Patent Publication Number: US-2007108902-A1

Title: Plasma display panel

Description:
CLAIMS OF PRIORITY  
      This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. §119 from an application for PLASMA DISPLAY PANEL earlier filed in the Korean Intellectual Property Office on 7 Sep. 2005 and there duly assigned Ser. No. 10-2005-0083107. 
    
    
     BACKGROUND OF THE INVENTION  
      1. Field of the invention  
      The present invention relates to a plasma display panel. More particularly, the present invention relates to a delta type plasma display panel capable of improving a bright room contrast by balancing colors representing a picture image.  
      2. Description of the Prior Art  
      As generally known in the art, a plasma display panel (PDP) refers to a display device for realizing an image using a visible light ray, which is generated when a fluorescent member is excited by means of a vacuum ultraviolet ray radiated from plasma derived from a gas discharge. Such a PDP makes it possible to fabricate a large screen of above 60 inches with a thickness less than 10 cm. In addition, since the PDP is a self-emissive display device similar to a CRT (cathode ray tube), the PDP has superior color reproducing characteristics while preventing the image from being distorted regardless of the viewing angle. In addition, the fabrication process for the PDP is easier than that of a liquid crystal display (LCD), so the PDP can be produced at a low cost. Due to these advantages s of the PDP, the PDP has been extensively used as a flat display device in next-generation industrial fields and as a TV display device at home.  
      Such a PDP generally includes a front substrate having a plurality of display electrodes and a rear substrate having a plurality of address electrodes crossing the display electrodes. Both display electrodes and address electrodes may be referred to as discharge electrodes. In addition, a plurality of barrier ribs are provided between the front substrate and the rear substrate in order to define a plurality of discharge areas. The barrier ribs are classified into stripe type barrier ribs, matrix type barrier ribs and delta type barrier ribs.  
      In the case of a PDP having the delta type barrier ribs, a pixel is defined by three discharge cells that are adjacent to each other. In addition, each discharge cell is constructed with a red (R) fluorescent layer, a green (G) fluorescent layer or a blue (B) fluorescent layer. In general, three address electrodes are allocated to one pixel in the delta type PDP. In order to produce a high definition PDP, a barrier rib structure capable of reducing capacitance between address electrodes, and an electrode structure capable of restricting an increase of the discharge voltage are necessary. Therefore, a rotary delta type barrier rib structure has been suggested. According to the rotary delta type PDP, two address electrodes may be allocated to one pixel. In other words, for the three adjacent discharge cells that define one pixel, one address electrode is commonly allocated to two discharge cells selected from the three discharge cells and a different address electrode is allocated to the remaining discharge cell.  
      Hereinafter, the operation of a PDP having the above structure will be briefly described. First, a discharge cell is selected by applying an electric signal to a Y display electrode of the display electrodes and an address electrode. Then, an electric signal is applied to an X electrode of the display electrodes followed by the Y electrode, so the surface-discharge is generated from the surface of the front substrate, thereby generating ultraviolet rays. The ultraviolet rays excite the fluorescent layer of the selected discharge cell, so that visible light rays are radiated from the fluorescent layer, thereby realizing still images or dynamic images.  
      The PDP operating in this manner exhibits a contrast ratio which can be classified into a bright room contrast and a dark room contrast. The bright room contrast refers to the contrast of an image displayed by a PDP, when a light source of 150 lux or greater exists at the exterior of the PDP and the PDP receives the effect of the external light generated from the light source. The dark room contrast refers to the contrast an image displayed by a PDP when a light source of 21 lux or less exists at the exterior of the PDP and the PDP receives no substantial effect from the external light generated from the light source.  
      In general, viewers watch the PDP in a bright room, instead of a dark room, so the bright room contrast must be improved in order to enhance the image quality of the PDP. Therefore, it is necessary to reduce the reflection brightness of the PDP. Accordingly, the internal structure of the PDP must be modified to reduce the reflection brightness of the PDP such that the bright room contrast of the screen can be improved.  
      The general delta type PDP or the rotary delta type PDP, however, has the following problems related to the effective picture area of the PDP.  
      The effective picture area refers to an area of a front panel with the exception of a part covered by a bezel of a front case. In other words, the effective picture area is that part of a screen area that is revealed to outside. Contemporary effective picture areas have rectangular shape.  
