In our fast paced world of ever changing technology, it’s easy to forget that we have an amazingly intelligent product that many people use every day, without even noticing how clever it is! It’s coming up for fifty years old, it works without flicking a switch or having to think about it…….. so what is this super smart piece of technology? The humble photochromic lens of course!
So here’s the history lesson – glass photochromic lenses appeared in the mid-sixties. They had a light tint when you were indoors, and then went dark when you stepped outside – how cool is that?! UV in sunlight triggered the change. The only disadvantage was that as they were glass, as all lenses were in those days, they were heavy, and of course could break if dropped. The lenses were slower to react than our modern versions, and over time, stayed darker in all light conditions. In 1986, the first plastic photochromic lens arrived, giving safer, lighter weight photochromics. The glass versions had been available in several different colour options, but these new fangled plastics came in light brown which then darkened to blue – choosing a matching frame was a challenge!
Now here’s the science lesson – the lenses work thanks to colourless molecules within the material that are excited by UV radiation. This breaks a chemical bond within the molecules, and they go dark! They fade back when the UV stimulus disappears, and you go back indoors.
Finally, here’s the practical lesson – what can these lenses do for you? Well, if you like one pair of specs for everything, photochromics give you clear lenses and sunglasses all in one. You don’t have to swap glasses around, and you only need to carry one pair with you, whatever the weather. Since 1986 several new versions of the material have been developed, and thankfully they are now available in grey or brown. Each new generation of lenses are faster reacting too.
So if you wear photochromics, or may choose them next time, take a moment to appreciate these quietly hard working, amazing lenses. That’s all for today’s lesson – class dismissed!