US 3660711 A
A high pressure xenon discharge lamp whose envelope has tubular portions extending from an enlarged central portion, the ends of the tubular portions being sealed by internal metal shells closed at their inner ends, in which the electrode rods are embedded in glass stems whose outer ends are attached to the tubular portions of the envelope and whose inner ends are spaced from the tubular portions, allowing the tubular portions to be of sufficient diameter for the lamp to be supported from the ends of the tubular portions while avoiding excessive thickening of the walls of the tubular portions.
Description (OCR text may contain errors)
i United States Patent 1151 3,660,711
Stanyon et a]. 1 May 2, 1972 54] XENON LAMP  m References Cited  Inventors: Horace Edward Stanyon; Kenneth Buckley UNITED STATES PATENTS Rebinson; Eric John George of 2,965,790 l2/l960 lttig et al .313/217 London, England 2,781,470 2/1957 Bellott  Assignee: Thorn Lighting Limited, London, England Pnmary Examiner-Roy Lake  Filed: Mar. 17, 1970 Assistant Examiner-Darwin R. Hostetter Attorney-Laurence Burns  Appl. No.: 20,173
57 ABSTRACT Foreign Application Priority Data A high pressure xenon discharge lamp whose envelope has tubular portions extending from an enlarged central portion, the Mar. 19, 1969 Great Brltam ..l4,525/69 ends of the tubular portions being Sealed y internal metal shells closed at their inner ends, in which the electrode rods 52 US. Cl ..313/220, 313/184, 313/217, are embedded in glass stems whose outer ends are attached to 313/244 the tubular portions of the envelope and whose inner ends are  lnt.Cl. ..H01j61/36 spaced from the tubular portions, allowing the tubular por-  Field of Search ..313/184, 217, 220, 331 tions to be of sufiicient diameter for the lamp to be supported from the ends of the tubular portions while avoiding excessive thickening of the walls of the tubular portions.
3 Claims, 2 Drawing Figures Patented May 2, 1972 HORACE EDWARD STANYON KENNETH BUCKLEY ROBINSON ERIC JOHN GEORGE BEESON INVENTORS BY; g
ATTORNEY XENON LAMP The present invention relates to high-pressure xenon discharge lamps such as compact source or short are xenon lamps.
These lamps are generally designed to operate with an internal gas pressure of many atmospheres. The lamp envelope, which is generally made of fused silica, and the seals through which current-carrying leads enter the lamp are designed to contain this high pressure and to avoid thermal stresses in the lamp body which could result in lamp failure by bursting. Since the lamps are normally used in static equipment mechanical strength is a secondary consideration. However when the existing lamps are subject to vibration or shock they tend to fail by cracking at certain weak points in the envelope.
One particular point of weakness is where the envelope surrounds the electrode structure, which is of rod formation. While the central portion of the envelope is bulbous, and commonly spherical, the portions surrounding the electrode structures are tubular and are reduced in diameter to engage and support the electrode structures. Since the lamp is normally supported at the outer ends of the tubular portions of the envelope these reduced diameter sections are points of weakness. The diameter cannot be increased by increasing the wall thickness since this results in increased risk of thermal stresses which will also weaken the lamp.
In accordance with the present invention there is provided a high-pressure xenon discharge lamp having electrode structures of rod formation supported within tubular portions of the envelope extending from a central enlarged portion of the envelope, in which part of the length of each of the electrode structures is embedded in a stem whose outer end is supported within the tubular portion of the envelope and whose inner end is spaced from the tubular portion of the envelope.
Where the outer ends of the tubular portions of the envelope are closed by tubular metal shells sealed within the tubular portions the outer end of the stem is supported by the closed inner end of the metal shell and by the wall of the tubular portion. The inner ends of the stems can be located with respect to the tubular portions by projections.
To increase the mechanical strength at the ends of the envelope from which the lamp is supported a metal cap is fitted on the end of the envelope and is secured to a metal rod which extends into the shell closing the end of the envelope and is packed tightly with heat-resisting material. A recess at the outer end of the rod serves for the mechanical support of the rod and electrical connection is made by way of the cap and molybdenum foils sealed between the envelope and the tubular shell.
