UV Light and Terpenoids

[knna]

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

This graph shows how a ozone column reduction of 20% affect expected UVB irradiance. High elevation areas have such reduction of ozone column as well.

You can see how as all UVB irradiation is increased, it does little on most range, but below 300nm is when the difference is huge.

I believe, but this is pure speculation, that 288-292nm plays an esential role on the effect of UVB on plants. Maybe a reduced irradiance of just that narrow range could make the difference. But no way of testing it, AFAIK. Some day in the future maybe we have UVB LEDs with most emission between 285-300nm, but that would be the only way of testing and using it if result practical. Surely not avalaible on the near future (at not outrageous cost).

 

[knna]

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.

Likely no any lamp with using an standard glass is going to be able to emit UVB enough to be noticeable by plants. Well, maybe for 0.1uE/m2, just below the lamp...but I doubt it. Normal glasses are almost fully opaque to wavelenghts below 365nm or so. Very little is able to go out the glass.

It would be required some manufacturer decided to release a CMH using an special glass somewhat transparent to UVB (as those use on pet bulbs), for horticulture. More likely, specific for MJ growing.

Distance is critical with UVB floros/CFLs. They are less efficient emitting UVB than mercury vapor lamps, and emits diffused light. Too far and they achieve very little effective UVB irradiance. Too close and you notice the deleterious effect of excess UVB. But the right distance is a matter of just few cm, probably no more than 2" closer or farer.

 

[Donald Mallard]

Hi greeninthethumb ,, i didnt read the whole thread ,,, but ,,
just wondering if much testing has been done in tropical zones?? ,, i notice most tests are using un natural light ,, is it the same as the tropical sun??

Id love to know why erb grown in the tropics is often stronger , particularly sativas grown in the tropics vs those grown indoors or in temperate climates ..

 

[VerdantGreen]

how about interference? i read someone claiming that the weak light from the uv tubes would be 'cancelled out' by the stronger light from an hps?. i was dubious about that but im no expert.

 

[spurr]

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

I have a bunch more PDFs to upload, I will try to do so in the next few days. Probably later today, once I download a few more and scan a few from hardcover annual journal reviews.

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).

Great. Let us know when it's done. I attached a PDF to this post you might find interesting and useful, it's one 3rdEye asked me for:

"Influence of PAR and UV-A in Determining Plant Sensitivity and Photomorphogenic Responses to UV-B Radiation"
Krizek, Donald T
Photochemistry and Photobiology 79(4):307-315. 2004​

Do you have all the Caldwell papers on UV-b? He has co-authored nearly a dozen papers on UV-b, I could get all of them tomorrow if you don't have them. And you do have his following paper for finding UV-b(be), yes?

"Solar UV irradiance and the growth and development of higher plants"
Photophysiology (Edited by A. C. Giese), Vol. 6, pp. 131-177​

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.

Yes, below 1 makes sense, but I think it will be close enough for our use. My conversion of 13.4 kJ/m^2 UV-b(be) into into uW/cm^2 UV-b (applied over X area) was close enough to elicit a strong increase in THC.

Vitalux emits (new) 1% of input energy as UV-B (3W from a 300W lamp). 3 W*h is 3600J (1W=1J/s).

Where did you get that figure of 1%?

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.

In the study by J.Lydon, et al. (1987), they measured kJ as irradiance (i.e. kJ/m^2), not as radiance. That is why they were able to provide two different levels of UV-b to the plants (by moving the lamp closer and further from the canopy*). Thus, distance to canopy needs to be considered too. A 300w lamp one foot from canopy will provide higher irradiance at canopy than the same lamp two feet from canopy, albeit in a smaller area, even thought the radiance (at the lamp) will be the same at both distances. Thus, a 300w lamp one foot from canopy would be used for a shorter time period to reach the same daily irradiance, ex. ~13 kJ/m^2, than a 300w lamp two feet from canopy.

* J.Lydon, et al., (1987) wrote:

"Individual plant heights were adjusted to maintain a uniform canopy, while the lamp/plant distance was maintained at 0.25 [meter] (0.08 mm CA filtered lamps) or 0.35 [meter] (0.13 mm CA and Mylar filtered lamps)."​

Also, area isn't a necessary factor to hold, ex. we don't need to use meter^2. And it's better not to use meter^2 because UV-b meters usually measure incident radiation (i.e. irradiance) in centimeter^2 (as microWatts). High radiance (wattage) mercury vapor UV-b lamps are very directional with small irradiance footprints (unlike lower radiance UV-b fluorescent tubes). That said, we can use uW/cm^2, as I have done, over a larger area to find the UV-b irradiance at canopy over any area we choose and still equal ~13 kJ/m^2 (for that smaller area). For example, using a goal of 124 uW/cm^2/3-hour (which equals 13.4 kJ/m^2/3-hour) I measured the irradiance over a 2 foot circumference under the Osram (due to its directionality of irradiance footprint). That means if we can provide ~124 uW/cm^2/3-hour over every centimeter^2 within X area we can come close to providing the same irradiance over a smaller area as is provided via. 13.4 kJ/m^2.

In the study by J.Lydon, et al. (1987), the workers used a daily dose of UV-b (weighted to UV-b(be)) over a 3 hour period, or a 6 hour period, I am not 100% sure. Their use of the phrase "on either side of solar noon" is a bit confusing, they could mean they used UV-b for 3 hours either before or after solar noon; or they could mean they used UV-b for a total of 6 hours by 3 hours before and after solar noon. But either way it doesn't matter, it's the daily dose (irradiance) of UV-b that matters, i.e. 13.4 kJ/m^2.

J.Lydon, et al. (1987) wrote:

"Ultraviolet-B radiation was provided for 3h on either side of solar noon, resulting in a daily UV-B(be) dose of 0, 6.7, or 13.4 effective kJ/m^2 UV-B(be). The highest dose was equivalent to the daily weighted UV-B dose received under clear sky conditions and minimum solar zenith in Colombia, South America (0" latitude, 3 km elevation, Julian [June] date 80, Green er al., 1980)."​

That is why to reach 13.4 kJ/m^2 over a whole day we could use 62 uW per cm^2 for 6-hours (ex. over a meter^2; i.e. 62 uW every cm^2 over m^2 for 6 hours), or 124 uW per cm^2 for 3-hours, or 248 uW per cm^2 for 1.5-horus, etc. We can modify area and time and still achieve an equivalent daily irradiance of 13.4 kJ/m^2 over a whole day.


Math:

for 3 hours of daily irradiation over a meter^2 as watt:​

1. (13.4kJ/m^2/3hr) / 3 = 4470 J/m^2/hr
2. (4470 J/m2/hr) / (60*60) = 1.24 J/m^2/sec (ie. 1.24 W/m^2/3-hours; i.e. 1,240,000 uW/m^2)

for 3 hours of daily irradiation over a cm^2 as micoWatt:​

• (1.24 W/m2) / (100x100) = 1.24e^-4 W/cm^2 (ie. 124 uW/cm^2/3-hours; i.e. 0.000124 W/cm^2)

for 6 hours of daily irradiation over a meter^2 as watt:​

1. (13.4kJ/m^2/6hr) / 6 = 2233.333 J/m^2/hr
2. (2233.333 J/m2/hr) / (60*60) = 0.62 J/m^2/sec (ie. 0.62 W/m^2/6-hours; i.e. 620,000 W/m^2)

for 6 hours of daily irradiation over a cm^2 as micoWatt:​

• (0.62 W/m^2) / (100x100) = 6.2e^-5 W/cm^2 (ie. 62 uW/cm^2/6-hours; i.e. 0.000062 W/m^2)

I think using microWatt as uW/cm^2, or as uW/m^2 i.e. (uW/cm^2)*(100*100), is better than kJ (as kJ/meter^2) because the good UV-b meters mostly use uW/cm^2 as the quantification of irradiance. What I did was convert 13.4 kJ/m^2/3-hour (and 13.4 kJ/m^2/6-hour) from the study by J.Lydon, et al. (1987) into micro-Watt/cm^2/X-hour. My conversion was not 100% accurate because of the factors you and I wrote about, i.e. weighting of photons, etc., but it was effective to increase THC in my tests.

