Abstract: A discharge lamp which maintains a high lumen maintenance factor even when operated for a long time is obtained in a discharge lamp which has a silica glass discharge vessel and a pair of opposed electrodes in the discharge vessel and in which the discharge vessel is filled with at least 0.15 mg/mm3 mercury, a rare gas with argon as the main component, and 2×10?4 ?mole/mm3 to 7×10?3 ?mole/mm3 bromine by meeting the following conditions when feeding a direct current of 5 mA between the electrodes and a glow discharge produced: 1.0×10?4?b/a?1.2×10?1??Condition (1) c/a?1.4×10?1??Condition (2) d/a?1.2×10?2??Condition (3) e/a?1.4×10?2??Condition (4) where a is the emission intensity of the argon with a wavelength of 668 nm, b is the emission intensity of OH with a wavelength of 309 nm, c is the emission intensity of hydrogen (H) with a wavelength of 656 nm, d is the emission intensity of C2 with a wavelength of 517 nm, and e is the emission intensity of CH with a wavelength of 431 nm.

Abstract: A discharge lamp which maintains a high lumen maintenance factor even when operated for a long time is obtained in a discharge lamp which has a silica glass discharge vessel and a pair of opposed electrodes in the discharge vessel and in which the discharge vessel is filled with at least 0.