Looks like this study is about people with mild vision problems. As I said before, I know some people with more limited vision (myopia with more than 10 diopter

Looks like this study is about people with mild vision problems. As I said before, I know some people with more limited vision (myopia with more than 10 diopters, optical nerve damage, etc), and all of them prefer light letters on dark background. Myself I can hardly read on paper or a paper-white screen. Whatever science may say, this is how I experience it! :)