[atonement]

Try to avoid reading in pitch dark and especially don't crank up the brightness if you can't. Dark mode helps but only so much. Years ago I made the mistake of reading ebooks in my mobile in pitch dark and despite dark mode and minimum brightness I had developed issues with my eye sight which warranted a visit to the ophthalmologist. Afterwards I almost never read in complete darkness and the issues gradually resolved. Read extensively thereafter on my LCD smartphone for years and never had an issue.
A high quality LCD like in an iPad is fine. OLED should be better but ofc e-ink is the best.
I do not use the frontlight in my PW3 even during night time. I prefer to have a background light source.