Abstract: An LED lamp arrangement adapted to replace a fluorescent lamp in a luminaire having a ballast for supplying power to the lamp. The LED lamp arrangement comprises a plurality of LEDs arranged in a plurality of groups, wherein the groups of LEDs are connectable in a plurality of circuit configurations, including at least a first circuit configuration, and a second circuit configuration having a different circuit arrangement of the groups of LEDs in which at least a portion of the groups of LEDs are connected into the circuit differently than in the first circuit configuration. The LED lamp arrangement further comprises a first circuit adapted to generate an output indicating whether the ballast is a magnetic ballast or a non-magnetic ballast, and a second circuit adapted to change a connection of the plurality of groups of LEDs between the first circuit configuration and the second circuit configuration on the basis of the output of the first circuit.