I'm new to beardies and hear mixed feelings on whether I should leave the lamp on at night or not, I turn the UV striplight off, apparently upto the point when I got him yesterday the previous owner was turning the heatlamp off at night, some have suggested a red light at night.
The cool down at night is natural and healthy for your dragon and he will do fine in temperatures down to the low sixties. If it does get too cold, then it's best to use a ceramic heat emitter - a ceramic disk that screws into a normal light socket and puts off heat without any light. This way the heat source is above your dragon's head so there's no risk of your dragon being burned, and it doesn't put off any light. Dragon's sleep can be disrupted by any light in their tank, even the red ones, so it is suggested that _all_ lights be turned off at night.