What I did was use a UV-b meter (Solarmeter 6.2, here) to measure irradiance of the lamp to find at what distance from canopy the lamp provided ~124 uW/cm^2 (over ~2 foot circumstance). And then I ran the lamp(s) for 3 hours a day starting at mid daylength under HID in an attempt to mimic when plants would get most UV-b in nature, around midday.

The major problem with high intensity (radiance) mercury vapor UV-b lamps is they are very directional, thus they have a small irradiance footprint. Neither the Osram or the MegaRay are able to irradiate a meter^2 with high irradiance UV-b. That is why they are hard to use, they have small footprints. I attached my UV-b lamp to a light mover and that worked OK, but then I bought a few more lamps so I had bigger and more even footprint of UV-b irradiance at canopy and didn't have to use the light mover.

I chose the Osram because it is less directional than the MegaRay, thus the Orasm has a bigger footprint with more even irradiance (less extreme irradiance peaks within the footprint). The MegaRay has an even smaller high irradiance footprint than the Osram, with more extreme irradiance peaks within the footprint.

• I am sure you have seen it, but if not, check out this comparison of the Osram and MegaRay: http://www.uvguide.co.uk/zoolamps.htm

If you are going to use data from the work by the folks at UV Guide UK, it's important to know they used the same UV-b meter I used. And the Soloarmater 6.2 (UV-b meter) master NIST traceable calibration was done using a pair of typical tanning lamps peaking at 350 nm UVA with ~7% UVB. A spectrum similar (but not exact) to noon tropical sun. So the spectral response of the Solarmeter 6.2, and of the data from the UV-b mercury vapor guide above, is not flat, as would be found in a good quantum sensor (for PPFD).

RE: source of UV-b irradiance in the study by J.Lydon, et al. (1987):

UV-b irradiance came from a filtered Westinghouse FS-40 sunlamp, as described in the work of Mirecki and Teramura (1984). FS-40 lamps are "phototherapy" UVB lamps with lots of irradiance below solar 290 nm. The lamps were fitted with either presolarized 0.08 mm or 0.13 mm cellulose acetate (UV-b transmitting) or 0.13 mm Mylar Type A (as control filters).


RE: absolute uW:

The spectroradiometer used to quantitate the UV-b irradiance by J.Lydon, et al. (1987) was an Optronic Laboratories, Inc. Model 742 spectroratiometer. And as you wrote, the spectroradiometer data was weighted with a generalized plant action spectrum for UV-b(be) (Calwell, et al, 1971), and normalized at 300 nm.


RE: daily Uv-b irradiance:

In the study by J.Lydon, et al. (1987) the workers used a daily UV-b irradiance (as kJ/m^2) equivalent to the daily weighted UV-b irradiance under clear sky conditions and minimum solar zenith in Columbia, South America at 0' latitude, 3 km elevation, June, 1980 (Green, et al., 1980).

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).

Yes I agree about increased time period to account for unweighted to weighted UV-b irradiance. But, we still need to consider distance to canopy as I noted above. Using watts alone (per meter^2) will not work because it doesn't measure irradiance at canopy, unless using so-called "PAR watts" (i.e. Watt/meter^2 as irradiance measured with a Pyranometer), but "PAR watts" is not a good measurement of light (irradiance) for plants.

Measuring irradiance of UV-b at canopy with a UV-b light meter is the best option. We can measure uW/cm^2 over a meter^2 to find Watt/m^2 of UV-b, ex. ((uW/cm^2)*(100*100))/1,000,000. That is why I converted 13.4 kJ/m^2/3-hour into 124 uW/cm^2/3-hour, so I could measure the UV-b irradiance and know what I am providing.

Meaning that, have you compared the UV-B chamber with a control with 100W more?

I do not understand your question, could you elaborate for me? I measured by uW/cm^2, and I tried to make the irradiance over a meter^2 (using a light mover) as close to 1.24 watt (UV-b) as I could by using 124 uW/cm^2 as a goal, i.e. ((124 uW/cm^2)*(100*100))/1,000,000. But due to the heterogeneous irradiance footprint from mercury vapor UV-b lamps I was not able to due so, even with the light mover, so I had to add more lamps to provide greater homogeneity in terms of canopy irradiance.

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.

Tested what? True quantification of THC by mg per gram of dry weight bud as in the study by J.Lydon, et al. (1987)? If so, no, not yet. I used comparative TLC (Thin Layer Chromatography), and with that it's hard to say very accurately the percent increase of THC in terms of spot density (not by mg/Gram). That said, the THC increase by comparing spot destiny was > ~15-20% vs. non-UV-b irradiated cananbis.

I plan to use quantitative HPTLC (High Performance TLC) and Gas Chromatography, to re-test effects of the same UV-b irradiance early in the coming year, once I move and get my new rooms setup.

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).

Yup, the workers used 30 days of irradiation during veg before starting the experiment (i.e. quantitating THC by mg/gram). Then the workers used at least 40 more days of UV-b irradiance during the experiment, for a total of at least 70 days of UV-b irradiation. I too used more than 70 days of UV-b irradiation starting during veg (for about three weeks) until harvest (for about 8 weeks).

J.Lydon, et al. (1987) wrote:

"Vegetative or flowering plants were exposed to UV-B radiation for 30 days prior to the start of the experiment. At that time, plants were trimmed to a uniform height. Vegetative and floral meristems developed while plants were irradiated for an additional 40 days.
...
Vegetative drug-type plants (10 plants per treatment) were exposed to UV-B radiation during the months of November and December 1983 when the plants were 9 months old; average total daily photosynthetic photon flux density** (PPFD between 400 and 700 nm), recorded with a LI-COR LI-550 printing calculator equipped with a LI-COR LI-185 quantum sensor, was 11.4 mol m^2***, and average daily maximum/minimum air temperature were 25/20°C. The natural photoperiod was extended to 16h with a 1000W General Electric Hg vapor lamp to inhibit flowering.

Reproductive drug-type plants (10 plants per treatment) were irradiated during the months of February and March 1984 when the plants were 11 months old, the average total daily PPFD was 13.5 mol m^2****, and average daily maximum/minimum air temperatures were 28/23"C."​

** "total daily" PPFD is termed DLI (Daily Light Integral).

*** mol/m^2/day is DLI, and 11.4 mol/m^2/16-hour day = ~198 PPFD (which is very low, cannabis has highest rate of photosynthesis under 1,500 PPFD. Greater than ~1,600 PPFD is light saturation point for cannabis).

**** 13.5 mol/m^2/6-hour day = 625 PPFD (I used 6 hour average daylength as found in Mississippi, the location of the study I believe, from February to March. That said, 625 PPFD is also very low, far too low for ideal yield and growth rate of cannabis)

FWIW,
Here is a big post of mine about ideal PPFD and DLI for cannabis, backup by four different studies all finding ideal PPFD fro cannabis is ~1,500:
https://www.icmag.com/ic/showpost.php?p=4052410&postcount=473

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?)

Yes. I tested using UV-b only in flowering and via. comparative TLC I found more THC in cannabis that was irradiated during veg and flowering vs. only during flowering.

 

[spurr]

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.

Most likly you had it too close, that is why I suggest people buy a Uv-b meter, such as the Solarmeter 6.2.

 

[spurr]

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.

I also bet you might have either provided too much instantaneous UV-b or too much daily dose of UV-b. That is why I did the math I wrote out above, and used a UV-b light meter to know I was providing an ideal 'ball park' range of UV-b as instantaneous and daily irradiance.

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

I will upload some more papers today or tomorrow, but yes, UV-b does help growth, as does UV-a, both in terms of "cryptochrome" mediated photoreactions, etc.

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

I doubt to noticeable degree. An important factor is to provide high PPFD (irradiance in PAR range; 400-700 nm) when using UV-b due to the deleterious effects UV-b can have on plant morpholgoies/growth/tissue. The key to irradiating a canopy with UV-b is to know the UV-b wavelengths provided and how much UV-b you are providing (as instantaneous UV-b and daily net rate (dose) of UV-b).

