Patent Publication Number: US-2013229596-A1

Title: Led substrate, backlight unit, and liquid crystal display device

Description:
TECHNICAL FIELD 
     The present invention relates to an LED substrate including a plurality of LEDs, a backlight unit including the LED substrate, and a liquid crystal display device including a liquid crystal display panel and the backlight unit that is disposed behind the liquid crystal display panel. 
     BACKGROUND ART 
     A liquid crystal display device including a transmissive liquid crystal display panel includes a backlight unit that is disposed behind the liquid crystal display panel to project light thereonto. Aside (edge) backlight unit is known as this kind of backlight unit, which includes a light guide plate having a plate shape that is made from a transparent material such as an acrylate resin, and a light source that includes a cold cathode tube (fluorescent lamp) or an LED (Light-Emitting Diode) that is disposed along one side or more than one side of the light guide plate. The side backlight unit described above has an advantage such that a thin profile thereof can be easily achieved compared with a direct backlight unit including a light source disposed behind a liquid crystal display panel. 
     In particular, a liquid crystal display device that includes an LED as a light source of a side backlight unit has the advantages of long life and high luminous efficiency, and thus has been receiving attention.  FIG. 13  is an exploded perspective view showing a schematic configuration of a liquid crystal display device including this kind of side backlight unit including LEDs.  FIG. 14  is a cross-sectional view showing a relevant portion of the same. 
     As shown in  FIG. 13 , a liquid crystal display device  100  includes a bezel  102 , a liquid crystal display panel  103 , and a backlight unit  104 . 
     The bezel  102  has a square frame shape with an opening so as to cover edge portions of the liquid crystal display panel  103 , and is arranged to, together with a backlight chassis  114 , ensure strength of the entire liquid crystal display device  100 . The liquid crystal display panel  103  includes two glasses that are bonded together, and liquid crystals are filled in a space between the glasses. The liquid crystal display panel  103  is capable of displaying an image on its front face. 
     The backlight unit  104  includes the backlight chassis  114  having the shape of a box of low height. The chassis  114  houses optical sheets  107  to  109 , a light guide plate  111 , a reflection sheet  113 , and two LED substrates  120 . 
     As shown in  FIG. 14 , the light guide plate  111  includes a light incidence surface  111   a  arrange to obtain light from the LEDs  121  of the LED substrates  120 , and a light emitting surface  111   b  arrange to emit the light upward (in a direction to project the light), which is obtained from the light incidence surface  111   a . The light incidence surface  111   a  is defined by a given side surface of the light guide plate  111 , and the light emitting surface  111   b  is defined by a front surface of the light guide plate  111 . 
     The reflection sheet  113  is disposed so as to cover a back surface  111   c  of the light guide plate  111 , which is the opposite surface to the light emitting surface  111   b . The optical sheets  107  to  109  define optical sheets such as a diffusion sheet and a lens sheet, and are disposed above the light emitting surface  111   b  of the light guide plate  111 . 
     The optical sheets  107  to  109 , the light guide plate  111  and the reflection sheet  113  are stacked and fixed onto a bottom plate  114   a  of the backlight chassis  114  by a frame  105 . 
     In addition, the LEDs  121  provided to the LED substrates  120  are disposed close to the light incidence surface  111   a  of the light guide plate  111 . Further, light emitting surfaces  121   d  of the LEDs  121  are disposed along the light incidence surface  111   a  of the light guide plate  111 , having a given space therebetween so as to be opposed to the light incidence surface  111   a . In this case, the two LED substrates  120  are fixed so as to be disposed laterally while standing on a fixing plate  115  having the shape of the letter “L” that is provided so as to stand on the bottom plate  114   a  in the vicinity of a side wall  114   b  of the backlight chassis  114 . 
     Each LED substrate  120  includes wiring patterns  131 ,  132  and  133  that are formed on a radiating plate made from metal such as aluminum while sandwiching therebetween an insulating layer, and the LEDs  121  are disposed on each LED substrate  120  so as to be connected to the wiring patterns  131 ,  132  and  133 , as shown in  FIG. 15 . 
     In this case, four LEDs  121  are disposed linearly along a longitudinal direction of each LED substrate  120 , and connected to one another in series by the connecting patterns  131  and  132 . 
     The first LED  121  from the right end of each LED substrate  120  is connected to one end of the light source pattern  131 . The other end of the light source pattern  131  is connected to a light-source-side terminal (positive terminal)  141  of a substrate connector  140  disposed at the right end of each LED substrate  120 . 
     The first LED  121  from the left end of each LED substrate  120  (the fourth LED  121  from the right end) is connected to one end of the ground pattern  133 . The other end of the ground pattern  133 , which extends from the left end of each LED substrate  120  so as to be folded back in a rightward direction along the longitudinal direction of each LED substrate  120 , is connected to a ground-side terminal (negative terminal)  142  of the substrate connector  140 . 
     In this case, the substrate connectors  140  have a configuration of being connected to a power substrate  118  included in the liquid crystal display device  100  via cable connectors  150  and cables  161  and  162  arranged to be fitted and connected to the substrate connectors  140 . 
     In the LED substrates  120  having the configuration described above, the substrate connectors  140  connected to the LEDs  121  are disposed at either different ones of right and left ends of the LED substrates  120 . Thus, when the two LED substrates  120  are disposed laterally as shown in  FIG. 16 , the substrate connectors  140  of the LED substrates  120  are disposed so as not to be adjacent to each other by disposing the LED substrate  120  to the left, on which the substrate connector  140  is disposed at the left end, and disposing the LED substrate  120  to the right, on which the substrate connector  140  is disposed at the right end. This configuration allows a distance P 2  between the first LED  121  from the right end of the left LED substrate  120  and the first LED  121  from the left end of the right LED substrate  120  to be equal to a distance P 1  between the adjacent LEDs  121  (P 2 =P 1 ). Thus, the light from the LEDs  121  of the two LED substrates  120  can uniformly enter the light incidence surface  111   a  of the light guide plate  111 . 
     In this case, if the LED substrate  120  is disposed to the left, on which the substrate connector  140  is disposed at the right end, and the LED substrate  120  is disposed to the right, on which the substrate connector  140  is disposed at the right end as shown in  FIG. 17A , a problem arises such that the cable connector  150  and the cables  161  and  162  arranged to be fitted and connected to the substrate connector  140  of the left LED substrate  120  interfere with a left end portion or the LED  121  of the right LED substrate  120 . 
     In addition, the ends of the LED substrates  120  on the sides of the substrate connectors  140  are longer by a size of the substrate connectors  140 , so that a distance P 3  between the first LED  121  from the right end of the left LED substrate  120  and the first LED  121  from the left end of the right LED substrate  120  is longer than the distance P 1  between the adjacent LEDs  121  (P 3 &gt;P 1 ) as shown in  FIG. 17A . Thus, the light from the LEDs  121  of the two LED substrates  120  cannot uniformly enter the light incidence surface  111   a  of the light guide plate  111 , which causes a problem such that luminance on the light emitting surface  111   b  of the light guide plate  111  becomes nonuniform. 
