Abstract:
An exemplary backlight module ( 4 ) includes a frame ( 44 ) and a light guide plate ( 40 ) received in the frame. The light guide plate has a top light emitting surface ( 404 ). The frame and an end ( 408 ) of the light guide plate cooperatively define a gap ( 46 ) therebetween. The gap has a narrowed exit ( 462 ) adjacent to the light emitting surface, whereby light beams are prevented from either or both of leaking out from the end of the light guide plate and leaking out from the gap via the narrowed exit.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to backlight modules such as those used in liquid crystal displays (LCDs), and more particularly to a backlight module with a thermal expansion gap configured to prevent excess light exiting therefrom.  
       GENERAL BACKGROUND  
       [0002]     Liquid crystal displays are commonly used as display devices for compact electronic apparatuses, because they not only provide good quality images but are also very thin. Because liquid crystal molecules in a liquid crystal display do not emit any light themselves, the liquid crystal molecules have to be lit by a separate light source so as to clearly and sharply display text and images. Therefore, liquid crystal displays usually require a backlight module.  
         [0003]     Referring to  FIG. 8 , a typical backlight module  8  includes a light guide plate  80 , a light source  82 , and a plastic frame  84 . The light guide plate  80  and the light source  82  are received in the plastic frame  84 . The light guide plate  80  includes a side light incident surface  802 , a top light emitting surface  804  adjoining the light incident surface  802 , a bottom surface  806 , and a side surface  808  at an opposite side of the light guide plate  80  to the light incident surface  802 . The light source  82  is located adjacent to the light incident surface  802  of the light guide plate  80 , and includes an illuminator  822  and a reflector  824  partially enclosing the illuminator  822 . The plastic frame  84  has an inner side surface  842  opposite and parallel to the side surface  808  of the light guide plate  80 . The inner side surface  842  and the side surface  808  are both planar. A gap  86  is defined between the side surface  808  and the inner side surface  842 . The gap  86  provides room for the plastic frame  84  and the light guide plate  80  to expand during stability tests performed on the backlight module  8  and when the backlight module  8  is used in high temperature conditions.  
         [0004]     In operation of the backlight module  8 , light beams emitted from the illuminator  822  are transmitted into the light guide plate  80  through the light incident surface  802 , and are converted by the light guide plate  80  to form a surface light source at the light emitting surface  804 . During this process, some light beams may be emitted from the side surface  808  and strike the inner side surface  842  of the plastic frame  84 . Some of the light beams striking the inner side surface  842  are absorbed thereat, and other light beams are reflected back into the gap  86  and may emit from the backlight module  8  via the gap  86 . When this occurs, the brightness of the backlight module  8  in an area between the light guide plate  80  and the plastic frame  84  appears stronger than would otherwise be the case. That is, a uniformity of brightness of the backlight module  8  is degraded. Moreover, some of the light beams emitted from the side surface  808  of the light guide plate  80  transmit to a bottom of the gap  86  and are absorbed by the plastic frame  84  thereat. Such light beams are lost, and thus a light utilization ratio of the backlight module  8  is decreased.  
         [0005]     What is needed, therefore, is a backlight module that can overcome the above-described deficiencies. What is also need is a liquid crystal display employing such a backlight module.  
       SUMMARY  
       [0006]     In a preferred embodiment, a backlight module includes a frame and a light guide plate received in the frame. The light guide plate has a top light emitting surface. The frame and an end of the light guide plate cooperatively define a gap therebetween. The gap has a narrowed exit adjacent to the light emitting surface, whereby light beams are prevented from either or both of leaking out from the end of the light guide plate and leaking out from the gap via the narrowed exit. The end can also be jagged for preventing light beams from leaking out from the light guide plate therethrough.  
         [0007]     Other aspects, advantages and novel features will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]     The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present backlight module and liquid crystal display. In the drawings, like reference numerals designate corresponding parts throughout various views, and all the views are schematic.  
         [0009]      FIG. 1  is a side, cross-sectional view of a backlight module according to a first embodiment of the present invention.  
         [0010]      FIG. 2  is a side, cross-sectional view of a backlight module according to a second embodiment of the present invention.  
         [0011]      FIG. 3  is a side, cross-sectional view of a backlight module according to a third embodiment of the present invention.  
         [0012]      FIG. 4  is a side, cross-sectional view of a backlight module according to a fourth embodiment of the present invention.  
