That's a weird area - with my Kindle paperwhite I don't even turn on the backlight at night - it's basically staring at a static image. It's also built so that you don't really have device attention issues, There's little in the way of digital distraction, your choice is to read a book, or read a book. I feel like it's basically the same as a book at that point.

I would argue that an ereader that simply displays ebooks is less of a "screen" than a smartphone.

But I read 90 books a year on an ereader, so perhaps I'm biased.