Abstract:
A backlight assembly capable of reducing light loss is presented. The backlight assembly includes a plurality of substrate units and a plurality of reflective members on the substrate units arranged to form an adjacent area where two reflective members are closest to each other. The adjacent area is on one of the substrate units. A display device incorporating the backlight assembly is also presented.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of Korean Patent Application No. 10-2009-0085516 filed on Sep. 10, 2009, the content of which is herein incorporated by reference in its entirety. 
       FIELD OF INVENTION 
       [0002]    The present invention refers generally to a backlight assembly for a display device. 
       BACKGROUND 
       [0003]    Liquid crystal display (LCD) devices are commonly used today as monitors for televisions, computers, laptops, mobile phones, and personal digital assistants (PDAs), among other devices. Typically, liquid crystal display devices include a display panel and a backlight assembly. The backlight assembly provides light to the display panel, and the display panel includes a layer of liquid crystal molecules sandwiched between transparent substrates to modulate light transmission, thereby displaying the desired images. 
         [0004]    There are a few different types of backlight assemblies, such as an edge-type backlight assembly where the light sources are positioned along one or more edges of a light guide plate, and a direct-type backlight assembly where the light sources are underneath the display panel. Typically, a backlight assembly includes a substrate unit to which light sources are coupled and a reflective member positioned on the substrate unit to redirect stray light toward the display panel. 
         [0005]    Even with the reflective member, some light is still lost (i.e., not directed toward the display panel to enhance image brightness). A way of further reducing light loss is desired. 
       SUMMARY 
       [0006]    In one aspect, the invention is a backlight assembly that includes a plurality of substrate units and a plurality of reflective members disposed on the substrate units, wherein at least one of the reflective members is larger than one of the substrate units and at least one of the reflective members is smaller than or the same size as one of the substrate units. 
         [0007]    In another aspect, the invention is a backlight assembly that includes a plurality of substrate units and a plurality of reflective members on the substrate units arranged to form an adjacent area where two reflective members are closest to each other, wherein the adjacent area is on one of the substrate units. 
         [0008]    In yet another aspect, the invention is a backlight assembly that includes a plurality of substrate units arranged next to one another and a reflective member arranged on the substrate units such that an edge of one of the substrate units and an edge of the reflective member covering the substrate unit are at non-overlapping locations. 
         [0009]    In yet another aspect, the invention is a display device that includes a panel that display images and a backlight assembly coupled to the panel and providing light to the panel. The backlight assembly includes a plurality of substrate units and a plurality of reflective members on the substrate units arranged to form an adjacent area where two neighboring reflective members are closest to each other, wherein the adjacent area is on one of the substrate units. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is an exploded perspective view of a display of the invention. 
           [0011]      FIG. 2  is a cross sectional view showing the coupling member of the display device shown in  FIG. 1 . 
           [0012]      FIG. 3  is a cross sectional view showing the coupling member extending through the coupling holes of the display device shown in  FIG. 1 . 
           [0013]      FIG. 4  is a cross sectional view of the substrate units and conventional reflective members in a conventional display device. 
           [0014]      FIG. 5   a  is a perspective view of the substrate units and the reflective members in accordance with the invention. 
           [0015]      FIG. 5   b  is a cross sectional view of the substrate units and reflective members of the embodiment shown in  FIG. 5   a.    
           [0016]      FIGS. 6   a  and  6   b  are perspective views showing substrate units and reflective members coupled to the substrate units in accordance with another embodiment of the present invention. 
           [0017]      FIG. 7  is a perspective view showing substrate units  150   a ,  150   b ,  150   c ,  150   d  and reflective members  140   a ,  140   b ,  140   c ,  140   d  in accordance with yet another embodiment of the invention. 
           [0018]      FIG. 8  is a cross sectional view showing substrate units and reflective members in accordance with yet another embodiment of the invention. 
