Abstract:
A surface light source ( 30 ) has a light source ( 23 ), and a light guide plate ( 20 ) for introducing light beams from the light source out. The light guide plate includes an incident surface ( 211 ) for introducing light beams in; an emitting surface ( 214 ) for uniformly transmitting light beams out; and a bottom surface ( 212 ) opposite to the emitting surface for reflecting the light beams in directions toward the emitting surface. Furthermore, a color filter ( 22 ) is provided and disposed on the emitting surface of the light guide plate, which has a color layer ( 222 ) for a full color display.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a surface light source and a light guide plate used in the surface light source, and particularly to a surface light source and a light guide plate having a color filter. 
   2. Prior Art 
   In general, liquid crystal displays (LCDs) have two main advantages in comparison with cathode ray tubes (CRTs): LCDs are thin, and have low power consumption. It has been said that LCDs might one day completely replace CRT display devices, and LCDs have aroused great interest in many industries in recent times. In general, an LCD needs a surface light source to provide even light for a clear display. 
     FIG. 5  shows a conventional LCD  100 , which comprises a liquid crystal panel  101  and a back light source  102  emitting light beams into the liquid crystal panel  101 . The liquid crystal panel  101  has a first substrate  2 , a Thin Film Transistor (TFT) substrate  7 , and a liquid crystal layer  5  installed between the first substrate  2  and the TFT substrate  7 . An top polarizer  1  and a bottom polarizer  8  are mounted on outsides of the first substrate  2  and the TFT substrate  7 , respectively. A color filter  3  and a transparent electrode layer  4  are stacked on an inside of the first substrate  2  in that order from top to bottom. The transparent electrode layer  4  is made from Indium Tin Oxide (ITO). A TFT electrode  6  is disposed on the TFT substrate  7 . The back light system  102  comprises a prism plate  9 , a diffuser  10 , a light guide plate  11 , and a light source  12  emitting light beams into the light guide plate  11 . The prism plate  9  and the diffuser  10  are stacked on the light guide plate  11  from top to bottom in that order. The light guide plate  11  changes directions of the incoming light beams, and transmits the light beams into the liquid crystal panel  101 . 
     FIG. 6  shows the color filter  3  disposed on the first substrate  2 . The color filter  3  comprises: a black matrix  14  formed on the first substrate  2  in a lattice pattern using a method such as photolithography; a color layer  13  filling and covering spaces defined in the black matrix  22  with color materials such as dyes, organic pigments or inorganic pigments, the color layer  13  being formed using photolithography; and a resin film layer  15  covering the color layer  13  and the black matrix  14 . In the LCD  100 , the color filter  3  is always disposed on the first substrate  2  of the LCD panel  101 , and is an important element for realizing a high quality color display. However, the process for manufacturing the color filter  3  on the first substrate  2  is complex. Therefore, the cost of the first substrate  2  is correspondingly high. 
   A new light guide plate providing the function of color filtering is desired to overcome the above-described problems. 
   SUMMARY OF THE INVENTION 
   An object of the present invention is to provide a light guide plate having a color filter. 
   Another object of the present invention is to provide a back light system using a light guide plate having a color filter. 
   To achieve the above objects, a surface light source according to the present invention has a light source, and a light guide plate for transmitting light beams received from the light source. The light guide plate includes an incident surface for receiving the light beams; an emitting surface for uniformly transmitting light beams out; and a bottom surface opposite to the emitting surface for reflecting the light beams in directions toward the emitting surface. A color filter is disposed on the emitting surface of the light guide plate. The color filter has a color layer for a full color display. 
   Other objects, advantages and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings, in which: 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic, side sectional view of a light guide plate in accordance with a first embodiment of the present invention; 
       FIG. 2  is a top elevation of a color layer of a color filter of the light guide plate of  FIG. 1 ; 
       FIG. 3  is a schematic, side sectional view of a light guide plate in accordance with a second embodiment of the present invention; 
       FIG. 4  is a schematic, side sectional view of a surface light source in accordance with the present invention; 
       FIG. 5  is a schematic, side sectional view of part of a conventional liquid crystal display; and 
       FIG. 6  is a schematic, enlarged, inverted view of a color filter of the liquid crystal display of  FIG. 5 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Hereinafter, preferred embodiments of the present invention will be explained in detail with reference to the accompanying drawings. 
   Referring to  FIG. 1 , a light guide plate  20  in accordance with the first embodiment of the present invention comprises a substrate  21 , and a color filter  22  disposed on and adjacent to the substrate  21 . As shown, the substrate  21  may be generally rectangular or square. Alternatively, the substrate  21  may be wedge-shaped or have another suitable shape. The substrate  21  is made from a transparent glass or synthetic resin. Various kinds of highly transparent synthetic resin may be used, such as acrylic resin, polycarbonate resin, vinyl chloride resin, etc. 
