EP0895653B1 - Electric radiation source and irradiation system with this radiation source - Google Patents

Abstract

PCT No. PCT/DE97/01989 Sec. 371 Date May 6, 1998 Sec. 102(e) Date May 6, 1998 PCT Filed Sep. 8, 1997 PCT Pub. No. WO98/11596 PCT Pub. Date Mar. 19, 1998A radiation source, in particular a discharge lamp suitable for operating a dielectrically hindered pulsed discharge by means of a ballast, has at least one electrode separated by dielectric material from the inside of the discharge vessel. By appropriately designing at least one of the electrodes and/or the dielectric material, local field reinforcement areas are created, so that during the pulsed mode of operation one or more dielectrically hindered individual discharges are generated exclusively in these areas, maximum one individual discharge being generated in each area. These areas are obtained in particular by shortening the spacing in locally limited areas, for example by providing on one of the electrodes hemispherical projections which extend towards the counter-electrode. This measure achieves a timestable discharge structure with a high useful radiation effectiveness uniformly distributed throughout the discharge vessel.

Description

Technical field

The invention relates to an electrical radiation source according to the preamble of claim 1. The invention also relates to an irradiation system with this radiation source and with a voltage source according to the preamble of claim 15.

In operation, the radiation source emits by means of a dielectric barrier Discharge incoherent radiation. A dielectric barrier discharge is generated by using one or both of the two with the voltage source connected electrodes of the discharge arrangement by a dielectric is separated from the discharge inside the discharge vessel or are (one-sided or two-sided dielectric discharge).

Under incoherently emitting radiation sources are here UV (U ltra v iolet) - and IR (I nfra r ot) emitters as well as discharge lamps which emit visible light in particular, to understand.

Radiation sources of this type are suitable, depending on the spectrum of the emitted radiation, for general and auxiliary lighting, such as home and office illumination or backlighting of displays, such as LCDs (L iquid C rystal D isplays), for the transport and signal lighting, as well as for UV radiation, e.g. disinfection or photolytics.

State of the art

The invention is based on WO 94/23442 and those disclosed therein Operating mode for dielectrically disabled discharges. This mode of operation uses a basically unlimited sequence of voltage pulses, which are separated from each other by dead times or break times. critical for the efficiency of the generation of useful radiation are among others Pulse shape and the duration of the pulse or dead times. To be favoured for this mode of operation narrow, e.g. used strip-like electrodes, which can be dielectrically impeded on one or both sides. Stand up For example, two elongated electrodes in parallel opposite one another Large number of similar, in plan view, that is perpendicular to the plane in which the two electrodes are arranged, delta-like (Δ) discharge structures generated, which are lined up along the electrodes and themselves widen in the direction of the (current) anode. In the case of changing Polarity of the voltage pulses of a double-sided dielectric barrier Discharge appears to be a superimposition of two delta-shaped structures. Because these discharge structures prefer repetition frequencies generated in the kHz range, the viewer takes only one of the temporal Resolution of the human eye corresponding to "medium" discharge structure true, in the shape of an hourglass. The number of each Discharge structures is inter alia due to the electrical power can be influenced. The disadvantage, however, is that some Discharge structures may have their respective location along the electrodes can change spontaneously, causing some instability of the Radiation distribution results. In addition, the discharge structures also accumulate in partial areas of the discharge vessel, whereby the Power distribution in relation to the total volume of the discharge vessel can be very uneven.

A variety of radiation sources for the are from the patent literature Operation using alternating voltage is known. Here, too, the individual Discharge structures change their location spontaneously. In addition, you can also do not predict exactly where an individual is Single discharge will ignite. The emergence of the individual discharges shows rather, a spatial and temporal stochastic behavior.

In DE 40 10 809 A1, for example, there is a high-power radiator with one another parallel, strip or wire-shaped electrodes disclosed. In the respective longitudinal direction of two directly adjacent electrodes different polarity, no place is special compared to the neighboring places excellent. As a result, they ignite between these electrodes Single discharges a degree of freedom, corresponding to a common one Dimension of the parallel, elongated electrodes.

EP 0 254 111 B1 describes a radiator with a first transparent and a second flat metal electrode, e.g. known a metal layer. The transparent electrode is a transparent, electrically conductive layer or implemented as a wire mesh. In the first case, i.e. if there are two flat If the electrodes face each other, the individual discharges therefore have two Degrees of freedom, corresponding to the respective two dimensions of the two Electrode surfaces. In the second case, the individual discharges can be anywhere along the warp or weft threads of the wire mesh, always have another degree of freedom.

