On the occurrence of ‘bead lightning’ phenomena in long laboratory sparks

•For the first time, the occurrence of bead patterns in the channel of laboratory sparks was reported.•Depending on the geometry some regions of the channel decays faster than the other sections.•A possible mechanism for the occurrence of beads in decaying states of lightning flashes is proposed.

The formation of bead lightning, where the lightning channel appears to break up into luminous fragments, is still an object of speculation. Here we report similar observations in laboratory discharges. Analysis of time resolved photographs shows that the discharge channel exhibits a ‘bead pattern’ in the decaying stage of the discharge and the occurrence of loops in the channel sections where the bead pattern is observed. This result presents the first evidence that the rapid cooling of non-uniform channel sections could lead to the formation of beads. It is suggested that periodically occurring non-uniform channel sections could explain the bead pattern of lightning discharges.