WO2005083745A1

WO2005083745A1 - Flat fluorescent lamp

Info

Publication number: WO2005083745A1
Application number: PCT/KR2005/000513
Authority: WO
Inventors: Tae-Young Lim; Young-Muk Kim; Min-Su Lim; Myoung-Ho Lee
Original assignee: Youyang Airport Lighting Equipment Inc.
Priority date: 2004-02-27
Filing date: 2005-02-26
Publication date: 2005-09-09
Also published as: KR100650491B1; JP4606456B2; JP2007525806A; CN1965387A; KR20050087493A

Abstract

The present invention relates to a flat fluorescent lamp with stable discharge and uniform brightness. The flat fluorescent lamp comprises a front panel 110 with a fluorescent material 111 applied thereto; a rear panel 170 including a reflecting plate 120, first and second electrode portions 130 and 140 printed to be electrically insulated, a dielectric layer 150 and a fluorescent material 160; and a support 180 for supporting the front and rear panels 110 and 170 and maintaining a sealed state. Each of the first and second electrode portions 130 and 140 is formed of a pair of strip leads 131 and 141 to construct the same electrode, a plurality of protrusions P are symmetrically formed to protrude outward on the pair of strip leads, and the first and second electrode portions are disposed alternately. Since each of two electrodes driven by an AC power source comprises the pair of strip leads to have the same electrode structure, there are advantages in that the number of discharge at the two electrodes can be increased as compared with conventional driving by a DC power source, and the brightness and uniformity are improved.

Description

FLAT FLUORESCENT LAMP

Technical field The present invention relates to a flat fluorescent lamp, and more particularly, to a flat fluorescent lamp with stable discharge and uniform brightness.

Background Art In the prior art regarding flat fluorescent lamps, there have been disclosed a flat fluorescent lamp with opposite electrodes arranged thereon, and a surface discharge type of flat fluorescent lamp with linear electrodes arranged on one side thereof. As for commercially available flat fluorescent lamps, there is a flat fluorescent lamp using dielectric barrier discharge, which is available from Osram GmbH in Germany. Fig. 7 is a sectional view showing the structure of a conventional flat fluorescent lamp with opposite electrodes arranged thereon, wherein front and rear panel units 10 and

20 are fixed to a support frame 30 to define a discharge space filled with an inert gas. The front panel unit 10 comprises a transparent electrode layer 11, a front glass substrate 12 and a front fluorescent layer 13, which are sequentially stacked one above another. The rear panel unit 20 comprises a rear glass substrate 21, an electrode layer 22, a dielectric layer 23 and a rear fluorescent layer 24, which are sequentially stacked one above another. Such a conventional flat fluorescent lamp with opposite electrodes arranged thereon is characterized by efficiently converting ultraviolet rays emitted upon discharge into visible rays through arrangement of the fluorescent layers 13 and 24 in the front and rear panel units 10 and 20. However, since electrons and cations generated upon gaseous discharge collide directly against the fluorescent layers and thus cause sputtering of the fluorescent layers, there are problems in that the life of the fluorescent lamp is shortened and brightness uniformity thereof is deteriorated. Next, Fig. 8 shows another example of a conventional flat fluorescent lamp, i.e. a surface discharge type flat fluorescent lamp with linear electrodes arranged on one side thereof. In the fluorescent lamp of Fig. 8, front and rear panel units 40 and 50 are fixed to a support frame 60 to define a discharge space filled with an inert gas. The front panel unit 40 comprises a front glass substrate 42 with a fluorescent layer 41 applied to a bottom surface thereof. The rear panel unit 50 comprises a rear glass substrate 51, linear electrodes 52, and dielectric layers 53 for electrically insulating the linear electrodes 52 and lowering a discharge starting voltage, which are sequentially stacked one above another. In the flat fluorescent lamp with the linear electrodes arranged on one side thereof, the electrodes are placed on only one of the glass substrates of the flat fluorescent lamp, contrary to the flat fluorescent lamp of Fig. 7. Since electrons and cations do not collide directly against the fluorescent layer in case of the arrangement of the linear electrodes on one side, there are advantages in that sputtering of the fluorescent layer 41 and the linear electrodes 52 is prevented, thereby prolonging the life of the fluorescent lamp. However, since such a flat fluorescent lamp uses the linear electrodes, there are problems in that a lighting voltage becomes high and power consumption increases.

