A low-pressure mercury vapor discharge lamp has a light-transmitting
discharge vessel (10) enclosing, in a gastight manner, a discharge space
(11) provided with a filling of mercury and a rare gas. The discharge
vessel (10) comprises discharge means for maintaining a discharge in the
discharge space (13). At least a part of an inner wall (12) of the
discharge vessel (10) is provided with a protective layer (16). The
discharge vessel (10) is provided with a luminescent layer (17)
comprising a luminescent material. The luminescent layer (17) further
comprises inorganic softening particles (27) with a softening point above
450.degree. C. The size of the softening particles (27) is in the range
from 0.01 to 10 gm. Preferably, the softening particles (27) are selected
from the group formed by strontium borate, barium borate, yttrium borate,
yttrium-strontium borate and calcium pyrophosphate.