Patent Publication Number: US-2023152630-A1

Title: Illumination device and display device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2021-186415, filed Nov. 16, 2021, the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate generally to an illumination device and a display device. 
     BACKGROUND 
     For example, a display device such as a liquid crystal display device comprises a display panel with pixels and an illumination device such as a backlight that illuminates the display panel. The illumination device comprises a light source that emits light and a light guide to which light from the light source is emitted. The light from the light source is made incident on the light guide from a side surface of the light guide, propagates the inside of the light guide, and is emitted from an emission surface corresponding to one of main surfaces of the light guide. 
     For example, a configuration in which two light guides overlap is also known. In conventional illumination devices, however, there is a problem that the light partially escapes from the light guide before made incident from the side surface of the light guide and emitted from the emission surface, resulting in the decrease in emission efficiency. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is an exploded perspective view showing a configuration example of a display device of a first embodiment. 
         FIG.  2    is a plan view of the illumination device shown in  FIG.  1   . 
         FIG.  3    is a cross-sectional view of the display device shown in  FIG.  1   . 
         FIG.  4    is a perspective view showing an example of a configuration of each of reflective layers. 
         FIG.  5    is a schematic diagram showing an example of the change in reflectance of S-polarized light and P-polarized light with respect to angles of incidence of the S-polarized light and P-polarized light made incident on a light guide from air. 
         FIG.  6    is a schematic diagram showing an example of the P-polarized light made incident from air to the light guide. 
         FIG.  7    is a schematic diagram showing an example of the change in reflectance of the S-polarized light and the P-polarized light with respect to angles of incidence of the S-polarized light and the P-polarized light made incident on the light guide from air. 
         FIG.  8    is a schematic diagram showing an example of P-polarized light made incident from the light guide to air. 
         FIG.  9    is a cross-sectional view showing a configuration example of an illumination device of a comparative example. 
         FIG.  10    is a perspective view showing an example of a configuration of each of reflective layers corresponding to the illumination device of  FIG.  9   . 
         FIG.  11    is a view showing an example of the change in luminance of the illumination device of  FIG.  9    in a direction Y with respect to a distance X in a case where P-polarized light and S-polarized light are made incident. 
         FIG.  12    is a cross-sectional view showing an example of the arrangement of the light source with respect to the light guide of the illumination device shown in  FIG.  3   . 
         FIG.  13    is a cross-sectional view showing an example of the arrangement of the light source with respect to the light guide of the illumination device shown in  FIG.  3   . 
         FIG.  14    is a cross-sectional view showing an example of the arrangement of the light source with respect to the light guide of the illumination device according to modified example 1. 
         FIG.  15    is a cross-sectional view showing an example of the arrangement of the light source with respect to the light guide of the illumination device according to modified example 1. 
         FIG.  16    is a cross-sectional view showing a display device according to a second embodiment. 
         FIG.  17    is a cross-sectional view showing an example of the arrangement of the light source with respect to the light guide of the illumination device according to the second embodiment. 
         FIG.  18    is a cross-sectional view showing an example of the arrangement of the light source with respect to the light guide of the illumination device according to the second embodiment. 
         FIG.  19    is a cross-sectional view showing an example of the arrangement of the light source with respect to the light guide of the illumination device according to modified example 2. 
         FIG.  20    is a cross-sectional view showing an example of the arrangement of the light source with respect to the light guide of the illumination device according to modified example 2. 
     
    
    
     DETAILED DESCRIPTION 
     In general, according to one embodiment, an illumination device comprises a first light guide having a first side surface, a second side surface located on a side opposite to the first side surface in a first direction, a first main surface, and a first opposed surface located on a side opposite to the first main surface in a second direction intersecting the first direction and a first light source opposed to the first side surface to emit first P-polarized light to the first side surface, the first side surface is inclined to the first main surface and the first opposed surface, the first light source is inclined to a first straight line perpendicular to the first side surface. 
     According to another embodiment, a display device comprises the illumination device and a display panel displaying an image, the display panel is opposed to the first main surface. 
     According to the configuration described above, an illumination device and a display device capable of improving an emission efficiency can be provided. 
     Embodiments will be described hereinafter with reference to the accompanying drawings. 
     The disclosure is merely an example, and proper changes in keeping with the spirit of the invention, which are easily conceivable by a person of ordinary skill in the art, come within the scope of the invention as a matter of course. In addition, in some cases, in order to make the description clearer, the widths, thicknesses, shapes and the like, of the respective parts are illustrated schematically in the drawings, rather than as an accurate representation of what is implemented. However, such schematic illustration is merely exemplary, and in no way restricts the interpretation of the invention. In addition, in the specification and drawings, structural elements which function in the same or a similar manner to those described in connection with preceding drawings are denoted by like reference numbers, detailed description thereof being omitted unless necessary. 
     In the embodiments, a transmissive liquid crystal display device is disclosed as an example of the display device DSP. In addition, an illumination device used as a backlight of a transmissive liquid crystal display device is disclosed as an example of the illumination device. A main configuration disclosed in the embodiments can be applied to a liquid crystal display device comprising not only a transmissive function, but also a reflective function reflecting external light and using the external light for the display, an electronic paper display device with electrophoretic elements and the like, a display device utilizing micro-electromechanical systems (MEMS), a display device employing electrochromism, or the like. Furthermore, the main configuration disclosed in the embodiments can also be applied to an illumination device used for applications other than the backlight. 
     First Embodiment 
       FIG.  1    is an exploded perspective view showing a configuration example of a display device DSP according to the embodiment.  FIG.  1    shows a direction X, a direction Y (first direction), and a direction Z (second direction). The direction X, the direction Y, and the direction Z are orthogonal to each other but may intersect at an angle other than 90 degrees. The direction X and the direction Y correspond to directions parallel to a main surface of a substrate constituting a liquid crystal display device (hereinafter often simply referred to as a display device) DSP, and the direction Z corresponds to a thickness direction of the display device DSP. In the present specification, a direction from a first substrate SUB 1  to a second substrate SUB 2  is referred to as an upper side (or, more simply, upwardly) and a direction from the second substrate SUB 2  to the first substrate SUB 1  is referred to as a lower side (or, more simply, downwardly). According to “a second layer above a first layer” and “a second layer under a first layer”, the second layer may be in contact with the first layer or may be separated from the first layer. It is assumed that an observation position at which the display device DSP is to be observed is set at a tip side of an arrow indicating the third direction Z, and viewing toward an X-Y plane defined by the direction X and the direction Y from this observation position is referred to as planar view. The X-Z plane is defined by the direction X and the direction Z. The Y-Z plane is defined by the second direction and the direction Z. IN addition, a “length of a predetermined substance, object, or area in the direction X and the direction Y” is often referred to as a “width”, and a “length of a predetermined substance, object, or area in the third direction” is often referred to as a “thickness” or a “height”. 
     The display device DSP comprises a display panel PNL, an illumination device IL, an IC chip  1 , and a wiring board  2 . 
     The display panel PNL comprises a first substrate SUB 1  and a second substrate SUB 2 . The first substrate SUB 1  and the second substrate SUB 2  are opposed to each other. A display function layer (liquid crystal layer LC to be described later, in the embodiment) is provided between the substrates SUB 1  and SUB 2 . The display panel PNL includes a display area DA and a non-display area NDA. The display area DA is an area where images are displayed. The display area DA is located substantially in the center of the area where the first substrate SUB 1  and the second substrate SUB 2  are opposed to each other. The non-display area NDA is an area where no images are displayed and is located outside the display area DA. The display panel PNL comprises, for example, a plurality of pixels PX arrayed in a matrix in the display area DA. 
     The IC chip  1  and the wiring board  2  often read signals from the display panel PNL, but mainly function as signal sources which supply signals to the display panel PNL. The IC chip  1  and the wiring board  2  are located in the non-display area NDA. In the example shown in  FIG.  1   , the IC chip  1  and the wiring substrate  2  are located on a mounting portion MT of the first substrate SUB 1  extending outside from a substrate side edge (or often referred to as a substrate end portion) of the second substrate SUB 2 . The wiring board  2  is, for example, a foldable flexible printed board. The IC chip  1  may be provided on the wiring board  2 . 
     The illumination device IL illuminates the display panel PNL. The illumination device IL comprises a light guide LG 1 , a light guide LG 2 , a plurality of light sources LS 1 , and a plurality of light sources LS 2 . The light guide LG 2 , the light guide LG 1 , the first substrate SUB 1 , and the second substrate SUB 2  are arranged in order of description toward the tip side of the arrow in the direction Z. 
     The light guide LG 1  is an insulating substrate such as a glass substrate or a plastic substrate. The light guide LG 1  is formed of a substrate formed of a material containing acrylic resin, for example, an acrylic substrate. The light guide LG 1  is formed in a flat plate shape parallel to the X-Y plane. The light guide LG 1  has a main surface  1 A opposed to the display panel PNL, an opposed surface  1 B located on a side opposite to the main surface  1 A in the direction Z, a side surface SF 1 , and a side surface SF 2  located on a side opposite to the side surface SF 1  in the direction Y. The main surface  1 A and the opposed surface  1 B are, for example, parallel to the X-Y plane and are provided parallel to each other. The main surface  1 A and the opposed surface  1 B may be non-parallel to each other. The side surface SF 1  and the side surface SF 2  are opposed to each other in the direction Y. The side surface SF 1  is, for example, non-parallel to the X-Z plane. The side surface SF 2  is, for example, parallel to the X-Z plane. The side surface SF 1  and the side surface SF 2  are, for example, provided non-parallel to each other. The side surface SF 1  and the side surface SF 2  may be provided parallel to the X-Z plane and parallel to each other. The light guide LG 1  has a thickness T 1 . The thickness T 1  is equal to a length from the opposed surface  1 B to the main surface  1 A in the direction Z. 
     The plurality of light sources LS 1  are arranged at intervals in the direction X. In the example shown in  FIG.  1   , the plurality of light sources LS 1  are opposed to the side surface SF 1 . In addition, the plurality of light sources LS 1  are spaced apart in the direction X and arranged along the side surface SF 1 . 
     The light guide LG 2  is an insulating substrate such as a glass substrate or a plastic substrate. The light guide LG 2  is formed of, for example, the same material as the light guide LG 1 . The light guide LG 2  may not be formed of the same material as the light guide LG 1 . The light guide LG 2  is formed of a substrate formed of a material containing acrylic resin, for example, an acrylic substrate. The light guide LG 2  is formed in a flat plate shape parallel to the X-Y plane. The light guide LG 2  has a main surface  2 A opposed to the opposed surface  1 B, an opposed surface  2 B located on a side opposite to the main surface  2 A in the direction Z, a side surface SF 3  arranged with the side surface SF 1  in the direction Z, and a side surface SF 4  located on a side opposite to the side surface SF 3  in the direction Y and arranged with the side surface SF 2  in the direction Z. The main surface  2 A and the opposed surface  2 B are, for example, parallel to the X-Y plane and are provided parallel to each other. The main surface  2 A and the opposed surface  2 B may be non-parallel to each other. The side surface SF 3  and the side surface SF 4  are opposed to each other in the direction Y. The side surface SF 3  is, for example, parallel to the X-Z plane. The side surface SF 4  is, for example, non-parallel to the X-Z plane. The side surface SF 3  and the side surface SF 4  are, for example, provided non-parallel to each other. The side surface SF 3  and the side surface SF 4  may be provided parallel to the X-Z plane and parallel to each other. The light guide LG 2  has a thickness T 2 . The thickness T 2  is equal to a length from the opposed surface  2 B to the main surface  2 A in the direction Z. 
     The plurality of light sources LS 2  are arranged at intervals in the direction X. In the example shown in  FIG.  1   , the plurality of light sources LS 2  are opposed to the side surface SF 4 . In addition, the plurality of light sources LS 2  are spaced apart in the direction X and arranged along the side surface SF 4 . 
     The light sources LS 1  and LS 2  are, for example, laser light sources such as semiconductor lasers that emit polarized laser light. The light sources LS 1  and LS 2  are not limited to the light sources emitting laser light, but may be, for example, light emitting diodes. 
     The light sources LS 1  and LS 2  may comprise a plurality of light emitting elements that emit light of different colors. For example, each of the light sources LS 1  and LS 2  comprises three light emitting elements that emit red, green, and blue light, respectively. When comprising three light emitting elements that emit red, green, and blue light, the light sources LS 1  and LS 2  can obtain light of a mixture of these colors (for example, white color). 
       FIG.  2    is a plan view of the illumination device IL shown in  FIG.  1   . As shown in  FIG.  2   , the illumination device IL includes a first area A 1 , a second area A 2 , and a boundary BO between the first area A 1  and the second area A 2 . The first area A 1  has a length LN 10  in the direction Y, and the second area A 2  has a length LN 20  in the direction Y. The length LN 10  is equal to the length LN 20 . The length LN 10  may not be equal to the length LN 20 . The terms “same”, “identical”, “equivalent”, and “equal” mean indicate that a plurality of target objects, spaces, areas or the like are the same in physical quantity, material, configuration (structure) or the like, and are slightly different to the extent that they can be regarded as substantially the same. In the example shown in  FIG.  2   , each of the light guide LG 1  and light guide LG 2  is located in the entire first area A 1  and the entire second area A 2 . In other words, each of the main surface  1 A, the opposed surface  1 B, the main surface  2 A, and the opposed surface  2 B shown in  FIG.  2    is located in the first area A 1  and the second area A 2 . The side surface SF 1  and the side surface SF 3  are located in the first area A 1 , and the side surface SF 2  and the side surface SF 4  are located in the second area A 2 . The boundary BO corresponds to each of a middle part between the side surface SF 1  and the side surface SF 2  and a middle part between the side surface SF 3  and the side surface SF 4 . For example, the boundary BO corresponds to a middle part between a leading part opposite to a tip side of an arrow indicating the direction Y of the side surface SF 1  and a leading part on a tip side of an arrow indicating the direction Y of the side surface SF 2 . For example, the boundary BO corresponds to a middle part between a leading part opposite to a tip side of an arrow indicating the direction Y of the side surface SF 3  and a leading part on a tip side of an arrow indicating the direction Y of the side surface SF 4 . 
