HIGH-PRESSURE DISCHARGE LAMP, IN PARTICULAR HIGH-PRESSURE SODIUM-VAPOR LAMP, WITH IMPROVED IGNITABILITY

Abstract

A high-pressure discharge lamp with a burner unit which has a discharge vessel which encloses a discharge space and in which two electrodes are arranged opposite one another, wherein the electrodes each have an electrode support and an electrode tip, wherein the electrode tips are located opposite one another to form an electric arc during operation of the high-pressure discharge lamp, wherein at least a first one of the electrodes is configured as a coil electrode which has an electrode support and an electrode coil formed by a wire wound around the electrode support, wherein an exposed end of the electrode support forms the electrode tip, and wherein the electrode coil is arranged in a tip region of the electrode support adjacent to the electrode tip in the discharge space, and wherein an antenna to which voltage can be applied is routed along an outer surface of the discharge vessel. The electrode coil of the first electrode has a protrusion that protrudes beyond the outer circumference of the electrode coil toward the antenna.

Claims

1. A high-pressure discharge lamp with a burner unit which has a discharge vessel which encloses a discharge space and in which two electrodes are arranged opposite one another, wherein the electrodes each have an electrode support and an electrode tip, wherein the electrode tips are located opposite one another to form an electric arc during operation of the high-pressure discharge lamp, wherein at least a first one of the electrodes is configured as a coil electrode which has an electrode support and an electrode coil formed by a wire wound around the electrode support, wherein an exposed end of the electrode support forms the electrode tip, and wherein the electrode coil is arranged in a tip region of the electrode support adjacent to the electrode tip in the discharge space, and wherein an antenna to which voltage can be applied is routed along an outer surface of the discharge vessel, wherein the first electrode has a protrusion that protrudes beyond the outer circumference of the electrode coil toward the antenna.

2. The high-pressure discharge lamp according to claim 1, wherein the lamp is selected from the group consisting of a metal halide lamp and a high-pressure sodium-vapor lamp, a high-pressure sodium-vapor lamp with a gas filling pressure of more than 360 mbar, a high-pressure sodium-vapor lamp with a gas filling pressure of more than 470 mbar, a high-pressure sodium-vapor lamp with a gas filling pressure of more than 580 mbar, a high-pressure sodium-vapor lamp with a gas filling pressure of more than 700 mbar, and a high-pressure sodium-vapor lamp with a gas filling pressure of 580 mbar to 850 mbar.

3. The high-pressure discharge lamp according to claim 1, wherein the protrusion has at least one of the following characteristics: it is located at a rear end region of the electrode coil facing away from the electrode tip; it is formed from a section of the wire of the electrode coil; it is formed as a wire loop; it is formed by an end section of the wire that is not wound around the electrode support; it protrudes from an outer coil layer, which is wound onto an inner coil layer at least in some sections; it protrudes beyond the outer circumference of the electrode coil by a length in the range of 0.5 mm to 1.8 mm; the free end of the protrusion is arranged close to the inner surface of the discharge vessel, but keeps a distance from it.

4. The high-pressure discharge lamp according to claim 1, wherein the antenna has at least one of the following characteristics: it is configured as a passive antenna not directly electrically connected to the electrodes; it is capacitively or resistively coupled to the electrodes; it is capacitively coupled to a lamp ignition voltage on the side of the first electrode via a capacitor unit, in particular a triple capacitor; it has a first antenna ring integral with the other sections of the antenna and formed by routing the antenna around the outer circumference of the discharge vessel in the region of the first electrode.

5. The high-pressure discharge lamp according to claim 4, wherein the first antenna ring is arranged in a region whose width in a longitudinal direction of the lamp extending through the electrode supports is in a range of at most ±4 mm with respect to the free end of the protrusion.

6. The high-pressure discharge lamp according to claim 4, wherein the distance in a radial direction between the first antenna ring and the free end of the protrusion essentially corresponds to the wall thickness of the discharge vessel.

7. The high-pressure discharge lamp according to claim 6, wherein the distance in the radial direction between the first antenna ring and the free end of the protrusion is in a range of 0.65 mm to 0.9 mm.

