Patent Publication Number: US-2012026423-A1

Title: Edge-lit backlight module and lcd using the same

Description:
TECHNICAL FIELD OF THE INVENTION 
     The present invention relates to a liquid crystal displaying technique, more particularly, to an edge-lit backlight module for a liquid crystal display (LCD), which is able to realize good local dimming, and to an LCD using such an edge-lit backlight module. 
     BACKGROUND OF THE INVENTION 
     Nowadays, liquid crystal displays (LCDs) are becoming the main stream of displaying technique, and are being widely applied to various electronic products such as a mobile phone, a PDA, a digital camera, a computer screen, a notebook screen and the like. A backlight module is one of the crucial components being a deciding factor of the quality of the LCD. Generally, the illuminating light source of the backlight module is implemented by an electro-luminance (EL) element, a light emitting diode, or a cold cathode fluorescent lamp. Among the above three light sources, LEDs are widely utilized in small LCD devices due to the small volume, light weight and excellent controllability. 
     LED backlight modules can be classified into types of direct-lit backlight modules and edge-lit backlight modules according to the disposal of the light sources thereof. In a direct-lit backlight module, LED dice are evenly disposed under a liquid crystal panel and server as the light source, thereby uniformly transmitting the backlight all over the screen. 
       FIG. 1  is a schematic diagram showing an application example of a conventional direct-lit LED backlight module. For sake of simplification and clarity, some components are omitted in the drawings. As shown, in an LCD, a light source constituted by an LED matrix  20  is disposed under a liquid crystal glass  10 . The LED matrix  20  comprises a number of LED dice  201  arranged in columns and rows. The liquid crystal glass  10  comprises liquid crystal being sandwiched therein. The liquid crystal glass has been used in various applications. Since it is not the focus of the present invention, the details thereof are omitted herein. 
     In such a structure, the LED dice  201  are arranged under the liquid crystal glass  10  to provide the liquid crystal glass  10  with illumination light. Accordingly, local dimming can be easily realized. In this example, the liquid crystal glass  10  is divided into regions A 1  to A 6 , B 1  to B 6 , C 1  to C 6  and D 1  to D 6 . By controlling the LED dice corresponding to the respective regions, the local dimming of each region can be achieved. The LED matrix  20  can transfer the heat thereof directly to a back plate (not shown) to accomplish heat dissipation. However, a great quantity of the LED dice is necessary for such a structure, and more electrical power is consumed thereof. Furthermore, the finished LCD will have a greater thickness since there is a layer of the LED matrix  20 . 
       FIG. 2  is a schematic diagram showing an application example of a conventional edge-lit LED backlight module. As shown, LED light bars  22 ,  24  are disposed at the two long sides of a liquid crystal glass  11  respectively. Taking the LED light bar  24  as an example, the LED light bar  24  comprises a plurality of LED dice  241 . In this example, the LED light bar  22  is used to control the luminance of each of the regions A 1  to A 6  of the liquid crystal glass  11 ; the LED light bar  24  is used to control the luminance of each of the regions B 1  to B 6  of the liquid crystal glass  11 . The edge-lit LED backlight module requires fewer LED dice. However, the number of regions of the edge-lit backlight module in which the local dimming can be realized is considerably less than that of the direct-lit backlight module shown in  FIG. 1  since only the LED light bars  22 ,  24  which are disposed at the two sides of the liquid crystal glass  11  are used for illumination and the illuminating range of each LED die is limited. 
     Therefore, an improved backlight module is required to solve the existing problems of the current technique. 
     SUMMARY OF THE INVENTION 
     A main objective of the present invention is to provide an edge-lit backlight module, which can achieve local dimming for multiple regions with limited power consumption. 
     Another objective of the present invention is to provide a liquid crystal display (LCD) comprising an edge-lit backlight module, which can achieve local dimming for multiple regions with limited power consumption. 
     To achieve the foregoing objectives, the present invention provides an edge-lit backlight module. The edge-lit backlight module comprises a light guide plate divided into several sections, the light guide plate, which is composed of the sections, is formed as a ladder shape so that each section has a side edge exposed; and a plurality of light sources, each of the light sources is disposed at the exposed side edge of one of the sections of the light guide plate for illuminating the section. 
