide plate 15. The first prism sheet 16 has a sheet-shaped first substrate 16A and a first prism 16B provided on the first substrate 16A. A pair of principal surfaces in the first substrate 16A include a third principal surface 16A1 and a fourth principal surface 16A2. The third principal surface 16A1 is a principal surface on the front side of the first substrate 16A opposite to the light guide plate 15, and emits light toward the light guide plate 15. The fourth principal surface 16A2 is a principal surface on the back side of the first substrate 16A opposite to the light absorbing sheet 17.

[0045] The first substrate 16A is formed of a substantially transparent synthetic resin, specifically, for example, a crystalline transparent resin material such as PET, which is the same as the second substrate 18A. The first prism 16B is formed of a substantially transparent ultraviolet curing 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. The ultraviolet curing 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] like Figure 3 As shown, the first prism 16B is arranged on the fourth principal surface 16A2 on the back side of the first substrate 16A. In detail, the first prism 16B is arranged in a form protruding from the fourth principal surface 16A2 of the first substrate 16A along the Z-axis direction toward the back side (the light absorbing sheet 17 side). The cross-sectional shape of the first prism 16B cut along the X-axis direction is roughly triangular (roughly mountain-shaped), and extends in a straight line along the Y-axis direction (first direction). In the fourth principal surface 16A2 of the first substrate 16A, a plurality of first prisms 16B are arranged along the X-axis direction (second direction). The plurality of first prisms 16B are arranged continuously along the X-axis direction substantially without any intervals. The first prism 16B has a first base 16B1 parallel to the X-axis direction and a pair of first oblique sides 16B2 and 16B3 rising from both ends of the first base 16B1. One side in the X-axis direction ( Figure 3 The left side of the x-axis direction is set as the first hypotenuse 16B2 on one side, and the other side ( Figure 3 The hypotenuse on the right side) is set as the first hypotenuse 16B3 of the other side.

[0047] like Figure 3As shown, in the first prism 16B, the inclination angle (first base angle) θ10 of the first hypotenuse 16B2 on one side relative to the first base 16B1 is the same as the inclination angle (second base angle) θ11 of the first hypotenuse 16B3 on the other side relative to the first base 16B1. That is, the cross-sectional shape of the first prism 16B is a symmetrical shape, forming an isosceles triangle. Specifically, the inclination angles θ10 and θ11 of a pair of first hypotenuses 16B2 and 16B3 in the first prism 16B relative to the first base 16B1 are preferably in the range of 40° to 50°, with 45° being the most preferred. In contrast, in the first prism 16B, the angle (third vertex angle) θ12 formed by a pair of first hypotenuses 16B2 and 16B3 is preferably in the range of 80° to 100°, with 90°, i.e., a right angle, being the most preferred. In addition, the height dimensions of the multiple first prisms 16B arranged along the X-axis direction, the width dimension of the first base 16B1, the inclination angles of the first oblique sides 16B2 and 16B3 relative to the first base 16B1, etc. are all approximately the same, and the arrangement intervals between adjacent first prisms 16B are also approximately constant and arranged at equal intervals.

[0048] According to this composition, Figure 2 As shown, during the process of light emitted from LED 13 and incident on the light-entering end surface 15A of the light guide plate 15 propagating in the light guide plate 15, in the second main surface 15C, when reaching the first inclined surface 22A having an inclination rising from the opposite side of LED 13 to the LED 13 side in the Y-axis direction, although more light is reflected on the first inclined surface 22A, the remaining light is refracted and emitted from the first inclined surface 22A to the back side. Among them, the light reflected by the first inclined surface 22A is directed toward the first main surface 15B, and is reflected or emitted again by the first main surface 15B. On the other hand, the light emitted from the first inclined surface 22A is directed toward the first prism sheet 16. The light from the first inclined surface 22A toward the first prism sheet 16 is reflected or incident on the first prism sheet 16 at the third main surface 16A1 (the interface between the first substrate 16A and the air layer) of the first prism sheet 16. When the light reflected by the third principal surface 16A1 of the first prism sheet 16 is incident on the second principal surface 15C of the light guide plate 15 , it is emitted directly from the first principal surface 15B or emitted from the first principal surface 15B after propagating in the light guide plate 15 .

[0049] like Figure 3As shown, the light incident on the first prism sheet 16 is reflected at the first base 16B1 (interface between the first substrate 16A and the first prism 16B) in the first prism 16B, or reflected at a pair of first oblique edges 16B2 and 16B3 in 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. In detail, the light incident on the third main surface 16A1 of the first substrate 16A passes through any of the following paths: being totally reflected at the interface between the first substrate 16A and the first prism 16B, or being incident on the first prism 16B and reflected by the first oblique edge 16B2 on one side and then traveling toward the first oblique edge 16B3 on the other side and then being reflected by the first oblique edge 16B3 on the other side, or being reflected by the first oblique edge 16B3 on the other side and then traveling toward the first oblique edge 16B2 on one side and then being reflected by the first oblique edge 16B2 on one side, and then being emitted from the third main surface 16A1 to the front side (light guide plate 15 side). When the light emitted from the first prism sheet 16 toward the front side enters the second principal surface 15C of the light guide plate 15 , it is emitted directly from the first principal surface 15B or emitted from the first principal surface 15B after propagating in the light guide plate 15 .

[0050] In addition, when the light reaches the second main surface 15C during the propagation in the light guide plate 15, the light refracted by the first inclined surface 22A is given an angle corresponding 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 the present embodiment, among the outgoing light from the second main surface 15C of the light guide plate 15, the light on the first prism sheet 16 side ( Figure 2 The lower side of the light guide plate 15 includes light with an angle of up to about 10° (80° relative to the Z-axis direction). That is, the outgoing light from the second principal surface 15C of the light guide plate 15 has a high directivity such that the light with an angle of about 10° relative to the Y-axis direction on the first prism sheet 16 side has a peak brightness, and almost no diffuse light is included. As a result, the outgoing light from the second principal surface 15C of the light guide plate 15 is mirror-reflected at the third principal surface 16A1 of the first prism sheet 16 or the first bottom edge 16B1 of the first prism 16B with a high efficiency (specifically, the average reflectivity of the P wave and the S wave is about 40%), and is effectively totally reflected at a pair of first oblique edges 16B2 and 16B3 of the first prism 16B, and almost no diffuse light is included in any reflected light. As a result, the outgoing light from the backlight device 12 is unlikely to include light emitted within the range of "+50° to +80°", that is, side lobe light. Through the above, it is possible to limit the emission angle of light without using a conventional blind, and to reduce side lobe light.

