I have the traditional two light at the left and at the right of my garage door. The are on the same circuit with the porch light that has a PIR sensor (turns on when move is detected).
So it is power source-->switch--Porch light--first light--second light
In the evening when we turn these lights on from inside the first light is flashing like those on the police cars :-), it keeps doing that for a while (can't say how long, it is not a regular interval) and then it stops flashing and it is solid on. Sometimes the same light turn off and stays like that
What could be the reason for this?