UV-C for mold control"7 watt light for a exposure of 60 seconds about 4 inches away from the affected leaves followed by a 4-hour dark period"

physics and technical background with experience coming through... First off, don't listen to anyone trying to send you to www.randomnobodywithoutascientificopinion.com/blog or who cannot fully discuss the nuances of implementing the UV spectrum in your rooms. We are talking about the electromagnetic spectrum, not celebrities or buzzfeed, why are we not using scientific sources if we need to defer to experts rather than experience? There is a reason UV light has been used in industry for decades and decades across the globe... There is also a reason your average joe is scared of it. UV light when discussed as a photon packet can be viewed as a projectile. The size of photons is directly correlated with what they can interact with. Think red flowers appearing so because of their interaction with red versus non-red photons... UV light, the entire band of A/B/C, are all REALLY MFing close to DNA in size. UV-C is perfection, directly obliterating DNA each hit. This is the mechanism behind cancer and mutations with UV light, as well as the entire mechanism for sterilizing (as a function of time). You have to keep in ming you're talking photons per area over time, which quickly leads you into probability density curves and calculus... Long story short, you're getting close to leaving regular physics with apples and arrows and getting into much more advanced stuff, despite optics being solely geometry. You got some wild answers down here, just as a second warning. Mold repairing DNA is indeed a factor, however mold is not an application which UV light is typically leveraged for....unless encased in an O3 bubble...which is elementary knowledge. The 3D nature of our universe results in shadowing effects at the local level...aka think of two molds stacked as spores...the photon is not hitting the second one. Think of a pile of mold casting a shadow over some mold locally, photons do not land.... This is why we throw away sponges, instead of putting them under a UV flashlight. If you are trying to clean something you cannot see or on a porous surface, then use ozone to flush the photons through. If you can directly see what you want to clean, then you can apply UV light. UV-B is relatively safe as hell compared to UV-C and still has incredulous destruction capacity for pathogens on the scale of bacteria and molds. Now for your use case? Using UV-C outside? UV is an extremely high energy photon. Inverse square/that simple geometry coming back into the picture means UV photons travel on the order of feet usually... If you are into flower already and outside, UV is not your answer. Full stop, just forget about it. That is only for the PM part. Budrot is almost always a user error, where you didn't use sterile instruments (be it your hands or your tools). Proper UV use cases for cannabis: 1. During daytime to introduce extra stress or shift slightly from cannabinoids to volatiles. 2. In ducting to scrub air into the tent. (this is a big mold prevention one) 3. In ducting to scrub/mix scent. 4. In dry/cure environments in intermittent bursts outside of the C band, to prevent pests/pathogens in a high priority /no downtime capacity environment. (this is a big mold prevention one) 5. During iso-shifts to cheat shifts. Proper Ways to Fight PM 1. Have a robust living web and genetics and let the plant say no thank you to the PM. 2. Grow indoors and control your environment. Dew point theory and stuff is not a suggestion... We use this for storing artifacts, meats, cheeses, produce, books, and on and on. You will never control the variables that go into that outside... 3. Spray sulfur or similar products as a preventative rather than prescriptive solution. Proper Ways to Fight Budrot 1. OpSec with instruments/plant wounds I actually have worked with the US Patent Office and multiple startups with UV devices. As well as regularly use them in my tents for a variety of purposes. And the formal background in, well, physics. I would say Ultraviolet's response is def the most robust, with everything ringing scientifically correct. The only caveat I would have with this is where are you getting your UV photons from? We have diodes now that do pretty well and we have the old solid to vapor spectral line mercury trick lamps.... Make sure you have zero leak. Most sources of UV will also emit a visible purple to them. This purple WILL be within your plant's range and will begin to awaken it. The true UV will not. The old mercury lamps emit right on point once vaporized internally, just make sure your ballast math is correct. Most I have seen can be ran of a royer oscillator, which has an expired patent.

