Timers, photocells, and astronomical clocks.
Learning Track · Module 1: The network · Step 3 of 101
Showing content for Europe. Change the region at the top of the page.
- Fixed timer. It switches at the same clock time every day. Sunset changes during the year, so lights come on too early or too late. Do not use this method.
- Photocell. A light sensor switches the circuit or the luminaire when it gets dark. It follows the real sky, but dirt, damage, or a bad position make it fail.
- Astronomical clock. It calculates sunset and sunrise from the date, latitude, and longitude. You can add an offset, for example on 10 minutes after sunset.
USA: In the USA, most lights have their own twist-lock photocell (ANSI C136.10). Many photocells fail "on", which causes day burning. Specify fail-off photocells where the utility permits.
Europe, Middle East, South Asia: Many cabinet controllers use the astronomical clock as the main source and a light sensor for very dark days South Asia: , for example in heavy monsoon cloud Middle East: , for example during dust storms.
Night length depends on latitude. Europe: In northern Europe, a winter night can be more than 17 hours and a summer night less than 5. Middle East: Near 25° N, nights range from about 10.5 to 13.5 hours. South Asia: Near 23° N, nights range from about 10.5 to 13.5 hours. USA: At 40° N, nights range from about 9 to 15 hours. Find your burn hours with the burn hours tool.
Note
When a photocell fails closed, lights burn into the day. See Day burning.
Sources
- ANSI C136.10 Locking-type photocontrol devices and mating receptacles
- UL 773 Plug-in, locking type photocontrols
Changes: 30 October 2026: First publication: guides for Europe, the Middle East, South Asia, and the USA; failure library; tender clause library; comparisons; tools; downloads. See the changelog. Found a mistake? Report it.