People who wear prescription eyeglasses are not always willing to carry around a second pair of prescription lenses to wear outdoors. To tackle this problem, eyeglass manufacturers have introduced a type of specialty lens designed to transition from clear to dark when exposed to sunlight.
Eliminating the need to tote around a pair of prescription sunglasses to wear outdoors, and protection from UV light.
Problems associated with Transistion Lenses
Generally, transistion lenses do not work well when driving because the car's windshield blocks UV light; as a result, there is nothing to trigger the lenses to darken to block glare.