You need to get a temperature gun so you can check the different temperatures in the enclosure. They are not expensive. I got mine from Amazon.com. I put the link below of the one I purchased. Also placing a UVB light on top of a screen filters out a lot of the UVB so your tortoise will not be getting sufficient UVB.
https://www.amazon.com/gp/product/B00837ZGRY/?tag=exoticpetnetw-20
https://www.amazon.com/gp/product/B00837ZGRY/?tag=exoticpetnetw-20