     The light source LS 1  emits light toward the side surface SF 1  in an emission direction DL 1 . The intensity of the light emitted from the light source LS 1  is the highest at the optical axis AX 1 , and the emission direction DL 1  is parallel to the optical axis AX 1 . The light source LS 2  emits light toward the side surface SF 4  in the emission direction DL 2 . The intensity of the light emitted from the light source LS 2  is the highest at the optical axis AX 2 , and the emission direction DL 2  is parallel to the optical axis AX 2 . 
       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 comprises a liquid crystal layer LC, a seal SE, a polarizer PL 1 , and a polarizer PL 2 . 
     The liquid crystal layer LC and the seal SE are located between the first substrate SUB 1  and the second substrate SUB 2 . The seal SE bonds a first substrate SUB 1  and a second substrate SUB 2 , and seals a liquid crystal layer LC between the first substrate SUB 1  and the second substrate SUB 2 . 
     The polarizer PL 1  is bonded to a lower surface of the first substrate SUB 1 . The polarizer PL 2  is bonded to an upper surface of the second substrate SUB 2 . A polarization axis of the polarizer PL 1  and a polarization axis of the polarizer PL 2  are, for example, orthogonal to each other. 
     The illumination device IL further comprises a reflective layer P 1 , a reflective layer P 2 , a diffusion sheet DS, a prism sheet PS, and a reflective sheet RS. A plurality of, for example, two prism sheets PS may be provided to overlap in the direction Z. 
     The diffusion sheet DS is located between the display panel PNL and the light guide LG 1 . The diffusion sheet DS diffuses light made incident on the diffusion sheet DS to uniform the luminance of the light. The prism sheet PS is located between the diffusion sheet DS and the light guide LG 1 . For example, the prism sheet PS focuses light emitted from the main surface  1 A of the light guide LG 1 , in the direction Z. The prism sheet PS is composed of a plurality of prisms continuously arranged in the direction Y. The plurality of prisms of the prism sheet PS protrude toward the main surface  1 A in the direction Z. The prisms of the prism sheet PS have a triangular cross-sectional shape parallel to the Y-Z plane. The cross-sectional shapes of each prism of the prism sheet PS parallel to the Y-Z plane are similar to each other. A bottom angle of the prisms of the prism sheet PS may be hereinafter referred to as an inverted prism bottom angle. The reflective sheet RS is opposed to the opposed surface  2 B of the light guide LG 2 . For example, the reflective sheet RS reflects the light leaking from within the light guide LG 2  and makes the light incident on the light guide LG 2  again. 
     In the illumination device IL, the side surface SF 1  is a slope that extends toward a direction between the side opposite to the tip of the arrow indicating the direction Y and the tip side of the arrow indicating the direction Z. In other words, the side surface SF 1  is a slope that extends from the inside to the outside of direction Y according to the direction Z from the lower side to the upper side. In  FIG.  3   , the main surface  1 A extends to a side opposite to the tip of the arrow indicating the direction Y with respect to the opposed surface  1 B. The side surface SF 1  may be a slope that extends in a direction between a side opposite to the tip of the arrow indicating the direction Y and a side opposite to the tip of the arrow indicating the direction Z. In other words, the side surface SF 1  may be a slope that extends from the inside to the outside of the direction Y according to the direction Z from the upper side to the lower side. In  FIG.  3   , the opposed surface lB may extend to a side opposite to the tip of the arrow indicating the direction Y with respect to the main surface  1 A. 
     The side surface SF 1  is inclined at an acute angle to the main surface  1 A and at an obtuse angle to the opposed surface  1 B. In other words, the side surface SF 1  is inclined at an acute angle to the main surface  1 A. In addition, the side surface SF 1  is inclined at an obtuse angle to the opposed side  1 B. For example, the side surface SF 1  is inclined at an angle smaller than 90° with respect to the main surface  1 A and at an angle larger than 90° (degrees)—Brewster&#39;s angle. The side surface SF 1  may be inclined at an obtuse angle with respect to the main surface  1 A and at an acute angle with respect to the opposed surface  1 B. In other words, the side surface SF 1  may be inclined at an obtuse angle with respect to the main surface  1 A. In addition, the side surface SF 1  may be inclined at an acute angle with respect to the opposed surface  1 B. For example, the side surface SF 1  may be inclined at an angle larger than 90° with respect to the main surface  1 A and at an angle smaller than 90° (degrees)—Brewster&#39;s angle. 
     In the illumination device IL, the side surface SF 4  is a slope that extends toward a direction between the tip side of the arrow indicating the direction Y and the tip side of the arrow indicating the direction Z. In other words, the side surface SF 4  is a slope that extends from the inside to the outside of direction Y according to the direction Z from the lower side to the upper side. In  FIG.  3   , the main surface  2 A extends to the tip side of the arrow indicating the direction Y with respect to the opposed surface  2 B. The side surface SF 4  may be a slope that extends in a direction between the the tip side of the arrow indicating the direction Y and a side opposite to the tip of the arrow indicating the direction Z. In other words, the side surface SF 4  is a slope that extends from the inside to the outside of the direction Y according to the direction Z from the upper side to the lower side. In  FIG.  3   , the opposed surface  2 B may extend to the side of the arrow indicating the direction Y with respect to the main surface  2 A. 
     The side surface SF 4  is inclined at an acute angle to the main surface  2 A and at an obtuse angle to the opposed surface  2 B. In other words, the side surface SF 4  is inclined at an acute angle with respect to the main surface  2 A. In addition, the side surface SF 4  is inclined at an obtuse angle to the opposed surface  2 B. For example, the side surface SF 4  is inclined at an angle smaller than 90° with respect to the main surface  2 A and at an angle larger than 90°—Brewster&#39;s angle. The side surface SF 4  may be inclined at an obtuse angle with respect to the main surface  2 A and at an acute angle with respect to the opposed surface  2 B. In other words, the side surface SF 4  may be inclined at an obtuse angle with respect to the main surface  2 A. In addition, the side surface SF 4  may be inclined at an acute angle with respect to the opposed surface  2 B. For example, the side surface SF 4  may be inclined at an angle larger than 0° with respect to the main surface  2 A and at an angle smaller than 90°—Brewster&#39;s angle. 
     Each of the reflective layer P 1  and the reflective layer P 2  is a layer including a plurality of prisms, which will be described below in detail. 
     The reflective layer P 1  is located on the opposed side  1 B. The reflective layer P 1  extends from the second area A 2  to a predetermined position between the boundary BO and the side surface SF 1  beyond the boundary BO, in the direction Y. The reflective layer P 1  may extend within the second area A 2 . The reflective layer P 1  includes an end portion E 10  on the tip side of the arrow indicating the direction Y and an end portion E 11  on the side opposite to the end portion E 10  in the direction Y. The end portion E 10  is located between the boundary BO and the side surface SF 2 . The end portion E 10  is located on the side surface SF 2  side between the boundary BO and the side surface SF 2 . The end portion E 10  is close to the side surface SF 2 . For example, the end portion E 10  overlaps with the side surface SF 2 . The end portion E 10  may not overlap with the side surface SF 2 . The end portion E 11  is located between the side surface SF 1  and the boundary BO. The end portion E 11  is located on the boundary BO side between the side surface SF 1  and the boundary BO. The end portion E 11  is located near the boundary BO. The end portion E 11  may be located between the side surface SF 2  and the boundary BO. The end portion E 11  may be located on the boundary BO side between the side surface SF 2  and the boundary BO. For example, the end portion E 10  corresponds to the position of the prism closest to the side surface SF 2 , of the plurality of prisms included in the reflective layer P 1  (prisms PA to be described below). For example, the end portion E 11  corresponds to the position of the prism closest to the side surface SF 1 , of the plurality of prisms included in the reflective layer P 1  (prisms PA to be described below). 
     The reflective layer P 2  is located on the opposed surface  2 B. The reflective layer P 2  extends from the second area A 2  to a predetermined position between the boundary BO and the side surface SF 4  beyond the boundary BO. The reflective layer P 2  may extend within the second area A 2 . The reflective layer P 2  includes an end portion E 20  and an end portion E 21  on the side opposite to the end portion E 20 . The end portion E 20  is located between the side surface SF 3  and the boundary BO. The end portion E 20  is located on the side surface SF 3  side between the side surface SF 3  and the boundary BO. The end portion E 20  is close to the side surface SF 3 . For example, the end portion E 20  overlaps with the side surface SF 3 . The end portion E 20  may not overlap with the side surface SF 3 . The end portion E 21  is located between the boundary BO and the side surface SF 4 . The end portion E 21  is located on the boundary BO side between the boundary BO and the side surface SF 4 . The end portion E 21  is located near the boundary BO. The end portion E 21  may be located between the side surface SF 3  and the boundary BO. The end portion E 21  may be located on the boundary BO side between the side surface SF 3  and the boundary BO. For example, the end portion E 20  corresponds to the position of the prism closest to the side surface SF 3 , of the plurality of prisms included in the reflective layer P 2  (prisms PA to be described below). For example, the end portion E 21  corresponds to the position of the prism closest to the side surface SF 4 , of the plurality of prisms included in the reflective layer P 2  (prisms PA to be described below). 
     The reflective layer P 1  and the reflective layer P 2  overlap with each other in the direction Z in the boundary BO and the vicinity of the boundary BO. The reflective layer P 1  and the reflective layer P 2  may not overlap with each other in the direction Z in the boundary BO and the vicinity of the boundary BO. 
     The light source LS 1  is separated from the side surface SF 1 . The emission direction DL 1  of the light source LS 1  is the direction that intersects a line parallel to a center line passing the center of the thickness T 1  of the light guide LG 1  and extending in the direction Y. The light source LS 2  is separated from the side surface SF 4 . The emission direction DL 2  of the light source LS 2  is the direction that intersects a line parallel to a center line passing the center of the thickness T 2  of the light guide LG 2  and extending in the direction Y. 
     Light L 1  emitted from the light source LS 1  is not reflected at all or almost at an interface between the side surface SF 1  and an air layer, but is made incident on the light guide LG 1  from the side surface SF 1  and is refracted on the side surface SF 1 . Light traveling toward the opposed surface  1 B, of the light L 1  made incident on the light guide LG 1  is reflected (for example, total reflection) at the interface between the light guide LG 1  and the air layer. In addition, light traveling toward the main surface  1 A, of the light L 1  made incident on the light guide LG 1  is reflected (for example, total reflection) at the interface between the light guide LG 1  and the air layer. Thus, in the area where the reflective layer P 1  is not provided, of the first area A 1 , the light L 1  travels toward the tip side of the arrow indicating the direction Y, inside the light guide LG 1 , while repeatedly reflected on the main surface  1 A and the opposed surface  1 B (for example, total reflection). The angle of the total reflection condition is a constant value calculated by subtracting a critical angle which is calculated based on the refractive index of the light guide LG 1  and the refractive index of the air layer, from 90°, and is 48° in a case where the light guide LG 1  is formed of, for example, glass. When the angle formed between the light and the main surface or opposed surface is smaller than or equal to the angle of total reflection condition, the light is totally reflected on the main surface or opposed surface. In contrast, when the angle formed between the light and the main surface or opposed surface is larger than the angle of total reflection condition, the light deviates from the total reflection condition and is extracted from the main surface or opposed surface, which is the emission surface. 
     Light traveling toward the reflective layer P 1 , of the light L 1  traveling inside the light guide LG 1 , is reflected on the prisms of the reflective layer P 1  such that its traveling direction is changed. The light reflected on the prisms of the reflective layer P 1  deviates from the total reflection condition of the main surface  1 A and is emitted from the main surface  1 A. The light emitted from the main surface  1 A illuminates the display panel PNL through the prism sheet PS and the diffusion sheet DS. In other words, in the area where the reflective layer P 1  is not provided (or the area close to the side surface SF 1 ), of the first area A 1 , emission of the light L 1  incident from the side surface SF 1 , from the light guide LG 1  toward the display panel PNL, is suppressed. 
     Similarly, light L 2  emitted from the light source LS 2  is not reflected at all or almost at the interface between the side surface SF 4  and the air layer, but is made incident on the light guide LG 2  from the side surface SF 4  and is refracted on the side surface SF 4 . Light traveling toward the opposed surface  2 B, of the light L 2  made incident on the light guide LG 2  is reflected (for example, total reflection) at the interface between the light guide LG 2  and the air layer. In addition, light traveling toward the main surface  2 A, of the light L 2  made incident on the light guide LG 2  is reflected (for example, total reflection) at the interface between the light guide LG 2  and the air layer. Thus, in the area where the reflective layer P 2  is not provided, of the second area A 2 , the light L 2  travels toward the side opposite to the tip side of the arrow indicating the direction Y, inside the light guide LG 2 , while repeatedly reflected on the main surface  2 A and the opposed surface  2 B (for example, total reflection). 
