Author Topic: Cheapest way to check if a UVC bulb is as advertised?  (Read 7205 times)

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Offline pipe2nullTopic starter

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Cheapest way to check if a UVC bulb is as advertised?
« on: April 03, 2020, 10:46:21 am »
The topic says it all.  There probably is no cheap way to do it if you don't have the right equipment, but I don't know since I've never had reason to measure light/UV emissions before.

I ordered a small variety of different UVC bulbs for pandemic purposes.  I figure replacement UVC bulbs for use in products from larger companies are probably as advertised, at least the official replacement parts.  But then there are some LED UVC lights, with convenient household light bulb screw connectors, that claim to emit 254nm UVC at various power output.  At first I thought it was total BS, but apparently UVC LEDs are a thing now.

"Ideally", I'd like to know what wavelengths are actually emitting, and how much of the advertised 3.5W, 30W, 60W, 100W, etc power is actually being emitted at 254nm UVC.  It would also be useful to measure the same info for replacement UVC bulbs for normal commercial products as well.  Also, even if 254nm exist, also would like to verify that no lower wavelengths are emitted that produce ozone.

But that's "ideally".  :-DD   Is there a cheap way to do this?
 

Offline Siwastaja

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Re: Cheapest way to check if a UVC bulb is as advertised?
« Reply #1 on: April 03, 2020, 11:05:06 am »
About the LEDs,

UVC LED bulbs that advertise multi-watt numbers and don't cost a fortune are likely just scams, or just rated by the input power, which is meaningless. The state-of-the-art UVC LED efficiency being somewhere around 2-3% and the cost somewhere around $1000/W for output power. So they are in the same spot now as white LEDs in mid-to-late 1990's.

Also, you don't want to buy 254nm UVC LEDs, because that's not the optimum wavelength. With LEDs, you have the choice for 275 or 285 nm products.
« Last Edit: April 03, 2020, 11:07:18 am by Siwastaja »
 

Offline jpanhalt

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Re: Cheapest way to check if a UVC bulb is as advertised?
« Reply #2 on: April 03, 2020, 11:11:49 am »
One can find various inorganic compounds that fluoresce when exposed to short wavelengths.  Orange and green are will known and used in TLC (thin-layer chromatography) plates like this: https://www.coleparmer.com/i/kinesis-telos-aluminum-backed-tlc-plate-with-gf254-indicator-silica-200-x-200-mm-20-pk/0647587?PubID=VV&persist=True&ip=no&gclid=EAIaIQobChMIgZXynY7M6AIVm4FaBR3k5QaWEAAYAiAAEgJl7fD_BwE

There might be some organic compounds too, but the inorganic compounds are more common and stable.  Now,of course,there are lots of fluorescent organic compounds, but most of them, e.g., fluorescein and rhodamine, fluoresce when excited by longer wavelength light.
 

Offline NiHaoMike

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Re: Cheapest way to check if a UVC bulb is as advertised?
« Reply #3 on: April 03, 2020, 01:33:45 pm »
Get an old EPROM and see how long it takes to erase.
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Offline pipe2nullTopic starter

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Re: Cheapest way to check if a UVC bulb is as advertised?
« Reply #4 on: April 03, 2020, 07:39:50 pm »
So, moral of the story is UVC LED products currently sold on Amazon are ALL? scams since it is not currently possible to produce them within consumer price ranges???  I was and still am skeptical of those products, but doing actual measurements confirm reality, up to the limits of your testing ability, which is my current issue.

Does anyone know a good de-rating factor to use for "should probably be as advertised" UVC replacement bulbs for commercial products, the actual glass bulbs with...  I think mercury?  By "de-rating factor" I mean the actual power output in the germicidal range given the advertised overall power consumption of the bulb.  I have one "replacement" bulb on the way that is advertised as 3.5W, but I reasonably assume that is the power requirement and not the actual emitted UVC power.  I'll have the same issue with any other bulb I order.

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Offline artag

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Re: Cheapest way to check if a UVC bulb is as advertised?
« Reply #5 on: April 03, 2020, 07:51:44 pm »
If you watch Big Clive's channel, it would seem that the easy way to test it is to expose yourself to it  :o for a few minutes and see how bad a sunburn you get.

But from a video he's only released on Patreon so far, it would seem that fakes are indeed very common.



