Ultraviolet - Sun vs Flashlight compared

Everytime I play with UV flashlight I feel uncomfortable because of the fear that it might be too dangerous for for eyes and skin, I have done some research about how the intensity of UV flashlight compared to the Sun’s UV but i got no answer. So i decided to test it my self and find the answer.
The UV flashlight being tested is Convoy S2 ,LEUVA33W70RL00 LED ,7135*5, zwb2 filter installed.
The Sun being tested is Melbourne’s autumn Sun, at around 2pm, clear sky.

Test 1: Light goes direct to the light meter sensor through a zwb2 filter to filter out visible light.


Test 1 result:

Sun: 472 Lux
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Convoy UV hotspot at ~1m: 648 lux
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Test 2: Light goes through zwb2, the UV light up the fluorescent powder, the light emitted from fluorescent powder is mearsured.
Reason for test 2: I thought that the zwb2 filter might allow some other wavelengths other than 365nm such as deep red or infrared to go through. This will overestimate the amount of UV in sunlight. So i did a second test, measured the the UV indirectly through fluorescent powder with the intention that wavelength longer than UV will be absorbed by fluorescent powder rather than be converted into another wavelength.





The fluorescent powder is placed at the bottom of the cup, light goes through one hole with zwb2 filter, the emitted light from fluorescent powder will be measured from another hole.
Test 2 result:


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Conclusion

  1. The intensity of UV from the UV flashlight (hotspot at 1m) is roughly equal to UV from the sun.
  2. Indirect UV such as UV reflected from wall is negligible, zero lux measured my method used in test 1, about 30cm away, so it seems to be safe playing UV flashlight around house, BUT wear your protective glasses, because you usually play with UV in the dark, when your eyes’ aperture is wide open, so your retina will received a lot of reflected UV.

Test limitations:

  • The sun light might be much more dangerous because it contains shorter UV wavelengths which are filtered out by zwb2 filter and was not reflected in the measurement.
    -Similar, the UV flashlight might be much worse than the sun UV because it *might *contain shorter wavelengths which might not be filtered out by zwb2 filter and these shorter wavelengths cannot be measured by the lightmeter, therefore the dangerous level was not reflected in the measurements.

I hope anyone with knowledge can help me with the limitations above and point out other defects in my tests. Now i feel comfortable play with my UV light.

Thank you for this test, it is very interesting.

Thanks for the test, very interesting. However I am afraid that it is not a true test to the real damage that a UV flashlight can do. Think that the eyes (pupil) will react differently to the outdoor sunlight, and to a flashlight that emits in a narrow spectrum used indoor.

Nice set of tests. I can think of a couple of shortcomings but they may not alter the outcome in the end.

Although the amount of UV from the sun may be comparable to the UV from the flashlight at a short distance, people are not usually looking straight into the sun so what your eyes experience is mostly reflected UV (which can still be a lot). And as you already pointed out, the pupil of your eyes are fully contracted in the sun, while fully open when watching the flashlight in the dark, allowing 36 times more light into the eyes.

So yes, wear glasses. Because I can feel UV light as pain in my retina, I can confirm that while the amount of UV from the source may be equivalent, the way people behave and how your eyes work, a high power 365nm UV flashlight, like the UV S2+, does allow much more UV into the eyes than the sun.

The observation of djozz is very important. Because of the amount of visible light outside, your pupils will contract and therefore limit not only the quantity of visible light but also the quantity of invisible light, like 365nm UV light. Indoors your pupils will be more dilated, and because your pupils will not contract with UV light, the UV light will hit your open eyes with full force!

Your conclusion about indirect UV light needs some clarification. To be sure, I have tested this a moment ago. Take your UV light and position yourself in front of a mirror. Then shine your light into the mirror. BUT ONLY AFTER holding a piece of white (printer) paper in front of you, between your eyes and the light and the mirror. You will notice the typical blue-ish glow shining through the paper. That’s UV light, reflected in the mirror! The same warning goes for the glass in windows, and in a more moderate way, for clean shiny kitchen and/or bathroom tiles.
So unless you are able to avoid all these surfaces at home: always wear protective glasses!

