A light source (S) is powered by a two-wire power supply line (10) in which is interposed a switch (T) to control the transfer of said power supply to said light source (S), thus regulating the luminosity of the source (S). Downstream of the switch (T) there is a capacitance (C) crossed by a charge current when said switch (T) is closed. A pre-charge stage (P) that limits such a charge current to a given value is interposed between the switch (T) and the capacitance (C).
