Patent Publication Number: US-2005122044-A1

Title: Flat lamp

Description:
BACKGROUND OF THE INVENTION  
      This application claims the priority of Korean Patent Application Nos. 2003-87169, and 2004-83973, filed on Dec. 3, 2003, and on Oct. 20, 2004, respectively, in the Korean Intellectual Property Office, the disclosures of which are incorporated herein in their entireties by reference.  
      1. Field of the Invention  
      The present invention relates to a flat lamp, and more particularly, to a flat lamp capable of lowering a discharge voltage and improving luminance efficiency.  
      2. Description of the Related Art  
      Flat lamps, which are usually developed as back lights of liquid crystal displays (LCDs), have developed from edge-light or direct-light type flat lamps using conventional cold cathode fluorescent lamps, to surface-discharge or facing-discharge type flat lamps in which the entire space below a light emitting surface is a discharge space in consideration of luminance efficiency, the uniformity of brightness, and the like. Although a surface-discharge flat lamp has the advantage of having a stable discharge compared to a facing-discharge flat lamp, the entire brightness of the surface discharge flat lamp is inferior to that of the facing-discharge flat lamp.  
       FIG. 1  illustrates a lower substrate  10  of a conventional surface-discharge type flat lamp. Referring to  FIG. 1 , a plurality of spacers  15  are arranged on the lower substrate  10  to define a plurality of discharge cells in a discharge space between the lower substrate  10  and an upper substrate (not shown) and to maintain a distance between the lower substrate  10  and the upper substrate constant. In addition, a pair of first and second electrodes  11  and  12  is arranged in each of the discharge cells on the lower substrate  10 . In this structure, when predetermined voltages are applied to the first and second electrodes  11  and  12 , gas discharge occurs within each of the discharge cells.  
      In general, when gas discharge is used, the longer the discharge path, the more luminance efficiency increases. However, increasing the discharge path creates an increase in a discharge voltage and has a bad influence on cost and longevity. Therefore, in a flat lamp with the above-described structure, when making the discharge path long by placing the first and second electrodes  11  and  12  far apart, efficiency might be increased but the problem that the discharge voltage increases remains.  
      A flat lamp to solve such problems is illustrated in  FIG. 2 . Referring to  FIG. 2 , a pair of first and second electrodes  21  and  22  is formed in each discharge cell on a lower substrate  20 . In addition, first and second auxiliary electrodes  23  and  24  are disposed between the first and second electrodes  21  and  22 . The first and second electrodes  21  and  22  are connected to the first and second auxiliary electrodes  23  and  24 , respectively, by resistance layers  27  and  28 , respectively. In the above-described structure, the start of discharge is propelled by applying a voltage to the first and second auxiliary electrodes  23  and  24 . However, such a flat lamp needs an additional process of forming the resistance layers  27  and  28 . Furthermore, heat loss by the resistance layers  27  and  28  occurs, and a difference in brightness is generated between a portion having the auxiliary electrodes  23  and  24  and a portion having no auxiliary electrodes  23  and  24 .  
     SUMMARY OF THE INVENTION  
      The present invention provides a flat lamp which reduces a discharge voltage by arranging a pair of electrode portions each consisting of a plurality of electrodes in each discharge cell, so that luminance efficiency is increased.  
      According to an aspect of the present invention, there is provided a flat lamp including: an upper substrate and a lower substrate arranged to face each other with a certain distance, forming at least one discharge cell between the upper and lower substrates; and a pair of first and second electrode portions formed in each of the discharge cells on at least one of the upper and lower substrates. Each of the first and second electrode portions comprises a plurality of electrodes.  
      The electrodes of the first electrode portion and the electrodes of the second electrode portion may be arranged in a sequence which is symmetrical with respect to a center line between the first and second electrode portions.  
      The electrodes of the first and second electrode portions may be formed with identical widths. As going farther from the center line between the first and second electrode portions, the electrodes of each of the first and second electrode portions may become wider.  
