Well, I had the dreaded "LED headache" return today. In the late afternoon I worked with a colleague at their desk for under 5 minutes. They have a Dell U2713H and had the settings of 11% brightness, 50% contrast, "Standard" Pre-Set mode.
I've had a terrible headache for 3 hours now, which I would describe more as a "brain ache" as it feels deep in the head. My eyeballs ache a lot, and even blinking seems to make them a bit uncomfortable. I can't think very well and I'm kinda dopey and woozy. This is not the first occurrence of this happening with this VDU model and length of time. Literally 5 minutes (300 seconds) is all it takes for hours of grief.
Remember, this was after I mentioned I went about a month with no issues worth writing home about when using my trusty Dell U2410. Like hpst, I'm convinced this issue in particular has to be a technology issue, since I can look at other displays without these seemingly neurological symptoms occurring.
The frustrating thing is that none of us here can find out what the link is, and we've been looking for it for years now...