They speculate that the harmful component of e-readers is the blue-shifted illumination. I’d be curious if newer e-readers with temperature controllable backlights set to “warm” mitigates some of this sleep harm
Also the kindles use significantly less light that aren’t emitted directly into your eyes (rather up/down on the screen). That’s what I thought this study was at first. I have a non illuminated kindle for years and I’m wondering the same thing for when I inevitably have to replace it. A built in warm & dim light is convenient especially if it doesn’t adversely affect things. If not back to candles for me!