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saywherefore t1_jckuspk wrote

Sunlight can be a useful tool for sterilising things. For example you can sterilise water by leaving it in bright sunlight in a plastic bottle. Or you can put a mattress in the sun to reduce the number of mites in it.

Think about how sunlight bleaches fabrics and other materials that are left out for an extended period - that is the same mechanism at work.

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WesPeros t1_jckv5kr wrote

UV light from Sun does damage many things, but keep in mind, most of the Sun's UV light gets blocked by the Earth's ozone, only small fraction reaches the surface. Human made radiation is much more intense than the one received by the Sun

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frustrated_staff t1_jckwp2x wrote

It's about intensity and time. UV radiation used for disinfection is very high intensity and short duration. Thus makes it useful for disinfecting at scale. UV from sunlight is, however, low(er) intensity, long duration, so, while it can disinfect, its not good for doing so at scale. You'd probably be surprised at just how "clean" a sidewalk is, in all honesty: if not exposed to the sun's rays, it'd be a lot less "clean", which is not to say that its clean at all, just that it would be a lot worse without the sun

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jon_hendry t1_jcl0acq wrote

Because it takes time, and additional fresh bacteria and whatnot can land on the exposed surface all the time.

I suspect that even 1/8th of an inch under the surface there would be a much higher bacterial and viral load because of the moisture and being shielded from the sun.

A bit of sidewalk under, say, a quartz glass dome would probably be pretty much sterilized after a few days in the sun, from UV and heat.

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redligand t1_jcl1u6p wrote

Replying to Doormatty (#2,254,478)

Solar disinfection is used effectively in remote communities in the developing world. The effect is amplified by leaving the bottles on reflective surfaces. It's not great and it takes hours but it is effective.

See here for an academic source: https://link.springer.com/referenceworkentry/10.1007/978-3-319-70061-8_125-1#:~:text=Solar%20disinfection%2C%20or%20SODIS%2C%20refers,at%20least%206%E2%80%938%20h.

Wiki: https://en.m.wikipedia.org/wiki/Solar_water_disinfection

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Foxs-In-A-Trenchcoat t1_jclazfo wrote

UV irradiation works by ripping apart DNA, which then kills microbes. This is also how it gives you skin cancer. Organisms have evolved ways to prevent and repair this DNA damage with varying amounts of efficiency. A bacteria called Deinococcus radiodurans is the most efficient.

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KnoWanUKnow2 t1_jclfzmv wrote

It does.

But mane-made light is more effective because it is more powerful. Our atmosphere blocks a lot of the sun's UV rays. Also organisms evolved with sunlight, so they have developed mechanisms to resist and repair the damage.

But enough sunlight will kill most microorganisms.

However, your skin has pores. Sidewalks have micro-fissures. There are places where microorganisms can hide from direct sunlight.

So the sun will deplete their numbers, but won't eradicate them.

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ThisTooWillEnd t1_jcljs8p wrote

Replying to saywherefore (#2,254,264)

Importantly, the water must be very clear for this to work. If you just put some dirty lake water in a bottle and put it in the sun, the water will still be both unclean and full of life. Filter first, then UV treat.

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mook1178 t1_jclo52f wrote

Replying to KnoWanUKnow2 (#2,255,485)

>But enough sunlight will kill most microorganisms.

I have read studies that homes with open window curtains during the day actually have less bacteria and mold. UV sterilization was their reason why.

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ProfessionalDaikon16 t1_jclpxfi wrote

When we use UV radiation it isn’t blocked by anything and hits the bacteria directly. After about 15-20 minutes the DNA is too damaged to allow the bacteria to replicate and thrive. The UV radiation we receive is mostly blocked by the ozone layer so most of the energy isn’t enough to do enough damage. If it could do the type of damage you’re inquiring about, life wouldn’t be able to survive at all.

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echawkes t1_jcls73x wrote

The frequency of radiation used to sterilize things (like operating rooms in a hospital) is in the UVC range. UVC light is completely blocked by the earth's atmosphere: the UV light you are exposed to on the earth's surface is UVA and UVB.

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PerpetuallyLurking t1_jclt72k wrote

Well, we keep touching them. That doesn’t help. Neither would nighttime. Even if the radiation was consistently strong enough to sterilize the sidewalk, as soon as someone walks on it at nighttime, you’ve got bacteria waiting for morning. Never mind all the northern sides of buildings that don’t see direct sunlight.

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KoalaGrunt0311 t1_jcm4e2o wrote

UV is denoted in at least 4 different wavelengths: A, B, C, and Far C. UV lights for sterilization purposes are designed to put out UV C at a specific measurable distance at a large enough intensity to disrupt the DNA in bacteria and virus.

