Abstract:
A surface light source device includes a light source body to generate light in response to an electric signal, which has a space filled with a discharge gas to generate the light, and a light diffusion part to diffuse the light generated from the light source body to output diffused light. The light diffusion part is integrally formed with the light source body. The light source body includes a first substrate through which the diffused light is output, a second substrate disposed to face the first substrate, in which a space is formed between the first and second substrates, at least one partition disposed between the first and second substrates, in which the space is regionally divided by the at least one partition, a sealing member disposed between the first and second substrates to seal the space, and a voltage applying part to provide the electric signal to excite the discharge gas in the space.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a device for providing light in image display devices, and more particularly, to a surface light source device providing light having enhanced luminance and uniform luminance distribution and to a image display apparatus employing the surface light source device.  
         [0003]     2. Description of the Related Art  
         [0004]     A liquid crystal display device generally includes a liquid crystal adjusting part and a light providing part. The light providing part provides light to the liquid crystal adjusting part. The liquid crystal adjusting part adjusts the optical properties of the liquid crystal so as to display images using the light provided from the light providing part.  
         [0005]     The liquid crystal adjusting part includes pixel electrodes, a common electrode and the liquid crystal interposed between the pixel electrodes and the common electrode. The common electrode and the respective pixel electrodes are disposed facing each other. A thin film transistor (TFT) is electrically connected to a pixel electrode, and the thin film transistor operates as a switching device. A pixel voltage is applied to the pixel electrode via the thin film transistor. A reference voltage is applied to the common electrode. Thus, electric field is formed between the pixel electrode and the common electrode, so that the arrangement of the liquid crystal between the pixel electrode and the common electrode is adjusted. The pixel electrodes and the common electrode are made of electrically conductive and transparent material, such as indium tin oxide (ITO).  
         [0006]     The light providing part provides the light to the liquid crystal adjusting part. Then the light passes through the pixel electrode, the liquid crystal and the common electrode in sequence, so that the light is transformed into image light that contains image information.  
         [0007]     Thus, the display quality of a liquid crystal display device depends on luminance and uniformity of the light generated from the light providing part. As the luminance and the uniformity increase, the display quality is improved.  
         [0008]     In general, a light providing part adopts a cold cathode fluorescent lamp (CCFL) or a light emitting diode (LED) and others. The cold cathode fluorescent lamp generates high luminance light, having a long lifespan, and white color. The light emitting diode also generates light with high luminance and has low power consumption.  
         [0009]     However, the cold cathode fluorescent lamp and the light emitting diode generate non-uniform light. Thus, for using as a light source of display the cold cathode fluorescent lamp or the light emitting diode needs an additional member, such as a light guide plate, a light diffusion member, a prism sheet, etc, to generate light with uniform luminance distribution. As a result, there is an inevitable increase in volume and weight of the liquid crystal display device.  
       SUMMARY OF THE INVENTION  
       [0010]     The above disclosed and other drawbacks and deficiencies of the conventional light sources are overcome or alleviated by a surface light source device and the display apparatus employing the same according to the present invention. In one embodiment, a surface light source device includes a light source body to generate light in response to an electric signal, in which the light source body has a space filled with a discharge gas to generate the light, and a light diffusion part to diffuse the light generated from the light source body to output diffused light. The light diffusion part may be integrally formed with the light source body. The light source body may include a first substrate through which the diffused light is output, a second substrate disposed to face the first substrate, in which a space is formed between the first and second substrates, at least one partition disposed between the first and second substrates, in which the space is regionally divided by the at least one partition, a sealing member disposed between the first and second substrates to seal the space, and a voltage applying part to provide the electric signal to excite the discharge gas in the space. A fluorescent layer may be coated on the surfaces of the first and second substrates, the at least one partition and the sealing member, which define the space of the light source body.  
         [0011]     The light diffusion part may include a light diffusion pattern formed on a surface of the first substrate to diffuse the light generated from the light source body. In an embodiment where the first substrate has first and second surfaces opposite to each other and the first surface is in contact with the space and the at least one partition, the light diffusion pattern includes a plurality of convex surfaces successively formed on the second surface.  
         [0012]     In other embodiments, the light diffusion pattern may include a plurality of convex members formed on the second surface such that density of the convex members is higher at a first area through which the light passes than at a second area adjacent to the at least one partition; a plurality of convex members formed on the second surface such that the convex members have a larger size at an area adjacent to the at least one partition that at an area through which the light passes; a plurality of convex surfaces successively formed on the first and/or second surface; a plurality of V-shaped grooves successively formed on the second surface; a plurality of protrusion members discretely formed on the second surface, each of which has a cross-sectional view of a polygonal shape; or a plurality of grooves discretely formed on the second surface, each of which has a cross-sectional view of a polygonal shape.  
