Measuring UV-C For About $5

Looking to sterilize something? Give it a good blast of the old UV-C. Ultraviolet radiation in the shortest wavelength band breaks down DNA and RNA, so it’s a great way to kill off any nasties that are lurking. But how much UV-C are you using? [Akiba] at Hackerfarm has come up with the NukeMeter, a meter that measures the output of their UV-C sterilizer the NukeBox. It is built around a $2.50 sensor and a $3 Arduino.

The NukeMeter is built around a GUVA-S12SD UV sensor breakout board. This sensor is really designed for UV-A detection, but a quick look at the spec sheet revealed that it is sensitive to UV across all of the bands. So, it can be used as a UV-C sensor if you know how sensitive it is to this particular frequency band.

However, the sensor is not that sensitive to UV-C light, so [Akiba] had to do a bit of minor surgery on the circuitry that surrounds the sensor to tweak the output. The sensor was designed to measure relatively low levels of UV light (such as sunlight), and now they are blasting it with a shedload of radiation, so they have to effectively disable one of the op-amps that normally scales the output up, which involves replacing a couple of resistors. That’s a bit of a pain to do with surface mount components, but it is doable with a steady hand and a small tip soldering iron.

Next, an Arduino takes the voltage output of the sensor and converts it into a light level. The mathematics of how this works are all well detailed in the post, but it isn’t complicated, and the source code is here.

Using this, [Akiba] was able to measure how the lights performed, how quickly they warmed up and how much the light level varies along the length of the fluorescent tube.

One caveat to bear in mind here: [Akiba] designed this to measure the output of the low-pressure mercury vapor lamps they are using at Hackerfarm, which output a very narrow frequency band, peaking at 250 nM. This design would not work for a more broadband output or for one which mixed UV-C with UV-A and UV-B. For that, you would need a more sophisticated design that would probably cost more than $5.

SAFETY NOTE: Don’t mess with UV-C light sources unless you have a good idea of what you are doing and are sure that the light is contained, e.g. in a sealed box, maybe with interlocks. Remember that you also rely on DNA, and inadvertently zapping your own DNA can cause all sorts of unpleasantness.  

89 thoughts on “Measuring UV-C For About $5

  1. I was wondering about creating own sterilisation box, i have a toddler so it would be neat to sanitise toys and anything that mnight end up in her mouth curently we use biling water and alcohol based sanitiser but leaving things in UV box for night would be better- of course it would have to have locking mechanism and power cut-off if lid is lifted probably over engineered with backups you know toddlers and their tiny hands are good at opening things they arent supposed to open.

    1. Nice idea but, please beware as many bacteria hide in fats and oils (they can move into them) – the fats of which attenuates UV-C to a fair degree. Also beware that a virus, depending on conjunctive compatabilities with other microbes can embed in bacterial membrane fluids reducing viral degradation and which also offer some protection from UV as well.
      In the food industry high intensity pulses of white light offer useful local surface (flash) heating to kill all sorts of microbes, so UV-C in conjunction could then offer a higher probabilistic approach to sterilisation with far greater confidence and more so with feedbacks of various types.
      Then of course one would be tempted to set up a small microbe lab with Petri dishes and incubator, reagents with such things as various formulations of peptone waters, great fun ;-)

      1. Interesting the food industry model – what kind pulses of white light are they, what range? Like stroboscope lights? I wander if that is building enough temperature on the surface to degrade the bacterias or viruses

        1. It’s a very tightly controlled feedback industrial process misyly designed for assembly line production speed. Ie Very high intensity non infrared across wide visible spectra shone on surface regions (with timing control for depth so as not to significantly affect texture or other related food quality issues) targeted for are ranging sterilisation with real time feedback of localised heating effects. Ie visible light is absorbed by the surface of the food, heats up very rapidly, emits infra red for feedback controls which dynamically adjusts how long the bright white light operates for. Optional to repeat so could be viewed as stroboscopic after the event but, not as a design requirement per se.

