Relative perceived contrast is important in vision. Most displays are backlit LCD and their black is actually a mid to light grey; it only appears moderately b

Relative perceived contrast is important in vision. Most displays are backlit LCD and their black is actually a mid to light grey; it only appears moderately black in contrast to bright white. The white of white text on black isn't enough brightness to make the black truly black, reducing effective contrast and making it harder to read. It's much better on OLED and other non-backlit displays with higher contrast ratios. (CRTs in the days of DOS and terminals were white on black mostly for ergonomic reasons; it is easier to read.) The lighting in the room is a factor too. I like dark mode in dim lighting and light when it's bright in the room.