Investing in new lights LED or HID?

[secondtry]

Osram Ultra Vitalux 300w: ($90) (the UV-b lamp I use)
http://www.bulborama.com/store/Medi...MP-TANNING-BULB-230-VOLTS-300-WATTS-p711.html


Voltage Converter 1,000w: ($60) (should have 5-10% extra unused watts)
http://www.voltageconverters.com/itemdesc.asp?ic=VC1000W


Poultry Brooder Reflector/Fixture: ($20) (heavy-duty, must be rated for at least 250 watts)
http://www.teksupply.com/farm/suppl...&division=TekSupply&pageId=ItemDetail&isDoc=N

Study:
"The Use of Dome Refcors with Mercury Vapor Lamps"
http://www.uvguide.co.uk/mercvapourreflectortests.htm
​

UV-b Meter:
Here is a good UV-b meter for $180; the same one used in the studies above (from UVGuide.co.uk); it reports UV-b irridiance from 280-320 nm as uW/cm^2 http://www.solarmeter.com/model62.html

 

[secondtry]

On the topic of ideal PPFD for cannabis to reach Pnmax (maximum rate of photosynthesis)

Another good and recent study on ideal PPFD for cannabis; yet again showing why LEDs are not up to the job considering that they will not emit 1,500 PPFD at what I consider to be a reasonable distance of grater than a few inches from canopy (and that's only an unproven claim of the new plasma LEDs):


Zlatko Mehmedic, Suman Chandra, Hemant Lata, Ikhlas A. Khan and Mahmoud A. ElSohly (2009)

"EFFECT OF LIGHT INTENSITY ON PHOTOSYNTHETIC CHARACTERISTICS OF FOUR HIGH ∆9-THC YIELDING VARIETIES OF CANNABIS SATIVA"
International Association for Cannabis as Medicine; IACM 5th Conference on Cannabinoids in Medicine. 2-3 October 2009, Cologne, Germany​

ABSTRACT:

Cannabis sativa L. (Cannabaceae), an annual herb is the natural source of cannabinoids that mainly accumulates in glandular trichomes of the plant. Due to the allogamous (cross fertilization) nature of Cannabis sativa it is very difficult to maintain the efficacy of selected high THC yielding elite varieties if grown from seeds under field conditions. Thus, the indoor cultivation, under controlled environmental conditions, using vegetative propagation of selected high yielding female clones can be a better alternative for its mass propagation. In the present study, plants of four drug type Cannabis varieties namely HPM, MX, K2 and W1 were grown indoor, under controlled environmental conditions (25 ± 3oC, 55 ± 5 % RH and ~ 700 ± 24 μmol/m^2/s^-1 light at plant canopy level). Gas and water vapour characteristics of these plants were studied at different Photosynthetic Photon Flux Density (PPFD; 000, 500, 1000, 1500 and 2000 μmol/m^2/s^-1) for their efficient indoor cultivation. An increasing trend in photosynthesis (PN), transpiration (Tr) and stomatal conductance (gCO2) was observed with increase in PPFD up to 2000 μmol/m^2/s^-1 in all the varieties at optimum growth temperature (25 ± 3oC). However, the magnitude of increase and maximum rate of PN (PN max) varied with the varieties. Highest rate of photosynthesis was observed in W1 followed by MX, K2 and HPM. Water Use efficiency (WUE) in W1, MX and HPM increased with light up to highest level tested, whereas, in K2 highest WUE was observed at 1500 μmol/m^2/s^-1. Our results show that this species is able to use high level of PPFD for its PN and therefore, may be cultivated in under bright indoor light (~1500 to 2000 μmol/m^2/s^-1) for better growth and biomass.The strict control of other environmental factors however, should be maintained for the higher yield.
*Supported by the National Institute on Drug Abuse (NIDA) contract # N01DA-5-7746

 

[medmaker420]

What I love about all the diagrams and pretty pictures is that in the end that has zero to do with ability of the grower. No matter how amazing a specific light, frequency or what have you in the end it comes down to the skill of the grower.

Most growers going for quality and weight go with hps setups over led ANY DAY. Whether or not hid is within the perfect spectrum to grow BETTER than anything else really doesn't matter BECAUSE they work.

Don't fix what aint broke and trying to run lights that cost $400+ for 1XX watts give or take is FUNNY at best BUT some people love spending money on the latest and supposed greatest.

If I were going from cfl I would FOR SURE go for mh,cmh,hps over led anyday.

 

[secondtry]

Hello,

What I love about all the diagrams and pretty pictures is that in the end that has zero to do with ability of the grower. No matter how amazing a specific light, frequency or what have you in the end it comes down to the skill of the grower.

I disagree. For example, if two growers with the same skill and strain (ie., clone), using the same growing method except for lighting irridiance (same lamp/reflector/ballast) where grower A is using 1,300-1,500 PPFD and grower B is using 500-700 PPFD in the end grower A will see greater growth, yield and quality.

I believe PPFD (irridiance within PAR range) is more important than the spectral quality of the light (i.e., the SPD) because the differences in Pn between wavelengths within PAR is not so huge if using broad-band white light (i.e,. HID); tho we do want to provide the full PAR range, and peaks in green is good for Pn (that is why I like the Horitlux Blue).

It's about photosynthesis and we want the rate of photosynthesis (Pn) to be at or just below Pnmax and that is what 1,300-1,500 PPFD offers. There are other considerations like noon-break phenomenon and Pn-peaks, but those can be mitigated somewhat by controlling/manipulating DLI (Daily Light Integral- see next post), VPD (Vapor Pressure Deficit) and Rubiso activase, media and air temp, etc. many terms are new to many people so they sound hard and confusing, but they really are not at all. Calculating VPD is very easy, I gave links on page two with an on-line calculator, and PPFD is simple too (but it's about $400-500 for the units), DLI and 3-DLI is only a bit of basic math...

Most growers going for quality and weight go with hps setups over led ANY DAY. Whether or not hid is within the perfect spectrum to grow BETTER than anything else really doesn't matter BECAUSE they work.

Yea but they can work better, i.e., most growers do one of three things: 1) don't provide enough PPFD leading to low/ish Pn (rate of photosynthesis); 2) provide too much PPFD leading to photoinhibition; and 3) offer too few wavelengths within PAR ragne, far-red range and UV ranges, these ranges effect biochemical responses in cannabis, it's about quality more so than quantity (yield). In any of those cases the yield and/or quality suffers, as does the resistance to disease, stresses, etc. IMO spectral quality is important, but irridiance within PAR (ie., PPFD) is more important; IMO both must be considered.