[0051] Next, the light absorbing sheet 17 will be described in detail. Figures 1 to 3As shown, the light absorbing sheet 17 is arranged in a form in which its main surface is parallel to each main surface of the light guide plate 15 or 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 to overlap with the fourth main surface 16A2 of the first prism sheet 16 over substantially the entire area. The light absorbing sheet 17 is made of, for example, PET having a black surface, and has a higher light absorption than either the light guide plate 15 or the first prism sheet 16. Of the pair of main surfaces of the light absorbing sheet 17, the main surface on the front side is arranged toward the fourth main surface 16A2 of the first prism sheet 16, and becomes a light absorbing main surface (fifth main surface) 17A that absorbs light.

[0052] According to such a configuration, the light emitted from the fourth main surface 16A2 of the first prism sheet 16 toward the back side is directed toward the light absorbing sheet 17 and is effectively absorbed by the light absorbing main surface 17A. Here, the light emitted from the fourth main surface 16A2 of the first prism sheet 16 mostly has characteristics close to diffuse light, so by absorbing the light with the light absorbing sheet 17, the emission angle of the emitted light of the backlight device 12 can be better limited. Thus, further reduction of side lobe light can be achieved. In addition, the amount of emitted light from the fourth main surface 16A2 of the first prism sheet 16 is very small, so even if it is absorbed by the light absorbing sheet 17, the effect on the brightness of the emitted light of the backlight device 12 is very slight.

[0053] Next, in order to verify the superiority of the backlight device 12 and the liquid crystal display device 10 of the present embodiment, the following comparative experiments 1 and 2 are conducted. First, comparative experiment 1 is described. Comparative experiment 1 obtains the light distribution of the outgoing light of each backlight device of the following embodiment 1 and comparative examples 1 to 4. Embodiment 1 is a backlight device 12 having the same structure as that described before comparative experiment 1. Comparative examples 1 to 4 are backlight devices having a different structure from that of embodiment 1. Specifically, the backlight devices of comparative examples 1, 2, and 4 have, in addition to LEDs as light sources, Figure 7 As shown, at least a light guide plate 1, a light reflecting sheet 2 stacked on the back side of the light guide plate 1, a light diffusing sheet 3 stacked on the front side of the light guide plate 1, and a prism sheet 4 stacked on the front side of the light diffusing sheet 3. The light guide plate 1 provided in the backlight device of comparative examples 1, 2, and 4 has a light reflecting portion 5 on the main surface 1B on the back side that rises toward the front side by diffusing and reflecting light. The light reflecting portion 5 is composed of a rough surface (fine concave-convex) selectively provided on the main surface 1B on the back side of the light guide plate 1. A portion of the light diffused and reflected by the light reflecting portion 5 is emitted from the main surface 1A on the front side of the light guide plate 1. The surface of the light reflecting sheet 2 is white and has high light reflectivity. Through the light reflecting sheet 2, the light emitted from the main surface 1B on the back side of the light guide plate 1 can be diffused and reflected and then incident on the light guide plate 1. The light diffusing sheet 3 contains a diffusing agent that diffuses and reflects light. The prism sheet 4 is the same as the third prism sheet 19 described before comparative experiment 1 (refer to Figure 3) has roughly the same structure as the prism sheet, so the detailed description of the structure of the prism sheet 4 is omitted here.

[0054] The backlight device of Comparative Example 1 has Figure 7 In addition to the structure shown in the figure, the louver is also provided as in the past. In the backlight device of Comparative Example 1, the louver is stacked on the surface side relative to the prism sheet 4. The louver is a structure in which the light-shielding part and the light-transmitting part are alternately arranged along the Y-axis direction, and the emission angle of the light passing through the light-transmitting part is limited by the two light-shielding parts sandwiching the light-transmitting part. On the other hand, the backlight device of Comparative Example 2 adopts the structure shown in the figure. Figure 7 The backlight device of Comparative Example 4 has Figure 7 In addition to the structure shown in the figure, a first prism sheet 16 is also provided (see Figure 2 as well as Figure 3 In the backlight device of Comparative Example 4, the first prism sheet 16 is arranged to be sandwiched between the light guide plate 1 and the light reflecting sheet 2 (see Figure 7 On the other hand, the backlight device of Comparative Example 3 is configured as follows: Figure 2 as well as Figure 3 ) The first prism sheet 16 is removed, and a light reflecting sheet 2 is provided (refer to Figure 7 ) instead of the light absorbing sheet 17. As shown in Example 1 and Comparative Example 3, in addition to LED 13, Figure 2 and Figure 3 The type of backlight device including the light guide plate 15, the second prism sheet 18 and the third prism sheet 19 shown in the figure is referred to as "Type A". Figure 7 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 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. Example 1 can be said to be a configuration of Type A with the first prism sheet 16 and the light absorbing sheet 17. Comparative Example 3 can be said to be a configuration of Type A with the light reflecting sheet 2 but without the first prism sheet 16.

[0055] In Comparative Experiment 1, the brightness of the emitted light was measured with the LEDs lit using the backlight devices of Example 1 and Comparative Examples 1 to 4 described above, and a graph of the light distribution (brightness angle distribution) in the Y-axis direction was prepared. The experimental results of the light distribution in Comparative Experiment 1 are shown in FIG. Figure 8 shown. Figure 8 In the graph showing the light distribution, the horizontal axis is the angle in the Y-axis direction relative to the front direction (Z-axis direction) (unit: "°"), and the vertical axis is the relative brightness (unit: "%) based on the peak brightness (100%). Figure 8The positive and negative signs "- (negative)" given to the angle of the horizontal axis of the backlight device 12 indicate that the backlight device 12 is viewed from the front and the Y-axis direction (vertical direction) is 0° (front direction) relative to the reference value. Figure 6 The lower side (opposite side of the windshield FG side) of the backlight device 12 is indicated by “+ (positive)”, which indicates that the backlight device 12 is viewed from the front and the Y-axis direction is 0° (front direction) relative to the reference value. Figure 6 On the upper side (windshield FG side). Figure 8 In the figure, the curve graph of Example 1 is illustrated by a solid line, the curve graph of Comparative Example 1 is illustrated by a dotted line, the curve graph of Comparative Example 2 is illustrated by a single-dot chain line, the curve graph of Comparative Example 3 is illustrated by a thick double-dot chain line, and the curve graph of Comparative Example 4 is illustrated by a thin double-dot chain line.

