It is also not clear cut that other than the incandescent bulb use of electricity is actually prohibited. The Hazon Ish ruled that the completion of a circuit is considered ‘makke bapatish’ or ‘boneh’. But one can argue reasonably that it is not so.
It's been assur for long enough that everyone just holds `lo plugh' when it comes to electricity. Yes an incandescent is prohibited, a hotplate is prohibited. An eInk display is technically alright, as is an LCD watch. But there's way to many gray areas between those. What about LED bulbs? Some get hot enough to be a problem, some do not.
I've had this idea that if we could ever get e-ink displays to actually be paper like (i.e. in thickness, and bendability and hatever other features you attach to paper books) it be interesting for observant jews an people who just like books to be able to sell "placeholder" e-ink books. i.e. books filled with programmable eink pages that you can flip through like a regular book. One would download a book and program it, and then just read it like a traditional book, flipping pages as you go. once done, you download another book to it and all the pages get reprogrammed.
