Comment by dkga

Could be related to the light spectrum. Kindles aren't really "screen" like the others; they do have background light but you can turn it off and use it with its paper-like screen (which is what I do and really like it). But traditional screens have blue light as part of the normal light they emit, which is known to disrupt sleeping patterns. When I am using my cell phone or computer right before sleeping, I usually turn on colour filtering to make my whole cell phone be tinted red. This helps wonders. I found this page that explains how this can be done: [0].

[0]: https://ios.gadgethacks.com/how-to/keep-your-night-vision-sh...