Lighting and display devices

Abstract

To allow luminance uniformity to be improved.SOLUTION: An illuminating device IL comprises: a light guide plate LG comprising a first side surface, a second side surface opposed to the first side surface, a principal surface 1A, and an opposed surface 1B opposed to the principal surface; a light source opposed to the first side surface; a reflection layer; and first and second prisms PM1 and PM2 provided on the opposed surface. The light guide plate becomes thicker as going toward the second side surface. The opposed surface comprises a first inclined surface SLP1, a second inclined surface SLP2, a third inclined surface SLP3, a fourth inclined surface SLP4, a first flat surface PLN1, and a second flat surface PLN2. Cross-sectional shapes of the first and second prisms are formed in triangular shapes. The first prism is arranged on the first flat surface. The second prism is arranged on the second flat surface. A first height of the first prism is smaller than a second height of the second prism. The sum of the first height, a third height of the first inclined surface, and a fourth height of the second inclined surface is larger than the sum of the second height, a fifth height of the third inclined surface, and a sixth height of the fourth inclined surface.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] FIELD OF THE INVENTION The present invention relates to a lighting device and a display device. [Background technology]

[0002] For example, a display device such as a liquid crystal display device includes a display panel having pixels and an illumination device such as a backlight that illuminates the display panel. The illumination device includes a light source that emits light and a light guide plate onto which the light from the light source is irradiated. The light from the light source enters the light guide plate from a side surface of the light guide plate, propagates through the light guide plate, and exits from an exit surface corresponding to one of the main surfaces of the light guide plate. For example, a configuration including a single light guide plate with a reflective layer provided on the side opposite the light source is also known. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-26905 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present embodiment is to provide a lighting device and a display device. [Means for solving the problem]

[0005] An illumination device according to one embodiment includes a light guide plate having a first side surface, a second side surface facing the first side surface in a first direction, a main surface, and an opposing surface facing the main surface in a second direction intersecting the first direction; a light source facing the first side surface and emitting light toward the first side surface; a reflective layer provided on the second side surface; a first prism provided on the opposing surface; and a second prism provided on the opposing surface closer to the second side surface in the first direction than the first prism, wherein the thickness of the light guide plate in the second direction increases from the first side surface to the second side surface in the first direction, and the opposing surface has a first inclined surface, a second inclined surface located closer to the second side surface in the first direction than the first inclined surface, and a third inclined surface located closer to the second side surface in the first direction than the second inclined surface. a fourth slope located closer to the second side surface than the third slope, a first plane connecting the first slope and the second slope and parallel to the main surface, and a second plane connecting the third slope and the fourth slope and parallel to the main surface, the cross-sectional shapes of the first prism and the second prism are formed in a triangular shape protruding to the side opposite the opposing surface in the second direction, the first prism is disposed on the first plane, the second prism is disposed on the second plane, a first height of the first prism in the second direction is smaller than a second height of the second prism in the second direction, and a sum of the first height, a third height of the first slope in the second direction, and a fourth height of the second slope in the second direction is greater than a sum of the second height, a fifth height of the third slope in the second direction, and a sixth height of the fourth slope in the second direction.

[0006] An illumination device according to another embodiment includes a light guide plate having a first side surface, a second side surface facing the first side surface in a first direction, a main surface, and an opposing surface facing the main surface in a second direction intersecting the first direction and parallel to the main surface; a light source facing the first side surface and emitting light to the first side surface; a reflective layer provided on the second side surface; a first prism group provided on the opposing surface; and a second prism group provided on the opposing surface closer to the second side surface in the first direction than the first prism group, wherein the first prism group includes a first prism, a second prism located closer to the second side surface than the first prism in the first direction, and a second prism located closer to the second side surface than the first prism in the first direction. the second prism group has a fourth prism, a fifth prism located closer to the second side surface than the fourth prism in the first direction, and a sixth prism located closer to the second side surface than the fifth prism in the first direction, and a first height of the second prism in the second direction is smaller than a second height of the fifth prism in the second direction, and a sum of the first height, a third height of the first prism in the second direction, and a fourth height of the third prism in the second direction is greater than a sum of the second height, a fifth height of the fourth prism in the second direction, and a sixth height of the sixth prism in the second direction.

[0007] and a reflective layer provided on the second side, wherein a first length of the first side in the third direction is smaller than a second length of the second side in the third direction, the second light source is disposed between the first light source and the third light source, and a first light intensity ratio of the first light source to the third light source is larger than a second light intensity ratio of the second light source. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is an exploded perspective view showing an example of the configuration of a display device according to a first embodiment. [Figure 2] FIG. 2 is a plan view of the lighting device shown in FIG. [Figure 3] FIG. 3 is a cross-sectional view of the display device shown in FIG. [Figure 4] FIG. 4 is a cross-sectional view showing an example of the arrangement of prisms according to the first embodiment. [Figure 5] FIG. 5 is a schematic diagram showing an example of a change in the effective height of a prism relative to the position of the light guide plate according to the first embodiment. [Figure 6] FIG. 6 is a cross-sectional view showing an example of the arrangement of prisms according to the first modification. [Figure 7] FIG. 7 is a cross-sectional view showing an example of the arrangement of prisms according to the second modification. [Figure 8] FIG. 8 is a cross-sectional view of the display device according to the second embodiment. [Figure 9] FIG. 9 is a cross-sectional view showing an example of the arrangement of a group of prisms according to the second embodiment. [Figure 10]FIG. 10 is a plan view of the lighting device according to the third embodiment. [Figure 11] FIG. 11 is a plan view of an illumination device according to the third modification. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments will be described with reference to the drawings. The disclosure is merely an example, and appropriate modifications that a person skilled in the art can easily make while maintaining the gist of the invention are naturally included within the scope of the present invention. Furthermore, the drawings may be more schematic than the embodiments to clarify the description, but they are merely examples and do not limit the interpretation of the present invention. Furthermore, in this specification and each drawing, components that perform the same or similar functions as those described above with respect to the previous drawings are designated by the same reference numerals, and redundant detailed descriptions may be omitted.

[0010] In the embodiments, a transmissive liquid crystal display device is disclosed as an example of a display device DSP. Also, as an example of an illumination device, an illumination device used as a backlight for a transmissive liquid crystal display device is disclosed. The main configuration disclosed in the present embodiment can also be applied to a liquid crystal display device that has a reflective function that reflects external light and uses the reflected light for display in addition to a transmissive function, an electronic paper display device having an electrophoretic element, a display device that applies MEMS (Micro Electro Mechanical Systems), or a display device that applies electrochromism. The main configuration disclosed in the present embodiment can also be applied to an illumination device used for purposes other than backlighting.

[0011] (First embodiment) FIG. 1 is an exploded perspective view showing an example of the configuration of a display device DSP according to this embodiment. FIG. 1 shows direction X (third direction), direction Y (first direction), and direction Z (second direction). Directions X, Y, and Z are perpendicular to each other, but may intersect at an angle other than 90 degrees. Directions X and Y correspond to directions parallel to the main surfaces of the substrates constituting the liquid crystal display device (hereinafter sometimes simply referred to as a display device) DSP, and direction Z corresponds to the thickness direction of the display device DSP. In this specification, the direction from the first substrate SUB1 to the second substrate SUB2 is referred to as the "upper side" (or simply "up"), and the direction from the second substrate SUB2 to the first substrate SUB1 is referred to as the "lower side" (or simply "lower"). When referring to a "second layer above the first layer" and a "second layer below the first layer," the second layer may be in contact with the first layer or spaced apart from the first layer. The observation position for observing the display device DSP is at the tip of the arrow indicating direction Z, and viewing from this observation position toward the XY plane defined by directions X and Y is called planar viewing. The X-Z plane is defined by directions X and Z. The Y-Z plane is defined by directions Y and Z. Also, the "length of a specified substance, object, or region in directions X and Y" is sometimes called "width," and the "length of a specified substance, object, or region in direction Z" is sometimes called "thickness" or "height."

[0012] The display device DSP includes a display panel PNL, an illumination device IL, an IC chip 1, and a wiring board 2. The display device DSP has a display area (or active area) DA and a non-display area (or non-active area) NDA. The display area DA is an area where an image is displayed. The non-display area NDA is an area where no image is displayed, and is located outside the display area DA.

[0013] The display panel PNL comprises a first substrate SUB1 and a second substrate SUB2. The first substrate SUB1 and the second substrate SUB2 face each other. A display function layer (in this embodiment, a liquid crystal layer LC, which will be described later) is provided between the substrates SUB1 and SUB2. In the display panel PNL, a display area DA is located approximately in the center of the area where the first substrate SUB1 and the second substrate SUB2 face each other. The display panel PNL comprises, for example, a plurality of pixels PX arranged in a matrix in the display area DA.

[0014] The IC chip 1 and wiring board 2 mainly function as a signal source that supplies signals to the display panel PNL, although they may also read signals from the display panel PNL. The IC chip 1 and wiring board 2 are located in the non-display area NDA. In the example shown in FIG. 1, the IC chip 1 and wiring board 2 are mounted on a mounting portion MT of the first substrate SUB1 that extends outward from one substrate side edge (sometimes referred to as a substrate end) of the second substrate SUB2. The wiring board 2 is, for example, a bendable flexible printed circuit board. The IC chip 1 may be provided on the wiring board 2.

[0015] The illumination device IL faces the display panel PNL and illuminates the display panel PNL. The illumination device IL includes a light guide plate LG, a plurality of light sources LS, and a reflecting layer RF. The illumination device IL, the first substrate SUB1, and the second substrate SUB2 are arranged in the order shown toward the tip of the arrow in the direction Z.

[0016] The light guide plate LG is an insulating substrate such as a glass substrate or a plastic substrate. The light guide plate LG is formed of a substrate made of a material containing acrylic resin, for example, an acrylic substrate. The light guide plate LG is formed in a flat plate shape extending in the XY plane. The light guide plate LG has a main surface 1A facing the display panel PNL, a facing surface 1B located opposite the main surface 1A in the Z direction, a side surface SF1, and a side surface SF2 located opposite the side surface SF1 in the Y direction. The facing surface 1B faces the main surface 1A in the Z direction, and the main surface 1A is, for example, parallel to the XY plane. The facing surface 1B has, for example, a portion non-parallel to the XY plane. In other words, for example, the facing surface 1B has a portion non-parallel to the main surface 1A. Note that the main surface 1A and the facing surface 1B may be parallel to each other. The side surface SF1 corresponds to the end face of the light guide plate LG opposite the tip of the arrow in the Y direction. The side surface SF1 is sometimes referred to as a light incident surface. The side surface SF2 faces the side surface SF1 in the direction Y. The side surface SF2 corresponds to the end surface of the light guide plate LG at the tip side of the arrow in the direction Y. The side surface SF2 is sometimes referred to as the anti-light incident surface. The side surfaces SF1 and SF2 face each other in the direction Y. The side surfaces SF1 and SF2 are, for example, parallel to the XZ plane and parallel to each other. Note that the side surfaces SF1 and SF2 may be non-parallel to the XZ plane and non-parallel to each other.