         [0013]     In another embodiment, the light diffusion part includes a plurality of light diffusion members disposed on a surface of the first substrate through which the diffused light is output. The light diffusion members may have a substantially identical size or various sizes and are attached on the surface of the first substrate by adhesive, or have a substantially identical size and are securely held by a binder which is coated on the surface of the first substrate.  
         [0014]     In another embodiment, a display device displaying images in response to electrical signals externally provided includes a display panel to display the images, a surface light source device to provide surface light to the display panel, in which the surface light source device includes a light source body to generate light in response to an electric signal, the light source body having a space filled with a discharge gas to generate the light, and a light diffusion part to diffuse the light generated from the light source body to output diffused light, in which the light diffusion part is integrally formed with the light source body, and a receiving container to receive and securely hold the display panel and the surface light source device.  
         [0015]     These and other objects, features and advantages of the present invention will become apparent from the following detailed description of illustrative embodiments thereof, which is to be read in connection with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]     This disclosure will present in detail the following description of exemplary embodiments with reference to the following figures wherein:  
         [0017]      FIG. 1  is a perspective view illustrating a surface light source device according to an exemplary embodiment of the present invention;  
         [0018]      FIG. 2  is a cross-sectional view of the surface light source device taken along line A-A′ in  FIG. 1 ;  
         [0019]      FIG. 3A  is a plan view of the first substrate in  FIG. 2 ;  
         [0020]      FIG. 3B  is a plan view of the second substrate in  FIG. 2 ;  
         [0021]      FIG. 4  is an exploded perspective view of the light source body in  FIG. 1 ;  
         [0022]      FIG. 5  is an exploded perspective view illustrating a light source body according to another embodiment of the present invention;  
         [0023]      FIG. 6  is a schematic cross-sectional view illustrating a surface light source device according to another exemplary embodiment of the present invention;  
         [0024]      FIG. 7  is a schematic cross-sectional view illustrating a surface light source device according to another exemplary embodiment of the present invention;  
         [0025]      FIG. 8  is a schematic cross-sectional view illustrating a surface light source device according to another exemplary embodiment of the present invention;  
         [0026]      FIG. 9  is a schematic cross-sectional view illustrating a surface light source device according to another exemplary embodiment of the present invention;  
         [0027]      FIG. 10  is a schematic cross-sectional view illustrating a surface light source device according to another exemplary embodiment of the present invention;  
         [0028]      FIG. 11  is a schematic cross-sectional view illustrating a surface light source device according to another exemplary embodiment of the present invention;  
         [0029]      FIG. 12  is a schematic cross-sectional view illustrating a surface light source device according to another exemplary embodiment of the present invention;  
         [0030]      FIG. 13A  is a schematic cross-sectional view illustrating a surface light source device according to another embodiment of the present invention;  
         [0031]      FIG. 13B  is an enlarged view of portion ‘A’ in  FIG. 13A ;  
         [0032]      FIG. 14A  is a schematic cross-sectional view illustrating a surface light source device according to another embodiment of the present invention;  
         [0033]      FIG. 14B  is a schematic cross-sectional view illustrating a surface light source device according to another embodiment of the present invention; and  
         [0034]      FIG. 15  is an exploded perspective view illustrating an image display apparatus of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0035]     Detailed illustrative embodiments of the present invention are disclosed herein. However, specific structural and functional details disclosed herein are merely representative for purposes of describing exemplary embodiments of the present invention.  
         [0036]      FIG. 1  is a perspective view showing a surface light source device according to an exemplary embodiment of the present invention, and  FIG. 2  is a cross-sectional view of the surface light source device taken along line A-A′ in  FIG. 1 . Referring to  FIGS. 1 and 2 , the surface light source device includes a light source body  100  and a light diffusion part  200 . The light source body  100  has an inner space  136  filled with a discharge gas  152  from which light is generated.  
         [0037]     The light diffusion part  200  is formed on the surface of the surface light source device  300 , though which the light  280  exits. The light diffusion part  200  transforms the light  280  into diffused light  290 . The diffused light  290  has higher and more uniform luminance than that of the light  280  generated from the discharge gas  152  in the space  136  of the light source body  100 . The light source body  100  includes first and second substrates  110  and  120 , a sealing member  130 , a partition  140  and a light generating part  150 .  
         [0038]      FIG. 3A  is a plan view of the first substrate  110  in  FIG. 2 . Referring to  FIGS. 2 and 3 A, the first substrate  110  is transparent. For example, a glass substrate may be used as the first substrate  110 . The first substrate  110  has a plate shape. The first substrate  110  includes a first sealing region  112  and a light exiting region  114 . The first sealing region  112  surrounds the light exiting region  114 .  
