Look about your work environment. It is possible that your light environment is just not good. I used to have photo sensitivity and frequent headaches at a previous work.
Then, I realized that the cause was bad light conditions. It was not that I was in the dark, but for example sun light was coming from a window at 90 degrees with my screen.
And despite being sufficient light in total all around, it was like that the direction of my screen where I was looking was the darkest.
Don't know about anything else, but it simply looks better to me - staring at a darker screen feels easier on my eyes than a highly white, lumnious one.
And if anything, that leads me to look at my devices even more!