UV Light and Terpenoids

Don't know if this has been discussed.
At some professional vegetable greenhouses I know they block out uv-b with special curtains/glass coatings because studies show uv reduces chlorophyll and thereby mass growth. In flower greenhouses they are experimenting with higher levels by use of artificial lighting, because uv also reduces stretch and make the plant produce higher levels of anthocyanin (color), valued more than mass growth in their case.

Hey superpedro,

The point you bring up is very valid, in terms of UV-b effecting levels of Chl A and/or B. That is an example of what I meant when I wrote Uv-b is deleterious to plant tissue, esp. under lower light levels. I wouldn't use UV-b if I used less than ~600 PPFD.

To the point you made about "reduces stretch", do you have references you can cite for us? I ask because reduction of plant stretching is better controlled, in terms of light color, by modifying the red to far-red ratio intracanopy than by adding UV-b AFAIK. I would be very interested to read any legit references you have about Uv-b light and plant stretch. TIA!

Using reptile type UVB fluorescents definitely makes plants grow more compact and stocky, but that will be due to the 380nm-450nm light they also produce. They also promote the production of some pigments which makes cannabis flowers take on purple colours. When I did an experiment with UVB fluoros, the side of the cola facing the UV lamp turned purple, the other side stayed green.

I know some people claim Uv-b reduces stretch, but this is an advanced botany forum, thus the standard of info/claims is much higher than the rest of the forum at ICmag. Simply stating it makes them stretch less by looking at cananbis plants, without proper controls and scientific method testing isn't sufficient for this forum, IMO; and not does it meet the forum goals as I understand them.

I think it's very important to make sure we provide legit academic references (whenever possible) for our claims, and not make claims based on simple observation without accounting for many factors that affect growth/stretch. We should strive to use analytical methods, not simply and very fallible observation.

This is an example of a good reference. In this study it is shown that cryptochrome processes (blue light receptors that use UV-B and blue light in PAR range) can make a plant grow/stretch more in lower light gardens. Thus, UV-b wouldn't make plants stretch less in some circumstances:

"Phototropins Promote Plant Growth in Response to Blue Light in Low Light Environments"
Atsushi Takemiy, Shin-ichiro Inoue, Michio Doi, Toshinori Kinoshita and Ken-ichiro Shimazaki
The Plant Cell 17:1120-1127 (2005)
(full text) http://www.plantcell.org/cgi/content/full/17/4/1120

Hi spurr,

I just read a few of your posts in the red:f-red thread, and I was very interested to read your posts in this thread shortly after. I believe we will have a lot to talk about in the future and I am very glad to make your acquaintance. My mind works like yours =D

I researched UV-B and cannabis extensively about 5/6 years ago, back when Overgrow was still going strong. I wrote a research paper on the subject using all of the sources that I could find at the time. It is definitely a little out-dated now, but I still think you would enjoy reading it:
http://mrnice.nl/forum/showthread.php?t=3508

I'm very happy that you have quantifiable experiments suggesting the link and look forward to any other research about this subject you could point me to.

Take it easy

Excellent contributions. Thank you everyone

spurr you mention UV-B having a negative effect on plants below a certain irradiance level (in this case 800PPFD). Which experience or papers did you derive your observation from? Have you found ratios or maximum levels of exposure?

Another question that seems to fit here is whether UV-B actually increases total production of THC or is the seeming increase only due to the difference in loss of vegetative mass. It still would result in a increase in THC versus weight/volume which is a good thing in most cases as i gather it.

3rdEye said:

Excellent contributions. Thank you everyone

spurr you mention UV-B having a negative effect on plants below a certain irradiance level (in this case [edit 600PPFD]). Which experience or papers did you derive your observation from? Have you found ratios or maximum levels of exposure?

Click to expand...