           [0019]      FIG. 9  is a cross sectional view showing coupling holes formed on a reflective member, a substrate unit, and a lower receiving container, and a coupling member coupled to the coupling holes in accordance with another embodiment of the invention. 
           [0020]      FIG. 10  is a cross sectional view showing coupling holes formed on a reflective member, a substrate unit, and a lower receiving container, and a coupling member coupled to the coupling holes in accordance with an embodiment of the invention. 
           [0021]      FIG. 11A  is a perspective view showing a backlight assembly in accordance with another embodiment of the invention. 
           [0022]      FIGS. 11B and 11C  show details of the reflective cover in  FIG. 11A . 
       
    
    
     DETAILED DESCRIPTION 
       [0023]      FIG. 1  is an exploded perspective view of a display device  100  of the invention. As shown, the display device  100  includes a display panel assembly  30 , an upper receiving container  20 , and a backlight assembly  10 . The display panel assembly  30  includes a liquid crystal display panel  31 , a printed circuit board  36  and flexible films  34 ,  35  connecting the printed circuit board  36  to the liquid crystal display panel  31 . The liquid crystal display panel  31  may include an upper substrate  33 , a lower substrate  32 , and a liquid crystal layer disposed between the two substrates  32 ,  33 . The printed circuit board  36  may include a plurality of chips generating signals for driving the liquid crystal panel  31 , and the flexible films  34 ,  35  may transfer the signals to the liquid crystal panel  31 . 
         [0024]    The backlight assembly  10  includes a middle frame  110 , optical sheets  120 , an optical plate  130 , reflective members  140   a ,  140   b , substrate units  150   a ,  150   b  and a lower receiving container  160 . 
         [0025]    The substrate units  150   a ,  150   b  includes a substrate  152  and a plurality of point light sources  154  disposed on the substrate  152 . A circuit may be formed on the substrate  152 . The point light sources  154  may be mounted on the substrate  152  and connected to the circuit. The shape of the substrate  152  comprises a rectangular frame shape. The upper surface of the substrate units  150   a ,  150   b  may include a reflective material. For example, the upper surface of the light surface blocks  150   a ,  150   b  can be coated by a reflective material. The point light sources  154  comprise light emitting diodes (LEDs). The point light sources  154  may be disposed on the substrate  152  in various arrangements to improve luminance uniformity of the backlight assembly  10 . For example, the point light sources  154  may be disposed uniformly on the substrate  152  in a matrix or a zigzag configuration. 
         [0026]    The substrate units  150   a ,  150   b  are disposed adjacent to each other. A neighboring area  153  between the substrate units  150   a ,  150   b  may include a gap, as it is difficult to assemble the substrate units  150   a ,  150   b  without a gap in a real mass-production line. 
         [0027]    The reflective members  140   a ,  140   b  are disposed on the substrate units  150   a ,  150   b . The reflective members  140   a ,  140   b  reflect the light generated by the point light sources  154  that propagates away from the display panel assembly  30 . The number of the reflective members  140   a ,  140   b  may be the same as the number of the substrate units  150   a ,  150   b . Each of the reflective members  140   a ,  140   b  includes a plurality of openings  142  corresponding to the point light sources  154  to expose the point light sources  154 . Each of the substrate units  150   a ,  150   b  further includes a coupling hole  181  to be coupled to the coupling member  170 . The reflective members  140   a ,  140   b  are coupled to the substrate units  150   a ,  150   b.    
         [0028]    Adhesive materials may be disposed between the reflective members  140   a ,  140   b  and the substrate units  150   a ,  150   b  to keep the parts in place. 
         [0029]    The substrate units  150   a ,  150   b  and the reflective members  140   a ,  140   b  are coupled to the lower receiving container  160  by the coupling member  170 . The coupling member  170  may be formed of a reflective material, such as polycarbonate, although this is not a limitation of the invention. Polycarbonate has good reflectivity, heat-resistance and intensity. The coupling member  170  may include a screw or an adhesive tape. 
