Gas discharge lamp

Abstract

A gas discharge lamp has an inner bulb with a discharge vessel with two sealing sections thereon, from which electrodes protrude into the discharge vessel, each electrically connected with a conductor in the associated sealing section to supply current to the electrodes. The lamp also has an outer bulb surrounding the discharge vessel, leaving a cavity therebetween. Close to at least one of the electrodes in or near a transitional area between the discharge vessel and the associated sealing section on an outside of the inner bulb is arranged potential-free a conductive structure which on application of a voltage to the electrodes influences the electrical field adjacent the electrodes such that a discharge arc travels from the electrode first in the direction of a wall section of the discharge vessel adjacent the electrode and then over the inside of the wall toward the other electrode.

Claims

1. A gas discharge lamp comprising: an inner bulb with a quartz glass discharge vessel and a first sealing section and a second sealing section arranged on the discharge vessel, a first electrode and a second electrode protruding from the respective first and second sealing sections into the discharge vessel which are each electrically connected in the respective first and second sealing sections with a conductor in order to supply current to the first and the second electrodes, an outer bulb which surrounds the discharge vessel leaving a cavity between the discharge vessel and the outer bulb, and a unitary conductive ring coating, the unitary conductive ring being arranged potential-free in surrounding relation about at least a portion of the first sealing section and in spaced relation from the discharge vessel on an outside of the inner bulb, said unitary conductive ring coating on said first sealing section insulated from said second sealing section, wherein the second sealing section has no conductive ring thereabout, the first sealing section ring, on application of a voltage to the first and the second electrodes, influencing the electrical field present in the area of the first electrode such that a discharge arc travels from the first electrode first in the direction of a section of a wall of the discharge vessel adjacent to the first electrode and then along the wall toward the second electrode.

2. A gas discharge lamp as claimed in claim 1, wherein the conductive ring comprises a coating applied to the inner bulb, the coating comprising small conductive areas and/or particles isolated from each other.

3. A gas discharge lamp as claimed in claim 1, wherein the cavity between the outer bulb and the discharge vessel is filled with a gas.

4. A gas discharge lamp as claimed in claim 3, wherein the gas is one of the group He, Ne, Ar, Kr, Xe, F2, Cl2, Br2, I2, N2, O2 or a mixture thereof.

5. A gas discharge lamp as claimed in claim 1, wherein a pressure in the cavity between the outer bulb and the discharge vessel lies between 0.1 kPa and 100 kPa, preferably between 40 kPa and 80 kPa.

6. A gas discharge lamp as claimed in claim 2, wherein the coating comprises palladium particles.

7. A gas discharge lamp, comprising: an inner bulb with a glass discharge vessel and a first sealing section and a second sealing section arranged at opposing ends of said discharge vessel, a first electrode and a second electrode protruding from said respective first and second sealing sections into said discharge vessel, each of said first and second electrodes electrically connected in said respective first and second sealing sections with a conductor in order to supply current to said first and second electrodes, an outer bulb which surrounds said discharge vessel leaving a cavity between said discharge vessel and said outer bulb, a unitary conductive ring coating at a transitional area between said discharge vessel and said first sealing section arranged potential-free and in surrounding relation of at least a portion of said first sealing section, said unitary conductive ring coating on said transitional area being insulated from said second sealing section, wherein said second sealing section has a transitional surface which is free of conductive material, said first sealing section ring, on application of a voltage to said first and second electrodes, influencing the electrical field present in the area of said first electrode such that a discharge arc travels from said first electrode first in the direction of a section of a wall of the discharge vessel adjacent to said first electrode and then along said wall toward said second electrode.

Description

(1) These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter. The same components are identified with identical reference numerals. In the drawings:

(2) FIG. 1 is a diagrammatic side view of a first embodiment example of a gas discharge lamp according to the invention with associated lamp holder, where the gas discharge lamp is shown in cross section,

(3) FIG. 2 is a section through the gas discharge lamp according to FIG. 1 in a first phase during ignition of the discharge arc,

(4) FIG. 3 is a section through the gas discharge lamp according to FIGS. 1 and 2 in a second phase during ignition of the discharge arc,

(5) FIG. 4 is a section through the gas discharge lamp according to FIGS. 1 to 3 in stationary mode after ignition,

(6) FIG. 5 is a top view with a section through the outer bulb in a second embodiment example of a gas discharge lamp according to the invention,

(7) FIG. 6 is a view of a gas discharge lamp according to FIG. 5 with a gas filling between the inner and outer bulbs in a first ignition phase,

(8) FIG. 7 is a top view with a section through the outer bulb in a third embodiment example of a gas discharge lamp according to the invention,

(9) FIG. 8 is a section through a fourth embodiment of a gas discharge lamp according to the invention,

(10) FIG. 9 is a top view with a section through the outer bulb in a fifth embodiment of a gas discharge lamp according to the invention.