 
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Offline Siwastaja

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Re: Cheapest way to check if a UVC bulb is as advertised?
« Reply #6 on: April 03, 2020, 08:27:02 pm »
So, moral of the story is UVC LED products currently sold on Amazon are ALL? scams since it is not currently possible to produce them within consumer price ranges???

Well, I see very little reason why a consumer should be buying germicidal UVC bulbs off Amazon. It's better if they are audiophoolery equivalent and either emit UVA, or just a few dozen mW UVC maximum, so people won't injure themselves with them.

I simply don't see how an average or even technically oriented person could use such bulbs. Very advanced hobbyists / scientists / engineers are of course different. But we want to see specs. Which, for UVC LEDs, are available when you buy the LEDs from proper distributors. And they suck at a bit over 2% efficiency.
 
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Offline pipe2nullTopic starter

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Re: Cheapest way to check if a UVC bulb is as advertised?
« Reply #7 on: April 03, 2020, 08:52:28 pm »
If you watch Big Clive's channel, it would seem that the easy way to test it is to expose yourself to it  :o for a few minutes and see how bad a sunburn you get.
Heh...  And you quantify the power output by how many layers of skin peal off!   :-DD  I have a limit of exposable patches of skin, so I'm thinking I'll skip that testing method.

At the end of the day, I'm trying to find (legitimate) UVC sources that are powerful enough to kill COVID-19 in psuedo-real-time, fast enough to sterilize air at or above typical peak airflow rate of breathing, primarily the exhale part.  I read a couple studies on SARS-CoV, and the minimum UVC exposure for that virus appears to be somewhere between 0.1 J/cm2 to 1.5J/cm2 depending on a bunch of factors including if the virus is on a surface or in some other medium, etc.  I'm still searching for better/more applicable data on exposure times.  But based on those numbers alone, it might be feasible to use UVC to sterilize breathing air in psuedo-real-time, but a lot depends on the power and geometry of the bulb plus the geometry of the enclosure (AKA reactor, I think it's referred to).  There are a lot of different projects going on that are considering use of UVC, so the info I'm looking for applies to more projects than my own.

And for these efforts to be of any use, need to be able to acquire the bulbs in a reasonable amount of time, not months or years, thus bulbs available on Amazon (if some of them are powerful enough) would be ideal.  But if there are other recommended suppliers, I will check them out.  Thanks!
 

Offline jpanhalt

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Re: Cheapest way to check if a UVC bulb is as advertised?
« Reply #8 on: April 03, 2020, 08:59:31 pm »
There are lots of established ways to measure UV emission spectrum.  You are too cheap to do it.  I suggested a practical alternative. "Fluorescent" TLC plates are in every organic chemistry lab in the US.   One telephone call.  Or, are you an inveterate,paranoid, DIY'er who expects something for free?

EDIT: The chemical to make those TLC plates is less than $1.00 per gram on eBay, and you need about 1 mg.
« Last Edit: April 03, 2020, 10:02:38 pm by jpanhalt »
 

Offline Siwastaja

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Re: Cheapest way to check if a UVC bulb is as advertised?
« Reply #9 on: April 03, 2020, 09:05:35 pm »
I bought some UVC LEDs from Digikey for the same purpose you describe. Yes, they were expensive, and yes, I do realize with my napkin math that with 60mW output power, the disinfection rate of air will be something between maybe 70% and 99% but definitely no more. I'm combining it with a HEPA filter (I happen to have quite a few from a previous project), though. Proper mechanical filtering is what all those masks are doing, and as you may know, proper masks are really good stopping viruses, no UV needed.
 
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Re: Cheapest way to check if a UVC bulb is as advertised?
« Reply #10 on: April 03, 2020, 09:07:18 pm »
You can buy air filters with germicidal bulbs installed https://asept-air.com/ca/shop/life-cell-1550-uv/
Any sort of replacement germicidal bulb from a genuine company is going to be legit, something like this for example: https://www.amazon.com/Ultraviolet-Water-Purifier-Bulb-Sterilizer/dp/B07K7Z1P63

These are ridiculously powerful and should not be operated outside of a good light sealed chamber, eg stainless steel.
They also heat up fast, and UV output can drop if the bulb overheats, not to mention burning up.

