[UVC SAFETY WARNING] First tests and experiments with a 265 nm UVC LED

[Stefano]

[UV SAFETY] UV-C Light Is Dangerous

NEVER look at a UV-C light.

NEVER let UV-C light hit your skin directly or by reflection.

UV-C light can cause:

• severe burns of the eyes and the skin, and
• DNA damage from broken chromosomes.

When working with UV-C illumination, you MUST:

• cover up completely, and
• have strong ventilation.

---

 

 

I bought 5 pcs 1 W 265 nm LEDs on eBay. I can later put a link for purchase if someone is interested (as always, I have no affiliation with the seller).

 

Link: https://www.ebay.com/itm/254318067890

 

I ordered the LEDs already soldered to a 20 mm copper star PCB, since my soldering skills are not that great and I don't have a heat gun or solder paste. I took one out for testing, I don't know how I will use the other four but I wanted to also build a 265 nm torch, so that's one use.

 

The LEDs are rated at 1 W input power and 8-10 mW output power. Efficiencies around 1% are typical at these very low wavelengths, so the numbers given make sense. They are rated at 150 mA of forward current.

 

I don't have a meter to measure the output power, but I can measure the input power. When the LED is cold, it requires 6.3 V to run 150 mA across it, and that's 0.945 W, very close to the advertised 1 W. For the tests done below I ran the LED at about 80-90 mA without an heatsink, and it became noticeably warm but not hot. I can run it at full power for a couple of minutes, but then it becomes too hot, so a small heatsink is required. A downside of the very low efficiency is that almost all power (~99%) is converted into heat, while an efficient 365 nm LED can reach 50% efficiency, so only half the power becomes heat.

 

The LEDs also have a lens on top, which must be made of quartz or similar, and according to the seller the view angle is 60-80°. I measured ~64.5°.

 

All photos were taken with my smartphone. For the 365 nm shots I used a 365 nm LED torch with a ZWB2-like filter, which is the first UV torch I bought. I could have used the Convoy, but I usually keep it safe and use it only when I need an intense beam.

 

This is how the LEDs arrived. The "holder" on top was longer and bent, and I cut away the excess portion with a pair of pliers. They probably gave me half of a 5x2 array.

 

Looking at the LED with a pair of polycarbonate goggles on, the chip appeared bluish while the lens appeared more violet. Looking at the spectrum with a diffraction grating I saw a full rainbow from violet to red. The output actually appears to be quite clean, but filtering it would improve it for sure. Also, very carefully, very briefly and with the LED at low power I looked at it without protection, and it looked no different than with protection. That was to be expected, as my cornea and lens completely block UVC. I am very aware of the dangers of UVC light, and I always used eye protection while working with this LED, and avoided getting my skin too close to it. The output is very low, mercury-vapor lamps are about 35% efficient (source here) and so a 3 W mercury lamp is already ~100 times more powerful than one of my LEDs, but I am still careful.

 

The output, while being low, is still usable. Combining several of these LEDs together would be better, but just one of them is enough at close range. In my limited experience, I noticed most things have very similar fluorescence behaviours under 365 nm longwave UVA and 265 nm shortwave UVC light. Paper still fluoresces bright blue, yellow and orange highlighters behave like normal, and most things appear basically the same. There was one big difference which I liked a lot, and that's banknotes.

 

This is a 20 € banknote under normal light (it should be the new one):

 

The same banknote under 365 nm UV:

 

The fluorescence appears greenish, but is actually yellow.

 

Now, under 265 nm UV:

 

The color changes to a beautiful deep orange. It reminds me of older Euro banknotes, which had yellow and orange fluorescing inks. Also, there is an hidden "€" symbol visible under UVC but not under UVA or visible light, so this color change may be intended.

 

Another nice thing is that, finally, glass appears opaque. Some plastics are surprisingly (partially) transparent, but most aren't, and all glass I found around isn't. I tried with a quartz crystal, which is the only quartz thing I have around, at it looks to be transparent (it should be). A paper sheet was put under the pieces of glass to "see" the otherwise invisible UV light.

 

Below an (empty) glass.

