Abstract:
In the present invention, a backlight ( 3 ) serving as a planar light source unit is equipped with: multiple LEDs ( 12 ); and a bottom plate ( 11   a ) having a mounting surface ( 11   a   1 ). The multiple LEDs ( 12 ) are two-dimensionally arranged on the mounting surface ( 11   a   1 ) within a rectangular area (RA) that is smaller than the bottom plate ( 11   a ). In addition, the arrangement density of the LEDs in the rectangular area (RA) is lower at the center part (Rc) than at the peripheral part (Rp). The rectangular area (RA) has a corner area, where at least one LED ( 12 ) is provided, at each of the four corners thereof. The LEDs ( 12 ) positioned in the respective corner areas are installed such that the central axes of the LEDs lean toward the periphery side of the rectangular area (RA) with respect to the direction perpendicular to the mounting surface ( 11   a   1 ).

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a planar light source device in which a plurality of light sources are disposed two-dimensionally in a rectangular region on a mounting surface and to a liquid crystal display device that includes the planar light source device. 
       BACKGROUND ART 
       [0002]    Conventionally, as a planar light source device that illuminates a liquid crystal panel, a so-called illumination device of direct type, which is disposed right under a rear surface of the liquid crystal panel, is proposed. As a light source of such an illumination device, it is possible to use a tube-like light source (e.g., cold-cathode tube lamp) as in patent documents 1 to 3 or use a point light source (e.g., LED (light emitting diode) as in a patent document 4. Especially, an LED is advantageous in longevity and low power consumption, and in recent years, many LEDs are used as light sources of illumination devices. 
         [0003]    In the meantime, when humans watch a screen of a liquid crystal panel, they watch more carefully the screen center than the screen peripheral. Because of this, in a case of using LEDs as the light source, even if the disposition density of the LEDs is made low at the peripheral portion, visual brightness unevenness is not conspicuous. As described above, by partially changing the disposition density of the LEDs, it is possible to secure the brightness of a necessary region (screen center) and achieve low cost by reducing the number of LEDs mounted. 
         [0004]    When changing partially the disposition density of the LEDs, in the patent document 4, as shown in  FIG. 25 , LED boards  102  mounting a plurality of LEDs  101  are disposed in parallel, and disposition intervals of the LED boards  102  are partially changed. Specifically, in a central portion Rc in an arrangement direction of the LED boards  102 , the interval of neighboring LED boards  102  is made narrow, while in an outside peripheral portion Rp with respect to the central portion Rc in the arrangement direction of the LED boards  102 , the interval of neighboring LED boards  102  is made wide. As described above, it is conceivable that by adjusting the interval of the LED boards  102  to change partially the disposition density of the LEDs, it is also possible to easily deal with a size change of an illumination device  100 . 
         [0005]    Besides, in the illumination device in the patent document 4, a reflection sheet  103  is disposed on a bottom plate (mounting surface) of a backlight chassis where the LED board  102  is mounted. The reflection sheet  103  has an opening portion for exposing the LED  101  and is disposed on the bottom plate to cover the LED board  102 . An edge portion  103   a  of the reflection sheet  103  rises obliquely from the bottom plate. As described above, by disposing the reflection sheet  103 , even if the LED  101  is not disposed on a peripheral portion of the bottom plate, it is possible to illuminate a screen peripheral portion of a liquid crystal panel by means of light that is emitted from the LED  101  and reflected by the edge portion  103   a  of the reflection sheet  103 . Accordingly, it is possible to achieve low cost by further reducing the number of LEDs  101  mounted. 
       CITATION LIST 
     Patent Literature 
       [0000]    
       
         PLT1: International Publication No. 2009/004840 pamphlet (see claim 1, FIG. 5 and the like). 
         PLT2: International Publication No. 2009/004841 pamphlet (see claim 1, FIG. 5 and the like). 
         PLT3: International Publication No. 2010/146920 pamphlet (see claim 1, FIG. 11, FIG. 12 and the like). 
         PLT4: International Publication No. 2010/146921 pamphlet (see claims 1, 2, paragraphs [0005], [0008], [0035], [0036], FIG. 7 and the like). 
       
     
       SUMMARY OF INVENTION 
     Technical Problem 
       [0010]    In the meantime, in  FIG. 25 , the LEDs  101  are disposed in a region on the bottom plate where the edge portion  103   a  of the reflection sheet  103  does not exist, that is, a rectangular region of V1 (cm) height×H1 (cm) width. On the other hand, the bottom plate of the back chassis has a size of V2 (cm) height×H2 (cm) width, where V1&lt;V2, and H1&lt;H2. As describe above, because of the reduction in the number of LEDs  101  mounted, if the size (V1×H1) of the disposition region for the LEDs  101  becomes smaller than the size (V2×H2) of the bottom plate and the disposition density of the LEDs  101  in the disposition region becomes lower in the peripheral portion Rp than in the central portion Rc, the light has difficulty in reaching four corners of the screen of the liquid crystal panel from LEDs  101   a  to  101   d  at four corners of the disposition region. As a result of this, as shown in  FIG. 26 , a phenomenon easily occurs, in which the brightness in four-corner regions  201   a  to  201   d  of the screen of the liquid crystal panel declines. 
         [0011]    The present invention has been made to solve the above problems, and it is an object of the present invention to provide: a planar light source device that is able to alleviate the brightness declining at the four corners of an illumination region of an illumination target even in a structure in which a plurality of light sources are disposed such that the disposition density becomes lower in a peripheral portion than in a central portion in a small region that is smaller than a size of a bottom plate; and a liquid crystal display device that includes the planar light source device. 
       Solution to Problem 
       [0012]    A planar light source device according to an aspect of the present invention comprises: a plurality of light sources, and a bottom plate that has a mounting surface on which the plurality of light sources are mounted, wherein the plurality of light sources are two-dimensionally disposed in a rectangular region of the mounting surface that is smaller than a size of the bottom plate, and disposition density of the light sources in the rectangular region is lower in a peripheral portion than in a central portion, wherein the rectangular region has, at four corners thereof, corner regions where at least one of the light sources is disposed, and the light source located in each of the corner regions is disposed such that a central axis thereof inclines from a direction perpendicular to the mounting surface toward an outer peripheral side of the rectangular region. 
         [0013]    A planar light source device according to another aspect of the present invention comprises: a plurality of light sources, and a bottom plate that has a mounting surface on which the plurality of light sources are mounted, wherein the plurality of light sources are two-dimensionally disposed in a rectangular region of the mounting surface that is smaller than a size of the bottom plate, and disposition density of the light sources in the rectangular region is lower in a peripheral portion than in a central portion, the planar light source device further comprising a diffusion lens that is disposed correspondingly to each of the plurality of light sources and diffuses light emitted from the light source, wherein the rectangular region has, at four corners thereof, corner regions where at least one of the light sources is disposed, and the diffusion lens corresponding to the light source located in each of the corner regions is disposed such that a central axis thereof is located at a position closer to an outer peripheral side of the rectangular region than a light emitting portion of the light source. 
         [0014]    A planar light source device according to still another aspect of the present invention comprises: a plurality of light sources, and a bottom plate that has a mounting surface on which the plurality of light sources are mounted, wherein the plurality of light sources are two-dimensionally disposed in a rectangular region of the mounting surface that is smaller than a size of the bottom plate, and disposition density of the light sources in the rectangular region is lower in a peripheral portion than in a central portion, the planar light source device further comprising a diffusion lens that is disposed correspondingly to each of the plurality of light sources and diffuses light emitted from the light source, wherein the rectangular region has, at four corners thereof, corner regions where at least one of the light sources is disposed, and the diffusion lens corresponding to the light source located in each of the corner regions is disposed such that a central axis thereof inclines from a direction perpendicular to the mounting surface toward an outer peripheral side of the rectangular region. 
         [0015]    A liquid crystal display device according to still another aspect of the present invention comprises: the above planar light source device, and a liquid crystal panel that modulates light supplied from the planar light source device to perform display. 
       Advantageous Effects of Invention 
       [0016]    According to the present invention, by suitably setting the disposition angles of the light sources located in the four corner regions of the mounting surface, the mounting positions and mounting angles of the diffusion lenses corresponding to the light sources, even in the structure in which to achieve low cost by reduction in the number of the light sources mounted, the disposition region for the light sources is made smaller than the size of the bottom plate and the disposition density of the light sources in the disposition region is made lower in the peripheral portion than in the central portion, it is possible to alleviate the brightness declining at the four corners of the illumination region by means of illumination from the light source in each of the corner regions. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0017]      FIG. 1A  is a cross-sectional view showing a schematic structure of a liquid crystal display device according to an embodiment 1 of the present invention. 
           [0018]      FIG. 1B  is a plan view of a backlight of the above liquid crystal display device. 
           [0019]      FIG. 2  is a cross-sectional view of a diffusion lens of the above backlight. 
           [0020]      FIG. 3A  is a plan view showing schematically a division example when a rectangular region on which a plurality of LEDs are disposed is divided into a plurality of regions on a bottom plate of the above backlight. 
