mikeh said:gtc said:mikeh said:gtc, yes, you got idea.....
Ideally you want to create same basking temperature as with regular basking lights. I would go with 95F for arid species. Because the heat output of T5HO is not as intense the height to create this basking temp will depend on weather you have closed chamber and size or open table and room temperature. It could be anything from 10"-18", that will also determine strength and number of UVB tubes.
If you provide some details I can give you better idea on tubes.
The attached photo is not current, I have covered about 90-95% of the top now in order to keep humidity at basking zone between 25-30% and 60-70% in rest of enclosure. I use a 160W powersun mvb now.
Due to the climate my greek lives about 9 months indoors and always sleeps indoors.
I am considering changing to your setup after reading all these interesting posts, especially when in about 2 years I plan to make a very large indoor enclosure and I wish to have large basking zones.
My biggest concern is if uvb tubes (compared to mvb) can provide enough uvb for adequate vit D synthesis in torts that dont get a lot outside time. Also since the future indoor enclosure will be open and about 3 yards by 6 yards I wonder if the tubes will be able to produce a hot enough basking temp?
On your biggest concern of UVB: T5HO UVB tubes are superior to MVBs. They mimic suns spectrum better then MVBs and last much longer. MVBs (Mega Ray may be the exception) are known to fail within as little as one month, rendering them useless for UVB. T5HO Arcadia D3+ are good for up to one year. In short T5HO tubes are better choice for UVB.
For your current set up 24" T5HO quad fixture seems ideal. Fixture placed in the middle with most of the enclosure covered as you have now. This would increase your basking area humidity to 45%-55% with rest remaining at your current levels.
Here is link to a hydrofarm fixture.
It comes with grow lights. This will allow you to determine at what height you will set the fixture to obtain desired basking temp. The ideal height will then determine what strength UVB tube(s) are appropriate.
Heights 10"-12" will yield lover UVB tubes such as Zoomed 5% or Arcadia D3+ 6%.
Height of 15-18" will yeild higher UVB tubes, Zoomed 10% or Arcadia D3+12%.
Either set up with two uvb tubes placed in the outer positions of the fixture seem ideal, with grow lights on the inside positions.
For your future 3yards by 6yards enclosure you would need 4' 6-8tube fixture or maybe even creating two basking areas with two large fixtures.
If your tortoise spends hours on end under the MVB you have, it is having a drying effect on its carapace not only by lowering humidity to very low levels under the bulb but also by IRA spectrum the heat bulbs produce. It is suggested this may be one of the factors contributing to pyramiding, that's what this thread is about.
Since T5HO lights don't dry out the humidity it would seem they don't produce as high of IRA spectrum thus not having this negative effect on the shell, although testing is needed. Hopefully one of our members will test them with rest of the heat lights in next couple of months to give us better answers.
First of all, thank you for the great info. I found a place in my country that sells the exact same fixture you recommended (it costs 300 dollars here though).
Its funny, I went for a mvb + ceramic base with dome + zoomed light stand (which I paid over 600 dollars for here, everything is so cheap in the USA ) since I read that mvb's produced a better spectrum that T5 tubes. My last powersun lasted for the full 9 months I used it, and I just bought a new one a month ago. Do you think that pyramiding is possible even if I go from 90% cover to 100% cover and increase the humidity to maybe 35-40% under the bulb? If so I will go ahead that buy the new setup right away. Otherwise I am considering waiting 9 more months and when the time comes to replace my mvb to switch to your setup. The most important thing the the well being of my tortoise.