I bought a pair of sunglasses while on vacation in Mexico. I am quite certain that the sunglasses are not made by the manufacturer indicated by the trademark on the glasses. (For one thing, the trademark was easily scraped off using my thumbnail.)
So, I know that the glasses are counterfeit. Is there a way for me to determine if the lenses truly protect my eyes from unwanted UV light?
You can get UV cards that change color when exposed to UV rays. I’d probably start with one of those, confirm it changes color in the sun, then see if it changes color if it’s covered with the sunglasses.
ETA, I’m not vouching for this, it’s just the first one I saw. If you watch BigCliveDotCom on youtube, he uses these from time to time, but I couldn’t tell you what brand he uses/prefers.
https://www.amazon.com/QuantaDose-Light-Power-Visibility-Technology/dp/B08KZZ54BZ
You also want to distinguish between different kinds of UV. UV-B, the higher frequency kind, is blocked by ordinary glass (and probably a lot of other materials). UV-A, which is more prevalent in sunlight, requires more special materials to block.
Blue Lizard brand sunscreen has either a label or a cap (I forget which) that changes color when exposed to UV light. I don’t know if it distinguishes between UVA and UVB or not, though.
EDITED TO ASK: How much did these fake shades cost? It might be cheaper than some of the solutions recommended in this thread.
I would get a UV LED flashlight (they are really cheap these days), and use a “blued” t-shirt, or a piece of fluorescent paper, and see how much the lens attenuates the UV.
I bought some amber UV-tinted goggles to use with a very high-power UV resin curing light, and I wanted to see how much UV they actually blocked, and this is what I did.
The thing is, almost all sunglasses will block harmful UV rays. The hard part is making materials that transmit harmful UV rays. I know – I’ve had tp do it.
Virtually all plastics and glasses block light below 300 nm, and most block it below 400 nm.
Here’s the transmission of acrylic, for instance. It stops at 400 nm.
“UV acrylic” transmits below 400 nm, but you have to pay extra for it.
Here’s a bunch of different plastics. Note that, except for the UV acrylic, they stop at 400 nm:
Here’s PMMA (plexiglas)
Polycarbonate (the stuff my eyeglasses are made of) stops at 390 nm
Virtually all sunglasses block beloe 380 nm
I had thought that plexiglass was just the most common brand name for acrylic.
So said another way, purported special UV blocking features of sunglasses are pure marketing ouffery devoid of substance.
In other news, Dasani sells the wettest water.
I’ve got one, that’s the way to go. It has sections that react to different freq/wavelengths to distinguish, say, UV-A vs C. It was a couple bucks on Amazon at the time, more now!
I confess I first misunderstood how they worked and thought it laggily charged up like glow in the dark phosphors. I was leaving it in direct sunbeams for a minute and rushing it inside to see the reaction: none found. Then, I tried it in a UV-C chamber and found the same unreacted card when I took it out for inspection.