I use a day light bulb for my rtb, its on a cycle of 12/12..but I dont mind turning off the light, cause i am not that lazy. Upon occassion, Caleb does come out and bask in his "sun", mind you, not for long periods of time, but he does do it. He is more active at night for sure after it is dark, although, last evening, he was out and about cruising his cage around 6 PM, which his light is still on. With the cycle I run my light, he does not seem stressed out, he eats fine, is not nippy or nervous... he does just great. Now I have never heard that they need the light to maintain healthy skin, but I have heard they need it, but have yet to hear a good explanation why. But, it is possible that it is used to let them know there is a day and night... heck, I am not sure, but I have given Caleb his own "sun" and he does just fine. Plus it provideds some heat to his warm side in the day time.