In the early ’80’s current was expensive, costing a consumer on the average about twenty cents per kilowatt hour. The cost has gradually come down and the general average rate for which current is sold for lighting purposes is now about 4½ cents. During the period 1880 to 1905 the average efficiency of carbon lamps throughout their life increased from about one to over 2¾ lumens per watt and their list price decreased from one dollar to twenty cents. The average amount of light obtained for one cent at first was about five candlepower hours and in 1904 it was increased to over thirty-six at the average rate then in effect. The next year with the more efficient Gem lamp 44 candle-hours could be had for one cent. In 1906 the amount was increased to 50 with the tantalum lamp and with the tungsten lamp in 1907, even at its high price of $1.50, the amount was further increased to 63. Since then the average cost of current has been reduced but slightly, but the efficiency of the tungsten lamp has materially increased and its cost reduced so that it is now possible to obtain, with the ordinary 40-watt lamp 170 candle-hours for a cent. If the gas-filled tungsten lamp were used the amount of light now obtained for a cent would depend upon the size, which, for the 1000-watt lamp, would be 382 candle-hours.
STATISTICS REGARDING THE PRESENT DEMAND FOR LAMPS
In the United States there are about 350 million incandescent and about two hundred thousand magnetite arc lamps now (1923) in use. They are increasing about 10 per cent each year. The annual demand for incandescent lamps for renewals and new installations is over 200 millions, exclusive of miniature lamps. The use of incandescent lamps in all other countries put together is about equal that in the U. S.
The average candlepower of standard lighting lamps has increased from 16, which prevailed during the period prior to 1905, to over 60. The average wattage has not varied much during the past twenty-odd years, the average lamp now consuming about 55 watts. This indicates that the public is utilizing the improvement in lamp efficiency by increased illumination. The present most popular lamp is the 40-watt size which represents 20 per cent of the total demand. Second in demand is the 25-watt at 18 per cent and third, the 50-watt at 15 per cent of the total in numbers. While the aggregate demand of all the gas-filled tungsten lamps is a little over 20 per cent in numbers, they represent, on account of their greater efficiency and wattage, over half the amount of total candlepower used. In the United States about 85 per cent of all lamps are for the 110-volt range. About 5 per cent for 220 volts, 2 per cent for street series lighting, 3 per cent for street railway and 5 per cent for trainlighting and miscellaneous classes of service.
SELECTED BIBLIOGRAPHY
Alglave and Boulard, “The Electric Light,” translated by T. O’Connor Sloane, edited by C. M. Lungren, D. Appleton & Co., New York, 1884.
Barham, G. Basil, “The Development of the Incandescent Electric Lamp,” Scott Greenwood & Son, London, 1912.
Dredge, James, “Electric Illumination,” 2 vols., John Wiley & Sons, New York, 1882.
Durgin, William A., “Electricity—Its History and Development,” A. C. McClurg & Co., Chicago, 1912.
Dyer & Martin, “Edison, His Life and Inventions,” 2 vols., Harper & Bros., New York, 1910.