Effect of ultraviolet on breakdown voltage

The effect of ultraviolet light upon the breakdown voltage of sphere gaps subjected to impulse voltages is considered in this paper. It is shown that, especially for the smaller gaps and corresponding lower voltages, more accurate voltage measurements result when ultraviolet light is used. Photoelectric emission from the surface of the spheres is believed to be the cause of the improved accuracy. Without ultraviolet light, variations in the number of free electrons affect the result.