Every bulb, fixture and enclosure is different. The only way to set the height correctly is with a Solarmeter 6.5. I run several of these bulbs, and the usual distance is around 18-20 inches. That should put you in the ballpark and not do damage from being too close. You only need to run this bulb for a few hours mid day. No need to run it 12 hours a day.How far from baby hermmans tort back? This is what I have