      The discharge cells may be defined by spacers. The spacers may be disposed such that the discharge cells are enclosed.  
      Alternatively, the spacers may be disposed such that adjacent discharge cells are connected to each other. One end of each of the spacers may be separated from a frame that forms exterior walls of the discharge cells. Both ends of each of the spacers may be separated from a frame that forms exterior walls of the discharge cells. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which:  
       FIG. 1  illustrates a conventional flat lamp;  
       FIG. 2  illustrates another conventional flat lamp;  
       FIG. 3  is a plan view of a lower substrate of a flat lamp according to an embodiment of the present invention;  
       FIG. 4  is a cross-sectional view illustrating a portion of the flat lamp of  FIG. 3 ;  
       FIG. 5  is a cross-sectional view illustrating a modified example of the flat lamp according to the embodiment of the present invention;  
       FIG. 6  is a cross-sectional view illustrating another modified example of the flat lamp according to the embodiment of the present invention;  
       FIG. 7  is a plan view illustrating the lower substrate of the flat lamp according to another embodiment of the present invention;  
       FIG. 8  is a cross-sectional view illustrating a portion of the flat lamp of  FIG. 7 ;  
       FIG. 9  is a cross-sectional view illustrating a modified example of the flat lamp according to another embodiment of the present invention;  
       FIG. 10  is a cross-sectional view illustrating the flat lamp according to still another embodiment of the present invention; and  
       FIGS. 11 and 12  are a plan view and a graph, respectively, to compare brightness and efficiency of a flat lamp according to the present invention with those of a conventional flat lamp.  
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings.  
       FIG. 3  is a plan view illustrating a lower substrate of a flat lamp according to an embodiment of the present invention and  FIG. 4  is a cross-sectional view illustrating a portion of the flat lamp of  FIG. 3 .  
      Referring to  FIGS. 3 and 4 , a lower substrate  100  and an upper substrate  120  are arranged to face each other with a certain distance between the two substrates. In general, the lower substrate  100  and the upper substrate  120  are made of glass. At least one discharge cell  130 , where plasma discharge occurs, is formed between the lower and upper substrates  100  and  120  and filled with a discharge gas. The discharge cell  130  is defined as a discharge space formed between a pair of a cathode and an anode. A frame (not shown) surrounds a space between the lower and upper substrates  100  and  120 .  
      In addition, at least one spacer  115  is arranged between the lower and upper substrates  100  and  120  so as to maintain a distance between the lower and upper substrates  100  and  120  constant and to define the discharge cells  130  within the space between the lower and upper substrates  100  and  120 . One or both ends of each of the spacers  115  may be disposed apart from the frame so that a part of each of the discharge cells  130  is open. On the other hand, both ends of each of the spacers  115  may be closely attached to the frame so that the discharge cells  130  can be enclosed. A phosphor layer (not shown) that generates visible light by being excited by ultraviolet rays generated due to discharge may be formed on an inner wall of each of the discharge cells  130 .  
      A plurality of discharge electrodes are formed on an upper surface of the lower substrate  100  to make discharge occur within the discharge cells  130 . More specifically, a pair of a first electrode portion  111  and a second electrode portion  112  is formed on the upper surface of the lower substrate  100 . The first electrode portion  111  is comprised of first electrodes  111   a ,  111   b , and  111   c , and the second electrode portion  112  is comprised of second electrodes  112   a ,  112   b , and  112   c . The first electrodes  111   a ,  111   b , and  111   c  are connected to a first common line  140 , and the second electrodes  112   a ,  112   b , and  112   c  are connected to a second common line  150 . Although the first and second electrode portions  111  and  112  shown in  FIGS. 3 and 4  each have three electrodes, each of the first and second electrode portions  111  and  112  may be constituted of two or four or more electrodes.  