         [0039]     The first substrate  110  includes a first surface  111  and a second surface  113 . The first and second surfaces  111  and  113  are formed facing each other. The first substrate  110  has side surfaces  115  connecting the first and second surfaces  111  and  113 . The number of the side surfaces  115  is three or more and determines the shape of the first substrate  110 . In this embodiment, for example, the number of the side surfaces  115  is four. Thus, the first substrate  110  and the first and second surfaces  111  and  113  have a rectangular shape.  
         [0040]      FIG. 3B  is a plan view of the second substrate  120  in  FIG. 2 . Referring to  FIGS. 2 and 3 B, the second substrate  120  is transparent. For example, a glass substrate may be used as the second substrate  120 . The second substrate  120  has a plate shape. The second substrate  120  includes a second sealing region  122  and a light generating region  124 . The second sealing region  122  surrounds the light generating region  124 .  
         [0041]     The second substrate  120  includes a third surface  121  and a fourth surface  123 . The third and fourth surfaces  121  and  123  are formed facing each other. The second substrate  120  also has side surfaces  125  connecting the third and fourth surfaces  121  and  123 . The number of the side surfaces  125  is three or more and determines the shape of the second substrate  120 . In this embodiment, for example, the number of the side surfaces  125  is four. Thus, the second substrate  120  and the third and fourth surfaces  121  and  123  have a rectangular shape.  
         [0042]     Referring again to  FIG. 2 , the sealing member  130  is disposed at the first sealing region  112  of the first substrate  110  and the second sealing region  122  of the second substrate  120 , so that a space is formed between the light exiting region  114  of the first substrate  110  and the light generating region  124  of the second substrate  120 . The sealing member  130  is formed along an edge of the first and second substrates  110  and  120 . The sealing member  130  comprises the same material as that of the first and second substrates  110  and  120 . Thus, for example, the sealing member  130  comprises glass.  
         [0043]     The sealing member  130  includes first and second sealing layers  132  and  134 . The first sealing layer  132  is formed at a first surface  130   a  of the sealing member  130 , which faces the first sealing region  112  of the first substrate  110 . The second sealing layer  134  is formed at a second surface  130   b  of the sealing member  130 , which faces the second sealing region  122  of the second substrate  120 .  
         [0044]      FIG. 4  is an exploded perspective view of the surface light source device  300 . Referring to  FIGS. 2 and 4 , the partitions  140  divide the space formed between the light exiting region  114  of the first substrate  110  and the light generating region  120  of the second substrate  120  to form a light generating space  136 . The partitions  140  each have a bar shape and have first and second end portions  141  and  142  that are respectively disposed at the ends of each partition.  
         [0045]     In  FIG. 4 , the first direction is the longitudinal direction of the partitions  140 , and the second direction is substantially perpendicular to the first direction. The partitions  140  are arranged in the second direction and parallel with each other. The partitions  140  have a substantially identical longitudinal length L 1  that is shorter than a first directional length L 2  of the light generating region  124 .  
         [0046]     One of the first and second end portions  141  and  142  of the respective partitions  140  is in contact with the sealing member  130 . For example, the odd numbered partitions  143  of the partitions  140  are in contact with the sealing member  130  at their first end portions  143 , respectively, and the even numbered partitions  144  are in contact with the sealing member  130  at their second end portions  142 , respectively. Thus, the partitions  140  are disposed in zigzag shape, so that the light generating space  136  divided by the partitions  140  is connected to form a serpentine shape. Therefore, a pressure of the discharge gas injected via an injection hole  126  and disposed in each of the light generating spaces  136  is substantially identical in the light generating space  136 .  
         [0047]     Referring to  FIGS. 2 and 4 , the light generating part  150  is divided by the partitions  140  to form the light generating spaces  136 . The light is generated from the discharge gas  152  in the light generating space  136 . The light generating part  150  includes first and second fluorescent layers  154  and  156 , the discharge gas  152  and a voltage applying part  158 .  
         [0048]     The first fluorescent layer  154  is formed on the first surface  111  of the first substrate  110 . The first fluorescent layer  154  is formed either on the entire area or partial areas of the first surface  111 . In other words, the first fluorescent layer  154  is formed on the entire first surface  111  of the first substrate  110  or on selected areas of the first surface  111  of the first substrate  110 .  
         [0049]     In this embodiment, the first fluorescent layer  154  is formed on selected partial areas of the first surface  111  of the first substrate  110 . In particular, the first fluorescent layer  154  is not formed on the areas of the first surface  111  on which the partitions  140  are attached. The first fluorescent layer  154  that partially covers the first surface  111  may be formed using a printing method. The first fluorescent layer  154  transforms an invisible light, such as ultraviolet light, into visible light  280  (hereinafter, referred to as light).  
