Electric lamp and discharge devices – With gas or vapor – Envelope with particular structure
Reexamination Certificate
2000-10-19
2003-03-11
Patel, Vip (Department: 2879)
Electric lamp and discharge devices
With gas or vapor
Envelope with particular structure
C315S058000, C315S324000
Reexamination Certificate
active
06531822
ABSTRACT:
The present invention relates to a flat radiator lamp for dielectric barrier discharges, which can be used, in particular, for backlighting of display devices, principally liquid crystal display screens.
As regards the prior art, reference may be made firstly to the following applications of the same applicant, which form the technical basis for the following invention, and whose disclosure is included here:
DE 196 36 965.7=WO 97/01989
DE 195 26 211.5=WO 97/04625 and
DE-P 43 11 197.1=WO 94/23442.
In accordance therewith, there are known for dielectric barrier discharges flat radiator lamps in the case of which the discharge vessel filled with a gas fill consists essentially of a base plate and a cover plate which are connected by a frame. In this design, the spacing between the two plates is conspicuously smaller than their width and length.
The frame need not necessarily in this case be designed as a separate component, but is defined in the case of this invention by the fact that it outwardly seals the discharge volume, filled up by the gas fill, in the plane of the plates and between them. For example, the frame can also be formed by a cambered outer edge one of the two plates such that, to a certain extent, the frame forms the edge of a trough whose flat middle part is the base plate or cover plate.
Also known from the third printed publication mentioned above are spacers which support the two plates of the discharge vessel with respect to one another, but are intended in this prior art to bear or contain the electrodes of the lamp (compare
FIGS. 4
a
and
4
b
).
EP 0 521 553 A2 may also be mentioned as prior art; it exhibits a flat gas discharge lamp with a reduced-pressure fill, which is protected against implosion by the stability of walls of the base and cover plates which are of sufficiently thick dimension.
Furthermore, this document shows the possibility of buffer gas fills for producing an atmospheric pressure of the gas fill, as is also shown by the publication entitled “A Flat Fluorescent Lamp With Xe Dielectric Barrier Discharges” by T. Urakabe, S. Harada, T. Saikatsu and M. Karino (Special Issue “The Seventh International Symposium on the Science & Technology of Light Sources” J. Light & Vis. Env., Vol. 20, No. 2, 1996, pages 20-25).
Spacers in the form of ribs, respectively traversing virtually the entire width of the flat reflector, between the plates, which use alternating cutouts to define in relation to a frame of the discharge vessel a discharge channel of overall meandering shape for a conventional Hg discharge are disclosed in “Flat Lamp Technology for LCDs” by R. Hicks and W. Halstead, SPIE, Volume 2219, Cockpit Displays (1994). The precise cross section and dimensions of length of the discharge channel defined by these spacers are essential for the—so-called wall-stabilized—Hg discharge.
Comparable examples from the commercial prior art are disclosed in data sheets of the manufacturer Thomas Electronics, Inc. (100 Riverview Drive, Wayne, N.J. 07470) “Flat Fluorescent Lamps for LCD-Backlighting”.
Finally, the second printed publication cited at the beginning discloses an electrode arrangement in which the anodes and cathodes are of strip-type design and arranged on the base plate parallel to one another in an alternating fashion, that is to say offset from one another.
This invention is based on the technical problem of improving a flat radiator lamp of the type represented at the beginning with regard to stability and light-emitting properties.
In a somewhat more general formulation than at the beginning, the inventive solution of this problem is therefore based as preamble on a flat radiator lamp for dielectric barrier discharges having a discharge vessel, which is filled with a gas fill and has an essentially flat base plate, an essentially flat and at least partially transparent cover plate, a frame connecting the plates and at least one spacer supporting the two plates with respect to one another, and having anodes and cathodes which are at least partially of strip type and are arranged substantially offset in parallel with one another in a projection on a flat plane, a dielectric layer being arranged between the anodes and the gas fill.
In this case offset in parallel means that an adjacent, essentially parallel cathode strip piece essentially exists for each anode strip piece and vice versa.
The invention solves this technical problem by virtue of the fact that the spacer is completely separated from the frame by an interspace and is arranged in the projection between the electrode strips at least with its seating surfaces with the plates—or else entirely.
Consequently, the invention proceeds from the conventional concept of spacers which are connected as ribs on at least one side to the frame of the discharge vessel. According to the invention, it has been realized, rather, that an adequate stabilizing effect of the spacers is also possible when the spacers are connected only to the plates, but not directly to the frame. Specifically, the important loads occur perpendicular to the planes of the plates such that there is no need for the spacers to be straight and to be anchored on the frame.
Moreover, in the case when a spacer is connected to the frame the problem also arises that obscurations accumulate at the contact point owing to the absorption in the frame and the spacer and owing to the radiation component lacking from the corresponding part of the discharge vessel. The obscuration problem of a spacer or the frame can be countered per se in each case by suitable measures. Reference may be made in this regard to the parallel application “Leuchtstofflampe mit Abstandshaltern und lokal verdünnter Leuchtstoffschichtdicke” [“Fluorescent lamp with spacers and locally thinned fluorescent layer thickness”], whose disclosure is included here in relation to possible solutions in this regard. However, when spacers and frame meet at the contact point it becomes very difficult to compensate for the obscuration. This aspect plays a particular role in the case of the preferred field of application of this invention, specifically flat radiator lamps for background lighting of flat display devices, in particular liquid crystal display screens.
A further advantage of the invention is in this case the good gas flow dynamics inside the discharge vessel in the case of evacuation during the production process. Thus, for the purpose of cleaning and filling a lamp according to the invention, instead of the conventional vacuum furnace method (not represented here in more detail) it is also possible to use solutions with exhaust tubes in the case of which the discharge vessel is exhausted via the exhaust tube with the aid of a vacuum pump accompanied by heating (possibly locally progressing in the case of large lamps), and is then filled via the exhaust tube. The essential disadvantage of the vacuum furnace solution consists, in particular, in the substantial outlay in the case of large-size lamps which are of great technical interest, in particular in conjunction with a relatively large display device, and can also be produced relatively easily with the aid of the technology, employed here, of flat radiator lamps with dielectric barrier discharge.
Furthermore, the spacers according to the invention have the advantage that, by renouncing the continuous rib geometry in connection with the frame, it is possible to find “local solutions” for spacers which can be adapted to the geometric design of the electrode structure. Particularly in the context of optimizing the uniformity of light emission with regard to the abovementioned application areas, it is necessary to have the maximum possible freedom available when designing the electrode geometry.
Surprisingly, according to the invention it has been found that the electrode geometry, depending on the geometric size of the desired spacers, can be designed taking little or virtually no account of the local positions of the spacer(s). Contrary to expectation, it has also emerged that arran
Hitzschke Lothar
Vollkommer Frank
Berck Ken
Clark Robert F.
Patel Vip
Patent-Treuhand-Gesellschaft fuer elektrische Gluehlampen mbH
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