     The light L 2  traveling toward the reflective layer P 2 , of the light L 2  traveling inside the light guide LG 2 , is reflected on the prisms of the reflective layer P 2  such that its traveling direction is changed. The light reflected on the prisms of the reflective layer P 2  deviates from the total reflection condition of the main surface  2 A and is emitted from the main surface  2 A. The light emitted from the main surface  2 A illuminates the display panel PNL through the light guide LG 1 , the prism sheet PS, and the diffusion sheet DS. In other words, in the area where the reflective layer P 2  is not provided (or the area close to the side surface SF 4 ), of the second area A 2 , emission of the light L 2  incident from the side surface SF 4 , from the light guide LG 2  toward the display panel PNL, is suppressed. 
     The display panel PNL is illuminated in the first area A 1  mainly by the light L 2  from the light source LS 2 . The display panel PNL is illuminated in the second area A 2  mainly by the light L 1  from the light source LS 1 . 
     In general, light beams from a plurality of light sources arranged at intervals travel inside the light guide while each diffused, but these light beams are not mixed sufficiently in the vicinity of the light sources. For this reason, in a display device using such light as illumination light, there is a risk that stripe-shaped non-uniformity in luminance or chromaticity deviation resulting from differences in intensity may be visually recognized when the display area is watched in planar view. The difference in intensity of illumination light is smaller at a position more separated from the light source. 
     In the example shown in  FIG.  3   , in the area where the reflective layer P 1  is not provided, of the first area A 1 , the light L 1  made incident from the side surface SF 1  is confined within the light guide LG 1 , and its incidence on the display panel PNL is suppressed. In the first area A 1 , the light L 1  from the light source LS 1  is hardly made incident on the display panel PNL, but the light L 2  from the light source LS 2  illuminates the display panel PNL. The second area A 2  is separated from the side surface SF 1  in a distance sufficient for the light L 1  to be mutually mixed. For this reason, in the second area A 2 , the degradation of display quality (illumination quality) resulting from non-uniformity in luminance and chromaticity deviation of the illumination light can be suppressed. 
     Similarly, in the area where the reflective layer P 2  is not provided, of the second area A 2 , the light L 2  made incident from the side surface SF 3  is confined within the light guide LG 2  and its incidence on the display panel PNL is suppressed. In the second area A 2 , the light L 2  from the light source LS 2  is hardly made incident on the display panel PNL, but the light L 1  from the light source LS 1  illuminates the display panel PNL. The first area A 1  is separated from the side surface SF 4  in a distance sufficient for the light L 2  to be mutually mixed. For this reason, in the first area A 1 , the degradation of display quality (illumination quality) resulting from non-uniformity in luminance and chromaticity deviation of the illumination light can be suppressed. 
     Furthermore, the reflective layer P 1  extends to the first area A 1  beyond the boundary BO and the reflective layer P 2  extends to the second area A 2  beyond the boundary BO. For this reason, the situation where the luminance level of the light emitted from the illumination device IL decreases in the vicinity of the boundary BO can be avoided. When the end portion E 11  of the reflective layer P 1  and the end portion E 21  of the reflective layer P 2  are located at the boundary BO, the luminance level of the light emitted from the illumination device IL may be lowered in the vicinity of the boundary BO. 
       FIG.  4    is a perspective view showing an example of a configuration of the reflective layer P 1  and the reflective layer P 2 .  FIG.  4    corresponds to  FIG.  3   . Constituent elements necessary for explanations alone are shown in  FIG.  4   . 
     In the example shown in  FIG.  4   , the reflective layer P 1  includes a plurality of prisms PA (first prisms). In the reflective layer P 1 , the plurality of prisms PA are intermittently arranged in the direction Y. The reflective layer P 2  includes a plurality of prisms PB (second prisms). In the reflective layer P 2 , the plurality of prisms PB are intermittently arranged in the direction Y. The plurality of prisms PA are provided on the opposed surface  1 B. The plurality of prisms PB are provided on the opposed surface  2 B. For example, the prisms PA are formed integrally with the light guide LG 1 . Similarly, the prisms PB are formed integrally with the light guide LG 2 . 
     The prisms PA protrude from the opposed side  1 B toward the main surface  2 A. In other words, the prisms PA protrude toward the side opposite to the tip side of the arrow indicating the direction Z. The prisms PA have a triangular cross-sectional shape parallel to the Y-Z plane and extend in the direction X. For example, the cross-sectional shapes of the respective prisms PA parallel to the Y-Z plane are similar to each other. The prism PA has a slope SL 1  (first slope), a slope SL 2  (second slope), a reference plane BL 1 , and a vertex VT 1 . A height HA of the prism PA is a height of the prism PA in the normal direction of the reference plane BL 1  (opposed surface  1 B), and corresponds to a length in the direction Z from the reference plane BL 1  to the vertex VT 1 . 
     In the prism PA, the slope SL 1  is located on the side surface SF 2 , and the slope SL 2  is located on the side surface SF 1  side. The reference plane BL 1  is located on the same plane as the opposed surface  1 B. The vertex VT 1  corresponds to a point where the slope SL 1  and the slope SL 2  intersect. 
     A plurality of vertices VT 1  are arranged at regular intervals LG 30  in the direction Y. The interval LG 30  is, for example, 0.1 mm. In the example shown in  FIG.  4   , an angle α 1  formed between the slope SL 1  and the reference plane BL 1  is equal to an angle α 2  formed between the slope SL 2  and the reference plane BL 1 . The angle α 1  corresponds to one of internal angles in the cross-section of the prism PA, and the angle α 2  corresponds to one of the internal angles in the cross-section of the prism PA other than the angle α 1 . The angle α 1  and the angle α 2  may be referred to as prism angles of the prism PA. The cross-section of the prism PA is shaped in an isosceles triangle. The cross-section of the prism PA may not be shaped in an isosceles triangle. 
     In the example shown in  FIG.  4   , the height HA of each of the plurality of prisms PA becomes smaller from the side surface SF 2  toward the side surface SF 1 . In other words, the height HA of each of the plurality of prisms PA becomes larger as the prism PA is farther from the light source LS 1 . The height HA of each of the plurality of prisms PA may be the same. In the direction Y, the ratio of the prism PA (reference plane BL 1 ) per unit area in the X-Y plane increases and the ratio of the opposed surface  1 B per unit area in the X-Y plane decreases, from the end portion E 11  toward the end portion E 10 . In contrast, when light traveling in the light guide LG 1  progresses to the prism PA of the reflective layer P 1  and is emitted from the light guide LG 1 , the amount of light traveling in the light guide LG 1  decreases. As a result, the illumination device IL can irradiate the display panel PNL with the illumination light that has uniform luminance distribution in the second area A 2 . 
     The prism PB protrudes from the opposed surface  2 B toward the reflective sheet RS. In other words, the prism PB protrudes toward the side opposite to the tip side of the arrow indicating the direction Z. The prisms PB have a triangular cross-sectional shape parallel to the Y-Z plane and extend in the direction X. For example, the cross-sectional shapes of the respective prisms PA parallel to the Y-Z plane are similar to each other. The prism PB has a slope SL 3  (third slope), a slope SL 4  (fourth slope), a reference plane BL 2 , and a vertex VT 2 . A height HB of the prism PB is a height of the prism PB in the normal direction of the reference plane BL 2  (opposed surface  2 B), and corresponds to a length in the direction Z from the reference plane BL 2  to the vertex VT 2 . 
     In the prism PB, the slope SL 3  is located on the side surface SF 4  side, and the slope SL 4  is located on the side surface SF 3  side. The reference plane BL 2  is located on the same plane as the opposed surface  2 B. The vertex VT 2  corresponds to a point where the slopes SL 3  and the slope SL 4  intersect. 
     The plurality of vertices VT 2  are arranged at regular intervals LG 30  in the direction Y. In the example shown in  FIG.  4   , an angle α 3  formed by the slope SL 3  and the reference plane BL 2  is equal to an angle α 4  formed by the slope SL 4  and the reference plane BL 2 . The angle α 3  corresponds to one of internal angles in the cross-section of the prism PB, and the angle α 4  corresponds to one of the internal angles in the cross-section of the prism PB other than the angle α 3 . The angle α 3  and the angle α 4  may be referred to as prism angles of the prism PB. The cross-section of the prism PB is shaped in an isosceles triangle. The cross-section of the prism PB may not be shaped in an isosceles triangle. 
     In the example shown in  FIG.  4   , the height HB of each of the plurality of prisms PB is made smaller from the side surface SF 3  toward the side surface SF 4 . In other words, the height HB of each of the plurality of prisms PB becomes larger as the prism PB is farther from the light source LS 2 . The height HB of each of the plurality of prisms PB may be the same. In the direction Y, the ratio of the prism PB (reference plane BL 2 ) per unit area in the X-Y plane increases and the ratio of the opposed surface  2 B per unit area in the X-Y plane decreases, from the end portion E 21  toward the end portion E 20 . In contrast, when light traveling in the light guide LG 2  progresses to the prism PB of the reflective layer P 2  and is emitted from the light guide LG 2 , the amount of light traveling in the light guide LG 2  decreases. As a result, the illumination device IL can irradiate the display panel PNL with the illumination light that has uniform luminance distribution in the first area A 1 . 
       FIG.  5    is a schematic diagram showing an example of the change in reflectance of S-polarized light and P-polarized light with respect to angles of incidence of the S-polarized light and P-polarized light made incident on a light guide from air. In  FIG.  5   , the vertical axis indicates the reflectance of light, and the horizontal axis indicates the angle of incidence of light [° (degree)].  FIG.  5    shows a change in reflectance Rp 1  of the P-polarized light to the angle of incidence of the P-polarized light made incident on a light guide formed of the same material as the light guides LG 1  and LG 2  from air (hereinafter often referred to as a change in reflectance of the P-polarized light made incident on the light guide from air), and a change in reflectance Rs 1  of the S-polarized light to the angle of incidence of the S-polarized light made incident on a light guide formed of the same material as the light guides LG 1  and LG 2  from air (hereinafter often referred to as a change in reflectance of the S-polarized light made incident on the light guide from air). The P-polarized light corresponds to a component of light whose electric vector oscillates in the plane of incidence. The S-polarized light corresponds to a component of the light whose electric vector oscillates perpendicularly to the plane of incidence. 
     In the example shown in  FIG.  5   , the change in reflectance Rp 1  of the P-polarized light made incident on the light guide from air becomes smaller as the angle of incidence of the P-polarized light made incident on the light guide from air changes from 0° to 55.9°. In other words, the reflectance of the P-polarized light made incident on the light guide from air becomes smaller as the angle in incidence of the P-polarized light made incident on the light guide from air becomes from 0° to 55.9°. 
     In the example shown in  FIG.  5   , when the angle of incidence of the P-polarized light made incident on the light guide from air is 55.9°, the change in reflectance Rp 1  of the P-polarized light made incident on the light guide from air is zero. In other words, when the angle of incidence of the P-polarized light made incident on the light guide from air is 55.9°, the reflectance of the P-polarized light made incident on the light guide from air is 0. In other words, when the angle of incidence of the P-polarized light made incident on the light guide from air is 55.9°, the P-polarized light made incident on the light guide from air is not reflected at all at the boundary between the air and the light guide, but is entirely made incident on the light guide from air. The angle of incidence at which the reflectance (or the reflection intensity) of the P-polarized light thus becomes zero (0%) is referred to as the Brewster&#39;s angle. In the example shown in  FIG.  5   , when the P-polarized light is made incident on the light guide from air, the Brewster&#39;s angle is 55.9°. 
     In the example shown in  FIG.  5   , the change in reflectance Rp 1  of the P-polarized light made incident on the light guide from air is larger as the angle of incidence of the P-polarized light made incident on the light guide from air becomes larger than 55.9°. In other words, the reflectance of the P-polarized light made incident on the light guide from air becomes larger as the angle of incidence of the P-polarized light made incident on the light guide from air becomes larger than 55.9°. 
     In addition, when the angle of incidence of the P-polarized light made incident on the light guide from air is in a range of 49.0° or more and 62.0° or less, then the reflectance of the P-polarized light made incident on the light guide from air is 0.005 (0.5%) or less. In other words, when the angle of incidence of the P-polarized light made incident on the light guide from air is in a range of 49.0° or more and 62.0° or less, the P-polarized light made incident on the light guide from air is not substantially reflected at the boundary between the air and the light guide, but is substantially made incident on the light guide from air. 
     In the example shown in  FIG.  5   , the change in reflectance Rs 1  of the S-polarized light made incident on the light guide from air becomes larger as the angle of incidence of the S-polarized light made incident on the light guide from air becomes larger than 0°. In other words, the reflectance of the S-polarized light made incident on the light guide from air becomes larger as the angle of incidence of the S-polarized light made incident on the light guide from air becomes larger than 0°. In other words, the rate of reflection of the S-polarized light made incident on the light guide from air, at the boundary between the air and the light guide becomes larger as the angle of incidence of the S-polarized light made incident on the light guide from air becomes larger than 0°. 
