Abstract: An electronic visible light sensor is employed to detect the presence or lack of sunlight. The simple, digital light/dark data from the sensor is fed to electronic circuits which control security and other devices dependent upon day and night status. These circuits are directed and controlled in turn by associated electronic circuits that gather data which measures the length of the solar night, that is, between dusk and dawn, and by deduction, the length of the day. Given that these time periods vary daily and in a regular fashion, the result will necessarily differ by a few minutes each and every day during the 365 day solar year. The resulting day/night time data is used to estimate, with say, a four to ten minute accuracy, taken against the Universal Coordinated Time System, to establish start/stop times, durations and cycles of security and other devices dependent upon the presence or lack of sunlight relative to UCT designated within the universally accepted twenty-four day.