The Brightness setting is somewhat better in this respect – the majority of LCD monitors control the brightness of the screen by changing the luminosity of the backlight lamps, so this setting has no relation to the matrix and doesn’t affect the response time in any way. Monitors with matrix-controlled brightness exist, though. For example, Sony’s products have an independent “Backlight” setting for adjusting the luminosity of the backlight lamps and a “Brightness” setting for the matrix. If you use the latter, the response time will be changing (measurements show that the response time may grow up considerably at low Brightness settings).
The asymmetry of the response time should be taken into consideration, too. I mean the ratio of the pixel rise and pixel fall times. For example, if we take two monitors with a total response time of 30 milliseconds, but one has 25/5msec pixel rise/fall times (typical for TN matrices) and another has 15/15msec times (this is typical for MVA and PVA matrices), they will display moving objects in a different manner. Particularly, thin black lines moving on a white background will seem thinner than should be on the screen of the first monitor.
The same lines will keep their thickness on the screen of the second monitor, although becoming a little lighter. The latter effect is better on the eyes, so an MVA matrix would seem faster than a TN one when scrolling text, their full response times being equal. This is another confirmation of my point that it’s wrong to compare matrices of different types by their total response time only – you must also know the pixel rise to pixel fall ratio, at least.
Users are often asking if it is possible to measure the response time without any special equipment. Alas, it is not. The maximum you can do is to launch a dynamic game and evaluate the image subjectively (“it suits me” or “it doesn’t suit me”). Users who are trying to estimate the response time by means of special tests that usually use a white square running on a black background (for example, Passmark Monitor Test) make one mistake, at least. The blurriness of the box is only indicative of black-to-white-to-black transitions, but it is not a crucial factor contributing to the monitor’s responsiveness in the majority of cases, as I explained above. Moreover, users often carry over their experience with CRT monitors to LCD ones, evaluating the response time by the trail behind the moving square.
Due to the specifics of the CRT technology (the pixel lights up very fast, but produces an exponential graph when fading out), the box will have sharp edges and a barely visible and rather long trail (the “tail” of the exponential function that’s describing the pixel’s fading-out). LCD monitors won’t necessarily have this trail, since they are usually described with quite another function, without the long tail. Some people even claim that modern LCD monitors have surpassed CRT ones, basing on this criterion. But they should take a look at the front and rear edges of the box – it is them that are the true indication of the matrix’s responsiveness. The figure below illustrates the typical white square moving on a black background from left to right: the picture taken on a CRT monitor is above (sharp edges, but a visible trail), the one taken on a typical LCD monitor is below (no visible trail, but fuzzy edges):