FLAT FLUORESCENT LAMPAND ELECTRODE STRUCTURE

THEREOF

Technical Field

[1] The present invention relates to a flat fluorescent lamp and an electrode structure thereof, and more particularly, to a flat fluorescent lamp and an electrode structure thereof wherein a thickness of the lamp can be minimized and the brightness uniformity of the lamp can be improved. Background Art

[2] As a prior art of a flat fluorescent lamp, there are disclosed a flat fluorescent lamp with opposite electrodes arranged thereon and a surface discharge type flat fluorescent lamp with line electrodes arranged on one surface thereof. A flat fluorescent lamp using dielectric barrier discharge manufactured by Osram GmbH of Germany has been commercially available.

[3] Hereinafter, a related art flat fluorescent lamp will be described with reference to

Figs. 16 and 17.

[4] A fluorescent lamp of Fig. 16 includes a front glass substrate 10, a rear glass substrate 20, and a support frame 30 for forming a discharge space between the glass substrates, which is filled with inert gas.

[5] A phosphor layer 11 is applied to a lower surface of the front glass substrate 10.

[6] Electrodes 21 formed with protrusions for partial discharge, a dielectric layer 22 for electrically isolating the electrodes 21 from one another and decreasing a breakdown voltage, and a phosphor layer 23 are sequentially laminated on the rear glass substrate 20.

[7] Fig. 17 is a view showing a planar structure of electrodes provided in the fluorescent lamp of Fig. 16. Each of the electrodes 21 consists of an anode 21a and a cathode 21b and is driven in DC impulse mode.

[8] The anode 21a and the cathode 21b are composed of a plurality of strip leads, respectively. Particularly, the anode 21a is composed of a pair of strip leads, and each strip lead of the cathode 21b is positioned most adjacent to the pair of the strop leads of the anode 21a. The strip lead of the cathode 21b is formed with a plurality of needle- shaped protrusions for partial discharge.

[9] In the related art flat fluorescent lamp, when a DC impulse is applied to the anode

21a and the cathode 21b, delta-shaped partial discharge is generated between the strip leads of the anode 21a and the protrusions P of the strip leads of the cathode 21b, so that ultraviolet rays are emitted.

[10] However, in the related art flat fluorescent lamp, the anode consisting of a pair of strip leads is different from the cathode consisting of a strip lead formed with a plurality of protrusions in view of their electrode structure shapes. Therefore, there is a problem in that the brightness uniformity is deteriorated due to asymmetry of the electrode structures.

[11] In particular, there is a problem in that the brightness uniformity is reduced by the brightness difference caused from the partial discharge at the needle-shaped protrusions.

Disclosure of Invention Technical Problem

[12] The present invention is conceived to solve the aforementioned problems in the prior art. An object of the present invention is to provide a flat fluorescent lamp which provides stable discharge and uniform brightness distribution by solving the brightness difference caused from partial discharge at the needle-shaped protrusions in an electrode structure of a flat lamp and has a discharge tube structure capable of minimizing the thickness of a fluorescent lamp panel.

Technical Solution

[13] According to an aspect of the present invention, there is provided an electrode structure of a flat fluorescent lamp, which includes a discharge tube in the form of a flat plate with a certain thickness in which gas is filled and sealed, conductive electrode portions printed in the discharge tube, a dielectric layer applied to the electrode portions and the discharge tube, and a phosphor applied to the dielectric layer. The electrode portions include a plurality of strip electrodes which are uniformly arranged in parallel with each other on a surface in the discharge tube, and voltages of opposite polarities are applied to the most adjacent strip electrodes, respectively, when discharge occurs.

[14] According to another aspect of the present invention, there is provided an electrode structure of a flat fluorescent lamp, which includes a discharge tube in the form of a flat plate with a certain thickness in which gas is filled and sealed, conductive electrode portions printed in the discharge tube, a dielectric layer applied to the electrode portions and the discharge tube, and a phosphor applied to a portion of the dielectric layer. The electrode portions include a plurality of electrode groups consisting of at least two strip electrodes which are uniformly arranged on a surface in the discharge tube, and voltages of opposite polarities are applied to the most adjacent electrode groups of the strip electrodes, respectively.

