Visit the following link for a description of our testing methodology and equipment and an explanation of the specified and measured parameters of LCD monitors. The article is called Xbit Labs Presents: LCD Monitors Testing Methodology Indepth. That article is going to help you if you feel overwhelmed by the numbers and terms used in this roundup.
Starting with this article we added brightness uniformity measurements to our standard testing procedure. The details of this test are described in the above linked testing methodology coverage, but in brief the main idea of brightness uniformity measurement is as follows. We use a sensitive photo-sensor to take the readings for screen brightness with 3cm increments for 19-inch monitors and proportionally larger increments for larger models. The measurements are taken in two modes: when only white color is displayed and only black, because of specific LCD matrix features (since in one case it is the electric field that holds the crystals in a certain position, while in another case the crystals are held by special grooves on the panel glass plates, the brightness uniformity for white and black colors is determined by two different factors). After that the deviation in % for each spot is calculated for both data arrays in relation to the arithmetic mean value. The obtained deviation results are used to build two brightness diagrams showing the brightness distribution over the entire screen surface which are then applied to the schematic monitor image (for more illustrative picture). This will help you get a better idea what this unevenness we talked about looks in reality on your display.
Here it is important to understand that we do not try to emulate the exact look of the monitor on these diagrams – these are just diagrams with some reference colors, and not monitor photos. Some reviewers may use different colors – green, yellow, orange, red, etc. - for different deviation levels (with 5% or 10% increments), however, we believe it makes things very hard to perceive, because you will have to remember all the way through the article that the yellow color stands for darker areas on the screen, while red – for lighter areas. That is why in our reviews we will use the closest to natural representation: lighter areas will be colored lighter, while darker areas – darker. However, we changed the brightness scale to make the images more illustrative, i.e. if the brightness of two dots on the diagram differs by the factor of 3, it doesn’t mean that in reality their brightness is also 3 times different – please check the scale showing the actual brightness deviation percentage and the colors we use.
So, the diagrams above serve to estimate the brightness uniformity: the distribution over the monitor screen, what areas are darker – corners or center, etc. For the sake of quantitative comparison between different monitor models we always provide percentage values in the text of the review: average deviation and maximum deviation. Speaking of particular numbers, if the deviation is within 5% it is considered a good result, within 7-8% - acceptable, and over 8% poor.