If the light occasionally flickers when the engine is hot and idling, that's not much cause for concern.

If it flickers when the revs are up (even a little - like 1000 or higher) then it *could* be something to worry about. If it does that, first check the wiring - the insulation has a hard life being shaken around by the engine and baked by the exhaust pipe. Next, think about swapping the pressure switch - they are cheap, easy to swap (with the engine cold - they sit right behind the downpipe!), and occasionally get flaky. Oh, and (of course) make sure it has sufficient oil in the engine - it will slosh the oil away from the picup in corners if it gets a little low. Try to avoid using the oil light as an 'add oil now' sensor. Also, replace the oil filter. Even if they get blocked, they are suposed to be spring loaded and bypass the filter without reducing flow much (dirty oil is better than no oil) but you never know.

If it still persists on flickering it high rpms when it has oil in it I'd suggest attaching an oil pressure gauge so you can get a better indication of what is going on - even temporarily if need be. You can get cheap ones for ~$20. If you are having low oil pressure (and it has to be *very* low usually to turn the light on if the oil light switch is working properly) at higher rpms there's no doubt about it, something is seriously amiss inside the engine. Pehaps the bearings are really worn, prehaps an o-ring on the oil feed tube (from the pump to the block) has popped out. Perhaps the pump has been sucking in crud in has worn itself out. Hard to tell without pulling the motor.

Don't try to 'cure' a low oil pressur issue with thicker oil, though. The bearings need flow to survive, and with a normal viscosity the pressure is a good indication fo the flow they are receiving. But add thicker oil and the flow will drop, even if the pressure sounds good. The flow cools the bearings, and to me that is more important than the lubrication the oil provides.
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I'm JohnMc, and I approved this message.