         [0013]      FIG. 5  is a side, cross-sectional view of a backlight module according to a fifth embodiment of the present invention.  
         [0014]      FIG. 6  is a side, cross-sectional view of a backlight module according to a sixth embodiment of the present invention.  
         [0015]      FIG. 7  is an exploded, side cross-sectional view of a liquid crystal display according to a seventh embodiment of the present invention.  
         [0016]      FIG. 8  is a side, cross-sectional view of a conventional backlight module. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0017]     Reference will now be made to the drawings to describe the preferred embodiments in detail. [ 0018 ] Referring to  FIG. 1 , a backlight module  1  according to a first embodiment of the present invention includes a light guide plate  10 , a light source  12 , and a frame  14 . The light guide plate  10  and the light source  12  are received in the frame  14 . The light guide plate  10  includes a side light incident surface  102 , a top light emitting surface  104  perpendicular to the light incident surface  102 , a bottom surface  106 , and a side surface  108  at an opposite side of the light guide plate  10  to the light incident surface  102 . The side surface  108  is planar, and maintains a predetermined acute angle relative to the light emitting surface  104 . The light source  12  is located adjacent to the light incident surface  102 , and includes an illuminator  122  and a reflector  124  partially enclosing the illuminator  122 . The frame  14  has an inner side surface  142  adjacent to the side surface  108 . The inner side surface  142  is planar, and is perpendicular to the light emitting surface  104 . Thus a right-angled substantially trapezoid-shaped gap  16  is defined between the light guide plate  10  and the frame  14 . The gap  16  has a narrow top exit  162  coplanar with the light emitting surface  104 , and a wide bottom exit  164  opposite to the top exit  162 . The light guide plate  10  can be made from polycarbonate (PC) or polymethyl methacrylate (PMMA), and can be manufactured by an injection molding method. The frame  14  can be made from white polycarbonate, plastic, or any other suitable material. The illuminator  122  can be a cold cathode fluorescent lamp (CCFL), or at least one light emitting diode (LED).  
         [0018]     In operation, light beams emitted from the illuminator  122  are transmitted through the light incident surface  102  into the light guide plate  10 , and are then converted by the light guide plate  10  to serve as a surface light source at the light emitting surface  104 . During this process, some light beams strike the side surface  108  of the light guide plate  10 , with incident angles of the light beams being greater than a critical angle of the side surface  108 . With the above-described configuration, substantially total reflection occurs at the side surface  108 , whereby the light beams are prevented from leaking out from the side surface  108 . Thus a brightness of the backlight module  1  at the top exit  162  between the light guide plate  10  and the frame  14  is not unduly strong, and a high level of brightness uniformity of the backlight module  1  can be achieved. Moreover, because the light beams are prevented from leaking out from the light guide plate  10  through the side surface  108 , there is little or no loss of light at the bottom exit  164 . Instead, the light reflected at the side surface  108  transmits within the light guide plate  10  toward the light emitting surface  104 . Thus the overall light utilization ratio of the backlight module  1  is increased.  
         [0019]     Referring to  FIG. 2 , a backlight module  2  according to a second embodiment of the present invention is similar to the backlight module  1 . However, a light guide plate  20  of the backlight module  2  has an outwardly curved side surface  208 . The backlight module  2  has advantages similar to those described above in relation to the backlight module  1 .  
         [0020]     Referring to  FIG. 3 , a backlight module  3  according to a third embodiment of the present invention is similar to the backlight module  1 . However, a light guide plate  30  of the backlight module  3  has a jagged side surface  308 , thus defining a plurality of V-shaped grooves  305  thereat. When light beams in the light guide plate  30  strike the side surface  308 , most of the light beams are reflected back by surface portions defining the V-shaped grooves  305 , and transmit toward a top light emitting surface  304  perpendicular to the side surface  308  or a bottom surface  306  opposite to the light emitting surface  304 . That is, most of the light beams can be prevented from leaking out from the side surface  308  of the light guide plate  30 .  
