Simple answer: can't tell. If there's 1200m RVR in rain or snow then there's very, very slim chance of seeing anything, but If you have RVR1200 with SKC then it all depends on the thickness of mist layer. In second case, visibility above mist is often 9999 and as you descend towards the runway you can often clearly see full length of approach and runway lights, until you plunge into mist - sudden reduction in visibility leads to illusion of pitching up and if one doesn't expect it, pushing the nose down and firm arrival are guaranteed.
Even worse awaits those foolish enough to try IFR approach into fogbound field which is below RVR minima, just because they see the lights. With low lying thick fog, they might be able to see everything down to and even below minima, just to loose it all in the flare.