Title of Invention

"FLAT RADIATOR"

Abstract The invention relates to flat radiator having dielectrically impeded, strip-like cathodess (12;15) and anodes (8;9a) which are arranged alternately next to one another on the wall of the discharge vessel (14) has in each case an additional anode (9b) between neighbouring cathodes (12;12,15), thus arranging an anode pair (9) in each case between the cathodes (12;12,15). The cathodes (15) have nose-like extensions (28) which face the respectively neighbouring anodes (8) and are arranged more densely in a spatially increasing fashion in the direction of the edges (26,27) of the flat radiator (13). In an alternative embodiment, the two anode strips (9a,9b.) of each anode pair (9) are widened in the direction of the edges (26,27) of the flat radiator (13) at one end in the direction of the respective partner strip (9a or 9b).Owing to these measures, the surface luminous density of the flat radiator (13) is largely constant towards the edges (26,27,29,30) in pulsed operation.
Full Text -1A-

Technical field
The invention proceeds from a flat radiator^
Furthermore,
the invention relates to a system composed of this flat radiator and a voltage source,
The designation "flat radiator" is understood here to mean radiators having a flat geometry and which emit light, that is to say visible electromagnetic radiation, or ultraviolet (UV) or vacuum ultraviolet (VUV) radiation.
Depending on the spectrum of the emitted radiation, such radiation sources are suitable for general and auxiliary lighting, for example home and office lighting or background lighting of displays, for example LCDs (Liquid Crystal Displays), for traffic lighting and signal lighting, for UV irradiation, for example sterilization or photolysis.
At issue here are flat radiators which are operated by means of dielectrically impeded discharge. In this type of radiator, either the electrodes of one polarity or all electrodes, that is to say of both polarities, are separated from the discharge by means of a dielectric layer (discharge dielectrically impeded at one end or two ends), see, for example, WO 94/23442 or EP 0 363 832. Such electrodes are also designated as "dielectric electrodes" below for short.

- 2 -Prior art
DE-A 195 26 211 discloses a flat radiator in which strip-shaped electrodes are arranged on the outer wall of a discharge vessel. The radiator is operated with the aid of a train of active power pulses separated from one another by pauses. Consequently, a multiplicity of individual discharges, which are delta-like (A) in top view, that is to say at right angles to the plane in which the electrodes are arranged, burn in each case between neighbouring electrodes. These individual discharges are lined up next to one another along the electrodes, widening in each case in the direction of the {instantaneous) anode. In the case of alternating polarity of the voltage pulses of a discharge dielectrically impeded at two ends, there is a visual superimposition of two delta-shaped structures. The number of the individual discharge structures can be influenced, inter alia, by the electric power injected.
In accordance with the equidistantly arranged strips, the individual discharges are - assuming an adequate electric input power - distributed virtually uniformly inside the planar-like discharge vessel of the -radiator. However, it is disadvantageous in this solution that the surface luminous density drops sharply towards the edge. The reason for this is, inter alia, the missing contributory radiation at the edge from the neighbouring regions outside the discharge vessel.
A further disadvantage is that the individual discharges preferentially are formed between the anodes and only one of the two respectively directly neighbouring cathodes. Evidently, individual discharges do not form simultaneously on both sides of the anode strips independently of one another. Rather, it cannot be predicted by which of the two neighbouring cathodes

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the discharges will be formed in each case. Referring to the flat radiator as a whole, this results in a non-uniform discharge structure, and consequently in a temporally and spatially non-uniform surface luminous density.
A uniform surface luminous density is, however, desirable for numerous applications of such radiators. Thus, for example, the back lighting of LCDs requires a visual uniformity whose depth of modulation does not exceed 15 %.
Representation of the Invention
It is the object of the present invention, to provide a
flat radiator having strip-like electrodes in

accordance with the features of the invention and whose surface luminous density is virtually uniform up to the edge.
The term "strip-like electrode" or "electrode strip" for short is to be understood here and below as an elongated structure which is very thin by comparison with its length and is capable of acting as an electrode. The edges of this structure need not necessarily be parallel to one another in this case. In particular, substructures along the longitudinal sides of the strips are also to be included. Moreover, a strip can also have a pattern, for example a zig-zag pattern or square-wave pattern.
The basic idea of the invention consists in using an adapted electrode structure to balance the fall, typical for flat radiators, in luminous density from the middle to the edges. The electrode structure is

