Well, as per Nodge's post ( #2 ) I strongly suggest you sort this ASAP - as it'll kill the engine if the sensor is telling the truth ....
A gauge is the only way to know for sure - preferably a capillary one, and preferably Durite, IMO.
I had to do this myself on a tractor the other day - oil light on at tickover ..... engine orft, gauge connected, and oil pressure is 60 psi
..... new switch fitted, and no problem ..... was all of £4.58 for a new, genuine one, so ...
Weirdly, this is the second one I have had fail in recent times - SWMBO's D1 oil pressure switch let go big style a few months ago = oil everywhere - and I do mean EVERYWHERE
- took longer to clean up the mess than it did to fit the new switch
I'd also suggest genuine / OEM filters only too - e.g. the donaldson filter for this tractor has no non return valve - and the genuine one does. I've no words for the stupidity this demonstrates ......