EP1118099A1

EP1118099A1 - Dimmable discharge lamp for dielectrically impeded discharges

Info

Publication number: EP1118099A1
Application number: EP99957252A
Authority: EP
Inventors: Frank Vollkommer; Lothar Hitzschke
Original assignee: Patent Treuhand Gesellschaft fuer Elektrische Gluehlampen mbH
Current assignee: Osram GmbH
Priority date: 1998-10-01
Filing date: 1999-09-28
Publication date: 2001-07-25
Anticipated expiration: 2019-09-28
Also published as: JP4695760B2; KR20010075527A; JP2002527859A; ATE429707T1; HUP0103743A2; CN1320270A; HUP0103743A3; CN1246878C; US6636004B1; TW494440B; WO2000021116A1; KR100555602B1; EP1118099B1; CA2346009A1; DE19845228A1; DE59915011D1; CA2346009C

Abstract

According to the invention, the discharge distances in discharge lamps for dielectrically impeded discharges are shortened to less than 3 mm, whereby dead times of a pulsed active-power launching can be increased to times approximately greater than 50 ms so that the dimming properties of the discharge lamp are drastically improved.

Description

Dimmable discharge lamp for dielectric barrier discharges

Technical field

The present invention relates to 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 an electrode arrangement with at least one anode and at least one cathode. Since the discharge lamp is designed for dielectrically impeded discharges, there is at least one dielectric layer between the anode and the discharge medium. The anode and the cathode thus define a discharge distance between them in which dielectrically impeded discharges can be generated.

The terms anode and cathode should not be understood to mean that the discharge lamp would only be suitable for unipolar operation. It can also be designed for a bipolar power supply, in which case there is at least no electrical difference between the anode or cathodes. In this application, the statements for one of the two electrode groups therefore apply to both electrode groups in the case of a bipolar power supply.

The discharge lamps considered here have a large number of promising areas of application. An important example is the backlighting of flat-screen systems, especially LCDs (Liquid Crystal Displays). Another point is the backlighting or lighting of signaling devices and signal lamps themselves. With regard to these two latter points, reference is made to the disclosure content of EP 0 926 705 A1 referred to here. Furthermore, reference is made to W098 / 43277, also with regard to the backlighting of flat screens, the disclosure content of which is also referred to.

State of the art

Since discharge lamps for dielectrically impeded discharges can be designed in a wide variety of sizes and geometries and at the same time achieve a relatively high efficiency while avoiding the typical disadvantages of classic discharge lamps with a mercury-containing filling, they are promising candidates for a large number of different technical fields of application.

Many technical efforts have been made to maximize parameters such as the luminous efficacy, the luminous flux, the luminance, the homogeneity of the luminance, etc.

Presentation of the invention

The invention is based on the technical problem of improving a discharge lamp for dielectrically impeded discharges in such a way that its possible uses are further increased and a corresponding operating method for the discharge lamp is specified.

According to the invention, this problem is solved by a discharge lamp with a discharge vessel containing a discharge medium, an electrode arrangement with at least one anode and at least one cathode, which define a discharge distance, and with a dielectric layer between at least the anode and the discharge medium, characterized in that the discharge distance is 3 mm or less,

and by a method for operating such a discharge lamp, in which a dead time between active power pulses of a pulsed power supply is more than 50 μs, preferably more than 100 μs, 500 μs, 1 ms,

and finally by a method for operating such a discharge lamp, in which the power coupled into the discharge lamp is changed by changing a dead time between active power pulses of a power supply operated in a pulsed manner.

First of all, the invention is based on the knowledge that there are a number of applications in which, in addition to or instead of the qualities required at the outset, it is essential that the discharge lamp can be operated with a very low luminous flux. For this purpose, it was necessary in the invention to improve the properties of the lamp in such a way that it allows the coupling in of very low supply powers. This is possible according to the invention in that the discharge distance between the electrodes is chosen to be particularly small. According to the invention, this discharge distance between cathodes and anodes is 3 mm or less, preferably 2 mm, 1.5 mm, 1 mm, 0.8 mm or less and particularly preferably 0.6 mm and less.

It is important here that electrode pairs with such a small discharge distance do not have to occur exclusively in the discharge lamp. Larger discharge distances can also be used in the same discharge lamp, because it is then possible, if necessary, to operate the lamp only with the small discharge distance according to the invention. The main advantage of the short discharge distances is that they allow particularly long dead times between the individual active power pulses in a pulsed power supply, without locally undesirably high current densities.

