This is a brief followup to Post #1658., where I checked the UV protection provided by some eyeglasses, sunglasses, and car window glass.
Here, I’m validating that using an actual UV meter, marketed for safe tanning practices.
I’ll keep it short, because a) the results are boring but b) not quite as boring as multiple pictures of a meter showing “0.0”.
Bottom line: The meter totally validated the findings of the prior post. The objects that appeared to block UV, based preventing a $20 bill from glowing brightly, or preventing UV-sensitive material from darkening, scored a big round zero on the UV index meter.
I got a reading of 0.0 when the sensor was covered by those lenses, versus a reading of 6.0 on the UV Index for direct sunlight. The meter only reads to the nearest 0.5 UV Index increment. So I can’t be sure these objects block all incoming UV energy. But I can be assured that they block almost all of it.
There are just two things worth noting.
First, the UV sensitive strip on the $20 is so sensitive that it doesn’t take much energy to make it glow, if only a little bit. So you may still see some small residual glow, using that test, when the material you are testing is well within its specifications for blocking (most of) incident UV light. It’s the bright glow — as above — that’s the dead giveaway that little of the incident UVA energy is being blocked.
Second, my non-UV-protected glasses — the ones you see flunking the $20 bill test above — actually block about half of incoming UVA/UVB energy. That was an expected result, as the plastic most commonly used for eyeglass lenses actually blocks UVB pretty well. It just fails to block UVA. So that cheapo-UV-flashlight test really is strictly a test for UVA blocking. If it’s critical that you know the fraction of UV energy blocked across the entire UV spectrum, you’ll need to step up your game and buy a meter.
Otherwise, the cheapo UV flashlight and a $20 works just fine. The cheapo UV flashlight and the UV-sensitive cards are easier to read. And the meter is overkill for almost anyone who is simply trying to get a handle on whether or not they have significant UV protection in their eyewear or in their car windows.
Basically, if the security strip of a $20 bill glows strongly, or the UV-sensitive cards darken noticeably,when illuminated by the UV flashlight, the material you are shining the light through provides inadequate UV protection. Any testing more complicated than that is overkill, for purposes of choosing your sunglasses or window tinting.