 

[spurr]

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)

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

What they are writing is very low irradiance of UV-b, i.e. less than 1 microMole per meter^2 per second, has little effect upon plant photoreactions to UV-b in terms of "plant's resistance to UV-B stress and to other biotic stress types". What that means is we need to provide sufficient level of UV-b to elicit a response, such as increasing THC. And rest assured, ~13 kJ/m^2/3-hour is much more than 1 umol/m^2/second.


FWIW,

microMole is also called [FONT=Arial, Helvetica, sans-serif]microEinstein[/FONT], and 1 umol = 1 photon, with energy per photon not withstanding in this example; i.e. lower wavelength photons (ex. blue) hold more energy than higher wavelength photons (ex. red). A photon is also called quanta.

 

[B. Friendly]

light spectrum most definantly has an effect on the plant, plus what goes in determines what comes out.

you will not get anything new, but the amounts of this and that cannabinoid would be altered.

grow a plant in Cali, Hawaii, BC and Amsterdam and you'll notice different effects from your herb.

there will be a difference in your bud if you use HPS or MH bulbs, so obviously there is a light spectrum difference on your MJ.

What is so hard to wrap your head around??????

 

[spurr]

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).

Yes I thought it might be hard to do so, a 'ball park' figure is fine from my testing. I didn't bother trying to weight the photons and I still got strong increase in THC, as the old saying goes: close enough for horse-shoes and hand-grenades

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.

For close accuracy to the studies yes. However, UV-b range is ~280 nm to ~315 nm, and as long as we provide sufficient irradiance within UV-b there is a strong increase in THC (as found from my testing). I think trying to use plant action spectra weighted UV-b might not be worth the effort. I would rather test with a good UV-b meter, such as the Solarmeter 6.2, and attempt to provide 13 kJ/m^2/3-hour UV-b irradiance per day (unweighted for plants). In fact, that is just what I did, via. ~124 uW/cm^2/3-hour and I did see an increase in THC, a worthwhile increase from TLC assay and from smoking the bud (got me and my friends noticeably higher)

I plan to conduct more testing this coming year, with quantification of THC. I will be using the Solarmeter 6.2 UV-b meter, or a different UV-b meter that does not weight photons at all (like a good quantum sensor), to find ideal level of UV-b irradiance as instantaneous irradiance (by rate of photosynthesis using "chlorophyll fluorometry") and as daily dose of UV-b (by rate of photosynthesis and net rate of photosynthesis using chlorophyll fluorometry, and by THC production, flavonoid production and possibly even terpenoid production, etc).

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.

Yup. That is why I think my testing with a commonly available (high irradiance) UV-b lamps and a good UV-b meter, irrespective of plant action spectra in UV-b range, might be a good way to go. That way, the data and findings are usable by most all cannabis growers...and easy to comprehend and put into action.

Using properly weighted UV-b(be) is best, for sure, but also most difficult and would stop many cananbis growers from trying to supply sufficient/ideal UV-b; at least in my opinion. This is similar to the point that using PPFD, and not Quantum Flux Density or Yield Photon Flux is sufficient for measuring PAR range light for plants. Mostly because the quantum yield (effect upon photosynthesis of plants) difference between blue, green and red is not huge; and under high irradiance white light, green light has been found to drive rate of photosynthesis more than blue and even red light (that goes to flaws in the work of Keith McCree and Katsumi Inada; re: they both used monochromatic lighting to make each of their plant action spectra).

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.

I have not seen studies finding that, they do however tend to find chemotype III plants (i.e. hemp, C.sativa), which is a different species than what we grow (i.e. chemotype I; C.indica), has little THC increase from UV-b. However, I have tested UV-b on a few different varieties of cannabis, and they all showed an increase in THC. In the work of J.Lydon, et al., (1986 and 1987), they used strains from a Jamaican variety of drug bio-type (chemotype I) cannabis. I assume the Jamaican variety they used was not from a linage of cannabis from a high UV-b irradiance elevations (i.e. > ~7,000 feet), thus, that seems to indicate response to Uv-b in terms of THC production is not variety, nor overly race (i.e. ecotype) dependent.

FWIW, the word "strain" is a misnomer when we mean "race" or "variety". The word "strain" is synonymous with "cultivar" (with a semantic caveat not wroth mentioning here).

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

Yes, see the most recent paper I uploaded about PAR and UV-a effect upon plant photoreactions to UV-b.

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:

The studies by J.Lydon, et al. (1986 and 1987) used low levels of PPFD and Daily Light Integral (DLI), see my post here decribing the PPFD and DLI they used. The PPFD and DLI used by J.Lydon, et al., is much lower than most cannabis growers provide who use HID > ~400 watt. And the PPFD and DLI used by J.Lydon, et al., is lower than many growers provide who grow with high irradiance LED panels. I think I recall you try to use ~800 PPFD, yes? If so, you are using more than J.Lydon, et al., used in their studies.

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.

Pretty close, DLI was 11.4 mol/m^2 for 16-hour day (for veg), which equals ~198 PPFD; and 13.5 mol/m^2 for ~ 6-hour day (for flowering), which equals 625 PPFD.


FWIW, using the term "PAR" when we mean "PPFD" is a misnomer. PAR used to be the term for umol/m^2/second, but for a couple of decades it has been changed to PPFD, mostly thanks to Keith McCree. PAR, as a measrue of irradaince, is used for watt/meter^2 (ex. with a Pyranometer); and PAR is also used to for non-irradiance when used to qualify the wavelength range that most efficiently drive rate of photosynthesis (i.e. 400-700 nm). However, photobiologists have been arguing that PPFD is also a misnomer, due to the use of the word "density"*. I for one think using PPFD is fine, and there is no need to change the term for umol/m^2/second, yet again.

* Topic 9.1: "Working with Light"
A Companion to Plant Physiology, Fifth Edition by Lincoln Taiz and Eduardo Zeiger
http://5e.plantphys.net/article.php?ch=t&id=131

"The flat sensor measurement of photosynthetically active radiation (PAR, 400 to 700 nm) may also be expressed on the basis of energy (W/m–2) or quanta (umol/m–2/s–1) (McCree 1981). It is important to note that PAR is an irradiance-type measurement [i.e. "PAR watts" as W/m^2 from a Pyranometer]. In research on photosynthesis, when PAR is expressed on a quantum basis, it is often given the special term photosynthetic photon flux density PPFD). However, it has been suggested that the term "density" be discontinued (Holmes et al. 1985) because within the International System of Units (Système Internationale d'Unités, or SI units) "density" can mean area or volume. Moreover, area is contained within the term flux. PPFD has in some cases been shortened to PPF, but it is not clear whether this abbreviation represents an irradiance-type or a spherical measurement."
​

Translating it [DLI as 10-11mols/sq meter-day] 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.

Yup, for sure, over 1,000 PPFD is the best goal. FWIW, if we convert the two different DLIs used in the study, 11.4 mol/m^2 for 16-hour day (for veg), and 13.5 mol/m^2 for ~ 6-hour day (for flowering), we come up with the two following PPFD figures under a 12 hour daylength:

1). 11.4 mol/m^2 for 16-hour day (for veg in the study) equals ~198 PPFD. So then, PPFD of 11.4 mol/m^2/12 hours would come to ~264 PPFD (i.e. ~264 umol/m^2/second).

2). 13.5 mol/m^2 for ~ 6-hour day (for flowering in the study) equals 625 PPFD. So then, PPFD of 13.5 mol/m^2/12 hours would come to ~313 PPFD (i.e. ~313 umol/m^2/second).
​

On the other hand, 13KJ UVB/240uE has a noticeable larger effect than 13 KJ UVB/600uE or 13KJUVB/1000uE.

I am not sure that is correct. If we use lower PPFD (ex. 240 umol/m^2/second) with 13 kJ/m^2/day of UV-b, I think the effect on growth and morphology of the plant (not in terms of THC content) would be more deleterious than if we used used 600 PPFD or 1,000 PPFD with 13 kJ/m^2/day of UV-b.