      The first electrodes  111   a ,  111   b , and  111   c  and the second electrodes  112   a ,  112   b , and  112   c  are disposed in a sequence which is symmetrical with respect to the center line between the first and second electrode portions  111  and  112 . The first and second electrodes  111   a ,  111   b ,  111   c ,  112   a ,  112   b , and  112   c  have the same widths. However, the first electrodes  111   a ,  111   b , and  111   c  and the second electrodes  112   a ,  112   b , and  112   c  may be disposed in a sequence which is asymmetrical with respect to the center line between the first and second electrode portions  111  and  112 .  
      In the flat lamp having the above-described structure, when predetermined voltages are applied to the first electrode portion  111  and the second electrode portion  112 , start discharge occurs between the first and second electrodes  111   a  and  112   a , which are closest to each other. By making the distance between the first and second electrodes  111   a  and  112   a  narrower than in a conventional flat lamp, discharge voltage can be lowered. Next, a main discharge occurs between the first electrodes  111   a ,  111   b , and  111   c  and the second electrodes  112   a ,  112   b , and  112   c . When the average distance between the first and second electrode portions  111  and  112  is made wider than that in the conventional flat lamp, the average discharge path becomes longer and thus luminance efficiency improves.  
       FIG. 5  illustrates a modified example of a flat lamp according to an embodiment of the present invention. Referring to  FIG. 5 , a pair of a first electrode portion  111 ′ and a second electrode portion  112 ′ is formed on the bottom surface of the lower substrate  100  for each of the discharge cells  130 . The first electrode portion  111 ′ is made up of three first electrodes  111   a ′,  111 ′ b ,  111 ′ c , and the second electrode portion  112 ′ is made up of three second electrodes  112 ′ a ,  112 ′ b , and  112 ′ c.    
       FIG. 6  illustrates another modified example of a flat lamp according to the embodiment of the present invention. Referring to  FIG. 6 , a pair of the first and second electrode portions  111  and  112  are formed in each of the discharge cells  130  on the top surface of the lower substrate  100 . As described above, the first electrode portion  111  is comprised of the first electrodes  111   a ,  111   b , and  111   c , and the second electrode portion  112  is comprised of the first electrodes  112   a ,  112   b , and  112   c . In addition, a pair of third and fourth electrode portions  113  and  114  is formed in each of the discharge cells  130  on the bottom surface of the upper substrate  120 . The third electrode portion  113  is constituted of third electrodes  113   a ,  113   b , and  113   c , and the fourth electrode portion  114  is constituted of fourth electrodes  114   a ,  114   b , and  114   c . Although  FIG. 6  illustrates the first, second, third, and fourth electrode portions  111 ,  112 ,  113 , and  114  each comprising three electrodes, each of the first through fourth electrode portions  111  through  114  may be comprised of two or four or more electrodes.  
      The first electrodes  111   a ,  111   b , and  111   c  and the second electrodes  112   a ,  112   b , and  112   c  are arranged in a sequence which is symmetrical with respect to the center line between the first and second electrode portions  111  and  112 . The third electrodes  113   a ,  113   b , and  113   c  and the fourth electrodes  114   a ,  114   b , and  114   c  are arranged in a sequence which is symmetrical with respect to the center line between the third and fourth electrode portions  113  and  114 . In addition, the first and second electrodes  111   a ,  111   b ,  111   c ,  112   a ,  112   b , and  112   c  are formed with identical widths. The third and fourth electrodes  113   a ,  113   b ,  113   c ,  114   a ,  114   b , and  114   c  are formed with identical widths.  
      In the flat lamp having the above-described structure, since gas discharge occurs between the first and second electrode portions  111  and  112  and also between the third and fourth electrode portions  113  and  114 , discharge can be smoothly carried out.  
       FIG. 7  is a plan view illustrating a portion of a lower substrate  200  of a flat lamp according to another embodiment of the present invention.  FIG. 8  is a cross-sectional view illustrating a portion of the flat lamp of  FIG. 7 .  
