GB2151072A

GB2151072A - Compact low-pressure discharge lamp

Info

Publication number: GB2151072A
Application number: GB8430210A
Authority: GB
Inventors: Manfred Schindler; Dr Wolfgang Pabst; Dr Horst Lange; Dr Manfred Rehmet
Original assignee: Patent Treuhand Gesellschaft fuer Elektrische Gluehlampen mbH
Current assignee: Osram GmbH
Priority date: 1983-12-07
Filing date: 1984-11-29
Publication date: 1985-07-10
Also published as: GB8430210D0; JPS60140645A; FR2556500A1; DE3344270A1

Abstract

A compact low-pressure discharge lamp 1 comprises a cylindrical envelope 2 and a substantially star-shaped insert member 4 which forms, by means of partitions, a winding discharge path with at least three discharge chambers extending along the envelope - parallel to the lamp axis - the insert member 4 having a resilient action in the radial direction transversely to the longitudinal axis of the lamp on the individual partitions between adjacent discharge chambers bear tightly against the envelope 2 without a rigid connection, the contact being effected along a line in each case. <IMAGE>

Description

SPECIFICATION Compact low-pressure discharge lamp The in'Jntion relates to a compact low-pressure discharge lamp having a cylindrical envelope of glass, a substantially star-shaped insert member which forms, by means of partitions, a winding discharge path with at least three discharge chambers extending along the envelope as well as an additional cavity situated in the centre--each parallel to the lamp axis -, a filling of mercury and at least one rare gas, two electrodes of highmelting-point metal and a cap fitted to the envelope at one end.

Compact low-pressure discharge lamps of this type have been developed to an increased extent in recent years in order to meet the need for current-saving alternative light sources for incandescent lamps. In these lamps, the sealing between insert member and envelope represents aAgreat problem. It has actually been found that even with a rigid insert member with extremely narrow tolerances, of metal for example, sufficiently wide gaps or crevices still remain between the edges of the partitions bearing against the envelope and the envelope, through which a cross discharge can develop. In DE-OS 29 36 488, the formation of such gaps which allow the discharge through is prevented in that the edges of the partitions are provided with short flanges which bear flat against the envelope.

This measure requires additional expenditure on labour and costs, however.

Even the rigid connection of an insert member of glass to the envelope by fusion or soldering leads to problems because the formation of flaws, cracks and splits can occur when the lamp is in operation as a result of strains appearing after manufacture. In addition, here too, additional operations are necessary and the glass insert member leads to a greater weight of the lamp. A compact lowpressure discharge lamp is known from the DE-OS 31 06 721 wherein a curved discharge path is formed by a thin-walled glass member between an outer and an inner member-both likewise of glass.The resulting slitlike spaces between inner or outer member and the thin-walled glass member, which se zasutc ih- indiviåt3al discharge paths from one another, are so dimensioned in this case that the length of the slit is greater than its width by at least the factor 1 0. It is true that a cross discharge is avoided as a result but darker areas, visible from the outside, a high manufacturing cost and likewise a great weight must be accepted with this lamp.

The invention secks to provide a compact low-pressure discharge lamp wherein gaps between insert member and envelope are kept so small that they cannot be penetrated by the discharge. In addition, the lamp should also preferably be a low-voltage construction which does not lead to the formation of any flaws or cracks during the manufacture and operation of the lamp. No additional operations should be necessary to provide these advantages and the weight of the lamp should remain as low as possible.

According to the invention, there is provided a compact low-pressure discharge lamp having a cylindrical envelope of glass, a substantially star-shaped insert member which forms, by means of partitions, a winding discharge path with at least three discharge chambers extending along the envelope as well as an additional cavity situated in the centreeach parallel to the lamp axis-a filling of mercury and at least one rare gas, two electrodes of high-melting-point metal as well as a cap fitted to the envelope at one side, wherein the insert member has a resilient action in the radial direction transversely to the longitudinal axis of the lamp and the individual partitions between adjacent discharge chambers bear tightly against the envelope without a rigid connection, the contact being effected along a line in each case.

As a result of the resilient characteristics of the insert member, such a close contact of the partitions with the envelope may be established that the possibility of penetration at these contact points is no longer open to the discharge. This contact is particularly close, as a result of the satisfactory spring characteristics, which are extremely uniform in particular, if each discharge chamber is bounded by its own partition. An insert member so formed may very easily be introduced into the envelope by contraction towards the axis of symmetry.

