Abstract:
A backlight module ( 3 ) includes a light source group ( 31 ) and a light guide plate ( 32 ). The light source group includes at least a light sources (not labeled), the light guide plate has a light input surface ( 321 ) for receiving light and a light output surface ( 322 ) for emitting light. The light source group faces the light input surface, which is a curved and its curvature matches with the light distribution of the light source group.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a backlight module, and particularly to one used in a liquid crystal display (LCD).  
           [0003]    2. Description of Prior Art  
           [0004]    In a backlight type LCD, light beams are applied to a display member from the rear of the display member. Portions of the display member selectively allow transmission of the light beams therethrough, while other portions are opaque and prevent transmission of the light beams. The transmitted light beams are seen by an observer as displayed information. Important characteristics of the LCD include its long working lifetime, low power consumption, and brightness and uniformity of the emitted light rays. High brightness and uniform illumination help an LCD provide good display performance.  
           [0005]    Referring to FIG. 6, a conventional backlight module  1  comprises a light source group  11  and a light guide plate  12 . The light source group  11  comprises several light emitting diodes (LEDs) (not labeled). The light guide plate  12  has a light input surface  121  and a light output surface  122 . Because each LED emits light over a certain range of angles, a scope of illumination  13  of the light source group  11  is the sum of the contributions of each LED&#39;s output light. Nevertheless, the illumination scope generally cannot cover the whole light guide plate  12 . The hatched areas  14  in FIG. 6 show parts of the light guide plate  12  that are not illuminated. These parts are known as ‘dark zones.’ The existence of dark zones diminishes the performance of the backlight module  1 .  
           [0006]    Referring to FIG. 7 and FIG. 8, China Patent No. 98206129 issued on Nov. 10, 1999 discloses another kind of backlight module  2 . The backlight module  2  comprises a light source group  21  and a light guide plate  22 . The light source group  21  comprises three light emitting diodes (LEDs, not labeled), and the light guide plate  22  has a light input surface  221  and a light output surface  222 . The light input surface  221  defines three U-shaped grooves, each matching with a corresponding LED. Thus each LED faces a concave surface of the corresponding U-shaped groove, and light beams passing through the concave surface cover a larger area of the light guide plate  22  in comparison with the above-described backlight module  1 . Even so, the backlight module  2  still exhibits dark zones  24 .  
           [0007]    It is desired to provide a backlight system and a light guide plate used therein which overcome the above-described problems.  
         SUMMARY OF THE INVENTION  
         [0008]    An object of the present invention is to provide a backlight module which enjoys full illumination of a light guide plate thereof, there being no dark zones in the light guide plate.  
           [0009]    To achieve the above object, a backlight module of present invention comprises a light source group and a light guide plate. The light source group comprises a plurality of point light sources such as LEDs. The light guide plate has a light input surface for receiving light, and a light output surface for emitting light. The light source group faces the light input surface. The light input surface is curved such that it matches a distribution of light of the light source group.  
           [0010]    Because the light input surface matches the light distribution of the light source group, divergent light emitted from the light source group reaches the entire light input surface. Thus the light guide plate is entirely illuminated, and has no dark zones.  
           [0011]    Other objects, advantages, and novel features of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings, in which: 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    [0012]FIG. 1 is a top elevation of a backlight module according to a first embodiment of the present invention;  
         [0013]    [0013]FIG. 2 is similar to FIG. 1, but schematically shows a scope of illumination of the backlight module;  
         [0014]    [0014]FIG. 3 is an isometric view of a backlight module according to a second embodiment of the present invention;  
         [0015]    [0015]FIG. 4 is an exploded, front elevation of a backlight module according to a third embodiment of the present invention;  
         [0016]    [0016]FIG. 5 is an exploded, isometric view of a backlight module according to a fourth embodiment of the present invention;  
         [0017]    [0017]FIG. 6 is a top elevation of a conventional backlight module, schematically showing a scope of illumination thereof;  
         [0018]    [0018]FIG. 7 is an exploded, isometric view of another conventional backlight module; and  
         [0019]    [0019]FIG. 8 is substantially an assembled, top elevation of the backlight module of FIG. 7, schematically showing a scope of illumination thereof. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0020]    Referring to FIG. 1 and FIG. 2, a backlight module  3  according to the first embodiment of the present invention comprises a light source group  31  and a light guide plate  32 . The light source group  31  comprises three point light sources such as LEDs (not labeled). The light guide plate  32  is generally parallelepiped-shaped, and has a light input surface  321  for receiving light and an opposite light output surface  322  for emitting light. The light source group  31  faces the light input surface  321 . The light output surface  322  is a plane surface. The light input surface  321  is spherically concave. That is, a top elevation of the light guide plate  32  shows the light input surface  321  having an arcuate profile (see FIG. 1), and a side elevation of the light guide plate  32  also shows the light input surface  321  having an arcuateaccurate profile.  
