A few weeks ago I noticed an interesting phenomenon which I've been able to reproduce quite reliably - whenever there's a lot (by a lot I mean really a lot) of ambient light, I feel significantly less eye strain from screens.
I've made this discovery because of a light therapy device I purchased recently in order to improve my worsening insomnia during winter months because days in my country get quite dark and gloomy at this time of the year. I have a device Beurer TL 80 (it produces 10k lux at 20cm, but I sit farther than that) and sometimes I would place it on my desk to make me more alert (which works really well) and regulate my circadian rhythm (my sleep did seem to improve right after getting this device, but it's hard to tell because I'm doing other things too).
I wonder whether this has something to do with the constricted pupils or because intense ambient light makes the light coming from the screen less noticeable by the eyes.
I don't know whether this could be achieved with strong natural light too.