Photochromic spectacle lenses have advanced considerably since the first ones were developed by Roger Araujo at Corning Glass works in the 1960's. For many years photochromic lenses could only be produced in a glassy material, but then plastic versions started to become available, although initially these changed from a light tint to a dark tint very slowly and faded even more slowly. Attempts were made by American Optical in the 1980's but it was not until the 1990's that the Transitions company (created jointly by PPG and Essilor) released the first CR39 photochromic and, in 1996, they introduced their third generation product, enabling the lenses to be made in a grey colour and with a reasonable speed of reaction. The latest versions have even better performance with short reaction times and can change from very pale to very dark.
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