Timocracy,
approach visibility minima criteria is the slant distance at the MDA from a std 3 deg profile to the runway threshold plus 160 metres (I think - verify for yourself). So if you're at MDA inbound of an appch, on correct profile and can see 2... almost 3 lights spaced at 60m, then it's likely that you'll have the min vis for the appch.
Use your common sense and some rules of thumb, some of which you may find here and you'll be right.