UV question autoflowers

Good evening everyone.
I have been using my Spider Farmer UVA bars with my SF light which is my dedicated autoflower tent.
Recently someone told me I should move the UV bars to my photoperiod tent as UV won’t do anything for the Autoflowers.
I couldn’t figure out why that would be, I mean theoretically they are the same as the photos just on a timer.
Has anyone heard this or is it some bro science myth spread around?
I’ll gladly move my UV bars to my photoperiods if it would have more of an impact.
Thanks in advance.
@dbrn32 I know you are the light guru any thoughts?


Your lights should do everything for an auto that they would a photo. I’m not convinced it’s a lot when talking about uv specifically though.


As far as that goes, photo or auto react the same. IMHO :wink:


I read on the net that UVA light really doesnt do anything for plant growth as it makes the plant go into a defensive mode and produce trichomes to protect itself. If theres any truth or fact behind that theory I haven’t a clue. I run a UVA for basically the whole grow not sure if it’s beneficial or not. All I grow is photos


Thanks and thats what I figured and yea I’m not sure what it anything it does but figured couldn’t hurt.
I thought it seemed weird he said it wouldn’t do anything with autoflowers but said would make a huge difference with my photos. I was just like hmm doubt it :joy:


The uv makes a difference if used correctly. The difference is in the trichomes but it isnt something that will magically turn trash into stash by any means but it does help just not so much for growth

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I’m interested any advice.

This is the only reason I turn it on and only the last 3 weeks leading up to harvest :love_you_gesture:


That’s where I start with the UVB around week 6 I’m all ears…lol @OGIncognito

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Only my 3rd run under this light and using the IR/UV that came as a separate function. The manufacturer recommended 25% at week 1 bumping that up gradually. I’ve had 1 run that way and one run and harvest using the last 3 weeks. The jury is still out, my note taking has gone to :poop: as well. The harvest using the IR/UV the last 3 weeks was pretty frosty , dense and super loud but could also be strain related :love_you_gesture:


I have both lights and going off of what hellraiser had to say but really haven’t understood them except for the research I do. Still figuring out the best way to use them. GroBro Thanks :metal:


There is uva and uvb used and they are different. Uvb is stronger and should only be used 1/2 to 1 hour a day usually at the end of the light cycle during the last 3-4 weeks. Because its on a different light schedule its a little more of a pain but not that bad. Uva is a little more friendly to work with and is much more popular. You have it turn on with your main flowering light for the full 12 or 18 hours, whichever you are running and i start running mine at 3-3 1/2 weeks after light flip. Cannabis produces trichomes as a means of its protection against sun, rain, and wind eg.getting a sunburn/windburn so cranking up some uv and a slight breeze help your plants produce more and bigger trichs which is where the good stuff is. It wont make a higher thc content, but it will make more of it. In college i grew some that had lower thc content than some other dudes but it was better smoke none the less from having more and bigger trichs and alot better cure

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Appreciate the input! Just thinking about my next grow in August making a plan with the lights.

@GrowingIs4Everyone Didn’t mean to Hijack ya :v:

No problem man, just be aware that if you decide on uvb more problems can arise since it would be on a separate timer such as if the uvb would stay on for some reason it could mess up your light cycle or worse burn your plants up. Its an ugly trade for reduced electrical costs which isnt that much to begin with if you ask me


I have a couple of 8 program timers for the UV’S Sometimes ya have to trust technology. :beers: Ya when I was running far red lights at the end of the light cycle I was fooling around with the electrical and plugged them into the wrong outlet ( put the internet on the timer ) and revegged my plant.


Man I miss @Hellraiser I wish he’d return.

We started with uva about the same time… I also experimented with the uvb.

We both found the uva in veg does seem it can produce heartier leaves… But no real effect that benefits the final grow other than a stronger plant.

I started off with the idea that in nature plants can’t escape uva, b or, C.

To save on electricity and having to worry about remembering the uva is on… I stopped using it in veg.

Using uva starting shortly after the acclimation of flowering light switch… A week or two… For 12 hours per day. Has shown me that my buds are super crystally… Tricome filled. Versus just doing it the last three weeks of flower or none at all. However, I’ve had phenotypes that just don’t produce the density of tricomes no matter what.

The uvb… That gets very very tricky… I left a couple plants directly under uvb never rotating around the tent for even coverage… Just directly under it… Ruined the buds… They were funky… Hard as rocks, tasted funny, and small.

What I postulated as the highest sun if the day I was trying to replicate the highest uvb per day a plant could when the day was at its hottest and brightest… From a hour to two hours per day… In fact he middle of my light cycle… I found very little affect.

So little so that I have stopped using uvb due to accidentally getting exposed to uvb forgetting to turn off the light or forgetting it’s on all together. No reefer is worth cancer.

Uvc… Just don’t. To scary… The time amount of exposure is so short…burns, Cancer or cell death isn’t worth it.

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I agree I’ve not noticed any difference in anything other then tje one light I have with uv (spiderfarmer se3000 "upgraded with uv) has produced the most purple to sometimes black plant’s :man_shrugging:.
It may be bias but im convinced there has to be something triggering a “sun tan” effect or something :sweat_smile: I don’t get dark colors as often under my bigger lights without uv :man_shrugging:


Right, you would have to be in lab type of setting and tracking all sorts of variables to say anything for sure either way. The scientific attemps to prove this have come back with mixed reviews. Some support varying wavelengths below 400nm to be beneficial to plant response, and others don’t. The most supportive document I’ve reviewed showed thc increase from something like 20% to 21%. This is a 5% increase in thc content, but not the move from 20% thc to 25% thc that some think.

From my perspective, the available information makes it hard to suggest people spend their money on uv lighting.


I cant help but Wondering if say the uv40 bars grom hlg, how effective would they be at preventing or possibly treating things like WPM, algae, or maybe some pests :thinking:
Uv is use to sanitize stuff.

I have 2 of the hlg bars but im unconvinced of the cannabis claims. But if it made it impossible for bad stuff to live it could be worth.

If it was effective at actually treat some things, it would definitely be worth have just incase we got some PWM with tent stuffed full :thinking: