A low-pressure mercury-vapor discharge lamp, which is equipped with Hg or
amalgam, has a pumping tube opening (4) with constricted cross-section or
lumen. A solid body in the pumping tube (3) prevents the mercury from
emerging into the discharge space. At the same time, the particular shape
of the constriction and of the solid body, respectively, makes it possible
for Hg vapor to diffuse through-passages between the pumping tube and the
solid body into discharge vessel.