The brand manufacturers have created many brand names for photochromic lenses. These include Transitions, Reactolite, Reactions and Graduations. However, they are all photochromic lenses. The most common photochromic brands are 1. Transitions Lenses. They are the most popular brand of photochromic lenses today. They are available in a variety of options including Standard Plastic, Polycarbonate, 1.6 and 1.67 Lenses. They are the fastest reacting lens on the market, reacting into sunglasses within 30 seconds of UV exposure. 2. Reactolite Lenses. Reactolite is a brand name given to a Glass photochromic lens. They do not react as well as the transitions and are much heavier to wear. However, they work much better behind a car windscreen than the Transitions. Source: http://www.eyekit.co/information/sunglasses/about-sunglass-lenses/what-are-photochromic-lenses.html