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configured for this purpose to the effect that the electric power density increases towards the edges of the flat radiator.
In a first embodiment, the strip-shaped electrodes are arranged next to one another on a common wall of the discharge vessel (type I). This produces in operation an essentially planar-like discharge structure. The advantage is that shadows owing to the electrodes on the opposite wall are avoided. Instead of a single anode strip, as previously, two mutually parallel anode strips, that is to say an anode pair, are arranged in each case between the cathode strips. The result of this is to eliminate the problem outlined at the beginning that, in the quoted prior art, in each case only individual discharges of one of two neighbouring cathode strips burn in the direction of the individual anode strips situated therebetween.
In the following explanation of the principle of a first realization according to the invention of an electrode structure for a flat radiator of type I, reference is made to the diagrammatic representation in Figure 1. In order to be able to discern the details more effectively, only a section of the electrode region is shown. The aim to be achieved is to construct the individual discharges in operation in a spatially more dense fashion towards the edges 1-3 of the flat radiator than in the remaining part of the discharge vessel. For this purpose, the cathode strips 4 are specifically shaped in such a way that they have spatially preferred root points for the individual discharges. These preferred root points are realized by nose-like extensions 6 facing the respectively neighbouring anode 5. Their effect is locally limited intensifications of the electric field, and consequently that the delta-shaped individual discharges 7 ignite exclusively at these points. The extensions 6 are arranged more densely in the direction

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of the narrow sides of the cathodes 4,4', that is to say in the direction of the edges 1,3 oriented perpendicular to the electrode strips 4,5. Typically, the mutual spacing between the extensions 6 at the edges 1,3 is only half as large as in the middle. In the direct vicinity of the corner points ' of the flat radiator, the spacing between the extensions 6 is finally reduced to about a third. An individual anode strip 5' is preferably arranged in each case in the direct neighbourhood of the edges 2 orientated parallel to the electrode strips 4,5 (the corresponding opposite second edge of the flat radiator is not represented in the selected detail of Figure 1) . Consequently, during operation the base sides of the delta-shaped (A) individual discharges lined up along these individual anode strips 5' are in each case in the direct neighbourhood of the corresponding edges 2. As a result, the drop in luminous density is also relatively slight as far as the vicinity of these edges 2. Furthermore, to provide support it is additionally possible for the extensions 8, facing the two individual anode strips 5' , of the directly neighbouring cathode strips 4' to be arranged more densely overall than in the case of the remaining cathode strips 4. However, the mean power density is less than othe maximum achievable power density. Consequently, with this solution, as well, it is not possible to achieve a maximum luminous density averaged over the entire flat radiator.
The second principle for realizing an electrode structure for a flat radiator of type I aims to increase the luminous density of the individual discharges to a greater extent the nearer they are arranged to the edge. This is achieved (compare the partial diagrammatic representation of the principle in Figure 2) by virtue of the fact that the two anode strips 9a, 9b of each anode pair 9 are widened in the direction of the edges 10,11 orientated perpendicular

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thereto, of the flat radiator. Typical values for the widening amount to a factor of approximately two for the edge regions of the flat radiator and to a factor of about three for the corner regions.
In a first variant, the anode strips are widened asymmetrically with respect to their longitudinal axis in the direction of the respective anodic partner strip 9b or 9a. Owing to this measure, the respective spacing d from the neighbouring cathode 12 remains constant throughout despite widening of the anode strips 9a,9b. Consequently, during operation the ignition conditions for all the individual discharges (not represented) are also the same along the electrode strips 9,12. It is ensured thereby that the individual discharges are formed in a fashion lined up along the entire electrode length (assuming an adequate electric input power).
In a second variant (not represented), the anode strips are widened in the direction of the respective neighbouring cathode. However, in this case the widening is only relatively weakly formed. This prevents the discharges from forming exclusively at the point of maximum width of the anode strip, that is to say at the point of the striking distance which is oshortest in this case. The widening is distinctly smaller than the striking distance, typically approximately one tenth of the striking distance. Furthermore, both widening variants can also be combined, that is to say the widening is formed both in the direction of the respective anode partner strip and in the direction of the neighbouring cathode.
An increasing electric current density, and thus also an increasing luminous density of the individual discharges is achieved along the widening, with the result that it is possible effectively to balance the luminous density distribution up to the edges 10,11. However, it is no longer possible to realize the

