Cheapest way to check if a UVC bulb is as advertised? - Page 1
Forum section: electronics / projects

author: pipe2null
author_rank: Regular Contributor
timestamp: April 03, 2020, 10:46:21 am
content: 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".Is there a cheap way to do this?

author: Siwastaja
author_rank: Super Contributor
timestamp: April 03, 2020, 11:05:06 am
content: 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.

author: jpanhalt
author_rank: Super Contributor
timestamp: April 03, 2020, 11:11:49 am
content: 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_BwEThere 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.

author: NiHaoMike
author_rank: Super Contributor
timestamp: April 03, 2020, 01:33:45 pm
content: Get an old EPROM and see how long it takes to erase.

author: pipe2null
author_rank: Regular Contributor
timestamp: April 03, 2020, 07:39:50 pm
content: So, moral of the story is UVC LED products currently sold on Amazon areALL? 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 usefor "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.

author: artag
author_rank: Super Contributor
timestamp: April 03, 2020, 07:51:44 pm
content: If you watch Big Clive's channel, it would seem that the easy way to test it is to expose yourself to itfor 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.

author: Siwastaja
author_rank: Super Contributor
timestamp: April 03, 2020, 08:27:02 pm
content: Quote from: pipe2null on April 03, 2020, 07:39:50 pmWell, 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.

author: pipe2null
author_rank: Regular Contributor
timestamp: April 03, 2020, 08:52:28 pm
content: Quote from: artag on April 03, 2020, 07:51:44 pmHeh... And you quantify the power output by how many layers of skin peal off!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!

author: jpanhalt
author_rank: Super Contributor
timestamp: April 03, 2020, 08:59:31 pm
content: 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.

author: Siwastaja
author_rank: Super Contributor
timestamp: April 03, 2020, 09:05:35 pm
content: 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.

author: thm_w
author_rank: Super Contributor
timestamp: April 03, 2020, 09:07:18 pm
content: You can buy air filters with germicidal bulbs installedhttps://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/B07K7Z1P63These 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.pdfBe incredibly careful with skin or eye exposure.

author: Someone
author_rank: Super Contributor
timestamp: April 03, 2020, 09:12:57 pm
content: Quote from: pipe2null on April 03, 2020, 10:46:21 amCheaply 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.

author: Ian.M
author_rank: Super Contributor
timestamp: April 03, 2020, 09:30:37 pm
content: 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.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: April 03, 2020, 09:40:06 pm
content: Smell of ozone.

author: jpanhalt
author_rank: Super Contributor
timestamp: April 03, 2020, 09:52:02 pm
content: 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

author: pipe2null
author_rank: Regular Contributor
timestamp: April 03, 2020, 10:40:13 pm
content: Lots of good feedback, thanks!Quote from: Someone on April 03, 2020, 09:12:57 pmYea... That is what I figured, thus my inclusion of the "" 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_wThanks 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 theW/cm2 of the UVC/germicidal emissionto 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 pmVery 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.

author: Zero999
author_rank: Super Contributor
timestamp: April 03, 2020, 11:06:07 pm
content: Quote from: Siwastaja on April 03, 2020, 08:27:02 pmYes, 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.pdfI knowyou said in the other threadthat 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.

author: LaserSteve
author_rank: Super Contributor
timestamp: April 03, 2020, 11:38:32 pm
content: 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

author: thm_w
author_rank: Super Contributor
timestamp: April 04, 2020, 12:37:28 am
content: Quote from: pipe2null on April 03, 2020, 10:40:13 pmQuotehttp://www.iuva.org/UV-FAQshttps://aem.asm.org/content/78/6/1666.shorthttps://pubs.acs.org/doi/abs/10.1021/es070056uExhausting 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/S0021850208001729https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1477932/

author: pipe2null
author_rank: Regular Contributor
timestamp: April 04, 2020, 01:22:02 am
content: @thm_wThanks 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 toefficientlykill 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.

author: Someone
author_rank: Super Contributor
timestamp: April 04, 2020, 01:24:39 am
content: Quote from: pipe2null on April 03, 2020, 10:40:13 pmA 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.Quote from: LaserSteve on April 03, 2020, 11:38:32 pmThat will help pick the emission wavelengths (assuming the fluorescent material lines up with the emission) but doesn't help with quantifying the source energy.

author: Siwastaja
author_rank: Super Contributor
timestamp: April 04, 2020, 06:35:17 am
content: Quote from: Zero999 on April 03, 2020, 11:06:07 pmYes, 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.