     In order to prevent these problems, when the two LED substrates  120  are disposed laterally as shown in  FIG. 16 , the LED substrates  120  of two different kinds are prepared, on which the substrate connectors  140  are disposed at either different ones of right and left ends, and disposed so as to have the configuration that the LED substrate  120  is disposed to the left, on which the substrate connector  140  is disposed at the left end, and the LED substrate  120  is disposed to the right, on which the substrate connector  140  is disposed at the right end. A prior art literature of the present invention relates to is provided below. 
     CITATION LIST 
     Patent Literature 
     
         
         PTL 1: JP2004-103993 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     However, because each of these LED substrates  120  has a configuration of including the ground pattern  133  that is adjacent to the LEDs  121 , which are disposed linearly along the longitudinal direction of the LED substrate  120  and connected to one another in series, in a width direction of the LED substrate  120 , and extends in the longitudinal direction of the LED substrate  120 , there is a problem in downsizing the LED substrates  120  in the width direction (direction perpendicular to the longitudinal direction). 
     Because of this configuration, the width of the LED substrates  120  is much wider than the width of the LEDs  121  included on the LED substrates  120 . Thus, the backlight chassis  114  has a configuration such that a convex portion  114   c , which defines a portion of the bottom plate  114   a  that is protruded downward by a width for including the ground patterns  133  of the LED substrates  120 , is provided, the fixing plate  115  stands on the convex portion  114   c , and the LED substrates  120  are fixed to the fixing plate  115 , as shown in  FIG. 14 . However, the convex portion  114   c , which is protruded downward from the bottom plate  114   a  of the backlight chassis  114 , hinders achieving a thin profile of the backlight unit  104 , in other words, hinders achieving a thin profile of the liquid crystal display device  100 . 
     In particular, a thin profile of the liquid crystal display device  100  has been highly required recently in order to improve the design property of a liquid crystal display device such as a wall-hanging liquid crystal display device, so that the LED substrates  120  are desired to be downsized in width. 
     In addition, accompanied by recent increases in the size of a screen of the liquid crystal display panel  103 , the backlight unit  104  increases in size, in other words, the area of the light guide plate  111  increases, so that three or more than three LED substrates  120  are sometimes desired to be disposed laterally along the light incidence surface  111   a  of the light guide plate  111 . 
     However, because the LED substrates  120  of two different kinds described above have the configurations that the substrate connectors  140  connected to the LEDs  121  are disposed at either different ones of right and left ends of the LED substrates  120 , the three or more than three LED substrates  120 , when disposed laterally, have a problem such that the distance between the adjacent LEDs  121  of the two adjacent LED substrates  120  is not equal to the distance between the adjacent LEDs  121  of each LED substrate  120 . 
     For example, when the three LED substrates  120  are disposed laterally as shown in  FIG. 17B , the LED substrate  120  is disposed to the left, on which the substrate connector  140  is disposed at the left end, and the LED substrate  120  is disposed in the middle, on which the substrate connector  140  is disposed at the right end. Thus, distances P 1  (=P 2 ) between the LEDs  121  of the two LED substrates  120  can be made uniform. However, a distance P 3  between the first LED  121  from the right end of the middle LED substrate  120 , on which the substrate connector  140  is disposed at the right end, and the first LED  121  from the left end of the right LED substrate  120 , on which the substrate connector  140  is disposed at the right end, is longer than the distance P 1  between the adjacent LEDs  121  (P 3 &gt;P 1 ) as shown in  FIG. 17B , which causes a problem of nonuniform distances between the LEDs  121  of the two LED substrates  120 . 
     The present invention is made in view of the problems described above, and an object of the present invention is to provide an LED substrate including a plurality of LEDs that is capable of being downsized in width, and a plurality of the LED substrates that are capable of being disposed laterally in an efficient fashion such that the distances between the adjacent LEDs are uniform, a backlight unit including the LED substrates, and a liquid crystal display device including the backlight unit. 
     Solution to Problem 
     To achieve the objects and in accordance with the purpose of the present invention, an LED substrate of a preferred embodiment of the present invention includes a radiating plate made from metal that has a rectangular shape long in aright/left direction, an insulating layer disposed on an upper surface of the radiating plate, a connector disposed in the middle on an upper surface of the insulating layer and including a first light-source-side terminal, a second light-source-side terminal and a ground-side terminal, a first LED group including a plurality of LEDs that are disposed to the left of the connector on the upper surface of the insulating layer linearly along a longitudinal direction of the radiating plate and connected to each another in series, a second LED group including a plurality of LEDs that are disposed to the right of the connector on the upper surface of the insulating layer linearly along the longitudinal direction of the radiating plate and connected to each other in series, a first light source pattern disposed in the middle on the upper surface of the insulating layer and connected to the first LED from the right in the first LED group, a second light source pattern disposed in the middle on the upper surface of the insulating layer and connected to the first LED from the left in the second LED group, a first ground pattern disposed at a left end on the upper surface of the insulating layer and connected to the first LED from the left in the first LED group, and a second ground pattern disposed at a right end on the upper surface of the insulating layer and connected to the first LED from the right in the second LED group, wherein the LED substrate further includes a third ground pattern disposed in the middle on the upper surface of the insulating layer, wherein the first light source pattern is connected to the first light-source-side terminal of the connector, wherein the second light source pattern is connected to the second light-source-side terminal of the connector, wherein the third light source pattern is connected to the ground-side terminal of the connector, wherein the first ground pattern is connected to the radiating plate via a first screw made from metal that is inserted in a first through-hole provided to the first ground pattern and the radiating plate, wherein the second ground pattern is connected to the radiating plate via a second screw made from metal that is inserted in a second through-hole provided to the second ground pattern and the radiating plate, and wherein the third ground pattern is connected to the radiating plate via a third screw made from metal that is inserted in a third through-hole provided to the third ground pattern and the radiating plate. 
     It is preferable that the metal from which the radiating plate is made defines aluminum, and the first, second and third screws define sheet-metal screws. In addition, it is preferable that conductive pastes are applied to inner surfaces of the first, second and third through-holes. 
     It is preferable that the LED substrate further includes a first conductive tape, one end of which is attached to the first ground pattern, and the other end is attached to the radiating plate, wherein the first ground pattern and the radiating plate are connected via the first conductive tape, a second conductive tape, one end of which is attached to the second ground pattern, and the other end is attached to the radiating plate, wherein the second ground pattern and the radiating plate are connected via the second conductive tape, and a third conductive tape, one end of which is attached to the third ground pattern, and the other end is attached to the radiating plate, wherein the third ground pattern and the radiating plate are connected via the third conductive tape. 
