Working on a ground school lesson plan got me wondering. I see standard VASI and PAPI light systems all the time. I can only think of one airport where I've seen a pulsating VASI (Portage WI). I have never seen a tri-color VASI or an "alignment of elements" system. IOW it appears these three are very rare. Just how common are the pulsating VASI, tri-color VASI, and alignment of elements systems? Are there certain areas of the country where they are more common?