The issues of Uv-b deleterious effects upon plant tissue when PPFD is low(ish) is from many papers and studies and reviews. In nature, Uv-b makes up only a small fraction of the photons reaching a plant, so if we increase that fraction too much it effects them in a negative manner. I can upload some papers on the topic. I still have to upload the other papers I have too...so much to do, so little time!

When I wrote 600 PPFD that was my best guess for cannabis, considering 600 PPFD is fairly low irradiance for cananbis if Uv-b is high.

3rdEye said:

Another question that seems to fit here is whether UV-B actually increases total production of THC or is the seeming increase only due to the difference in loss of vegetative mass. It still would result in a increase in THC versus weight/volume which is a good thing in most cases as i gather it.

Click to expand...

The increase in THC is not relative to biomass, even though an increase in THC in X area (ex. per meter^2) was also found. I see no decrease in biomass (flower size or yield) when I use Uv-b vs. not using Uv-b. The deleterious effects of Uv-b is generally upon plant tissue directly, not total biomass AFAIU.

Uv-b and Uv-a also provide other benefits to plants, like blue light mediated responses such as increasing stomatal conductance, phototropism, aiding in photoperiodism, etc.

hades said:

Hi spurr,

Click to expand...

hades said:

I just read a few of your posts in the red:f-red thread, and I was very interested to read your posts in this thread shortly after. I believe we will have a lot to talk about in the future and I am very glad to make your acquaintance. My mind works like yours =D

Click to expand...

Great, nice to meet you! I'll PM you my email address.

hades said:

I researched UV-B and cannabis extensively about 5/6 years ago, back when Overgrow was still going strong. I wrote a research paper on the subject using all of the sources that I could find at the time. It is definitely a little out-dated now, but I still think you would enjoy reading it:
http://mrnice.nl/forum/showthread.php?t=3508

Click to expand...

Thanks, I'll check it out for sure, I love reading sound info on this topic. I am a member at Mrnice, as gojo. Sadly, because Mrnice forum doesn't offer HTTPS I refuse to post there (because I use a proxy and my unencrypted data can be intercepted via. packet sniffers).

hades said:

I'm very happy that you have quantifiable experiments suggesting the link and look forward to any other research about this subject you could point me to.

Take it easy

Click to expand...

Will do. I promise I will upload the relevant UV-b papers I have tomorrow. And I'll check out your thread too, I assume you have some of the same papers already

@ All,

Here are some papers about UV-b and cannabis, in the next few posts I will upload papers about UV-b and plants in general (that are comparable to effects on cannabis), such as flavonoid and terpenoid issues, rate of photosynthesis, PPFD (Photosynthetic Photon Flux Density; i.e. irradiance within PAR rage) issues, etc.

After I upload the papers I have (I still need to download a few more), I will post info about how to supply proven daily irradiance of UV-b to increase THC, and a good UV-b meter for testing irradiance, etc.

Some of the studies and papers I uploaded and posted in this post I am sure people have read before. A few cite the seminal work of J.Lydon, A.H. Teramura and C.B. Coffm (Photochemistry and Photobiology, Vol.46, No.2, pp. 201-206, 1987). Search for key words "cannabis", "uv" and "cannabinoid" in the PDFs if you don't want to read them in full.


~Papers and book online~


Chemical ecology of Cannabis
Pate, D.W., 1994.
Journal of the International Hemp Association 2: 29, 32-37.
http://www.hempfood.com/iha/iha01201.html


The Greenhouse Effect: Impacts of Ultraviolet-B (UV-B) Radiation, Carbon Dioxide (CO2),and Ozone (O3) on Vegetation
S. V. Krupa and R. N. Kickert
Environmental Pollution, Vol.61 (1989) pp.263-393
http://www.file-upload.net/download-3023921/The-Greenhouse-effect.zip.html

• I uploaded this to a Russian file host, the passphrase to decrypt file: "ilovecanna" (without quotes)

Advances in hemp research: Ultraviolet Radiation
By Paolo Ranalli
Psychology Press, 1999
http://books.google.com/books?ei=U8...nces+in+hemp+research&q=ultraviolet+radiation



~Uploaded papers~


The effect of ultraviolet radiation on the accumulation of medicinal compounds in plants
Wen Jing Zhang and Lars Olof Björn
Fitoterapia 80 (2009) 207–218

• That paper is a must read, it covers cannabinoids specifically, but also terpenoids, flavonoids, etc. The authors cite some of the papers I uploaded to this thread.

