A study of the characteristics of low voltage arc discharges in cesium vapor led to the development of a practical lamp that was used in a successful communication system using infra-red radiation. The radiated energy is confined almost entirely to the cesium resonance lines at 8521 and 8944 angstroms. Data are presented that give structural details, operating characteristics, infra-red output, and efficiencies of several lamps of different sizes. Excellent modulability is attained throughout the audiofrequency range with current modulation up to 100 percent.
N. C. BEESE, "Cesium Vapor Lamps," J. Opt. Soc. Am. 36, 555-557 (1946)