[0056] The experimental results of comparative experiment 1 are described below. Figure 8 In each of the light distributions of Comparative Examples 1, 2, and 4, the peak angle as the angle of peak brightness is "+3°", and the half-value width is wider than the half-value width of the light distribution of Example 1. It can be inferred that the reason why the half-value width of each of the light distributions of Comparative Examples 1, 2, and 4 is wider than the half-value width of the light distribution of Example 1 is because the light is diffusely reflected by the light reflecting sheet 2, the light diffusing sheet 3, and the light reflecting portion 5 respectively provided in the backlight device of type B. On the other hand, in the light distribution of Example 1, the peak angle as the angle of peak brightness is "+6°". In the light distribution of Comparative Example 3, the peak angle as the angle of peak brightness is "+8°". The half-value widths of each of the light distributions of Example 1 and Comparative Example 3 are narrower than the half-value widths of Comparative Examples 1, 2, and 4, respectively. It can be inferred that the reason why the half-value widths of the light distributions of Example 1 and Comparative Example 3 are narrower than those of Comparative Examples 1, 2, and 4 is that, in addition to the high light focusing effect in the Y-axis direction provided by the two prism sheets 18 and 19 provided in the backlight device of type A, almost no diffuse reflection occurs in any of the light guide plate 15 and the prism sheets 18 and 19. It can be inferred that the reason why the peak angle of the light distribution of Comparative Example 3 is larger than the peak angle of the light distribution of Example 1 is that, since the first prism sheet 16 is not provided, in addition to the absence of the reflected light of the first prism sheet 16, the light is also affected by the diffuse reflection of 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 that even if the light is diffusely reflected by the light reflecting sheet 2, the light diffusing sheet 3, and the light reflecting portion 5 of the type B backlight device, the light emission angle range is well limited by the louver in the Y-axis direction. According to the light distribution of Comparative Example 2 and Comparative Example 4, the side lobe light has a relative brightness of approximately 20% or more, and the reflection caused by the side lobe light is easily visually recognized. The reason is presumed to be that Comparative Example 2 does not have a structure for limiting the emission angle range of the light diffusely reflected by the light reflecting sheet 2, the light diffusing sheet 3, and the light reflecting portion 5 of the type B backlight device. 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 that of the light distribution of Comparative Example 1. The reason is speculated to be that diffuse reflection is hardly generated in the light guide plate 15 and the prism sheets 18 and 19 of the type A backlight device, and in particular, the light emitted from the first inclined surface 22A toward the back side is given an appropriate angle, so that the light can be efficiently specularly reflected or totally reflected by the first prism sheet 16. Furthermore, it is speculated that absorbing the diffuse light emitted from the first prism sheet 16 by the light absorption sheet 17 also helps to suppress the side lobe light. In the light distribution of Comparative Example 3, although the side lobe light is suppressed compared with the light distribution of Comparative Examples 2 and 4, the side lobe light is slightly increased compared with the light distribution of Example 1 and Comparative Example 1. The reason is speculated to be that because Comparative Example 3 is a type A backlight device, the range of the light emission angle is limited, but in addition to the absence of reflected light from the first prism sheet 16, the light is also diffusely reflected by the light reflection sheet 2.

[0058] Next, comparative experiment 2 is described. Comparative experiment 2 extracts the ratio of side lobe light from the light distribution obtained using each backlight device of Example 1 and Comparative Examples 1 to 4 described in Comparative Experiment 1. In Comparative Experiment 2, the brightness of the emitted light is measured in a state where the LED is turned on using each backlight device of Example 1 and Comparative Examples 1 to 4. On the basis of obtaining the light distribution in the Y-axis direction, the relative brightness (unit is "%) at each angle of +50°, +60°, +70°, and +80° in the light distribution in the Y-axis direction is extracted. The relative brightness at each angle of +50°, +60°, +70°, and +80° is based on the peak brightness at the peak angle (100%). Here, the significance of extracting the relative brightness at each angle of +50°, +60°, +70°, and +80° is to provide an index related to whether the "reflection" caused by the side lobe light (light emitted in the range of +50° to +80°) is easy to be visually recognized. That is, in order to make “reflection” difficult to be visually recognized, the relative brightness at each of the angles of +50°, +60°, +70°, and +80° is preferably 3% or less.

[0059] Compare the experimental results of Experiment 2 Fig. 9 As shown in the table. Fig. 9 In the table, information related to the configuration of Example 1 and Comparative Examples 1 to 4 (peak angle, backlight type, presence or absence of louvers, presence or absence of first prism 16, presence or absence of light absorbing sheet 17, presence or absence of light reflecting sheet 2) and relative brightness at angles of +50°, +60°, +70°, and +80° as experimental results are shown. The peak angle of Example 1 is "+6°", that of Comparative Examples 1, 2, and 4 is "+3°", and that of Comparative Example 3 is "+8°". The backlight type is the type of the backlight device, which is either type A or type B mentioned above. Only Comparative Example 1 has louvers. Example 1 and Comparative Example 4 have first prism 16. Only Example 1 has light absorbing sheet 17. Comparative Examples 1 to 4 have light reflecting sheet 2.