      A PDP may include display areas, which include the discharge cells exclusively and which are capable of displaying images using discharge electrodes when a discharge voltage is applied, and non-display areas, which are non-emissive areas aligned at outer portions of the display areas.  
      In a delta type PDP having a rectangular effective picture area, if the rectangular effective picture area is established to cover the entire display areas, empty spaces (i.e., non-display areas) may be undesirably formed, because the shape of the delta type barrier ribs will inevitably result in a mismatch between the effective picture area and the display areas.  
      The empty spaces are typically coated with a dielectric layer or a fluorescent layer. The dielectric layer and the fluorescent layer are white in color, so they exhibit superior reflection brightness in response to the incidence of external light onto the empty spaces. If the empty spaces have superior reflection brightness, the bright room contrast of the PDP may be degraded, thereby lowering the image quality of the PDP.  
      In order to solve the above problem, the pixels defined by the hexagonal discharge cells are shifted with respect to the effective picture area, such that the spaces which were originally the empty spaces, i.e., the spaces in the effective picture area that were originally not covered by the pixels, will be covered by the pixels. In this case, however, a part of the pixels, that was originally belonging to the display areas, deviates from the effective picture area. Such a deviation of the pixels may be incurred in the general delta type PDP.  
      As mentioned above, according to the delta type PDP, one pixel is defined by three adjacent discharge cells and each discharge cell radiates visible rays of red, green or blue colors. In addition, the delta type PDP generates various colors by mixing the visible rays. If a part of the pixel deviates from the effective picture area, however, a part of the red, green or blue color may not be viewed by the viewers, and therefore an input color signal may not match with an output color signal. For this reason, a color unbalance may occur at the edge portions of the effective picture area, so that it is difficult to exhibit the desired color, which is intended to be seen by the optical facilities of the viewers.  
     SUMMARY OF THE INVENTION  
      It is therefore an object of the present invention to provide an improved delta type plasma display panel.  
      It is another object of the present invention to provide an improved delta type plasma display panel in order to solve one or more of the above-mentioned problems occurring in the prior art.  
      It is still another object of the claimed invention is to provide a delta type plasma display panel capable of improving a bright room contrast by balancing colors representing a picture image.  
      In order to accomplish the above objects, according to one aspect of the present invention, a plasma display panel may be constructed with front and rear substrates aligned opposite to each other, a plurality of barrier ribs provided between the front and rear substrates in order to define a plurality of discharge areas such that a pixel is formed by three adjacent discharge cells radiating visible rays having different colors and being aligned in a triangular pattern, a plurality of electrodes aligned on at least one of the front substrate, the rear substrate, and the barrier ribs corresponding to the discharge cells, and a fluorescent layer formed in the discharge cells. The plasma display panel includes display areas as a set of pixels, which are emissive areas, and non-display areas which are non-emissive areas aligned outside of the display areas, and an external light absorber is provided in the non-display areas.  
      According to the exemplary embodiment of the principles of the present invention, the plasma display panel has a rectangular effective picture area which includes the entire display areas absorber is provided in the non-display areas located in the effective picture area.  
      At this time, an external light absorber is provided in either a front surface or a rear surface of the front substrate corresponding to the non-display areas. The external light absorber area includes a recess having a depth, in which the recess is formed in a front surface of the front substrate corresponding to the non-display areas and is filled with light shielding materials. The external light absorber may be disposed on the barrier ribs forming the discharge cells, the fluorescent layer or a dielectric layer corresponding to the non-display areas.  
      In addition, a dummy wall is formed in the non-display areas located in the effective picture area, in which the dummy wall extends from a barrier rib forming an outermost portion of the display areas and the external light absorber is provided on the dummy wall.  
      The external light absorber is made from a material having a surface color of black.  
      According to another aspect of the present invention, a plasma display panel is constructed with front and rear substrates aligned opposite to each other, barrier ribs provided between the front and rear substrates in order to define a plurality of discharge areas such that a pixel is formed by three adjacent discharge cells radiating visible rays having different colors and being aligned in a triangular pattern, a plurality of kinds of electrodes aligned on at least one of the front substrate, the rear substrate, and the barrier ribs corresponding to the discharge cells, and a fluorescent layer formed in the discharge cells, wherein the plasma display panel includes display areas, which are emissive areas, and non-display areas which are non-emissive areas aligned outside of the display areas, and an effective picture area is established by covering the entire display areas, exclusively.  
