I was recently told by one eye doctor that if I get a pair of glasses with polycarbonate lenses, they don’t need any sort of extra UV coating, because they’ll screen out UV by themselves. Does anyone else know any details about this?
My optometrist told me the same thing.
I’m always surprised about claims that various glasses or plastics are opaque to UV. The truth is that almost all glasses and plastics block light at wavelengths of 300 nm or above. Usually the cutoff is even higher. In fact, you really have to work at it to find glasses and especially plastics that will transmit below that wavelength. These exist – UV quartz, UV polycarb, polychlorotrifluoroethylene – but you’re not likely to stumble across a pair of glasses made of any of this stuff. In my experience,m you have to pay extra for reliable UV transmission.
According to my source (Tokyo Optical web site, so probably somewhat biased) UV light up to 400nm can increase risk of cataracts. Most glass lenses have a cutoff around 340nm. Polycarbonate has a cutoff around 380nm so it’s pretty safe, but an extra anti-UV coating can bring the cutoff up to 400nm.
Former 1-hour glasses retailer lab tech here:
I don’t have any detailed data, but I know that we didn’t sell the anti-UV coating option on our polycarb lenses. And since we’d try to sell pretty much anything that was useful enough to not result in a lawsuit, I’d have to say that the polycarb lenses had about as much UV opacity as plastic lenses with an anti-UV coating.
Works for me.
So what we need is the absorbtion curves for “plastic” (probably PMMA acrylic), versus polycarbonate.
Here’s one version, but it’s not detailed enough below 500nM:
Hey, I have some laser lab glasses with “UV SAFETY” stamped on the sides with big letters. They’re polycarb for shatter-resistance, but also have a distinctly yellow tinge, as if they contained a dye which was absorbing the VISIBLE blue end of the spectrum. This points out that “opaque” is a matter of degree. Something that is 99% “opaque” to ultraviolet might not be so safe if you’re working with molecular fluorescence experiments using many-watts UV lasers.