[0060] The experimental results of comparative experiment 2 are described below. Fig. 9 , the relative brightness of Comparative Examples 2 to 4 exceeds 3% at any angle of +50°, +60°, +70°, and +80°, so it can be said that the reflection caused by the side lobe light is easy to see. Among them, the relative brightness of Comparative Examples 2 and Comparative Examples 4 at each angle of +50°, +60°, and +70° exceeds 20%, which can be said to have a tendency to be particularly easy to visually identify the reflection. In Comparative Example 3, although the relative brightness at each angle exceeds 3% as a reference value, it is suppressed to below 5%, and the reflection is suppressed compared with Comparative Examples 2 and 4. The reason is that although Comparative Example 3 does not have the first prism sheet 16, it is type A, so it is speculated that the directivity of the emitted light becomes higher. In addition, although Comparative Example 4 has the first prism sheet 16, the side lobe light is generated the most. It is speculated that the reason is that in the backlight device of type B, since a large amount of diffuse reflected light is generated, it is difficult to limit the range of the light emission angle even if the first prism sheet 16 is used in combination. On the other hand, it can be said that in Example 1 and Comparative Example 1, at any angle of +50°, +60°, +70°, and +80°, the relative brightness is less than 3%, and the reflection caused by the side lobe light is difficult to be fully seen. Comparative Example 1 can suppress the side lobe light the most. The reason is speculated to be that the blinds well limit the range of the light emission angle. In contrast, although Example 1 does not use blinds, the side lobe light is suppressed to a level close to that of Comparative Example 1. It is speculated that the reason is that by using the first prism sheet 16 and the light absorbing sheet 17 in the backlight device of type A, it is possible to limit the range of the light emission angle while suppressing the generation of diffuse reflected light. In this way, Example 1 can fully suppress the reflection caused by the side lobe light at a low cost without using blinds.

[0061] As described above, the backlight device (illumination device) 12 of the present embodiment includes: an LED (light source) 13; a light guide plate 15, wherein at least a portion of its outer peripheral end surface is opposite to the LED 13 and is a light incident end surface (first end surface) 15A into which light is incident, one main surface of which is set as a first main surface 15B, and the other main surface of which is set as a second main surface 15C; and a first prism sheet 16, wherein one main surface of which is set as a third main surface 16A1 arranged toward the second main surface 15C, and the other main surface of which is set as a fourth main surface 16A2, and an inclined first inclined surface 2 is provided on the second main surface 15C of the light guide plate 15. 2A, the inclined first inclined surface 22A rises from the opposite side of LED 13 toward the LED 13 side in a first direction including a direction from LED 13 toward the light guide plate 15, and a plurality of first prisms 16B extending along the first direction and arranged along the second direction are provided on the fourth main surface 16A2 of the first prism sheet 16, the second direction intersecting with the first direction and along the fourth main surface 16A2, the first prism 16B has a first base 16B1 parallel to the second direction and a pair of first oblique sides 16B2 and 16B3 rising from both ends of the 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 in the light guide plate 15. When the light propagating in the light guide plate 15 reaches the first inclined surface 22A on the second main surface 15C, more light is reflected on the first inclined surface 22A, and the remaining light is refracted and emitted from the first inclined surface 22A, which has an inclination rising from the opposite side of the LED 13 to the LED 13 side in the first direction. The light reflected by the first inclined surface 22A is directed toward the first main surface 15B, and is reflected again by the first main surface 15B or emitted. The light emitted from the first inclined surface 22A is directed toward the first prism sheet 16. The light directed toward the first prism sheet 16 is reflected by the third main surface 16A1 of the first prism sheet 16 or is incident on the first prism sheet 16. When the light reflected by the third principal surface 16A1 of the first prism sheet 16 is incident on the second principal surface 15C of the light guide plate 15, it is directly emitted from the first principal surface 15B, or it is emitted from the first principal surface 15B after propagating in the light guide plate 15. The light incident on the first prism sheet 16 is reflected at the first base 16B1 of the first prism 16B, or it is reflected by a pair of first oblique edges 16B2 and 16B3 in the first prism 16B, thereby being emitted from the first prism sheet 16 toward the second principal surface 15C of the light guide plate 15. When the light emitted from the first prism sheet 16 to the light guide plate 15 side is incident on the second principal surface 15C of the light guide plate 15, it is directly emitted from the first principal surface 15B, or it is emitted from the first principal surface 15B after propagating in the light guide plate 15.

[0063] In addition, the light refracted by the first inclined surface 22A reaches the second main surface 15C during the propagation in the light guide plate 15, and is refracted at an angle corresponding to the refractive index of the light guide plate 15 and the inclination angle of the first inclined surface 22A relative to the first direction. That is, the outgoing light from the second main surface 15C of the light guide plate 15 contains almost no diffuse light. Therefore, the light reflected by the third main surface 16A1 of the first prism sheet 16, the light reflected by the first bottom edge 16B1 of the first prism 16B, and the light reflected by the pair of first inclined edges 16B2 and 16B3 of the first prism 16B also contain almost no diffuse light, so it is difficult for the outgoing light of the backlight device 12 to contain side lobe light emitted at an angle close to the first direction. As a result, the outgoing angle of light can be limited without using a shutter as in the past, and the side lobe light can be reduced.

[0064] In addition, a light absorbing sheet 17 is provided, one of the main surfaces of which is a light absorbing main surface (fifth main surface) 17A arranged toward the fourth main surface 16A2, and has a higher light absorptivity than either the light guide plate 15 or the first prism sheet 16. The light emitted from the fourth main surface 16A2 of the first prism sheet 16 is directed toward the light absorbing sheet 17. The light absorbing sheet 17 has a higher light absorptivity than either the light guide plate 15 or the first prism sheet 16, so that the light emitted from the fourth main surface 16A2 can be effectively absorbed at the light absorbing main surface 17A. Here, the light emitted from the fourth main surface 16A2 of the first prism sheet 16 mostly has a characteristic close to diffuse light, so by absorbing the light with the light absorbing sheet 17, the emission angle of the emitted light of the backlight device 12 can be more effectively limited, and the side lobe light can be further reduced. In addition, the amount of light emitted from the fourth principal surface 16A2 of the first prism sheet 16 is small, and therefore, even if it is absorbed by the light absorbing sheet 17 , the influence on the brightness of the light emitted from the backlight device 12 is very slight.

