i'm not really sure what it is, but attempting to get to the bottom of it. lately i haven't been using it much/at all in widescreen, so i'm not sure exactly when it happened but...
last night i was playing a ps2 game and i set my controller down for a minute and dozed off for about 3 hours (it was at 4:3 screen size). today i noticed a vertical line that is darker and extends about 2/3 of the way from the top down and approximately 1/8" wide that falls just off the edge of the 4:3 area in the display (you can't see it when watching a 4:3 ratio source)
it was a used tv, built august 2008.
the pixels still display color, but it's a shade darker than the surrounding pixels. i did some reading up on it and tried cranking the brightness/backlight to max and then displaying a white image and when i do that, the line vanishes (which says to me that they are at least able to light up).
i read up on various methods and a few methods they outlined were to like display a white image that fills the entire screen and leave it on that for a few hours and/or run a few different programs with a computer connected to it that will get the pixels uniform again.
i have read a few things on applying pressure to the screen but they all warned that it could easily do more harm than good.
i ran the applet here for about half an hour and it seemed to reduce it slightlyhttp://www.jscreenfix.com/basic.php