       FIG.  6    is a schematic diagram showing an example of the P-polarized light made incident on a light guide LG 10  from air. The light guide LG 10  formed of the same material as the light guides LG 1  and LG 2  is shown in  FIG.  6   . The light guide LG 10  is formed in a flat plate shape parallel to the X-Y plane. The light guide LG 10  has an upper main surface  10 A, an opposed surface  10 B located on a side opposite to the main surface  10 A in the direction Z, and a side surface SF 10 . The main surface  10 A and the opposed surface  10 B are, for example, parallel to the X-Y plane and are provided parallel to each other. The main surface  10 A and the opposed surface  10 B may be non-parallel to each other. The side surface SF 10  is, for example, parallel to the X-Z plane. P-polarized light L 10  made incident on the light guide LG 10  from air is shown in  FIG.  6   . 
     In the example shown in  FIG.  6   , the P-polarized light L 10  is made incident on the light guide LG 10  from air at an angle of incidence=55.9°. In other words, the P-polarized light L 10  is made incident on the side surface SF 10  of the light guide LG 10  from air at the angle of incidence=55.9° with respect to a straight line perpendicular to the side surface SF 10 . As represented by the change in reflectance Rp 1  of the P-polarized light made incident on the light guide from air in  FIG.  5   , when the P-polarized light L 10  is made incident on the side surface SF 10  of the light guide LG 10  from air at an angle of incidence (Brewster&#39;s angle)=55.9°, the P-polarized light L 10  is not reflected on the side surface SF 10 , but is entirely made incident on the light guide LG 10 . In other words, when the P-polarized light L 10  is made incident on the side surface SF 10  at an angle=55.9° to a straight line perpendicular to the side surface SF 10 , the P-polarized light L 10  is not reflected on the side surface SF 10 , but is entirely made incident on the light guide LG 10 . 
       FIG.  7    is a schematic diagram showing an example of the change in reflectance of the S-polarized light and the P-polarized light with respect to the angles of incidence of the S-polarized light and the P-polarized light made incident on the light guide from air. In  FIG.  7   , the vertical axis indicates the reflectance of light, and the horizontal axis indicates the angle of incidence of light [°].  FIG.  7    shows a change in reflectance Rp 2  of the P-polarized light to the angle of incidence of the P-polarized light made incident on air from a light guide formed of the same material as the light guides LG 1  and LG 2  (hereinafter often referred to as a change in reflectance of the P-polarized light made incident on air from the light guide), and a change in reflectance Rs 2  of the S-polarized light to the angle of incidence of the S-polarized light made incident on air from a light guide formed of the same material as the light guides LG 1  and LG 2  (hereinafter often referred to as a change in reflectance of the S-polarized light made incident on air from the light guide). 
     In the example shown in  FIG.  7   , the change in reflectance Rp 2  of the P-polarized light made incident on air from the light guide becomes smaller as the angle of incidence of the P-polarized light made incident on air from the light guide changes from 0° to 33.5°. In other words, the reflectance of the P-polarized light made incident on air from the light guide becomes smaller as the angle of incidence of the P-polarized light made incident on air from the light guide changes from 0° to 33.5°. 
     In the example shown in  FIG.  7   , when the angle of incidence of the P-polarized light made incident on air from the light guide is 33.5°, the change in reflectance Rp 2  of the P-polarized light made incident on air from the light guide becomes 0. In other words, when the angle of incidence of the P-polarized light made incident on air from the light guide is 33.5°, the reflectance of the P-polarized light made incident on air from the light guide becomes 0. In other words, when the angle of incidence of the P-polarized light made incident on air from the light guide is 33.5°, the P-polarized light made incident on air from the light guide is not reflected at all at the boundary between the light guide and air, but is entirely made incident on air from the light guide. In the example shown in  FIG.  6   , when the P-polarized light is made incident on air from the light guide, the Brewster&#39;s angle is 33.5°. 
     In the example shown in  FIG.  7   , the change in reflectance Rp 2  of the P-polarized light made incident on air from the light guide is larger as the angle of incidence of the P-polarized light made incident on air from the light guide becomes larger than 33.5°. In other words, the reflectance of the P-polarized light made incident on air from the light guide is larger as the angle of incidence of the P-polarized light made incident on air from the light guide becomes larger than 33.5°. 
     In addition, when the angle of incidence of the P-polarized light made incident on air from the light guide is in the range of 30.0° or more and 35.5° or less, the reflectance of the P-polarized light made incident on air from the light guide is 0.005 or less. In other words, when the angle of incidence of the P-polarized light made incident on air from the light guide is in the range of 30.0° or more and 35.5° or less, the P-polarized light made incident on air from the light guide is not substantially reflected at the boundary between the light guide and the air, but is substantially made incident on air from the light guide. 
     In the example shown in  FIG.  7   , the change in reflectance Rs 2  of the S-polarized light made incident on air from the light guide is larger as the angle of incidence of the S-polarized light made incident on air from the light guide becomes larger than 0°. In other words, the reflectance of the S-polarized light made incident on air from the light guide is larger as the angle of incidence of the S-polarized light made incident on air from the light guide becomes larger than 0°. In other words, the rate of reflection of the S-polarized light made incident on air from the light guide, at the boundary between the light guide and air becomes larger as the angle of incidence of the S-polarized light made incident on air from the light guide becomes larger than 0°. 
       FIG.  8    is a schematic diagram showing an example of the P-polarized light made incident on air from the light guide LG 10 . The light guide LG 10  is shown in  FIG.  8   . P-polarized light L 11  made incident on air from the light guide LG 10  is shown in  FIG.  8   . 
     In the example shown in  FIG.  8   , the P-polarized light L 11  is made incident on air from the light guide LG 10  at an angle of incidence=33.5°. In other words, the P-polarized light L 11  is made incident on the main surface  10 A at the angle of incidence=33.5° with respect to a straight line perpendicular to the main surface  10 A, from the light guide LG 10  to air. As indicated by the change in reflectance Rp 2  of the P-polarized light made incident on air from the light guide in  FIG.  8   , when the P-polarized light L 11  is made incident on air from the light guide LG 10  at an angle of incidence (Brewster&#39;s angle)=33.5° from the main surface  10 A, the P-polarized light L 11  is not reflected on the main surface  10 A, but is entirely made incident on air. In other words, when the P-polarized light L 10  is made incident on the main surface  10 A at an angle=33.5° to a straight line perpendicular to the main surface  10 A, the P-polarized light L 11  is not reflected on the main surface  10 A, but is entirely made incident on air. 
       FIG.  9    is a cross-sectional view showing a configuration example of an illumination device ILc of a comparative example. As shown in  FIG.  9   , the illumination device ILc of the comparative example has a third area A 3 , a fourth area A 4 , and a boundary BOc between the third area A 3  and the fourth area A 4 . A length of the third area A 3  in the direction Y is equal to a length of the fourth area A 4  in the direction Y. The length of the third area A 3  in the direction Y may not be equal to the length of the fourth area A 4  in the direction Y. 
     The illumination device ILc comprises a diffusion sheet DS, a prism sheet PS, a light guide LG 3 , a plurality of light sources LS 3 , a reflective layer P 3 , a light guide LG 4 , a plurality of light sources LS 4 , a reflective layer P 4 , and a reflective sheet RS. The reflective sheet RS, the reflective layer P 4 , the light guide LG 4 , the reflective layer P 3 , the light guide LG 3 , the prism sheet PS, and the diffusion sheet DS are arranged in the mentioned order toward the tip side of the arrow indicating the direction Z. 
     The diffusion sheet DS is located on the light guide LG 3 . The prism sheet PS is located between the diffusion sheet DS and the light guide LG 3 . For example, the prism sheet PS focuses light emitted from the light guide LG 3 , in the direction Z. 
     The light guide LG 3  is an insulating substrate such as a glass substrate or a plastic substrate. The light guide LG 3  is formed of, for example, the same material as the light guides LG 1  and LG 2 . The light guide LG 3  is formed in a flat plate shape parallel to the X-Y plane. The light guide LG 3  has a main surface  3 A opposed to the display panel PNL, an opposed surface  3 B located on a side opposite to the main surface  3 A in the direction Z, a side surface SF 5 , and a side surface SF 6  located on a side opposite to the side surface SF 5  in the direction Y. The main surface  3 A and the opposed surface  3 B are, for example, parallel to the X-Y plane and are provided parallel to each other. The main surface  3 A and the opposed surface  3 B may be non-parallel to each other. The side surfaces SF 5  and SF 6  are, for example, parallel to the X-Z plane and are provided parallel to each other. The side surfaces SF 5  and SF 6  may be non-parallel to each other. 
     The light guide LG 3  is located in the entire third area A 3  and the entire fourth area A 4 . In other words, the main surface  3 A and the opposed surface  3 B shown in  FIG.  9    are located in the third area A 3  and the fourth area A 4 . The side surface SF 5  is located in the third area A 3 , and the side surface SF 6  is located in the fourth area A 4 . The boundary BOc corresponds to a middle part between the side surface SF 5  and the side surface SF 6 . 
     A plurality of light sources LS 3  are arranged at intervals in the direction X. In the example shown in  FIG.  9   , the plurality of light sources LS 3  are opposed to the side surface SF 5 . In addition, the plurality of light sources LS 3  are spaced apart in the direction X and arranged along the side surface SF 5 . 
     The light sources LS 3  are separated from the side surface SF 5 . The light sources LS 3  emit light L 3  toward the side surface SF 5  in the emission direction DL 3 . The emission direction DL 3  of the light sources LS 3  is the direction that intersects a line parallel to a center line passing the center of the thickness of the light guide LG 3  and extending in the direction Y. 
     The reflective layer P 3  is a layer including a plurality of prisms, which will be described below in detail. The reflective layer P 3  is located on the opposed surface  3 B. The length of the reflective layer P 3  in the direction Y is 70.6 mm. The reflective layer P 3  extends from the fourth area A 4  to a predetermined position between the boundary BOc and the side surface SF 5  beyond the boundary BOc, in the direction Y. The reflective layer P 3  may extend within the fourth area A 4 . The reflective layer P 3  includes an end portion E 30  on the tip side of the arrow indicating the direction Y and an end portion E 31  on the side opposite to the end portion E 10  in the direction Y. The end portion E 30  is separated from the side surface SF 6  to a side opposite to the tip side of the arrow indicating the direction Y by 0.66 mm. The end portion E 31  is located between the side surface SF 5  and the boundary BOc. The end portion E 31  is located on the boundary BOc side between the side surface SF 5  and the boundary BOc. The end portion E 31  is located near the boundary BOc. The end portion E 31  is located between the boundary BOc and the side surface SF 6 . For example, the end portion E 30  corresponds to the position of the prism closest to the side surface SF 6 , of the plurality of prisms included in the reflective layer P 3  (prisms PC to be described below). For example, the end portion E 31  corresponds to the position of the prism closest to the side surface SF 5 , of the plurality of prisms included in the reflective layer P 3  (prisms PC to be described below). 
     The light guide LG 4  is an insulating substrate such as a glass substrate or a plastic substrate. The light guide LG 4  is formed of, for example, the same material as the light guide LG 3 . The light guide LG 4  may not be formed of the same material as the light guide LG 3 . The light guide LG 4  is formed in a flat plate shape parallel to the X-Y plane. The light guide LG 4  has a main surface  4 A opposed to the opposed surface  3 B, an opposed surface  4 B located on a side opposite to the main surface  4 A in the direction Z, a side surface SF 7  arranged with the side surface SF 5  in the direction Z, and a side surface SF 8  located on a side opposite to the side surface SF 7  in the direction Y and arranged with the side surface SF 6  in the direction Z. The main surface  4 A and the opposed surface  4 B are, for example, parallel to the X-Y plane and are provided parallel to each other. The main surface  4 A and the opposed surface  4 B may be non-parallel to each other. The side surface SF 7  and the side surface SF 8  are opposed to each other in the direction Y. The side surfaces SF 7  and SF 8  are, for example, parallel to the X-Z plane and are provided parallel to each other. The side surfaces SF 7  and SF 8  may be non-parallel to each other. 
     The light guide LG 4  is located in the entire third area A 3  and the entire fourth area A 4 . In other words, the main surface  4 A and the opposed surface  4 B shown in  FIG.  9    are located in the third area A 3  and the fourth area A 4 . The side surface SF 7  is located in the third area A 3 , and the side surface SF 8  is located in the fourth area A 4 . The boundary BOc corresponds to a middle part between the side surface SF 7  and the side surface SF 8 . 
     The plurality of light sources LS 4  are arranged at intervals in the direction X. In the example shown in  FIG.  1   , the plurality of light sources LS 4  are opposed to the side surface SF 8 . In addition, the plurality of light sources LS 4  are spaced apart in the direction X and arranged along the side surface SF 8 . 
     The light sources LS 4  are separated from the side surface SF 8 . The light sources LS 4  emit light L 4  toward the side surface SF 8  in the emission direction DL 4 . The emission direction DL 4  of the light sources LS 4  is the direction that intersects a line parallel to a center line passing the center of the thickness of the light guide LG 4  and extending in the direction Y. 
     The light sources LS 3  and LS 4  are, for example, laser light sources such as semiconductor lasers that emit polarized laser light. The light sources LS 3  and LS 4  are not limited to the light sources emitting laser light, but may be, for example, light emitting diodes. 
     The light sources LS 3  and LS 4  may comprise a plurality of light emitting elements that emit light of different colors. For example, each of the light sources LS 3  and LS 4  comprises three light emitting elements that emit red, green, and blue light, respectively. When comprising three light emitting elements that emit red, green, and blue light, the light sources LS 3  and LS 4  can obtain light of a mixture of these colors (for example, white color). 