[0017] The plurality of light sources LS are arranged at intervals in the direction X. In the example shown in FIG. 1, the plurality of light sources LS each face the side surface SF1. The plurality of light sources LS are also arranged along the side surface SF1 at intervals in the direction X. Note that the plurality of light sources LS may also be arranged continuously in the direction X along the side surface SF1.

[0018] The light source LS is, for example, a laser light source such as a semiconductor laser that emits polarized laser light. However, the light source LS may also be a non-polarized light source. Furthermore, the light source LS is not limited to one that emits laser light, and may also be, for example, a light emitting diode.

[0019] The plurality of light sources LS may each include a plurality of light-emitting elements that emit light of different colors. For example, the plurality of light sources LS each include three light-emitting elements that emit red, green, and blue light. Note that the plurality of light sources LS may each include light-emitting elements other than three light-emitting elements that emit red, green, and blue light. When the plurality of light sources LS includes three light-emitting elements that emit red, green, and blue light, the plurality of light sources LS can obtain light of a mixed color (e.g., white) of these colors.

[0020] The reflective layer RF is made of a material that reflects light. The reflective layer RF is provided at the end of the light guide plate LG opposite the light source LS in the direction Y. In the example shown in FIG. 1, the reflective layer RF is provided on the side surface SF2 of the light guide plate LG. For example, the reflective layer RF is applied to, bonded to, or adhered to the side surface SF2 of the light guide plate LG.

[0021] FIG. 2 is a plan view of the lighting device IL shown in FIG. 1. As shown in FIG. 2, the light guide plate LG has a first region A1, a second region A2, and a boundary BO between the first region A1 and the second region A2. The first region A1 has a length LN10 in the direction Y, and the second region A2 has a length LN20 in the direction Y. The lengths LN10 and LN20 are the same. When the lengths LN10 and LN20 are the same, the boundary BO corresponds to the center position of the width of the light guide plate LG in the direction Y. Note that the lengths LN10 and LN20 do not have to be the same. The terms "same," "identical," "equivalent," and "match" not only refer to the physical quantities, materials, or configurations (structures) of multiple target objects, spaces, regions, etc. being exactly the same, but also include slight differences that can be considered to be substantially the same. 2, side surface SF1 is located at the end of the first region A1 opposite to the tip of the arrow in direction Y, and side surface SF2 is located at the end of the second region A2 on the tip side of the arrow in direction Y. Boundary BO corresponds to the midpoint between side surface SF1 and side surface SF2.

[0022] The light source LS emits light in an emission direction DL toward the side surface SF1. The intensity of the light emitted by the light source LS is highest on the optical axis AX, and the emission direction DL is parallel to the optical axis AX. The light emitted from the light source LS in the emission direction DL and incident on the light guide plate LG from the light incident surface (side surface) SF1 (hereinafter sometimes referred to as outgoing light) travels in the emission direction DL. Hereinafter, the term "outgoing light" may also be used to mean "the chief ray of the outgoing light." A portion of the outgoing light is guided within the light guide plate LG and reflected by the reflective layer RF (or the anti-light incident surface SF2) in a reflection direction RD, which is the opposite direction to the emission direction DL. The light reflected by the reflective layer RF (or the anti-light incident surface SF2) (hereinafter sometimes referred to as returning light) travels in the reflection direction RD. Hereinafter, the term "returning light" may also be used to mean "the chief ray of the return light." The intensity of the return light is greatest on the optical axis AX, and the reflection direction RD is parallel to the optical axis AX. Note that the intensity of the return light does not have to be greatest on the optical axis AX, and the reflection direction RD does not have to be parallel to the optical axis AX.

[0023] Fig. 3 is a cross-sectional view of the display device DSP shown in Fig. 1. As shown in Fig. 3, the display panel PNL further includes a liquid crystal layer LC, a seal SE, a polarizing plate PL1, and a polarizing plate PL2.

[0024] The liquid crystal layer LC and the seal SE are located between the first substrate SUB1 and the second substrate SUB2. The seal SE bonds the first substrate SUB1 and the second substrate SUB2 together, and seals the liquid crystal layer LC between the first substrate SUB1 and the second substrate SUB2.

[0025] The polarizer PL1 is bonded to the lower surface of the first substrate SUB1. The polarizer PL2 is bonded to the upper surface of the second substrate SUB2. The polarization axis of the polarizer PL1 and the polarization axis of the polarizer PL2 are, for example, perpendicular to each other.

[0026] The illumination device IL further includes prisms PM (PM1, PM2, PM3, ...), a diffusion sheet DS, a prism sheet PS, and a reflection sheet RS. Note that a plurality of prism sheets PS, for example, two prism sheets PS, may be provided stacked in the direction Z.

[0027] The diffusion sheet DS is located between the display panel PNL and the light guide plate LG. The diffusion sheet DS diffuses light incident on the diffusion sheet DS to uniformize the brightness of the light. The prism sheet PS is located between the diffusion sheet DS and the light guide plate LG. The prism sheet PS, for example, focuses light emitted from the main surface 1A of the light guide plate LG in direction Z. The prism sheet PS is composed of multiple prisms arranged continuously in direction Y. The multiple prisms of the prism sheet PS protrude toward the main surface 1A in direction Z. The prisms of the prism sheet PS have a triangular cross-sectional shape (hereinafter simply referred to as the cross-sectional shape) parallel to the Y-Z plane. The cross-sectional shapes of the prisms of the prism sheet PS are similar to each other. Hereinafter, the base angle of the prism of the prism sheet PS may be referred to as the inverse prism base angle. The reflection sheet RS faces the opposing surface 1B of the light guide plate LG. The reflective sheet RS reflects, for example, light leaking from the light guide plate LG and makes the light enter the light guide plate LG again.

[0028] In the example shown in FIG. 3 , the height in the Z direction of the side surface SF1 is smaller than the height in the Z direction of the side surface SF2. In other words, the height in the Z direction of the side surface SF2 is greater than the height in the Z direction of the side surface SF1. The thickness of the light guide plate LG increases as it progresses toward the tip of the arrow in the Y direction. In other words, the thickness of the light guide plate LG increases from the side surface SF1 to the side surface SF2 in the Y direction. Here, the thickness of the light guide plate LG corresponds to the length in the Z direction between the main surface 1A and the opposing surface 1B. In the light guide plate LG, the opposing surface 1B is inclined downward with respect to the main surface 1A. In other words, in the light guide plate LG, the opposing surface 1B is inclined toward the side opposite to the tip of the arrow in the Z direction with respect to the main surface 1A. The opposing surface 1B is inclined downward with respect to the main surface 1A as it progresses toward the tip of the arrow in the Y direction. In other words, the opposing surface 1B is inclined toward the side opposite to the tip of the arrow in the Z direction with respect to the main surface 1A as it progresses toward the tip of the arrow in the Y direction. FIG. 3 shows positions (hereinafter sometimes simply referred to as positions) Pss, Ps1, Psc, Ps2, and Pse of the light guide plate LG in the direction Y. Position Pss corresponds to the position of side surface SF1 in the direction Y. Position Pse corresponds to the position of side surface SF2 in the direction Y. Position Psc corresponds to an intermediate position between positions Pss and Pse in the direction Y. Position Ps1 corresponds to a position between positions Pss and Psc in the direction Y. Position Ps2 corresponds to a position between positions Psc and Pse in the direction Y.

[0029] Position Ps1 is located closer to side surface SF2 than position Pss in direction Y. Position Psc is located closer to side surface SF2 than position Ps1 in direction Y. Position Ps2 is located closer to side surface SF2 than position Psc in direction Y. Position Pse is located closer to side surface SF2 than position Ps2 in direction Y.

[0030] The prisms PM are arranged at intervals in the direction Y on the lower side of the light guide plate LG. In other words, the prisms PM are arranged at intervals in the direction Y on the opposing surface 1B of the light guide plate LG. The prisms PM are arranged or formed so that their height increases toward the tip of the arrow in the direction Y. In other words, the prisms PM are formed or arranged so that their height decreases toward the opposite side of the tip of the arrow in the direction Y. The prisms PM have a shape that protrudes downward (inverted prism shape). In other words, the prisms PM have a shape that protrudes on the side opposite the opposing surface 1B in the direction Z. The cross-sectional shape of the prisms PM is a triangular shape that protrudes downward (inverted triangle). In other words, the cross-sectional shape of the prisms PM is a triangular shape that protrudes on the side opposite the opposing surface 1B in the direction Z. The shape of the prisms PM may be a shape other than an inverted prism shape. The cross-sectional shape of the prisms PM may be a shape other than a triangle (inverted triangle). The plurality of prisms PM may be formed separately from the light guide plate LG, or may be formed integrally with the light guide plate LG.

[0031] In the example shown in FIG. 3, the prism PM includes prisms PM1, PM2, and PM3. The prism PM may include four or more prisms, or may include two or less prisms. The prisms PM1, PM2, and PM3 are arranged below the light guide plate LG at intervals in the direction Y. In other words, the prisms PM1, PM2, and PM3 are arranged on the opposing surface 1B of the light guide plate LG at intervals in the direction Y. The prism PM1 is arranged at a position Ps1 on the light guide plate LG. The prism PM2 is arranged at a position Psc on the light guide plate LG. The prism PM3 is arranged at a position Ps2 on the light guide plate LG. The multiple prisms PM may be arranged at predetermined positions on the light guide plate LG in the direction Y other than the positions Ps1, Psc, and Ps2.

[0032] The light source LS is spaced apart from the side surface SF1. The light source LS emits light toward the side surface SF1 of the light guide plate LG. The outgoing light emitted from the light source LS enters the light guide plate LG from the side surface SF1. The outgoing light that enters the prism PM travels upward within the light guide plate LG. Furthermore, the outgoing light that is guided through the light guide plate LG and reaches the reflective layer RF is reflected by the reflective layer RF. The return light that is reflected by the reflective layer RF and enters the prism PM, and a portion of the return light that enters the opposing surface 1B, travel upward within the light guide plate LG.

