Applicant has disclosed a method for controlling on and off times for streetlights by synchronizing these intervals to recent local daylight conditions without any human intervention. The preferred method comprises: sensing, via a photocell, when dusk and dawn occurs; and then, timing or counting the dusk and dawn times per 24-hour cycle, recording that dusk and dawn data, calculating the average dusk-to-dawn interval for a plurality of preceding 24-hour cycles; predicting, the next dusk time; and turning on the streetlight for a preselected percentage of the calculated average dusk-to-dawn interval. Future “on” time periods are repeatedly calculated as a percentage of the dark periods determined on one or several immediately prior nights, and so varies with the seasons. Unlike the prior art, Applicant's streetlight control does not require field programming or field inputs from the installer or time knowledge. It also does not require any external or internal precision clock or calendar.