Further, since each fluorescent lamp should have two linear electrodes having different polarities, there are problems in that a distance between electrodes in a large area lamp increases to cause the rise of a discharge starting voltage and discharge stability cannot be secured. Figs. 9 and 10 show a further example of a conventional flat fluorescent lamp, wherein a fundamental discharge concept thereof is the same as the fluorescent lamp of Fig. 7 and anode electrodes are in pairs for dielectrically hindered discharge. The fluorescent lamp of Fig. 9 comprises a support frame 90 to define a discharge space filled with an inert gas between front and rear panel units 70 and 80. The front panel unit 70 comprises a front glass substrate 72 with a fluorescent layer 71 applied to a bottom surface thereof. The rear panel unit 80 comprises a rear glass substrate 81, linear electrodes 82, a dielectric layer 83 for electrically insulating the linear electrodes 82 and lowering a discharge starting voltage, and a fluorescent layer 84, which are sequentially stacked one above another. Fig. 10 shows the planar configuration of the linear electrodes provided in the fluorescent lamp of Fig. 9, wherein each of the linear electrodes 82 includes anodes 82a and a cathode 82b and is driven in a DC impulse manner. The anodes 82a and the cathode 82b are formed of strip leads. Particularly, the anodes 82a are in pairs, and a strip lead of one cathode 82b is disposed most adjacent to a relevant pair of anodes 82a. The strip lead of the cathode 82b is formed with a plurality of needle-shaped protrusions P for partial discharge. In such a conventional flat fluorescent lamp, when a DC impulse is applied to the anodes 82a and the cathode 82b, delta-shaped partial discharge occurs between the strip leads of the anodes 82a and the protrusions P of the strip lead of the cathode 82b to emit visual rays. However, since in such a conventional flat fluorescent lamp, the anodes formed of the pair of strip leads and the cathode formed of one strip lead with the plurality of protrusions have different electrode structures, there is a problem in that brightness uniformity is deteriorated due to asymmetry of the electrode structures. That is, there is a problem in that a great difference in brightness is shown between a discharge starting portion of the cathode and a portion thereof where discharge is not dense.

Disclosure of Invention Accordingly, the present invention is conceived to solve the problems in the prior art. An object of the present invention is to provide a flat fluorescent lamp of which two electrodes have the same electrode structure and which is driven by an AC power source to achieve stable discharge and uniform brightness distribution. The flat fluorescent lamp of the present invention comprises a front panel with a fluorescent material applied thereto; a rear panel including a reflecting plate, first and second electrode portions printed to be electrically insulated, a dielectric layer and a fluorescent material; and a support for supporting the front and rear panels and maintaining a sealed state. Each of the first and second electrode portions is formed of a pair of strip leads to construct the same electrode, a plurality of protrusions are symmetrically formed to protrude outward on the pair of strip leads, and the first and second electrode portions are disposed alternately.

Brief Description of Drawings Fig. 1 is a partially cut-away perspective view of a flat fluorescent lamp of the present invention. Fig. 2 is a view showing a preferred example of an electrode structure provided in the flat fluorescent lamp according to the present invention. Fig. 3 is a view showing a preferred example of spacers provided in flat fluorescent lamp according to the present invention. Fig. 4 is a view showing another example of the flat fluorescent lamp according to the present invention. Fig. 5 a view showing a preferred example of a driving circuit for driving the flat fluorescent lamp according to the present invention. Fig. 6 is a view showing waveforms of input and output signals of the driving circuit of Fig. 5. Figs. 7 to 10 show a variety of examples of conventional flat fluorescent lamps.