 

Visible light:

 

365 nm UV:

 

265 nm UV:

 

Old magnifying glass, visible light:

 

365 nm UV:

 

265 nm UV:

 

About filtering, 360-type glass doesnt work, as it blocks UVC. 340-type glass, although it reaches deeper, absorbs UVC almost completely. The only option is to use the 330-type (Hoya U-330, UG5, ZWB3 and so on) as it transmits 265 nm well while blocking most visible light and some IR. Not perfect, but does something. The best thing would be to use a dichroic filter, but those are hard to find with good peak transmissions.

 

As a reference, here is the normalized transmission curve of 1.5 mm thick UG5 glass:

 

As a test, I tried with 2 mm thick ZWB2 glass:

 

Visible light:

 

365 nm UV:

 

265 nm UV:

 

About the beam pattern... it isn't very uniform. I hoped for something better, but this is what I have:

 

Not too bad, but could have been nicer. One thing these LEDs are great for is collimation with a (quartz/fused silica) lens. LEDs with an already partially collimated output (like this one, which has a ~60° viewing angle) are great to be used this way as you don't waste any light with a sufficiently "strong" lens (a lens with a pronounced curvature which has a short focal length while being relatively wide). The LED is also quite small, and this allows for narrow beams. If you want to use a parabolic reflector, it is much better if not mandatory to remove the lens instead.

 

Overall, a nice LED.

[Cadmium]

Stefano, Cool tests!

[microbat52]

Im really intrigued about the bank note, I thought lamps for bank notes were usually in the 390s nm, I cant imagine anyone expecting bankers to use uvc.

[Stefano]

Thanks Steve

 

[Stefano]

Im really intrigued about the bank note, I thought lamps for bank notes were usually in the 390s nm, I cant imagine anyone expecting bankers to use uvc.

Usually for banknotes you need to go lower than the 390s to see the patterns clearly, and between 365 and 395 nm there is a huge difference. They aren't like highlighters which work well under violet or even blue light, and I think this is actually a good test to see if your UV source is "good" UV.

 

To me it makes sense that they included inks for UVC exitation, this makes counterfeiting even more difficult.

 

Just found this: https://www.dnb.nl/echtofvals/en/all-features/europa/20/uv/index.html

 

Quote: "If you use special UV light (UV-C), a large € symbol becomes visible in the centre of the banknote." So yes, this is an intended feature and an additional proof my LEDs are true UVC.

[bvf]

Good work, Stefano. I don't think you explain it, but I assume in the shots of the glass and magnifying glass you're actually photographing the fluorescence from paper or something and the shadow cast by the glass - is that correct?

[Stefano]

Yes, I am using the fluorescence from the paper to see the UV light. They aren't reflected UV photos, although somewhat similar.

[Cadmium]

Stefano, I'm fascinated with your 265nm UVC LED tests.

(DANGER DANGER - reminder to anyone reading, this is not something you should mess with unless you know the danger first)

Personally, I can't remember many UVIVF examples that were posted using UVC and UVB except the topic Pylon did way back in 2015.

(there may have been others, but this is the one that I remember when I think of UV-A/B/C visual fluorescence compared)

Took me a while to search for it, finally found it, he has some interesting example comparing UVIVF using UVC, UVB, and UVA.

https://www.ultravio...ndpost__p__9890

Fore more DANGER DANGER warnings about UVC, read page 1 of that topic. You really need to be SCARED of this stuff, otherwise you will mutate, or worse.

[Andy Perrin]

Wow, blast from the past! The tests are very interesting. Shining it in your eye still seems like a bad idea to me (I wouldn't do that with a mercury lamp either!). Stefano, could you rig up a fluorescent screen image, with a pinhole? I take it you are using your phone for the photos, but there are long exposure apps for the phone. It would be kind of like my relay lens setup that I originally used for the SWIR imaging, and probably the same issue with signal to noise problems, but it might be worth a shot. Or you could probably find a quartz singlet online for not too much. You could color the paper with a highlighter to get higher output.

[dabateman]

That link is fun. I wouldn't call 350nm UVB, to me that is still UVA.

UVB is 290nm to 320nm mostly. small range but dangerous. From 320nm to 380nm I think mostly as UVA. 380nm to 405nmish is still technically UVA, but looks different so I think of it as UVblue.

