The application discloses a retrofit LED lamp (16) for replacing a fluorescent lamp in fixture having a magnetic or an electronic ballast (2). The retrofit LED lamp comprises a retrofit lamp connector (1; 1′, 2; 2′) for electrically connecting the retrofit lamp (16) to the ballast (2) of the fixture. Impedances (8,9) are connected between connector points of the retrofit lamp connector (1; 1′, 2; 2′) which correspond with connector points of filaments of the fluorescent lamp replaced. Rectifying circuitry (4,5) is coupled to the retrofit lamp connector (1; 1′, 2; 2′) for rectifying an AC current received from the ballast (2) via the retrofit lamp connector (1; 1′, 2; 2′). LED circuitry (3) is coupled to the rectifying circuitry (4, 5). The Led circuitry (3) comprises LEDs for emitting light when energized by the rectified current received from the rectifying circuitry (4, 5). A flicker reduction circuit (6) is connectable in parallel over the LED circuitry (3) for reducing an AC component in the rectified current through the LED circuitry (3) so as to reduce a flickering of the emitted light. A switch (7) for connecting the flicker reduction circuit (6) in parallel over the LED circuitry (3). A switch control circuit (10) controls the switch (7) to keep the flicker reduction circuit disconnected during a delay period, preferably longer than 10 msec, at a begin of a start-up of the LED retrofit lamp (16) and to continuously connect the flicker reduction circuit (6) after the delay period in case the retrofit lamp (16) is energized by a magnetic ballast.