Best Mode for Carrying out the Invention Figs. 1 to 6 show a flat fluorescent lamp of the present invention, wherein Fig. 1 is a partially cut-away perspective view of the flat fluorescent lamp of the present invention, Fig. 2 is a view showing a preferred example of an electrode structure provided in the flat fluorescent lamp according to the present invention, Fig. 3 is a view showing a preferred example of spacers provided in flat fluorescent lamp according to the present invention, Fig. 4 is a view showing another example of the flat fluorescent lamp according to the present invention, Fig. 5 a view showing a preferred example of a driving circuit for driving the flat fluorescent lamp according to the present invention, and Fig. 6 is a view showing waveforms of input and output signals of the driving circuit of Fig. 5. Preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The flat fluorescent lamp of the present invention shown in Fig. 1 comprises a front panel 110, a rear panel 170 and a support 180 for defining a discharge space between the front and rear panels 110 and 170. The front panel 110 has a fluorescent material 111 applied a bottom surface thereof that serves a light-exiting surface through which light generated from the fluorescent lamp exits. The rear panel 70 comprises a reflecting plate 120, first and second electrode portions 130 and 140, a dielectric layer 150 and a fluorescent material 160. The reflecting plate 120 disposed on a top surface of the rear panel 170 enhances use efficiency of light by reflecting light toward the light-exiting surface and also causes the entire light-exiting surface of the fluorescent lamp to have uniform brightness distribution by controlling the amount of reflected light of total incident light. The first and second electrode portions 130 and 140 are printed on a top surface of the reflecting plate 120 such that they are electrically insulated from each other. The dielectric layer 150 electrically insulates the first and second electrode portions 130 and 140 and limits an electric current. The fluorescent material 160 is applied to a top surface of the dielectric layer 150. An inert gas is filled into a discharge chamber defined by the front plate 110, the rear plate 170 and the support 180. However, it is preferred that the inert gas do not contain mercury. Specifically, xenon (Xe) gas, argon (Ar) gas containing Xe gas, neon (Ne) gas, or krypton (Kr) gas may be filled thereinto. To maintain the uniform brightness property in the present invention, a gap between the front and rear plates should be kept constant. If such a gap is not kept constant, a non-emitting area is produced in micro discharge. To compensate this, the fluorescent lamp preferably has a thickness of 3mm or greater. More preferably, the gap between the front and rear plates is in a range of 3 to 8mm. Fig. 2 is a view showing a preferred example of an electrode structure provided in the flat fluorescent lamp according to the present invention, wherein each of the first and second electrode portions 130 and 140 in the present invention is formed of a pair of strip leads 131 or 141 to construct the same electrode structure, a plurality of protrusions P symmetrically protrude outward on the pair of strip leads 131 or 141, and the first and second electrode portions 130 and 140 are arranged alternately. A plurality of first and second electrode portions 130 and 140 are connected to primary electrodes 132 and 142 provided outside of the discharge chamber, respectively.