     The reflective layer P 4  is a layer including a plurality of prisms, which will be described below in detail. The reflective layer P 4  is located on the opposed side  4 B. The length of the reflective layer P 4  in the direction Y is 70.6 mm. The reflective layer P 4  extends from the third area A 3  to a predetermined position between the boundary BOc and the side surface SF 8  beyond the boundary BOc, in the direction Y. The reflective layer P 4  may extend within the fourth area A 4 . The reflective layer P 4  includes an end portion E 40  on a side opposite to the tip side of the arrow indicating the direction Y and an end portion E 41  on a side opposite to the end portion E 40  in the direction Y. The end portion E 40  is separated from the side surface SF 7  to the tip side of the arrow indicating the direction Y by 0.66 mm. The end portion E 41  is located between the boundary BOc and the side surface SF 8 . The end portion E 41  is located on the boundary BOc side between the boundary BOc and the side surface SF 8 . The end portion E 41  is located near the boundary BOc. The end portion E 41  may be located between the boundary BOc and the side surface SF 7 . For example, the end portion E 40  corresponds to the position of the prism closest to the side surface SF 7 , of the plurality of prisms included in the reflective layer P 4  (prisms PD to be described below). For example, the end portion E 41  corresponds to the position of the prism closest to the side surface SF 8 , of the plurality of prisms included in the reflective layer P 4  (prisms PD to be described below). 
     The reflective layer P 3  and the reflective layer P 4  overlap with each other in the direction Z in the boundary BOc and the vicinity of the boundary BOc. The reflective layer P 3  and the reflective layer P 4  may not overlap with each other in the direction Z in the boundary BOc and the vicinity of the boundary BOc. 
     The reflective sheet RS is opposed to the opposed surface  4 B of the light guide LG 4 . For example, the reflective sheet RS reflects the light leaking from within the light guide LG 4  and makes the light incident on the light guide LG 4  again. The reflective sheet RS may not be provided. 
     The light L 3  emitted from the light sources LS 3  is not reflected at the interface between the side surface SF 5  and the air layer, but is made incident on the light guide LG 3  from the side surface SF 5  and is refracted on the side surface SF 5 . Light traveling toward the opposed surface  3 B, of the light L 3  made incident on the light guide LG 3  is reflected at the interface between the light guide LG 3  and the air layer. In addition, light traveling toward the main surface  3 A, of the light L 3  made incident on the light guide LG 3  is reflected at the interface between the light guide LG 3  and the air layer. Thus, in the area where the reflective layer P 3  is not provided, of the third area A 3 , the light L 3  travels toward the tip side of the arrow indicating the direction Y, inside the light guide LG 3 , while repeatedly reflected on the main surface  3 A and the opposed surface  3 B. 
     Light traveling toward the reflective layer P 3 , of the light L 3  traveling inside the light guide LG 3 , is reflected on the prisms of the reflective layer P 3  such that its traveling direction is changed. The light reflected on the prisms of the reflective layer P 3  deviates from the total reflection condition of the main surface  3 A and is emitted from the main surface  3 A. The light emitted from the main surface  3 A illuminates the display panel PNL through the prism sheet PS and the diffusion sheet DS. In other words, in the area where the reflective layer P 3  is not provided (or the area close to the side surface SF 5 ), of the third area A 3 , emission of the light L 3  incident from the side surface SF 5 , from the light guide LG 3 , is suppressed. 
     Similarly, the light L 4  emitted from the light sources LS 4  is not reflected at the interface between the side surface SF 8  and the air layer, but is made incident on the light guide LG 4  from the side surface SF 8  and is refracted on the side surface SF 8 . Light traveling toward the opposed surface  4 B, of the light L 4  made incident on the light guide LG 4  is reflected at the interface between the light guide LG 4  and the air layer. In addition, light traveling toward the main surface  4 A, of the light L 4  made incident on the light guide LG 4  is reflected at the interface between the light guide LG 4  and the air layer. Thus, in the area where the reflective layer P 4  is not provided, of the fourth area A 4 , the light L 4  travels toward a side opposite to the tip side of the arrow indicating the direction Y, inside the light guide LG 4 , while repeatedly reflected on the main surface  4 A and the opposed surface  4 B. 
     The light L 4  traveling toward the reflective layer P 4 , of the light L 4  traveling inside the light guide LG 4 , is reflected on the prisms of the reflective layer P 4  such that its traveling direction is changed. The light reflected on the prisms of the reflective layer P 4  deviates from the total reflection condition of the main surface  4 A and is emitted from the main surface  4 A. The light emitted from the main surface  4 A illuminates the display panel PNL through the light guide LG 3 , the prism sheet PS, and the diffusion sheet DS. 
       FIG.  10    is a perspective view showing an example of the configuration of the reflective layer P 3  and the reflective layer P 4 , which corresponds to the illumination device ILc of  FIG.  9   .  FIG.  10    corresponds to  FIG.  9   . The only constituent elements necessary for explanations are shown in  FIG.  10   . 
     In the example shown in  FIG.  10   , the reflective layer P 3  includes a plurality of prisms PC. In the reflective layer P 3 , the plurality of prisms PC are intermittently arranged in the direction Y. The reflective layer P 4  has a plurality of prisms PD. In the reflective layer P 4 , the plurality of prisms PD are intermittently arranged in the direction Y. The plurality of prisms PC are provided on the opposed surface  3 B. The plurality of prisms PD are provided on the opposed surface  4 B. For example, the prisms PC are formed integrally with the light guide LG 3 . Similarly, the prisms PD are formed integrally with the light guide LG 4 . 
     The prisms PC protrude from the opposed surface  3 B toward the main surface  4 A. In other words, the prisms PC protrude toward the side opposite to the tip side of the arrow indicating the direction Z. The prisms PC have a triangular cross-sectional shape parallel to the Y-Z plane and extend in the direction X. For example, the cross-sectional shapes of the respective prisms PC parallel to the Y-Z plane are similar to each other. The prism PC has a slope SL 5 , a slope SL 6 , a reference plane BL 3 , and a vertex VT 3 . A height HC of the prism PC is a height of the prism PC in the normal direction of the reference plane BL 3  (opposed surface  3 B), and corresponds to a length in the direction Z from the reference plane BL 3  to the vertex VT 3 . 
     In the prism PC, the slope SL 5  is located on the side surface SF 6  side, and the slope SL 6  is located on the side surface SF 5  side. The reference plane BL 3  is located on the same plane as the opposed surface  3 B. The vertex VT 3  corresponds to a point where the slopes SL 5  and the slope SL 6  intersect. 
     A plurality of vertices VT 3  are arranged at regular intervals LG 32  in the direction Y. The interval LG 32  is, for example, 0.1 mm. In the example shown in  FIG.  10   , the angle between the slope SL 5  and the reference plane BL 3  is 15°, and the angle between the slope SL 6  and the reference plane BL 3  is 35°. The angle between the slope SL 5  and the slope SL 6  is 130°. R of the tip of apex VT 3  is 0.015 mm. 
     In the example shown in  FIG.  10   , a height HC of each of the plurality of prisms PC is constant. The height HC of each of the plurality of prisms PC may be smaller from the side surface SF 6  toward the side surface SF 5 . In other words, the height HC of each of the plurality of prisms PC may become higher the farther the prism PC is from the light source LS 3 . 
     The prisms PD protrude from the opposed surface  4 B toward the reflective sheet RS. In other words, the prisms PD protrude toward the side opposite to the tip side of the arrow indicating the direction Z. The prisms PD have a triangular cross-sectional shape parallel to the Y-Z plane and extend in direction X. For example, the cross-sectional shapes of the respective prisms PD parallel to the Y-Z plane are similar to each other. The prism PD has a slope SL 7 , a slope SL 8 , a reference plane BL 4 , and a vertex VT 4 . A height HD of the prism PD is a height of the prism PD in the normal direction of the reference plane BL 4 , and corresponds to a length in the direction Z from the reference plane BL 4  to the vertex VT 4 . 
     In the prism PD, the slope SL 7  is located on the side surface SF 8  side, and the slope SL 8  is located on the side surface SF 7  side. The reference plane BL 4  is located on the same plane as the opposed surface  4 B. The vertex VT 4  corresponds to a point where the slopes SL 7  and the slope SL 8  intersect. 
     A plurality of vertices VT 4  are arranged at regular intervals LG 32  in the direction Y. In the example shown in  FIG.  10   , the angle formed between the slope SL 7  and the reference plane BL 4  is 15°, and the angle formed between the slope SL 8  and the reference plane BL 4  is 35°. The angle formed between the slope SL 7  and the slope SL 8  is 130°. R of the tip of the vertex VT 4  is 0.015 mm. 
     In the example shown in  FIG.  10   , the height HD of each of the plurality of prisms PD is constant. The height HC of each of the plurality of prisms PD may be smaller from the side surface SF 7  toward the side surface SF 8 . In other words, the height HC of each of the plurality of prisms PD may be larger as the prism PD is farther from the light sources LS 4 . 
       FIG.  11    is a view showing an example of the change in luminance of the illumination device ILc of  FIG.  9    in the direction Y with respect to the distance X in a case where the P-polarized light and the S-polarized light are made incident. In  FIG.  11   , the vertical axis indicates the luminance of the illumination device ILc, and the horizontal axis indicates a distance×[mm] from the side surfaces SF 5  and SF 7  of the illumination device ILc to the tip side of the arrow indicating the direction Y.  FIG.  11    shows a change in luminance LMp 1  of the illumination device ILc to the distance x in a case where the P-polarized light is emitted from the light sources LS 3  and LS 4  in the illumination device ILc including the reflective sheet RS (often referred to as a change in luminance of the illumination device ILc including the reflective sheet RS in a case where the P-polarized light is emitted), a change in luminance LMp 2  of the illumination device ILc to the distance x in a case where the P-polarized light is emitted from the light sources LS 3  and LS 4  in the illumination device ILc not including the reflective sheet RS (often referred to as a change in luminance of the illumination device ILc not including the reflective sheet RS in a case where the P-polarized light is emitted), a change in luminance LMs 1  of the illumination device ILc to the distance x in a case where the S-polarized light is emitted from the light sources LS 3  and LS 4  in the illumination device ILc including the reflective sheet RS (often referred to as a change in luminance of the illumination device ILc including the reflective sheet RS in a case where the S-polarized light is emitted), and a change in luminance LMs 2  of the illumination device ILc to the distance x in a case where the S-polarized light is emitted from the light sources LS 3  and LS 4  in the illumination device ILc not including the reflective sheet RS (often referred to as a change in luminance of the illumination device ILc not including the reflective sheet RS in a case where the S-polarized light is emitted). In  FIG.  11   , each of the change in luminance LMp 1  of the illumination device ILc including the reflective sheet RS in a case where the P-polarized light is emitted, the change in luminance LMp 2  of the illumination device ILc not including the reflective sheet RS in a case where the P-polarized light is emitted, the change in luminance LMs 1  of the illumination device ILc including the reflective sheet RS in a case where the S-polarized light is emitted, and the change in luminance LMs 2  of the illumination device ILc not including the reflective sheet RS in a case where the S-polarized light is emitted, includes the luminance of the light reflected on the reflective layer P 3  and the luminance of the light reflected on the reflective layer P 4 . 
     In the example shown in  FIG.  11   , the change in luminance LMpl of the illumination device ILc including the reflective sheet RS in a case where the P-polarized light is emitted, is larger than the change in luminance LMs 1  of the illumination device ILc including the reflective sheet RS in a case where the S-polarized light is emitted, and the change in luminance LMs 2  of the illumination device ILc not including the reflective sheet RS in a case where the S-polarized light is emitted. In other words, the luminance of the illumination device ILc including the reflective sheet RS in a case where the P-polarized light is emitted from the light sources LS 3  and LS 4 , is larger than the luminance of the illumination device ILc including the reflective sheet RS in a case where the S-polarized light is emitted from the light sources LS 3  and LS 4 , and the luminance of the illumination device ILc not including the reflective sheet RS in a case where the S-polarized light is emitted from the light sources LS 3  and LS 4 . 
     The change in luminance LMp 2  of the illumination device ILc not including the reflective sheet RS in a case where the P-polarized light is emitted, is substantially equal to the change in luminance LMs 1  of the illumination device ILc including the reflective sheet RS in a case where the S-polarized light is emitted. In other words, the luminance of the illumination device ILc not including the reflective sheet RS in a case where the P-polarized light is emitted from the light sources LS 3  and LS 4 , is substantially equal to the luminance of the illumination device ILc including the reflective sheet RS in a case where the S-polarized light is emitted from the light sources LS 3  and LS 4 . 
     The change in luminance LMs 1  of the illumination device ILc including the reflective sheet RS in a case where the S-polarized light is emitted is larger than the change in luminance LMs 2  of the illumination device ILc not including the reflective sheet RS in a case where the S-polarized light is emitted. In other words, the luminance of the illumination device ILc including the reflective sheet RS in a case where the S-polarized light is emitted from the light sources LS 3  and LS 4  is larger than the luminance of the illumination device ILc not including the reflective sheet RS in a case where the S-polarized light is emitted from the light sources LS 3  and LS 4 . 
     The luminance of the light reflected on the reflective layer P 4  is substantially equal to the luminance of the light reflected on the reflective layer P 3 , in each of the change in luminance LMp 1  of the illumination device ILc including the reflective sheet RS in a case where the P-polarized light is emitted and the change in luminance LMp 2  of the illumination device ILc not including the reflective sheet RS in a case where the P-polarized light is emitted. In other words, the P-polarized light has a small interface reflection of the emitted light. 
