We currently don’t measure viewing angles due to technical reasons, yet one note is necessary.
Like with the response time parameter, there are two methods to measure the viewing angles of an LCD matrix: by a reduction of the contrast ratio to 10:1 or to 5:1. Obviously, the latter method yields bigger numbers due to a milder limiting condition and it is generally used to measure viewing angles of TN matrixes that have traditionally had narrow viewing angles. So, if you are comparing a TN-based monitor with specified viewing angles of 160 degrees with a monitor on a *VA or S-IPS matrix with specified viewing angles of 178 degrees, keep it in mind that the angles are measured according to different methods. If measured according to the “honest” method with a contrast drop to 10:1, the viewing angles of TN matrixes are going to shrink to 130-140 degrees.
The poor vertical viewing angle of TN matrixes looks like this (the screen displays horizontal gradients from the TFTTest program):
View of the screen straight ahead
View of the screen slightly from beneath
View of the screen slightly from above
As you can see, when viewed from below (and the angle is not too big – it roughly corresponds to a man sitting at a distance of 60cm from the monitor deflecting his head by 10cm up and down from the central point) the top part of the image gets dark as if the displayed gradients were shifted to the right and had a bigger dark part, which is not the case.
This is the reason why TN matrixes suit but badly for portrait mode. The poor viewing angle when viewed from below becomes a poor viewing angle from the right or left when you turn the screen around into the portrait orientation, which is downright unacceptable.
This strong distortion of the image as you change your angle of view is typical of TN matrixes only. S-IPS, MVA and PVA matrixes are much better from this aspect.