A circuit (100; 200; 400) comprising: a first series interconnection of a first light-emitting diode group, a first transistor, and a first resistor; and a second series interconnection of a second light-emitting diode group, a second transistor, and a second resistor, wherein: the second series interconnection is connected between a drain terminal and a source terminal of the first transistor, and the first and second light-emitting diode groups are selectively activated by a variable voltage applied across the first series interconnection; the circuit further comprising: a rectifier receiving an AC driving voltage at a pair of input terminals, rectifying the received AC driving voltage, and outputting the rectified voltage as the variable voltage at a pair of output nodes, and wherein: a cathode of the first light-emitting diode group is coupled to the drain terminal of the first transistor, characterised in that; an anode of the first light-emitting diode group is coupled to one of the pair of output nodes of the rectifier; the source terminal of the first transistor is coupled to a first terminal of the first resistor; and a gate terminal of the first transistor is coupled to a second terminal of the first resistor and to the other of the pair of output nodes of the rectifier. a first series interconnection of a first light-emitting diode group, a first transistor, and a first resistor; and a second series interconnection of a second light-emitting diode group, a second transistor, and a second resistor, wherein: the second series interconnection is connected between a drain terminal and a source terminal of the first transistor, and the first and second light-emitting diode groups are selectively activated by a variable voltage applied across the first series interconnection; the circuit further comprising: a rectifier receiving an AC driving voltage at a pair of input terminals, rectifying the received AC driving voltage, and outputting the rectified voltage as the variable voltage at a pair of output nodes, and wherein: a cathode of the first light-emitting diode group is coupled to the drain terminal of the first transistor, characterised in that; an anode of the first light-emitting diode group is coupled to one of the pair of output nodes of the rectifier; the source terminal of the first transistor is coupled to a first terminal of the first resistor; and a gate terminal of the first transistor is coupled to a second terminal of the first resistor and to the other of the pair of output nodes of the rectifier. the second series interconnection is connected between a drain terminal and a source terminal of the first transistor, and the first and second light-emitting diode groups are selectively activated by a variable voltage applied across the first series interconnection; the circuit further comprising: a rectifier receiving an AC driving voltage at a pair of input terminals, rectifying the received AC driving voltage, and outputting the rectified voltage as the variable voltage at a pair of output nodes, and wherein: a cathode of the first light-emitting diode group is coupled to the drain terminal of the first transistor, characterised in that; an anode of the first light-emitting diode group is coupled to one of the pair of output nodes of the rectifier; the source terminal of the first transistor is coupled to a first terminal of the first resistor; and a gate terminal of the first transistor is coupled to a second terminal of the first resistor and to the other of the pair of output nodes of the rectifier. a cathode of the first light-emitting diode group is coupled to the drain terminal of the first transistor, characterised in that; an anode of the first light-emitting diode group is coupled to one of the pair of output nodes of the rectifier; the source terminal of the first transistor is coupled to a first terminal of the first resistor; and a gate terminal of the first transistor is coupled to a second terminal of the first resistor and to the other of the pair of output nodes of the rectifier.