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maximum luminous density in the middle region of the flat radiator owing to the increase in luminous density in the edge regions thereof. The advantage by comparison with the first solution is, however, that -assuming an adequate electric input power - it is possible to achieve the maximum spatial density of the individual discharges everywhere inside the discharge vessel, . that is to say in this case the individual discharges are essentially directly adjacent to one another.
Moreover, the two principles for realizing the specific electrode shaping can also be combined with one another (compare Figure 3a}.
In the case of the anode widening, the cathodes need not necessarily be provided with extensions, as is shown merely by way of example in Figure 2. Rather, the cathodes can also be designed as simple parallel strips in the case of the widened anode strips.
In order to minimize the drop in the surface luminous density at the edge, an experimental optimization of the dense packing of the extensions and/or of the anode widening is required in the concrete individual case.
In a further embodiment, the anode strips and cathode strips are arranged on mutually opposite walls of the discharge vessel (type II). During operation, the discharges consequently burn from the electrodes of one wall through the discharge chamber to the electrodes of the other wall. In this arrangement, each cathode strip is assigned two anode strips in such a way that, viewed in cross-section with respect to the electrodes, the imaginary connection of cathode strips and corresponding anode strips respectively yields the shape of a "V". The result of this is that the striking distance is greater than the spacing between the two walls. As has been shown, it is possible using this

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arrangement to achieve a higher UV yield than if anodes and cathodes are arranged alternately next to one another on only one common wall. According to the present state of knowledge, this positive effect is ascribed to reduced wall losses. The double anode strips are preferably arranged on the top plate, which serves primarily to couple out light, and the cathode strips are arranged on the base plate of the flat radiator. The advantage is the low shading of the useful light emitted by the top plate, since the anode strips are designed to be narrower than the cathode strips. For tne purpose of as small as possible a drop in luminous density at the edge, as in the case of the type I flat radiator the cathode strips have extensions which are arranged increasingly more densely towards their narrow sides. As an addition or an alternative to this, the widening of the anode strips, already likewise explained in the case of the type I flat radiator, towards the edge of the flat lamp is also advantageous.
Description of the accompanying drawings
The invention is to be explained below in more detail with the aid of an exemplary embodiment. In the figures:
Figure 1 shows a diagrammatic representation for explaining the principle of a first shaping of the electrodes according to the invention,
Figure 2 shows a diagrammatic representation for explaining the principle of a second shaping of the electrodes according to the invention,
Figure 3a shows a diagrammatic representation of a partially cut away top view of a flat radiator according to the invention, and

_ 9 _
Figure 3b shows a diagrammatic representation of a side view of the flat radiator of Figure 3a.
Figures 3a,3b show in a diagrammatic representation a top view and side view [sic] of a flat fluorescent lamp, that is to say a flat radiator, which emits white light during operation. This flat radiator is suitable for normal lighting or for background lighting of displays, for example LCD (Liquid Crystal Display). Features similar to those in Figures 1 and 2 . are denoted below by means of the same reference numerals.
The flat radiator 13 comprises a flat discharge vessel 14 with a rectangular base face, four strip-like metallic cathodes 12, 15 (-) and dielectrically impeded anodes {+), of which three are constructed as elongated double anodes 9 and two are constructed as individual strip-shaped anodes 8. The discharge vessel 14 for its part comprises a base plate 18, a top plate 19 and a frame 9. The base plate 18 and top plate 19 are connected in a gas-tight fashion to the frame 20 by means of glass solder 21 in such a way that the interior 22 of the discharge vessel 14 is of cuboid construction. The base plate 18 is larger than the top plate 19 in such a way that the discharge vessel 14 has a free-standing circumferential edge. The inner wall of the top plate 19 is coated with a mixture of fluorescent materials (not visible in the representation), which converts the UV/VUV radiation generated by the discharge into visible white light. In one variant (not represented), in addition to the inner wall of the top plate, the inner wall of the base plate and of the frame are additionally also coated with a mixture of fluorescent materials. Furthermore, one light-reflecting layer each, made from A12O3 and TiO2, respectively, is applied to the base plate.
The cutout in the top plate 19 serves merely representational purposes and reveals the view onto a