[15] According to a further aspect of the present invention, there is provided an electrode structure of a flat fluorescent lamp, which includes a discharge tube in the form of a

flat plate with a certain thickness in which gas is filled and sealed, conductive electrode portions printed in the discharge tube, a dielectric layer applied to the electrode portions and the discharge tube, and a phosphor applied to the dielectric layer. The electrode portions include a plurality of strip electrodes which are uniformly arranged in parallel with each other on a surface in the discharge tube, nonconductive regions are formed within peripheral edges of the strip electrodes, and voltages of opposite polarities are applied to the most adjacent strip electrodes, respectively, when discharge occurs.

[16] According to a still further aspect of the present invention, there is provided a flat fluorescent lamp in which gas is filled and sealed, which comprises a front plate to which a phosphor is applied; a rear plate on which a reflection plate, first and second conductive electrode portions printed to be electrically insulated from each other, a dielectric layer, and a phosphor are sequentially provided; and a support portion for supporting the front and rear plates, thereby allowing an airtight discharge space to be formed between the front and rear plates, wherein the first electrode portion includes a plurality of first strip electrodes which are positioned in the discharge space in parallel with one another, and a first lead electrode, which is positioned out of the discharge space such that a plurality of the first electrodes are joined to the first lead electrode, and the second electrode portion includes a plurality of second strip electrodes, which are positioned one by one between the first electrodes in parallel with one another, and a second lead electrode, which is positioned out of the discharge space such that a plurality of the second electrodes are joined to the second lead electrode.

[17] According to a still further aspect of the present invention, there is provided a flat fluorescent lamp in which gas is filled and sealed, which comprises a front plate to which a phosphor is applied; a rear plate on which a reflection plate, first and second conductive electrode portions printed to be electrically insulated from each other, a dielectric layer, and a phosphor are sequentially provided; and a support portion for supporting the front and rear plates, thereby allowing an airtight discharge space to be formed between the front and rear plates, wherein the first electrode portion includes a plurality of first electrodes, which are arranged in parallel with one another in the discharge space and into which at least two parallel strip electrodes are grouped together, and a first lead electrode, which is positioned out of the discharge space such that the first electrodes are joined to the first lead electrode; and the second electrode portion includes a plurality of second electrodes, which are arranged in parallel with one another and into which parallel strip electrodes equal in number to the number of the strip electrodes in each first electrode are grouped together to be symmetric with the adjacent first electrode, and a second lead electrode, which is positioned out of the discharge space such that a plurality of the second electrodes are joined to the second

lead electrode. Advantageous Effects

[18] According to the flat fluorescent lamp of the present invention as described above, strip electrodes are arranged to be symmetric one to one or in groups consisting of two or more electrodes in a discharge tube. Thus, the brightness difference due to partial discharge at the needle-shaped protrusions caused from the conventional electrode structure can be eliminated. Therefore, there are advantages in that it is possible to provide stable discharge and uniform brightness distribution and to minimize the thickness of the fluorescent lamp panel.