      According to the exemplary embodiment of the principles of the present invention, a front case surrounding the plasma display panel is provided such that an entire non-display area is covered with the bezel of the front case. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      A more complete appreciation of the invention, and many of the attendant advantages thereof, will be readily apparent as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings in which like reference symbols indicate the same or similar components, wherein:  
       FIG. 1  is a schematic view illustrating empty spaces formed in a contemporary delta type PDP having a rectangular effective picture area;  
      FIG. 2  is a schematic view illustrating a contemporary delta type PDP in which pixels have been shifted in order to cover empty spaces;  
       FIG. 3  is a partially enlarged perspective view illustrating a PDP constructed as one embodiment of the principles of the present invention;  
       FIG. 4  is a front view of the PDP shown in  FIG. 3 ;  
       FIG. 5  is a partially enlarged perspective view illustrating a PDP constructed as another embodiment of the principles of the present invention; and  
       FIG. 6  is a front view of a PDP constructed as still another embodiment of the principles of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       FIG. 1  is a front view of a rotary delta type plasma display panel (PDP)  100  having a contemporary rectangular effective picture area  300 . Herein, effective picture area  300  refers to an area of a front panel with the exception of a part covered with a front case. That is, effective picture area  300  is a screen area that displays images viewed by the optical facilities of the viewers.  
      A PDP includes display areas  332  capable of displaying images using discharge electrodes, to which a discharge voltage is applied, and non-display areas  330 , which are non-emissive areas aligned at outer portions of display areas  332 .  
      As shown in  FIG. 1 , in delta type PDP  100  having rectangular effective picture area  300 , if rectangular effective picture area  300  is established to cover entire display areas, empty spaces  330  (i.e., non-display areas) may be undesirably formed because the shape of delta type barrier ribs  170  will inevitably result in a mismatch between effective picture area  330  and display areas  332 .  
      Although  FIG. 1  shows empty spaces  330  (i.e., non-display areas) formed in rotary delta type PDP  100  having hexagonal discharge cells  191 ,  192  and  193 , in which each hexagonal discharge cell is formed in such a way that upper and lower end portions  328  of the hexagonal discharge cell are horizontal lines when viewed from the front of the hexagonal discharge cell, empty spaces  330  can also be formed in the general delta type PDP having hexagonal cells  191 ,  192  and  193 , in which each hexagonal cell is formed in such a way that left and right end portions of the hexagonal cell are vertical lines when viewed from the front of the discharge cell, because in this arrangement, effective picture area  300  does not match with display areas  332  either.  
      Such empty spaces  330  are typically coated with a dielectric layer or a fluorescent layer. The dielectric layer and the fluorescent layer are white in color, so they exhibit superior reflection brightness in response to the incidence of external light onto non-display areas  330  (i.e., empty spaces). If non-display areas  330  have superior reflection brightness, the bright room contrast of the PDP may be degraded, thereby lowering the image quality of the PDP.  
      In order to solve the above problem, pixels  190  defined by three hexagonal discharge cells  191 ,  192  and  193  have been shifted with respect to effective picture area  300 , as shown in  FIG. 2 , such that empty spaces  330  in effective picture area  300  can be covered by pixels  190 .  
      Referring to  FIG. 2 , pixels  190  defined by three hexagonal discharge cells  191 ,  192  and  193  have been shifted with respect to effective picture area  300  such that empty spaces  330  in effective picture area  300  that were originally not covered by pixels  190  can be covered by pixels  190 . In this case, however, a part of pixels  190  that was originally belonging to display areas  332  deviates from effective picture area  300 . Although  FIG. 2  only shows the rotary delta type PDP, such a deviation of the pixel may be incurred in the general delta type PDP.  
      As mentioned above, according to the delta type PDP, one pixel is defined by three adjacent discharge cells and each discharge cell radiates visible rays of red, green or blue colors. In addition, the delta type PDP generates various colors by mixing the visible rays. If a part of the pixel deviates from effective picture area  300 , however, an input color signal may not match with an output color signal. For this reason, a color unbalance may occur at the edge portions of effective picture area  300 , so that it is difficult to exhibit the desired color, which is intended to be seen by the viewers.  
