Abstract:
Several optical mechanism designs for making luminance of the outer portion of a back light module of edge lighting type to become higher than luminance of the inner portion of the back light module are disclosed in accordance with the present invention. The disclosed optical mechanism designs can cooperate with each other to enhance the optical effect of the back light module. Additionally, the back light modules of the present invention are feasible for use in various scanners or liquid crystal displays.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to back light modules, and more particularly, to back light modules whose outer portion has higher luminance than inner portion thereof.  
         [0003]     2. Description of the Prior Art  
         [0004]     A back light module is one of the key components for the liquid crystal display (LCD) or the scanner. The back light module comprises light sources and other optical devices for reflecting or refracting light to provide uniform light output. The light source of the back light module is typically a cold cathode fluorescent lamp (CCFL) or light emitting diode (LED). In general, the back light module can be divided into two groups, the edge lighting type and the direct lighting type. The two groups are categorized by the positions of the light sources thereof.  
         [0005]     In the conventional art, the main concept of designing both the edge lighting type and the direct lighting type is to provide a uniform light output from the back light module, i.e., to uniform the luminance distribution of the back light module. Unfortunately, such a design concept may negatively affect the performance of some applications.  
         [0006]     For example, suppose that a conventional back light module having uniform luminance distribution is employed in a scanner as a back light source required for scanning transparencies, and positive or negative films. The brightness of the outer portion of a scanned image received by an optical module of the scanner is usually lower than the brightness of the inner portion of the scanned image due to the optical characteristics or mechanical designs of the optical module, and thereby reducing the scanning quality of the scanner.  
       SUMMARY OF THE INVENTION  
       [0007]     An exemplary embodiment of a back light module of edge lighting type is disclosed comprising: a light guide plate (LGP) for scattering incident light to a light output surface; a diffuser positioned on the light output surface of the light guide plate for diffusing light from the light output surface; a reflecting layer positioned on a reflection surface of the light guide plate for reflecting light into the light guide plate; and a light emitting device for emitting light to at least one side of the light guide plate, wherein the outer portion of the light emitting device along a first axis having higher luminous intensity than the inner portion thereof.  
         [0008]     Another exemplary embodiment of a back light module of edge lighting type is disclosed comprising: a light emitting device for emitting light; a light guide plate (LGP) for scattering light from the light emitting device to a light output surface, wherein a plurality of reflection patterns (or referred to as reflection elements) being formed on a reflection surface of the light guide plate so that the outer portion of the light guide plate has higher luminance than the inner portion of the light guide plate; a diffuser positioned on the light output surface of the light guide plate for diffusing light from the light output surface; and a reflecting layer positioned on the reflection surface of the light guide plate for reflecting light into the light guide plate.  
         [0009]     Another exemplary embodiment of a back light module of edge lighting type is disclosed comprising: a light emitting device for emitting light; a light guide plate (LGP) for scattering light from the light emitting device to a light output surface; a diffuser positioned on the light output surface of the light guide plate for diffusing light from the light output surface, wherein the outer portion of the diffuser has higher light transmittance than the inner portion of the diffuser; and a reflecting layer positioned on a reflection surface of the light guide plate for reflecting light into the light guide plate.  
         [0010]     Another exemplary embodiment of a back light module of edge lighting type is disclosed comprising: a light guide plate (LGP) for scattering incident light to a light output surface; a diffuser positioned on the light output surface of the light guide plate for diffusing light from the light output surface; a reflecting layer positioned on a reflection surface of the light guide plate for reflecting light into the light guide plate; a light emitting device for emitting light to the light guide plate; and a reflector positioned on a side of the light emitting device such that the light emitting device being disposed between the reflector and the light guide plate, the reflector for reflecting light from the light emitting device to the light guide plate; wherein the outer portion of the reflector has higher reflectivity or larger reflecting area than the inner portion of the reflector.  
         [0011]     Thereto, another exemplary embodiment of a back light module of edge lighting type is disclosed comprising: a light guide plate (LGP) for scattering incident light to a light output surface; a diffuser positioned on the light output surface of the light guide plate for diffusing light from the light output surface; a reflecting layer positioned on a reflection surface of the light guide plate for reflecting light into the light guide plate; a light emitting device for emitting light to the light guide plate; and two reflectors positioned on a side of the light emitting device with each corresponding to one of two ends of the light emitting device such that the light emitting device being disposed between the two reflectors and the light guide plate, the two reflectors for reflecting light emitted from the two ends of the light emitting device to the light guide plate.  