[0065] In addition, it comprises: a second prism sheet 18, one principal surface of which is a second light emitting principal surface (seventh principal surface) 18A1, and the other principal surface of which is a second light incident principal surface (eighth principal surface) 18A2 arranged toward the first principal surface 15B; and a third prism sheet 19, one principal surface of which is a third light emitting principal surface (ninth principal surface) 19A1, and the other principal surface of which is a third light incident principal surface (tenth principal surface) 19A2 arranged toward the second light emitting principal surface 18A1, a plurality of second prisms 18B extending along the second direction and arranged along the first direction are arranged on the second light emitting principal surface 18A1 of the second prism sheet 18, and a plurality of third prisms 19B extending along the second direction and arranged along the first direction are arranged on the third light emitting principal surface 19A1 of the third prism sheet 19. When the light emitted from the first principal surface 15B of the light guide plate 15 is incident on the second light incident principal surface 18A2 of the second prism sheet 18, the multiple second prisms 18B extending along the second direction in the second light emitting principal surface 18A1 selectively apply a focusing effect on the first direction, and the light is emitted from the second light emitting principal surface 18A1. When the light emitted from the second light emitting principal surface 18A1 of the second prism sheet 18 is incident on the third light incident principal surface 19A2 of the third prism sheet 19, the multiple third prisms 19B extending along the second direction in the third light emitting principal surface 19A1 selectively apply a focusing effect on the first direction, and the light is emitted from the third light emitting principal 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 limited, and the side lobe light can be further reduced.

[0066] In addition, the second prism 18B has a second base 18B1 arranged in the first direction, and a pair of second oblique sides 18B2 and 18B3 rising from both ends of the second base 18B1, and the second oblique side 18B2 on the LED 13 side in the first direction, i.e., the second LED side oblique side 18B2, of the pair of second oblique sides 18B2 and 18B3, forms a larger angle with the second base 18B1 than the second oblique side on the opposite side to the LED 13 side in the first direction, i.e., the second LED opposite side oblique side 18B3. Thus, among the pair of second oblique sides 18B2 and 18B3 in the second prism 18B, it is more difficult for light incident on the second light incident principal surface 18A2 of the second prism sheet 18 to be irradiated on the second oblique side 18B2 on the LED 13 side in the first direction than on the second oblique side 18B3 on the opposite side to the LED 13 side in the first direction. Here, if the incident light of the second prism sheet 18 is irradiated to the second hypotenuse on the LED 13 side, that is, the second LED side hypotenuse 18B2, there is a tendency that the light will not rise when it exits the second prism 18B and will easily become the side lobe light. Therefore, if the incident light of the second prism sheet 18 is difficult to directly contact the second hypotenuse on the LED 13 side, that is, the second LED side hypotenuse 18B2, the generation of side lobe light can be suppressed. In addition, most of the incident light of the second prism sheet 18 is refracted and emitted by the second hypotenuse on the opposite side of the LED 13 side, that is, the second LED opposite side hypotenuse 18B3, and is incident on the third prism sheet 19, and is easily effectively utilized.

[0067] In addition, the third prism 19B has a third base 19B1 arranged in the first direction and a pair of third oblique sides 19B2 and 19B3 rising from both ends of the third base 19B1, and the angles formed by the pair of third oblique sides 19B2 and 19B3 and the third base 19B1 are equal. Among the light incident on the third light incident principal surface 19A2 of the third prism sheet 19, the light irradiated on the third oblique side 19B3 on the opposite side of the LED 13 side in the first direction, that is, the third LED opposite side oblique side 19B3, is refracted and emitted there, or is reflected there and directed toward the third oblique side on the LED 13 side, that is, the third LED side oblique side 19B2. Here, the angles formed by the pair of third oblique sides 19B2 and 19B3 and the third bottom side 19B1 are equal, so when the light reflected by the third oblique side on the opposite side of the LED 13 side, that is, the third LED opposite side oblique side 19B3, is irradiated to the third oblique side on the LED 13 side, that is, the third LED side oblique side 19B2, it is easy to be reflected there and return to the second prism sheet 18 side. The light (returning light) returned to the second prism sheet 18 side reaches the third prism sheet 19 again by reflection in the backlight device 12, etc., and is raised and emitted by any one of the pair of third oblique sides 19B2 and 19B3 in the third prism 19B. As a result, the utilization efficiency of light can be improved.

[0068] In addition, a plurality of first inclined surfaces 22A are arranged side by side along the first direction, and the plurality of first inclined surfaces 22A are configured to have a larger area as they are farther away from the LED 13. Most of the light reaching the second main surface 15C during propagation in the light guide plate 15 is reflected by the first inclined surface 22A. The plurality of first inclined surfaces 22A arranged along the first direction are configured to have a larger area as they are farther away from the LED 13, so the more light is reflected by the first inclined surface 22A as it is farther away from the LED 13. As a result, the amount of light emitted from the first main surface 15B of the light guide plate 15 is uniformed in the first direction, which is preferable in terms of suppressing uneven brightness.

[0069] In addition, the liquid crystal display device (display device) 10 of the present embodiment includes: the backlight device 12 described above; and a liquid crystal panel (display panel) 11 that performs display using light from the backlight device 12. According to the liquid crystal display device 10 having such a structure, the light emission angle can be limited without using a conventional blind, so that a display with excellent display quality can be achieved.

[0070] <Second Embodiment> pass Figures 10 to 13 The second embodiment will be described. In the second embodiment, a case where a light reflecting sheet 23 is used instead of the light absorbing sheet 17 is exemplified. In addition, regarding the same structure, operation, and effect as those of the first embodiment, repeated description will be omitted.

[0071] like Fig.10 As shown, the backlight device 112 of this embodiment includes a light reflecting sheet 23 instead of the light absorbing sheet 17 described in the first embodiment (see Figure 2 as well as Figure 3 ). The light reflecting sheet 23 is configured to overlap with the first prism sheet 116 on the back side (the opposite side of the light guide plate 115 side). The light reflecting sheet 23 is configured in a form in which its main surface is parallel to the main surfaces 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 overlapped with the fourth main surface 116A2 of the first prism sheet 116 over the entire area. The light reflecting sheet 23 is made of, for example, PET having a white surface, and has a higher light reflectivity than either the light guide plate 115 or the first prism sheet 116. The main surface on the front side of the pair of main surfaces of the light reflecting sheet 23 is set to be arranged toward the fourth main surface 116A2 of the first prism sheet 116 to become the light reflecting main surface (sixth main surface) 23A that reflects light.