      Referring to  FIGS. 7 and 8 , the lower substrate  200  and an upper substrate  220  are arranged to face each other with a certain distance between the two substrates. At least one spacer  215  is arranged between the lower and upper substrates  200  and  220  to define discharge cells  230  in a space between the lower and upper substrates  200  and  220 . The spacers  215  may be disposed either to open a part of each of the discharge cells or to enclose the discharge cells  230 , as described above.  
      A pair of first and second electrode portions  211  and  212  is arranged in each of the discharge cells  230  on the top surface of the lower substrate  200 . The first electrode portion  211  is constituted of first electrodes  211   a  and  211   b , and the second electrode portion  212  is constituted of second electrodes  212   a  and  212   b . In  FIGS. 7 and 8 , the first and second electrode portions  211  and  212  are each constituted of two electrodes. However, each of the first and second electrode portions  211  and  212  may be constituted of three or more electrodes.  
      The first electrodes  211   a  and  211   b  and the second electrodes  212   a  and  212   b  are arranged in a sequence which is symmetrical with respect to the centre line between the first and second electrode portions  211  and  212 . As going farther from a centre line in between the first and second electrode portions  211  and  212 , the first electrodes  211   a  and  211   b  become wider, and the second electrodes  212   a  and  212   b  also become wider. The first electrodes  211   a  and  211   b  and the second electrodes  212   a  and  212   b  may be arranged in a sequence which is asymmetrical with the centre line between the first and second electrode portions  211  and  212 .  
      In the flat lamp having the above-described structure, when predetermined voltages are applied to the first and second electrode portions  211  and  212 , a start discharge occurs between the first electrode  211   a  of the first electrode portion  211  and the second electrode  212   a  of the second electrode portion  212 , which are close to each other. Next, a main discharge occurs between the first and second electrodes  211   a  and  211   b  and the second electrodes  212   a  and  212   b . Since the widths of the first and second electrodes  211   b  and  212   b , which are far from each other, are greater than those of the first and second electrodes  211   a  and  212   a , which are close to each other, the average discharge path can be greater than the prior art, thus improving luminance efficiency.  
       FIG. 9  illustrates a modified example of a flat lamp according to another embodiment of the present invention. Referring to  FIG. 9 , a pair of first and second electrode portions  211  and  212  is formed in each of the discharge cells  230  on the top surface of the lower substrate  200 . As described above, the first electrode portion  211  is comprised of the first electrodes  211   a  and  211   b , and the second electrode portion  212  is comprised of the second electrodes  212   a  and  212   b . In addition, a pair of third and fourth electrode portions  213  and  214  is formed in each of the discharge cells on the bottom surface of the upper substrate  220 . The third electrode portion  213  consists of third electrodes  213   a  and  213   b , and the fourth electrode portion  214  consists of fourth electrodes  214   a  and  214   b . Although each of the first through fourth electrode portions  211  through  214  illustrated in  FIG. 9  is comprised of two electrodes, it may be comprised of three or more electrodes.  
      The first electrodes  211   a  and  211   b  and the second electrodes  212   a  and  212   b  are arranged in a sequence which is symmetrical with respect to the center line between the first and second electrode portions  211  and  212 . As going farther from a centre line in between the first and second electrode portions  211  and  212 , the first electrodes  211   a  and  211   b  become wider, and the second electrodes  212   a  and  212   b  also become wider. Similarly, as going farther from a centre line in between the third and fourth electrode portions  213  and  214 , the third electrodes  213   a  and  213   b  become wider, and the fourth electrodes  214   a  and  214   b  also become wider.  
       FIG. 10  is a cross-sectional view illustrating a portion of a flat lamp according to still another embodiment of the present invention. Referring to  FIG. 10 , a lower substrate  300  and an upper substrate  320  are arranged to face each other with a certain distance between the two substrates. At least one spacer  315  is arranged between the lower and upper substrates  300  and  320  to define discharge cells  330  in a space between the lower and upper substrates  300  and  320 .  
