Dr. Mercola likes to over-dramatize things so that he can sell his products. It's pretty much Scare Tactics 101 with him. It's not that he's necessarily wrong about things, but he goes too far and makes his readers think that they have a bunch of health problems to deal with even though they felt just fine before reading his articles. Even when he's not trying to sell one or more of his products, it's like he's one of those tin foil hat people. Y'know what I mean?
I don't know who this Dr. Jack Kruse is, but I would bet he kinda does the same thing.
I don't have any problems with leaving f.lux set to 6500K all day, and I literally LIVE at my computer (I spend all day at my computer, every single day). All you have to do is make sure your indoor lighting in your computer room is blended fairly well with the brightness of your monitor and vice versa. Oh, and of course, don't sit too close - like, you know, keep a distance between your monitor and your eyes of like say 2-3 feet or more.
I don't know if you can see how paranoid these 2 "doctors' are making you be, but it seems to me they have taken away your ability to just relax and enjoy your computer and your life. Try to stop listening to them so much. You're not going to hurt your eyes by simply using a computer. I mean really, look at the rest of the world. Or, look at me. I've been living at my computer for YEARS but I don't have any problems.