The quality of my PowerBook and 20" Cinema Display screens has degraded over time, they became noticeably yellowish and darker due to the wear of the backlight (I assume). Neither of those screens is LED-backlit. I'm wondering, how do the LED-backlit screens used in current Apple products degrade over time? Do they similarly become yellowish, give less light, ...? How long does it take for the effect to become obvious, or what's the expected life time of these screens?
This Engadget article shows photos of a direct comparison:
Also interesting could be the Advantages and Disadvantages sections of the Wikipedia article on LEDs (link):
I've had my 2007 MBP17 backlights replaced a couple times.
With that model, you could place downward pressure on the closed device. That apparently causes blobby regions of the backlight to appear overtly grayer. I carried my MBP17 in a padded backpack with stuff in it that compressed the unit while carrying. Whoops.
Another failure mode I saw was the backlighting dimmed in largely vertical areas; text over at the top-left of the panel and below over time became harder to read. The effect is considerably less obvious than the first problem.
(Normally, the screen center looks brightest and the edges look a little dimmer, but I can see the left side of the screen as brightly as the center by moving my head to the left. When it doesn't seem a little brighter by doing that, you may have a backlight issue.)
There may be other failure modes, these are the ones I've seen. For me, the degradation is slow and involved areas of the backlight becoming less bright.