           [0021]      FIG. 3B  is a descriptive view showing an address of each division region in the above division example. 
           [0022]      FIG. 4  is a descriptive view showing schematically LEDs disposed in four corner regions of the above rectangular region and a brightness distribution of light emitted from the LEDs via diffusion lenses. 
           [0023]      FIG. 5A  is a plan view showing schematically another division example of the above rectangular region. 
           [0024]      FIG. 5B  is a descriptive view showing an address of each division region in the above division example. 
           [0025]      FIG. 6  is a plan view showing another structure of the above backlight. 
           [0026]      FIG. 7  is a plan view showing still another structure of the above backlight. 
           [0027]      FIG. 8  is a plan view showing still another structure of the above backlight. 
           [0028]      FIG. 9  is a plan view of a backlight according to an embodiment 2 of the present invention. 
           [0029]      FIG. 10  is a descriptive view showing schematically LEDs disposed in four corner regions of a rectangular region on which a plurality of LEDs are disposed on a bottom plate of the above backlight and a brightness distribution of light emitted from the LEDs via diffusion lenses. 
           [0030]      FIG. 11  is a plan view showing schematically another division example of the above rectangular region. 
           [0031]      FIG. 12  is a plan view showing another structure of the above backlight. 
           [0032]      FIG. 13  is a plan view showing still another structure of the above backlight. 
           [0033]      FIG. 14  is a plan view showing still another structure of the above backlight. 
           [0034]      FIG. 15  is a plan view of a backlight according to an embodiment 3 of the present invention. 
           [0035]      FIG. 16  is a descriptive view showing schematically LEDs disposed in four corner regions of a rectangular region on which a plurality of LEDs are disposed on a bottom plate of the above backlight and a brightness distribution of light emitted from the LEDs via diffusion lenses. 
           [0036]      FIG. 17  is a plan view showing schematically another division example of the above rectangular region. 
           [0037]      FIG. 18  is a plan view showing another structure of the above backlight. 
           [0038]      FIG. 19  is a plan view showing still another structure of the above backlight. 
           [0039]      FIG. 20  is a plan view showing still another structure of the above backlight. 
           [0040]      FIG. 21  is a cross-sectional view showing another disposition example of an LED and a diffusion lens in a corner region of the above rectangular region. 
           [0041]      FIG. 22  is a cross-sectional view showing still another disposition example of an LED and a diffusion lens in a corner region of the above rectangular region. 
           [0042]      FIG. 23  is a cross-sectional view showing still another disposition example of an LED and a diffusion lens in a corner region of the above rectangular region. 
           [0043]      FIG. 24  is a cross-sectional view showing still another disposition example of an LED and a diffusion lens in a corner region of the above rectangular region. 
           [0044]      FIG. 25  is a plan view showing a structure of a conventional backlight. 
           [0045]      FIG. 26  is a plan view showing schematically a display screen of a liquid crystal panel illuminated by the backlight. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiment 1 
       [0046]    An embodiment 1 of the present invention is described based on drawings as follows. In the meantime, there is a case where structures common to each embodiment are indicated by the same member numbers and description of them is skipped. 
         [0047]      FIG. 1A  is a cross-sectional view showing a schematic structure of a liquid crystal display device  1  according to the present embodiment, and  FIG. 1B  is a plan view of a backlight  3  of the liquid crystal display device  1 . In the meantime, in  FIG. 1B , for the sake of convenience, illustration of a diffusion plate  15  and an optical sheet  16  described later is skipped. As shown in these drawings, the liquid crystal display device  1  has a liquid crystal panel  2  and a backlight  3 . 
         [0048]    The liquid crystal panel  2  is a liquid crystal display element that modulates light supplied from the backlight  3  to display an image, and composed by sandwiching a liquid layer by means of a pair of boards. One board is provided with a source wiring and a gate wiring disposed to cross each other at right angles, a switching element (e.g., TFT: Thin Film Transistor) that performs ON/OFF of driving of a pixel enclosed by the source wiring and the gate wiring adjacent to each other, a pixel electrode connected to the switching element and the like. The other board is provided with a color filter formed of color filters of R (red), G (green), and B (blue) disposed correspondingly to each pixel, a common electrode common to each pixel and the like. Besides, a side of each board facing the liquid crystal layer is provided with an orientation film that orients liquid crystal molecules, while an outer side (opposite to the liquid crystal layer) of each board is provided with a light polarization plate that transmits predetermined polarized light only. 
         [0049]    The backlight  3  is a planar light source device (illumination device) of direct type that is disposed right under a rear surface of the liquid crystal panel  2  and illuminates the liquid crystal panel  2  in a planar manner. The backlight  3  includes a backlight chassis  11 , LEDs  12  as a plurality of light sources, an LED board  13 , a diffusion lens  14 , a diffusion plate  15 , an optical sheet  16 , a reflection sheet  17 , and a not-shown circuit board. The above circuit board is a circuit board that controls light emission from the LED  12 , but may include a circuit board for driving the liquid crystal panel  2  and other boards (power source board, control board). 
         [0050]    The backlight chassis  11  is a chassis member that is formed by bending a sheet metal into a predetermined shape, has a bottom plate  11   a  and a side plate  11   b . The bottom plate  11   a  is formed into a rectangular shape when viewing from top, and on one surface of which (surface facing the liquid crystal panel  2 ) the plurality of LEDs  12  are mounted via the LED board  13 . Hereinafter, this surface is called a mounting surface  11   a   1  on which the plurality of LEDs  21  are mounted. The side plate  11   b  is connected to an outer peripheral portion (four side edge portions of the bottom plate  11   a ) of the bottom plate  11   a  to rise substantially upright from the bottom plate  11   a.    
         [0051]    The LEDs  12  are each a light emitting diode (point light source) that has a light emitting portion  12   a  (see  FIG. 2 ) and mouthed in a line on the LED board  13  as a mounting board. A plurality of the LED boards  13  are disposed in parallel on the bottom plate  11   a . In this way, the plurality of LEDs  12  are disposed two-dimensionally on the bottom plate  11   a . In the present embodiment, because the reflection sheet  17  described later is provided with an edge portion  17   b , on the bottom plate  11   a , a disposition region for the LEDs  12  is a rectangular region RA smaller than a size of the bottom plate  11   a.    
         [0052]    Here, two directions parallel to the mounting surface  11   a   1  of the bottom plate  11   a  and perpendicular to each other are defined as an H direction (first direction) and a V direction (second direction), respectively. In the meantime, the H direction corresponds to, for example, a long-edge direction of the rectangular region RA, while the V direction corresponds to a short-edge direction of the rectangular region. The size of the rectangular region RA is H1 (cm)×V1 (cm), while the size of the bottom plate  11   a  is H2 (cm)×V2 (cm), where H1&lt;H2, V1&lt;V2. As described above, the rectangular region RA is one size smaller than the size of the bottom plate  11   a.    
         [0053]    Besides, on the bottom plate  11   a , the disposition interval of the LED boards  13  is narrow in a central portion Rc in the arrangement direction of the LED boards  13  and wide in an outer peripheral portion Rp with respect to the central portion Rc in the arrangement direction. As a result of this, the disposition density of the LEDs  12  is high in the central portion Rc of the rectangular region RA and low in the peripheral portion Rp. As described above, by partially changing the disposition density of the LEDs  12 , it is possible to secure an illumination brightness in a necessary region (central region Rc) and to achieve low cost by reducing the number of LEDs  12  mounted as a whole. Besides, by adjusting the disposition interval of the LED boards  13  to partially change the disposition density of the LEDs  12 , it is also possible to easily deal with a size change of the backlight  3 . 
         [0054]    The diffusion lens  14  is disposed on the LED board  13  correspondingly to each of the plurality of LEDs  12  and diffuses the light emitted from each LED  12 . In the meantime, a detailed structure of the diffusion lens  14  is described later. By disposing the diffusion lens  14 , the light from the LED  12  is diffused by the diffusion lens  14 ; accordingly, even in a case where the interval between neighboring LEDs  12  is large, dot-like unevenness becomes unlikely to occur in a brightness distribution by each LED  12 . As a result of this, it is possible to achieve low cost by further reducing the number of LEDs  12  mounted. In the meantime, in a case where it is possible to amply reduce the number of LEDs  12  mounted by adjusting the above disposition interval of the LED boards  13 , it is also possible to employ a structure in which the diffusion lens  14  is not disposed. 
         [0055]    The diffusion plate  15  further diffuses and averages the light emitted from each LED  12  via the diffusion lens  14 , is formed into a flat plate shape and disposed at a position closer to the liquid crystal panel  2  than the diffusion lens  14 . The optical sheet  16  outputs the light, which passes through the diffusion plate  15 , as planar light and is composed to include a lens sheet, a prism sheet, a retroreflection sheet and the like. Respective end portions of the diffusion plate  15  and optical sheet  16  are supported by the side plate  11   b  of the backlight chassis  11  via end portions of the reflection sheet  17 . 
