Patent Publication Number: US-2007121345-A1

Title: Bottom-lighting type backlight module

Description:
1. TECHNICAL FIELD  
      The present invention relates to a bottom-lighting type backlight module for use in, for example, a liquid crystal display (LCD).  
     2. BACKGROUND  
      In a liquid crystal display device, liquid crystal is a substance that does not itself illuminate light. Instead, the liquid crystal relies on reflecting light from a light source, thereby displaying images and data. In the case of a typical liquid crystal display device, a backlight module powered by electricity supplies the needed light.  
      Typically, there are two types of backlight systems: an edge lighting type and a bottom-lighting type. The edge-lighting type of backlight system is widely used in small and medium size liquid crystal display for merits on small weight, thin body and low energy cost. Large size liquid crystal display seldom uses the edge-lighting backlight system because the results based on the merits mentioned above is poor. Furthermore, the large size edge-lighting type backlight system seldom satisfies the requirement of light brightness and optical uniformity. Nowadays, the market demand for larger size liquid crystal display has increased progressively. Therefore, the bottom-lighting type of backlight system needs to be developed to satisfy the market demand.  
      Referring to  FIGS. 5 and 6 , a typical bottom-lighting backlight module  10  is shown. The backlight module  10  includes a frame  11 , a reflective plate  12 , a number of cold cathode fluorescent lamps  13 , a light diffusion plate  14 , a first light diffusion sheet  15 , a prim sheet  16 , and a second light diffusion plate  17 . The frame  11  is a rectangular housing, which includes a base  111  and a plurality of sidewalls  112  extending from the periphery of the base to define an opening (not labeled). The reflective plate  12  is disposed on the base  111  of the frame  11 . The light diffusion plate  14 , the first light diffusion sheet  15 , the prim sheet  16  and the second light diffusion sheet  17  are stacked on the opening of the frame  11  in order. The cold cathode fluorescent lamps  13  are positioned in the frame  11  under the light diffusion plate  14 . A thickness of the light diffusion plate  14  is in a range of about 2 to 3 centimeters, and is much larger than both that of the first and second light diffusion sheet  15  and  17 . Therefore, the light beams emitted from the cold cathode fluorescent lamps  13  are substantially diffused in the light diffusion plate  14 , and finally surface light beams are output from the second light diffusion sheet  17 . It is noted that the light diffusion plate  14  is significantly needed to improve the backlight module  10 &#39;s optical uniformity.  
      However, the light diffusion plate  14  is typically manufactured by uniformly dispersing a plurality of light diffusion particles  142  into transparent resin matrix materials  141 . The light diffusion particles  142  may be selected from a group comprising of silicon dioxide (SiO 2 ) particles and titanium dioxide (TiO 2 ) particles. Because the light beams are diffused at the light diffusion particles  142  many times in the light diffusion plate  14 , a part of the light energy would have been consumed in the light beam&#39;s diffusing process, thus a light brightness of the backlight module is decreased. In addition, the light diffusion plate  14  costs much in manufacturing the backlight module  10 .  
      What is needed, therefore, is a bottom-lighting type backlight module that overcome the above mentioned disadvantage.  
     SUMMARY  
      A bottom-lighting type backlight module according to a preferred embodiment includes a frame, a light guide member and a plurality of linear light sources. The light guide member includes a light incident surface and an opposite light emitting surface facing away from the light incident surface. The frame includes a base facing toward and spaced from the light incident surface of the light guide member, and a plurality of elongated projections formed on the base, every two adjacent projections and the base cooperatively defining an elongated groove therebetween. The linear light sources are arranged between the light guide member and the frame with each light source received in a corresponding one of the grooves.  
      Other advantages and novel features will become more apparent from the following detailed description of the preferred embodiments, when taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Many aspects of the bottom-lighting backlight module can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, the emphasis instead being placed upon clearly illustrating the principles of the present backlight module. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.  
       FIG. 1  is a schematic, perspective view of a bottom-lighting type backlight module according to a first preferred embodiment;  
       FIG. 2  is a schematic, cross-sectional view of the bottom-lighting type backlight module taken along a line II-II of  FIG. 1 ;  
       FIG. 3  is a partially enlarged, cross-sectional view of the bottom-lighting type backlight module of  FIG. 1  and showing light beams reflected and refracted therein;  
       FIG. 4  is a schematic, cross-sectional view of a bottom-lighting type backlight module according to a second preferred embodiment;  
       FIG. 5  is a schematic, cross-sectional view of a conventional bottom-lighting type backlight module; and  
       FIG. 6  is a schematic, partially enlarged cross-sectional view of a diffusing plate of the bottom-lighting type backlight module of  FIG. 5 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      Reference will now be made to the drawings to describe preferred embodiments of the present bottom-lighting backlight module, in detail.  
