UVC sterilization LEDs as seen by my camera

[Fandyus]

As some of you might have heard (not sure I ever mentioned it publicly), I am hearing impaired. Not severely but it is enough to warrant the use of Widex hearing aids to amplify the sounds so that I can hear the world clearly. I own a Widex DRY-GO UV Electronic Drying Station for daily maintenance (mostly disinfection and drying out any liquids such as sweat so that they don't reach the electronics or clog the microphone).

https://www.widex.biz/axapta/documents/9 502 3571 001 01.pdf

I wanted to see if my camera picked up anything when the UV cycle was on, so I pointed it on the device. It picked up a faint green glow, which I believe is either an extension of the peak, or UV induced UV fluorescence of the materials within.

And before you ask, I checked with Widex themselves and was re-assured the device's UVC won't harm me if it's just on with me in the room and that it complies with all EU safety regulations. I imagine a lot of you would be alarmed have I not mentioned this.

 

This is what the whole setup looks like lit by a 365nm torch. Please do excuse the grime, I'm sure you're all aware UV amplifies any surface irregularities a lot. I'm definitely gonna have to clean it after seeing this image, though. (perhaps it's depositions created by the vapors coming through every night, the device uses heated air)

 

This is an image from when the UVC was on. ZWB2 filter+IR blocking was used. ISO 400, f/3.5 Industar 50-2, 479s exposure.

here are the two images overlaid just for the sake of it

What do you guys think?

[Doug A]

Neat and educational images. Wouldn't have expected the green. 

Thanks for sharing,

Doug A

[Fandyus]

28 minutes ago, Doug A said:

Neat and educational images. Wouldn't have expected the green. 

Thanks for sharing,

Doug A

No problem, Doug, I'm glad you've seen something new.

And yes, the green is how shorter UV wavelengths are usually seen by cameras. The color usually starts turning green at around 350nm. But there's been a lot of talk about how you can't actually determine the wavelength by looking at the false UV color.

[Cadmium]

Not that important, but I don't trust most of those UV sterilization items. There are so many of those type of things out there these days.

I stay away from anything that claims to be "sterilization" stuff... you don't want that stuff around where you might see it.

Keep in mind even if they emit UVC, they will likely emit a wider range including UVB and UVA and Visible. But maybe not, just saying.
Still an interesting test.

[colinbm]

It could well be a UVC LED under the bottom of the tray.
UVC LEDs have a lot of leak into the visible blue range, so you maybe seeing with your camera & filters some UVA.

[Fandyus]

4 hours ago, Cadmium said:

Not that important, but I don't trust most of those UV sterilization items. There are so many of those type of things out there these days.

I stay away from anything that claims to be "sterilization" stuff... you don't want that stuff around where you might see it.

Keep in mind even if they emit UVC, they will likely emit a wider range including UVB and UVA and Visible. But maybe not, just saying.
Still an interesting test.

I do trust this one. It's Widex, they basically only make expensive things for medical purposes, I don't think they'd put something out that they weren't sure about.

I never really saw any visibly blue glow, but I wear polycarbonate prescription glasses most of the time so I suspect my exposure (if any) isn't high anyway. Thhe LEDs are likely to be extremely weak and never really get closer to my face than 50cm and 99% of the time it's more then that. Plus the UVC LEDs are rigged to switch off if the lid of the device is opened.

[Cadmium]

I am just saying because it is very dangerous and anyone reading this should be aware of how dangerous it is.
 

[dabateman]

I would suspect the lid to have some type of blocking material that gets excited by the UVC to show its on. 

As we know many materials and rocks will glow when excited by UVc.

Your ZWB2 filter and your choice of lens will not pick up much light below 330nm at all, even that might be stretching that. To know what the green is, stack a long pass visible filter over your setup and see if its still there. If so then also try a IR filter. 

You might be seeing UVA, visible or IR.

[Fandyus]

2 minutes ago, dabateman said:

I would suspect the lid to have some type of blocking material that gets excited by the UVC to show its on. 

As we know many materials and rocks will glow when excited by UVc.

Your ZWB2 filter and your choice of lens will not pick up much light below 330nm at all, even that might be stretching that. To know what the green is, stack a long pass visible filter over your setup and see if its still there. If so then also try a IR filter. 

You might be seeing UVA, visible or IR.

It is very unlikely to be a leak. This stack from what I noticed never really picks up any light it shouldn't unless you're dealing with something like a candle flame. The lid contains no such materials, the holes are there for ventilation purposes so blocking them would he shooting yourself in the foot. The UVC cycle is indicated by a flashing visible LED located inside.

