Abstract:
A backlight unit ( 49 ) of a display device ( 69 ) having a liquid crystal display panel ( 59 ) is provided with a chassis ( 41 ), a diffusion plate ( 43 ) supported by the chassis, and a light source which irradiates the diffusion plate with light. The light source is constructed by combining a plurality of mounting substrates ( 21 ) provided with an LED ( 22 ) which serves as the light-emitting element and a diffusion lens ( 24 ) for covering the LED. Connectors ( 25 A) are mounted on matching edges of the plurality of mounting substrates to electrically connect the substrates. The connectors are placed so as not to interfere with the illumination light region in which the LED imparts brightness to the diffusion plate. In order to achieve this state of non-interference, a beveled part ( 26 ) is formed on the side of the connectors facing the LED.

Description:
TECHNICAL FIELD 
       [0001]    The present invention is related to an illumination device, a display device including the illumination device, and a television receiver having the display device. 
       BACKGROUND ART 
       [0002]    Display devices using a display panel such as a liquid crystal display panel, which does not emit light itself, typically incorporate an illumination device that illuminates the display panel from behind. Various types of light sources including cold cathode tubes and light emitting elements are used as the light source of such an illumination device. Examples of such light emitting elements include light emitting diodes (hereinafter referred to as “LEDs”), organic electroluminescence elements, inorganic electroluminescence elements, among which LEDs are used the most commonly today. The light sources of the illumination device disclosed in Patent Literature 1 are also LEDs. 
         [0003]    In the illumination device disclosed in Patent Literature 1, as shown in  FIG. 8 , LEDs  122  are mounted on the mounting board  121 , and further, lenses  124  each covering a corresponding one of the LEDs  122  are attached to the mounting board  121 . The mounting board  121 , the LED  122 , and the lens  124  together form a light emitting module mj. The lenses  124  are each formed in a shape of a hemisphere dome with even thickness, and transmit light emitted from the LEDs  122  without significant refraction. Thus, if the LEDs  122  face upward as shown in  FIG. 8 , a large part of the light proceeds in a direction close to the vertical direction. 
       CITATION LIST 
     Patent Literature 
       [0000]    
       
         Patent Literature 1: JP-A-2008-41546 
       
     
       SUMMARY OF INVENTION 
     Technical Problem 
       [0005]    Only a single mounting board  121  is illustrated in  FIG. 8 , but a case of illuminating a large area may require a configuration in which a plurality of mounting boards  121  are connected to each other with connectors. The illumination device of  FIG. 8  is originally designed as a backlight of a liquid crystal display device, and irradiates a diffusion plate with light from a large number of LEDs  122  to give the diffusion plate even brightness; here, if a plurality of mounting boards  121  are connected to each other with connectors, the connectors may block the light from the LEDs  122  to cast their shadows onto the diffusion plate. 
         [0006]    The present invention has been made in view of the foregoing, and an object of the present invention is, with respect to an illumination device that irradiates a diffusion plate with light from a light source built as a combination of a plurality of mounting boards on which light emitting elements are mounted, to prevent connectors used for connecting the mounting boards to each other from causing uneven brightness of the diffusion plate. 
       Solution to Problem 
       [0007]    According to a preferred embodiment of the present invention, in an illumination device including a diffusion plate and a light source which irradiates the diffusion plate with light, the light source is configured by combining a plurality of mounting boards on each of which a light emitting element is mounted, connectors are attached to corresponding edges of the plurality of mounting boards to electrically connect the mounting boards to each other, and the connectors are placed in a state in which the connectors do not interfere with an irradiation light region in which the light emitting element imparts brightness to the diffusion plate. 
         [0008]    With this configuration, light that imparts brightness to the diffusion plate is not blocked by the connectors, and thus the diffusion plate does not suffer from uneven brightness caused by the connectors. 
         [0009]    According to a preferred embodiment of the present invention, the illumination device configured as described above further includes a diffusion lens that covers the light emitting element. Here, light from the diffusion lens forms the irradiation light region. 
         [0010]    With this configuration, the light from the diffusion lens is not blocked by the connectors, and thus the diffusion plate does not suffer from uneven brightness caused by the connectors. 