digikey has UVC photodiodes, if you want to measure the true output.
There were some digital sensors as well but it looks like the one I was looking at will not work, germicidal peak is 270nm this one measures 350nm peak, but others may exist: https://www.vishay.com/docs/84277/veml6070.pdf

Be incredibly careful with skin or eye exposure.
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Re: Cheapest way to check if a UVC bulb is as advertised?
« Reply #11 on: April 03, 2020, 09:12:57 pm »
"Ideally", I'd like to know what wavelengths are actually emitting, and how much [energy] is actually being emitted at 254nm UVC.  It would also be useful to measure the same info for replacement UVC bulbs for normal commercial products as well.  Also, even if 254nm exist, also would like to verify that no lower wavelengths are emitted that produce ozone.

But that's "ideally".  :-DD   Is there a cheap way to do this?
Cheaply quantifying spectral energy, not really possible. Doing it below 300nm, another order of magnitude more expensive at least. Without an accurate and stable spectral output the cheap methods to quantify energy are all useless.
 

Offline Ian.M

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Re: Cheapest way to check if a UVC bulb is as advertised?
« Reply #12 on: April 03, 2020, 09:30:37 pm »
There's no real problem working with UVC bulbs so long as you aren't stupid.  When I built an EPROM eraser using a 4W T5 UVC tube, I started off with a 4W fluorescent torch which had a Royer converter driving an ordinary white 4W T5 fluorescent tube, and did a quick check it was compatible with the UVC tube I had bought 'Big Clive' style, switched on and observed from the other side of the room - Inverse Square law is your friend, and *DONT* stare at it!

Then I built an enclosure with a draw with a black felt light seal  and antistatic foam for the EPROM(s), a draw interlock microswitch and a timer and status indicators,  with aluminum foil tape to protect various plastic parts from UVC degradation, and tested it with the visible white tube.  The UVC tube didn't get refitted until I was 100% satisfied with the control electronics, and that there was no significant light leakage (by observation in a dark room).

Re: the OP's UV intensity comparison problem, probably the cheapest hobbyist friendly option would be to time the 'bit-rot' of a UV erasable EPROM.  Program it all '0' then time till half the bits have become '1'.  However you mustn't apply power while the EPROM is being exposed to UV, so its going to require you to rig up some sort of servo controlled shutter to obscure its window while you are powering and reading the EPROM.

Otherwise, if you want a better measurement of optical intensity vs wavelength,  its DIY optics bench territory - build a spectrometer with a fused quartz prism rotated by a precision servo with a high sensitivity wide-band photodiode as the detector, then calibrate it using a source with a known spectrum and intensity e.g. direct noon sunlight at (near) sea level on an absolutely cloudless high pressure summer day.  Be prepared to move the photodiode further from the prism to reduce the intensity (inverse square law again).  Stray light is your absolute enemy - in addition to a light tight enclosure with a matte black interior, you'll probably want tubes with the best optical flat black coating you can afford round the optical paths, and inner enclosures with the same coating round the prism and detector.
« Last Edit: April 04, 2020, 12:09:29 am by Ian.M »
 
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Offline mikeselectricstuff

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Re: Cheapest way to check if a UVC bulb is as advertised?
« Reply #13 on: April 03, 2020, 09:40:06 pm »
Smell of ozone. 
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Offline jpanhalt

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Re: Cheapest way to check if a UVC bulb is as advertised?
« Reply #14 on: April 03, 2020, 09:52:02 pm »
Are you sure ozone doesn't require a shorter wavelength? 

Low pressure mercury lamps in quartz envelops do produce ozone, but that is mostly from the small amount of shorter wavelengths they produce. https://www.oxidationtech.com/ozone/ozone-production/uv-lamp.html
 

Offline pipe2nullTopic starter

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Re: Cheapest way to check if a UVC bulb is as advertised?
« Reply #15 on: April 03, 2020, 10:40:13 pm »
Lots of good feedback, thanks!

Cheaply quantifying spectral energy, not really possible. Doing it below 300nm, another order of magnitude more expensive at least. Without an accurate and stable spectral output the cheap methods to quantify energy are all useless.
Yea...  That is what I figured, thus my inclusion of the " :-DD" emoji next to the word "ideally" in the OP.   ;)
A spectrum analyzer or VNA is on my to-buy list, but wasn't intending on picking one of those up until next year.  I think I read somewhere that SAs are used with a special probe for wavelength measurements?  I have a scope and a miscellaneous assortment of bits n pieces, had hoped cobbling together a makeshift probe for use with my existing scope might have been possible, but I really did not expect it.

