>> When I worked on the rigs. The control room operators would keep the
>> same screens on their monitors 24 hours a day. After a few years you
>> could see the ghost images burnt into the screens.

Someone had installed plasma screens above every gate in Munich airport 
when I used to go there a lot. When a flight was not departing it just 
showed a default static "Lufthansa" logo. As you can imagine all the 
screens ended up with a horrible ghost image on them. Plasma screens are 
possibly the worst for burn-in.

> I've seen a ghost image burned into the screen on an iMac. Which is
> weird, because I didn't think LCDs even *do* that! o_O

They will easily burn if the time-average voltage across the pixel is 
not zero volts (they switch between + and - every frame). Obviously 
exactly zero volts is impossible, but the further away from zero you are 
the faster you will burn in that pixel. So it depends on the quality of 
your driver electronics.

If you're destructively-minded you may have realised that if you were to 
display black one frame and white the next frame, then repeat, this will 
create a massive non-zero average voltage on the pixel. And yes this 
will cause damage eventually. Note that screens don't normally do all 
pixels with the same polarity, it might do one column +, one column - 
(or row by row, or in a checkerboard pattern), then flip for the next 
frame. That's what this page is meant to figure out, assuming your 
monitor electronics are non-ideal then the pattern that matches will 
flicker slightly:

http://www.lagom.nl/lcd-test/inversion.php

> Now here's a question: Why does printing white text shift the
> corresponding scanlines left slightly?

On a CRT? I remember that if you drew a white rectangle around the edge 
of the screen, then flipped the inside between black and white and shape 
of the screen would change massively. I believe it's because the extra 
current needed to draw all the "white" slightly reduces the voltage from 
the PSU which is also used to control the timing/geometry, so the shape 
of the picture will change based on the average brightness of the image.

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