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 dead (resulting in a "dark" defect).
DPT was written to help me check my own screens (Couldn't find one that worked across multiple desktops so had to write my own!) by cycling through the three primary colours used (red,green,blue) and all on (white) and all off (black). Simply select a colour 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).
In most cases, a stuck or dead pixel is impossible to fix (some people rub them gently with a cloth etc. search the net for other ways), however most manufacturers have a policy which will specify that after X amount of dead/stuck pixels they will replace the screen free of charge (in warranty period). You can use DPT to help identify IF you have any pixels and how many in order to see if you qualify for a replacement screen/laptop... no guarantees though!
Note:
If you have problems downloading Dead Pixel Tester 2.20,
please try to stop using your download manager
and avoid right clicking on files. Also, check
your firewall settings, because some mirrors may
require that you do not block the HTTP
referrers.
Note:
If you have problems downloading Dead Pixel Tester 2.20,
please try to stop using your download manager
and avoid right clicking on files. Also, check
your firewall settings, because some mirrors may
require that you do not block the HTTP
referrers. 
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