UV-B RADIATION EFFECTS ON PHOTOSYNTHESIS, GROWTH AND CANNABINOID PRODUCTION OF TWO Cannabis sativa CHEMOTYPES
JOHN LYDON, ALAN H. TERAMURA and C. BENJAMIN COFFM
Photochemistry and Photobiology Vol.46, No.2, pp.201-206, 1987


Higher plants and UV-B radiation: balancing damage, repair and acclimation
Marcel A.K. Jansen, Victor Gaba and Bruce M. Greenberg
PII: S1360-1385(1998)01215-1


Photosynthesis and Cannabinoid Content of Temperate and Tropical Populations of Cannabis sativa
F.A. BAZZAZ, D.DUSEK, D.S. SEIGLER and A.W. HANEY
Biochemical Systematics and Ecology, 1975, Vol.3, pp. 15-18

• That paper cites an old paper from 1926 that found UV affects sex expression in cannabis. I uploaded this because it discuses UV (albeit just a little), I am not claiming UV-b effect sex expression in cananbis, but it might (I will look into UV-b and sex expression at a later time). This is uploaded for its historical value citing such as old paper (from 1926).

~I will try to get this PhD thesis paper by John Lydon this coming week; it is cited in the 2009 paper by Wen Jing Zhang and Lars Olof Björn: "The effect of ultraviolet radiation on the accumulation of medicinal compounds in plants"~


Effects of ultraviolet-B radiation on the growth, physiology and cannabinoid production of Cannabis sativa L.
J.Lydon
Ph.D. thesis, Univ. of Maryland, College Park, MD, USA. 1986. p. 117

Abstract

The concentration of cannabinoids in Cannabis sativa L. is correlated with high ultraviolet-B (UV-B) radiation environments. Tetrahydrocannabinolic acid [THC-A] and cannabidiolic acid [CBD-A], both major secondary products of C. sativa, absorb UV-B radiation and may function as solar screens. The object of this study was to test the effects of UV-B radiation on the physiology and cannabinoid production of C. sativa. Drug and fiber-type C. sativa were irradiated with three levels of UV-B radiation for 40 days in greenhouse experiments.

Physiological measurements on leaf tissues were made by infra-red gas analysis. Drug and fiber-type control plants had similar CO2 assimilation rates from 26' to 32'C. Drug-type control plant had higher dark respiration rates and stomatal conductances than fiber-type control plants.

The concentration of THC, but not of other cannabinoids, in both vegetative and reproductive tissues increased with UV-B dose in drug-type plants. None of the cannabinoids in fiber-type plants were affected by UV-B radiation. The increased level of THC found in leaves after irradiation may account for the physiological and morphological insensitivity to UV-B radiation in the drug-type plants. However, fiber plants showed no comparable change in the level of cannabidoil (CBD). Resin stripped from fresh fiber-type floral tissue by sonication was spotted on filter paper and irradiated continuously for 7 days. Cannabidiol (CBD) gradually decreased when irradiated but THC and cannabichromene did not.

Click to expand...

Enjoy!

indifferent said:

Aye, that Joe Knuc article is a joke.

Sam did indeed say that he was unable to find any benefit to UV light, he used UV fluoro tubes in a greenhouse.

Click to expand...

The problem with "UV Fluoro" tubes is: (1) they often lack sufficient UV-b irradiance to increase THC and flavonoids content in glandular trichomes; and (2) if they do not provide the proper wavelengths (within UV-B) the effect would be greatly diminished.

