Read here about the history of glass and what optimisations have emerged over the years for the spectacle lens industry.
Initially, the low-index CR 39 remained the only material used for plastic lenses. It was not until the mid-1980s that the development of plastic materials with a higher refractive index began.
Photochromic lenses gradually darken when exposed to an increasing intensity of short-wave light and return to their original state when the light is removed. They adapt automatically to changing light conditions and therefore provide optimum protection against glare in every situation.