Why doesn't my photochromic goggle get as dark as my friend's sunny-day goggle?

Photochromic goggles have a VLT range (e.g., 22%–80%) that spans from moderately dark to quite light, but they cannot achieve the extremely low VLT of a dedicated sunny lens (8–15%). This is a physical limitation of current photochromic technology—the molecules can only restructure so much. For the vast majority of sunny skiing conditions, the darkest state of a photochromic lens provides adequate glare protection. Only in extreme high-altitude or glacier conditions might you want a dedicated darker lens.