A short-arc discharge lamp (10) including a light-emitting tube (1) having at least 15 mg/cc of mercury sealed therein, an anode (2) and cathode (3) facing each other and disposed within the light-emitting tube (1), and a heat-release layer (6) covering a substantial portion of an outer surface of the cathode (3) so that when the short-arc discharge lamp (10) is provided with electricity having a current value of at least 50 A, an inter-electrode power value defined by a ratio Y/X is at least 500 W/mm, X being defined as a distance in millimeters between the anode (2) and the cathode (3), and Y being defined as an input power in Watts provided to the short-arc discharge lamp (10).