Abstract:
An exemplary light guide plate ( 31 ) includes a light incident surface ( 310 ), a light output surface ( 312 ) adjacent to the light incident surface, and a bottom surface ( 313 ) opposite to the light output surface. The bottom surface includes a plurality of W-shaped structures ( 314 ) thereat. With such configuration, the output light beams can be concentrated to make the intensity distribution of the output light beams to be even. A backlight module employing the light guide plate is also provided.

Description:
FIELD OF THE INVENTION 
   The present invention relates to a light guide plate for use in a liquid crystal display (LCD) or the like, and more particularly to a light guide plate having W-shaped structures at a bottom surface thereof. The invention also relates to a backlight module using the light guide plate. 
   BACKGROUND 
   A typical LCD device includes an LCD panel, and a backlight module mounted under the LCD panel for supplying light beams thereto. The backlight module mainly includes a light source and a light guide plate. The light guide plate is generally made of a transparent acrylic plastic, and is used for guiding light beams emitted from the light source in order to uniformly illuminate the LCD panel. 
   In order to diffuse the light beams and emit them uniformly from a top surface of the light guide plate, it is common for protrusions or recesses to be formed at a bottom surface of the light guide plate. Alternatively, a pattern of light diffusion dots may be formed on the bottom surface of the light guide plate. 
   Referring to  FIG. 7 , a conventional backlight module  20  includes a light guide plate  21 , a light source  22 , and a reflective sheet  23 . The light guide plate  21  includes a light incident surface  211 , a light output surface  213  adjacent to the light incident surface  211 , and a bottom surface  212  opposite to the light output surface  213 . The bottom surface  212  includes a plurality of parallel, regularly arranged V-shaped prisms  214 . The light source  22  is disposed adjacent to the light incident surface  211 , and the reflective sheet  23  is disposed adjacent to the bottom surface  212 . 
   Referring to  FIG. 8 , an exemplary optical path of a light beam transmitting in the backlight module  20  is shown. Light beams emitted by the light source  22  propagate within the light guide plate  21 , are reflected and refracted by the light guide plate  21  and the reflective sheet  23 , and exit from the output surface  213  to illuminate an associated liquid crystal display panel. 
   Also referring to  FIG. 9 , this shows a light intensity distribution graph of light beams output from the light guide plate  21 . In the graph, X, Y coordinate values are plotted. An angle between light beams output from the output surface  213  and a line normal to the output surface  213  is taken as a value of the X-coordinate, and a relative intensity of the light beams is taken as a value of the Y-coordinate. The curve A 1  denotes a relative intensity of the light beams in a first plane perpendicular to both the light output surface  213  and the light incident surface  211 . The curve B 1  denotes a relative intensity of the light beams in a second plane that maintains an angle of 45° relative to the first plane. The curve C 1  denotes a relative intensity of the light beams in a third plane that maintains an angle of 90° relative to the first plane. The curve D 1  denotes a relative intensity of the light beams in a fourth plane that maintains an angle of 135° relative to the first plane. According to  FIG. 9 , the V-shaped prisms  214  at the bottom surface  212  tend to concentrate the emitting angles of the output light beams. 
   The intensity of the output light beams located in the range of ±20° in each of the first, second, and fourth planes is greatest, and approaches a maximum value of 7. On the other hand, the intensity of the output light beams located in the range of ±20° in the third plane is low. Even the maximum value achieved at the angle of 0° is low—i.e. approximately 2 only. That is, with the configuration of the V-shaped prisms  214 , the output light beams cannot be satisfactorily concentrated in the third plane that is perpendicular to the light output surface  213  and parallel to the light incident surface  211 . In other words, the overall intensity distribution of the output light beams is not even. 
   Accordingly, what is needed is a light guide plate and a backlight module that can overcome the above-described deficiencies. 
   SUMMARY 
   A light guide plate includes a light incident surface, a light output surface adjacent to the light incident surface, and a bottom surface opposite to the light output surface. The bottom surface includes a plurality of W-shaped structures thereat. 
   A backlight module includes a light guide plate and a light source. The light guide plate includes a light incident surface, a light output surface adjacent to the light incident surface, and a bottom surface opposite to the light output surface. The light source is disposed adjacent to the light incident surface of the light guide plate. The bottom surface includes a plurality of W-shaped structures thereat. 