         [0011]    According to a preferred embodiment of the present invention, in the illumination device configured as described above, among edges of the connectors, at least an edge which is located on a side that faces the light emitting element is formed to be away from the light emitting element, to thereby impart to the connectors a shape which allows the connectors to be in a state in which the connectors do not interfere with the irradiation light region. 
         [0012]    With this configuration, it is possible to eliminate unevenness in brightness by changing the shape of the connectors, and thus the object of the present invention is easily achieved. 
         [0013]    According to a preferred embodiment of the present invention, in the illumination device configured as described above, among the edges of the connectors, at least the edge which is located on the side that faces the light emitting element is formed to be away from the light emitting element by forming a beveled part at the edge. 
         [0014]    With this configuration, the shape of the connectors is easily changed simply by forming the beveled part in the connectors. 
         [0015]    According to a preferred embodiment of the present invention, in the illumination device configured as described above, among the edges of the connectors, at least the edge which is located on the side that faces the light emitting element is formed to be away from the light emitting element by forming a rounded part at the edge. 
         [0016]    With this configuration, the shape of the connectors is easily changed simply by forming the rounded part in the connectors. 
         [0017]    According to a preferred embodiment of the present invention, in the illumination device configured as described above, among the edges of the connectors, at least the edge which is located on the side that faces the light emitting element is formed to be away from the light emitting element by forming a stepped part at the edge. 
         [0018]    With this configuration, the shape of the connectors is easily changed simply by forming the stepped part in the connectors. 
         [0019]    According to a preferred embodiment of the present invention, in the illumination device configured as described above, a height of the connectors is reduced, to thereby impart to the connectors a shape which allows the connectors to be in a state in which the connectors do not interfere with the irradiation light region. 
         [0020]    With this configuration, it is possible to eliminate uneven brightness by changing the size of the connectors, and thus the object of the present invention is easily achieved. 
         [0021]    According to a preferred embodiment of the present invention, in the illumination device configured as described above, the light emitting element is an LED. 
         [0022]    With this configuration, it is possible to obtain a bright illumination device by using LEDs brightness of which has recently been remarkably increased. 
         [0023]    According to a preferred embodiment of the present invention, a display device includes: any illumination device of the illumination devices configured as described above; and a display panel which receives light from the illumination device. 
         [0024]    With this configuration, it is possible to obtain a display device free from brightness unevenness stemming from the connectors. 
         [0025]    According to a preferred embodiment of the present invention, in the display device configured as described above, the display panel is a liquid crystal display panel. 
         [0026]    With this configuration, it is possible to obtain a liquid crystal display device free from brightness unevenness stemming from the connectors. 
         [0027]    According to a preferred embodiment of the present invention, a television receiver includes the display device configured as described above. 
         [0028]    With this configuration, it is possible to obtain a television receiver in which the screen is free from brightness unevenness stemming from the connectors. 
       Advantageous Effects of Invention 
       [0029]    According to the present invention, light from the light emitting element that imparts brightness to the diffusion plate is not blocked by the connectors, and thus the connectors do not cause uneven brightness, and this helps improve the quality of images displayed on the display device incorporating the display panel that receives light from the illumination device of the present invention. This further helps improve the image quality of the television receiver incorporating the display device. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0030]      FIG. 1  An exploded perspective view showing a display device including an illumination device according to a preferred embodiment of the present invention; 
           [0031]      FIG. 2  A sectional view showing a mounting-board joint portion of the illumination device according to a first embodiment; 
           [0032]      FIG. 3  A plan view showing the mounting-board joint portion of  FIG. 2 ; 
           [0033]      FIG. 4  A sectional view showing a mounting-board joint portion of an illumination device according to a second embodiment; 
           [0034]      FIG. 5  A sectional view showing a mounting-board joint portion of an illumination device according to a third embodiment; 
           [0035]      FIG. 6  A sectional view showing a mounting-board joint portion of an illumination device according to a fourth embodiment; 
           [0036]      FIG. 7  An exploded perspective view showing a television receiver; 
           [0037]      FIG. 8  An exploded perspective view showing a conventional illumination device; 
           [0038]      FIG. 9  A graph showing how illuminance differs in different directions of irradiation from an LED; and 
           [0039]      FIG. 10  A conceptual diagram showing how brightness of a plurality of LEDs gathers. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0040]    A description will be given of an embodiment of the configuration of a display device provided with an illumination device according to a preferred embodiment of the present invention, based on  FIGS. 1 to 3 . In  FIG. 1 , a display device  69  is illustrated as being horizontally placed with a display surface thereof up. 