Providing ideal PPFD and spectral quality can allow for more a full expression of the strain (ie., the individual plant/clone of a particular variety like the variety NL #5). To me it makes sense to try an offer ideal PPFD. Offering too much PPFD hinders plant and wastes dollars and the same can be written if the grower provides too little PPFD in terms of what (cannabis quality and quantity) one could have produced.

Don't fix what aint broke and trying to run lights that cost $400+ for 1XX watts give or take is FUNNY at best BUT some people love spending money on the latest and supposed greatest.

I think that's it, people buy LEDs for the wow factor and the skill of the snake-oil salespeople...funny part is what I am writing about is way more advanced than what LEDs offer.

If I were going from cfl I would FOR SURE go for mh,cmh,hps over led anyday.

Did you not like reading about UV-b? That is something people often ask about but very few people have real info which as been researched and applied; I have done all three and provided info on that. Adding 375 uW/cm^2 of UV-b has been found to increase (total) THC content in cannabis flowers by around 20-30% and in leaf by around 40-60%. Not only that but UV-b positively effects secondary metabolite production of cannabis (other than cannabinoids) and of other plants such as flavinoids, terpenoids, etc. For a grand total of $150 or so you can provide near ideal irridiances of UV-b, see my previous post/s. I use the leafs for extracts so the greater the content of THC-A and other secondary metabolites the better IMO.


HTH

 

[secondtry]

On the topic of modifying the daylength and circadian rhythm to increase Pnnet, carbon assimilation and probably yield:

I wrote this in my big post on page two but I think people might have missed it; my next post will be about Daily Light Integral (DLI) and Vapor Pressure Deficit (VPD)

1. I use a 28 hour dirunal (length of daylength and nightlight; usually 24 hours) for flowering as 16 hr/12 hr (daylength/nightlength). I apply an hour of dark at/past noon to help reduce noon-break and amount and/or intensity of Pn (rate of photosynthesis) peaks, both of which are mostly due mostly to DLI (Daily Light Intregral), VPD (Vapor Pressure Deficit) and air and media temperature.

2. I use a 20 hour diurnal for preflowering with 8 hr/12 hr (daylength/nightlength). This helps keeps stretch to a minimum while still offering sufficient Pn. I try to also use a DIFF of 0 (zero) during preflowering to keep stretch to a minimum.​

I am basing these claims on proven scientific theory (re: carbon assimilation, DIFF, etc) and a couple of assumptions concerning the effect of an hour of dark at/post mid-day.




A few references:

16 hr Daylength: Diurnal Pn, circadian rhythms and carbon assimilation

1. “SUPPLEMENTAL LIGHTING OF GREENHOUSE VEGETABLES: LIMITATIONS AND PROBLEMS RELATED TO LONG PHOTOPERIODS,”
http://www.actahort.org/members/showpdf?booknrarnr=481_54


2. “LIGHT PERIOD REGULATION OF CARBOHYDRATE PARTITIONING,”
http://ncr101.montana.edu/Light1994Conf/1_6_Janes/Janes text.htm


3. “REGULATION OF ASSIMILATE PARTITIONING BY DAYLENGTH AND SPECTRAL QUALITY,”
http://ncr101.montana.edu/Light1994Conf/1_2_Britz/Britz text.htm


4. “Factors affecting the rate of photosynthesis,”
http://web.archive.org/web/20030306020209/http://www.geocities.com/CapeCanaveral/Hall/2385/rate.htm


5. “Independent Circadian Regulation of Assimilation and Stomatal Conductance in the ztl-1 Mutant of Arabidopsis,”
http://www.jstor.org/pss/1514476


6. “Environmental effects on circadian rhythms in photosynthesis and stomatal opening,”
http://www.springerlink.com/content/m275226261246h24/


7. “Circadian Rhythms in Photosynthesis : Oscillations in Carbon Assimilation and Stomatal Conductance under Constant Conditions,”
http://www.plantphysiol.org/cgi/content/abstract/96/3/831


8. “COORDINATING PHOTOSYNTHETIC ACTIVITY: CIRCADIAN RHYTHMS,”
http://www.tiem.utk.edu/bioed/webmodules/circadianrhythm.html


9. “859.pdf,”
http://www.plantphysiol.org/cgi/reprint/102/3/859.pdf



​

Noon break and multi-peak Pn and diurnal Pn changes

1. “Physiology of woody plants,”
http://books.google.com/books?id=lE...summary_r&cad=0#v=snippet&q=peak noon&f=false


2. “Study on the Diurnal Changes of Net Photosynthetic Rate and the Impact Factors of Stevia rebaudiana Bertoni in Autumn,”
http://www.scialert.net/pdfs/ajpp/2009/18-23.pdf


3. “DAILY CHANGES IN THE PHOTOSYNTHETIC RATE AND CHLOROPHYLL FLUORESCENCE IN FOUR COLORED LEAF PRUNUS TAXA,”
http://www.actahort.org/books/769/769_56.htm


4. “Effects of different light transmission rate on American ginseng's photosynthesis,”
http://www.ncbi.nlm.nih.gov/pubmed/15146635


5. “Diurnal changes in net photosynthetic rate in potato in two environments,”
http://www.springerlink.com/content/t7k256132141w668/


6. “lec21.pdf,”
http://www.plant.uoguelph.ca/courses/pbio-3110/documents/lec21.pdf
​

Rubisco

1. “Rubisco Activase,”
http://4e.plantphys.net/article.php?ch=8&id=81


2. “When the Lights Go Out"

(contrary to the claims of the authors blue PAR photons do not offer grater Pn than red PAR photons)​

http://thegardeninghub.spaces.live.com/blog/cns!3413DF10CC8C202A!231.entry


3. “Robust Plants' Secret? Rubisco Activase!,”
http://www.ars.usda.gov/is/AR/archive/nov02/plant1102.htm​

 

[NiteTiger]

Wait...

Hello,
I disagree. For example, if two growers with the same skill and strain (ie., clone), using the same growing method except for lighting irridiance (same lamp/reflector/ballast) where grower A is using 1,300-1,500 PPFD and grower B is using 500-700 PPFD in the end grower A will see greater growth, yield and quality.