With regard to the operation, reference is first made to the method with the pulsed active power coupling

WO 94/23442 and DE-P 4311 197.1,

the disclosure content of which is hereby incorporated by reference.

In this operating method, dead times occur between individual pulses in which the discharge lamp is supplied with active power, during which no discharge burns in the discharge lamp. The discharge does not have to burn continuously during the active power coupling pulses; just as little is it necessary for the discharge to end immediately after the end of the active power coupling. In any case, certain dead times without discharges occur in the operation of the lamp between the discharge ignitions.

If the dead times between the discharges are now greatly extended, the average power coupled into the lamp and thus also the average emitted light power are reduced, at least as long as the amount of energy coupled in per pulse is not increased to compensate. Rather, it is preferred in the invention that - even in the case of a power setting which is still dealt with below - the energy coupled in per active power pulse remains essentially constant, ie is not changed consciously. Of course, it can change somewhat as a result of the change in the electrical parameters and discharge parameters as a result of the extension of the dead time, but this does not detract from the invention. Based on the current state of knowledge, it is to be regarded as a purely empirical result that particularly long dead times are possible with the small discharge distances according to the invention. Rather, it was expected that the dielectric would be destroyed by arcing because the excessive dead times between the individual active power pulses means that there is practically no physical coupling. In the "normally long" dead times, a single discharge structure forms an ionization of the discharge medium, which is broken down after the discharge pulse has extinguished. The next discharge pulse then ignites in a still somewhat pre-ionized region of the discharge medium, which also means that the pulsed mode of operation is aimed for temporal and local homogeneity of the overall discharge image results.

If the dead times become too long, this coupling no longer takes place between the individual discharge pulses at normal discharge intervals, so that each discharge pulse is comparable to a re-ignition, which initially shows an arc-shaped discharge. The arcs repeated with each pulse make permanent operation of the lamp and efficient homogeneous light generation completely impossible, the discharge lamp i. a. rather damaged and thereby destroyed earlier.

It was also surprising that the invention also does not result in any significant acoustic problems. In the case of "conventional" discharge distances, annoying whistling noises were found at frequencies which are too low, that is to say frequencies in the audible range, which arise by coupling the pulse frequency of the discharges to the discharge vessel via various mechanisms which are not of interest here the small discharge distances with a reduced coupling on the one hand and on the other hand presumably due to the already greatly reduced performance, such problems practically no longer occur.

On the one hand, the invention relates to an operating method in which, as stated above, particularly long dead times are used, in particular longer than the values already mentioned. This also includes an operation of the discharge lamp with only this low power or the long dead time.

Above all, however, the invention is directed to an operating method in which the dead time between the active power pulses can be set in order to set the lamp power, which corresponds to a dimming method if it can be adjusted during lamp operation.

It follows from the above description that the invention relates in this respect on the one hand to the new design of the discharge lamp, but on the other hand also to new features of an operating method for this discharge lamp.

In principle, it is preferred in this invention to provide one or more further discharge distances in a discharge lamp in addition to the small discharge distance according to the invention. It is particularly preferred, in particular in combination with an auxiliary ignition function described below, or independently of this, to be able to operate these electrode groups separately with different discharge distances. Then different power levels can be operated with different electrode groups or different combinations of electrode groups during operation, and so optimal operating parameters can be selected in each case.

For the division of the electrode arrangement into separately operable groups, the disclosure content of DE 198 17479 AI is referred to. In particular, groups of electrodes with a larger discharge distance can be used for higher powers of the discharge lamp, because better efficiency can generally be achieved with the larger discharge distances. In any case, the small discharge distances according to the invention are not really advantageous with regard to the efficiency of the light generation. However, this is generally of lesser interest when the aim is to achieve particularly small outputs, in which the absolute losses occurring due to deteriorated efficiency are small anyway.

A major problem with the efficiency of gas discharge lamps is, in particular, the heat balance, which, however, does not play a critical role in the deterioration in efficiency mentioned here for small outputs because, as stated, the losses are small in absolute terms.

If a significantly lower power is then to be set - whether after the discharge lamp has been switched on again or in the sense of a dim function during operation - an electrode group (or several electrode groups) with the small discharge distance according to the invention is used below a certain power. If only discharges are operated over the small discharge distance, considerable reductions in lamp power are possible.

