Patent Publication Number: US-2010124075-A1

Title: Edge Type Back Light Module and Display Device Using the Same

Description:
This application claims the benefit of Taiwan application Serial No. 97144575, filed Nov. 18, 2008, the subject matter of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates in general to an edge type back light module and a display device using the same, and more particularly to an edge type back light module without reflective plate and a display device using the same. 
     2. Description of the Related Art 
     A liquid crystal display device mainly includes a display panel, an edge type back light module, a driving display unit, and a frame. The edge type back light module is located at one side of the display panel for providing a uniformed light source to the display panel of the liquid crystal display device. The light source is further divided into side type back light module and direct type back light module. Let the side type back light module be taken for example. The linear light source or the point light source is disposed on the lateral side of an optical film such as a light guide plate (LGP) or a diffusion film for increasing the uniformity and laminating efficiency of the light the LGP and the diffusion film. 
     Despite the efficiency of the light source is increased by the use of the optical films, light leakage from the bottom of the LGP still occurs. The efficiency of the light source will be increased further if the light leakage can be reflected back to the LGP and used again. Therefore, a reflector is normally disposed on the bottom of the frame of the edge type back light module for reflecting the light leakage back to the LGP. 
     However, the disposition of the reflective plate incurs extra cost, moreover, the reflective plate merely reflects the light leakage, and there is no control regarding at what angle is the light leakage emitted from the LGP. 
     SUMMARY OF THE INVENTION 
     The invention is directed to an edge type back light module without a reflective plate. The light guide portion, disposed on the frame surface of the edge type back light module, reflects the light leakage back to the light guide plate (LGP) and further guides the light leakage to be emitted from the LGP at a predetermined angle, hence dispensing with the use of reflective plate and saving the cost relevant to the reflective plate. The frame is made from a material such that the reflection rate on the frame surface ranges from 65% to 100%, but the composition of the material is not defined here. 
     According to a first aspect of the present invention, an edge type back light module is provided. The edge type back light module is adjacent to a display panel of a display device. The edge type back light module includes a LGP, a light source and a frame. The LGP has a light-receiving surface, a light-emitting surface and a light-reflecting surface opposite to the light-emitting surface. The light-emitting surface faces the display panel. The light source is adjacent to the light-receiving surface of the LGP for emitting a light. The frame has a frame surface and a light guide portion. The frame surface faces the light-reflecting surface of the LGP. The light guide portion is disposed on the frame surface. After a portion of the light contacts the light guide portion, the light guide portion guides the portion of the light to be emitted from the light-emitting surface. 
     According to a second aspect of the present invention, a display device is provided. The display device includes a display panel and aforementioned edge type back light module. 
     The invention will become apparent from the following detailed description of the preferred but non-limiting embodiments. The following description is made with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a display device according to a first embodiment of the invention; 
         FIG. 2  shows a part of enlarged light guide portion of  FIG. 1 ; 
         FIG. 3  shows a light guide portion of  FIG. 2  being a recess; 
         FIG. 4  shows a first implementation of a light guide portion of  FIG. 2 ; 
         FIG. 5  shows a light guide portion of  FIG. 4  being a recess; 
         FIGS. 6A and 6B  show a second implementation of a light guide portion of  FIG. 2 ; 
         FIG. 7A  shows an extension path of a light guide portion of an embodiment of the invention; 
         FIG. 7B  shows another implementation of an extension path of a light guide portion of  FIG. 7A ; 
         FIGS. 8A and 8B  show another implementation of the frame of  FIG. 1 ; 
         FIGS. 8C and 8D  show another implementation of the frame of  FIG. 8A to 8B ; 
         FIG. 9  shows a display device according to a second embodiment of the invention; and 
         FIG. 10  shows a display device according to a third embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Two embodiments are disclosed below as exemplifications of the invention. However, the two embodiments are for exemplification only, not for limiting the scope of protection of the invention. Besides, secondary embodiments are omitted for highlighting the technical features of the invention. 
