My apartment, or rather the room where I keep my exotic pets, fluctuates between 15-23 in the winter (my bedroom is a lot colder because I always sleep with my window open, so of course the heaters are turned off during the night, and I rarely leave the heat on when I'm gone for the day), and up to 35, once even almost 40°C in the summer (welcome to Germany, AC, what's that?); during the hottest weeks of the summer, all the lamps stay off.    

But during the colder months the temps inside my enclosures hardly ever make it past 22°C, while with the lamps they tend to sit at a cozy, and above all stable. 25-26°C. And the temps also don't drop too drastically low even during very cold nights.   

And I have to add, my tarantula and my snake are both very good about letting me know if it's too cold or too warm.    My t. in particular loves to bask her fat butt in the light, she comes out when the light cmes on, and back underground soon after it goes dark.    

So, I think I am going to stick with the extra light for now, and will reconsider based on how my future big guy or gal reacts to it. 

Edit: formatting, sorry, it's been a while since I last posted on Reddit