Abstract:
A surface light source device of a backlight unit for a liquid crystal display is provided. The surface light source device includes: a main body having a first panel, and a second panel between which an inner space is formed; and at least one partition wall for partitioning the inner space into a plurality of discharge spaces. The second panel includes a plurality of convex parts formed at the discharge spaces to be outwardly convex, and outermost convex parts have a larger outer curvature radius than other convex parts between the outermost convex parts.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a light source device; and, more particularly, to a surface light source device having an inner space partitioned into discharge spaces by a plurality of partition walls.  
       DESCRIPTION OF RELATED ARTS  
       [0002]     Liquid crystals have electrical and optical characteristics in that the arrangement of the liquid crystals varies with a direction of electric field applied thereto and a light transmittance thereof varies with the arrangement thereof.  
         [0003]     A liquid crystal display (LCD) device includes a backlight unit, and a liquid crystal control unit for controlling liquid crystals. The liquid crystal control unit includes a plurality of pixel electrodes and a common electrode.  
         [0004]     The backlight unit for an LCD device provides light to liquid crystals. The light emitted from the backlight unit passes through pixel electrodes, liquid crystals, and a common electrode sequentially. The light passing through the liquid crystals forms an image. The quality of the image depends on the luminance uniformity of the light, and the resolution of the image is determined by the number of the pixel electrodes.  
         [0005]     A backlight unit for an LCD device may use cold cathode fluorescent lamps (CCFLs) of a tube shape or light emitting diodes (LEDs) of a dot shape as a light source device. However, the cold cathode fluorescent lamp (CCFL) and the light emitting diode (LED) have bad luminance uniformity. In order to overcome such a shortcoming, a surface light source device has been introduced, recently. The surface light source device is classified into a surface light source device with an independent partition wall and a surface light source device with an integrated partition wall.  
         [0006]      FIG. 1  is a perspective view illustrating a surface light source device according to a related art.  FIG. 2  is a cross-sectional view illustrating the surface light source device shown in  FIG. 1 .  
         [0007]     Referring to  FIG. 1  and  FIG. 2 , the surface light source device includes a main body  100  having an inner space, a plurality of partition walls  111  partitioning the inner space of the main body  100 , and electrodes  130  formed at both sides of the main body  100 .  
         [0008]     The main body  100  includes a second panel  110  having the plurality of partition walls  111 , a first panel  120  facing the second panel  110 . A frit  101  and  102  is formed between the peripheries of the first and second panels  110  and  120  for sealing the main body  100 . Discharge gas is injected into the discharge space  140 .  
         [0009]     The second panel  110  includes a protective layer (not shown) and a fluorescent layer (not shown), which are sequentially formed on an inner surface thereof. The first panel  120  also includes a florescent layer (not shown) formed on an inner surface thereof. In addition, a reflective layer  150  is formed on the inner surface of the first panel  120  to reflect light generated in the discharge space  140  toward the second panel  110 .  
         [0010]     A partition wall may be integrally formed on at least one of the panels. In  FIG. 1 , the partition wall  111  is integrally formed on the second panel  110 . However, independent partition walls may be interposed between the first and second panels.  
         [0011]     The electrodes  130  are formed on both sides of the main body  100  to apply power into the discharge space  140  for exciting the discharge gas. The excited discharge gas emits ultraviolet rays, and the emitted ultraviolet rays excite the florescent layers to generate visible rays.  
         [0012]     The luminance is high at a central area of the surface light source device because the visible rays are overlapped at the central area. However, the overlap of the visible rays is small at both edges of the surface light source device. Accordingly, the luminance is low at both edges.  
       SUMMARY OF THE INVENTION  
       [0013]     It is, therefore, an object of the present invention to provide a surface light source device with high luminance uniformity.  
