Alonefire safety glasses?

[Jody Barends]

I bought an Alonefire H42 UV torch and keen to test it out. It comes with a pair of yellow glasses that's labelled UV 400. However, one reviewer on Amazon mentions that these glasses are not effective at all as protection against 365nm and other UV-A wavelengths because it is labelled as UV 400. I am a bit lost because I thought the UV 400 meant that it protects against all wavelengths under 400nm. Can anyone with an Alonefire torch clear this up?

[otoien]

Shine your UV torch though the safety glasses towards a piece of white paper in a dark room. If effective you should not see any fluorescence from the paper. 

[Andy Perrin]

Two things:

Quote

It comes with a pair of yellow glasses that's labelled UV 400. However, one reviewer on Amazon mentions that these glasses are not effective at all as protection against 365nm and other UV-A wavelengths because it is labelled as UV 400. I am a bit lost because I thought the UV 400 meant that it protects against all wavelengths under 400nm. 

That Amazon reviewer doesn't understand that shorter than 400nm is UV. Ignore the review.

 

 

On 5/13/2023 at 2:21 PM, otoien said:

Shine your UV torch though the safety glasses towards a piece of white paper in a dark room. If effective you should not see any fluorescence from the paper. 

Wait, UV torches are EXTREMELY intense. The UV400 rating means that it filters at least 99% of the light less than 400nm. But that means it allows 1% through, which is just an OD2 filter. That's not very much filtration at all relative to what that torch puts out! [*] I would certainly expect to see paper fluoresce through that with such a hefty torch. Of course since OD2 is the minimum, it's possible those glasses will filter more than that, but they are not required to just to get that label. I don't think this is a good test, although if it passes it, it definitely means the glasses are working, and much better than they are required to!

 

As a quick experiment, I have a pair of UVEX UV blocking safety glasses that are rated to block 99.9% of UVA-UVC, which corresponds to OD3. When I shine my Nemo torch through it at a piece of white paper, I still see a faint glow. There would be quite a bit of glow at OD2, which allows 10x as much light through as OD3.

 

[*] OD2 may not be enough to stop a super-strong torch from making paper fluoresce at point-blank range, but it's probably enough to protect your eyes from the sun, which is what the UV400 label is aimed at presumably. That is to say, the glasses might be fine even if they fail the paper glow test, if you don't push them to the limit by shining the torch directly in your eyes.

[otoien]

It is a quick initial test  based on my own experience with shining a Covoy though my polycarbonate UV-safety glasses. I would have to look very hard to see any coming though to cause fluorescence. My reading glasses attenuates it, but to a much lesser degree, would not be good protection. While 100% absorption is of course desirable, just going outside in the sun one gets exposed to a considerable amount of UV. So unless one are working with it turned on for hours or looking straight into it, a 0.1 to 1 percent getting though does not seem like a disaster? But I guess it depends on what UV source is being used - some of the more powerful ones discussed here lately could seem pretty scary.  Perhaps more of a concern is stray UV getting in from the side if not sealing well against the face?

[ulf]

The 365nm wavelength is also not that dangerous, compared to some shorter wavelengths.

Here I posted a screenshot from from the IEC/EN 62471 standard safety document:

It looks like 365nm hazard is just about 3 times as high as deep violet at 400nm.

An OD2 attenuation will be quite enough to keep you safe as long as you are not directing the beam towards your goggles protected eyes for a longish time.  However that torch is powerful with maybe 7W 365nm optical output so be careful!

 

Real protection goggles have a better coverage on the sides to protect from specular reflections from the side, but as long as you are not directing the beam at mirrors and polished surfaces it will be OK.

 

The final result from the standard above ends in a calculation of power density and as the intensity decays fast from torches as they are not focussed like a laser beam the power is rather quickly reduced. 

[Andy Perrin]

I think people are misreading my comment. It's not that OD2 or 3 is not enough (I think it's fine), it's that judging by fluorescence is a bad way to check glasses. And glasses are not safety goggles. You should buy goggles that protect the sides and list the level of blocking so you know what it is. UVEX has in the past been a good source for them, they are my favorite company for this kind of thing because of the documentation and testing they do.

[Andrea B.]

Here are a couple of points we try to emphasize. This summarizes some of the info above.

And feel free to debate these points further. Or add other useful info.

 

• At a minimum you want 99% protection throughout the 330-400 nm range
  in which we usually make UV reflective photographs or illuminate subjects for fluorescence photos.
   
• Wrap-around goggles that fit to the head or glasses with side shields
  are necessary to protect against reflections from UV-flashes or UV-torches
  which could enter the eyes from the side.
   
• If using a UV-flash, close your eyes when you fire the flash. 

 

Here is the UVEX Safety Page Link:  LINKIE

There is a lot of info there about occupational safety and standards.

To actually buy a pair of UVEX, google around to see what the best deals are.

 

In the beginner's BEST list I also mention the very inexpensive McMaster-Carr Panoramic Safety Glasses.

(I don't know if they ship outside the US.)

 

Added:  The glasses which came with the Alonefire torch are likely meant for use during nighttime expeditions looking for fluorescent mushrooms and scorpions when you are aiming the torch well ahead of you and less likely to encounter stray reflections.