Our empirical results show that theI‐Vrelationship of flash lamps operating in the preionized mode with peak current density higher than 2 kA/cm2follows Marotta’s formulaV=K0i0.85, and reduces to Gonz’s equationV=K0i0.5for current density lower than 0.6 k A/cm2. At a high‐current, short‐pulse system, the inductanceLfand the equivalent negative resistancedLf/dtacross the flash tube becomes more significant than the inductance of the external circuit. The plasmaz‐pinch equation can successfully solve these time‐variation terms.