     First Embodiment 
     Referring to  FIG. 1 , a display device according to a first embodiment of the invention is shown. The display device  100  includes a display panel  102  (LCD, EPD, EWD . . . ) and an edge type back light module  104 , which is adjacent to the display panel  102 . The edge type back light module  104  includes a LGP  106 , a light source  108 , a frame  110 , a first brightness enhancement film (BEF)  122 , a diffusion film  124  and a second BEF  126 . 
     The diffusion film  124  is located between the LGP  106  and the second BEF  126 . The second BEF  126  is located between the first BEF  122  and the diffusion film  124 . The first BEF  122 , the second BEF  126  and the diffusion film  124  are adjacent to the light-emitting surface  114  of the LGP  106 . 
     The LGP  106  has a light-receiving surface  112 , a light-emitting surface  114  and a light-reflecting surface  116  opposite to the light-emitting surface  114 . The light source  108  is adjacent to the light-receiving surface  112  of the LGP  106  for emitting a light L. The light-emitting surface  114  faces the display panel  102 . The frame  110  has a frame surface  118  and a light guide portion  120 . The frame surface  118  faces the light-reflecting surface  116  of the LGP  120 . 
     Referring to  FIG. 2 , a part of enlarged light guide portion  120  of FIG. 
       1  is shown. The light guide portion  120  is disposed on the frame surface  118  and projected from the frame surface  118 . The light guide portion  120  is used for guiding the light leakage L 1  to be emitted from the light-emitting surface  114  after a portion of the light L, such as the light leakage L 1  of the LGP  106 , contacts the light guide portion  120 . A predetermined angle A 1  is contained between the outgoing direction of the light leakage L 1  emitted from the light-emitting surface and the normal line LN of the light-emitting surface  114 . When the predetermined angle A 1  is preferably controlled to be within the range of 35 to 65 degrees, the light leakage L 1  pass through the diffusion film  124 , the second BEF  126 , and the first BEF  122  sequentially and then L 1  can be eventually emitted towards the display panel  102  in a direction perpendicular to the first BEF  122 . Thus, the display luminance is the brightest, and the display quality is the best. Preferably, the light leakage L 1  is the peak of the light leakage of the LGP  106 . 
     As indicated in  FIG. 2 , the cross-section of the light guide portion  120  is a trapezoid, wherein the angle A 2  contained between the lateral side  128  of the trapezoid and the bottom side  130  of the trapezoid ranges from 5 to 90 degree. 
     In the present embodiment of the invention, the light guide portion  120  is projected from the frame surface  118 . However, in other embodiments, the light guide portion  120  can be a recess. Referring to  FIG. 3 , a cross-section of the light guide portion  132  is a trapezoidal recess. The angle A 3  contained between the lateral side  134  of the trapezoid and the bottom side  136  of the trapezoid ranges from 90 to 175 degrees. 
     By use of the light guide portion  120 , the light leakage L 1  is reflected back to the LGP  106  so as to increase the efficiency of the light source. Moreover, the light guide portion  120  also guides the light leakage L 1  to be emitted from the LGP  106  at a predetermined angle A 1 . Apart from saving the use of the reflective plate in conventional display module, the light guide portion of the invention further meets optical requirements. 
     Referring to  FIG. 4 , a first implementation of a light guide portion of  FIG. 2  is shown. The light guide portion  138  is a protrusion projected from the frame surface  118 , wherein the cross-section of the light guide portion  138  is a triangle. The vertex angle A 3  of an apex T 1  of the triangle ranges from 30 to 175 degrees. The apex T 1  faces the light-reflecting surface  116 . 
     Referring to  FIG. 5 , a light guide portion of  FIG. 4  being a recess is shown. The cross-section of the light guide portion  140  is a triangular recess. The vertex angle A 4  of an apex T 2  of the triangle ranges from 30 to 175 degrees. The apex A 4  faces the direction away from the light-reflecting surface  116  (illustrated in  FIG. 2 ). 
