Abstract: The invention relates to an energy-saving operating method and an apparatus for energy-saving operation of a fluorescent tube, especially a T5 fluorescent tube. In a first operating mode, heat current is applied to an incandescent filament at one end of the fluorescent tube. Moreover, in the first operating mode, another heat current is applied to another incandescent filament at an end of the fluorescent tube opposite to said one end. The other incandescent filament is connected to energy-saving circuitry. In a second operating mode, the application of the heat current to the incandescent filament and of the other heat current and the other incandescent filament is interrupted. Monitoring means are provided, which are comprised by electronic circuitry, to monitor an operating parameter of the other incandescent filament in the first and second operating modes.