UV LASER danger?

[Robert Dyer]

I'm interested in this discussion, and I want to have a clearer understanding of the dangers of LASERs that are being described here. Most importantly I don't want to be one of the blissfully ignorant people carelessly wielding my UV LASER, or any wavelength LASER for that matter. But I also don't want to be Chicken Little, declaring that, "The Sky is Falling!" There are many much more experienced and knowledgeable optical people here than I, so resources abound, and I bow to their input.

 

In the 80's I worked around research LASERs a lot. In fact our company required all of us to have periodic "LASER eye-exams" to ensure we hadn't sustained any retinal damage. The exam consisted of pupil dilation and then a photograph was taken of our retinas. However, as it turned out, the bright flash of light to illuminate our unprotected retinas for the photograph was found to be more damaging statistically than the incidence of LASER damage, so the periodic exams were discontinued. Ain't science grand!?! :))

 

I want to be clearer about the specific conditions we are talking about for damage to the eye. I've also heard that long-term exposure to blue light is supposed to harm the eye, but mostly I've heard of that through a decade-old flurry of late night infomercials for blue-blocker sunglasses. I haven't seen the research. I'm not claiming it's false, I just haven't chased it down. I wear sunglasses outside anyway, (NOT blue-blockers!) and I have since I first started wearing contact lenses in the early 70's.

 

But regarding LASERs, what I remember is that the danger of LASER light specifically is not just due to the power, but also due to the collimated nature of the beam. What I remember is that when our eyes are at infinity focus, collimated light is concentrated to the smallest possible spot on the retina. So any collimated beam of light has the potential to cause retinal damage due to the focus of our lens. Therefore green and red LASERs, and even bright collimated LED lights, are potentially damaging to the retina. And also, reflections of collimated light off of specular surfaces such as mirrors or other polished surfaces, retains the collimation.

 

However, I also seem to remember that a non-specular (diffuse) reflection of a LASER beam off of a surface, limits the collimated nature of the light. Also that the scattering by the diffuse reflection distributes the power through some (non-uniform) reflective function, over 2Pi steradians of solid angle, reducing the amount of light (power) that can enter the pupil.

 

Therefore I'm a little skeptical about drawing too many conclusions about eye damage from the "apparent" intensity of a UV LASER spot on a diffuse surface. One is the lack of collimation, and the other is fluorescence. When shining any of my LASER pointers on the surfaces of my office (being careful to stay away from specular surfaces) the apparent intensity varies from surface to surface. Most of this is due to the specific wavelength reflectance/absorption (attenuation) of particular surfaces, but I think this variation is even more true of the UV LASER because of fluorescence.

 

There is no better example of that than printer paper. Manufacturers are big on putting fluorescing brighteners in their paper to obtain better whites. Even good ol' Mom used to put Bluing in the wash water to make our white shirts appear whiter. And if any of you remember poster black-lights, they always made our clothes "glow" brighter from other laundry soap ingredients.

 

What I'm curious about is the effects of fluorescence on both true and apparent beam power. First of all, is the spot "apparently" brighter due to the fact that the new wavelengths are always down-shifted (in energy, not wavelength) from UV to wavelengths our eye is more responsive to? And second, how much power of the UV light is absorbed in the fluorescence process (attenuation)?

 

Again, I'm not trying to insult anyone or cast disparaging words, I just want to ask the question of degree. I'm not asking if the danger is real. I'm asking HOW real? Have these phenomena been measured with instruments, or are they mostly anecdotal and the result of the amazing, highly adapted, VERY complex, and easily-fooled process of human vision?

 

Robert

[Dan Beavers]

What is the label on the laser? Check out
http://www.national-laser.com/laser-classification.htm for appropriate
considerations. I think that florescence is only going to change the
frequency and not the intensity. I wonder if the frequency changes are
taken into account in the classification process.

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[Dave Stoft]

It's good to be both concerned about safety and skeptical. I'd suggest there's a practical way to think about the degree of concern. It takes only a 10-deg-C rise in retinal temp to cause damage and 400nm tends to cause clouding and retinal damage and the rated exposure levels for the cornea are near 1mW/cm^2. A pocket laser beam is small (~1mm) so a "5mW" laser produces roughly 100x5mW in a cm^2 area -- or simply 500x the allowable exposure limit for the eye. Next, consider that pocket lasers are notoriously inaccurate at meeting their specs,  so probably multiply that by 5x. Clearly, direct exposure for any length of time is a very bad thing.