I do not put much faith in the trails by Sam (I'm not trying to be rude, just honest) mostly because he never (to my knowledge) listed the UV-b irradiance as uW/cm^2/day (or any other quantification). Thus, we have no way to know if he conducted worthwhile trial(s).

We must measure and report the UV-b irradiance per day, and the wavelengths provided, to offer worthwhile data.

indifferent said:

Two great points Sam made that folks need to bear in mind:

1. If UV was truly important in the production of resin and potency, then all indoor grown bud would lack resin and potency as fluoros and HIDs don't produce UV.

Click to expand...

UV-b isn't needed for cananbis to form various secondary metabolites like cananbinoids (i.e. THC), flavonoids, etc. However, providing sufficient irradiance of UV-b will increase THC levels, and flavonoid levels too; even trepenoids levels AFAIU.

indifferent said:

2. A high altitude cultivar such as a Highland Nepalese will have the same high if grown at sea-level with a lower UV level, the nature of the high and potency being genetically pre-determined.

Click to expand...

No, that is a bit mixed up. The quantity of cannabinoids (at least THC) is a phenotypic expression, that means it is controlled by genetics and the growing environment (~50/50). However, the "chemotype" (ratio of cannabinoids to each other) is a genotypic expression, the drug bio-types we grow with high THC are chemotype I. That means the ratio of cannabinoids to each other are little affected by the environment.

I can post references to very good peer-reviewed published papers if people are interested.

indifferent said:

Apart from the research done by Raphael Mechoulam in Israel where he exposed CBD acids in a petri dish to UV light at 285nm and got a small proportion to convert into THC acids, has anyone ever published any proper scientific work on this subject?

Click to expand...

Yup, see this post of mine: https://www.icmag.com/ic/showpost.php?p=4056279&postcount=169


From the seminal work of J.Lydon, A.H. Teramura and C.B. Coffm (Photochemistry and Photobiology, Vol.46, No.2, pp. 201-206, 1987):

The researchers looked at the two main species of Cannabis spp. humans grow: (1) drug bio-type, the kind we grow, i.e., "indica" = C. indica and "sativa" = C. indica indica; and (2) the non-drug bio-type grown for fibre, i.e., "hemp" = C. sativa.

The researchers found that drug bio-type had increases in THC from UV-b irradiance. They found THC increases of about 15-32% in flowers and about a 22-48% in leafs.

I have highlighted the most relevant sections from the paper. The study found no increase in quantity of CBD (cannabidiol); only an increase in THC.

I have tested growing with sufficient level of UV-b irradiation, and I used comparative Thin Layer Chromatography to test the effects. In my tests, the irradiated plants did produce more THC, without a doubt. For my tests I converted the UV-b irradiance from the study below, the same UV-b that is found in nature near the equator, in summer, over 3 hours at noon time at ~9,000 foot elevation. Granted, my conversion is only approximate (but 'good enough' IMO) due to the different light sources (sun vs. lamp), and the different "absolute irradiance" calibrations of the spectroradiometer used by J.Lydon, et al. (1987), and the UV-b meter I used (a Solarmeter 6.2, here).

I converted 13.4 kilo-Joules/meter^2/3-hour (from J.Lydon, et al., 1987) into micro-Watt/cm^2/3-hour. My math, after converting the max daily irradiance used by J.Lydon, et al. (1987), that provided the most THC, came to 124 uW/cm^2/3-hour. Or, the same daily irradiance of UV-b can be supplied via. 248 uW/cm^2/1.5-hours; or 62 uW/cm^2/6-hours, etc.