[0033] 4 is a cross-sectional view showing an example of the arrangement of the prisms PM according to this embodiment, and only the configuration necessary for explanation is shown in FIG. The light guide plate LG has a plurality of inclined surfaces SLP and a plurality of flat surfaces PLN on the opposing surface 1B side. In other words, the opposing surface 1B has a plurality of inclined surfaces SLP and a plurality of flat surfaces PLN. The inclined surfaces SLP correspond to surfaces extending in a direction intersecting with direction Y. In other words, the inclined surfaces SLP correspond to surfaces extending in a direction intersecting with the main surface 1A in the YZ plane. The flat surfaces PLN correspond to surfaces extending parallel to direction Y. The flat surfaces PLN correspond to surfaces extending parallel to the main surface 1A. On the opposing surface 1B, the inclined surfaces SLP and flat surfaces PLN are arranged alternately. To prevent visible streaks, the light guide plate LG has prism structures, each of which combines at least one inclined surface SLP and at least one prism PM, provided at regular intervals. In other words, the light guide plate LG is provided with a prism structure, each of which is a combination of at least one slope SLP and at least one prism PM, at a predetermined density so that streaks are not visible. In the example shown in Fig. 4, the light guide plate LG has a plurality of prism structures, each of which is a combination of two slopes SLP and one prism PM disposed between the two slopes SLP. Note that the light guide plate LG may have a prism structure, each of which is a combination of a number other than two slopes SLP and a number other than one prism PM.

[0034] The multiple slopes SLP are formed, for example, to contribute to the return light. In other words, the multiple slopes SLP are formed to contribute only to the return light without contributing to the outgoing light. Note that the multiple slopes SLP may be formed to contribute to the outgoing light. Furthermore, the multiple slopes SLP may be formed to contribute to both the outgoing light and the return light. The multiple slopes SLP are arranged so that they are positioned lower as they proceed toward the tip of the arrow in the direction Y. In other words, the thicknesses of the multiple light guide plates LG corresponding to the multiple slopes SLP increase as they proceed toward the tip of the arrow in the direction Y.

[0035] The heights of the multiple slopes SLP are set according to the heights of the multiple prisms PM. The multiple slopes SLP are arranged or formed so that the sum of the height of each slope SLP, the height of each of the other slopes SLP adjacent to each slope SLP in the direction Y with each prism PM sandwiched therebetween, and the height of each of the prisms PM arranged between each slope SLP and each of the other slopes SLP increases as one progresses toward the opposite side from the tip end in the direction Y. The multiple slopes SLP are arranged or formed, for example, so that the height decreases as one progresses toward the tip end in the direction Y. Furthermore, for example, among the multiple slopes SLP, two adjacent slopes SLP forming a pair in the direction Y are arranged or formed so that the heights of the two paired slopes SLP decrease as one progresses toward the tip end in the direction Y.

[0036] The sizes (e.g., length or area) of the plurality of slopes SLP are set according to the sizes (e.g., length or area) of the plurality of prisms PM. The lengths of the plurality of slopes SLP are set according to the side lengths of the cross-sectional shapes of the plurality of prisms PM (hereinafter, sometimes simply referred to as side lengths). The plurality of slopes SLP are arranged or formed so that the sum of the length of each slope SLP, the length of each other slope SLP adjacent to each slope SLP in the direction Y with each prism PM sandwiched therebetween, and the length of each side of each prism PM arranged between each slope SLP and each other slope SLP increases as one progresses toward the opposite side from the tip end in the direction Y. The plurality of slopes SLP are arranged or formed, for example, so that the length decreases as one progresses toward the tip end in the direction Y. Furthermore, for example, among the plurality of slopes SLP, two pairs of slopes SLP adjacent to each other in the direction Y are arranged or formed so that the lengths of the two pairs of slopes SLP decrease as one progresses toward the tip end in the direction Y.

[0037] 4, the plurality of slopes SLP include slopes SLP1, SLP2, SLP3, SLP4, SLP5, and SLP6. The plurality of slopes SLP1 to SLP6 are arranged in the order shown on the tip side of the arrow in the direction Y.

[0038] The inclined surfaces SLP1 to SLP6 are each inclined at an angle θ1 downward toward the tip end in the direction Y. In other words, the inclined surfaces SLP1 to SLP6 are each inclined at an angle θ1 downward toward the side surface (opposite light-incident surface) SF2. The angle θ1 is, for example, an angle equal to or greater than the chief ray angle of outgoing light incident from the light-incident surface SF1 to the light guide plate LG. The angle θ1 is preferably an angle that maximizes the number of chief rays in the normal direction to the display panel PNL in relation to the shape of the prism, the refractive index of the material of the light guide plate LG, and the refractive index of the material of the prism PM. The heights of the inclined surfaces SLP1 to SLP6 may be different. The lengths of the inclined surfaces SLP1 to SLP6 may be different.

[0039] The slopes SLP1 and SLP2 correspond to the slopes of a right triangle with an inclination angle θ1 and a height Sh1. That is, the heights of the slopes SLP1 and SLP2 are the same. The heights of the slopes SLP1 and SLP2 may be different. The lengths of the slopes SLP1 and SLP2 are the same. The lengths of the slopes SLP1 and SLP2 may be different. The slopes SLP1 and SLP2 are arranged at a position Ps1. In other words, the slopes SLP1 and SLP2 are arranged at a distance from each other in the direction Y at the position Ps1. The slopes SLP1 and SLP2 are adjacent to each other with the position Ps1 sandwiched between them. The slope SLP2 is located closer to the tip of the arrow in the direction Y than the slope SLP1. In other words, the slope SLP2 is located closer to the side surface SF2 than the slope SLP1 in the direction Y. The slope SLP2 is located on the opposite side of the slope SLP1 from the tip of the arrow in the direction Z. In other words, the slope SLP2 is located below the slope SLP1. That is, the thickness of the light guide plate LG corresponding to the slope SLP2 is greater than the thickness of the light guide plate LG corresponding to the slope SLP1.

[0040] The slopes SLP3 and SLP4 correspond to the slopes of a right triangle with an inclination angle θ1 and a height Sh2. That is, the heights of the slopes SLP3 and SLP4 are the same. The heights of the slopes SLP3 and SLP4 may be different. The lengths of the slopes SLP3 and SLP4 are the same. The lengths of the slopes SLP3 and SLP4 may be different. The length of the slopes SLP3 and SLP4 is shorter than the lengths of the slopes SLP1 and SLP2. The slopes SLP3 and SLP4 are located at a position Psc. In other words, the slopes SLP3 and SLP4 are located at a distance in the direction Y at the position Psc. The slopes SLP3 and SLP4 are adjacent to each other with the position Psc between them. The slope SLP3 is located closer to the tip of the arrow in the direction Y than the slope SLP2. In other words, the slope SLP3 is located closer to the side surface SF2 than the slope SLP2 in the direction Y. The slope SLP3 is located on the opposite side of the slope SLP2 from the tip of the arrow in the Z direction. In other words, the slope SLP3 is located below the slope SLP2. That is, the thickness of the light guide plate LG corresponding to the slope SLP3 is greater than the thickness of the light guide plate LG corresponding to the slope SLP2. The slope SLP4 is located on the opposite side of the slope SLP3 from the tip of the arrow in the Z direction. In other words, the slope SLP4 is located below the slope SLP3. That is, the thickness of the light guide plate LG corresponding to the slope SLP4 is greater than the thickness of the light guide plate LG corresponding to the slope SLP3. The height Sh2 is smaller than the height Sh1. For example, the height Sh2 is 2 / 3 times the height Sh1.

[0041] The slopes SLP5 and SLP6 correspond to the slopes of a right triangle with an inclination angle θ1 and a height Sh3. That is, the heights of the slopes SLP5 and SLP6 are the same. The heights of the slopes SLP5 and SLP6 may be different. The lengths of the slopes SLP5 and SLP6 are the same. The lengths of the slopes SLP5 and SLP6 may be different. The lengths of the slopes SLP5 and SLP6 are shorter than the lengths of the slopes SLP3 and SLP4. The slopes SLP5 and SLP6 are located at position Ps2. In other words, the slopes SLP5 and SLP6 are located at a distance from each other in the direction Y at position Ps2. The slopes SLP5 and SLP6 are adjacent to each other with position Ps2 sandwiched between them. The slope SLP5 is located closer to the tip of the arrow in the direction Y than the slope SLP4. In other words, the slope SLP5 is located closer to the side surface SF2 than the slope SLP4 in the direction Y. The slope SLP5 is located on the opposite side to the tip of the arrow in the direction Z than the slope SLP4. In other words, the slope SLP5 is located below the slope SLP4. In other words, the thickness of the light guide plate LG corresponding to the slope SLP5 is greater than the thickness of the light guide plate LG corresponding to the slope SLP4. The slope SLP6 is located closer to the tip of the arrow in the direction Y than the slope SLP5. In other words, the slope SLP6 is located closer to the side surface SF2 than the slope SLP5 in the direction Y. The slope SLP6 is located on the opposite side to the tip of the arrow in the direction Z than the slope SLP5. In other words, the slope SLP6 is located below the slope SLP5. In other words, the thickness of the light guide plate LG corresponding to the slope SLP6 is greater than the thickness of the light guide plate LG corresponding to the slope SLP5. The height Sh3 is smaller than the heights Sh1 and Sh2, for example, the height Sh3 is 1 / 3 times the height Sh1.

[0042] The multiple flat surfaces PLN reflect incident light so as to guide the light within the light guide plate LG. The multiple flat surfaces PLN are arranged or formed at intervals on the tip side of the arrow in the direction Y. The multiple flat surfaces PLN are arranged or formed so as to be located on the opposite side of the tip side of the arrow in the direction Z as they move toward the tip side of the arrow in the direction Y. The multiple flat surfaces PLN are arranged in a step-like manner descending downward at intervals in the direction Y. In other words, the thicknesses of the multiple light guide plates LG corresponding to the multiple flat surfaces PLN increase as they move toward the tip side of the arrow in the direction Y. The widths of the multiple flat surfaces PLN in the direction Y may be the same or different. For example, the widths of the multiple flat surfaces PLN in the direction Y may be set according to the heights of the two adjacent slopes SLP on both sides in the direction Y and the heights of the prisms PM arranged on each flat surface PLN.

