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I have also come across sunglasses fitted with "mineral glass lenses" which claim to filter 100% of UVA and UVB without the need for a UV coating, e.g.:

OTIS standard lenses are all made from mineral glass that is scratch-resistant, environmentally friendly and distortion free. They have a fixed tinting that won’t peel or fade over time and block 100% of harmful UVA, UVB and HEV light, providing superior protection from solar damage, while maintaining true colour and depth perception.

Treatments

  • Mineral glass offering the clearest vision [...]

Protection

  • Category 3
  • UV Protection: 100%
  • Infra-Red: Up to 90%
  • Visible light absorption: Up to 90%
  • Blue Light Filter: Up to 93%

These lenses don't have any surface treatment other than an anti-reflective coating on the interior.

Do mineral glass lenses protect against UV radiation?

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    This feels like a physics question as much as anything: a visible tint is, by definition, an absorption (or reflection) of frequencies that are visible to our eyes; absorption of frequencies that aren't visible to our eyes is by definition not visible. So a lens might appear completely transparent to "visible light", but filter most UV frequencies; and another might filter some visible frequencies (thus, appear tinted) but not block any UV frequencies (which we can't see).
    – IMSoP
    Oct 8, 2023 at 13:33
  • Welcome to Skeptics! I focussed the question onto the main claims, and avoided getting distracted by tints, your understanding of polycarbonates, etc.
    – Oddthinking
    Oct 8, 2023 at 14:17
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    Seems like an easy thing to test.
    – Schwern
    Oct 8, 2023 at 18:05
  • Thanks @Oddthinking, but the claim I was confused about was the one being made in the articles I had linked about tint colour not having any bearing on UV protection. as I've seen amber-coloured glass being used to store light-sensitive materials, .
    – user51462
    Oct 8, 2023 at 22:06
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    @user51462 I don't see that claim being made in the articles. They don't say that tint doesn't matter, they just say that their glasses use mineral glass, and that they block UV. Any glass inherently blocks a lot of UV radiation regardless of tinting or treatment. Glass is pretty much opaque to UVB in particular. UVA is blocked to a lesser degree based on various factors such as lamination, tinting, coatings, etc. Can you clarify the actual claim you're questioning?
    – barbecue
    Oct 8, 2023 at 22:45

1 Answer 1

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Most glasses block some amount of UV light, particularly the "harder" UV like UVC and UVB. UVC is not really relevant in the context of sunlight at normal altitudes, as the atmosphere, in particular ozone in the upper layers, filters it out.

Now, for the UVB and UVA parts that e.g. suncream needs to block to protect your skin; what about the glass that protects your eyes?

Let's first define the UV-regions:

  • UV-A goes from about 315-390 nm, has longer wavelengths and less energy and does not penetrate as deeply into tissue
  • UV-B goes from about 280-315 nm, has shorter wavelengths and thus more energy and does penetrate deeper into tissue, can cause damage there (sunburn, skin cancer)
  • UV-C 100-280 nm, really high energy UV. Very damaging to tissue but usually not an issue with sunlight.

If we look at the following chart from Edmund Optics (a reputable seller of optical equipment and related fields)

transmission chart from Edmund Optics

we see transmission curves for different types of glass. As you can see, all of them start to let less and less light through the deeper we go into the UV. In particular, B270 seems to be a common mineral glass used in corrective glasses. It lets about 90% of 360 nm (which is UV-A light) through, and about 50% of 320 nm light, which is almost in the UV-B region.

So it lets some UV light through, but not all of it. That means that a ordinary, untinted pair of glasses is still better sunlight protection than no glasses, but by far not as good as sunglasses that follow the ANSI Z87.1 or UV400 guideline (explained here), which lets virtually no light below 380 or 400 nm pass through.

Addendum: for your application - you said you saw "sunglasses fitted with "mineral glass lenses"" - I think the white, untinted glass alone would not necessarily offer enough UV protection, depending on the glass type. As we can see, there are glasses that offer more UV blocking, but these glasses are not really that common to the best of my knowledge. You didn't tell us if the glasses were also tinted, which, again depending on the technique used, might block UV. Your best bet is to look for any kind of certification according to respectable governing bodies like the FDA in the United States or the CE sign in the European Union.

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  • Also it would be useful to annotate the chart to show visible, UV-A and UV-B bands. But thanks for the great answer. Oct 10, 2023 at 12:15
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    I realize it's no longer part of the question, but one might also point out that dark lenses (traditional sun glasses) don't necessarily block UV. By not blocking UV, they actually cause more damage than non-tinted glasses (or no glasses at all) since they block the colours that cause the pupils to contract, allowing more light into the eye than if one didn't wear them. Oct 10, 2023 at 13:30
  • Aren't most glasses lenses made from polycarbonate or pmma these days? They absorb UV pretty completely up to 300-350nm iirc
    – CJR
    Oct 10, 2023 at 14:10
  • @RayButterworth: [citation-needed]
    – Oddthinking
    Oct 10, 2023 at 15:48
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    @Oddthinking does this count? Also this one Oct 10, 2023 at 18:42

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