         [0056]    The reflection sheet  17  has an opening portion  17   a  from which each LED  12  is exposed, is disposed on the bottom plate  11   a  to cover the LED board  13 , and reflects the light, which is emitted from the LED  12  and directly enters the reflection sheet, and the light, which is emitted from the LED  12  and reflected by the diffusion plate  15  and the like to enter the reflection sheet, again to the liquid crystal panel  2 . In this way, it is possible to improve use efficiency of the light emitted from the LED  12 . 
         [0057]    The reflection sheet  17  has the edge portion  17   b  that rises obliquely from the bottom plate  11   a  outside the rectangular region RA. In other words, the edge portion  17   b  is located to surround the rectangular region RA. An end portion (outer peripheral portion) of the edge portion  17   b  is supported from under by the side plate  11   b  of the backlight chassis  11 . 
         [0058]    By disposing the reflection sheet  17 , even if the LEDs  12  are not disposed on the outer peripheral portions of the bottom plate  11   a , it is possible to illuminate screen peripheral portions of the liquid crystal panel  2  by means of the light that is emitted from the LEDs  12  and reflected by the edge portion  17   b  of the reflection sheet  17 . Accordingly, it is possible to achieve low cost by further reducing the number of LEDs  12  mounted all the more because the LEDs  12  are not disposed on the peripheral portions of the bottom plate  11   a.    
         [0059]    Next, details of a structure of the above diffusion lens  14  are described.  FIG. 2  a cross-sectional view of the diffusion lens  14 . 
         [0060]    The diffusion lens  14  has a lens portion  14   a  and a plurality of leg portions  14   b  (e.g., three) that support the lens portion  14   a  on the LED board  13 , and is formed into a rotator shape (circular shape when viewing from top) as a whole. The leg portions  14   b  are disposed at an equal interval (e.g., angle interval of 120°) in a direction along an outer circumference of the lens portion  14   a , and mounted at predetermined of the LED board  13  positions by means of an adhesive (not shown), for example. By adjusting a length of each leg portion  14   b , it is possible to adjust a mounting angle of the diffusion lens  14  to the LED board  13 ; however, in the present embodiment, the lengths of the leg portions  14   b  are all the same. As a result of this, a central axis (optical axis) C of the diffusion lens  14  is perpendicular to the mounting surface  11   a  of the bottom plate  11   a.    
         [0061]    The lens portion  14   a  has a light output surface (upper surface)  14   c  and a lower surface  14   d . The light output surface  14   c  is formed into a concave shape recessed toward the LED  12  at a central region close to the central axis C and formed into a convex shape raised oppositely to the LED  12  in an outer circumferential region with respect to the central region in a lens radial direction. Besides, in the lower surface  14   d , a portion opposite to the LED  12  has a concave portion  14   e  that is recessed oppositely to the LED  12 . 
         [0062]    According to such structure of the diffusion lens  14 , the light emitted from the LED  12  is changed (diffused) in travelling direction to the outside by the concave portion  14   e  and the light output surface  14   c , so that a light expansion angle becomes large. 
         [0063]    In the meantime, the shapes of the light output surface  14   c  and lower surface  14   d  of the diffusion plate  14  are not limited to the above shapes, and whatever shapes may be employed if the shapes diffuse (enlarge the light expansion angle) the light emitted from the LED  12 . Accordingly, for example, it is also possible to compose the diffusion lens  14  without disposing the concave portion recessed toward the LED  12  at the central region of the light output surface  14   c , and also possible to compose the diffusion lens  14  without forming the concave portion  14   e  in the lower surface  14   d.    
         [0064]    Next, a structure, which alleviates a brightness decline at the screen four corners of the liquid crystal panel  2  as an illumination target, is described. 
         [0065]      FIG. 3A  is a plan view showing schematically a division example when the rectangular region RA on which the plurality of LEDs  12  are disposed is divided into a plurality of regions on the bottom plate  11   a , and  FIG. 3B  is a descriptive view showing addresses of the plurality of divided regions (hereinafter, also called a division region). In  FIG. 3A , the rectangular region RA is divided into, for example, 7 regions in the H direction (long-edge direction) and into, for example, 4 regions in the V direction (short-edge direction); accordingly,  FIG. 3B  shows a total of 28 regions R ij , where i is an integer of 1 to 4 and corresponds to a number of a row parallel to the H direction, while j is an integer of 1 to 7 and corresponds to a number of a column parallel to the V direction. 
         [0066]    Here, for the sake of convenience for the following description, in the rectangular region RA, regions R 11 ·R 17 ·R 41 ·R 47  located in the four corners are called corner regions P 1 . Besides, in the rectangular region RA, regions located in outermost peripheral portions including the four corner regions P 1 , namely, regions R 11  to R 17 , regions R 21 ·R 27 , regions R 31 ·R 37 , and regions R 41  to R 47  are called outer peripheral regions P 2 . Further, in the rectangular region RA, the remaining regions except for the corner regions P 1  and outer peripheral regions P 2 , namely, regions R 22  to R 26  and regions R 32  to R 36  located (surrounded by the outer peripheral regions P 2 ) inside the outer peripheral regions P 2  are called central regions P 3 . In  FIG. 3B , to facilitate the identification of the corner regions P 1 , outer peripheral regions P 2  and central regions P 3 , these three kinds of regions are indicated by symbols of o, Δ, and □, respectively. 
         [0067]    In the present embodiment, one LED  12  is disposed in each of the four corner regions P 1 . Besides, the above diffusion lens  14  is disposed correspondingly to each LED  12 ; accordingly, one diffusion lens  14  is disposed in each corner region P 1 . 
         [0068]      FIG. 4  shows schematically the LEDs  12  disposed in the four corner regions P 1  and a brightness distribution of the light emitted from the LEDs  12  via the diffusion lenses  14 . In the present embodiment, the LED  12  located in each corner region P 1  is disposed such that a central axis D thereof inclines from a direction perpendicular to the bottom plate  11   a  (mounting surface  11   a   1 ) toward the outer peripheral side of the rectangular region RA, especially toward each apex of the four corners of the rectangular region RA. In the meantime, in  FIG. 3A , an arrow attached to the LED  12  indicates the direction in which the central axis D of the LED  12  inclines, and other drawings appearing in the present embodiment are illustrated in the same way as this. Besides, as to the LED  12  with no arrow attached, the central axis D is in the direction perpendicular to the bottom plate  11   a.    
         [0069]    In the meantime, the central axis D of the LED  12  has the same meaning as a central axis (optical axis) of the light flux emitted from the LED  12 . In other words, an axis, which passes through the light emitting portion  12   a  of the LED  12  and a position where intensity (radiation intensity) of the light emitted from the LED  12  becomes the highest, is defined as the central axis D of the LED  12 . 
         [0070]    Here, in the present embodiment, to incline the central axis D of the LED  12  as described above, the LED  12  is mounted on the LED board  13  via a support member  18 . The support member  18  is formed into a triangle pole shape that has a right triangle in cross section and disposed sideways on the LED board  13 . Accordingly, by disposing the LED  12  onto a surface of the support member  18  inclined by an acute angle to the LED board  13  and disposing the support member  18  onto the LED board  13  such that a normal of the surface of the support member  18  faces each apex of the four corners of the rectangular region RA, it is possible to incline the central axis D of the LED  12  as described above. 
         [0071]    As described above, in the four corner regions P 1 , by disposing the LED  12  such that the central axis D of the LED  12  inclines toward the outer peripheral side of the rectangular region RA, as shown in  FIG. 4 , in the brightness distribution of the light emitted from each LED  12  in each corner region P 1 , it is possible to raise the illumination brightness on the side (outer peripheral side of the rectangular region RA) toward which the central axis D inclines with respect to an axis (e.g., central axis C of the diffusion lens  14 ) that passes through the LED  12  (light emitting portion  12   a ) and is perpendicular to the mounting surface  11   a   1 . In this way, even in the structure in which low cost is achieved by reduction in the number of LEDs  12  mounted, namely, even in the structure in which the disposition region for the LEDs  12  is made smaller than the size of the bottom plate  11   a  and the disposition density of the LEDs  12  in the disposition region is made lower in the peripheral portion Rp than in the central portion Rc, it is possible to alleviate the brightness declining at the four corners of the illumination region by means of the illumination by the LED  12  in each corner region P 1 . 
         [0072]    Especially, in a case where the number of LEDs  12  mounted is further reduced, or in a case where thickness reduction of the backlight  3  is pursued, the brightness at the four corners of the illumination region easily declines; accordingly, as described above, the structure in which the LED  12  inclines to alleviate the brightness decline at the four corners becomes very effective. 
         [0073]    Besides, in the liquid crystal display device  1  that illuminates the liquid crystal panel  2  by means of the backlight  3  having the above structure, it is possible to alleviate the brightness declining at the four corners of the screen of the liquid crystal panel  2 ; accordingly, it is possible to improve display quality. 
