[paulca]

The amount of oil in the sump is fairly irrelevant. The ability for the engine to pump oil around the galleries is much more important.

If the engine cannot pick up oil to pump round the galleries then the oil pressure light will illuminate.

You would expect that many, many miles before an engine actually runs dry the "Low Oil Pressure" light would be blinking on and off and finally stay on.

EDIT: I had an oil pump failure on a motorbike on the way to work. I immediately got the low oil pressure light, plus the high water temp light and low battery light. Confused by all these warmings I carried on to work and back home without issue. When the mechanic looked into it, the wiring for all 3 lights was meant to bring all on for any of the 3 failures. There was no engine damage though.