     In accordance with the present invention, in an embodiment, each of the top surface and the bottom surface of the light guide plate, which is composed of sections, is formed as a ladder shape, and two adjacent sections are jointed with each other in different levels to partially overlap. 
     In another embodiment, one of the top surface and the bottom surface of the light guide plate, which is composed of sections, is formed as a ladder shape and the other surface is flat so that each section has a side edge exposed. One of two adjacent sections of the light guide plate has a slot at the side edge for engaging with the other one section, while the remaining portion of the side edge is exposed, and the reserved thickness of the exposed portion of the side edge is able to define a space which is sufficient for disposing the light source. 
     In accordance with the present invention, in the edge-lit backlight module, the overlapping portions of the adjacent sections and also the adjacent sections of the light guide plate can be separated by setting a reflective layer. 
     In accordance with the present invention, the light sources in the edge-lit backlight module are implemented by LED light bars. 
     To achieve the above objectives, the present invention provides a liquid crystal display comprising a liquid crystal panel and the edge-lit backlight module described above. 
     The liquid crystal display further comprises a back plate, which is formed as ladder-like to be adaptable for receiving the light guide plate and the light sources. 
     To make the present invention more manifest and understandable, preferred embodiments will be described in detail in conjunction with the appending drawings: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram showing an application example of a conventional direct-lit LED backlight module. 
         FIG. 2  is a schematic diagram showing an application example of a conventional edge-lit LED backlight module. 
         FIG. 3  is a schematic diagram showing a perspective view of an edge-lit backlight module in accordance with a first embodiment of the present invention. 
         FIG. 4  is a schematic diagram showing a sectional view of the edge-lit backlight module of  FIG. 3 . 
         FIG. 5  is a schematic diagram showing a sectional view of an edge-lit backlight module in accordance with a second embodiment of the present invention. 
         FIG. 6  is a schematic diagram of a perspective view showing the edge-lit backlight module in combination with a back plate of an LCD in accordance with the present invention. 
         FIG. 7  is a schematic diagram showing a sectional view of an edge-lit backlight module in accordance with a third embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     To make the forgoing objectives, features, and advantages more manifest and understandable, preferred embodiments of the present invention will be described in detail in conjunction with the appending drawings. Further, the directional terms described in the present invention such as “above”, “under”, “front”, “rear”, “left”, “right”, “internal”, “external”, “side”, “bottom”, “top” or the like only indicate the directions with reference to the drawings. Thus, those directional terms are only used for describing and understanding the present invention rather than limiting the scope of the present invention. 
     Generally speaking, a liquid crystal display (LCD) comprises at least a liquid crystal panel (e.g. a liquid crystal glass) and a backlight module. The backlight module is utilized for illuminating the liquid crystal panel. The backlight module usually comprises a light source or light sources, a light guide plate and other optical films such as a reflector film, a diffuser film, a polarizer film and the like. The light guide plate is generally made of transparent material such as optical PMMA (Polymethyl Methacrylate). The light guide plate is used to scatter the light from the light source(s) all over the displaying panel of the LCD. The above structure can be disposed on a back plate of the LCD. In the present invention, the light guide plate is designed to have a specific geometrical structure and the light sources are adaptively disposed so as to achieve the effect of local dimming for multiple regions without significantly increasing power consumption. 
     Please refer to  FIG. 3  and  FIG. 4 .  FIG. 3  is a schematic diagram showing a perspective view of an edge-lit backlight module in accordance with a first embodiment of the present invention, and  FIG. 4  is a schematic diagram showing a sectional view of this edge-lit backlight module. According to the present invention, a light guide plate (LGP)  100  is divided into several sections such as the four sections: Section A  110 , Section B  120 , Section C  130  and Section D  140  shown in the drawings. Distinguishable from a conventional LGP, those LGP sections  110  to  140  are not disposed on the same plane. At least two adjacent sections are disposed at different levels to form a ladder shape. For example, Section A  110  and Section B 120  form a ladder shape. Section A is at the higher level while Section B  120  is at the lower level. Section C  130  and Section D  140  also form a ladder shape. Section D  140  is at the higher level while Section C  130  is at the lower level. In the present embodiment, the adjacent Section B  120  and Section C  130  are disposed side by side on the same plane. 