Finally, in EP 0 312 732 B1 there is a radiator with two, each consisting of one Wire network existing, mutually parallel electrodes known. Here the individual discharges can each be somewhere along two opposite each other standing and mutually parallel warp or weft threads of both Wire networks are created. Each individual individual discharge therefore has in turn a degree of freedom corresponding to the one common dimension of parallel warp or weft threads.

EP-A-0 578 953 describes a high-performance radiator in the form of a coaxial one Double tube arrangement disclosed. An outer electrode in the form of a Wire mesh extends over the entire circumference of the outer quartz tube. A helical inner electrode is inserted into the inner quartz tube. The inside of the inner quartz tube is filled with a coolant felt that has a high dielectric constant and except for cooling also serves to couple the inner electrode to the inner quartz tube. in the Space between the two tubes, the discharge space, is formed Apply a variety of AC voltage between the electrodes Discharge channels. To improve the ignition behavior at the first Ignition or after longer breaks in operation means are provided that due to local field distortion or field elevation at one point in the discharge space to force an initial spark. By the resulting UV radiation and the charge carriers of this local discharge will then the reliable ignition of the entire discharge volume is enforced. The following are disclosed as suitable means for field distortion: a dent in the interior or Outer tube that is about half the gap to the other Pipe reaches; a ball of dielectric material in the discharge space; one on the inner surface of the outer tube or the outer surface of the inner tube melted quartz drops; in elongated Spotlights two or more these balls; also is that Combination of ball (s) and dents or humps possible.

Presentation of the invention

The invention has for its object to eliminate the disadvantages mentioned and a radiation source with one with respect to the total volume of their discharge vessel more even power distribution as well as with a in particular also to specify a more stable overall discharge over time. On Another aspect of the invention is the improvement of the efficiency of the production of useful radiation.

This object is achieved by the characterizing features of claim 1 solved. Particularly advantageous versions of the Invention are described in the subclaims.

Another object of the invention is to provide an irradiation system which contains said radiation source. This task will according to the invention by the characterizing features of claim 15 solved.

The basic idea of the invention is local by means of a multitude limited amplifications of the electric field specifically spatially preferred To create starting points for the individual discharges. The individual discharges are forced to the places of these local field reinforcements and remain essentially stationary there, i.e. they have none Degree of freedom more to move to a location in the immediate vicinity. As a result, the overall structure of the discharge is largely temporal stable. The specific form of the individual discharges only plays a subordinate role Role. The delta and hourglass-shaped ones mentioned at the outset are true Individual discharges due to their high efficiency in generating useful radiation particularly suitable. Nevertheless, the invention is not limited to single discharges shaped in this way.

The points for local field reinforcement can be implemented by various measures, as the following simplified analysis shows. If U (t) denotes the time-varying voltage applied to two electrodes arranged at a distance d , this results in an electric field between the electrodes with the approximate strength E (t) = U (t) / d. Consequently, the local field amplifications E (t; r = r _i ) = U (t) / d (r _i ) can be achieved by locally shortening the electrode spacing d (r) at the corresponding points r _i , where i = 1,2, 3, ... n and n denote the total number of field reinforcements.

In addition, the electric field strength E (r) in the discharge space can be influenced by the capacitive effect of the dielectric layer (s) of the disabled electrode (s). Because of the capacitive effect of the dielectric, the electric field strength E (r) in the discharge space is weakened. Local field reinforcements E (r = r _i ) according to the invention are consequently also due to locally limited reductions in the (total) thickness b (r _i ) and / or through increases in the relative dielectric constant (s) ε (r _i ) of the dielectric layer (s) the corresponding places r _i can be realized.

The locations of local field strengthening are therefore due to the targeted structure at least one of the electrodes and / or the dielectric material is created. The geometrical extent of the places is on the concrete Dimensions of the individual discharges matched. Under the Designation "structure" are both form, structure, material and understand spatial arrangement and orientation.