     The luminance of the light reflected on the reflective layer P 4  is substantially equal to the luminance of the light reflected on the reflective layer P 3  according to the change in luminance LMs 1  of the illumination device ILc including the reflective sheet RS in a case where the S-polarized light is emitted, but the luminance of the light reflected on the reflective layer P 4  is smaller than the luminance of the light reflected on the reflective layer P 3  according to the change in luminance LMs 2  of the illumination device ILc not including the reflective sheet RS in a case where the S-polarized light is emitted. In other words, the S-polarized light has large interface reflection when the emitted light reflected on the reflection layer P 4  passes through the light guide LG 3 . 
     As described above, as light emitted from the light sources of illumination devices, for example, illumination devices IL and ILc, rather than S-polarized light P-polarized light should be used. 
       FIG.  12    is a cross-sectional view showing an example of the arrangement of the light source LS 1  relative to the light guide LG 1  of the illumination device IL shown in  FIG.  3   . According to the inventors&#39; study, when two inverted prism bottom angles of the prisms of the prism sheet PS are set at 61.3°, the refractive index n of the light guide is 1.5, the angle of total reflection condition of the incident light is 48°, and the radiation angle  5  of the incident light is 6.5°, the emission efficiency of the illumination device IL can be improved to 90% by setting the angle between the incident light and the main and opposed surfaces of the light guide to 26.5°, setting bottom angles α 1  of prisms PA and PB to 15° and, furthermore, setting apex angles of the prisms PA and PA to 130°. 
     In the example shown in  FIG.  12   , the light source LS 1  emits P-polarized light L 1  In the example shown in  FIG.  12   , the light source LS 1  is arranged on the tip side of the arrow indicating the direction Z to the light guide LG 1  such that the P-polarized light is made incident at an angle of incidence close to the Brewster&#39;s angle at which the reflectance to the side surface SF 1  is less than or equal to 0.005 (hereinafter often referred to as a Brewster&#39;s approximate angle), for example, Brewster&#39;s approximate angle=56°, in the Y-Z plane. In other words, the light source LS 1  is arranged on the tip side of the arrow indicating the direction Z to the light guide LG 1  such that the P-polarized light is made incident on the main surface  1 A side at an angle=56° to a straight line (normal) perpendicular to the side surface SF 1  at which the reflectance to the side surface SF 1  is less than or equal to 0.005 (0.5%), in the Y-Z plane. The light source LS 1  may be arranged on the tip side of the arrow indicating the direction Z to the light guide LG 1  such that the P-polarized light is made incident on the side surface SF 1  at the Brewster&#39;s angle=55.9°, in the Y-Z plane. In other words, the light source LS 1  may be arranged on the tip side of the arrow indicating the direction Z to the light guide LG 1  such that the P-polarized light is made incident on the main surface lA side at the angle=55.9° to the straight line perpendicular to the side surface SF 1 , in the Y-Z plane. 
     In the example shown in  FIG.  12   , the light source LS 1  is arranged to be displaced (or shifted) from the main surface  1 A to the tip side of the arrow indicating the direction Y. In other words, the light source LS 1  is positioned more closely to the tip side of the arrow indicating the direction Y than to the main surface  1 A. The light source LS 1  is arranged at a position separated from the main surface  1 A of the light guide LG 1  toward the tip side of the arrow indicating the direction Z in a distance HL 1 . An emitting portion LSP 1  of the light source LS 1  that emits the P-polarized light L 1  is positioned on an upper side of a center line which passes a center of the height of the main surface  1 A and the opposed surface  1 B of the light guide LG 1  and which is parallel to the main surface  1 A and the opposed surface  1 B, in the direction Z. 
     In  FIG.  12   , the side surface SF 1  is formed to be inclined to the main surface  1 A at an angle=82.9° and inclined to the opposed surface  1 B at an angle=97.1°, in the Y-Z plane. In other words, the side surface SF 1  is formed to be inclined to the main surface  1 A at an angle=82.9°, in the Y-Z plane. In addition, the side surface SF 1  is formed to be inclined to the opposed surface  1 B at an angle=97.1°, in the Y-Z plane. 
     In the example shown in  FIG.  12   , the light source LS 1  emits the P-polarized light L 1  from the main surface  1 A side toward the side surface SF 1  at the Brewster&#39;s approximate angle=56° , in the direction Z. The P-polarized light L 1  emitted from the light source LS 1  is made incident on the side surface SF 1  at the Brewster&#39;s approximate angle=56° from the main surface  1 A side in the direction Z. In other words, the P-polarized light L 1  emitted from the light source LS 1  is made incident of the side surface SF 1  at an angle=56° to the straight line perpendicular to the side surface SF 1  from the main surface  1 A side in the direction Z. The P-polarized light L 1  made incident on the light guide LG 1  from air is refracted at the boundary between the air and the side surface SF 1  at a refraction angle=33.6° to travel at an angle=26.5° with respect to the opposed side lB. In other words, the P-polarized light L 1  made incident on the light guide LG 1  from the side surface SF 1  is refracted at an angle of 33.6° to the opposed surface  1 B side with respect to a straight line perpendicular to the side surface SF 1 , on the side surface SF 1 , to travel at 26.5° with respect to the opposed surface  1 B. 
       FIG.  13    is a cross-sectional view showing an example of the arrangement of the light source LS 2  relative to the light guide LG 2  of the illumination device IL shown in  FIG.  3   . 
     In the example shown in  FIG.  13   , the light source LS 2  emits the P-polarized light L 2 . In the example shown in  FIG.  13   , the light source LS 2  is arranged on the tip side of the arrow indicating the direction Z to the light guide LG 2  such that the P-polarized light is made incident at the Brewster&#39;s approximate angle at which the reflectance to the side surface SF 4  is less than or equal to 0.005 (0.5%) to the side surface SF 4 , for example, at the Brewster&#39;s approximate angle=56°, in the Y-Z plane. In other words, the light source LS 2  is arranged on the tip side of the arrow indicating the direction Z to the light guide LG 2  such that the P-polarized light is made incident on the main surface  1 A side at an angle=56° to a straight line perpendicular to the side surface SF 4  at which the reflectance to the side surface SF 4  is less than or equal to 0.005, in the Y-Z plane. The light source LS 2  may be arranged on the tip side of the arrow indicating the direction Z to the light guide LG 2  such that the P-polarized light is made incident on the side surface SF 4  at the Brewster&#39;s angle=55.9°, in the Y-Z plane. In other words, the light source LS 2  may be arranged on the tip side of the arrow indicating the direction Z to the light guide LG 2  such that the P-polarized light is made incident on the main surface  1 A side at the angle=55.9° to the straight line perpendicular to the side surface SF 4 , in the Y-Z plane. 
     In the example shown in  FIG.  13   , the light source LS 2  is arranged to be displaced (or shifted) from the main surface  2 A to a side opposite to the tip side of the arrow indicating the direction Y. In other words, the light source LS 2  is positioned more closely to the tip side of the arrow indicating the direction Y than to the main surface  2 A. The light source LS 2  is arranged at a position separated from the main surface  2 A of the light guide LG 2  toward the tip side of the arrow indicating the direction Z in a distance HL 1 . An emitting portion LSP 2  of the light source LS 2  that emits the P-polarized light L 2  is positioned on an upper side of a center line which passes a center of the height of the main surface  2 A and the opposed surface  2 B of the light guide LG 2  and which is parallel to the main surface  2 A and the opposed surface  2 B, in the direction Z. 
     In  FIG.  13   , the side surface SF 4  is formed to be inclined to the main surface  2 A at an angle=82.9° and inclined to the opposed surface  2 B at an angle=97.1°, in the Y-Z plane. In other words, the side surface SF 4  is formed to be inclined to the main surface  2 A at an angle=82.9°, in the Y-Z plane. In addition, the side surface SF 4  is formed to be inclined to the opposed surface  2 B at an angle=97.1°, in the Y-Z plane. 
     In the example shown in  FIG.  13   , the light source LS 2  emits the P-polarized light L 2  from the main surface  2 A side toward the side surface SF 4  at the Brewster&#39;s approximate angle=56°, in the direction Z. The P-polarized light L 2  emitted from the light source LS 2  is made incident on the side surface SF 1  at the Brewster&#39;s approximate angle=56° from the main surface  2 A side in the direction Z. In other words, the P-polarized light L 2  emitted from the light source LS 2  is made incident on the side surface SF 4  at an angle=56° on the main surface  2 A side to the straight line perpendicular to the side surface SF 4 , from the main surface  2 A side in the direction Z. The P-polarized light L 2  made incident on the light guide LG 2  from air is refracted at the boundary between the air and the side surface SF 4  at a refraction angle=33.6° to travel at an angle=26.5° with respect to the opposed surface  2 B. In other words, the P-polarized light L 2  made incident on the light guide LG 2  from the side surface SF 4  is refracted at an angle of 33.6° to the opposed surface  2 B side with respect to a straight line perpendicular to the side surface SF 4 , on the side surface SF 4 , to travel at 26.5° with respect to the opposed surface  2 B. 
     According to the embodiment, the illumination device IL comprises a light guide LG 1 , a light guide LG 2 , a plurality of light sources LS 1 , and a plurality of light sources LS 2 . The light guide LG 1  has a main surface  1 A opposed to the display panel PNL, an opposed surface  1 B located on a side opposite to the main surface  1 A in the direction Z, a side surface SF 1 , and a side surface SF 2  located on a side opposite to the side surface SF 1  in the direction Y. The side surface SF 1  and the side surface SF 2  are opposed to each other in the direction Y. The side surface SF 1  is non-parallel to the X-Z plane. The side surface SF 2  is parallel to the X-Z plane. The side surface SF 1  and the side surface SF 2  are provided non-parallel to each other. The side surface SF 1  is a slope that extends from the inside to the outside of the direction Y according to the direction Z from the lower side to the upper side. The side surface SF 1  is formed to be inclined at an angle=82.9° to the main surface  1 A. The light guide LG 2  has a main surface  2 A opposed to the opposed surface  1 B, an opposed surface  2 B located on a side opposite to the main surface  2 A in the direction Z, a side surface SF 3  arranged with the side surface SF 1  in the direction Z, and a side surface SF 4  located on a side opposite to the side surface SF 3  in the direction Y and arranged with the side surface SF 2  in the direction Z. The side surface SF 3  and the side surface SF 4  are opposed to each other in the direction Y. The side surface SF 3  is parallel to the X-Z plane. The side surface SF 4  is non-parallel to the X-Z plane. The side surface SF 3  and the side surface SF 4  are provided non-parallel to each other. The side surface SF 4  is a slope that extends from the inside to the outside of the direction Y according to the direction Z from the lower side to the upper side. The side surface SF 4  is formed to be inclined at an angle=82.9° to the main surface  2 A. 
     A plurality of light sources LS 1  are opposed to the side surface SF 1 . The light sources LS 1  emit the P-polarized light L 1 . The light source LS 1  is arranged more closely to the tip side of the arrow indicating the direction Z than to the light guide LG 1  such that the P-polarized light is made incident at the Brewster&#39;s approximate angle=56° at which the reflectance to the side surface SF 1  is less than or equal to 0.005. A plurality of light sources LS 2  are opposed to the side surface SF 4 . The light sources LS 2  emit the P-polarized light L 2 . The light source LS 2  is arranged more closely to the tip side of the arrow indicating the direction Z than to the light guide LG 2  such that the P-polarized light is made incident at the Brewster&#39;s approximate angle=56° at which the reflectance to the side surface SF 4  is less than or equal to 0.005. Therefore, the illumination device IL can improve the efficiency of emission of the light emitted from the light sources LS 1  and LS 2 , from the light guides LG 1  and LG 2 . For this reason, the display device DSP can also improve the emission efficiency. 
     Next, the display device DSP and the illumination device IL of modified examples of the first embodiment, and other embodiments will be described. In the modified examples and other embodiments to be described below, the same portions as those of the display device DSP and the illumination device IL of the first embodiment described above will be denoted by the same reference numerals, and their detailed descriptions will be omitted or simplified, and portions different from those of the display device DSP and the illumination device IL of the first embodiment will be mainly described in detail. The same effects as those of the above-described embodiment can also be obtained in the modified examples and other embodiments. 
     MODIFIED EXAMPLE 1 
     The illumination device IL according to modified example 1 of the first embodiment is different from the illumination device IL of the first embodiment in configuration of the light sources LS 1  and LSF 2 . 
       FIG.  14    is a cross-sectional view showing an example of the arrangement of the light source LS 1  relative to the light guide LG 1  of the illumination device IL according to modified example 1. 
     In the example shown in  FIG.  14   , the light source LS 1  is arranged on a side opposite to the tip side of the arrow indicating the direction Z to the light guide LG 1  such that the P-polarized light is made incident at the Brewster&#39;s approximate angle=56° at which the reflectance to the side surface SF 1  is less than or equal to 0.005 (0.5%), in the Y-Z plane. In other words, the light source LS 1  is arranged on a side opposite to the tip side of the arrow indicating the direction Z to the light guide LG 1  such that the P-polarized light is made incident on the opposed surface  1 B side at an angle=56° to a straight line perpendicular to the side surface SF 1  at which the reflectance to the side surface SF 1  is less than or equal to 0.005, in the Y-Z plane. The light source LS 1  may be arranged on a side opposite to the tip side of the arrow indicating the direction Z to the light guide LG 1  such that the P-polarized light is made incident on the side surface SF 1  at the Brewster&#39;s angle=55.9°, in the Y-Z plane. In other words, the light source LS 1  may be arranged on a side opposite to the tip side of the arrow indicating the direction Z to the light guide LG 1  such that the P-polarized light is made incident on the opposed surface  1 B side at the angle=55.9° to the straight line perpendicular to the side surface SF 1 , in the Y-Z plane. 
