A single-ended fluorescent lamp having a partitioned envelope is coupled to a threaded screw-in type base and a module that contains a miniaturized electronic circuit which permits the lamp to be started and operated on direct current from an AC power source. The resulting compact fluorescent lamp unit can thus be used as a direct replacement for incandescent lamps in fixtures that are designed for residential and commercial lighting. Cataphoretic pumping and accumulation of the mercury vapor in the vicinity of the cathode during DC operation and short-circuiting of the partition by the arc discharge are both prevented by a diaphragm assembly at the electrode-end of the envelope which includes a porous gasket of fibrous material that is permeable to mercury vapor but constitutes an impenetrable barrier to the arc. The porous gasket also provides a manufacturing advantage since it establishes a connecting passageway between the tubulated sealed end of the envelope and the envelope proper which permits vapor and gaseous impurities to be quickly evacuated from the envelope before it is charged with fill gas, dosed with mercury and tipped-off.