To UVB or not to UVB??

[ForumToker]

So there are a few recent and very good discussions on the boards by some grow artisans regarding UVB lighting but no definitive conclussions from what I can find. I figure, what the hell, and just ordered one from Amazon as an addition to my flowering gear. My problem is that I am currently on my first indoor grow and have no comparables to go by.

Question is, has anyone personally tested UVB lighting in at least a mostly-controlled setting and seen a possitive or negative response in THC development or any other noticeables? If so, can you share your set-up and experience?

Thanks in advance and happy growing!!

 

[nuggetgrower]

Question is, has anyone personally tested UVB lighting in at least a mostly-controlled setting and seen a possitive or negative response in THC development or any other noticeables? If so, can you share your set-up and experience?

I have not done a controlled test, but I used a UVB bulb to boost UVB with my CFL's and the results were good.

Too much UVB and you can harm your plants, too little and you may have slightly less THC production. So depending on what your bulbs are putting out for UVB already, the added UVB may be a good thing for you.

 

[ForumToker]

Too much UVB and you can harm your plants, too little and you may have slightly less THC production. So depending on what your bulbs are putting out for UVB already, the added UVB may be a good thing for you.

Thanks for the quick reply Nugget!!

You mention CFL... What's your current mix CFL's to UVB? How bigs your grow area and grow itself? I'm trying to avoid the burning issues you mentioned.

I'm still in Veg but going flower next week. 3 plants in a small closet with 6 40w 2700k and 2x 26w 6500k CFL's. The light I ordered is a 10% UVB 20w 24" flourescent tube style light. How does that mix sound to you? Where and how far away in your experience should I place the UVB light? Any ideas on hours, i.e. 12/12 with the others or less?

Thanks again man!

 

[ForumToker]

Also, when did you initiate the UVB? Was it from start of flowering through harvest or any variation?

 

[ForumToker]

Anyone else have any experience with UVB?

 

[nuggetgrower]

Thanks for the quick reply Nugget!!

You mention CFL... What's your current mix CFL's to UVB? How bigs your grow area and grow itself? I'm trying to avoid the burning issues you mentioned.

I'm still in Veg but going flower next week. 3 plants in a small closet with 6 40w 2700k and 2x 26w 6500k CFL's. The light I ordered is a 10% UVB 20w 24" flourescent tube style light. How does that mix sound to you? Where and how far away in your experience should I place the UVB light? Any ideas on hours, i.e. 12/12 with the others or less?

Thanks again man!

Your mix sounds good. Try to put the UVB in a place where the light can spread throughout the grow space and give a little extra UVB to all plants. I have mine on the same timer, but if you find it is too much you may want to cut back hours on the UVB light.

I would introduce the UVB bulb when you begin flowering. The added UVB should increase resin production.

 

[ForumToker]

Thanks a ton Nugget!! I do appreciate your help and I'll fire one up in your honor in a few months!!

 

[ForumToker]

If anyone is still following, I found an interesting read on http://www.greenmanspage.com/guides/thc.html
(5) "Pate (1983) indicated that in areas of high ultraviolet radiation exposure, the UVB (280-320 nm) absorption properties of THC may have conferred an evolutionary advantage to Cannabis capable of greater production of this compound from biogenetic precursor CBD.* The extent to which this production is also influenced by environmental UVB has also been experimentally determined by Lydon et al. (1987)."

*****The writer's own experience allow for a more specific conclusion: If the UVB photon is missing from the light stream(a), or the intensity as expressed in µW/cm2 falls below a certain level(b), the phytochemical process will not be completely energized with only UVA photons which are more penetrating but less energetic, and the harvested resin spheres will have mostly precursor compounds and not fully realized THC(c).

*****(a)Examples of an environment where the UVB photon would be missing from the light stream include all indoor cultivation illuminated by HID bulbs and in glass or corrugated fiberglass covered greenhouses.

*****(b)"The maximum UVB irradiance near the equator (solar elevation angle less than 25 deg.) under clear, sunny skies is about 250 µW/cm2.* It was observed that the daily solar UVB in Riyadh, Saudi Arabia (N24.4Lat.) decreased from September to December by about 40% (Hannan et al. 1984).* The further a person is from the tropics, the less UVB radiation there is: the average annual exposure of a person living in Hawaii is approximately four times that of someone living in northern Europe."* Below are some UVB readings taken in Hoyleton, Illinois, on a clear sunny day in June by David Krughoff as reported in Reptile Lighting 2000.