Can you link me to the grow please? Otherwise it is nothing but theorycrafting, and shouldn't be stated as fact.

Offering too much PPFD hinders plant and wastes dollars and the same can be written if the grower provides too little PPFD in terms of what (cannabis quality and quantity) one could have produced.

Link to a grow please.

Did you not like reading about UV-b? That is something people often ask about but very few people have real info which as been researched and applied; I have done all three and provided info on that. Adding 375 uW/cm^2 of UV-b has been found to increase (total) THC content in cannabis flowers by around 20-30% and in leaf by around 40-60%.

Link required.

I have heard subjective accounts of a change in the 'high', but have not seen a definitive test that supports that claim. This is a very bold claim and will change the face of growing. I would think that if that had been -proven-, everyone would have UV-b lights in their grow right now.

Not only that but UV-b positively effects secondary metabolite production of cannabis (other than cannabinoids) and of other plants such as flavinoids, terpenoids, etc.

Link please.

If you can't provide definitive proof of these statements, then they should not be presented as fact. Especially point 3.

 

[secondtry]

On the topic of the amount of photons over a day:
(copyright secondtry)



DLI ("Daily Light Integral") is essentially the number of photons within the wavelength range of 400-700 nanometers per square meter per hour (by seconds per hour) of light per day (eg. "daylength").[1]

Most often DLI is a function of Photosynthetic Photon Flux (PPF; umol per square meter, often mistermed as PAR irradiance) multiplied by seconds per hour, not Photosynthetic Photon Flux Density (PPFD; umol per square meter per second). Using PPF for DLI is a problem because PPF is a imperfect plant photon quantitation and simply converting PPF into seconds per hour per daylength is not as accurate as PPFD quantitation. Thus all measurements are presented as "PPFD DLI", unless otherwise noted. PPFD is also an imperfect plant photon quantitation, however, it seems the most accurate for laymen field use.

DLI is an important consideration for a few reasons, for example: 1) to maximize plant photosynthesis and associated growth without wasted photons (eg. electricity for HID); 2) maximize growth to power consumption/cost, ideal DLI can be lower than maximum DLI; and 3) prevent leaf and plant stress and damage from too great DLI.

It has been found that DLI a pretty a ideal quantitation, however, it is practically impossible to accurately achieve a specific DLI as basis as a projection in the future (i.e., as a goal to achieve each day). Thus DLI is not suggested, it has been found that 3-day LI (3-DLI) is more achievable at a goal, and nearly as accurate as DLI. In fact, the most ideal integral irridiance quantitation (without projection) according to Seginer, Louis and Loslovich (2004) is: "a strategy using feedback from the difference between actual and reference light trajectory, without forecasting". Everything considered, 3-day LI seems the best option for laymen field usage.[2][3]


How-to calculate the DLI or 3-DLI from PPFD reading use the following equations:
(taken from Specmeters Support Knodwlgebase link http://support.specmeters.com/kb/index.php?ToDo=view&questId=102&catId=13 )

• DLI = PPFD x (3,600 x daylength) / 1,000,000

• 3-DLI = (PPFD x (3,600 x daylength) / 1,000,000) x 3

Where:

• PPFD is the reading as μmol/m^2/s (400-700 nm) from a quntum sensor like I link I linked to

• 3,600 is the number of seconds in an hour

• Daylength is the period (in hours) of light per diurnal period.

• 1,000,000 is the number of μmols per mole

Example DLI:

1,500 x (3,600 x 12) / 1,000,000 = 64.8 mol/m^2/day (or 64.8 moles/day)

​

One should attempt to take several PPFD measurements throughout the daylength and average them, using the average as the PPFD in the equations above.

-----------------------------------

Ideal PPFD

The following PPFD, ADT (Average Daily Temperature) and CO2 levels can achieve ideal and/or maximum rate of photosynthesis (PNmax), water use efficiency (WUE), rate of transpiration (E), leaf stomatal conductance (gs) and "decrease in intercellular CO2 concentration (Ci) and therefore, in the ratio of intercellular CO2 to ambient CO2 concentration (Ci/Ca)" for Cannabis spp. drug biotype cultivars[5]:

(In my next post I will write about Vapor Pressure Deficit which also needs to be taken into consideration)

• PPFD = 1,300-1,500
• ADT = 25-30'C
• CO2 = 750 to 1,000 PPM

Potentially ideal and/or maximum DLI and 3-day LI goals:

Vegetative stage, 24 hour diurnal with 16 hour daylength with one hour of darkness in middle of daylength:

• DLI: 1,500 x (3,600 x 15) / 1,000,000 = 81 mol/m^2/day

• 3-DLI: (1,500 x (3,600 x 15) / 1,000,000) x 3 = 243 mol/m^2/3-day

Pre-Flowering stage, 20 hour diurnal with 8 hour daylength:

• DLI: 1,500 x (3,600 x 8) / 1,000,000 = 43.2 mol/m^2/day

• 3-DLI: (1,500 x (3,600 x 8) / 1,000,000) x 3 = 129.6 mol/m^2/3-day

Flowering state, 28 hour diurnal with 16 hour daylength with one hour of darkness in middle of daylenght:

• DLI: 1,500 x (3,600 x 15) / 1,000,000 = 81 mol/m^2/day

• 3-DLI: (1,500 x (3,600 x 15) / 1,000,000) x 3 = 243 mol/m^2/3-day

Possible indicators of too great DLI and 3-day LI

Because exactly identifying the ideal DLI and 3-day LI is nearly impossible for all cultivars it is suggested one watches plant response, quantitates Pn and semi-quantitativly assays Rubisco over time. In terms of leaf/plant photoadaptation to light irridiance changes a common time frame seems to be day/s to a week. Visual signs of photoinhibition from too much PPFD over the whole day (like a human skin sunburn at the beach from 1 hr vs. 4 hr in the sun) often manifests as negative responses in the form of leaf tip burning, leaf bleaching and burning, the inward curling of leaf blades and the upward angling of leafs; in both latter cases the plant is reducing the surface are of the leaf to reduce the amount of photons striking the leaf.