         [0074]    Besides, the LED  12  located in each corner region P 1  is disposed such that the central axis D thereof inclines toward each apex of the four corners of the rectangular region RA; accordingly, it is possible to surely supply the light to the four corners of the illumination region by means of the illumination by the LED  12  in each corner region P 1 . Accordingly, it is possible to surely alleviate the brightness declining at the four corners of the illumination region. 
         [0075]    In the meantime, the above effects are obtainable even in a case where the diffusion lens  14  is not disposed over the light emitting side of the LED  12 . However, in the case where the diffusion lens  14  is disposed, the light from the LED  12  is diffused by the diffusion lens  14 , so that the brightness decline at the four corners of the illumination region becomes less conspicuous; accordingly, in this point, it is desirable to employ the structure in which the diffusion lens  14  is disposed. 
         [0076]    Besides, in the backlight  3  of direct type that illuminates the liquid crystal panel  2  from right under, brightness unevenness (e.g., brightness decline at the four corners of the screen) easily occurs in the liquid crystal panel  2  compared to an edge-light type that shines light onto an end surface of a light guide plate to illuminate the liquid crystal panel  2  in a planar manner. Accordingly, the above structure, which alleviates the brightness decline at the four corners of the screen by disposing and inclining the LED  12  in each corner region P 1 , becomes very effective. 
         [0077]    Besides, in the case where the LED  12  is used as the light source of the backlight  3 , the brightness decline due to the reduction in the number of light sources mounted easily occurs at the four corners of the screen compared to a case where a tube-like light source (e.g., cold-cathode tube) is used. Accordingly, in the case where the LED  12  is used as the light source, the above structure, which alleviates the brightness decline at the four corners of the screen by disposing and inclining the LED  12  in each corner region P 1 , becomes very effective. 
         [0078]    Besides, in the case where the diffusion sheet  17  is disposed in the backlight  3 , as described above, it is possible to illuminate the screen peripheral portion of the liquid crystal panel  2  by means of the light reflected by the edge portion  17   b  of the reflection sheet  17 . However, in this case, the LED  12  is not disposed on the peripheral portion of the bottom plate  11   a ; accordingly, it is possible to reduce the number of LEDs  12  mounted, but the light has difficulty in reaching the four corners of the screen of the liquid crystal panel  2 . Accordingly, in the case where the liquid crystal panel  2  is illuminated by means of the edge portion  17   b  of the reflection sheet  17  (case where the reduction in the number of LEDs  12  mounted is achieved), to alleviate the brightness decline at the four corners of the screen, the structure which inclines the LED  12  in each corner region P 1  becomes very effective. 
         [0079]    In the meantime, hereinbefore, the structure is described, in which one LED  12  is disposed in each division region of the rectangular region RA and one LED  12  in the corner region P 1  is inclined; however, a structure may be employed, in which a plurality of LEDs  12  are disposed in each division region and the plurality of LEDs  12  in the corner region P 1  are inclined. In other words, in the case where the total number of LEDs  12  is constant, a structure may be employed, which relatively reduces the number of division regions, increases the number of LEDs  12  disposed in one division region, and inclines the plurality of LEDs  12  in the corner region P 1 . Hereinafter, this point is described more specifically. 
         [0080]      FIG. 5A  is a plan view showing schematically another division example of the rectangular region RA, and  FIG. 5B  is a descriptive view showing an address of each division region. In  FIG. 5A , the rectangular region RA is divided into, for example, 3 regions in the H direction and into, for example, 3 regions in the V direction; accordingly,  FIG. 5B  shows a total of 9 regions R ij , where i is an integer of 1 to 3 and corresponds to a number of a row parallel to the H direction, while j is an integer of 1 to 3 and corresponds to a number of a column parallel to the V direction. 
         [0081]    Here, in the rectangular region RA, regions R 11 ·R 13 ·R 31 ·R 33  located in the four corners are called the corner regions P 1 . Besides, in the rectangular region RA, regions located in the outermost peripheral portions including the four corner regions P 1 , namely, regions R 11  to R 13 , regions R 21 ·R 23 , regions R 31  to R 33  are called the outer peripheral regions P 2 . Further, in the rectangular region RA, regions except for the corner regions P 1  and outer peripheral regions P 2 , namely, a regions R 22  located (surrounded by the outer peripheral regions P 2 ) inside the outer peripheral regions P 2  is called the central regions P 3 . In  FIG. 5B , to facilitate the identification of the corner regions P 1 , outer peripheral regions P 2  and central regions P 3 , these three kinds of regions are indicated by symbols of o, Δ, and □, respectively. 
         [0082]    In the case where the total number of LEDs  12  is the same as in  FIG. 3A  and  FIG. 3B  and the number of division regions in the rectangular region RA is reduced as in  FIG. 5A  and  FIG. 5B , the number of LEDs  12  disposed in one division region increases from the case of  FIG. 3A  and  FIG. 3B . In this example, two LEDs  12  are disposed in each corner region P 1 . In the meantime, the above diffusion lens  14  is disposed correspondingly to each LED  12 ; accordingly, also two diffusion lenses  14  are disposed in each corner region P 1 . 
         [0083]    As described above, by disposing the plurality of LEDs  12  in the corner regions P 1  such that the central axis D inclines toward the outer peripheral side of the rectangular region RA, the amount of the light supplied to the four corners of the illumination region by the plurality of LEDs  12  in the corner regions P 1  increases compared to the structure in which one LED  12  is inclined. Accordingly, it is possible to more alleviate the brightness decline at the four corners of the illumination region. 
         [0084]    From the above description, it can be said preferable if the rectangular region RA in which the LEDs  12  are disposed has, at the four corners, the corner regions P 1  in each of which at least one LED  12  is disposed and the LED  12  located in each corner region P 1  is disposed such that the central axis D thereof inclines toward the outer peripheral side of the rectangular region RA. 
         [0085]    Besides, to secure a high illumination brightness at the central portion of the illumination region while alleviating the brightness decline at the four corners of the illumination region by means of the LEDs  12  in the four corner regions P 1 , it is necessary to illuminate the central portion of the illumination region by means of LEDs  12  in the central region of the rectangular region RA while preventing the central axes D of the LEDs  12  in the central region from inclining toward the outer peripheral side of the rectangular region RA. At this time, for example, if the rectangular region RA is divided into a total of four regions with divided into 2 regions in the H direction and divided into 2 regions in the V direction, all of these four regions become the corner regions P 1  that include each apex of the four corners, and the central axes D of all the LEDs  12  incline toward the outer peripheral side. In other words, in this case, it is impossible to allow a region, in which the central axis D of the LED  12  does not incline, to exist in the rectangular region RA. 
         [0086]    Accordingly, in the present embodiment, by dividing the rectangular region RA into at least 9 regions with divided into 3 or more regions in the H direction and divided into 3 or more regions in the V direction, it is possible to surely alleviate the brightness decline at the four corners of the illumination region by means of the LED  12  in each corner region P 1  while surely achieving improvement in the illumination brightness at the central portion of the illumination region by means of the LED  12  located in a region (e.g., central region P 3 ) except for each corner region P 1 . At this time, each corner region P 1  becomes a region where both-end regions when the rectangular region RA is divided into three or more regions in the H direction and both-end regions when the rectangular region RA is divided into three or more regions in the V direction overlie each other. 
         [0087]    Besides, hereinbefore, the example is described, in which each central axis D of the LED  12  in each corner region inclines toward each corresponding apex of the four corners from the direction perpendicular to the bottom plate  11   a  (mounting surface  11   a ); however, if the central axis D inclines toward the outer peripheral side of the rectangular region RA, the inclination direction is not limited to the direction toward each apex of the four corners. 
         [0088]      FIG. 6  is a plan view showing another structure of the backlight  3 , and  FIG. 7  is a plan view showing still another structure of the backlight  3 . As shown in  FIG. 6  and  FIG. 7 , the LED  12  in each corner region P 1  may be disposed such that the central axis D thereof inclines from the direction perpendicular to the bottom plate  11   a  (mounting surface  11   a   1 ) toward a long edge or a short edge of the rectangular region RA. 
         [0089]    Besides,  FIG. 8  is a plan view showing still another structure of the backlight  3 . The LEDs  12  located in the outer peripheral region P 2  (see  FIG. 3B ,  FIG. 5B ) may be disposed such that each central axis D inclines from the direction perpendicular to the bottom plate  11   a  (mounting surface  11   a   1 ) toward the outer peripheral side (long edge, short edge) of the rectangular region RA. 
         [0090]    In this case, in the brightness distribution of the light emitted from the LED  12  in the outer peripheral region P 2 , it is possible to raise the brightness on the side (outer peripheral side of the rectangular region RA) toward which the central axis D inclines with respect to the axis that passes through the LED  12  and is perpendicular to the mounting surface  11   a   1 . In this way, it is possible to alleviate the brightness declining not only at the four corners of the illumination region but also at the outer peripheral portion, and for example, it is possible to alleviate frame-shaped brightness unevenness occurring on the display screen of the liquid crystal panel  2 . Accordingly, it is possible to further reduce the number of light sources in the outer peripheral region. In addition, by illuminating the central portion of the illumination region by means of the LEDs  12  located in the region (central region P 3 ) inside the outer peripheral region P 2 , it is possible to obtain the above effects while securing the brightness at the central portion. 