     According to the present invention, the sections of the LGP  100  are disposed at different levels, so that it is possible to dispose a light source at a side edge of each section. As shown in the drawings, a bar-like light source (e.g. an LED light bar  210 ) is disposed at a side edge of Section A  110 . Section B  120  is disposed at a level different from Section A  110 , and therefore a space is made at the side edge of Section B to dispose the light bar such as an LED light bar  220 . Similarly, an LED light bar  240  is disposed at a side edge of Section D  140 . Section C  130  and Section D  140  are disposed at different levels so that a space is made at a side edge of Section C  130  to dispose an LED light bar  230 . 
     The width of each of the sections: Section A  110 , Section B  120 , Section C  130  and Section D  140  is relative to the illuminating range of each light source (i.e. the light bars  210 ,  220 ,  230 ,  240 ). 
     By dividing the LGP into several sections and disposing the sections at different levels to form a ladder shape, spaces are created beside the side edges of the sections to install the light bars such as LED light bars. The local dimming of each section is achieved by controlling the corresponding light source. Therefore, a backlight module with a large area can be produced and excellent local dimming can be accomplished at the same time. Furthermore, in comparison with the conventional direct-lit backlight module, the edge-lit backlight module in accordance with the present invention does not need to use so many light source elements (e.g. LED dice), and accordingly the power consumption can be reduced. 
       FIG. 5  is a schematic diagram showing a sectional view of an edge-lit backlight module in accordance with a second embodiment of the present invention, in which the same reference numbers indicate the same components. As in the previous embodiment, the LGP  100  is composed of four sections: Section A  110 , Section B  120 , Section C  130 , Section D  140 , in which Section A  110  is adjacent to Section B  120 , and Section A  110  is at the higher level while Section B  120  is at the lower level; Section B is adjacent to and joined with Section C  130  and is located at the same level (the lower level) with Section C  130 ; Section C  130  is adjacent to and joined with Section D  140 , and Section C  130  is located at the lower level while Section D  140  is located at the higher level; and Section D  140  is at the same level (the higher level) with Section A  110 . 
     As shown, in order to have the LGP  100  keep a certain degree of strength, Section B  120  and Section A  100  partially overlap at the joint to form an overlapping portion. In this overlapping portion, in addition to the corresponding LED light bar  220 , Section B  120  is also influenced by the LED light bar  210  corresponding to Section A  110 . This is because the illuminating range of the LED light bar  210  extends to the end of Section A  100 , that is, the portion overlapped by Section B  120 . Similarly, the portion of Section A  110 , which is overlapped by Section B  120 , in addition to the corresponding LED light bar  210 , is also influenced by the LED light bar  220  corresponding to Section B. Therefore, a phenomenon referred to as “clutter” occurs. 
     To prevent the light of the corresponding light source for Section B  120  (i.e. the LED light bar  220 ) from entering into Section A  110 , and in the meanwhile prevent the light of the corresponding light source for Section A  110  (i.e. the LED light bar  210 ) from entering into Section B  120 , in the present embodiment, a reflective layer  115  is provided at the bottom of Section A  110  and also at the side of one end of Section A  110  which is opposite to the end near the LED light bar  210  (i.e. the end located at the overlapping portion) to separate Section A  110  from Section B  120  at the overlapping portion. Similarly, a reflective layer  135  is provided on the bottom of Section D  140  and also at the side of an end of Section D  140  in the overlapping portion. At the overlapping portion, Section A  110  is separated from Section B by using the reflective layer  115 . Similarly, at the overlapping portion, Section C  130  is separated from Section D  140  by using the reflective layer  135 . A reflective layer  125  is provided at the junction between Section B  120  and Section C  130  to separate these two sections, thereby avoiding interference of the lights from the respective light sources corresponding to these sections. Accordingly, Section A  110 , Section B  120 , Section C  130  and Section D  140  form a continuous planar light source jointly, and each of the sections can be controlled individually and independently. 
