What strength uvb for tegus?

We are getting Ssra's 4 foot intermediate cage set up, and I just realized that I don't recall reading about the strength of the uvb bulb you should use. I will probably use a megaray, but if I go with arcadia should I use the 12% desert bulb or the 6% jungle? So far, he has had the 12% bulb, but he is only 7 months old and has been hibernating for 4 of them =(

Thank you