Circuit arrangement for an optical monitoring system, the circuit arrangement comprising - a driver circuit configured to generate at least one driving signal for driving a light source; - a detector terminal for receiving a detector current (Id), in particular from an optical detector; - a current source configured and arranged to generate at the detector terminal a reduction current (Ir), wherein an amplitude of the reduction current (Ir) - is given by a base value whenever none of the at least one driving signal assumes a value suitable for activating the light source; and - is given by a sum of the base value and a reduction value otherwise; - a processing unit configured to generate an output signal depending on a combination of the detector current (Id) and the reduction current (Ir); characterized in that it further comprises - a control unit configured and arranged to - determine whether a value of a signal depending on the combination of the detector current (Id) and the reduction current (Ir) lies within a predefined first range at a time when the amplitude of the reduction current (Ir) is given by the sum of the base value and the reduction value and/or lies within a predefined second range at a time when the amplitude of the reduction current (Ir) is given by the base value; and - adapt the at least one driving signal if the value of the signal depending on the combination of the detector current (Id) and the reduction current (Ir) does not lie within the first range and/or does not lie within the second range. - a driver circuit configured to generate at least one driving signal for driving a light source; - a detector terminal for receiving a detector current (Id), in particular from an optical detector; - a current source configured and arranged to generate at the detector terminal a reduction current (Ir), wherein an amplitude of the reduction current (Ir) - is given by a base value whenever none of the at least one driving signal assumes a value suitable for activating the light source; and - is given by a sum of the base value and a reduction value otherwise; - is given by a base value whenever none of the at least one driving signal assumes a value suitable for activating the light source; and - is given by a sum of the base value and a reduction value otherwise; - a processing unit configured to generate an output signal depending on a combination of the detector current (Id) and the reduction current (Ir); characterized in that it further comprises - a control unit configured and arranged to - determine whether a value of a signal depending on the combination of the detector current (Id) and the reduction current (Ir) lies within a predefined first range at a time when the amplitude of the reduction current (Ir) is given by the sum of the base value and the reduction value and/or lies within a predefined second range at a time when the amplitude of the reduction current (Ir) is given by the base value; and - adapt the at least one driving signal if the value of the signal depending on the combination of the detector current (Id) and the reduction current (Ir) does not lie within the first range and/or does not lie within the second range. - determine whether a value of a signal depending on the combination of the detector current (Id) and the reduction current (Ir) lies within a predefined first range at a time when the amplitude of the reduction current (Ir) is given by the sum of the base value and the reduction value and/or lies within a predefined second range at a time when the amplitude of the reduction current (Ir) is given by the base value; and - adapt the at least one driving signal if the value of the signal depending on the combination of the detector current (Id) and the reduction current (Ir) does not lie within the first range and/or does not lie within the second range.