         [0050]     The second fluorescent layer  156  is formed on the surface of the partition  140 . The second fluorescent layer  156  is also formed on the third surface  121  of the second substrate  120 . The second fluorescent layer  156  that covers the surface of the partition  140  and the third surface  121  of the second substrate  120  may be formed using a spray method. The second fluorescent layer  156  also transforms the invisible light into the visible light  280 .  
         [0051]     The discharge gas  152  is injected into the light generating space  136  defined by the first and second substrates  110  and  120  and the partitions  140 . The discharge gas  152  emits the invisible light when the discharge gas  152  is electrically discharged. The discharge gas includes mercury (Hg). The discharge gas may further include argon (Ar), xenon (Xe), krypton (Kr), or a mixture thereof.  
         [0052]     Referring again to  FIGS. 1 and 2 , the voltage applying part  158  provides a discharge voltage to electrically discharge the discharge gas  152  in the light generating space  136 , so that the invisible light is generated. The voltage applying part  158  includes first and second electrodes  158   a  and  158   b . Both the first and second electrodes  158   a  and  158   b  may be disposed inside the light source body  100 . One of the first and second electrodes  158   a  and  158   b  may be disposed outside the light source body  100 , or both the first and second electrodes  158   a  and  158   b  may be disposed outside the light source body  100 . In this embodiment, both the first and second electrodes  158   a  and  158   b  are disposed outside the light source body  100 .  
         [0053]     The voltage applying part  158  applies the discharge voltage in the range from a few kV to a few tens kV to the light generating space  136 . Thus, the discharge gas of the light generating space  136  becomes in an exited state and returns to a stable state to generate the invisible light.  
         [0054]     The light  280  exits from the light source body  100  via both the first and second substrates  110  and  120  of the light source body  100  because the first and second fluorescent layers  154  and  156  are formed on the first and second substrates  110  and  120 , respectively, which are transparent. Since the light source body  100  emits light through both the substrates  110  and  120 , it may be used for an display device having different display regions in different directions. For example, a mobile phone has main and sub display panels disposed in two different directions. The light source body  100  may be used in the mobile phone to provide light to the main and sub display panels in different directions.  
         [0055]     In the embodiment of  FIG. 2 , a light reflecting layer  128  is added to reflect light toward the first substrate  110  of the light source body  100 . The light reflecting layer  128  is interposed between the second fluorescent layer  156  and the third surface  121  of the second substrate  120 , so that the light  280  exits from only the first substrate  110  of the light source body  100 . As a result, the luminance of the light  280  exiting the first substrate  110  is enhanced. The light reflecting layer  128  reflects the light  280  that travels to the third surface  121  of the second substrate  120  toward the first surface  111  of the first substrate  110 . The light reflecting layer  128  comprises aluminum oxide (Al 2 O 3 ) or titanium oxide (TiO 3 ).  
         [0056]     The light diffusion part  200  of the surface light source device  300  diffuses the light  280  to transform the light  280  into the diffused light  290  that has a uniform luminance. The light diffusion part  200  includes a light diffusion pattern  210  formed on the second surface  113  of the first substrate  110 . The second surface  113  of the first substrate  110  is embossed to form the light diffusion pattern  210 . In other words, the light diffusion pattern  210  has a number of convex surfaces successively formed on the second surface  113  of the first substrate  110 . The light diffusion pattern  210  diffuses the light  280  to increase uniformity of the luminance.  
         [0057]     To form the light diffusion part  200  on the second surface  113  of the first substrate, a sand blaster method may be used such that the second surface  113  is subjected to impact of sand particles, or a grinding method may be used such that the second surface  113  is grinded to form the light diffusion pattern  210 . Chemical, such as hydrogen fluoride (HF), may be used to form the light diffusion pattern  210 .  
         [0058]     According to the present embodiment, the light source body  100  generates the light  280  having two-dimensions, and the light diffusion pattern  210  diffuses the light  280  to increase the uniformity of the luminance. Thus, a display device (e.g., liquid crystal display) improves its display quality by employing the surface light source device having above described structure.  
         [0059]      FIG. 5  is an exploded perspective view illustrating a light source body according to anther embodiment of the present invention. In  FIG. 5 , the same parts as those shown in  FIG. 4  are represented with like reference numerals and a detailed description thereof will be omitted to avoid description duplication.  
         [0060]     In this embodiment, the partitions  145  have a substantially identical length L 3  that is substantially same as a first directional length L 4  of the light generating region  124 . Thus, first and second end portions  141   a  and  141   b  of the respective partitions  145  are in contact with the sealing member  130 .  
         [0061]     When the first and second end portions  141   a  and  142   a  make contact with the sealing member  130 , the light generating space is completely divided. In this case, the discharge gas needs to be separately injected in each light generating space, and each light generating space may have different pressure of the discharge gas.  
