Abstract: An electronic switch comprising at least one switching device 70,72, a reference frequency source 58, a microprocessor 50 and means for applying to the microprocessor inputs representative of at least the current time and date and the latitude at which the time switch is to be used 31-36, the microprocessor being 50 responsive to the reference frequency source 58 and the current time and date inputs to implement a real time clock and calendar 62, and being arranged to calculate from the date provided by said real time clock and calendar and from the latitude input the respective times of at least one of sunrise and sunset at said location on each of a plurality of days, and to operate the switching device 70,72 at respective switching times dependent upon the calculated times.