      Referring to  FIGS. 1 through 3 , a bottom-lighting type backlight module  20  in accordance with a first preferred embodiment is shown. The backlight module  20  includes a frame  21 , a light guide member  24 , and a plurality of linear light sources  26 . The frame  21  includes a base  211  and a plurality of sidewalls  212  extending from the periphery of the base  211  to define an opening  213 . The light guide member  24  is disposed on the opening  213  of the frame  21 . The linear light sources  26  are arranged in the frame  21  along a Y direction, under the light guide member  24 . The base  211  of the frame  21  defines a plurality of projections  214  extending out therefrom towards the opening  213  along the Y direction parallel to the linear light sources  26 .  
      Each projection  214  is an elongated rod having two side surfaces (not labeled). The side surfaces may be configured to be either a flat surface or a curving surface. In the embodiment, the side surface of each projection  214  is the curving surface. Curving surfaces of the two adjacent projections  214  and the base  211  cooperatively define a plurality of elongated grooves  215  arranged side by side. Each groove  215  receives a corresponding linear light source  26  therein.  
      The light guide member  24  is a rectangular sheet, which includes a flat surface  242  facing the frame  21  and a prism surface  243  opposite to the flat surface  242 . The prism surface  243  defines a plurality of prism structures (not labeled) thereon. The prism structures each extend along an X-direction and are configured to be parallel (or at least essentially parallel) to each other. An angle between the X direction with respect to the Y direction is configured to be in a range from about 10 to about 80 degrees. A shape of each prism structure may be selected from an elongated V-shaped protrusion or an elongated semi-circular protrusion. In this embodiment, each prism structure is configured to be an elongated V-shaped protrusion. It is also said that the angle is defined by an axis of the elongated side of the prism structure with respect to an axis of the linear light source  26 .  
      The light guide member  24  may be selected from one of a prism sheet and a transparent plate having a prism surface. A material of the light guide member  24  may be formed of transparent resin materials, such as polymethyl methacrylate (PMMA), polycarbonate (PC), and a combination thereof.  
      Also referring to  FIG. 3 , in use, not only will the light guide member  24  directly above the linear light sources  26  have more incidence of light and illumination, other portions of the light guide member  24  above the left and right sides of the corresponding light sources  26  will also have more incidence of light and illumination because more light rays are reflected by the curving surface of elongated grooves  215  facing corresponding linear light sources  26 . With the help of the light guide member  24  (i.e. the prism structures and the angle defined by an axis of the elongated side of the prism structure with respect to an axis of the linear light source  26  is configured to be in the range from about 10 to about 80 degrees), a part of light rays that incident at a portion of the light guide member  24  above the linear light sources  26 , would be total reflected at the prism surface  243 , thus, illumination of the portion of the light guide member  24  above the linear light sources  26  is decreased. In addition, light emitting angles of a plurality of light rays that incident at other portions of the light guide member  24  above the left and right sides of the corresponding light sources  26 , would be decreased for reducing reflection and increasing the illumination of the other portions of the light guide member  24 . Therefore, a uniform and high brightness optical performance of the backlight module  20  is obtained without the help of a conventional light diffusion plate, so as to decrease the cost of the backlight module  20 .  
      Referring to  FIG. 4 , a bottom-lighting type backlight module  30  in accordance with a second preferred embodiment is shown. The backlight module  30  includes a frame  31 , a light guide member  34 , and a plurality of linear light sources  36 . The backlight module  30  is similar in principle to the backlight module  20 , except that the backlight module  30  further includes a transparent supporting plate  32 , a light diffusion film  33  and a reflecting polarizer sheet  35 .  
      The transparent supporting plate  32  is positioned on the opening of the frame  31  under the light guide member  34 , so as to support the light guide member  34 . The light diffusion film  33  is disposed between the light guide member  34  and the transparent supporting plate  32 . The light diffusion film  33  not only may be formed on an upper surface of the transparent supporting plate  32 , but also may be formed on a flat surface of the light guide member  34  adjacent to the transparent supporting plate  32 . Compared with the typical light diffusion plate, a thickness of the light diffusion film  33  is smaller, thus few light energy would be lost when the light passes through the light diffusion film  33  and a more uniform optical performance would be obtained. The reflecting polarizer sheet  35  is positioned on the light guide member  34  for further improving light brightness of the backlight module  30 .  
      A material of the transparent supporting plate  32  may be selected from a group comprising of glass and transparent resin materials. The light diffusion film  33  may be manufactured by depositing an oil ink film having a plurality of diffusion particles on the upper surface of the transparent supporting plate  32  or on the flat surface of the light guide member  34 . Alternatively, the light diffusion film  33  and the transparent supporting plate  32  may be integrally formed by etching a plurality of microstructures having light diffusion capability on the upper surface of the transparent supporting plate  32 .  
      Finally, while the present invention has been described with reference to particular embodiments, the description is illustrative of the invention and is not to be construed as limiting the invention. Therefore, various modifications can be made to the embodiments by those skilled in the art without departing from the true spirit and scope of the invention as defined by the appended claims.