   Other advantages and novel features will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. In the drawings, all the views are schematic. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an exploded, side view of a backlight module according to a first embodiment of the present invention, the backlight module including a light guide plate, a reflective sheet, and two light sources, the light guide plate defining a plurality of W-shaped structures. 
       FIG. 2  is essentially an enlarged view of part of the light guide plate and reflective sheet of  FIG. 1 , showing essential optical paths thereof. 
       FIG. 3  is a graph showing light intensity distribution of light beams output from the backlight module of  FIG. 1 . 
       FIG. 4  is a side view of a backlight module according to a second embodiment of the present invention. 
       FIG. 5  is a side view of a backlight module according to a third embodiment of the present invention. 
       FIG. 6  is a side view of a backlight module according to a fourth embodiment of the present invention. 
       FIG. 7  is an exploded, side view of a conventional backlight module, the backlight module including a light guide plate, a reflective sheet, and a light source. 
       FIG. 8  is essentially an enlarged view of part of the light guide plate and reflective sheet of  FIG. 7 , showing essential optical paths thereof. 
       FIG. 9  is a graph showing light intensity distribution of light beams output from the backlight module of  FIG. 7 . 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   Referring to  FIG. 1 , a backlight module  300  according to a first embodiment of the present invention includes two light sources  30 , a light guide plate  31 , and a reflective sheet  32 . The light sources  30  may be cold cathode fluorescent lamps. 
   The light guide plate  31  includes two light incident surfaces  310  and  311 , a light output surface  312  adjacent to both the light incident surfaces  310  and  311 , and a bottom surface  313  opposite to the light output surface  312 . 
   The bottom surface  313  includes a plurality of generally W-shaped structures  314  thereat. In the illustrated embodiment, the W-shaped structures  314  are a plurality of rectilinear protrusions, each having a W-shaped profile. Each of the W-shaped structures  314  spans from one lateral side of the light guide plate  31  to an opposite lateral side of the light guide plate  31 . All the W-shaped structures  314  have a same height and a same shape, are parallel to the light incident surfaces  310  and  311 , and are continuously arranged one beside the other. Each of the W-shaped structures  314  has two generally symmetrically opposite elongate prisms (not labeled). Each prism includes a pair of flat surfaces (not labeled), and spans between the opposite lateral sides of the light guide plate  31 . In each W-shaped structure  314 , one of the prisms forms an apex angle α, and the other prism forms an apex angle γ. The angle α and angle γ are each greater than an angle β formed between the two prisms. In the illustrated embodiment, the angle α and angle γ are equal to each other. In alternative embodiments, the angle α and angle γ can be different from each other. The W-shaped structures  314  may be formed at the bottom surface  313  by molding or by a cutting method. 
   The light sources  30  are disposed adjacent to the light incident surfaces  310  and  311  respectively, and the reflective sheet  32  is disposed immediately below the bottom surface  313 . 
   Also referring to  FIG. 2 , this shows essential optical paths of light beams transmitting in the backlight module  300 . Light beams emitted by the light sources  30  propagate within the light guide plate  31 , are reflected and refracted at the W-shaped structures  314  and the reflective sheet  32 , and subsequently exit from the light output surface  312  of the light guide plate  31 . The W-shaped structures  314  are used to evenly concentrate the emitting angles of the output light beams, particularly in directions generally perpendicular to the light output surface  312 . 
   Referring to  FIG. 3 , this shows a light intensity distribution graph of light beams output from the light guide plate  31 . In the graph, X, Y coordinate values are plotted. An angle between light beams output from the output surface  312  and a line normal to the output surface  312  is taken as a value of the X-coordinate, and a relative intensity of the light beams is taken as a value of the Y-coordinate. The curve A 2  denotes a relative intensity of the light beams in a first plane perpendicular to both the light output surface  312  and the light incident surface  311 . The curve B 2  denotes a relative intensity of the light beams in a second plane that maintains an angle of 45° relative to the first plane. The curve C 2  denotes a relative intensity of the light beams in a third plane that maintains an angle of 90° relative to the first plane. The curve D 2  denotes a relative intensity of the light beams in a fourth plane that maintain an angle of 135° relative to the first plane. According to  FIG. 3 , the W-shaped structures  314  at the bottom surface  313  tend to concentrate the emitting angles of the output light beams. 