UV-B RADIATION EFFECTS ON PHOTOSYNTHESIS, GROWTH and CANNABINOID PRODUCTION OF TWO Cannabis sativa CHEMOTYPES
J.Lydon, A.H. Teramura and C.B. Coffm
Photochemistry and Photobiology, Vol.46, No.2, pp. 201-206, 1987

• In this paper the authors refer to drug bio-type (chemotype I; high THC) and non-drug bio-type (chemotype III; high CBD) plants as under C. sativa L. But, current genetic and chemotype testing (Mahlberg and Hillig, et al.) found that is most probably not correct. Drug bio-types (incl. what we call indica and sativa) are now under C. indica; and hemp (non-drug bio-types) are under C. sativa.
• Also see the PhD thesis paper I cited above by John Lydon, 1986.

(excerpt from the paper)

ABSTRACT

The effects of UV-B radiation on photosynthesis, growth and cannabinoid production of two greenhouse-grown C. sativa chemotypes (drug and fiber) were assessed. Terminal meristems of vegetative and reproductive tissues were irradiated for 40 days at a daily dose of 0, 6.7 or 13.4 kJ/m^2 biologically effective UV-B radiation. Infrared gas analysis was used to measure the physiological response of mature leaves, whereas gas-liquid chromatography was used to determine the concentration of cannabinoids in leaf and floral tissue.

There were no significant physiological or morphological differences among UV-B treatments in either drug or fiber-type plants. The concentration of 9-tetrahydrocannabinol (THC), but not of other cannabinoids, in both leaf and floral tissues increased with UV-B dose in drug-type plants. None of the cannabinoids in fiber-type plants were affected by UV-B radiation.

The increased levels of 9-THC in leaves after irradiation may account for the physiological and morphological tolerance to UV-B radiation in the drug-type plants. However, fiber plants showed no comparable change in the level of cannabidiol [CBD] (a cannabinoid with UV-B absorptive characteristics similar to THC). Thus the contribution of cannabinoids as selective UV-B filters in C. sativa is equivocal.

Only the THC content in leaf and floral tissues of drug-type plants increased significantly with UV-B radiation. Regression analysis indicated that there was a significant linear increase in THC with UV-B dose in these tissues (Fig.3). The concentration of THC in leaf tissue increased by 22% and 48% with a total daily UV-B dose of 6.7 and 13.4 effective kJ/m^2, respectively, as compared to controls. The same levels of UV-B radiation resulted in a 15% and 32% increase in THC, respectively, in floral tissues.

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FWIW,

I use Osram Ultra VitaLux 300w UV-b mercy vapor lamps. First I had one setup on my Light-Rail 3.5 light mover, but then I bought a few more to more evenly irradiate the canopy. The Osram runs off of 230v, so to use it in the U.S. (120v household outlets) we need a down-converter:




And here is a great site about UV-b, tons of great info, I have been in contact with those who run the site. They are great guys and very knowledgeable:


I plan to test other UV-b lamps in the future, those with lower wattage.

Very interesting topic, and one that could pay off if you know what you're doing.... I tell you what, with the drought here this year, we saw more late summer and early fall sunshine than we ever get, and the cannabis turned out potent as can be....

Thanks for your hard work guys. Got my plenty of winter reading now...

Outstanding info, spurr!! Thanks a lot for sharing it.

Im introducing on a Excel sheet the sensibility curve from Caldwell, used to calculate UV-B (BE) on those studies, and be able to obtain it from the spectra of Vitalux and Megaray lamps (most used). But likely, conversion from radiometric UV-B irradiance to UV-B (BE) index is going to be below 1, due its normalized to effect for 300nm, and easily 75% of the output of such lamps is between 300 and 310nm, where effect (conversion value to UV-B (BE) lower than 1) is lower than at 300nm.


Vitalux emits (new) 1% of input energy as UV-B (3W from a 300W lamp). 3 W*h is 3600J (1W=1J/s). So in order to achieve a daily irradiance of 13KJ (13000 J), its required 3.6h of a 300W lamp a day for each sq meter. As conversion from radiometric UV-B to UV-B (BE) is below 1 (Ill came with a figure later) likely you would need to use a 300W lamp about 4.5-5h a day on each sq meter to achieve that irradiance (or normalized to 12h lighting, a little over 100W/sq meter). With floro tubes, which only puts out about 0.03% of input energy as UV-B on best cases, likely wattage required to achive those UV-B irradiances is going to be too high.

