An induction RF fluorescent lamp includes a lamp envelope with a re-entrant cavity both covered on a partial vacuum side with phosphor and filled with a working gas mixture; a power coupler on the non-vacuum side of said re-entrant cavity comprising a ferromagnetic core overwound with at least one turn of an electrical conductor; an electronic ballast, wherein the ballast converts mains frequency voltage and current to a power coupler frequency voltage and current, the electronic ballast providing the voltage and current to the power coupler through at least two of a plurality of electrical terminals of the electronic ballast; a capacitor electrically connected between the ferromagnetic core and at least one of the plurality of electrical terminals of the electronic ballast, wherein the magnitude of the impedance of the capacitor is high at the mains frequency and the magnitude of the impedance of that same capacitor is low at the operating frequency of the RF fluorescent lamp.