Patent Publication Number: US-2007115688-A1

Title: Backlight module having matrix of light tubes and liquid crystal display having same

Description:
FIELD OF THE INVENTION  
      The present invention relates to backlight modules such as those used in liquid crystal displays (LCDs); and more particularly to a backlight module having a matrix of light tubes, and a liquid crystal display including the backlight module.  
     GENERAL BACKGROUND  
      Liquid crystal displays are commonly used as displays for compact electronic apparatuses, because they not only provide good quality images with little power but are also very thin. The liquid crystal in a liquid crystal display does not emit any light itself. The liquid crystal has to be lit by a light source so as to clearly and sharply display text and images. Thus, a backlight module is generally needed for a liquid crystal display.  
      There are generally two kinds of backlight modules, namely direct-type backlight modules and side-edge backlight modules. A large-sized liquid crystal display generally requires very high brightness, which is difficult for a side-edge backlight module to achieve. On the contrary, a direct-type backlight module can generally provide enough brightness for a large-sized liquid crystal display. Therefore, direct-type backlight modules are more popularly used in large-sized liquid crystal displays.  
      Light tubes are generally used as light sources for direct-type backlight modules. A popular kind of light tube is the cold cathode fluorescent lamp (CCFL). In a typical direct-type backlight module, a plurality of linear light tubes are horizontally arranged in parallel and cooperatively serve as a light source. A length of the light tubes corresponds to a size of the backlight module. That is, the larger the size of the backlight module, the greater the length of each light tube. Due to inherent limitations in the manufacturing of light tubes, it is difficult to manufacture light tubes that are very long. In another typical direct-type backlight module, a plurality of linear light tubes are vertically arranged in parallel and cooperatively serve as a light source. However, gaseous mercury in the light tubes is heavier than other constituents. The gaseous mercury is liable to drift down and concentrate in bottom end portions of the light tubes due to the effect of gravity. Thus, the uniformity of light eventually output by the backlight module is liable to be diminished.  
      What is needed, therefore, is a backlight module that can overcome the above-described deficiencies. What is also needed is a liquid crystal display employing such a backlight module.  
     SUMMARY  
      In one preferred embodiment, a backlight module includes a diffusing film, a frame, and a plurality of light tubes. The frame includes a bottom wall. The diffusing film is received in the frame. The light tubes are located between the diffusing film and the bottom wall of the frame. The light tubes are arranged in a matrix.  
      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  
      The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the described embodiments. In the drawings, like reference numerals designate corresponding parts throughout various views, and all the views are schematic.  
       FIG. 1  is an exploded, side cross-sectional view of a liquid crystal display according to a first embodiment of the present invention, the liquid crystal display including a plurality of linear light tubes.  
       FIG. 2  is essentially a top plan view of the light tubes and an inverter of the liquid crystal display of the first embodiment, showing the light tubes arranged in a matrix having two columns and four rows and showing electrical connections therebetween.  
       FIG. 3  is similar to  FIG. 2 , but showing a corresponding view in the case of a liquid crystal display according to a second embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
      Reference will now be made to the drawings to describe the preferred embodiments in detail.  
      Referring to  FIG. 1 , a liquid crystal display  1  according to a first embodiment of the present invention is shown. The liquid crystal display  1  includes a liquid crystal panel  10 , and a backlight module  12  located adjacent to the liquid crystal panel  10 .  
      The liquid crystal panel  10  includes an upper substrate  102 , a lower substrate  104 , and a liquid crystal layer  106  sandwiched between the upper substrate  102  and the lower substrate  104 . The upper substrate  102  and the lower substrate  104  are transparent, and are generally made from glass or quartz.  
      The backlight module  12  is a direct-type backlight module, and includes a brightness enhancement film (BEF)  14 , a diffusing film  16 , and a plurality of light tubes  18 , arranged in that order from top to bottom. The BEF  14  is located adjacent to the lower substrate  104  of the liquid crystal panel  10 . The backlight module  12  further includes a frame  19  receiving the BEF  14 , the diffusing film  16 , the light tubes  18 , and the liquid crystal panel  10 .  
      The frame  19  has a generally U-shaped cross-section, and includes a bottom wall (not labeled). The bottom wall is coated with reflective material for reflecting light beams emitted from the light tubes  18 . A plurality of holders  192  inwardly extends from the bottom wall of the frame  19 . The holders  192  are arranged in four parallel lines on the bottom wall, corresponding to an arrangement of two columns of the light tubes  18  (see below). Each of the holders  192  is configured for fittingly supporting and securely holding one of opposite end portions of a corresponding light tube  18 . In the illustrated embodiment, each holder  192  includes a stem (not labeled) perpendicularly extending from the bottom wall, and an arc-shaped receptacle (not labeled) at a top of the stem. The receptacle is configured for fittingly supporting and securely holding the end portion the corresponding light tube  18 .  
