EP2394291A1

EP2394291A1 - High-pressure discharge lamp

Info

Publication number: EP2394291A1
Application number: EP10721803A
Authority: EP
Inventors: Klaus Stockwald
Original assignee: Osram GmbH
Current assignee: Osram GmbH
Priority date: 2009-06-22
Filing date: 2010-05-27
Publication date: 2011-12-14
Also published as: CN102804330A; US20120146497A1; DE102009029867A1; WO2010149458A1; JP2012531022A

Abstract

The invention relates to a high-pressure discharge lamp, wherein a fin-like structure (10 is mounted on each of the ends of the ceramic discharge vessel, serving to cool the discharge vessel. The fins comprise undercuts and are preferably combined with an ignition aid.

Description

Title: High pressure discharge lamp

Technical area

The invention relates to a high-pressure discharge lamp according to the preamble of claim 1. Such lamps are in particular high-pressure discharge lamps with a ceramic discharge vessel for general lighting.

State of the art

US Pat. No. 4,970,431 discloses a sodium high-pressure discharge lamp in which the bulb of the discharge vessel is made of ceramic. At the cylindrical ends of the discharge vessel fin-like extensions are attached, which are used for heat dissipation.

WO2007 / 082885 discloses ceramic discharge vessels which have fin-like projections at the end of the ceramic discharge vessel. However, these do not have a specific shape.

Presentation of the invention

The object of the present invention is to provide a high-pressure discharge lamp whose discharge vessel is effectively cooled.

This object is achieved by the characterizing features of claim 1.

Particularly advantageous embodiments can be found in the dependent claims. The high pressure discharge lamp is equipped with a ceramic elongate discharge vessel. The discharge vessel defines a lamp axis and has a central portion and two end portions, each sealed by seals, with electrodes anchored in the seals extending into the discharge volume enveloped by the discharge vessel, and also a filling, preferably containing metal halides, in the Discharge volume is housed. In this case, sits on at least one end portion of a fin-like structure which extends axially parallel to the outside and is substantially spaced from the seal itself. The seals are tubular capillaries or plug-shaped seals. The use of ceramic gradient cermets, longitudinally or axially as known per se, is also possible for this purpose.

In the case of ceramic high-pressure lamps with increased burner load in the back of the electrode (for example due to altered convection currents along the colder burner interior areas), the outer surface for radiation cooling can be dimensioned to set a cold spot temperature. For the flexible adjustment of the surface radiating in the NIR, axis-parallel fin structures (for example fin-like, integral projections on the burner vessel) have proven to be favorable, because they are relatively easy to produce and can be dimensioned in a wide range of surface area.

Depending on the length / diameter extent of the burner end, the structures must be extended to the closure area become. The longitudinal fin structure acts as a thermal bridge to the burner end.

The advantage of fins or fins is their targeted adaptability. The wall thicknesses of the fin structures can be specifically adapted, in particular reduced, and the number of fins can be increased in order to achieve a sufficient cooling effect with simultaneously limited heat flow in all cases.

It turns out that the number of fins only up to a number of 3 to a maximum of 8 to a meaningful radiation characteristic, which acts cooling, and that the wall thickness of the fins can not be made arbitrarily thin. The locally effective

Cooling effect is distributed over a comparatively large end area. It should preferably a

Wall thickness of about 25-50% of the average occurring at the burner wall thickness, in particular of the central part, are not exceeded, in order to produce larger quantities of production technology with little waste.

The cooling effect is decisively improved in that the fins are designed with an undercut such that the burner end facing the end of the fin structure does not make contact with the closure wall, so the capillary or the stopper has. This avoids that over the axial length LH of the undercut a heat flow passes to the seal or the burner end. Thus, a loss-determining heat transfer through the fin in this area is avoided. This results in a relatively effective cooling in the region of the attachment point of the extended cooling surfaces of these fins or fins. The axial length of the attachment point is denoted by LA.

Advantages :

1. Flexible design of the approach zone of the integral cooling elements (fin structures).

2. Wall thickness of the cooling structure need not be significantly reduced because the cooling element does not automatically act as a thermal bridge, but only in the area of the attachment point.

