A low voltage hydrogen discharge tube giving an intense continuous spectrum in the ultraviolet is described. The variation of the intensity of the continuum with pressure, current and discharge voltage has been determined. Fora given power consumption 220 volts was found to be more efficient in exciting the continuum than 1200 volts. The hot cathode made it possible to maintain discharges at much higher pressures with 1200 volts than was possible with a cold cathode.
The manner in which the relative intensities of the continuum, secondary and series spectra of hydrogen vary with pressure and discharge voltage, indicates that they are largely excited by electron impact rather than by recombination.
A. E. SMITH and R. DUDLEY FOWLER, "A Low Voltage Source of Ultraviolet Continuum," J. Opt. Soc. Am. 26, 79-81 (1936)