      A pair of first and second electrode portions  311  and  312  is arranged in each of the discharge cells  330  on the top surface of the lower substrate  300 . The first electrode portion  311  consists of first electrodes  311   a ,  311   b ,  311   c , and  311   d , and the second electrode portion  312  consists of second electrodes  312   a ,  312   b ,  312   c , and  312   d . In addition, the first electrodes  311   a ,  311   b ,  311   c , and  311   d  and the second electrodes  312   a ,  312   b ,  312   c , and  312   d  are arranged in a sequence which is symmetrical with respect to the center line between the first and second electrode portions  311  and  312 . The first and second electrodes  311   a ,  311   b ,  311   c ,  311   d ,  312   a ,  312   b ,  312   c , and  312   d  have identical widths. In  FIG. 10 , the first and electrode portions  311  and  312  each consist of four electrodes, but each may consist of a number of electrodes greater than one, other than four. As going farther from a centre line in between the first and second electrode portions  311  and  312 , the first electrodes  311   a ,  311   b ,  311   c , and  311   d  may become wider, and the second electrodes  312   a ,  312   b ,  312   c , and  312   d  also may become wider.  
      A pair of third and fourth electrode portions  313  and  314  is arranged in each of the discharge cells  330  on the bottom surface of the upper substrate  320 . The third and fourth electrode portions  313  and  314  each consist of a number of electrodes smaller than the number of electrodes of each of the first and second electrodes  311  and  312 . That is, the third electrode portion  313  is comprised of third electrodes  313   a  and  313   b , and the fourth electrode portion  314  is comprised of fourth electrodes  313   a  and  313   b . The third electrodes  313   a  and  313   b  and the fourth electrodes  314   a  and  314   b  are arranged in a sequence which is symmetrical with respect to the center line between the third and fourth electrode portions  313  and  314 . The third and fourth electrodes  313   a ,  313   b ,  314   a , and  314   b  have identical widths. In  FIG. 10 , the third and fourth electrode portion  313  and  314  each consist of two electrodes, but each may consist of one or more electrodes. If two or more electrodes are employed, the effects of the present invention will be present for the third and fourth electrodes  313  and  314 , as well. As going farther from a centre line in between the third and fourth electrode portions  313  and  314 , the third electrodes  313   a  and  313   b  may become wider, and the fourth electrodes  314   a  and  314   b  also may become wider.  
      In the flat lamp having the above-described structure, visible light generated due to discharge is less blocked by the electrodes formed on the upper substrate  320  than in the other flat lamps described above, if the electrodes are not transparent to visible light.  
       FIGS. 11 and 12  are a view and a graph, respectively, for comparing the brightness and efficiency of a flat lamp according to the present invention with those of a conventional flat lamp.  
       FIG. 11  illustrates a flat lamp in which an electrode arrangement according to the present invention and a conventional electrode arrangement are both applied. In  FIG. 11 , area A is one to which the electrode arrangement according to the present invention is applied and area B is one to which the conventional electrode arrangement is applied. In area A of this example, a first electrode portion  117 , consisting of two electrodes  117   a  and  117   b , and a second electrode portion  118 , consisting of two electrodes  118   a  and  118   b , are arranged in each discharge cell. In area B, a first electrode  17  and a second electrode  18  are arranged in each discharge cell. Such an electrode arrangement is applied to both the upper and lower substrates.  FIG. 12  is a graph illustrating the brightness and efficiency of the flat lamp shown in  FIG. 11 . Referring to  FIG. 12 , the brightness improves by 8% and the efficiency improves approximately over 40% in the electrode arrangement according to the present invention compared to the conventional electrode arrangement.  
      As described above, in the flat lamp according to the present invention, the discharge voltage can be reduced by arranging a pair of electrode portions each consisting of a plurality of electrodes in each discharge cell, and the average discharge path can be lengthened. Thus, the brightness and luminance efficiency are improved.  
      While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.