Patent ID: 7573203

Claim:
A mercury-free high-pressure discharge lamp comprising: a light-transmissive airtight envelope enclosing therein a discharge space; a pair of electrodes sealed inside the light-transmissive airtight envelope and facing the discharge space; and an ionization medium filled in the light-transmissive airtight envelope, which includes primary halide, accessory halide and rare gas while substantially excluding mercury therefrom, wherein the primary halide includes at least thulium bromide having an innumerable emission spectrum primarily around the peak of a luminosity efficiency curve; the accessory halide includes one or more metal halides including a halide of Magnesium (Mg), Iron (Fe), Cobalt (Co), Chromium (Cr), Zinc (Zn), Nickel (Ni), Manganese (Mn), Aluminum (Al), Antimony (Sb), Bismuth (Bi), Beryllium (Be), Rhenium (Re), Gallium (Ga), Titanium (Ti), Zirconium (Zr) or Hafnium (Hf) or any combination thereof which primarily contributes to fix lamp voltage; the amounts of thulium halide and the accessory halide in the ionization medium satisfy following relations, 30<A<90 0<B<20 where “A” represents the mass percentage of the thulium halide to the whole of halides and “B” represents the mass percentage of the accessory halide to the whole of halides.