Usually the basking lamp heat is enough to provide heat for the outlying areas. If you use a temperature gun to measure temperatures around the enclosure, you will know how you are doing. They're inexpensive from hardware stores and Amazon.
I thought it was but knew it sounded stupid asking the question, i have a temp gun and all appears ok just need to get them to eat more and the humidity up a little but I've just got some orchid bark. thanks for the help, how long have you kept tortoises for?