Originally Posted by
vfpamp
Well, there are several papers testing the quality of the UV protection in the market. I remember this one because I was one of the reviewers
https://biomedical-engineering-onlin...938-016-0209-7
I also did test glasses sold in the US myself a few years ago using a similar procedure with similar results. We ended up not publishing because there wasn't anything new we could say...
So it is entirely possible I missed something in this paper, but I don't see anything to back up "Eyeglasses UV coatings wear off on average in about 1 year for a 4hr/day use, faster in the tropics." This paper seems to be aimed at the tests themselves being inadequate in their current state. Both in duration and intensity. It does say this
"The exposure of sunglasses to the sun may deteriorate their UV protection and alter the category under which they are classified (lenses may become lighter when overexposed to the sun) over time."
It doesn't cite a source for how much UV deterioration or how long it takes to deteriorate. The other papers I found also said similar things but no cited source for the previous studies. ANSI Z80.3-2015 RESISTANCE TO RADIATION TEST only references change in luminous transmittance after irradiation, not UV degradation. ISO 12312-1:2013 limits to the amount of relative change to luminous transmission, but then stats "the UV requirements for the initial τv shall continue to be satisfied. I don't know what the Brazilian standards say.
From the paper:
"In our previous investigations on sunglasses standards, limits and insertion of missing requirements have been suggested for ocular safety. In this paper, we evaluate the degradation of the lenses (category and ultraviolet protection) as sunglasses are exposed to solar radiation for periods considered still within its lifetime. Our study includes 44 unbranded sunglasses: 12 were submitted to a solar simulator (0.46 suns) for 2500 h and spectroscopy was performed every 25 h. The remaining 32 were submitted to a 10-sun solar simulator for 962 h of exposure, and transmittance spectroscopy and UV protection evaluation have been done. These exposure conditions are equivalent to wearing sunglasses for a period over 2 years, for 2 h daily. Standards require 50 h exposure as the aging test. Under this condition, only one lens failed the requirement. However, our longer-term irradiation (sunglasses desired lifetime period exposure) experiment in solar simulator shows that the majority of lenses will eventually fail the standard requirement, suggesting the revision of such aging test.(emphasis mine) Additionally, there has not been any significant alteration on UV protection. Summarizing, current parameters, for the resistance to radiation test for sunglasses on standards, is ineffective for ocular safety within its lifetime. In summary, current parameters for the resistance to radiation test for sunglasses, required by ISO 12312-1 standard, are ineffective for sunglasses average lifetime required by population."
Also:
It is also important to understand the lifetime of the optical properties of sunglasses. The exposure of sunglasses to the sun may deteriorate their UV protection...(emphasis mine)
Where is the data for the above statements in bold? Maybe there was a table or paragraph I missed somewhere, or didn't understand, a reference I didn't read. The other thing about this particular paper that doesn't really jive is that I saw no mention of what type of sunglasses they are referring to, other than plano. Polarized, tinted, material, etc. There are some 20 -30 year old sunglasses I brought out from my basement and tested with two different simple UV meters, that all still showed 0-1% UV transmittance, and show no degradation after years of wearing, plano and Rx. How can this be if they should be unsafe after 2 years for 2 hours per day? I would also like to reiterate my question of, who is using UV coatings? Is there a mass market of cheap UV coated sunglasses I am unaware of that degrades over time, or do all sunglasses lose their ability to safely block UV with prolonged sun exposure? That would necessarily imply that all clear glasses are unsafe to wear in a much shorter time span since they are worn outside much longer than sunglasses for the average glasses wearer, I would assume. Does the average Joe need to replace their Rx lenses every 6 months do to loss of UV protection?
There has to be something I am missing here. It's probably simple and staring me in the face and I am going to look like an idiot, but it won't be the first time.
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