      Hereinafter, embodiments of a plasma display panel (PDP) according to the present invention will be described with reference to the accompanying drawings.  
       FIG. 3  is a partially enlarged perspective view illustrating a PDP constructed as one embodiment of the principles of the present invention.  
      Referring to  FIG. 3 , PDP  100  according to the principles of the present invention is constructed with a front substrate  110 , a rear substrate  140  opposite to front substrate  110 , barrier ribs  170  defining a space  125  between front and rear substrates  110  and  140  such that three discharge cells  191 ,  192  and  193  radiating visible rays having different colors are aligned in space  125  in a triangular pattern to form one pixel  190 , a plurality of discharge electrodes including display electrodes  120  and address electrons  150  aligned on at least one of front substrate  110 , rear substrate  140  and barrier ribs  170  corresponding to discharge cells  191 ,  192  and  193 , a fluorescent layer  165  formed in discharge cells  191 ,  192  and  193 , and an external light absorber  200  formed in a non-display areas  330 . Discharge cells  191 ,  192  and  193  are filled with discharge gas for generating vacuum ultraviolet rays through plasma discharge.  
      In the following description, the direction which is perpendicular to and directed toward front substrate  110  (that is, the +Z direction in  FIG. 3 ) is referred to as an upper direction, and the direction which is perpendicular to and directed toward to rear substrate  140  (that is, the −Z direction in  FIG. 3 ) is referred to as a lower direction.  
      A front panel  115  is constructed with a front substrate  110 , display electrodes  120 , an upper dielectric layer  130  and a protective layer  135 . Front substrate  110  is made of a transparent material, such as soda glass. In addition, Y display electrodes  122  and X display electrodes  124  are aligned on rear surface  112  of front substrate  110  and they are parallel to each other. Y and X display electrodes  122  and  124  are aligned in the Y direction of the substrate sequentially and seriatim. A pair of Y and X display electrodes  122  and  124  are allocated to each discharge cell. Y and X display electrodes  122  and  124  are covered with an upper dielectric layer  130 , which is protected by a protective layer  135 .  
      A rear panel  145  is constructed with a rear substrate  140 , address electrodes  150  and a lower dielectric layer  160 . Rear substrate  140  is made of a transparent material, such as soda glass and forms PDP  100  together with front substrate  110 . Address electrodes  150  are formed at a front surface  162  of rear substrate  140  and aligned in a direction which is perpendicular to Y and X display electrodes  122  and  124 , i.e., the Y direction in  FIG. 3 , and a lower dielectric layer  160  covers address electrodes  150 . Barrier ribs  170  are provided on lower dielectric layer  160 . A fluorescent layer  165  is formed on dielectric layer  160  and on parts of sidewalls  168  of barrier ribs  170 .  
      As shown in  FIG. 3 , barrier ribs  170  can be formed on an entire surface of lower dielectric layer  160  with a thickness or in a position separated from rear panel  145 . Barrier ribs  170  may form discharge cells having various shapes, such as a triangular shape, a rectangular shape, a lozenge shape, a pentagonal shape or a hexagonal shape. Although  FIG. 3  shows barrier ribs  170  forming hexagonal shaped discharge cells  191 ,  192  and  193 , the present invention is not limited to this shape. That is, the present invention is applicable for various delta type barrier ribs  170  forming discharge cells in various shapes. Barrier ribs  170  forms a space between front and rear panels  115  and  145  while defining discharge cells  191 ,  192  and  193 .  
      In delta type barrier ribs  170 , three discharge cells  191 ,  192  and  193  radiating visible rays having different colors are adjacent to each other in a triangular pattern, thereby forming one pixel  190 . Herein, two address electrodes  150  are allocated to one pixel  190  defined by delta type barrier ribs  170 . That is, one address electrode (e.g. address electrode  151 ) is commonly allocated to two discharge cells (e.g. discharge cells  192  and  193 ) selected from three discharge cells  191 ,  192 , and  193  and a different address electrode (e.g. address electrode  152 ) is allocated to the remaining discharge cell (e.g. discharge cell  191 ).  