[colinbm]

If people get frightened with this cleaner, they should be more scared of fluorescent lights which they have used all their lives, because they are UVC & have Mercury too.

 

[Fandyus]

25 minutes ago, colinbm said:

If people get frightened with this cleaner, they should be more scared of fluorescent lights which they have used all their lives, because they are UVC & have Mercury too.

 

The mercury sure is an issue but doesn't the glass and phosphor coating block all UVC?

[enricosavazzi]

Given that the PDF does not seem to mention that the machine uses UVC LEDs, and that these LEDs are still quite expensive, I am inclined to think that the machine actually uses a cheaper design with a small/miniature mercury tube with fused silica glass envelope to generate UV, and a UV-pass filter to eliminate the VIS emission (and also leak NIR). A small mercury tube can be easily fed from USB power via an internal voltage multiplier and electronic starter.

 

This would explain the false-green either as UVA around 320-340 nm, or as  IR leaking through the filter of the machine. The UVC would be mostly the 254 nm line, but mercury tubes also emit several weak lines in the 300-340 nm range and a strong line at 365 nm, together with dozens of other lines across the UV-VIS-NIR spectrum up to more than 1,000 nm.

[Cadmium]

At the bottom of the link it says UV-C, but I don't see it saying LED's anywhere.

If that pic is shot in UV, then the green could be lower UV-A (340nm green for example).

A tube would require replacement, so it should say somewhere how to do that.

[JMC]

Fandyus, in your original post you said "ZWB2 filter+IR blocking was used" for the 'UVC' image. What did you use for IR blocking, and what were the thicknesses of the filters you used?

[Fandyus]

.

15 minutes ago, JMC said:

Fandyus, in your original post you said "ZWB2 filter+IR blocking was used" for the 'UVC' image. What did you use for IR blocking, and what were the thicknesses of the filters you used?

ZWB2 + QB39

I believe they're both 2mm, I've never observed any leaks except while imaging a candle which is quite a push. Even looking at the sun with the filter stack while polycarbonate was inserted in front of the filters made the sun turn deep violet but no red or green or anything.

[JMC]

1 hour ago, Fandyus said:

.

ZWB2 + QB39

I believe they're both 2mm, I've never observed any leaks except while imaging a candle which is quite a push. Even looking at the sun with the filter stack while polycarbonate was inserted in front of the filters made the sun turn deep violet but no red or green or anything.

Ok thanks. Based on that, then you're not going to be seeing any UVC through those filters when stacked together - the QB39 will block anything that low. You may be seeing some UVB which would account for the green, but even that would be low levels. If it is, as has been mentioned above, a small mercury lamp rather the LEDs, then you are most likely picking up longer wavelength light (UVA and vis) and the end result is something with looks green. Very difficult to be certain without getting a spectrum of the light itself.

[Fandyus]

2 hours ago, enricosavazzi said:

Given that the PDF does not seem to mention that the machine uses UVC LEDs, and that these LEDs are still quite expensive, I am inclined to think that the machine actually uses a cheaper design with a small/miniature mercury tube with fused silica glass envelope to generate UV, and a UV-pass filter to eliminate the VIS emission (and also leak NIR). A small mercury tube can be easily fed from USB power via an internal voltage multiplier and electronic starter.

 

This would explain the false-green either as UVA around 320-340 nm, or as  IR leaking through the filter of the machine. The UVC would be mostly the 254 nm line, but mercury tubes also emit several weak lines in the 300-340 nm range and a strong line at 365 nm, together with dozens of other lines across the UV-VIS-NIR spectrum up to more than 1,000 nm.

 

35 minutes ago, JMC said:

Ok thanks. Based on that, then you're not going to be seeing any UVC through those filters when stacked together - the QB39 will block anything that low. You may be seeing some UVB which would account for the green, but even that would be low levels. If it is, as has been mentioned above, a small mercury lamp rather the LEDs, then you are most likely picking up longer wavelength light (UVA and vis) and the end result is something with looks green. Very difficult to be certain without getting a spectrum of the light itself.

It honestly makes a lot of sense, though until now I assumed LEDs were used, when I'm home, I'll try to peek in when it's turned off, see if I can see a tube.

Edit: also, even if the filter stack could pass UVC, it would be filtered by the lens, and even if the lens was quartz, it's more then likely my camera would not respond to UVC at all due to microlenses or the Bayer array and such, I never really implied that I could be seeing UVC.

[JMC]

Fandyus, yes indeed, I didn't mention the lens or the camera, but based on the filters you mentioned UVC wont be getting through those.