Landscape lighting systems can be controlled in several different ways. Photocells detect when the sun has set and turn the system on, and then turn it off when the sun rises. (On at dusk, off at dawn). Timers allow you to program when you want the lights to come on and when you want them to go off.
There is even a version of timer that varies the on and off times slightly to make it look like the system is being activated by a person, even when you’re away. Photocells and timers can also be used together, for example to turn the system on at dusk and to turn it off at a prescribed hour.