3. A shorter burner zone can be cooled more effectively via the fin attachment, thus setting a lesser efficiency-reducing heat flow into the seal ends.

4. In the region of the undercut, preferably an ignition aid contact can be made on the end closure surface (for example ignition auxiliary contact), which has a small distance from the internal power supply. This distance is essentially given by the wall thickness of the seal. It is preferably in the range 0.6 to 1, 1 mm.

In the case of ceramic high-pressure lamps with increased burner load in the back of the electrode (eg due to altered convection currents along the colder burner interior areas), the outer surface for radiation cooling can be dimensioned to set a cold spot temperature. For flexible adjustment of the surface radiating in the NIR, axis-parallel fin structures (eg fin-like, integral approaches to the burner vessel) proved to be favorable, which are relatively easy to produce.

Depending on the length / diameter extent of the burner end, the structures must be extended to the closure area. Here, the longitudinal fin structure acts as

Thermal bridge to the burner end. The burner end is preferably designed so that it tapers for sealing, so that here Finns can be well recognized.

The application of the invention relates in particular to highly efficient ceramic lamps with very high luminous efficiencies and high radiation conversion efficiency.

In particular, high wall loads of the burner surface of 35-45 W / cm ^{2 are achieved} on the inner surface. Further, gas convection is altered by stable adjustment and use of longitudinal or associated acoustic resonances derived therefrom, as known in the art, such that enhanced suppression of plasma segregation by diffusion processes occurs. Gas flows from the center of the developing high-pressure plasma are directed to the inner end surfaces in the rear electrode space.

This leads to an increased heating of the cold-spot acting end surfaces.

It turns out that especially for certain, in particular Na / Ce-based

Metallhalogenidfüllungen to achieve particularly high Luminous efficiencies, ie high radiation conversion efficiency (efficiency of the generation of visible radiation in the visual spectral range in relation to the input electrical power) and visual efficiency (adjustment of the spectral radiation distribution to the eye sensitivity, ie lumen output in relation to the radiation power generated in the visual spectral range) a certain temperature range of End surfaces to adjust the resulting metal halide vapor pressure is necessary and should not be exceeded.

This is essentially in the range between 980-1080 ⁰ C. In particular, typically less than 1050 ⁰ C, in the aforementioned average wall loads.

Luminous efficiencies of up to 160 lm / W can be achieved with very good color rendering of> 80.

With appropriate design of the burner vessel and the filling composition can be

Achieve discharge efficiencies of> 50% (conversion of electrical power into visual radiation) and visual efficiencies of> 320 lm / W _vls for the lamp _spectrum .

The burner vessels used are burners with a high aspect ratio of inner length and inner diameter (expressed by an aspect ratio of in particular 3 to 8), which then also leads to an increased plasma arc length between the electrode tips and leads to corresponding ignition difficulties.

The surface usable for end cooling via NIR radiation is located substantially in the region of Burner, which encloses the electrode back space, and in the subsequent part of the closure end construction.

Eien any surface enlargement can be done by increasing the mass of the closure zone, but at the same time means an increase in the cross-sectional area for leading into the closure ends heat flow.

Although enlarged projections for surface enlargement with circumferential heat accumulation grooves (annular cooling) are suitable for increased NIR radiation while simultaneously reducing the amount of heat flowing away to the ends, they produce increased shadowing of the light intensity radiated into the end zones and thus lead to an efficiency increase. Reduction.

Achsparallel running fin structures have been found to be the best possible and easiest to produce surface structure for local NIR surface cooling.

The increased arc length in the discharge vessel with high aspect ratio leads to an increased demand

Ignition field strength for the initiation of lamp operation. at

Lamps with ceramic lamp vessel (typically made of

AI2O3), the seals are end constructions, which are formed as thin tubular closure zones. To Zündfeldstärkeerniedrigung and initiation of the ignition can by capacitively coupled auxiliary discharges in the

End structures are initiated the ignition. For this purpose, contacting in the immediate vicinity of at least one electrode or power supply to the electrode tip is the most favorable. When using Zündhilfungskontaktierungen (wires and / or conductive coatings) the best possible contact in the area of the electrode shaft is the most favorable.

