I use light bulbs (common incandescent) in the room and they burn out periodically, ca. one bulb in 4 months burns out. Very often, exactly at the moment when it happens, I see an arc (blueish light flash) in the switch, so the bulb always burns when being switched on. I don't see an arc anytime the bulb is normally switched, but only when the bulb burns out.
Question: does the bulb burn after the arc appears, or is it vice versa - when the filament burns it causes the arc in the switch?
My thought is that the bulb burns simply because of worn out filament, but why is there almost always an arc in the switch at this moment?