High-pressure discharge lamp and lighting system

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PROBLEM TO BE SOLVED : To provide a high-pressure discharge lamp and a lighting system equipped with the same excellent in high emission efficiency and a high luminous flux maintenance factor, without the use of halides of rare-earth metal of Dy, Ho, and Tm.SOLUTION : The high-pressure discharge lamp is structured of a translucent ceramic airtight vessel 1, a pair of electrodes 2, mercury, rare gas and metal halides. The metal halides contain sodium halide (NaX), thallium halide (TlX), cerium halide (CeX) and calcium halide (CaX), not containing dysprosium halide (DyX), holmium halide (HoX) nor thulium halide (TmX), and a discharge medium with a volume of cerium (Ce) of 1 to 3 mol% to the total sealed volume of the metal halides, a mol ratio of sodium (Na) to thallium (Tl), Na/Tl, of 2 to 5, and a mol ratio Ca/(Na+Tl) of 0.2 to 1.4, and with a correlated color temperature of 3, 500 to 4, 500 K.