pylkko wrote:Tablet's and other computers generally have some kind of backlighterd display. Perhaps and LCD or AMOLED, which means that there is a large lamp shining light, and on top of that is a layer of pixels that can change the light in different wys to form an image. E-book readers tend to have E-ink displays, which do not have a lamp, but the image is created by dark or coloured specks that can be turned on or of with electric current and which reflect light. (https://en.wikipedia.org/wiki/Electronic_paper). This is the reason that they cause less eye fatigue and are so aesthetically pleasing. You can buy linux controllable E-ink displays. People often control these with Raspberry pi's and simiar to make low power displays of information (news, calendar, weather that kind of stuff)
However, I believe that all commercial (not DIY) E-book readers -- or at least do not know of one that is not -- organized so that the content that you buy is "not yours". That is, there is a server somewhere, and when you pay for a book, you unlock access to it on that server for youtself. This means you cannot read your own made documents, pirated stuff, and need to have a mobile connection. You also cannot just give the book to a friend, for example. According to Wikipedia, Amazon Kindle has a service where you can email stuff to Amazon and they will put ot into your account (https://en.wikipedia.org/wiki/Amazon_Kindle). This is the reason that I do not have one of these readers although I like the displays.
If you googled that far you might just have found a little something called "calibre". You know the little program for Win/Linux/Mac that talks to pretty much all of the ebook readers out there ( and even tablets with ereader software ) and lets you put your own books on the reader. It even helpfully converts pretty much any format out there to any other format so you can guarantee that your reader can read the book.
I only occasionally turn the wifi on my kindle paperwhite on, and that is only if I have books lined up in kindle unlimited to download. ~600 books on it right now, 10 from kindle unlimited, 0 from being bought on amazon, and ~590 bought / pirated from other places and DRM free. So no, you don't ever HAVE to turn on the wifi.
As for the rest of the discussion about backlights - the kindle paperwhite / nook glow ( if they still make it? ) are e-ink displays with lighting. You can read in the dark just as well as you can in direct sunlight. I actually find the default ~50% brightness on mine WAY too bright. 10% is plenty to read with in dark areas, and saves the battery quite a bit. At 10% backlight I can go 3-5 weeks with wifi off and reading 3-5 hours a day between charges.