From data product services:
Dead Pixel Tester - TFT screens have thousands of pixels, on a 1024x768 monitor, there are three cells for each pixel - one each for red, green, and blue - which amounts to nearly 2.4 million cells (1024x768x 3 = 2,359,296). There's only a slim chance that all of these will be perfect; more likely, some will be stuck on (creating a "bright" defect) or off (resulting in a "dark" defect). Simply select a color then closely inspect your monitor in each of the primary colours checking for pixels that are not operating as expected. Stuck pixels (always on) are easier to noticed then pixels that are not on due to their size (normally under .5mm).