author: Zero999
author_rank: Super Contributor
timestamp: April 04, 2020, 07:40:30 am
content: Quote from: Siwastaja on April 04, 2020, 06:35:17 amI 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.

author: Siwastaja
author_rank: Super Contributor
timestamp: April 04, 2020, 07:48:49 am
content: 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'slikelythere 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.

author: borjam
author_rank: Unknown
timestamp: April 04, 2020, 08:31:05 am
content: 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

author: LaserSteve
author_rank: Super Contributor
timestamp: April 04, 2020, 10:29:55 am
content: For measuring lasers above about 15-20 mW, we use what is basically a Absorber mounted on a Pelter element in reverse, which is the core of many laser power meters. While it is possible for a Hobbyist to build one, the issue is that they respond to pretty much "EVERYTHING" around them. Which is why my post above stresses finding the wavelength.Carbon black in the form of Black Krylon Engine Paint is generally a good start for the absorber, with a decent instrumentation amp circuit on the Peltier. Calibration, however, is an art form, with the classic means being a heater coil. You need a massive heat sink on the other side of the array.UV low pass glass filters or dichroric filters don't grow on trees, making this task a bit difficult. Fluorescence conversion can be anything but linear unless you have in-organic phosphors. SO:If you've got 100$ to spend you can get a GaP photodiode from Thorlabs. If you go GaP, I hope you can find a decent Ampere per Watt curve for a representative device.Part number is FGAP71Photonics is easy, but accurate quantitative photonics is difficult and expensive.Steve

author: Zero999
author_rank: Super Contributor
timestamp: April 04, 2020, 05:32:09 pm
content: Quote from: LaserSteve on April 04, 2020, 10:29:55 amI would have thought you'd want high pass, not low pass filters, unless your source has considerable energy above the useful germicidal frequencies, although it would produce a lot of ozone, if that were the case. I think lots of those cheap UV lamps will really be black light and there will still be a significant thermal IR blackbody, which would both be picked up by a bolometer. Cooling would reduce the blackbody emission, but it will affect the efficiency of the lamp.

author: LaserSteve
author_rank: Super Contributor
timestamp: April 04, 2020, 06:47:25 pm
content: I have attached an optical "Shortpass" typical graph from the Edmund Optics website. Optics uses the terminology just a little differently:

author: pipe2null
author_rank: Regular Contributor
timestamp: April 04, 2020, 07:22:46 pm
content: What do you think of these photodiodes?$30-ish on digikey with reduced responsive range, no filter required for UVC/germicidal detection range but only "0.076 mm2" active area:https://media.digikey.com/pdf/Data%20Sheets/Photonic%20Detetectors%20Inc%20PDFs/SD008-2171-112.pdf$350-ish on digikey, has "1 cm2" active area but has normal response to visible light, requires filter etc.:https://optodiode.com/pdf/UVG100.pdf

author: Zero999
author_rank: Super Contributor
timestamp: April 04, 2020, 08:59:48 pm
content: Quote from: pipe2null on April 04, 2020, 07:22:46 pmThe big sensor has a greater response in the near IR, than UV, so it would be a challenge to filter.The current from the small UV-only sensor is tiny, but the data sheet specifies it with a 306nm source, which it has little sensitivity to: only 68fA at 10mW/cm². Going by the response graph, it should be 25 to 30 times more sensitive to germicidal wavelengths, but it still isn't very much. It will be fun designing a circuit to work at such low currents, an ultra low bias current op-amp is a must a lens or parabolic mirror could be used to provide more gain, but the former might be expensive/difficult to get hold of and the reflectivity of some metals might not be as good at such short wavelengths, making the latter difficult to do.

author: pipe2null
author_rank: Regular Contributor
timestamp: April 04, 2020, 11:08:14 pm
content: So... I'm thinking I need to split this into 2 different projects to consider, and then choose one to proceed with, depending on cost, benefit, and likelihood of success building this myself. In either case, I am assuming that the measurements/readings would be obtained with a scope and/or cheap dmm, 'cause that's what I have:Solution 1: Cheapo UVC detector: $30 photodiode + parts for ultra low bias current amplifier (haven't messed with op amps in a looong time)https://media.digikey.com/pdf/Data%20Sheets/Photonic%20Detetectors%20Inc%20PDFs/SD008-2171-112.pdfThe only real benefit I can think of for this is declaring the UVC LED products available on Amazon as scams. Or not? Seems likely, but don't know for sure since nobody's bothered testing them.Solution 2: Germicidal Power "probe": $350 photodiode + $225 BP filter + parts for whatever glue is needed to get a decent measurement using scope/dmmUse 10mm x 10mm active area photodiode:https://optodiode.com/pdf/UVG100.pdfPlus a bandpass filter similar to:https://www.edmundoptics.com/p/254nm-cwl-40nm-fwhm-25mm-mounted-diameter/22476/I could be off my rocker, but I'm thinking you could reasonably measure the actual power of germicidal UV emissions with something like this? Can it be done without a UVC test source with known output (reference) for calibration?Thoughts? Any better alternatives I should consider that hasn't been posted?

