Having a light on at night disrupts a tortoises (and other durinal animals) day/night cycle. If you have to use a heat source a non-light emitting ceramic heater would be a better choice.
It also depends upon the species and the temperature within it's enclosure whether or not it even needs a night time heat source. Not all do.
Thats what i thought, im doing the TT course and theres a question about light heating for hatchlings but i wasnt sure if it meant a black light or a bright daylight one, I knew that you shouldnt have lights on at night but as it said heat source i wasnt sure if it could also mean the heat emiters, Thanks anyway guys,