Meaning that, have you compared the UV-B chamber with a control with 100W more? In the sense of knowing if worth more using the supplement with UV-B or standard lighting. If enhancement is 25% more THC per dry weight, surely it worth it, but I would like to know if you tested it.

An important note about procedure on Lydon experiments is they not used UV-B just during blooming, but at least for one month earlier, and plants used were old, maintained on veg for several months (about 9).

Oldmac posted a little ago (cannabis.com) his results with 3 chambers carefully designed to have same irradiance and he observed a consistent increase in yield of 2 of 3 strains tested when using UV-B along both veg and bloom, while chamber only supplemented during bloom harvested in line with control chamber (no UVB). Unfortunately, he dont have equipment to measure THC content.

Spurr, have you noticed this as well ? (using UV-B during veg giving the best results?)

I noticed a premature aging effect caused by a 26w reptile 10.0 UVB tube placed 10cm from a plant. I put this down to the UVA. The trichomes on the side of the plant nearest the lamp went brown, not amber but brown, while the trichomes on the other side stayed clear, this was 4-6 weeks before the plant (a 14 week Oaxacan) was ripe. I have macro pics somewhere, have to dig em out.

similar story here, the Blueberry buds near my t5 UV reptile tubes - its a stretcher and they are only an inch or so away in places - have definitely had some reaction. purplish color and the leaves curling upwards (although the purple may be to do with cold temps too) normally i spin the plants around every few days so different bits are near the tubes but these are just too tall!
nice to see the tubes can have some effect though.

interesting to hear that it helps to use UV in veg though, makes sense - i need to try and sort that out.

i guess the effectiveness of UV to increase resin/thc my be strain/variety dependent to a degree??

I found this interesting, but I wouldn't know how to translate the numbers to real world applications.

Low UV-B fluence rates (<1 µmol m-2 s-1) cause no or very low amounts of CPDs that are below the limit of detection but stimulate protective and photomorphogenetic responses (Batschauer et al., 1996Go; Kim et al., 1998Go; Frohnmeyer et al., 1999Go) that affect the plant's resistance to UV-B stress and to other biotic stress types (Kim et al., 1998Go; Ballaré, 2003Go).

Click to expand...

Found here:

Ultraviolet-B Radiation-Mediated Responses in Plants. Balancing Damage and Protection Hanns Frohnmeyer and Dorothee Staiger
http://www.plantphysiol.org/cgi/content/full/133/4/1420

I couldnt be able to get an exact figure, because the equation I found for converting UV-B irradiance to UV-B BE index is not accurate (result a curve with less slope).

But all points up to the shorter wavelenghts of UV-B having by far the most pronounced effect, and all weighting functions have higher or lower curve slope, but all shows way larger effect for the 280-300nm range. So in order to match any index used on those studies, we need to use higher radiometric irradiance higher.

Notice that the main difference between high elevation and equatorial areas respect temperate climates is mostly on the UVB short cut off, and way less on the total amount of irradiance on the UVB range. It seems cut off on temperate climates about 292-293nm is way less effective than cut off at 288nm, when total irradiance not vary excessively (about 1.5x more irradiance at lower cutoff achieves effect one order of magnitude higher). So its really difficult to make any assumptions about UVB irradiance we need to use.

If almost all studies about UVB get a similar conclusion is about the variability of effect between plant species and more yet, between varieties of same specie. We have many evidences that UVB effect on cannabis is strongly strain dependent. From no effect to very sensitive.

Other generalized consensus between botanists is UVB effects are dependent of other factors (humidity, CO2 and specially, light intensity on visible and UVA spectrums):

It seems UVA effect is opposite to UVB effect, and thus using UVA (as many people does for MJ) is counterproductive.

