Wow, 1200K feels amazing! It's like silk.
This won't sound good to start off, but I've been awake for over 45 hours now (I've been doing a huge project, but I've had like a half a dozen little 10-minute naps in my chair). It's nighttime now, and needless to say, comibined with being awake for so long, my eyes simply do not want any blue light. Period. I just sat down after taking a good long shower. I had the lights dimmed very nicely in the bathroom, but now I'm at my computer.
So, I turn the ocmputer on and I get blasted by 6500K with 100% monitor brightness. Ouch! LOL For the first time ever, I finally know what people mean when they say that it hurts. It really does if the conditions are right! I immediately selected 1200K, and wow... just wow. Even with my monitor at 100% brightness, selecting 1200K was like getting naked and then slipping into a warm silk bed! (or a cool silk bed if you're too warm) Then I pressed Alt+Page Down and followed that with lowering my monitor's brightness all the way and it became even more comfortable. WOW. Now I get it. Finally.
So, Michael, Lorna, thank you. F.lux truly is the best. I'm glad that I had this little experience even though it's been a bit unpleasant up until now. lol
Edit: In case someone wants to recommend Darkroom Mode, I can't really use that because the Negative effect makes a few key things become nearly impossible to see in my little world on my computer. However, I'm trying it right now and it does feel even better than 1200K because the background on the f.lux forum is black now.