In order to ensure a transition that is as continuous as possible or a smooth dimming behavior, the discharge lamp is preferably designed in such a way that the power ranges possible with the different discharge distances overlap one another. In this case, when switching from one discharge distance to the other, there may be jumps in efficiency and thus discontinuous luminous flux jumps with a steady course of the power. By adapting the dimming behavior of a ballast with corresponding jumps in performance to compensate for jumps in efficiency when switching between discharge distances these small discontinuities can also be corrected if they are annoying.

Finally, it is also possible to ignite discharges over all the existing discharge distances in the full-load operation of the discharge lamp and thus to achieve a further power gain through the discharges over the small discharge distances. This does not necessarily have to be associated with a loss in efficiency if, according to the following explanation, an arrangement is selected in which a certain ignition aid function is present between different discharge paths. This can reduce the so-called case losses.

With regard to the electrode arrangement of the discharge lamp, a special embodiment of the invention consists in that in addition to an anode and a cathode (further anodes and cathodes may be present), a further electrode is provided, which is assigned to the anode and the cathode for the dielectric barrier discharge is, namely the cathode in the small discharge distance according to the invention and the anode in a larger discharge distance. As a result, the additional electrode can act as an anode with regard to the small discharge distance and as a cathode with regard to the larger discharge distance. This has the particular advantage that the “build-up” of electrons in front of the anode from the discharge over the short discharge distance caused by the special functioning of the dielectric barrier discharge prepares the discharge over the longer discharge distance to a certain extent, in that the pent-up electrons from the cathode active electrode to facilitate the ignition of this further discharge.

In this context, it is particularly preferred that the discharges are not only operated together over the smaller and the larger discharge distance, ie simultaneously in the sense of macroscopic times. the, but that there is also a fixed phase relationship between the active power pulses for the two discharges, which is selected in a suitable manner with regard to the described ignition support function of the discharge over the smaller distance for the discharge over the larger distance.

In this context, it is helpful to clarify that the discharge over the small discharge distance is very easy to ignite because of this short discharge distance, even with small outputs. In this respect, it makes sense to support the comparatively difficult to ignite discharge over the larger discharge distance, in that in the region of the cathode, i. H. there is already an accumulation of electrons on the dielectric and immediately above the dielectric. (In this embodiment, the electrode under consideration here must be covered with a dielectric because, among other things, it acts as an anode.)

In particular, it should be noted that the described auxiliary ignition function also enables the discharges to be operated over the larger discharge distance with significantly longer dead times. Especially in connection with the fixed phase relationship described above, this means practically that the small discharge distance is still switched on in the area of "conventional" powers, with the ignition aid function also dimming down the discharges over the larger distance far below the conventionally achievable power range In the case of very low powers, an even lower power can then be set under certain circumstances by operating the discharges exclusively with the small discharge distance.

Another possibility, which is aimed in the same direction, is to replace this "double-function electrode" by two electrodes. One of these electrodes is assigned as an anode to that in the small one Discharge distance provided cathode, the other of these electrodes is assigned as a cathode to the anode provided in the larger discharge distance. If these two electrodes are sufficiently close together, an auxiliary ignition function in the sense already described is also possible.

According to a further aspect, the measures according to the invention which have already been described are supplemented by an embodiment of the electrode arrangement in favor of dimmability even with conventional discharge distances. For this purpose, the electrode arrangement is made inhomogeneous along a so-called control length, so that an arc voltage of the discharges changes within the control length. For the sake of brevity, reference can be made to the previous German patent application "Dimmable discharge lamp for dielectrically impeded discharges" dated September 29, 1998, file number 19844720.5. The disclosure content of this application is again included here.

In this context, a sinusoidal curve of at least some of the electrodes is preferred, the inhomogeneity being a change in the discharge distance and thus in the operating voltage.

As already mentioned, the method according to the invention for power adjustment or dimming method uses the dead time between individual active power pulses of a pulsed power supply as parameters for influencing the power. In the context of this invention, two specific variants for the configuration of a corresponding electronic ballast are preferred. These two variants are summarized in claims 13 and 14. For further details, reference is once again made to advance registrations, specifically to the registrations “electronic ballast for discharge lamp with dielectric barrier discharge - Li ¬

gen "198 39329.6 and 198 39 336.9, which, like all other cited applications, come from the same applicant. The disclosure content of these applications is also hereby incorporated by reference. The electronic ballasts described there according to the forward converter principle or according to the blocking / forward converter principle are described in clocked a primary circuit switch - there designated TQ - which is switched by a control device - there SE - so the dead time can be influenced by appropriate selection of the electrical parameters of the ballasts and the discharge lamp by appropriate intervention in the control logic of this control device The value of the dead time can be influenced by an external influence of a reference variable of this control device for the time definition.