[0072] According to such a configuration, the light emitted from the fourth main surface 116A2 of the first prism sheet 116 toward the back side is effectively reflected by the light reflecting main surface 23A toward the light reflecting sheet 23. Although the amount of light emitted from the fourth main surface 116A2 of the first prism sheet 116 is small, by reflecting the light using the light reflecting sheet 23, the brightness of the light emitted from the backlight device 112 can be improved.

[0073] Next, the following comparative experiments 3 to 5 are carried out. First, comparative experiment 3 is described. In comparative experiment 3, the light distribution of the outgoing light of the backlight device of Example 2 is obtained. Example 2 is a backlight device 112 having the same structure as that described previously in this paragraph. That is, Example 2 is a type A backlight device, which differs 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, as in comparative experiment 1, the backlight device of Example 2 is used to measure the brightness of the outgoing light with the LED turned on, and a graph of the light distribution (brightness angle distribution) in the Y-axis direction is prepared. The experimental results of the light distribution in comparative experiment 3 are shown as follows. Fig.11 shown. Fig.11 The light distribution curve is shown in Figure 2. Figure 8 Same. Fig.11 In addition to the graph of Example 2, for reference, the experimental results of Comparative Experiment 1, that is, the graphs of Example 1 and Comparative Example 3, are also recorded. Fig.11 In the figure, 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 double dashed line.

[0074] The experimental results of comparative experiment 3 are described below. Fig.11 , the angle of peak brightness, i.e., the peak angle, of the light distribution of Example 2 is "+9°", and the half-value width is slightly wider than the half-value width of the light distribution of Example 1, and is equal to the half-value width of Comparative Example 3. The reason why the half-value width of the light distribution of Example 2 is slightly wider than the half-value width of the light distribution of Example 1 is presumably because the light is diffusely reflected by the light reflection sheet 23 of Example 2, thereby slightly widening the light emission angle range. The peak angle of the light distribution of Example 2 is larger than the peak angle of the light distribution of Example 1 (+6°) and the peak angle of the light distribution of Comparative Example 3 (+8°). In the light distribution of Example 2, the side lobe light is fully suppressed to a level close to that of the light distribution of Example 1, and the side lobe light is light emitted within the range of "+50° to +80°".

[0075] Next, comparative experiment 4 is described. In comparative experiment 4, the ratio of side lobe light is 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 is used to measure the brightness of the emitted light while the LED is turned on, and the light distribution in the Y-axis direction is obtained. On this basis, the relative brightness (unit is "%) at each angle of +50°, +60°, +70°, and +80° in the light distribution in the Y-axis direction is extracted. As described in comparative experiment 2, in order to make it difficult to visually recognize the "reflection", it is preferred that the relative brightness at each angle of +50°, +60°, +70°, and +80° is less than 3%.

[0076] Comparison of the experimental results of Experiment 4 Fig.12 As shown in the table. Fig.12 In the table, in addition to the experimental results of Example 2, the experimental results of Comparative Experiment 2, i.e., the experimental results of Example 1 and Comparative Example 3, are also recorded as reference. Fig.12 In the table, Fig. 9 Similarly, the table illustrates information related to the structure of Examples 1, 2 and Comparative Example 3 (peak angle, backlight type, presence or absence of blinds, presence or absence of first prism sheet 16, presence or absence of light absorption sheet 17, presence or absence of light reflection sheet 2) and the relative brightness at each angle of +50°, +60°, +70°, and +80° as experimental results.

[0077] The experimental results of Comparative Experiment 4 are described below. Fig.12 Although Example 2 exceeds 3% as the reference value at +60° and +70°, it is suppressed to less than 3% at +50° and +80°. That is, compared with Example 1 where Example 2 is less than 3% at all angles, the reflection is easy to visually recognize, but compared with Comparative Example 3 where it exceeds 3% at all angles, the reflection is suppressed. The reason for this result is speculated to be that Example 2 is common to Example 1 in the point of being a backlight device of type A and the point of having the first prism sheet 116, so even if light is diffusely reflected by the light reflecting sheet 23, the light emission angle range can be limited to a certain extent. In this way, Example 2 can achieve low cost without using blinds, and on the basis of obtaining the brightness improvement effect of the light reflecting sheet 23, the reflection caused by the side lobe light can be suppressed to a certain extent.

[0078] Next, comparative experiment 5 is described. In comparative experiment 5, based on the light distribution of the outgoing light of each backlight device of Examples 1 and 2 obtained in the same manner as in the above-mentioned comparative experiment 3, the vertical axis in the light distribution curve graph is set to "brightness" of the absolute value. In comparative experiment 5, as in comparative experiment 1, each backlight device of Examples 1 and 2 is used to measure the brightness of the outgoing light with the LED lit, and a curve graph of the light distribution in the Y-axis direction is prepared. The experimental results of the light distribution in comparative experiment 5 are as follows. Fig.13 shown. Fig.13 In the light distribution curve shown in the figure, the horizontal axis is the angle of the Y-axis direction relative to the front direction (Z-axis direction) (unit: "°"), and the vertical axis is the brightness (unit: "cd / m 2 ").exist Fig.13 In the figure, the curve graph of Example 2 is shown by a solid line, and the curve graph of Example 1 is shown by a dashed line.

[0079] The experimental results of Comparative Experiment 5 are described below. Fig.13 The peak brightness of the light distribution of Example 1 is slightly lower than 2000 cd / m 2 In contrast, the peak brightness of the light distribution of Example 2 is 2300 cd / m 2 That is, the peak brightness of the light distribution of Example 2 is higher than that of Example 1. The reason is presumably that, in Example 1, the light absorbing sheet 17 absorbs the light emitted from the first prism sheet 16 to the back side and is not used as the emitted light, while in Example 2, the light reflecting sheet 23 reflects the light emitted from the first prism sheet 16 to the back side and is used as the emitted light. Thus, according to Example 2, the effect of improving the peak brightness of the emitted light can be obtained.

[0080] As described above, according to the present embodiment, the light reflecting sheet 23 is provided, one of the main surfaces of which is the light reflecting main surface (sixth main surface) 23A arranged toward the fourth main surface 116A2, and has a higher light reflectivity than either the light guide plate 115 or the first prism sheet 116. The light emitted from the fourth main surface 116A2 of the first prism sheet 116 is directed toward the light reflecting sheet 23. The light reflecting sheet 23 has a higher light reflectivity than either the light guide plate 115 or the first prism sheet 116, and therefore, the light emitted from the fourth main surface 116A2 can be effectively reflected at 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 using the light reflecting sheet 23, the brightness of the light emitted from the backlight device 112 can be improved.