The discharge chambers may be bounded by a one-piece partition of the insert member which may have a concave curvature in crosssection, directed towards the discharge chamber. In this case, the chamber walls formed by the partitions do not have any corners with acute angles and so render possible a very uniform coating, which is easy to provide, with reflecting and fluorescent substances- as stated below. In addition, the individual discharge chambers can be completely filled by the discharge so that a very uniform and largely complete conversion into visible light takes place.

As a result of the manufacture of the insert member from one piece, a simplification in the production process may be additionally achieved because then only one welding or soldering operation still has to be effected. If the insert member is formed from a tube, even this operation can be completely omitted.

It is naturally also conceivable to provide a resilient insert member comprising three or more plane partitions which are welded or stuck together in the form of a star at the axis of symmetry. In this case, the width of the individual partition is somewhat greater than the inner radius of the associated envelope so that, after introduction into the envelope, the resilient walls bear tightly against the envelope with a slight arching-perpendicular to the longitudinal axis of the lamp. Further forms of the insert member also of one piece are conceivable none of which has as satisfactory a spring characteristic, however, or is so simple to introduce into the envelope as the form of embodiment given first.

In addition, a cover plate, which bears tightly against the envelope without a rigid connection, can be provided at the end of the insert member remote from the lamp cap.

With the aid of this cover plate and the closed end of the envelope, an additional discharge chamber is thus formed which renders possible a further lengthening of the discharge path. Two apertures in the cover plate ensure the necessary connection to the other discharge chambers. It is also conceivable, however, to accommodate one or both electrodes in this space.

The insert member preferably consists of metal and sheet metals with metal alloys of chromium and/or nickel with iron have proved particularly suitable because of their satisfactory spring characteristics.

In addition, such alloys have a similar coefficient of expansion to that of the glass of the envelope so that no stresses occur.

If the insert member of metal is provided with a cover plate, this may comprise a metal alloy or glass with a coefficient of expansion substantially as large as that of the insert member. In this manner, further possible stresses are avoided. Both parts are then connected to one another by means of glass solder.

It is also conceivable to rn3nufacture the insert member and possibly the cover plate of plastics material. All the plastics materials so far known, which have sufficiently satisfactory resilient properties, have neveftheless proved usable only to a limited extent because these plastics materials either release gases, are not stable under UV radiation or shrink.

Towards the lamp cap, the envelope may be soldered or fused to a base plate of metal or glass which has a similar coefficient of expansion to the envelope in order to achieve a construction as free from stress as possible.

The base plate and the insert member may be connected by means of glass solder in pre cisely the same manner as the insert member and the cover plate, so that the formation of grooves, otherwise usual, can be dispensed with.

The individual discharge chambers may be connected to one another by apertures so that a winding discharge path results which passes once through all the chambers. A possible control of the discharge can be seen from the drawing.

All the sides of the internal assembly, consisting of insert member, base plate and possibly cover plate, adjacent to the discharge may carry a reflecting and fluorescent coating. As a result of the coating of the base plate, spar; from advantages from the light poiilt of view, thermal advantages are also achieved in particular because then any ballast integrated in the cap-see below cxperiences less heating. In addition, the envelope may be coated with a fluorescent substance on its inside.

The compact low-pressure discharge lamp can be operated with an external starter and ballast. It is also possible, however, to integrate this device in the lamp and the chamber situated in the centre of the lamp offers itself for this purpose, for example, which chamber is formed, as mentioned above, in the insert member with the concavely curved walls.

The invention will now be described in greater detail, by way of example, with reference to the drawings, in which: Figure 1 shows a side view, partially in section, of a preferred form of compact lowpressure discharge lamp according to the invention; Figure 2 shows a section through a compact low-pressure discharge lamp as shown in Figure 1 at the position I; and Figure 3 shows a section through a compact low-pressure discharge lamp as shown in Figure 1 at the position II.

The drawings show a preferred form of a single-cap compact low-pressure discharge lamp 1 with a total length of 165 mm and a maximum outside diameter of 55 mm. The lamp 1 comprises an envelope 2 with a length of 100 mm and a cap 3 with a length of 65 mm containing the starter and ballast.

In the envelope 2 there are an insert member 4 and a cover plate 5-each consisting of one piece of Ni-Fe sheet metal 0.1 or 0.3 mm thick-which are connected to one another by glass solder and together form a winding discharge path. The insert member 4 is so shaped that each of the discharge chambers a to C and e to g is bounded by a partition of the insert member 4. In this case, the individual partition has a concave curvature directed towards the discharge chamber and bears very tightly against the envelope 2 as a result of the satisfactory spring characteristics of the insert member 4. The envelope 2 is closed in a gastight manner by a base plate 6 with a raised edge which embraces the end of the envelope 2 open towards the lamp cap 3.