Those negative morphological effects can occur when the maximum DLI or 3-day LI has been surpassed. Reducing the daylength will reduce the DLI and 3-day LI while still allowing for Pnmax from ideal PPFD. Thus one can simply use a "trial and error" methodology to identify the ideal DLI and 3-day LI for individual cultivars. Until accomplishing that goal using the previously presented DLI and 3-day LI seems wise. The following are major indicators of too great DLI and/or 3-day LI[2][3][6]:

(I use the upward angling of leaf as indication of light saturation because it's is temporary and seems to be a quick response)

• Leaf bleaching
• Leaf tip burn and leaf burn
• Vertical angling leafs to limit photon interception
• Inward curled leaf blades to limit photon interception

References:

[1] "Daily Light Integral Defined"
Author(s): Erik Runkle; 2006
Department of Horticulture at Michigan State University, East Lansing, MI
http://www.onhort.com/articles/070_gpn1106.pdf (full PDF)


[2] "STRATEGIES FOR A CONSTANT DAILY LIGHT INTEGRAL IN GREENHOUSES"
Author(s): Ido Seginer; Louis D. Albright; Ilya Ioslovich; 2004
Acta Hort. (ISHS) 691:117-124
http://www.actahort.org/books/691/691_12.htm


[3] "Improved Strategy for a Constant Daily Light Integral in Greenhouses"
Author(s): Ido Seginer; Louis D. Albright; Ilya Ioslovich; 2005
Biosystems Engineering. Volume 93, Issue 1, January 2006, Pages 69-80
http://www.gwri-ic.technion.ac.il/pd..._Seginer/5.pdf (full PDF)


[4] "Light Management in Greenhouses I. Daily Light Integral: A useful tool for the U.S. Floriculture industry"
Author(s): Jim E. Faust; circa 2005
FIRST Research Report
http://www.specmeters.com/pdf/articles/A051.pdf (full PDF)


[5] "Photosynthetic response of Cannabis sativa L. to variations in photosynthetic photon flux densities, temperature and CO2 conditions"
Author(s): Suman Chandran, Hemant Lata, Ikhlas A. Khan and Mahmoud A. Elsohly; 2008
Physiology and Molecular Biology of Plants. Volume 14, Number 4 / October, 2008.
http://www.springerlink.com/content/a3527u6018823x43/


[6] "Light Management in Greenhouses II. Plant Growth Responses to Daily Light Intergrals"
Author(s): Jim E. Faust; circa 2005
FIRST Research Report
http://www.specmeters.com/pdf/articles/A051.pdf (full PDF)


[7] "How to calculate Daily Light Integral (DLI) with a Quantum Light Meter"
Formula taken from Jim Faust‚ Light Management I (of III) article found in Spectrums articles section (#A050)
http://support.specmeters.com/kb/index.php?ToDo=view&questId=102&catId=13​

 

[yellowbluegreen]

I've got a bunch of 100w incandescent bulbs that I'm going to try. 1,000 watts of retro, baby!

 

[secondtry]

Hey NT,

(I like your nik, reminds me of when I was kid)

Secondtry wrote:

Hello,
I disagree. For example, if two growers with the same skill and strain (ie., clone), using the same growing method except for lighting irridiance (same lamp/reflector/ballast) where grower A is using 1,300-1,500 PPFD and grower B is using 500-700 PPFD in the end grower A will see greater growth, yield and quality.

Wait...

Can you link me to the grow please? Otherwise it is nothing but theorycrafting, and shouldn't be stated as fact.

You will find I prefer well documented studies to side-by-side grows where the scientific method is not taken into consideration. I don't ever use threads as evidence, sorry but it's rare that posts are well referenced enough and based upon proven scientific theory (and can prove it).

Here are some studies I already posted in this thread, the first discusses PPFD in regards to Pn (rate of photosynthesis) along with growth and yield (biomass) of cannabis; the last two discuss ideal PPFD for Pnmax which should be the goal for growing, not yield. Photosynthesis tends to be the lynch pin which holds other process (like growth, yield, secondary metabolite production, etc) together and the stronger the pin (higher Pn) the more it can hold (yield); crappy analogy I know but I hope it helps:

1. "Effect of Light Intensity on Photosynthetic Characteristics of Four High Delta9-THC Yielding Varieties of Cannabis Sativa"
https://www.icmag.com/ic/showpost.php?p=3247505&postcount=42


2. “Thidiazuron-induced high-frequency direct shoot organogenesis of Cannabis sativa L.,”
http://springerlink.com/content/3028210397611640/


3. “Photosynthetic response of Cannabis sativa L. to variations in photosynthetic photon flux densities, temperature and CO2 conditions,”
http://www.springerlink.com/content/a3527u6018823x43/
​

NT wrote:

Secondtry wrote:

Offering too much PPFD hinders plant and wastes dollars and the same can be written if the grower provides too little PPFD in terms of what (cannabis quality and quantity) one could have produced.

Link to a grow please.

See the studies I linked to above and the post above this one (link) where I discuss DLI, the effects of photoinhibition. All of this is very well documented, just not by cannabis growers, but heck, most of us still use Lux to measure lamps...

NT wrote:

secondtry wrote:

Did you not like reading about UV-b? That is something people often ask about but very few people have real info which as been researched and applied; I have done all three and provided info on that. Adding 375 uW/cm^2 of UV-b has been found to increase (total) THC content in cannabis flowers by around 20-30% and in leaf by around 40-60%.

Link required.

I have heard subjective accounts of a change in the 'high', but have not seen a definitive test that supports that claim. This is a very bold claim and will change the face of growing. I would think that if that had been -proven-, everyone would have UV-b lights in their grow right now.