 

I have been slow this year, but have been hoping to do that properly. look at 254nm induced fluorescence vs 303nm induced fluorescence vs 370nm induced fluorescence. I made my filter setup with furnace fittings to cover my bulbs. Its just my filters are tinny, so will output a tight spot of light. Still need to think about it.

I have good Mercury 254nm and Mercury 303nm source lamps. Its just that the output is broad. Leds would be cleaner and maybe cheaper as filters are tricky.

[Cadmium]

I have never used any UV other than 365nm for UVIVF or UVIIRF (I have used green visual light for UVIIRF also, but that is beside the point here).

I find the different fluorescence examples quite interesting, and the money/note that Stefano posted above, pretty interesting,

UVC, danger, danger!

Stay safe, Stefano...

[Stefano]

Stefano, could you rig up a fluorescent screen image, with a pinhole? I take it you are using your phone for the photos, but there are long exposure apps for the phone. It would be kind of like my relay lens setup that I originally used for the SWIR imaging, and probably the same issue with signal to noise problems, but it might be worth a shot. Or you could probably find a quartz singlet online for not too much. You could color the paper with a highlighter to get higher output.

I actually did build something very similar, using a car headlight lens, a cardboard box and baking paper colored yellow with a highlighter to make it sensitive to UV, but the image quality was very poor and I never used it. Nice idea though, I will try that.

[Stefano]

You too, Stefano...

I have actually thought about using gloves when handling the LED, even if probably sunlight mutates more cells than a few tenths of mW/cm² of UVC. But I always use goggles, there's no excuse for that.

[Cadmium]

With UVC, you need to cover everything on your body, or be in an underground concrete bunker, with your LED's in a separate room, or a separate country.

UVC can not shine on anything that is alive, skin, cloths that it would pass through, holes...

read that scary stuff on the first page. Start with this link if you don't read the whole page from the top, then read what JCDowdy writes...

https://www.ultravio...ndpost__p__9168

 

You MUST isolate all parts of your body from UVC. See the picture of David in his hood...

They use UVC to kill things, it can cause other dangerous thing to happen to you even if it doesn't kill you.

And it can seriously damage certain materials. It isn't something we encounter naturally. You must handle it like you would something more dangerous.

 

There is no UVC in sunlight.

 

Oooo! Bernard changed his picture!

[bvf]

Oooo! Bernard changed his picture!

 

Well spotted! I took the head shot to see if a patch of solar keratosis which had been treated would show up in UV. It didn't but I thought I'd use the mugshot for UVP. I tried adding a sign around my neck to make it look like a police mugshot, but alas the cropping by the UVP site has cut most of this out.

[bvf]

With UVC, you need to cover everything on your body, or be in an underground concrete bunker, with your LED's in a separate room, or a separate country.

UVC can not shine on anything that is alive, skin, cloths that it would pass through, holes...

read that scary stuff on the first page. Start with this link if you don't read the whole page from the top, then read what JCDowdy writes...

https://www.ultravio...ndpost__p__9168

 

You MUST isolate all parts of your body from UVC. See the picture of David in his hood...

They use UVC to kill things, it can cause other dangerous thing to happen to you even if it doesn't kill you.

And it can seriously damage certain materials. It isn't something we encounter naturally. You must handle it like you would something more dangerous.

 

There is no UVC in sunlight.

 

 

So now I'm getting frightened! David forced me to buy a 254nm (but at least it's not 245nm, as Stefano corrected me) hand-held illuminator, and now you're telling me I'm going to die horribly.

 

Just how dangerous are these things? (https://www.ebay.co.uk/itm/4W-Shortwave-254nM-Ultraviolet-Lamps-Stamps-Phosphorescence-UV-Light-with-Filter/324087830892?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649). It's a consumer product sold without any safety warnings or controls.

[Stefano]

Exposures to the eyes or skin for a couple of minutes (even less) will give you photokeratitis (snow blindness or welder'd eye) and burn your skin quite badly, not something you can't recover from, but not pleasant at all. You have to dress like in David's profile picture.

[Stefano]

Also, keep in mind that a 4 W shortwave mercury lamp is more than 100x more powerful than one of my LEDs at full power.

[dabateman]

Bernard Don't Panic. You should wear gloves and eye protection. You should wear a long sleeved 100% cotton shirt.

