The design of the materials used in both photochromic glasses and fluorescent lamps has therefore naturally lead to the situation where photochromic lenses should generally not darken with indoor light sources.įor a more hands-on approach to this whole topic, I highly recommend this excellent video. Meanwhile, a good visible light source should create visible photons, and avoid wasting energy on harmful UV photons. For instance, when you’re driving in Transitions lenses, you’re at the mercy of the lens and how dark it gets in that particular environment. One of the perks of sunglasses is that you can control the darkness of the lenses. Good eye-wear glasses block invisible and damaging UV photons present in sunlight, but shouldn't block visible photons. Sunglasses are the original outdoor eyewear that offers sun protection for your eyes. Unsurprisingly, this is an entirely intentional property. Lastly, I'll briefly address why this process happens in sunlight, but not indoors. This simple fact (plus a lot of auxiliary processes) was the basis of the main forms of photography all throughout the 19th and 20th century.īecause of this, the classic examples of photosensitive compounds are the silver halides ( $\ce$, making it dark. Silver salts have been isolated and manipulated for centuries, so it's surely been known they have a tendency to darken in light for a long time. Photochromic sunglasses are a smart new application of very old knowledge. My goal here is to provide some insight into the chemical/physical mechanisms at work. As mentioned in the comments, this topic can become exceedingly complex if all the aspects of current-gen photochromic lenses are brought to the table (and I'm sure a lot of it is locked away in trade secrets).
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