GB749448A - Electronic fluorescent illuminating lamp - Google Patents

Abstract

749,448. Fluorescent discharge lamps. SEBEL SOC. ANON. April 16, 1953 [April 22, 1952; Jan. 28, 1953], No. 10476/53. Class 39 (1). A fluorescent lamp of the high-vacuum type has an anode 14, Fig. 1, coated on the tube wall and carrying a fluorescent coating 6 and two grids 12, 13 screening the indirectly heated cathode 2 from the anode 14, grid 12 being at cathode potential or slightly negative relatively thereto and grid 13 being positive relatively to the cathode grids 12, 13 being of the same pitch and having aligned elements so that the elements of grid 13 are in the electronic shadow of grid 12. The negative grid 12 focuses the beam so that the positive grid collects few electrons, i.e. about 3-5 per cent. The cathode and grids can be arranged coaxially in a cylindrical prismatic or parallolepipedic form. In Fig. 1 the cathode and grids are carried by mica washers 10, 11; the grids may be helices of circular or rectangular section secured to bars 15. Grid 13 may be connected to anode 14 which may be formed by spraying. If the fluorescent coating 6 emits ultra-violet light, the upper wall of the bulb can be coated with a photoluminescent substance to transform the ultra-violet to visible light. Alternatively the anode may be formed by the tube wall which is made of conductive glass. In this case the fluorescent coating may be over the whole inner surface of the tube. The heater 9 is of tungsten coated with alumina. To avoid extinction of fluorescence due to infra-red rays produced by the cathode, the cathode and grids are made flat and parallel to one another but extend perpendicular to the tube axes, Fig. 2 (not shown), so that the infra-red rays pass out through the uncoated portion of the envelope.