author: Someone
author_rank: Super Contributor
timestamp: April 05, 2020, 01:52:26 am
content: Quote from: pipe2null on April 04, 2020, 11:08:14 pmThose ideas still can't measure the output power of the source as:a) its spectral distribution is unknownb) its spatial distribution is unknownYou really need to read some introductory texts on optics and/or spectroscopy and/or radiometry.There are specific instruments to measure irradiance at a target surface, and more specialised tools that apply weightings for specific measures:https://www.intl-lighttech.com/products/ilt2400-uvgi-0You can't just magic something up out of parts unless you understand what the parts do and most importantly, what you are trying to measure. This thread is like the rush of people making radiation measuring equipment after the Fukushima Daiichi accident, you can measure "something" but its unlikely to be either what you think you are measuring, comparable to any specific units, or useful to assess safety.

author: Smokey
author_rank: Super Contributor
timestamp: April 05, 2020, 02:11:43 am
content: Seriously.... just stick to the easy problems like making an open source ventilator!

author: james_s
author_rank: Super Contributor
timestamp: April 05, 2020, 03:00:52 am
content: The easiest way is probably to sniff for ozone, the UVC lamps I have produce rather copious amounts of it. You can't cheat on the spectrum of a mercury discharge, the only corner they could cut on a "fluorescent" tube is to make the envelope out of glass rather than quartz. If it's glass it won't produce ozone so if it does you can be reasonably sure that it's producing UVC. Be careful as ozone is fairly toxic in high concentrations, along with the UV radiation being hazardous to biological organisms. Don't forget to keep your pets from being exposed too. It will also fade and degrade fabrics and polymers.

author: NiHaoMike
author_rank: Super Contributor
timestamp: April 05, 2020, 03:09:02 am
content: Quote from: Ian.M on April 03, 2020, 09:30:37 pmI remember an experiment that involved repeatedly reading an EPROM while it's being exposed to UV. I forgot how much UV was used, but the EPROM was constantly powered during the whole process.Quote from: james_s on April 05, 2020, 03:00:52 amSome UVC lamps are filtered to block the really short ozone forming UV.

author: pipe2null
author_rank: Regular Contributor
timestamp: April 05, 2020, 07:03:13 am
content: In all seriousness, I am REALLY not trying to beat a dead horse.Quote from: Someone on April 05, 2020, 01:52:26 ama) AFAIK (please correct if I am wrong), it doesn't matter if there are 1 or 15 different emitted wavelengths as long as they are all within the germicidal region. If there is emission outside the germicidal range, then it doesn't matter for this application. There is the issue of ozone creation at <200nm wavelengths which is outside of the band pass region of the filter, but for simplicity can leave that one single "measurement" to a sniff check. For wavelengths that get attenuated toward the edges of the band pass region, well, I'm still thinking on that. The intended purpose of the measurement for this application is to establish the minimum W/cm2 I can expect from an off the shelf product that doesn't come with a datasheet, so error due to attenuation that results in a measured value that is lower than reality is on the the conservative side of the line.b) Well... Isn't this an issue no matter what you are using to measure, DIY or NIST traceable light meter? Most (but not all) of the UVC sources that might be useful are cylindrical, so hopefully that will reduce the complexity a little bit. You make a good point though, relating point measurements back to the overall output pattern...Quote from: Someone on April 05, 2020, 01:52:26 amI wholeheartedly agree. If you have any recommendations on a technical ref book on the measurement of radiating sources/patterns/etc, especially if it includes the simplified equations for typical geometries (point samples -> total), I would appreciate it. I ordered a technical reference for UVGI and its application to air and surface disinfection earlier this week. It should have some basics on UVC source performance data, but I don't think it will have much on measurement.Thanks for the pointer to the ILT2400. Yep, that would take care of what I'm trying to do (at least once I get the tech reference info). $3000 is a bit much for short term use, but I found a place that will rent it. $420 for 2 weeks seems a bit steep, and I'll likely need it for longer than that, so the rental price is getting pretty close to the cost of the bandpass filter and fancy photodiode. Hmm...

