[maskros]

Because astigmatism or other refractive vision errors.

Think about how astigmatism affects vision, then take into account the effect on pupil size based on incoming brightness, and how this affects the depth of field, and you may understand why.

[walteweiss]

Sorry, still don’t understand. Would appreciate ELI5 or other kind of explanation.

[arcanemachiner]

Some people have conditions that make dark mode text harder to read, not easier. Astigmatism is one of them. Also, myopia.

It can cause "halation" which is like a foggy glow around objects which are brighter than their relative surroundings. Like a streetlight at night, or white text on a black background.

I have this to some degree but I still prefer dark mode most of the time.

[walteweiss]

Thank you for the explanation. I thought it’s the other way: the dark mode somehow provokes your eyesight to become worse. For me, I used white-on-black since the dawn of time (with CTR displays) and even then it was much easier on my eyes. Right now, I have an iPhone’s frontal sensors dirty (have a broken screen) and it manages auto-brightness wrongly to some degree. I have a dark theme all the time, and I tried to make it automatic (light during the daytime and dark during the nighttime, obviously). So so so horrible to me! Switched it back almost immediately.