In a post I wrote a while back about dark mode and variable fonts, Gerhard Großmann made this rather lovely comment:
In typography it’s well known that luminous letters on dark backgrounds tend to look bolder. Unfortunately I know the technical term only in German – „Überstrahlung“, which could be translated as blooming or flare. If somebody knows the English term, please comment! I found a good explanation of this effect in a German article about legibility on computer screens. My translation of the relevant part: “Bright areas outshine (flare/bloom into) darker ones, so that a bright background eats away dark letters from the outside and the font seems to be less bold – vice versa bright text seems to be bolder on dark backgrounds.” Besides on computer screens this effect occurs on luminous or reflective road signage, too [...]. It’s also helpful to slightly (!) letter-space white text on black backgrounds. As always in typography there’s more than one possibility to compensate the numerous subtle optical phenomenons.
Subtle. Optical. Phenomenons. Heck yes.