[0081] <Third Embodiment> In addition, through Figures 14 to 16A third embodiment will be described. In the third embodiment, an example is given in which the configuration of the light guide plate 215 is changed. In addition, regarding the same structure, operation, and effect as those of the first embodiment, repeated description will be omitted.

[0082] In the backlight device 212 of this embodiment, Fig.14 As shown, the material and refractive index of the light guide plate 215 are changed compared with the first embodiment. The light guide plate 215 of this embodiment has a refractive index lower than that of the light guide plate 15 described in the first embodiment (see Figure 2 as well as Figure 3 ) high. Specifically, in the present embodiment, the light guide plate 215 uses, for example, PC (polycarbonate) as a synthetic resin material, and its refractive index is, for example, about 1.52. In this way, the angle assigned when light is incident on the light guide plate 215 or when light is emitted from the light guide plate 215 is different from that in the first embodiment. In addition, the critical angle of the light guide plate 215 is also different from that in the first embodiment. Therefore, in the present embodiment, the angle (peak angle) at which the peak brightness is achieved in the light distribution of the emitted light from the backlight device 212 is "+4°".

[0083] Next, comparative experiments 6 and 7, which are the same as comparative experiments 1 and 2 described in the first embodiment, are performed. In comparative experiment 6, the following light distribution of the outgoing light of the backlight device of Example 3 is obtained. Example 3 is a backlight device 212 having the same structure as that described previously in 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, as in comparative experiment 1, the backlight device of Example 3 is used to measure the brightness of the outgoing light with the LED turned on, and a graph of the light distribution (brightness angle distribution) in the Y-axis direction is prepared. The experimental results of the light distribution in comparative experiment 6 are shown as follows. Fig.15 shown. Fig.15 The light distribution curve shown is Figure 8 Same. 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 recorded as references. Fig.15 In the figure, 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 dotted line.

[0084] The experimental results of Comparative Experiment 6 are described below. Fig.15In the light distribution of Example 3, the angle at which the peak brightness is reached, i.e., the peak angle, is "+4°", and the half-value width is slightly wider than the half-value width of the light distribution of Example 1. The reason why the half-value width of the light distribution of Example 3 is slightly wider than the half-value width of the light distribution of Example 1 is presumably because the refractive index of the light guide plate 215 of Example 3 is higher than the refractive index of the light guide plate 15 of Example 1, so that the light emission angle range is slightly widened. Although 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, it is smaller than the peak angle (+6°) of the light distribution of Example 1. In the light distribution of Example 3, the light emitted within the range of "+50° to +80°", i.e., the side lobe light, is suppressed sufficiently low to approach the level of the light distribution of Example 1.

[0085] Next, comparative experiment 7 is described. In comparative experiment 7, the ratio of side lobe light is extracted from the light distribution obtained by using the backlight device of Example 3 described in comparative experiment 6. In comparative experiment 7, similarly to comparative experiments 2 and 4, the brightness of the emitted light is measured with the LED lit using the backlight device of Example 3 to obtain the light distribution in the Y-axis direction. On this basis, the relative brightness (unit is "%) at each angle of +50°, +60°, +70°, and +80° in the light distribution in the Y-axis direction is extracted. As described in comparative experiment 2, in order to make it difficult to visually recognize "reflection", it is preferred that the relative brightness at each angle of +50°, +60°, +70°, and +80° is less than 3%.

[0086] Compare the experimental results of Experiment 7 Fig.16 As shown in the table. Fig.16 In the table, in addition to the experimental results of Example 5, the experimental results of Comparative Experiments 2 and 4, that is, the experimental results of Examples 1 and 2 and Comparative Example 1, are also recorded as reference. Fig.16 In the table, Fig. 9 Similarly, the table shows information related to the structure of Examples 1 to 3 and Comparative Example 1 (peak angle, backlight type, presence or absence of blinds, 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 relative brightness at each angle of +50°, +60°, +70°, and +80° as experimental results.

[0087] The experimental results of Comparative Experiment 7 are described below. Fig.16In Example 3, the relative brightness is suppressed to less than 3% at any angle of +50°, +60°, +70°, and +80°. In detail, in Example 3, the side lobe light is slightly more than that in Example 1 at all angles, but the side lobe light is suppressed compared with Example 2. The peak angle of the light distribution of Example 3 is closer to the value of the peak angle of the light distribution of Comparative Example 1 than Examples 1 and 2. In this way, in Example 3, the peak angle of the light distribution is close to that of Comparative Example 1, and the side lobe light is suppressed to a degree close to that of Example 1.

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

[0089] (1) In the third embodiment, the case where the material and refractive index of the light guide plate 215 are changed from the first embodiment is shown, but in addition to this, the peak angle of the light distribution of the outgoing light can be adjusted by changing, for example, the material and refractive index of the second prism sheet 18 from the first embodiment, or by changing the inclination angles θ1 and θ2 formed by each of the second oblique sides 18B2 and 18B3 and the second base 18B1, and the angle θ3 formed by a pair of second oblique sides 18B2 and 18B3 from the first embodiment. In addition, in the configurations described in the various embodiments, the specific value of the peak angle (θvp) of the light distribution of the outgoing light can be appropriately changed in addition to the above.

[0090] (2) In the first prism sheets 16 and 116 , specific values ​​of the inclination angles θ10 and θ11 formed between the first oblique sides 16B2 and 16B3 and the first base 16B1 and the angle θ12 formed between the pair of first oblique sides 16B2 and 16B3 may be changed as appropriate.

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

[0092] (4) In the third prism sheet 19, specific values ​​of the inclination angles θ4 and θ5 formed between the third oblique sides 19B2 and 19B3 and the third base 19B1 and the angle θ6 formed between the pair of third oblique sides 19B2 and 19B3 may be changed as appropriate.

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

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

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

[0096] (8) The number of LEDs 13 and 113 to be installed, the arrangement interval of the first light guide plate lenses 20, the contact angle of the first light guide plate lenses 20, and the vertex angle of the second light guide plate lenses 21 may be changed as appropriate.

