UV curing lights & eye protection

[precisionworks]

Quite a few CPF members set their own trits with Norland Optical Adhesive (NOA61). A wide variety of UV curing methods are used but all have one common feature - longwave UV (UV-A) is generated by these light sources & this can cause eye irritation or eye damage. The Norland site says this:

NOA 61 is cured by ultraviolet light with maximum absorption within the range of 320-380 nanometers with peak sensitivity around 365nm.

Some specialty lights like the one I use have a bandpass filter & there's very little UV emitted above or below 365nm:



Different wavelengths affect different parts of the eyes. Longer wavelengths of ultraviolet light (UV-A), which range from 315nm to 400nm are absorbed principally in the lens of the eyeball. Overexposure of the eyes to UV-A can cause a condition called "welders flash" or "arc flash". In can become apparent quickly or it may take up to 12 hours to notice. The symptoms of this are the feeling of sand in the eyes & this usually goes away within 36-72 hours. I can tell you that it isn't any fun Repeated exposure can also cause permanent damage to the lens of the eye & may eventually require cataract surgery.

Protective eyewear is rated by Optical Density (OD) at a specific wavelength. The most common (& lowest cost) eyewear transmits 0.01% of the 365nm wavelength. This is equal to OD4.

Greater optical densities are available in laser protective eyewear and can be as high as OD9 with transmission of 0.0000001%. After my first flash burn with the larger UV curing lamp I purchased OD7 protective glasses (190-532nm) & have had no recurrence of any eye problems.

NOTE - some long time users of UV curing lamps have experienced no eye problems. Other people may be more sensitive. YMMV.



$58 delivered on eBay, pretty much the going price for new laser protective glasses.



If you do decide to buy protective eyewear look for a high VLT (visible light transmission). Mine are rated at 50% & are similar to wearing very lightly tinted sunglasses. Clear glasses are also available with 93% VLT.

[Norm]

I've noticed most ordinary safety glasses offer some protection from UV and my spectacles will cast a shadow if you shine a UV light at them.

I use a florescent Pet urine detector light for curing Norland and it sets quite quickly. Search ebay for "UV BLACKLIGHT Torch LIGHT Pet Stain DETECTOR Handheld Ultraviolet"

Norm

[precisionworks]

... most ordinary safety glasses offer some protection from UV...

Norm, I thought that my ANSI Certified (similar to CE certified) polycarbonate safety glasses might do the job. It is well documented that clear polycarbonate lenses provide some protection from both UV-B and UV-A up to 380nm. Even thought I wear my safety glasses 100% of the time that I'm in the shop they did not work in this situation.

The light is extremely powerful & has an energy output of 21,700 µW/cm² at 2 inches distance. Quite a bit of that energy is reflected from a machined titanium surface. Most members don't use a light with that output so this may not be an issue for them.

[fyrstormer]

I tested my prescription glasses once, using the same McGizmo UV light engine I use to cure Norland. I believe McGizmo's UV light engine runs at 365nm.



Honestly, my recommendation is to set up a batch of lights that need to be cured at the same time, turn the UV lamp on a low setting if that's possible, and walk away. It doesn't matter how bright the light is if you're not standing where it can hit you.

[precisionworks]

my recommendation is to set up a batch of lights that need to be cured at the same time, turn the UV lamp on a low setting if that's possible, and walk away.

That is good advice. Avoidance is certainly the safest route.

The merc vapor lamp takes about five minutes to ignite & reach full brightness. I flip the switch on & set a couple of cardboard baffles between the lamp & the area where the Norland is applied (about three feet away). To "quick set" a trit I reach around the end baffle & push the flashlight under the lamp that's supported by the holder. About ten seconds gets a good preset and I never have to look at the UV lighted area.

[precisionworks]

These images are all shot at the same exposure (4 seconds, f/16, ISO200).

