dart leader (lightning)

A dart leader is a dart of light which is seen to propagate down the same channel as the first flash (return stroke) channel in a lightning strike. Occurring 40 to 60 milliseconds after the first flash, it propagates at about one-hundredth the speed of light and is associated with a 1,000-ampere current. Once it reaches near the ground, the increase in the electric field causes a return stroke along the path of the dart leader (but in the opposite direction). It is distinguished from a stepped leader in that there is no branching off the original channel path.