I use 2 double 4 foot fixtures with grow lights PLUS one single 4 foot UVB fixture in a 4x8 enclosure. All are T5 fixtures. I also have 2 65 watt incadescent basking bulbs in there.I was planning on building a 4x8 or 4x10 enclosure within the next couple of months. Would 1 48'' UVB light be okay or would I need to get 2 to cover the whole length of the enclosure?