[JumpCrisscross]

It’s also exposure to natural light. Myopia jumps when kids are exposed to artificial lighting [1]. It seems some constant is hard coded into our genes to calibrate our eyes to the Sun’s light. (Artificial natural light, despite sounding like an oxymoron, can help.)

[1] https://pubmed.ncbi.nlm.nih.gov/38766340/

[robwwilliams]

Yes, this is the main factor. Luminance and spectrum however are reasonable secondary factors and highlighted in the reference above.