         [0030]    The backlight assembly  10  may further include a heat spreader (not shown) disposed between the substrate units  150   a ,  150   b  and the lower receiving container  160 . The heat spreader may include a coupling mechanism formed on an area of the heat spreader corresponding to the coupling holes  181 ,  182 ,  183 . 
         [0031]    The diffuser plate  130  is disposed over the reflective members  140   a ,  140   b  and diffuses the light generated by the substrate units  150   a ,  150   b.    
         [0032]    The optical sheets  120  are disposed over the diffuser plate  130  and diffuse and collimate the light supplied by the diffuser plate  130 . The optical sheets  120  may include a diffuser sheet and a prism sheet. 
         [0033]    The middle frame  110  is disposed over the diffuser plate  130  and coupled to the lower receiving container  160  to receive the diffuser plate  130 , the optical sheets  120 , the reflective members  140   a ,  140   b  and the substrate units  150   a ,  150   b . The display panel assembly  30  is disposed on the middle frame  110 . 
         [0034]    The lower receiving container  160  includes a base plate and a plurality of sidewalls extending from the base plate to receive the diffuser plate  130 , the optical sheets  120 , the reflective members  140   a ,  140   b  and the substrate units  150   a ,  150   b . The coupling hole  183  is formed on the base plate. 
         [0035]    The upper receiving container  20  covers the edges of the display panel assembly  30  and is coupled to the lower receiving container  160 . 
         [0036]      FIG. 2  is a cross sectional view showing the coupling member  170  of the display device shown in  FIG. 1 .  FIG. 3  is a cross sectional view showing the coupling member  170  extending through the coupling holes of the display device shown in  FIG. 1 . 
         [0037]    Referring to  FIGS. 2 and 3 , the coupling member  170  includes a head portion  172 , a pillar portion  174  protruding from the head portion  172 , and a hook portion  176  extending from the pillar portion  174 . The outer surface of the hook portion  176  includes an upper inclined surface  176   a  and a lower inclined surface  176   b . The shape of the head portion  172  may be a circle (when viewed from the top). The width of the pillar portion  174  is smaller than the diameter of the head portion  172 . Coupling holes  181 ,  182 , 183  are formed on the reflective members  140   a ,  140   b , the substrate units  150   a ,  150   b  and the lower receiving container  160 . The diameter W 2  of the coupling holes  181 ,  182 ,  183  are smaller than the maximum width Wmax of the hook portion  176 . The width W of the hook portion  176  gets smaller when the hook portion  176  passes through the coupling holes  181 ,  182 ,  183  and bends toward the pillar portion  174 . The coupling holes  181  may be formed on areas close to the edges of the reflective members  140   a ,  140   b . Coupling holes  182  may be formed on areas between the point light sources  154 . The coupling holes  181 ,  182 , and  183  are aligned so that the coupling member  170  can extend through all three layers of holes to fix the parts together. 
         [0038]      FIG. 4  is a cross sectional view of the substrate units  150   a ,  150   b  and conventional reflective members  240   a ,  240   b  in a conventional display device. As shown, the size of the reflective members  240   a ,  240   b  and the size of the substrate units  150   a ,  150   b  corresponding to the reflective members  240   a ,  240   b  are substantially the same. The neighboring area  153  of the substrate units  150   a ,  150   b  is not covered by the reflective members  240   a ,  240   b . As a result, most of the light that falls into the gap between the conventional reflective members  240   a ,  240   b  end up propagating into the neighboring area  153  that includes a gap between the substrate units  150   a ,  150   b . This localized loss of light causes a dark area in the image that is displayed. 