      Barrier ribs  170  can be fabricated through a screen-printing, a sandblasting, a lifting-off, or an etching scheme. The present invention, however, does not limit the fabrication processes for fabricating barrier ribs  170 . In addition, barrier ribs  170  are made from glass including an element selected from the group of Pb, B, Si, Al and O. Preferably, barrier ribs  170  are made from a dielectric material including a filler, such as ZrO 2 , TiO 2 , or Al 2 O 3 , and a pigment, such as Cr, Cu, Co or Fe. The present invention, however, does not limit the materials for making barrier ribs  170  and barrier ribs  170  can be made from various dielectric materials. Barrier ribs  170  are white in color, so they produce superior reflection brightness in response to the incidence of external light onto barrier ribs  170 . If barrier ribs  170  have superior reflection brightness, however, the bright room contrast of PDP  100  may be degraded, thereby lowering the image quality of PDP  100 . For this reason, a black stripe layer  174  is formed on an front surface  172  of barrier ribs  170  or a part of front panel  115  corresponding to front surface  172  of barrier ribs  170  in order to improve the bright room contrast.  
      Upper dielectric layer  130  is constructed with display electrodes  120  and covers the entire rear surface  112  of front substrate  110 . Upper dielectric layer  130  can be formed by uniformly screen-printing paste, which mainly includes glass powder having a low melting point, onto the entire rear surface  112  of front substrate  110 . As is generally known in the art, upper dielectric layer  130  is transparent and serves as a capacitor during the discharge operation. In addition, upper dielectric layer  130  restricts the current and has a memory function. A protective layer  135  may be constructed on upper surface  132  of rear dielectric layer  130  in order to discharge a greater amount of secondary electrons during the discharge operation while reinforcing endurance of upper dielectric layer  130 . Protective layer  135  can be formed through an electron beam process or a sputtering process using MgO or equivalent material. The present invention, however, does not limit the materials and fabrication processes for protective layer  135 .  
      Lower dielectric layer  160  is constructed with address electrodes  150  and covers the entire front surface  142  of rear substrate  140 . Lower dielectric layer  160  may be made from a material similar to the material forming upper dielectric layer  130 .  
      Address electrodes  150  are aligned on front surface  142  of rear substrate  140 , parallel to each other and spaced apart from each other. Address electrodes  150  substantially cross display electrodes  120 . Each address electrode  150  extends in the Y direction (see,  FIG. 3 ) while passing through discharge cells  191 ,  192  and  193  radiating visible rays with different colors. Address electrode  150  is fabricated by the sputtering, screen-printing, or photolithograph technique using Ag paste or equivalent material. The present invention, however, does not limit the materials and fabrication processes for the address electrode  150 .  
      Display electrodes  120  are aligned on rear surface  112  of front substrate  110 , parallel to each other and spaced apart from each other. Each display electrode  120  includes a pair of Y and X display electrodes  122  and  124 . Preferably, display electrodes  120  are made from one selected from the group of indium tin oxide (ITO) (an oxide layer of In), SnO 2  (an oxide layer of Sn), and equivalent materials having superior light transmittance characteristics in order to improve the aperture ratio of front substrate  110 . The present invention, however, does not limit the materials from which display electrodes  120  are made. In addition, display electrodes  120  are mainly fabricated by a sputtering process. The present invention, however, does not limit the fabrication processes for display electrodes  120 . Meanwhile, a low-resistance bus electrode (not shown) can be provided on the surface of the display electrode  120  in order to restrict the voltage drop. Such a low-resistance bus electrode may be made from one selected from the group of Cr—Cu—Cr, Ag and equivalent materials. The present invention, however, does not limit the materials for the low-resistance bus electrode.  
      In the meantime, although it is not illustrated in figures, display electrodes  120  are aligned along barrier ribs  170  in the X direction (see,  FIG. 3 ) while substantially crossing address electrodes  150 . Therefore, three adjacent discharge cells  191 ,  192  and  193  coated with fluorescent layers  165  having different colors are aligned on the basis of Y and X display electrodes  122  and  124 . The reason for aligning display electrodes  120  on barrier ribs  170  or in barrier ribs  170  instead of in the areas where barrier ribs  170  are not substantially presented, is to solve a problem derived from a narrow discharge space in the high definition PDP, because when display electrodes  120  are aligned on or in barrier ribs  170 , display electrodes  120  do not occupy too much discharge spaces. Thus, a pair of display electrodes  120  are allocated to each pixel  190  defined by the barrier ribs  170 .  
