The traditional method of creating stage lightning is with a flash pot. A small charge of flash powder, containing the flammable metal magnesium, is ignited in a container by an electric spark.
Alternatively, photographic flash bulbs or carbon arc lamps may be used.
Forked lightning can be simulated by projecting a photographic slide of a lightning flash onto ‘sky’ scenery.
Most flash effects on stage are controlled by the fire regulations.
Picture Credit : Google