Electronics > Projects, Designs, and Technical Stuff
Cheapest way to check if a UVC bulb is as advertised?
pipe2null:
Lots of good feedback, thanks!
--- Quote from: Someone on April 03, 2020, 09:12:57 pm ---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.
--- End quote ---
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.
--- Quote from: Siwastaja 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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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.
Zero999:
--- Quote from: Siwastaja on April 03, 2020, 08:27:02 pm ---
--- Quote from: pipe2null 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???
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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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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.
LaserSteve:
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.
Steve
thm_w:
--- Quote from: pipe2null on April 03, 2020, 10:40:13 pm ---@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.
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--- 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.
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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/
pipe2null:
@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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