I have found that java moss is a plant that can survive and thrive with little or no specific light supply. My own experience with it, as a livebearer fanatic keeper, is that java moss thrives even when I use it in a tank that gets only North facing exposure and the tank has no supplemental lighting. I actually had a clump of java moss that I used in an emergency situation in a fish room with only a northern exposure to sunlight that not only survived but thrived in a tank with no supplemental lighting. That stuff was great for a tank that needed to provide temporary housing for livebearers. It also provided me a source of algae-free cover for my other tanks since it kept right on growing in those conditions.