     Thus, the light guide portions  138  and  140  with a triangular cross-section control the predetermined angle A 1  to be within the range of 35 to 65 degrees, so that the light leakage L 1 , after being emitted towards the diffusion film  124 , is emitted from the first BEF  122  in a direction perpendicular to the first BEF  122 . Due to the manufacturing factors, the vertex angle T 1  of the light guide portion  138  and the vertex angle T 2  of the light guide portion  140  may be in the shape of a circular arc, not a sharp angle. Nevertheless, the function of the light guide portion of the invention is not affected. 
     In the present embodiment of the invention, the cross-section of the light guide portion is exemplified by a triangle or a trapezoid. However, in other embodiments, the cross-section of the light guide portion can be a polygon (not illustrated). 
     Referring to  FIGS. 6A and 6B , a second implementation of a light guide portion of  FIG. 2  is shown. In  FIGS. 6A and 6B , the light guide portion is exemplified by a recess. However, the light guide portion  142  can be a protrusion projected from the frame surface  118 . As indicated in  FIG. 6A , the cross-sectional silhouette S 1  of the light guide portion  142  is a curve, which can be a portion of a circular curve, such as an arc curve in which the ratio of width X 1  to height Y 1  ranges from 0.1 to 10. Or, in another implementation, the curve can be a portion of an elliptical curve (not illustrated), in which the ratio of width X 1  to height Y 1  also ranges from 0.1 to 10. Or, as indicated in  FIG. 6B , the light guide portions  186  are interconnected and the cross-sectional silhouette S 4  of the light guide portions  186  is a curve, which can be a portion of a circular curve, such as a circular curve in which the ratio of width X 2  to height Y 2  also ranges from 0.1 to 10. Or, in another implementation, the curve can be a portion of an elliptical curve (not illustrated), in which the ratio of width X 2  to height Y 2  also ranges from 0.1 to 10. 
       FIG. 7A  shows the frame  110  viewed along the direction V 1  of  FIG. 1 . In  FIGS. 7A and 7B , the extension path of the light guide portion  120  is a straight line substantially parallel to or perpendicular to one side  146  of the LGP  106 . Referring to  FIG. 7A , the extension path of the light guide portion is parallel to one side  146  of the frame  110 . Referring to  FIG. 7B , the light guide portion  148  is a straight line, and the extension path of the light guide portion  148  is substantially perpendicular to one side  152  of the frame  150 . Alternatively, the extension path of the light guide portion does not have to be a straight line. The light guide portion can be an arc or a wave-shaped (not shown in FIG). In other embodiments, the extension path of the light guide portion can be continuous in particular segments only, and is not limited to the exemplification in the present embodiment of the invention. 
     In the present embodiment of the invention, the frame surface  118  is exemplified by a plane. However, in other embodiments, the curvature of the frame surface  118  corresponds to the curvature of the LGP  106 . Referring to  FIGS. 8A and 8B , another implementation of the frame of  FIG. 1  is shown. As indicated in  FIG. 8A , the frame surface  160  and a surface  164  of the LGP  162  are both a curved surface, the silhouette of the curved surface of the frame surface  160  corresponds to the silhouette of the surface  164  of the LGP  162 . As indicated in  FIG. 8B , the frame surface  166  and a surface  170  of the LGP  168  are both a curved surface, and the silhouette of the curved surface of the frame surface  166  corresponds to the silhouette of the surface  170  of the LGP  168 . Referring to  FIGS. 8C and 8D , another implementation of the frame of  FIGS. 8A to 8B  is shown. As indicated in  FIG. 8C , the frame surface  172  is a curved surface, and a surface  176  of the LGP  174  is a plane. As indicated in  FIG. 8D , the frame surface  178  is a curved surface, and a surface  182  of the LGP  180  is a plane. The curvature on the appearance of the frame surface  172  of  FIG. 8C  differs with that of the frame surface  178  of  FIG. 8D . 