Brief Description of the Drawings [19] Fig. 1 is a partially cut away perspective view of a flat fluorescent lamp according to the present invention. [20] Fig. 2 is a view showing a preferred example of a drive circuit for driving the flat fluorescent lamp of the present invention. [21] Fig. 3 is a view showing waveforms of input and output signals of the drive circuit shown in Fig. 2. [22] Fig. 4 is a view showing an electrode structure of the flat fluorescent lamp according to a first preferred embodiment of the present invention. [23] Fig. 5 is a view showing an experimental example of the brightness uniformity of the flat fluorescent lamp according to the first embodiment of the present invention. [24] Fig. 6 is a view showing the brightness uniformity of a related art flat fluorescent lamp for the comparison with that of the flat fluorescent lamp according to the first embodiment of the present invention. [25] Fig. 7 is a graph showing the current characteristics according to an electrode width in the first embodiment of the present invention. [26] Fig. 8 is a graph showing the efficiency characteristics according to an electrode width in the first embodiment of the present invention. [27] Fig. 9 is a graph showing the efficiency characteristics and breakdown voltage according to a gap between electrodes in the first embodiment of the present invention. [28] Fig. 10 is a graph showing the relationship between the brightness and pressure according to a gap between electrodes in the first embodiment of the present invention. [29] Fig. 11 is a view showing an electrode structure of a flat fluorescent lamp according to a second embodiment of the present invention. [30] Fig. 12 is a graph showing current waveforms according to the respective electrode structures of the first and second embodiments of the present invention. [31] Fig. 13 is a graph showing the brightness characteristics according to the respective electrode structures of the first and second embodiments of the present invention.

[32] Figs. 14 and 15 are views showing an electrode structure according to modified embodiments of the present invention.

[33] Fig. 16 is a sectional view of a related art flat fluorescent lamp.

[34] Fig. 17 is a view showing an electrode structure of the related art flat fluorescent lamp. Best Mode for Carrying Out the Invention

[35] <First Embodiment

[36] Hereinafter, a first embodiment of the present invention will be described in detail with reference to the accompanying drawings.

[37] Referring to Fig. 1, a flat fluorescent lamp of the present invention includes front and rear plates 110 and 120 made of a glass substrate and a support portion 130 for supporting the front and rear plates 110 and 120, thereby forming a discharge space.

[38] A discharge tube, which is formed by the front plate 110, the rear plate 120 and the support portion 130, is filled with inert gas. More specifically, xenon (Xe) gas, xenon (Xe) gas including neon (Ne), argon (Ar) or krypton (Kr), or the like may be filled in the discharge tube, but mercury (Hg) should not preferably be filled therein.

[39] A phosphor 111 is applied to a lower surface of the front plate 110. Thus, the front plate 110 becomes a light-emitting surface through which light generated from the fluorescent lamp is emitted.

[40] The rear plate 120 is provided with a reflection plate 140, electrode portions 150 and 160 composed of a plurality of strip electrodes, a dielectric layer 170, and a phosphor 180.

[41] The reflection plate 140 provided on the upper portion of the rear plate 120 reflects the light toward the light-emitting surface, thereby enhancing the light use efficiency. In addition, the reflection plate 140 controls an amount of all incident lights to be reflected, thereby causing the whole light-emitting surface of a backlight to have uniform brightness distribution.

[42] The dielectric layer 170 electrically insulates the electrode portions 150 and 160 from each other and limits an electric current.

[43] The phosphor 180 is applied to an upper surface of the dielectric layer 170.

[44] Meanwhile, in the embodiment of the present invention, the discharge space is formed by providing the support portion 130 on peripheral edges of the front and rear plates 110 and 120 therebetween. However, the discharge space may be formed by bonding the peripheral edges of the front and rear glass plates using an injection method of frit glass without providing an additional support portion between the front and rear plates. At this time, a plurality of spacers may be provided in the space between the front and rear plates, so that the front and rear plates are kept spaced apart

by a certain gap between each other. To increase the light-emitting efficiency, a phosphor may be applied to the spacers.

[45] Since the discharge space is formed by the injection method in a state where such an additional support portion is not used, there is an advantage in that it is possible to thin the fluorescent lamp panel.

[46] In the flat fluorescent lamp of the present invention, the electrode portions consist of a plurality of strip electrode uniformly arranged in parallel with one another on a plane within the discharge tube. It is the technical feature that voltages of opposite polarities are applied to the most adjacent strip electrodes when the discharge occurs.

[47] In the present invention, it is preferred that paste for use in the electrode portions have a small work function, strong resistance to ion bombardment and superior conductivity, be easily adsorbed to a dielectric material, and do not need a specific post- process such as an activation or aging process. As a material for the electrodes, conductive paste such as silver (Ag), nickel (Ni) or copper (Cu) may be used.

