Abstract:
A plurality of reflecting structures are provided at the corner portions of a backlight module, so that the dark areas occurring at the corner portions or edges of the backlight module are prevented from forming, thereby uniforming the luminance performed by the display.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
   This application is a continuation-in-part of U.S. Ser. No. 11/278,619, filed on Apr. 4, 2006, which claims the priority of Taiwan Patent Application No. 094143406. 
   This application claims the benefit from the priority of Taiwan Patent Application No. 095145678 filed on Dec. 7, 2006, the disclosures of which are incorporated by reference herein in their entirety. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a backlight module, especially to a direct backlight module and a liquid crystal display (LCD) using the same, whereby the undesired dark areas on the corners and/or edges of the display can be efficiently reduced, resulting in a uniform overall luminance. 
   2. Descriptions of the Related Art 
   Liquid crystal displays (LCDs) have become the most popular displays because of the light weight and good displaying quality. The backlight module is an important illumination structure of the LCD. Controlling the transmissive light provided from the backlight module in association with the liquid crystal cells in a matrix of a panel, and appropriately controlling switches, make the brightness and quality of the images presented on the display be determined. Light emitting diodes (LEDs) widely serve as the light source of the backlight module because of the low power consumption, light weight and high luminance. Therefore, LEDs have gradually become substitutes for fluorescent lamps when selecting light sources for the backlight module. 
     FIG. 1  is a perspective view of a conventional LCD, which comprises an LCD panel  30 , a front frame  20  disposed on the LCD panel  30 , a backlight module  10  having an LED array  103  disposed on a back bezel  101 , and a frame assembly  102  disposed along the edges of the back bezel  101 . The backlight module  10  is a direct type backlight module. There are a plurality of optical films  40  disposed between the LCD panel  30  and the backlight module  10  for enhancing the efficiency of light usage and luminance promotion. The optical films  40  can be diffusing films, prism films, acrylic films and/or light enhancing films. 
   Generally, the LCD panel  30  comprises an upper glass substrate, a lower glass substrate, and a liquid crystal layer (not shown) disposed therebetween. The upper glass substrate and the lower glass substrate can be a color filter substrate and an active (or passive) array substrate, respectively. The voltage difference between the upper and the lower glass substrates makes the liquid crystal in the liquid crystal layer rotate or tilt accordingly. Therefore, the light transmitting through the LCD panel  30  will be controlled and will then produce images on the LCD panel  30 . 
   The LED array  103  can be constituted by individually packaging a plurality of single LEDs or by integrally packaging a module that has a plurality of LEDs. A printed circuit board (not shown) is electrically connected to the LED array  103  for supplying power. The LEDs of the LED array  103  can be red, green, blue, or white LEDs, depending on the requirements of the LCD panel  30 . 
   The material of the frame assembly  102  and the back bezel  101  can be light reflective. The inner walls thereof can also be made of reflective materials or have reflective films adhered thereon to reflect the light projected from the LED array  103 . 
   Nevertheless, there is no light source disposed on the corner or edge portions of the backlight module because the undesired dark areas may occur in those parts, thereby causing the brightness of the overall backlight module to not be uniform. Additional light sources that are disposed on the corner or edge portions of the backlight module make the design and manufacturing procedures more complicated. Thus, it is not facilitated to control the uniformity of the brightness by adding light sources at the edges and corners. 
   SUMMARY OF THE INVENTION 
   The primary objective of this invention is to provide a direct backlight module. By disposing a reflector on the corner portions of the backlight module, the undesired dark areas on the corner portions or the edges of the backlight module can be reduced. 
   Another objective of this invention is to provide an LCD comprising a direct backlight module. By disposing a reflector on the corner portions of the backlight module, the brightness of the backlight module can be more uniform, resulting in the enhancement of the overall quality of the LCD. 
   The detailed technology and preferred embodiments implemented for the subject invention are described in the following paragraphs accompanying the appended drawings for people skilled in this field to well appreciate the features of the claimed invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view showing a conventional LCD; 
       FIG. 2  is a perspective view showing an LCD according to the present invention; 
       FIG. 3  is a perspective view showing an LED backlight module according to the present invention; 
       FIG. 4A  to  FIG. 4D  are reflectors of different configurations according to the present invention; 
       FIG. 5A  is an experimental diagram showing the light intensity (in nit), in view of each area measured from the conventional backlight module; 
       FIG. 5B  is an experimental diagram showing the light intensity (in nit), in view of each area measured from the backlight module according to the present invention; 
       FIG. 6  is a schematic view illustrating the comparison between the representative optical paths of the present invention and the prior art at the corner portion of the backlight module; 
       FIG. 7  is a schematic view illustrating a preferred embodiment of the present invention; 
       FIGS. 8A and 8B  are schematic views illustrating other preferred embodiments of the present invention; 
       FIGS. 9A and 9B  are schematic views illustrating still a further preferred embodiment of the present invention; 
       FIGS. 10A and 10B  are schematic views illustrating yet a further preferred embodiment of the present invention; and 
       FIGS. 11A ,  11 B and  11 C are schematic views illustrating the alternative tubular light sources of the backlight module of the present invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 2  is a perspective view of the LCD according to the present invention. The LCD comprises an LCD panel  30 , a front bezel  20  disposed above the LCD panel  30 , and a backlight module  10  that has at least one light source. Preferably, at least one light source should be an LED array  103  disposed on the back bezel  101 . A frame  102  is disposed along the two adjacent edge portions of the back bezel  101 . The frame  102  and the back bezel  101  form at least one corner portion. There are a plurality of optical films  40  disposed between the LCD panel  30  and the backlight module  10  for enhancing the efficiency of light usage and luminance promotion. The optical films  40  can be diffusing films, prism films, acrylic films and/or light enhancing films. 
