This question already has an answer here:
I am trying to compare a VASI-4 light system with a PAPI lights. I know that 2White-2Red is the pattern that indicates that the aircraft is on the glideslope; more reds mean lower and more white means higher than the desired glideslope height. With relations to that, how should the VASI lights be on a correct/incorrect approach?
P.S. My question is specific to VASI-4 light system aka 2-bar VASI.
UPDATE I found this from FAA that may very well be the answer, but an explanation would be great.