       Embodiment 2 
       [0091]    An embodiment 2 of the present invention is described based on drawings as follows. 
         [0092]      FIG. 9  is a plan view of the backlight  3  according to the present embodiment. In the meantime, in  FIG. 9 , for the sake of convenience, the illustration of the diffusion plate  15  and optical sheet  16  is skipped. In the present embodiment, instead of inclining the LED  12  located in each corner region P 1  of the rectangular region RA in the structure according to the embodiment 1, the position of the diffusion lens  14  corresponding to the above LED  12  is deviated with respect to the LED  12 . In more detail, the diffusion lens  14  corresponding to the LED  12  in each corner region P 1  is disposed such that the central axis C thereof inclines toward the outer peripheral side of the rectangular region RA, especially toward each apex of the four corners of the rectangular region RA with respect to the light emitting portion  12   a  of the LED  12 . 
         [0093]    In the meantime, in  FIG. 9 , an arrow attached to the diffusion lens  14  indicates the direction in which the diffusion lens  14  deviates with respect to the LED  12 , and other drawings appearing in the present embodiment are illustrated in the same way as this. Besides, as to the diffusion lens  14  with no arrow attached, the central axis C does not deviate (passes through the light emitting portion  12   a ) from the light emitting portion  12   a  of the LED  12 . 
         [0094]      FIG. 10  shows schematically the LEDs  12  disposed in the four corner regions P 1  and a brightness distribution of the light emitted from the LEDs  12  via the diffusion lenses  14 . In the present embodiment, the central axis C of the diffusion lens  14  corresponding to the LED  12  in each corner region P 1  is located at a position closer to the outer peripheral side of the rectangular region RA than the light emitting portion  12   a  of the LED  12 , so that in the above brightness distribution, it is possible to raise the brightness on the outer peripheral side (side toward which the diffusion lens  14  deviates) of the rectangular region RA compared to the case where the diffusion lens  14  is not deviated. In this way, even in the structure in which to achieve low cost by reduction in the number of LEDs  12  mounted, the disposition region for the LEDs  12  is made smaller than the size of the bottom plate  11   a  and the disposition density of the LEDs  12  in the disposition region is made lower in the peripheral portion Rp than in the central portion Rc, it is possible to alleviate the brightness declining at the four corners of the illumination region by means of the illumination by the LED  12  in each corner region P 1 . 
         [0095]    Especially, in the corner region P 1 , the diffusion lens  14  is disposed such that the central axis C of the diffusion lens  14  is located at a position closer to each apex of the four corners of the rectangular region RA than the light emitting portion  12   a  of the LED  12 ; accordingly, it is possible to surely supply the light to the four corners of the illumination region by means of the illumination by the LED  12  in each corner region P 1  and to surely alleviate the brightness declining at the four corners of the illumination region. 
         [0096]    Here,  FIG. 11  is a plan view showing schematically another division example of the rectangular region RA of the backlight  3  according to the present embodiment. In the meantime, in  FIG. 11 , for the sake of convenience, the illustration of the diffusion plate  15  and optical sheet  16  is skipped. As shown in the drawing, to dispose a plurality of the LEDs  12  in one division region, the rectangular region RA on the bottom plate  11   a  may be divided into 3×3 regions, namely, a total of 9 regions, and the diffusion lenses  14  corresponding to the plurality of LEDs  12  (two in  FIG. 11 ) in each corner region P 1  may be disposed such that the central axes C are located at positions closer to the outer peripheral side of the rectangular region RA than the light emitting portions  12   a  of the LEDs  12 . 
         [0097]    In this case, the amount of the light that is emitted from the LEDs  12  in the corner regions P 1  and supplied to the four corners of the illumination region via the diffusion lenses  14  increases compared to the structure in which only one diffusion lens  14  in the corner region P 1  is deviated toward the outer peripheral side. Accordingly, it is possible to more alleviate the brightness decline at the four corners of the illumination region. 
         [0098]    From the above description, it can be said preferable if the rectangular region RA in which the LEDs  12  are disposed has, at the four corners, the corner regions P 1  in each of which at least one LED  12  is disposed and the diffusion lens  14  corresponding to the LED  12  located in each corner region P 1  is disposed such that the central axis C thereof is located at a position closer to the outer peripheral side of the rectangular region RA than the light emitting portion  12   a  of the LED  12 . 
         [0099]    Besides, if the diffusion lens  14  is disposed in each corner region P 1  such that the central axis C of the diffusion lens  14  is located at a position closer to the outer peripheral side of the rectangular region RA than the light emitting portions  12   a  of the LEDs  12 , the direction, in which the diffusion lens  14  deviates with respect to the light emitting portion  12   a , is not limited to the direction toward each apex of the four corners. 
         [0100]      FIG. 12  is a plan view showing another structure of the backlight  3  according to the present embodiment, and  FIG. 13  is a plan view showing still another structure of the backlight  3 . As shown in  FIG. 12  and  FIG. 13 , the diffusion lens  14  in each corner region P 1  may be disposed such that the central axis C thereof is located at a position closer to the long edge or the short edge of the rectangular region RA than the light emitting portion  12   a.    
         [0101]    Besides,  FIG. 14  is a plan view showing still another structure of the backlight  3 . The diffusion lens  14  corresponding to the LED  12  located in the outer peripheral region P 2  (see  FIG. 3B ,  FIG. 5B ) may be disposed such that the central axis C is located at a position closer to the outer peripheral side (long edge, short edge) of the rectangular region RA than the light emitting portions  12   a.    
         [0102]    In this case, in a brightness distribution of the light that is emitted from the LED  12  in the outer peripheral region P 2  and obtained via the diffusion lens  14 , it is possible to raise the brightness on the outer peripheral side (side toward which the diffusion lens  14  deviates) of the rectangular region RA with respect to the axis (e.g., central axis D) that passes through the light emitting portion  12   a  of the LED  12  and is perpendicular to the mounting surface  11   a   1  compared to the case where the diffusion lens  14  is not deviated. In this way, it is possible to alleviate the brightness declining not only at the four corners of the illumination region but also at the outer peripheral portion, and it is possible to alleviate the frame-shaped brightness unevenness occurring on the display screen of the liquid crystal panel  2 , for example. Accordingly, it is possible to further reduce the number of light sources in the outer peripheral region. In addition, by illuminating the central portion of the illumination region by means of the LEDs  12  located in the region (central region P 3 ) inside the outer peripheral region P 2 , it is possible to obtain the above effects while securing the brightness at the central portion. 
       Embodiment 3 
       [0103]    An embodiment 3 of the present invention is described based on drawings as follows. 
         [0104]      FIG. 15  is a plan view of the backlight  3  according to the present embodiment. In the meantime, in  FIG. 15 , for the sake of convenience, the illustration of the diffusion plate  15  and optical sheet  16  is skipped. In the present embodiment, instead of inclining the LED  12  located in each corner region P 1  of the rectangular region RA in the structure according to the embodiment 1, the diffusion lens  14  corresponding to the above LED  12  is inclined and disposed. In more detail, the diffusion lens  14  corresponding to the LED  12  in each corner region P 1  is disposed such that the central axis C thereof inclines from the direction perpendicular to the mounting surface  11   a  (bottom plate  11   a ) toward the outer peripheral side of the rectangular region RA, especially toward each apex of the four corners of the rectangular region RA. Besides, in the present embodiment, the above diffusion lens  14  is disposed such that the central axis C thereof passes through the light emitting portion  12   a  of the LED  12 . 
         [0105]    In the meantime, in  FIG. 15 , an arrow attached near the diffusion lens  14  indicates a direction in which the central axis C of the diffusion lens  14  inclines from the direction perpendicular to the mounting surface  11   a   1 , and other drawings appearing in the present embodiment are illustrated in the same way as this. Besides, as to the diffusion lens  14  with no arrow attached, the central axis C does not incline (direction perpendicular to the mounting surface  11   a   1 ). 
         [0106]    Here, in the present embodiment, to incline the central axis C of the diffusion lens  14  as described above, the length of the leg portion  14   b  of the diffusion lens  14  is adjusted. For example, by forming the length of the leg portion  14   b  of the plurality of leg portions  14   b  furthest from the outer peripheral side of the rectangular region RA to be longer than the leg portion  14   b  closest to the outer peripheral side of the rectangular region RA, it is possible to incline the central axis C from the direction perpendicular to the bottom plate  11   a  toward the above outer peripheral side. In the meantime, also as to the leg portions  14   b  other than the above leg portion, the length may be suitably adjusted in accordance with the inclination direction and inclination angle of the central axis C. 
