I'll add that I also began experiencing severe eyestrain after buying the SP3. I've been using computers heavily for 20 year s with no eye strain problems so this was a shock.
I wasn't sure what the cause was so I stopped using my desktop & tablets, and only iPad & iPhone. The worst symptoms disappear right away, most are completely gone within a few days. The DPI/size is definitely not the cause because I am able to remote in to my desktop from my iPad, which makes for a really miniaturized display.
I did have a SP2 for a year, but I almost always ran it on maximum brightness. The SP3, I have almost always ran dim because the screen was bigger and tints more toward blue (flu.x appears to crash the video card.) I really appreciate the info in this thread &
Ullit's graphs.
Another interesting thing is I have mostly switched to LED bulbs in my house. Now I wonder if that is optimal.