Therefore, attaching a Zünddrahtschlaufe or a coating in the foremost region, preferably first third of the lengths LH, the undercut of the fin structure is particularly favorable, since at this point inside the capillary the smallest inner gap width occurs in the gas space.

Alternatively (possibly in addition to the above-mentioned methods), interconnects running between the fins and bridging the burner length (for example made of cermet, platinum or conductive carbon layers which extend into the region of the undercut) may be used as ignition aids.

The fin undercut is particularly effective when the undercut length LH is at least the size of the minimum fin wall thickness WS, preferably a multiple thereof, in particular 3 to 10 times the wall thickness WS.

A particularly advantageous embodiment of the invention lies in the consideration of the following aspects:

- The seal is a capillary (tubular cylindrical) with implementation, the electrode shaft is partially recessed in the capillary and with a certain minimum distance between the shaft and capillary is maintained. It should be at least 10 μm and should not exceed 50 μm. - At least three fins are attached to the end of the discharge vessel, which have an undercut (preferably parallel to the capillary);

- The root of the approach of the undercut (rear root) is in the area of the electrode shaft in

Area of the seal. The Midnestabstand from the opening of the capillary to the discharge volume is 1 mm in the direction of implementation; Preferably, this rear root is in the rearmost third of the shaft, but still spaced from the end of the shaft; the rear part of the shaft can be reinforced with a helix, etc.

In a particularly particularly preferred embodiment, the undercut is used for a starting aid. It is true that an ignition aid (realized as a wire or line) in the area between the rear root and the end of the shaft acts so that sufficient to ignite increased electric field strength is generated.

Although the connection between the fin and the discharge vessel itself may lie to a small extent on the capillary, this is only in the sense that the thermal bridge is not significantly displaced thereby onto the capillary. Looking at the axial length of the entire lug length LA of the fin, the lying on the capillary portion should preferably at most up to 40%, preferably not more than 25%, the axial length LA make up,. Best results are achieved if this part does not exceed 15%.

In particular, the invention relates to lamps with an increased aspect ratio of up to 8 or even lamps which have been shortened Have structures for the seals. The end region preferably has a tapering inner contour in the electrode rear space. That is, the central portion has a maximum or constant inner diameter ID and the end portions have a smaller inner diameter to which they taper.

The fin-like structure is preferably formed around the electrode construction or at the end region. The discharge vessel typically consists of aluminum-containing ceramics such as PCA or also YAG, AlN, or A1YO3. A freestanding cooling structure substantially spaced from the seal is used, which in particular is itself formed of ceramic and, in particular, is an integral part of the end region.

The invention is particularly suitable for highly loaded metal halide lamps in which the ratio between the inner length IL and the maximum inner diameter ID of the discharge vessel, the so-called aspect ratio IL / ID, is between 1.5 and 8.

It can be seen that in these torch molds, when they have tapered end portions running towards the end, local end cooling is effective. This improves the filling distribution in the burner because the filling preferably deposits in the region behind the electrodes in the so-called electrode back space and thus leads to improved color stability and also to increased light output. Especially when using fillings containing Na and / or Ce, extremely high luminous efficiencies with high color rendering can be achieved. It turns out that if a suitable operating Method, for example DE-A 102004004829, the performance curve of the lamp can be favorably influenced, so that a luminous efficacy of more than 150 lm / W can be achieved while maintaining a color rendering index Ra> 80 long-term stable.

Irrespective of the wall thickness distribution between the electrodes, the temperature gradient of highly loaded burners, which typically reach a wall load of at least 30 W / cm ² in the region of the axial length between the electrodes, can be influenced and adjusted by the choice of the starting point for the cooling structure. Thus, the constancy of the color temperature and the yield of the resulting metal halide lamp can be significantly improved.