[0043] 4, the plurality of planes PLN include planes PLN1, PLN2, and PLN3. The plurality of planes PLN1 to PLN3 are arranged on the tip side of the arrow in the Y direction in the order described.

[0044] The plane PLN1 is located at position Ps1. The plane PLN1 is disposed between the slopes SLP1 and SLP2. The slopes SLP1, PLN1, and SLP2 are disposed consecutively in the order listed in the direction Y. The plane PLN1 is connected to the end of the slope SLP1 on the tip side of the arrow in the direction Y and is connected to the end of the slope SLP2 on the opposite side to the tip side of the arrow in the direction Y. The slope SLP1 is inclined from the plane PLN1 at an angle θ1 to a height Sh1 upward, opposite to the tip side of the arrow in the direction Y. The slope SLP2 is inclined from the plane PLN1 at an angle θ1 to a height Sh1 downward, toward the tip side of the arrow in the direction Y.

[0045] The plane PLN2 is located at position Psc. The plane PLN2 is located below the plane PLN1. In other words, the thickness of the light guide plate LG corresponding to the plane PLN2 is greater than the thickness of the light guide plate LG corresponding to the plane PLN1. The plane PLN2 is located between the slopes SLP3 and SLP4. The slopes SLP3, PLN2, and SLP4 are arranged consecutively in the order listed in the direction Y. The plane PLN2 is connected to the end of the slope SLP3 on the tip side of the arrow in the direction Y and to the end of the slope SLP4 on the opposite side to the tip side of the arrow in the direction Y. The slope SLP3 is inclined from the plane PLN2 at an angle θ1 to a height Sh2, opposite to the tip side of the arrow in the direction Y and downward. The slope SLP4 is inclined from the plane PLN2 at an angle θ1 to a height Sh2, toward the tip side of the arrow in the direction Y and downward.

[0046] The plane PLN3 is located at position Ps2. The plane PLN3 is located below the plane PLN2. In other words, the thickness of the light guide plate LG corresponding to the plane PLN3 is greater than the thickness of the light guide plate LG corresponding to the plane PLN2. The plane PLN3 is located between the slopes SLP5 and SLP6. The slopes SLP5, PLN3, and SLP6 are arranged consecutively in the order listed in the direction Y. The plane PLN3 is connected to the end of the slope SLP5 on the tip side of the arrow in the direction Y and to the end of the slope SLP6 on the opposite side to the tip side of the arrow in the direction Y. The slope SLP5 is inclined from the plane PLN3 at an angle θ1 to a height Sh3 upward, opposite to the tip side of the arrow in the direction Y. The slope SLP6 is inclined from the plane PLN3 at an angle θ1 to a height Sh3 downward, toward the tip side of the arrow in the direction Y.

[0047] The prisms PM are arranged or formed on the planes PLN, respectively. The prisms PM are formed, for example, to contribute to both the outgoing light and the returning light. Note that the prisms PM may be formed, for example, to contribute to only one of the outgoing light and the returning light.

[0048] The height of the prism PM is set according to the heights of the two slopes SLP adjacent to both sides of the plane PLN on which the prism PM is arranged in the direction Y. In other words, the height of the prism PM is set according to the heights of the two slopes SLP adjacent to each other in the direction Y, sandwiching the prism PM therebetween. The multiple prisms PM are arranged or formed so that their heights increase as they move toward the tip of the arrow in the direction Y. Furthermore, the multiple prisms PM are arranged or formed so that the sum of the height of each prism PM and the heights of the two slopes SLP adjacent to each other in the direction Y, which form a pair, increases as they move away from the tip in the direction Y. In other words, the multiple prisms PM are arranged or formed so that the sum of the height of each prism PM and the heights of the two slopes SLP adjacent to each other in the direction Y, which form a pair, sandwiching the prism PM therebetween increases as they move away from the tip in the direction Y.

[0049] The side length of the prism PM is set according to the lengths of the two slopes SLP adjacent to both sides of the plane PLN on which the prism PM is arranged in the direction Y. In other words, the side length of the prism PM is set according to the lengths of the two slopes SLP adjacent to each other in the direction Y, sandwiching the prism PM therebetween. The multiple prisms PM are arranged or formed so that the side lengths increase as one progresses toward the tip of the arrow in the direction Y. Furthermore, the multiple prisms PM are arranged or formed so that the sum of the side length of each prism PM and the lengths of the two slopes SLP of each pair adjacent to each prism PM in the direction Y increases as one progresses toward the opposite side from the tip side in the direction Y. In other words, the multiple prisms PM are arranged or formed so that the sum of the side length of each prism PM and the lengths of the two slopes SLP of each pair adjacent to each prism PM in the direction Y, sandwiching each prism PM therebetween, increases as one progresses toward the opposite side from the tip side in the direction Y.

[0050] In the example shown in FIG. 4, the prism PM1 is disposed on the plane PLN1. The cross-sectional shape of the prism PM1 is an isosceles triangle (inverted triangle) with two base angles inclined at an angle θ1 with respect to the plane PLN1 and a height Ph1. The apex of the cross-sectional shape of the prism PM1 is located at a position Ps1. For example, the height Ph1 is smaller than the height Sh1. For example, the height Ph1 is 1 / 3 times the height Sh1. For example, the length of a side of the prism PM1 is smaller than the length of the slope SLP1. The length of a side of the prism PM1 is the same as the lengths of the slopes SLP5 and SLP6, for example. Note that the prism PM1 does not necessarily have to be disposed on the plane PLN1. The height Ph1 may be larger than the height Sh1. The length of a side of the prism PM1 may also be larger than the length of the slope SLP1.

[0051] The prism PM2 is disposed on the plane PLN2. The cross-sectional shape of the prism PM2 is an isosceles triangle (inverted triangle) with two base angles inclined at an angle θ1 with respect to the plane PLN2 and a height Ph2. The apex of the cross-sectional shape of the prism PM2 is located at a position Psc. The height Ph2 is greater than the height Ph1. For example, the height Ph2 is twice the height Ph1. For example, the height Ph2 is the same as the height Sh2. The length of each side of the prism PM2 is greater than the length of each side of the prism PM1. For example, the length of each side of the prism PM2 is the same as the lengths of the inclined surfaces SLP3 and SLP4. Note that if the prism PM1 is not disposed on the plane PLN1, the prism PM2 does not have to be disposed on the plane PLN2. Furthermore, the height Ph2 does not have to be the same as the height Ph2.

[0052] Prism PM3 is disposed on plane PLN3. The cross-sectional shape of prism PM3 is an isosceles triangle (inverted triangle) with two base angles inclined at angle θ1 with respect to plane PLN2 and a height Ph3. The apex of the cross-sectional shape of prism PM3 is located at position Ps2. Height Ph3 is greater than heights Ph1 and Ph2. For example, height Ph3 is three times the height Ph1. Height Ph3 is 3 / 2 times the height Ph2. For example, height Ph3 is greater than height Sh3. For example, height Ph3 is three times the height Sh3. The side length of prism PM3 is greater than the side length of prism PM2. For example, the side length of prism PM3 is the same as the lengths of slopes SLP1 and SLP2. If the prisms PM1 and PM2 are not disposed on the planes PLN1 and PLN2, respectively, the prism PM3 does not have to be disposed on the plane PLN3. Furthermore, the height Ph3 may be smaller than the height Sh3.

[0053] FIG. 5 is a schematic diagram showing an example of the change in the effective height of the prism PM with respect to the position of the light guide plate LG according to this embodiment. In FIG. 5, the horizontal axis represents the position of the light guide plate LG in the direction Y, and the vertical axis represents the effective height of the prism PM (hereinafter, sometimes referred to as the effective prism height). For outgoing light, the effective prism height corresponds to the height of the components contributing to the outgoing light, and for return light, it corresponds to the height of the components contributing to the return light. In this embodiment, the effective prism height corresponds to the height of the prism PM contributing to the outgoing light, and for return light, it corresponds to the sum of the height of the prism PM contributing to the return light and the height of two slopes adjacent to and sandwiching the prism PM in the direction Y. On the horizontal axis of FIG. 5, the position of the light guide plate LG is the position toward the side surface SF2 of the light guide plate LG in the direction of the tip of the arrow, and the position toward the side surface SF1 of the light guide plate LG in the direction opposite to the tip of the arrow. The horizontal axis of FIG. 5 indicates positions Pss, Ps1, Psc, Ps2, and Pse. On the vertical axis of FIG. 5, the effective prism height increases toward the tip of the high arrow and decreases toward the tip of the low arrow. FIG. 5 also shows the change in effective prism height OBL with respect to the position of the light guide plate LG corresponding to outgoing light (hereinafter also referred to as the change in effective prism height corresponding to outgoing light), and the change in effective prism height RTL with respect to the position of the light guide plate LG corresponding to returning light (hereinafter also referred to as the change in effective prism height corresponding to returning light). The change in effective prism height OBL with respect to outgoing light enters the light guide plate LG from the side surface SF1 in the direction Y of the light guide plate LG. The change in the effective prism height RTL corresponding to the return light corresponds to the change in the sum of the height of the prism PM relative to the return light reflected by the side surface SF2 in the direction Y of the light guide plate LG and the heights of the two adjacent slopes SLP sandwiching this prism PM in the direction Y.

[0054] 5, in the light guide plate LG of this embodiment, the change OBL in the effective prism height corresponding to the outgoing light increases from position Pss to position Pse. In other words, the prisms PM are provided on the opposing surface 1B of the light guide plate LG so that the height increases as the prisms progress toward the tip of the arrow in direction Y.

[0055] 5, in the light guide plate LG of this embodiment, the change RTL in the effective prism height corresponding to the return light increases from position Pse to position Pss. In other words, the prism PM and the slopes SLP are provided on the opposing surface 1B of the light guide plate LG so that the sum of the height of the prism PM and the heights of the two slopes SLP adjacent to each other in direction Y and sandwiching the prism PM therebetween increases as one moves in the direction opposite to the tip of the arrow in direction Y.

[0056] Generally, in a light guide plate LG, light output from the side closer to the light incident surface SF1 is suppressed, and light output from the side farther from the light incident surface SF1 is increased. In the light guide plate LG of the present embodiment described above, the prisms PM contribute to the output of outgoing light, and the prisms PM and the slopes SLP contribute to the output of returning light. In the light guide plate LG shown in FIG. 4, since there is a risk of insufficient light mixing, the outgoing light is actively output from a point on the tip side of the arrow in direction Y where sufficient light mixing has been achieved. Therefore, the light guide plate LG of this embodiment can suppress brightness deviations in both directions Y and X.

