Not good to have a light on at night.
If you want to take the chill out of the air, use a ceramic heat lamp (just heat, no light) or some other heat source that you can set up to be safe - (so it can't ignite anything or be knocked over or burn them if they touch it). Been researching this a lot. When my two seem cold (already they seem cold here in NJ - either because there's only two of them or because they are not cold hardy or because they are under the weather, not sure which), I use ceramic heat lamp (or lamps) suspended high over them and not where the lamps can touch anything. Basically just takes the edge off the cold and in prior winters was necessary to keep their water from freezing. I am seriously thinking about ordering a heater called edenPURE that is marketed as the safest - researching.........
JJ