A CHE Emits heat and no light. It is what is recommended if you need to add heat during the night.
They can feel ambient heat around an area, so if a heating pad is giving off heat, the dragon will know that side is warmer than the cooler side.
The problem is, they don't detect heat from their bellies, so your dragon laying ontop of where the heat is coming from, is a big risk, as its much hotter at the belly than it is 2 or so inches off the heat rock.
-Brandon