The ultraviolet characteristics of a 0.5-kw d.c. arc through high pressure xenon were investigated. The lamp has a quartz envelope and contains pure xenon under a pressure of roughly 20 atmospheres when operating; its general characteristics have been described by Schulz. The absolute spectral radiance between 2000A and 5000A was measured photographically by comparison with the positive crater of a spectroscopically pure carbon arc. An ultraviolet radiance contour map of the arc stream was obtained by analysis of direct photographs. It was found that the lamp radiates a smooth ultraviolet continuum, which extends to the air cut-off and is interrupted by only a few weak lines. The radiance of the central spot exceeds that of the carbon crater by a factor of 23 at 2500A, 12 at 3000A, and 6 at 3500A. Comparison with other ultraviolet-continuum sources shows the xenon arc to be unusually intense.
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