Patent Publication Number: US-2007097709-A1

Title: Liquid crystal display and backlight module having light guide plate integrally formed with point illuminator

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 light guide plate integrally formed with a point illuminator.  
     GENERAL BACKGROUND  
      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 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. Therefore, liquid crystal displays typically require a backlight module.  
      Referring to  FIG. 3 , a typical backlight module  30  includes a diffusing film  32 , a light guide plate (LGP)  34 , and a reflective film  36 , arranged in that order from top to bottom. The backlight module  30  further includes a light emitting diode (LED)  38  adjacent to a light incident surface  342  of the light guide plate  34 . The light guide plate  34  further includes a bottom surface  344  perpendicularly connecting with the light incident surface  342 , and a light emitting surface  346  opposite to the bottom surface  344 . A plurality of dots  348  inwardly extend from the bottom surface  344 . That is, the dots  348  are in the form of depressions.  
      The backlight module  30  employs the LED  38  as a light source. The LED  38  is recyclable and has low power consumption. Moreover, the dots  348  can reflect and diffuse light beams striking thereat, which can improve the uniformity of light emission of the backlight module  30 . In a process of assembling the backlight module  30 , a step of precisely aligning the LED  38  with the light incident surface  342  of the light guide plate  34  is needed. This step is problematic, and may lead to inefficiency and increased cost in manufacturing the backlight module  30 . Further, light beams emitted from the LED  38  transmit into the light guide plate  34  through the light incident surface  342 , and then propagate to the bottom surface  344  or the light emitting surface  346 . The longer the propagation distance of the light beams, the lower the ratio of light utilization of the backlight module  30 . That is, the backlight module  30  may be considered to have an unsatisfactory ratio of light utilization.  
      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 light guide plate, and at least one point illuminator. The light guide plate includes a main body. The main body includes a bottom surface, and a diffraction grating structure at a top of the main body. The at least one point illuminator is integrally formed in contact with the light guide plate without intervening space or substance therebetween except at a bottom of the at least one point illuminator. The bottom of the at least one point illuminator corresponds in position to the bottom surface.  
      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 an exemplary embodiment of the present invention, the liquid crystal display including a backlight module, the backlight module including a light guide plate.  
       FIG. 2  is a top plan view of the light guide plate of the backlight module of the liquid crystal display of  FIG. 1 .  
       FIG. 3  is an exploded, side cross-sectional view of a conventional backlight module. 
    
    
     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 an exemplary embodiment of the present invention is shown. The liquid crystal display  1  includes a liquid crystal panel  10 , and a backlight module  11  adjacent to an underside of the liquid crystal panel  10 . The backlight module  11  includes a diffusing film  12 , a light guide plate  13 , a point illuminator  14 , a flexible printed circuit (FPC) board  15 , and a reflective film  16 , arranged generally in that order from top to bottom.  
      Referring also to  FIG. 2 , the light guide plate  13  includes a main body  130 . The main body  130  includes a bottom surface  132 . The reflective film  16  is positioned adjacent to the bottom surface  132 . A plurality of prism structures  136  are formed at a top of the main body  130 , opposite to the bottom surface  132 . The diffusing film  12  is positioned adjacent to the prism structures  136 . The prism structures  136  are annular and concentric, thus defining a center (not labeled) thereof. In the illustrated embodiment, the center defined by the prism structures  136  corresponds to a center of the bottom surface  132 . A density of distribution of the prism structures  136  progressively increases away from the center of the prism structures  136 . In particular, a distance between an acme (not labeled) of each prism structure  136  and a corresponding nearest acme (not labeled) of an adjacent prism structure  136  progressively increases away from the center of the prism structures  136 . Further, a height of the prism structures  136  increases away from the center of the prism structures  136 . That is, the acmes of the prism structures  136  all lie in a single common plane, with a depth of grooves between adjacent prism structures  136  increasing away from the center of the prism structures  136 . Thus the prism structures  136  are arranged so that they form a so-called fresnel diffraction grating structure. The light guide plate  13  can be made from polycarbonate (PC) or polymethyl methacrylate (PMMA), and can be manufactured by an injection molding method.  
      In the illustrated embodiment, the point illuminator  14  is an LED  14 . The LED  14  is integrally formed in the light guide plate  13  at the center of the bottom surface  132  of the main body  130 . A bottom of the LED  14  is flush with the bottom surface  132 . The FPC  15  is electrically connected with the LED  14 , and abuts the bottom surface  132 .  
      The light guide plate  13  integrally formed with the LED  14  can be made according to the following steps. First, the LED  14  is electrically connected with the FPC  15 , and the LED  14  alone is placed in a mold. Second, the light guide plate  13  is formed in the mold by an injection molding method, with withal portions of the LED  14  except a bottom face thereof directly encased by the light guide plate  13 .  
      In operation of the liquid crystal display  1 , light beams emitted from the LED  14  propagate to the main body  130  directly, and are uniformly refracted or reflected by the prism structures  136 . Some light beams emit from the light guide plate  13  through the prism structures  136 , propagate to the diffusing film  12 , and reach the liquid crystal panel  10  after being diffused by the diffusing film  12 . Other light beams are reflected by the prism structures  136 , and emit from the light guide plate  13  through the bottom surface  132 , and propagate to the reflective film  16  adjacent the bottom surface  132 . These light beams are then reflected back into the light guide plate  13  by the reflective film  16 , and finally reach the liquid crystal panel  10  after being diffused by the diffusing film  12 .  
      The light guide plate  13  includes the LED  14  integrally formed therein, and light beams from the LED  14  propagate to the prism structures  136  of the light guide plate  13  directly over relatively short distances. That is, compared to the above-described conventional light guide plate  34 , propagation distances of the light beams are greatly reduced, thus obtaining an improved ratio of light utilization for the backlight module  11 . Further, the prism structures  136  of the main body  130  form the so-called fresnel diffraction grating structure, whereby light beams passing therethrough are uniformly diffracted. This provides improved uniformity of light output by the backlight module  11 , and improved performance for the liquid crystal display  1 .  
      Further or alternative embodiments may include the following. In one example, two or more point illuminators can be provided at the bottom surface of the light guide plate. In such case, a physical center of distribution of the point illuminators corresponds to the center of the prism structures. In another example, the FPC can be replaced with a printed circuit board (PCB). In a still further example, side surfaces of the light guide plate between the top thereof and the bottom surface can be coated with a reflective material, for further improving a ratio of light utilization of the backlight module.  
      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.