         [0062]     In the embodiment of  FIG. 5 , such problem is solved by forming a through-hole  146  in the respective partitions  145 . The light generating spaces  136   a  are connected to each other via the though holes  146 . Thus, the discharge gas is injected into the light generating spaces  136   a  via the injection hole  126 .  
         [0063]      FIG. 6  is a schematic cross-sectional view illustrating a surface light source device according to another exemplary embodiment of the present invention. The surface light source device  300  of the present embodiment is substantially same as the one in  FIG. 2 , except for the light diffusion part. Thus, in  FIG. 6 , the same parts as those shown in  FIG. 2  are represented with like reference numerals and a detailed description thereof will be omitted to avoid description duplication.  
         [0064]     Referring to  FIG. 6 , a light diffusion part  220  formed on the second surface  113  of the first substrate  110  includes first and second light diffusion patterns  222  and  224 . The first and second light diffusion patterns  222  and  224  are formed on first and second regions  114   a  and  114   b  of the light exiting region  114  respectively. The first region  114   a  is disposed above the light generating space  136 , and the second region  114   b  is disposed above the partition  140 .  
         [0065]     The first light diffusion pattern  222  of the first region  114   a  has first convex members each having a predetermined size, and a predetermined number (M) of the first convex members are formed at a unit area. The second light diffusion pattern  224  of the second region  114   b  has second convex members each having a predetermined size, and a predetermined number (N) of the second convex members are formed at a unit area. In this embodiment, the sizes of the first and second convex members are substantially identical, and the number (M) of the first convex members is smaller than the number (N) of the second convex members. In other words, the second region  114   b  has a higher density of the convex members than in the first region  114   a . As a result, the luminance at the second region  114   b  increases up to a level substantially equal to the luminance at the first region  114   a.    
         [0066]     According to the present embodiment, the light diffusion pattern  220  is formed on the light source body  100 , such that the first and second light diffusion patterns  222  and  224  each have a different density of the convex members at which the light is diffused. The first light diffusion pattern  222  formed above the light generating space  136  has relatively sparse convex members, and the second light diffusion pattern  224  formed above the partition  140  has relatively dense convex members. As a result, the luminance of the diffused light  290  becomes uniform at the first and second regions  114   a  and  114   b  of the light exiting region  114 .  
         [0067]      FIG. 7  is a schematic cross-sectional view illustrating a surface light source device according to another exemplary embodiment of the present invention. The surface light source device  300  of the present embodiment is substantially same as the one in  FIG. 2 , except for the light diffusion part. Thus, in  FIG. 7 , the same parts as those shown in  FIG. 2  are represented with like reference numerals and a detailed description thereof will be omitted to avoid description duplication.  
         [0068]     Referring to  FIG. 7 , the light diffusion part  200  formed on the second surface  113  of the first substrate  110  has a light diffusion pattern  211  including first and second light diffusion patterns  225  and  226 . The first and second light diffusion patterns  225  and  226  are formed at the first and second regions  114   a  and  114   b , respectively, of the light exiting region  114 . The first region  114   a  is disposed above the light generating space  136 , and the second region  114   b  is disposed above the partition  140 .  
         [0069]     The first light diffusion pattern  225  has convex members of a first size, and a number (M) of the convex members are formed at a unit area of the first region  114   a . The second light diffusion pattern  226  has convex members of a second size that is larger than the first size, and a number (N) of the convex members are formed at a unit area of the second region  114   b . In this embodiment, the numbers (M and N) of the convex members of the first and second light diffusion patterns  225  and  226  are substantially same. Thus, the luminance at the second region  114   b  increases up to a level substantially equal to the luminance of the first region  114   a.    
         [0070]     According to the present embodiment, the light diffusion part  221  is formed on the light source body  100 , such that the convex members of the first light diffusion pattern  225  have a different size than those of the second light diffusion pattern  226 . In other words, the convex members of the first light diffusion pattern  225  formed above the light generating space  136  have a relatively small size, and the convex members of the second light diffusion pattern  226  formed above the partition  140  has a relatively large size. Thus, the luminance of the diffused light  290  becomes uniform at the first and second regions  114   a  and  114   b.    
         [0071]      FIG. 8  is a schematic cross-sectional view illustrating a surface light source device according to another exemplary embodiment of the present invention. The surface light source device  300  of the present embodiment is substantially same as the one in  FIG. 2 , except for the light diffusion part. Thus, in  FIG. 8 , the same parts as those shown in  FIG. 2  are represented with like reference numerals and a detailed description thereof will be omitted to avoid description duplication.  
