What is the purpose of UV flashlights?

PaladinNO

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One question regarding UV...I find a lot online regarding eye protection against UV exposure, but little to nothing on how different coloured lenses / filters works on how the eye perceives things under UV light.

I know a yellow lens improves contrast, and makes everything more...soothing, for lack of a better word, for the eyes in low light conditions (which is why I have yellow lens covers on all the lights on my car - MUCH better when driving at night in the winter).

For example, I have a Sofirn SF15 UV penlight, 365 nm. It's good, it's basic, and it lights up any...excessive staining with its fairly weak but wide beam.
And I have a Sofirn SF16 UV, also 365 nm. It has a much more narrow and intensive beam, and lights up much more and in better detail but in a smaller area.

However, I just tested the SF15 with yellow safety glasses...and wow, it lights up everything the SF16 did, but at the much larger area.

And my question is simple: how come? How does this work? It's like the yellow glasses worked as an UV amplifier for my eyes. And my brain blew 2 fuses trying to understand what happened.

EDIT:
Now I know the difference between SF15 and SF16: the SF16 have a UV filter.
 
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PhotonWrangler

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First of all, you're lucky that your brain has backup fuses. :)

By viewing the fluorescence through yellow glasses, you're increasing the visual contrast by filtering out any shorter wavelengths towards the blue end of the spectrum.

I just ran a quick test with a couple of fluorescent items, a blue LED and a pierce of amber colored plastic to simulate the yellow glasses. One of the items fluoresces a bright yellow-green while the other fluoresces blue. They both look bright to my naked eye, but when I look at them thru the amber plastic, the yellow-green item appears much brighter, but it's because the blue item looks like dull grey by comparison. I've increased the contrast in a narrow part of the visible spectrum.
 

PaladinNO

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By viewing the fluorescence through yellow glasses, you're increasing the visual contrast by filtering out any shorter wavelengths towards the blue end of the spectrum.
Very interesting! So the yellow glasses makes the brain think it sees things better UV by reducing the blue light which would otherwise partially "overwhelm" the UV, or the part of the spectrum that makes stains illuminate.

This also explains the difference between the Sofirn SF15 and SF16 I mentioned above. The SF16 has a UV-filter, which I assume works the same way as the yellow glasses.

I was certain a yellow lens somehow added something to change the perception, but it's the other way: a yellow lens removes something.
A new day, and new knowledge. Thank you very much. :)

I know so-called "gaming glasses" uses a yellow lens, which they say decreases fatigue by reducing the blue light exposure. I had no idea UV also contained this much blue light.

Makes sense though, considering 365 nm (UVA) is so close to blue light in the spectrum.
1711450396062.png


I got a pair of clear and yellow lens 3M SecureFit 3700 (SF3701SGAF and SF3703SGAF) on order to do some more testing.

"UV protection with good colour recognition. This product conforms to the requirements of the standard,
providing UV protection for the complete specified range (210nm – 365nm)"

Says they will block 99.9% of the UV spectrum, but I assume that only means protecting the eyes from the UV exposure, and not affect how the eyes sees things under UV, which is what I am after here.

Now I want a Fenix LD32 UVC even more, to see how stains would look under an even lower wavelength (254 nm).

----------------------

Another question then: how does the power (mW) of the UV LED work? Does a more powerful UV LED make stains glow more, or does it just produce more "useless" blue light?
If it's the latter (which I suspect, since it won't have a UV filter), it won't matter, because now I know I will need to use yellow glasses anyway.


I ask because now I am considering another Emisar Noctigon K9.3 (21700), with UV LEDs on the second channel. Better spread than the Sofirn SF16 (18650), and much more power and runtime than the SF15 (2x AAA) penlight.
 
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yellow

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Ahhh,
its all in the wavelength...

I have a cheapo "1 W" UV insert in one of my 18650 hosts, that barely lights up anything more than white paper,
while the 3 5mm led of the aftermarket led ring of the A2 brightly Show the whole picture of hidden color.

... dunno if I wanted to know/see it
;)
 

Brian Ski

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Where does black light fit in the UV spectrum above?? I bought a black light when my outdoor UV light died and the Black light did almost nothing to make the Glow in the dark paint light. I ended up putting the LED in the Black light to get it to light up.
 

