Hello Richard,
I think one pixel should live as much as its refresh rate, which depends on your monitor and screen card.
According to me, the lifetime of one pixel should be as follows:
Pixel lifetime= 1/refresh_rate ,for example, if refresh rate is 70Hz, the lifetime of the pixel should be 1.428 *10^-2 sn.
These colors can be recorded. Only one sample should be taken for every 1.428 *10^-2 sn(this lifetime depends on your screen and monitor card) from screen.
Maybe, some web sites can help you about this topic http://www.hugoson.com/www.hugoson.se/index.php?show=3118_ENG&&page_anchor=http://www.hugoson.com/www.hugoson.se/p3118/p3118_eng.php
http://www.practical-home-theater-guide.com/LCD-Tv.html
Best Regards
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