The distance reductions Δd (r _i ) are achieved by specially shaped or structured electrodes, which are also suitably arranged spatially to one another. The specific design of the electrode configuration is matched to the shape or symmetry of the discharge vessel. In addition, when using bipolar voltage pulses, it should be taken into account that the electrodes of different polarity alternately act as cathode or anode and, consequently, should ideally be of completely the same design. If unipolar voltage pulses are used, on the other hand, it is expedient to structure or shape only the cathode in a targeted manner, since the “tips” of the delta-shaped individual discharges start there.

For cuboid or flat discharge vessels are suitable two or more substantially elongated electrodes that are parallel to each other are arranged. For the advantageous effect of the invention Structuring the electrode doesn't matter if the electrodes are all outside or inside, on one side or on opposite sides Sides of the discharge vessel are arranged. It is only important that either at least the electrodes of one polarity (one-sided dielectric disabled discharge) or the electrodes of both polarities (Dielectric barrier discharge on both sides) by a dielectric Layer are separated from the discharge.

At least the electrodes of one polarity are provided at regular intervals in the vessel plane with formations which extend in the direction of the counterelectrode (s) in such a way that a predeterminable number n of distance reductions Δd (r _i ) with i = 1,2,3, ... n is reached. Rod-shaped electrodes with nose-like shapes or "zigzag" and rectangular shapes are suitable, for example.

Semicircular or hemispherical shapes are particularly cheap, because in this case - in contrast to rectangular or triangular shapes - Both a defined shortest distance is realized as well undesirable peak effects can be avoided.

The shapes or shapes of the respective electrodes are dimensioned such that the local field reinforcements E ( r _i ) thereby achieved are on the one hand sufficiently high to reliably generate the individual discharges at only these points r _{i of} the distance reductions Δd (r _i ) . On the other hand, the partial volume of the discharge vessel claimed by the shapes or by the shape of the electrode cannot be used by the individual discharges themselves. Given the requirement to create a discharge vessel that is as compact as possible or an efficiently used vessel volume, a relatively small reduction in distance should therefore be aimed for. An acceptable compromise can therefore be found in individual cases.

Typical relationships between the shortening of the distance Δd (r _i ) and the effective striking distance w for the individual discharges are in the range between approx. 0.1 and 0.4. The effective distance w is the respective distance d (r _i ) between adjacent electrodes of different polarity at points r _i , ie w = d ( r _i ) -b, reduced by the thickness b of the dielectric .

A combination is particularly suitable for cylindrical discharge vessels consisting of a helical and one or more elongated electrodes. The helical electrode is preferably centrally axially inside of the discharge vessel arranged. The elongated electrode or electrodes are at a predeterminable distance from the outer surface of the electrode coil, for example on the outer wall of the cylinder jacket of the discharge vessel, preferably arranged parallel to the longitudinal axis of the cylinder. By this targeted shaping and arrangement of the electrodes is a multitude separate locations with shortened electrode spacing created. The pitch - i.e. the distance within which the helix is one complete revolution - is preferably about the size of that maximum transverse expansion - in delta-like forms this corresponds to the Foot width - of the individual discharges or larger, to overlap the individual discharges to prevent.

DE 41 40 497 A1 already contains a high-power radiator, in particular for ultraviolet light, disclosed with a helical inner electrode. However, this inner electrode is only used for coupling of a pole of an AC voltage source to a distributed additional capacitance acting molded body. The coupling of the alternating electrical field is preferred by a liquid with high dielectric constant, preferably demineralized water (ε = 81). Besides, that is Counter electrode realized in the form of a wire mesh. Each locally on the Individual discharges of the type described at the beginning of limited field reinforcements do not result from this configuration. Hence neither generation or separation according to the invention Single discharges possible.

To complete the radiation source to an irradiation system are the electrodes of the radiation source alternating with the two poles connected to a pulse voltage source. The pulse voltage source delivers voltage pulses interrupted by pauses, such as in WO 94/23442.

Another aspect of the invention is the overlap of individual discharges to be largely prevented or at least restricted. It It has been shown that the efficiency for the production of useful radiation increases with decreasing overlap. On the other hand lets by moving together or overlapping the individual discharges the volume of electrical discharge that can be coupled into the discharge vessel increase. Therefore, a suitable compromise between the Level of performance (greater overlap) and level of efficiency (less overlap) to choose. Depending on the requirement, either the absolute value of the radiant power or the efficiency of the Radiant power, i.e. in the case of visible radiation, the height of the Luminous flux or the luminous efficacy, weighted more.