Also, in that study by J.Lydon, et al., I think they used ~625 PPFD for flowering with UV-b, not 240 PPFD, because I think they used a 6 hour daylength for flowering. I think they used 6 hour daylength for flowering because they didn't mention supplemental (increased) daylength hours from HID in flowering, only for veg. However, in that study they did use ~240 PPFD (i.e. more accurately ~264 PPFD) with Uv-b, for veg only, because they used a 16 hour daylength.

Of course, I am forming my opinion about PPFD during flowering on the average hours of daylight found in Mississippi (i.e. 6) from February to March; and I could be wrong about my assumption. I will email J.Lydon this week to ask how long the daylength was for flowering.

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).

Very good point.

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.

I would not take the results "with a gain of salt", I do however agree the exact percentage increase of THC as mg to gram of dry bud is not a very accurate example of what we would see. I write that because I use ~1,100 PPFD for flowering, thus for flowering (under 12 hour daylength) I provide ~46 mol/m^2/day. And I found a very worthwhile increase in THC when using ~1,000 PPFD in veg (i.e. ~61 mol/m^2/17 hour daylength) and ~1,1000 PPFD in flowering (i.e. ~46 mol/m^2/12 hour daylength). Although, I didn't use weight of THC to compare results, I used comparative spot density via. TLC.

 

[spurr]

@ all,

The paper I uploaded titled "Influence of PAR and UV-A in Determining Plant Sensitivity and Photomorphogenic Responses to UV-B Radiation" was not complete, it lacks the references second, some images/tables, and had formatting errors such as "12 kJ m^sup -2^ day^sup -1^" instead of "12 kJ m^-2 day^-1". I will try to get a better copy of the paper tomorrow:

Influence of PAR and UV-A in Determining Plant Sensitivity and Photomorphogenic Responses to UV-B Radiation
Krizek, Donald T
Photochemistry and Photobiology 79(4):307-315. 2004​

FWIW, in biology the use of "^-1", as in "day^-1" or "second^-1", means the same thing as writing "day" and "second". So, when PPFD is written as "umol/meter^2/second^-1" it's the same as writing "umol/meter^2/second".

 

[knna]

I have a bunch more PDFs to upload, I will try to do so in the next few days. Probably later today, once I download a few more and scan a few from hardcover annual journal reviews.

Yes, its very interesting, resuming previous studies on a very meaningful way. I always loved Krizek, I had read many of his articles. But I didnt know this one.

This is due I have never focused my research on UV effects, but on other lighting topics. I need to select what I want and can do, and some reason let me to give up experimenting with UVB. The practical difficulties (little lamps available, short lived, very difficult to work with narrow bands without using filters...) and personal reasons (high family susceptibility to retina disease).

But Ive been always been very interested on the topic, so I chimed in when I saw the excellent info you gave. Ill try to help on what I can, but not experimenting myself.

Great. Let us know when it's done. I attached a PDF to this post you might find interesting and useful, it's one 3rdEye asked me for:

"Influence of PAR and UV-A in Determining Plant Sensitivity and Photomorphogenic Responses to UV-B Radiation"
Krizek, Donald T
Photochemistry and Photobiology 79(4):307-315. 2004​

Do you have all the Caldwell papers on UV-b? He has co-authored nearly a dozen papers on UV-b, I could get all of them tomorrow if you don't have them. And you do have his following paper for finding UV-b(be), yes?

"Solar UV irradiance and the growth and development of higher plants"
Photophysiology (Edited by A. C. Giese), Vol. 6, pp. 131-177​

I have about half dozen of Cadwell articles. I tried to get "Solar UV..." but I was unable to find it. The equation I got was cited on other article as the Cadwell one, but after introducing it on the Excel sheet, I realized it not matched with graphs showing it.

The weighting equation is:

W(λ)=2.618*(1-(λ/331.3)^2)*exp{(300-λ)/31.08}

for 286<λ<313nm.

Anyway, my only interest was to find the radiometric irradiance equivalent to those 13.4KJ/m2. And for other studies that uses same weighting function. Any weighting function has proven to accurately represent plants responses to UV-B. This one pretended to be a generalized UVB induced damage action spectrum, but later studies showed that longer wl plays an higher role than initially thought (maybe the equation I has represent a curve with less slope proposed later by Cadwell taking it into account). But other effects of UVB has their own weighting functions.

And we dont have a minimal idea of the action spectrum of THC enhancement reaction of cannabis. So we must work with radiometric units not weighted and compare when using different UVB spectrum if those with more energy on shorter wavelength actually has an higher effect,and if so, how many more effective, if just slightly or with an order of magnitude of difference.

Yes, below 1 makes sense, but I think it will be close enough for our use. My conversion of 13.4 kJ/m^2 UV-b(be) into into uW/cm^2 UV-b (applied over X area) was close enough to elicit a strong increase in THC.

Any weighting is going to give a figure below radiometric power, that is sure. But as we actually dont know what weighting function is more adequate for THC enhancement, the best we can do is experiments with figures reasonably near, as you did. And observe results.

Research with cannabis should be able to find what irradiances produce weird and undesired reactions, in order growers are aware of minimal distances at which use each type of lamp. Once found that limit, all is experiment with figures below it and check if enhancement is actually lineal on true growing conditions or using relatively low irradiances may get a good enhancement effect.

Where did you get that figure of 1%?

Directly for your link to the Vitalux bulb. It states 3W output in a hour. How accurate is it, I dont know. It appeared rather high to me, but I have never weighted the emission of a UVB bulb. Surely Ill do as soon as I have some time for it and find and accurate spectrograph with reliable lm output.

Unfortunately my spectroradiometer is not UVB, reach up to a minimun of 340nm, and little accuracy below 360.

In the study by J.Lydon, et al. (1987), they measured kJ as irradiance (i.e. kJ/m^2), not as radiance. That is why they were able to provide two different levels of UV-b to the plants (by moving the lamp closer and further from the canopy*). Thus, distance to canopy needs to be considered too. A 300w lamp one foot from canopy will provide higher irradiance at canopy than the same lamp two feet from canopy, albeit in a smaller area, even thought the radiance (at the lamp) will be the same at both distances. Thus, a 300w lamp one foot from canopy would be used for a shorter time period to reach the same daily irradiance, ex. ~13 kJ/m^2, than a 300w lamp two feet from canopy.

Yeah, usually studies are done measuring irradiance at top canopy. Its the easier way of doing it.

I prefered to use an alternative way when studying our indoor grows. Kind of reverse thinking. When using high reflective walls, and radiance is known, its possible to calculate the average irradiance of the area and more yet, the light density for the plants volume. As total photosynthesis is strongly related to photons available, this procedure gives aditional very valuable info, as we know the effect of a given number of photons on a given area.

I prefer to go to irradiance from radiance, instead of radiance from irradiance. Actually I use both methods, but using just the second, as usual, is incomplete, IMHO.

On the other hand, studies on a greenhouse cant do that. But giving the DLI at top canopy underestimate actual photons available for plants use, because the side lighting (not in the Lydon study, they surrounded plants stand with mylar) and diffuse lighting.

So adjusting irradiance by raising the lamp works, but depending of footprint of lamp, actually photons available may decrease on lower degree, if light initially going out is bounced back on side walls.

The assumption of top irradiance correlating with total photons available is based on some conditions that not always apply (a fault I see on many botanical studies). What has been proven is total photosynthesis of whole plant correlates with amount of photons absorbed (on a plant with LAI over 3, almost all photons available, reduced by reflectance on a small degree). On field, there is a direct correlation between top irradiance and photons available, but on grow chambers, it not always apply.

That is a general reflexion that probably dont apply at all to Lydon experiment: actual reflectance of UVB by mylar is low. Im just trying to explain why I prefer to know amount of photons available for plants use, and tend to think on those terms. Of course I look too at local irradiances used, I just point up that only top irradiance data is incomplete very often. Not only for the reasons explained, but due uneven light distribution, specially when using HIDs without a diffusing filter (as on our grow areas).