In the combination of the described operating method according to the invention and the described discharge lamps according to the invention, the invention relates to an illumination system with such a discharge lamp and a correspondingly designed electronic ballast, the latter not necessarily according to claims 13 and 14.

As a preferred application come - as already mentioned at the beginning - for. B. screens, signal lamps, lighting and backlighting of signaling devices, etc. into consideration. In general terms, this area of application can be summarized with information displays of any kind. When displaying information, the readability of the information from the display device plays a very important role under various environmental conditions. This concerns above all the freedom from glare in rather dark ambient conditions and the readability in brighter surroundings or stray light. A wide, adjustable output range of the discharge lamps is of great importance for adaptation. This particularly affects the area of traffic engineering, e.g. B. lamps in the interior of vehicles. In addition, reference is made to the disclosure content of EP 0 926 705 AI (already cited). Furthermore, as already mentioned, monitors and screens come into consideration. There, adjustment ranges for the luminous flux are required, typically 1: 100, which discharge lamps without the invention (previously typically 1: 5) cannot even come close to. Office automation is also an option, for example lamps in scanners.

Description of the drawings

Concrete exemplary embodiments of the invention are described in more detail below, which are shown schematically in the figures. Individual features disclosed can be essential to the invention, either individually or in combinations other than those shown. In detail shows:

Figure 1 is a schematic representation of an electrode arrangement according to the invention;

FIG. 2 shows a schematic illustration of a further electrode arrangement according to the invention;

FIG. 3 shows a schematic illustration of yet another electrode arrangement according to the invention;

FIG. 4 shows a schematic illustration of yet another electrode arrangement according to the invention;

FIG. 5 shows a schematic illustration of a section of a further electrode arrangement according to the invention;

FIG. 6 shows a schematic illustration to explain the electrode arrangement from FIG. 5. In the electrode arrangement shown in Figure 1 as the first embodiment of the invention, twelve numbered electrode strips are shown, which are deposited on a wall, not shown, of a flat radiator discharge vessel. You can of course also in different ways on different walls, z. B. the opposite plate inside of a flat radiator discharge vessel.

The electrode strips 1 and 2, 5 and 6, 7 and 8 and 11 and 12 each have a distance of 4 mm from each other, which is a larger discharge distance in the sense of the introduction to the description. In contrast, the electrode strips 2, 3, 4, 5, on the one hand, and 8, 9, 10, 11, on the other, are at a distance of 0.4 mm, that is to say small distances according to the invention. The electrode strips 6 and 7 are spaced apart by approximately 2-3 mm.

According to the polarity of the individual electrode strips shown in the right-hand side of FIG. 1, the following operating mode is possible: The outer electrode strips 1 and 12 and the middle electrode strips 6 and 7 are at a positive potential, that is to say are connected as anodes. The inner electrode strips 3, 4, 9, 10 in the closely spaced groups of four are at negative potential, that is to say they are cathodes. The remaining electrode strips 2, 5, 8, 11 are at a potential between the above-mentioned potentials, however, significantly closer to the negative potential. For the sake of simplicity, this is indicated by 0 in FIG. The respective potentials can be switched, i.e. H. the electrode strips 1-12 do not have to be supplied with electricity at the same time.

According to the invention, discharges can now be operated via the discharge distances between the electrode pairs 2 and 3, 4 and 5, 8 and 9 and 10 and 11 in a dimming area of the flat radiator with very low powers or luminous fluxes. Since these electrode distances with 0.4 mm are extremely short, these discharges are very easy to ignite and can even be controlled according to this invention with dead times in the range of 1 ms and above. By shortening or lengthening the dead times, the flat radiator can be dimmed even at very low power levels.

It should also be added that, as already mentioned, the efficiency of the discharges, which has deteriorated significantly, over the large discharge distances, in addition to the relative reduction in supply power (compared to the full load of the flat radiator), results in an even greater reduction in the emitted luminous flux. In order to specify a magnitude that is not to be understood as restrictive, the efficiency of the discharges over the short discharge distance of 0.4 mm is in this example about a factor of 5 worse than for the more powerful discharges over the larger discharge distance of 4 mm.

