in LED backlighting - and this means that unit to unit variance is higher than you might think, even with very high quality screens Even the most minute difference in white will seen by even an untrained human eye. In particular, the way white balance and chromatic adaptation work with the human eye - means that we extraordinarily sensitive to differences in white tones (i.e.your desktop background, or a white screen) - your eye will pick even slight difference in those tones.
Here are some of the reasons it doesn't work the way we naturally expect: Like most things in life, solving this problem is far more complex than it initially looks. There's are many reasons why multiple monitor calibration does not achieve a visual match between screens.