Precisely because your argument of being possible to adjust irradiance by adjusting distance to lamp is why I did the math based on radiance. Knowing the total radiance of the lamp, you can know what area you can cover giving an average irradiance with a know lamp.

Thats why I adjusted to m2. Converting to irradiance, but not actual ones as you can measure on a point of the grow with the light meter, but average values for the full area to being lit. Its a way of calculating the lamp power required to use in order to get the average irradiances you look for on a given area.

Of course, how averages irradiances translates to actual irradiances depends of the pattern of light distribution of the lamp. If the lamp is very directional, as you well say its the case of these mercury vapor lamps, in order to get a large footprint for the lamp, distance of use becomes unpractical, first, and second, distribution is anyway very uneven, with spots directly perpendicular to the lamp with high irradiances, way higher than the average, and edges areas, much lower than average. If distance required to lit the area becomes too large, or the light distribution too uneven, then is required to use more lamps of less power each.

This problem of footprint/distance as related to average irradiance is not exclusive of UVB lighting, is a general topic for indoor lighting. Any HID suffer of this problem, but however many people uses it successfully, still when they are actually growing with way higher irradiances below the lamp than at the grow edges.

Florescent tubes produces a way even lighting. But AFAIK, UVB tubes are less efficients than MV.

* J.Lydon, et al., (1987) wrote:

"Individual plant heights were adjusted to maintain a uniform canopy, while the lamp/plant distance was maintained at 0.25 [meter] (0.08 mm CA filtered lamps) or 0.35 [meter] (0.13 mm CA and Mylar filtered lamps)."​

Also, area isn't a necessary factor to hold, ex. we don't need to use meter^2. And it's better not to use meter^2 because UV-b meters usually measure incident radiation (i.e. irradiance) in centimeter^2 (as microWatts). High radiance (wattage) mercury vapor UV-b lamps are very directional with small irradiance footprints (unlike lower radiance UV-b fluorescent tubes). That said, we can use uW/cm^2, as I have done, over a larger area to find the UV-b irradiance at canopy over any area we choose and still equal ~13 kJ/m^2 (for that smaller area). For example, using a goal of 124 uW/cm^2/3-hour (which equals 13.4 kJ/m^2/3-hour) I measured the irradiance over a 2 foot circumference under the Osram (due to its directionality of irradiance footprint). That means if we can provide ~124 uW/cm^2/3-hour over every centimeter^2 within X area we can come close to providing the same irradiance over a smaller area as is provided via. 13.4 kJ/m^2.

Its just a problem of units. But conceptually is all the same (always you understand that when I refer to average figures, Im using a math tool, but Im not refering to actual irradiances as measured with a light meter).

Irradiance official unit is W/m2. You can convert any unit on a equivalent one you prefer because its more meaningful for you. Always the conversion is well done, its the same.

For example, if I talk of 3W/m2.

1m2=10000 cm2
1W=1000000 uW (microwatts).

So 3*1000000/10000=3*100=300 uW/m2.

Its the same to express irradiance as 3W/m2 or 300uW/cm2. Of course an irradiance measurement is only valid for the point it was taken, and the size area of the detector, with is way closer to 1cm2 than to 1 m2. But when you express it, its indifferent the unit you use, alway you know its only valid for the exact point it was taken. More yet, for the exact orientation of the sensor. If you measure irradiance at same point but with sensor turned 90º, usually figure obtained is very different.

That limitation is obliges to use irradiance measurements, a great tool, with caution. It only represent a point of space on a given orientation. Thus scaling from it is dangerous, while scaling from radiance to irradiance, provided light distribution pattern of lamp is well known, can be very accurate, and a actual representation of photons available.

You prefer to use uW/cm2 because that way you are aware of the small size for which an irradiance measurement is valid.I prefer to use W/m2, knowing that its only valid for the small point when its measured, because offer an insightful way of knowing how much power to use on a given space. But both units are the same, and both ways correct.

If we use daily figures of irradiance required, we just need to divide them by the hours with lamp on.

In the study by J.Lydon, et al. (1987), the workers used a daily dose of UV-b (weighted to UV-b(be)) over a 3 hour period, or a 6 hour period, I am not 100% sure. Their use of the phrase "on either side of solar noon" is a bit confusing, they could mean they used UV-b for 3 hours either before or after solar noon; or they could mean they used UV-b for a total of 6 hours by 3 hours before and after solar noon. But either way it doesn't matter, it's the daily dose (irradiance) of UV-b that matters, i.e. 13.4 kJ/m^2.

J.Lydon, et al. (1987) wrote:

"Ultraviolet-B radiation was provided for 3h on either side of solar noon, resulting in a daily UV-B(be) dose of 0, 6.7, or 13.4 effective kJ/m^2 UV-B(be). The highest dose was equivalent to the daily weighted UV-B dose received under clear sky conditions and minimum solar zenith in Colombia, South America (0" latitude, 3 km elevation, Julian [June] date 80, Green er al., 1980)."​

That is why to reach 13.4 kJ/m^2 over a whole day we could use 62 uW per cm^2 for 6-hours (ex. over a meter^2; i.e. 62 uW every cm^2 over m^2 for 6 hours), or 124 uW per cm^2 for 3-hours, or 248 uW per cm^2 for 1.5-horus, etc. We can modify area and time and still achieve an equivalent daily irradiance of 13.4 kJ/m^2 over a whole day.

I understood it as they used UVB supplementation for three hours, at the time of solar noon, thus from 1.5h before to 1.5h later. Anyway, as they stated daily dose on KJ, which conversion is to Wh (or KWh), conversion to time used is straightforward. If UVB-BE wasnt used, we could do a fast coversion.

What I did was use a UV-b meter (Solarmeter 6.2, here) to measure irradiance of the lamp to find at what distance from canopy the lamp provided ~124 uW/cm^2 (over ~2 foot circumstance). And then I ran the lamp(s) for 3 hours a day starting at mid daylength under HID in an attempt to mimic when plants would get most UV-b in nature, around midday.

And you did well.

All our talk about calculating power used for a given area is for those that dont have a UVB meter (most), and as for guideline to decide what lamp to use on a given space.

But the pudding is on use a lamp and that it gives the irradiances we are looking for. And measuring it is the only way of knowing for sure you are using the right irradiance, not high, not low.

Ideally, for other growers incorporating to UVB experimentation with more confidence, a table of measurements of irradiance along a grid at some different distances would be very useful (kind of pico and others did for HPS's hood)

The major problem with high intensity (radiance) mercury vapor UV-b lamps is they are very directional, thus they have a small irradiance footprint. Neither the Osram or the MegaRay are able to irradiate a meter^2 with high irradiance UV-b. That is why they are hard to use, they have small footprints. I attached my UV-b lamp to a light mover and that worked OK, but then I bought a few more lamps so I had bigger and more even footprint of UV-b irradiance at canopy and didn't have to use the light mover.

I chose the Osram because it is less directional than the MegaRay, thus the Orasm has a bigger footprint with more even irradiance (less extreme irradiance peaks within the footprint). The MegaRay has an even smaller high irradiance footprint than the Osram, with more extreme irradiance peaks within the footprint.

Yes, if lamps used are too powerfull and directional, only alternatives is to use a light rail, or more lamps of less power. If you found that irradiance provided by a single 300W lamp is valid for a large grow area, those are the options. And yes, looking for the lamps with wider beam angle help giving a more evenly light distribution and reducing distance to lit a given footprint.

I continue tomorrow,its too late here.

 

[spurr]

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.

Very true, and in the two studies by J.Lydon (his PhD thesis and the work in 1987), he/they found increasing UV-b irradiance increased THC content. So it seems to provide highest increase in THC from UV-b, not to mention other medical compounds from cannabis like flavonoids and possibly terpnoinds, more UV-b is better, up to saturation point. And the saturation point of UV-b is probably > ~14 or 15 kJ/m^2/day. In nature, the highest UV-b found is ~14-15 kJ/m^2/day, but that's not very common, more often the highest found is ~12 kJ/m^2 (D.T. Krizek, 2004).