     In another aspect of the present invention, a backlight unit of a preferred embodiment of the present invention includes a light guide plate having a plate shape, an LED substrate disposed on a side surface of the light guide plate, and a chassis made from metal and arranged to house the light guide plate and the LED substrate, wherein the LED substrate includes a radiating plate made from metal that has a rectangular shape long in a right/left direction, an insulating layer disposed on an upper surface of the radiating plate, a connector disposed in the middle on an upper surface of the insulating layer and including a first light-source-side terminal, a second light-source-side terminal and a ground-side terminal, a first LED group including a plurality of LEDs that are disposed to the left of the connector on the upper surface of the insulating layer linearly along a longitudinal direction of the radiating plate and connected to each other in series, a second LED group including a plurality of LEDs that are disposed to the right of the connector on the upper surface of the insulating layer linearly along the longitudinal direction of the radiating plate and connected to each other in series, a first light source pattern disposed in the middle on the upper surface of the insulating layer and connected to the first LED from the right in the first LED group, a second light source pattern disposed in the middle on the upper surface of the insulating layer and connected to the first LED from the left in the second LED group, a first ground pattern disposed at a left end on the upper surface of the insulating layer and connected to the first LED from the left in the first LED group, and a second ground pattern disposed at a right end on the upper surface of the insulating layer and connected to the first LED from the right in the second LED group, wherein the LED substrate further includes a third ground pattern disposed in the middle on the upper surface of the insulating layer, wherein the first light source pattern is connected to the first light-source-side terminal of the connector, wherein the second light source pattern is connected to the second light-source-side terminal of the connector, wherein the third light source pattern is connected to the ground-side terminal of the connector, wherein the first ground pattern is connected to the radiating plate via a first screw made from metal that is inserted in a first through-hole provided to the first ground pattern and the radiating plate, wherein the second ground pattern is connected to the radiating plate via a second screw made from metal that is inserted in a second through-hole provided to the second ground pattern and the radiating plate, and wherein the third ground pattern is connected to the radiating plate via a third screw made from metal that is inserted in a third through-hole provided to the third ground pattern and the radiating plate. 
     It is preferable that the metal from which the radiating plate is made defines aluminum, and the first, second and third screws define sheet-metal screws. In addition, it is preferable that conductive pastes are applied to inner surfaces of the first, second and third through-holes. 
     It is preferable that the backlight unit further includes a first conductive tape, one end of which is attached to the first ground pattern, and the other end is attached to the radiating plate, wherein the first ground pattern and the radiating plate are connected via the first conductive tape, a second conductive tape, one end of which is attached to the second ground pattern, and the other end is attached to the radiating plate, wherein the second ground pattern and the radiating plate are connected via the second conductive tape, and a third conductive tape, one end of which is attached to the third ground pattern, and the other end is attached to the radiating plate, wherein the third ground pattern and the radiating plate are connected via the third conductive tape. 
     It is preferable that the backlight unit further includes a fixing plate made from metal that is disposed to stand on the chassis, wherein the LED substrate is fixed to the fixing plate by the first, second and third screws, and wherein the radiating plate is electrically connected to the chassis via the fixing plate. 
     It is preferable that the backlight unit further includes a thermal conductive sheet disposed between the fixing plate and the radiating plate of the LED substrate. It is also preferable that the thermal conductive sheet possesses electrical conductivity. 
     Yet, in another aspect of the present invention, a liquid crystal display device of a preferred embodiment of the present invention includes a liquid crystal display panel, and the backlight unit of the above-described embodiment of the present invention that is disposed behind the liquid crystal display panel. 
     Advantageous Effects of Invention 
     In the LED substrate, the backlight unit and the liquid crystal display device having the configurations described above, the radiating plate, which is made from metal and disposed under the LEDs that are connected in series while sandwiching therebetween the insulating layer, is used as a ground wire for the LEDs. Thus, it is unnecessary to provide a ground pattern shown in  FIG. 15  and explained above in the description of Background Art, which is adjacent to the LEDs, which are disposed linearly along the longitudinal direction of the LED substrate and connected to one another in series, in the width direction of the LED substrate, and extends linearly along the longitudinal direction of the LED substrate. 
     Thus, downsizing (decreasing) in width of the LED substrate by a width that is required in order to include the ground pattern disposed linearly along the longitudinal direction of the LED substrate can be achieved, whereby a thin profile of the backlight unit, in other words, a thin profile of the liquid crystal display device can be achieved, which improves the design property of the liquid crystal display device. 
     In addition, the LED substrate of the present invention has the configuration that the connector arranged to supply power to the LEDs is disposed in the middle of the LED substrate, which is different from the configuration of the LED substrate  120  explained above in the description of Background Art that the substrate connector  140  is disposed at either one of right and left ends of the LED substrate  120 . Thus, the right and left ends of the LED substrate of the present invention can have the same shape. 
     Thus, the distances between the LEDs of the plurality of LED substrates can be made uniform even when the plurality of LED substrates are disposed laterally, which prevents the problem that the distance P 3  between the LEDs  121  of the two adjacent LED substrates  120  is longer than the distance P 1  between the LEDs  121  of each LED substrate  120 , which is shown in  FIGS. 17A and 17B  and explained above in the description of Background Art. 
     In addition, because the right and left ends of the LED substrate of the present invention have the same shape owing to the configuration that the connector is disposed in the middle of the LED substrate, the LED substrates of one kind having an above-described configuration can suffice when two, three or more than three LED substrates are disposed laterally. Thus, it is unnecessary to prepare LED substrates of two different kinds on which substrate connectors are disposed at either different ones of right and left ends of the LED substrates, which are conventionally used, whereby the number of components can be reduced to save a cost. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is an exploded perspective view showing a schematic configuration of a liquid crystal display device of a preferred embodiment of the present invention. 
         FIG. 2  is an enlarged cross-sectional view showing a relevant portion of the liquid crystal display device shown in  FIG. 1  after being assembled. 
         FIG. 3  is an external perspective view showing a schematic configuration of an LED substrate of a preferred embodiment of the present invention. 
         FIG. 4  is a front plan view showing the LED substrate shown in  FIG. 3 . 
         FIG. 5A  is a vertical cross-sectional view showing the LED substrate shown in  FIG. 3 , and  FIG. 5B  is a longitudinal cross-sectional view showing a substrate connector of the LED substrate shown in  FIG. 5A  on the side of a ground-side terminal. 
         FIG. 6A  is a cross-sectional view showing the LED substrate shown in  FIG. 5A , where sheet-metal screws are inserted in the LED substrate, and  FIG. 6B  is a cross-sectional view showing the LED substrate shown in  FIG. 5B , where a sheet-metal screw is inserted in the LED substrate. 
