GB966608A - Improvements in or relating to low pressure mercury vapour electric discharge lamps - Google Patents

Abstract

966,608. Fluorescent discharge lamps. GENERAL ELECTRIC CO. Ltd. July 2, 1962 [April 6, 1961], No. 12380/61. Addition to 828,015. Heading H1D. A low-pressure mercury vapour and rare gas fluorescent discharge lamp has the envelope provided at one or each end with a narrow tube extending outwards from the main discharge space, the outer end of the tube being closed, the tube containing an amalgam of mercury with a metal or alloy, and the tube length, the amalgam composition and the position of the amalgam within the tube being such that in normal operation of the lamp the temperature attained by the amalgam is such that the fractional mercury vapour pressure above the amalgam is less than the saturated vapour pressure of free mercury at the temperature attained by any part of the envelope between the electrodes. The length of the tube containing the amalgam and the position of the amalgam within the tube can be such that in normal operation of the lamp the temperature attained by the amalgam is less than that attained by any part of the envelope between the electrodes. The tube 9 containing the amalgam can consist of a glass tube 9 extending from the pinched re-entrant front tube 6 and the amalgam can be in the form of a coating 11 on the inner surface of the tube or in the form of a pellet or pellets in the tube. Methods of forming the amalgam from a pellet or separate pellets of mercury and the amalgamating metal or alloy are described. A plug of glass wool permeable to mercury vapour but not to liquid mercury can be present in the tube 9. The tube 9 can be covered by the cap 8 carrying the terminals 7. The tube containing the amalgam can be tipped-off at such a distance from the end of the envelope that in normal operation the end of the tube is maintained at a temperature which is lower than that of any other part of the envelope, as described in Specification 854,513, the amalgam heing deposited close to the tipping-off region and retained in position by a plug of glass wool. Cadmium, in the weight ratio of 8 to 1 of mercury, is the amalgamating metal preferred but aluminium, lead, tin, zinc, gold, silver, copper and barium are also referred to. The rare gas filling can be argon at a pressure of about 3 mms. Fillings of neon or a mixture of neon and argon are also referred to. The end of the envelope containing the tube 9 can be cooled as described in Specifications 835,144, 854,514 and 854,647.