# Too Much UV-B Light Damaging to Plants?



## Justin00 (May 9, 2011)

before i post my big long explanation of the entire situation for everyone to dredge thru ill ask the question short and sweet first.

Can UV-B lights damage your plants? (2 UV-B-10 CFLs @ about 6 inches from tops)


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## IVIars (May 9, 2011)

people say anything over 5-6 hours could actually cause less thc


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## Sensibowl (May 13, 2011)

Justin00 said:


> before i post my big long explanation of the entire situation for everyone to dredge thru ill ask the question short and sweet first.
> 
> Can UV-B lights damage your plants? (2 UV-B-10 CFLs @ about 6 inches from tops)


I think you need to worry about anything that's too much of something. Whiel plants would get the UVB rays outside, you never want to OD on anythign in the grow room. Stick to moderate amounts of everything and plants will respond better.

HTere are some sweet lighting setups on Advanced Nutrients' site. I didn't realize they had so much stuff until recently. Lots of new stuff, it seems.

I'm thinking about ramping up my grow room and your post really got me thinking about the kind of lights I need.

good lcuk!


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## Cali.Grown>408 (May 13, 2011)

well look at all the uvb coming from the sun...you can go outside and get sunburnt and go in your grow room and try to get sunburnt but u wont..i can guarantee the uvb is stronger outside and your plants are actually loving it..outdoor plants get about 8-11 hours of uvb a day to by the way plus i've been using uvb for years and i usually keep it on 8-11 hours a day


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## vh13 (May 13, 2011)

Those UV bulbs can cast more UV light on your plants then the sun if they're too close.

I used to know how much UV light the sun casts per square foot, and the wattage per square foot that a UV bulb would correspond to... there is an appropriate wattage for the square footage of the grow space... but I don't remember anymore, so now you know what to research.


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## herbderby (May 13, 2011)

i run 4 13w repitsun cfls and a 2 foot reptisun t8, both uvb 10.0.

i do this for all of flower(12 hours a day) and my resin production is excellent.


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## Cali.Grown>408 (May 13, 2011)

vh13 said:


> Those UV bulbs can cast more UV light on your plants then the sun if they're too close.
> 
> I used to know how much UV light the sun casts per square foot, and the wattage per square foot that a UV bulb would correspond to... there is an appropriate wattage for the square footage of the grow space... but I don't remember anymore, so now you know what to research.



read the thread..he has 2-10.0 uvb's..that's nothing, not even close to how much the sun puts out


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## vh13 (May 13, 2011)

Did you read the original post? Maybe you didn't notice there was no indication of wattage.


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## Gastanker (May 13, 2011)

I run 8 10.0 tubes right up against my plants. Works wonders.







Still doesn't compare to the sun though.


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## Cali.Grown>408 (May 13, 2011)

vh13 said:


> Did you read the original post? Maybe you didn't notice there was no indication of wattage.


so disregard your 1st post then right LOL


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## Icemud (May 15, 2011)

I've read that UV-B is actually good for your plants for raising the THC levels by making the plant produce more resin and trichomes to protect itself from the UV-B. I have read that many will switch from a HPS to a MH during the last few weeks of flowering to achieve this effect and raise the potency of their buds. I also have read that if you use a 2:1 ratio of HPS with MH you will achieve your best results. Anyone ever tried this. I am only on my 1st grow ever, but have tried to do everything with the most accurate and best information available, so I am running 1 400MH for my UV-B (enhanced blue spectrum Ushio) and a 600w HPS for my far red.... Lets see how these ladies do!

My question...How harmful to the human eye is a MH bulb, for limited exposure....maybe 2x 10 minute exposures daily.... should I wear protective eyewear? high spf lotion?? can't be worse than the socal sun we get!! Any insight?