Since the primary electrodes 132 and 142 do not greatly affect electrical properties, or properties of discharge generated within the discharge chamber, the configurations of the primary electrodes in the present invention are not limited to specific configurations. It is preferred that the protrusions P be formed equidistantly on the strip leads 131 and 141. Meanwhile, the present invention is characterized in that an end of each of the strip leads 131 and 141 is positioned outside of an inner contact interface between the rear panel 170 and the support. For reference, reference numeral 180a designates a region to which the support is fixed. It can be seen that the end of each of the strip leads 131 and 141 extends at least up to the region to which the support is fixed. Since the ends of the strip leads are positioned outside of the discharge space, they do not affect the discharge generated within the discharge chamber. Thus, it is possible to obtain a stable discharge property. That is, the ends and intermediate portions of the strip leads are prevented from performing discharge in different discharge manners, so that the same brightness uniformity can be obtained between the center and edges of the fluorescent lamp. In the present invention, the protrusions symmetrically formed on both sides of each strip lead take the shape of a needle. Referring to the partially enlarged view in Fig. 2, a tip PI of each protrusion P preferably has a predetermined radius of curvature. Although the curved tip PI has a disadvantage in that the discharge starting voltage increases, there are advantages in that an effective area for discharge is enlarged, the concentration of an electric filed is reduced to widen a discharge path, a problem of heat generation due to instantaneous discharge can be solved, and the life of the lamp can be prolonged. Further, in addition to the tip PI of the protrusion, an intermediate portion P2 and a lower portion P3 of the protrusion are also formed to have predetermined radii of curvature, thereby preventing discharge from being generated at other portions except the tip PI of the protrusion. It is preferred that the radii of curvature of the curves defined in the protrusion be in a range of R0.1 to R0.8. Next, the spacing between most adjacent strip leads of the first and second electrode portions should be properly maintained. That is, if the spacing between adjacent strip leads of the first and second electrode portions is too small, it is possible to lower the discharge starting voltage. However, there is a disadvantage in that a discharge current rapidly increases, resulting in lowering of discharge efficiency. On the contrary, if the spacing between adjacent strip leads is large, the discharge starting voltage increases, resulting in the occurrence of a non-emitting area. Therefore, proper spacing between the electrodes is very important in determining brightness, efficiency, and the performance of an inverter. The present invention is characterized in that the spacing dl between most adjacent strip leads 131 and 141 of the first and second electrode portions 130 and 140 is 2 to 10mm. Next, it is preferred that the spacing between a pair of strip leads constructing the same electrode be maintained to be minimum spacing. If the spacing between a pair of strip leads constructing the same electrode is large, a non-emitting area increases, resulting in deterioration of brightness uniformity. The present invention is characterized in that the spacing d2 between a pair of strip leads constructing the same electrode is 1 to 7mm. Further, the present invention is characterized in that the width of each strip lead is

0.1 to 1mm. Since there is a great difference in pressure of the interior and exterior of the discharge chamber in the flat fluorescent lamp of the present invention, spacers capable of providing support between the front and rear panels can be added. It is preferred that such spacers minimize shades to prevent deterioration of brightness uniformity. Fig. 3 is a view showing a preferred example of the spacers provided in flat fluorescent lamp according to the present invention. Spacers 200 each of which comprises a hexahedron 210 and a sphere 220 can be added between the front and rear panels 110 and 170. It is preferred that a ratio of the sphere 220 to the hexahedron 210 be determined to minimize hindrance to uniformity and brightness. Fluorescent materials 211 and 221 are applied to surfaces of the hexahedron 210 and the sphere 220 to improve light-emitting efficiency. Fig. 4 is a view showing another example of the flat fluorescent lamp according to the present invention, wherein the rear panel is further provided with a heat-dissipating member with superior thermal conductivity to facilitate heat dissipation. The heat-dissipating member includes a heat-dissipating sheet or silicone that is mounted on a back surface of the rear panel 170 to facilitate rapid heat conduction. Moreover, in the flat fluorescent lamp of the present invention, a light-diffusing member is additionally mounted on a top surface of the front panel to compensate the influence of differences in brightness between micro discharge regions of different electrodes, thereby improving brightness and uniformity. The light-diffusing member includes a diffusion sheet 410 or a prism sheet 420. The present invention is characterized in that the flat fluorescent lamp is driven by a square wave pulse type AC power source. Since polarities of the AC power source are considered as performing the same function, the polarities of the first and second electrode portions are not separately discriminated from each other. Fig. 5 a view showing a preferred example of a driving circuit for driving the flat fluorescent lamp according to the present invention, wherein a high-voltage square wave AC pulse is output by combining four high speed FETs with a transformer. That is, the square wave AC pulse can be obtained by inputting proper signals into gates of the respective FETs in a state where a DC voltage +V is applied to drains Ql and