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.

How did you calculate that data? Could you please cite your reference? I am interested in your math.

You seem to be referring to radiance via. lack of density (area), not irradiance, correct? Those figures are for umoles/second, not umoles/area/second. I ask because radiance is not very useful considering it does not account for distance to canopy, nor area, both of which greatly affect level of irradiance at canopy.

What I mean is X umol/second (uE) at lamp doesn't well correlate to Y umol/area/second at canopy (via. inverse square law) if we are using a point source light within a reflector (esp. 'pebbled' reflector), or that passes through a "collimating" lens. The same holds true for point source light that becomes diffuse via. diffuse transmission, for example, passing through opal glass.

The problem with mercury vapor lamps like the Osram and MegaRay, is the bulb is within a reflector and the light passes through collimating lens. Not only that, but the Osram lamp face is made of opal glass and thus provides diffuse transmission. Also, using the inverse square law is generally most accurate when the irradiated area is large, relative to the size of the bulb. That is why incandescent and HID lamps can be used with the inverse square law when they are not placed in a reflector. However, both the Osram and the MegaRay are 'flood' style UV-b lamps, they are very directional in terms of a small footprint, they do not provide direct light, they provide diffuse light. Thus, the inverse-square law is not really applicable (in terms of worthwhile accuracy) for either lamp, at least in my opinion.

Considering the issues about the Osram and MegaRay 'zoo' UV-b lamps I listed above, using the inverse square law is not valid, IMO anyway. That is why I used a UV-b meter, and why I suggest others use a UV-b meter too. What matters is the irradiance at canopy, not radiance at lamp, because radiance at the lamp can't be converted into irradiance at canopy with those two lamps with a reasonable degree of accuracy using the inverse square law, at least in my opinion.

I would be interested to read your opinion on those topics.


Here is a great reference work:

"The Light Measurement Handbook"
by Alex Ryer
http://homepages.inf.ed.ac.uk/rbf/CVonline/LOCAL_COPIES/LIGHTMEASUREMENT/handbook.pdf
​

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

The problem with the Osram, but especially the MegaRay, is they are both 'flood' style lamps, thus they have small irradiance footprints. Both have ~2 foot circumference of high irradiance, no mater how far the lamp is placed from the canopy. That is why they are hard to use to irradiate a big canopy (ex. square meter), unless they are attached to a light mover, of unless we use may of them in an array.

FWIW, I choose the Osram for to two main reasons: (1) the irradiance footprint is more homogeneous than that of the MegaRay; and (2) the owner of MegaRay is a major asshole.

 

[spurr]

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.

FWIW, you can sometimes find used Solarmeter 6.2 UV-b meters on E-bay for pretty cheap, or you can buy a new one for ~$200. Using a UV-b meter is the best option, I believe.

 

[spurr]

Yes, its very interesting, resuming previous studies on a very meaningful way. I always loved Krizek, I had read many of his articles. But I didnt know this one.

This is due I have never focused my research on UV effects, but on other lighting topics. I need to select what I want and can do, and some reason let me to give up experimenting with UVB. The practical difficulties (little lamps available, short lived, very difficult to work with narrow bands without using filters...) and personal reasons (high family susceptibility to retina disease).

Yea I agree, too much to study and implement with too little time. I am mostly interested in PAR range light and issues of light quality and quantity (PPFD) in terms of rate of photosynthesis, stomatal conductance, Co2 fixation, etc. But UV-b is also very interesting.

But Ive been always been very interested on the topic, so I chimed in when I saw the excellent info you gave. Ill try to help on what I can, but not experimenting myself.

Great, I am very happy to have you chime in, you know a lot, for sure

I continue tomorrow,its too late here.

Great, looking forward to it. I am about to sign off too, I will read the rest of your post/s tomorrow.

Best, spurr

 

[knna]

Before continuing with other topics, I would like to clarify the point about using radiance as a tool to calculate irradiance, and how both things correlates.

Radiance refers to light emitted for the lamp. Its an absolute figure, its total emission. Either in optical Watts (or mW, or uW, its the same), either in photons, usually micromols of photons per second (which I usually abbreviate for uE and skip s^-1 for simplicity, as when using the low umol figure is almost always for second time frame; when not, I state it).

On the other hand, irradiance refers to the lighted area. It only makes sense as a figure of density. The true figure that should be used for photon/watts density is for volume: W/m^3 or uE/m^3 (ill skip ^ from now on, I think m2 and m3 is clear enough to use them, and saves lots of time writing about it on a forum). But as there is no instruments able to do an straightforward measurement of W/m3 (or uW/cm3 or whatever), botanist studies uses W/m2, or uE/m2, a density over area basis.

When studying a single leaf, with almost no thickness, it makes sense to study irradiance on a area basis. And at the end, it we could measure the actual irradiance at each leaf of the grow area, it would be perfect. But its not practical, almost impossible to do, to take a thousand measurements, some for each leaf of the plant.

So taking a measurement of irradiance at top canopy is the most practical way of know the light plants are receiving, but its very incomplete when studying whole plant reactions. Only works as a good indicator of how much light plant is getting, but not is valid to know accurately how many light actually is used for the whole plant. It would require to make hundreds of measurements at top canopy to know it (each for an area size of detector), and integrate all measurements on an average irradiance/whole area lit.

But when we know absolute rradiance on a closed grow area, specially if wall reflectivity is high, we can calculate very accurately that average irradiance, but simply dividing total radiance by surface area of the grow. Result is a virtual figure, but which accurately says the average irradiance on the grow area.

Not only that, its a tool which allows to calculate light density based on volume (W/m2, or uE/cb ft).

For plants reactions closely related to total amount of photons incident to plant matter, it gives the better info. I dont know if actually, UVB driven reaction is of this nature. For Lydon study, it seem so, but maybe just irradiance level at tip of plant is what drives the reaction. A question about this would be: have you noticed if THC enhancement varies from parts of the plant receiving more UVB to other parts receiving less? (measured irradiance at leaves of each part).

Knowing the average irradiance is very useful, yes, but measuring too actual local irradiances (and better yet, according to leaves orientation) is required too to drive good experiments. Without knowing the average irradiance, its possible to get valid conclusion from experiments, as far as you have at least local irradiance measurements which put things in perspective.

But calculated average irradiance is very useful calculating what lamp you need to use and how to place it. More yet, with known lamp's light distribution pattern, its is possible to know actual irradiances at each point of the grow area (at any height), very accurately if you use a lighting simulation sofware.

Its as simple as irradiance saying how many photons (or watts) are falling on a given area (of the detector, when measured). Unit used to express it is irrelevant, as far as conversion is done right. No matter if its stated on W/m2, or uW/cm2 (or using uE/m2...), it just refers and is valid for the area of the detector, on the actual orientation it was taken.

With virtual calculation of average irradiance, you get the same, a figure of W (or photons) falling on a given area (no matter if which time frame is referred, it could by second, hour, or day, all them easily converted to any of the others). But referred to the whole area being lit (and being able to make it referred to the whole volume being lit).

How average irradiance actually translates to irradiance depend of the light distribution pattern of the lamp, and according to it we need to decide how to place lamps. For example, if the grown area is long and narrow, it could be achieved a relatively even irradiance distribution, with figures not too far of average, by placing two lamps at each side of the room, maybe placed with angle and not in perpendicular.

All depends of lamp/reflector(if any) used, size and shape of the room. Im very used to find solutions to this topic, if you let me know how is the grow area to be lit and light distribution of lamps used I can suggest good ways to achieve the required irradiance levels required as more evenly as possible (how much is possible depend of how concentrated is the output of lamp).

 

[knna]

How did you calculate that data? Could you please cite your reference? I am interested in your math.

Please, for those not inclined to maths, skip directly this post.

Its not required at all for experimenting with UVB, or for lighting a grow, or for growing at all. Just for those who likes to know things in deep and likes maths.

