In a country like the Philippines where the tropical weather is as fun as it is UV ridden, transition eyeglasses are almost a necessity. Not only do they protect your eyes from harsh UV rays but they also help your eyes fight brightness by turning a shade darker in the sun. But if you’ve ever seen transition lenses in action, you’d know that they are completely transparent indoors and turn a very relaxing shade in the sun. So how does it happen?
In 1965, Donald Stooky and Roger Araujo, both chemists, discovered that certain compounds behave differently when exposed to UV light and from there, the first transition lenses were distributed under the brand name Bestlite. After a couple more years, improvement in the photochromatic lenses as they are also called made way for photogray lenses.
Photogray lenses are eyeglasses with a film cover made of a compound of silver and copper chloride that, when exposed to UV, yield a chemical reaction that causes it to turn gray and absorbs the UV rays in the process, returning to its original state. If you wear transition lenses in the Philippines, what you are looking at actually are chemical reaction taking effect literally in front of your eyes.
Downsides to transition lenses are that they will react to UV rays so if you are in a car that has UV protected windows & windshields, the lenses might only turn about 10-30% darker than because of reduced UV exposure—they block UV rays but don’t necessarily adjust to cater to your preferred brightness. But if you’re a regular commuter in the Philippines, transition eyeglasses are very helpful tools that protect your eyes both from UV damage and intense brightness.
Also: they are called transition lenses because the most famous brand for them was called Transitions (in the same way we call photocopies Xerox), and the real name of the coated material are photochromatic lenses.