         [0041]    The display device  69  uses a liquid crystal display panel  59  as a display panel. The liquid crystal display panel  59  and a backlight unit  49  that illuminates the liquid crystal display panel  59  from behind are accommodated in a single housing. The housing is formed by combining a front housing member HG 1  and a rear housing member HG 2 . 
         [0042]    The liquid crystal display panel  59  is formed by fixing an active matrix substrate  51  that includes a switching element such as a thin film transistor (TFT) and a counter substrate  52  that is located opposite to the active matrix substrate  51  to each other with an unillustrated seal member placed therebetween, and filling the space between the active matrix substrate  51  and the counter substrate  52  with liquid crystal. 
         [0043]    Polarization films  53  are fixed one to each of the light receiving side of the active matrix substrate  51  and the light output side of the counter substrate  52 . The liquid crystal display panel  59  forms an image by making use of variation in light transmittance resulting from tilting of liquid crystal molecules. 
         [0044]    The backlight unit  49 , which embodies the illumination device according to the present invention, has the following configuration. That is, the backlight unit  49  includes light emitting modules MJ, a chassis  41 , a reflection seat  42 , a large-size diffusion plate  43 , a prism seat  44 , and microlens sheet  45 . 
         [0045]    The light emitting modules MJ each include a mounting board  21 , an LED  22  as a light emitting element, a diffusion lens  24 , and a built-in reflection sheet  11 . 
         [0046]    Now, a description will be given of the importance of the diffusion lens  24 . Take, for example, the illumination device disclosed in Patent Literature 1. Although the illumination device shown in  FIG. 8  includes lenses  124  incorporated therein, since light from each of the LEDs  122  is emitted in a small range of directions, a large number of light emitting modules mj need to be arranged in a high density. This increases the cost for preparing and mounting the components, making the illumination device expensive as a whole. 
         [0047]    Recently, the brightness of LEDs has been significantly increased, so that it is now possible to obtain a sufficient amount of light to cover the entire screen with a comparatively small number of LEDs. However, if a small number of high-brightness LEDs are sparsely arranged, it is impossible to prevent uneven brightness, and thus, it is preferable to use a lens that is highly capable of diffusing light (such a lens will herein be referred to as “diffusion lens”) in combination with each LED. 
         [0048]      FIG. 9  is a graph showing how illuminance (unit: Lux) differs in different irradiation directions in a case of a bare LED and in a case of an LED combined with a diffusion lens. In the case of the bare LED, the illuminance is highest at an angle of 90°, which is the angle of the optical axis, and sharply decreases farther away from there. In contrast, in the case of the LED combined with a diffusion lens, illuminance of a certain level or higher can be secured in a wider area, and the peak of illuminance can be set at an angle that is different from the angle of the optical axis. Needless to say, the pattern of illuminance shown in the figure can be changed as desired by accordingly designing the diffusion lens. 
         [0049]      FIG. 10  conceptually shows how brightness of a plurality of LEDs gathers. In the figure, the solid-line waveforms indicate the brightness of LEDs each combined with a diffusion lens, while the broken-line waveforms indicate the brightness of bare LEDs. The horizontal lines among the waveforms indicate widths (full width at half maximum) of the waveforms at brightness of levels half the peak levels. In the case of the LEDs each combined with a diffusion lens, each wave can have a large width, and thus it is easy to generate integrated, collective brightness as flat brightness as shown in the upper part of the figure. In contrast, in the case of the bare LEDs, the waveforms each have a high peak but have a narrow width, and thus it is impossible to avoid generation of waves in the brightness made by gathering the waveforms. Unevenly bright images are not desirable, so it is almost indispensably necessary to adopt the LED combined with a diffusion lens. 