         [0107]      FIG. 16  shows schematically the LEDs  12  disposed in the four corner regions P 1  and a brightness distribution of the light emitted from the LEDs  12  via the diffusion lenses  14 . In the present embodiment, the central axis C of the diffusion lens  14  corresponding to the LED  12  in each corner region P 1  inclines to lean from the direction perpendicular to the mounting surface  11   a   1  (bottom plate  11   a ) toward the outer peripheral side of the rectangular region RA, so that in the above brightness distribution, it is possible to raise the brightness on the outer peripheral side (side toward which the diffusion lens  14  inclines) of the rectangular region RA with respect to the axis (e.g., central axis D of the LED  12 ) that passes through the light emitting portion  12   a  and is perpendicular to the mounting surface  11   a   1  compared to the case where the diffusion lens  14  does not incline. In this way, even in the structure in which to achieve low cost by reduction in the number of LEDs  12  mounted, the disposition region for the LEDs  12  is made smaller than the size of the bottom plate  11   a  and the disposition density of the LEDs  12  in the disposition region is made lower in the peripheral portion Rp than in the central portion Rc, it is possible to alleviate the brightness declining at the four corners of the illumination region by means of the illumination by the LED  12  in each corner region P 1 . 
         [0108]    Especially, in the corner region P 1 , the diffusion lens  14  is disposed such that the central axis C thereof inclines from the direction perpendicular to the mounting surface  11   a   1  (bottom plate  11   a ) toward each apex of the four corners of the rectangular region RA; accordingly, it is possible to surely supply the light to the four corners of the illumination region by means of the illumination by the LED  12  in each corner region P 1  and to surely alleviate the brightness declining at the four corners of the illumination region. 
         [0109]    Here,  FIG. 17  is a plan view showing schematically another division example of the rectangular region RA of the backlight  3  according to the present embodiment. In the meantime, in  FIG. 17 , for the sake of convenience, the illustration of the diffusion plate  15  and optical sheet  16  is skipped. As shown in the drawing, to dispose a plurality of the LEDs  12  in one division region, the rectangular region RA on the bottom plate  11   a  may be divided into a plurality of regions (e.g., a total of 9 regions of 3×3) and the diffusion lenses  14  corresponding to the plurality of LEDs  12  (two in  FIG. 17 ) in each corner region P 1  may be disposed such that the central axes C incline from the direction perpendicular to the mounting surface  11   a   1  (bottom plate  11   a ) toward the outer peripheral side of the rectangular region RA. 
         [0110]    In this case, the amount of the light that is emitted from the LEDs  12  in the corner region P 1  and supplied to the four corners of the illumination region via the diffusion lenses  14  increases compared to the structure in which only one diffusion lens  14  in the corner region P 1  is inclined toward the outer peripheral side. Accordingly, it is possible to more alleviate the brightness decline at the four corners of the illumination region. 
         [0111]    From the above description, it can be said preferable if the rectangular region RA in which the LEDs  12  are disposed has, at the four corners, the corner regions P 1  in each of which at least one LED  12  is disposed and the diffusion lens  14  corresponding to the LED  12  located in each corner region P 1  is disposed such that the central axis C thereof inclines from the direction perpendicular to the mounting surface  11   a   1  (bottom plate  11   a ) toward the outer peripheral side of the rectangular region RA. 
         [0112]    Besides, in each corner region P 1 , if the diffusion lens  14  is disposed such that the central axis C of the diffusion lens  14  inclines from the direction perpendicular to the mounting surface  11   a   1  (bottom plate  11   a ) toward the outer peripheral side of the rectangular region RA, the direction in which the diffusion lens  14  inclines is not limited to a direction toward each apex of the four corners of the rectangular region RA. 
         [0113]      FIG. 18  is a plan view showing another structure of the backlight  3 , and  FIG. 19  is a plan view showing still another structure of the backlight  3 . As shown in  FIG. 18  and  FIG. 19 , the diffusion lens  14  in each corner region P 1  may be disposed such that the central axis C thereof inclines from the direction perpendicular to the mounting surface  11   a   1  (bottom plate  11   a ) toward the long edge or the short edge of the rectangular region RA. 
         [0114]    Besides,  FIG. 20  is a plan view showing still another structure of the backlight  3 . The diffusion lens  14  corresponding to the LED  12  located in the outer peripheral region P 2  (see  FIG. 3B ,  FIG. 5B ) may be disposed such that the central axis C inclines from the direction perpendicular to the mounting surface  11   a   1  (bottom plate  11   a ) toward the outer peripheral side (long edge, short edge) of the rectangular region RA. 
         [0115]    In this case, in a brightness distribution of the light that is emitted from the LED  12  in the outer peripheral region P 2  and obtained via the diffusion lens  14 , it is possible to raise the brightness on the outer peripheral side (side toward which the diffusion lens  14  inclines) of the rectangular region RA with respect to the axis (e.g., central axis D of the LED  12 ) that passes through the light emitting portion  12   a  and is perpendicular to the mounting surface  11   a   1  compared to the case where the diffusion lens  14  does not incline. In this way, it is possible to alleviate the brightness declining not only at the four corners of the illumination region but also at the outer peripheral portion, and it is possible to alleviate the frame-shaped brightness unevenness occurring on the display screen of the liquid crystal panel  2 , for example. Accordingly, it is possible to further reduce the number of light sources in the outer peripheral region. In addition, by illuminating the central portion of the illumination region by means of the LEDs  12  located in the region (central region P 3 ) inside the outer peripheral region P 2 , it is possible to obtain the above effects while securing the brightness at the central portion. 
         [0116]    [Supplement] 
         [0117]    It is of course possible to compose the backlight  3  and the liquid crystal display device  1  by suitably combining the above embodiments. Hereinafter, combinations of the embodiments are described. 
         [0118]      FIG. 21  is a cross-sectional view showing another disposition example of the LED  12  and diffusion lens  14  in the corner region P 1  of the rectangular region RA. As shown in the drawing, the backlight  3  may have a structure obtained by combining the embodiments 1 and 2. In other words, the backlight  3  may be structured in such a way that (1) the LED  12  in each corner region P 1  is disposed such that the central axis D thereof inclines from the direction perpendicular to the mounting surface  11   a   1  (bottom plate  11   a ) toward the outer peripheral side of the rectangular region RA and (2) the diffusion lens  14  in each corner region P 1  is disposed such that the central axis C thereof is located at a position closer to the outer peripheral side of the rectangular region RA than the light emitting portion  12   a  of the LED  12 . 
         [0119]    In this structure, in the brightness distribution of the light that is emitted from the LED  12  in each corner region P 1  and obtained via the diffusion lens  14 , even in a case where the inclination angle (inclination angle to the direction perpendicular to the mounting surface  11   a   1 ) of the central axis D of the LED  12  is small, because of the above disposition of the diffusion lens  14 , it is possible to raise the brightness on the outer peripheral side (side toward which the diffusion lens  14  deviates) of the rectangular region RA with respect to the axis that passes through the light emitting portion  12   a  and is perpendicular to the mounting surface  11   a   1 . In this way, even in the case where the inclination angle of the central axis D of the LED  12  is small, it is possible to surely obtain the effect of alleviating the brightness declining at the four corners of the illumination region. Besides, in a case where the inclination angle of the central axis D of the LED  12  is enlarged, it is possible to further alleviate the brightness declining at the four corners of the illumination region in cooperation with the above disposition of the diffusion lens  14 . 
         [0120]    Besides,  FIG. 22  is a cross-sectional view showing still another disposition example of the LED  12  and diffusion lens  14  in the corner region P 1  of the rectangular region RA. As shown in the drawing, the backlight  3  may have a structure obtained by combining the embodiments 1 and 3. In other words, the backlight  3  may be structured in such a way that (1) the LED  12  in each corner region P 1  is disposed such that the central axis D thereof inclines from the direction perpendicular to the mounting surface  11   a   1  (bottom plate  11   a ) toward the outer peripheral side of the rectangular region RA and (2) the diffusion lens  14  in each corner region P 1  is disposed such that the central axis C thereof inclines from the direction perpendicular to the mounting surface  11   a   1  (bottom plate  11   a ) toward the outer peripheral side of the rectangular region RA. 
         [0121]    In this structure, in the brightness distribution of the light that is emitted from the LED  12  in each corner region P 1  and obtained via the diffusion lens  14 , even in a case where the inclination angle of the central axis D of the LED  12  is small, it is possible to raise the brightness on the outer peripheral side (side toward which the diffusion lens  14  inclines) of the rectangular region RA with respect to the axis that passes through the light emitting portion  12   a  and is perpendicular to the mounting surface  11   a   1 . In this way, even in the case where the inclination angle of the central axis D of the LED  12  is small, it is possible to surely obtain the effect of alleviating the brightness declining at the four corners of the illumination region. Besides, in a case where the inclination angle of the central axis D of the LED  12  is enlarged, it is possible to further alleviate the brightness declining at the four corners of the illumination region in cooperation with the above disposition of the diffusion lens  14 . 
