Abstract:
A direct-type backlight unit is provided for improving a dark area problem on the diffusion plate. The direct-type backlight unit includes an optical sheet; a diffusion plate for supporting the optical sheet; a bottom plate, disposed below the diffusion plate; a plurality of light emitting devices (LEDs), disposed between the diffusion plate and the bottom plate; a plurality of supporting elements, disposed between the diffusion plate and the bottom plate and fixed on the bottom plate, each supporting element including: a top portion having a light transmissive section through which light emitted by the LEDs pass; and a bottom portion, fixed on the bottom plate.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a direct-type backlight unit and a liquid crystal display using the same, and more particularly to a support structure which can improve a dark area problem. 
       BACKGROUND OF THE INVENTION 
       [0002]    Recently, a direct-type backlight unit using light emitting diodes (LEDs) is capable of local dimming, has high luminance uniformity and no mercury pollution problem, such that the direct-type backlight unit becomes popular. The direct-type backlight unit can be implemented by two conventional methods. In the first method, a surface mount type LED is adopted, but this method normally requires a large number of LEDs. On the other hand, in the second method, a surface mount type LED and a second lens are used together, which can reduce the number of LEDs used. However, no matter what method is used, it requires a support structure to support the diffusion plate for preventing deformation of the diffusion plate caused by thermal expansion, handling and transportation, which may reduce optical performance and damage LEDs if the height of a cavity accommodating the diffusion plate and the LEDs is low. 
         [0003]    Please refer to  FIG. 1 , it is a structure view of a conventional direct-type backlight unit. The backlight unit comprises: an optical sheet  940 , a diffusion plate  960 , a bottom plate  910 , a plurality of LEDs, and a plurality of support structures  930 . For convenience of explanation,  FIG. 1  only shows two LEDs  920  and a support structure  930 . 
         [0004]    The optical sheet  940  is disposed on the diffusion plate  960 ; the bottom plate  910  is disposed below the diffusion plate  960 ; the LEDs  920  are disposed between the diffusion plate  960  and the bottom plate  910 ; the support structure  930  is disposed between the diffusion plate  960  and the bottom plate  910 , and one end of the support structure  930  is fixed on the bottom plate  910  and the other end of the support structure  930  is contacted with the diffusion plate  960 . 
         [0005]    Please refer to  FIG. 3 , it is a luminous intensity distribution curve of the LED  920  with an additional secondary lens. The black line  8  in the  FIG. 3  shows an LED having bat-type light field with different luminous intensities in different angles. In addition, from  FIG. 3 , the light intensity in the two lateral sides is stronger than that of the middle portion in the LED. 
         [0006]    Please see  FIG. 2 , when the LEDs  920  emit light, the light is emitted into a bat shape. However, the light is blocked by the support structure  930  and can&#39;t pass through, resulting in a dark area  950  on the diffusion plate  960 . 
         [0007]    Therefore, it is required to provide a novel backlight unit and a crystal display device using the same in order to solve the dark area problem on the diffusion plate. 
       SUMMARY 
       [0008]    In order to overcome the dark area problem on the optical sheet caused by the support structure in the conventional backlight unit, one objective of the present invention is to provide a novel backlight unit which can solve the problem of light blocked by the support structure, resulting in a dark area on the diffusion plate and the downgrade of picture quality. 
         [0009]    In order to overcome the dark area on the diffusion plate caused by the support structure of the backlight unit in the conventional liquid crystal display, another objective of the present invention is to provide a novel backlight unit which can solve the problem of light blocked by the support structure, resulting in a dark area on the diffusion plate and the downgrade of picture quality. 
         [0010]    To achieve the above-mentioned objectives, the present invention is directed to provide a direct-type backlight unit which comprises an optical sheet; a diffusion plate for supporting the optical sheet; a bottom plate, disposed below the diffusion plate; a plurality of light emitting devices (LEDs), disposed between the diffusion plate and the bottom plate; and a plurality of supporting elements, disposed between the diffusion plate and the bottom plate and fixed on the bottom plate, each supporting element including: a top portion, having a light transmissive section through which light emitted by the LEDs pass; and a bottom portion, fixed on the bottom plate. 
         [0011]    In an embodiment, the volume proportion of the light transmissive section in the supporting element is greater than 20% of the total volume of the top portion. 