[0057] According to this embodiment, the illumination device IL includes a light guide plate LG, a plurality of light sources LS, a reflective layer RF, and a plurality of prisms PM. The light guide plate LG has a main surface 1A located on the display panel PNL side, a facing surface 1B located on the opposite side of the main surface 1A in the Z direction, a side surface SF1, and a side surface SF2 located on the opposite side of the side surface SF1 in the Y direction. The side surface SF1 and the side surface SF2 face each other in the Y direction. The main surface 1A extends parallel to the Y direction. The facing surface 1B has a plurality of inclined surfaces SLP and a plurality of flat surfaces PLN. The inclined surfaces SLP are inclined downward at an angle θ1 toward the tip of the arrow in the Y direction. The inclined surfaces SLP are arranged or formed so that their heights and lengths decrease toward the tip of the arrow in the Y direction. The flat surfaces PLN are connected to two adjacent inclined surfaces SLP on both sides in the Y direction. The cross-sectional shape of the multiple prisms PM is an isosceles triangle (inverted triangle) having two base angles θ1 that are the same as the inclination angle θ1 of the slope SLP. The multiple prisms PM are respectively arranged on multiple flat surfaces PLN. The multiple prisms PM are arranged or formed, for example, so that the height and length of their sides increase as they proceed toward the tip of the arrow in the direction Y. The multiple prisms PM and multiple slopes SLP are formed or arranged so that the sum of the height and length of each prism PM and the heights and lengths of two pairs of slopes SLP adjacent to each other in the direction Y with each prism PM sandwiched therebetween increases as they proceed away from the tip of the arrow in the direction Y.

[0058] The multiple light sources LS face the side surface SF1. The light sources LS emit light toward the side surface SF1. In the light guide plate LG of this embodiment, the prisms PM contribute to the output of outgoing light, and the prisms PM and the slopes SLP contribute to the output of returning light. Because there is a risk of insufficient light mixing, the outgoing light is actively output from a point toward the tip of the arrow in direction Y where sufficient light mixing is achieved. Therefore, the light guide plate LG of this embodiment can suppress brightness deviations in both directions Y and X. Since the illumination device IL is composed of a single light guide plate LG, it can be made thin. Furthermore, the illumination device IL can ensure in-plane brightness uniformity. Therefore, the illumination device IL can improve brightness uniformity. In other words, the display device DSP can also improve brightness uniformity.

[0059] Next, display devices DSP and illumination devices IL according to modified examples and other embodiments of the first embodiment will be described. In the modified examples and other embodiments described below, the same parts as those of the display device DSP and illumination device IL according to the first embodiment will be given the same reference numerals, and detailed description thereof will be omitted or simplified. The detailed description will focus on parts that differ from the display device DSP and illumination device IL according to the first embodiment. Note that the same effects as those of the above-described embodiments can also be obtained in other modified examples and other embodiments.

[0060] (Variation 1) The illumination device IL according to the first modification of the first embodiment differs from the illumination device IL of the first embodiment in the configuration of the light guide plate LG. Fig. 6 is a cross-sectional view showing an example of the arrangement of the prisms PM according to Modification 1. Fig. 6 shows only the configuration necessary for explanation. The multiple prism groups PMG are arranged at intervals in the direction Y on the lower side of the light guide plate LG. In other words, the multiple prism groups PMG are arranged at intervals in the direction Y on the opposing surface 1B of the light guide plate LG. The multiple prism groups PMG are arranged or formed on multiple planes PLN, respectively. The multiple prism groups PMG include multiple prisms PM. The multiple prism groups PMG are, for example, made up of multiple prisms PM lined up consecutively in the direction Y. Note that the multiple prism groups PMG may also be, for example, made up of multiple prisms PM lined up at intervals in the direction Y.

[0061] The height of the prism group PMG is set according to the heights of the two slopes SLP adjacent to both sides of the plane PLN on which the prism group PMG is arranged in the direction Y. In other words, the height of the prism group PMG is set according to the heights of the two slopes SLP adjacent to each other in the direction Y, sandwiching the prism group PMG therebetween. For example, the height of the prism group PMG corresponds to the sum of the heights of the multiple prisms PM included in the prism group PMG. The multiple prism groups PMG are arranged or formed so that their heights increase as they move toward the tip of the arrow in the direction Y. Furthermore, the multiple prism groups PMG are arranged or formed so that the sum of the height of each prism group PMG and the heights of each pair of slopes SLP adjacent to each prism group PMG in the direction Y increases as they move toward the opposite side from the tip in the direction Y. In other words, the multiple prism groups PMG are arranged or formed so that the sum of the height of each prism group PMG and the height of each pair of adjacent inclined surfaces SLP sandwiching each prism group PMG in direction Y increases as one progresses in the direction opposite the tip side in direction Y.

[0062] The length of each side of the prism group PMG is set according to the lengths of the two slopes SLP adjacent to both sides of the plane PLN on which the prism group PMG is arranged in the direction Y. In other words, the length of each side of the prism group PMG is set according to the lengths of the two slopes SLP adjacent to each other in the direction Y, sandwiching the prism group PMG therebetween. For example, the length of each side of the prism group PMG corresponds to the sum of the lengths of the sides of the multiple prisms PM included in the prism group PMG. The multiple prism groups PMG are arranged or formed so that the length of each side increases as one moves toward the tip of the arrow in the direction Y. Furthermore, the multiple prism groups PMG are arranged or formed so that the sum of the length of each side of each prism group PMG and the length of each pair of slopes SLP adjacent to each prism group PMG in the direction Y increases as one moves toward the opposite side from the tip in the direction Y. In other words, the multiple prism groups PMG are arranged or formed so that the sum of the length of the side of each prism group PMG and the length of each pair of adjacent inclined surfaces SLP sandwiching each prism group PMG in direction Y increases as one progresses in the direction opposite the tip side in direction Y.

[0063] In the example shown in FIG. 6, the prism group PMG has a prism group PMG1. The prism group PMG1 is arranged on a plane PLN1. The prism group PMG1 includes three prisms PM1. The prism group PMG1 may include two prisms PM1, or may include four or more prisms PM1. The prism group PMG1 is made up of three prisms PM1 lined up consecutively in the direction Y. The prism group PMG1 may also be made up of three prisms PM1 lined up at intervals in the direction Y. The prism group PMG1 may also be made up of a plurality of prisms PM with different heights that are similar to each other.

[0064] The heights of the plurality of slopes SLP are set according to the heights of the plurality of prism groups PMG. The plurality of slopes SLP are arranged or formed so that the sum of the height of each slope SLP, the height of each of the other slopes SLP adjacent to each slope SLP in the direction Y with each prism group PMG sandwiched therebetween, and the height of each of the prism groups PMG arranged between each slope SLP and each of the other slopes SLP increases as one proceeds in the direction opposite to the tip side in the direction Y. Such a first modification also has the same effects as the first embodiment.

[0065] (Variation 2) The illumination device IL according to the second modification of the first embodiment differs from the illumination devices IL according to the first embodiment and the first modification in the configuration of the light guide plate LG.

[0066] Fig. 7 is a cross-sectional view showing an example of the arrangement of the prism PM according to Modification 2. Fig. 7 shows only the configuration necessary for explanation. The planes PLN include planes PLN on which prisms PM or prism groups PMG are arranged, and planes PLN on which prisms PM or prism groups PMG are not arranged.

[0067] In the example shown in FIG. 7, prism PM2 is arranged on plane PLN2. Prism PM3 is arranged on plane PLN3. No prism PM is arranged on plane PLN1. Since no prism PM is arranged on plane PLN1, prism PM2 does not have to be arranged. Furthermore, if prism PM2 is not arranged on plane PLN2, prism PM3 does not have to be arranged on plane PLN3. Such a second modification also has the same effects as the first embodiment.

[0068] (Second embodiment) The display device DSP according to the second embodiment differs from the display devices DSP according to the first embodiment, the first modification, and the second modification in the configuration of the light guide plate LG of the illumination device IL.

[0069] FIG. 8 is a cross-sectional view of a display device DSP according to the second embodiment. 8, the thickness of the light guide plate LG is constant in the direction Y. In the light guide plate LG, the opposing surface 1B is parallel to the main surface 1A.

[0070] The plurality of prism groups PMG are arranged at intervals in the direction Y on the lower side of the light guide plate LG. In other words, the plurality of prism groups PMG are arranged at intervals in the direction Y on the opposing surface 1B of the light guide plate LG. The prism group PMG includes at least one prism PM (hereinafter also referred to as a round-trip prism) formed to contribute to the outgoing light and the returning light, and at least one prism PM (hereinafter also referred to as a returning prism) formed to contribute only to the returning light.

[0071] In the example shown in FIG. 8 , the prism group PMG includes prism groups PMG4, PMG5, and PMG6. The prism group PMG may include four or more prism groups, or may include two or less prism groups PMG. The prism groups PMG4, PMG5, and PMG6 are arranged below the light guide plate LG at intervals in the direction Y. In other words, the prism groups PMG4, PMG5, and PMG6 are arranged on the opposing surface 1B of the light guide plate LG at intervals in the direction Y. The prism group PMG4 is arranged at a position Ps1 on the light guide plate LG. The prism group PMG5 is arranged at a position Psc on the light guide plate LG. The prism group PMG6 is arranged at a position Ps2 on the light guide plate LG. The multiple prism groups PMG may be arranged at predetermined positions on the light guide plate LG in the direction Y other than the positions Ps1, Psc, and Ps2.

[0072] Fig. 9 is a cross-sectional view showing an example of the arrangement of the prism group PMG according to the second embodiment. Fig. 9 shows only the configuration necessary for explanation. The height of the round trip path prism PM is set according to the heights of the other prisms PM in each prism group PMG. The multiple round trip path prisms PM included in each of the multiple prism groups PMG are arranged or formed so that their height increases as they proceed toward the tip of the arrow in the direction Y. Furthermore, the multiple prism groups PMG are arranged or formed so that their height increases as they proceed in the direction opposite to the tip of the arrow in the direction Y. In other words, the multiple prism groups PMG are arranged or formed so that the sum of the height of at least one round trip path prism PM and the height of at least one return path prism PM increases as they proceed in the direction opposite to the tip of the arrow in the direction Y.