         [0021]     Referring to  FIG. 4 , a backlight module  4  according to a fourth embodiment of the present invention is similar to the backlight module  1 . However, a light guide plate  40  of the backlight module  4  includes a top light emitting surface  404 , a bottom surface  406  opposite to the light emitting surface  404 , and a side surface  408  between the light emitting surface  404  and the bottom surface  406 . The side surface  408  is planar, and is perpendicular to the light emitting surface  404  and the bottom surface  406 . A frame  44  of the backlight module  4  has an inner side surface  442  adjacent to the side surface  408  of the light guide plate  40 . The inner side surface  442  is planar, and maintains a predetermined obtuse angle relative to the light emitting surface  404  of the light guide plate  40 . Thus, a right-angled substantially trapezoid-shaped gap  46  is defined between the light guide plate  40  and the frame  44 . The gap  46  has a narrow top exit  462  coplanar with the light emitting surface  404 , and a wide bottom exit  464  opposite to the top exit  462 .  
         [0022]     With this configuration, at least some if not most of light beams that emit from the side surface  408  strike the inner side surface  442 . The light beams that strike the inner side surface  442  are either absorbed or reflected. Most of the reflected light beams transmit either toward a bottom surface (not labeled) of a frame portion of the backlight module  4  that adjoins the frame  44 , or back into the light guide plate  40  through the side surface  408 . Most of the light beams that strike the bottom surface of the frame portion are either absorbed, or reflected toward the inner side surface  442  or back into the light guide plate  40  through the side surface  408 . That is, most of the light beams in the gap  46  do not leak out from the top exit  462  thereof. Thus, a brightness of the backlight module  4  at the top exit  462  between the light guide plate  40  and the frame  44  is not unduly strong, and a high level of brightness uniformity can be achieved for the backlight module  4 . Moreover, at least some of the light beams that emit from the side surface  408  of the light guide plate  40  are directly or indirectly reflected back into the light guide plate  40  through the side surface  408 . As a result, the light utilization ratio of the backlight module  4  is improved.  
         [0023]     Referring to  FIG. 5 , a backlight module  5  according to a fifth embodiment of the present invention is similar to the backlight module  4 . However, a frame  54  of the backlight module  5  has an outwardly curved inner side surface  542 . The backlight module  5  has advantages similar to those described above in relation to the backlight module  4 .  
         [0024]     Referring to  FIG. 6 , a backlight module  6  according to a sixth embodiment of the present invention is similar to the backlight module  4 . However, a frame  64  of the backlight module  6  has a jagged inner side surface  642 , thus defining a plurality of V-shaped grooves  644  thereat. When light beams from a light guide plate  60  of the backlight module  6  strike the inner side surface  642 , the light beams are either absorbed or reflected by surface portions defining the V-shaped grooves  644 . Most of the reflected light beams transmit either toward a bottom surface (not labeled) of a frame portion of the backlight module  6  that adjoins the frame  64 , or back into the light guide plate  60  through a side surface (not labeled) thereof. Most of the light beams that strike the bottom surface of the frame portion are either absorbed, or reflected toward the inner side surface  642  or back into the light guide plate  60  through the side surface thereof. That is, most of the light beams in a gap  66  between the light guide plate  60  and the inner side surface  642  do not leak out from a top exit (not labeled) of the gap  66 .  
         [0025]     Referring to  FIG. 7 , a liquid crystal display  7  according to a seventh embodiment of the present invention is shown. The liquid crystal display  7  includes a liquid crystal panel  68  and the above-described backlight module  1 . The backlight module  1  is positioned adjacent to the liquid crystal panel  68 . The liquid crystal display  7  has a high level of brightness uniformity. In alternative embodiments, the backlight module  1  can be replaced with any one of the above-described backlight modules  2  to  6 .  
         [0026]     Further or alternative embodiments may include the following. In one example, the light guide plate may include two or three side surfaces, each oriented at an oblique angle relative to the light emitting surface thereof. In another example, the light guide plate may include two or three side surfaces each perpendicular to the light emitting surface. In such case, the frame receiving the light guide plate can have two or three oblique inner side surfaces adjacent to the side surfaces of the light guide plate respectively. In a further example, a plurality of diffusing dots may be arranged at the bottom surface of the light guide plate for improving the uniformity of brightness of the backlight module. In still further examples, any of the above-described inner side surfaces of the respective frames and any of the side surfaces of the above-described light guide plates may be combined in a single backlight module. With such configurations, light beams leaking out from respective gaps can be further decreased or even eliminated.  
         [0027]     It is believed that the present embodiments and their advantages will be understood from the foregoing description, and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the examples hereinbefore described merely being preferred or exemplary embodiments of the invention.