By avoiding contact between the cooling structure and the seal (in this case, an electrode passage capillary), effective cooling is ensured at the point of attachment of the cooling structure and, at the same time, heat flow to the seal is avoided. This reduces the losses at the ends and increases the temperature gradient in the region of the seal.

This applies in particular to metal halide lamps which contain at least one of the halides of Ce, Pr or Nd, in particular together with halides of Na and / or Li. Otherwise, color temperature fluctuations due to distillation effects occur here.

Preference is also given to the application in lamps with a high aspect ratio of 2 to 6 and lamps with targeted excitation of acoustic resonances, the repeal used by longitudinal segregation in the vertical burning position.

As the material of the piston PCA or any other conventional ceramic can be used. The choice of filling is in principle subject to no particular restriction.

Depending on the filling composition, discharge vessels for high-pressure lamps with approximately uniform wall thickness distribution and slim-running end shapes have hitherto exhibited partially high color spread due to the strong distribution of the metal halide filling in the interior of the discharge vessel. Typically, the filling condenses in the area behind a line, which is determined by projection of the electrode tip on the inner burner surface. The filling position on a zone of the surface in the interior of the discharge vessel, which corresponds to a narrow temperature range, and in the residual volumes of the capillaries is not yet sufficiently accurately adjustable.

Previous discharge vessels often have a shape with increased wall thickness at the end faces, e.g. in cylindrical burner shapes, thereby creating an enlarged end surface. Another problem is the increased by the wall thickness-dependent specific emission coefficient of the ceramic radiation of IR radiation during operation of the discharge vessel in the evacuated or gas-filled outer envelope.

In this way, an occupancy of the inner wall with filling concentrate is produced by a heat sink effect at the end of the discharge vessel, which determines the vapor pressure of the metal halides used in the discharge vessel in such a way that that in ceramic lamp systems, a satisfactory value of the dispersion of the color temperature of at most 75 K for larger groups of lamps the same operating performance is adjustable.

Spherical discharge vessels, or those with hemispherical end shapes or conically tapering end shapes or elliptically shaped end shapes and cylindrical center part with a relatively high aspect ratio of IL / ID of about 1.5 to 8, result in particularly serious problems. Due to the tapered transition into the capillary, partially insufficient cooling effects at the end of the discharge vessel and thus an insufficient determination of the temperature, which is not sufficient for a precise filling deposit in a narrow temperature range of the inner wall.

In the case of a burner geometry which has no cooling structure, see FIG. 8 of WO2007 / 082885, a very small temperature gradient is produced by the burner body to the closure structure, which results in preferential distillation of the filling in the feedthrough structure.

Another known solution (Figure 10) are simple fins or fin-like formations. Although these increase the cooling surface, they form a thermal bridge between the burner end and the seal, in particular if short cooling lengths are preferred and the cooling structure has an increased number of cooling ribs. These disadvantages are avoided by the cooling structure according to the invention.

In a preferred embodiment of the invention, the cooling structure is wholly or partly covered with a coating. provided. It consists of a material having in the near infrared (NIR), in particular in the wavelength range between 1 and 3 microns, compared to the ceramic material of the cooling structure an increased hemispherical emissivity ε in the temperature range 650-1000 ⁰ C. The coating should preferably be applied in the region of the transition between the end of the discharge vessel and the seal.

High-temperature-resistant coatings with hemispherical emission coefficients ε, preferably ε ≥ 0.6, are suitable as coating materials. Among them is graphite, mixtures of A12O3 with graphite, mixtures of A12O3 with carbides of the metals Ti, Ta, Hf, Zr, as well as of semi-metals such as Si. Also suitable are mixtures which additionally contain other metals for adjusting any desired electrical conductivity.

Of course, both measures can be suitably combined with each other, so that a part of the surface radiation increase takes place via an enlargement of the surface by the fin-like structure and at the same time a part by the coating of parts of this fin-like structure or of the adjacent colder sealing regions.

