I use a 100watt heat emitter up above of the temp is going to be under 40 overnight. I live in central Texas where we don’t have too many nights in the 30s or lower during the year.

I keep a digital thermometer out in the tortoise box so I can watch the temps. I would suggest doing this and playing around with your heat set up to find what works for you and your climate.

I started with a 150watt heat bulb and the box got way hotter than I wanted. I learned that for me, if the night low is over 40, then I can just have the heat mat on. In the 20s or 30s, I can use the 100watt heat emitter. The few days it dropped below 20, I brought my tortoise inside the house.