@thm_w
Thanks for the info.  Prior to pandemic, I bought a floor-standing air purifier with UVC.  At least for the model I bought, if you pop off the cover and check out how it works, only a tiny percentage of the total volume of air passing through the unit gets any UVC exposure at all, and the duration of exposure is very short.  For the replacement germicidal bulbs, the only numbers I have seen are power consumption, but I need the W/cm2 of the UVC/germicidal emission to relate back to virus-killing professional studies that use numbers like 0.1J/cm2 or 4000 uW/cm2 for 15 minutes, etc.  I saw various photodiodes on digikey, I'll have to look at those a bit more in depth.

I bought some UVC LEDs from Digikey for the same purpose you describe. Yes, they were expensive, and yes, I do realize with my napkin math that with 60mW output power, the disinfection rate of air will be something between maybe 70% and 99% but definitely no more. I'm combining it with a HEPA filter (I happen to have quite a few from a previous project), though. Proper mechanical filtering is what all those masks are doing, and as you may know, proper masks are really good stopping viruses, no UV needed.
Very cool!  The direction I was going is mostly for sterilizing exhaled-and-aerosolized viruses from sick people who need to use a CPAP/BiPAP, whether because a ventilator is not available or if they normally use a CPAP on a regular day but can't now without broadcasting nasty bits all over the place.  There are a massive number of people out there who have CPAP or BiPAP machines at home.  With enough UVC exposure, shouldn't need a filter, and with the various shortages of medical supplies, having an all-electric solution would be a good thing.  And, as you pointed out, you can always add a filter later.  Might be able to do something similar with inhaled air, but that's not my main objective.

 

Offline Zero999

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Re: Cheapest way to check if a UVC bulb is as advertised?
« Reply #16 on: April 03, 2020, 11:06:07 pm »
So, moral of the story is UVC LED products currently sold on Amazon are ALL? scams since it is not currently possible to produce them within consumer price ranges???

Well, I see very little reason why a consumer should be buying germicidal UVC bulbs off Amazon. It's better if they are audiophoolery equivalent and either emit UVA, or just a few dozen mW UVC maximum, so people won't injure themselves with them.

I simply don't see how an average or even technically oriented person could use such bulbs. Very advanced hobbyists / scientists / engineers are of course different. But we want to see specs. Which, for UVC LEDs, are available when you buy the LEDs from proper distributors. And they suck at a bit over 2% efficiency.
Yes, mercury lamps are much more efficient, than UVC LEDs. Going by the data sheet, 30% seems to be fairly typical. Of course this doesn't taken into account the losses in the ballast, but an electronic ballast will have similar losses to a switched mode LED driver.
https://www.ushio.com/files/specifications/germicidal-low-pressure-mercury-arc.pdf

I know you said in the other thread that UVC LEDs have a more optimal spectrum, but it's still isn't enough to offset it. I imagine LEDs might work out better if they need to be switched on and off very frequently, such as in a water dispenser, where the mercury vapour lamp would probably be on continuously, as people wouldn't want to wait for it to warm up, but that's about it. LEDs also don't give off any ozone which can also be responsible for the sterilising effect, especially in applications where some of the surfaces will be shaded. I know ozone is often unwanted and there are doped quartz lamps which filter it out.

I agree about investing in UVC LEDs, but I consider them too immature for use in all but the most niche applications. Mercury lamps are a mature, efficient, tried and tested technology.
« Last Edit: April 04, 2020, 07:27:51 am by Zero999 »
 

Offline LaserSteve

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Re: Cheapest way to check if a UVC bulb is as advertised?
« Reply #17 on: April 03, 2020, 11:38:32 pm »
A metalized, reflective mode. diffraction grating and something that is florescent is all you need. It helps if you have a neon lamp (NE2 is fine), HG based germicidal lamp,  or a old CFL lamp for rough calibration.

Quartz, Fused Silica, or Calcium Fluoride  prisms are out there, but would be a pain in the neck to use compared to a  1200 LPI grating.