         FIG. 7  is an external perspective view showing the LED substrate and a fixing plate to which the LED substrate is to be fixed. 
         FIG. 8A  is a vertical cross-sectional view showing the LED substrate and the fixing plate shown in  FIG. 7 , and  FIG. 8B  is a longitudinal cross-sectional view showing the substrate connector of the LED substrate shown in  FIG. 8A  on the side of the ground-side terminal. 
         FIG. 9  is a plan view showing three LED substrates that are laterally disposed. 
         FIG. 10A  is a vertical cross-sectional view showing the LED substrate of a first modified embodiment, and  FIG. 10B  is a longitudinal cross-sectional view showing the substrate connector of the LED substrate shown in  FIG. 10A  on the side of the ground-side terminal. 
         FIG. 11A  is a vertical cross-sectional view showing the LED substrate of a second modified embodiment, and  FIG. 11B  is a longitudinal cross-sectional view showing the substrate connector of the LED substrate shown in  FIG. 11A  on the side of the ground-side terminal. 
         FIG. 12  is a plan view showing the LED substrate of a third modified embodiment. 
         FIG. 13  is an exploded perspective view showing a schematic configuration of a conventional liquid crystal display device. 
         FIG. 14  is an enlarged cross-sectional view showing a relevant portion of the liquid crystal display device shown in  FIG. 13  after being assembled. 
         FIG. 15  is a front plan view showing a conventional LED substrate. 
         FIG. 16  is a plan view showing two conventional LED substrates that are laterally disposed. 
         FIG. 17A  is a plan view showing two conventional LED substrates that are laterally disposed, and  FIG. 17B  is a plan view showing three conventional LED substrates that are laterally disposed 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     A detailed description of an LED substrate, a backlight unit, and a liquid crystal display device of preferred embodiments of the present invention will now be provided with reference to the accompanying drawings. 
       FIG. 1  is an exploded perspective view showing a schematic configuration of a liquid crystal display device  1  of a preferred embodiment of the present invention.  FIG. 2  is an enlarged cross-sectional view showing a relevant portion of the liquid crystal display device  1 . The liquid crystal display device  1  includes a bezel  2 , a liquid crystal display panel  3  and a backlight unit  4  as shown in  FIGS. 1 and 2 . 
     The bezel  2  has a square frame shape with an opening so as to cover edge portions of the liquid crystal display panel  3 , and is arranged to, together with a backlight chassis  14  to be described later, ensure strength of the entire liquid crystal display device  1 . The liquid crystal display panel  3  includes two glasses that are bonded together, and liquid crystals are filled in a space between the glasses. The liquid crystal display panel  3  is capable of displaying an image on its front surface. 
     The backlight unit  4  defines a so-called side (edge) illuminating device. The backlight unit  4  includes a frame  5 , optical sheets  7  to  9 , a light guide plate  11 , a reflection sheet  13 , the backlight chassis  14 , a fixing plate  15 , and three LED substrates  20  as shown in  FIG. 1 . The frame  5  has a square frame shape with an opening, and is arranged to fix the optical sheets  7  to  9 , the light guide plate  11  and the reflection sheet  13 , which are stacked in this order from the top, to the backlight chassis  14 . The optical sheets  7  to  9 , the light guide plate  11  and the reflection sheet  13  define optical members arranged to adjust the properties (e.g., refraction, diffraction, reflection) of light that enters the liquid crystal display panel  3  from LEDs  21  included on the LED substrates  20 . 
     The backlight chassis  14  is made of a metal plate such as aluminum that possesses electrical conductivity. The backlight chassis  14  has the shape of a box of low height that is formed through bending processing of the metal plate. The backlight chassis  14  houses the optical sheets  7  to  9 , the light guide plate  11 , the reflection sheet  13 , the fixing plate  15 , and the LED substrates  20 . 
     The light guide plate  11  has a rectangular shape when seen in a plan view, and is preferably made of a transparent plate having a thickness of about 3 to 4 mm. The light guide plate  11  includes alight incidence surface  11   a  arrange to obtain light from the LEDs  21 , and a light emitting surface  11   b  arrange to emit the light upward (in a direction to project the light) obtained from the light incidence surface  11   a . The light incidence surface  11   a  is defined by a given side surface of the light guide plate  11 , and the light emitting surface  11   b  is defined by a front surface of the light guide plate  11 . 
     The light guide plate  11  is arranged to repeatedly reflect the light, which enters from the light incidence surface  11   a , between the light emitting face (front face)  11   b  and a back surface  11   c , which is the opposite surface to the light emitting surface  11   b , to planarly diffuse the light inside the light guide plate  11 . The light guide plate  11  includes a plurality of scattering members (not shown) on the back surface  11   c , which are arranged to scatter the light, which enters from the light incidence surface (side surface)  11   a , and emit the light from the light emitting surface (front surface)  11   b . The scattering members are preferably provided thereon by dotting paint containing a white pigment in a printing method on the back surface  11   c  of the light guide plate  11 , or are preferably provided thereon by forming a plurality of concave portions on the back surface  11   c  of the light guide plate  11 . 
     In addition, the LEDs  21  provided to the LED substrates  20  are disposed close to the light incidence surface  11   a  of the light guide plate  11 . Further, light emitting surfaces  21   d  of the LEDs  21  are disposed along the light incidence surface  11   a  of the light guide plate  11 , having a given space therebetween so as to be opposed to the light incidence surface  11   a . In the present embodiment, the three LED substrates  20  are fixed so as to be disposed laterally while standing (erecting) on the fixing plate  15  having the shape of the letter “L” that is provided so as to stand on a bottom plate  14   a  in the vicinity of a side wall  14   b  of the backlight chassis  14 . 
     The reflection sheet  13  is disposed so as to cover the back surface  11   c , which is the opposite surface to the light emitting surface  11   b . In the present embodiment, the reflection sheet  13  is disposed on the bottom plate  14   a  of the backlight chassis  14 . The reflection sheet  13  is arranged to reflect the light, which is emitted from the back surface  11   c  of the light guide plate  11 , toward the light guide plate  11 . The reflection sheet  13  preferably defines a resin sheet having a thickness of about 0.1 to 2 mm. The reflection sheet  13  is preferably painted white to increase use efficiency of the light and to enhance brightness of the light on the light emitting surface  11   b  of the light guide plate  11  by efficiently reflecting the light, which is emitted from the back surface  11   c  of the light guide plate  11 , toward the light guide plate  11 . 
     The three optical sheets  7  to  9  define resin sheets, which have a thin rectangular shape when seen in a plan view. The three optical sheets  7  to  9  are defined by a stack of the polarization selective reflection sheet  7 , the lens sheet  8 , and the diffusion sheet  9 , which have a thickness of about 0.1 to 0.5 mm, and are stacked in this order from the top and disposed on the light guide plate  11 . 