         [0014]     In accordance with an aspect of the present invention, there is provided a surface light source device including: a main body having a first panel, and a second panel between which an inner space is formed; and at least one partition wall for partitioning the inner space into a plurality of discharge spaces, wherein the second panel includes a plurality of convex parts formed at the discharge spaces to be outwardly convex, and outermost convex parts have a larger outer curvature radius than other convex parts between the outermost convex parts. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]     The above and other objects and features of the present invention will become better understood with regard to the following description of the preferred embodiments given in conjunction with the accompanying drawings, in which:  
         [0016]      FIG. 1  is a perspective view illustrating a surface light source device according to a related art;  
         [0017]      FIG. 2  is a cross-sectional view of the surface light source device shown in  FIG. 1 ;  
         [0018]      FIG. 3  is a perspective view illustrating a surface light source device according to one embodiment of the present invention;  
         [0019]      FIG. 4  is a cross-sectional view of the surface light source device of  FIG. 3 ;  
         [0020]      FIG. 5  is a graph for comparing beam angles of light emitted from outermost discharge spaces of surface light source devices according to a related art and the present invention;  
         [0021]      FIG. 6  is a graph showing the luminance distribution of surface light source devices according to a related art and the present invention;  
         [0022]      FIG. 7  is a view showing the luminance distribution in surface light source devices according to a related art and the present invention; and  
         [0023]      FIG. 8  is an exploded perspective view of a backlight unit having the surface light source device according to the embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0024]     Hereinafter, a surface light source device and a backlight unit having the same will be described in more detail with reference to the accompanying drawings.  
         [0025]      FIG. 3  is a perspective view illustrating a surface light source device according to one embodiment of the present invention, and  FIG. 4  is a cross sectional view of the surface light source device of  FIG. 3 .  
         [0026]     Referring to  FIG. 3  and  FIG. 4 , the surface light source device includes a main body, a plurality of partition walls  221   a , and electrodes  231  and  232 .  
         [0027]     The main body includes a first panel  210  and a second panel  220  facing each other. An inner space is formed between the first and second panel  210  and  220 . A discharge gas is injected into the inner space. The partition walls  221   a  partition the inner space of the main body into a plurality of discharge spaces. The electrodes  231  and  232  are formed at both sides of the surface light source device  200  to cover both ends of the discharge spaces  240 .  
         [0028]     The partition walls  221   a  may be formed at the same time when the second panel  220  (or the first panel  210 ) is formed. Or, independent partition walls  221   a  may be interposed between the first and second panels  210  and  220 . Each of the partition walls  221   a  has a width w and forms a dark area. Passage holes (not shown) may be formed at the partition walls  221   a.    
         [0029]     The second panel  220  includes a plurality of convex parts  221   b  forming discharge spaces  240  between the first and second panels  210  and  220 . The convex parts  221   b  form a bright area where light generated in a discharge space  240  is emitted.  
         [0030]     The convex parts  221  connect the partition walls  221   a . Outer curvature radiuses A and A′ of the outermost convex parts  221   b  are larger than curvature radiuses B and B′ of other convex parts  221   b  formed between the outermost convex parts.  
         [0031]     The luminance at the central area of the surface light source device  200  is generally greater than the luminance at both edges thereof due to the difference in an amount of the light overlap. Therefore, in the present invention, the outermost convex parts  221   b  are formed to have comparatively larger outer curvature radiuses than the other convex parts  221   b  between the outermost convex parts. Preferably, the outer curvature radius of the outermost convex parts has 1.5 times larger than the curvature radius of the other convex parts. This compensates the luminance difference. In a word, the present invention improves the luminance uniformity of the surface light source device  200  by altering the curvature radius of the convex parts  221   b.    
         [0032]     A florescent layer (not shown) is formed on inner surfaces of the panels, and a discharge gas is injected to excite the florescent layer. A mercury gas is generally used as the discharge gas. The discharge gas emits an ultra violet ray after being excited by the applied power. The UV ray excites the florescent layer to generate a visible ray. Also, a reflective layer  250  is formed at the inner surface of the first panel  210  and reflects the generated light in one direction. The reflective layer  250  is deposited on the first panel  210 . The reflective layer  250  may be formed on the second panel  220 .  
         [0033]     The electrodes  231  and  232  are formed at both sides of the surface light source device  200  and apply the discharge voltage to each of the discharge spaces  240 . The luminance difference can be compensated by expanding both ends of the outermost discharge spaces  240  to be wider than other discharge spaces. Parts  231   a  and  232   a  of the electrodes  231  and  232  at the outermost discharge spaces are formed to have a larger area than parts  231   b  and  232   b  at the other discharge spaces.  
         [0034]     Both ends of the outermost discharge spaces are horizontally expanded, which improves the luminance at the outermost discharge surface.  