However, if the light is diffuse by scattering like the specular reflection off a far wall, the inverse-square rule comes closer to the reduced levels with distance. The problem is that specular reflection intensities are very difficult to calculate. However, it is clear that a reduction of at least 2500x minimum is a very good idea.

So, the simple answer is to ensure no "significant direct reflections" allow exposure toward a human and it's best to 1) provide some eye protection (it's relatively cheap) and 2) cover it up when in use. Not paranoid, just practical as sloppiness can have very bad and permanent side effects.

[Dave Stoft]

I did a little more checking and _real_ UV protection glasses are quite expensive (the kind you'd use in a laser lab) so if the $10 variety were provided, they might be just as an added precaution relative to scattering. This suggests the best route is to completely cover the UV exposure region during measurements and add clear warning labels and notation about potential dangers of misuse.

[Jeffrey Warren]

I think the steps Dave's laid out are prudent and reasonable. We're still designing the final Oil Testing Kit package, but putting a clear warning on the website is also an important step, as folks are likely building the kit on their own as well. 

In this case, the staff of PL are very interested in posting accurate safety information, but I do want to point out that I don't think there's any special qualification that ought to prevent Hank or others from simply sharing their warnings on the wikis and mailing lists. Hank - you don't have to be able to say exactly what would guarantee eye safety to help people be safer. 

But thanks for the input you've already shared on the issue: 

> I would not trust "yellow glasses" that are not rated specifically safe for this wavelength

> NOTE:   All the rated protection I've found for wavelengths in this range appears to be dark green!
> If you want to collect the discussion somewhere, and include a pointer to that with a warning that there are concerns and no assurance that any exposure to this band is safe -- it might be useful to do that.

Good observations, and as to your latter suggestion, that's what I'd hope you could help out with. 

Also, I've seen "uv protective glasses" for sale for around $10 each, but would guess they're available for less. Any leads? 

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[Dave Stoft]

You might want to consider adding a laser warning lable for Class-III on the device itself. Also, IF some form of $10 glasses were included or suggested you should note that they are not sufficient to protect the eyes from direct beam exposure (direct or reflected from 'highly reflective' object) -- to prevent such assumptions of "complete protection" by non-technical or uninformed users. The "real" glasses for lab use do provide such protection -- which is why the are about $200.

[Jeffrey Warren]

Good suggestions - I definitely think it's just a good idea to tell people never to shine the laser or a reflection of it in their eyes, ever. I don't think providing yellow UV-filtering glasses is an invitation to do so, but the warnings should make it extra clear. 

As to the yellow glasses, they may not stop a direct or reflected beam in the eye, but they're quite good at reducing scattered UV that might make it out of the OTK attachment and are a good extra layer of protection, as my earlier tests showed. 

[Hank Roberts]

It's a long shot, but I've emailed the 'corresponding author' of this recent paper to ask if she has any suggestion to make about how to approach this.

http://archopht.jamanetwork.com/article.aspx?articleID=1810015
March 2014
Ocular Safety of Recreational Lasers
Glenn Yiu, MD, PhD1; Sujit Itty, MD1; Cynthia A. Toth, MD1

[Hank Roberts]

P.S., I understand this thread is going to focus on "UV LASER" danger.

Note the earlier thread about the 405nm "blu-ray" laser is covering a wider subject -- the blu-ray "violet" emitters are recently common and cheap; the illuminated spot is barely visible but does not look bright to our vision, while the 405nm photons are energetic enough to be a concern.

Each person will have a range across which you'll want increasingly brighter and more powerful light to see anything at all.

[Jeff Hecht]

Laser safety is a complex topic. Separate rules cover the safe USE of lasers and the sale of products containing lasers. I write about lasers, so I have a general knowledge of laser safety, but I think you need a real expert to give you guidance.

The Food and Drug Administration has complex rules covering the sales of products containing lasers. That may make it impractical to package a laser with the spectroscopy kit. A starting point for digging into those rules is at http://www.fda.gov/Radiation-EmittingProducts/RadiationEmittingProductsandProcedures/HomeBusinessandEntertainment/LaserProductsandInstruments/default.htm 

Major labs and companies have laser safety officers responsible for the safe use of lasers, and they may be the most accessible source of help. The Department of Energy sponsors annual meetings of laser safety officers, and you can find a list of papers presented at last year's conference at https://lasers.llnl.gov/nif-workshops/laser-safety-officer-2014/agenda. That includes links to papers and a list of attendees with their affiliations. With some digging, you should be able to find someone who could give you advice on the right way to do things, or point you to someone else who could help.

