Abstract:
The present invention relates to a direct type backlight module providing a planar backlight source, wherein it adopts several light-emitting elements, and the light emitted from the light-emitting elements directly illuminates a diffuser, or is reflected by a reflector, and then the reflected light illuminates the diffuser. Via light-compensating elements installed between any two neighboring light-emitting elements, the present invention solves the brightness defects occurring in the portions between any two neighboring light-emitting elements and further increases the brightness and uniformity of a planar backlight source.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a direct type backlight module, particularly to a direct type backlight module, which has a promoted brightness and uniformity via providing additional light-compensating elements to improve the brightness defects occurring in the regions between any two neighboring light-emitting elements.  
       BACKGROUND OF THE INVENTION  
       [0002]     Generally speaking, a backlight module refers to an assembly of parts that provides a backlight source for the product. The typical application thereof is the backlight source of a flat panel display, such as a liquid crystal display LCD. The light-emitting elements currently used by a backlight module include: electron luminescence (EL), cold cathode fluorescent lamp (CCFL), and light-emitting diode (LED). According to the position for the backlight source, a backlight module can be divided into the direct type and the edge-side type.  
         [0003]     The light-emitting elements currently used by the direct type backlight module include: multiple light-emitting diodes arranged into an array, and multiple cold cathode fluorescent lamps arranged in parallel.  
         [0004]     Please refer to  FIG. 1 . A conventional direct type backlight module  10  is composed of a reflector  12 , a plurality of CCFLs  14  and a diffuser  16 . The light emitted from the CCFL  14  illuminates the diffuser  16  directly, or is reflected by the reflector  12 , and by the fog effect of the diffuser  16 , a planar backlight source having a uniform brightness is provided.  
         [0005]     In the conventional direct type backlight module  10 , the brightness of the regions most close to the CCFLs  14  is higher than that of the regions far from the CCFLs  14 , which induces brightness defects (i.e. a shadow phenomenon) at the regions between any two neighboring CCFLs  14  and further influences the brightness uniformity of the planar light source of the conventional direct type backlight module  10 .  
         [0006]     As shown in  FIGS. 2 and 3 , a conventional technology utilizes a modified surface of the reflector  14  to improve the brightness defect, such as a zigzag surface  12   a  as shown in  FIG. 2 , or a wave-like surface  12   b  as shown in  FIG. 3 . Although improving the brightness defects occurring in the regions between any two neighboring CCFLs  14 , those methods will increase the difficulty of compacting the backlight module.  
         [0007]     Another conventional technology for improving the brightness defect is to install light-shielding elements  18  above the CCFLs  14 , as shown in  FIG. 4 , or to print light-shielding patterns  19  on some portions of the bottom surface of the diffuser  16 , wherein those portions are ones most close to the CCFLs  14 , as shown in  FIG. 5 , in order to reduce the orthogonal light energy of the CCFLs  14 . Those methods can improve the total performance of uniformity; however, the total brightness of the backlight module decreases as the orthogonal light energy is shielded.  
         [0008]     Besides, if a viewer observes the direct type backlight module  10  shown in  FIG. 5  from a non-orthogonal viewing angle (i.e. angle θ with respect to the normal), the non-uniformity of the brightness will become even more serious as the relative position of the CCFLs  14  and the light-shielding pattern  19  shifts, as shown in  FIG. 6 . The light-shielding element  18  as shown in  FIG. 4  has the non-uniform problem when a viewer observes the direct type backlight module  10  form a non-orthogonal viewing angle. Further, the printed light-shielding pattern  19  also has a problem of the color deterioration resulting from an ink aging.  
       SUMMARY OF THE INVENTION  
       [0009]     One objective of the present invention is to provide a direct type backlight module for improving the insufficient brightness occurring between any two neighboring light-emitting elements and further to increase the total performance of the brightness and uniformity.  
         [0010]     To achieve the objective mentioned above, in the present invention, light-compensating elements are installed at the regions between any two neighboring light-emitting elements to improve the brightness defects occurring in the regions between any two neighboring light-emitting elements so as to increase the brightness and uniformity of a planar backlight source.  
         [0011]     Also to achieve the objectives mentioned above, the present invention utilizes a structure of total-reflection prisms to realize the aforementioned light-compensating element. In one preferred embodiment of the present invention, the light-compensating elements are disposed at the positions that are above the regions between any two neighboring CCFLs and intervene between the diffuser and the CCFLs. In another preferred embodiment of the present invention, the structures of total-reflection prisms are formed directly onto some regions of the bottom of the diffuser, wherein those regions correspond to the positions intervening between any two neighboring CCFLs. The light emitted from two lateral sides of the CCFL is guided to some regions of the diffuser, wherein those regions correspond to the positions intervening between any two neighboring CCFLs, in order to compensate the brightness in those regions and increase the total performance of the brightness and uniformity.  