8. The high-pressure discharge lamp according to claim 1, wherein the second electrode is configured like the first electrode.

9. The high-pressure discharge lamp according to claim 1, wherein a second antenna ring is provided which is integral with the other sections of the antenna and is formed by routing the antenna around the outer circumference of the discharge vessel at a distance from the first antenna ring.

10. The high-pressure discharge lamp according to claim 9, wherein the second antenna ring is arranged at a distance from the electrode coil of the second electrode and in the region of the outer end of the discharge vessel adjacent to the second electrode.

11. The high-pressure discharge lamp according to claim 1, having at least one of the following characteristics: the discharge vessel is made of ceramic; the discharge vessel is arranged in an outer bulb, the outer bulb being socketed either at one or both ends; it is configured for plant lighting.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The invention is explained in more detail below with reference to embodiment examples shown in the figures, without limiting the invention to these embodiment examples. Like parts or functionally like parts are designated by like reference numerals in the figures. Recurring parts are not designated separately in each figure. In the schematic figures:

[0026] FIG. 1: is a side view of a high-pressure discharge lamp according to the invention;

[0027] FIG. 2: is a side view of the discharge vessel of the high-pressure discharge lamp of FIG. 1;

[0028] FIG. 3: shows the discharge vessel according to FIG. 2 rotated by 90°;

[0029] FIG. 4: is a detailed side view of the first electrode;

[0030] FIG. 5: is a view of the first electrode in an axial direction, with one end of the wire forming the protrusion;

[0031] FIG. 6: is a view of the first electrode in an axial direction, with a wire loop forming the protrusion;

[0032] FIG. 7: is a side view of the burner unit of a high-pressure discharge lamp;

[0033] FIG. 8: shows the burner unit according to FIG. 4 rotated by 90°; and

[0034] FIG. 9: is a detailed side view of an end section of the burner unit with the first electrode.

DETAILED DESCRIPTION

[0035] FIG. 1 shows a high-pressure discharge lamp 5, specifically a high-pressure sodium-vapor discharge lamp for plant lighting. The high-pressure discharge lamp 5 comprises an outer bulb 50, which is made of quartz glass, for example, and in which a burner unit 1 is accommodated. As is usual with high-pressure discharge lamps 5, the outer bulb 50 comprises at each end along the longitudinal direction L of the lamp a seal 52, for example a pinch, which seals the outer bulb 50 in a gas-tight manner and through which outer connections 53 for electrically connecting the high-pressure discharge lamp 5 are routed to the outside. Furthermore, a getter 51 is arranged in the outer bulb 50 to remove impurities in the outer bulb 50.

[0036] The burner unit 1 comprises a discharge vessel 10 made, for example, of ceramic, which is shown in more detail in FIGS. 2 and 3. The view in FIG. 2 is rotated 90° to the left compared to the view in FIG. 3. The discharge vessel 10 is essentially configured as a hollow cylinder and encloses a discharge space 11, which is closed in a gas-tight manner at each of its end faces by a seal 12, which in turn each have a lead-through for an electrode connection. The wall of the discharge vessel 10, which is made of a ceramic, for example, has an outer surface 100 and an inner surface 101, which are spaced apart from one another by the wall thickness of the discharge vessel 10. An antenna 2 is arranged on the outer surface 100 of the discharge vessel 10. The antenna 2 is made of a conductive material applied to the outer surface 100 of the discharge vessel 10, and its main body extends in the longitudinal direction L of the high-pressure discharge lamp 5. In the region of the ends of the discharge vessel 10, the antenna has a first antenna ring 20 and a second antenna ring 21 made of conductive material. The antenna 2 including the antenna rings 20, 21 is integral, so that the antenna rings 20, 21 are electrically conductively connected to each other. Such antennas 2 are generally known in the prior art. However, as will be discussed in more detail below, in the present embodiment, the first antenna ring 20 is positioned farther from the adjacent end of the discharge vessel 10 and toward the center of the discharge vessel than the second antenna ring 21 is positioned from its associated end of the discharge vessel 10. This will be explained in more detail below.