         [0012]     These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]      FIG. 1  is a simplified diagram of a back light module of the edge lighting type according to one embodiment of the present invention.  
         [0014]      FIG. 2  is a schematic diagram illustrating a luminous intensity distribution of a light emitting device of  FIG. 1  according to one embodiment of the present invention.  
         [0015]      FIG. 3  is a diagram showing different embodiments of the light emitting device of  FIG. 1  in accordance with the present invention.  
         [0016]      FIG. 4  is a diagram showing reflection patterns/elements on a light guide plate of  FIG. 1  according to one embodiment of the present invention.  
         [0017]      FIG. 5  and  FIG. 6  are other embodiments of the back light module of the edge lighting type in accordance with the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0018]     Please refer to  FIG. 1 , which shows a simplified diagram of a back light module  100  of the edge lighting type according to one embodiment of the present invention. As shown, the back light module  100  comprises a light guide plate (LGP)  110 ; a diffuser  120  position on a light output surface  112  of the LGP  110 ; a reflecting layer  130  positioned on a reflection surface  114  of the LGP  110 ; and a light emitting device  140  for emitting light to at least one side of the LGP  110 . The LGP  110  is arranged for scattering and guiding incident light to the light output surface  112 . Then, the diffuser  120  diffuses light from the light output surface  112 . The reflecting layer  130  is utilized for reflecting light into the LGP  110  to increase the light usage efficiency. The LGP  110  is generally made by acrylic resin, but this is not a restriction of the practical applications. Additionally, the LGP  110  can be planar or wedge-shaped.  
         [0019]      FIG. 2  illustrates a luminous intensity distribution of the light emitting device  140  according to one embodiment of the present invention. As shown, in this embodiment, the outer portion  140 A and  140 B of the light emitting device  140  along a first axis  10  have higher luminous intensity than the inner portion  140 C of the light emitting device  140 . This configuration results in the two ends of the LGP  110  receiving more light than the middle portion (i.e., the inner portion) of the LGP  110 . As a result, the luminance of the outer portion of the LGP  110  along a second axis  12  is higher than the luminance of the inner portion thereof, i.e., the LGP  110  has a concave-down luminance distribution. Preferably, the LGP  110  has an arc-shaped luminance distribution such as a curve  16  shown in  FIG. 1 .  
         [0020]      FIG. 3  shows three different embodiments of the light emitting device  140  in accordance with the present invention. In implementations, the light emitting device  140  may be a lamp having a bended shape such as a U-shaped lamp  310  shown in  FIG. 3 . The U-shaped lamp  310  can be implemented with a cold cathode fluorescent lamp (CCFL). A light emitting device  320  shown in  FIG. 3  is an alternative embodiment. As shown, the light emitting device  320  comprises a straight lamp  332  (e.g., a straight CCFL) and a plurality of luminance units  324  for enhancing the luminous intensity of the outer portion of the light emitting device  320 . The plurality of luminance units  324  can be a plurality of electro luminances (ELs), a plurality of light emitting diodes (LEDs), or a combination of the two. A light emitting device  330  shown in  FIG. 3  is another embodiment. The light emitting device  330  is composed of a plurality of luminance units  332 . Similarly, the plurality of luminance units  332  can be a plurality of ELs, a plurality of LEDs, or a combination of the two. It can be appreciated by those of ordinary skill in the art that the luminous intensity of the outer portion of the light emitting device  330  along the axis  10  can become higher than the inner portion of the light emitting device  330  by properly adjusting the arrangement density (i.e., spacing) of the plurality of luminance units  332 .  
         [0021]     Please note that the light emitting device  140  can also be implemented with other design choices. In addition, the number of light emitting devices employed in the back light module  100  is not a restriction of the present invention, i.e., two, or more than two, sets of light emitting devices may be employed as the light source in the back light module  100 .  
         [0022]     In the previous embodiment, the back light module  100  enhances the luminance of the outer portion thereof (or the outer portion of the LGP  110 ) by utilizing the light emitting device  140  whose outer portion has higher luminous intensity than the inner portion. In practice, the back light module  100  can obtain the same optical characteristic by adopting other optical mechanisms.  
         [0023]     For example, a plurality of reflection patterns (or referred to as reflection elements) are typically formed on the reflection surface  114  of the LGP  110  for destroying total reflection of light so that the incident light can be guided to the light output surface  112 . The reflection patterns/elements formed on the reflection surface  114  of the LGP  110  can be properly designed such that the outer portion of the LGP  110  has higher luminance than the inner portion thereof. Further details will be explained with reference to  FIG. 4 .  
