EP0265266A1

EP0265266A1 - Electric discharge lamp

Info

Publication number: EP0265266A1
Application number: EP87309354A
Authority: EP
Inventors: Miklos Csapody; Janos Spielmann
Original assignee: Tungsram Rt
Current assignee: Tungsram Rt
Priority date: 1986-10-23
Filing date: 1987-10-22
Publication date: 1988-04-27
Anticipated expiration: 2007-10-22
Also published as: DE3770574D1; EP0265266B1; JPS63110545A; HU196014B; HUT44875A

Abstract

Electric discharge lamp, particularly one of an output not exceeding 400 W, comprising a tube (1) made of a translucent material and sealed at two ends by respective closing elements (2), electrodes (7) arranged oppositely on respective electrode rods (8) in the interior of the tube (1) for defining a discharge space and lead-in conductors (4) for supplying electric current to the electrodes (7), fixed by means of mechanical deformation to the respective electrode rod (8), at least one lead-in conductor (4) including a hollow part for containing a liquid phase filling composition and having at least one capillary connecting the discharge space and the interior of the hollow space for ensuring a path of transportation of the filling composition when it is in vapour phase, wherein the lead-in conductor (4) is fastened by flattening to the electrode rod (8) on its section (10) lying in the interior of the tube (1).

Description

BACKGROUND OF THE INVENTION

The present invention relates to an electric discharge lamp, particularly but not exclusively to such a lamp having an output not exceeding 400 W, and comprising a tube made of a translucent material and sealed at two ends by respective closing elements, electrodes arranged oppositely one another on respective electrode supports in the interior of the tube for defining a discharge space and lead-in conductors for supplying electric current to the electrodes, fixed to the respective electrode supports, at least one lead-in conductor including a hollow part for containing a liquid phase filling composition and having at least one capillary connecting the discharge space and the interior of the hollow space for ensuring a path of transportation of the filling composition when it is in vapour phase. The construction of the invention relates mainly to high pressure sodium vapour lamps.
The disclosure of the DE-A1 27 54 001 describes an electric discharge lamp, more exactly a discharge vessel made of a ceramic material based on polycrystalline alumina. The tube-shaped vessel is sealed by closing elements made of polycrystal-alumina, too. The closing elements are bored and their holes carry lead-in conductors made of a metal having a coefficient of thermal expansion approximately equal to that of the alumina. The lead-in conductors, made particularly of niobium, are connected to the electrodes of the discharge vessel and at least one of them constitutes an exhaust tube. By means of a seal the elements are connected together and the seal ensures hermetic closing. The discharge vessel contains a filling composed of sodium and mercury and a starting gas including a noble gas. The lead-in conductor is fastened by mechanical means to an electrode rod wherein the electrode rod has a long section placed within the exhaust type lead-in conductor passing through the closing element. The lead-in conductor joins the electrode rod at its part lying outside the discharge tube. The joint is made by mechanical flattening. During the manufacture of the discharge tube the lead-in conductor serves as a pumping (evacuation) pipe and as a tube for introducing the filling composition into the interior of the discharge tube. After finishing the process of manufacturing the interior of the discharge tube the lead-in conductor is hermetically closed as far from the discharge tube as possible. This closure is made also by means of mechanical flattening. Hence, the lead-in conductor is closed by flattening at both ends and the inner space, i.e. the interior of the lead-in conductor is used for storing the liquid state filling composition. By means of capillaries formed at the flattened part of the electrode rod it is possible to realise communication paths between the space of the discharge in the tube and the reservoir (interior of the lead-in conductor), whereby filling composition in vapour phase can be introduced into the discharge space.
This solution has the disadvantage that the flattened part required for fixing the electrode rod and located outside the discharge tube results in an increased length of the exhaust tube, i.e. the lead-in conductor and this length is excessive. A longer lead-in conductor is more expensive than a shorter one, and this fact can be better appreciated when one takes into account that the lead-in conductor is of (rather expensive) niobium. What is more, the so-called cold point of the tube is, in arrangements of the kind described above, too far from the heat source of the discharge, i.e. from the discharge arc and the electrodes. Therefore special measures have to be taken for assuring the required temperature of this cold point, and especially for discharge tubes having an output not exceeding 400 W.
The solution in practice to date has in most cases bee n to apply special heat-reflecting surfaces at both ends of the discharge tube, resulting in increased costs of manufacture and in creating thermal contact between the surface of the ceramic tube wall and the elements carrying the heat-reflecting surfaces. Such thermal contacts lead to a large scatter of discharge tube parameters.
Another possibility is to heat up the interior of the discharge tube and this is expensive.