From these points of view, the maximum transverse expansion has to be considered of the individual discharges standardized distance in the range of approx. 0.5 to 1.5 proved to be suitable. Here, standardized distances of e.g. 0.5, 1 and 1.5 that the central axes of adjacent partial discharges by half, the single or one and a half times their maximum transverse extent from each other are removed, which is an overlap, a touch without Overlap or a spacing of the partial discharges corresponds. in the Case of spaced partial discharges, i.e. that between the partial discharges is a discharge-free area, a mutual influence of the Partial discharges can be largely excluded.

Description of the drawings

Fig. 1

eine Prinzipdarstellung einer Entladungsanordnung für eine gepulste, einseitig dielektrisch behinderte Entladung mit zwei nebeneinander angeordneten Elektroden mit lokalen Verkürzungen des Elektrodenabstandes,

Fig. 2

eine Variation der Anordnung aus Figur 1 mit zwei Anoden und sägezahnförmiger Kathode,

Fig. 3

eine weitere Variation der Anordnung aus Figur 1 mit zwei Anoden und stufenförmiger Kathode,

Fig. 4

ein Ausführungsbeispiel eines Flachstrahlers mit einer Kathode mit nasenartigen Fortsätzen,

Fig. 5a

ein Ausführungsbeispiel einer zylindrischen Entladungslampe mit einer spiralförmigen Kathode in Seitenansicht,

Fig. 5b

den Querschnitt entlang A-A der in Figur 5a gezeigten Entladungslampe,

Fig. 5c

einen Teil eines Längsschnittes entlang B-B der in Figur 5a gezeigten Entladungslampe,

Fig. 6a

eine schematische Darstellung einer teilweise durchbrochenen Draufsicht einer erfindungsgemäßen Flachlampe mit auf der Bodenplatte angeordneten Elektroden mit lokalen Verkürzungen des Elektrodenabstandes,

Fig. 6b

eine schematische Darstellung einer Seitenansicht der Flachlampe aus Figur 6a.

The invention is explained in more detail below with the aid of a few exemplary embodiments. Show it

Fig. 1

1 shows a schematic diagram of a discharge arrangement for a pulsed discharge which is dielectrically impeded on one side and has two electrodes arranged next to one another with local reductions in the electrode spacing,

Fig. 2

1 shows a variation of the arrangement from FIG. 1 with two anodes and a sawtooth-shaped cathode,

Fig. 3

1 shows a further variation of the arrangement from FIG. 1 with two anodes and a stepped cathode,

Fig. 4

an embodiment of a flat radiator with a cathode with nose-like extensions,

Fig. 5a

an embodiment of a cylindrical discharge lamp with a spiral cathode in side view,

Fig. 5b

the cross section along AA of the discharge lamp shown in Figure 5a,

Fig. 5c

FIG. 5a shows a part of a longitudinal section along BB of the discharge lamp shown in FIG. 5a,

Fig. 6a

1 shows a schematic representation of a partially broken top view of a flat lamp according to the invention with electrodes arranged on the base plate with local reductions in the electrode spacing,

Fig. 6b

is a schematic representation of a side view of the flat lamp of Figure 6a.

Figure 1 serves primarily to explain the principle of the invention - namely the targeted localization of the individual discharges of a pulsed dielectrically disabled discharge using local field amplifiers - and based on local shortening of the electrode spacing of a discharge arrangement 1. For this purpose, Figure 1 shows a longitudinal section of the Discharge arrangement 1 with two arranged parallel to each other at a distance d elongated electrodes 2,3 in a schematic representation. A first one 2 of the two electrodes 2, 3 is covered by a dielectric layer 4 adjacent discharge space, which extends between the two electrodes 2, 3 Cut. The second metallic electrode 3, however, is uncoated. This is a one-sided dielectric barrier Discharge arrangement that is particularly efficient with unipolar voltage pulses is operated. The polarity is chosen so that the dielectric handicapped electrode 2 as the anode and the unhindered electrode 3 consequently act as a cathode.

