lots of information on SPS and LPS par , but very little on softies which I presume is because they can thrive in a wide range of lighting. Since most tank bottoms (where softies tend to be allocated - lps middle or sps top) are in the 50-100 par range, that is what I have always presumed, but I see them do well on what has to be 250 par, including mine which seemed to show no preference in that 50 -250 range .
Lots of leather or soft coral tanks using low end and stock lighting fixtures.