author: LaserSteve
author_rank: Super Contributor
timestamp: April 05, 2020, 07:59:03 am
content: Check your PMs, Pipe2Null. I just sent you a link to overstock from a reputable optical filter manufacturer.Steve

author: Zero999
author_rank: Super Contributor
timestamp: April 05, 2020, 11:48:17 am
content: Quote from: pipe2null on April 04, 2020, 11:08:14 pmIs there any reason why your application requires LEDs i.e. having many on/off cycles, free from mercury (by the way low pressure germicidal lamps contain tiny amounts of mercury), no glass to shatter etc.? If not, just use mercury lamps. They're much cheaper and more efficient, than LEDs, given the same power ratings.

author: NiHaoMike
author_rank: Super Contributor
timestamp: April 05, 2020, 04:52:10 pm
content: Are there cold cathode or even capacitive coupled germicidal lamps available? The filaments are the main failure points of fluorescent lamps, and with no phosphor to degrade, a capacitive coupled germicidal lamp should last "forever".

author: james_s
author_rank: Super Contributor
timestamp: April 05, 2020, 05:02:21 pm
content: There's no reason one couldn't be made however I've never seen one. Properly cared for cathodes (filaments) can last a very, very long time. If you are going for long life, avoid instant start as that blows material off the cathodes every time it starts. Better electronic ballasts have what's called programmed start, they preheat the cathodes then gently apply the high voltage to strike the lamp, a good quality lamp on one of those can last tens of thousands of hours.I've used electronic ballasts designed for those triple tube compact fluorescent lamps to run small germicidal tubes with good success. I replaced the failed ballast chokes in the ozonator in my hot tub with one almost 15 years ago and it's still going.

author: pipe2null
author_rank: Regular Contributor
timestamp: April 05, 2020, 07:11:46 pm
content: Thanks everyone for the great feedback!Quote from: LaserSteve on April 05, 2020, 07:59:03 amAwesome, thanks! I'm checking it out.Quote from: Zero999 on April 05, 2020, 11:48:17 amMy purpose related to UVC is 2 parts:Part #1) There are a lot of people out there desperately trying to hack together something to sterilize one thing or another. There is a pretty long thread started by a guy who was trying to effectively sterilize the face masks his (medical professional) wife has to re-use. I am not in any way an expert on these things, but I can work to find the right information and post it so those with no other choice but to hack something together might have a reasonable chance at succeeding. I've seen posts where someone says to bake it at 60 degrees C for a while, but I found a study on SARS that required a minimum temperature of 75 degrees, so...As far as the UVC LED products on Amazon go, I have been told by multiple people that it is not possible to produce a UVC LED light product with a useful LED count that can sell as low as $50 or $100. If those products are scams, not only are desperate people getting cheated out of money, but the sterilization they believe is occurring is NOT, so, if they are indeed scams then the continued sales of those products actually promotes the spread of COVID-19. I kinda think that's a bad thing...Part #2) I had a crazy idea to use a powerful enough UVC source to sterilize exhaled air in psuedo-real-time from infected people who need to use CPAP/BiPAP/etc for one reason or another. This includes (possibly healthy) people who normally use CPAP on a daily basis but have stopped due to warnings related to COVID-19 being expelled as an aerosol. Theoretically at least, it might be possible to do this with zero filters, which are in short supply globally. I should have a "textbook" on UVGI for surface and air sterilization tomorrow, so that should have most of the important info needed. The problem is availability of UVC sources with minimal lead time, and which ones might be suitable. I freely admit that it isBass Ackwardto design a "UVC light in a can" aka "bio reactor" based on what UVC source "just happens" to be locally available instead of the other way around. Which brings us back to products currently listed on Amazon. And back to Part #1 since anyone attempting to use UVC for something important has the same problem I'm currently facing.As for the current thread:I would appreciate recommendations on a "technical reference/textbook"that contains the right information to measure the output of UVC/radiating sources, preferably one that contains the "cheat sheet" equations to use for typical geometries so you can calculate total output based on point samples taken at specific positions around the UVC source. Hopefully I will not end up needing it, but there is a lead time so I should order it asap. Worst case it will be a welcome addition to my library. Decades ago, I vaguely recall I got a degree in EE, but after many professional years only on the software side of things... Well, saying that I have a lot of relearning and catching up to do is a gross understatement.