The cathode 3 has four nose-like extensions 9-12, which face the anode 2. As a result, locally limited reinforcements of the electric field are generated at the locations of the extensions 9-12. These targeted field reinforcements have the effect that - assuming a sufficiently high electrical power - a delta-shaped individual discharge 5-8 starts at each of these extensions 9-12. In order to prevent or at least limit undesired migration of the starting points for the tips of the individual discharges 5-8 on the extensions 9-12, the transverse extension s of the respective extension, ie the extension along the cathode 3, is relatively small compared to the width f of the Foot of a single discharge. The transverse extension s is typically about 1/10 of the foot width f . Another important measure is the lateral extent of the extensions 9-12, ie the extent in the direction of the shortest distance to the opposite anode 2 - that is, the shortening of the distance Δd ( r _i ) previously explained in the description. The respective distance between the extensions 9-12 and the anode - minus the dielectric layer 4 - thus gives the effective striking distance w for the individual discharges 5-8. Consequently, the lateral dimensions aus are dimensioned such that a sufficient field gain E (t) = U (t) / w is achieved when the electrode voltage U ( t ) is applied, in order to ensure that the individual discharges 5-8 are reliably applied. Typically, the ratio of lateral expansion Schlag and effective stroke length w is in the range between approx. 0.1 and 0.4.

The distances between adjacent individual discharges 5-8 can be influenced by the distances a of the associated extensions 9-12. To clarify this concept, the distances between the successive extensions 9-12 and consequently also the associated individual discharges 5-8 are selected differently in FIG. It is also assumed that the delta-shaped individual discharges 5-8 have the shape of an equilateral triangle. The mutual distance between the first two extensions 9 and 10 corresponds exactly to half the foot width f of the two associated individual discharges 5 and 6, corresponding to a distance of 0.5 normalized to the foot width f . Consequently, these two individual discharges 5 and 6 overlap in the overlap region 13. The mutual distance between the second and third extensions 6 and 7 corresponds to the entire foot width f of the two associated individual discharges 6 and 7, corresponding to a standardized distance of 1. Consequently, these two close Individual discharges 6 and 7 directly adjacent to one another, without overlap, but also without discharge-free space between the foot areas of the two individual discharges 6 and 7. The mutual spacing of the third and fourth extensions 11 and 12 is finally greater than the foot width f of the two associated individual discharges 7 and 8, corresponding to a normalized distance greater than 1. Consequently, these two individual discharges 7 and 8 are separated from one another by a discharge-free space between their foot areas.

In Figures 2 and 3 are variations of the discharge arrangement of Figure 1 with two anodes arranged parallel to each other schematically shown. Identical features are provided with the same reference numbers.

In Figure 2 the local reductions in the electrode spacing are complete a "zigzag" arranged centrally in the plane of the two anodes 2a, 2b - or sawtooth-shaped cathode 14, for example made of a metal wire bent, realized. The six points 15-20 of the cathode 14 point alternating with one or the other of the two anodes 2a, 2b. To this Way is achieved that with appropriate electrical power at everyone the prongs 15-20 apply a delta-shaped individual discharge 21-26. The ends at the "odd-numbered points", i.e. the first point 15 and at the individual buttocks 17 and 19 starting after the next but one 21, 23, 25 on one anode 2a. The ones in between or the next following "even-numbered" spikes 16, 18, 20 starting individual discharge 22,24,26, however, end at the opposite one Anode 2b. The mutual distances of the individual discharges are through the corresponding distances between the points can be influenced. In Figure 2 are the distances between the next but one neighboring points 15, 17; 17.19 or 16, 18 and 18, 20 were chosen to be the same size as the foot width of the individual discharges 21-26. As a result, both are "odd" as well the "even-numbered" individual discharges 21, 23, 25 and 22, 24, 26 each immediately lined up adjacent to each other on both sides of the cathode 14.

In FIG. 3, only the cathode 27 has been changed compared to FIG. 1, specifically in such a way that a centrally between the two anodes 2a, 2b Sequence of four stages 28-31, for example bent from a metal wire, extends. Steps 28-31 alternate with one anode 2a and other anodes 2b oriented, so that these steps as local shortenings function of the electrode gap.

The discharge arrangement in FIG. 3 is particularly suitable for "curtain-like" discharge structures, such as those under certain discharge conditions, e.g. relatively low pressure of the gas or gas mixture can be generated within the discharge vessel. Under these Under special conditions, no delta-shaped individual discharges are formed out. Rather, then burn between levels 28,30 and adjacent anode 2a on the one hand and between steps 29, 31 and adjacent anode 2b, on the other hand, each have rectangular discharges 32.34 and 33.35, respectively.