         [0012]     The preferred embodiments and detailed technical contents of the present invention will be stated below in co-operation with the drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]      FIG. 1  is a structural diagram of a conventional direct type backlight module.  
         [0014]      FIG. 2 ˜ FIG. 5  are structural diagrams of other conventional direct type backlight modules.  
         [0015]      FIG. 6  is a schematic diagram showing that the conventional direct type backlight module shown in  FIG. 5  is observed from the view of a different angle.  
         [0016]      FIG. 7  is a structural diagram of the direct type backlight module according to the present invention.  
         [0017]      FIG. 8  is a schematic diagram showing the optical path of the direct type backlight module according to the present invention.  
         [0018]      FIG. 9  is a diagram of a preferred embodiment of the light-compensating element according to the present invention.  
         [0019]      FIG. 10  is a diagram of a preferred embodiment of the arc-type light-compensating element according to the present invention.  
         [0020]      FIG. 11A ˜ FIG. 11C  are diagrams of preferred embodiments of the geometric designs of the light-compensating element&#39;s contour according to the present invention.  
         [0021]      FIG. 12  is a diagram of a preferred embodiment that the present invention&#39;s light-compensating elements are disposed onto a transparent planar plate.  
         [0022]      FIG. 13  is a diagram of the prismatic plates is integrated with the diffuser.  
         [0023]      FIG. 14  is a schematic diagram of the brightness values measured at several points in a conventional direct type backlight module.  
         [0024]      FIG. 15  is a schematic diagram of the brightness values measured at several points in the direct type backlight module according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0025]      FIG. 7  shows a structural diagram of the structure of a first preferred embodiment, wherein the direct type backlight module  100  that utilizes a CCFL  120  as a light source. The direct type backlight module  100  of the present invention comprises a reflector  110 , a plurality of CCFLs, a diffuser  130  and a plurality of light-compensating elements  140 .  
         [0026]     A plurality of CCFLs  120  is disposed inside the reflector  110  and arranged in parallel with each other in an appropriate spacing. The diffuser  130  is placed over the reflector  110  and positioned above the CCFLs  120 . The diffuser  130  is an optical plate, which provides the light with a fogging effect, has an incident face  131  fronting the CCFLs and an exit face  132  opposite to the incident face  131 , and the light emitted from the exit face  132  of the diffuser  130  has a uniform brightness. The light-compensating elements  140  are disposed at regions corresponding to those positions between any two neighboring CCFLs  120  and interpose between the diffuser  130  and the CCFLs  120 .  
         [0027]     The reflector  110  is used to reflect a part of the light emitted from the CCFLs  120  to the diffuser  130 . The reflector  110  is a metallic material, or is disposed with a reflective material  112  on the surface of the reflector  110 . Referring to  FIG. 8 , the light-compensating elements  140  are used to condense and guide the light emitted from any two neighboring CCFLs  120  toward some regions of the diffuser  130 , wherein those regions correspond to the positions between any two neighboring CCFLs  120 , in order to improve the defects of insufficient brightness occurring between any two neighboring CCFLs  120  and further to increase the total brightness and uniformity.  
         [0028]     Please refer to  FIG. 9 , the light-compensating element  140  is realized via a prismatic plate, and an optical total-reflection prism plate would be a better choice thereof; it can be made of a transparent material, such as a glass, or an acrylic, etc. The prismatic plate is of a planar shape, which is disposed above the region between two neighboring CCFLs  120  and interposes between the diffuser  130  and the CCFLs  120  via supporting elements or means (not shown in the drawings).  
         [0029]     The bottom of the prismatic plate, i.e. the incident face, possesses a plurality of prisms  142  arranged side by side. After the incidence into the prism  142 , the light emitted from the CCFL  120  will be condensed and guided onto a region of the diffuser  130  according to principle of refraction and total reflection, wherein the region corresponds to the position between two neighboring CCFLs  120 . Further, the vertex angle  144  of the prism  142  can be modified according the incident angle of the light emitted from the CCFL  120 . For example, taking the central line A of the prismatic plate as the reference line, the vertex angle  144  of the prism  142  close to the central line A is designed to be different from that of the prism  142  far away from the central line A. In this embodiment, the vertex angle  144  of the prism  142  close to the central line A is designed to be larger than that of the prism  142  far away from the central line A, which helps increase the light-condensing effect.  
