Thanks for the replies! I was just a bit worried that without light from a window, they would lose their rhythm of when to be active or asleep, or that total darkness (without moonlight) would make it hard for them to move around.
On a related note - what is the best night-time viewing light to use: Red light or blueish "moon" light? I'd be looking for LEDs since I already have heating covered. Or can either be used provided it's dim?