[0097] (9) The materials and refractive indexes of the first prism sheets 16 and 116 , the second prism sheets 18 , and the third prism sheets 19 may be changed as appropriate in addition to those described above.

[0098] (10) The material and refractive index of the light guide plates 15, 115, and 215 may be changed as appropriate in addition to those described above.

[0099] (11) The specific cross-sectional shape of the first light guide plate lens 20 may be changed appropriately. For example, the cross-sectional shape of the first light guide plate lens 20 may be a triangle.

[0100] (12) The specific cross-sectional shape of the second light guide plate lens 21 may be changed as appropriate. For example, the cross-sectional shape of the second light guide plate lens 21 may be a semicircular shape (cylindrical lens) or the like.

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

[0102] (14) Besides the structure in which the thickness of the light guide plate 15 , 115 , or 215 is constant over the entire length, the thickness of the light guide plate 15 , 115 , or 215 may be reduced as the distance from the LED 13 increases, and the opposite main surfaces may be inclined.

[0103] (15) The planar shape of the light guide plate 15, 115, 215 may be a trapezoid, an inverted trapezoid, an arc, a semicircle, a semi-ellipse, a trapezoid with an arc-shaped upper base, etc. In addition to a square, the planar shape of the light guide plate 15, 115, 215 may be a trapezoid, an inverted trapezoid, an arc, 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 may also be changed.

[0104] (16) LED 13 may be a top-emitting type in addition to a side-emitting type.

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

[0106] (18) A reflective polarizer may be installed on the main surface of the back side (outer side) of the array substrate constituting the liquid crystal panel 11 instead of the polarizer. The reflective polarizer includes: a polarizing layer having a specific polarization axis (transmission axis), a multilayer film formed by alternately stacking layers with different refractive indices, a protective layer, etc. The polarizing layer has a polarization axis and an absorption axis orthogonal to the polarization axis, thereby selectively transmitting linear polarized light parallel to the polarization axis and converting circularly polarized light into linear polarized light along the polarization axis. The polarization axis of the polarizing layer is orthogonal to the polarization axis of the polarizing plate installed on the main surface of the outer side of the CF substrate. The multilayer film is a multilayer structure and has a reflective characteristic in which the reflectivity of the s-wave contained in the light is substantially higher than the reflectivity of the p-wave. By having a multilayer film, the reflective polarizer can reuse the s-wave absorbed by the polarizing layer by reflecting it to the back side, thereby improving the utilization efficiency (and thus brightness) of light.

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

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

[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 principal surface, 15C…Second principal surface, 16, 116…First prism sheet, 16A1…Third principal surface, 16A2, 116A2…Fourth principal surface, 16B…First prism, 16B1…First base, 16B2, 16B3…First hypotenuse, 17…Light absorbing sheet, 17A…Light absorbing Main surface (fifth main surface), 18…second prism sheet, 18A1…second light-emitting main surface (seventh main surface), 18A2…second light-entering main surface (eighth main surface), 18B…second prism, 18B1…second base, 18B2, 18B3…second hypotenuse, 19…third prism sheet, 19A1…third light-emitting main surface (ninth main surface), 19A2…third light-entering main surface (tenth main surface), 19B…third prism, 19B1…third base, 19B2, 19B3…third hypotenuse, 22A…first oblique surface, 23…light reflecting sheet, 23A…light reflecting main surface (sixth main surface).

Claims

1. A lighting device, characterized in that: It has: light source; A light guide plate, at least a portion of its outer peripheral end surface is opposite to the light source and is a first end surface for incident light, one main surface is a first main surface, and the other main surface is a second main surface; as well as The first prism sheet has one principal surface which is a third principal surface arranged toward the second principal surface, and the other principal surface which is a fourth principal surface. The second main surface of the light guide plate is provided with an inclined first slope, the first slope rising from the opposite side of the light source to the light source side in a first direction including a direction from the light source toward the light guide plate, A plurality of first prisms are disposed on the fourth principal surface of the first prism sheet, the plurality of first prisms extend along the first direction and are arranged in a second direction intersecting the first direction and along the fourth principal surface, The first prism comprises: a first base parallel to the second direction; and a pair of first oblique sides rising from both ends of the first bottom side.

2. The lighting device according to claim 1, characterized in that: The lighting device includes a light absorbing sheet having one main surface which is a fifth main surface arranged toward the fourth main surface and having a higher light absorptivity than either the light guide plate or the first prism sheet.

3. The lighting device according to claim 1, characterized in that: The lighting device includes a light reflecting sheet having one main surface which is a sixth main surface arranged toward the fourth main surface and having higher light reflectivity than either the light guide plate or the first prism sheet.

4. The lighting device according to any one of claims 1 to 3, characterized in that: The lighting device comprises: a second prism sheet, one of the principal surfaces of which is the seventh principal surface, and the other principal surface of which is the eighth principal surface disposed toward the first principal surface; and The third prism sheet has one principal surface which is the ninth principal surface and the other principal surface which is the tenth principal surface arranged toward the seventh principal surface. A plurality of second prisms are disposed on the seventh principal surface of the second prism sheet, and the plurality of second prisms extend along the second direction and are arranged in an array along the first direction. A plurality of third prisms are disposed on the ninth principal surface of the third prism sheet, and the plurality of third prisms extend along the second direction and are arranged in an array along the first direction.

5. The lighting device according to claim 4, characterized in that: The second prism includes: a second base parallel to the first direction; and a pair of second oblique sides rising from both ends of the second base, 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 the second base side than the second oblique side on the opposite side to the light source side in the first direction.

6. The lighting device according to claim 4, characterized in that: The third prism includes: a third base parallel to the first direction; and a pair of third hypotenuses rising from both ends of the third base, An angle formed between a pair of the third oblique sides and the third base is equal.

7. The lighting device according to any one of claims 1 to 3, characterized in that: A plurality of the first inclined surfaces are arranged along the first direction, and the first inclined surfaces are configured such that the farther away from the light source, the larger the area.

8. A display device, characterized in that: It includes: The lighting device according to any one of claims 1 to 3; as well as A display panel that performs display using the light from the lighting device.

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