Filament circuits (1) for lamps (5) powered via ballasts (6) comprise first filament-inputs (11) coupled to first ballast-outputs, second filament-inputs (12) coupled to second ballast-outputs, first circuits (13) comprising resistive components, second circuits (14) comprising reactive components, direct-current paths between the first and second filament-inputs (11, 12) whereby series configurations of the first and second circuits (13, 14) comprise these direct-current paths, and filament-outputs (15) coupled to a driver-input of a driver (3) for driving a light source (4) of the lamp (5). These filament-outputs (15) may correspond with the first filament-inputs (11), or with the second filament-inputs (12). The resistive components may comprise first resistors (16). The reactive components may comprise first capacitors (17) with the second circuits (14) comprising parallel configurations of the first capacitors (17) and second resistors (18), or the reactive components may comprise inductors (20). The first circuits (13) may comprise parallel configurations of the first resistors (16) and second capacitors (19).