   There are reflectors  104  disposed on the corner portions of the back bezel  101 . The reflectors  104  are provided for reducing dark areas occurring on the corners or edges of the backlight module and for increasing the uniformity of the luminance. The reflectors  104  can be disposed on the areas adjacent to the edges of the back bezel  101  as well. 
   The LCD panel  30  comprises an upper glass substrate, a lower glass substrate, and a liquid crystal layer (not shown) disposed therebetween. The upper glass substrate and the lower glass substrate can be a color filter substrate and an active (or passive) array substrate, respectively. The voltage difference between the upper and the lower glass substrates make the liquid crystal in the liquid crystal layer rotate or tilt accordingly. Therefore, the light transmitted through the LCD panel  30  will be controlled and will then produce images on the LCD panel  30 . 
   The LED array  103  can be constituted by individually packaging a plurality of single LEDs or by integrally packaging the same in advance into a module that has a plurality of LEDs. A printed circuit board (not shown) is electrically connected to the LED array  103  to provide electrical power. The LEDs of the LED array  103  can be red, green, blue, white or other colors, depending on what the LCD panel  30  requires. 
   The material of the frame  102  and the back bezel  101  could be reflective materials. The inner walls thereof can be made of reflective materials or have reflective films adhered thereon to reflect the light emitted from the LED array  103 . 
     FIG. 3  is a perspective view of an LED backlight module  10  according to the preferred embodiment of the present invention. As shown in  FIG. 3 , there is a frame  102  (including four assembled elements or only a single element) disposed along four edge portions of the back bezel  101  of the backlight module  10 . Four reflectors  104  are disposed on the four corner portions formed by the frames  102  and the back bezel  101 . The contact area between the reflectors  104  and the back bezel  101  is about, but not limited to, 2% to 10%, preferably, about 4% to 8%, of the planar area of the back bezel  101 . 
   The reflector  104  can be made of silver or polyethylene terephthalate (PET) resin, or similar materials comprising the same. The reflector  104  and the back bezel  101  can be formed integrally into one piece, then assembled with the frame  102 . Alternatively, the reflector  104 , the back bezel  101  and the frame  102  can be formed integrally into one piece to constitute the desired structure. It is understandable that the method employed for manufacturing the reflector  104  can be through a computer numerical control (CNC) process or a press process if the reflectors  104  are made of metal. The well-known CNC process includes inputting orders or numerical values to the computer. According to the input orders or numerical values, devices connected to the computer, for example, operate when creating, chamfering, drilling, moving, pressing, sticking or forming additional elements onto the workpiece or elements. Advantages thereof include saved time, precision, low cost and no need for molds. Alternatively, the reflector  104  can be formed on the backlight module by adding it onto the corner portion. The reflector  104  can be made according to the above-mentioned CNC process. The reflectors  104  and the back bezel  101  can be formed integrally. The reflectors  104  and the frame  102  can be formed integrally too. 
   As shown in  FIG. 4A  to  FIG. 4D , the reflector  104 , for example, can be pyramid-shaped, which comprises a body that has a reflective surface formed thereon. The reflective surface reflects lights with its original material property, or by a reflective film additionally adhered thereon. An alternative way to reflect light is to apply or coat at least one layer of reflective material, for example, silver, barium sulfate, polyethylene terephthalate (PET) resin or the combination thereof, onto the reflective surface of the reflector  104 . 
   As shown in  FIG. 4A , a curved surface of the reflector  104   a  projects convexly out of the corner portion. In  FIG. 4B , a curved surface of the reflector  104   b  projects concavely into the corner portion. In  FIG. 4C , a reflective surface of the reflector  104   c  is a flat plane. In  FIG. 4D , a curved surface of the reflector  104   d  is a regularly or an irregularly curved face. It is understandable that the shape or structure of the reflective surface of the reflector  104  is not limited, provided that its configuration provides the basic functions to better reflect lights to eliminate the dark areas occurring at the edge and corner portions. 