author: james_s
author_rank: Super Contributor
timestamp: April 05, 2020, 07:24:33 pm
content: LEDs are pretty much a non-starter, at least right now. Currently nothing we know of comes close to a low pressure mercury discharge for generating copious amounts of UV. The lamps are essentially identical to conventional fluorescent lamps but without the fluorescent part, or at higher power densities there are high pressure mercury discharge lamps available up into the kilowatts. They are quite efficient at producing UV, one of the reasons mercury vapor lamps have been considered inefficient is that much of their output is UV which is not useful for illumination.

author: helius
author_rank: Super Contributor
timestamp: April 05, 2020, 08:46:43 pm
content: In another thread on UV-C disinfection, a poster mentioned that the base of an EPROM eraser could be removed, transforming it into a shortwave ultraviolet lamp. I have one of the same units, so I did the same.One of the things I noticed is that its ABS plastic housing fluoresces bright green under the UV-C rays. This is at least an indication that the proper wavelengths are being output from the tube. The rated power of the tube appears to be 8 W (the ballast is rated for 2, 4, or 8 W), and at 30% spectral efficiency that is about 2.5 W of UV radiation.BTW, the discussion above about "instant start" vs "programmed start" is good. This unit has "manual start"! The power switch does preheat as long as it is held down, and kicks when released.

author: Zero999
author_rank: Super Contributor
timestamp: April 05, 2020, 08:51:40 pm
content: Quote from: helius on April 05, 2020, 08:46:43 pmIf you have a known good lamp, then I agree the fluorescence of the plastic is a good indication that it works, but plastics often fluoresce at longer non-germicidal UVA wavelengths, so it's not a test to prove an unknown lamp doesn't just produce UVA and no UVC, unless you're sure it only fluorescences under UVC.Quote from: james_s on April 05, 2020, 05:02:21 pmGoogling for electrodeless germicidal brings up a few microwave excited mercury vapour lamp.Quote from: james_s on April 05, 2020, 07:24:33 pmYes go with mercury vapour for UVC. By the way nearly all modern mercury vapour lamps used for visible lighting use phosphors to boost the efficiency and are therefore really fluorescent lamps, even though they're not known as such. This is evident from the fact they're opaque/translucent white when unpowered. See the example linked below:https://www.bltdirect.com/venture-mercury-blended-lamps-delux-mbf-mbfudl-50w-e27?adcid=pla&gclid=EAIaIQobChMInZ_Kh5PS6AIVCPlRCh1EQwIDEAQYBSABEgIr2PD_BwEQuote from: pipe2null on April 05, 2020, 07:11:46 pmHow about a non-electronic solution? You want to test it kills bacteria so how about testing it on some harmless bacteria, such as yeast? Culture a small amount on an agar dish, expose it to the lamp, then see how much it continues to grow afterwards.QuoteThat's not a crazy idea. I like it. There are small UVC lamps available. Something the size of a small neon indicator lamp would be good, but I've had a quick look and couldn't find anything that small. The smallest I could find is a 2W filament pre-heated mercury vapour lamp, which won't be that efficient, but still much better than LEDs. You should avoid lamps that produce ozone, which is bad for the lungs, unless there's some kind of filter to remove it.https://www.amazon.co.uk/GTL-2-Screw-Germicidal-Light-GTL2/dp/B06ZZ8GH24QuoteSorry, I can't help you there. I'd just go with data sheets. If you're going to make enough of them, it might be worth talking to a manufacturer, but I expect they'll be very busy, given the current crisis.

author: james_s
author_rank: Super Contributor
timestamp: April 05, 2020, 09:07:16 pm
content: Quote from: Zero999 on April 05, 2020, 08:51:40 pmYes I'm well aware of this, there is a long history to phosphored mercury lamps, you can see the reddish or pinkish glow when they first start up before they warm up and appear white. The phosphor is not perfect though, only some of the UV is converted into useful light and the phosphor itself does absorb some visible light as well. You can be fooled too, I have at least one inexpensive Chinese mercury vapor lamp which is printed with the /DX (deluxe white) suffix but the coating is only a diffusing powder, it does not actually fluoresce.The best lamp related website I know of iswww.lamptech.co.uk. It's an excellent site all around IMO, very good information density, clean layout without any scripts. Lots of good info without any fluff.