Lamp comprising a conductor embedded in the quartz glass envelope of the lamp

Abstract

A lamp comprising an envelope (1) of quartz glass surrounding the light source of the lamp is described, wherein an electric conductor (8), for example, an electrode rod, is at least partly embedded in the quartz glass material of the envelope (1). At the conductor (8) is provided with protrusions (15) forming a brush-like structure at this surface. The protrusions (15) preferably have an average length of between 10 m and 35 m.

Claims

1. A lamp, comprising: an envelope of a quartz glass material defining a discharge space; and an electric conductor that is at least partly embedded in the quartz glass material of the envelope, wherein the electric conductor comprises: a surface; one or more recesses in at least a portion of the surface of the electric conductor; and flexible dendritic protrusions on the portion of the surface of the electric conductor at edges of the one or more recesses, the flexible dendritic protrusions forming a brush-like structure on the portion of the surface of the electric conductor, wherein an average material density of the brush-like structure is between 20% and 80% of a solid structure of the same material, thereby providing a mechanical flexibility and deformation potential that is substantially higher than that of the solid structure of the same material.

2. A lamp as claimed in claim 1, wherein the flexible dendritic protrusions have an average length of between 10 m and 35 m.

3. A lamp as claimed in claim 1, wherein the brush-like structure on the surface of the electric conductor extends in a zone of less than 25 m wide.

4. A lamp as claimed in claim 1, wherein the portion of the surface of the electric conductor is treated by a laser beam by which material of the electric conductor is locally detached and forms the flexible dendritic protrusions on the portion of the surface of the electric conductor.

5. A lamp as claimed in claim 1, wherein the material of the electric conductor is tungsten, tungsten alloy, or doped tungsten.

6. A lamp as claimed in claim 1, wherein the material of the electric conductor is a metal other than tungsten from the group of refractory metals such as Mo, Ta, Re, In, in a pure, doped, or alloyed quality.

7. A lamp as claimed in claim 1, wherein the electric conductor is an electrode rod which is partly embedded in the quartz glass material of the envelope.

8. A lamp as claimed in claim 7, wherein the lamp is a high-pressure gas discharge lamp, and the electrode rod is embedded in a sealed portion of the envelope.

9. A lamp as claimed in claim 1, wherein the one or more recesses comprise one or more helical grooves or pits.

10. A lamp as claimed in claim 1, wherein the one or more recesses have a width A and a pitch B, the pitch B is greater than the width A to provide areas of the surface between recesses, the flexible dendritic protrusions are formed at the edges of the one or more recesses in the areas of the surface between the recesses.

11. A method of manufacturing a lamp, comprising: rotating an electrode rod about its longitudinal axis; and directing one or more laser beam pulses onto at least a portion of a surface of the electrode rod during said rotating, by which material of the electrode rod is locally detached and forms one or more recesses in the portion of the surface of the electrode rod and flexible dendritic protrusions on the portion of the surface of the electrode rod at edges of the one or more recesses, the flexible dendritic protrusions forming a brush-like structure on the portion of the surface of the electrode rod, wherein an average material density of the brush-like structure is between 20% and 80% of a solid structure of the same material, thereby providing a mechanical flexibility and deformation potential that is substantially higher than that of the solid structure of the same material.

12. A method as claimed in claim 11, wherein said directing one or more laser beam pulses forms one or more helical recesses in the portion of the surface of the electrode rod.

13. A method as claimed in claim 12, wherein the one or more helical recesses comprise one or more helical grooves or pits.

14. A method as claimed in claim 11, further comprising applying a gas flow during said directing one or more laser beam pulses.

15. A method as claimed in claim 11, wherein the one or more recesses have a width A and a pitch B, the pitch B is greater than the width A to provide areas of the surface between recesses, the flexible dendritic protrusions are formed at the edges of the one or more recesses in the areas of the surface between the recesses.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the drawings,

(2) FIG. 1 shows a gas discharge lamp;

(3) FIG. 2 is a schematic sectional view of a part of the lamp;

(4) FIG. 3 shows the brush-like surface of the electrode rod;

(5) FIG. 4 is a schematic sectional view of the surface of the electrode rod; and

(6) FIG. 5 shows the brush-like surface of another electrode rod.

(7) The Figures are diagrammatic representations, showing only parts that are relevant to the invention.

DESCRIPTION OF EMBODIMENTS

(8) FIG. 1 shows a gas discharge lamp having an envelope 1 of quartz glass. The envelope 1 accommodates a gas discharge space 2 which is filled with, for example, mercury, sodium iodide, scandium iodide, xenon and/or other gases. The envelope 1 is surrounded by a transparent outer envelope 3.