         [0122]    Besides,  FIG. 23  is a cross-sectional view showing still another disposition example of the LED  12  and diffusion lens  14  in the corner region P 1  of the rectangular region RA. As shown in the drawing, the backlight  3  may have a structure obtained by combining the embodiments 2 and 3. In other words, the backlight  3  may be structured in such a way that (1) the diffusion lens  14  corresponding to the LED  12  in each corner region P 1  is disposed such that the central axis C thereof is located at a position closer to the outer peripheral side of the rectangular region RA than the light emitting portion  12   a  of the LED  12  and (2) the diffusion lens  14  is disposed such that the central axis C thereof inclines from the direction perpendicular to the mounting surface  11   a   1  (bottom plate  11   a ) toward the outer peripheral side of the rectangular region RA. 
         [0123]    In this structure, in the brightness distribution of the light that is emitted from the LED  12  in each corner region P 1  and obtained via the diffusion lens  14 , even in a case where the deviation amount of the diffusion lens  14  from the light emitting portion  12   a  is small, it is possible to raise the brightness on the outer peripheral side of the rectangular region RA with respect to the axis (e.g., central axis D of the LED  12 ) that passes through the light emitting portion  12   a  and is perpendicular to the mounting surface  11   a   1 . In this way, even in the case where the deviation amount of the diffusion lens  14  from the light emitting portion  12   a  is small, it is possible to surely obtain the effect of alleviating the brightness declining at the four corners of the illumination region. Besides, in a case where the deviation amount of the diffusion lens  14  is enlarged, it is possible to further alleviate the brightness declining at the four corners of the illumination region in cooperation with the above inclination of the diffusion lens  14 . 
         [0124]    Besides,  FIG. 24  is a cross-sectional view showing still another disposition example of the LED  12  and diffusion lens  14  in the corner region P 1  of the rectangular region RA. As shown in the drawing, the backlight  3  may have a structure obtained by combining all the embodiments 1 to 3. In other words, the backlight  3  may be structured in such a way that (1) the LED  12  in each corner region P 1  is disposed such that the central axis D thereof inclines from the direction perpendicular to the mounting surface  11   a   1  (bottom plate  11   a ) toward the outer peripheral side of the rectangular region RA, (2) the diffusion lens  14  corresponding to the LED  12  in each corner region P 1  is disposed such that the central axis C thereof is located at a position closer to the outer peripheral side of the rectangular region RA than the light emitting portion  12   a  of the LED  12 , further (3) the diffusion lens  14  is disposed such that the central axis C thereof inclines from the direction perpendicular to the mounting surface  11   a   1  (bottom plate  11   a ) toward the outer peripheral side of the rectangular region RA. 
         [0125]    In this structure, in the brightness distribution of the light that is emitted from the LED  12  in each corner region P 1  and obtained via the diffusion lens  14 , even in a case where at least one of the inclination angle of the LED  12 , the deviation amount of the diffusion lens  14  and the inclination angle of the diffusion lens  14  is small, it is possible to raise the brightness on the outer peripheral side of the rectangular region RA and to alleviate the brightness declining at the four corners of the illumination region. Besides, it is possible to significantly alleviate the brightness declining at the four corners of the illumination region by means of a synergy effect of the inclination of the LED  12 , the deviation of the diffusion lens  14  and the inclination of the diffusion lens  14 . 
         [0126]    In the meantime, the planar light source device and liquid crystal display device represented in each embodiment are expressible as follows. 
         [0127]    A planar light source device according to one embodiment of the present invention comprises a plurality of light sources, and a bottom plate that has a mounting surface on which the plurality of light sources are mounted, wherein the plurality of light sources are two-dimensionally disposed in a rectangular region of the mounting surface that is smaller than a size of the bottom plate, and disposition density of the light sources in the rectangular region is lower in a peripheral portion than in a central portion, wherein the rectangular region has, at four corners thereof corner regions where at least one of the light sources is disposed, and the light source located at each of the corner regions is disposed such that a central axis thereof inclines from a direction perpendicular to the mounting surface toward an outer peripheral side of the rectangular region. 
         [0128]    According to the above structure, in the brightness distribution of the light emitted from the light source in each corner region, it is possible to raise the brightness on the side (outer peripheral side of the rectangular region) toward which the central axis inclines with respect to the axis that passes through the light source and is perpendicular to the mounting surface. In this way, even in the structure in which to achieve low cost by reduction in the number of light sources mounted, the disposition region for the light sources is made smaller than the size of the bottom plate and the disposition density of the light sources in the disposition region is made lower in the peripheral portion than in the central portion, it is possible to alleviate the brightness declining at the four corners of the illumination region by means of the illumination by the light source in each corner region. 
         [0129]    In the above planar light source device, the light source located in each of the corner regions may be disposed such that the central axis thereof inclines from the direction perpendicular to the mounting surface toward each apex of the four corners of the rectangular region. 
         [0130]    In this case, it is possible to surely supply the light to the four corners of the illumination region by means of the illumination by the light source in each corner region and to surely alleviate the brightness declining at the four corners of the illumination region. 
         [0131]    The above planar light source device may include a diffusion lens that is disposed correspondingly to each of the plurality of light sources and diffuses the light emitted from the light source. 
         [0132]    In this case, the light from the light source is diffused by the diffusion lens; accordingly, the brightness decline at the four corners becomes more inconspicuous. Besides, even in a case where the interval between neighboring light sources is large, dot-like unevenness becomes unlikely to occur in the brightness distribution by each light source; accordingly, it is possible to achieve low cost by further reducing the number of light sources mounted. 
         [0133]    In each of the corner regions of the above planar light source device, the diffusion lens may be disposed such that a central axis thereof is located at a position closer to the outer peripheral side of the rectangular region than the light emitting portion of the light source. 
         [0134]    In this structure, in the brightness distribution of the light that is emitted from the light source and obtained via the diffusion lens, it is possible to raise the brightness on the outer peripheral side (side toward which the diffusion lens deviates) of the rectangular region with respect to the axis that passes through the light emitting portion of the light source and is perpendicular to the mounting surface. In this way, even in the case where the inclination angle of the central axis of the light source is small, it is possible to surely alleviate the brightness declining at the four corners of the illumination region. 
         [0135]    In each of the corner regions of the above planar light source device, the diffusion lens may be disposed such that the central axis thereof inclines from the direction perpendicular to the mounting surface toward the outer peripheral side of the rectangular region. 
         [0136]    In this structure, in the brightness distribution of the light that is emitted from the light source and obtained via the diffusion lens, it is possible to raise the brightness on the side (outer peripheral side of the rectangular region) toward which the central axis of the diffusion lens inclines with respect to the axis that passes through the light emitting portion of the light source and is perpendicular to the mounting surface. In this way, even in the case where the inclination angle of the central axis of the light source is small, it is possible to surely alleviate the brightness declining at the four corners of the illumination region. 
         [0137]    In the above planar light source device, when the rectangular region is divided into an outermost peripheral region including each of the corner regions and an inner region with respect to the outermost peripheral region, the light source located in the outermost peripheral region may be disposed such that the central axis thereof inclines from the direction perpendicular to the mounting surface toward the outer peripheral side of the rectangular region. 
         [0138]    In this case, in the brightness distribution of the light emitted from the light source in the outermost peripheral region in the rectangular region, it is possible to raise the brightness on the side (outer peripheral side of the rectangular region) toward which the central axis inclines with respect to the axis that passes through the light source and is perpendicular to the mounting surface. In this way, it is possible to alleviate the brightness declining not only at the four corners of the illumination region but also at the outer peripheral portion, and it is possible to alleviate the frame-shaped brightness unevenness occurring. In addition, by illuminating the central portion of the illumination region by means of the light sources located in the region inside the outermost peripheral region, it is possible to obtain the above effects while securing the brightness at the central portion. 
         [0139]    A planar light source device according to another embodiment of the present invention comprises a plurality of light sources, and a bottom plate that has a mounting surface on which the plurality of light sources are mounted, wherein the plurality of light sources are two-dimensionally disposed in a rectangular region of the mounting surface that is smaller than a size of the bottom plate, and disposition density of the light sources in the rectangular region is lower in a peripheral portion than in a central portion, the planar light source device further comprising a diffusion lens that is disposed correspondingly to each of the plurality of light sources and diffuses light emitted from the light source, wherein the rectangular region has, at four corners thereof, corner regions where at least one of the light sources is disposed, and the diffusion lens corresponding to the light source located in each of the corner regions is disposed such that a central axis thereof is located at a position closer to an outer peripheral side of the rectangular region than a light emitting portion of the light source. 
         [0140]    According to the above structure, in the brightness distribution of the light that is emitted from the light source in each corner region and obtained via the diffusion lens, it is possible to raise the brightness on the outer peripheral side (side toward which the diffusion lens deviates) of the rectangular region with respect to the axis that passes through the light emitting portion of the light source and is perpendicular to the mounting surface. In this way, even in the structure in which to achieve low cost by reduction in the number of light sources mounted, the disposition region for the light sources is made smaller than the size of the bottom plate and the disposition density of the light sources in the disposition region is made lower in the peripheral portion than in the central portion, it is possible to alleviate the brightness declining at the four corners of the illumination region by means of the illumination by the light source in each corner region. 