         [0035]     In  FIG. 3 , the distances between the discharge spaces, that is, the widths of the partition walls, are the same as one another, and both ends of the discharge spaces are formed to be bent.  
         [0036]     However, only the outermost discharge spaces among a plurality of discharge spaces may be formed to be bent. In this case, both ends of the outermost discharge space may be expanded outwardly.  
         [0037]      FIG. 5  is a graph for comparing beam angles of light emitted from the outermost discharge spaces of surface light source devices according to a related art and the present invention. The beam angle denotes an angle between a normal line of the light emitting surface and a light proceeding direction. In graphs of  FIG. 5 , an X axis denotes an angle from the normal line, and a Y axis denotes luminance. As shown, the luminance shows a Gaussian distribution. The graph a) of  FIG. 5  shows a beam angle of light emitted from the outermost discharge spaces of a surface light source device according to the related art. As shown in the graph a) of  FIG. 5 , the highest luminance point is over the center of the outermost discharge space. The graph b) of  FIG. 5  shows a beam angle of the light emitted from the outermost discharge spaces of a surface light source device according to the present invention. As shown in the graph b) of  FIG. 5 , the highest luminance point is tilted outwardly from the center of the outermost discharge space.  
         [0038]     The amount of the light overlap at the edges of the surface light source device is generally smaller than that at the central area. Therefore, the luminance at the edges of the surface light source is comparatively low. Therefore, the present invention modifies the beam angle of the outermost discharge spaces by altering the outer curvature radius thereof. As a result, the luminance difference is compensated.  
         [0039]      FIG. 6  is a graph showing the luminance distribution of surface light source devices according to a related art and the present invention.  
         [0040]     Referring to  FIG. 6 , a solid line denotes the luminance distribution of light emitted from the surface light source device according to the present invention, and a dotted line denotes the luminance distribution of light emitted from the surface light source device according to the related art. In  FIG. 6 , an X axis denotes the distance from a center of a surface light source device, and a Y axis denotes the luminance of the light.  
         [0041]     As shown in  FIG. 6 , luminances are different at both edges of the surface light source devices. According to the dotted line, the luminance is greatly dropped at both edges of the surface light source device. On the contrary, the solid line shows that the luminance increases at both edges of the surface light source.  
         [0042]      FIG. 7  is a view showing luminance distribution in surface light source devices according to a related art and the present invention.  
         [0043]     The picture a) of  FIG. 7  shows the luminance distribution of light emitted from the surface light source device according to the related art, and the picture b) of  FIG. 7  shows the luminance distribution of light emitted from the surface light source device according to the present invention. As shown in the picture a) of  FIG. 7 , the dark area where the luminance is low is formed at the edges of the surface light source device according to the related art. On the contrary, the dark area is not shown in the picture b) of  FIG. 7 . That is, the luminance is not dropped at the edges of the surface light source device according to the present invention.  
         [0044]      FIG. 8  is an exploded perspective view of a backlight unit having the surface light source device according to the embodiment of the present invention.  
         [0045]     Referring to  FIG. 8 , the backlight unit includes a surface light source device  500 , a top case  515 , a bottom case  510 , an optical sheet  530  and an inverter  540 .  
         [0046]     The surface light source device  500  includes first discharge spaces  501  being the outermost discharge spaces, and second discharge spaces  502  formed between the first discharge spaces  501 . The convex parts forming the first discharge spaces  501  have a larger outer curvature radius than other convex parts forming the second discharge spaces  502  in order to compensate the luminance difference.  
         [0047]     The bottom case  510  provides a space to safely house the surface light source device  500 . The top case  515  is assembled to the bottom case  510  to prevent the surface light source device  500  and the optical sheet  530  from being separated.  
         [0048]     The inverter  540  is disposed at the back of the bottom case  510  and generates a discharge voltage to drive the surface light source device  500 . The discharge voltage is supplied to each of the electrodes of the surface light source device  500  through wires. The optical sheet  530  may include a diffusion sheet for uniformly diffusing light emitted from the surface light source device  500  and a prism sheet for collimating the diffused light.  
         [0049]     As described above, the surface light source device according to the present invention compensates the luminance difference by modifying the outermost convex parts to have a larger outer curvature radius than other convex parts.  
         [0050]     While the present invention has been described with respect to certain preferred embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the spirits and scope of the invention as defined in the following claims.