(9) The envelope 1 of the lamp is provided with two sealed portions 4, 5 at opposite ends of the envelope 1. Each sealed portion 4, 5 comprises a molybdenum foil member 6, 7 embedded in the quartz glass material of the envelope 1. Each molybdenum foil member 6, 7 is connected to the end of an electrode rod 8, 9, and the other end of each electrode rod 8, 9 projects into the gas discharge space 2. The electrode rods 8, 9 are made of tungsten which may comprise an additive, e.g. ThO.sub.2, at least at their surfaces.

(10) Each of the two molybdenum foil members 6, 7 is also connected to lead-out wires 10, 11, respectively, which project outside the quartz glass material of the envelope 1, so that they can be connected to means for supplying electric power. The electric power is supplied to the electrode rods 8, 9 through the molybdenum foil members 6, 7.

(11) The lamp is provided with a cap 12 in order to connect the lamp to a lamp holder. The cap 12 of the lamp is provided with contact elements (not shown) to be connected to corresponding contact members in the lamp holder, so that electric power can be supplied through these contact members from the lamp holder to the lamp. Lead-out wire 10 is connected to one of said contact elements and the other contact element is connected to an electric current guiding rod 13 in order to supply electric power to lead-out wire 11.

(12) FIG. 2 is a schematic sectional, exploded view of a part of the lamp, which part is indicated by circle 17 in FIG. 1. The sealed portion 4 of the quartz glass material of the envelope 1 of the lamp comprises the molybdenum foil member 6 which is connected to the end of electrode rod 8. The other end of electrode rod 8 projects into the gas discharge space 2 of the envelope 1 of the lamp.

(13) A part of the cylindrical electrode rod 8 is embedded in the sealed portion 4 of the quartz glass envelope 1 of the lamp. The surface of this part of the electrode rod 8 is provided with a helical groove 14 which is indicated in FIG. 2 by backward-slashed lines. Protrusions are present along the two edges of the groove 14 are, so that a brush-like structure at the surface of the electrode rod 8 is obtained.

(14) FIG. 3 represents a portion of the electrode rod 8, wherein the brush-like structure of the surface of the electrode rod 8 is shown. The brush-like structure comprises hair-like protrusions 15 of the material of the electrode rod 8, which protrusions are located at the edge of the helical groove 14 in the cylindrical surface of the electrode rod 8.

(15) The brush-like structure extends in a zone of less than 25 m wide, aside the groove 14, and is typically 15 m to 25 m high, with a dendritic, fibrous and/or conical shape. The protrusions 15 in the zone have an average material density of between 20% and 80%, while the dendritic, fibrous or conical shape has a material density close to 100%. The protrusions 15 have such a height over cross-section ratio that their mechanical flexibility and deformation potential is substantially higher than that of a solid structure of the same dimension.

(16) The brush-like structure shown in FIG. 3 is created by means of an operation with a laser beam directed onto the surface of the electrode rod 8, while the electrode rod 8 is rotating about its axis, so that the helical groove 14 is obtained. In this way, the material of the electrode rod 8 is locally detached and forms the hair-like protrusions 15 of the brush-like structure as shown in FIG. 3.

(17) FIG. 4 shows diagrammatically the grooves 14 and the protrusions 15. In this example, the grooves 14 have a width A of about 25 m and a depth C of about 75 m. The distance B between the grooves 14 is about 100 m, and the protrusions 15 have a length D (i.e. height) of about 20 m.

(18) FIG. 5 shows a cylindrical electrode rod 8 whose surface is treated by means of a pulsating laser beam, so that pits 18 are created in the surface of the electrode rod 8, and the protrusions 15 are located at the edges of the pits 18. The operation is performed by a Q-switched nanosecond YAG laser IR 1064 nm. The pulse length is about 16 ns and the pulse frequency is 33 Hz. The average power is 9.6 W (80% of a 12 W system). The pits have a dimension of about 25 m. During the operation, the electrode rod 8 rotates at a speed of 1000 rpm. Furthermore, a gas flow (air or argon) is applied in order to allow for traces of oxygen, as oxygen is part of the reaction to obtain the desired brush-like structure.

(19) Due to the brush-like structure of the surface of the electrode rod 8, there will be some space between the electrode rod 8 and the quartz glass material of the sealed portion 4 of the envelope 1 of the lamp, so that the electrode rod 8 can expand a little more than the quartz glass material. Furthermore, due to the brush-like structure, there is a good heat-conducting contact between the material of the electrode rod 8 and the quartz glass material of the sealed portion 4 of the envelope 1 of the lamp. The risk of occurrence of cracks in the quartz glass is thus considerably reduced.

(20) The embodiment of the lamp as described above is only an example of a gas discharge lamp according to the invention; many other embodiments are possible, such as embodiments wherein only some portions of the embedded part of the conductor are provided with the brush-like structure, or wherein portions of the surface of the lead-out wires are provided with the brush-like structure.