Or the sun/daylight while being outside? I'd guess that's some orders of magnitude more.

Ironically you need to be exposed to the strong light outside (as a child), otherwise you will need glasses.

Yep, I really regret spensing so much time of my youth indoors in front of a monitor... At age 19 I can experience the loss in sight quality already. It is recommended to spend AT LEAST 2 hours everyday outside in daylight to prevent myopia. I did not follow that recommendation and regret it sorely.

The evidence around this appears to be most strong for actually having a long focal distance as being one of the most important factors (as opposed to the lux) - unless the evidence has significantly changed.

I mean there’s probably a pretty strong correlation between being outside and having a long focal distance, but my understanding was that when attempting to control for this (ie rise of increase in apartment living, first in Japan and then other Asian cities) its tightly correlated to not focusing on things a long way away

Yep, that's correct. If you're spending many hours a day in front of a phone or monitor for months or years you'll have accumulated a lot of very short focal length time, so to say.

I’d imagine most discomfort is eye strain rather than brightness. The way VR headsets work right now it’s important to have your eye correctly positioned and the headset adjusted for your own distance between pupils.