What does the world look like at UVC?

[Andy Perrin]

Thanks, Jonathan, that’s pretty much what I was expecting. There is no 250nm sunshine. Ergo any signal must be out of band.

[JMC]

No problem folks.

 

I have no doubt that with a 256nm lamp, the story will be very different. I did have one on order - a tube to fit one of my BlakRay lamps - but it never arrived, and I eventually got my money back. If I ever end up getting one I'll give it a go.

[dabateman]

Excellent!

Thank you Jonathon. Now I don't have to repeat my test. Also its been raining today. So would have to wait any way.

 

However, one thing I do need to test is with my portable 254nm light outside. I wonder what the difference will look like.

[Bill De Jager]

Sure, but I'm sure if you were out in the open it would fade by the time you were tens of meters away, like in fog. I mean you can SEE in fog usually in a steamy bathroom for example. But outdoors things go white. I imagine things would go black in UVC.

 

Here is the absorption coefficient of all the major atmospheric gases:

 

Sigh... I forgot that the original question referred to sunlight. Yes, the ozone layer filters out just about all solar radiation under 300nm.

 

However, my understanding is that O2 doesn't come into play until ~200nm. The graph you provided lumps the two gases together which is not helpful. I don't see any other gas that would cause a fog-like appearance at 250 nm. Sunlight should be insignificant to none, while strong sources on the earth's surface should provide good illumination at close distances with attenuation primarily due to distance rather than absorption or scattering.

[Andy Perrin]

Yeah, I took the graph I put on here before as meaning that O3 and O2 had similar spectra, but it seems they meant the MIXTURE of the two gases had that spectrum. As you say, unhelpful. I did manage to dig this one up, and yes, in fact O2 doesn't absorb until under 200nm:

cite: http://www.cnofs.org...985/Chptr22.pdf

 

So no fog-like effect, but things will be dark outdoors because there is no sunshine at all, and very few man-made sources of UVC.

[Stefano]

What a strange place the world is at these wavelengths! Basically a UVC lamp is a little torch shining light in a obscure world. Corona discharges may be the only (weak) light source in this band.

[Bill De Jager]

I would also expect UV-C from lightning, given that the associated plasma runs around 50000 K.

[Avalon]

Can anybody advice test to separate UV-A from UV-C radiation? I have only seen that postage stamps seems to exhibit different fluoresce with postage stamps and not always there big difference between 254nm and 365nm. Does 254nm or 265-280nm produce ozone? I have quartz lamps which produce ozone but UVC waves can be very short.

 

https://chsopensource.org/category/multispectral-imaging/uv-fluorescence/page/2/

[Cadmium]

Avalon, I am no expert on that, so I Googled it, according tho one link:

 

"Ozone is produced naturally by UV light created from sunlight.

UV light wavelengths shorter than 240 nm will create ozone via photolysis of the oxygen molecule.

UV light wavelengths between 240-280 nm will destroy ozone via photolysis of the ozone molecule."

 

https://www.oxidatio...on/uv-lamp.html

 

Here is another link, these are all just from Google. so I recommend people investigate these questions because I am no expert, just curious also.

I do have some germicidal UV for my aquariums, which I use occasionally, and I have no idea really for sure if they create much ozone or not.

http://www.uvresources.com/blog/the-ultraviolet-germicidal-irradiation-uv-c-wavelength/

[dabateman]

Can anybody advice test to separate UV-A from UV-C radiation? I have only seen that postage stamps seems to exhibit different fluoresce with postage stamps and not always there big difference between 254nm and 365nm. Does 254nm or 265-280nm produce ozone? I have quartz lamps which produce ozone but UVC waves can be very short.

 

https://chsopensource.org/category/multispectral-imaging/uv-fluorescence/page/2/

 

Yes buy some rocks. There are some that only fluorescence under short wavelengths, 254nm. Others only at long wavelengths, 365nm. That could help you.

 

[Avalon]

Not much expert in mineralogy, can you name few rock examples? I recall earlier seeing different band ultraviolet photography including UV-C in someone forum post in room with furniture but can't find now.

[ulf]

You can find several by searching at eBay:

 

Short wave fluorescent:

https://www.ebay.com...cent+mineral+SW

 

Long wave fluorescent:

https://www.ebay.com...cent+mineral+LW

[Andy Perrin]

Can anybody advice test to separate UV-A from UV-C radiation? I have only seen that postage stamps seems to exhibit different fluoresce with postage stamps and not always there big difference between 254nm and 365nm. Does 254nm or 265-280nm produce ozone? I have quartz lamps which produce ozone but UVC waves can be very short.

 

https://chsopensourc...escence/page/2/

 

There are some truly fantastic (in the sense of "unbelievable, and not in a good way") prices on that website. They are selling a tiny Arduino board to allow a Gigapan head to interface with a PC for 490€! Like, that must be about $40US of equipment there...and only very basic electronics and programming skills to put it together.

https://chsopensource.org/product/shooting-adapter-for-pano-infrared-reflectography-bellini/

[Avalon]

I guess calcite crystal is best mineral worth getting. It produces different fluorescence in UV-C, UV-B and UV-A. Will optical calcite work or it has to have impurities? https://www.ebay.com/itm/1pc-Iceland-Spar-Optical-Calcite-Quartz-Crystal-Mineral-Specimen/363059470341?hash=item548807e005%3Ag%3AUgUAAOSw3C5e2hh-&LH_BIN=1

[colinbm]

I guess calcite crystal is best mineral worth getting. It produces different fluorescence in UV-C, UV-B and UV-A. Will optical calcite work or it has to have impurities? https://www.ebay.com...5e2hh-&LH_BIN=1

 

And in IR too....https://link.springer.com/article/10.1134/S0020168506110136