[0073] The side length of a round trip path prism PM is set according to the side lengths of the other prisms PM in each prism group PMG. The multiple round trip path prisms PM are arranged or formed so that the side lengths increase as they proceed toward the tip of the arrow in the direction Y. Furthermore, the multiple prism groups PMG are arranged or formed so that the side lengths increase as they proceed in the direction opposite to the tip of the arrow in the direction Y. In other words, the multiple prism groups PMG are arranged or formed so that the sum of the side length of at least one round trip path prism PM and the side length of at least one return path prism PM increases as they proceed in the direction opposite to the tip of the arrow in the direction Y.

[0074] In the example shown in FIG. 9 , the prism group PMG4 is disposed at position Ps1. The prism group PMG4 includes prisms PM4, PM5, and PM6. In the prism group PMG4, the prisms PM4, PM5, and PM6 are arranged consecutively in the order shown on the tip side of the arrow in the direction Y. The prism PM5 is disposed at a distance from the tip side of the prism PM4 in the direction Y, and the prism PM6 is disposed at a distance from the tip side of the prism PM5 in the direction Y. In other words, the prism PM5 is disposed at a distance closer to the side surface SF2 than the prism PM4 in the direction Y, and the prism PM6 is disposed at a distance closer to the side surface SF2 than the prism PM5 in the direction Y. Alternatively, the prism PM5 may be disposed consecutively from the tip side of the prism PM4 in the direction Y, and the prism PM6 may be disposed consecutively from the tip side of the prism PM5 in the direction Y. In other words, prism PM5 may be arranged contiguous to prism PM4 on the side surface SF2 side in the direction Y, and prism PM6 may be arranged contiguous to prism PM5 on the side surface SF2 side in the direction Y. Prism PM5 is located between prisms PM4 and PM6 in the direction Y in prism group PMG4. Prisms PM4 and PM6 correspond to return path prisms. Prism PM5 corresponds to a forward / backward path prism. The cross-sectional shape of prisms PM4 and PM6 is a triangle (inverted triangle) having a height Ph4 and an apex where a side (first long side) inclined at an angle θ1 with respect to opposing surface 1B toward the tip of the arrow in the direction Y and downward and a side (first short side) inclined at an angle θ2 with respect to opposing surface 1B larger than the angle θ1 intersect. In other words, the cross-sectional shape of the prisms PM4 and PM6 is a triangle (inverted triangle) having a height Ph4, with a vertex at the intersection of a first long side located closer to the light-incident surface SF1 than the first short side and inclined toward the first short side at an angle θ1 with respect to the opposing surface 1B, and a first short side located closer to the anti-light-incident surface SF2 than the first long side and inclined toward the first long side at an angle θ2 with respect to the opposing surface 1B. θ2 is greater than θ1. θ2 is preferably 90° to reduce luminance loss. The length of the first long side is greater than the length of the first short side.The cross-sectional shape of the prism PM5 is an isosceles triangle (inverted triangle) with two base angles inclined at an angle θ1 with respect to the opposing surface 1B and a height Ph5. The apex of the cross-sectional shape of the prism PM5 is located at a position Ps1. For example, the height Ph4 is greater than the height Ph5. For example, the height Ph4 is three times the height Ph5.

[0075] The prism group PMG5 is disposed at position Psc. The prism group PMG5 includes prisms PM7, PM8, and PM9. The prisms PM7, PM8, and PM9 are arranged consecutively in the order shown on the tip side of the arrow in the direction Y. The prism PM8 is disposed at a distance from the tip side of the prism PM7 in the direction Y, and the prism PM9 is disposed at a distance from the tip side of the prism PM8 in the direction Y. In other words, the prism PM8 is disposed at a distance closer to the side surface SF2 than the prism PM7 in the direction Y, and the prism PM9 is disposed at a distance closer to the side surface SF2 than the prism PM8 in the direction Y. Alternatively, the prism PM8 may be disposed consecutively from the tip side of the prism PM7 in the direction Y, and the prism PM9 may be disposed consecutively from the tip side of the prism PM8 in the direction Y. In other words, prism PM8 may be arranged contiguously with prism PM7 on the side surface SF2 side in the direction Y, and prism PM9 may be arranged contiguously with prism PM8 on the side surface SF2 side in the direction Y. Prism PM8 is located between prisms PM7 and PM9 in the direction Y. Prisms PM7 and PM9 correspond to return path prisms. Prism PM8 corresponds to a forward / backward path prism. The cross-sectional shape of prisms PM7 and PM9 is an inverted triangle (inverted triangle) having a vertex where a side (second long side) inclined at an angle θ1 with respect to the opposing surface 1B toward the tip of the arrow in the direction Y and downward and a side (second short side) inclined at an angle θ2 with respect to the opposing surface 1B larger than the angle θ1 toward the opposite side of the tip of the arrow in the direction Y and downward. In other words, the cross-sectional shape of the prisms PM7 and PM9 is a triangle (inverted triangle) having a height Ph6 and an apex at which a second long side, which is located closer to the light-incident surface SF1 than the second short side and inclined toward the second short side at an angle θ1 with respect to the opposing surface 1B, intersects with a second short side, which is located closer to the anti-light-incident surface SF2 than the second long side and inclined toward the second long side at an angle θ2 with respect to the opposing surface 1B. The length of the second long side is greater than the length of the second short side. The length of the second long side is less than the length of the first long side. The length of the second short side is also less than the length of the first short side.The cross-sectional shape of the prism PM8 is an isosceles triangle (inverted triangle) with two base angles inclined at an angle θ1 with respect to the opposing surface 1B and a height of Ph7. The apex of the cross-sectional shape of the prism PM8 is located at position Psc. For example, the height Ph6 is smaller than the height Ph4. For example, the height Ph6 is 2 / 3 times the height Ph4. The height Ph7 is larger than the height Ph5. For example, the height Ph7 is twice the height Ph5. The sum of the heights of the prisms PM7 to PM9 (2×Ph6+Ph7) is smaller than the sum of the heights of the prisms PM4 to PM6 (2×Ph4+Ph5). In other words, the sum of the heights of the prisms PM4 to PM6 (2×Ph4+Ph5) is larger than the sum of the heights of the prisms PM7 to PM9 (2×Ph6+Ph7). The length of the equilateral sides of prism PM8 is greater than the length of the equilateral sides of prism PM5. For example, the length of the equilateral sides of prism PM8 is twice as long as the length of the equilateral sides of prism PM5 and is the same as the length of the second long sides of prisms PM7 and PM9. The sum of the lengths of the two second long sides of prisms PM7 and PM9 and the length of the equilateral sides of prism PM8 is less than the sum of the lengths of the two first long sides of prisms PM4 and PM6 and the length of the equilateral sides of prism PM5. In other words, the sum of the lengths of the two first long sides of prisms PM4 and PM6 and the length of the equilateral sides of prism PM5 is greater than the sum of the lengths of the two second long sides of prisms PM7 and PM9 and the length of the equilateral sides of prism PM8.

[0076] The prism group PMG6 is disposed at position Ps2. The prism group PMG6 includes prisms PM10, PM11, and PM12. The prisms PM10, PM11, and PM12 are arranged consecutively in the order shown on the tip side of the arrow in the direction Y. The prism PM11 is disposed at a distance from the tip side of the prism PM10 in the direction Y, and the prism PM12 is disposed at a distance from the tip side of the prism PM11 in the direction Y. In other words, the prism PM11 is disposed at a distance closer to the side surface SF2 than the prism PM10 in the direction Y, and the prism PM12 is disposed at a distance closer to the side surface SF2 than the prism PM11 in the direction Y. Alternatively, the prism PM11 may be disposed consecutively from the tip side of the prism PM10 in the direction Y, and the prism PM12 may be disposed consecutively from the tip side of the prism PM11 in the direction Y. In other words, prism PM11 may be arranged contiguously with prism PM10 on the side surface SF2 side in the direction Y, and prism PM12 may be arranged contiguously with prism PM11 on the side surface SF2 side in the direction Y. Prism PM11 is located between prisms PM10 and PM12 in the direction Y. Prisms PM10 and PM12 correspond to return path prisms. Prism PM11 corresponds to a forward / backward path prism. The cross-sectional shape of prisms PM10 and PM12 is an inverted triangle having a height Ph8 and an apex where a side (third long side) inclined at an angle θ1 with respect to the opposing surface 1B toward the tip of the arrow in the direction Y and downward intersects with a side (third short side) inclined at an angle θ2 with respect to the opposing surface 1B larger than the angle θ1 toward the opposite side of the tip of the arrow in the direction Y and downward. In other words, the cross-sectional shape of the prisms PM10 and PM12 is a triangle (inverted triangle) having a height Ph8 and an apex at which a third long side, which is located closer to the light-incident surface SF1 than the third short side and inclined toward the third short side at an angle θ1 with respect to the opposing surface 1B, intersects with a third short side, which is located closer to the anti-light-incident surface SF2 than the third long side and inclined toward the third long side at an angle θ2 with respect to the opposing surface 1B. The length of the third long side is greater than the length of the third short side. The length of the third long side is less than the length of the second long side. The length of the third short side is also less than the length of the second short side.The cross-sectional shape of the prism PM11 is an isosceles triangle (inverted triangle) with two base angles inclined at an angle θ1 with respect to the opposing surface 1B and a height of Ph9. The apex of the cross-sectional shape of the prism PM11 is located at position Ps2. For example, the height Ph8 is smaller than the heights Ph4 and Ph6. For example, the height Ph8 is 1 / 3 times the height Ph4. For example, the height Ph8 is 1 / 2 times the height Ph6. The height Ph9 is larger than the heights Ph5 and Ph7. For example, the height Ph9 is 3 times the height Ph5. For example, the height Ph9 is 3 / 2 times the height Ph7. The sum of the heights of the prisms PM10 to PM12 (2 × Ph8 + Ph9) is smaller than the sum of the heights of the prisms PM7 to PM9 (2 × Ph6 + Ph7). In other words, the sum of the heights of prisms PM7 to P9 (2×Ph6+Ph7) is greater than the sum of the heights of prisms PM10 to PM12 (2×Ph8+Ph9). The length of the equilateral sides of prism PM11 is greater than the lengths of the equilateral sides of prisms PM5 and PM8. For example, the length of the equilateral sides of prism PM11 is three times the length of the equilateral sides of prism PM5, and is three times the length of the third long sides of prisms PM10 and PM12. The sum of the lengths of the two third long sides of prisms PM10 and PM12 and the length of the equilateral sides of prism PM11 is less than the sum of the lengths of the two third long sides of prisms PM7 and PM9 and the length of the equilateral sides of prism PM8. In other words, the sum of the lengths of the two third long sides of prisms PM7 and PM9 and the length of the equal sides of prism PM8 is greater than the sum of the lengths of the two third long sides of prisms PM10 and PM12 and the length of the equal sides of prism PM11.