I have a very good Excel sheet that is able to calculate almost all parameters you want to know from a given spectrum, you just need to introduce the spectrum. This is an explanation of the way of calculating micromols of photons of each wavelength on a given energy. Excel sheet do it for you, you just introduce wavelenght figure and its done.

All needed to perform the calculation is the plank equation and Avogadro number.

In order to know how many energy carries a photon of a given wavelenght, I use the Planck's equation:

E=hc/λ (derived from the basic E=hv), where:

E=Energy of the photon on J/s.

h=Planck constant= 6.62606896*10^-34

c=speed of light in vacuum= 299792458 m/S~ 3*10^8 m/s

λ= wavelenght, in meters.

As we usually use nanometers to note wavelength, and a nanometer is 10^-9 meters, equation is as follow:

E=(6.62606896*10^-34 * 2.99792458*10^8 )/(λ*10^-9), which result on

E=1.9864455 * 10^-16 /λ

as the energy of a photon of wavelength λ expressed in nm.

Avogadro number says how many particles are a mol. Its 6.02214179* 10^23. For a micromol (1/1000000 mol), its same number multiplied by 10^17.


So in order to know how many photons of wavelength λ holds on 1 watt (W=J/s), Q, expressed on micromols of photons:

Q(λ)= (1/E)/6.02214179 *10^17 = λ/119.58658357 micromols of photons of wavelength λ (nm) on 1 Watt.

BTW, as I did it I realized I did the calculation for the Excel sheet with less decimals so I get a coefficient of ~123.1, meaning sheet results was 2.9% lower than reality. I have to change it, when done Ill upload it.

 

[spurr]

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.

Here is an interesting paper I found the other day, I will get it in full text sometime this week:

"Use of UV radiation for control of height and conditioning of tomato transplants (Lycopersicon esculentum Mill.)"
Giuseppe Del Corso and Bartolomeo Lercari
Scientia Horticulturae Volume 71, Issues 1-2, November 1997, Pages 27-34
​

 

[spurr]

Before continuing with other topics, I would like to clarify the point about using radiance as a tool to calculate irradiance, and how both things correlates.

They only correlate well (i.e. with a high degree of accuracy), if using inverse square law, when the light source is a point source (ex. HID lamp, incandescent lamp, single LED, LED array depending upon the far-field conditions, etc). Non-point source would be a fluorescence tube lamp (long kind), a LED array on a panel (unless the distance to canopy is sufficient relative to array size, i.e. "far-zone" and "far-field" conditions, in that case a LED array can be a directional point source light*), etc.

However, a point source light (ex. HID lamp) that is within a reflector (esp. a 'pebbled' reflector that makes very diffuse light) or that passes through a collimating lens, means the accuracy/reliability of using inverse square law to find irradiance from radiance is not sufficient for analytical work. This is why scientists use quantum sensors in the case of PAR range light to find unweighted PPFD (i.e. umol/m^2/second), even when using LAI (Leaf Area Index) to find whole canopy PPFD figures.

If the distance to illuminated area (ex. canopy) from light source is not far enough relative to the size of the light source (e.g. five-times rule), the accuracy of using inverse square law is also reduced**. Those reasons are the main reasons I don't like trying to use radiance to find irradiance; it's just not accurate enough, at least in my opinion.

* "LED array: where does far-field begin?"
Ivan Moreno, Ching-Cherng Sun

"Intensity definition only applies to point sources. However, in theory, any LED array can be modeled as a directional point source if a far-field condition is met. Geometrically, a solid angle must have a point as its apex; therefore, the strict definition of intensity applies only to a point source. In practice, however, the radiation emanating from a source whose dimensions are negligible in comparison with the distance from which it is detected may be considered as coming from a point.

Depending on the working distance, both the optical modeling and the experimental characterization of a light source must be performed in a different way. Basically, there are two working conditions: near-field and far-field. In near field a source is modeled as an extended area, and it is usually assumed that the distance to the illuminated target is shorter than 5 times the maximum source dimension.

A far-field approach assumes that the target is farther from the source than this nominal separation, and the source can be modeled or measured as an emitting point. However, this rule of thumb fails for LED arrays because of: the discrete nature of the source, and the wide variety of both array geometries and intensity distributions (LEDs are available in many different beam patterns). Then, a general definition of the far-field condition is necessary to correctly delimitate the near zone from the far zone."
​

** "LED array: where does far-field begin?"
Ivan Moreno, Ching-Cherng Sun

In the far zone, an extended light source can be easily simulated or measured as a point source with specific angular intensity distribution. As a rule of thumb, it is usual to assume the far-zone begins at a distance of five times the largest dimension of the light source. In that region, the measured radiant intensity or luminous intensity is practically independent upon distance from the source. Hence, an answer to the question “where does far-field begin?” involves computing the intensity of an arbitrary extended source, which must be compared with an equivalent point source

The “five times” rule of thumb is valid for a source with circular shape and Lambertian emission (L=constant). This rule states that for a distance 5 times the source diameter, the error from using the inverse-square law is 1%. The set up for this condition considers a detector located on the optical axis, i.e. θ=0. Therefore, this condition is equivalent to get an error of 1% when using I(θ=0,φ=0)∞ instead of I(r,θ=0,φ=0).
​

Radiance refers to light emitted for the lamp. Its an absolute figure, its total emission. Either in optical Watts (or mW, or uW, its the same), either in photons, usually micromols of photons per second (which I usually abbreviate for uE and skip s^-1 for simplicity, as when using the low umol figure is almost always for second time frame; when not, I state it).

On the other hand, irradiance refers to the lighted area. It only makes sense as a figure of density. The true figure that should be used for photon/watts density is for volume: W/m^3 or uE/m^3 (ill skip ^ from now on, I think m2 and m3 is clear enough to use them, and saves lots of time writing about it on a forum). But as there is no instruments able to do an straightforward measurement of W/m3 (or uW/cm3 or whatever), botanist studies uses W/m2, or uE/m2, a density over area basis.

Yup. For plant science, in terms of light, density is over a 2-dimensional (horizontal) area, as in meter^2. But it is possible to use volume (i.e. m^3) instead of density (i.e. m^2) with a quantum sensor; i.e. whole canopy "PPFD-I" (PPFD-Interception). This topic is important not only for a better understanding of how plants use photons, but for PPFD Radiation Use Efficiency (e.g. PPFD-RUE).

See:

"Crop productivity in relation to interception of photosynthetically active radiation"
M.V.K. Sivakumar and S.M. Virmani
Agricultural and Forest MeteorologyVolume 31, Issue 2, May 1984, Pages 131-141


"The influence of plant spacing on light interception and use in greenhouse tomato (Lycopersicon esculentum Mill.): A review"
A. P. Papadopoulos and S. Pararajasingham
Scientia HorticulturaeVolume 69, Issues 1-2, 31 March 1997, Pages 1-29
​

The problem with using volume in place of density is the LAI of whole canopies is not standard, thus the irradiance by volume is hard to measure and report as a figure for people to use when the LAI is different in different gardens. And if we consider some growers use reflective walls (like you mentioned) and some do not, the use of volume in place of density is even more difficult as a general guide. That is why using PPFD, or umol/foot^2/second, is a better guide for people because it doesn't account for many factors that are different in each garden (e.g. LAI, plant spacing, etc.)

See:

"Ground‐based measurements of leaf area index: a review of methods, instruments and current controversies"
J. Exp. Bot. (2003) 54 (392): 2403-2417
Nathalie J. J. Bréda
http://jxb.oxfordjournals.org/content/54/392/2403.full.pdf+html
​

FWIW, I for like to write out the area and time to avoid confusion. I knew you used uE as uE/second, a la, umol or umol/second. Using either uE (microEinstein) or umol (micromole) are basically synonymous, but in plant science, umol is the most often used term, so to avoid confusion that is what I use too.

When studying a single leaf, with almost no thickness, it makes sense to study irradiance on a area basis. And at the end, it we could measure the actual irradiance at each leaf of the grow area, it would be perfect. But its not practical, almost impossible to do, to take a thousand measurements, some for each leaf of the plant.

