First of all, the only rime to start worrying is when the light comes on whilst you are under load.
Mine came on on tickover for years, until I fitted the correct oil pressure switch! It needs to be a 'down to 5psi before it kicks in' type. There are many different types which kick in at various psi ratings. For instance, a Triumph twin one is set to kick in at 8-10 psi.
Take the switch to a motor factor and ask him to supply one the same shape and thread with a 5 psi rating.
There were other problems that contributed to the problem, which I solved first so if the problem doesn't go away with a new switch then let us know.
Does your bike have the Devimead/SRM bearing conversion?
Chris