      Fluorescent layer  165  has components capable of generating visible light rays upon receiving ultraviolet rays. The red fluorescent layer formed in the discharge cell radiating a visible ray having a red color is made from fluorescent materials, such as Y(V,P)O 4 :Eu. The green fluorescent layer formed in the discharge cell radiating a visible ray having a green color is made from fluorescent materials, such as Zn 2 SiO 4 :Mn. In addition, the blue fluorescent layer formed in the discharge cell radiating a visible ray having a blue color is made from fluorescent materials, such as BAM:Eu. Accordingly, fluorescent layer  165  is divided into red, green and blue fluorescent layers formed in adjacent discharge cells  191 ,  192  and  193 , respectively. In addition, adjacent discharge cells  191 ,  192  and  193  formed with the red, green and blue fluorescent layers  165  are combined with each other, thereby forming a unit pixel  190  in order to realize a color image.  
      In the meantime, discharge gas, such as Ne—Xe or He—Xe, is injected into a discharge cell defined by front and rear panels  115  and  145  and barrier ribs  170 .  
      Two address electrodes  150  are allocated to one pixel  190  defined by barrier ribs  170 . One address electrode  150  may be commonly allocated to the red and green fluorescent layers  165  and the other address electrode  150  may be allocated to the blue fluorescent layer  165 . It is possible, however, to commonly allocate one address electrode  150  to the green and blue fluorescent layers  165  while allocating the other address electrode  150  to the red fluorescence layer  165 . In addition, it is also possible to commonly allocate one address electrode  150  to the blue and red fluorescent layers  165  while allocating the other address electrode  150  to the green fluorescence layer  165 .  
      Discharge cells  191 ,  192  and  193  are defined by lower dielectric layer  160  formed on the front surface  142  of rear substrate  140 , barrier ribs  170  and upper dielectric layer  130 . Discharge gas (e.g. mixing gas made from Xe and Ne) is filled into discharge cells  191 ,  192  and  193  in order to generate the plasma discharge. In addition, as mentioned above, fluorescent layers  165  radiating visible rays of different colors upon receiving the ultraviolet rays generated by the plasma discharge are formed at corresponding areas of discharge cells  191 ,  192  and  193 , respectively. The width or length of discharge cells  191 ,  192  and  193  may vary depending on the light emitting efficiency of fluorescent layers  165 .  
      In addition, PDP  100  includes display areas  332  and non-display areas  330 . An external light absorber  200  is formed in non-display areas  330 . Referring to  FIG. 3 , external light absorber  200  is formed in non-display areas  330  provided at a front surface  114  of front substrate  110  (that is, a front surface of front substrate  110  when the PDP is uprightly installed).  
      Hereinafter, detail description will be made with respect to external light absorber  200 .  
       FIG. 4  is a front view of the PDP shown in  FIG. 3 .  
      Referring to  FIG. 4 , a PDP  100  constructed as one embodiment of the principles of the present invention includes display areas  332  (emissive areas) as a set of pixels and non-display areas  330  (non-emissive areas) aligned at outer portions of the display areas. In addition, external light absorber  200  is formed in non-display areas  330  in order to reduce the reflection brightness of PDP  100  in response to the incidence of the external light.  
      Herein, the term “display area” refers to an area to which the discharge voltage is applied through a plurality of discharge electrodes so that ultraviolet rays are generated in the process of plasma discharge and the visible rays are radiated when the fluorescent molecules in the fluorescent layer formed in the discharge cell are excited by the ultraviolet rays and then drop to the ground state in terms of energy, thereby realizing the image.  
      In addition, the term “non-display area” refers to an area located outside of the display areas and the sustain discharge is not generated between X and Y display electrodes  124  and  122 . X electrodes  124 , Y electrodes  122  and address electrodes  150  may extend into the non-display areas from the display areas, so that terminals of the above electrodes area are electrically connected to an external terminal of a signal transferring unit, such as a flexible printed cable.  
      According to the present invention, delta type barrier ribs  170  are employed so that the boundary lines between display areas  332  and non-display areas  330  are curved.  
