The RBTA will move to where every he wants and is getting the most light. I don't know what the min for them are cause I had one in my 75 under 4 65watts PCs and he didn't make it. Not saying that it was the lights cause there could have been 1000 other factors. So cant answer your light question but on the RBTA it doesn't matter were you stick him under which lights cause he will move when he wants to.