[user5994461]

Colors, brightness and angle of vision.

Without going into specifics, the shortest way to get a good screen is probably to buy an IPS display (it's barely more expensive). Pretty sure all IPS display are at least okay.

The cheapest displays are TN because it's cheaper to manufacture, sadly that technology has very bad angle of vision, move a feet to the left and another feet and you'll see the image looking different, it also has a more limited rendering of colors. Not great.

Typically you realize how bad a screen is when you try to calibrate it (looking at a few pictures is enough, no need for expensive equipment). With a really shitty screen, you will notice that the display literally cannot render half the colors.

For example looking at a picture with 16 shades from pure white to pure black, the 4 first levels of white look the same.

Typically that's the part where you have to adjust brightness/contrast until it's showing a difference. If you have a really shitty screen, there's no settings where half the colors will render. The example above being extremely skewed toward bright white will slowly destroy your eyes, being too bright and removing details/contrasts.

[karmakaze]

I don't know how true of a problem this still is. Are most LCDs now not typically TFT/CCFL? Quality still varies, but I haven't had trouble with even cheap displays if you can use the included controls or software to adjust the gamma or dark/light response. I used to use the Norman Koren test patterns[0] before using a Mac with included wizard.

It's likely much more common for people not to know or try to see how much difference settings can make.

[0] http://www.normankoren.com/makingfineprints1A.html

[bluedino]

IPS, TN, now you have this pentile shit

[daneel_w]

But neither color accuracy nor poor viewing angle are issues that cause strain on the eyes. Blinding brightness certainly can, but are there really screens these days which cannot be dimmed-down enough? I have a hard time believing it.