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« Last Edit: April 03, 2020, 11:40:08 pm by LaserSteve »
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Online thm_w

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Re: Cheapest way to check if a UVC bulb is as advertised?
« Reply #18 on: April 04, 2020, 12:37:28 am »
@thm_w
Thanks for the info.  Prior to pandemic, I bought a floor-standing air purifier with UVC.  At least for the model I bought, if you pop off the cover and check out how it works, only a tiny percentage of the total volume of air passing through the unit gets any UVC exposure at all, and the duration of exposure is very short.  For the replacement germicidal bulbs, the only numbers I have seen are power consumption, but I need the W/cm2 of the UVC/germicidal emission to relate back to virus-killing professional studies that use numbers like 0.1J/cm2 or 4000 uW/cm2 for 15 minutes, etc.  I saw various photodiodes on digikey, I'll have to look at those a bit more in depth.

Quote
    Most scientists and engineers in the UV business now use the units "mJ/cm2" (millijoule per square centimeter) or "J/m2" (joule per square meter) for UV dose (the correct term is "fluence"). The units "J/m2" are used in most parts of the world except for North America, where "mJ/cm2" are used (1 mJ/cm2 = 10 J/m2. The old term "mW-s/cm2" (milliwatt-second per square centimeter) is equivalent to "mJ/cm2", since a "W-s" is the same as a "J" (joule). Note that 1000 microwatt = 1 milliwatt.

    Note that the term "dose" ("dosage" is a word that is redundant with "dose" and should be discouraged) is normally applied in situations where the radiation is totally absorbed (e.g., UV in sunlight absorbed by the skin to cause sun tanning or sun burning). Since less than 1% of the UV incident on a microorganism is absorbed, the term "dose" is not appropriate for this situation. This is why the term "fluence" (which is defined in terms of UV "incident" on a tiny sphere from all directions) is more appropriate.

    The units "mW/cm2" (for fluence rate or irradiance) are often confused (as you have in your question) with the units "mJ/cm2" (for fluence or UV dose). The "fluence" (UV dose) is obtained by multiplying the "fluence rate" (or irradiance) (units "mW/cm2") by the exposure time in seconds.

http://www.iuva.org/UV-FAQs
https://aem.asm.org/content/78/6/1666.short
https://pubs.acs.org/doi/abs/10.1021/es070056u


Exhausting the air outside would be simplest solution if it is possible, say on a rooftop far from any humans with some HEPA filtering.
Heating the air is also possible but could take a lot more power. Normal breathing 5L/min, an 858D can do that at 400C with ~400W.
https://www.sciencedirect.com/science/article/pii/S0021850208001729
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1477932/
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Offline pipe2nullTopic starter

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Re: Cheapest way to check if a UVC bulb is as advertised?
« Reply #19 on: April 04, 2020, 01:22:02 am »
@thm_w
Thanks again, even more really good info.  That will take me some time to dig all the way through. 

The 2 studies I was referring to list "0.1J/cm2" and "4016 μW/cm2 at 2 cm for 15 min", respectively, for the 2 non-air mediums used in the study to reduce SARS-CoV counts below what they were able to detect in their respective labs.  I have not been able to find similar studies on COVID-19 yet.  Which I find odd...  There are tons of researchers working on all kinds of things, but I haven't seen any concrete studies, even preliminary results, that focus on how to efficiently kill COVID-19 specifically.  Lots of speculation and (pun intended) gross overkill, but no actual professional studies months into a pandemic.  Knowing the minimum exposure required, or preferably the curve, would be very useful.  I could easily have missed something though.

A couple days ago I ordered "Ultraviolet Germicidal Irradiation Handbook: UVGI for Air and Surface Disinfection" by Kowalski and I should get it Monday.  It was recommended by KaneTW in another thread.  Hopefully that will answer most of my other questions.
 

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Re: Cheapest way to check if a UVC bulb is as advertised?
« Reply #20 on: April 04, 2020, 01:24:39 am »
Lots of good feedback, thanks!

Cheaply quantifying spectral energy, not really possible. Doing it below 300nm, another order of magnitude more expensive at least. Without an accurate and stable spectral output the cheap methods to quantify energy are all useless.
Yea...  That is what I figured, thus my inclusion of the " :-DD" emoji next to the word "ideally" in the OP.   ;)
A spectrum analyzer or VNA is on my to-buy list, but wasn't intending on picking one of those up until next year.  I think I read somewhere that SAs are used with a special probe for wavelength measurements?  I have a scope and a miscellaneous assortment of bits n pieces, had hoped cobbling together a makeshift probe for use with my existing scope might have been possible, but I really did not expect it.
A spectrum analyser measures RF/audio frequencies in a voltage source, visible light frequencies are over the terahertz gap at 500THz, UV even further. There aren't practical circuits at these frequencies so all the "processing" has to be done in optics.