[0037] FIG. 4 shows an electrode using the first electrode 3 as an example. The second electrode 4 (see FIGS. 7 and 8) may be configured in the same manner as the first electrode 3. The first electrode 3 comprises an electrode support 30 with an electrode tip 31. Specifically, the electrode support 30 is an integral rod with one end forming the electrode tip 31. A wire 33 is wound onto the electrode support 30 in a tip region 32 as an electrode coil 34. Both the electrode support 30 and the wire 33 forming the electrode coil 34 are made of tungsten, for example. In this case, the electrode coil 34 consists of a continuous, integral wire 33 which, in the embodiment example shown, is wound around the electrode support 30 in two coil layers 37,38. Specifically, the wire 33 forms an inner coil layer 37, which in the embodiment example shown consists of twelve turns wound from a middle region of the electrode support 30 toward the electrode tip 31 with a clockwise direction of rotation, and an outer coil layer 38 counter-directionally wound onto the inner coil layer 37 back from the electrode tip, which in the embodiment example shown consists of nine turns with a counter-clockwise direction of rotation. However, the directions of rotation could also be reversed. The tip region 32, in which the electrode coil 34 is located, extends from the electrode tip 31 toward the rear end of the electrode support 30 and occupies about two-thirds of the total length of the electrode support. The electrode coil 34 is set back relative to the electrode tip 31, so that in a free tip region 32-1, an end region of the electrode support 30 is exposed and is not wrapped by the electrode coil.

[0038] In order to ensure a uniform arc discharge within the burner unit 1, it is desired for the electric arc to continuously attach to the electrode tip 31 during operation of the high-pressure discharge lamp 5. If this is not the case, the lamp flickers during operation. For this reason, the electrode coil is usually slightly set back on the electrode support relative to the electrode tip. Furthermore, it is avoided in the prior art to have protrusions that protrude beyond the electrode coil 34, as they can cause the electric arc to attach to them instead of the electrode tip 31. Contrary to this previous effort, a protrusion 35 is provided on electrode 3, which protrudes by a length E beyond the electrode coil 34. The length E is measured as the distance of the outermost point of the protrusion 35 from the outer circumference of the electrode coil 34 indicated by the dashed line, measured in a radial direction, starting from the center axis of the electrode support 30 (see also FIG. 5). In the embodiment shown, the protrusion 35 is formed by the end section 351 of the wire 33 of the outer coil layer 38. In other words, a piece of wire 33 is left protruding outward after the outer coil layer 38 of the electrode coil 34 has been created from it. This piece of wire 33 is not wound around the electrode support 30 and onto the inner coil layer 37, and therefore its free end 352 protrudes from the electrode coil 34.

[0039] The protrusion 35 reduces the distance between the electrode 3 and the antenna 2 by the length E of the protrusion 35, measured in the radial direction R, starting from the center axis M of the electrode support 30, between the outer circumference of the electrode coil 34 and the outermost point of the protrusion 35. In this case, the length E is greater than the diameter (thickness) C of the electrode coil 34 in the radial direction R. The closer proximity of the electrode 3 to the antenna facilitates the escape of electrons, which in turn improves the ignitability of the high-pressure discharge lamp 5. To prevent the electric arc from attaching to the protrusion 35 during operation of the high-pressure discharge lamp 5, the protrusion 35 is spaced apart from the electrode tip 31 by a distance A in the longitudinal direction L of the high-pressure discharge lamp 5. Although the protrusion 35 is still in the tip region 32, in the region of the electrode coil 34, but is located in a middle region of the electrode support 30, i.e. at about half its length. With respect to the electrode coil 34, the protrusion 35 is located in a rear end region 36 thereof, at about one-third of the total length of the electrode coil in the longitudinal direction L, and at the end of the outer coil layer 38 facing away from the electrode tip 31. Such an arrangement of the protrusion 35 reliably prevents the electric arc from attaching to it.