I already posted link on page two, but I will post it/them again below; I have no idea why people are not using UV-b, myself and few people I know are, I figured all this stuff out like two years ago and wrote all about it at CW. I have used UV-b but have no personal unbiased data, however, I recently purchased all needed tools along with the mobile phase, stationary phase, reagent (fast BB) and preservation phase needed for me to analytically semi-quantitatively assay cannabinoids of cannabis flowers and extract using TLC (Thin Layer Chromatography) and the JustTLC program. I have put together a method to do just that from what NATO uses and is suggests by DEA, etc. Thus along with the study below I will have unbiased analytical results of Total THC, CBD, CBC, etc, and I can test for some specific terpenoids and flavinoids too from UV-b at specific irridiance

Here are a few good studies about increase in Total THC. The first one is the study I cited for the info about increase in Total THC in leaf and flower:

1. “UV-b Radiation Effects on Photosynthesis, Growth and Cannabinoid Production of Two Cannabis Sativa Chemotypes,"
http://www3.interscience.wiley.com/journal/120019839/abstract


2. “Photochemical studies of marijuana (Cannabis) constituents,”
http://www3.interscience.wiley.com/journal/113338818/abstract


3. “Chemical ecology of Cannabis,”
http://www.hempfood.com/Iha/iha01201.html
​

Here are other good papers on teh topic of UV-b:

1. “LIGHTING CONSIDERATIONS IN CONTROLLED ENVIRONMENTS FOR NONPHOTOSYNTHETIC PLANT RESPONSES TO BLUE AND ULTRAVIOLET RADIATION,”
http://ncr101.montana.edu/Light1994Conf/3_1_Caldwell/Caldwell text.htm


2. “REQUIREMENTS OF BLUE, UV-A, AND UV-B LIGHT FOR NORMAL GROWTH OF HIGHER PLANTS, AS ASSESSED BY ACTION SPECTRA FOR GROWTH AND RELATED PHENOMENA,”
http://ncr101.montana.edu/Light1994Conf/3_3_Hashimoto/Hashimoto text.htm


3. “Screening of visible and UV radiation as a photoprotective mechanism in plants,”
http://www.springerlink.com/content/g82t5p3k803p3162/


4. “Field testing of biological spectral weighting functions for induction of UV-absorbing compounds in higher plantst,”
http://cat.inist.fr/?aModele=afficheN&cpsidt=15756317
​

NT wrotre:

secondtry wrote:

Not only that but UV-b positively effects secondary metabolite production of cannabis (other than cannabinoids) and of other plants such as flavinoids, terpenoids, etc.

Link please.

If you can't provide definitive proof of these statements, then they should not be presented as fact. Especially point 3.

I already did provide the proof of scientific theory, I understand it was a huge post but all you are asking for is there, and lots more As for "point 3" I do not know what you are referring to. I know I have references for if I wrote it as a proven statement unless it was a typo.


Thanks for reading! I fear many people are not even doing that.

All the best

 

[secondtry]

I've got a bunch of 100w incandescent bulbs that I'm going to try. 1,000 watts of retro, baby!

Errr, you are joking right?

 

[phattybudz]

Obviously there have been LED claims in the past that were hype and most people agree they are good for veg but not flower (at least the old technology,) but there are new panels being made by ledgirl and another company that clearly ripped her name off (hydrogrowled is ledgirl, growledhydro is another company putting out new high wattage panels.)

So the question is are these new panels better for flowering?
If they match or beat yield by hps with good buds, then a higher initial cost would be justified by longer life and lower energy costs over time. Most of this has been stated though, personally I'm waiting to see what Blazeoneup thinks about them... his test is here: https://www.icmag.com/ic/showthread.php?t=160480&page=4
If you don't know Blaze, he's posted numerous tutorials and big grows; I respect his judgement more than any of the small-scale testers that have posted results so far (no offense guys, I just haven't seen you pump out fat commercial-size results before. So I am going to wait and see how that pans out before I drop a cent on LEDs.

 

[secondtry]

Hello,

Obviously there have been LED claims in the past that were hype and most people agree they are good for veg but not flower (at least the old technology,)

I disagree. Higher PPFD up to about 1,500 offers higher Pn and greater growth; thus I would suggest using 1,300-1,500 PPFD for veg and flower. I think the difference is the low irridiance is only really noticed by us during flowering.

but there are new panels being made by ledgirl and another company that clearly ripped her name off (hydrogrowled is ledgirl, growledhydro is another company putting out new high wattage panels.)

The LED panels made by LEDGirl are the LEDs I was referring to this while time. I tried to have a nice and productive conversation about this with her two weeks ago but she removed all my posts after it became clear she was beyond her depth of understanding. For example, she claims specific PPFD data from her LEDs by converting from irridiance (lux?) reported by the LED manufacture, there are at least two problems with that: 1) there is no way to convert accurately from lux to PPFD, or PPF (mis-termed as PAR irradiance) to PPFD, etc; and 2) the starting data (lux?) was from a second hand source. Also, on her PPFD page she seems to suggest one should use 500-700 PPFD for cannabis (read: tomatoes) and that is not correct as I have shown.

To reach over 1,300 PPFD a setup from LEDGirl (even the near 300w setup) would have to be placed inches from the canopy (I assume), IF it can reach 1,000 PPFD in the first place.

As the study from Kennedy Space Center showed, adding 25% green LED to a LED panel increased growth and is suggested. All LED panels I know of are missing that point, to use green LEDs. The reason IMO is that most LED developers like LEDGirl mistakenly use the absorption spectra of leaf extracts of chlorophyll A&B which is found in vitro in a spectrophotometer (IIRC). That is not how leafs and PPFD works outside in vivo, and is why I wrote we need to use the PAS (Photosynthesis Action Spectrum) when comparing SPD of lamps, not the absorption spectra of chlorophyll A&B.

So the question is are these new panels better for flowering?

See my previous comments. I will have my new PPFD meter and hand-held reader in a month and I offer anyone who has one of these new LED panels from LEDGirl to send it to me so I can test it, then I will send it back.

I make that offer to LEDGirl: Lets get real PPFD data on your new 300w panels. If you send me one I will test it and report the findings and send it back to you right away...let do it!


HTH

 

[secondtry]

On the topic room RH and Vapor Pressure Deficit (which effects Pn, transpiration, carbon assimilation, etc):


We should probably be using VPD for measurement, not RH when growing plants like cannabis, we want a VPD of 0.8-1.0 kPa, i.e., 8-10 mb(ar). Below I will quote heavily from a paper I attached to this post entitled: "Understanding Humidity Control in Greenhouse". When keeping VPD between 0.8-1.0 kPa we should be able to lower the intensity/amount of Pn-peaks throughout the day and allow for greater Pnnet (the net rate of photosynthesis over a day), hopefully also mitigating the noon-break. The range of 0.45-1.25 kPa is the minimum and maximum range of VPD for best growth according to Autogrow Systems Ltd (link). The problem being is keeping VPD from 0.8-1.0 kPa means a high RH, around 70-80% in some instances. The VPD effects the opening and closing of leaf stomata, adjusting VPD to 0.8-1.0 kPa increases the openness of stomata and thus the amount of transpiration, Co2 uptake and rate of photosynthesis, etc.