         [0141]    Besides, the light from the light source is diffused by the diffusion lens; accordingly, the brightness decline at the four corners becomes more inconspicuous. Besides, even in the case where the interval between neighboring light sources is large, the dot-like unevenness becomes unlikely to occur in the brightness distribution by each light source; accordingly, it is possible to achieve low cost by further reducing the number of light sources mounted. 
         [0142]    In the above planar light source device, the diffusion lens may be disposed such that the central axis thereof is located at a position closer to each apex of the four corners of the rectangular region than the light emitting portion of the light source. 
         [0143]    In this case, it is possible to surely supply the light to the four corners of the illumination region by means of the illumination by the light source in each corner region and to surely alleviate the brightness declining at the four corners of the illumination region. 
         [0144]    In the above planar light source device, the diffusion lens may be disposed such that the central axis thereof inclines from the direction perpendicular to the mounting surface toward the outer peripheral side of the rectangular region. 
         [0145]    In this structure, in the brightness distribution of the light that is emitted from the light source and obtained via the diffusion lens, it is possible to raise the brightness on the side (outer peripheral side of the rectangular region) toward which the central axis of the diffusion lens inclines with respect to the axis that passes through the light emitting portion of the light source and is perpendicular to the mounting surface. In this way, even in the case where the deviation amount of the diffusion lens with respect to the light source (light emitting portion) is small, it is possible to alleviate the brightness declining at the four corners of the illumination region. 
         [0146]    In the above planar light source device, when the rectangular region is divided into the outermost peripheral region including each of the corner regions and the inner region with respect to the outermost peripheral region, the diffusion lens corresponding to the light source located in the outermost peripheral region may be disposed such that the central axis thereof is located at a position closer to the outer peripheral side of the rectangular region than the light emitting portion of the light source. 
         [0147]    In this case, in the brightness distribution of the light that is emitted from the light source in the outermost peripheral region in the rectangular region and obtained via the diffusion lens, it is possible to raise the brightness on the outer peripheral side (side toward which the diffusion lens deviates) of the rectangular region with respect to the axis that passes through the light emitting portion of the light source and is perpendicular to the mounting surface. In this way, it is possible to alleviate the brightness declining not only at the four corners of the illumination region but also at the outer peripheral portion, and it is possible to alleviate the frame-shaped brightness unevenness occurring. In addition, by illuminating the central portion of the illumination region by means of the light sources located in the region inside the outermost peripheral region, it is possible to obtain the above effects while securing the brightness at the central portion. 
         [0148]    A planar light source device according to still another embodiment of the present invention comprises a plurality of light sources, and a bottom plate that has a mounting surface on which the plurality of light sources are mounted, wherein the plurality of light sources are two-dimensionally disposed in a rectangular region of the mounting surface that is smaller than a size of the bottom plate, and disposition density of the light sources in the rectangular region is lower in a peripheral portion than in a central portion, the planar light source device further comprising a diffusion lens that is disposed correspondingly to each of the plurality of light sources and diffuses light emitted from the light source, wherein the rectangular region has, at four corners thereof, corner regions where at least one of the light sources is disposed, and the diffusion lens corresponding to the light source located in each of the corner regions is disposed such that a central axis thereof inclines from a direction perpendicular to the mounting surface toward an outer peripheral side of the rectangular region. 
         [0149]    According to the above structure, in the brightness distribution of the light that is emitted from the light source in each corner region and obtained via the diffusion lens, it is possible to raise the brightness on the side (outer peripheral side of the rectangular region) toward which the central axis of the diffusion lens inclines with respect to the axis that passes through the light source and is perpendicular to the mounting surface. In this way, even in the structure in which to achieve low cost by reduction in the number of light sources mounted, the disposition region for the light sources is made smaller than the size of the mounting surface and the disposition density of the light sources in the disposition region is made lower in the peripheral portion than in the central portion, it is possible to alleviate the brightness declining at the four corners of the illumination region by means of the illumination by the light source in each corner region. 
         [0150]    Besides, the light from the light source is diffused by the diffusion lens; accordingly, the brightness decline at the four corners of the illumination region becomes more inconspicuous. Besides, even in the case where the interval between the neighboring light sources is large, the dot-like unevenness becomes unlikely to occur in the brightness distribution by each light source; accordingly, it is possible to achieve low cost by further reducing the number of light sources mounted. 
         [0151]    In the above planar light source device, the diffusion lens may be disposed such that the central axis thereof inclines from the direction perpendicular to the mounting surface toward each apex of the four corners of the rectangular region. 
         [0152]    In this case, it is possible to surely supply the light to the four corners of the illumination region by means of the illumination by the light source in each corner region and to surely alleviate the brightness declining at the four corners of the illumination region. 
         [0153]    In the above planar light source device, when the rectangular region is divided into the outermost peripheral region including each of the corner regions and the inner region with respect to the outermost peripheral region, the diffusion lens corresponding to the light source located in the outermost peripheral region may be disposed such that the central axis thereof inclines from the direction perpendicular to the mounting surface toward the outer peripheral side of the rectangular region. 
         [0154]    In this case, in the brightness distribution of the light that is emitted from the light source in the outermost peripheral region in the rectangular region and obtained via the diffusion lens, it is possible to raise the brightness on the side (outer peripheral side of the rectangular region) toward which the central axis of the diffusion lens inclines with respect to the axis that passes through the light emitting portion of the light source and is perpendicular to the mounting surface. In this way, it is possible to alleviate the brightness declining not only at the four corners of the illumination region but also at the outer peripheral portion, and it is possible to alleviate the frame-shaped brightness unevenness occurring. In addition, by illuminating the central portion of the illumination region by means of the light sources located in the region inside the outermost peripheral region, it is possible to obtain the above effects while securing the brightness at the central portion. 
         [0155]    In the above planar light source device, when two directions parallel to the mounting surface and perpendicular to each other are defined as a first direction and a second direction, each of the corner regions may be a region where both-end regions when the rectangular region is divided into three or more regions in the first direction and both-end regions when the rectangular region is divided into three or more regions in the second direction overlie each other. 
         [0156]    In this case, it is possible to surely alleviate the brightness decline at the four corners of the illumination region by means of the light source located in each corner region while securing the illumination brightness in a region other than the four corners of the illumination region by means of the light source located in a region other than the corner region, and possible to alleviate the brightness unevenness of the entire illumination region. 
         [0157]    The above planar light source device may be of direct type that illuminates an illumination target from right under in a planar manner by means of the plurality of light sources. 
         [0158]    In the case of the direct type, the brightness decline easily occurs at the four corners of the illumination region because of the reduction in the number of light sources mounted compared to an edge-light type; accordingly, the structure according to each embodiment of the present invention becomes effective. 
         [0159]    In the above planar light source device, the plurality of light sources each may be formed of a light emitting diode. 
         [0160]    In the structure that uses an LED as the light source, the brightness decline easily occurs at the four corners of the illumination region because of the reduction in the number of light sources mounted compared to a structure that uses a tube-like light source (e.g., cold-cathode tube); accordingly, the structure according to each embodiment of the present invention becomes effective. 
         [0161]    The above planar light source device may further include a reflection sheet that has an opening portion from which each of the plurality of light sources is exposed, is disposed on the bottom plate, and reflects the light emitted from the light source, wherein the reflection sheet may have an edge portion that rises obliquely from the bottom plate on the outer side of the rectangular region. 
         [0162]    In the structure in which the peripheral portion of the illumination region is illuminated by means of the light that is emitted from the light source and reflected by the edge portion of the reflection sheet, the light source is not disposed in the peripheral portion of the bottom plate to form the edge portion; accordingly, it is possible to reduce the number of light sources mounted, but the light has difficulty in reaching the four corners of the illumination region. Accordingly, the structure according to each embodiment of the present invention, which is able alleviate the brightness decline at the four corners of the illumination region, becomes very effective in the case of achieving reduction in the number of light sources mounted by means of the illumination that uses the edge portion of the reflection sheet. 
         [0163]    The liquid crystal display device represented in the embodiments of the present invention includes the above planar light source device and a liquid crystal panel that modulates the light supplied from the planar light source device to perform display. 
         [0164]    In this structure, it is possible to alleviate the brightness declining at the four corners of the screen of the liquid crystal panel and improve the display quality. 
       INDUSTRIAL APPLICABILITY 
       [0165]    The planar light source device according to the present invention is usable for a backlight of a liquid crystal display device, for example. 
       REFERENCE SIGNS LIST 
       [0000]    
       
         
           
               1  quid crystal display device 
               2  liquid crystal panel 
               3  backlight (planar light source device) 
               11   a  bottom plate 
               11   a   1  mounting surface 
               12  LED (light source, light emitting diode) 
               14  diffusion lens 
               17  reflection sheet 
               17   a  opening portion 
               17   b  edge portion 
             C central axis 
             D central axis 
             P 1  corner region 
             P 2  outer peripheral region (outermost peripheral region) 
             P 3  central region 
             RA rectangular region 
             Rc central portion 
             Rp peripheral portion