         [0039]    The gap (a) may be larger than 0.3 mm. As can be seen, the gap between the light reflective members  240   a ,  240   b  (i.e., the gap in the adjacent area) is larger than 0.3 mm. During the assembly process of the backlight assembly, another gap may form between an end of the substrate unit  150   a / 150   b  and an end of the reflective member  240   a / 240   b  that covers the substrate unit  150   a / 150   b . The gap (b) between an end of the substrate unit  150   a / 150   b  and an end of the reflective member  240   a / 240   b  can be controlled more precisely than the gap (a) between the substrate units  150   a ,  150   b . For example, the gap (b) may be larger than 0.2 mm. Since the gap (a) between the substrate units  240   a ,  240   b  may be 0.4 mm or longer, so the gap between the reflective members  240   a  and  240   b  may be larger than 0.7 mm (0.3 mm+2(0.2 mm)). 
         [0040]    In the conventional backlight assembly of  FIG. 4 , one of the ways light is lost is by falling into the gap between reflective sheets  240   a ,  240   b . As the gap between the substrates  150   a ,  150   b  overlaps the gap between the reflective sheets  240   a ,  240   b , the combined depth of the gaps is deep. Furthermore, there is no reflective material at the bottom of the gap between the substrates  150   a ,  150   b , making it unlikely that the light that goes into this deep gap will be recovered. The deep gap resulting from the combination of the gap at the reflective layer and the gap at the substrate unit layer is responsible for significant light loss. 
         [0041]    Covering the gap between the substrate units  150   a ,  150   b  with a reflective member that is large enough to cover multiple substrate units has been contemplated. However, this is likely to be an impractical solution because the large size of the reflective member would make it difficult to attach the reflective member to a plurality of substrate units without forming wrinkles Furthermore, one of the factors that affect the price of the reflective member is its size. So, use of large reflector in a backlight assembly translates to an increase in the manufacturing cost. Moreover, when one of the substrate units stops to function properly and needs replacing, the reflective member has to be removed to change the substrate unit to a new one. Through the removal and reattachment process, the reflective member can become easily become damaged. 
         [0042]    The invention offers a way to eliminate or reduce light loss to the deep gap that is approximately as deep as the combined thicknesses of the substrate layer and the reflective layer without the disadvantages associated with using a large reflective member. For example, the invention includes a backlight assembly that uses a plurality of light reflective members  140   a ,  140   b  to reduce light loss. The sizes of the reflective members may vary so that the gaps in the reflective layers do not align with the gaps in the substrate layer. This way, light that enters the gap in the reflective layer will only travel a short way down before being reflected back out by the reflective coating on the substrate surface. By avoiding the use of a large reflective member, high manufacturing cost and complicated substrate replacement/repair process can be avoided. 
         [0043]      FIG. 5   a  is a perspective view of the substrate units  150   a ,  150   b  and the reflective members  140   a ,  140   b  of the invention. In this embodiment, the reflective members  140   a ,  140   b  are of different sizes. The reflective members  140   a ,  140   b  are disposed close to each other, forming an adjacent area  143 . In this embodiment, a first reflective member  140   a  covers the neighboring area  153  of the substrate units  150   a ,  150   b . The first reflective member  140   a  is larger than a first substrate unit  150   a  that it covers, and a second reflective member  140   b  is smaller than a second substrate unit  150   b  that is covered by the second reflective member  140   b . The reflective members  140   a ,  140   b  do not overlap each other, making the upper surface of the reflective members  140   a ,  140   b  substantially flat. The adjacent area  143  of the reflective members  140   a ,  140   b  is disposed on one of the substrates units, so the adjacent area  143  of the reflective members  140   a ,  140   b  does not align or overlap with the neighboring area  153  of the substrate units  150   a ,  150   b.    
         [0044]    The adjacent area  143  of the reflective member  140   a ,  140   b  may include a gap. The reflective members  140   a ,  140   b  comprise a reflective sheet or film, so the reflective members  140   a ,  140   b  are thinner and more flexible than the substrate units  150   a ,  150   b . The gap in the adjacent area  143  of the reflective members  140   a ,  140   b  can be controlled more precisely than the gap in the neighboring area  153  of the substrate units  150   a ,  150   b  during the assembly process because of the characteristic of the reflective members  140   a ,  140   b.    
