Hi Kathy!
I use two fixtures that are designed specifically for reptile tank use. One has two incandescent fixtures that will hold up to 150 watts each, the other has two incandescent 150 watt fixtures, and one 15 watt fluorescent fixture. Each bulb has its own switch and cord so you can put them on timers individually. I run two day (one incandescent and the fluorescent for color rendering) and one or two night bulbs during the day depending on temperature, turn off the day incandescent and turn on the remaining moonglow bulbs (leaving the fluoro on) for 30 minutes or so to simulate sunset, then turn off the fluorescent bulb. The great thing about these fixtures is that you can change the bulbs out to higher or lower wattages for different house temperatures.
ESU and Fluker's both make these. I have found them at Petco and Pet Club, and an example also online at:
http://www.reptiledirect.com/index.asp? ... ProdID=150
After having run a simulated natural night/day cycle for a couple of weeks now, I am utterly convinced that it is extremely beneficial to crabs. My crabs used to come out any old time late at night, but it would vary like they were confused as to what time it was. Now, my eccies run around all day, alternately basking and hiding, and my other crabs come out soon after "nightfall." They are more active because the air temperature in my tank is higher, staying between 74 and 78 degrees in the daytime and 70 to 74 degrees at night.
Bill has a gap in his glass lid that his lights sit over, so he uses lower wattages than I do. Because of my tank construction, I have my fixtures sitting on top of glass panels, so I need higher wattages to get through the glass.
The only issue with overhead lighting is that humidity tends to drop. I have compensated for this with a TropicAire Terrarium Mister. It circulates humid air by way of a pump into the tank by a perforated tube. I have to use two of them because my tank is so big, but I've got it so the humidity stays between 75 and 80%.
You can get a mister at:
http://www.kazabee.com/html/reptile_accessories.html
I got mine at Petco, but Bill at Kazabee sells them $5 cheaper. And he's a bigtime crabber, the guy who got me on this lighting crusade in the first place.
The problem with UTHs is that the heat doesn't get to the air, and sometimes barely warms the substrate. Crabs will hibernate if the temperatures go below 68 degrees. They'll be happier, healthier, and more active if you can keep their substrate AND air temperatures in an acceptable range for them at all times.
Good luck, and if you have more questions, Bill posts to Yahoo hermies. He likes to answer questions.
Kerie