          For various food types in a high speed production assembly line the degree of visible light heating assessed via sample testing initially as part of the production design for a specific food product and for several criteria; antibacterial antiviral efficacy, food colour changes, texture changes, chemical composition changes and whatever else could impact food quality, sale-ability, shelf life etc which doesn’t reduce sales but, which reliably sterilised the very worst bacteria as a start eg spore former bacteria such as bacillus, clostridium and of course all viruii, fortunately viruii generally far more fragile to flash heating than bacteria. It’s a comparatively sophisticated balancing act tuned to specifics taking into account a fair number of commercial vs safety criteria…

        1. UV-C the higher frequency (shorter wavelength) is effective and depending upon its intensity eg if higher reduces time for viral (and other life form) damage but, you don’t want UV-C on or near your pets on skin or especially anywhere near your eyes. Also damages insects eg pollinators. Also be careful with artificial UV-C sources as reflects well so wear protection eg in labs etc.
          Causes skin cancer, eye damage in fact all life eventually degraded unless deep in water though some hardened bacteria surprisingly resistant.
          We get a little from sunlight, places like Australia have high skin cancer rates from UV-C further south especially when closer to Antarctica ie our southern ozone hole still not recovered to what it was decades ago though even fully a ‘recovered’ ozone levels there or anywhere are not 100% protection against UV-C as some would still be getting to Earth’s surface anywhere on the planet.

    2. The problem with that is that most toys have a lot of plastic and plastic becomes brittle from UV exposure, so that could lead to swallowable bits breaking off. I’d recommend sticking with your current washing regime.

    3. In addition to regular physical cleaning and cycles in the dishwasher (for those that can survive), I have set up a small ozone box for disinfection of baby/toddler toys. I’ve been thinking about adding a UV-C light as well. Ozone seems to work very well to get into all the nooks and crannies where mold likes to grow on outdoor toys.

      1. Just be aware UV-C will break down the plastic, first by fading but then breaking down the polymer itself and cracking/powdering on the surface. Just think of what happens to plastic left out in the sun for a long time, but on an accelerated rate. You could pump ozone through an aquarium air stone in water and make ozonated water which is a good sterilizer. Not sure how you’d do this without the specialized generator though designed for water.

      2. Ozone will get into nooks and crannies but is an intense oxidizer and will destroy rubber and plastics very fast. I know people with CPAP machines and they sterilize them daily with UV. The manufacturers void warranty if you do it with ozone. Lots of plastic and rubber in those med devices. Ozone does work wonders it getting out odors though. Just have to use the right methods for the right applications within constraints and consider the trade-offs.

  2. The diode chip itself may be sensitive down to UV-C but you will probably get pretty terrible attenuation a that wavelength and there is a pretty good chance the resin will solarize and change as you use it. You can get photodiodes that are windowless that will work down there accurately and be pretty stable. Though I am betting they are not cheap. We used them on some of the laser pulse detectors at work.

    1. This is absolutely true. I am involved in UV-C research and we tried using a breakout board with these sensors and found the output to be unstable over time and the response was not systematic, rather random. In short, this is not a good option for UV-C. There are other sensors that are solar blind and accurate for UV-C.

    2. The same company making the sensor cited here makes a UV-C band device. Time for someone to write a new updated article and an opportunity for someone to make a new sensor board. Digi-key sells the chip for $18. It’s more than $5 but not worth being a cheap skate if you are trying to kill a health impacting virus and messing with potentially dangerous UV-C light, right?

  3. Would it be possible to make breathing equipment that could be carried in a backpack using uv-c light to sanitize the air that passes? Like a long tube where air is sucked throught with a lot of uv-c leds on all sides, powered by a battery pack.

    1. In theory that should be doable, start it off with a filter to catch particles large enough to occlude the light. After that it all comes down to a balance of tube-length to brightness and battery capacity.
      I think that 2,5m should be long enough, so you could get that with a 20cm diameter coil with 4 loops.
      UV-based water filters use about 40-80W so an air-filter should in theory require less, lets say 25W. You can easily get 50Wh with lithium batteries without taking up too much space.