(11) The embodiment example shown in the figureswithout restricting the invention to thisis an MPXL lamp used for preference which is constructed in the conventional manner with an inner bulb 2 and an outer bulb 10 surrounding this inner bulb 2. The inner bulb 2 here comprises the actual discharge vessel (burner) 3 of quartz glass which on two opposite sides has quartz glass end pieces 8 molded on the discharge vessel 3. Immediately adjacent to the discharge vessel 3, the quartz glass end pieces 8 are formed as sealing sections 4, 5. Electrodes 6, 7 protrude from these sealing sections 4, 5 into the discharge vessel 3. In the sealing sections the electrodes 6, 7 are each connected with a relatively thin, short conductor film section 9 which in turn is connected at the other end with a supply line 17, 18. In the area of the sealing sections 4, 5 the quartz glass end pieces 8 are crimped together so that the conductor film sections 9 are tightly enclosed in the sealing sections 4, 5. The sealing sections 4, 5 are therefore normally referred to as pinches. This ensures that the discharge vessel 3 is sealed airtight or gas-tight to the environment.

(12) In the interior 11 of the discharge vessel 3 the inert gas is under relatively high pressure. Because of this inert gas between the two electrodes 6, 7 on ignition of the lamp a discharge arc forms which then in stationary operation can be maintained with a voltage which is very low in relation to the ignition voltage. Normally the ignition voltage is of the order of 20 kV and the operating voltage for stationary operation in the area of less than 100 V.

(13) The outer bulb 10 serves primarily to screen the UV radiation occurring because of the physical processes in the discharge vessel 3 close to the desired light spectrum. Normally this outer bulb 10 is also made of quartz glass and connected at the ends with the quartz glass end pieces 8 of the inner bulb 2 through which the supply lines 17, 18 of the electrodes 6, 7 are guided outwards. The connecting points between the outer bulb 10 and the quartz glass end pieces 8 of the inner bulb 2 are normally called rolls. Preferably this connection is designed gastight and the gap 12 between the inner bulb 2 and the outer bulb 10 is filled with a gas or gas mixture, where applicable also with air.

(14) FIG. 1 shows how the lamp 1 is normally held in a base 21. The gas discharge lamp 1 is here connected via a holder 22 with the base 21 and with this forms a common lamp unit. It can thus be used in various types of headlamp which have a corresponding receptacle for the holder, in particular vehicle headlamps.

(15) As shown in FIG. 1 the supply line 17 arranged on the base side electrode 6 is guided directly to the base 21. The conductor 18 connected with the electrode 7 lying remote from the base 21 is connected with an external electrical return line 19 which runs outside the outer bulb 10 past the lamp 1 back to the base 21. This return line 19 is guided in the part running parallel to the lamp bulb 12 within an insulating ceramic tube 20 which serves for support or mechanical stabilization of the return line 19.

(16) As can be seen from FIG. 1, on the electrode 6 arranged in the vicinity of the base 21, on the outside on the inner bulb 2 directly in the transitional area between the discharge vessel 3 and the sealing section 4 in which the electrode 6 is connected with the supply line 17 with the conductor film 9 in between, is a conductive structure 13. This is a simple ring 13 of conductive material which is guided once about the inner bulb 2 along this transitional area. A top view of this conductive structure 13 is shown in FIG. 5. In FIG. 5 corresponding conductive structures 13, 13 are arranged symmetrically on the two electrodes 6, 7, where in contrast in FIG. 1 such a conductive ring 13 is arranged only about the electrode 6, close to the base, to which the high voltage is applied in the ignition process. The conductive structure 13 is insulated from other parts and thus not laid to a particular prespecified potential. The conductive ring 13 can comprise a simple coating, for example of a conductive paint such as palladium or a paint comprising individual palladium particles.