The base plate 6, with a thickness of 0.5 mm-of the same material as the insert mem ber 4 and the cover plate 5-carries the electrodes 7, 8 and is likewise connected to the insert member 4 by means of glass solder.

There is no rigid connection between insert member 4 or cover plate 5 and the envelope 2.

The discharge begins at the electrode 7 in the discharge chamber a, passes via an aperture at the top in the insert member 4 into the chamber b, via an aperture 9 at the bottom into the chamber C and an aperture 10 in the cover plate 5 into the chamber deformed from cover plate 5 and envelope 2. From there, the discharge arc passes via the aperture 11 into the chamber e via an aperture 1 2 at the bottom into the chamber fand via an aperture 1 3 at the top into the chamber g to the electrode 8. The insert member 4, the cover plate 5 and the base plate 6 are each provided with a reflecting and fluorescent coating 14 at the sides adjacent to the discharge. The envelope 2 is provided with a fluorescent coating 1 5 at its inside, both coatings comprising a three-band mixture of fluorescent substances.

The cap 3 comprises plastics material and has an edge 1 6 for the insertion of the envelope 2. It also has opening slits 1 7 to cool the starter and ballast and an E 27 thread 1 8 for screwing the compact lowpressure discharge lamp 1 into a conventional incandescent lamp holder.

The low-pressure discharge lamp has a lamp voltage of about 75 V with a power of 1 5W and an operating frequency of about 45 kHz. It achieves a light yield of more than 60 1 m/W with a colour reproduction of stage 1 according to DIN 5035.

Claims

1. A compact low-pressure discharge lamp having a cylindrical envelope of glass, a substantially star-shaped insert member which forms, by means of partitions, a winding discharge path with at least three discharge chambers extending along the envelope as well as an additional cavity situated in the centre - each parallel to the lamp axis-a filling of mercury and at least one rare gas, two electrodes of high-melting-point metal as well as a cap fitted to the envelope at one side, wherein the insert member has a resilient action in the radial direction transversely to the longitudinal axis of the lamp and the individual partitions between adjacent discharge chambers bear tightly against the envelope without a rigid connection, the contact being effected along a line in each case.

2. A lamp as claimed in Claim 1, wherein each of the discharge chambers is bounded by its own partition.

3. A lamp as claimed in Claims 1 and 2, wherein each of the discharge chambers is bounded by a one-piece partition of the insert member, and this partition has a concave curvature in cross-section, directed towards the discharge chamber.

4. A lamp as claimed in any one of Claims 1 to 3, wherein the whole insert member is made of one piece.

5. A lamp as claimed in any one of Claims 1 to 4, wherein a cover plate is provided on the end of the insert member remote from the lamp cap, which cover plate bears tightly against the envelope without a rigid connection.

6. A lamp as claimed in any one of Claims 1 to 5, wherein the insert member comprises metal.

7. A lamp as claimed in any one of Claims 1 to 6, wherein the cover plate comprises glass.

8. A lamp as claimed in any one of Claims 1 to 6, wherein apart from the insert member, the cover plate also comprises of metal.

9. A lamp as claimed in any one of Claims 1 to 8, wherein the insert member and the cover plate are connected by means of glass solder.

10. A lamp as claimed in any one of Claims 1 to 5, wherein the insert member and/or the cover plate comprise plastics material.

11. A lamp as claimed in any one of Claims 1 to 10, wherein the envelope is sealed off from the lamp cap in a gastight manner by a base plate of metal.

1 2. A lamp as claimed in any one of Claims 1 to 10, wherein the envelope is sealed off from the lamp cap in a gastight manner by a base plate of glass.

1 3. A lamp as claimed in Claim 11 or 12, wherein the insert member and the base plate are connected by means of glass solder.

14. A lamp as claimed in Claims 11,12 or 13, when appendent directly or indirectly to Claim 5, wherein the base plate and/or the cover plate have a reflecting or fluorescent coating on their sides adjacent to the discharge.

1 5. A lamp as claimed in any one of Claims 1 to 14, wherein the envelope has a fluorescent coating on its interior.

1 6. A compact low pressure discharge lamp substantially as described herein with reference to the drawings.