If you use standard automatic light controller then you know that it is mechanical clock based switch or electronic with ambient light detector. Mechanical one require regular time adjusting since sunset time variates during year. Second one would be OK – it senses darkness with LDR and then turns on the lights. But things happen, LDR may get covered with objects or simply dark clouds my trigger the lights. Anyway there is another solution – smart clock that keeps track of sunset times.
Paulo decided to build lighting timer using sunset and sunrise time calculating algorithm. So lights are turned on time no matter what season is currently on. Additionally Arduino based devices is equipped with 7 segment display, couple push buttons for setting time, battery backed RTC. Lights are turned on by using mechanical relay.