voltages v 3 v 4 v 5 etc persist over time intervals t 3 t 4 t 5 etc in each case the time interval ending when the microcontroller 74 has determined that the load current is stable note that although the voltage reductions illustrated in fig3 b are fixed by the microcontroller 74 at set voltage levels that differ from the preceding voltage value by a fixed percentage the time intervals t 1 t 2 t 3 etc are unpredictable the time interval required to permit load current to resume a stable value may depend upon ambient conditions the inherent characteristics of the luminaires in the load etc and as a result these various time intervals t 1 t 2 t 3 etc are quite variable in length and not necessarily correlatable with the voltage values v 1 v 2 v 3 etc in order to give effect to a progressive voltage reduction as illustrated in fig3 a and 3b the microcontroller 74 performs a series of monitoring and comparison operations and provides a number of output control signals as better understood with reference to the flow chart of fig4 the flowchart of fig4 graphically depicts the human and microcontroller operations and decisions to be effected referring.