[0077] With the configuration of the light guide plate LG shown in FIG. 9, the illumination device IL according to the second embodiment can reproduce the substantial height changes OBL and RTL of the prism PM relative to the position of the light guide plate LG shown in FIG.

[0078] According to the second embodiment, the illumination device IL includes a light guide plate LG, a plurality of light sources LS, a reflecting layer RF, and a plurality of prism groups PMG. The light guide plate LG has a main surface 1A located on the display panel PNL side, an opposing surface 1B located opposite the main surface 1A in direction Z and parallel to the main surface 1A, a side surface SF1, and a side surface SF2 located opposite the side surface SF1 in direction Y. The plurality of prism groups PMG are arranged on the opposing surface 1B at intervals in direction Y. The prism group PMG includes at least one round-trip path prism PM formed to contribute to both outgoing light and return light, and at least one return prism formed to contribute only to return light. The plurality of round-trip path prisms PM included in each of the plurality of prism groups PMG are arranged or formed so that their heights and side lengths increase toward the tip of the arrow in direction Y. Furthermore, the prism groups PMG are arranged or formed so that their heights and sides increase in the direction opposite to the tip of the arrow in the direction Y. This allows the illumination device IL to improve brightness uniformity, which in turn allows the display device DSP to improve brightness uniformity.

[0079] (Third embodiment) The illumination device IL according to the third embodiment differs from the illumination devices IL according to the first embodiment, modified example 1, modified example 2, and second embodiment in the configurations of the light source LS and the light guide plate LG.

[0080] Fig. 10 is a plan view of an illumination device IL according to a third embodiment. As shown in Fig. 10, the illumination device IL according to the third embodiment has a display area DA and a non-display area NDA. In the example shown in Fig. 10, the display area DA has an octagonal shape. However, the display area DA may be formed in a shape other than an octagonal shape.

[0081] In the example shown in FIG. 10, the light guide plate LG has a third region A3, a fourth region A4, and a fifth region A5. The third region A3, the fourth region A4, and the fifth region A5 are arranged consecutively in the order shown on the tip side of the arrow in the X direction. The third region A3 corresponds to the region at the end opposite the tip side of the arrow in the X direction, and the fifth region A5 corresponds to the region at the end side of the arrow in the X direction. The fourth region A4 corresponds to the region between the third region A3 and the fifth region A5 in the X direction. The fourth region A4 is located in the center (or inside) in the X direction, and the third region A3 and the fifth region A5 are located at the ends (or outside) in the X direction.

[0082] In the example shown in FIG. 10 , the light guide plate LG has a side surface SF1, a side surface SF2 opposite to the side surface SF1, a side surface SF3 intersecting with the side surface SF2, a side surface SF4 intersecting with the side surface SF2 and opposite to the side surface SF3, a sloped surface CP1 connecting the side surfaces SF1 and SF3, and a sloped surface CP2 connecting the side surfaces SF1 and SF4. When viewed from above, the light guide plate LG is formed into a hexagonal shape with two notches formed by cutting out two corners opposite the tip of the arrow in the direction Y from a square. For example, when viewed from above, the light guide plate LG is formed into a hexagonal shape with sloped surfaces CP1 and CP2 formed by cutting out two corners opposite the tip of the arrow in the direction Y from a square. Note that the light guide plate LG may be formed into a shape other than a hexagonal shape when viewed from above. For example, when viewed in a plane, the light guide plate LG may have a shape having a recess with a radius (R) formed by cutting out at least one of the two corners of a rectangle on the side opposite the tip of the arrow in direction Y.

[0083] The length of the side surface SF1 in the direction X is shorter than the length of the side surface SF2 in the direction X. The side surface SF1 corresponds to, for example, the end surface opposite the tip of the arrow in the direction Y of the fourth region A4. Note that the side surface SF1 may correspond to, for example, the end surface opposite the tip of the arrow in the direction Y of a region other than the fourth region A4. The side surface SF2 corresponds to, for example, the end surface at the tip of the arrow in the direction Y of the third region A3 to the fifth region. Note that the side surface SF2 may correspond to, for example, the end surface at the tip of the arrow in the direction Y of at least one of the third region A3 to the fifth region. The side surfaces SF3 and SF4 extend parallel to the direction Y in a planar view. The side surfaces SF3 and SF4 are parallel in a planar view. The lengths of the side surfaces SF3 and SF4 in the direction Y are the same. Note that the lengths of the side surfaces SF3 and SF4 in the direction Y may be different.

[0084] The slope CP1 is a surface connecting the end of the side surface SF1 opposite the tip of the arrow in the X direction with the end of the side surface SF3 opposite the tip of the arrow in the Y direction. In a plan view, the slope CP1 extends obliquely from the end of the side surface SF1 opposite the tip of the arrow in the X direction toward the end of the side surface SF3 opposite the tip of the arrow in the Y direction, in a direction opposite to the tip of the arrow in the X direction and toward the tip of the arrow in the Y direction. For example, in a plan view, the slope CP1 extends obliquely at an angle of 45° from the end of the side surface SF1 opposite the tip of the arrow in the X direction toward the end of the side surface SF3 opposite the tip of the arrow in the Y direction. For example, in a plan view, the slope CP1 may extend obliquely at an angle other than 45° from the end of the side surface SF1 opposite the tip of the arrow in the X direction toward the end of the side surface SF3 opposite the tip of the arrow in the Y direction. The slope CP1 corresponds to, for example, the end surface of the third region A3 opposite the tip of the arrow in the Y direction. The slope CP1 may correspond to, for example, an end surface other than the third region A3 opposite the tip of the arrow in the Y direction.

[0085] The slope CP2 is a surface connecting the end of the side surface SF1 on the tip side of the arrow in the X direction with the end of the side surface SF4 on the opposite side from the tip of the arrow in the Y direction. In a plan view, the slope CP2 extends obliquely from the end of the side surface SF1 on the tip side of the arrow in the X direction toward the end of the side surface SF4 on the opposite side from the tip side of the arrow in the Y direction, toward the tip side of the arrow in the X direction and toward the tip side of the arrow in the Y direction. For example, in a plan view, the slope CP2 extends obliquely at an angle of 45° from the end of the side surface SF1 on the tip side of the arrow in the X direction toward the end of the side surface SF4 on the opposite side from the tip side of the arrow in the Y direction. Note that the slope CP2 may also extend obliquely at an angle other than 45° from the end of the side surface SF1 on the tip side of the arrow in the X direction toward the end of the side surface SF4 on the opposite side from the tip side of the arrow in the Y direction, toward the tip side of the arrow in the X direction and toward the tip side of the arrow in the Y direction. The slope CP2 corresponds to, for example, the end face of the fifth region A5 opposite to the tip of the arrow in the direction Y. Note that the slope CP2 may correspond to, for example, the end face of a region other than the fifth region A5 opposite to the tip of the arrow in the direction Y.

[0086] In the example shown in FIG. 10 , the multiple light sources LS include light sources LS1, LS2, LS3, LS4, LS5, and LS6. The light sources LS1 to LS6 are arranged in the listed order in the direction X. To uniformize the brightness in the third region A3, the fourth region A4, and the fifth region A5, the light intensity of the light sources LS1 to LS6 arranged on the edge side (or outer side) in the direction X is greater than the light intensity of the light sources LS arranged in the center (or inner side) in the direction X. In other words, to uniformize the brightness in the third region A3, the fourth region A4, and the fifth region A5, the light intensity ratio of the light sources LS arranged on the edge side (or outer side) in the direction X is greater than the light intensity ratio of the light sources LS arranged in the center (or inner side) in the direction X. For example, the light intensities of the light sources LS1 and LS6 are greater than the light intensities of the light sources LS2 to LS5 to uniformize the brightness in the third region A3, the fourth region A4, and the fifth region A5. In other words, for example, the light intensity ratio of the light sources LS1 and LS6 is greater than the light intensity ratio of the light sources LS2 to LS5 in order to make the brightness uniform in the third area A3, the fourth area A4, and the fifth area A5.

[0087] In order to uniform the brightness in the third region A3, the fourth region A4, and the fifth region A5, the light sources LS1 to LS6 may have gradually increasing light intensities from the light source LS arranged in the center (or inside) in the direction X toward the light source LS arranged on the end (or outside) side in the direction X. In other words, in order to uniform the brightness in the third region A3, the fourth region A4, and the fifth region A5, the light sources LS1 to LS6 may have gradually increasing light intensity ratios from the light source LS arranged in the center (or inside) in the direction X toward the light source LS arranged on the end (or outside) side in the direction X. For example, in order to uniform the brightness in the third region A3, the fourth region A4, and the fifth region A5, the light intensities of the light sources LS2 and LS5 are greater than the light intensities of the light sources LS3 and LS4, and the light intensities of the light sources LS1 and LS6 are greater than the light intensities of the light sources LS2 and LS5. In other words, for example, to uniform the brightness in the third area A3, the fourth area A4, and the fifth area A5, the light intensity ratio of light sources LS2 and LS5 is greater than the light intensity ratio of light sources LS3 and LS4, and the light intensity ratio of light sources LS1 and LS6 is greater than the light intensity ratio of light sources LS2 and LS5.

[0088] For example, the light intensities of the outgoing light beams emitted from light sources LS1 to LS6 are set so that the light intensity ratio of the outgoing light beams emitted from light sources LS1 to LS6 is 3:1:1:1:1:3. In a configuration that combines the configuration of this embodiment with the configuration of the first or second embodiment, the light intensities of the outgoing light beams emitted from light sources LS1 to LS6 can be set so that the light intensity ratio of the multiple return light beams corresponding to the multiple outgoing light beams emitted from light sources LS1 to LS6 is 6:2:2:2:2:6.

