I find that nighttime alertness is artificially (and undesirably) propped up by having the sum total of the world's knowledge at my fingertips. The LED brightness exacerbates. I haven't RCT'd tbis, but my best guess is that excessive nighttime alertness is 2/3 due to content availability, 1/3 screen (and perhaps ambient) brightness. I take active steps to have both passively cut off after a certain time.
Great point, I feel often the same. The brain so often goes into a mode of "ah yeah, now is the time to google that one thing I was wondering earlier today", or "I just want to confirm this one small detail about thing X", and then my phone is pointed straight into the eyeballs again.