         [0072]     Referring to  FIG. 8 , the light diffusion part  200  is formed on the second surface  113  of the first substrate  110 . The light diffusion part  200  includes light diffusion members  230 . Each of the light diffusion members  230  has a spherical particle shape. The light diffusion members  230  has a refractivity that is, for example, different from that of the first substrate  110 . The refractivity of the light diffusion members  230  may be also different from the refractivity of air. The light diffusion members  230  have a substantially identical size. The light diffusion members  230  are attached on the second surface  113  of the first substrate  110  by adhesive.  
         [0073]     The light  280  generated from the discharge gas in the light generating space  136  passes through the first surface  111  of the first substrate  110 , and arrives at the light diffusion members  230 . Then, the light  280  is reflected or refracted by the light diffusion members  230 , so that the light  280  is transformed into the diffused light  290  that has a uniform luminance.  
         [0074]     According to the present embodiment, the light diffusion part  200  includes the light diffusion members  230  for diffusing the light  280  generated from the discharge gas of the light generating space  136  to uniformize the luminance of the light.  
         [0075]      FIG. 9  is a schematic cross-sectional view illustrating a surface light source device according to another exemplary embodiment of the present invention. The surface light source device of the present embodiment is substantially same as the one in  FIG. 2 , except for the light diffusion part. Thus, in  FIG. 9 , the same parts as those shown in  FIG. 2  are represented with like reference numerals and a detailed description thereof will be omitted to avoid description duplication.  
         [0076]     Referring to  FIG. 9 , the light diffusion part  200  is formed on a second surface  113  of the first substrate  110 . The light diffusion part includes light diffusion members  240 . The light diffusion members  240  have a spherical particle shape. The light diffusion members  240  have a refractivity that is, for example, different from that of the first substrate  110 . The refractivity of the light diffusion members  240  may be also different from the refractivity of air. In this embodiment, the light diffusion members  240  each have a different size. The light diffusion members  240  with various sizes are attached on the second surface  113  of the first substrate  110  by adhesive.  
         [0077]     The light  280  generated from the discharge gas in the light generating space  136  passes through the first surface  111  of the first substrate  110 , and arrives at the light diffusion members  240 . Then, the light  280  is reflected or refracted by the light diffusion members  240 , so that the light  280  is transformed into the diffused light  290  that has a uniform luminance.  
         [0078]     According to the present embodiment, the light diffusion part  200  includes the light diffusion members  240  with various sizes for diffusing the light  280  generated from the discharge gas of the light generating space  136  to uniformize the luminance of the light.  
         [0079]      FIG. 10  is a schematic cross-sectional view illustrating a surface light source device according to another exemplary embodiment of the present invention. The surface light source device  300  of the present embodiment is substantially same as the one in  FIG. 2 , except for the light diffusion part. Thus, in  FIG. 10 , the same parts as those shown in  FIG. 2  are represented with like reference numerals and a detailed description thereof will be omitted to avoid description duplication.  
         [0080]     Referring to  FIG. 10 , the light diffusion part  200  is formed on the second surface  113  of the first substrate  110 . The light diffusion part  200  includes a light diffusion member  250 . The light diffusion member  250  includes beads  252  and a binder  254 . The beads  252  have a spherical particle shape, and the binder  254  fixes the beads  252  in the light diffusion member  250 .  
         [0081]     The beads  252  are transparent and have a refractivity that is, for example, different from that of the first substrate  110 . The beads  252  may have a substantially same size or different sizes. The binder  254  has fluidity and adhesiveness to securely hold the beads  252  on the second surface of the first substrate. The refractivity of the binder  254  is different from that of the beads  252 . The binder  254  is disposed to coat the second surface  113  of the first substrate  110 .  
         [0082]     According to the present embodiment, the light diffusion part  200  includes the light diffusion member  250  having the beads  252  with a substantially same size and the binder  254  coated on the second surface  113  of the first substrate  110  to diffuse the light  280  generated from the discharge gas in the light generating space  136 . As a result, the diffused light has a uniform luminance distribution.  
         [0083]      FIG. 11  is a schematic cross-sectional view illustrating a surface light source device according to another exemplary embodiment of the present invention. The surface light source device  300  of the present embodiment is substantially same as the one in  FIG. 2 , except for the light diffusion part. Thus, in  FIG. 11 , the same parts as those shown in  FIG. 2  are represented with like reference numerals and a detailed description thereof will be omitted to avoid description duplication.  
         [0084]     Referring to  FIG. 11 , the light diffusion part  200  has a light diffusion pattern  260  formed on the first surface  111  of the first substrate  110 . The first surface  111  is embossed to form the light diffusion pattern  260 . In other words, the light diffusion pattern  260  has a number of convex surfaces successively formed on the first surface  111  of the first substrate  110 . In this embodiment, the light diffusion pattern  260  has no convex surface at the region of the first surface  111 , where the first sealing layer  132  is attached. The light diffusion part with the light diffusion pattern  260  diffuses the light from the light generating space  136  so as to increase the luminance of the light output from the first substrate.  