   The intensity of the output light beams located in the range of ±20° in each of the first, second, and third planes is greatest, and approaches a maximum value of 7. The intensity of the output light beams located in the range of ±20° in the fourth plane is less, and approaches a value of 5. Unlike with the conventional backlight module  20 , the W-shaped structures  314  of the light guide plate  31  provide relative uniformity of output light beams across all of the first, second, third and fourth planes that are perpendicular to the light output surface  312 . That is, an overall intensity distribution of the output light beams is relatively even. 
   Referring to  FIG. 4 , a backlight module  400  according to a second embodiment of the present invention has a structure similar to that of the backlight module  300  of the first embodiment. The backlight module  400  includes a light guide plate  41 , and a pair of light sources (not labeled) at two opposite ends of the light guide plate  41  respectively. The light guide plate  41  includes a plurality of W-shaped structures  414  at a bottom surface thereof. In the illustrated embodiment, the W-shaped structures  414  are a plurality of rectilinear protrusions, each having a W-shaped profile. All of the W-shaped structures  414  are spaced apart from each other various distances, and are symmetrically distributed at two opposite sides of a transverse centerline (not shown) of the bottom surface of the light guide plate  41 . That is, a density of distribution of the W-shaped structures  414  progressively increases along a direction from each end of the light guide plate  41  to the centerline of the bottom surface of the light guide plate  41 . Each of the W-shaped structures  414  has two elongate prisms (not labeled) which are shaped differently from each other. Each prism includes a pair of flat surfaces (not labeled), and spans between two opposite lateral sides of the light guide plate  41 . The angles of the prisms of each of the W-shaped structures  414  may be configured to enable all the W-shaped structures  414  to have varying shapes. The arrangement of the W-shaped structures  514  helps ensure that an intensity of output light beams over a whole of a light output surface (not labeled) of the light guide plate  41  is uniform. That is, an overall intensity distribution of the output light beams is relatively even. 
   Referring to  FIG. 5 , a backlight module  500  according to a third embodiment of the present invention is shown. The backlight module  500  has a structure similar to that of the backlight module  300  of the first embodiment. However, the backlight module  500  includes a single light source  50  and a light guide plate  51 . The light guide plate  51  includes a light incident surface  510 , and a bottom surface  513  adjacent to the light incident surface  510 . The bottom surface  513  includes a plurality of W-shaped structures  514  thereat. In the illustrated embodiment, the W-shaped structures  514  include a plurality of portions of the light guide plate  51  having grooves defined therein. Each W-shaped structure  514  includes a pair of grooves that provide the W-shaped structure  514  with a W-shaped profile. The W-shaped structures  514  are spaced apart from each other various distances. In particular, a density of the W-shaped structures  514  progressively increases along a direction away from the light incident surface  510 . Further, heights of the W-shaped structures  514  progressively increase along the direction away from the light incident surface  510 . The arrangement and varying configurations of the W-shaped structures  514  help ensure that an intensity of output light beams over a whole of a light output surface (not labeled) of the light guide plate  51  is uniform. That is, an overall intensity distribution of the output light beams is relatively even. 
     FIG. 6  shows a backlight module according to a fourth embodiment of the present of the present invention. The backlight module  600  has a structure similar to that of the backlight module  300  of the first embodiment. However, the backlight module  600  includes a plurality of W-shaped structures  614  at a bottom surface of a light guide plate  61 . Each of the W-shaped structures  614  has two generally symmetrically opposite elongate prisms (not labeled). Each prism has a pair of curved surfaces (not labeled), and spans between opposite lateral sides of the light guide plate  61 . In the illustrated embodiment, the prisms in each W-shaped structure  614  have a same shape but are symmetrically opposite from each other. In an alternative embodiment, the prisms in each W-shaped structure  614  can be different from each other. In another alternative embodiment, the W-shaped structures  614  can be spaced apart from each other. The backlight module  600  has advantages similar to those described above in relation to the backlight module  300  of the first embodiment. 
   Various modifications and alterations are possible within the ambit of the invention herein. For example, the W-shaped structures may be other kinds of protrusions or grooves or a combination of protrusions and grooves. The protrusions and/or grooves may be continuously arranged, or alternately arranged. With these configurations, the backlight module may provide substantially uniform intensity of output light beams. That is, an overall intensity distribution of the output light beams is relatively even. 
   It is to be understood, however, that even though numerous characteristics and advantages of the present embodiments have been set out in the foregoing description, together with details of the structures and functions of the embodiments, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.