(17) This conductive ring structure 13 ensures that the ignition voltage can be reduced substantially. The action mechanism of this ring structure 13 is shown in FIGS. 2, 3 and 4. On application of an electrical voltage to the electrodes 6, 7, the ring structure 13 modifies the electrical field created in the discharge vessel 3 so that, in a first phase, a discharge arc 15 is initially established from the electrode 6, subject to a high voltage, towards an adjacent wall section of the discharge vessel 3. In a further phase, this discharge arc 15 is propagated along the inside of the wall of the discharge vessel 3 as shown in FIG. 3. When finally the discharge arc 15 has reached the opposite electrode 7, as shown in FIG. 4 in a third step the discharge arc 15 forms directly between the electrodes. Although thus the conductive structure 13 arranged according to the invention on the outside of the inner bulb 3 ensures that the discharge arc 15 is first diverted along the wall of the discharge vessel 3 instead of traveling directly along the shortest connection between the two electrodes 6, 7, the ignition voltage can be substantially reduced by this procedure. The reason is that on a surface discharge along the wall, substantially better mechanisms can be used to generate free charge carriers. In a pure volume discharge without surface contact it is considerably more difficult to generate electrons and ions. When finally the discharge arc 15 traveling along the wall generates enough free charge carriers in the inert gas, the discharge arc 15 can easily form between the two electrodes 6, 7.

(18) FIGS. 5 and 6 show a further variant of the invention which also leads to a substantial reduction in the ignition voltage. In this variant, corresponding ring structures 13, 13 showing a sufficient high conductivity are arranged about the two electrodes 6, 7. The space 12 between the inner bulb 3 and the outer bulb 10 is filled with argon or an argon mixture. The gas pressure lies below atmospheric pressure. With such a low gas pressure an ignition can occur between different potentials with relatively low voltage. As is evident from the cross sections shown in FIGS. 2 to 4, the conductive ring structures 13, 13 are arranged relatively close to the electrodes 6, 7. They are therefore capacitatively coupled with the electrodes 6, 7 concerned. If a voltage is applied to the electrodes 6, 7 this also leads to the creation of a potential difference between the two conductive ring structures 13, 13 arranged at opposite ends of the discharge vessel 3. If this potential difference is large enough, a discharge 16 occurs in the space 12 between the inner bulb 2 and the outer bulb 10 because of the relatively low gas pressure. This discharge 16 acts like a plasma antenna and causes further field changes in the discharge vessel 3 so that after the predischarge 16 in the outer bulb 10 the actual desired discharge is formed between the electrodes 6, 7. As soon as the discharge in the inner bulb 2 has ignited, the voltage between the conductive ring structures 13, 13 coupled merely capacitatively with the electrodes 6, 7 falls such that the discharge 16 in the outer bulb 10 is extinguished.

(19) FIG. 7 shows a further variant in which the two conductive ring structures 13, 13 arranged symmetrical to each other about the respective electrodes 6, 7 are connected together by a thin, electrically conductive strip 14 running over the outside of the discharge vessel 3 preferably so that the two ring structures 13, 13 always have the same potential. The conductivity of the electrically conductive strip 14 is preferably sufficiently high, so as to ensure equalisation of the potentials of the annular structures. It has been found that this structure also helps improve the ignition behaviour.

(20) In FIG. 8 a further embodiment is shown, which closely resembles the first embodiment shown in FIGS. 1 to 4. Here, however, the conductive ring structure 13 is applied to the end of the pinch 4 facing away from the discharge vessel 3, with the advantage that the temperature in that region is not so high. Furthermore, a conductive coating is used here which, as described above, comprises solitary conductive particles such as palladium.

(21) In the embodiment shown in FIG. 9, such a coating is also used. However, instead of a ring, a conductive structure 13 in the form of strip is applied on the outside of the quartz glass end piece 8, along the longitudinal axis of the lamp in the region of the pinch 4 (over the conductor film 9).

(22) Finally it is pointed out that the lamp constructions shown in the figures and the description are merely embodiment examples that can be varied by the person skilled in the art without leaving the scope of the invention.

(23) For the sake of completeness it is also pointed out that the use of the indefinite article a or an does not exclude the possibility of the features concerned also being present in multiples.