         [0085]      FIG. 12  is a schematic cross-sectional view illustrating a surface light source device according to anther embodiment of the present invention. The surface light source device  300  of the present embodiment is substantially same as the one in  FIG. 2 , except for the light diffusion part. Thus, in  FIG. 12 , the same parts as those shown in  FIG. 2  are represented with like reference numerals and a detailed description thereof will be omitted to avoid description duplication.  
         [0086]     Referring to  FIG. 12 , the light diffusion part has first and second light diffusion patterns  270  and  280  formed on the first and second surfaces  111  and  113 , respectively, of the first substrate  110 . The first surface  111  is embossed to form the first diffusion pattern  270  such that a number of convex surfaces are successively formed on the first surface  111  of the first substrate  110 . The second surface  113  is embossed to form the second diffusion pattern  280  such that a number of convex surfaces are successively formed on the second surface  113  of the first substrate  110 .  
         [0087]     In this embodiment, the light generated from the discharge gas of the light generating space  136  is diffused by the first light diffusion pattern  270 , and then diffused again by the second light diffusion pattern  280 . As a result, the light output from the first substrate  110  has a uniform luminance.  
         [0088]      FIG. 13A  is a schematic cross-sectional view illustrating a surface light source device according to another embodiment of the present invention, and  FIG. 13B  is an enlarged view of portion ‘A’ in  FIG. 13A . The surface light source device in  FIG. 13A  is substantially same as the one in  FIG. 2 , except for the light diffusion part. Thus, in  FIG. 13A , the same parts as those shown in  FIG. 2  are represented with like reference numerals and a detailed description thereof will be omitted to avoid description duplication.  
         [0089]     Referring to  FIGS. 13A and 13B , the light diffusion part  200  diffuses the light  280  generated from the discharge gas of the light generating space  136  to transform the light  280  into the diffused light  290 . The light diffusion part  200  has a light diffusion pattern  295  formed on the second surface  113  of the first substrate  110 . The light diffusion pattern  295  has a number of V-shaped grooves formed on the second surface  113  of the first substrate  110 .  
         [0090]     The V-shaped grooves are spaced apart each other by about 50 μm. The surface of the light diffusion pattern  295  is rough. For example, the surfaces of the V-shaped grooves are embossed as shown in  FIG. 13B . Thus, the traveling direction of the light  130  generated from the discharge gas in the light generating space  136  is adjusted by the V-shaped grooves, and the light  130  is diffused by the rough surfaces of the V-shaped grooves to transform the light  130  into the diffused light  290 . As a result, uniformity of the luminance increases. The V-shaped grooves may be formed, for example, by compressing the second surface  113  of the first substrate  110 , when being heated, with a stamp having a negative or positive pattern.  
         [0091]      FIG. 14A  is a schematic cross-sectional view illustrating a surface light source device according to another embodiment of the present invention, and  FIG. 14B  is a schematic cross-sectional view of a surface light source device modified from the embodiment in  FIG. 14A . The embodiments of the surface light source device are substantially same as the one in  FIG. 2 , except for the light diffusion part. Thus, in  FIGS. 14A and 14B , the same parts as those shown in  FIG. 2  are represented with like reference numerals and a detailed description thereof will be omitted to avoid description duplication.  
         [0092]     Referring to  FIG. 14A , the light diffusion part  200  diffuses the light  280  generated from the discharge gas in the light generating space  136  so as to transform the light  280  into the diffused light  290 . Thus, uniformity of the luminance increases. The light diffusion part  200  includes a light diffusion pattern  298  formed on the second surface  113  of the first substrate  100 . The light diffusion pattern  298  has a number of protrusion members each having, for example, a prism shape. The protrusion members are discretely formed on the second surface  113  such that the adjacent protrusion members are apart each other by a predetermined distance. The protrusion members each may have a prism shape with a cross-sectional view of a triangular shape, a rectangular shape, a pentagonal shape or other polygonal shape. The light diffusion pattern  298  may also have a rough surface to increase the diffusion effect with respect to the light  280 . In this case, the traveling direction of the light  280  is adjusted by the protrusion members, and the light  280  is diffused by the rough surface of the light diffusion pattern  298 . As a result, the diffused light  290  has a uniform luminance distribution.  
         [0093]     Referring to  FIG. 14B , the light diffusion part  200  includes a light diffusion pattern  299  having a number of grooves. The second surface  113  of the first substrate  110  is partially recessed to form the grooves that are discretely formed such that the adjacent grooves are apart each other by a predetermined distance. The grooves of the light diffusion pattern  299  each have a cross-sectional view of a polygonal shape, such as a triangular shape, a rectangular shape, a pentagonal shape, etc.  