      So yeah I’d say it’s quite doable, as long as my assumptions are correct. Though it might be more convenient to just use a scuba tank. Using a UV-filter might also cause the air you breathe in to be VERY ionized, which I think isn’t healthy.

      1. Yes, thats true. So not really a good idea, only if you can de-ionize the air before inhaling it. I guess filtering the air by letting it pass through a filter with water (like the one on a compressor where the water catches all particles) would be a better and easier option. The filter could then be constantly bombarded with uv light so it kills whatever is caught in it.

        1. I was going to reply that UV-C LEDs also don’t exist but I found out they actually do, but aren’t very efficient and are obscenely expensive. You should look specifically for UV lamps designed for HVAC systems that block the lower UV-C wavelengths that produce ozone. Ozone can be very harmful to your lungs, essentially like chlorine gas which would be extremely counter productive. Here’s some info:

        2. It’s not the ionization of the air that will get you; it’s the ozone. If you wanted to build such a thing you would need to use some catalytic process to eliminate the ozone, which is really quite bad for you.

          1. I’ve read about using titanium dioxide in conjunction with UV-C to catalytically eliminate even more chemicals. I’m not sure if this also helps break down some of the ozone. Something I’m interested to try and build though; I couldn’t find any sources of the TiO2 pellets that were used in the study I remember seeing, so I ended up buying some titanium mesh, which I hope to just oxidize by heating to the right temp, hopefully producing a layer of TiO2 on the outside surface. Not sure how durable this is or if this process even makes sense. But that’s what experimentation is all about :)

          2. Actually, while it makes sense to look at the process of ionization – which is in truth, not harmful to humans or strands of RNA, DNA in the instant of ionization – the result of that ionization is Ozone. If I were teaching a flow diagram of UV radiation for sterilization/sanitation, I would include such a flow chart showing each potential bulb’s process of producing the necessary wavelengths. And immediately after the box with the wavelengths produced, I would have a question tree “Ionize Oxygen” and the yes answer would go to a box saying “Find another source if in a residence or around children & susceptible people & animals as Ozone is hazardous in quantity and in duration of exposure.” If the answer is no – then I would have the UV-C wavelength question tree following and if it isn’t in the 250-260 nm range, I would (or not stable around the 254 nm wavelength touted as most genetically disruptive), I would quash that option as well.

            You see, while Ozone is not Ionization – therefore you are right – Ozone is the product and so, like a mobius strip, Ionization results in Ozone so you really can’t separate the two out without sounding sophomoric or professorial. In medicine we may ‘split hairs’, but when something is harmful, we call it like it is.

      2. I’m trying to Google the maximum length of an air hose, but can’t find a suitable reference.
        Pretty sure there’s a length limit – if you inhale AND exhale via the same tube, you never get fresh air.

        Logical solution – exhaled air vents via a different path.

      1. Some bulbs generate ozone and some don’t. If the bulb emits light < 240nm, it will produce some ozone. The most ozone is produced around 185nm which most germicidal bulbs block.

    2. UV-C lights interact with Oxygen producing Ozone (~0.5%), which is a powerful oxidant that is not safe to breath. Long term effects of even very low concentrations of ozone would be permanent damage to the upper respiratory tract, the lungs and ultimately early death from lung disease.

      You would either need to filter through something that is expendable (needs continual replacing ¥¥¥/€€€/$$$/£££) that neutralises this powerful oxidant, while still leaving all oxygen, or add a delay between UV-C exposure and the air entering lungs of about ~4 hours for this highly corrosive, unstable molecule to slowly breakdown into more stable Oxygen molecules.

      1. I wouldn’t want to breathe straight from it, but for room filter for clearing ozone, I might think of passing it through a bunch of steel wool, with a coffee filter after it to catch rust dust and fragments of steel. Would need continual monitoring to determine when it needed replacement. Depends how much ozone you were making, I’d consider that style more as a bit of insurance against low amount rather than one that can get rid of a real high ozone concentration.

