Blacklights (UV-A bulbs) are extremely inefficient, and produce very little PAR. It will make particular corals fluoresce, but probably won't contribute much - if anything - in way of health. Blacklights aren't good candidates for night lights. In nature, there is no UV radiation at night, and this would at best, be unnatural for your livestock and at worst, be detrimental to certain dinural/nocturnal patterns. Personally, I say don't bother with them.