An electrodeless fluorescent lamp employs a glass envelope made from a single linear tube or bulb and a reentry cavity disposed on the envelope axis and sealed to the envelope. The envelope is filled with inert gas and mercury vapor. Phosphor and protective coatings are disposed on the inner surfaces of the envelope and the cavity. An induction coil of A few turns made from silver coated copper wire is wrapped around the envelope in its axial direction. The inductively-coupled axially uniform plasma is generated inside the envelope. The discharge electric field and current form a closed-loop path inside the envelope along its walls. The introduction of the reentry cavity decreases the lamp wall loading without loosing lamp power efficiency and efficacy. The lamp is operated at frequencies from 50 kHz to 200 MHz and RF power from 5 W to 2000 W without the use of ferrite inside of the reentry cavity.