CD 1964098 E&MP27.076
September 9, 1939
Dr. Harvey C. Rentschler, Director of Research, Westinghouse Lamp Company, showing a positive column, hot cathode sodium vapor lamp which he demonstrated for the first time in this country during the January Science Forum of the New York Electrical Society when he talked on “Scientific Conquests of 1931.
This sodium lamp, recently developed in Germany by Dr. M. Pirani, Director of Research, the Osram Company, Berlin, is the most efficient light source yet developed. It has an efficiency of 70 percent, which is three to four times as efficient as Neon light, and gives six times as much light for the same current as the 40-watt tungsten lamp.
The increased efficiency of the sodium-vapor lamp is due to the fact that practically all the radiation from the element sodium falls very nearly in that part of the spectrum which is most sensitive to the eye. Thus, 70 percent of the electric energy passed through the vaporized sodium is converted into light.
Original Caption by Science Service