Electric Discharge Lamps

Abstract

AT the tenth annual conference at Margate of the Association of Public Lighting Engineers, a paper was read on September 5 by Mr. G. H. Wilson on electric discharge lamps and their applications to public lighting. These lamps, which mark a considerable advance in the efficiency of light production, emit light not because any solid is made ‘white hot’ (as in the case of the filament of the ordinary electric lamp) but because a gas or vapour is ‘excited’ electrically. When a suitable gas at low pressure is sealed into a glass tube having an electrode at either end, it conducts electricity and light is emitted, the colour of which depends upon the gas used. Mercury vapour produces a blue light, helium an ivory white, sodium a yellow light, and nitrogen a buff colour. The earlier experimental types of discharge lamp were developed for the efficient production of coloured light and are available to-day for decorative purposes, but efforts have been made, with considerable success, to produce lamps which give white light or light approaching white in colour. Development is continuing at a rapid rate, and the experimental lamps of to-day will, in all probability, be the practical lamps of to-morrow. Mr. Wilson gave technical details of the lamps which have actually been in successful use in outdoor installations. They give from two to three times the light of an ordinary electric lamp for the same current and enjoy a longer life. Practical installations have been erected at Croydon, Wembley and elsewhere, and these have shown that the new lamp can be applied successfully to public lighting. A high degree of visibility is attained, and objects on the roadway can be clearly seen for an unusually long distance.