Don't know about anyone else, but for my Paperwhite and Deb's Nexus, you don't need lights at all.
I believe that the Kindle Paperwhite display is e-paper, but has a built-in light. The Nexus is a tablet with a conventional backlit LCD screen. Neither of these is a typical e-book reader, which has an e-paper display and needs to be lit to be readable, just like printed paper.