     FIG. 5A  is an experimental diagram showing the light intensity (in nit) which is measured by each unit area at the light output from a backlight module of the existing art  FIG. 5B  is a diagram according to the present invention that corresponds to  FIG. 5A . With reference to these two diagrams, it can be observed that the light intensity of corner portions C 1 , C 2  and C 3  of the backlight module is generally lower than that of the central area; therefore, the luminance of the light output is not uniform. For example, it can be found in  FIG. 5A  that the lowest light intensity (nit) is about 5722 nit, which is about 81% of the highest one, 7069 nit. Turning to  FIG. 5B , the lowest light intensity (nit) is about 5929 nit, which is about 85% of the highest one, 7016 nit. In conclusion, the decrease in the highest light intensity (nit) is merely about 0.75% which makes no substantial influence on the image quality. On the other hand, the increase in the uniformity of the luminance is 4%, which apparently improves the output quality of the image. The backlight module according to the present invention can increase the efficiency of light usage and luminance promotion, and ultimately, increase the uniformity of the luminance provided by the backlight module. 
     FIG. 6  is a schematic view illustrating the optical paths along the vertical cross-section at the corner portion of the present invention. The dash lines show a representative optical path as in the conventional technology without any reflector. After the back bezel  101  and the frame  102  partially reflect the light, the light will travel toward the central area of the panel. On the other hand, the solid lines show a representative optical path of the present invention having the reflectors  104 . After the reflectors  104  reflect the light, the reflected light will be guided toward the corner portion or the periphery area of the frame  102 . This helps to enhance the brightness at the corner portion or the periphery area, and promote the luminance uniformity of the panel. 
   A preferable embodiment of the present invention is that the frame  102  is partially formed with the back bezel  101  integrally. In specific, as shown in  FIG. 7 , the frame  102  comprises two opposite first frame portions  102   a  and two opposite second frame portions  102   b , in which the first frame portions  102   a  is formed by extending integrally and bending from the back bezel  101 . In manufacture, the back bezel  101  and the first frame portions  102   a  can be simultaneously formed and then be bended by sheet metal works. As shown in  FIG. 7 , the first frame portions  102   a  are longer than the second frame portions  102   b.    
   To further illustrate the connection between the first frame portions  102   a  and the second frame portions  102   b , the first frame portion  102   a  has two opposite end portions  106   a  and  106   b , and the second frame portion  102   b  has two opposite end portions  106   c  and  106   d . One of the end portions  106   a  and  106   b  of the first frame portion  102   a  is affixed to one of the end portions  106   c  and  106   d  of the second frame portion  102   b . The structure as mentioned for connection can be altered in any way that can perform the similar functions.  FIG. 8A  illustrates another preferable embodiment of the present invention. In specific, the first frame portion  102   a  has bending portions  102   c  at the end portions  106   a  and  106   b  respectively, for connecting with the end portions  106   c  and  106   d  of the second frame portions  102   b . Alternatively, as shown in  FIG. 8B , bending portions  102   d  extends from the end portions  106   c  and  106   d  of the second frame portions  102   b  respectively, for connecting with the first frame portion  102   a . Those skilled in this field can easily implement variations as to the connection according to the demands, and the abovementioned connecting manner includes screwing, riveting or any other known skills, which are not limited and superfluously addressed. Accordingly, the first frame portions  102   a , the second frame portions  102   b  and the back bezel  101  can be formed to define the aforesaid four corner portions therewith. As shown in  FIG. 8A  and  FIG. 8B , the first frame portions  102   a  are longer than the second frame portions  102   b.    
   Still another embodiment of the present invention is shown in  FIG. 9A  and  FIG. 9B . Both of the first frame portions  102   a  and the second frame portions  102   b  are formed with the back bezel  101  integrally and subsequently bended to form the backlight module  10  to come with the reflectors  104 . Further, as shown in  FIG. 10A , the first frame portions  102   a , the second frame portions  102   b  and the reflectors  104  are formed by extending integrally and bending from the back bezel  101 . After the sheet metal works are performed, the backlight module  10  as shown in  FIG. 10B  can be formed. Alternatively, it will be practicable that the reflectors  104  are not integrated with the back bezel  101  but with the frame  102  (not shown) instead. 
   It is noted that adopting light emitting diodes (LEDs) as the light source in the direct backlight module  10  in the aforementioned embodiments is only for exemplified, but not limited. Various tubular light sources  103   a  can be used, for example, straight tubes as shown in  FIG. 11A , U-shape tubes as shown in  FIG. 11B , or hybrid tubes by combining those types as shown in  FIG. 11C . The tubular light source  103   a  is selected from the group consisting of a cold cathode fluorescent lamp (CCFL), a hot cathode fluorescent lamp (HCFL), and an external electrode fluorescent lamp (EEFL). 
   The above disclosure relates to the detailed technical contents and inventive features thereof. People skilled in this field may proceed with a variety of modifications and replacements based on the disclosures and suggestions of the invention as described without departing from the characteristics thereof. Although such modifications and replacements are not fully disclosed in the above descriptions, they have substantially been covered in the following claims as appended.