I've got a 3x3x7 room. I'm gonna yank the mylar off the walls, I think it was brighter without it, I just put another coat of flat white paint on before this grow. I've got a cheep 3-in-1 light-moisture-pH meter, but I don't think it's sharp enough to tell the difference. The mylar reflects the black pots and it just kinda looks darker than the white walls.