Transitions. My personal favorite is transitions xtraactive which is one of the few photochromic lenses to actually darken in the car. Most lenses that darken automatically are activated by ultraviolet light and need to be directly expsed to uv light in order to activate/darken. The transition xtraactive lenses have a slight tint indoors but will darken in the car as well as outdoors.
Photochromic lenses. Check info in this website below. Http://www. Viziooptic. Com/eyeglass-prescription-lenses/introduction-to-color-changing-eyeglass-lenses-transition-lenses-photochromic-lenses. Aspx.