[48] Such a flat fluorescent lamp of the present invention is characterized in that it is driven by AC square-wave pulse power.

[49] Since the polarities of the AC pulse power perform the same function in the present invention, the polarities of the first and second electrode portions are not particularly distinguished from each other.

[50] Specifically, referring to Fig. 2 showing a preferred example of a drive circuit for driving the flat fluorescent lamp of the present invention, four high speed FETs and a transformer are combined to output high AC square-wave pulse power.

[51] When appropriate signals are input to gates of the respective FETs in a state where

DC voltage (+V) is applied to drains Ql and Q3, the AC square- wave pulse power can be obtained. Referring to Fig. 3a, a voltage of about +V is generated at both ends of a primary side of the transformer when Q3 and Q4 are simultaneously turned on, while a voltage of about -V is generated at both the ends of the primary side of the transformer when Ql and Ql are simultaneously turned on.

[52] Fig. 3 (a) and (b) show waveforms of gate input signals and an output voltage of the drive circuit of Fig. 2, respectively. The output voltage generated at the primary side of the transformer is increased and thus applied the first and second electrode portions.

[53] Fig. 4 is a view showing the first preferred embodiment of the planar structure of the electrode in the flat fluorescent lamp according to the present invention. The electrode consists of the first and second electrode portions 150 and 160 to which voltages of opposite polarities are applied.

[54] Specifically, the first electrode portion 150 includes a plurality of first strip electrodes 151, which are positioned in the discharge space in parallel with one another, and a first lead electrode 152, which is positioned out of the discharge space

such that a plurality of the first electrodes are joined to the first lead electrode.

[55] The second electrode portion 160 may include a plurality of second strip electrodes

161, which are positioned one by one between the first strip electrodes in parallel with one another, and a second lead electrode 162, which is positioned out of the discharge space such that a plurality of the second electrodes are joined to the second lead electrode.

[56] In the meantime, reference numeral 130a shown in Fig. 4 designates a portion to which the support portion 130 is fixed. Respective ends of the first and second electrodes extend at least up to a portion in which the support portion 130 is positioned, so that the ends of the electrodes should not be exposed in the discharge space.

[57] Since the ends of the strip electrodes are positioned out of the discharge space, the ends of the strip electrodes have no influence on the discharge generated in the discharge space. Thus, it is possible to obtain the stable discharge characteristics. That is, it is possible to obtain the same brightness uniformity in the center and peripheral edges of the lamp by preventing the ends and intermediate portions of the strip electrodes from being discharged in different discharge modes.

[58] As described in the prior art, a plurality of the needle-shaped protrusions are formed on the conventional strip electrodes such that discharge positions can be uniformly distributed between the electrodes. It is for the purpose of obtaining the certain brightness uniformity by appropriately distributing the needle-shaped protrusions such that the uniform discharge can be performed between the electrodes by causing the discharge to begin at the tips of the needle-shaped protrusions and predicting a discharge path.

[59] However, in the related art electrode structure, electric field is concentrated at the needle-shaped protrusions or the tips of the electrodes. Particularly, there is a problem in that the discharge becomes unstable since the electric field is further concentrated at the tips as it is higher. Further, in the related art electrode structure having the needle- shaped protrusions, shadow areas in which the brightness is partially deteriorated occur according to positions of the needle-shaped protrusions. Thus, there is another problem in that the brightness uniformity is deteriorated.

[60] On the other hand, in the related art electrode structure having the needle-shaped protrusions, when the lamp operates with the tips subjected to the high electric field for a long time, damage of the electrodes are accelerated, thus causing life span of the lamp to be shortened. In addition, the phosphor is deteriorated and thus the dielectric layer is damaged. Thus, there is a problem in that the stable discharge is not obtained.

