A high-intensity discharge lamp connected to a lighting device has various
superior emission properties such as efficiency. The discharge lamp
includes a translucent ceramic discharge vessel, in which a pair of
electrodes and a discharge medium are inserted. The lamp further includes
an outer jacket, in which the arc tube is disposed, and a pair of feeder
members. The discharge medium has metal halides including those of Na, Tl
and Tm or Na, Tl, In and Tm, and the ratio (MTm/M) of the weight of the
gross sealed mass M of the metal halides to the filled mass MTm of the Tm
halide is about 0.4.ltoreq.MTm/M.ltoreq.0.9. The deviation in
chromaticity (d.u.v.) on the x-y chromaticity coordinates (CIE 1931) for
the overall operating position during the life of the lamp is within the
range of about -0.006 to +0.010.