Correlation between brightness and channel currents of electrical discharges

Channel brightness of 500 mm long electrical discharges were measured by analyzing a set of digitized images taken by 3 cameras placed symmetrically around a discharge gap at a radial distance of 200 cm from the axis of the spark. The sparks were generated between a steel rod and a plane electrode. The distribution of the brightness across the channel represented a Gaussian distribution. A linear correlation was seen between the channel brightness measured by different cameras looking at the same spark channel. No correlation was seen between the channel brightness and the channel depth (direction perpendicular to the camera plane). The measured peak current and the brightness of the main spark channel show a high degree of correlation (R-2=0.97). The sum of brightness of branches was equal to the brightness of the parent channel. One can use this result to calculate the relative distribution of branch currents in complex electrical discharges including natural lightning flashes. If the current in the parent channel is known, branch currents can be calculated by measuring the optical intensities using photographic techniques.