[61] However, the electrode structure of the flat fluorescent lamp of the present invention employs the linear strip electrodes in which additional protrusions are not

formed while the protrusion portions at which the discharge begins are excluded and the strip electrodes are arranged to be symmetric one to one on a whole surface of the discharge tube. Thus, it was confirmed that the present invention allows the brightness uniformity to be considerably increased as compared with the conventional electrode structure with the needle-shaped protrusions in which the discharge is generated only at specific positions of the electrodes.

[62] Specifically, Fig. 5 is a view showing an experimental example of the brightness uniformity of the flat fluorescent lamp according to the present invention. The brightness uniformity has been measured in a state where a surface light source is divided into nine equal areas. The numerals in parentheses designate brightness [cd/m ² ] in the respective measured areas.

[63] The brightness has been measured for each of the areas Al to A9 obtained by dividing the whole surface light source into nine equal areas. It is understood that average brightness is 5,831cd/m and that the ratio of the brightness in the lowest area

A9 to the brightness in the highest area A2 is 95% according to the definition of uniformity of the surface light source. [64] Fig. 6 is a view showing the brightness uniformity of the related art flat fluorescent lamp having the electrode structure formed with the needle-shaped protrusions for the comparison with that of the flat fluorescent lamp according to the present invention.

Similarly to Fig. 5, the brightness uniformity has been measured in a state where a surface light source is divided into nine equal areas. [65] The brightness has been measured for each of the areas Al to A9 obtained by dividing the whole surface light source into nine equal areas. It is understood that average brightness of the conventional fluorescent lamp is 5,593cd/m and that the ratio of the brightness in the lowest area B9 to the brightness in the highest area B5 is 88% according to the definition of uniformity of the surface light source.

[66] That is, if the present invention is compared with the prior art, the conventional fluorescent lamp has the brightness uniformity of 88%, whereas the fluorescent lamp of the present invention has the brightness uniformity of 95%. Thus, it has been confirmed that the brightness uniformity of the present invention is considerably higher as compared with that of the conventional electrode structure with the needle- shaped protrusions.

[67] The flat fluorescent lamp of the present invention has a technical feature that the thickness of each of the first electrode and the second electrode is 5 to 15D. In addition, the electrodes are preferably manufactured so that the deviation in thickness of each of the electrodes is 1/2 or less.

[68] This is to prevent the electric field from being concentrated at both sides of the electrode and thus the electrodes from being damaged in a case where both sides of the

electrode are excessively thin due to the large difference in thickness between the middle and both sides of the electrode. This can also be optimized within a range in which stable discharge can be preformed in consideration of technical and economical aspects when an electrode is manufactured using a printing method.

[69] Next, the flat fluorescent lamp of the present invention has a technical feature in that the width of each electrode is within a range from 0.3 to 1 mm.

[70] Referring to Fig. 7, in the embodiment of the present invention, heat is apt to be generated in the electrode when the electrode width is 0.3 mm or less. Further, a peak value of displacement current increases in proportion to the electrode width, and thus, the capacitance of the electrode increases due to the increase in area of the electrode as the electrode width is increased when the electrode width is 1 mm or more. Thus, there is a problem in that even in a case of discharge current, a peak value of the current and a current holding time are increased as the electrode width is increased, so that large reactive power, which does not contribute to emit light, is increased due to excessive current flow.

[71] The applicant of the present invention for solving this problem has confirmed that the electrode width is preferably determined to be within the range from 0.3 to 1 mm after measuring discharge efficiency characteristics according to electrode widths.

[72] Fig. 8 is a graph showing the discharge efficiency characteristics according to electrode widths. It can be shown from this figure that the discharge efficiency is decreased when the electrode width is out of the range of 0.3 to 1 mm.

[73] The present invention also has a technical feature in that the distance between the two adjacent electrodes is 3 to 10 mm.

[74] Specifically, the distance between the two electrodes should be considered together with a pressure in the discharge tube. In consideration of the Paschen's law, the pressure in the discharge tube should be adjusted according to the distance between the two electrodes.

[75] According to the Paschen's law, a breakdown voltage Vf can be expressed as a function of a gap d between the electrodes and a mean free path λe, i.e. Vf = f(d/λe).

