In order to construct a most intense source of the continuous spectrum of hydrogen, the most favorable conditions were systematically investigated. The intensity varied linearly with the current density except for very high current densities where it varied less rapidly. The pressure for a maximum of intensity was found to be a function of the current density and practically varied from 1 to 2 mm. A study of the relation of the intensity to length, surface, and cross section of the capillary was made. On the basis of these results a powerful source of the continuum was constructed. This source was compared with the positive crater of the carbon arc and found to be superior in intensity below 2925A.
NOYES D. SMITH, "Intensity of the Continuous Spectrum of Hydrogen," J. Opt. Soc. Am. 28, 40-45 (1938)