I have yet to do a grow with a VPD as low as 1.0 kPa but this next grow I am shooting for 1.0-1.2 kPa which means I will need to use humidifiers (impeller style are best) to raise RH and also I will need to exhaust of air on regular basis, maybe once an hour or once every two hours after which point the Co2 tank will turn on to raise the Co2 to 1,000 ppm. My main worry of course is high humidity in late flowering but I will try to keep RH below 75% with strong air movement and reoccurring air changes. At the bottom of this post I offer links to products which allow for fully automated control of RH and temperature, and hence VPD in a room...on the cheap.

The most accurate way to calculate VPD is to use air temperature, RH and leaf temperature. According to E. T. Linacre (1967) leaf temperature is higher than air temperature when air temperature is lower than the so-called "equality temperature" of 30'C (86'F), and in a paper by Nobuoka Takshi et al,. (circa 1997) the authors explain how an increased air movement lowers the temperature of the leaf and increases transpiration. According to Chandra, et al., (2008) ideal air temperature for Pnmax of cannabis is 30'C when irridiance is 1,500 PPFD.




Here are two different scenarios where I took VPD into consideration, most growers should fit into either of the daylength category; these are just very simple examples, YMMV (calculated with this page: link)

(the following data was calculated from referenced studies on cannabis (i.e., ideal PPFD, Co2 and air temp) and higher green plants (i.e., VPD), I didn't randomly choose these data except for RH and leaf temp-tho both the latter are based upon science)

[Daylength] Here is what seems to be reasonable figure (although it should be a range) for achieving ideal VPD while also achieving ideal PPFD, Co2, air temp and just over ideal RH...all of those equate to Pnmax and Pnnetmax of cannabis:

• VPD = 1.03 kPa
• PPFD = 1,300-1,500
• Co2 = 800-1,000 ppm
• Air relative humidity = 70%
• Air temperature = 30'C (86'F)
• Leaf temperature = 29'C (84'F)

[Daylength] Here is my best judgment on ideal VPD (although it should be a range) in less than ideal PPFD which means lower air temperature (and decreased Pn in cannabis):

• VPD = 1.19 kPa
• PPFD = < 1,200
• Co2 = 300-400 ppm (no addition of Co2)
• Air relative humidity = 75%
• Air temperature = 25'C (77'F)
• Leaf temperature = 27'C (80'F)

"Understanding Humidity Control in Greenhouse"

What is Vapor Pressure Deficit?

Relative humidity is still the most commonly used measurement for greenhouse control, even though it is not a perfect indication of what the plants ‘feel’. Plants respond to the difference between humidity levels at the the leaf stomata and the humidity levels of the surrounding air. At the same relative humidity levels, but at different temperatures, the transpiration demand for water from the leaves may be double (See Figure 3.) Therefore, another kind of measurement, called the Vapour Pressure Deficit is often used to measure plant/air moisture relationships. Some environmental control companies now offer VPD measurements as a part of their humidity management programs.

Role of Humidity

The main plant mechanism for coping with humidity is the adjustment of the leaf stomata. Stomata open and close in response to vapour pressure deficit, opening wider as humidity increases. When humidity levels drop to about 8 grams/m^3 (12 mb VPD) the stomata apertures on most plants close to about 50% to help guard against wilting. This also reduces the exchange of C02, thereby affecting photosynthesis. Tables 1 & 2 (See Page 8) outline vapour pressure deficits (the difference between saturated air and air at various relative humidities). Although different crops vary in their response to humidity levels, a VPD range of 8 - 10 mb has been suggested as an optimum range. VPD can be used for both dehumidifying and humidifying, but it is particularly useful for humidifying.

Photosynthesis

Humidity levels indirectly affect the rate of photosynthesis because C02 is absorbed through the stomatal openings. At higher daytime humidity levels, the stomata are fully opened allowing more C02 to be absorbed for photosynthesis. Photosynthetic levels can vary by about 5% between VPD’s of 2-10 mb.

Products Needed:


1. Accurate hygrometer:

I like synthetic hair models, below are a few good models/brands. This comes calibrated but I like to double check and adjust if needed as so: fully soak a towel then wring it out so it's fully wet but not dripping water, then wrap it around the hygrometer fro 60 minutes, remove the hygrometer and adjust the hydrometer to 99% RH (or use the salt method).

Hygrometer/Thermometer ($60) accurate to +/- 5% and +/- 2' F
http://www.partshelf.com/taylor5565.html

Hygrometer($41) accurate to +/- 5%
http://www.a3bs.com/weather/precision-hair-hygrometer-u14293,p_83_860_862_0_1065_image_full.html

Hygrometer($75) accurate to +/- 4%
http://www.robertwhite.com/cgi-loca...0&categ=rw_thermo_hygrometers&nav_bar=weather
​

2. Infrared Leaf Thermometer ($35):

http://www.horticulturesource.com/product_info.php?products_id=4657



3. Humidifier impeller style: (reduce VPD)

I use 2 in a room that is 10x12 to raise RH over 80%, can get these at Walmart, etc:
http://www.kaz.com/kaz/store/product/77e8cc17f66a13b695100097a33ddebc/



4. Humidistat and thermostat (auto-control of humidifier and heater):

I have used this for mycology and it worked well, I spoke with ZooMed and they claim a +/- 3% accuracy in RH score. I also use a ceramic space heater rated under 1,000 watts with this controler so when the RH drops below 70% the controller will turn on the humidifiers and turn off the humidifier once RH is at 70% and if the temperature drops below 30'C the controller will turn on the space heater and turn it off once the temperature is at 30'C.
http://www.reptiledirect.com/zoomed-hygrotherm.aspx



P.S. I have lots of references in cast anyone is interested in reading more.


I hope someone finds this as interesting as I do

 

[Zombo]

Hello,

....

See my previous comments. I will have my new PPFD meter and hand-held reader in a month and I offer anyone who has one of these new LED panels from LEDGirl to send it to me so I can test it, then I will send it back.
HTH

I might be up for that, as I just set up a new closet for dwc/scrog, and I believe Cammie's 126w unit will fit the bill perfectly. I'd like to bring her in on this, as what I'm thinking is I buy a brand new unit, she ships it to you, you test it, then ship it to me (you pay the shipping cost, of course).