[76] Since the mean free path λe is in inverse proportion to the pressure P, the breakdown voltage Vf can be expressed by means of a single variable showing a ratio of a gap d to a mean free path λe from the Paschen's law. It can be understood that the same value of d/λe exhibits the same discharge characteristics.

[77] Fig. 9 is a graph showing the efficiency characteristics and breakdown voltage according to a gap between the electrodes in the first embodiment of the present invention. It can be shown from this figure that the breakdown voltage is increased at a high rate as a gap between the electrodes is increased, whereas a change in the efficiency is relatively small as compared with the rate of increase in the breakdown

voltage.

[78] Next, Fig. 10 is a graph showing the relationship between the brightness and the pressure according to a gap between the electrodes in the first embodiment of the present invention. It can be shown from this figure that a large amount of gas can be filled in the discharge tube as a gap between the electrodes is narrow, whereas the brightness tends to be considerably decreased when the gap between the electrodes is wide and a gas pressure is high.

[79] To obtain the stable discharge characteristics as well as the high brightness, it is preferred that a distance between the two adjacent electrodes be within a range from 1 1 o 10 mm according to this embodiment of the present invention.

[80] To minimize the influence caused from the brightness difference between the discharge areas between the fine electrodes, a well-known diffusion sheet can be employed in the flat fluorescent lamp of the present invention. At this time, a film used to increase the brightness may be considered to have the same function as the diffusion sheet.

[81] In addition, the flat fluorescent lamp of the present invention can be further provided with a radiation plate for allowing heat to be easily radiated. The radiation plate can be mounted to a rear surface of the rear plate. A radiation sheet or silicone may be mounted to perform effective heat conduction.

[82]

Mode for the Invention

[83] <Second Embodiment

[84] In general, the efficiency of a lamp is in proportion to brightness and in inverse proportion to power consumption. To increase the efficiency of a lamp, therefore, the power consumption should be reduced and the brightness should be increased.

[85] In the meantime, it is preferred that an electrode width be increased to enhance the brightness. However, the power consumption are increased together with the brightness when only the electrode width is increased in the electrode structure in which the electrode is in the form of a single strip as in the first embodiment. Thus, it is difficult to expect the increase in the lamp efficiency even if only the electrode width is increased.

[86] Therefore, the second embodiment of the present invention is characterized in that the brightness is increased by setting the electrode width to be larger and power consumption is also reduced by minimizing the areas of the electrodes such that a lamp with high efficiency can be provided.

[87] Hereinafter, the second embodiment of the present invention will be specifically described in detail with reference to the accompanying drawings.

[88] The constitutions of the flat fluorescent lamp according to the second embodiment of the present invention are the same as those of the first embodiment, except the electrode structure. Therefore, the details described in the first embodiment will be omitted herein and their differences will be mainly described below.

[89] The present invention has a technical feature in that the flat fluorescent lamp has such an electrode structure that at least two parallel strip electrodes are in each group and uniformly arranged on a surface in a discharge tube, and voltages of opposite polarities are applied to the two adjacent groups of strip electrodes, respectively. Hereinafter, a preferred example of the electrode structure in which three strip electrodes are in a group and arranged to be 3:3 symmetric with three strip electrodes in another adjacent group will be described.

[90] As shown in Fig. 11, the electrode structure of the flat fluorescent lamp of the present invention consists of first and second electrode portions 210 and 220 made of conductive materials, which are provided on an inner surface of a rear plate 200 and to which voltages of opposite polarities are applied, respectively

[91] The first electrode portion 210 includes a plurality of first electrodes 211 which are provided in parallel with one another within and into which three strip electrodes are grouped together, and a first lead electrode 212 which is positioned out of the discharge space such that a plurality of the first electrodes 211 can be joined thereto.

[92] The second electrode portion 220 includes a plurality of second electrodes 221 which are provided in parallel with one another between the two adjacent groups of the first electrodes 211 and into which three strip electrodes are grouped together, and a second lead electrode 222 which is positioned out of the discharge space such that a plurality of the second electrodes 221 can be joined thereto.