     In the present embodiment, the diffusion sheet  9  is used to diffuse the light emitted from the light guide plate  11 , allowing uniformalization of brightness distribution of the light. The lens sheet  8  is used to gather the light emitted from the diffusion sheet  9 , allowing enhancement of front brightness of the light. The polarization selective reflection sheet  7  is used to selectively reflect the light emitted from the lens sheet  8  so that the light is not absorbed by a polarizing plate (not shown) that is attached on the underside of the liquid crystal display panel  3 . 
     The backlight unit  4  is capable of converting the light from the LEDs  21  into planate light with the use of the optical sheets  7  to  9 , the light guide plate  11  and the reflection sheet  13 , and projecting the light onto a back surface of the liquid crystal display panel  3 . A power board  18  arranged to supply power to the LED substrates  20 , and a control board  19  arranged to drive the liquid crystal display panel  3  are provided behind the backlight chassis  4 . 
     Next, a description of the LED substrates  20  of the present embodiment of the present invention will be provided with reference to  FIGS. 3 to 7 . Each of the LED substrates  20  includes a radiating plate  22  made from metal such as aluminum that possesses electrical conductivity as shown in  FIGS. 3 to 7 . The radiating plates  22  have a long rectangular shape. Insulating layers  23  are disposed on upper surfaces of the radiating plates  22 . The plurality of LEDs  21  (four LEDs  21  per LED substrate  20  in the present embodiment) disposed linearly along a longitudinal direction of the LED substrates  20  (the radiating plates  22 ) are disposed on the insulating layers  23 . 
     In the present embodiment, the radiating plates  22  function as base members of the LED substrates  20 , and function to curb an increase in temperature caused by heat generation of the LEDs  21 . The radiating plates  22  are attached and fixed to the fixing plate  15  while sandwiching therebetween a thermal conductive sheet  16  that has adhesive faces on both sides. The fixing plate  15  has the shape of the letter “L”, is made from metal such as aluminum that possesses electrical conductivity, and is disposed so as to stand on the bottom plate  14   a  of the backlight chassis  14  (see  FIG. 2 ). 
     Thus, the heat generated by the LEDs  21  is conveyed to the bottom plate  14   a  of the backlight chassis  14  via the radiating plates  22  of the LED substrates  20 , the thermal conductive sheet  16  and the fixing plate  15 , so that the temperature of the LEDs  21  is curbed not to increase excessively. The fixing plate  15  is attached to the bottom plate  14   a  of the backlight chassis  14  by a fixation screw  17 . 
     Each of the LEDs  21  has a package structure such that an LED chip  21   a  that emits blue light is encapsulated in a transparent resin into which a yellow fluorescent material is mixed, for example, and is capable of emitting white light from its top surface, i.e., the light emitting surface  21   d . In the present embodiment, the light emitting surfaces  21   d  are disposed parallel to plate faces (surfaces) of the LED substrates  20 . 
     A first ground pattern  34 , a connecting pattern  33 , a first light source pattern  31 , a third ground pattern  36 , a second light source pattern  32 , a connecting pattern  33 , and a second ground pattern  35  that define wiring patterns are provided in this order from the left on each insulating layer  23  as shown in  FIGS. 3 ,  4  and  5 A. The two LEDs  21  that are disposed in an area of a left half from the middle of the LED substrate  20  (a first LED group  21 A) are connected to each other in series by the connecting pattern  33 , and the two LEDs  21  that are disposed in an area of a right half from the middle of the LED substrate  20  (a second LED group  21 B) are connected to each other in series by the connecting pattern  33 . 
     To be specific, a positive electrode (anode electrode)  21   b  of the first LED  21  from the left in the first LED group  21 A and a negative electrode (cathode electrode)  21   c  of the second LED  21  from the left in the first LED group  21 A are connected by the connecting pattern  33 , and a positive electrode (anode electrode)  21   b  of the first LED  21  from the right in the second LED group  21 B and a negative electrode (cathode electrode)  21   c  of the second LED  21  from the right in the second LED group  21 B are connected by the connecting pattern  33 , as shown in  FIG. 5A . 
     A white coating such as a white solder resist is printed on the surfaces of the LED substrates  20  in a silk printing method so that the surfaces are coated with the coating (not shown). The silk printing method is defined by a method of covering a subject to be printed with a silk that functions as a screen, in which an opening with a given pattern is formed, and then printing ink in the subject through the opening, which is also called as a silk screening method. 
     In the present embodiment, the white coating is printed on the surface of each LED substrate  20  except the areas where the LEDs  21  and the first, second and third ground patterns  34 ,  35  and  36  are disposed. Thus, the white coating reflects the light that comes back to the LED substrates  20  from the light incidence surface  11   a  of the light guide plate  11 , which increases use efficiency of the light. 
     In addition, a substrate connector  40  is provided to each LED substrate  20 . The substrate connectors  40  are disposed in the almost middles of the LED substrates  20  between the first LED groups  21 A and the seconds LED group  21 B. The substrate connectors  40  are used to supply electric source (power) to the LEDs  21 , and each substrate connector  40  includes a first male light-source-side terminal (positive terminal)  41 , a second male light-source-side terminal (positive terminal)  42  and a male ground-side terminal (negative terminal)  43 . 
     In the present embodiment, the substrate connectors  40  have a configuration of being connected to the power board  18  of the liquid crystal display device  1  via cable connectors  50  and cables  61 ,  62  arranged to be fitted and connected from below to the substrate connectors  40 . 
     In the present embodiment, each substrate connector  40  is disposed such that its fitting surface faces downward in a direction parallel to a width direction of each LED substrate  20  (in a lateral direction) so that each connector  50  is fitted and connected thereto from below as shown in  FIG. 4 . The first light-source-side terminal  41 , the ground-side terminal  43  and the second light-source-side terminal  42  are disposed in this order from the left to the right in a connector housing of each substrate connector  40 . 
     Each cable connector  50  includes a first female light-source-side terminal (positive terminal)  51 , a second female light-source-side terminal (positive terminal)  52 , and a female ground-side terminal (negative terminal)  53 , which are arranged to be fitted and electrically connected to the first light-source-side terminal  41 , the second light-source-side terminal  42  and the ground-side terminal  43  of each substrate connector  40 , respectively, as shown in  FIG. 4 . In the present embodiment, each cable connector  50  has a configuration such that the first light-source-side terminal  51 , the ground-side terminal  53  and the second light-source-side terminal  52  are disposed in this order from the left to the right in a connector housing of each cable connector  50  so as to correspond to each substrate connector  40  to which each cable connector  50  is to be connected. 
     A crimping portion  51   a  of the first light-source-side terminal  51  of each cable connector  50  is connected to an end portion of the first light-source-side cable  61 , a crimping portion  52   a  of the second light-source-side terminal  52  of each cable connector  50  is connected to an end portion of the second light-source-side cable  62 , and a crimping portion  53   a  of the ground-side terminal  53  of each cable connector  50  is connected to an end portion of the ground-side cable  63 . 
