yes - it will lead to eyestrain.

Less light means your pupils will dilate.

When your pupils dilate you must flex the physical lens of your eyes to focus on the screen. Less of what you see is in focus, especially up close.

Constantly focusing and refocusing can lead to eyestrain and headaches.

Meanwhile a brighter screen allows your pupils to contract, and with small pupils more of what you see is naturally and optically in focus.

This is depth of field and is most familiar to folks who have set the aperture and focus in a DSLR (or SLR in the old days)

This is less noticeable to younger folks because their lenses are much more flexible. But as people age, their lenses become less flexible and it is harder to focus up close. It might be like squeezing a tennis ball for an hour. This is why people buy reading glasses - to set the natural focus of their eyes closer to them.

If you buy reading glasses it's quite common to get a higher correction for very close like an ipad ~ 18" and a different lower correction for a computer ~ 24-30".

You are not alone. I've tried several times to use dark themes and dark modes. I just can't do it, I feel less productive because I'm hunting for UI elements to click in programs more often, and the lower contrast between text and background makes everything just that much harder to read for me.

Do you happen to have an astigmatism?

I’m not sure if my personal anecdotes will apply to you but I’ve found dark color schemes with gray text over a blue background (ex. Solarized Dark) to be infinitely more usable than something with a black background with white text.

Same here. I tried multiple times (low contrast, high contrast) because I love the aesthetic and also I usually write code in dark but when looking at a dark theme for more than 5 minutes I start to get dizzy, my eyes hurt, I get a headache. I always assumed it was because if my astigmatism, even got correcting glasses but no luck. I ended up with light theme, low brightness and Flux.

I always prefer dark mode but I'd guess you're actually the majority, otherwise we wouldn't have dark mode this late in the game. What I observed around my personal circle is people who started wearing glasses at a young age are more likely to prefer dark mode. I'm not sure if it is coincidence or a real cause.

Likewise; it's particularly bad when I view a light on dark website, I often have to use reader mode or invert the screen colors.

For regular reading I can deal with light mode, but for code I can't make it work at all. Because of how much less syntax coloration "pops" against a light background, the code all runs together into a mush that's difficult to read at any reasonable speed.