         [0050]    In view of the above, the light emitting module MJ is provided with the diffusion lens  24 . 
         [0051]    Each of the mounting boards  21  have a shape of elongate rectangle, and on its upper surface which is formed as a mount surface  21 U, a plurality of electrodes (not shown) are formed to be arranged at predetermined intervals in the length direction. The LEDs  22  are mounted on the electrodes. The mounting board  21  functions as a common mounting board for the plurality of LEDs  22 . That is, a plurality of units each composed of a LED  22 , a diffusion lens  24 , and a built-in reflection sheet  11  are arranged at predetermined intervals along the length direction on the mounting board  21  as shown in  FIG. 1 . 
         [0052]    The diffusion lens  24  is circular in plan, and has a plurality of legs  24   a  on a lower surface thereof. The tips of the legs  24   a  are bonded to the mount surface  21 U of the mounting board  21  with an adhesive, and thereby the diffusion lens  24  is attached to the mounting board  21 . The presence of the legs  24   a  generates a gap between the mounting board  21  and the diffusion lens  24 . An air flow passes through the gap, and the LED  22  is cooled by the air flow. Incidentally, on the condition that heat dissipation is secured, it is possible to use an integrally molded light emitting module in which an LED is embedded in a diffusion lens. 
         [0053]    Various types of LEDs can be used as the LED  22 . For example, it is possible to use an LED that is formed by combining a blue light-emitting LED chip with a fluorescent substance that emits yellow fluorescence on receiving light from the LED chip, the LED generating white light by mixing the blue light and the yellow light emitted by them. It is also possible to use an LED that is formed by combining a blue light-emitting LED chip with fluorescent substances that respectively emit green fluorescence and red fluorescence on receiving light from the LED chip, the LED generating white light by mixing the blue light, the green light, and the red light emitted by them. 
         [0054]    It is also possible to use an LED that is formed by combining a red light-emitting LED chip, a blue light-emitting LED chip, and a fluorescent substance that emits green fluorescence on receiving blue light from the blue light-emitting LED chip, the LED generating white light by mixing the red light, the blue light, and the green light emitted by them. 
         [0055]    It is also possible to use an LED that is formed by combining a red light-emitting LED chip, a green light-emitting LED chip, and a blue light-emitting LED chip, the LED generating white light by mixing the red light, the green light, and the blue light emitted by them. 
         [0056]      FIG. 1  shows a case where mounting boards  21  each having five LEDs  22  arranged thereon and mounting boards  22  each having eight LEDs  22  arranged thereon are used in combination. Each of the mounting boards  21  with five LEDs  22  is coupled to any one of the mounting boards  21  with eight LEDs  22  through the connection of connectors  25  which are each attached to one far-end edge of a corresponding one of the mounting boards  21  (it goes without saying that the connectors  25  are separated into male and female connectors). 
         [0057]    A plurality of pairs each composed of one mounting board  21  having five LEDs  22  and one mounting board  21  having eight LEDs  22  are arranged on the chassis  41  in parallel with each other. On each of the mounting boards  21 , the LEDs  22  are aligned along the longer-side direction of the chassis  41 , that is, along the direction indicated by arrow X in  FIG. 1 , and the pairs each composed of two mounting boards  21  are aligned along the shorter-side direction of the chassis  41 , that is, along the direction indicated by arrow Y in  FIG. 1 , as a result of which the LEDs  22  are arranged to form a matrix. The mounting boards  21  are fixed to the chassis  41  by appropriate means such as swaging, bonding, screwing, or riveting. 
         [0058]    The built-in reflection sheet  11  is disposed between the mounting board  21  and the diffusion lens  24 . The built-in reflection sheet  11  is fixed to the mount surface  21 U at a position that faces the bottom surface of the diffusion lens  24 . The built-in reflection sheet  11  has a higher optical reflectance than the mounting board  21 . The built-in reflection sheet  11  is also circular in plan and concentric with the diffusion lens  24 . In diameter, the built-in reflection sheet  11  is larger than the diffusion lens  24 . 