UV C at this intensity is not safe to be directly in contact with, though glass does limit how much UV C passes through. Depending on the size of the room, UV disinfection lights need to be ran multiple times in different positions because of shadows and distance. They're really only good for about 8 ft wide areas.

Far UV C is in trial phases and is a specific wavelength at the end of the UV C range that is both safe for skin exposure because it only affects the top layer of the epidermis, which is already dead, while at the same time being more destructive to the baddies to the point of being considered safe to treat surgical site infections or being built into normal light fixtures.

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SGBotsford t1_jcm4op9 wrote

You can. Take a dirty dish, wipe it clean with paper towels, then set it in direct sun for 20 minutes.

You can investigate how well this works by first creating a bunch of culture dishes. Jar lids set on a cookie sheet work ok, cover the sheet with cling wrap. Fill the lids with jello made according to directions, but add a half teaspoon of water soluble garden fertilizer to the batch of jello. Miracle gro is great.

Boil your lids before filling them. Bleach the cookie sheet.

Divide your lids into 5 groups:

Group 1: Using a clean Q-tip, draw a line on a culture plate. If doing multiple plates, use a fresh end each time.

Group 2: This time use dishes from the dishwasher. Rub the q-tip on the freshly washed dish then on the culture plate.

Group 3: Like group 2,but dishes from the cupboard.

Group 4: Dishes that you ahve "sun washed"

Group 5: Your kitchen floor. 'cause, why not?"

​

Put the cling wrap over the tray and set it somewhere warm Top of the fridge is out of the way.

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TX_B_caapi t1_jcm646v wrote

We’re really good at finding the specific wavelength and intensity to denature nucleic acids at a specific distance. If you brought a filthy object close enough to the sun to replicate our little monkey toy’s intensity at that wavelength, the object would most certainly be cleansed.

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Jealous_Distance2794 t1_jcm67mk wrote

UV from the sun is UVA (320÷400nm) and UVB (280÷320nm) which are, especially UVA, less effective for disinfection than UVC wich doesn't reach earth surface as it is absorbed by ozone. UVB can still disinfect but needs much more time than UVC, as in water disinfection https://en.m.wikipedia.org/wiki/Solar_water_disinfection but since its less effective it requires at least 6 hours, while UVC only takes seconds Wastewater Technology Fact Sheet: Ultraviolet Disinfection. Reason for this is that DNA, the target molecule of UV, has peak absorption in the UVC band at about 260nm and that's close to the 254nm emitted by germicidal lamps https://www.bmglabtech.com/en/application-notes/uv-absorbance-dna-quantitation/

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One_Planche_Man t1_jcm69jz wrote

Remember that nature is constantly moving. Dirt, debris, and bacteria move into an exposed area faster than it can be sterilized. For this to work, you have lay something out for a long time and have it not be disturbed, which simply doesn't happen in nature. Also remember that your skin is constantly touching things and excreting moisture and oils.

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RareBrit t1_jcmcq8x wrote

It’s something that’s known and studied in the earth sciences, particularly environmental microbiology. For example on a sandy beach that has been contaminated by raw sewage the sand that has been exposed to sunlight the longest will have a faecal bacteria count lower than that which has been exposed the shortest period of time. A properly collected and processed set of samples can therefore be used to support a prosecution.

As an aside most bacterial contamination on cleaner beaches comes from dogs, so yeah, clear up after your pooches please people.

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CarneDelGato t1_jcmefde wrote

Replying to WesPeros (#2,254,283)

> Human made radiation is much more intense than [the radiation from] the sun

I assume you mean for the sake of using it as disinfectant. I was in San Juan this week and I’m reasonably sure my sun burns are not from human-sourced radiation.

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Fskn t1_jcmfee3 wrote

Replying to CarneDelGato (#2,257,392)

For the sake of anything

U.V from the sun is inherently filtered out to a very large degree by the atmosphere, you cant get around that on the ground.

U.V we generate with whatever technology is only subjected to what we decide it to be.

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Oudeis16 t1_jcmoiig wrote

If fire cooks food, why isn't my steak grilled if I wave it over a candle?

If sound can damage eardrums, why am I not deafened by the pitter-patter of rain?

If alcohol kills germs, how can I get sick when I'm drunk?

There's an application of UV that will sterilize. That doesn't mean the simple existence of any kind of UV will fully sterilize all things.

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nriabko t1_jcmq3fm wrote

There are more UV photons per unit area in artificial UV versus solar. UV kills living things because it breaks apart DNA molecules (specifically, it creates thymine and cytosine dimers which prevent DNA transcription and replication and create mutations in the sequence), and the cells die if they sustain enough damage, and artificial UV is so concentrated that it does this much more quickly than the sun, since cells do have the ability to repair DNA damage. It’s like the difference between playing catch with your friend or having the whole class throw dodgeballs at you all at once.