    3. There is also the issue that it will take time to kill the virus. i.e. the air path under UVC has to be sufficiently long before you can be sure that all/most virus are destroyed.
      >In general, many research reports suggest that it will take about 10 to 15 minutes using a standard UV bulb. Personally, I would increase the time to a minimum of 30 minutes unless you know the energy output of the bulb at the distance where the surface sterilization is required.

      tl;dr Either you have some UVC source so powerful that it kills instantaneously (battery won’t cut it and your lungs will be fried by ozone) or an air path of hoses for 15+ minutes. This idea isn’t portable.

      1. It is not accurate to claim a time. It is a dosage, so it’s intensity integrated over time, or dosage = J/cm^2.
        Bulb power is watts, which is J/second. So you have to know your bulb wattage, then use a coefficient to get the UV-C band power from that, which is typically 0.3 to 0.4 for low pressure mercury UV C bulbs. With that, you have a compute the surface area this UV-C specific power will distribute across. Valid approximation is to know the distance from the bulb to your object ( r ) then compute the surface area of a sphere where the light spreads across: 4*PI*r^2. So dosage on the safe side would be:
        dosage = exposure_time * bulb_power * 0.3 / ( 4*PI*dist_to_object^2)

        Then solve for exposure_time:
        exposure_time = dosage * 4*PI*dist_to_object^2 / (0.3 * bulb_power )

        Known effective 99% UV-C kill dosage for SARS-CoV-1 is 0.1 J/cm^2. Estimate that SARS-CoV-2 is at worst case twice that at 0.2 J/cm^2. So if you object is 20 cm away from the light and you are using a 13w bulb:

        exposure_time = 0.2 J/cm^2 * 4 * PI * (20cm)^2 / ( 0.3 * 13 J/sec ) = 258 seconds

        So 5 minutes (300 seconds) with a 13w UV-C lp mercury bulb at 20 cm distance would be plenty. If you over expose you will have the trade-off of more quickly destroying materials that are subject to UV damage.

  4. One of the companies that makes UV sterilization lamps (UVDI, which Clorox rebadges and markets under its own name) also sells UV sensitive exposure metering cards. They’re pretty expensive though, $560 for 50.

    “Clorox 29-6053 Dose Verify UV-C Surface Dose Verification Cards”

    1. That definitely sounds like a 50$ product with a 500$ certificate. On the plus side, if I’m not mistaken you should be able to reuse metering cards as they shouldn’t go off unless you fuck up anyways.

  5. My wife was leaving amazon boxes on the front porch for a few days and other things like mail and groceries, so I made a UVC kill box to put that stuff in. I wondered if the UVC bulbs were really UVC and how effective they really are. Love to be able to test this. any ideas? with covid-19 it is one of our lines of defense.

    1. A basic test would be does it shred the DNA of any living organisms exposed to it, which is what UV-C does best breakdown molecular bonds. It is why it is so dangerous.

      Does it kill bacteria growing in a home made UV transparent Petri dish (day old soup left in “fresh” air).
      Or is kill bread mold ?
      Or …

    2. UVC LED won’t cut it. You’ll need a germicidal bulb (google for that)

      Based on wy experience of EPROM erasers that uns on UVC
      It would have a quartz casing, with a filament coated with mercury. When you light it up, the filament heats up and you’ll eventually see a discharge grow instead. It’ll smell of ozone around it after a while.

          1. And how do you think it generates Ozon? If with a generator you would see it if taken apart. If by uv light, then why use some that are under 200nm (to generate Ozon) and not some above. It critique doesn’t make sense and is unbiased.