Camera lens is directly aimed at trits with no barrier (note intense blue background & brightness of trits):



View through my shop safety glasses looks identical:



Through clear laser glasses with OD6 & 93% VLT. Blue background is still visible but less intense:



Through the amber laser glasses that I use, OD7 and 50% VLT. Blue background is totally gone, brightness of both the titanium parts & the trits is much less:



I'm not at all certain that the photos prove or disprove anything. The 365nm wavelength is right at the edge of the visible spectrum:



It seems that the amber glasses do the best job but that may be just my perception.

[fyrstormer]

The amber glasses block the blue wavelengths as well as the ultraviolet wavelengths. Whether this means they are better at blocking ultraviolet than optically-clear glasses, I have no idea, and that would no doubt need to be tested using a spectrometer. However, it occurs to me that blocking the blue wavelengths might give you a false sense of security because you don't see the angry purple color that might make you think "I shouldn't be looking at this", and if there's any deficiency in the glasses' UV-blocking ability, you'll end up exposing yourself to more UV because of that.

[precisionworks]

if there's any deficiency in the glasses' UV-blocking ability, you'll end up exposing yourself to more UV

With the CE certification & a retail price over $400 these seem well suited for the job. Still have to be careful any time the glasses aren't being worn when the light is turned on. "Sand in the eyes" is the least fun I've had in a long time

[fyrstormer]

Yeah, it's a uniquely unpleasant sensation.

In regards to the amber color of your glasses, all I was saying is the amber color and the consequent blue-blocking ability can't be relied on as an indicator of superior UV-blocking ability as well. That same amber coloring is added to nighttime driving glasses to reduce the blueness of oncoming headlights, but those glasses have no UV protection at all. The certification is what really matters. I'm sure you know this since you obviously did your research; I'm just stating it for the benefit of anyone else who might read this thread.

UV-blocking coatings are also available on optically-clear lenses, if for some reason the amber tint becomes undesirable. My prescription glasses darken when exposed to 400nm light, but when I'm sitting in my car I can have the sun shining directly in my face and my glasses won't react at all. Obviously my windshield has a good UV-blocking coating, as do most car windows nowadays.

[RedLED]

What about the 3M glasses? I always seem to trust Minnesota Mining and Manufacturing.

[RedLED]

With the CE certification & a retail price over $400 these seem well suited for the job. Still have to be careful any time the glasses aren't being worn when the light is turned on. "Sand in the eyes" is the least fun I've had in a long time

Sand in the eyes, that was us like metal shop in Junior high, that us what our shop teacher told us.

You know back in the days when men were men and women were glad of it! The 70s, when you could use an Arc welder as a kid.

Can you imagine the people who run schools these days even thinking of letting kids that age use an Arc welder! well, we did in the 1970s.

Now, they would need the horse size tablets of Xanax (like a Salvo) which they would wash down with vodka, to calm down enough to think about a screwdriver, or my god ,,, a hammer!

I remember being the first one to cut Ninja stars on the box and pan brake in the machine shop because of the TV show Kung FU! And they were horrified of them, it caught on, and there were so many stuck up in the suspended ceiling tiles the custodians gave up, and gave up laughing!

[Str8stroke]

Ninja stars! Made me laugh. I was a product of the 80's shop teacher, he was probably in his mid 70's back then. One of our shop projects was to make a knife! It had to be sharp enough to cut paper to make a passing grade! LOL They all looked like prison shanks!

Now, if some sissy classmate over heard a kid talking plans of making a blade in shop they would lock down the school, SWAT would be called in (Tanks & Tear Gas), and kid hand cuffed, possibly tazed, and interrogated with out parental consent, Expelled and charged with Making Terroristic Threats. The parents would be charged with Child Neglect or something stupid. Then the SS comes knocking. Social Services illegally kidnap all the other kids in the house that are obviously in grave danger. This of course is all for their own safety and safety of others.

Back to UV curing. I use mother nature. The sun seems to really do the trick quickly. I just make sure it isn't on a windy day. I don't want debris in my Norland.