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part of the anodes 8,9 and cathodes 12,15. The anodes 8,9 and cathodes 12,15 are arranged alternately and in parallel on the inner wall of the base plate 18. The anodes 8,9 and cathodes 12,15 are in each case extended at one of their ends and are guided to the outside on the baseplate 18 from the interior 22 of the discharge vessel 14 on both sides in such a way that the associated anodic or cathodic feedthroughs are arranged on mutually opposite sides of the baseplate 18. At the edge of the baseplate 18, the electrode strips 8,9,12,15 merge in each case into a cathode-side 23 or anode-side 24 bus-like conductor track. The two conductor tracks 23,24 serve as contacts for connecting with an electric voltage source (not represented). In the interior 22 of the discharge vessel 14, the anodes 8,9 are completely covered with a glass layer 25 (see also Figures 1 and 2), whose thickness is approximately 250 urn.
The double anodes 9 respectively comprise two mutually parallel strips, as already represented in detail in Figure 2. In the direction of the edges 2 6,27 orientated at right angles to them, the two anode strips 9a, 9b of each anode pair 9 are widened at one end in the direction of the respective partner strip 9b or 9a. The anode strips 9a, 9b are approximately 0.5 mm wide at the narrowest point, and approximately 1 mm wide at the widest point. The mutually largest spacing gmax {compare Figure 2) of the two strips of each anode pair 9 is approximately 4 mm, while the smallest spacing gmin is approximately 3 mm. The two individual anode strips 8 are in each case arranged in the direct vicinity of the two edges 29,30 of the flat radiator 13 which are parallel to the electrode strips 8,9,12,15.
The cathode strips 12; 15 have nose-like extensions 28 which face the respectively neighbouring anode 8; 9. As a result of them, there are locally limited intensifications in the electric field and,

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consequently, the delta-shaped individual discharges (not represented in Figure 3a, 3b but compare Figure 1) ignite exclusively at these points. The extensions 28 of the two cathodes 15, which are the direct neighbours of the edges 29, 30 of the flat radiator 13 which are parallel to the electrode strips 8,9,12,15, are arranged more densely along the respective longitudinal sides, facing the said edges 29, 30, in the direction of the narrow sides of the cathodes 15. The spacing d (compare Figure 2) between the extensions 28 and the respective directly neighbouring anode strip is approximately 6 mm.
The electrodes 8,9,12,15 including the feedthroughs and supply leads 23,24 are constructed respectively as cohering cathode-side or anode-side structures resembling conductor tracks. The structures are applied directly to the base plate 18 by means of the silk-screen printing technique.
A gas filling, of xenon with a filling pressure of 10 kPa is located in the interior 22 of the flat radiator 13.
One variant (not represented) differs from the flat radiator represented in Figures 3a, 3b merely in that not only the anodes but also the cathodes are separated from the interior of the discharge vessel by a dielectric layer (discharge dielectrically impeded at both ends).
In a complete system, the anodes 8,9 and cathodes 12,15 of the flat radiator 13 are connected via the contacts 24 and 23, respectively, to one pole each of a pulsed voltage source (not represented in Figures 3a,3b). During operation, the pulsed voltage source supplies unipolar voltage pulses which are separated from one another by pauses. In this case, a multiplicity of individual discharges are formed (not represented in

- 12 -
Figures 3a,3b), which burn between the extensions 28 of the respective cathode 12;15 and the corresponding directly neighbouring anode strip 8;9.
The invention is not restricted to specified exemplary embodiments. It is also possible in addition, to combine features of different exemplary embodiments.

13 We Claim
1. Flat radiator(13) having an at least partially transparent discharge vessel
which is closed and filled with a gas filling or open and flowed through by a gas
filling and consists of electrically non-conducting material, and having strip-like
electrodes (8;9;12;15) comprising anodes and cathodes arranged on a wall of
the discharge vessel (14), at feast the anodes (8,9) being separated in each case
from the interior of the discharge vessel (14) by a dielectric material (25),
characterized in that the cathodes (15) having nose-like extensions(28) facing
neighbouring anodes (8), the extensions being arranged more densely in a
spatially increasing fashion in the direction of the respective two narrow sides of
the cathodes (15).
2. Flat radiator as claimed in claim 1, wherein each anode pair (9) has two
anode strips (9a, 9b) which are widened in the direction of the edges (10,11)
oriented perpendicular to the flat radiator.
3. Flat radiator as claimed in claim 1, wherein the strip-like electrodes
(8;9;12;15)are arranged next to one another on a common inner wall of the
discharge vessel (14), and wherein the anodes (9) are arranged in pairs
between neighbouring cathode strips (12,12;12,15)
4. Flat radiator as claimed in claim 3, wherein the two anode strips (9a, 9b) of
each anode pair (9) are widened in the direction of their respective two narrow
sides and asymmetrically with respect to their longitudinal axis in the direction of
the respective partner strip (9b, 9a), so that the respective spacing (d) from the
neighbouring cathode(12, 15) is constant throughout, the luminous density of
the individual discharges increasing in operation towards the edges (26, 27).
5. Flat radiator as claimed in claim 1, wherein in that the electrode strips (9, 12)
are arranged on the inner wall of the discharge vessel (14), at least the anode
strips (9a, 9b) being completely covered by a dielectric layer (25),

