Dimmable discharge lamp for dielectrically impeded discharges

Electric lamp and discharge devices: systems – High frequency starting operation for fluorescent lamp

Reexamination Certificate

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C315S2090SC, C315SDIG007, C315S278000, C315S246000

Reexamination Certificate

active

06376989

ABSTRACT:

TECHNICAL FIELD
The present invention relates to an operating method for a discharge lamp which is designed for dielectrically impeded discharges. For this purpose, the discharge lamp has a discharge vessel filled with a discharge medium, and at least one anode and at least one cathode. A dielectric layer is provided at least between the anode and the discharge medium, in order to produce dielectrically impeded discharges.
The terms anode and cathode are not to be understood in this application such that the invention is limited to unipolar operation. In the bipolar case, there is, at least electrically, no difference between anodes and cathodes, and so the statements for one of the two electrode groups then hold for all electrodes.
PRIOR ART
As promising fields of application for the discharge lamps considered here, mention may be made by way of example of the backlighting of flat display screen systems, or the backlighting of signal devices and signal lamps themselves. Reference is made in a supplementary fashion regarding the two last-named points to the disclosure content, hereby referred to, of EP-A-0 926 705. Furthermore, this invention is also suitable for lamps such as the copier lamp, represented in DE-A-197 18 395, with internal electrodes, and to the linear lamp, described in German application 198 17 475.6, with external electrodes. The disclosure content of the cited applications is respectively referred to hereby.
Because of the fact that discharge lamps for dielectrically impeded discharges can be designed in a very large multiplicity of the most varied sizes and geometries and, moreover, avoid the typical disadvantages of classic discharge lamps with mercury-containing filling in conjunction with a relatively high efficiency, it is expected that such discharge lamps will be used increasingly both with regard to their quantitative spread and with regard to their fields of use.
Reference is made to the following documents from the prior art:
DE 196 36 965 A1 exhibits discharge lamps for dielectrically impeded discharges which consequently exhibit a dielectric layer between at least the anode and the discharge medium. In accordance with this document, defined attachment points for individual discharges are created by localized field forcings. The homogeneity of the power distribution is intended thereby to be improved both in regard to time and in regard to space.
DE 197 11 893 A1 largely corresponds to the document just cited, and takes the teaching thereof further by using a denser arrangement of the attachment points in the edge region of the lamp or, alternatively, by increasing the current density through individual discharges burning there to counteract edge darkening by widening the anodes.
DE 41 40 497 C2 exhibits an ultraviolet high-power radiator with dielectrically impeded discharges in which the electric power converted in the edge region is increased by varying the discharge spacing or the dielectric capacitance in order to improve the homogeneity of the UV emission.
DE 42 22 130 A1 is concerned within the framework of dielectrically impeded discharges with the starting aid function of local field distortion structures, for example quartz drops melted onto discharge vessel walls, or dents or humps in the walls.
U.S. Pat. No. 5,760,541 describes a discharge lamp with strip-shaped electrodes whose geometric shape leads to a field modulation in the discharge lamp owing to sinusoidal edges, cutouts and other possibilities. The aim thereby is to eliminate temporal fluctuations in a bright/dark distribution in the discharge lamp in order to permit a temporally constant spatial correction of these heterogeneities for the benefit of applications in scanning devices for transparent media.
DE 196 28 770 relates to measures for optimizing the power output of a traveling-wave tube amplifier element at transponder level for satellite applications, in order to stabilize the output power of the overall amplifier system with regard to changes in the operating point, ageing, frequency changes, temperature fluctuations etc.
GB 2 139 416 describes the spatial modulation of the emission of radiation from an electron irradiation device by means of specific spatial arrangements of permanent magnets and magnetic materials.
U.S. Pat. No. 4,584,501 describes a discharge display in which various discharge paths are switched by mechanically actuated flaps, and optical effects are produced by multiple reflections by using semipermeable mirrors.
DE 198 17 479, published after the priority date, relates to the division of the electrode arrangement in a silent discharge lamp into different groups, which can be operated separately.
DE 43 11 197 describes the pulsed operating method, which is essential for the discharge lamps considered here, and the coordination of parameters in order to produce a specific type of discharge.
SUMMARY OF THE INVENTION
This invention is based on the technical problem of providing a further contribution to widening and improving the possibilities of use of discharge lamps for dielectrically impeded discharges.
This problem is solved according to the invention by means of an operating method for a discharge lamp having a discharge vessel, containing a discharge medium, an electrode arrangement with an anode and a cathode, and having a dielectric layer between at least the anode and the discharge medium, the electrode arrangement being inhomogeneous along a control length in a way which varies a burning voltage, by virtue of the fact that it defines along the control length a discharge spacing which varies monotonically at least in a local mean value, and it holds for the quantitative ratio between a difference between a maximum arcing distance d
max
between the electrodes in the control length and a minimum arcing distance d
min
between the electrodes in the control length and this control length that: (d
max
−d
min
)/SL≦0.6, and an electric parameter of the power supply of the discharge lamp is varied during operation in order to control the power of the discharge lamp.
Furthermore, the invention also relates to a lighting system having the discharge lamp described and having a ballast designed for the method just mentioned.
Preferred design variants relating to the operating method according to the invention and to the lighting system according to the invention are specified in the dependent claims.
Some of these refinements of the invention are also associated with further technical features of the discharge lamp. To this extent, the invention likewise relates to the correspondingly configured discharge lamp.
As is already to be gathered from the preceding general formulation of the invention, the invention is directed toward power control in discharge lamps with dielectrically impeded discharges. It provides for this purpose at least one control length along the course of the electrode in the discharge lamp. This term denotes a segment of the electrode structure along which inhomogeneous discharge conditions exist. The aim of this inhomogeneity in the discharge preconditions is for a burning voltage of the discharge to vary monotonically along the control length, but at least to vary monotonically in an effective mean value. A particular discontinuous possibility for monotonic variation in the burning voltage is still to be examined further below.
In this case, the term burning voltage relates, in particular, to a minimum burning voltage which corresponds not to the starting voltage of an individual discharge, but to the minimum voltage with which a discharge structure can be maintained at a specific point of the electrode arrangement.
In the case of this invention, it is preferred to consider an operating method in which the active power is injected into the discharge lamp in a pulsed way. Reference is made for this purpose to WO 94/23442 and DE-P 43 11 197.1.
The disclosure content of these applications is hereby also referred to.
In conjunction with this pulsed active-power injection, in this case restarting does not mean restarting of

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