Overall, there are a number of advantages when using a fin-like structure in the case of ceramic discharge vessels:

1. Effective cooling, which can be pinpointed; 2. Reduction of longitudinal heat flow into the seal;

3. significantly increased flexibility of the surface adjustment in the end region;

4. reduction of shading effects in the solid angle range of the electrode feed;

5. Adjustability of effective local thermostatic effect by means of relatively small surface areas.

These properties are particularly important for highly loaded forms of discharge vessels with a small overall surface and possibly increased aspect ratio, since under these conditions a local cooling by heat flow over relatively large wall cross-sectional areas becomes difficult.

The total mass of the discharge vessel increases only insignificantly by this type of fin-like structure and thus remains below a critical value that would adversely affect the start-up behavior of the lamp during ignition. There is thus a sophisticated compromise between good ignition and effective cooling. This measure allows a very high color stability under the conscious acceptance of a bad isotherm. This is done in departure from the previous objective of the best possible isotherm and allows to precisely determine the zone of condensation of the filling by deliberately designing a temperature gradient.

The cooling effect can be controlled in particular by the maximum radial height of the fin-like structure, as ever according to approach level the derivative is carried out from another temperature level.

A particular advantage of such a fin-like structure is that not only does it effectively cool, but it is also easy to manufacture using modern manufacturing techniques such as injection molding, slip casting or rapid prototyping.

Brief description of the drawings

In the following, the invention will be explained in more detail with reference to several embodiments. The figures show:

1 shows a high-pressure discharge lamp with discharge vessel;

FIG. 2 shows a detail of the discharge vessel from FIG. 1 in perspective (FIG. 2 a) and in a longitudinal section (FIG. 2 b);

FIG. 3 shows a section through the end region of FIG. 2; FIG.

FIG. 4 shows a further exemplary embodiment of an end region of a discharge vessel with ignition strip;

5 shows a further embodiment of an end region of a discharge vessel with ignition wire;

FIG. 6 shows a section through the end region of FIG. 5.

Preferred embodiment of the invention

1 shows a metal halide lamp 1. It consists of a tubular discharge vessel 2 made of ceramic, in two electrodes are inserted (not visible). The discharge vessel has a central part 5 and two ends 4. At the ends sit two seals 6, which are designed as capillaries. Preferably, the discharge vessel and the seals are integrally made of a material such as PCA.

The discharge vessel 2 is surrounded by an outer bulb 7, which terminates a base 8. The discharge vessel 2 is in the outer bulb by means of a frame which includes a short and long power supply 11 a and II b, supported. At the burner end sits in each case a fin-like structure 10, which rotates about the seal 6.

Figure 2a shows a fin-like structure 10 in perspective view in conjunction with a capillary 6. Instead of a capillary, a short stopper can be used.

Figure 2b and 2c shows a longitudinal section of a discharge vessel, each rotated by 90 °. The fin-like structure 10 of four fins 11 is integrally formed on the outside in the tapered end portion 5 of the discharge vessel 2 and extends in the entire axial extent LF far in the direction of the capillary 6. The fin or fin 11 has a projection or bridge portion 12 with the axial Length LA connecting it to the end of the discharge vessel. This approach essentially extends beyond the tapering end 5. The front, near-discharge root point WF of the fin does not necessarily attach to the outer wall of the middle part of the discharge vessel, but it can also deeper, only behind the center part, in the region of the tapered End 5, set. The rear discharge-distant root point WH sits here at the end of the tapered area, where, for example, the capillary begins. This posterior root point WH may lie on the beginning of the capillary, in particular on the front tenth of the length of the capillary. It is important that the rear root point WH axially at least 1 mm distance from the end of the inner volume, here represented by the end face 13, has. This distance is denoted by DD in FIG. 2b.

In particular, the front root point WF of the fin-like structure 10 sets at the tapered end portion and extends axially outwardly, with the bridge portion terminating at about the level of the capillary. The bridge area may still extend slightly over the capillary. The fin 11 is provided with an undercut 15. The root WH of the undercut sits where the bridge area ends. In most cases, the edge 16 of the undercut is parallel to the capillary 6, so that its distance from the capillary is constant, which facilitates the production. However, it is also possible that the distance increases somewhat outwardly, preferably an angle of 1 to 10 ° is preferred here against the axis, which facilitates demolding, without the desired cooling effect suffers, on the largest possible total area per mm Finn length is based.

