Patent ID: 6858987

Claim:
A flash lamp unit comprising a flash lamp having mercury sealed in a discharge container, wherein preheating means is provided for preheating said flash lamp; and the quantity of contained mercury in said flash lamp is in the range of 0.2 to 55 mg/cm 3 , and said flash lamp is ignited under the conditions satisfying the Formula (1) presented below: W 1 =Q /( V×Δt )≧2.1×10 4 ×H 0.25 (1) where W 1 is the average power density (W/cm 3 ) in the flash lamp, Q is the flash power quantity (J), V is the internal volume (cm 3 ) of the discharge container, Δt is the half-power width (sec), and H is the quantity (mg/cm 3 ) of contained mercury.