      Although  FIG. 4  shows the rotary delta type PDP  100  having hexagonal discharge cells  191 ,  192  and  193 , in which each hexagonal discharge cell is formed in such a way that upper and lower end portions  328  of the hexagonal discharge cell are horizontal lines when viewed from the front of the hexagonal discharge cell, the present invention is also applicable for the general delta type PDP having hexagonal cells, in which each hexagonal cell is formed in such a way that left and right end portions of the hexagonal discharge cell are vertical lines when viewed from the front of the discharge cell. In addition, the present invention is also applicable for PDP  100  in which two address electrodes  150  are allocated to one pixel  190 . Although rotary delta type PDP  100  may be constructed with two address electrode  150  allocated to one pixel  190 , the rotary delta type PDP is not limited to this arrangement. In other words, the rotary delta type PDP may be constructed with two display electrodes, i.e. X and Y display electrodes  124  and  122 , allocated to one pixel. In addition, the present invention is also applicable for the PDP having polygonal discharge cells, rather than the hexagonal discharge cells.  
      Referring again to  FIG. 4 , PDP  100  has a rectangular effective picture area  300  including entire display areas  332  and a part of non-display areas  330  adjacent to display areas  332 . In other words, rectangular effective picture area  300  includes not only entire display areas  332 , but also a part of non-display areas  330 .  
      In addition, external light absorber  200  is provided in non-display areas  330  formed in rectangular effective picture area  300 . In delta type PDP  100  having rectangular effective picture area  300 , if rectangular effective picture area  300  is established with entire display areas  332 , empty spaces may be inevitably formed due to the shape of delta type barrier ribs. The empty spaces correspond to non-display areas  330 .  
      Such empty spaces  330  are typically coated with a dielectric layer or a fluorescent layer. The dielectric layer and the fluorescent layer are white in color, so they exhibit superior reflection brightness in response to the incidence of the external light onto non-display areas  330  (i.e. empty spaces). If non-display areas  330  have superior reflection brightness, the bright room contrast of PDP  100  may be degraded, thereby lowering the image quality of PDP  100 .  
      For this reason, external light absorber  200  is provided in empty spaces  330  in order to improve the bright room contrast by reducing the reflection brightness in response to the incidence of external light onto empty spaces  330 .  
      External light absorber  200  can be formed on rear surface  112  or front surface  114  of front substrate  110  corresponding to non-display areas  330 . In this case, the reflection brightness of the PDP with respect to the external light can be effectively reduced if external light absorber  200  covers the entire non-display areas  330 , which are formed in effective picture area  300 , of rear surface  112  or front surface  114  of the front substrate  110 . At this time, as shown in  FIG. 4 , the width of external light absorber  200  is periodically changed at the uppermost and lowermost sides and/or the rightmost and leftmost sides of discharge cells  191 ,  192  and  193 .  
      In addition, external light absorber  200  can be formed with a recess having a depth. In this case, recess  118  having depth A as shown in  FIG. 3  is formed in front surface  114  of front substrate  110  corresponding to non-display areas  330  and is filled with light shielding materials. The external light maybe incident slantwise into the discharge cells in non-display areas  330  from display areas  332 . If external light absorber  200  has recess  118  with depth A, however, the external light is shielded by the light shielding materials filled in recess  118  before the external light is incident into the discharge cells in non-display areas  330 .  
      In addition, external light absorber  200  can be formed on barrier ribs  170  forming discharge cells  191 ,  192  and  193 , fluorescent layer  165 , or dielectric layer  130  or  160 , in the areas corresponding to non-display areas  330 . In this case, the reflection brightness of the PDP with respect to the external light can be effectively reduced if external light absorber  200  covers entire light projection areas of barrier ribs  170 , fluorescent layer  165  or dielectric layer  130  or  160  in such a manner that the entire surface of non-display areas  330  formed in effective picture area  300  can be covered with external light absorber  200 .  
      In order to reduce the bright room contrast by using external light absorber  200 , it is preferred if a discharge cell in non-display areas  330  formed with external light absorber  200  has a reflection brightness lower than an average reflection brightness of the discharge cells realizing the image.  
      Therefore, external light absorber  200  is preferably made from a material having a superior light absorption property. More preferably, external light absorber  200  is made from a material having a surface color of black.  
       FIG. 5  is a partially enlarged perspective view illustrating a PDP  100  constructed as another embodiment of the principles of the present invention. Since PDP  100  shown in  FIG. 5  is substantially identical to PDP  100  shown in  FIGS. 3 and 4 , the following description will focus on the difference between PDP  100  shown in  FIG. 5  and PDP  100  shown in  FIGS. 3 and 4 .  