   The substrate  21  defines a light incident surface  211 , a light emitting surface  214  adjacent to the light incident surface  211 , and a bottom surface  212  adjacent to the light incident surface  211  and opposite to the light emitting surface  214 . A large number of scattering dots  213  are disposed on the bottom surface  212 . The scattering dots  213  reflect and diffuse light beams in directions toward the light emitting surface  214  of the light guide plate  20 . The scattering dots  213  are projections, whose sizes increase with increasing distance away from the light incident surface  211 . In an alternative embodiment, the scattering dots  213  may be uniformly sized, with a density of distribution of the scattering dots  213  increasing exponentially with increasing distance away from the light incident surface  211 . 
   The color filter  22  includes a black matrix  221  disposed on the light emitting surface  214  of the substrate  21  in a lattice pattern, a color layer  222  filling spaces defined in the black matrix  221 , and a light shielding layer  223  covering and, as seen from  FIGS. 2–4  generally on the color layer  222  and the black matrix  221 . 
   The color layer  222  is printed into and covers the spaces in the black matrix  221  by using photolithography. A plurality of color filter elements of red (R), green (G) and blue (B) is thus formed in a predetermined pattern, such as the deltoid pattern shown in  FIG. 2 . Alternatively, the pattern may be a striped pattern or a mosaic pattern. In the deltoid pattern, the color filter elements in any row are displaced one and a half places relative to the color filter elements in each of the adjacent rows. In the striped pattern, each of columns of the pattern is a same color. In the mosaic pattern, the color filter elements are aligned in regular rows and columns. Any three consecutive color filter elements in any row have the colors R, G and B, and any three consecutive color filter elements in any column have the colors R, G and B. Generally, a deltoid pattern is preferable for medium and small sized LCD panels, and can provide LCD displays with natural looking color images. The color filter elements of R, G and B are made from color materials such as dyes, organic pigments or inorganic pigments, and have a thickness in the range from 1.0 to 3.0 μm. In the preferred embodiment, the color filter elements of R are made from anthraquinone, and the color filter elements of G and B are made from phthalocyanine. 
   The black matrix  221  is usually made from a metal chromium film or a resin material having a thickness in the range from 1.0 to 2.0 μm, by using a desired patterning technique such as photolithography. The black matrix  221  blocks light beams, and functions to cut down on reflections and improve the reproduction of black on the LCD display. The result is color that is more true to life and with enhanced contrast, thus providing an exceptional screen image. 
   The light shielding layer  223  is made from an epoxy resin film or a titanium dioxide film. Each of such films has shielding characteristics, to protect the light guide plate  20  from ultraviolet wavelength light beams originating from the external environment. That is, propagation of ultraviolet wavelength light beams to the color layer  222  is prevented by the provision of the light shielding layer  223 . Direct decomposition of the color filter elements is restricted, and fading is prevented. 
   In operation, when light beams from a light source are introduced into the light guide plate  20  via the light incident surface  211 , the light beams are reflected and diffused by the bottom surface  212  and scattering dots  213  in directions toward the light emitting surface  214 . The color filter  22  is employed as an optical element for a full color display, with each three adjacent color filter elements of R, G and B constituting one pixel unit. Light beams are respectively passed through one of the R, G and B color filter elements contained in each pixel to achieve the full color display. 
   Referring to  FIG. 3 , a light guide plate  40  according to a second embodiment of the present invention is similar to the light guide plate  20  of the first embodiment. However, the light guide plate  40  comprises a large number of scattering dots  213 ′ that are micro lenses. 
     FIG. 4  shows a surface light source  30  according to the present invention. The surface light source  30  utilizes the light guide plate  20  to introduce light beams from a light source  23  into a liquid crystal display (not shown). The light source  23  is a cold cathode fluorescent lamp (CCFL) or a light emitting diode (LED), and is disposed adjacent to the light incident surface  211  of the light guide plate  20 . In an alternative embodiment, the light guide plate  20  may define two opposite light incident surfaces including the light incident surface  211 . The surface light source  30  may comprise two light sources  23  disposed adjacent to the light incident surfaces of the light guide plate  20  respectively, for providing high luminance. 
   In summary, the light guide plates  20 ,  40  and the surface light source  30  provide the color filter  22  therein. An LCD panel employing the surface light source  30  does not have to provide its own color filter. This can simplify the manufacturing process of the LCD panel and reduce costs accordingly. 
   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.