6. Flat radiator as claimed in claim 1, wherein the electrodes (8;9;12;15)
comprising feedthroughs and supply leads (23, 24) are constructed as in each
case functionally different subregions of a continuous cathode-side or anode-side
structure resembling a conductor track.
7. Flat radiator as claimed in claim 1, wherein at least a part of the inner wall of
the discharge vessel has a layer made from a fluorescent material or a mixture of
fluorescent materials.
8. System comprising a flat radiator as claimed in claims 1 or 8, and an electric
pulsed voltage source which is suitable for delivering voltage pulses separated
from one another by pauses during operation.
9. Fiat radiator having an at least partially transparent discharge vessel which is
closed and filled with a gas filling or open and flowed through by a gas filling and
consists of electrically non-conducting material, and having strip-like electrodes
comprising anodes and cathodes arranged on a wall of the discharge vessel, at
least the anodes being separated in each case from the interior of the discharge
vessel by a dielectric material, and the anodes being widened in the direction of
the respective anode partner strip and in the direction of the neighbouring
cathode.
The invention relates to flat radiator having dielectrically impeded, strip-like cathodess (12;15) and anodes
(8;9a) which are arranged alternately next to one another on the wall of the discharge vessel (14) has in each case an additional anode (9b) between neighbouring cathodes (12;12,15), thus arranging an anode pair (9) in each case between the cathodes
(12;12,15). The cathodes (15) have nose-like extensions (28) which face the respectively neighbouring anodes (8) and are arranged more densely in a spatially increasing fashion in the direction of the edges (26,27) of the flat radiator (13). In an alternative embodiment, the two anode strips (9a,9b.) of each anode pair (9) are widened in the direction of the edges (26,27) of the flat radiator (13) at one end in the direction of the respective partner strip (9a or 9b).Owing to these measures, the surface luminous density of the flat radiator (13) is largely constant towards the edges (26,27,29,30) in pulsed operation.

Documents:

00459-cal-1998 abstract.pdf

00459-cal-1998 claims.pdf

00459-cal-1998 correspondence.pdf

00459-cal-1998 description(complete).pdf

00459-cal-1998 drawings.pdf

00459-cal-1998 form-1.pdf

00459-cal-1998 form-2.pdf

00459-cal-1998 form-3.pdf

00459-cal-1998 form-5.pdf

00459-cal-1998 g.p.a.pdf

00459-cal-1998 letters patent.pdf

00459-cal-1998 priority document others.pdf

00459-cal-1998 priority document.pdf

459-CAL-1998-CORRESPONDENCE 1.1.pdf

459-CAL-1998-OTHERS.pdf

459-CAL-1998-PA.pdf


Patent Number 206414
Indian Patent Application Number 459/CAL/1998
PG Journal Number 17/2007
Publication Date 27-Apr-2007
Grant Date 27-Apr-2007
Date of Filing 19-Mar-1998
Name of Patentee PATENT-TREUHAND-GESELLSCHAFT FUR ELEKTRISCHE GLUEHLAMPEN MBH
Applicant Address HELLABRUNNER STR. 1, 81543 MUENCHEN, GERMANY
Inventors:
# Inventor's Name Inventor's Address
1 FRANK VOLLKOMMER NEURIEDERSTR, 18, 82131 BUCHENDERF
2 LOTHAR HITZSCHKE THEODOR-ALT-STR. 6, 81737, MUENCHEN;
3 SIMON JEREBIC WEIDENER STR., 7, 81737 MUENCHEN, GERMANY
PCT International Classification Number H01J 61/92
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 19711893.3 1997-03-21 Germany