Thanks for all that stuff, very useful background for me.
To respond to deptrai's legitimate "why are you asking??" question, I guess I am trying to get a feel for whether routine training gives line pilots the impression that if they can see a few lights at DH and are not too seriously mis-aligned, it is actually OK to continue, because it's been repeatedly demonstrated to them that whenever they do, the visual sequence that unfolds DOES pretty quickly provide enough information to get onto the runway.
While that may be the case in a lot, even the majority, of real-world cases, it doesn't represent the dangerous cases where the aircraft's vertical trajectory is actually too steep, but the actual visual cues don't give enough information to detect it, in the patchy fog/blowing snow/ heavy rain etc., or indeed the fact that RVR reports don't actually tell you what you'll see at DH.
Given the commercial pressure to minimise simulator time I suspect that it isn't normally the case that instructors are expected to demonstrate these variable conditions. I seem to recall that a lot of that type of stuff was what we did when we first started getting into the Cat 2 /3 trials etc. using the fairly primitive systems that Alf refers to, but I don't imagine it's part of many recurrent or even initial qualification training syllabi today.
(As an aside, I vividly remember thinking my career was over during a conversion course exercise with an early visual system. This used a physical terrain model on a rolling carpet loop, with a monochrome TV camera moving on a gantry to represent "aircraft position". During maintenance this had somehow been left hooked up with left-to-right reversal (mirror image), so when we came back to do engine cuts on takeoff, rudder inputs caused the visual presentation to go in the opposite direction to the instruments, with very rapid visual negative feedback, and repeated ground loops .....!)
Anyway my concern is whether we are really training pilots to make the ACTUAL decision needed at DH, i.e. judge "position and rate of change of position relative to desired flight path". Or is the training regime acclimatising them to a rather benign situation which leads to over-confidence, and assumptions that if
1) the RVR is said to be at or above your minima, and
2) you are reasonably close to the vertical profile, and
3) you can see almost any lights at all,
then you'll be OK to continue down. Because that does seem to be a factor in a lot of accidents which are still going on.