     Second Embodiment 
     Referring to  FIG. 9 , a display device according to a second embodiment of the invention is shown. The second embodiment differs with the first embodiment in that, the edge type back light module  304  of the second embodiment partly or completely replaces the first BEF  122 , the diffusion film  124  and the second BEF  126  of the first embodiment with a dual brightness enhancement film (DBEF)  302 , which is adjacent to the light-emitting surface  114  of the LGP  106 . Referring to  FIG. 1 , the first BEF  122  can be replaced by a multi-functioned brightness enhancement film (not illustrated) such as a brightness enhancement film-reflective polarizer (BEF-RP). As for other similarities, the same designations are used and are not repeated here. 
     When the DBEF  302  is used, if the predetermined angle A 1  is preferably controlled at 0 degree, the light leakage L 1  can be emitted from the DBEF  302  in a direction perpendicular to the DBEF  302  and emitted towards the display panel  102 . Thus, the display has the brightest luminance. When the BEF-RP (not illustrated) is used and the light guide portion has suitable design, the predetermined angle of the light emitted from the light-emitting surface of the LGP is preferably controlled to be within the range of 35 to 65 degrees, the display luminance has the brightest luminance. The predetermined angle of the light emitted from the light-emitting surface refers to the peak of the light intensity. 
     After the light leakage L 1  (illustrated in  FIG. 2 ) contacts the light guide portions such as the light guide portion  120 ,  132 ,  138 ,  140 ,  142 ,  148 , or  186 , the light guide portion guides the light leakage L 1  to be emitted from the light-emitting surface  114 . The outgoing direction of the light leakage L 1  emitted from the light-emitting surface  114  is perpendicular to the light-emitting surface, so that the light leakage L 1  is emitted from the first BEF  122  in a direction perpendicular to the first BEF  122  and emitted towards the display panel  102 . 
     Third Embodiment 
     Referring to  FIG. 10 , a display device according to a third embodiment of the invention is shown. The third embodiment differs with the first embodiment in that, the edge type back light module  402  of the third embodiment dispenses with one of the first BEF  122  and the second BEF  126  of the first embodiment. In the present embodiment of the invention, the second BEF  126  is dispensed with for exemplification. As for other similarities, the same designations are used and are not repeated here. 
     When the first BEF  122  is combined with the diffusion film  124 , if the predetermined angle A 1  of the light emitted from the light-emitting surface  114  is controlled to be within the range of 15 to 45 degrees, the light leakage L 1  is emitted from the first BEF  122  in a direction perpendicular to the BEF  122  and emitted towards the display panel  102 . Thus, the display has the brightest luminance. The predetermined angle A 1  of the light emitted from the light-emitting surface  114  refers to the peak of the light intensity. 
     After the light leakage L 1  contacts the light guide portion such as the light guide portion  120 ,  132 ,  138 ,  140 ,  142 ,  148 , or  186 , the light guide portion guides the light leakage L 1  to be emitted from the light-emitting surface  114 . The angle contained between the outgoing direction of the light leakage L 1  emitted from the light-emitting surface  114  and the normal direction of the light-emitting surface LN ranges from 15 to 45 degrees, so that the light leakage L 1  is emitted from the first BEF  122  in a direction perpendicular to the first BEF  122  and emitted towards the display panel  102 . 
     The edge type back light module and the display device using the same disclosed in the above embodiments of the invention have many advantages exemplified below: 
     (1) Compared with the conventional frame, the frame of the present embodiment of the invention dispenses with the use of the reflective plate, hence saving the cost relevant to the reflective plate, such as the material cost, the design cost, and the cost of manufacturing and adhering the reflective plate. 
     (2) The light guide portion not only reflects the light leakage back to the LGP but also guides the light leakage to be emitted from the LGP at a predetermined angle, further meeting the optical requirement of the optical film. 
     (3) The light guide portion of the present embodiment of the invention is not subject to the number of the optical film. The light guide portion of the invention still meets the optical requirements regardless how many BEFs or diffusion films are used in the first embodiment, the second embodiment and the third embodiment. 
     While the invention has been described by way of example and in terms of a preferred embodiment, it is to be understood that the invention is not limited thereto. On the contrary, it is intended to cover various modifications and similar arrangements and procedures, and the scope of the appended claims therefore should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements and procedures.