         [0021]    The spherically concave configuration of the light input surface  321  matches an overall distribution of light emitted from the light source group  31 . That is, divergent light beams emitted from the LEDs of the light source group  31  reach every part of the light input surface  321 , and thus every region in the light guide plate  32 . Thus a scope of illumination  33  as represented by overlapping ovals in FIG. 2 covers the whole light guide plate  32 , and the light guide plate  32  has no dark zones.  
         [0022]    Referring to FIG. 3, a backlight module  4  according to a second embodiment of the present invention uses a generally wedge-shaped light guide plate  42 . In other respects, the backlight module  4  is similar to the backlight module  3  of the first embodiment. The backlight module  4  further comprises a light source group  41 , and the light guide plate  42  comprises a light input surface  421  and a light output surface  422 . The light input surface  421  is spherically concave, so that a curvature of the light input surface  421  matches an overall distribution of light distribution emitted from the light source group  41 . Divergent light beams emitted from LEDs of the light source group  41  reach every region in the light guide plate  42 , so that the light guide plate  42  has no dark zones.  
         [0023]    Referring to FIG. 4, a backlight module  5  according to a third embodiment of the present invention comprises a diffusing plate  56  and a brightness enhancing film  57 , in addition to a light guide plate  52  and a light source group  51 . The diffusing plate  56  is disposed between the brightness enhancing film  57  and the light guide plate  52 , to receive and diffuse light beams emitted from a light output surface  522  of the light guide plate  52 . The diffused light beams then enter the brightness enhancing film  57 . The light guide plate  52  also has a light input surface  521  opposite to the light output surface  522 , to receive light emitted from the light source group  51 . The light source group  51  comprises four point light sources such as LEDs (not labeled). Unlike in the backlight modules  3 ,  4  of the first and second embodiments in which the light output surfaces  322 ,  422  are adjacent the light input surfaces  321 ,  421 , in the backlight module  5  the light output surface  522  is opposite to the light input surface  521 .  
         [0024]    Referring to FIG. 5, a backlight module  6  according to a fourth embodiment of the present invention comprises a reflecting plate  65 , a diffusing plate  66  and a brightness enhancing film  67 , in addition to a light guide plate  62  and a light source group  61 . The reflecting plate  65  is disposed adjacent a bottom surface  623  of the light guide plate  62 , which is opposite to a top light output surface  622  of the light guide plate  62 . The diffusing plate  66  is disposed between the brightness enhancing film  67  and the light guide plate  62 . The light source group  61  comprises three point light sources such as LEDs (not labeled).  
         [0025]    As described above, each backlight module  3 ,  4 ,  5 ,  6  has a spherically concave light input surface  321 ,  421 ,  521 ,  621 , whose curvature matches light distribution of the light source group  31 ,  41 ,  51 ,  61 . Because the divergent light beams emitted from the light source group  31 ,  41 ,  51 ,  61  reach every part of the light input surface  321 ,  421 ,  521 ,  621 , the whole light guide plate  32 ,  42 ,  52 ,  62  is illuminated and has no dark zones.  
         [0026]    In the backlight modules  4 ,  5  according to the third and fourth embodiments, the brightness enhancing film  57 ,  67  can be replaced by a prism plate instead.  
         [0027]    According the requirements of particular applications, the backlight module of the present invention may take forms other than the embodiments described above. For example, a linear light source may be used instead of a light source group comprising point light sources. In such case, the light input surface may be configured accordingly. In particular, instead of being spherically concave, the light input surface may be cylindrically concave. That is, a top elevation of the light guide plate shows the light input surface having a linear profile, and a side elevation of the light guide plate shows the light input surface having an arcuate profile. Still other types of light input surfaces may be configured according to need. Further, two or several light input surfaces may be employed instead of only one light input surface. Yet, another alternation may include to keep the light input surface straight while arranging the group of light sub-sources to disperse in a concave manner.  
         [0028]    It is also to be generally understood that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.