the present invention relates to a circuit for controlling at least one led and to a light - and / or signal element including said circuit , wherein the circuit facilitates an optimum utilization of any input voltage provided by an energy source and provides constant light intensity of the leds independent from an input voltage . for this purpose , the circuit contains a step - up converter arranged in the circuit in a way such that the step - up converter outputs a voltage adapted to a forward voltage of the at least one led at a constant current independent from an input voltage provided by the energy source .