      Referring to  FIG. 5 , PDP  100  constructed as another embodiment of the principles of the present invention includes display areas  332  (emissive areas) as a set of pixels  190  and non-display areas  330  (non-emissive areas) aligned at outer portions of display areas  332 . In addition, external light absorber  200  is formed in non-display areas  330  located in effective picture area  300  in order to reduce the reflection brightness of the PDP with respect to the external light.  
      In this case, a dummy wall  180  is formed in non-display areas  330  located in effective picture area  300 . Dummy wall  180  extends from a barrier rib  170  forming an outermost portion of display areas  332  in order to reduce the space of the discharge cells corresponding to non-display areas  330  and external light absorber  200  is provided on dummy wall  180 .  
      Although dummy wall  180  can be formed separately from barrier ribs  170 , it is preferred to integrally form dummy wall  180  with barrier ribs  170  in order to facilitate the fabrication process for PDP  100 .  
      If dummy wall  180  is not provided in non-display areas  332  of effective picture area  300 , the pre-discharge, such as the address discharge, may be generated in the discharge cell belonging to the non-display areas. If electric charges are abnormally charged in the discharge cell belonging to the non-display areas, an abnormal discharge may be undesirably generated. If dummy wall  180  is provided in non-display areas  330  located in effective picture area  300 , however, the space causing the pre-discharge or the abnormal discharge can be removed before the discharge occurs.  
      In addition, since external light absorber  200  is formed on dummy wall  180 , the external light incident onto non-display areas  330  is absorbed by external light absorber  200  so that the reflection brightness of the PDP with respect to the external light can be reduced, thereby improving the bright room contrast.  
      At this time, the reflection brightness of the PDP with respect to the external light can be effectively reduced if external light absorber  200  covers the entire light projection areas of dummy wall  180  formed in non-display areas  330  in such a manner that the entire surface of non-display areas  330  formed in effective picture area  300  can be covered by external light absorber  200 .  
       FIG. 6  is a front view of PDP  100  constructed as still another embodiment of the principles of the present invention. Since PDP  100  shown in  FIG. 6  is substantially identical to PDP  100  shown in  FIGS. 3 and 4 , the following description will focus on the difference between the PDP shown in  FIG. 6  and the PDP shown in  FIGS. 3 and 4 .  
      Referring to  FIG. 6 , PDP  100  constructed as still another embodiment of the principles of the present invention includes display areas  332  (emissive areas) as a set of pixels and non-display areas  330  (non-emissive areas) aligned at outer portions of display areas  332 . In addition, PDP  100  has an effective picture area  310  including entire display areas, exclusively. In other words, the display areas  332  match with effective picture area  310 .  
      Referring back to  FIG. 2 , the contemporary PDP employs rectangular effective picture area  300 , in which a part of pixels that was originally belonging to the display areas deviates from effective picture area  300 , so a color unbalance may occur at the edge portions of effective picture area  300 . Thus, the contemporary PDP may not produce the desired color, which is intended to be seen by the viewer. To solve the above problem, according to the principles of the present invention, effective picture area  310  is aligned corresponding to a curved boundary line  331  formed between display areas  332  and non-display areas  330 . In this case, the color balance can be obtained even in the edge portions of effective picture area  310  and non-display areas  330  are not formed in effective picture area  310  (i.e. display area  332  matches with effective picture area  310 ), thereby preventing the external light from being reflected from the non-display areas.  
      In order to establish the effective picture area  310  including entire display areas exclusively, front case  400  surrounding the PDP may cover the entire non-display areas  330 .  
      Accordingly, it is possible to improve the bright room contrast by balancing the colors representing the image.  
      As described above, the PDP constructed as an embodiment of the principles of the present invention employs effective picture area  310  including entire display areas  332  exclusively, so that the color balance can be obtained even in the edge portions of effective picture area  310 . In addition, if non-display areas  330  is provided in effective picture area  310 , external light absorber  200  is provided in non-display areas  330  so that the reflection brightness of the external light incident into non-display areas  330  can be reduced, thereby improving the bright room contrast of the PDP.  
      Although a preferred embodiment of the present invention has been described for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.