I currently use the 63w unit, but am not willing to send it to you and lose the use of it (I also have a 90w "UFO", however, I've not tried it out, test grow is pending). I'm willing to "take one for the team" so to speak, just because I'm an ex-LASER/Electro-Optics guy, who loves getting raw data on this stuff. I was going to buy a 126w anyhow, this will just delay my having the unit in hand.

 

[secondtry]

Hello,

Sure, sounds good to me. Although I won't be able to test for about 3-4 weeks, I am pretty busy for the next couple of weeks. If you plan to buy it next month or at the end of March I'm game; and sure I'll pay shipping. I would like to compile a large database of PPFD tests.

Thanks

 

[secondtry]

More info on "midday depression" (a.k.a. "noon-break") and Pn-peaks:


A very quick into:
Midday depression is when rate of photosynthesis (Pn) drops as does carbon assimilation, etc. The main goal of a grower should be to reduce the intensity and/or occurrence of midday depression and the intensity and/or number of Pn-peaks. The goal is to have plants achieve high Pn all day long at a fairly consistent rate. The flowing paper is very good and covers the topics really well, the paper offers more info of directly applicable nature than I have found so far.

The following paper is only in hardcover so I will go get the book tomorrow and photocopy the paper, then I will upload it. It is definitely worth the effort, one can read the whole paper on Google-book, well every page but the second page. That paper just answered a lot of the questions and I a few assumption I had.


Da-Quan Xu and Yun-Kang Shen

"Midday Depression of Photosynthesis"
Handbook of photosynthesis. v. 1996 - 1997. pp 451-460.​

http://books.google.com/books?id=MU...hotosynthesis&q=noon#v=snippet&q=noon&f=false

I. Introduction

Midday depression of photosynthesis occurs in many plants and significantly affects crop yields. Since it was discovered at the beginning of the century [1], many studies have been carried out, and several hypotheses, such as feedback inhibition of photosynthesis resulting from assimilate accumulation, stomatal closure, enzyme deactivation, and reversible decline in photochemical activity, have been proposed to explain the phenomenon [1-4]. In recent years, midday depression has been scrutinized with modern techniques. However, its casual mechanism is still not established [4]. Based on available data, the ecological, physiological, and biochemical factors related to midday depression are analyzed and the possible mechanisms and adaptive importance are discussed in this chapter.

II. THE PHENOMENON

A. Pattern of Diurnal Variation for Photosynthesis

Under natural conditions there are two typical patterns of photosynthetic diurnal course [5]. One is one-peaked, i.e., net photosynthetic rate increases gradually with the increase in sunlight intensity in the morning, reaches its maximum around noon, then decreases gradually with the decrease in sunlight intensity in the afternoon. Another is two-peaked, i.e., there are two peak values of net photosynthetic rate, one in late morning and another in late afternoon with a depression around noon, the so-called midday depression of photosynthesis, as shown in Figure 1 (curves 1 and 2).

 

[Blue Tail]

secondtry,

Wow... thanks very much for your OP on the Luxim LIFI's. And everything else you've posted since. This is great information... can't thank you enough. Keep it coming. I for one will read it all.

BT

 

[NiteTiger]

Secondtry, you missed what I was trying to say, I think, because the link you provided actually proves my point. Theory should not be presented as fact.

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 Δ9-tetrahydrocannabinol (Δ9-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 Δ9-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 (a cannabinoid with UV-B absorptive characteristics similar to Δ9 THC). Thus the contribution of cannabinoids as selective UV-B filters in C. sativa is equivocal.

In short, they were testing to see if the THC production was linked to UVB exposure - attempting to test the 'sunscreen' theory. No where does it state any specific amount of increase, certainly not 20-30%. In fact, the researchers themselves said it - Equivocal.

Do not present theory as fact. Be able to show real-world proven results before you say 'this has been proven'. I appreciate you bringing this research to IC, but realistically it is no more than interesting reading.

 

[secondtry]

Hey NT,

Can you please stop trying to lecture me? And drop your slightly condescending attitude? I spend at least 4-5 hours everyday researching and trying to figure all this stuff out, please do not assume I am an average ICer, I am not. I have a very high bar for info I present, and how I present it...

NT wrote:

secondtry, you missed what I was trying to say, I think, because the link you provided actually proves my point. Theory should not be presented as fact.

I did no such thing, you are mistaken. The links I provided show increases of Total THC from UV-b (Allwardt, et al, 1971 and Lydon, et al., 1986), and UV-c (Allwardt, et al, 1971), but UV-b is more safe to work with. I will go over each link one by one below to help explain matters. However, I never presented the THC increase as fact, I presented nothing as fact, this is what I wrote (verbatim): "has been found to increase (total) THC content". That is a FAR cry from what you claim I am doing. In science there is no fact, the closest thing to fact is proven scientific theory. What I presented is that increased levels of UV-b irridiance have been shown to increase Total THC, and that is a very true statement. I also cited quantitated increases in Total THC which was found in the work of Lydon, et al., (1986).

NT wrote:

In short, they were testing to see if the THC production was linked to UVB exposure - attempting to test the 'sunscreen' theory. No where does it state any specific amount of increase, certainly not 20-30%. In fact, the researchers themselves said it - Equivocal.

Below is the study (#1) you are referring to, and it seems you only read the abstract, no? When conducting research it's best to at least have access to the full text, if not read the whole paper, reading only abstracts doesn't cut it IMO. I have full text of almost every paper for which I have references, and I have read them all. I will upload the full text of the papers by Allwardt, et al., and by Lydon, et al., later today. The last paper by D.Pate is full text so I don't need to upload it.


1.
--------------------------------------------------------------------------------------------------------------

In the following work the researchers looked at the three main species of Cannabis spp. humans grow: 1) drug biotype, the kind we grow, i.e., "indica" = C. indica and "sativa" = C. indica indica; and 2) the non-drug biotype grown for fibre, i.e., "hemp" = C. sativa.

The researchers found that drug biotype had increases in THC from UV-b irridiance, this study is whence came the figures of about 20-30% THC increase in flower and about a 40-60% THC increase in leaf (granted those figures are from memory but they are close enough, and why I use the word "about"). The fibre non-drug biotype cultivars did not show the same response to UV-b, and according to D.Pate (1994) and other researchers most drug biotype variates and races of the two species C. indica and C. indica indica developed in geographical regions naturally higher in UV-b.

