Discussion on “transformation of electric power into light,” and “new types of incandescent lamps,” New York, November 23, 1906

Herschel C. Parker: The problem of the transformation of electric power into light is of equal importance to the physicist and to the electrical engineer. When an electrical engineer experiments on the problem, he is experimenting in the domain of physics; when a physicist works on the problem, he is an electrical engineer, if his experiments are successful; if not, he is simply a physicist. There are only two or three points in Dr. Steinmetz´s beautiful paper on which I am capable of saying anything that will interest you. The first is the fact that it is not the melting point of refractory substances that gives a high efficiency, but it is the point of disintegration or vaporization, shown by the tungsten filament and tantalum filaments which have a much lower melting point than carbon, but are much more difficult of vaporization, and hence show a great increase in efficiency. Mr. Walter G. Clark and I have been experimenting for a number of years on the subject of incandescent lighting, and we hope in the near future to present before the Institute some of these results which we think are of interest. A certain filament with which we have been experimenting, one substance of which is supposed to have a melting point of about 1400° cent., has shown an efficiency in experimental lamps of about one watt per candle, with an average life of 700 to 1200 hours. The vapor-tension of this substance is remarkably low; that is, it is almost impossible to vaporize the substance. This bears out in a remarkable manner the statement of Dr. Steinmetz. Another point about this filament is that if at the low temperature of 1800° or 1900° cent., it will give an efficiency of one watt per candle, we certainly must believe that some substances have a considerable selective radiation in the solid form, notwithstanding what the experiments of Messrs. Waidner and Burgess have shown regarding the tungsten and tantalum filaments.