In one variant, the step-like cathode is additionally of a thin one dielectric layer coated (not shown). That way is one Dielectric barrier arrangement realized on both sides. So that's one efficient operation with bipolar voltage pulses possible. Change in the process the alignment of the delta-shaped individual discharges constantly the changing polarity of the voltage pulses in the opposite direction. With typical pulse repetition frequencies in the range of a few tens Kilohertz creates the visual impression of "hourglass-shaped" individual discharges (not shown).

There are also many other suitable shapes for the cathode conceivable that the inventive feature of locally limited shortenings of the electrode spacing. In particular, the electrodes also in the form of conductor tracks on an inner or outer wall of the Discharge vessel can be printed, such as in the EP 0 363 832 A1. Essential for the beneficial effect of The invention is merely the additional means for local field amplification an average per single discharge. You can also use the electrodes instead of being arranged spatially just as well in one plane.

Figures 4a and 4b show a schematic representation of an embodiment of an irradiation system with flat radiator 36 and electrical supply device 37, partly in longitudinal section or in cross section. The electrode arrangement is similar to that shown in FIG. 1 to explain the inventive idea. The radiator 36 consists of an elongated cuboidal discharge vessel 38 made of glass. Xenon is located in the interior of the discharge vessel 38 with a filling pressure of approximately 8 kPa. A first electrode 39 (cathode) connected to the negative pole of the supply device 37 (cathode) is arranged centrally in the longitudinal axis of the discharge vessel 38. On the outer walls of the two narrow side surfaces 40a, 40b parallel to the longitudinal axis, a further strip-shaped electrode 41a, 41b (anode) made of aluminum foil connected to the positive pole of the supply device 37 is arranged. The cathode 39 consists of a metal rod which is provided with three pairs of nose-like extensions 42a, 42b-44a, 44b at a mutual spacing of approximately 15 mm. The two extensions of each pair 42a, 42b-44a, 44b are oriented in the opposite direction and towards each of the two anodes 41a, 41b. The extensions 42a, 42b-44a, 44b are semicircular with a diameter of approximately 2 mm. The lateral expansion ℓ in the direction of the respective anode is therefore approx. 1 mm. Together with an effective stroke distance ω of approx. 9 mm, this results in a value of approx. 0.11 for the quotient ℓ / w . In operation, the supply device 37 delivers a sequence of negative voltage pulses with widths (full width at half height) of approx. 1 μs and a pulse repetition frequency of approx. 80 kHz. Thus, a delta-shaped individual discharge 45a, 45b-47a, 47b can be generated on each of the extensions 42a, 42b-44a, 44b within the discharge vessel 38. Each individual discharge begins with its tip on an extension and widens as far as the opposite side wall 40a, 40b, which acts as a dielectric layer, on the outer wall of which the associated anode 41a, 41b is fastened.

FIG. 5a shows the side view, FIG. 5b the cross section and FIG. 5c shows a partial longitudinal section of a further embodiment of a discharge lamp 48. Its outer shape resembles conventional lamps with an Edison base 49. An elongated inner electrode 51 is arranged centrally within the circular cylindrical discharge vessel 50 made of 0.7 mm thick glass. The discharge vessel 50 has a diameter of approximately 50 mm. The inside of the discharge vessel 50 is filled with xenon at a pressure of 173 hPa. The inner electrode 51 is formed from metal wire as a right-handed spiral. The respective diameters of the metal wire and the helix 51 are 1.2 mm and 10 mm, respectively. The pitch h - ie the distance within which the helix makes one complete turn - is 15 mm. This value corresponds approximately to the foot width f of the delta-shaped individual discharges. On the outer wall of the discharge vessel 50, four outer electrodes 52a-52d in the form of 8 cm long conductive silver strips are attached equidistantly and parallel to the longitudinal axis of the coil. Consequently, there are four equidistant locations 53a-53d per turn on the outer surface of the spiral electrode 51, which are immediately adjacent to the corresponding outer electrodes 52a-52d. The tip of a delta-shaped individual discharge 54a-54d starts at these four points with the shortest stroke length w and widens up to the inner wall of the discharge vessel 50 in the direction of the outer electrodes 52a-52d. These locations of the shortest pitch are repeated from turn to turn and along the outer electrodes 52a-52d. In this way, the individual discharges burn in a deliberate manner, separated from one another, in two planes intersecting perpendicularly in the longitudinal axis of the lamp, each plane passing through two opposite outer electrodes 52a, 52c and 52b, 52d. In addition, the targeted choice of h = f ensures that the individual discharges along the outer electrodes 52a-52d do not overlap one another.