     The first light source pattern  31  is connected to the positive electrode (anode electrode)  21   b  of the first LED  21  from the right in the first LED group  21 A, and is also connected to a tip  41   a  of the first light-source-side terminal (positive terminal)  41  of the substrate connector  40  as shown in  FIGS. 3 ,  4  and  5 A. The second light source pattern  32  is connected to the positive electrode (anode electrode)  21   b  of the first LED  21  from the left in the second LED group  21 B, and is also connected to a tip  42   a  of the second light-source-side terminal (positive terminal)  42  of the substrate connector  40 . The third ground pattern  36  having a square shape (a substantially rectangular shape) that is disposed above the substrate connector  40  is connected to a tip  43   a  of the ground-side terminal (negative terminal)  43  of the substrate connector  40 . 
     In addition, the first ground pattern  34  having a square shape (a substantially rectangular shape) that is disposed at the left end of each LED substrate  20  is connected to the negative electrode (cathode electrode)  21   c  of the first LED  21  from the left in the first LED group  21 A. Further, the second ground pattern  35  having a square shape (a substantially rectangular shape) that is disposed at the right end of each LED substrate  20  is connected to the negative electrode (cathode electrode)  21   c  of the first LED  21  from the right in the second LED group  21 B. 
     A first through-hole  34   a  that goes through the first ground pattern  34 , the insulating layer  23  and the radiating plate  22  is formed in the middle of the first ground pattern  34  as shown in  FIGS. 3 ,  4  and  5 A. A second through-hole  35   a  that goes through the second ground pattern  35 , the insulating layer  23  and the radiating plate  22  is formed in the middle of the second ground pattern  35 . A third through-hole  36   a  that goes through the third ground pattern  36 , the insulating layer  23  and the radiating plate  22  is formed in the middle of the third ground pattern  36 . 
     In each LED substrate  20  having the configuration described above, the light-source-side terminal  41  of the substrate connector  40  is electrically connected to the LEDs  21  in the first LED group  21 A by the first light source pattern  31  and the connecting patterns  33 , while the first ground pattern  34  is not connected to the third ground pattern  36 . Thus, the negative electrode (cathode electrode)  21   c  of the first LED  21  from the left in the first LED group  21 A is yet to be connected to the ground-side terminal  43  of the substrate connector  40 . 
     In a similar manner, the light-source-side terminal  42  of the substrate connector  40  is electrically connected to the LEDs  21  in the second LED group  21 B by the second light source pattern  32  and the connecting patterns  33 , while the second ground pattern  35  is not connected to the third ground pattern  36 . Thus, the negative electrode (cathode electrode)  21   c  of the first LED  21  from the right in the second LED group  21 B is yet to be connected to the ground-side terminal  43  of the substrate connector  40 . 
     Thus, a first sheet-metal screw  71  and a third sheet-metal screw  73  that are made from metal that possesses electrical conductivity are inserted into the first through-hole  34   a  of the first ground pattern  34  and the third through-hole  36   a  of the third ground pattern  36 , respectively, so that the first ground pattern  34  is electrically connected to the radiating plate  22  disposed thereunder via the first sheet-metal screw  71 , and the third ground pattern  36  is electrically connected to the radiating plate  22  disposed thereunder via the third sheet-metal screw  73 , which allows the first ground pattern  34  and the third ground pattern  36  to be electrically connected to each other via the first sheet-metal screw  71 , the radiating plate  22  and the third sheet-metal screw  73 , as shown in shown in  FIGS. 3 ,  5 A and  5 B. 
     In a similar manner, a second sheet-metal screw  72  and the third sheet-metal screw  73  that are made from metal that possesses electrical conductivity are inserted into the second through-hole  35   a  of the second ground pattern  35  and the third through-hole  36   a  of the third ground pattern  36 , respectively, so that the second ground pattern  35  is electrically connected to the radiating plate  22  disposed thereunder via the second sheet-metal screw  72 , and the third ground pattern  36  is electrically connected to the radiating plate  22  disposed thereunder via the third sheet-metal screw  73 , which allows the second ground pattern  35  and the third ground pattern  36  to be electrically connected to each other via the second sheet-metal screw  72 , the radiating plate  22  and the third sheet-metal screw  73 , as shown in shown in  FIGS. 3 ,  5 A and  5 B. 
     Thus, the two LEDs  21  that are connected in series in the first LED group  21 A are made connected in series between the first light-source-side terminal  41  and the ground-side terminal  43  of the substrate connector  40 , and the two LEDs  21  that are connected in series in the second LED group  21 B are made connected in series between the second light-source-side terminal  42  and the ground-side terminal  43  of the substrate connector  40  as shown in  FIGS. 6A and 6B . 
     In other words, because each LED substrate  20  has the configuration that the first ground pattern  34  disposed at the left end of the LED substrate  20  and the second ground pattern  35  disposed at the right end of the LED substrate  20  are electrically connected to the third ground pattern  36  that is connected to the ground-side terminal  43  of the substrate connector  40  via the first sheet-metal screw  71 , the second sheet-metal screw  72 , the radiating plate  22  and the third sheet-metal screw  73 , it is unnecessary to provide the ground pattern  133  shown in  FIG. 15  and explained above in the description of Background Art, which is adjacent to the LEDs  121 , which are connected to one another in series in the longitudinal direction of the LED substrate  120 , in the width direction of the LED substrate  120 , and extends along the longitudinal direction of the LED substrate  120 . 
     Thus, downsizing (decreasing) in width of each LED substrate  20  by a width that is required in order to include the conventional ground pattern  133  disposed linearly along the longitudinal direction of the LED substrate  120  can be achieved by using the radiating plate  22  made from metal as a ground wire for the LEDs  21 , the radiating plate  22  being disposed under the LEDs  21  connected in series while sandwiching therebetween the insulating layer  23 . 
     That is, downsized in their width direction (direction perpendicular to the longitudinal direction), the LED substrates  20  can be housed in the backlight chassis  14  as shown in  FIG. 2  without providing the convex portion  114   c  shown in  FIG. 14  and explained above in the description of Background Art, which defines the portion protruded downward from the bottom plate  114   a  of the backlight chassis  114 . 
     Thus, the height of the backlight chassis  14  (the height from the bottom plate  14   a ) can be reduced compared with a conventional backlight chassis as shown in  FIG. 2 , which can achieve a thin profile of the backlight unit  4 , and a thin profile of the liquid crystal display device  1 . 
     It is also preferable to have a configuration such that normally-used screw holes are provided instead of the first through-hole  34   a  of the first ground pattern  34 , the second through-hole  35   a  of the second ground pattern  35 , and the third through-hole  36   a  of the third ground pattern  36 , and normally-used screws are provided instead of the first sheet-metal screw  71 , the second sheet-metal screw  72 , and the third sheet-metal screw  73 . 