A metalized, reflective mode. diffraction grating and something that is florescent is all you need. It helps if you have a neon lamp (NE2 is fine), HG based germicidal lamp,  or a old CFL lamp for rough calibration.

Quartz, Fused Silica, or Calcium Fluoride  prisms are out there, but would be a pain in the neck to use compared to a  1200 LPI grating.
That will help pick the emission wavelengths (assuming the fluorescent material lines up with the emission) but doesn't help with quantifying the source energy.
 

Offline Siwastaja

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Re: Cheapest way to check if a UVC bulb is as advertised?
« Reply #21 on: April 04, 2020, 06:35:17 am »
Yes, mercury lamps are much more efficient, than UVC LEDs. Going by the data sheet, 30% seems to be fairly typical. Of course this doesn't taken into account the losses in the ballast, but an electronic ballast will have similar losses to a switched mode LED driver.
https://www.ushio.com/files/specifications/germicidal-low-pressure-mercury-arc.pdf

I know you said in the other thread that UVC LEDs have a more optimal spectrum, but it's still isn't enough to offset it. I imagine LEDs might work out better if they need to be switched on and off very frequently, such as in a water dispenser, where the mercury vapour lamp would probably be on continuously, as people wouldn't want to wait for it to warm up, but that's about it. LEDs also don't give off any ozone which can also be responsible for the sterilising effect, especially in applications where some of the surfaces will be shaded. I know ozone is often unwanted and there are doped quartz lamps which filter it out.

I agree about investing in UVC LEDs, but I consider them too mature for use in all but the most niche applications. Mercury lamps are a mature, efficient, tried and tested technology.

Yes, you are right. Except for the very short duty intermittent applications where the LEDs make real engienering sense, UVC LEDs are still more of an interesting concept, like white LEDs somewhere 1998 or so. But, if the pandemic increases funding for their development, it's quite likely we see the series of similar breakthroughs what happened in white LEDs within just 5-10 years around 2000.
 

Offline Zero999

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Re: Cheapest way to check if a UVC bulb is as advertised?
« Reply #22 on: April 04, 2020, 07:40:30 am »
Yes, you are right. Except for the very short duty intermittent applications where the LEDs make real engienering sense, UVC LEDs are still more of an interesting concept, like white LEDs somewhere 1998 or so. But, if the pandemic increases funding for their development, it's quite likely we see the series of similar breakthroughs what happened in white LEDs within just 5-10 years around 2000.
I hope so, but don't hold your breath. LED efficiency hasn't gone up equally for all wavelengths. There has been a massive increase in the efficiency of UVA and blue LEDs, but green and yellow still lag significantly. In theory it should be possible to produce make shorter wavelengths more efficiently, than longer ones, because a higher forward voltage should mean less I2R losses inside the semiconducting materials, but it doesn't always work out that way.
 

Offline Siwastaja

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Re: Cheapest way to check if a UVC bulb is as advertised?
« Reply #23 on: April 04, 2020, 07:48:49 am »
Yes, because it's a matter of finding the right materials and processes, with physical constraints, it can't be predicted. More resources and funding means higher chances, but the plain old luck is still part of the equation. It's likely there is a breakthrough, but no one can guarantee it.

You could say that yellow LEDs are still more inefficient because there is much less need, hence less funding for their development than for blue (i.e., white) LEDs, but it may not be that way, it's also a possibility that you just can't make them any better.
 

Offline borjam

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Re: Cheapest way to check if a UVC bulb is as advertised?
« Reply #24 on: April 04, 2020, 08:31:05 am »
I have an old EPROM eraser, a hobby unit for two chips maximum.

It indeed erases them in 15 minutes or so, and once turned on you can smell ozone. Which means that ionizing radiation is indeed being emitted.

It also degraded anti static foam.

So I guess the presence of ozone is a good hint. Moreover that ozone itself is bad for germs adding insult to injury :)
 


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