[0089] According to the third embodiment, the illumination device IL includes a light guide plate LG, a plurality of light sources LS, a reflective layer RF, and a plurality of prisms PM. The light guide plate LG has a side surface SF1, a side surface SF2 opposite to the side surface SF1, a side surface SF3 intersecting with the side surface SF2, a side surface SF4 intersecting with the side surface SF2 and opposite to the side surface SF3, a sloped surface CP1 connecting the side surfaces SF1 and SF3, and a sloped surface CP2 connecting the side surfaces SF1 and SF4. When viewed from above, the light guide plate LG has a hexagonal shape with sloped surfaces CP1 and CP2 formed by cutting out two corners opposite the tip of the arrow in the direction Y from a rectangular shape. When two illumination devices IL (or display devices DSP) according to this embodiment are used for virtual reality (VR) or the like, a space for accommodating a nose can be formed in the sloped surface CP1 or CP2. The length of the side surface SF1 in the direction X is shorter than the length of the side surface SF2 in the direction X. The lengths of the side surfaces SF3 and SF4 are the same. The inclined surface CP1 connects the end of the side surface SF1 opposite the tip of the arrow in the direction X with the end of the side surface SF3 opposite the tip of the arrow in the direction Y. The inclined surface CP2 connects the end of the side surface SF1 opposite the tip of the arrow in the direction X with the end of the side surface SF4 opposite the tip of the arrow in the direction Y. The multiple light sources LS are arranged in the direction X along the side surface SF1. The light intensity ratio of the multiple light sources LS arranged at the end of the direction X is greater than the light intensity ratio of the light sources LS arranged in the center in the direction X. Therefore, the illumination device IL can improve the brightness uniformity. In other words, the display device DSP can also improve the brightness uniformity.

[0090] (Variation 3) The illumination device IL according to Modification 3 of the third embodiment differs from the illumination devices IL of the first embodiment, Modification 1, Modification 2, second embodiment, and third embodiment in the configuration of the light guide plate LG.

[0091] FIG. 11 is a plan view of an illumination device IL according to the third modification. In the example shown in FIG. 11, the density of the prisms PM on the outer side of the light guide plate LG in the direction X is greater than the density of the prisms PM in the center (or inner side) in the direction X. For example, the density of the prisms PM in the third region A3 and the fifth region A5 is greater than the density of the prisms PM in the fourth region A4. The density of the prisms PM corresponds to the number of prisms arranged in a given area in a plan view. For example, in the third region A3 and the fifth region A5, the multiple prisms PM are arranged in the direction Y at an interval YD1. Furthermore, in the fourth region A4, the multiple prisms PM are arranged in the direction Y at an interval YD2 that is greater than the interval YD1.

[0092] The light intensity ratios of the multiple light sources LS may be the same or different. For example, the light intensity ratios of the multiple light sources LS may be the same. Furthermore, for example, as in the third embodiment described above, the light intensity ratio of the multiple light sources LS arranged at the end (or outer) sides in the direction X is greater than the light intensity ratio of the light sources LS arranged at the center (or inner) sides in the direction X. In this modified example 3, the same effects as those of the first embodiment, the second embodiment, the third embodiment, modified example 1, and modified example 2 are obtained.

[0093] All display devices that can be implemented by a person skilled in the art by appropriately modifying the design based on the display devices described above as embodiments of the present invention also fall within the scope of the present invention as long as they include the gist of the present invention.

[0094] Within the scope of the concept of the present invention, a person skilled in the art may conceive of various modifications, and these modifications are also understood to fall within the scope of the present invention. For example, even if a person skilled in the art appropriately adds or deletes components or modifies the design of the above-described embodiment, or adds or omits steps or modifies conditions, these modifications are also included within the scope of the present invention as long as they maintain the gist of the present invention.

[0095] Furthermore, with regard to other effects brought about by the aspects described in the above embodiments, those that are clear from the description in this specification or that can be appropriately thought of by a person skilled in the art are naturally understood to be brought about by the present invention. [Explanation of symbols]

[0096] PNL...display panel, SUB1...first substrate, SUB2...second substrate, LC...liquid crystal layer, SE...seal, PL1, PL2...polarizer, DS...diffusion sheet, PS...prism sheet, RS...reflective sheet, LG...light guide plate, 1A...main surface, 1B...opposing surface, SF1, SF2, SF3, SF4...side surface, PM...prism, LS1...light source, DL...emission direction, RD...reflection direction, AX...optical axis, SLP...slope, PLN...flat surface.

Claims

1. a light guide plate having a first side surface, a second side surface facing the first side surface in a first direction, a main surface, and an opposing surface facing the main surface in a second direction intersecting the first direction; a light source facing the first side surface and emitting light toward the first side surface; a reflective layer provided on the second side surface; a first prism provided on the opposing surface; a second prism provided on the opposing surface closer to the second side surface in the first direction than the first prism, the thickness of the light guide plate in the second direction increases from the first side surface to the second side surface in the first direction, the opposing surface has a first inclined surface, a second inclined surface located closer to the second side surface than the first inclined surface in the first direction, a third inclined surface located closer to the second side surface than the second inclined surface in the first direction, a fourth inclined surface located closer to the second side surface than the third inclined surface in the first direction, a first plane connecting the first inclined surface and the second inclined surface and parallel to the main surface, and a second plane connecting the third inclined surface and the fourth inclined surface and parallel to the main surface, the first prism and the second prism have cross-sectional shapes each having a triangular shape that protrudes to a side opposite the opposing surface in the second direction, the first prism is disposed on the first plane; the second prism is disposed on the second plane; a first height of the first prism in the second direction is smaller than a second height of the second prism in the second direction; a sum of the first height, a third height of the first inclined surface in the second direction, and a fourth height of the second inclined surface in the second direction is equal to the second height, a fifth height of the third inclined surface in the second direction, a height of the fourth inclined surface in the second direction and a sixth height of the fourth inclined surface in the second direction.

2. The cross-sectional shapes of the first prism and the second prism are formed into an isosceles triangle shape in which two base angles are a first angle. the first inclined surface and the second inclined surface are each inclined at the first angle with respect to the first plane; The lighting device according to claim 1 , wherein the third inclined surface and the fourth inclined surface are each inclined at the first angle with respect to the second plane.

3. a third prism disposed on a third plane; The illumination device according to claim 2 , wherein the third prism has a cross-sectional shape of an isosceles triangle having two base angles that are the first angle.

4. The lighting device according to claim 2 , wherein the opposing surface has a third plane that connects the second inclined surface and the third inclined surface and is parallel to the main surface.

5. The lighting device according to claim 2 , wherein the first angle is equal to or greater than a chief ray angle of light emitted from the light source and incident on the light guide plate through the first side surface.

6. the third height and the fourth height are the same; the fifth height and the sixth height are the same; The lighting device according to claim 1 , wherein the third height and the fourth height are greater than the fifth height and the sixth height.

7. the light guide plate has a third side surface that intersects with the second side surface, a fourth side surface that faces the third side surface in a third direction that intersects with the first direction and the second direction and intersects with the second side surface, a first surface that connects the first side surface and the third side surface, and a second surface that connects the first side surface and the fourth side surface, the light source includes a first light source, a second light source, and a third light source; a first length of the first side surface in the third direction is smaller than a second length of the second side surface in the third direction; the second light source is disposed between the first light source and the third light source in the third direction; The lighting device according to claim 1 , wherein a first light intensity ratio of the first light source and the third light source is greater than a second light intensity ratio of the second light source.

8. a light guide plate having a first side surface, a second side surface facing the first side surface in a first direction, a main surface, and an opposing surface facing the main surface in a second direction intersecting the first direction and parallel to the main surface; a light source facing the first side surface and emitting light toward the first side surface; a reflective layer provided on the second side surface; a first prism group provided on the opposing surface; a second prism group provided on the opposing surface closer to the second side surface in the first direction than the first prism group, the first prism group includes a first prism, a second prism positioned closer to the second side surface than the first prism in the first direction, and a third prism positioned closer to the second side surface than the second prism in the first direction, the second prism group includes a fourth prism, a fifth prism positioned closer to the second side surface than the fourth prism in the first direction, and a sixth prism positioned closer to the second side surface than the fifth prism in the first direction, a first height of the second prism in the second direction is smaller than a second height of the fifth prism in the second direction; a sum of the first height, a third height of the first prism in the second direction, and a fourth height of the third prism in the second direction is greater than a sum of the second height, a fifth height of the fourth prism in the second direction, and a sixth height of the sixth prism in the second direction.

9. The cross-sectional shapes of the second prism and the fifth prism are formed into an isosceles triangle shape in which two base angles are a first angle, 9. The lighting device according to claim 8, wherein the cross-sectional shapes of the first prism, the third prism, the fourth prism, and the sixth prism are formed into a triangular shape having a vertex where a first side inclined at the first angle with respect to the opposing surface intersects with a second side that is located closer to the second side surface than the first side in the first direction and is inclined at a second angle with respect to the opposing surface that is larger than the first angle.

10. 10. The lighting device of claim 9, wherein the second angle is 90 degrees.

11. the third height and the fourth height are the same; the fifth height and the sixth height are the same; The lighting device according to claim 8 , wherein the third height and the fourth height are greater than the fifth height and the sixth height.

12. the light guide plate has a third side surface that intersects with the second side surface, a fourth side surface that faces the third side surface in a third direction that intersects with the first direction and the second direction and intersects with the second side surface, a first surface that connects the first side surface and the third side surface, and a second surface that connects the first side surface and the fourth side surface, the light source includes a first light source, a second light source, and a third light source; a first length of the first side surface in the third direction is smaller than a second length of the second side surface in the third direction; the second light source is disposed between the first light source and the third light source in the third direction; 12. The lighting device according to claim 8, wherein a first light intensity ratio of the first light source and the third light source is greater than a second light intensity ratio of the second light source.

13. a light guide plate having a first side surface, a second side surface facing the first side surface in a first direction, a third side surface intersecting the second side surface, a fourth side surface facing the third side surface in a third direction intersecting the first direction and a second direction intersecting the first direction and intersecting the second side surface, a first surface connecting the first side surface and the third side surface, and a second surface connecting the first side surface and the fourth side surface; a first light source, a second light source, and a third light source facing the first side surface and emitting light toward the first side surface; a reflective layer provided on the second side surface, a first length of the first side surface in the third direction is smaller than a second length of the second side surface in the third direction; the second light source is disposed between the first light source and the third light source in the third direction; a first light intensity ratio of the first light source and the third light source is greater than a second light intensity ratio of the second light source; a plurality of prisms provided on the light guide plate; An illumination device, wherein a first density of prisms arranged on the outer side in the third direction is greater than a second density of prisms arranged in a central portion in the third direction.

14. A lighting device according to any one of claims 1 to 13; a display panel for displaying an image, The display device, wherein the display panel faces the lighting device.

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