…how does those glasses become shaded when foing into the sun and then once indoors or in shade they become clear again? What makes them do that?
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I don’t know how they do it now, but back in the day when this technology was invented, it was silver dissolved in the glass. The light made some of it come out of solution and thus the glass darkened. That was called photogray, it was replaced with Transitions.
Tiny molecules of silver halide and chloride are embedded within a photochromic lens which is invisible and clear until exposed to sunlight/UV rays.
A chemical process takes place when exposed to sunlight/UV and the molecules effectively move, change shape and absorb the light. This process changes the molecules and they darken to a sunglasses shade/tint.
The photochromic lens will remain in this ‘darkened’ sunglasses state whilst exposed to sunlight/UV and the molecules will reverse the process once the lenses are removed from the sunlight/UV rays returning to the original ‘transparent/clear’ lens.
https://www.onlineopticiansuk.com/photochromic-lenses-explained-i149
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