In a discharge tube for use in a housing for a vacuum, an improved optical radiation source is formed by a cathode and a hollow anode. The hollow anode has at least one first surface defining a hollow, partly closed space. The first surface is disposed for cooperation with the cathode. The hollow anode also has at least one second surface that also could cooperate with the cathode. Only the first of the first and second surfaces is conductive. Electrodes are respectively connected to the cathode and hollow anode.