That feild is much debated. I like to stick with UTH's and a dish of Calcium & D3 powder. I do plan on eventually making a naturalistic vivarium that simulates a dry, rocky, hillside just like in the middle east, that will have UVB and UVA lights during the day and ceramic heaters at night. The new book by Ron Tremper and Philipe De Vosjoli (sp?) breifly mentions this subject and states that sometimes leos will bask in the light right before they go off and right after they come on, as well as sometimes letting part of their body rest outside their burrow for short periods during the day. They state that this type activity may be how leos survive in the wild without dishes of cal-D3. Really its up to you to decide if you want to pay for expensive powder or expensive lights