In the area of the base of the discharge vessel 50, the outer electrodes 52a-52d are electrically conductively connected to one another by means of a conductive silver strip 52e attached to the outer wall in a ring. The inner wall of the discharge vessel 50 is coated with a phosphor layer 55. It is a three-band phosphor with the blue component BaMgAl ₁₀ O ₁₇ : Eu ²⁺ , the green component La-PO ₄ : (Tb ³⁺ , Ce ³⁺ ) and the red component (Gd, Y) BO ₃ : Eu ³⁺ . This results in a luminous efficacy of approx. 45 lm / W in pulse mode with voltage pulses of approx. 1.2 µs pulse width, each separated by 37.4 µs pause time. Compared to the lamp of the similar type disclosed in WO 94/23442, but with a stick electrode, ie without specific separation of the individual discharges, this corresponds to an increase in yield of approximately 12-13%.

In a variant is a ballast (not shown), which the for the operation of the lamp supplies the necessary voltage pulses in the lamp base 49 integrated.

Figures 6a, 6b show a schematic representation of a top view or Side view of a flat fluorescent lamp operating white light emitted. It is used as a backlight for an LCD (Liquid Crystal Display).

The flat lamp 56 consists of a flat discharge vessel 57 with a rectangular base, four strip-like metallic cathodes 58 (-) and dielectric anodes 59 (+). The discharge vessel 57 in turn consists of a base plate 60, a cover plate 61 and a frame 62. Base plate 60 and cover plate 61 are each gas-tightly connected to the frame 62 by means of glass solder 63 such that the interior 64 of the discharge vessel 57 is cuboid. The base plate 60 is larger than the cover plate 61 in such a way that the discharge vessel 57 has a circumferential free-standing edge. The inner wall of the ceiling plate 61 is coated with a phosphor mixture (not visible in the illustration), which converts the UV / VUV radiation generated by the discharge into visible white light. It is a three-band phosphor with the blue component BAM (BaMgAl ₁₀ O ₁₇ : Eu ²⁺ ), the green component LAP (LaPO ₄ : [Tb ³⁺ , Ce ³⁺ ]) and the red component YOB ([Y, Gd) BO ₃ : Eu ³⁺ ). The opening in the ceiling plate 61 is used for illustrative purposes only and provides a view of part of the cathodes 58 and anodes 59.

The cathodes 58 and anodes 59 are alternating and parallel on the inner wall the bottom plate 60 is arranged. The anodes 59 and cathodes 58 are each extended at one end and on the base plate 60 from the inside 64 of the discharge vessel 57 on both sides to the outside performed such that the associated anodic or cathodic bushings arranged on opposite sides of the base plate are. The electrode strips go on the edge of the base plate 60 58.59 each in the cathode-side 65 and anode-side 66 external power supply about. The outer power supply lines 65, 66 serve as contacts for connection to an electrical pulse voltage source (not ) Shown. The connection with the two poles of a pulse voltage source usually takes place as follows. First, the individual anodic and cathodic power supplies with each other connected, e.g. using a suitable connector (not shown) including connecting lines. Eventually the two become common anodic or cathodic connecting lines with the associated two poles of the pulse voltage source connected.

In the interior 64 of the discharge vessel 57, the anodes 59 are completely included a glass layer 67 covered, the thickness of which is approximately 250 microns.

The cathode strips 58 have nose-like, the respectively adjacent anode 58 facing semicircular extensions 68. They work locally limited reinforcements of the electric field and consequently that the delta-shaped Single discharges (not shown) exclusively on these Ignite the spots and then burn locally.

The distance between the extensions 68 and the respective immediately neighboring anode strips is approx. 6 mm. The radius of the semicircular Extensions 68 is approximately 2 mm.

The individual electrodes 58, 59 including bushings and outer ones Power supply lines 65, 66 are each in the form of a coherent interconnect Structures formed. The structures are using screen printing technology applied directly to the base plate 60.

In the interior 64 of the flat lamp 56 there is a gas filling made of xenon a filling pressure of 10 kPa.

The invention is not restricted to the specified exemplary embodiments. In particular, individual features of different exemplary embodiments be combined in a suitable manner.