Some vineyards have been experimenting with UV. Important to apply in darkness (does not state how long before you apply) and to give at least 4 hours of darkness after application. You can use keywords from the article to find specifics, i'm sure... The exact methedology is not given in the article but it's out there 'somewhere' and google can find it for you. My question would be -- does interrupting the dark cycle while also giving a long enough length of darkness after that interruption a problem for the plant? I would think as long as there is enough time after the interruption that hormone balance will maintain flower phase without a problem... unless there is some sort of lag in hormone production due to the short interruption. 12 hours is already more than necessary, and the ~11.5 hours after any UV interruption would be enough under normal circumstances. But, sounds like applying UV while lights are on is not too effective. The mold will just repair it's dna faster than you can kill it. Source: Original article: https://www.winespectator.com/articles/could-a-tool-to-combat-covid-also-protect-grapevines-from-mildew https://www.extension.iastate.edu/wine/using-ultraviolet-light-way-control-powdery-mildew/ ------------anecdote... From my own hellish experience with WPM, it is almost exclusively a self-inflicted problem indoors. If you don't have a wireless temp/rh probe, it can be an eye-opening experience to see what happens as the lights turn off and temperatures drop. I reduced my canopy size and bought a beefier dehum and never saw the problem again. I had tried many things up to that point. I had already given up when i downsized canopy for different reasons and "magically" didn't have wpm that cycle. That was the first cycle i had a wireless probe instead of relying on spot-checking the dehum's display. Even with the smaller canopy it struggled a bit after lights turned off, but only neared a high risk level of humidity before getting back down to dehum's target RH. Easy to deduce what was happening with a larger canopy and more moisture released. once the plants were large enough, i'd start hitting high-risk RH levels after lightsout, and see WPM by 5th week of flower, give or take a few days. It really was like clockwork for a couple years (2 grows/year and 6 months off). You can calculate this stuff or use a "dewpoint table" - even if you dont have a wireless probe to assess risk using operating temps and the temperature it'll fall too (ambient home temp)... e.g. 27C and 60% has a dewpoint of 18.57C. Now, as temps drop a dehum will kick on and start to pull moisture out of the air, but it isn't instant. If room temps fall to ~18C, RH will spike fairly high even if it manages to avoid dewpoint (100% RH). 30C and 60% is 21.39C dewpoint. Gets even easier to spike into a high-risk RH with warmer tents running at suggested VPD (RH should be higher than 60% at 30c even considering leaf temp offset) -- 65-70% would be mor approriate and now 30c/70% is 23.93c dewpoint. Warmer operating temps make this more of a concern because of higher "absolute" humidity. The dehum won't kick on until RH starts to go up, but there's still a tone of excess moisture relative to the ambient house temperature it will quickly drop down to after lights turn off. All the anecdotal options I tried are total bullshit... "cornell" formula, potassium bicarbonate solution, sodium bicarbonate solution, some sort of sulfur spray, various natural oils, neem, a combination of those, or even milk... i was so desperate that i sprayed my plants with fucking milk -- Embarassing. Those foliar spray 'solutions' just spread it around to the stems and anything else it dripped on... useless nonsense. Often made the problem worse and definitely didn't kill nor slow it down. Fun fact -- "Cornell" formula is named after a university but not based on any research, evidence or anything scientific whatsoever... just trying to hitch a ride on their coattails Even commercial fungicide options are not that effective. They can help partially reduce infection but don't remedy it. We, as a species, really don't have a good answer for fungus-related problems - agriculture, human health, or any other context... fungi are robust lifeforms. Evil little shits. Most effective option -- control the climate, imo. See fungus? Cut it out and give it a wide berth while doing so, then pray to some god that won't listen.

https://www.cleanlightdirect.com got a "Hobby set" but not sure how safe it is, with those glasses and gloves there not that much infos on the homepage so i would probably stick to @Ultraviolet solution

UVC is highly mutagenic, I would avoid it at all costs to avoid any user error and issues. UVA/UVB is a better option if it has to be used. Most fungicides don't work well, would also help to remove any leaves with heavy growth.

@Ultraviolet I belive i'm using UVa 385-395nm for 12h since the 2nd week after flip what can u tell me about it ?