New types of incandescent lamps

For a number of years the standard of electric lighting has been set by the carbon-filament lamp consuming initially 3.1-watts per candle-power. Progress there has been; but it has been chiefly in the way of minor improvements in the process of manufacture, rating of lamps, and in the way of a more general adoption by electric lighting companies of the 3.1 watts-per-candle lamp. This watt-per-candle consumption has been recognized as the minimum practicable undergood operating conditions. Any radical or considerable improvement in the lamp itself has seemed improbable of attainment. The degree of improvement which has been made in the carbon filament lamp has been indicated by data given by Mr. J. T. Marshall in a paper before the Franklin Institute∗. The continuous increase in the effective life of incandescent lamps burned at 3.1-watts per candle between the years 1888 and 1904, as given in Marshall´s paper, are shown in the curve, Fig. 1. The effective life at the present time is seen to be substantially two and one half times as great as the life in 1888. The advent of the osmium lamp cannot be said to have altered the state of affairs materially. In spite of its very high efficiency and long life, this lamp seems precluded from exercising any revolutionary influence on lighting practice, on account of its low voltage and most of all by the limitations of of the visible supply of the material of which the filament is composed.