I have a couple questions about UV that I was hoping someone could answer. First, a fairly easy question: is it more important to supplement with UV in veg or flowering or both? Second, is longwave (365nm) or shortwave (254nm) more important or should I use both?

Thanks for any help regarding the subject...

Also, is there a site to get the usable spectrum of lighting for stages of plants? I know what it is for corals (420-490nm because this is the major light that penetrates the water), but this is obviously different for plants. I know that cannabis plants do not absorb the green sprectrum (don't know the exact range), that veg needs bluer light range, and that flower needs more of the red spectrum, but are there exact values of absorption rate so that I can figure out the PUR (Photosynthetically Usable Radiation) for my lighting setups? PAR is very easy to discover, but PUR needs much more information.

Thanks again

Sounds like you have a good grasp on lighting. For land plants I dont think they would benefit much from any thing that goes below what an actinic light produces, which after that gets into the blacklight spectrum. I do run a couple actinic bulbs on my box as supplemental light. You might be able to ween some info from Light and Plants. And this has a good diagram for where the nm's fit into the process. http://www.littlegreenhouse.com/guide3.shtml

Thank you, that was helpful. The only problem is that I am looking for the spectrums for marijuana stages. I think mj is differing slightly from that graph and also the stages determine the amount of usable light spectrum (i.e. more blue during veg for rooting, more red/orange for flower). It's hard to give a generalization for plants with the amount of lighting prefernces, intensities, etc. and the fact that blooming is at different times for different species. One major benefit of corals is that although there are thousands of species, generally the lighting is the same(a little more shade here and there, a little more depth for some) but lighting stays relatively constant once you have it set up. Now when I say constant, I don't mean the cycle must be constant(I have a variable lighting program for my LED setup including random cloud cover, waxing and waning moonlights, dawn and dusk cycle, variable day length, etc.), I merely mean that there are no separate stages of their light cycle.

We use blue light in veg to lower auxin levels and this keeps the internodes from elongating and the plant compact. We use red in flowering because this does not suppress the auxin levels (as much) and auxins are vital for flowering. Green and far red (720-780nm) has also been shown to boost auxin levels. Green isn't absorbed as efficiently as red and far red has no photosynthesis benefit (far red can be used as a supplement).


Auxin - Wikipedia, the free encyclopedia

There is some anecdotal evidence by a guy named Raphael Mechoulam that suggests that UV light in the 235-285nm range helps in the biosynthesis of THC (Marijuanna Botany, pg 132-133)

As far as I know, actual and total PUR has never been empirically established for pot in controlled studies.

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Talk, without the empiricism to back up your statements, is dogmatic BS.

Thank you so much, techlead, this information is extremely helpful. So, in short UV supp would be mainly beneficial in veg state, correct? Would you then recommend using UV supplementation for flowering? Since greens rate of absorption is so low, green would not be a useful supplement at any stage, correct? Would you recommend using far red supp, or were you just saying it can be? Also, do you know of any studies including infrared for flowering suppl, or would it be too far out of rage to have any affect?

Again, thanks a bunch for your answers.

UV has no photosynthetic properties and would not be useful in veging. The only shown possible benefit of UV is as a supplement in flowering to possibly raise THC levels. Keep in mind that this is an area that has not been fully researched and I'd call more hypothesis than theory.

Photosynthesis - Wikipedia, the free encyclopedia

It remains to be seen the benefits of green light. In my own research you want to keep green light levels low since green light is going to cause elongation of the plants internodes. I've used high power green LEDs to increase the size of leaves but is nothing that I'd recommend to anyone at this point. My initial results (and personal belief) does show that green will boost hormonal levels, however, I've never done a bioassay of the leaf material to empirically back my claim up.

I haven't done enough experiments with far red to give any empirical statements on its benefit for pot.

There is no known benefit to adding IR to plants.

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Talk, without the empiricism to back up your statements, is dogmatic BS.

i believe veg is aroun 450nm and flower 650 just what ive read somewhere cant remember where so no link srry

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i dont see why i should be the criminal
how can somethin with no recorded fatalitys be illegal

In my own personal experience using various wavelengths of LEDs, I've found that the specific wavellength is not nearly as critical as these manufactuers claim. For example, I saw no difference in growth between 630nm and 660nm and mixed 630/660 and my HPS, which peaks at around 589nm, will easily outperform any LED currently on the market watt for watt (I've experimented with up to 15 watt LEDs).

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Talk, without the empiricism to back up your statements, is dogmatic BS.

no worries man as i already said this is from what ive read havnt used LEDs myself

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i dont see why i should be the criminal
how can somethin with no recorded fatalitys be illegal