Are dark themes bad for your eyes? Alan Kay seems to think so

'A dark close up display will induce dark adaptation while looking at it and light adaptation when looking elsewhere.'

Meaning keep the light from the monitor consistent with your surroundings, to avoid having to readjust.

Going a bit further into his point, the tests were done on a CRT not an LCD, where black is no light, not just a grey. LCD black is not really black so I don't think it 'induce(s) dark adaptation'. Even when we have OLEDS and low brightness text that would be dark enough trigger adaption monitors have an ambient lighting setting that would crank brightness to be clearly visible on a sunny day, adding light to the dark elements.

Finally I use dark mode, when working in the dark, exactly the 'troglodytish existence' he advices against.

I think the other question is in terms of readability: I've always found light background/dark text to be more readable.

Maybe it's because the "brighter" nature of a light background means my eyes squint more and focus better on the words? At least with a dark background, my eyes feel more relaxed but they kind of just wander around and I can't focus on the text as naturally.

Then again, I've found dark backgrounds to work really well when there's a lot of visual elements in the design of the page (i.e. not words to read but graphics to look at).

(Not a professional designer, I just occasionally design things for people and wonder these things -- would love input from someone more knowledgeable).

Using both in different programs is very uncomfortable.

:(