Oil light at idle

Need some educated guesses (which means, no, I have no idea what to test, so suggestions regarding proper testing are way premature at this juncture; thank you very much). My wife's 93 Taurus wagon displays a flickering oil pressure light at idle. I've checked the oil level; it's good. And the engine isn't running rough at idle, either. What are the other most likely reasons this light would flicker at idle? Thanks.

Bad oil pressure switch. Is it also leaking oil?

-Rod

Oil pump worn out. Oil pickup tube gunked up. Oil filter gunked up. Putting in a super light weight oil instead of the recommended or higher weight. Those are a few more.

Thank you both. For the record: using the specified oil; no noticeable oil leak. We do need to change the oil. That has to wait until we get back from a weekend out of town.