Photochromic lenses, also known as Transitions or Reactolite (or sometimes just Reactions) are lenses that have the abililty to change their depth of tint depending on the ambient lighting. Light when its dark, dark when its light !
These lenses offer the convenience of having just one pair of glasses for any lighting situation.
It must be understood that these lenses cannot react immediately to sudden light changes. For example, driving into an underground car-park on a sunny day. They do take a small time to lighten or darken. They offer full UV protection against harmful radiation and generally are availble in either grey or brown colours. A company called Serengeti do make sunglasses that incorporate both photochromic abilities and are also polarising. This gives the best of all worlds - a variable tint and reduction in glare.
