Playing with a UV torch/flashlight

[ChrisR]

Eye glasses (spectacles) and a UV torch (flashlight).
The Convoy S2+ torch has a "365nm" Nichia led, and a short-pass ZWB2 filter over it.
The glasses are photochromic (go dark in bright sunlight), so bear that in mind.

Here the torch is OFF, with normal room light from a CFL bulb.
Cheap white tissue paper, which weakly fluoresces white, with a high visibility, fluorescent yellow sticky paper tab. The type which comes in a set of colours.


The torch goes on. You can see the glasses severely attenuate the UV light. Where it spills around the lens, there is some glow from the white tissue paper. To the room light, the lens is clear.


Going closer, there's no space for room light to get the other side of the lens to reflect off the paper through the lens. The lens is darker, because the UV can't get through it.


the immediately-following shot shows the lens really is clear.
The glasses are reversed, but at all times they look the same from both sides.


With the torch from the front, again the yellow paper fluoresces where it's unprotected. Within about 2 seconds, see what's happened to the lens coating. It's gone dark where the UV hit it.



With the torch off, the lens stays dark for a while.


This shows that the UV light hasn't got through the lens, and that the photochromic coating is at the front. When the torch is shone from the rear, the coating doesn't have any UV getting to it.

With a 405nm laser:

No spectacles were (permanently) harmed in the making of this documentary.

[zzffnn]

The lenses are made of polycarbonate, not glass, right? Thank you for sharing!

[ChrisR]

Pass. Plastic, yes. I was told glass isn't used now.

BTW I went through all the various goggles and glasses in the jumbled box in school - all of them passes the fluorescent paper test.

Some £1 reading glasses don't stop as much, though.

[MarkSturtevant]

Interesting. Can the UV torch be used to induce fluorescence in various arthropods like scorpions and phalangids? Those can provide cool pictures.

[Choronzon]

[ChrisR]

The W.H.O. - http://www.who.int/uv/faq/uvhealtfac/en/index3.html , is much less alarming than some commentaters!
If you do damage, it hurts, but mends, it appears to say.
I've had Arc-eye, it hurts, but as they say, gets better when the sunburned cornea recovers..
Nothing so far from these torches though.

Interesting. Can the UV torch be used to induce fluorescence in various arthropods like scorpions and phalangids? Those can provide cool pictures.

yes - Lot of examples here, and Paul Berter's site.
Fresh out of scorpions in London though..


Some things glow dramatically (algae, bright red, rust bright orange (!!) and don't look at a WC!), but some things like wood and some leaves look the right color. I don't know why!

[banania]

Chris, if stuff looks the right color when illuminated with invisible light it can't be reflected light. And probably not transmitted either. There must be some sort of Stokes shift involved and fluorescence or more generally luminescence? Lots of stuff emit something visible when poked with longwave UV or near UV blue monochromatic light. I think your observation is very interesting and needs to be explained!

[ChrisR]

I first noticed a row of books. Some are about the "right" colour in UV.
Perhaps printing inks have some amount of fluorescers to make the colours bright, in red, green, whatever. Some natural things do the same though, which I can't explain.

As a separate question, why does so much fluff and dust glow?
"Limescale" and/or washing powders may be responsible for a lot.