This larger discharge distance between the electrode strips 1 and 2, 5 and 6, 7 and 8 and 11 and 12 in turn enables discharges to be ignited and operated, which in themselves correspond to the state of the art, and which radiate a high luminous flux with good efficiency to let.

With this invention, relative power changes in dimming of at least 10: 1 are typically possible. With appropriate design of the discharge distances and adjustable dead times, values of 20: 1, 50: 1 or even 100: 1 and more can be achieved. It should be noted that due to the already mentioned deterioration in efficiency in the discharges over the short discharge distances, actual relative luminous flux changes which are increased by the factor of the deterioration in efficiency can be achieved by the relative power changes mentioned. A typical value for this factor with a discharge distance of 0.4 mm is 5. This would enable the invention to achieve relative changes in luminous flux of 50: 1, at best also of 500: 1.

In a transition area between the high power range and the very low power range, the electrode arrangement shown can be operated simultaneously with discharges over the long and short discharge distances mentioned. The term at the same time does not refer to the individual active power pulses, but only to macroscopic times in the sense of switching the discharge lamp on or off. As a result, the electrons accumulated by the discharges over the short distances on the intermediate potential electrode strips 2, 5, 8, 11 help to ignite the discharges over the long discharge distances. As a result of this interaction according to the invention between the discharges, the dimmability of the discharges over the long discharge distances can be significantly expanded to lower powers.

In the case of even smaller outputs, the flat radiator can then only be operated with the discharges over the short discharge distances.

In this embodiment, the electrode strips 3, 4, 9 and 10 are each to be understood as a double cathode. This cathode separation can also be omitted, as exemplified by the second exemplary embodiment described below.

In Figure 1 it can also be seen that the electrode strips 6 and 7 are also to be understood as a pair formed anode. Regarding this twin anode technique, reference is made to DE 19711 892 AI by the same applicant. The electrode arrangement shown in FIG. 1 is of course only to be understood as a section of a possibly much larger electrode arrangement.

Figure 1 illustrates that the electrode strips 1-6 and 7-12 each define an "elementary cell" in the vertical direction in Figure 1, which can be repeated as often as desired.

FIG. 2 also shows a detail representation, specifically for a second exemplary embodiment according to the invention. The twin anodes 6 and 7 from FIG. 1 are replaced by sinusoidally selected anodes 13 and 17. For this purpose, reference is made to the patent application “Discharge lamp for dielectrically handicapped discharges with improved electrode configuration” by the same applicant on September 29, 1998, file number 19844721.3. The disclosure content of the cited applications is referred to in each case.

Furthermore, the double cathodes 3, 4, 9 and 10 from FIG. 1 are now each simple, namely as electrode strips 15 and 19.

In FIG. 2, the unit cell corresponds, for example, to electrode strips 15-19, where cathodes would form in pairs when they were placed against one another, but are combined in FIG. 2 to form individual electrode strips 15 and 19, respectively.

The discharge distances correspond to the previous exemplary embodiment, the discharge distance between the electrodes 13 and 14, 16 and 17 and 17 and 18 fluctuating locally. If it is assumed that the structure shown in FIG. 2 is continued upwards and downwards, that is to say that a sinusoidal electrode has neighboring electrodes in both directions, the upper and lower halves of a sinusoidal electrode 13 and 17 must be assigned to other neighbors. For electrode 17, for example, this means that the “mountains” (in the sense of FIG. 2) have a discharge distance to the electrode strip 16 and define the "valleys" to the electrode strip 18. These discharge distances vary between 3 and 4 mm.

The local change in the discharge distance not only offers an alternative to the twin anode configuration shown in FIG. 1, but is also suitable for a conventional dimming technique already referred to in the introduction to the description. Please refer to the registration mentioned there.

Of course, the alternatives shown here can also be combined differently, e.g. For example, cathodes could be provided in pairs in FIG. It is also conceivable to make the closely adjacent electrode strips sinusoidal in their small discharge spacing according to the invention or meandering in another way.

With regard to the further technological details of the gas discharge lamps, reference is made to the various applications cited. Some data are mentioned as examples: The electrode tracks were 0.6 mm wide. 80 μj of energy were injected per pulse. By varying the dead times, it was possible to vary between full powers in the range of 8 W (only with the large discharge distances) and 0.8 W (at 10 kHz) or 0.08 W (at 1 kHz). This corresponds to a dimming range of the luminous flux of 1: 500.

FIG. 3 shows a further exemplary embodiment, an electrode arrangement in a tubular discharge lamp being shown in a schematic cross-sectional illustration.

