How do light reactive lenses work?

Question

I know we learned about these in school but the finer points of the explanation have evaded my little grey cells!

Helpful diagrams would be very much appreciated.

Answer 1

The glass lenses usually use a silver halide, like silver chloride. In the presence of light, some of the silver precipitates into metallic silver. That's the basic black and white photographic chemistry, but without subsequent steps to make the image permanent. The plastic lenses use organic materials like oxazynes. That process is more complicated, see the second reference.