You should put up a mercury vapor bulb in the enclosure. Use a timer to control when it comes on so it simulates a normal length of day (7am to 5pm). You said the enclosure is 3.5 x 8, I would recommend the PUV-11 Bulb, the 100watt.
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Set up the distance so that the temp on the ground is in the mid 90's. (check this after the lamp has been on for one hour, no sooner.) Distance shouldn't be less than 9 inches.
That should get you straightened out for the day cycle.
For the night time, if you choose, you can do a similar thing with a ceramic heat emitter (35 watts is good) and set up the distance so the temp is in the high 70's. Again, use a timer here to pick up after the day one shuts off.
Good luck and keep posting, this tortoise is about to love you.
http://www.zoomed.com/db/products/EntryDetail.php?EntryID=109&DatabaseID=2&SearchID=1
Set up the distance so that the temp on the ground is in the mid 90's. (check this after the lamp has been on for one hour, no sooner.) Distance shouldn't be less than 9 inches.
That should get you straightened out for the day cycle.
For the night time, if you choose, you can do a similar thing with a ceramic heat emitter (35 watts is good) and set up the distance so the temp is in the high 70's. Again, use a timer here to pick up after the day one shuts off.
Good luck and keep posting, this tortoise is about to love you.