The numbers 21-25 refer to electrode strips that can be recognized in cross-section and are each covered with a dielectric layer. These electrode strips 21-25 are deposited on the inside of a glass cylinder discharge vessel with an inside diameter of 10.6 mm and an outer diameter of 12 mm. The arrangement shown enables different discharge distances to be realized, depending on which electrode strips are operated with which polarity. The following discharge distances are available in this example:

23-24: 0.5 mm 21-22: 1.5 mm 23-25: 4 mm 21-25: 8.3 mm 22-23: 10.5 mm

With the discharge distances between the electrode strips 23 and 24 on the one hand and 21 and 22 on the other hand, small discharge distances can thus be achieved according to the invention. In addition, three different larger discharge distances between 4 and 10.5 mm are possible. The efficiency of the discharges is further improved even in the area of larger discharge distances, so that the greatest discharge distance between the electrode strips 22 and 23 is optimal in this regard. On the other hand, relatively high voltages are required to ignite discharges across such discharge distances, and comparatively high powers have to be coupled in.

It can be seen that arrangements with multiple selection options can be implemented, in particular with spatial electrode geometries.

The ignition aid function mentioned at the outset can be represented here in two ways: on the one hand with the electrode strip 24 as the cathode, the electrode strip 23 as the intermediate electrode and the electrode strip 25 as the anode (in the sense of the symbols +, 0 and - from FIGS. 1 and 2). Furthermore, with the electrode strip 22 as the cathode, the electrode strip 21 as the intermediate electrode and the electrode strip 25 as the anode. Such a dimmable tube lamp is e.g. B. interesting as an edge lamp for flat screen backlighting.

FIG. 4 shows a further exemplary embodiment of an electrode pattern for a flat radiator lamp. Here three identical tooth-tooth-like electrode tracks are arranged relatively closely adjacent in parallel. In addition, a mirror image of a three-way arrangement parallel to it follows at a greater distance and so on. The two outer electrode tracks of each three-way arrangement or each mirror-image three-way arrangement are connected to common outer connecting tracks 26 and 27 to form electrode groups. Each middle electrode path, both of the three-way arrangements and the mirror-image three-way arrangements, is connected to a further outer connecting path 28 to form a further electrode group. The individual "saw teeth" are asymmetrical. They have a relatively long flat and a short steep ramp. Within each triple arrangement, the distance between the two outer electrode tracks and the inner electrode track between them is 3 mm and 2 mm, respectively. The smallest distance between The tips of the saw teeth of adjacent three-way arrangements are 6 mm, where the individual discharges (not shown) start when the connecting tracks 26 and 27 are connected as (current) cathode or anode (case I) In this case, it is not connected to any pole of an electrical supply source (floating or floating potential). In an operation intended for particularly small outputs, on the other hand, the connecting tracks 26 and 27 are connected together as a (current) cathode and the connecting track 28 as a (current) anode (case II) .This causes the individual discharges to burn only between the respective a m closest adjacent electrode tracks of every three-way arrangement, the individual discharges starting at the sawtooth tips and burning to the next adjacent central electrode track. Between the two Control variants for the three electrode groups 26-28 can be switched over in a manner known per se, for example electronically by means of relays or the like.

With the electrode pattern shown in FIG. 4 and the previously described alternative control variants, the following power ranges for a flat lamp can be covered in unipolar pulse operation.

U _s mean the pulse peak voltage, f the pulse repetition frequency and P the mean electrical power coupled into the flat lamp.

The electrode configuration can also be operated in bipolar alternating pulse operation if there is dielectric interference on both sides.

It is particularly noteworthy that by means of the short discharge distance of approx. 2 mm (case II) an arc-free discharge even at a relatively low pulse repetition frequency (here 8 kHz, ie 10 times less than in case I) and consequently a correspondingly low average electrical power can be achieved. In case I, the peak pulse voltage is the control variable for the electrical power consumption. As the voltage increases, the delta-shaped partial discharge initially at the tip (= smallest electrode distance of approx. 6 mm) of each "saw tooth" widens along the longer ramp (= increasing electrode distance) of the relevant saw toothed to a curtain-like widened structure in which individual delta-shaped partial discharges are no longer clearly recognizable.

In a variant of the illustration in FIG. 4, which is not shown, an essentially straight electrode track can be provided between the three arrangements. This makes it possible, using a suitable third control variant (case III), to implement an average electrode or discharge distance.

