High-pressure gas discharge lamp

Abstract: The high-pressure gas discharge lamp has within an outer envelope (1) a discharge vessel (6) and current supply conductors (10, 11), which are connected via current lead-­ through conductors (8, 9) to electrodes (7). The long current supply conductor (11) is enveloped in part by an insulator (12). The lamp is resistant to shocks due to the fact that the insulator (12) is laterally connected to the outer envelope (1).

Description: The invention relates to a high-pressure gas discharge lamp comprising an outer envelope sealed in a vacuum-tight manner and having a seal at a first end thereof, a lamp cap provided with contacts, in which the first end of the outer envelope is fixed, a discharge vessel sealed in a vacuum-tight manner and provided with an ionizable filling and with electrodes connected to a first and a second current lead-through conductor, respectively, which emanate from the discharge vessel near and remote from the first end of the outer envelope, respectively, a first and a second current supply conductor, which are connected to a respective contact of the lamp cap and extend through the seal at the first end of the outer envelope to the first and the second current lead-through conductor, respectively, a part of the second current supply conductor being enveloped within the outer envelope by an insulator which is connected to the outer envelope. Such a lamp is known, for example, from EP-A-0 209 345. This document describes a high pressure metal vapor discharge lamp in which undesirable discharges are prevented in the outer envelope by covering at least one of the current supply conductors by a glass tube connected to the seal of the outer envelope. In high-pressure gas discharge lamps to be used in an optical system, endeavours are made to give the outer envelope the smallest possible transverse dimensions. As a result, minimal limitations are imposed on the design of the optical system. Small transverse dimensions of the outer envelope result in that the second current supply conductor extends within the outer envelope at a small distance from the outer envelope. In certain high-pressure gas discharge lamps, it is necessary that a part of the second current supply conductor is surrounded by an insulator. This is the case if it must be prevented that small metal ions, such as ions of sodium, disappear from the filling due to the fact that U.V. radiation releases electrons from said current supply conductor, which electrons are deposited on the discharge vessel. The negative charge on the discharge vessel is conducive to migration of sodium ions through the wall of said vessel. An insulator around the second current supply conductor may alternatively be necessary to enlarge the smallest distance between bare parts of the first and the second current supply conductor in order to reduce or exclude the risk of flash-over. This is the case in lamps in which a very high voltage is used, for example, of several kV to several tens of kV for re-igniting the lamp in the hot state after a current interruption. In a lamp in which the second current supply conductor extends within the outer envelope at a small distance therefrom, the insulator around said current supply conductor can be located at such a small distance from the outer envelope that the lamp is highly sensitive to shocks and that even during manipulation, for example packing, of the lamp the insulator is liable to break. The invention has for its object to provide a lamp of the kind described in the opening paragraph, which has a construction more resistant to shocks. According to the invention, this object is achieved in that the insulator is laterally connected to the outer envelope. The connection may be established, for example, by means of an adhesive, for example a glass melting at a temperature lower than that of the outer envelope and of the insulator, such as lead borate glass or a glue. Another possibility consists in indenting the outer envelope, for example providing it with indentations on either side of the insulator. With an indentation or indentations the insulator is then enclosed against the wall of the outer envelope. Alternatively, it is possible to fuse the outer envelope with the insulator. By connecting the insulator to the outer envelope, it is achieved that the insulator and the outer envelope in the case of shocks or vibrations no longer can abut against each other at the area of the connection and at a certain distance therefrom. With the use of a second current supply conductor, which is surrounded by an insulator along a comparatively great length, a simple experiment can show whether it is desirable to secure said conductor at more than one point. Embodiments of lamps having a glass insulator secured to the seal of the outer envelope, which are suitable to be ignited or re-ignited at a very high voltage, for example 50 kV, are shown in the drawing. In the drawing: Figure 1 is a side elevation, partly broken away, of a lamp, Figure 2 is a sectional view taken on II-II in Figure 1, Figure 3 shows a variation of Figure 2. In Figure 1, the lamp has an outer envelope 1 of hard glass or glass having an SiO₂ content of at least 95% by weight, such as quartz glass, which is sealed in a vacuum-tight manner and has a pinched seal 2 at a first end 3 thereof. This end 3 is fixed (in the drawing by means of cement 13) in a lamp cap 4 of ceramic material carrying contacts 5. A discharge vessel 6 of glass having an SiO₂ content of at least 95% by weight, such as quartz glass, sealed in a vacuum-tight manner, has an ionizable filling, for example bromide, of a rare earth metal, such as dysprosium, holmium or thulium and mercury bromide, mercury iodide, caesium iodide, mercury and argon/krypton at a pressure of 50 mbar. Electrodes 7 are arranged in the discharge vessel 6 and these electrodes are connected to a first current lead-through conductor 8 and a second current lead-through conductor 9, which emanate from the discharge vessel near and remote from the first end 3 of the outer envelope 1, respectively. A first current supply conductor 10 and a second current supply conductor 11 are connected to a respective contact 5 at the lamp cap 4 and extend through the seal 2 at the first end 3 to the first and second current lead-through conductors 8 and 9, respectively. A part of the second current supply conductor 11 is enveloped within the outer envelope 1 by an insulator 12. The insulator in the drawing is a tube of glass, for example of glass having an SiO₂ content of at least 95% by weight, such as quartz glass. The insulator 12 is anchored in the seal 2 in that it is fused therewith. The insulator 12 may alternatively be secured to the seal 2 by means of a low melting-point glass, such as lead borate glass. The insulator 12 is connected also laterally to the outer envelope 1. As is shown in Figure 2, the outer envelope has a fused area 14 with the insulator 12, which without this fused area would extend at a very small distance from the outer envelope and would be destroyed when abutting against it. Due to the fused area, a rigid assembly is obtained. Due to the presence of the insulator 12, the smallest distance (a) between bare parts of the current supply conductors 10, 11 is more than twice the smallest distance between said bare parts (b) without the use of the insulator. Flash-over during ignition or re-ignition at, for example, 50 kV is thus prevented. Figure 3 shows an embodiment, in which the outer envelope 1 has indentations 24, which enclose the insulator 12.

