My notes on checking LCD pixels:
Explain to the sales droid that LCD
displays can have dead (or permanently
alive) pixels. It probably won't know
that knackered pixels are expected,
but the vast majority of displays are
perfect, so there's no harm in making
sure you get a perfect one. Unpack the
display and plug it into a PC in the
store. Now you need to check both a
completely white screen and a
completely black screen - because
knackered pixels can be knackered
either always on or always off. An LCD
'turns on' its pixel so it becomes
opaque - that is, black. A pixel is
'turned off' (goes clear) and lets the
white backlight through it to display
white. This is why LCD's are not as
good at displaying black as CRT's. The
backlight is always on, and the pixels
can have varying degrees of opaqueness
when turned on. This makes black more
of an uneven very dark gray (well,
uneven on my LCD anyway..newer ones
might be better at it)
To check always off, fire up Internet
Explorer, go to "about:blank" and
press F11 (full screen). This will
give you a page full of white. Scan
the page closely looking for "always
off" dead pixels.
Then, to test for always on pixels,
right click on the desktop and go to
screen saver. Select "Blank" and then
"Preview". Again, scan the blank
screen and this time look for "always
on" pixels - although these are much
easier to spot!
Then go to
javscript:void(document.bgColor='red'),
javscript:void(document.bgColor='green'),
and
javscript:void(document.bgColor='blue')
with Full Screen (F11) after each
color.
I knocked these notes together from some slashdot posts a few years ago.