Join Date: Nov 2010
Location: Mulberry, FL. USA
Of course the oil level should be checked when engine is cold, and level on a center stand or lift.
When changing oil, and filter, filling to sight glass is only for first reference, keeping track of how much is going in. Then is good crank the engine for a few seconds, shut it off, walk away for at least 30 mins, let oil settle back in the sump, and check again. It usually would need a little more.
All that said. After an oil change, is normal for the oil pressure light to stay on longer as the new oil is pushed into a empty oil filter, and other crevices, but after that, light should not be on if the amount of oil is in the ballpark.
....if you insists you have the right amount, then the oil pressure switch may be defective.