         [0012]    In an embodiment, the top portion of the supporting element is a spiral structure. 
         [0013]    In an embodiment, the top portion of the supporting element is a mesh structure. 
         [0014]    In an embodiment, the top portion and the bottom portion are integrally formed. 
         [0015]    To achieve the above-mentioned objectives, the present invention is directed to provide a liquid crystal display, which comprises a liquid crystal panel; and a direct-type backlight unit for providing light to the liquid crystal panel, including: an optical sheet; a diffusion plate for supporting the optical sheet; a bottom plate, disposed below the diffusion plate; a plurality of light emitting devices (LEDs), disposed between the diffusion plate and the bottom plate; and a plurality of supporting elements, disposed between the diffusion plate and the bottom plate and fixed on the bottom plate, each supporting element including: a top portion, having a top portion body and a light transmissive section through which light emitted by the LEDs pass; and a bottom portion, fixed on the bottom plate. 
         [0016]    In an embodiment, a volume proportion of the light transmissive section in the supporting element is greater than 20% of total volume of the top portion. 
         [0017]    In an embodiment, the top portion of the supporting element is a spiral structure. 
         [0018]    In an embodiment, the top portion of the supporting element is a mesh structure. 
         [0019]    In an embodiment, the top portion and the bottom portion are made of the same material and integrally formed. 
         [0020]    As a conclusion from the above, the effect of the direct direct-type backlight unit and a liquid crystal display using the same of the present invention lies in that: by using the light transmissive section of the support structure, the light emitted by the LEDs can pass through, so as to improve the dark area problem on the diffusion plate. 
         [0021]    The present invention will become more fully understood by reference to the following detailed description thereof when read in conjunction with the attached drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]      FIG. 1  is a partial structure view of a conventional direct-type backlight unit; 
           [0023]      FIG. 2  is a partial structure of a conventional direct-type backlight unit when LEDs emit light; 
           [0024]      FIG. 3  is a luminous intensity distribution curve of the LED with an additional secondary lens; 
           [0025]      FIG. 4  is a partial cross section view of a direct-type backlight unit according to a first embodiment of the present invention; 
           [0026]      FIG. 5  is a partial cross section view of a direct-type backlight unit according to a second embodiment of the present invention; 
           [0027]      FIG. 6  is a partial cross section view of a direct-type backlight unit according to a third embodiment of the present invention; and 
           [0028]      FIG. 7  is a perspective view of a liquid crystal display according to one embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0029]    Hereafter, the preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings. 
         [0030]      FIG. 4  is a partial cross section view of a direct-type backlight unit according to a first embodiment of the present invention. As shown in  FIG. 4 , the direct-type backlight unit  1  comprises optical sheets  140 , a diffusion plate  160 , a bottom plate  110 , a plurality of LEDs  120 , and a plurality of support structures  130 . For convenient explanation, in  FIG. 4 , two LEDs and one support structure  130  are shown. The support structure  130  includes a top portion  131  and a bottom portion  132 . 
         [0031]    The optical sheets  140  are disposed on the diffusion plate  160 ; the bottom plate  110  is disposed below the diffusion plate  160 ; the LEDs  120  are disposed between the diffusion plate  160  and the bottom plate  110 , and fixed on the bottom plate  110 ; the support structure  130  is disposed between the diffusion plate  160  and the bottom plate  110 , and the bottom portion  132  of the support structure  130  is fixed on the bottom plate  110 . The top portion  131  of the support structure  130  is a spiral structure and has a light transmissive section  133  through which light emitted from the LEDs  120  pass, such that the color of dark area  150  on the diffusion plate  160  become lighter. In addition, the volume ratio of the light transmissive section  133  is greater than 20% of the total volume of the top portion  131 . 
         [0032]    The optical sheets  140  stacked from bottom to top are a 0 degree prism sheet, a 90 degree prism sheet and a brightness enhancement film, but not limited thereto. The bottom plate  110  may be a reflective sheet in order to increase light use efficiency. The top portion  131  of the support structure  130  may be a spring or a hard material the same as that of the bottom portion  132 , such as an acrylic material, a plastic material or a metal material. 
