New Electric Lamps

Abstract

IN a paper read to the Royal Society of Arts on March 7, Mr. J. W. Hyde of the G.E.C. Research Laboratories, Wembley, gave a full account of the working of the new electric discharge lamps. The sodium discharge lamp is practically monochromatic and of a brilliant yellow colour. Hence coloured objects illuminated by it all appear to be various shades of brown. Its efficiency, about 40 lumens per watt, although three times that of the ordinary filament lamp, is yet only about a tenth of the maximum possible yellow light that could be obtained for the same power. It is well known that the efficiencies of all kinds of electric lamp vary with their life. The problem of candle power maintenance is one that constantly engages the attention of every lamp manufacturer. In spite of years of research, the light output of incandescent filament lamps still drops by a certain amount after several hundred hours burning. The candle power maintenance for the new lamps has now been raised to a reasonable figure, but it is recognised that considerable improvements are possible. It is rapidly approaching that of the filament lamp. At present there is no sign that the eminently simple and highly developed filament lamp will shortly be replaced by discharge lamps for purposes of indoor illumination; but it must be admitted that discharge lamps will play an ever increasing part in the future of electric lighting. Already there are 65 street lighting installations for which these lamps have been adopted. Street lighting is the one use of artificial lighting for which we have never produced enough light. The use of the new lamps is an excellent opportunity of improving the lighting of our streets at little, if any, increase in the cost.