GB569198A - Improvements in or relating to electric lamps - Google Patents

Abstract

569,198. Discharge apparatus. LEVY. H. R. July 29, 1943, Nos. 12330, 12331 and 16539. [Class 39 (i)] A lamp consists of an evacuated envelope having on opposite walls a photo-emissive layer 4, Fig. 1, and a luminescent layer 3 arranged so as to have a retroactive effect on one another. In the form shown, the envelope is of cylindrical annular shape, and the central space may be used to house an auxiliary light source such as an elongated incandescent filament lamp for use in combination with the photo-luminescent element and for starting the latter. Alternatively, the starting may be effected by any stray illumination or the incandescent lamp may be replaced by a gas discharge tube with or without a luminescent coating. The photoluminescent element may have an external luminescent layer 7 which is excited by radiation from the inner layer 3, and, in cases where this layer is of the short-wave ultra-violet type, the wall of the envelope is made permeable thereto, and the photo-emissive layer is selected for its response to such radiation. To increase the light output, two or more electrodes may be mounted between the photo-emissive and luminescent layers, Fig. 3 (not shown). These electrodes may be made secondary-electron or photo-electron emissive or both, and the luminescent layer may also be made secondaryelectron emissive. Fig. 4 shows an arrangement in which a gas discharge lamp 17 with a luminescent layer 19 has a window 20 facing a window 23 of a photo-luminescent lamp 18. They are associated with bridging plates 26, 27 of lightdiffusing material such as frosted glass. The lamp 18 may be enclosed by an outer envelope 29 containing a transparent electrolyte 28 which acts as a cooling medium and also may be earthed to act as an electrostatic shield. When used for A.C. working, both the inner and outer walls of the envelope may carry the luminescent material and the photo-emissive material, with or without auxiliary electrodes is mounted intermediate. The layers are made conductive by a backing of metal film or a mesh or similar electrode may be disposed near them. The luminescent material referred to in the description comprise zinc orthosilicate, zinc sulphide activated with copper, a mixture of zinc sulphide and zinc-cadmium sulphide, cadmium tungstate activated with uranium, and zinc sulphide containing two heavy metals such as copper and gadolinium.