The invention will now be described in more detail with the aid of an example illustrated in the accompanying drawings, in which:
FIG. 1 is a longitudinal section of a xenon arc lamp in accordance with the invention, and
FIG. 2 is a section on an enlarged scale of one limb of the lamp envelope, showing the end cap construction.
Referring first to FIG. 1, the lamp envelope has a central portion which in this instance is of spherical shape. It may alternatively be elongated or of isothermal shape and it may have an auxiliary starting probe fitted. The envelope has a uniform wall thickness of about 2 to 4 mm. which enables it to operate at temperatures of 800 C. and higher without any risk of bursting. The ends of the envelope are formed by tubular portions 11 and 12 of uniform diameter which are closed at their outer ends by tubular metal shells l3 and 14, respectively, sealed within the tubular portions of the envelope. The electrodes of the lamp have rods 15 and 16 which serve as supports and as electrical conductors. The rods 15 and 16 are located within the tubular portions 11 and 12, respectively, and in a conventional lamp would be in direct contact with the inner surface of a thickened portion of the wall of the tubular portion, the outside diameter of the tubular portion being reduced to avoid undue thickening and the consequent risk of thermal stresses.
In the construction shown, however, the rods 15 and 16 are embedded in respective stems l7 and 18 which are fixed at their outer ends between the closed inner end of the tubular metal shell 13 or 14 and the inner wall of the tubular portion 11 or 12. Projections 19 on the inner ends of the stems l7 and 18 engage the inner walls of the tubular portions 11 and 12 and thus locate the stems. In this way the tubular portions 11 and 12 of the envelope can have a uniform diameter of suffcient magnitude to achieve the required strength while the electrode rods are still firmly supported and the risk of thermal stresses is minimized. The thickened portion of the stem is at its outer end where the temperature is lower. The diameter of the tubular portions 11 and 12 can be up to half that of the bulb and with a wall thickness equal to or comparable with that of the bulb they can easily be annealed to eliminate thermal stresses.
The ends of the envelope are fitted with metal caps 20 having ferrules 21 formed with conical recesses 22 by means of which the lamp can be located and supported. As shown in FIG. 2 the ferrule 21 at each end of the lamp is screwed onto the end of a metal rod 23 which is disposed within the metal shell 14 (or 13) and is packed tight with heat-resistent material 24 such as asbestos.
The cap 20, which is secured to the outside of the tubular portion 12 by a heat-resisting cement, comprises a cylindrical sleeve which is brazed to a washer 25 which in turn is brazed to the rod 23. An external flexible current lead (not shown) is attached to a second washer 26. Current is conveyed to the electrode rod 16 by molybdenum foils 27 embedded in the seal between the tubular metal shell 14 and the portion 12 of the envelope. The leads from the foils are attached to the washer 25. Therefore the current is carried from washer 24 through the molybdenum foils 27 by way of the metal shell 14 to the electrode 16.
This end cap construction provides a large area of engagement between the metal supporting parts and the glass or silica parts and thus reduces the stress loading on the brittle silica under shock and vibration and reduces the risk of loosening of the caps.
The projections 19 are preferably omitted to allow some resilience in the support of the anode and cathode. This is found to result in the tube being less susceptible to shock or vibration. It is also difficult to ensure that the projections 19 are a tight fit in the tubular portion 1 l or 12 and if they are not the hammering of the projections against the tube will tend to weaken it.
1. A high pressure xenon discharge lamp comprising an envelope containing a fill gas and having tubular end portions and a central enlarged portion between said end portions, electrode structures of rod formation, and stems in each of which at least part of said electrode structures is embedded, each stem having an outer end which is sealed by a metal shell and supported within one of the tubular end portions of the envelope and an inner end which is disposed within, but spaced from the said tubular end portion by a series of projections; a metal end cap having an internal metal rod and a conical locating recess on its outer surface filled over the tubular end portions; and current conveying means fitted between said electrode and said metal end cap.
2. A lamp according to claim 1 where said metal rod secured to said end cap extends within the said tubular shell, and a body of heat-resisting material is packed between said metal rod and said tubular shell.
3. A lamp according to claim 1 where said current-carrying means comprises molybdenum foils sealed between said metal shell and the tubular metal end caps of the envelope.