Figure 5 shows sections, i.e. without external connecting tracks, a further exemplary embodiment of an electrode pattern according to the invention. The electrode pattern shown is of course only to be understood as a section of a possibly much larger electrode arrangement. This electrode pattern has the advantage over that of FIG. 5 that it manages with fewer electrode tracks and also has a good homogeneity of the luminance distribution, since — as will be explained further below — the individual discharges with short or long striking distances at almost the same positions burn. As a result, the spatial distribution of the discharge structure is largely retained when switching to the respective alternative control variant, with only a different overall luminance.

In FIG. 6, two electrode tracks (29, 30), each with a complex shape, are arranged relatively closely adjacent to one another. In operation, they are used to generate a discharge structure (not shown) with relatively small distances. At a greater distance from this two-way arrangement (29, 30) there follows a mirror-image two-way arrangement (31, 32) etc. The electrode tracks (30, 31; 32, 29), which are adjacent to one another at a greater distance, are used for production in operation a discharge structure (not shown) with relatively large striking distances. For the explanation of further details reference is also made below to FIG. 6. The schematic representation only serves to illustrate how the shapes of the electrode tracks (29-32) in FIG. 5 can be constructed. For this purpose, one initially thinks of two symmetrically sawtooth-shaped electrode tracks (33, 33 ') arranged parallel to one another. The length p of the base of a "sawtooth" is 14 mm, the height s above the base is 1 mm. At the "kinks" 35, 35 'of the double toothed line 33, 33', a portion of the sawtooth tip facing the adjacent electrode path is in each case replaced by a wedge-shaped constriction 36, 36 '. Half the width c of each throat 36, 36 'is 2 mm. The shortest distance b between the two electrode tracks in the area of the narrow points 36, 36 'is 1.5 mm in each case. Then the two-way arrangement 33, 33 'with the narrow points 36, 36' is mirrored and the mirror-image two-way arrangement 34, 34 'with the narrow points 38, 38' is obtained. This is repeated until the entire electrode configuration has been generated. If, in FIG. 6, the obsolete bridged parts are thought to be removed at all “kinks” 35, 35 ', 37, 37', the electrode configuration of FIG. 5 finally results.

In a variant (not shown) of the illustration in FIG. 5, the constrictions can also be curved instead of wedge-shaped. As a result, the control properties of the discharge in the region of the constriction are “softer”, similar to the arcs of the electrode tracks 13 and 17 in FIG. 2.

In addition, the constrictions of one of the two electrode tracks of each two-person arrangement according to FIG. 5 can also be dispensed with, ie every second electrode track is merely sawtooth-shaped. In extreme cases, every second electrode track can also be straight or at least essentially straight. In any case, this reduces the number of bottlenecks within each two-person arrangement and consequently the number of partial ent charges during operation. This variant is therefore particularly suitable for very low luminance levels in dimming mode.

A specific embodiment of a flat lamp (not shown) is described below. The flat lamp has two parallel glass plates (thickness: 2 mm, dimensions: 105 mm by 137 mm) as the main boundary walls. An electrode pattern, for example according to FIG. 4 or alternatively according to FIG. 5 or also a variant as a metal screen printing pattern, is applied to a base plate of the flat lamp. The actual electrode tracks are located within a frame (cross-sectional dimensions: height = width = 5 mm), which connects the base plate with a front plate and seals the discharge volume to the outside (inner surface of the base plate: 78 mm by 110 mm). All electrode tracks are covered with a glass solder layer with a thickness of 150 μm (unilateral discharge). A light-reflecting layer of Al ₂ θ3 or Ti0 ₂ follows on the base plate and frame. All inner surfaces have a three-band phosphor layer. A spherical support point is fitted centrally between the base and front plate. The electrode tracks are simply passed under the seal of the glass solder frame in an extension relative to their sections within their discharge volume. The inside of the discharge vessel is filled with a xenon filling at a pressure of 13 kPa.

Claims

claims

1. discharge lamp with a discharge vessel containing a discharge medium, an electrode arrangement with at least one anode (29; 32) and at least one cathode (30; 31) that define a discharge distance, and with a dielectric layer between at least the anode and the discharge medium,

characterized in that the discharge distance (b) is 3 mm or less.

2. Discharge lamp according to claim 1 with at least two separately operable electrode groups (26, 27; 26, 27, 28), of which at least one (26, 27, 28) has the small discharge distance and which differ from one another with respect to the discharge distance.