Claims: A high-pressure gas discharge lamp comprising an outer envelope (1) sealed in a vacuum-tight manner and having a seal (2) at a first end (3) thereof, a lamp vessel (4) provided with contacts (5), in which the first end (3) of the outer envelope (1) is fixed, a discharge vessel (6) sealed in a vacuum-tight manner and provided with an ionizable filling and with electrodes (7) connected to a first current lead-through conductor (8) and a second current lead-through conductor (9), which emanate from the discharge vessel (6) near and remote from the first end (3) of the outer envelope (1), respectively, a first current supply conductor (10) and a second current supply conductor (11), which are connected to a respective contact (5) of the lamp cap (4) and extend through the seal (2) at the first end (3) of the outer envelope (1) to the first current lead-through conductor (8) and the second current lead-through conductor (9), respectively, a part of the second current supply conductor (11) within the outer envelope (1) being enveloped by an insulator (12), which is connected to the outer envelope, characterized in that the insulator (12) is connected laterally to the outer envelope (1). A high-pressure discharge lamp as claimed in Claim 1, characterized in that the insulator (12) has a fused area (14) with an outer envelope (1). A high-pressure discharge lamp as claimed in Claim 1, characterized in that the outer envelope (1) has indentations (24), which enclose the insulator (12). A high-pressure discharge lamp as claimed in Claim 1, 2 or 3, characterized in that the insulator (12) is also secured to the seal (2) of the outer envelope (1).

Inventors: VERWIMP FRANS JAN DYMPHNA, VERWIMP, FRANS JAN DYMPHNA
Applicants: PHILIPS NV, N.V. PHILIPS' GLOEILAMPENFABRIEKEN
Application year: 1990
Main classification: H01J61
IPC codes: H01J61