**7am: **12 microwatts/cm2
**8am: **74 microwatts/cm2
**9am: 142 microwatts/cm2
10am: 192 microwatts/cm2
11am: 233 microwatts/cm2
12pm: 256 microwatts/cm2
**1pm: 269 microwatts/cm2
**2pm: 262 microwatts/cm2
**3pm: 239 microwatts/cm2
**4pm: 187 microwatts/cm2
**5pm: 131 microwatts/cm2
**6pm: **61 microwatts/cm2

*****(c)Cannabinoid pathway: Anywhere in this pathway UVB does a better job than UVA in energizing a phytochemical reaction that will produce more fully realized THC because "all cannabinolic compounds show an absorption maximum between 270 and 280 nm in the ultraviolet region."*

 

[jcdws602]

I use mine the last 2 weeks of flowering,the uv rays stresses the plant out so it produces resin like sunscreen to protect itself but at the same time decreases yield because the plant spends more energy producing resin than building mass,so I wait the last 2 weeks,after the explosion period.

 

[420OldSchoolDJ420]

Unless every other aspect of your grow is 100% dialed in ( CO2/Lum's/Heat/Nutes ETC ETC ETC ) I think they are a waste of time. But if everything else is 100% perfect I think it may increase yields maybe 10-15% max.

 

[jcdws602]

Unless every other aspect of your grow is 100% dialed in ( CO2/Lum's/Heat/Nutes ETC ETC ETC ) I think they are a waste of time. But if everything else is 100% perfect I think it may increase yields maybe 10-15% max.

Yields???...........no........... Thc production yes

 

[420OldSchoolDJ420]

errr.. yea that too. lol

 

[ForumToker]

From the documentation I have reviewed over the past few weeks, I do not continue to question whether or not UVB rays increase THC production, or more specifically trichome production... It's a fact, they do. At the absolute minimum, a cannabis plant that is lacking the appropriate amount of UVB rays will have a lower production of trichomes.

The amount of UVB rays a cannabis plant should receive throughout the day is posted in my last msg.

My only real question now is WHEN to hit our baby's with this light...?

If the main intent is harvesting the actual bud and not the overall plant itself (I think this is all our goals), it would seem to make since, as said by jcdws602, that an introduction of UVB late in the flowering cycle and through to harvest, would tend to the best results. UVB is radiation and the plant will spend more of it's energy protecting itself, by creating the trichomes, but possibly at the expense of flowering, thus lowering the potential overall yield. So we're faced with the question of is more better, or is less but better, better?

Good discussion... Anyone else have opinions on timing?

 

[chronicdice88]

ive been pondering this very question now for a few weeks. this thread is great thanks for all the info so far. personally i think it wont harm the yeild to much depending on wattage on the uvb. marijuana grows better on the places of the world where more uvb light is.. so mimicking nature as close as we can is key. some smaller grows might be lacking in uvb light? i dont know where to draw the line.. im using 3 26w cfls and a 150hps.. im thinkin some more uvb wont hurt? but the question is to start it right when flowering starts.. or just the last week? hmmmmmm

 

[TeaTreeOil]

Conventional fluorescents already emit UVB. It's less than 5% of the photon flux, but it's there. Also MH/MV emit plenty of UVB. HPS doesn't(less than 0.1%).

UVB evokes increased resin production. Which means better smoke. Not really an issue during veg. The start of 12/12 would be good.

 

[ForumToker]

im using 3 26w cfls and a 150hps.. im thinkin some more uvb wont hurt? but the question is to start it right when flowering starts.. or just the last week? hmmmmmm

Thanks for joining in Chronic! From what I have read CFL's, HPS and black lights emit zero usable UVB lighting. MH and reptile lights do however, with any brand 10% HO Reptile light being ideal. So your question shouldn't be one of to add more, but whether to add any.

The question of WHEN though....

 

[robert 14617]

what are the % of UVB from the T-5's i want to add some to my grow room(closet )with one 400watt hps

 

[ForumToker]

Not sure Robert. T5's aren't an option for me so I haven't been reading up on them. I do know it is going to depend on manufacturer, model, etc and they should have that info available either via the web or customer service line. I know that Desert Zilla makes a T5 which outputs 50 microwatts/second which may be a little much for a 12/12 regiment on cannabis.

 

[robert 14617]

Not sure Robert. T5's aren't an option for me so I haven't been reading up on them. I do know it is going to depend on manufacturer, model, etc and they should have that info available either via the web or customer service line. I know that Desert Zilla makes a T5 which outputs 50 microwatts/second which may be a little much for a 12/12 regiment on cannabis.

wow redirect T-5 bulbs give a higher output

 

[ForumToker]

wow redirect T-5 bulbs give a higher output

True that. However, I am unconvinced that this is a good thing...

You have to keep in mind that the sun gives off 0.07472mg/second of UVB at the hottest time of day in the hottest month in the northern US (average high of 88 degrees a day where this test was preformed). So 50mg/s from a T5 is what, give or take 669 times stronger? For comparison, The Zoo Med Reptisun 10% HO UVB light that I ordered gives off around 20mg/s.

Now bear in mind that I am certainly not debating the potential benefits of UVB lighting on cannabis, in fact I whole-heartedly agree with it. I am just curious as to what exposure they should have and at what point do we see diminished returns?

Damn it, I hate math! Where's an MIT grad when we need one?