     In the present embodiment, by inserting the first sheet-metal screw  71  into the first through-hole  34   a  of the first ground pattern  34  to electrically connect the first ground pattern  34  and the radiating plate  22  disposed under the first ground pattern  34 , a thread of the first sheet-metal screw  71  is engaged in the inner surface of the first through-hole  34   a  to be transformed to a female screw. Thus, it is unnecessary to form the first through-hole  34   a  as a screw hole. In addition, the first sheet-metal screw  71  can be electrically connected to the radiating plate  22  in a convincing way. 
     In addition, in a similar manner, by inserting the second sheet-metal screw  72  into the second through-hole  35   a  of the second ground pattern  35  to electrically connect the second ground pattern  35  and the radiating plate  22  disposed under the second ground pattern  35 , a thread of the second sheet-metal screw  72  is engaged in the inner surface of the second through-hole  35   a  to be transformed to a female screw. Thus, it is unnecessary to form the second through-hole  35   a  as a screw hole. In addition, the second sheet-metal screw  72  can be electrically connected to the radiating plate  22  in a convincing way. 
     In addition, in a similar manner, by inserting the third sheet-metal screw  73  into the third through-hole  36   a  of the third ground pattern  36  to electrically connect the third ground pattern  36  and the radiating plate  22  disposed under the third ground pattern  36 , a thread of the third sheet-metal screw  73  is engaged in the inner surface of the third through-hole  36   a  to be transformed to a female screw. Thus, it is unnecessary to form the third through-hole  36   a  as a screw hole. In addition, the third sheet-metal screw  73  can be electrically connected to the radiating plate  22  in a convincing way. 
     It is also preferable that first, second and third sheet-metal screws  81 ,  82  and  83  are used instead of the first, second and third sheet-metal screws  71 ,  72  and  73 , the first, second and third sheet-metal screws  81 ,  82  and  83  being longer than the first, second and third sheet-metal screws  71 ,  72  and  73 , and front ends of the first, second and third sheet-metal screws  81 ,  82  and  83  are inserted into through-holes  15   a  provided to the fixing plate  15  and the thermal conductive sheet  16  as shown in  FIGS. 7 ,  8 A and  8 B. This configuration allows not only electrical connection between the first ground pattern  34  and the radiating plate  22 , electrical connection between the second ground pattern  35  and the radiating plate  22 , and electrical connection between the third ground pattern  36  and the radiating plate  22 , but also attachment of the LED substrates  20  to the fixing plate  15 . 
     The backlight chassis  14  usually functions as a grounding member arranged to electrically ground the power board  18  arranged to supply power to the LED substrates  20  and the control board  19  arranged to drive the liquid crystal display panel  3 . Thus, in the configuration shown in  FIGS. 7 ,  8 A and  8 B, the first ground pattern  34 , the second ground pattern  35  and the third ground pattern  36  of each LED substrate  20  are electrically connected to the backlight chassis  14  that functions as the grounding member via the sheet-metal screws  81 ,  82  and  83 , the radiating plate  22  and the fixing plate  15 . Thus, electrical grounding properties of the first ground pattern  34 , the second ground pattern  35  and the third ground pattern  36  of each LED substrate  20  are improved, which allows stable power supply to the LEDs  21 . 
     If a thermal conductive sheet that possesses electrical conductivity is used as the thermal conductive sheet  16  that is sandwiched between the radiating plate  22  of the LED substrate  20  and the fixing plate  15 , electrical grounding properties of the first ground pattern  34 , the second ground pattern  35  and the third ground pattern  36  of each LED substrate  20  are further improved. 
     Openings  14   c  for connector insertion are provided to the bottom plate  14   a  of the backlight chassis  14 , the openings  14  being larger than the outer diameters of the cable connectors  50  such that the cable connectors  50  are insertable in and removable from the substrate connectors  40  of the LED substrates  20  that are fixed to the bottom plate  14   a  of the backlight chassis  14  as shown in  FIGS. 1 ,  7  and  8 B. This configuration allows easy handleability of the cable connectors  50 , and easy wiring of the cables  61 ,  62  and  63  to the power board  18  disposed behind the bottom plate  14   a.    
     As described above, the LED substrates  20  have the configuration that the substrate connectors  40  arranged to supply power to the LEDs  21  included on the LED substrates  20  are disposed in the middles of the LED substrates  20 , so that the right and left ends of the LED substrates  20  can have the same shape, especially in this case, the symmetrically same shape as shown in  FIG. 4 . Thus, distances between the LEDs  21  of the plurality of LED substrates  20  can be made uniform even when the plurality of LED substrates are disposed laterally. 
     When three LED substrates  20  are disposed laterally in the longitudinal direction thereof, distances P 2  between the adjacent LEDs  21  of the adjacent LED substrates  20  can be made equal to distances P 1  between the adjacent LEDs  21  of each LED substrate  20  as shown in  FIG. 9 . Thus, the three LED substrates  20  can be disposed such that the distances between the LEDs  21  are all uniform. 
     That is, the LED substrates  20  of the present invention do not have the configuration that the substrate connectors  140  are disposed at either different ones of right and left ends of the LED substrates  120 , which is shown in  FIG. 15  and explained above in the description of Background Art. Thus, the problem that a distance between the LEDs  121  of the two adjacent LED substrates  120  is longer, which is indicated as P 3  in  FIGS. 17A and 17B , can be prevented. Thus, the plurality of LED substrates can be disposed laterally in an efficient fashion such that the distances between the adjacent LEDs are all uniform. 
     In addition, owing to the configuration of the LED substrates  20  that the substrate connectors  40  are disposed in the middles of the LED substrates  20 , the LED substrates of one kind having this configuration can suffice when two, three or more than three LED substrates are disposed laterally. Thus, it is unnecessary to prepare the LED substrates  120  of two different kinds on which the substrate connectors  140  are disposed at different one ends of the right and left ends of the LED substrates  120  as shown in  FIG. 16 , which can reduce the number of components and save a cost. 
     Next, descriptions of first to third modified embodiments of the above-described embodiment will be provided with reference to  FIGS. 10A to 12 . Explanations of the same components as those in the above-described embodiment are omitted, and different respects are explained mainly, providing the same reference numerals as those in the above-described embodiment to the same components. 
       FIGS. 10A and 10B  are a view showing the LED substrate  20  of the first modified embodiment, where conductive pastes  74 ,  75  and  76  preferably made from solder are applied to inner surfaces of the first through-hole  34   a  of the first ground pattern  34 , the second through-hole  35   a  of the second ground pattern  35 , and the third through-hole  36   a  of the third ground pattern  36 . Inserting the sheet-metal screws  71 ,  72  and  73  into the through-holes  34   a ,  35   a  and  36   a , to the inner surfaces of which the conductive pastes  74 ,  75  and  76  are applied, can further improve electrical connection between the first ground pattern  34  and the radiating plate  22 , electrical connection between the second ground pattern  35  and the radiating plate  22 , and electrical connection between the third ground pattern  36  and the radiating plate  22 . 
