I feel for 888 who just wanted a rough answer.
Mate. In Aus we use HIALS that are called British Calvert. They are the ones with the bars. They are spaced evenly. The minima normally is past all the lead in bars and is overhead a point called the descion bars, were they turn all red and are 1000' from the threshold.
As most people here are talking. We don't COUNT the bars or edge lighting.
Just know some simple rules :
800 m - gota see at least the threshold green lights and a few white edge lights
1200m - gota see the papi/vasi lights
1500m - gota see the touchdown markings clearly plus a little more
There ya go.
Oh and not everyone does 120 knots either @ Vat. So bear that in mind.
Cheers
PS found this great little article just now. Not much on HOW to calculate vis, but gives a great insight to approach lighting. From this, you can develope your own methods.
Calvert Cross Bar Lighting System