      Referring also to  FIG. 2 , the plurality of light tubes  18  have substantially a same length and a same diameter, and are arranged in a matrix. In the illustrated embodiment, the light tubes  18  are substantially linear CCFLs, and the matrix has four rows and two columns. Each light tube  18  is horizontally arranged. The light tubes  18  in each column are arranged in parallel, with a substantially constant pitch between every two adjacent light tubes  18 . All the light tubes  18  are electrically connected with each other in a parallel. Each light tube  18  includes a first electrode  182  and a second electrode  184 . The first electrode  182  and the second electrode  184  are located at two opposite end portions (not labeled) of the light tube  18 , respectively. In each row of the matrix, the second electrode  184  of the light tube  18  in the first column is physically adjacent to the first electrode  182  of the corresponding light tube  18  in the second column. A distance between the second electrodes  184  of the light tubes  18  in the first column and the first electrodes  182  of the light tubes  18  in the second column is substantially constant. The first electrodes  182  of the light tubes  18  in the matrix are electrically connected with a first metal conductive wire  186 , which transmits a high voltage. The second electrodes  184  of the light tubes  18  in the matrix are electrically connected with a second metal conductive wire  188 , which transmits a low voltage. The first metal conductive wire  186  and the second metal conductive wire  188  are each electrically connected with an inverter  189 , which can convert a direct current (DC) voltage to an alternating current (AC) voltage.  
      The light tubes  18  are horizontally arranged, which can prevent gaseous mercury therein from concentrating in end portions thereof. Therefore the backlight module  12  using the light tubes  18  can achieve uniform optical performance. Further, the light tubes  18  are arranged in a matrix. That is, each row includes at least two light tubes  18 . For a large-sized liquid crystal display  1 , this can greatly reduce or eliminate the difficulty of otherwise having to manufacture particularly long light tubes. That is, the light tubes  18  need not be overly long, and are therefore relatively easy to manufacture. Thus the large-sized liquid crystal display  1  using the light tubes  18  can be readily manufactured.  
      Referring to  FIG. 3 , a liquid crystal display  2  according to a second embodiment of the present invention is similar to the liquid crystal display  1 . The liquid crystal display  2  includes a plurality of light tubes  28  arranged in a matrix. In the illustrated embodiment, the matrix has four rows and two columns. The light tubes  28  are substantially linear CCFLs, and are electrically connected with each other in a parallel. Each light tube  28  includes a first electrode  282  and a second electrode  284 . The first electrode  282  and the second electrode  284  are located at two opposite end portions (not labeled) of the light tube  28 , respectively. In each row of the matrix, the second electrode  284  of the light tube  28  in the first column is physically adjacent to the second electrode  284  of the corresponding light tube  28  in the second column. The first electrodes  282  of the light tubes  28  are electrically connected with a first metal conductive wire  286 , which transmits a low voltage. The second electrodes  284  of the light tubes  28  are electrically connected with a second metal conductive wire  288 , which transmits a high voltage. The first metal conductive wire  286  and the second metal conductive wire  288  are each electrically connected with an inverter  289 , which can convert a DC voltage to an AC voltage. The liquid crystal display  2  has advantages similar to those of the liquid crystal display  1 .  
      Further or alternative embodiments may include the following. In one example, the matrix may have three, four, or more desired columns, and one, two, three, five or more desired rows. In another example, when the matrix of light tubes  18  has four rows and two columns, only three parallel lines of the holders  192  may be arranged on the bottom wall of the frame  19  (instead of four lines). In such case, each of the holders  192  in a central line of the holders  192  is configured for fittingly supporting and securely holding the end portions of two corresponding adjacent light tubes  18  in the matrix. In other examples, the holders  192  can have any of various other suitable configurations for securely holding the end portions of the light tubes  18 . Further, the holders  192  at two sides of the matrix of light tubes  18  can extend from corresponding side walls (not labeled) of the frame  19  instead of from the bottom. wall of the frame  19 . Moreover, at least portions of the side walls of the frame  19  can be coated with reflective material for reflecting light beams emitted from the light tubes  18 , in addition to the bottom wall of the frame  19  being coated with reflective material.  
      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.