Simultaneously measured lightning return stroke channel-base current and luminosity

The time delay between lightning return stroke current and the resultant luminosity was measured for 22 return strokes in eight lightning flashes triggered by the rocket-and-wire technique during the summer of 2014 in Florida. The current-to-luminosity delay measured at the channel base at the 20% amplitude level ranged from 30 to 200ns with an average of 90ns and at the 50% amplitude level ranged from 30 to 180ns with an average of 94ns. The delays are significantly shorter than that predicted by Liang et al. (2014) from theory. The current-to-luminosity delays increase with increasing current risetime, current risetime varying from 190ns to 570ns, but the delay appears not to depend on the peak current value.