GB863467A - Improvements in or relating to low pressure electric discharge lamps - Google Patents

Abstract

863,467. Discharge lamps. GENERAL ELECTRIC CO. Ltd. May 21, 1958 [May 21, 1957], No. 16117/57. Class 39(1). A low pressure mercury vapour-rare gas discharge lamp having an inner coating 2 of fluorescent material and a heatable electrode 3 at each end, is provided at least at one end with a shield 10, Fig. 1, behind the electrode for restricting the transfer of heat from the space between the electrodes into the space between the shield and the adjacnt end of the envelope 1, the end of the envelope being closed by a re-entrant glass foot-tube 6 which is coaxial with the envelope into the pinched inner end 5 of which the electrode supports 4 are sealed, and the shield 10 being formed of glass and structurally integral with the foottube so as to be supported directly therefrom independently of the electrode supports. The shield 10 can be in the form of a glass disc sealed to a glass support rod 9 which is sealed directly into the pinch 5 between the electrode supports 4. Holes can be provided in the disc or slots extending inwardly from the edge of the disc for the passage of the electrode supports 4 which can also serve as supply leads. The disc can be planar, part-spherical or partcylindrical with its concave surface directed towards the adjacent electrode. In the construction shown in Fig. 2 the shield is in the form of a tubular glass member 11 sealed to the pinch 5 and flaring outwards at 12. The shield 11 and the foot-tube 6 can be formed from a single glass tube with the pinch 5 formed at an intermediate part of the tube. The disc 10, Fig. 1, or the flared end 12, Fig. 2, can be provided with a heat-reflecting metallic coating facing the adjacent electrode. The rare gas filling used for starting can consist wholly of neon or of a mixture of neon and argon at a few mms. pressure, e.g. 80% neon and 20% argon, or 60% neon and 40% argon, at a total pressure of about 2 mms., the percentages being in respect of the partial pressures.