PaladinNO

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Where does black light fit in the UV spectrum above?? I bought a black light when my outdoor UV light died and the Black light did almost nothing to make the Glow in the dark paint light.
"Black light" is typical 365 nm to my knowledge, but I've seen also seen a lot of the previously discussed 395 nm cheap stuff going around online.

395 nm doesn't do much, other than shine purple light on something. I've made that mistake myself, once upon a time.
 

alpg88

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395 works great to cure resin and glue, it makes white paper, and white cloth glow, not as good as lower wavelength, but it still does
 

PhotonWrangler

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395 works great to cure resin and glue, it makes white paper, and white cloth glow, not as good as lower wavelength, but it still does
395nm is near-UV. It can make things fluoresce, but with a fair amount of visible purple light which reduces the contrast. Blue LEDs can make things fluoresce, but with lots more visible light "pollution" as well. You really need to get 365nm or shorter wavelength to get rid of visible light from the source.
 

sledhead

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Seems like the right place to ask this question……. I'm assuming that the Total Eclipse glasses that are being sold are suitable for UV light protection…… even the cheap paper ones. Looking at the paper ones at B&H.
 

PhotonWrangler

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Seems like the right place to ask this question……. I'm assuming that the Total Eclipse glasses that are being sold are suitable for UV light protection…… even the cheap paper ones. Looking at the paper ones at B&H.
Cardboard eclipse glasses are OK provided they're rated for ISO 12312-2 protection, which allows for direct viewing of the sun.
 

alpg88

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Seems like the right place to ask this question……. I'm assuming that the Total Eclipse glasses that are being sold are suitable for UV light protection…… even the cheap paper ones. Looking at the paper ones at B&H.
Those "glasses" are nothing but strong tint, that will prevent sun to burn your retina, no different than a welding glass, it is not made to block uv, (it may accidently, but it also may not) actually blocking visible light is not an indicator it will block uv, black glass that is sold with uv flashlights is a uv pass filter.
Last eclipse I could not find any welding glass in stores, everything was sold out, i was not gonna buy a whole mask for that, so i took pieces of polycarbonate, and window tint film in our shop, put like 5-6 layers on the PC and it turned out just right for the purpose. no doubt those cheap "glasses" do not comply with any standards or regulation. just tint as dark as possible
 

Zenster

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But now we can add some craziness to what UV lights can do...
I saw a post on social media (credible, right?) that if you shine a UV light (in the dark of course) on the face of someone who's had Covid vaccines, then little white spots will show up on their face while unvaccinated people will show no such artifacts.
Personally, I use my UV light to try to see space aliens in the dark.
 

Monocrom

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Yeah, don't shine a UV light in someone's face. No reason to cause them eye damage. Also, the little white spots thing is BS.
 

acebeam

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What is the purpose(s) of UV flashlights? I use my flashlight to look for bedbugs between the hotel matress and boxspring. Does a UV light help in this respect?
The purpose of UV flashlights is to detect substances that fluoresce under ultraviolet light. Using a UV flashlight can help to identify bedbugs as they often fluoresce under UV light.
 
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Really late to the game here-
I use UV to look for a variety of things- lately though it's 'charging' the dogs UV-reactive frisbee so I can see it/throw it at night (because, why not play when I want to sleep).

Some plants glow different colors under UV (Clover is red- did you know that? That was a surprise) and then of course rocks and minerals.

I also use it to check out estate/garage sales on the off chance I see some yellow looking glass- uranium glass- just in case.

Get the right filter of the top to get rid of all of the leakage, and remember- they CAN hurt your eyes, so don't look into the beam.
 

michaelmcgo

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Scorpion's skin are said to glow in UV
(never been able to test myself) ;)
and as this seems to be such a curiosity:
Do "normal" bugs even glow under UV?
Does this "test" in a hotel makes sense?
Have You ever found anything
🤔
There was a family in a gorge of the Grand Canyon where we hiked into one night with a UV light. They were shining it on the canyon walls and the scorpions we lighting up like they were little AAA flashlights! Super bright purple, yellow, and green. We were even able to find tiny ones smaller than a dime. It was really cool.
 

PhotonWrangler

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Today I learned about Blaschko's Lines, the invisible stripes and patches that cover our skin. Apparently these can be revealed under UV light, although I don't know if this requires UVA, UVB or UVC. Anyway i went to the bathroom mirror with a 365nm UVA flashlight and checked, but I didn't see any stripes. Your mileage may vary.
 
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