[SAFETY WARNING] Fluorescence with UV-C Excitation - An Observation in the Bathroom

[Kai]

SAFETY WARNING: 

UV-C is dangerous to your eyes and your skin.

UVP DOES NOT SUPPORT USING UV-C ILLUMINATION.

[UV SAFETY] UV-C Light Dangers

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For some time now I have had a UV LED for experiments on the photoelectric effect, which was advertised with an emission of around 275nm (https://de.aliexpress.com/item/4001054028870.html). In any case, it triggers a photocurrent in zinc.
Now I have fitted this lamp with a ZWB3 filter and wanted to use it for fluorescence excitation. At first I used it to beam around the house in the dark. In the bathroom there was a surprise for me: The tiles are apparently printed with a material that fluoresces bluish white with 275 nm excitation, but not with excitation with 365 nm.

 

For comparison:
Tiles in white light

 

Tiles in white light, contrast enhanced (to see the surface structure)

 

Tiles at 275 nm irradiation

 

It also clearly shows that it is a screen print

 

Tiles at 365 nm irradiation 

 

[Stefano]

Those tiles look so cool under 275 nm light! I can totally see them in a bathroom colored that way.

[nfoto]

Interesting observation. How was it achieved?

[Fandyus]

Very nice! I'd however recommend color balancing the pictures. I know it would make them fall into false color territory but you could discover subtle nuances in the blue that is emitted. I tried but the jpeg can't be stretched that far.

[dabateman]

Be very careful with that 275nm Led. You are at about the most dangerous wavelength for you.

Always remember to cover up your skin and eyes.

 

But that looks really cool.  With everyone at home I haven't had much time to do similar tests around my house.

[Kai]

1 hour ago, nfoto said:

Interesting observation. How was it achieved?

 

In general: By chance.
Technique: Camera (unmodified) on tripod, manual focus on the joint, 50mm lens at f / 8, Hoya K2 filter (light yellow) as a UV/violet blocking filter, WB against aluminum with artificial light (warm white LED, high CRI).
1. Photo in artificial light
2. Room in the dark, long exposure, irradiation with the UV-LED with excitation filter:
- 275 nm LED with ZWB3
- 365 nm LED with ZWB 2 

[Andy Perrin]

This topic needs warnings added at the top, per our discussion of UVC. Also a discussion of what safety equipment was used to protect skin and eyes. 

[colinbm]

I like how the 275nm fluorescence brings out this extra details.
BUT a WARNING 275nm is the most dangerous UVC wavelength, much more dangerous then 254nm.

[Nate]

Cool comparison. I have no plans on having 275nm blasting around me, but I have a question. Does it emit a lot more heat than a 365 torch? I was dumb in the beginning and shined my 365nm on my skin and noticed lots of heat even from a foot away.

[colinbm]

4 minutes ago, Nate said:

Cool comparison. I have no plans on having 275nm blasting around me, but I have a question. Does it emit a lot more heat than a 365 torch? I was dumb in the beginning and shined my 365nm on my skin and noticed lots of heat even from a foot away.

No & that is another reason why it is dangerous, we can't feel it until it is way too late, while it is destroying DNA.

[Nate]

2 minutes ago, colinbm said:

we can't feel it until it is way too late

OK thanks. Another reason for me to stay away from that wavelength 

[lukaszgryglicki]

Where can I buy LED 275 nm? I definitely want one.

 

[dabateman]

9 hours ago, lukaszgryglicki said:

Where can I buy LED 275 nm? I definitely want one.

 

MaxMax sells them, also lots on Ebay.  They are still a bit expensive though.

It really is a dangerous wavelength,  maybe best to avoid. 275nm is 10x to 100x better at killing bacteria than a Mercury 254nm bulb. Thus why they are less power.  Common for some water sterilizer systems. I still prefer other sterilization methods though.

[colinbm]

11 hours ago, lukaszgryglicki said:

Where can I buy LED 275 nm? I definitely want one.

 

Before you buy what UVC safety gear do you have ?

[Andy Perrin]

Yeah, this is in the range where you should have no skin showing at all while you wave the torch around, and should have full head protection (like a polycarbonate face shield). You don't want to slowly blind yourself with reflections.

[ulf]

The optimal thing here is to completely AVOIDING doing it.