          2. I’ve been trained by an unfortunately large body of personal experience to not trust claims of low cost Chinese products. No criticism against the people, and sometimes the sellers are honestly not knowing they’re selling fakes. I deal with batteries a lot that are fake, and plenty of false claims on other electronics. This particular lamp just seems very unlikely given all the other real UV-C LEDs I’ve looked at. I highly doubt they managed to make both a 10x cost decrease and 10x performance increase without the rest of the industry catching on ;)

          3. @Justin Kenny — you nailed it. True UV-C LED’s are not cheap. I impulsively got one of those bulbs from Amazon, but then decided to try to verify their product and do some research. I emailed the sellers — got nothing, no reports, no manufacturer name or part, nothing.. I asked for a full refund and they only refunded 1/3 of their price in hopes that they don’t get caught. I had to go though Amazon customer service to get the seller to refund the full amount and I’ve been trying to flag all of these unfounded claims by these sellers who are obviously just taking advantage of the uncertainty that is all over the world.

    3. thought for detecting/measuring uvc – smear a regular phototransistor with something that fluoresces in uv (like a highligher marker) and put it behind a filter that blocks anything except uvc.

      1. I think finding the UV-C pass (or high pass, in frequency terms) filter would be quite difficult or exotic. The opposite is easy however. Maybe a subtract sort of function, with one identical sensor setup with a UV-C block filter, and one without, and take the difference in power between the two.

  6. I worked on trying to build the cheapest (but still reliable) UV index meter and found it frustrating you can buy a whole board from China with a GUVA-S12 for less than just buying the sensor. Roitner-Technik doesn’t offer much of a price cut until you get way up in quantities and even then it’s not close to the China price. I found you can use a UV LED instead and come pretty close to the GUVA response. You get less output, so you either have to adjust the op-amp gain or do it in code, and of course it isn’t calibrated. I also tried to omit the op-amp entirely and just read the discharge time after reverse-biasing the diode, but this varied way too much to be usable beyond maybe a low/high reading.

    Here’s the project:

  7. For those of you who want to play around UV C lamps…

    Youtube: Awesome flesh-burning death lamp (Germicidal UV E27 socket):

    There was an event in Honk Kong 2017 where the organizers have unknowingly used UV C lamps, because they look nice. The visitors later suffered from sunburn, lingering pain in their eyes and a heightened sensitivity to light, in what appears to be a case of ultraviolet light exposure. Source:

    1. I have seen a few variations on this theme and generally none of them have enough energy to actually kill anything. And it looks like the leds are limited life anyway so just use a fluorescent lamp.

  8. Lots of responses some with great knowledge and some with little knowledge. The UVC light I used is a bulb the type used in HVAC to kill mold and viruses. UVC is very dangerous and that is why I put it all in a case where you cannot see the light. My only question was I don;t trust chinese providers and how can I test it that it is in the correct wave length. I don;t care about ozone or not it is in garage away from people. erasing an eprom makes no sense to me I think they will be erased by any UV not just UVC so that doesn’t make sense for a test.

    1. From the wikipedia entry on eproms:
      The recommended erasure procedure is exposure to UV light at 253.7 nm of at least 15 Ws/cm2, usually achieved in 20 to 30 minutes with the lamp at a distance of about 2.5 cm.

    2. if all you care about is UV-C for killing stuff, just let it run for a while and then smell the air…ozone has a very distinct smell even in very low quantities and only UV-C will make it out of air…

    3. I bought a UVC light bulb end of February and bought agar petri dishes to swab something before and after applying the light from the light bulb. The amount of bacteria after 2 mins of exposure was definitely much lower, almost nil, so I’m pretty sure it works.

      I’m now trying to figure out a better way of using the light without burning or blinding myself. I bought goggles that protects from UV light (ANSI Z87.1+). I also bought a glass aquarium because glass is supplsed to blocks UVC light as well. But I have no means to detect whether or not the UVC light is actually being blocked (maybe the glass isn’t thick enough, maybe it’s the wrong type of glass, etc). I’ll probably resort to petri dishes as well but it’s a pain in the ass.

          1. Thanks that is what I read also 80% reflective. My box is enclosed large enough to have groceries in it and has 4 of the UVC lights at different places with all the sides lined with foil. I know it is not perfect but better than leaving the boxes on the porch for days. Everything that comes into the house, mail, amazon package, groceries goes into this box for 15 minutes which is over kill.

