People in this forum describe many different factors that affect whether eye strain occurs. However they usually fail to isolate one main factor which decides about it, because this depends on many different factors that affect each other. Monitor, computer, GPU, operating system and even HDMI cable affect whether there is eye strain or not. The fact that eye strain occurs depends on all factors taken together and how they affect each other. You can not find a monitor or a computer that will ensure no eye strain.

Often a monitor works well with one computer and the same monitor works badly with another computer. And vice versa often one monitor causes eye strain and another not even if they are connected to the same computer. So you cannot say that the cause is only monitor or only computer. Sometimes even HDMI cable used for connection decides whether eye strain will occur. Furthermore, often eye strain occurs only when using certain operating system or driver and does not occur while using another operating system (even if computer and monitor are the same).

People say that if they use this "bad" operating system in a virtual machine or via VNC, their eye strain does not occur. So the cause in this case are not colors/animations/fonts/pixels displayed by the operating system. The reason is also not temporal dithering, because even if it is turned off (and it was tested that it is actually turned off), the "bad" operating system still causes eye strain when running as host system and does not cause eye strain when running in virtual machine. So in this case eye strain is not caused by pixels (image) displayed by a given system, but it must be caused by something else.

Here are some interesting and surprising cases that affect eye strain:

HDMI cable: https://ledstrain.org/d/214-hdmi-vs-vga-cable-and-eyestrain/

Power supply: https://ledstrain.org/d/1106-intel-hd-graphics-eyestrain-and-using-laptop-without-power-supply-as-solution

Partitioning scheme: https://ledstrain.org/d/1087-i-am-using-linux-comfortably/15

Based on posts on this forum, I suspect that a very important factor affecting eye strain is electromagnetic interference (EMI). Electromagnetic interference can obviously cause flickering of backlight or pixel (they will dim and brighten with the frequency of interference). Electromagnetic interference is transmitted through air only for very close distance (because power falls very quickly), but it is also very well transmitted through each metal wire for long distance (even if that wire is not connected to anything and simply lies nearby). Even if the HDMI cable uses digital signal that transmit data without losses, the electromagnetic interference noise is still transmitted by this cable from computer to monitor and from monitor to computer. Thus high frequency electromagnetic noise generated by a new processor or GPU or SSD drive is transmitted through HDMI cable to the monitor. Even if the monitor would be wireless or connected via optical fiber (but such technologies probably do not exist), the electromagnetic noise still would be transmitted through electrical network in the building.

Once I observed an interesting phenomenon. When I connected a 5V power supply to an electric socket, my monitor began to flicker (it was not eye strain, but a very strong flickering that was clearly visible to every person). This happened even if this 5V power supply was connected far from the monitor in a completely different room. After disconnecting the power supply, the monitor stopped flickering immediately. The only logical explanation in this case is "dirty electricity" (harmonics and transients generated primarily by electronic devices and by non-linear loads) transmitted through the electric network in the building. So even if my neighbor in his apartment connected that power supply to the electric network, the monitor in my apartment would probably be flickering.

Therefore, I suppose that electromagnetic interference is really important factor influencing eye strain. Computer (CPU, GPU, hard drive, etc), monitor and operating system affect which frequencies of electromagnetic interference are generated. Different monitors can be affected differently by different electromagnetic noise frequencies (for example LED could be affected differently than CCFL) hence the difference in symptoms on different devices.

An easy way to hear low frequency electromagnetic interference is AM radio. Just put the radio near computer, monitor or HDMI cable. In this very simplified way, you can compare noise generated by different hardware and software.

What do you think about it? Maybe connecting monitor or computer to double-conversion UPS (which filters dirty electricity) would sometimes help?