         [0059]    The built-in reflection sheet  11 , which is a resin foam sheet containing a large number of fine air bubbles, exploits the interface reflection in the air bubbles to the full and has a high optical reflectance. Polyethylene-terephthalate (PET) foam sheets having a reflectance of 98% or more are available, and thus, it is desirable to adopt such a sheet. In the built-in reflection sheet  11 , there are formed through holes through which the legs  24   a  of the diffusion lens  24  are inserted. Incidentally, in  FIG. 3 , illustration of the built-in reflection sheet  11  is omitted. 
         [0060]    On the chassis  41 , a reflection sheet  42 , which is similar to the chassis  41  in plan, is superposed. The reflection sheet  42  is also a resin foam sheet similar to the built-in reflection sheet  11 . In the reflection sheet  42 , corresponding to the positions of the light emitting modules MJ, there are formed apertures  42 H 1  each having a shape of a circle that is sized such that the diffusion lens  24  can pass therethrough while the built-in reflection sheet  11  cannot. Further, in the reflection sheet  42 , corresponding to the positions of the connectors  25 , there are formed rectangular apertures  42 H 2  for the connectors  25  to protrude therethrough. 
         [0061]    In the backlight unit  49 , the connectors  25 , which electrically connect the mounting boards  21  to each other are placed in a state in which they do not interfere with the irradiation light region in which the LEDs  22  impart brightness to the diffusion plate  43 . LEDs  22  emit fractional light in the horizontal direction or a substantially horizontal direction as well, but such light is not expected to impart brightness to the diffusion plate  43  and is also weak, and thus is ignorable. It is assumed that the irradiation light region in this case is substantially the light area that is able to function as a backlight. Here, since the diffusion lenses  24  covers the LEDs  22 , light from the diffusion lenses  24  forms the irradiation light region. 
         [0062]    For the purpose of securely placing the connectors  25  in a state in which they do not interfere with the irradiation light region in which the LEDs  22  impart brightness to the diffusion plate  43 , the following shape is imparted to the connectors  25 . That is, among edges of the connectors  25 , at least one located on the side that faces an LED  22  is formed to be away from the LED  22 . 
         [0063]    In the illumination device of the first embodiment shown in  FIG. 2  and  FIG. 3 , the connectors  25  are denoted with an additional letter A. In the connectors  25 A, beveled parts  26  are formed at edges thereof, to thereby achieve an effect of keeping the edges away from the LEDs  22 . 
         [0064]    Since the connectors  25 A have their edges beveled into the beveled parts  26 , the connectors  25 A are placed in a state in which they do not interfere with the irradiation light region in which the LEDs  22  impart brightness to the diffusion plate  43 . As a result, uneven brightness attributable to the connectors  25 A is not observed in the diffusion plate  43 , and the quality of images displayed on the liquid crystal display panel  59  is improved. The size and the inclination angle of the beveled part  26  are so set as to help achieve the object of placing the edges of the connectors  25 A in a state in which they do not interfere with the irradiation light region in which the LEDs  22  impart brightness to the diffusion plate  43 . 
         [0065]    As shown in  FIG. 3 , in each of the connectors  25 A, three of the four sides of the top surface are each formed into the beveled part  26 , that is, excluding one side at which the connector  25 A contacts the counter connector  25 A. However, depending on the positional relationship between the matrix of the light emitting modules MJ and the connectors  25 A, it is possible, in each of the connectors  25 A, to form the beveled part  26  solely at the side that faces the nearest light emitting module MJ, with no beveled part  26  formed at either of the other two sides that are perpendicular to this side, that is, in  FIG. 3 , the upper and lower sides. 
         [0066]      FIG. 4  shows a second embodiment of the illumination device. The second embodiment is different from the first embodiment in connector shape. That is, each of connectors  25 B used in the second embodiment is formed such that a rounded part  27 , not a beveled part, is formed at an edge thereof that is located on a side that faces an LED  22 . 