     It is preferable to provide raised portions  74   a ,  75   a  and  76   a  that are prepared by providing the conductive pastes  74 ,  75  and  76  having a given thickness around inlets of the through-holes  34   a ,  35   a  and  36   a  into which the sheet-metal screws  71 ,  72  and  73  are to be inserted. Providing the raised portions  74   a ,  75   a  and  76   a  can improve electrical connection between screw heads of the sheet-metal screws  71 ,  72  and  73  and the first, second and third ground patterns  34 ,  35  and  36  via the raised portions  74   a ,  75   a  and  76   a , respectively. 
       FIGS. 11A and 11B  are views showing the LED substrate  20  of the second modified embodiment, where the LED substrate  20  includes first, second and third conductive tapes  77 ,  78  and  79  that are made preferably of conductive aluminum tapes having adhesive faces. In the present modified embodiment, one end of the first conductive tape  77  is attached to the front surface of the first ground pattern  34 , and the other end is attached to the back surface of the radiating plate  22  disposed under the first ground pattern  34  as shown in  FIG. 11A , whereby the first ground pattern  34  and the radiating plate  22  are electrically connected via the first conductive tape  77 . 
     In addition, in a similar manner, one end of the second conductive tape  78  is attached to the front surface of the second ground pattern  35 , and the other end is attached to the back surface of the radiating plate  22  disposed under the second ground pattern  35  as shown in  FIG. 11A , whereby the second ground pattern  35  and the radiating plate  22  are electrically connected via the second conductive tape  78 . 
     In addition, in a similar manner, one end of the third conductive tape  79  is attached to the front surface of the third ground pattern  36 , and the other end is attached to the back surface of the radiating plate  22  disposed under the third ground pattern  36  as shown in  FIG. 11A , whereby the third ground pattern  36  and the radiating plate  22  are electrically connected via the third conductive tape  79 . 
     Thus, this configuration allows not only electrical connection between the first ground pattern  34  and the radiating plate  22 , electrical connection between the second ground pattern  35  and the radiating plate  22 , and electrical connection between the third ground pattern  36  and the radiating plate  22  via the sheet-metal screws  71 ,  72  and  73 , but also electrical connection between the first ground pattern  34  and the radiating plate  22 , electrical connection between the second ground pattern  35  and the radiating plate  22 , and electrical connection between the third ground pattern  36  and the radiating plate  22  via the conductive tapes  77 ,  78  and  79 , which can further improve electrical connection between the first ground pattern  34  and the radiating plate  22 , electrical connection between the second ground pattern  35  and the radiating plate  22 , and electrical connection between the third ground pattern  36  and the radiating plate  22 . 
       FIG. 12  is a view showing the LED substrate  20  of the third modified embodiment, where the LED substrate  20  includes a convex portion  20   a  that is protruded downward from the middle of the LED substrate  20 . The substrate connector  40  and the third ground pattern  36  are disposed on the convex portion  20   a . The LED substrates  20  of the third modified embodiment are capable of being attached to the fixing plate  115  standing on the convex portion  114   c  of the conventional backlight chassis  114  shown in  FIG. 14  and explained above in the description of Background Art, and thus are used when the backlight chassis  114  has a height (space) enough to house the LED substrates in the standing position. 
     In the present modified embodiment, the substrate connector  40  is disposed such that a direction of insertion of the cable connector  50  into the connector  40  is made lateral (i.e., a direction parallel to the longitudinal direction of the LED substrate  20 ). The first light-source-side terminal  41  (positive terminal), the second light-source-side terminal (positive terminal)  42  and the ground-side terminal (negative terminal)  43  are disposed in this order from top down in a connector housing of the substrate connector  40 . Meanwhile, the first light-source-side terminal (positive terminal)  51 , the second light-source-side terminal (positive terminal)  52 , and the ground-side terminal (negative terminal)  53  are disposed in this order from top down in a connector housing of the cable connector  50  so as to correspond to the substrate connector  40  to which the cable connector  50  is to be connected. 
     Because each LED substrate  20  described above of the present modified embodiment has the configuration that the first ground pattern  34  and the second ground pattern  35  are provided at the left and right ends of the LED substrate  20  while the third ground pattern  36  is provided in the middle of the LED substrate  20 , and that the first ground pattern  34 , the second ground pattern  35  and the third ground pattern  36  are electrically connected to one another via the metallic radiating plate  22 , which is disposed thereunder while sandwiching therebetween the insulating layer  23 , and via the sheet-metal screws  71 ,  72  and  73 , the configuration can be used as a ground wire for the LEDs  21  that are connected in series. 
     Thus, downsizing (decreasing) in width of each LED substrate  20  by a width that is conventionally required in order to include the ground pattern  133  disposed linearly along the longitudinal direction of the LED substrate  120 , can be achieved, and thus the height of the backlight chassis  14  (the height from the bottom plate  14   a ) can be reduced compared with a conventional backlight chassis as shown in  FIG. 2 , which can achieve a thin profile of the backlight unit  4 , and a thin profile of the liquid crystal display device  1 . 
     In addition, the LED substrate  20  has the configuration that the substrate connector  40  arranged to supply power to the LEDs  21  is disposed in the middle of the LED substrate  20 , which is different from the configuration of the LED substrate  120  explained above in the description of Background Art that the substrate connector  140  is disposed at either one of right and left ends of the LED substrate  120 . Thus, the right and left ends of the LED substrate  20  can have the same shape. 
     Owing to the configuration of the LED substrates  20 , distances P 2  between the adjacent LEDs  21  of the adjacent LED substrates  20  can be made equal to distances P 1  between the adjacent LEDs  21  of each LED substrate  20  as shown in  FIG. 9 . Thus, the three LED substrates  20  can be disposed such that the distances between the LEDs  21  are all uniform. In addition, the LED substrates  20  of one kind having this configuration can suffice when two, three or more than three LED substrates are disposed laterally. 
     The foregoing description of the preferred embodiments of the LED substrate, the backlight unit and the liquid crystal display device of the present invention has been presented for purposes of illustration and description with reference to the drawings. However, it is not intended to limit the present invention to the embodiments, and modifications and variations are possible as long as they do not deviate from the principles of the present invention. For example, described above in the preferred embodiments is the configuration that the LED substrates  20  are disposed along one side of the light guide plate  11 ; however, the present invention is not limited to this configuration. Configurations such that the LED substrates  20  are disposed along two or four opposed sides of the light guide plate  11  are preferably used.