GB414391A - Improvements in and relating to electric discharge lamps - Google Patents

Abstract

414,391. Discharge lamps. BRITISH THOMSON-HOUSTON CO., Ltd., Crown House, Aldwych, and GENERAL ELECTRIC CO., Ltd., Magnet House, Kingsway, both in London.-(Assignees of Spanner, H. J. ; 117, Chausseestrasse, Berlin.) Feb. 1, 1933, No. 3125. Convention date, Feb. 1, 1932. [Class 39 (i).] The metal-vapour filling of the high-pressure lamp described in Specification 410,787 contains a trace of sodium in addition to metals such as mercury, cadmium and zinc, the quantities of the sodium and of the other metals being adjusted so that the main lines of their spectra are of the same order of magnitude and that a substantially white light is obtained. The envelope may be of "Duran" glass with a high silica content, this glass assuming a greenbrown tint after use of the lamp and fluorescing, due to the presence of sodium on its surface. The thermionic electrodes may be of tungsten or oxide-coated and may be heated by the discharge or independently. In manufacturing the lamp, the metals to be introduced are placed in chambers 4, 5, leading off the exhaust tube 3. The lamp is exhausted, rare gas is introduced, mercury is added by heating the chamber 5 and the lamp is outgassed by a heavy-current mercury-vapour discharge. After re-exhausting, the final filling of argon at 6 mm. pressure is introduced and the metals are distilled from the chambers 4, 5 until a photometric spectroscopic test indicates that the quantities of metals arc correct, the lamp being then sealed off.