         [0024]      FIG. 4  shows a diagram showing reflection patterns/elements on the reflection surface  114  of the LGP  110  according to one embodiment of the present invention. In this embodiment, the reflection patterns/elements on the reflection surface  114  of the LGP  110  is a plurality of reflector dots  410  printed on the reflection surface  114 . The plurality of reflector dots  410  has variety in size and arrangement density (or spacing). As shown in  FIG. 4 , the outer portion of the reflection surface  114  along the axis  12  has larger reflector dots than the inner portion and has higher arrangement density of reflector dots than the inner portion. This configuration results in the outer portion of the LGP  110  has higher luminance than the inner portion of the LGP  110 .  
         [0025]     Instead of the printed reflection dots, the reflection patterns/elements formed on the reflection surface  114  of the LGP  110  may be a plurality of microstructures such as micro-lens or v-cut grooves. Similarly, the luminance of the outer portion of the LGP  110  can become higher than that of the inner portion by properly arranging these microstructures. The method of creating micro-lens or v-cut grooves on the reflection surface  114  is well known in the art and further details are therefore omitted for brevity.  
         [0026]     In addition, the luminance distribution of the back light module  100  can be adjusted by modifying the design of the diffuser  120 . For example, in one embodiment, the diffuser  120  of the back light module  100  has non-uniform light transmittance distribution. Specifically, the diffuser  120  of this embodiment is purposefully designed such that the light transmittance of the outer portion of the diffuser  120  along a third axis  14  is better than that of the inner portion thereof. As a result, the back light module  100  can obtain the same optical characteristic as the foregoing embodiments, i.e., the luminance of the outer portion of the back light module  100  along the second axis  12  (or the third axis  14 ) will be higher than the luminance of the inner portion.  
         [0027]      FIG. 5  and  FIG. 6  are other embodiments of back light module of the edge lighting type in accordance with the present invention. A back light module  500  shown in  FIG. 5  and another back light module  600  shown in  FIG. 6  are similar to the back light module  100  described previously. Therefore, components that have the same implementations and operations are labeled the same. The difference among the back light modules  100 ,  500  and  600  will be explained in below.  
         [0028]     As shown in  FIG. 5 , the back light module  500  further comprises a reflector  510 . The reflector  510  is positioned on a side of the light emitting device  140  such that the light emitting device  140  is disposed between the reflector  510  and the LGP  110 . The reflector  510  is arranged for reflecting light from the light emitting device  140  to the LGP  110  to improve the light usage efficiency. In this embodiment, the reflectivity of the reflector  510  is not uniform. Instead, the outer portion of the reflector  510  has higher reflectivity than the inner portion of the reflector  510 . Accordingly, the outer portion of the reflector  510  has better reflecting performance than the inner portion. In other words, the reflector  510  not only increases the light usage efficiency of the LGP  110  but also exposes the outer portion of the LGP  110  to more light thereby enhancing the luminance of the outer portion of the LGP  110  along the axis  12 . Alternatively, the reflecting area of the outer portion of the reflector  510  can be designed to be larger than the reflecting area of the inner portion to reach or enhance the above optical effect.  
         [0029]     In the back light module  600 , two reflectors  610  and  620  are positioned on a side of the light emitting device  140  such that the light emitting device  140  is disposed between the two reflectors and the LGP  110 . As shown in  FIG. 6 , the two reflectors  610  and  620  are respectively arranged to correspond to the two ends of the light emitting device  140  for reflecting light emitted from the two ends of the light emitting device  140  to the LGP  110 . It should be appreciated by those of ordinary skill in the art that the luminance of the outer portion of the LGP  110  can become higher than that of the inner portion thereof due to the configuration of the two reflectors  610  and  620  illustrated in  FIG. 6 .  
         [0030]     Note that, the different optical mechanism designs mentioned above can function independently or co-operate with each other to enhance the optical effect.  
         [0031]     The disclosed back light module of the edge lighting type can be utilized as the back light source for various scanners and LCDs. For example, the back light module disclosed in accordance with the present invention can be applied in a scanner capable of scanning transparencies, and positive or negative films. The back light module disclosed in accordance with the present invention will significantly improve the fall off problems of the optical module caused by the optical characteristics or mechanical designs of the optical module.  
         [0032]     Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.