[93] Reference numeral 201 of Fig. 11 designates a portion where the support portion is fixed. Respective ends of the first and second electrodes extend at least up to the portion 201 in which the support portion is positioned, so that the ends of the electrodes should not be exposed in the discharge space.

[94] As previously described in the first embodiment, since the ends of the strip electrodes are positioned out of the discharge space, the ends of the strip electrodes have no influence on the discharge generated in the discharge space. Thus, it is possible to obtain the stable discharge characteristics.

[95] According to the present invention, the respective electrodes of the first and second electrode portions are arranged to be symmetric with one another in a state where the three strip electrodes are in each group as described above. Therefore, it is possible to decrease impedance value and power consumption.

[96] Here, the three strip electrodes each of which has the same width can be used.

However, it is possible that the two electrodes have the same width, but the other

electrode has a width wider or narrower than that of the two electrodes.

[97] For example, as shown in Fig. 11, the electrodes can be configured in such a manner that the width d2 of both side electrodes 211a and 211c among a group of the three electrodes is larger than the width dl of an intermediate electrode 21 Ib.

[98] Even in the second embodiment of the present invention, it is preferred that the width of each electrode is within the range from 0.3 to 1 mm as described in the first embodiment.

[99] In addition, referring to Fig. 11, it is preferred that the overall width D of the electrode portion consisting of the three electrodes in 3:3 symmetry be within a range from about 1 to 10 mm.

[100] Fig. 12 is a graph showing current waveforms measured under the same voltage condition according to the respective electrode structures of the first and second embodiments of the present invention. As compared with the electrode structure of the first embodiment having the 1 : 1 symmetry configuration, it can be confirmed that the electrode structure of the second embodiment having the 3:3 symmetry configuration has increased current when measured under the same voltage condition.

[101] Fig. 13 is a graph showing the brightness characteristics according to the respective electrode structures of the first and second embodiments of the present invention. Since the displacement current is high and the discharge current is low in the electrode structure of the first embodiment having the 1 : 1 symmetry configuration, it can be understood that the efficiency of the electrode structure of the second embodiment having the 3:3 symmetry configuration is higher by about 25% than that of the first embodiment under the same voltage condition.

[102] That is, the electrode structure into which a plurality of strip electrodes are grouped together as in the second embodiment of the present invention has increased current under the same voltage condition as compared with the single strip electrode and provides an advantage in that the brightness can be increased without change of its material property, thickness and the like. In addition, it is possible to obtain the increased efficiency since the increase in brightness is greater than the increase in power.

[103] In the meantime, Figs. 14 and 15 are views showing other modified embodiments of the electrode structure according to the present invention.

[104] Comparing the 3:3 symmetry strip electrode structure described in the second embodiment with the 1 : 1 symmetry strip electrode structure described in the first embodiment, it can be understood that the 3:3 symmetry strip electrode structure is the same as a structure in which two rectangular nonconductive regions are added to the 1:1 symmetry strip electrode structure to be symmetric with respect to the 1:1 symmetry electrode structure.

[105] Thus, by causing additional nonconductive regions to be added within the peripheral edges of the respective strip electrodes having the 1 : 1 symmetry strip electrode structure, the power consumption can be reduced and the efficiency of lamp can also be improved since the impedance can be lowered while still maintaining the high brightness uniformity of the 1 : 1 symmetry strip electrode. In addition, since the decrease in conductance of the electrode can be expected, there are advantages in that the displacement current can be reduced and the discharge current can also be increased even though the electrodes are disposed at the same intervals therebetween.

[106] As described above, the nonconductive regions formed on the portions within the peripheral edges of the respective strip electrodes can be made in various manners. For example, nonconductive regions (Fig. 14) may be formed on two or more positions within the peripheral edges of the respective strip electrodes as shown in Fig. 14, or curved nonconductive areas may be formed as shown in Fig. 15.