Electric lamp and discharge devices – Having heating means to control gas/vapor – gas or vapor... – Vapor generating
Patent
1997-01-24
1998-05-12
Patel, Nimeshkumar
Electric lamp and discharge devices
Having heating means to control gas/vapor, gas or vapor...
Vapor generating
313607, 313234, 313545, 315248, H01J 6504
Patent
active
057511101
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to an electrodeless low-pressure discharge lamp provided with a lamp vessel which is closed in a gastight manner, which surrounds a discharge space, which contains a filling of mercury and a rare gas, and which has a cavity and a collar where said cavity is open towards the exterior, an electric coil being accommodated in said cavity while a support with an amalgam is positioned in the discharge space.
Such a lamp is known from U.S. Pat. No. 4,622,495. A high-frequency magnetic field is generated by the electric coil during lamp operation, maintaining an electric discharge in the lamp vessel. The cavity and the collar are integrally formed from a glass tube. A portion of the lamp vessel surrounding the cavity is fused to the outer circumference of the collar. The amalgam is provided on a metal gauze which is fastened to the cavity by means of a rod. The electric discharge arising after lamp ignition heats the support with the amalgam, so that the latter releases mercury bound thereto. The released mercury vapor achieves that the light output rises quickly after ignition up to a value desired for nominal operation. It is a disadvantage, however, that the amalgam degenerates comparatively strongly during lamp life.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an electrodeless low-pressure discharge lamp of the kind described in the opening paragraph which has a construction which counteracts degeneration of the amalgam.
According to the invention, the electrodeless low-pressure discharge lamp of the kind described in the opening paragraph is for this purpose characterized in that the collar is made of metal and the support is fastened to the collar.
Amalgam temperature is dependent not only on the discharge temperature but also partly on the temperature of the location where the amalgam support is fastened to the lamp vessel. The temperature of the cavity to which the amalgam support is fastened in the known lamp rises comparatively slowly from room temperature to a value which may be higher by 200.degree. C. or more. The result of this is that the amalgam temperature after an initial steep rise increases further gradually and does not stop increasing until the cavity has assumed its equilibrium temperature. The amalgam temperature then assumes values which are higher than those necessary for the release of mercury, which causes a strong degeneration of the amalgam.
The metal collar to which the amalgam is fastened in the lamp according to the invention undergoes a substantially smaller temperature rise after lamp ignition. This renders it possible to position the amalgam such that it quickly assumes a temperature necessary for the release of mercury, while the subsequent temperature rise, and thus the extent to which the amalgam degenerates during life, is limited.
The collar may be made from a metal which has a coefficient of expansion corresponding to that of the glass of the lamp vessel, for example, in the case of lime glass a CrNiFe alloy, for example Cr 6%, Ni 42%, remainder Fe by weight. In a hard-glass lamp vessel, for example of borosilicate glass, it is possible to use, for example, a collar of Ni/Fe or NiCoFe, for example Ni 29%, Co 17%, remainder Fe by weight.
Suitable materials for forming an amalgam with mercury are, for example, indium or an alloy of lead and tin. The amalgam may be provided, for example, in an open capsule. It is favorable, however, when the amalgam constitutes a layer on a surface of the support. Suitable materials on which the amalgam may be provided are, for example, stainless steel, iron, nickel. An intermediate layer may be present between the amalgam and the surface of the support on which the amalgam is provided so as to promote the adhesion of the amalgam to the support, for example an intermediate layer of cobalt or an intermediate layer of an alloy of the amalgam-forming material and the support material.
The support may be, for example, a single body, for example a strip fastened at one
REFERENCES:
patent: 4622495 (1986-11-01), Smeelan
patent: 5412288 (1995-05-01), Borowiec et al.
patent: 5434482 (1995-07-01), Borowiec et al.
patent: 5559392 (1996-09-01), Cocoma et al.
Spaapen Antonius J.
Van Gennip Theodorus J.M.J.
Van Haastrecht Johannes T.J.
Egbert, III Walter M.
Patel Nimeshkumar
U.S. Philips Corporation
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