Q3. Referring to Fig. 6a, when Q3 and Q4 are simultaneously turned on, a voltage approximate to XV is produced at both ends of a primary side of the transformer. When Ql and Q2 are simultaneously turned on, a voltage approximate to '-V is produced at both ends of the primary side of the transformer. Figs. 6 (a) and (b) show a waveform of an input gate signal of the driving circuit of Fig. 5, and a waveform of an output voltage, respectively. The output voltage produced on the primary side of the transformer is boosted and then applied through the first and second electrode portions. In the flat fluorescent lamp of the present invention constructed as such, when the square wave AC pulses are applied to the first and second electrode portions 130 and 140, partial discharge is generated through the protrusions P between the respective strip leads 131 and 141 of the first and second electrode portions 130 and 140. Free electrons produced by the partial discharge generated between the strip leads excite Xe atoms filled into the discharge chamber, and the excited Xe atoms radiate ultraviolet rays and then become a ground state. The ultraviolet rays react with the fluorescent materials 111 and 160 applied on the front and rear panels 110 and 170 to emit visible rays. Table 1 below shows the comparison of a conventional flat fluorescent lamp and the flat fluorescent lamp of the present invention. Table 1

It can be seen from the comparison that the flat fluorescent lamp of the present invention has superior brightness uniformity, brightness and light-emitting efficiency. Further, it can also be seen that the life of the flat fluorescent lamp of the present invention is prolonged as compared with the conventional flat fluorescent lamp. According to the flat fluorescent lamp of the present invention described above, since each of two electrodes driven by an AC power source comprises a pair of strip leads to have the same electrode structure, there are advantages in that the number of discharge at the two electrodes can be increased as compared with conventional driving by a DC power source, and the brightness and uniformity are improved. Moreover, since needle-shaped protrusions with predetermined radii of curvature are formed on the strip leads of the respective electrodes, it is possible to beforehand determine discharge initiation and a discharge path. Therefore, stable discharge can be generated.

Claims

1. A flat fluorescent lamp, comprising: a front panel with a fluorescent material applied thereto; a rear panel including a reflecting plate, first and second electrode portions printed to be electrically insulated, a dielectric layer and a fluorescent material; and a support for supporting the front and rear panels and maintaining a sealed state; wherein each of the first and second electrode portions is formed of a pair of strip leads to construct the same electrode, a plurality of protrusions are symmetrically formed to protrude outward on the pair of strip leads, and the first and second electrode portions are disposed alternately.

2. The lamp as claimed in claim 1, wherein the protrusions are needle-shaped in a laterally symmetrical manner.

3. The lamp as claimed in claim 2, wherein a tip of each protrusion is curved.

4. The lamp as claimed in claim 2, wherein a tip and a lower end of each protrusion are connected to each other by a curve.

5. The lamp as claimed in claim 2, wherein a lower end of each protrusion is connected to a relevant one of the strip leads by a curve.

6. The lamp as claimed in any one of claims 3 to 5, wherein a radius of curvature of the curve in each protrusion is in a range of R0.1 to R0.8.

7. The lamp as claimed in claim 1, wherein spacing between the pair of strip leads constructing the same electrode is 1 to 7mm.

8. The lamp as claimed in claim 1, wherein spacing between most adjacent strip leads of the first and second electrode portions is 2 to 10mm.

9. The lamp as claimed in claim 1, wherein the protrusions are formed equidistantly on each strip lead.

10. The lamp as claimed in claim 1, wherein an end of each strip lead is placed outside of an inner contact interface between the rear panel and the support.

11. The lamp as claimed in claim 1 , wherein spacing between the front and rear panels is 3 to 8mm.

12. The lamp as claimed in claim 1, wherein spacers are further provided between the front and rear panels, each of the spacers including a hexahedron and a sphere that have a fluorescent material applied thereto.

13. The lamp as claimed in claim 1, wherein a heat-dissipating member is further attached to a back surface of the rear panel.

14. The lamp as claimed in claim 1, wherein a light-diffusing member is further attached to a top surface of the front panel, thereby improving uniformity.

15. The lamp as claimed in claim 1, wherein the first and second electrode portions are driven by applying AC power thereto.

16. The lamp as claimed in claim 15, wherein the AC power is in the form of a square wave pulse.