I wonder if it would give you a Tan or be useful for skin conditions etc

i doubt a flashlight has anywhere near the power of the sun…
it just doesn;t make sense

an AA battery? even an 18650, producing maybe 1 watt, through an LED that is what, 10% efficient?

especially reflected off indoor surfaces, most of which probably absorb it anyway

the sun delivers like 100 watts per square foot, of light, to earth, it would take 1000 watts of input power to LEDs, then concentrated in the same 1 square foot…

good experiment though.

i’d have done it too, if i’d thought about it :slight_smile:

wle

Am I correct in thinking Australia may have higher UV from the sun than Europe/USA due to ozone hole?

Clever tests and nice report. Thank you AnhTran.

It’s very nice to know that my test is interesting to you guys. I stated in my conclusion about the necessary of wearing UV protective glasses but I think I haven’t emphasised it enough. I think your skin is safe ( just don’t point the flashlight directly to you at close range and prolonged, and be aware of highly reflective surface as wle noted)

But please wear your UV protection glasses when using UV flashlight, djozz and Henk did an excellent job in explaining the reason.

I also found that my prescription glasses did quite a good job of filtering out the UV, i will post more test results here

would regular sunglasses work for UV protection? say, Oakleys or similar?

Thanks for the very interesting information and knowledge. :beer:

Test with my prescription glasses


They are probably plastic. This makes them much safer compared to actual glass.

Very interesting test. Actually, I’m somewhat surprised the flashlight is as strong in UV as sunlight. But, I suppose the 5x7135 configuration does produce a fairly strong beam. I still find it hard to believe that reflected UV flashlight light is much of a concern, unless you’re using it a lot.

Even more surprising is this comment:

I’m not sure what to make of that. I’ve never heard of such a thing. Closest is the sandpaper-effect that people get on their corneas from being exposed to UV-C. But that’s a real physical effect. UV should be basically invisible. Maybe some skin-burning after prolonged exposure on the retina, but that would be an after-effect.

Yes the result from my test is that the intensity is comparable, BUT only in terms of wavelength that is allowed to pass through zwb2 filter.

I think the Sun has much more damaging UV than flashlights because it is not filtered with any filter

Naw, I “feel” the same thing.

Always thought it was just my imagination, in that playing with my UV lights (shining on walls, floors, etc., to discover any… “leavings”), that I’d get a headachey feeling, or actually an eyeachey feeling, within just a few minutes.

Kinda like “sunlight headache” when you’re outdoors in bright sunlight, surrounded by light-colored sidewalks, walls, etc., and the brightness of the light all around you is just too overwhelming.

After I saw similar comments from people here, I decided it in fact wasn’t my imagination.

Are you sure it’s not from the visible violet light that is also emitted from the UV source?

Or, is it possible it’s an imaginary effect? Like people that claim they are sensitive to EMR from cell phones or wifi, but when they are actually given a blinded test, there’s no effect.

I dunno, maybe it is a real thing. I’m just surprised that something invisible could cause an immediate effect of pain. I get that extended exposure might cause pain, perhaps from a “sunburned” retina.

ZWB2 filter, too.

Wasn’t expecting any effect at all, as I’ve still got a few “black lights” (eggplant-purple fluorescent tubes) that never gave me any issues.

Playing with a bare UVLED in a ’501 host, I noticed the “headache” after a few min. Chalked it up to anything but the light. Every time I’d do it, though, same dealy.

S2+ with ZWB2 filter, same dealy. Okay, not a coincidence anymore… Ain’t violet light nor “leakage”, but whatever’s coming from the both the bare UVLED and now with the filter. That pretty much leaves UV.

That’s just it, I don’t want to get blinded, so I keep UVing to a minimum.

Wellp, I’m a bit of a hyperæsthete. Bright lights can give me migraines, loud sounds bother me (even soft sounds when it’s otherwise quiet). I gotta wear a baseball cap at work because the damned overhead fluorescents flicking at me in my peripheral vision will give me headaches/eyeaches by lunchtime.

I joked that I was part Reman, but nobody got it.

Anyway, it doesn’t surprise me that I’d be sensitive to UV.

Yeah, polycarbonate should filter something like 99%+ of UV. I was considering building a S2+ UV triple until I remembered. I know someone did it with a C8F once, would work much better lol. My other concern was that the Vf of the UV emitters tends to be pretty damn high, and I'd want some sort of compatible buck driver to do it.