Abstract
The history of electric lamp development has been one of steady improvement in the efficiency of production of light. The lamps used to-day for general lighting have 15 to 20 times the efficiency of those first developed some 70 years ago. This paper surveys recent achievements and indicates the probable lines of future developments. New types of carbon arc lamp are described. Filament lamps, on the whole, are unlikely to advance far beyond their present level of performance. (Discharge lamps, however, promise considerable development in various directions. Typical of progress in fluorescent lamps is the discovery of halophosphate phosphors giving white light from a single powder, having a high degree of chemical stability and already providing an improvement of more than 50 per cent in the average efficiency throughout life. Simplification of control gear and the rapid starting of lamps are other aspects under constant review and in which developments may be expected. High-pressure metal vapour lamps show improved colour-rendering properties, without loss of luminous efficiency, by the addition of cadmium and zinc vapours and the use of higher operating temperatures. They are already finding application in cinema and television studios and give promise of ultimate use in general lighting service. Other developments reviewed include high intensity flash discharge lamps for use in photographic studios, press photography, and similar work. The operating circuit can be adapted for using the lamps in stroboscopic examinations of moving machinery. Daylight colour matching fluorescent lamps and additions to the range of specialised discharge lamps used in laboratory work are also described.
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