Patent GB-929618-A (GB)
Title: Improvements in or relating to multiple-groove discharge lamps
IPC: H01J61/33
Filed: 1959-04-01
Abstract: 929,618. Discharge lamps. GENERAL ELECTRIC CO. April 1, 1959 [April 18, 1958; May 12, 1958 (2)], No. 11039/59. Class 39 (1). A low-pressure discharge lamp, such as a fluorescent lamp, comprises an elongated vitreous envelope 2 having electrodes 6 sealed into opposite ends and containing an inert starting gas and a metal vapour, the envelope having a generally circular cylindrical boundary and a plurality of relatively short longitudinallyextending channel-shaped grooves 10, 11 alternately arranged on opposite sides of the envelope and forming a generally kidney-shaped cross-section at least at the centre portions of the grooves, wherein the groove throw A is between <SP>2</SP>/ 3  and <SP>3</SP>/ 2  of the diameter of the envelope boundary, and wherein the grooves have slanting end walls in a longitudinal direction to form a generally sinusoidal discharge path, the width of this path, measured in the medial plane of the grooves, being such that the wall-to-wall spacing C measured between the slanting end walls of two adjacent grooves is in the range of 60-150% of the wall-to-wall spacing D in the grooved portions of the envelope. The wall-to-wall spacing C can be approximately 80% of the wall-to-wall spacing D and the groove throw A can be approximately equal to the diameter of the envelope boundary. The channel-shaped grooves can have, in a transverse plane, a generally rounded crosssection, Fig. 3, with an aperture angle B of at least 90 degrees, preferably 100 degrees. The slanting end walls of the grooves can be curved in cross-section, as shown at 15a, 16a in Fig. 4a, or substantially straight, as shown at 15b and 16b in Fig. 4b. At least one of the grooves can be asymmetrically located with respect to the diametral plane through the longitudinal axis of the envelope to provide a wider rail portion 13<SP>1</SP>, Fig. 5, on one side and a narrower rail portion 14<SP>1</SP> on the other side, thus producing regions of different operating temperature. Two differently asymmetrically located grooves can be provided of which one is displaced to one side and the other is displaced to the opposite side of the diametral plane and can be located near the centre of the envelope and three grooves throws apart. At least one of the grooves 10<SP>11</SP>, 11<SP>11</SP>, Fig. 7, can be provided with an upstanding narrow fin 25, 26 extending outwardly from the bottom wall of the groove to provide a constricted zone within the envelope. Alternatively a depression or short indentation can be provided in the bottom or inner wall of one or more of the grooves and project inwardly into the envelope space, preferably to one side of the medial plane of the groove. The starting gas can be one or more of the inert rare gases, e.g. argon at a pressure of 0.5-5 mm., or a mixture of argon and not over approximately 50% neon or helium within this pressure range. Preferably argon at a pressure of 1.4 mm. together with mercury at a partial pressure of 1-20 microns, preferably 6 microns, are used. Krypton and xenon are also referred to as starting gases. A phosphor coating 8 of alkaline earth halophosphate is provided on the inside of the envelope. Specifications 802,877 and 821,321 are referred to.