The axial length LH of the undercut is selected as far as possible so that it corresponds to at least 20% of the axial length LA of the projection or bridge region; preferably much more, it is preferably in a range of 35 to 150% of this length, in particular 50 to 110%. In this way, the greatest possible abstraction lende surface, namely the two side surfaces of a plate-like fin or fin 11, achieved, which is decoupled from the lug length LA of the fin and also the place of action of this approach. The longer the LA, the more effective the cooling compared to the cooling that a conventional fin achieves without undercutting.

FIG. 2d shows a section which illustrates the possibility of a differently selected radial length LR of the fin. Here a fin 10 is picked out, in the dashed line three different conceivable heights LRl, LR2 and LR3 are located. The greater the LR chosen, the shorter the axial total length of the fin can be to achieve approximately the same radiating surface.

A particularly effective cooling is based, according to FIG. 3, on the fact that the leadthrough 13 is completely sunk in the capillary 6 on the discharge side, the electrode shaft 14 extending into a depth ET into the capillary. In this case, a minimum distance of 20 microns between the capillary and the electrode shaft is maintained, so that the filling can extend into this gap. The rear root WH, which is at the same time the root of the neck of the undercut, should still lie in the area of the electrode shaft 14. Preferably, it lies in the last third of the length of the shaft, facing away from the discharge. But it should not be in the area of implementation 13. However, this root should still be arranged somewhat spaced from the rear end of the shaft, as a rule, a distance of 5 to 35% of the length of ET is well suited. The shaft still has a coil 17 in the rear area, which minimizes the gap. The electrode shaft has just in height the Zündhilfe a thickened part 17, so that here the gap to the capillary has an optimal width. In this way, ignition aid and cooling structure work together optimally.

In general, the root WH may well also lie in the tapering end region of the discharge vessel. Essential is their positioning relative to the rear end of the electrode shaft.

FIG. 4 shows a fin-like structure 10, which is advantageously combined with an ignition aid 18 on the outside of the discharge vessel. The ignition aid 18 is a ceramic primer on the outside of the discharge vessel, which runs parallel to the axis of the discharge vessel. For example, this is a sintered firing strip from a W-A12O3 cermet. Basically, such ignition strips are already known, see DE-A 199 01 987 and DE-A 199 11 727. the Zündstrich 18 extends from a fin-like structure 10 at a first end of the discharge vessel to the fin-like structure 10 at the second end. The primer 18 begins and ends just near the root WH of a fin, and it travels along the foot of the fin 11 along the bridge portion 12 so that the primer in this region is effectively protected by the fin 11 against damage during assembly.

Finally, it is also possible to combine the fin-type structure 10 with an auxiliary ignition wire 20, see FIG. 5 and also FIG. 3. In this case, the ignition wire 20 is quasi formed into a loop which projects into the undercut 21 of the fin 11 in the vicinity of rear root is fitted, whereby it is fixed at the same time. On In this way, the cooling mechanism and the ignition mechanism interact optimally. In this case, the gap width of the undercut can advantageously be selected just so that the Zündhilfsdraht the gap width or possibly also the wire thickness of the gap width is adjusted. This ensures the correct fit of the wire at the most effective point for ignition and also a fixation is not separately necessary. It may even be provided with corresponding notches in the wire to lock it in the wreath of the fins 11 of a structure 10 as best as possible.

FIG. 6 shows a plan view, FIG. 6a, and a detailed illustration, FIG. 6b, of a discharge vessel 30, in which the seal is realized by a capillary. There are four fins 31 evenly distributed around the circumference. Each fin 31 has an initial wall thickness Wl in the area of the front root point WV. The wall thickness of the fin 31 tapers rearwardly to a wall thickness W2, which is only 40 to 80% of the wall thickness Wl. The upper edge 32 of the fin is slightly bevelled.

If one were to use a ring-like structure instead of the fin-like structure, the cooling effect on the surface zone of the burner vessel would be more uniform, but the radiating surface would be considerably lower in relative terms, and a combination with a starting aid would not make sense. An ignition aid would be a hindrance in a ring-like structure rather.

