Oil light at cold start

Hi guys my oil light has always gone out quickly on my defender but recently decided to stay on for a second after starting

Any ideas what this could be?

I serviced her at the weekend but that didn't make any difference

Oil pump bolt? Or would it be all over by now?

Hi, IMO ignore that second cos it's irrelevant... even the oil spec or ambient temperature can make such small difference also it's a simple pressure switch which can get "tired" in time and react a bit slower, mine stays on 2 seconds since i own the car and no probs, as long as it comes on for self test then goes out and stays out while the engine is running it's not a problem...if you are stressed fit a pressure gauge

Thanks for your advise! May have it tested just to be sure