Oil light on at low revs?

an oil light or sometimes an "idiot light" (named for the lack of an analog oil pressure guage) can come on at a low idle for a couple reasons. But first know that the oil pump spins mechanically with the RPM's of the engine. the slower the engine turns the slower the pump turns. this is why the light goes out when you rev the engine, the pump creates more oil pressure in the system and satisfies the pressure switch that activates the light. just a couple of things that can cause this. a: high mileage, old worn out bearings with wide tolerances dont restrict the oil enough and it will just run out and back into the pan, with pressure dropping at each bearing. b: too thin of an oil weight, when your engine heats up, a thinner oil, possibly in conjunction with "a" can act like water and will run through the system much faster and with less effectiveness. similar to pouring something thin through a funnel and something thick through a funnel. c: worn out fuel pump,