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## cannawizard (May 15, 2011)

Icemud said:


> I've read that UV-B is actually good for your plants for raising the THC levels by making the plant produce more resin and trichomes to protect itself from the UV-B. I have read that many will switch from a HPS to a MH during the last few weeks of flowering to achieve this effect and raise the potency of their buds. I also have read that if you use a 2:1 ratio of HPS with MH you will achieve your best results. Anyone ever tried this. I am only on my 1st grow ever, but have tried to do everything with the most accurate and best information available, so I am running 1 400MH for my UV-B (enhanced blue spectrum Ushio) and a 600w HPS for my far red.... Lets see how these ladies do!
> 
> My question...How harmful to the human eye is a MH bulb, for limited exposure....maybe 2x 10 minute exposures daily.... should I wear protective eyewear? high spf lotion?? can't be worse than the socal sun we get!! Any insight?


**good info, uv-b is essential for thc+ production.. MH or HPS exposure to your eyes is safe, just dont stare into your lights  ..on a side note, MH bulbs do produce small amounts of uv-b, but not enough imho.


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## cannawizard (May 15, 2011)

Justin00 said:


> before i post my big long explanation of the entire situation for everyone to dredge thru ill ask the question short and sweet first.
> 
> Can UV-B lights damage your plants? (2 UV-B-10 CFLs @ about 6 inches from tops)


**too much of anything is bad 

2 uv-b cfls (im guessing your using iguana type fluro, you can actually put those bulbs as close as 2inchs, you'll just be limiting the area of exposure..)


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## cannawizard (May 15, 2011)

Cali.Grown>408 said:


> well look at all the uvb coming from the sun...you can go outside and get sunburnt and go in your grow room and try to get sunburnt but u wont..i can guarantee the uvb is stronger outside and your plants are actually loving it..outdoor plants get about 8-11 hours of uvb a day to by the way plus i've been using uvb for years and i usually keep it on 8-11 hours a day


**curious what kind of uv-b setups you've used/using, ultra violet lighting w/ cannabis has always been my 'cup of tea'


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## cannawizard (May 15, 2011)

IVIars said:


> people say anything over 5-6 hours could actually cause less thc


**Myth Busted**

you can expose cannabis w/ 24hrs of uv-b, and it will not lessen thc+ production. but if you pass the 600nm mark regarding uv-b intensity then some strains have shown to produce less thc+ (mainly due to stress)


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## Cali.Grown>408 (May 17, 2011)

cannawizard said:


> **curious what kind of uv-b setups you've used/using, ultra violet lighting w/ cannabis has always been my 'cup of tea'


the most i've ever used was 3-10.0 uvb lizard bulbs over 4 plants with a 400w hps...now i only have one 10.0 uvb under four plants and i just rotate them..i plain on adding one or two more again next grow


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## cannawizard (May 17, 2011)

Cali.Grown>408 said:


> the most i've ever used was 3-10.0 uvb lizard bulbs over 4 plants with a 400w hps...now i only have one 10.0 uvb under four plants and i just rotate them..i plain on adding one or two more again next grow


** i started on repti 10.0 uvb bulbs.. decent source of uv-b but i would recommend these bulbs instead :: http://www.amazon.com/Zoo-Med-PowerSun-Mercury-Vapor/dp/B0002AQDJ0/ref=pd_sim_k_6 ::
--it would be enough to cover your 400w setup


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## Justin00 (May 19, 2011)

ty for all the responses, i think from the info you guys gave that i can attribute all the damage to the spider mites. i am confidant at this point the light had no negative effect.


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## Bonzo Mendoza (Apr 14, 2012)

I have double 48 inch Reptisun bulbs along the edge of the MJ garden and the results are amazing.

The plants uder the uv-b tubes are stinky with resin and STICKY. They are easily the best plants in the garden - they are thicker and heavier and seemed to be filled with oil. I have several varieties but the plants that grew from Nirvana Bubbleicious (I only got four females out of ten regular seed package) seem to like the uv-b the best. The buds smell exactly like a piece of Bazooka bubble gum!!!

I have (sadly) some Nirvana Kaya Gold and Nirvana Super Skunk, (all total shit - waste of money - 6 fems out of 20 seeds - big worthless ditchweed plants). UV-B: no effect.

I got a great result with uv-b. I am going to get another fixtures a.s.a.p. (still have over a month of flowering to go).


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## Gastanker (Apr 14, 2012)

This bud is resting directly against a 10.0 UVB bulb with no concernable stress. 

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