Don't look at it. Just point it away from your self at all times. In Britain pants are underwear, so you should wear those too, but also what's over them. Slacks, dungarees or jeans? I am loosing my talk like a Brit. Need to watch more Dr. Who.

 

If you have read hitch highkers guide to the galaxy, those don't Panic glasses would be perfect.

 

Most important, don't point it at anyone, the light source. The reflecting light will not be as bad as the direct light. So if your covered, its cold outside anyways, you should be fine.

Do not start thinking you can tan yourself with it. Its only 4W not 25W but people get odd ideas at times.

 

It will slowly burn your eyes if you look at it. So goggles are recommended but also don't stare at it.

 

The fun thing about Ebay is you can order almost anything. So don't expect warnings or labels. Neither of my Convoys or Nemo's came with the yellow warning label that is required by the FDA. So don't expect anything.

[Stefano]

Well, I think UVC doesn't tan you, it just straight burns you. Anyway, as long as you are covered and your skin and eyes (your body in one word) are not exposed, you will be fine.

 

David, I don't know why you are saying the reflected light is less harmful. Yes, usually materials absorb UVC and reflections will be weaker, but reflected UVC photons are no different than direct ones.

 

Bernard, you have to be scared by UVC as you should be by powerful lasers, especially invisible IR ones. I built a 808 nm IR laser from my green DPSS laser, it appears as a faint red dot but it's anything but faint. That thing scares me, I should by a pair of safety goggles. In a similar way, UVC is completely invisible, and if your lamp is well filtered you may not notice it's on unless you have some fluorescing things around. Once you are safe it's kind of like using a Convoy or a Nemo, just with extra care.

[dabateman]

Stefano, as you know distance from source is part of the energetics. So if you have 2x (to thing and back) is less bad than x looking at the thing at that distance.

 

However, both are bad. So yes take precautions, and wear lots of 100% tight net cotton. I haven't tested wool, but cotton blocks. Polyester does not, not even UVA. So don't be rocking that old 1970s polyester leisure suit.

 

Bernard, why are you worried about 245nm?

DNA and RNA will absorb 260nm plus minus 10nm. So 255nm to 265nm is really dangerous. Will cause double strand breaks, cancer and cell death.

Similar most back bones of molecules will absorb 230nm. So 225nm to 235nm is really bad. This is why I will not jump into the 222nm band wagon. Too close to 225nm.

 

I am hoping for more 208nm lights which were shown as "safe". Also can be made cheaper with iodine.

[Stefano]

245 nm (which, BTW, is not what the lamp puts out) is still very dangerous. There are 245 nm LEDs on Thorlabs, but that's not relevant here. It's better not to expose any body part to UVC, whether it is the "safer" (still dangerous) 280 nm, or 265, 254, 222, 185. You may have two danger peaks at 265 nm (DNA) and 230 nm (molecules) but also what is in between should be treated with care.

[bvf]

I'm only worried about 245nm because I dyslexically confused it with 254nm. It's a complete red-herring - so forget it. The light source I have ordered is for 254nm.

 

But 254nm is on the edge of being very nasty from what you say. You give the danger range as 260 +/- 10nm, but from your next clause I assume you meant 260 +/- 5nm. But even so, 254nm is unpleasantly close.

[Stefano]

254 nm may not be the most dangerous wavelength, but it is nasty. Much worse than UVB, which we evolved under. 254 nm is alien light, is light that has never shined on the surface of the Earth.

 

There are a lot of stories of people who burned themselves using this lamps without knowing the dangers. People who looked at them or exposed their skin to them.

 

Photokeratitis is very painful, my dad experienced it many years ago because he welded without protection. They say it feels like having sand in your eyes. While I never had photokeratitis, I had actual sand in my eyes when I was a child, I think in primary school. I was playing in the sand at the beach and while digging I throwed sand in my eyes, and that was nasty, it really was. I felt it for days.

 

So wear eye and skin protection, as David said. Once you are protected there's no need to be worried, the fear you should have is that type of good fear that makes you act responsibly. Just that.

[dabateman]

Oh no its definitenly not a tight 254nm light and you should worry. I just scanned my portable 4W hand held light.

 

Full spectrum to see all the lines With the filter on (doesn't really filter much):

 

Spectrum not maxed out with filter on:

 

Spectrum with filter off, You can see the 185nm mercury line there at the bottom of the plot: