I recall that the DCA Flying Unit in the old days tested the T-VASIS for flyability down to 200 feet. It was assumed that no pilot would want to follow the lights any lower since it was a visual guide not a category 2 or 3 ILS.
For the same reason you should never consider switching from the ILS at Cat 1 height of 200 ft to the PAPI since the electronic glide slope is already there to give guidance.