SUMMARY OF THE INVENTION

An object of the invention is to provide a discharge lamp having a special lead-conductor for ensuring an advantageously arranged cold point while maintaining the existing facility of exhausting the interior of the discharge tube through the exhaust tube type lead-in conductor and storing the filling composition without the necessity of applying special measures for discharge tubes with an output not exceeding 400 W, particularly 150 W.
The invention is based on the recognition that the mechanical connection of the electrode support or rod and the lead-in conductor should be effected not outside the discharge tube but within it, in the interior, because in this way it is very simple to assure the required temperature of the cold point.
According to the invention, an electric discharge lamp, particularly but not exclusively on having an output not exceeding 400W, comprises a tube made of a translucent material and sealed at two ends by respective closing elements, electrodes arranged oppositely to one another on respective electrode supports, e.g. rods in the interior of the tube for defining a discharge space and lead-in conductors for supplying electric current to the electrodes, fixed by means of mechanical deformation to the respective electrode support, wherein at least one lead-in conductor includes a hollow part for containing a liquid phase filling composition and is equipped with at least one capillary connecting the discharge space and the interior of the hollow space for ensuring a path of communication of the filling composition when the latter is in a vapour phase, the lead-in conductor being fastened by flattening to the electrode support on a part thereof disposed in the interior of the tube for simplifying the process of manufacturing the discharge lamp and assuring the required cold temperature thereof without specific additional means.
In an advantageous embodiment of the proposed electric discharge lamp the lead-in conductor is made with a four-leaf clover shaped cross-section at its flattened part.
In a further advantageous embodiment of the proposed electric discharge lamp the lead-in conductor is fastened to the electrode rod by means of mechanical flattening and point pressure or spot welding.
The discharge lamp of the invention can be manufactured without any specific change of the conventional technological process. On the basis of the proposed lead-in conductor it is possible to realise high-pressure electric discharge lamps of higher and lower out-puts having the required cold point without special measures and being economic and reliable in production. The discharge lamp of the invention can be fixed in an outer vessel and advantageously equipped with an Edison-type screw thread.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be further described in more detail by way of examples and with reference to a preferred embodiment illustrated in the drawing, wherein:

Figure 1 is a cross-section of a part of the discharge lamp of the invention equipped with a novel lead-in conductor, and
Figure 2 is a cross-section II-II of the discharge lamp shown in Figure 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The preferred discharge lamp of the invention comprises (Figure 1) a discharge tube 1 made of polycrystall ine alumina. Each end part of the discharge tube 1 is closed by a closing element 2 made of a ceramic material based on alumina. The closing element 2 ensures hermetic closure of the discharge tube 1 by means of a seal 3 composed of metal oxides according to the known principles. The same seal is applied for fixing a lead-in conductor 4 in the closing element 2. The lead-in conductor 4 is of exhaust tube type element which is generally made of niobium.
The thin metal tube of the lead-in conductor 4 has an end part 5 which lies outside the discharge tube 1, it protrudes through the closing element 2. The end part 5 renders the pumping and filling process of the discharge tube 1 possible and after finishing this process it is hermetically closed by mechanical flattening. The lead-in conductor 4 has another end part 6 in the interior of the discharge tube 1 connected to an electrode 7 by means of an electrode rod 8 bearing the electrode 7. The electrode rod 8 is connected to the lead-in conductor by means of flattened part 10 prepared by mechanical deformation of the lead-in conductor 4.
According to the embodiment shown in Figure 1 the flattened part 10 can be prepared by means of a four-jaw press equipment and this results in a four-leaf clover form of the cross-section of the lead-in conductor at the flattened part 10, as shown in Figure 2. By flattening the lead-in conductor 4 the flattened part 10 is equipped with capillaries 9 with an inner diameter effective in hindering the flow of a liquid state filling composition applied in the discharge lamp and introduced into the lead-in conductor 4 at its section bounded by the flattened part 10 and the end part 5 lying outside the discharge tube 1. The capillaries 9 do, however, assure a path of communication for the vapour phase part of the filling composition between the interior of the discharge tube 1, more exactly the discharge space defined by the electrodes 7 and the interior of the lead-in conductor 4.
The process of manufacture of the discharge vessel and discharge lamp is well-known from the literature and the practice in all further details. It can be seen, however, that the flattened part 10 connecting the electrode rod 8 and the lead-in conductor 4 lies in this case in the interior of the discharge tube 1, contrary to the known solutions characterized by this connection locus lying outside the discharge tube. Moreover, the cold point or, in other words, the reservoir of the discharge lamp reaches also into the interior of the discharge tube 1, whereby its temperature can be increased without specific heating means. The advantage of this solution is appreciable, especially in the case of discharge lamps with an output not exceeding 400 W, particularly in the range 50 to 250 W.
The apparatus applied for flattening the lead-in conductor 4 to the electrode rod 8 preferably comprises means for point pressure welding, whereby electric contact of very high reliability can be ensured between the connected elements, because of a cohesive contact over the mechanical flattening.

Claims

1. An electric discharge lamp, preferably having an output not exceeding 400 W, comprising a tube (1) made of a translucent material and sealed at two ends by respective closing elements (2), electrodes (7) arranged oppositely on respective electrode supports (8) in the interior of the tube (1) for defining a discharge space, and lead-in conductors (4) for supplying electric current to the electrodes (7) fixed to the respective electrode support (8), at least one lead-in conductor (4) including a hollow part for containing a liquid phase filling composition and having at least one capillary (9) connecting the discharge space and the interior of the hollow space for ensuring a path of communication for the filling composition when it is in vapour phase, characterized in that the lead-in conductor (4) is fastened, e.g. by flattening, to the electrode support (8) on at a part of said conductor (4) which is disposed within the interior of the tube (1).

2. An electric discharge lamp according to claim 1, characterised in that the said part of the lead-in conductor (4) includes a flattened part (10) with a four-leaf clover shaped cross-section.

3. The electric discharge lamp according to claim 1 or 2, characterized in that the lead-in conductor (4) is fastened to the electrode support (8) by means of mechanical flattening and point pressure or spot welding.