         [0067]    The rounded part  27  is also effective in keeping edges away from the LEDs  22 . Thus, the connectors  25 B are placed in a state in which they do not interfere with the irradiation light region in which the LEDs  22  impart brightness to the diffusion plate  43 . As a result, uneven brightness attributable to the connectors  25 B is not observed in the diffusion plate  43 , and the quality of images displayed on a liquid crystal display panel  59  is improved. The size of the rounded part  27  is so set as to help achieve the object of placing the edges of the connector  25 B in a state in which they do not interfere with the irradiation light region in which the LEDs  22  impart brightness to the diffusion plate  43 . 
         [0068]    Like the beveled part  26  of the first embodiment, in each of the connectors  25 B, three of the four sides of the top surface may each be formed into the rounded part  27 , that is, excluding one side at which the connector  25 B contacts the counter connector  25 B, or it is possible to form the rounded part  27  solely at the side that faces the nearest light emitting module MJ. 
         [0069]      FIG. 5  shows a third embodiment of the illumination device. The third embodiment is different from the first and second embodiments in connector shape. That is, each of connectors  25 C used in the third embodiment is formed such that a stepped part  28  is formed at an edge thereof that is located on a side that faces an LED  22 . There is no particular limitation to the number of steps of which the stepped part  28  is formed. 
         [0070]    The stepped part  28  is also effective in keeping edges away from the LEDs  22 . Thus, the connectors  25 C are placed in a state in which they do not interfere with the irradiation light region in which the LEDs  22  impart brightness to the diffusion plate  43 . As a result, uneven brightness attributable to the connectors  25 C is not observed in the diffusion plate  43 , and the quality of images displayed on a liquid crystal display panel  59  is improved. The size and the inclination angle of the stepped part  28  are so set as to help achieve the object of placing the edges of the connectors  25 C in a state in which they do not interfere with the irradiation light region in which the LEDs  22  impart brightness to the diffusion plate  43 . 
         [0071]    In this case as well, like in the cases of the beveled part  26  and the rounded part  27 , three of the four sides of the top surface of each of the connectors  25 C may each be formed into the stepped part  28 , that is, excluding one side at which the connector  25 C contacts the counter connector  25 C, or it is possible to form the stepped part  28  solely at the side that faces the nearest light emitting module MJ. 
         [0072]      FIG. 6  shows a fourth embodiment of the illumination device. The approach taken in the fourth embodiment is different from those taken in the first to third embodiments. Specifically, in the fourth embodiment, connectors are formed with a reduced height to thereby shape them such that they do not interfere with an irradiation light region in which LEDs  22  impart brightness to a diffusion plate  43 . 
         [0073]    The connectors  25 D shown in  FIG. 6  are formed such that the height thereof itself is shorter than the maximum heights of the connectors of the first to third embodiments, and thus, the connectors  25 D are placed in a state in which they do not interfere with the irradiation light region in which the LEDs  22  impart brightness to the diffusion plate  43 . As a result, uneven brightness attributable to the connectors  25 D is not observed in the diffusion plate  43 , and the quality of images displayed on a liquid crystal display panel  59  is improved. 
         [0074]      FIG. 7  shows an example of the configuration of a television receiver in which a display device  69  is incorporated. A television receiver  89  is configured such that the display device  69  and a group of control boards  92  are housed in a cabinet composed of a front cabinet  90  and a rear cabinet  91  which are attached to each other, the cabinet being supported by a stand  93 . 
         [0075]    It is to be understood that the present invention may be carried out in any other manner than specifically described above as embodiments, and many modifications and variations are possible within the scope of the present invention. For example, the present invention is applicable to a connector for connecting mounting boards on which light emitting elements that are not covered with diffusion lenses are arranged. 
       INDUSTRIAL APPLICABILITY 
       [0076]    The present invention is widely applicable to illumination devices, display devices including the illumination devices, and television receivers provided with the display devices. 
       LIST OF REFERENCE SYMBOLS 
       [0000]    
       
         
           
               49  backlight unit 
               41  chassis 
               43  diffusion plate 
             MJ light emitting module 
               11  built-in reflection sheet 
               21  mounting board 
               22  LED 
               24  diffusion lens 
               25 ,  25 A,  25 B,  25 C,  25 D connector 
               26  beveled part 
               27  rounded part 
               28  stepped part 
               59  liquid crystal display panel 
               69  display device 
               89  television receiver