GB1199535A - Low-Pressure Sodium Vapour Discharge Lamp - Google Patents

Abstract

1,199,535. Metal-vapour lamps. PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd. 5 July, 1968 [10 July, 1967], No. 32169/68. Heading H1D. In a low-pressure sodium-vapour discharge lamp containing sodium not in vapour form in the operating condition of the lamp, and having the discharge tube mounted within an outer envelope exhausted to 10-<SP>3</SP> torr or below, substantially the whole of the non-vapourized sodium is contained in an appendage which lies entirely outside of, but opens into, the discharge space, the condition V > 0À5A#A being satisfied, where V is the volume of the protuberance in cm<SP>3</SP> and A is the area, in cm<SP>2</SP>, of the orifice between the protuberance and the discharge space; the appendage is disposed in the vicinity of an electrode of the lamp, is heated only by heat evolved in the lamp, and has no conductive connection to an electrode of the lamp in the inoperative condition. As shown, Fig. 6, the sodium may be contained in a re-entrant portion 54 of the discharge tube 51, the closed end of the protuberance being adjacent, and heated by, the electrode 53. In the embodiment of Fig. 4, in which the outer envelope is not shown, the protuberance 23 is so twisted with respect to the plane p which passes through both the axis of the discharge tube and the orifice 24 of the protuberance, that for any orientation of the lamp, a portion of the protuberance lies below the level of the orifice, whereby to ensure that the enclosed sodium, liquid under operating condition, is prevented from flowing into the discharge space. In further embodiments the protuberance communicates with one limb of a U-shaped discharge tube (Figs. 1 to 3, not shown), and may be in the form of a sodium container connected to the discharge tube by a supply tube (Fig. 5, not shown). The lamp may be manufactured by sealing the protuberance, containing the whole of the sodium required for the lamp filling, to the discharge tube such that it communicates with the latter via an orifice, and heating the protuberance.