I have 2 Zen Habitats and use a 24" fixtures w/ a Arcadia 12% bulb in one tank and a Reptisun 10.0 T 5 in the other tank - both are inside the tanks and approx 12-15 inches from basking decor- you can use a Arcadia 14% bulb but you need a low decor piece for it in the tank - I have the 14% in the one tank now that is getting changed out to the T5 next month -- that fixture at the moment is strapped to the top of the tank and basking decor piece is approx 18 inches --- the 14% bulb is a real strong bulb - I wanted to go w/ another Arcadia 12% but they were sold out so its getting switched to the Reptisun -- if you need to see the tank let me know I will post a pic of it
Karrie