Thyristor

A thyristor acts like a switch that remembers being turned on. A short pulse at gate G can start current from anode A to cathode K. If enough current flows, it stays on after the pulse ends.

Removing the gate signal does not switch it off. The main current must fall low enough; interrupting the supply is one way to do that.

At SparkVille’s kite festival, a short signal lights the hilltop beacon. The thyristor keeps it on until the keeper interrupts the current.