         [0045]      FIG. 5   b  is a cross sectional view of the substrate units  150   a ,  150   b  and reflective members  140   a ,  140   b  of the embodiment shown in  FIG. 5   a . As shown, one of the reflective members  140   a ,  140   b  covers the neighboring area  153  between the substrate units  150   a ,  150   b . The adjacent area  143  between the light reflective members  140   a ,  140   b  may include a gap (c). The gap (c) may be reduced to about 0.2 mm. So the gap (c) between the reflective members  140   a ,  140   b  according to the present embodiment is narrower than the gap between the reflective members  240   a ,  240   b  of the conventional display device shown on  FIG. 4 . 
         [0046]    The gap (c) between the reflective members  240   a ,  240   b  is disposed on a single substrate  152 . As described above, the upper surface of the substrate  152  may include a reflective material, so the upper surface of the substrate  152  reflects any light that propagates into the gap (c). Also, the reflective members  140   a ,  140   b  may be thinner than the substrates  152 , making the gap (c) shallower than the gap (b). With the reduced width and depth of gap (c) relative to the gap (a+2b) in the conventional device, the effect of a dark area caused by the gap between the reflective members is reduced. 
         [0047]      FIGS. 6   a  and  6   b  are perspective views showing substrate units  150   a ,  150   b ,  150   c  and reflective members  140   a ,  140   b ,  140   c  coupled to the substrate units  150   a ,  150   b ,  150   c  in accordance with another embodiment of the present invention. The display device shown in  FIGS. 6   a  and  6   b  includes three substrate units  150   a ,  150   b ,  150   c . Three reflective members  140   a ,  140   b ,  140   c  are disposed on the substrate units  150   a ,  150   b ,  150   c.    
         [0048]    In the embodiment of  FIG. 6   a , the reflective members  140   a ,  140   b ,  140   c  include first reflective members  140   a ,  140   c  larger than and covering the substrate units  150   a ,  150   c  and a second reflective member  140   b  smaller than and covering a portion of the substrate unit  150   b . The first reflective members  140   a ,  140   c  cover the neighboring areas  153  at the interfaces between substrate units  150   a ,  150   b ,  150   c.    
         [0049]    In the embodiment of  FIG. 6   b , the second reflective member  140   b  is larger than the substrate unit  150   b  that it covers and disposed between the first reflective members  140   a ,  140   c  smaller than the substrate units  150   a ,  150   c  corresponding to the first reflective members  140   a ,  140   c . The second reflective member  140   b  covers the neighboring areas  153  at the interfaces between the substrate units  150   a ,  150   b ,  150   c.    
         [0050]    The reflective members  140   a ,  140   b ,  140   c  do not overlap each other and the adjacent areas  143  at the interfaces of the reflective members  140   a ,  140   b ,  140   c  do not overlap with the neighboring areas  153  of the substrate units  150   a ,  150   b ,  150   c . The adjacent areas  143  and the neighboring areas  153  are at different locations in plan view. 
         [0051]      FIG. 7  is a perspective view showing substrate units  150   a ,  150   b ,  150   c ,  150   d  and reflective members  140   a ,  140   b ,  140   c ,  140   d  in accordance with yet another embodiment of the invention. As shown, the display device includes four substrate units  150   a ,  150   b ,  150   c ,  150   d  forming four neighboring areas  153 . Four reflective members  140   a ,  140   b ,  140   c ,  140   d  are disposed on the substrate units  150   a ,  150   b ,  150   c ,  150   d . The reflective members  140   a ,  140   b ,  140   c ,  140   d  include first reflective members  140   b ,  140   c  larger than the substrate units  150   b ,  150   c  and corresponding to the first reflective members  140   b ,  140   c  and second reflective members  140   a ,  140   d  smaller than the substrate units  150   a ,  150   d  and corresponding to the second reflective members  150   a ,  150   c . The bigger first reflective members  140   b ,  140   c  cover the boundaries  153 . 