Preferably, the radial height LR of the plate-like fin 11 is at least 50% of the difference between capillary fin. Re and maximum outer radius of the central region of the discharge vessel.

The distance between the fins should preferably be at least three to five times the mean wall thickness. The average wall thickness WM of a fin should in particular be at most 1/10 of the circumference, based on the maximum outer radius of the discharge vessel. This is to ensure that the radiation of one fin does not heat up the nearest fin.

In the case of an axially variable wall thickness, however, an average wall thickness is defined. For example, in the case of FIG. 6, WM = (Wl + W2) / 2.

The fins are usually plate-like, since they are the easiest to produce. However, more complicated structures of the fin are not excluded. The fins are designed substantially plate-like with an axial length LF = LA + LH and with a maximum height LR. In particular, they can also be terraced with different heights LR of subsections.

Essential features of the invention in the form of a numbered list are:

A high pressure discharge lamp comprising a ceramic longitudinally extending discharge vessel having an axis and having a central center portion and two tapered ends and an axis, the ends being closed by seals, which are preferably made as capillaries, electrode systems being used in the discharge. Seals are anchored, wherein a filling containing metal halides, housed in the discharge vessel, characterized in that at least one tapered end of a finned structure consisting of at least three fins sits, which has a neck with a front root point directly on the discharge vessel and a rear root point from which an undercut extends in the direction of the seal, wherein the axial length of the lug LA is selected and wherein the axial length LH of the undercut is at least 30% of LA.

2. High-pressure discharge lamp according to claim 1, character- ized in that the fins are designed substantially plate- tenartig with an axial length LF = LA + LH and with a maximum height LR.

3. High-pressure discharge lamp according to claim 1, character- ized in that the axial length LH is 80% to 180% of LA.

4. High-pressure discharge lamp according to claim 1, character- ized in that the electrode system has a shaft and a passage, wherein the shaft extends over a length ET to the capillary, wherein between the shaft and capillary a gap remains and wherein the rear root point in the area the length ET is.

5. High-pressure discharge lamp according to claim 4, character- ized in that the rear root point is located in the rear third of the length ET. 6. High-pressure discharge lamp according to claim 1, character- ized in that a discharge aid is attached to the discharge vessel, which generates a high electrical ignition strength sufficient locally for ignition on a local electrode system.

7. High-pressure discharge lamp according to claim 6, character- ized in that the starting aid is a Zündstrich, which extends axially outside the discharge vessel and ends in the immediate vicinity of the rear root point.

8. High-pressure discharge lamp according to claim 1, character- ized in that the ignition aid is a Zündhilfsdraht forming a loop which is fixed in the undercut.

Claims

claims

A high pressure discharge lamp comprising a ceramic elongated discharge vessel having an axis and a center central portion and two tapered ends and an axis, the ends being sealed by seals, preferably capillaries, with electrode systems anchored in the seals , wherein a filling containing metal halides, is housed in the discharge vessel, characterized in that at least one tapered end of a consisting of at least three fins fin-like structure sits, which has a neck with a front root point directly on the discharge vessel and with a rear root point, from which an undercut extends in the direction of the seal, wherein the axial length of the lug LA is selected and wherein the axial length LH of the undercut is at least 30% of LA.

2. High-pressure discharge lamp according to claim 1, character- ized in that the fins are designed substantially plate-like with an axial length LF = LA + LH and with a maximum height LR.

4. High-pressure discharge lamp according to claim 1, character- ized in that the electrode system has a shaft and a passage, wherein the shaft via a length ET extends into the capillary, wherein between the shaft and capillary a gap remains and wherein the rear root point is in the range of the length ET.

5. High-pressure discharge lamp according to claim 4, character- ized in that the rear root point is located in the rear third of the length ET.

6. High-pressure discharge lamp according to claim 1, characterized in that a discharge aid is attached to the discharge vessel, which generates a high sufficient for ignition electric field strength locally on an electrode system.