Check out the Center for Disease Control (CDC) figures on sleep in the USA map in this Stat report. Note how dark it gets up in our neck of the woods of Minnesota, i.e., us being able to sleep better.
Dark is good but even better is the cold according to this new YouTube video posted by the Wall Street Journal.
There being a sweet spot on temperature makes perfect sense to me, this being based on many sleepless nights camping in the cold or hot. However the worst night I can remember was an overnight ice-fishing outing with a bunch of boy scouts. They could not stop fiddling with the space heater, which cycled us from freezing to boiling for some hours before finally stabilizing at a reasonable temperature. That is when the farting began and the giggling commenced. The whole troop deserved a merit badge for flatulence. But I digress…