          2. Calculating direct exposure is pretty straight forward but what about the sides of items that get indirect exposure? I figure with losing 20% each time the UV bounces, we get 4 bounces (0.8+0.6+0.4+0.2 to expose the areas that don’t get direct exposure to the light. I am not sure how to work that into an exposure equation but it seems indirect exposure in a foil lined chamber is stronger than direct exposure from the bulb. And, of course, surfaces that get direct exposure from the bulb also get bouncy light so the foil is magnifying the effect of the UV light.

  9. The manufacturer of the UVA sensor also sells a solar-blind UVC sensor in an equivalent form factor. Why not just use the UVC sensor and skip all of the associated trouble with trying to adapt a UVA/visible sensor?

  10. I have heard and read a wide range of exposures for killing Covid-19 and SARS. I have been using this study, which isn’t perfect but seems close to our application:

    “Inactivation of viruses on surfaces by ultraviolet germicidal irradiation”,

    They say, “For 90% viral reduction, the UV dose was 1.32 to 3.20 mJ/cm2 for ssRNA,” … “For all four tested viruses, the UV dose for 99% viral reduction was 2 times higher than those for 90% viral reduction.”

    Covid-19 is an ssRNA virus so 99% dead takes 6.4 mJ/cm2 or 64 J/m2 of UV-C exposure.

    I am hoping to find good info so please comment if you have other sources and different data.

  11. One video with partially useful info, mentioned exposing groceries to UV. When this was done to green bananas they got “sunburnt.” So, I tried that with some fresh bananas and a strip of aluminum foil across a few. 40 minutes and no sunburn. So, the supposed 60w, UV-C led bulb was actually just a bright blue light. No UV-C. Germs/viruses/bananas doing fine. Me, not so much. The intensity of the blue light did briefly mess up my color perception. No ozone smell. Grrr

    1. my bananas did turn brown with only a 10 minute exposure. but it took a day or two for them to turn brown not instantly. the non exposed bananas did not turn brown. plus the uvc exposed bananas showed lines of the peel that did not turn because those parts were covered and protected from the uvc light

      1. I have a UVc sterelizer, just trying to find a way to test if it’s actually working. So far the unit doesn’t darken the lenses I have just asking around if they theoretically should. I don’t know if I have the skills to build the Arduino unit above but that could be an experience haha

        1. Big Clive on Youtube has done a series of videos recently on testing UV devices (and debunking fake LED ones), I recommend you watch it. He uses an Adafruit UV sensor to test his, and by putting a piece of normal glass in between the UV source and the sensor you can get a sense of how much UV it is emitting. If it’s got a clear glass tube, it’s most likely a real UV source. If it’s got LEDs, and they don’t have a brass casing and quartz glass window, it’s 99.9% likely to not be a real UV LED.

  12. from BrianD :
    ” Known effective 99% UV-C kill dosage for SARS-CoV-1 is 0.1 J/cm^2. Estimate that SARS-CoV-2 is at worst case twice that at 0.2 J/cm^2. So if you object is 20 cm away from the light and you are using a 13w bulb etc etc ”

    this is absolutely wrong…
    15w lamb (with x 0.3 irr. power) , at 20 cm distance / 5 min, aint gonna do nothing to c-19 at all…
    it would probably work at 2cm …
    perhaps 15 min is more suitable…

    please correct your post. u are going to get people sick…

    above post from Alan Kk is more accurate information.

    “Covid-19 is an ssRNA virus so 99% dead takes 6.4 mJ/cm2 or 64 J/m2 of UV-C exposure.”

    i have meter(s) test strips etc , and i have been testing all sort of UVC lights, with distance/power combination setting etc!

  13. Great article – your link takes us to the UV-A sensor in SMD 3528 package, however the same company also advertises a UV-C sensor in an SMD 3535 package. Not the exact same size, however the critical diemnsion of 3.5mm solder end to solder end remains the same. Do you fancy trying that modification? I’m after a simple relay trigger that UV-C is present so a 5VDC relay should do trick :-)

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