The more light that hits your eyes, the more your iris contracts. The smaller hole makes for a clearer image (think of a pinhole camera). People who like dark mode have good vision at screen distance. For some others, they need to strain their eyes more to focus at that distance.
For me, the best is to have dark text on a light enough background, enough screen brightness overall, and a well lit room (natural light is really good, as long as it isn't coming from behind me).
For me, the best is to have dark text on a light enough background, enough screen brightness overall, and a well lit room (natural light is really good, as long as it isn't coming from behind me).