     For enhancing the firmness and structural stability of the whole edge-lit backlight module, a back plate of an LCD (not shown) can be formed a specific shape according to the bottom profile of the ladder-like LGP  100  of the edge-lit backlight module in the present invention. The back plate secures the LGP  100  in coordination with a mold frame (not shown), as shown in  FIG. 6 , which is a schematic diagram of a perspective view showing the edge-lit backlight module in combination with the back plate of an LCD in accordance with the present invention. As shown, the back plate  50  of the LCD is formed as a ladder shape and defines a ladder-like receiving tray, which is suitable for receiving the ladder-like LGP  100  as well as the LED light bars  210  to  240  disposed at the side edges of the respective sections  110  to  140 . 
       FIG. 7  is a schematic diagram showing a sectional view of an edge-lit backlight module in accordance with a third embodiment of the present invention. In the present embodiment, the backlight module comprises a light guide plate (LGP)  300 . The LGP  300  comprises four sections: Section A  310 , Section B  320 , Section C  330  and Section D  340  and LED light bars  410 ,  420 ,  430  and  440  are disposed at the side edges of these sections, respectively. The difference between the present embodiment and the previous embodiments is that the shapes of the intermediate Section B  320  and Section C  330  are changed and cease to be simply rectangular as the previous embodiments. 
     As shown, in the present embodiment, Section B  320  is thicker and has a recess  324  at the left side edge for engaging with Section A  320 . After engaging with each other, the top surfaces of Section A  310  and Section B  320  are flat. In addition, the bottom surfaces of Section A  310  and Section B  320  form a ladder shape since these two sections have different thicknesses. A portion of the side edge below the recess  324  of Section B  320  is exposed. The reserved thickness below the recess  324  at the side edge of Section B is sufficient to dispose an LED light bar  420  at the left side edge of Section B  320  and in the meanwhile under Section A  310  to illuminate Section B. 
     Similarly, Section C  320  is thicker than Section D  340  and has a recess  334  at a side edge (i.e. the right side edge shown in the drawing) to engage with Section D  340 . After engaging with each other, the top surfaces of Section D  340  and Section C  330  are flat. In addition, the bottom surfaces of Section D  340  and Section C  330  form a ladder shape since these two sections have different thicknesses. A portion of the side edge (i.e. the right side edge shown in the drawing) below the recess  334  of Section C  330  is exposed. The reserved thickness below the recess  334  at the side edge of Section C is sufficient to dispose an LED light bar  430  at the right side edge of Section C  330  and in the meanwhile under Section D  340  to illuminate Section C. Section B  320  and Section C  330  have the same thickness and are shaped in mirror image symmetry. 
     Such a structure makes the LGP  300  firmer and easier to be secured. It is noted that the top surface of the LGP  300  described above is flat and the bottom surface is ladder-like. However, quite contrary, that is, it is also practicable that the top surface is ladder-like and the bottom surface is flat. In addition, the four LGP sections can be formed integrally. Further, as the previous embodiment, a reflective layer can be applied between two adjacent sections at the overlapping portion to avoid clutter phenomenon. The manner of implementation is similar to the previous embodiment, and therefore the description thereof is omitted herein. 
     As shown, in the present embodiment, the top surface of the LGP  300  of the edge-lit backlight module is flat, just as a general LGP, while the bottom surface thereof is ladder-like, by forming the LGP  300  such a specific shape, spaces are created to dispose the LED light bars  420  and  430  for illuminating Section B  320  and Section C  330 , respectively. 
     It is noted that the respective embodiments described above each comprises four sections, however, the present invention is not limited thereto. For example, the edge-lit backlight module LGP in accordance with the present invention may comprise three sections or more than four sections. 
     From the foregoing, while the present invention has been disclosed by describing the preferred embodiments, various modifications and alterations can be made by persons skilled in this art without departing from the spirit and realm of the present invention, and therefore the claimed scopes of the present invention to be protected should be according to the scopes defined in the appended claims.