Patent ID: 7489083

Claim:
A mercury-free arc tube for a discharge bulb comprising: a mercury-free arc tube main body including a closed glass sphere, wherein electrodes are oppositely provided and starting rare gases and metal halides are sealed in the closed glass sphere; and a cylindrical shroud glass tube that is airtightly integrated with the arc tube main body and surrounds the closed glass sphere, wherein an inert gas is sealed in the shroud glass tube surrounding the closed glass sphere, wherein the starting rare gas is sealed in the closed glass sphere in a pressure X within a range of 10 to 15 atm, and an amount M of sealed metal halide in the closed glass sphere is within a range of 10 to 20 mg/ml, the inert gas in the shroud glass tube is a mixed gas of a first inert gas and a second inert gas, and a thermal conductivity λ(W/m·K) of the mixed gas is adjusted within a range of a formula of ( X+ 0.42 M− 12)/160≦λ≦( X+ 0.32 M− 6.5)/144.