Abstract:
A light guide module ( 10 ) for use in a flat panel display ( 21 ) comprises a light guide pipe ( 20 ) having a light emitting surface ( 21 ), and a light incident surface ( 25 ) orthogonal to the light emitting surface. A light diffusion arrangement ( 30 ) is deployed over the light emitting surface and includes organic scattering balls ( 31 ) homogenously mixed within a bonding agent ( 33 ). At least a light source ( 60 ) is arranged adjacent the light incident surface to project light beams into the light guide module.

Description:
BACKGROUND OF INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a light guide module plate, and more particularly to a light guide module having a light diffusion arrangement over a light emitting surface, thereby providing uniform luminance distribution over the entire light emitting surface.  
           [0003]    2. Description of Related Art  
           [0004]    A liquid crystal display is capable of displaying a clear and sharp image over a wide area. It is thus used with various devices in which a message or picture needs to be illustrated. However, a liquid crystal itself does not emit light, therefore, it has to be back-lit by a light source to display the messages and/or pictures shown there.  
           [0005]    In an ideal liquid crystal display, the backlight provides light evenly across the entire surface. In addition, the apparatus has to meet the requirements of being small in size, light in weight, and bright enough, while having a low power consumption.  
           [0006]    U.S. Pat. No. 5,438,484 issued to Kanda et al. discloses a surface lighting device. A variety of prior art surface lighting devices are disclosed in FIGS.  1  to  5  of the Kanda patent. The light source arrangements in the surface lighting devices of FIGS.  1  to  5  are generally referred to as “edge-type” light sources. Kanda describes the disadvantages of the prior art surface lighting devices in detail, i.e., that the surface areas closer to the light sources are brighter than the central areas. According to Kanda&#39;s explanation in the specification, “However, as described above, the surface lighting device of an edge-type has a low luminance in the central portion between the light sources and a high luminance in the vicinity of the light sources as indicated by a broken line C shown in FIG. 9. This is because the light sources  1   a  and  1   b  emit diffusion light and make the vicinity of the light sources  1   a  and  1   b  bright while the light emitted from the light sources  1   a  and  1   b  mostly reach the opposite light source  1   b  and  1   a  to be diffused, respectively, thus making the vicinity of the light sources  1   a  and  1   b  brighter. As a result, it is inevitable that the effective light range (effective emission surface) of the foregoing lighting device will become narrower because its overall luminance must be adjusted to latch evenly as a backlight with the lowered luminance between the central portion of the light sources  1   a  and  1   b . Thus, a problem is encountered that the light utilization efficiency for the apparatus as a whole is reduced.” See Column  2 , lines  31  to  49 .  
           [0007]    Kanda provides a solution, as shown in FIGS.  11  to  16 , by providing “a light guide configured by a plural light transmitting members joined together, so that the junction surface therebetween crosses the light emitting surface.” As a result, according to Kanda, the luminance emitted from edge-type light sources is evenly distributed across the entire area.  
           [0008]    Kanda provides another solution in FIGS.  17  to  23 , typically shown in FIG. 23. In this application, the light source is arranged directly behind the diffusion board, instead of at the edge of a light guide, as shown in FIG. 1 of the Kanda patent. However, although this arrangement does provides a brighter central displaying area, it creates a problem of color chromaticity across the liquid crystal display. As explained by Kanda in Column  12 , lines  19 - 49 . Kanda then uses a “light source having preferably be more blueish than the standard color” to solve the “yellowish” problem.  
           [0009]    Aside from use of the “blueish light source”, it is noted that a “light curtain”, reference numeral  14  of FIG. 22, has also been used to reduce the luminance projected toward the display area immediately in front of the light source. It should be easy to appreciate that the more parts used within the liquid crystal display, the more laborious the effort needed to assemble the display. No doubt, the size and weight of the liquid crystal display will inevitably be increased.  
           [0010]    U.S. Pat. No. 5,881,201 issued to Khanarian discloses improved light pipes for backlighting liquid crystal display devices. The light pipes comprise transparent polymers with scattering centers. A preferred composition for such light pipes comprises a cycloolefin polymer containing scattering centers from suitable elastomers and inorganic fillers. The inventive light pipes offer superior scattering efficiency as well as spatial uniformity of scattering and uniformity of scattering across a wide wavelength range.  
           [0011]    Taiwan Utility Patent Publication No. 368081, typically shown in FIG. 6, discloses a backlight module  100  which generally includes a transparent light guide  110  with a reflective light enhancer  120  attached to a bottom surface thereof. The back light module  100  further includes a diffusion film  130  arranged on a top surface of the light guide. A fluorescent light  140  is arranged at an end of the light guide  110 . It can be readily appreciated that the light guide  110  is provided with a plurality of elongate printed lines  111  diverging away from the light source  140  located at the end of the light guide  110 . The back light module  100  further includes an end reflective enhancer  150  to homogeneously reflect the light beams so as to provide a uniform distribution of luminance over the light guide  110 .  
           [0012]    The diffusion film  130  functions to homogenously diffuse the light beams projected from the light source  140 . However, before the light beams reach the diffusion film  130 , the light beams have to travel through the light guide  110 , and be reflected by the reflective light enhancer  120 . It should be noted that before the light beams reach the diffusion film  130 , the light beams have to first be emitted from the light guide  110 , and then must enter the diffusion film  130 . The light guide  110  and the diffusion film  130  have different refractive indices and surely the energy of the light beam is exhausted during the transition. In addition, the diffusion film  130  is a separate element in addition to the light guide  110 , has to be manufactured separately. As such, the overall cost is inevitably increased.  