[0040] FIGS. 5 and 6 show two different embodiments of the protrusion 35 in an axial view of the electrode 3. In the embodiment shown in FIG. 5, the protrusion 35 is formed by an end section 351 of the wire 33, the free end 352 of which projects away from the electrode coil 34 and the electrode support 30. With respect to the electrode support 30 or the inner coil layer 37, the protrusion 35 projects tangentially. In the radial direction, it shortens the distance between the electrode 3 and the antenna 2 by the length E, as already described with reference to FIG. 4. FIG. 6 shows an alternative embodiment in which the protrusion 35 is formed by a wire loop 350 of the wire 33. Specifically, a middle section of the wire 33 is formed into a wire loop 350 away from and back to the inner coil layer 37. In the embodiment example shown, the wire 33 then ends after returning to the inner coil layer 37. However, it could also be further wound in further turns around the inner coil layer 37. It is also possible to squeeze the wire loop together such that the two halves of the loop are closer together or even touching. It is also possible to twist the two halves of the loop together to make the loop narrower and tapered in the region of the free end. The loop-shaped protrusion 35 likewise projects radially beyond the electrode 3 by the length E, thereby shortening the distance between the electrode 3 and the antenna 2.

[0041] FIGS. 7 and 8 show the burner unit 1 with the electrodes 3, 4 installed in the discharge vessel 10. As with FIGS. 2 and 3, the discharge vessel 10 is shown rotated by 90° between FIGS. 7 and 8. The electrodes 3, 4 are configured identically, are arranged in the discharge space 11 of the burner unit 1 and can each be electrically contacted with a contact pin 39, 49, which is led out of the discharge vessel 10 through the seal 12. As can be seen in FIGS. 7 and 8, the first antenna ring 20 of the antenna 2 is arranged along the longitudinal direction L of the high-pressure discharge lamp 5 at the level of the protrusion 35 of the first electrode 3. The second antenna ring 21 of the antenna 2, on the other hand, is spaced apart from the protrusion 45 of the second electrode 4 along the longitudinal direction L of the high-pressure discharge lamp 5 and is arranged offset outwardly toward the end of the discharge vessel 10 adjacent to the second electrode 4. In this manner, coupling between the second antenna ring 21 and the second electrode 4 is avoided, and short circuits are prevented.

[0042] The first electrode 3 is configured to be connected to the neutral conductor of a ballast. Furthermore, a capacitor unit 390, in the present embodiment a triple capacitor such as the applicant's “Triple Capacitor”, is provided on the side of the electrode 3. Via the capacitor unit 390, the antenna 2 is capacitively coupled to the ignition voltage on the side of the first electrode 3. The capacitor unit is configured as a triple capacitor and comprises three capacitor elements connected in parallel to each other, each with an inner conductor, a dielectric and an outer conductor. For example, the inner conductor is a niobium pin surrounded by a ceramic tube that forms the dielectric. Around the outer surface of the dielectric, the outer conductor is arranged as a coil, for example made of tungsten wire. The inner conductor is electrically conductively connected to the first electrode. The outer conductor, in turn, is electrically conductively connected to the antenna. The capacitor unit causes the high-frequency ignition pulse to be transmitted only at an attenuated level. The capacitance of the capacitor, and thus the desired ignition pulse, can be adjusted by suitably matching the dimensions of the dielectric, specifically the wall thickness of the ceramic tube, the coil and the pin. In this manner, the ignition voltage to start the lamp is lowered and the formation of the electric arc is assisted without the possibility of current flow through the antenna, which would bypass the electric arc and could damage or destroy the material of the discharge vessel.

[0043] The use of the capacitor unit 390 in conjunction with the antenna 2 and the protrusion 35 results overall in a significant improvement in the ignitability of the high-pressure discharge lamp 5, allowing its operation at increased gas filling pressure.

[0044] FIG. 9 shows an enlarged detailed view of the end of the burner unit 1 in which the first electrode 3 is arranged. In particular, it is apparent from the illustration that the first antenna ring 20 is arranged within a width W around the protrusion 35 in the longitudinal direction L of the lamp. The width W is, for example, 2 mm to each side of the protrusion 35 in the longitudinal direction L. This ensures that the protrusion 35 is as close as possible to the antenna 2, and more specifically to the first antenna ring 20. The distance D between the electrode 3 and the antenna 2 is therefore shortened by the length E of the protrusion 35. Due to this reduced distance D, the high-pressure discharge lamp 5 ignites with an ignition voltage that can be provided by conventional lamp sockets and ballasts, even with a very high gas filling pressure in the discharge vessel to achieve a high PAR value.