Here's how you check: Find a white image on google , save it to your camera roll...open the image in your camera roll. Tap the screen until the menu disappears and you only have a white background, make sure brightness is up and screen is clean of any fingerprints.....
Proceed to inspect!
I got lucky, my display is perfect, no back light problems, bleeds, uneven color, display is truely gorgeous.
While I was waiting to pick up my ipad, I inspected others and noticed a couple with a dark shadow on the left side of the display while in portrait mode .
Out of the four models I inspected, 3 of them had the issue, with varied degrees of darkness...only one out if the four was severe enough to warrant a replacement IMO.
I think it has to do with the magnet for the Smart Cover along the left side of the ipad.
If you put two ipad airs next to one another they attract and repel each other. A magnet can effect a display if close enough, correct? Since the bezels are smaller, the magnet may be closer to the internal display, creating these issues in some iPads.
that's my two cents!