Normally I wait a while to update my iPhone when a new version comes out, but last night I couldn't resist trying the new Night Shift feature on my 5S so I installed 9.3.1. What a difference, it's so much easier on my eyes late at night. Normally I would have turned my brightness down all the way, and even then my eyes would feel strained after a short amount of time so I'd find myself turning my phone slightly sideways and use the view angle to direct more of the light away from my eyes. Now I run Night Shift just slightly towards the warmer side of the slider with the brightness all the way down and and it's very comfortable on the eyes. A little adjustment is needed to get used to the hue at first but it wasn't a big deal for me at least. I'm not sure I buy into the "better sleep" marketing just yet, it's early to tell, but it sure does make it easier on the eyes in general. I wish my iPad mini had the same function now. Thank you Apple for a relatively minor, but very welcome feature.