(Also called continuous leader.) The leader which, after the first stroke, typically initiates each succeeding stroke of a multiple-stroke flash lightning. (The first stroke is initiated by a stepped leader.) The dart leader derives its name from its appearance on photographs taken with streak cameras. The dart leader's brightest luminosity is at its tip which is tens of meters in length, propagating downward at about 107 m s−1. In contrast to stepped leaders, dart leaders do not typically exhibit branching because the previously established channel's low gas density and residual ionization provide a more favorable path for this leader than do any alternative ones. Chalmers, J. A., 1957: Atmospheric Electricity, p. 239.
A dart leader (also known as a continuous leader; may have been referred to by Feynman as a dark leader ) is the cloud-to-ground movement of electrons which occurs just before a secondary lightning strike. The dart leader is similar to a step leader, because it is not as intense as the main strike, yet serves to ionize the air between the cloud and the ground, allowing electrical breakdown of the path of the lightning strike.