     In the example shown in  FIG.  14   , the light source LS 1  is arranged to be displaced (or shifted) from the opposed surface  1 B to a side opposite to the tip side of the arrow indicating the direction Y. In other words, the light source LS 1  is positioned more closely to the side opposite to the tip side of the arrow indicating the direction Y than to the opposed surface  1 B. The light source LS 1  is arranged at a position separated from the opposed surface  1 B of the light guide LG 1  toward the side opposite to the tip side of the arrow indicating the direction Z in a distance HL 1 . The emitting portion LSP 1  of the light source LS 1  that emits the P-polarized light L 1  is positioned on a lower side of a center line which passes a center of the height of the main surface  1 A and the opposed surface  1 B of the light guide LG 1  and which is parallel to the main surface  1 A and the opposed surface  1 B, in the direction Z. 
     In  FIG.  14   , the side surface SF 1  is formed to be inclined to the main surface  1 A at an angle=97.1° and inclined to the opposed surface  1 B at an angle=82.9°, in the Y-Z plane. In other words, the side surface SF 1  is formed to be inclined at an angle=82.9° to the opposed surface  1 B, in the Y-Z plane. In other words, the side surface SF 1  is formed to be inclined to the main surface  1 A at an angle=97.1°, in the Y-Z plane. 
     In the example shown in  FIG.  14   , the light source LS 1  emits the P-polarized light L 1  from the opposed surface  1 B side toward the side surface SF 1  at the Brewster&#39;s approximate angle=56°, in the direction Z. The P-polarized light L 1  emitted from the light source LS 1  is made incident on the side surface SF 1  at the Brewster&#39;s approximate angle=56° from the opposed surface  1 B side in the direction Z. The P-polarized light L 1  made incident on the light guide LG 1  from air is refracted at the boundary between the air and the side surface SF 1  at a refraction angle=33.6° to travel at an angle=26.5° with respect to the main surface  1 A. In other words, the P-polarized light L 1  made incident on the light guide LG 1  from the side surface SF 1  is refracted at an angle=33.6° to the main surface  1 A side with respect to a straight line perpendicular to the side surface SF 1 , on the side surface SF 1 , to travels at 26.5° to the main surface  1 A. 
       FIG.  15    is a cross-sectional view showing an example of the arrangement of the light source LS 2  relative to the light guide LG 2  of the illumination device IL according to modified example 1. 
     In the example shown in  FIG.  15   , the light source LS 2  is arranged on a side opposite to the tip side of the arrow indicating the direction Z to the light guide LG 2  such that the P-polarized light is made incident at the Brewster&#39;s approximate angle=56° at which the reflectance to the side surface SF 4  is less than or equal to 0.005 (0.5%), in the Y-Z plane. In other words, the light source LS 2  is arranged on a side opposite to the tip side of the arrow indicating the direction Z to the light guide LG 2  such that the P-polarized light is made incident on the opposed surface  1 B side at an angle=56° to a straight line perpendicular to the side surface SF 4  at which the reflectance to the side surface SF 4  is less than or equal to 0.005 (0.5%), in the Y-Z plane. The light source LS 2  may be arranged on a side opposite to the tip side of the arrow indicating the direction Z to the light guide LG 2  such that the P-polarized light is made incident on the side surface SF 4  at the Brewster&#39;s angle=55.9°, in the Y-Z plane. In other words, the light source LS 2  may be arranged on a side opposite to the tip side of the arrow indicating the direction Z to the light guide LG 2  such that the P-polarized light is made incident on the opposed surface  1 B side at the angle=55.9° to the straight line perpendicular to the side surface SF 4 , in the Y-Z plane. 
     In the example shown in  FIG.  15   , the light source LS 2  is arranged to be displaced (or shifted) from the opposed surface  2 B to a side opposite to the tip side of the arrow indicating the direction Y. In other words, the light source LS 2  is positioned more closely to the side opposite to the tip side of the arrow indicating the direction Y than to the opposed surface  2 B. The light source LS 2  is arranged at a position separated from the opposed surface  2 B of the light guide LG 2  toward the side opposite to the tip side of the arrow indicating the direction Z in a distance HL 1 . The emitting portion LSP 2  of the light source LS 2  that emits the P-polarized light L 2  is positioned on a lower side of a center line which passes a center of the height of the main surface  2 A and the opposed surface  2 B of the light guide LG 2  and which is parallel to the main surface  2 A and the opposed surface  2 B, in the direction Z. 
     In  FIG.  15   , the side surface SF 4  is formed to be inclined at an angle=82.9° to the opposed surface  2 B and at an angle=97.1° to the main surface  2 A, in the Y-Z plane. In other words, the side surface SF 4  is formed to be inclined at an angle=82.9° to the opposed surface  2 B, in the Y-Z plane. In other words, the side surface SF 4  is formed to be inclined to the main surface  2 A at an angle=97.1°, in the Y-Z plane. 
     In the example shown in  FIG.  15   , the light source LS 2  emits the P-polarized light L 2  from the opposed surface  2 B side toward the side surface SF 4  at the Brewster&#39;s approximate angle=56°, in the direction Z. The P-polarized light L 2  emitted from the light source LS 2  is made incident on the side surface SF 4  at the Brewster&#39;s approximate angle=56° from the opposed surface  2 B side in the direction Z. The P-polarized light L 2  made incident on the light guide LG 2  from air is refracted at the boundary between the air and the side surface SF 4  at a refraction angle=33.6° to travel at an angle=26.5° with respect to the main surface  2 A. In other words, the P-polarized light L 2  made incident on the light guide LG 2  from the side surface SF 4  is refracted at an angle=33.6° to the main surface  2 A side with respect to a straight line perpendicular to the side surface SF 4 , on the side surface SF 4 , to travel at 26.5° with respect to the main surface  2 A. 
     In such modified example 1, too, the same advantages as those of the first embodiment can be obtained. 
     Second Embodiment 
     A display device DSP according to the second embodiment is different from the display device DSP of the first embodiment in configuration of light sources LS 1  and LS 2  of an illumination device IL and the light guides LG 1  and LG 2  of the illumination device IL. 
       FIG.  16    is a cross-sectional view showing the display device DSP according to the second embodiment. 
     For example, a side surface SF 1  is inclined at an angle larger than 0° with respect to a main surface  1 A and at an angle smaller than 90°—Brewster&#39;s angle. In addition, for example, a side surface SF 4  is inclined at an angle larger than 0° with respect to a main surface  2 A and at an angle smaller than 90°—Brewster&#39;s angle. 
     Light L 1  emitted from the light source LS 1  is not reflected at all or almost at an interface between the side surface SF 1  and an air layer, but is made incident on the light guide LG 1  from the side surface SF 1  and is refracted on the side surface SF 1 . Light traveling toward the main surface  1 A, of the light L 1  made incident on the light guide LG 1  is reflected (for example, total reflection) at the interface between the light guide LG 1  and the air layer. In addition, light traveling toward an opposed surface  1 B, of the light L 1  made incident on the light guide LG 1  is reflected (for example, total reflection) at the interface between the light guide LG 1  and the air layer. Thus, in the area where the reflective layer P 1  is not provided, of the first area A 1 , the light L 1  travels toward the tip side of the arrow indicating the direction Y, inside the light guide LG 1 , while repeatedly reflected on the main surface  1 A and the opposed surface  1 B (for example, total reflection). 
     Similarly, light L 2  emitted from the light source LS 2  is not reflected at all or almost at the interface between the side surface SF 4  and the air layer, but is made incident on the light guide LG 2  from the side surface SF 4  and is refracted on the side surface SF 4 . The light traveling toward the main surface  2 A, of the light L 2  made incident on the light guide LG 2  is reflected (for example, total reflection) at the interface between the light guide LG 2  and the air layer. In addition, light traveling toward an opposed surface  2 B, of the light L 2  made incident on the light guide LG 2  is reflected (for example, total reflection) at the interface between the light guide LG 2  and the air layer. Thus, in the area where the reflective layer P 2  is not provided, of the second area A 2 , the light L 2  travels toward the side opposite to the tip side of the arrow indicating the direction Y, inside the light guide LG 2 , while repeatedly reflected on the main surface  2 A and the opposed surface  2 B (for example, total reflection). 
       FIG.  17    is a cross-sectional view showing an example of the arrangement of the light source LS 1  relative to the light guide LG 1  of the illumination device IL according to the second embodiment. 
     In the example shown in  FIG.  17   , the light source LS 1  is arranged at a position separated on a side opposite to the tip side of the arrow indicating the direction Y to the side surface SF 1  such that the P-polarized light is made incident at the Brewster&#39;s approximate angle at which the reflectance to the side surface SF 1  is less than or equal to 0.005 (0.5%) to the side surface SF 1 , for example, at the Brewster&#39;s approximate angle=56°, in the Y-Z plane. In other words, the light source LS 1  is arranged at a position separated on a side opposite to the tip side of the arrow indicating the direction Y to the side surface SF 1  such that the P-polarized light is made incident on the main surface  1 A side at an angle=56° to a straight line perpendicular to the side surface SF 1  at which the reflectance to the side surface SF 1  is less than or equal to 0.005, in the Y-Z plane. In other words, the light source LS 1  is arranged at a position separated on the side opposite to the tip side of the arrow indicating the direction Y to the side surface SF 1  such that the P-polarized light is made incident at an angle=4.1° to a center line which passes the center of the light guide LG 1  and which is parallel to the main surface  1 A and the opposed surface  1 B, in the Y-Z plane. 
     The light source LS 1  may be arranged at a position separated on the side opposite to the tip side of the arrow indicating the direction Y to the side surface SF 1  such that the P-polarized light is made incident on the side surface SF 1  at the Brewster&#39;s angle=55.9°, in the Y-Z plane. In other words, the light source LS 1  may be arranged at a position separated on a side opposed to the tip side of the arrow indicating the direction Y to the side surface SF 1  such that the P-polarized light is made incident on the main surface  1 A side at the angle=55.9° to the straight line perpendicular to the side surface SF 1 , in the Y-Z plane. 
     In the example shown in  FIG.  17   , the light source LS 1  is arranged between the main surface  1 A and the opposed surface  1 B in the direction Z. In other words, the light source LS 1  is arranged between heights of the main surface  1 A and the opposed surface  1 B, in the direction Z. The light source LS 1  is arranged within a range from the main surface  1 A to a position separated from a side opposite to the tip side of the arrow indicating the direction Z in a distance HL 2 . The light source LS 1  is arranged to be inclined on a lower side at an angle of 4.1° to a center line which passes a center of the height of the main surface  1 A and the opposed surface  1 B of the light guide LG 1  and which is parallel to the main surface  1 A and the opposed surface  1 B, in the direction Z. The emitting portion LSP 1  of the light source LS 1  that emits the P-polarized light L 1  is positioned on a lower side of a center line which passes a center of the height of the main surface  1 A and the opposed surface  1 B of the light guide LG 1  and which is parallel to the main surface  1 A and the opposed surface  1 B, in the direction Z. 
     In  FIG.  17   , the side surface SF 1  is formed to be inclined at an angle=29.9° to the main surface  1 A and at an angle=150.1° to the opposed surface  1 B, in the Y-Z plane. In other words, the side surface SF 1  is formed to be inclined to the main surface  1 A at an angle=29.9°, in the Y-Z plane. In addition, the side surface SF 1  is formed to be inclined to the opposed surface  1 B at an angle=150.1°, in the Y-Z plane. 
     In the example shown in  FIG.  17   , the light source LS 1  emits the P-polarized light L 1  from the opposed surface  1 B side toward the side surface SF 1  at the Brewster&#39;s approximate angle=56°, in the direction Z. The P-polarized light L 1  emitted from the light source LS 1  is made incident on the side surface SF 1  at the Brewster&#39;s approximate angle=56° from the opposed surface  1 B side in the direction Z. In other words, the P-polarized light L 1  emitted from the light source LS 1  is made incident on the side surface SF 1  at an angle=56° on the main surface  1 A side to the straight line perpendicular to the side surface SF 1 , in the direction Z. The P-polarized light L 1  made incident on the light guide LG 1  from air is refracted at the boundary between the air and the side surface SF 1  at a refraction angle=33.6° to travel at an angle=26.5° with respect to the main surface  1 A. In other words, the P-polarized light L 1  made incident on the light guide LG 1  from the side surface SF 1  is refracted at an angle of 33.6° to the opposed surface  1 B side with respect to a straight line perpendicular to the side surface SF 1 , on the side surface SF 1 , to travel at 26.5° with respect to the main surface  1 A. 
       FIG.  18    is a cross-sectional view showing an example of the arrangement of the light source LS 2  relative to the light guide LG 2  of the illumination device IL according to the second embodiment. 
