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 210-4 mole/mm3
to 710-3 mole/mm3 bromine by meeting the
following conditions when feeding a direct current of 5 mA between the electrodes
and a glow discharge produced:
1.010-4b/a1.210-1 Condition (1)
c/a1.410-1 Condition (2)
d/a1.210-2 Condition (3)
e/a1.410-2 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.