If you're worried about 405-nm lasers, I tested one with a pair of blue-blocking glasses from lowbluelights.com and found that they blocked the 405 nm light well enough that I saw no fluorescence from white paper when I shone the laser beam through them. You can try the same experiment with any kind of filter and material that fluoresces when illuminated with a laser source.

Jeff Hecht

[Jeffrey Warren]

Hi, all - I posted additional warnings and created a cover with flaps which is used to close off the sample chamber while using the laser. That, combined with the uv-reducing yellow glasses (see the test Jeff describes in attached image) should be plenty of protection. 

http://publiclab.org/wiki/oil-testing-kit#Scan

New cover: http://publiclab.org/wiki/oil-testing-kit-construction#Assembly

Thanks, all!

--

[Dan Beavers]

I added some minor edits to
http://publiclab.org/wiki/oil-testing-kit-warning

For the New cover link referenced in Jiff's email - The second and third
images are not in the same orientation so it was a little disruptive for
me to mentally rotate the third picture. Perhaps that is just my weird
mind and no one else has an issue.

On 2015-08-03 14:21, Jeffrey Warren wrote:
> Hi, all - I posted additional warnings and created a cover with flaps
> which is used to close off the sample chamber while using the laser.
> That, combined with the uv-reducing yellow glasses (see the test Jeff
> describes in attached image) should be plenty of protection.
>
> http://publiclab.org/wiki/oil-testing-kit#Scan
> New cover: http://publiclab.org/wiki/oil-testing-kit-construction#Assembly
>
> Thanks, all!
>

> Inline image 1
>
> On Tue, Jul 28, 2015 at 10:20 AM, Jeff Hecht <hech...@gmail.com
> <mailto:hech...@gmail.com>> wrote:
>
> Laser safety is a complex topic. Separate rules cover the safe USE
> of lasers and the sale of products containing lasers. I write about
> lasers, so I have a general knowledge of laser safety, but I think
> you need a real expert to give you guidance.
>
> The Food and Drug Administration has complex rules covering the
> sales of products containing lasers. That may make it impractical to
> package a laser with the spectroscopy kit. A starting point for
> digging into those rules is at
> http://www.fda.gov/Radiation-EmittingProducts/RadiationEmittingProductsandProcedures/HomeBusinessandEntertainment/LaserProductsandInstruments/default.htm
>
>
> Major labs and companies have laser safety officers responsible for
> the safe use of lasers, and they may be the most accessible source
> of help. The Department of Energy sponsors annual meetings of laser
> safety officers, and you can find a list of papers presented at last
> year's conference at
> https://lasers.llnl.gov/nif-workshops/laser-safety-officer-2014/agenda.
> That includes links to papers and a list of attendees with their
> affiliations. With some digging, you should be able to find someone
> who could give you advice on the right way to do things, or point
> you to someone else who could help.
>
> If you're worried about 405-nm lasers, I tested one with a pair of
> blue-blocking glasses from lowbluelights.com

> <http://lowbluelights.com> and found that they blocked the 405 nm

> light well enough that I saw no fluorescence from white paper when I
> shone the laser beam through them. You can try the same experiment
> with any kind of filter and material that fluoresces when
> illuminated with a laser source.
>
> Jeff Hecht
>
>
> On Monday, July 27, 2015 at 7:12:11 PM UTC-4, Hank Roberts wrote:
>
>
> P.S., I understand this thread is going to focus on "UV LASER"
> danger.
>
> Note the earlier thread about the 405nm "blu-ray" laser is
> covering a wider subject -- the blu-ray "violet" emitters are
> recently common and cheap; the illuminated spot is barely
> visible but does not look bright to our vision, while the 405nm
> photons are energetic enough to be a concern.
>
> Each person will have a range across which you'll want
> increasingly brighter and more powerful light to see anything at
> all.
>
> --
> Post to this group at plots-sp...@googlegroups.com

> <mailto:plots-sp...@googlegroups.com>

>
> Public Lab mailing lists (http://publiclab.org/lists) are great for
> discussion, but to get attribution, open source your work, and make
> it easy for others to find and cite your contributions, please
> publish your work at http://publiclab.org
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>
>

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[Dan Beavers]

Sorry cant spell Jeff.