         [0030]     Please refer to  FIG. 10 . The present invention modifies the shape of the light-compensating element  140  to achieve the aforementioned objective. The light-compensating element  140  is a prismatic plate and an arc shape. The incident face of the prismatic plate faces the curvature center of the arc in order to enable the light to project upward onto the diffuser  130  for increasing the light-condensing effect. Further, the top portion of the prismatic plate can be treated with a gradient fogging procedure, such as a sandblast or a coating, for reducing the dispersion of the prismatic plate or the image discontinuity occurring in the region corresponding to the edge of the prismatic plate.  
         [0031]     Please refer to the  FIGS. 11A, 11B  and  11 C, the geometric-shape design of the contour of the light-compensating element  140  enables the brightness generated by the light, which passes through the light-compensating element  140  and projects onto the diffuser  130  without a distinct border. The geometric shapes are continuous wave-like shape (shown in  FIG. 11A ), continuous arc shape (shown in  FIG. 11B ), and continuous zigzag shape (shown in  FIG. 11C ), all of which can improve the image discontinuity corresponding to the edge of the prismatic plate.  
         [0032]      FIG. 12  shows an embodiment that the light-compensating elements  140  of the present invention are disposed onto a transparent plate  150 . The transparent plate  150  is installed between the CCFLs  120  and the diffuser  130 , and a plurality of the light-compensating elements  140  are attached above the transparent plate  150 . It is to be appreciated by a person skilled in the art that if permitted by the design of the optical path, the light-compensating elements  140  can be directly disposed onto the diffuser  130  rather than onto the transparent plate  150 , and it has the same convenience of fixing.  
         [0033]     Referring to  FIG. 13 , the diffuser  130  and the prismatic plates are integrated into a unit. The direct type backlight module  100  of the present invention is not limited to utilize the independent dedicated light-compensating elements  140 , and total-reflection prism&#39;s structures  130   a  can also be adopted and directly formed in some regions of the diffuser  130 , wherein those regions correspond to the positions between any two neighboring CCFLs  120 . The total-reflection prism&#39;s structure  130   a  is equivalent to the prisms  142  of the prismatic plate in the aforementioned embodiment, and via the total-reflection prism&#39;s structures  130   a , the light is guided to some regions of the diffuser  130 , wherein those regions correspond to the positions between any two neighboring CCFLs  120 , in order to compensate the brightness defects occurring between any two neighboring CCFLs  120 .  
         [0034]      FIG. 14  is a schematic diagram of the brightness values measured at several points in a conventional direct type backlight module.  FIG. 15  is a schematic diagram of the brightness values measured at several points in the direct type backlight module of the present invention. Comparing  FIG. 15  with  FIG. 14 , it is obvious that each of the values measured at point  1  to point  13  in the backlight module of the present invention is larger than the corresponding one measured at the corresponding point in the conventional backlight module; for example, the brightness value at point  1  in the conventional one is 3452.7; however, the brightness value at point  1  in the present invention is 3690.8. According to that, it is further confirmed that via installing the light-compensating elements, the direct type backlight module of the present invention not only can improve the non-uniformity of the planar light source occurring in the conventional one but also can increase the total performance of brightness with about 10% increase thereof.  
         [0035]     In the present invention, via disposing the light-compensating elements in the regions corresponding to the positions between any two neighboring CCFLs, the light emitted from the lateral sides of the CCFLs is guided onto the diffuser&#39;s regions corresponding to the positions between any two neighboring CCFLs, so that the brightness between two neighboring CCFLs is compensated, and the light energy efficiency is also raised. Further, the total performance of the brightness and the uniformity is increased. It is to be appreciated by the persons skilled in the art that in the present invention, the light-compensating element is not limited to the prismatic plate and any other light-compensating element, which can guide the light emitted from the lateral sides of the CCFLs toward the region above the position between two neighboring CCFLs, is to be included within the scope of the present invention. Besides, the prismatic plates, or the like, can be integrated with the diffuser to directly form the structures of the total-reflection prisms on those diffuser&#39;s regions corresponding to the positions between any two neighboring CCFLs, which can also compensate the brightness between two CCFLs, raise the light energy efficiency and increase the total performance of the brightness and the uniformity.  
         [0036]     In conclusion, the present invention, wherein the light-compensating elements are disposed in the regions between any two neighboring CCFLs to guide the light emitted from the light-emitting elements toward the regions above any two neighboring CCFLs, has the following advantages: 
    1. Increasing the total brightness and the light-utilization efficiency of the light-emitting element;     2. Improving the uniformity no matter whether the backlight module observed from the orthogonal or the lateral view;     3. Being beneficial for the compacting of the backlight module as it is unnecessary to change the shape of the reflector.    
 
         [0040]     Furthermore, having described the invention in connection with certain specific embodiments thereof, it is to be understood that further modifications may now suggest themselves to those skilled in the art, it is intended to cover all such modifications as fall within the scope of the appended claims.