They way i look at it is in the wild they say there in there borrows alot and come out to hunt and bask so i guess they need the sun to digest there fod and to keep there body heat up.I my self use uvb on all the tegu's i've ever owned.Everybody has there own way of not using uvb,uva,but i my self use a mega ray bulb and change them every 6 months.Good luck