On the other hand, UVB irradiance effect seems to be related to total UVB-visible radiation. Many experiments are carried under very high UVB/visible ratios, an unrealistic situation for both field conditions or our indoor grows . So we should take some results with a grain of salt:

For example, the graph posted by spurr on post #170. Looking at experiment conditions, I found flowering was performed at a greenhouse on winter, with an average PAR irradiance of 10-11mols/sq meter-day. Translating it to a 12h indoor grow, its 240 micromols of photons (uE) per second per sq meter. Way lower than any of us uses (except maybe some LED grows, that are just a little over it). We often consider 500uE/m2 as minimum usable in order to obtain good budding (growers usually uses more, or a lot more). We know a MJ plant grow under such irradiances usually develop sparse small and airy buds, very little dense. On the other hand, 13KJ UVB/240uE has a noticeable larger effect than 13 KJ UVB/600uE or 13KJUVB/1000uE.

As result displayed in the graph is of weight of THC/weight of bud, if UVB irradiance results on increased resin production, that ratio (showed in the graph) enhances very quickly, but mostly due buds weight is low. As shown comparing leaves enhancement vs bud enhancement, 50 and 25% respectively (give or take).

So I would take with a grain of salt those exact figures. All this not mean results is not valid, and that increase of THC is linear with increasing UVB irradiance. But I believe the slope of such graph would be way less if done under our usual growing conditions. Anyway, it seems UVB may strongly enhance hash production off leaves and manicuring rests.

nice post knna - great to have you here

so presumably the difference in UVB wavelength between altitude and temperate is doe to the atmosphere filtering out UVB below 290nm? thinner atmosphere at high altitude will filter out those wavelengths below 290 less efficiently??

VG

messn'n'gommin' said:

I found this interesting, but I wouldn't know how to translate the numbers to real world applications.



Found here:

Ultraviolet-B Radiation-Mediated Responses in Plants. Balancing Damage and Protection Hanns Frohnmeyer and Dorothee Staiger
http://www.plantphysiol.org/cgi/content/full/133/4/1420

Click to expand...

There is proof of low irradiances able to trigger UVb mediated response. On other article of the linked by spurr (The effect of ultraviolet radiation on the accumulation of medicinal compounds in plants), it says there is evidence of two specific UVB receptors on plants, one with maximun peak sensivity 280-290nm requiring just 0.1uE/m2, and other with peak sensibility 300-310 with required fluence rate about 1uE/m2.

One thing is to trigger photomorphogenesis effects (thicker leaves, or thicker leaves epidermis, for example) and other to promote higher production of THC/resin. We still dont know if such low UVB fluence rates may trigger it.

But in case its enough, I can help translating it to figures for our real world:

-1 optical watt holds:

-2.27uE of 280nm
-2.32uE of 285nm
-2.36uE of 290nm
-2.4uE of 295nm
-2.44uE of 300nm
-2.48uE of 305nm
-2.52uE of 310nm
-2.56uE of 315nm

Average of UVB 280-315nm range, 2.42uE/Watt.

Using the vitalux 300W, which emits 3W, you have about 7.35uE. Way more than required to obtain 1uE/m2.

A 160W mercury vapor lamp should be more than enough to lit a large area with such low UVB levels

Thanks knna!

I can't find any info on UVR levels for the CMH lamps and was hoping that at least the 250w emitted enough to "qualify" as a low fluence rate UV-B source. But, a lack of quantifiable numbers makes it harder to do. So, now I'm thinking maybe (and by extension the 400w), but probably not, as either would probably emit considerably more UV-A.

Still, I have two Repti-sun 10.0 desert lamps I've used for the full 12 hours during flowering and way too close to the canopy, noticing a definite negative effect of yield. I think I'll add them to the mix this next run, but at less duration and a bit more distance.