Spectral Distribution of Energy Radiated from a New Type of Tungsten Mercury Arc

Abstract

This paper describes measurements with a quartz monochromator and thermopile of the energy flux from the tungsten mercury arc which is the source of radiation in the General Electric Sunlamp. Data are given on the energy flux radiated in each of the principal mercury lines below 6000A and a curve is given for the distribution of energy in the continuous spectrum between 2500 and 17000A. The maximum in the continuous spectrum curve comes at about 10600A where the energy flux in a 50A band is ${6.5}_9$ microwatts per ${\mathrm{cm}}^2$ at one meter distance from the center of the arc in a direction normal to the plane of the leads when the arc is operated with 115 volts on the primary of the transformer. The energy maximum corresponds to that of tungsten at about 2500°K but the shape of the curve below 5000A corresponds more closely to that of tungsten at 3250°K which is approximately the maximum temperature of the electrodes. For the radiation in a direction normal to the plane of the leads 1% of the total energy flux was found to lie between 2500 and 3200A, 1% between 3200 and 4000A, 10% between 4000 and 7600A, 46% between 7600 and 17000A, ${29.}_5$% between 17000A and the cutoff (roughly 40,000A) of a fused quartz plate 2.4 mm thick and the remaining ${12.}_5$% at longer wave-lengths.