Although an open window shade isn’t likely to bother anyone on most occasions, there are times when it can disrupt the sleep of an entire aircraft of people.
An article published on Traveller explains when flying from west to east (e.g Europe to Australia) passengers experience a short night, especially in summer.
"Cabin crew will often request that passengers lower their shades and the reason becomes obvious once the sun is in the sky," the article says.
Leaving one window open while the rest are closed floods the cabin with light, "and it doesn't stop when it hits the person sitting in the window seat."
And it isn't the ordinary light we're used to.
"This is the pure light of the high troposphere, unfiltered by smog or clouds, it's more intense than the "normal" daylight typically experienced at ground level even on a cloudless day.
"Sleepers without eye masks might be disturbed and anyone watching a video in close proximity might experience a desaturated screen, dulling the modest pleasure of the viewing experience."