I have several outside lights with built in day/night switches. The
switch turns the light on at night and off during the day. But, although
small, the switch modules use simple a CdS photocell and a triac switch circuit.
They almost always flutter the lamp at dawn and dusk. This
fluttering action is caused by the lack of hysteresis in the circuit. When the
CdS cell says that the light should turn on, the act of turning it on increases the
The photocell then says that it is not dark enough and turns the
light off again. This on/off cycle is repeated for perhaps 5 minutes twice
each day until finally it is either dark or light enough.
Then, the light remains stable. This flickering action
accelerates the failure rate of any light used in the fixture. In fact, I’ve
never be able to use any kind of compact fluorescent lamp other than a “dimmable”
type for fixtures with day/night switches.