         SUMMARY OF INVENTION  
         [0013]    It is an object of the present invention to provide a light guide module in which a light diffusion arrangement is deployed over a light emitting surface of light guide module so as to reduce the overall cost.  
           [0014]    In order to achieve the object set forth, a light guide module has a light emitting surface and a light incident surface orthogonal to the light emitting surface. A light diffusion arrangement is deployed on the light emitting surface and includes organic scattering balls homogenously mixed within a bonding agent. At least a light source is arranged adjacent the light guide to project light beams into the light guide module. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0015]    [0015]FIG. 1 is a perspective view of a light guide module in accordance with the present invention;  
         [0016]    [0016]FIG. 2 is a side view of FIG. 1;  
         [0017]    [0017]FIG. 3 is a top view of a FIG. 1;  
         [0018]    [0018]FIG. 4 is a bottom view of FIG. 1; and  
         [0019]    [0019]FIG. 5 is an exploded view of the light guide module of FIG. 1 together with a light source in accordance with the present invention.  
         [0020]    [0020]FIG. 6 is an exploded view of a prior art backlight module; 
     
    
     DETAILED DESCRIPTION  
       [0021]    Referring to FIG. 1, a light guide module  10  in accordance with the present invention generally includes a light pipe  20  and a light diffusion arrangement  30 . The light pipe  20  is made from transparent resin material or glass. The light pipe  20  generally includes an incident surface  25 , an emitting surface  21 , and a bottom surface  23  opposite to the emitting surface  21 . Since the incident surface  25  is located at an end of the light pipe  20 , the incident surface  25  intersects both the bottom surface  23  and the emitting surface  21 .  
         [0022]    Referring now to FIGS. 1, 2, and  3 , the emitting surface  21  of the light pipe  20  has the light diffusion arrangement  30 . The light diffusion arrangement  30  comprises a plurality of organic scattering balls  31  mixed with bonding agent  33  so as to evenly distribute luminance across the emitting surface  21 . The organic scattering balls  31  are evenly mixed within the bonding agent  33  and the mixture is then spread uniformly over the emitting surface  21  of the light pipe  20 . Material for making the organic scattering balls  31  can be selected from Polymethyl Methacrylate, Polycarbonate, and Methallocene Cyclic Olefin Copolymer having a grain size ranging from 10-15 mlcrometers. The bonding agent  33  is selected from acrylic adhesives.  
         [0023]    Now referring to FIG. 4, together with FIGS. 1 and 2, the light pipe  20  in accordance with the present invention further includes a dot-web  41  evenly distributed over the bottom surface  23  of the light pipe  20 . The dot-web  41  is made from highly refractive diffusion material so as to effectively refract and diffuse the light beams traveling within the light pipe  20  after the light beams enter the light pipe  20  from the incident surface  25 . The use of the dot-web  41  can prevent total-reflection of the light within the light pipe  20 .  
         [0024]    As stated above, the use of the organic scattering balls  31  can effectively diffuse the light beams emitted from the emitting surface  21  so as to provide an evenly distributed luminance across the emitting surface  21 . In addition, each of the scattering balls  31  has a limited surface contact with the emitting surface  21 . As a result, the light losses resulting from the scattering balls can be controlled to with a certain limit. Accordingly, the overall optical characteristics of the light pipe  20  are enhanced.  
         [0025]    It should be readily appreciated that the light pipe  20  can be embodied in a variety of forms. For example, a cross section of the light pipe can be a trapezoid configuration. In addition, the dot-web  41  can be arranged in different patterns based on its grain size and density. Typically, the grain size and density of the dot-web  41  can be increased in proportion to a distance from the incident surface  25 . When the dot-web  41  is varied, the grain size and density of the scattering balls can also be changed accordingly. The incident surface  25  of the light pipe can also be arranged with respect to the emitting surface  21 .  
         [0026]    Referring to FIG. 5, the backlight module  50  includes a light source  60  and a light guide module  10  as discussed above. The light source  60  is arranged adjacent to the incident surface  25  of the light pipe  20 . The light source  60  projects light beams into the light pipe  20  through the incident surface  25 , which beams travel within the light pipe  20 . Finally, the light beams are emitted from the light emitting surface  21  after they are diffused by the light diffusion arrangement  30 .  
         [0027]    The light diffusion arrangement  30  made according to the present invention adequately addresses the prior art issue and provides a simple implementation over the light guide emitting surface  21  featuring less energy loss and brighter luminance.  
         [0028]    Alternatively, a backlight module  50  can be embodied with two light sources  60  arranged adjacent two opposite ends (incident surfaces). When the second light source  60  is introduced, the overall luminance is further enhanced. In alternative embodiments, prism plates can be arranged adjacent to the light emitting surface  21  and/or the bottom surface  23 .  
         [0029]    The light guide module according to the present invention is made by the following steps, a) providing a light pipe  20  made from a dynthetic resin or glass; b) providing a mixture fully blended of the scattering balls  31  and bonding agent  33 ; c) deploying a layer of the mixture over an emitting surface  21  of the light pipe. The grain size of the scattering balls range from 10-50 micrometers, and material of the scattering balls selected from Polymethyl Methacrylate, Polycarbonate, and Methallocene Cyclic Olefin Copolymer. The method further comprises a step of forming a dot-web across the bottom surface of the light guide.  
         [0030]    It is to be understood, however, that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, 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.