The issue isn't brightness, it's distance to what you are looking at and focus on the retina. When your eyes can still bring far objects into focus, they produce a signal that causes your eyes to grow longer.
https://newsroom.uw.edu/news-releases/glasses-stop-myopia-ar...
The brightness of light is actually believed to be the main factor now. This seems a supported by animal studies, where animals are fitted with light-filtering goggles. Animals that receive brighter light develop normally, while animals that receive dimmer light develop myopia.
Do we really need VR headsets for this? Is there some material way in which just walking around outside, for free, is worse than strapping expensive electronics to your face and staying indoors?