That is why using area is good, vs. using volume: area is a more general measurement that growers can use. Ex. > 1,000 PPFD (up to light saturation of ~1,600 PPFD) is ideal for cannabis as an instantaneous irradiance, any grower can implement that for their garden to grow better cannabis in terms of 'top canopy' irradiance. If using volume, we need to account for LAI, sunfleck, whole canopy density, etc., to came up with an ideal 'whole canopy' figure for irradiance. And far, far fewer growers would be able to use that irradiance datum because their whole canopies are different.

I think, as do a majority of plant physiologists, that using PPFD is best, and then tell the grower to try for ideal plant spacing/LAI for greater irradiation intracanopy. It's also important to point out that younger leafs photosynthesize at a higher rates than older leaves, and younger leafs tend to be near/at the top of the whole canopy.

LAI and whole canopy structure has a lot to due with plant stretching in terms of red:far-red light ratio intracanopy, via. phytochrome responses. I started a thread on this topic here:

Control red to far-red light ratio to limit stretching
​

So taking a measurement of irradiance at top canopy is the most practical way of know the light plants are receiving, but its very incomplete when studying whole plant reactions. Only works as a good indicator of how much light plant is getting, but not is valid to know accurately how many light actually is used for the whole plant.

Exactly, that is why it's so good, it is a 'shoe that fits most growers'. And the other factors of RUE (Radiation Use Efficiency), like LAI, sunfleck (via. light mover), reflective walls, etc., is up the grower to try and optimize.

Here are some good papers (PDFs) about radiation, irradiance, LAI, PPFD-I, RUE, etc., at this good resource from the University of Guelph "Plant-BIO-3110 Crop Physiology" (link)

Solar radiation and irradiance
​

Interception of PPFD by a crop canopy (LAI, extinction coefficient (k), canopy reflectance, etc. A major flaw in that paper is the missed the fact under high irradaince white light green leaves absrob green photons to drive rate of photosynthesis often greater than blue and red photons under high irrdiacne white light)

Leaf net photosynthesis

Canopy photosynthesis I (Distribution of Absorbed PPFD within the Crop Canopy)

Canopy photosynthesis II (Whole Canopy CO2 Assimilation)

Canopy photosynthesis III (Whole Canopy Photosynthesis Calculations)
​

It would require to make hundreds of measurements at top canopy to know it (each for an area size of detector), and integrate all measurements on an average irradiance/whole area lit.

Using a standard quantum sensor, if measuring PPFD, it takes 144 measurements, one every 3" over 3'x3', then to find the average of the 144 measurements to find PPFD. That can be expanded into vertical measurements too, for volume, not only density, to see the whole canopy PPFD.

Some canopies are not a meter^2, many cannabis growers use small garden canopies, so it would take much fewer readings to find the irradiance over a smaller area, ex. umol/foot^2/second.

However, using an 'rod' quantum sensor, like the Li-cor Li-191, we can take much fewer readings to find PPFD. The Li-191 is a meter long and has 10 quantum sensors evenly spaced over the meter, it finds umol/meter/second by averaging the datum from all 10 quantum sensors.

But when we know absolute rradiance on a closed grow area, specially if wall reflectivity is high, we can calculate very accurately that average irradiance, but simply dividing total radiance by surface area of the grow. Result is a virtual figure, but which accurately says the average irradiance on the grow area.

Only if the caveats I wrote about in regard to point source light and inverse square law are meet. For an HID in a reflector using the inverse square law is not accurate enough, same for a LED array when the distance does not exceed the five-times rule (relative to size of LED array).

However, using inverse square law to find irradiance by volume still does not account for LAI, etc. Just like using a quantum sensor does not account for LAI, etc.

Basically, using radiation to find irradiance is a guessing game in terms of indoor cannabis grows. But using irradiance via. a light meter (ideally a quantum sensor) is not a guessing game, we know exactly the irradiance (either by density or volume).

Not only that, its a tool which allows to calculate light density based on volume (W/m2, or uE/cb ft).

But you would have to account for LAI, sunfleck, etc., to find volume in terms of intracanopy irradiance, and that is very hard to due in a general use application. Othweise you have a datum that does not represent the intracanopy irradiance of a whole canopy.

It's fairly trival to find irradiance by volume using a light meter, ex. umol/meter^3/second, or umol/foot^3/second. And it's more accurate than trying to use radiance to fine irradiance (by cubic volume). Here is an example using a UV-b meter to find two-dimensional (vertical) irradiance. The same directions apply to using a quantum sensor and can be easily modified to find 3-dimensional (length/width/depth, i.e. volume) irradiance:

"Make yourself a UV spread chart"
http://www.uvguide.co.uk/makingspreadcharts.htm
​

For plants reactions closely related to total amount of photons incident to plant matter, it gives the better info.

If that was the case, then using radiance (via. inverse square law) to get irradiance would be the scientific standard, but it's not. Doing as you suggest would not give a true representation of intracanopy irradiance, only give figure of irradiance by volume in an empty space. We will have to agree to disagree.

Knowing the average irradiance is very useful, yes, but measuring too actual local irradiances (and better yet, according to leaves orientation) is required too to drive good experiments. Without knowing the average irradiance, its possible to get valid conclusion from experiments, as far as you have at least local irradiance measurements which put things in perspective.

Yup, that is why using PPFD along with LAI is the scientific standard for 'whole canopy' irradiance, e.g. PPFD-I.

But calculated average irradiance is very useful calculating what lamp you need to use and how to place it. More yet, with known lamp's light distribution pattern, its is possible to know actual irradiances at each point of the grow area (at any height), very accurately if you use a lighting simulation sofware.

I agree, however, that is only true with point source light. And most cannabis growers do not use point source light because they use HID lamps inside a reflector, or LED array that does not exceed the five-times rule (i.e. far-field requirements), etc.

Its as simple as irradiance saying how many photons (or watts) are falling on a given area (of the detector, when measured). Unit used to express it is irrelevant, as far as conversion is done right.

That is only true if the SPD is known at the time of testing. Ex. converting PAR range W/m^2 from a spectroradiometer into PPFD (umol/m^2/second) is only possible if we know the SPD of the lamp, and that changes with age of lamp and power input, ex. using a magnetic ballast vs. digital ballast. Thus we can't use SPD of an HID lamp from a manufacture to find PPFD if the lamp is not brand new and if we are using a different ballast than used for to make the original SPD; along with issues of different reflectors.

With virtual calculation of average irradiance, you get the same, a figure of W (or photons) falling on a given area (no matter if which time frame is referred, it could by second, hour, or day, all them easily converted to any of the others). But referred to the whole area being lit (and being able to make it referred to the whole volume being lit).

That is true if we are talking about true point source light, but, most cannabis growers do not use true point source light, thus the inverse square law has a much higher margin of error. That is why I dont' suggest using radiance to find irradiance in indoor grows; it's just not accurate enough, IMO.

One can do as you suggest, for sure, but the accuracy of using inverse square law, when a lamp is in a reflector, is much reduced.

How average irradiance actually translates to irradiance depend of the light distribution pattern of the lamp, and according to it we need to decide how to place lamps. For example, if the grown area is long and narrow, it could be achieved a relatively even irradiance distribution, with figures not too far of average, by placing two lamps at each side of the room, maybe placed with angle and not in perpendicular.

All depends of lamp/reflector(if any) used, size and shape of the room. Im very used to find solutions to this topic, if you let me know how is the grow area to be lit and light distribution of lamps used I can suggest good ways to achieve the required irradiance levels required as more evenly as possible (how much is possible depend of how concentrated is the output of lamp).

In terms of UV-b lamps like the Osram or MegaRay, you can't use inverse square law due to the factors I wrote about; re: reflector, collimating lenses, etc.


Basically, we take opposite sides of the debate, you think using inverse square law is valid for indoor grows, and I do not. That is about the sum of our differences. I don't think I can convince you, and I don't think you can convince me. But I do really appreciate your input and efforts

 

[GreenintheThumb]

Sorry I've been really busy with work and haven't kept up with my own thread.

spurr I believe you said you saw an increase in thc production with uv-b light? How did you measure this effect?