         [0052]    The substrate units  150   a ,  150   b ,  150   c ,  150   d  have rectangular shapes. The first reflective members  140   b ,  140   c  have irregular pentagonal shapes that look like rectangles with a corner cut off. The second reflective members  140   a ,  140   d  have rectangular shapes. The first and second reflective members  140   a ,  140   b ,  140   c ,  140   d  do not overlap. The adjacent areas  143  of the reflective members  140   a ,  140   b ,  140   c ,  140   d  do not overlap or align with the neighboring areas  153  of the substrate units  150   a ,  150   b ,  150   c ,  150   d.    
         [0053]      FIG. 8  is a cross sectional view showing substrate units  150   a ,  150   b ,  150   c  and reflective members  140   a ,  140   b ,  140   c  in accordance with yet another embodiment of the invention. As shown, the reflective members  140   a ,  140   b ,  140   c  overlap each other in the adjacent areas  143  where the reflective members  140   a ,  140   b ,  140   c  meet. The reflective members  140   a ,  140   b ,  140   c  cover the neighboring areas  153  of the substrate units  150   a ,  150   b ,  150   c . In the example shown, the reflective member  140   c  is smaller than the reflective members  140   a  and  140   b , which are of substantially the same size. 
         [0054]      FIG. 9  is a cross sectional view showing coupling holes formed on a reflective member  140   a , a substrate unit  150   a  and a lower receiving container  160 , and a coupling member coupled to the coupling holes in accordance with another embodiment of the invention. As shown, the lower receiving container  160  includes a coupling hole  183 . A protruding portion  184  protruding from an inner surface of the coupling hole  183  contacts the hook portion  176  of the coupling member  170 . According to the present embodiment, the hook portion  176  of the coupling member  170  is bent toward the pillar portion  174  when compressed by the coupling hole  183 . 
         [0055]      FIG. 10  is a cross sectional view showing coupling holes formed on a reflective member  140   a , a substrate unit  150   a  and a lower receiving container  160 , and a coupling member coupled to the coupling holes in accordance with an embodiment of the invention. As shown, the hook portion  176  of the coupling member  170  includes at least one flat surface that contacts the bottom surface of the protruding portion  184 . Due to the increased contact area between the lower receiving container  160  and the hook portion  176 , the coupling member  170  is coupled the coupling hole  184  more securely. The head portion  172  covers the adjacent area  143  and the neighboring area  153  to prevent light loss. 
         [0056]      FIG. 11A  is a perspective view showing a backlight assembly in accordance with another embodiment of the invention. Details of a reflective cover  190  in  FIG. 11A  are shown in  FIGS. 11B and 11C . As shown, the reflective cover  190  includes a plate  191  and a plurality of coupling members  192  extending from the plate  191 . The lower receiving container  160  includes coupling holes  183  through which the coupling members  192  extend. 
         [0057]    The plate  191  is wide enough to cover the neighboring area  153 . The coupling mechanism, which may be similar to the coupling mechanism  170  shown in  FIG. 3 , extends through the neighboring area  153  and the coupling holes  183  to fix the plate  190  to the receiving container ( 184 ). The reflective cover  190  covers the neighboring area  153  and fixes the reflective members  140   a ,  140   b  and the substrate units  150   a ,  150   b  to the receiving container  184 . The reflective cover  190  may be made of polycarbonate. Although  FIG. 11B  shows the ends of the reflective members  140   a  and  140   b  as being flush with the ends of the substrate units  15   a  and  150   b , respectively, for simplicity of illustration, the reflective cover  190  can be used for any other situation. The plate  191  may be made wide enough to cover any gap between the reflective member  140   a ,  140   b  and any gap between the substrate units  150   a ,  150   b.    
         [0058]    Although the foregoing invention has been described in some detail by way of illustration and examples for purposes of clarity and understanding, it will be apparent that modifications and alternative embodiments of the invention are contemplated which do not depart from the spirit and scope of the invention as defined by the foregoing teachings and appended claims.