Quote Originally Posted by turtle420
Maybe I'm wrong, and maybe somebody can correct me, but I think that night-time should be colder than daytime... maybe 10 degrees colder (F)?

You are correct.
Without lights on it will always get a little colder at night.
With lights on you will have peak temps in hot parts of the day.
Most growrooms temps will vary because most people wont put in a AC/Heat unit to control it to the degree.
A good way to help any Temp problem is to run lights at night instead of day to keep temps down and keep it from getting to cold in the winter mths.
DFG