     In the example shown in  FIG.  18   , the light source LS 2  emits the P-polarized light L 2 . In the example shown in  FIG.  18   , the light source LS 2  is arranged at a position separated on a side opposite to the tip side of the arrow indicating the direction Y to the side surface SF 4  such that the P-polarized light is made incident at the Brewster&#39;s approximate angle at which the reflectance to the side surface SF 4  is less than or equal to 0.005 (0.5%) to the side surface SF 1 , for example, at the Brewster&#39;s approximate angle=56°, in the Y-Z plane. In other words, the light source LS 2  is arranged at a position separated on the tip side of the arrow indicating the direction Y to the side surface SF 4  such that the P-polarized light is made incident on the main surface  2 A side at an angle=56° to a straight line perpendicular to the side surface SF 4  at which the reflectance to the side surface SF 4  is less than or equal to 0.005, in the Y-Z plane. In other words, the light source LS 2  is arranged at a position separated on the tip side of the arrow indicating the direction Y to the side surface SF 1  such that the P-polarized light is made incident at an angle=4.1° to a center line which passes the center of the light guide LG 2  and which is parallel to the main surface  2 A and the opposed surface  2 B, in the Y-Z plane. 
     The light source LS 2  may be arranged at a position separated on the tip side of the arrow indicating the direction Y to the side surface SF 4  such that the P-polarized light is made incident on the side surface SF 4  at the Brewster&#39;s angle=55.9°, in the Y-Z plane. In other words, the light source LS 2  may be arranged at a position separated on the tip side of the arrow indicating the direction Y to the side surface SF 4  such that the P-polarized light is made incident on the opposed surface  2 B side at the angle=55.9° to the straight line perpendicular to the side surface SF 4 , in the Y-Z plane. 
     In the example shown in  FIG.  18   , the light source LS 2  is arranged between the main surface  2 A and the opposed surface  2 B in the direction Z. In other words, the light source LS 2  is arranged between heights of the main surface  2 A and the opposed surface  2 B in the direction Z. The light source LS 2  is arranged within a range from the main surface  2 A to a position separated from a side opposite to the tip side of the arrow indicating the direction Z in the distance HL 2 . The light source LS 2  is arranged to be inclined on a lower side at an angle of 4.1° to a center line which passes a center of the height of the main surface  2 A and the opposed surface  2 B of the light guide LG 2  and which is parallel to the main surface  2 A and the opposed surface  2 B, in the direction Z. The emitting portion LSP 2  of the light source LS 2  that emits the P-polarized light L 1  is positioned on a lower side of a center line which passes a center of the height of the main surface  2 A and the opposed surface  2 B of the light guide LG 2  and which is parallel to the main surface  2 A and the opposed surface  2 B, in the direction Z. 
     In  FIG.  18   , the side surface SF 4  is formed to be inclined to the main surface  2 A at an angle=29.9° and inclined to the opposed surface  2 B at an angle=150.1°, in the Y-Z plane. In other words, the side surface SF 4  is formed to be inclined to the main surface  2 A at an angle=29.9°, in the Y-Z plane. In addition, the side surface SF 4  is formed to be inclined to the opposed surface  2 B at an angle=150.1°, in the Y-Z plane. 
     In the example shown in  FIG.  18   , the light source LS 2  emits the P-polarized light L 2  from the opposed surface  2 B side toward the side surface SF 4  at the Brewster&#39;s approximate angle=56°, in the direction Z. The P-polarized light L 2  emitted from the light source LS 2  is made incident on the side surface SF 4  at the Brewster&#39;s approximate angle=56° from the opposed surface  2 B side in the direction Z. In other words, the P-polarized light L 2  emitted from the light source LS 2  is made incident on the side surface SF 4  at an angle=56° on the main surface  2 A side to the straight line perpendicular to the side surface SF 4 , from the opposed surface  2 B side in the direction Z. The P-polarized light L 2  made incident on the light guide LG 2  from air is refracted at the boundary between the air and the side surface SF 4  at a refraction angle=33.6° to travel at an angle=26.5° with respect to the main surface  2 A. In other words, the P-polarized light L 2  made incident on the light guide LG 2  from the side surface SF 4  is refracted at an angle of 33.6° to the opposed surface  2 B side with respect to a straight line perpendicular to the side surface SF 4 , on the side surface SF 4 , to travel at 26.5° with respect to the main surface  2 A. 
     The second embodiment also has the same advantages as those of the first embodiment and modified example 1. In addition, the thickness of the illumination device IL of the second embodiment can be made smaller than the thickness of the illumination device IL of the first embodiment. 
     MODIFIED EXAMPLE 2 
     The illumination device IL according to modified example 2 of the second embodiment is different from the illumination device IL of the first embodiment, modified example 1, and the second embodiment in configuration of the light sources LS 1  and LSF 2 . 
       FIG.  19    is a cross-sectional view showing an example of the arrangement of the light source LS 1  relative to the light guide LG 1  of the illumination device IL according to modified example 2. 
     In the example shown in  FIG.  19   , the light source LS 1  is arranged at a position separated on a side opposite to the tip side of the arrow indicating the direction Y to the side surface SF 1  such that the P-polarized light is made incident at the Brewster&#39;s approximate angle at which the reflectance to the side surface SF 1  is less than or equal to 0.005 (0.5%) to the side surface SF 1 , for example, at the Brewster&#39;s approximate angle=56°, in the Y-Z plane. In other words, the light source LS 1  is arranged at a position separated on a side opposite to the tip side of the arrow indicating the direction Y to the side surface SF 1  such that the P-polarized light is made incident on the opposed surface lB side at an angle=56° to a straight line perpendicular to the side surface SF 1  at which the reflectance to the side surface SF 1  is less than or equal to 0.005, in the Y-Z plane. In other words, the light source LS 1  is arranged at a position separated on the side opposite to the tip side of the arrow indicating the direction Y to the side surface SF 1  such that the P-polarized light is made incident at an angle=4.1° to a center line which passes the center of the light guide LG 1  and which is parallel to the main surface  1 A and the opposed surface  1 B, in the Y-Z plane. 
     The light source LS 1  may be arranged at a position separated on the side opposite to the tip side of the arrow indicating the direction Y to the side surface SF 1  such that the P-polarized light is made incident on the side surface SF 1  at the Brewster&#39;s angle=55.9°, in the Y-Z plane. In other words, the light source LS 1  may be arranged at a position separated on the side opposite to the tip side of the arrow indicating the direction Y to the side surface SF 1  such that the P-polarized light is made incident on the opposed surface  1 B side at the angle=55.9° to the straight line perpendicular to the side surface SF 1 , in the Y-Z plane. 
     In the example shown in  FIG.  19   , the light source LS 1  is arranged between the main surface  1 A and the opposed surface  1 B of the light guide LG 1 , in the direction Z. In other words, the light source LS 1  is arranged between heights of the main surface  1 A and the opposed surface  1 B, in the direction Z. The light source LS 1  is arranged within a range from a position separated from the opposed surface  1 B on the tip side of the arrow indicating the direction Z in a distance HL 2 , to the main surface  1 A. The light source LS 1  is arranged to be inclined on an upper side at an angle of 4.1° to a center line which passes a center of the height of the main surface  1 A and the opposed surface  1 B of the light guide LG 1  and which is parallel to the main surface  1 A and the opposed surface  1 B, in the direction Z. An emitting portion LSP 1  of the light source LS 1  that emits the P-polarized light L 1  is positioned on an upper side of a center line which passes a center of the height of the main surface  1 A and the opposed surface  1 B of the light guide LG 1  and which is parallel to the main surface  1 A and the opposed surface  1 B, in the direction Z. 
     In  FIG.  19   , the side surface SF 1  is formed to be inclined to the main surface  1 A at an angle=150.1° and inclined to the opposed surface  1 B at an angle=29.9°, in the Y-Z plane. In other words, the side surface SF 1  is formed to be inclined to the main surface  1 A at an angle=150.1°, in the Y-Z plane. In addition, the side surface SF 1  is formed to be inclined to the opposed surface  1 B at an angle=29.9°, in the Y-Z plane. 
     In the example shown in  FIG.  19   , the light source LS 1  emits the P-polarized light L 1  from the main surface  1 A side toward the side surface SF 1  at the Brewster&#39;s approximate angle=56°, in the direction Z. The P-polarized light L 1  emitted from the light source LS 1  is made incident on the side surface SF 1  at the Brewster&#39;s approximate angle=56° from the main surface  1 A side in the direction Z. In other words, the P-polarized light L 1  emitted from the light source LS 1  is made incident on the side surface SF 1  at an angle=56° on the opposed surface  1 B side to the straight line perpendicular to the side surface SF 1 , from the main surface  1 A side in the direction Z. The P-polarized light L 1  made incident on the light guide LG 1  from air is refracted at the boundary between the air and the side surface SF 1  at a refraction angle=33.6° to travel at an angle=26.5° with respect to the opposed side  1 B. In other words, the P-polarized light L 1  made incident on the light guide LG 1  from the side surface SF 1  is refracted at an angle of 33.6° to the main surface  2 A side with respect to a straight line perpendicular to the side surface SF 1 , on the side surface SF 1 , to travel at 26.5° with respect to the opposed surface  1 B. 
       FIG.  20    is a cross-sectional view showing an example of the arrangement of the light source LS 2  relative to the light guide LG 2  of the illumination device IL according to modified example 2. 
     In the example shown in  FIG.  20   , the light source LS 2  is arranged at a position separated on the tip side of the arrow indicating the direction Y to the side surface SF 4  such that the P-polarized light is made incident at the Brewster&#39;s approximate angle at which the reflectance to the side surface SF 4  is less than or equal to 0.005 (0.5%) to the side surface SF 1 , for example, at the Brewster&#39;s approximate angle=56°, in the Y-Z plane. In other words, the light source LS 2  is arranged at a position separated on the tip side of the arrow indicating the direction Y to the side surface SF 4  such that the P-polarized light is made incident on the opposed surface  2 B side at an angle=56° to a straight line perpendicular to the side surface SF 4  at which the reflectance to the side surface SF 4  is less than or equal to 0.005, in the Y-Z plane. In other words, the light source LS 2  is arranged at a position separated on the tip side of the arrow indicating the direction Y to the side surface SF 4  such that the P-polarized light is made incident at an angle=4.1° to a straight line which passes the center of the light guide LG 2  and which is parallel to the main surface  2 A and the opposed surface  2 B, in the Y-Z plane. 
     The light source LS 2  may be arranged at a position separated on the tip side of the arrow indicating the direction Y to the side surface SF 4  such that the P-polarized light is made incident on the side surface SF 4  at the Brewster&#39;s angle=55.9°, in the Y-Z plane. In other words, the light source LS 2  may be arranged at a position separated on the tip side of the arrow indicating the direction Y to the side surface SF 4  such that the P-polarized light is made incident on the opposed surface  2 B side at the angle=55.9° to the straight line perpendicular to the side surface SF 4 , in the Y-Z plane. 
     In the example shown in  FIG.  20   , the light source LS 2  is arranged between the main surface  2 A and the opposed surface  2 B in the direction Z. In other words, the light source LS 2  is arranged between heights of the main surface  2 A and the opposed surface  2 B in the direction Z. The light source LS 2  is arranged within a range from a position separated from the opposed surface  2 B on the tip side of the arrow indicating the direction Z in a distance HL 2 , to the main surface  2 A. The light source LS 2  is arranged to be inclined on an upper side at an angle of 4.1° to a center line which passes a center of the height of the main surface  2 A and the opposed surface  2 B of the light guide LG 2  and which is parallel to the main surface  2 A and the opposed surface  2 B, in the direction Z. An emitting portion LSP 2  of the light source LS 2  that emits the P-polarized light L 1  is positioned on an upper side of a center line which passes a center of the height of the main surface  2 A and the opposed surface  2 B of the light guide LG 2  and which is parallel to the main surface  2 A and the opposed surface  2 B, in the direction Z. 
     In  FIG.  20   , the side surface SF 4  is formed to be inclined to the main surface  2 A at an angle=150.1° and inclined to the opposed surface  2 B at an angle=29.9°, in the Y-Z plane. In other words, the side surface SF 4  is formed to be inclined to the main surface  2 A at an angle=29.9°, in the Y-Z plane. In addition, the side surface SF 4  is formed to be inclined to the opposed surface  2 B at an angle=150.1°, in the Y-Z plane. 
     In the example shown in  FIG.  20   , the light source LS 2  emits the P-polarized light L 2  from the main surface  2 A side toward the side surface SF 4  at the Brewster&#39;s approximate angle=56°, in the direction Z. The P-polarized light L 2  emitted from the light source LS 2  is made incident on the side surface SF 4  at the Brewster&#39;s approximate angle=56° from the main surface  2 A side in the direction Z. In other words, the P-polarized light L 2  emitted from the light source LS 2  is made incident on the side surface SF 4  at an angle=56° on the opposed surface  2 B side to the straight line perpendicular to the side surface SF 4 , from the opposed surface  2 B side in the direction Z. The P-polarized light L 2  made incident on the light guide LG 2  from air is refracted at the boundary between the air and the side surface SF 4  at a refraction angle=33.6° to travel at an angle=26.5° with respect to the opposed surface  2 B. In other words, the P-polarized light L 2  made incident on the light guide LG 2  from the side surface SF 4  is refracted at an angle of 33.6° to the main surface  2 A side with respect to a straight line perpendicular to the side surface SF 4 , on the side surface SF 4 , to travel at 26.5° with respect to the opposed surface  2 B. 
     The second embodiment also has the same advantages as those of the first embodiment and modified example 1. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.