3. Discharge lamp according to claim 2, in which the electrode arrangement contains at least one electrode (2), to which a cathode (3) in the small discharge distance is assigned on one side and an anode (1) in a larger one on the other side Discharge distance is assigned.

4. Discharge lamp according to claim 2 or 3, in which the electrode arrangement contains at least two closely adjacent electrodes, one of which is assigned to one side a cathode in the small discharge distance and the other to another side an anode in a larger discharge distance is.

5. Discharge lamp according to claim 2, 3 or 4, in which the electrode arrangement is inhomogeneous along a control length in a shape which changes a burning voltage over a larger discharge distance.

6. Discharge lamp according to claim 5, wherein at least one electrode (13; 17) has a substantially sinusoidal shape.

7. Discharge lamp according to claim 5, wherein at least one electrode (26; 27; 28; 29; 30; 31; 32) has a substantially sawtooth shape.

8. Discharge lamp according to claim 7, which has at least one arrangement of at least two electrodes (29, 30) with the small discharge distance and at least one mirror-image electrode arrangement (32, 31), the smallest mutual distances (g) of neighboring electrode arrangements being larger , as the smallest mutual distances (b) of the next neighboring electrodes (29; 30) within an arrangement (29, 30).

9. Discharge lamp according to claim 8, in which the small discharge distances (b) are realized by constrictions (36, 36 '; 38, 38') between the neighboring pairs of electrodes of each electrode arrangement, each constriction (36; 36 '; 38; 38 ') is formed between each two saw teeth of at least one electrode of each pair of electrodes.

10. Discharge lamp according to claim 9, wherein each constriction is arcuate or wedge-shaped.

11. A method for operating a discharge lamp according to one of the preceding claims, in which a dead time between active power pulses of a pulsed power supply is more than 50 μs.

12. The method, also according to claim 11, for operating a discharge lamp according to one of claims 1-10, in which the power coupled into the discharge lamp is changed by a dead time between active power pulses of a pulsed power supply is changed.

13. The method according to claim 12, wherein the energy coupled into the discharge lamp per active power pulse remains essentially constant.

14. The method according to claim 12 or 13, in which the discharge lamp is configured according to claim 2 and the power is set in a range of lower powers, while only electrode pairs are operated with the smaller discharge distance, and the power is set in a range of higher powers is operated while or only pairs of electrodes with the larger discharge distance.

15. The method according to claim 12, 13 or 14, in which the discharge lamp is configured according to claim 2 and electrode pairs with the smaller discharge distance are operated together with electrode pairs with a larger discharge distance.

16. The method according to claim 15, in which there is a fixed phase relationship between the active power pulses for the electrode pairs with the smaller discharge distance and the active power pulses for the electrode pairs with the larger discharge distance.

17. The method according to any one of claims 12-16, in which the discharge lamp is operated with a ballast which is constructed as a flux converter for impressing an external voltage pulse from a primary circuit via a transformer into a secondary circuit with the discharge lamp, in order to ignite in the discharge lamp and to effect an internal counter polarization, and has a switching device which is designed to interrupt the after the ignition primary-side current flow through the transformer for isolating the secondary circuit in order to allow the secondary circuit to oscillate, to draw off the charge which causes the external voltage across the discharge lamp and to lead to re-ignition by the internal counter-polarization in the discharge lamp, the switching device being designed to to change the dead time after the re-ignition until a new ignition in the discharge lamp in order to change the power coupled into the discharge lamp.

18. The method according to any one of claims 12-16, wherein the discharge lamp is operated with a ballast, which is constructed as a combined flyback / flux converter and has a switching device in a primary circuit, which is designed to interrupt the primary circuit-side current flow through a transformer for Injecting an external voltage pulse into a secondary circuit with the discharge lamp, in order to bring about an ignition and counter-polarization in the discharge lamp, and then to switch on the primary circuit-side current flow through the transformer again, in order to use a counter-voltage pulse to charge the external voltage across the discharge lamp subtract from the discharge lamp in order to bring about reignition with the aid of the internal counter-polarization in the discharge lamp,

wherein the switching device is designed to change the dead time after the re-ignition until it is re-ignited in the discharge lamp in order to change the power coupled into the discharge lamp.

19. Lighting system with a discharge lamp according to one of claims 1-10 and an electronic ballast, which is designed for a method according to one of claims 11-16.

20. Device for displaying information with a lamp according to one of claims 1-10.

21. Device according to claim 20 with a lighting system according to claim 19.