         [0094]     The grooves of the light diffusion pattern  299  may have a rough surface to increase the diffusion effect. The traveling direction of the light  280  is adjusted by the grooves, and the light  280  is diffused by the rough surface of the light diffusion pattern  299 . As a result, the diffused light  290  has a uniform luminance distribution.  
         [0095]     For example, the light diffusion patterns  298  and  299  in  FIGS. 14A and 14B  are formed using the following method. The light diffusion pattern  298  or  299  is exposed and developed on a photosensitive layer. Then, a metal layer is formed on the photosensitive layer by sputtering method. A light diffusion pattern shape is transcribed on a thin metal plate via the metal layer having the light diffusion pattern shape. Then, the metal plate having the light diffusion pattern shape is attached on a roller, so that a transcription roller is formed. The second surface  113  of the first substrate  110  is heated. The transcription roller rolls on the second surface  113 . As a result, the light diffusion pattern is formed.  
         [0096]     In the above description, the light diffusion pattern of the surface light source device of the present invention is explained with reference to the exemplary embodiments. It should be noted that the shape of the light diffusion pattern is not limited to the shapes described in the above embodiments and shown in the drawings. The light diffusion pattern may have various shapes and be readily modified within the scope of the present invention by one skilled in the art. For example, the light diffusion part may have an irregular pattern as well as a regular pattern.  
         [0097]     In the surface light source device of the present invention, since the light diffusion part is formed inside the light source body, the light is not totally reflected but exits from the light source body. Thus, the luminance of the surface light source device increases. For example, the surface light source device with the light diffusion part according to the present invention has the luminance of 3760 cd, while a conventional surface light source device has the luminance of 3300 cd.  
         [0098]     The surface light source device of the present invention may be employed in a display apparatus displaying images using the light separately provided. As an example, described below is a liquid crystal display apparatus including the surface light source device of the present invention.  
         [0099]      FIG. 15  is an exploded perspective view illustrating a liquid crystal display apparatus of the present invention. The liquid crystal display apparatus  700  includes a receiving container  400 , a surface light source device  300 , a liquid crystal display panel  500  and chassis  600 . The surface light source device  300  may be one of the embodiments described above. Thus, a detailed description of the light source device will be omitted.  
         [0100]     The receiving container  400  includes a bottom plate  410  and sidewalls  420 . The sidewalls  420  are disposed at edge portions of the bottom plate  410 . The bottom plate  410  and the sidewalls  420  form a receiving space. The receiving container  400  receives the surface light source device  300  and the liquid crystal display panel  500  such that the surface light source device  300  and the liquid crystal display panel  500  are securely held therein.  
         [0101]     The surface light source device  300  includes a light source body  100  and a light diffusion part  200 . The light source body  100  includes a space having a flat shape, and light is emitted from the space. The light diffusion part  200  is formed on a selected region of the light source body  100 , and the light exits the light source body  100  through the light diffusion part  200 . The light diffusion part  200  diffuses the light generated from discharge gas in the space of the light source body  100  so that the diffused light has a uniform luminance distribution.  
         [0102]     The liquid crystal display panel  500  transforms the light generated from the surface light source device into image light that contains image information. The liquid crystal display panel  500  includes a thin film transistor substrate  510 , a liquid crystal layer  520 , a color filter substrate  530  and a driver module  540 .  
         [0103]     The thin film transistor substrate  510  includes pixel electrodes, thin film transistors, gate lines and data lines. The pixel electrodes are arranged in a matrix form. Thin film transistors are electrically connected to the pixel electrodes respectively. In detail, a drain electrode of the thin film transistor is electrically connected to the pixel electrode. A gate electrode of the thin film transistor is electrically connected to the gate line. A source electrode of the thin film transparent is electrically connected to the source line.  
         [0104]     The color filter substrate  530  includes color filters and a common electrode. The color filters are disposed such that the color filter faces the pixel electrodes respectively. The common electrode is formed on the color filters. The liquid crystal layer  520  is interposed between the thin film transistor substrate  510  and the color filter substrate  530 .  
         [0105]     The chassis  600  enwraps the edge portions of the liquid crystal display panel  500 . The chassis  600  is combined with the receiving container  400 . The chassis  600  protects the liquid crystal display panel  500  to prevent the liquid crystal display panel from being broken and separating from the receiving container  400 .  
         [0106]     The surface light source device generates the light having uniform luminance in comparison with conventional light source devices, such as a light emitting diode or a cold cathode fluorescent lamp.  
         [0107]     Having described the exemplary embodiments of the surface light source device and the display device employing the same according to the present invention, modifications and variations can be readily made by those skilled in the art in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the present invention can be practiced in a manner other than as specifically described herein.