Examination of the light output of discharge tubes, using the multiplier-type photo-tube in conjunction with a cathode-ray oscillograph, is suggested as a powerful aid to the usual electrical measurements in understanding the behavior of electrical discharges in gases. Exhaustive experiments of this type are under way, the preliminary results of which are reported in this paper. A striking characteristic of these results is the appearance of oscillations not only in the voltage and current, but particularly in the light intensity. These oscillations appear to be very general, and are not due to the external circuit used. They are only of a few percent magnitude in the case of the voltage and current, but often nearly 100 percent in the case of the light intensity. It seems certain that the theory -of electrical discharges should in many cases be revised to take these oscillations into account.
H. Y. LOH and G. H. DIEKE, "Fluctuations in Gas Discharges," J. Opt. Soc. Am. 37, 837-845 (1947)