         [0033]      FIG. 5  is a partial cross section view of a direct-type backlight unit according to a second embodiment of the present invention. As shown in  FIG. 5 , the direct-type backlight unit  2  comprises optical sheets  240 , a diffusion plate  260 , a bottom plate  210 , a plurality of LEDs  220 , and a plurality of support structures  230 . For convenient explanation, in  FIG. 5 , two LEDs  220  and one support structure  230  are shown. The support structure  230  includes a top portion  231  and a bottom portion  232 . 
         [0034]    The optical sheets  240  are disposed on the diffusion plate  260 ; the bottom plate  210  is disposed below the diffusion plate  260 ; the LEDs  220  are disposed between the diffusion plate  260  and the bottom plate  210 , and fixed on the bottom plate  210 ; the support structure  230  is disposed between the diffusion plate  260  and the bottom plate  210 , and the bottom portion  232  of the support structure  230  is fixed on the bottom plate  210 . The top portion  231  of the support structure  230  may be a mesh structure and has a light transmissive section  233  through which light emitted from the LEDs  220  pass, such that the color of dark area  250  on the diffusion plate  260  become lighter. In addition, the volume ratio of the light transmissive section  233  is greater than 20% of the total volume of the top portion  231 . The optical sheets  240  stacked from bottom to top are a 0 degree prism sheet, a 90 degree prism sheet and a brightness enhancement film, but not limited thereto. The bottom plate  210  may be a reflective sheet in order to increase light use efficiency. The top portion  231  of the support structure  230  may be a hard material the same as that of the bottom portion  232 , such as an acrylic material, a plastic material or a metal material. 
         [0035]      FIG. 6  is a partial cross section view of a direct-type backlight unit according to a third embodiment of the present invention. As shown in  FIG. 6 , the direct-type backlight unit  3  comprises optical sheets  340 , a diffusion plate  360 , a bottom plate  310 , a plurality of LEDs  320 , and a plurality of support structure  330 . For convenient explanation, in  FIG. 6 , two LEDs  320  and one support structure  330  are shown. The support structure  330  includes a top portion  331  and a bottom portion  332 . 
         [0036]    The optical sheets  340  are disposed on the diffusion plate  360 ; the bottom plate  310  is disposed below the diffusion plate  360 ; the LEDs  320  are disposed between the diffusion plate  360  and the bottom plate  310 , and fixed on the bottom plate  310 ; the support structure  330  is disposed between the diffusion plate  360  and the bottom portion  332  of the support structure  330  is fixed on the bottom plate  310 . The top portion  331  of the support structure  330  may be three columns for supporting the optical sheets  340  and have a light transmissive section  333  in-between, and the light emitted from the LEDs  320  can pass through the light transmissive section  333 , such that the color of dark area  350  on the diffusion plate  360  become lighter. In addition, the volume ratio of the light transmissive section  333  is greater than 20% of the total volume of the top portion  331 . 
         [0037]    The optical sheets  340  stacked from bottom to top are a 0 degree prism sheet, a 90 degree prism sheet and a brightness enhancement film, but not limited thereto. The bottom plate  310  may be a reflective sheet in order to increase light use efficiency. The top portion  331  of the support structure  330  may be a hard material the same as that of the bottom portion  332 , such as an acrylic material, a plastic material or a metal material. 
         [0038]      FIG. 7  is a perspective view of a liquid crystal display according to the present invention. The liquid crystal display  4  comprises a liquid crystal panel  440  and a direct-type backlight unit  420 . The direct-type backlight unit  420  is used as a light source for providing light to the liquid crystal panel  440  in order to display an image. In one embodiment of the present embodiment, the direct-type backlight unit  420  may be a direct-type backlight unit disclosed in one of the first embodiment, the second embodiment, and the third embodiment. Here, the liquid crystal display  4  further includes a mold frame, a front frame, a back cover, and heatsinks; however, it will not be described herein because the above-mentioned elements and related structures are conventional art. 
         [0039]    From the above disclosure, the advantage of the direct-type backlight unit and the liquid crystal display using the same lie in that: by using the light transmissive section of the support structure, the light emitted by the LEDs can pass through, so as to improve the dark area problem on the diffusion plate. 
         [0040]    Although the present invention is disclosed through the above embodiments, the embodiments are not intended to limit the present invention. Equivalent replacements like variations and modifications made by any person skilled in the similar art without departing from the spirit and scope of the present invention shall still fall within the protection scope of the present invention.