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purpleoctopuppy t1_jcmr0ik wrote

Replying to TinyDemon000 (#2,257,798)

UV Index of 14 is 350 mW/m², a UV steriliser bulb I found online is 28 μW/cm² which is 280 mW/m² ... huh, those are pretty comparable.

(The bulb is measured at 1m, so in practice it'll probably be 16× stronger or more, but still I wasn't expecting comparable orders of magnitude. Also note different UV wavelengths)

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Ausoge t1_jcmuezg wrote

Replying to joyamazingpinoy (#2,258,098)

That will probably be more to do with moisture being able to escape - with open windows, your house will be a lot drier than if you keep them closed for weeks at a time. You wouldn't need to open windows to get the UV effect, just your curtains.

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brad_y t1_jcmuzj2 wrote

I see a lot of correct comments here. I work in the UVC disinfection industry and the best way I describe it to people is basically the Sun produces UV-A, UV-B, and UV-C. Because of C’s wavelength, it never makes it through earths atmosphere, thus nothing on earth has a resistance to it. It’s pretty cool how UVC has been used since the late 1800s to help with outbreaks and now it’s used in almost every operating room to quickly disinfect in between surgeries to prevent hospital acquired infections. Hope that helps!

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KoalaGrunt0311 t1_jcmwzus wrote

Replying to JonseyCSGO (#2,258,085)

I forget the full measurements for UV-C. I want to say UV-C is between 280 nm and 200 nm. After investigating, it looks like Far C is 222 nm with filters set for safety purposes at 233 nm.

Columbia University is the originators of the Far UV C concept and studies. Here's some starting research points.

https://www.cuimc.columbia.edu/news/new-type-ultraviolet-light-makes-indoor-air-safe-outdoors

And they have their technology licensed to USHIO.

https://www.ushio.com/product/care222-filtered-far-uv-c-excimer-lamp-module/

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purpleoctopuppy t1_jcn4ra3 wrote

Replying to fkenthrowaway (#2,258,267)

Yes definitely! That's why I mentioned different wavelength: sunlight is not an adequate replacement for a sterilising bulb.

I was just expecting it to be thousands of times stronger integrated across the UV spectrum that I was surprised, as I wasn't expecting to need to take that into account at the start!

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Daddyssillypuppy t1_jcn80im wrote

Replying to Historical_Tea2022 (#2,258,217)

We have light 'spf 15' ones but they're mostly face lotions and such that are meant to be worn under makeup or indoors.

For outdoors we have spf 30 or 50 generally. After 50 the protection doesn't increase much so spf100 isn't much better than the 50.

I know our sunscreens have to go through testing and meet regulations but I assume the rest of the world does that too.

We have a long long running TV add campaign called Slip, Slop, Slap, Seek, Slide.

Slip on a hat, Slop on sunscreen, Slap on a hat, seek shade, slide on sunglasses.

Edit- Slip on a Shirt

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palbertalamp t1_jcnh2rj wrote

Replying to Daddyssillypuppy (#2,259,030)

>Slip on a hat, Slop on sunscreen, Slap on a hat, seek shade, slide on sunglasses.

HA. Only two hats.

Amateur.

I too Slip on the first hat, Slap on the 2nd, but the trick is to Scrunch on the third hat to hold down the slippy slappy first two hats.

But then, I only go outside at night, so I keep losing hats in the dark , unless there's moonlight .of course

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IthinkIllthink t1_jcniiw4 wrote

Thank to everyone contributing.

I am going to use your concepts for a NDIS appeal at the AAT. (Australia).

The NDIS will not fund a path to a blind client’s clothesline (multiple falls) - “we only find 1 access path to a dwelling, and a clothesline path isn’t access”.

She is also immunocompromised and uses the Sun to sterilise clothes a sheets. “Why doesn’t she use a clothes dryer and a dehumidifier”.

This sub is gold. Thanks.

Edit: fixed typo, and added Australia

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gauchocartero t1_jcniwft wrote

Replying to Historical_Tea2022 (#2,258,217)

If you want to experience the most loving solar embrace visit the Altiplano in December and play a football match at 3500m! The sun is exactly directly overhead, and the UV index is over 20 every day. The crazy thing is, it’s the craddle of South American civilisation.

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wrechch t1_jcnp71z wrote

Replying to BlueFox5 (#2,259,819)

Almost all of Japan hangs their laundry and most prefer it because, and I quote my workers on this, "It smells cleaner." I still find it burdensome, personally. But you have to adjust.

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Sufficient_Primary45 t1_jcntxg2 wrote

Many Germans, most mornings, open all windows and shades, wipe the seals and place bedding on the sunny side of the home while starting their morning and then just before leaving pull in the bedding, make the bed, close the windows and leave for their day. On Saturdays they wash from their front door all the way to the center of the street. Just a little extra for your consideration.

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