Dimmable LED reading light unit, arrangement of power supply and dimmable LED reading light unit, method of operating a dimmable LED reading light unit in a power supply system and method of replacing a dimmable light unit by a dimmable LED reading light unit

A dimmable LED reading light unit according to exemplary embodiments of the invention, in particular for a passenger transportation vehicle, such as an airplane, a ship, a bus, or a railcar, comprises an input connectable to a potentiometer (6) being supplied with a constant supply voltage and outputting a direct voltage having a voltage intensity corresponding to a selected dimming rate; an electronic measuring and control unit (20) connected to at least one LED (22) and providing an operating current to the at least one LED (22); a resistor (12) having a predetermined resistance value; and an output (24) connectable to a ground line (4); the electronic measuring and control unit (20) and the resistor (12) being connected in parallel; wherein the electronic measuring and control unit (20) is configured to measure the partial voltage applied to it and the partial load current flowing through it; to determine the resistance value of the electronic measuring and control unit (20) based on the measured partial voltage and based on the measured partial load current; to determine the equivalent resistance value of the electronic measuring and control unit (20) and of the resistor (12) based on the predetermined resistance value of the resistor (12) and based on the determined resistance value of the electronic measuring and control unit (20); to determine the resistance value of the potentiometer (6) based on the equivalent resistance value of the electronic measuring and control unit (20) and of the resistor (12), based on the measured partial voltage and based on the constant voltage supplied to the potentiometer (6); to determine the dimming rate of the potentiometer (6) based on the determined resistance value of the potentiometer (6) and based on the predetermined nominal resistance value of the potentiometer (6); and to supply driving current to the at least one LED necessary to emit light with a luminous flux corresponding to the dimming rate of the potentiometer (6).