Claims (15)

1. Radiation source (36; 48; 56) which is suitable for operating a dielectrically obstructed, pulsed discharge, the radiation source (36; 48; 56) having an at least partially transparent discharge vessel, which is closed (38; 50) and filled with a gas filling, or which is open and is flowed through by a gas or gas mixture, which discharge vessel is made from an electrically nonconductive material and has electrodes (39, 41a, 41b; 51, 52a-52d; 58, 59), at least the electrodes of one polarity (41a, 41b; 52a-52d; 59) being separated from the interior of the discharge vessel by dielectric material (40a, 40b; 50; 67), and during the pulsed operation an electric field being generated in each case between the electrodes of opposite polarity, characterized in that the design of at least the electrodes of one polarity and/or of the dielectric material creates a multiplicity of sites for local amplification of the electric field in such a way that during the pulsed operation one or more dielectrically obstructed individual discharges are generated exclusively at these sites, at most one individual discharge being generated per site.
2. Radiation source according to Claim 1, characterized in that the mutual spacing of the individual sites for local amplification of the electric field is selected in such a way that the individual discharges essentially do not overlap.
3. Radiation source according to Claim 1, characterized in that the spacing of the individual sites for local amplification of the electric field, which spacing is normalized to the maximum transverse extent of the individual discharges, is in the range between approximately 0.5 and 1.5, preferably in the region between 0.9 and 1.3.
4. Radiation source according to one of Claims 1 to 3, characterized in that the design through which the sites for local field amplification are created is such that the electrodes of opposite polarity in each case have locally limited shortenings of the spacing.
5. Radiation source according to Claim 4, characterized in that the locally limited shortenings of the spacing are realized as nose-like protuberances (9-12; 42a; 42b-44a; 44b; 68).
6. Radiation source according to Claim 5, characterized in that the protuberances have the shape of a semicircle (68) or a hemisphere (42a; 42b-44a; 44b).
7. Radiation source according to Claim 1, characterized in that the discharge vessel (57) is shaped in a two-dimensional manner and the electrodes (58, 59) are of essentially elongated design.
8. Radiation source according to Claim 4, characterized in that the locally limited shortenings of the spacing are realized by means of an electrode (27) having the shape of a square wave.
9. Radiation source according to Claim 4, characterized in that the locally limited shortenings of the spacing are realized by means of a saw-tooth electrode (14).
10. Radiation source according to Claim 4, characterized in that the locally limited shortenings of the spacing are realized by means of a helical electrode (51) and at least one elongated counterelectrode (52a-52d), the counter electrode(s) (52a-52d) being arranged essentially parallel to the longitudinal axis of the helical electrode (51).
11. Radiation source according to Claim 10, characterized in that the pitch (h) of the helical electrode (51) corresponds at least to the maximum transverse extent (f) of the individual discharges (54a).
12. Radiation source according to Claim 4, characterized in that the ratio between the value of the local shortening of the spacing (l) and the striking distance (w) for the individual discharges is in the range of between approximately 0.1 and 0.4.
13. Radiation source according to Claim 1, characterized in that the design through which the sites for local field amplification are created is such that the dielectric material has appropriately locally limited shortenings of the thickness of the dielectric layer.
14. Radiation source according to Claim 1, characterized in that the design through which the sites for local field amplification are created is such that the dielectric material has appropriately locally limited increases in the relative dielectric constant.
15. Radiation system having a radiation source (36) and a voltage source (37), which voltage source (37) is capable of supplying a sequence of voltage pulses, the individual voltage pulses being separated from one another by off periods, which radiation source (36) is suitable for a dielectrically obstructed, pulsed discharge, the radiation source (36) having an at least partially transparent discharge vessel, which is closed (38) and filled with a gas filling, or which is open and is flowed through by a gas or gas mixture, which discharge vessel is made from an electrically nonconductive material and has electrodes (39; 41a; 41b), at least the electrodes of one polarity (41a; 41b) being separated from the interior of the discharge vessel by dielectric material (38), which electrodes (39; 41a; 41b) are connected to the voltage source (37), and during the pulsed operation an electric field being generated in each case between the electrodes of opposite polarity, characterized in that the design of at least the electrodes of one polarity and/or of the dielectric material creates a multiplicity of sites for local amplification of the electric field in such a way that during the operation of the voltage source (37) one or more dielectrically obstructed individual discharges are generated exclusively at these sites, at most one individual discharge being generated per site.

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