I have colored the important sentences from this abstract, they speak for themselves. The study found no increase in quantity of CBD (cannabidiol) within C. sativa, but we grow C. indica or C. indica indica. The very last sentence you noted only states that the study did not prove cannabinoids are filters for UV-b...however, that says nothing about the findings showing UV-b increased THC in drug biotype cultivars...

FWIW:
I have proposed in the past a hybrid of indica (C. indica) and sativa (C. indica indica) be classified as C. indicaxindica, ex. afghan x haze.



"UV-B RADIATION EFFECTS ON PHOTOSYNTHESIS, GROWTH and CANNABINOID PRODUCTION OF TWO Cannabis sativa CHEMOTYPES"

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 Δ9-tetrahydrocannabinol (Δ9-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 Δ9-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 (a cannabinoid with UV-B absorptive characteristics similar to Δ9 THC). Thus the contribution of cannabinoids as selective UV-B filters in C. sativa is equivocal.

2.
-------------------------------------------------------------------------------------------------------

In the following study the researchers found that CBD and THC are photoreactive and that CBD converts into THC under the wavelength range of 235-285 nm. While conversion of CBD to THC happens at other wavelengths (and plant age) I think this study shows UV-c and UV-b has an effect on THC. The lamp I use should emit photons in that range considering UV-b starts just below 290 nm and goes to 320 nm (or to 315 nm depending upon the reference material).

It should be noted that some sources cite 280 nm as the lowest UV-b wavelength, while other source cite 290 nm as the lowest UV-b wavelength. Considering UV-b has been found to increase THC (Lydons, et al., 1986) and the work of Allwardt, et al., (1971) found CBD converts to THC at the wavelengths of (at least) 235-285 nm I tend to believe UV-b starts closer to 280 nm than 290 nm. I would like to know for sure...


"Photochemical studies of marijuana (Cannabis) constituents"

Abstract

The marijuana (Cannabis) constituents, cannabidiol, (-)-9-trans-tetrahydrocannabinol, and (-)-9-trans-tetrahydrocannabinol were found to be photoreactive. The only interconversion of these cannabinoids detected by GLC, however, was the conversion of cannabidiol to (-)-9-trans-tetrahydrocannabinol. From a photoreaction mixture obtained by the irradiation of cannabidiol, a sample of (-)-9-trans-tetrahydrocannabinol was isolated and identified by GLC, optical rotation, NMR, and mass spectrometry. A yield of 16% was obtained. The activating energy for the conversion appears to be in the 235-285-nm wavelength area.

3.
--------------------------------------------------------------------------------------------

The following review by D.Pate (1994) he presents much and more of the same info I presented. I do not think I need to write about this paper because it is in the full text. I would suggest you read it if you have not, it's a good read. D.Pate discusses the same work by Lydon, et al, as I discussed above.


"Chemical ecology of Cannabis"

A preliminary investigation (Pate 1983) indicated that, in areas of high ultraviolet radiation exposure, the UV-B (280-315 nm) absorption properties of THC may have conferred an evolutionary advantage to Cannabis capable of greater production of this compound from biogenetic precursor CBD. The extent to which this production is also influenced by environmental UV-B induced stress has been experimentally determined by Lydon et al. (1987). Their experiments demonstrate that under conditions of high UV-B exposure, drug-type Cannabis produces significantly greater quantities of THC. They have also demonstrated the chemical lability of CBD upon exposure to UV-B (Lydon and Teramura 1987), in contrast to the stability of THC and CBC. However, studies by Brenneisen (1984) have shown only a minor difference in UV-B absorption between THC and CBD, and the absorptive properties of CBC proved considerably greater than either. Perhaps the relationship between the cannabinoids and UV-B is not so direct as first supposed. Two other explanations must now be considered. Even if CBD absorbs on par with THC, in areas of high ambient UV-B, the former compound may be more rapidly degraded. This could lower the availability of CBD present or render it the less energetically efficient compound to produce by the plant. Alternatively, the greater UV-B absorbency of CBC compared to THC and the relative stability of CBC compared to CBD might nominate this compound as the protective screening substance. The presence of large amounts of THC would then have to be explained as merely an accumulated storage compound at the end of the enzyme-mediated cannabinoid pathway. However, further work is required to resolve the fact that Lydon's (1985) experiments did not show a commensurate increase in CBC production with increased UV-B exposure.

-----------------------------------------------------------------------------------

NT wrote:

Do not present theory as fact. Be able to show real-world proven results before you say 'this has been proven'. I appreciate you bringing this research to IC, but realistically it is no more than interesting reading.

I did not present anything as fact, please see the two links below, they might help explain the myth of science "facts" better than I. AFAIR I never once wrote "this has been proven" about UV-b increasing THC, please do not put words in my mouth. I did however claim it has happened (which is a fact) and is very likely to happen again (which is near proven scientific theory). What I offer is real-word results, hell, I grow this way...

"Fact, Hypothesis, and Theory"
http://www.ruf.rice.edu/~bioslabs/studies/concepts/objectivity.html

"How Not to Do Science"
http://www.ruf.rice.edu/~bioslabs/studies/concepts/concepts.html#not
​

References:

1) John Lydon, Alan H. Teramura and C. Benjamin Coffman (1986)

"UV-B RADIATION EFFECTS ON PHOTOSYNTHESIS, GROWTH and CANNABINOID PRODUCTION OF TWO Cannabis sativa CHEMOTYPES"
Photochemistry and Photobiology. Volume 46 Issue 2, Pages 201 - 206
​

2) William H. Allwardt, Philip A. Babcock, Alvin B. Segelman, John M. Cross (1971)

"Photochemical studies of marijuana (Cannabis) constituents"
Journal of Pharmaceutical Sciences. Volume 61 Issue 12, Pages 1994 - 1996
​

3) David W. Pate (1994)

"Chemical ecology of Cannabis"
Journal of the International Hemp Association 2: 29, 32-37.
​

 

[secondtry]

I just edited and clarified my previous post a little, I didn't change anything of import except what is quoted below, the edited text is italicized:

In the following study the researchers found that CBD and THC are photoreactive and that CBD converts into THC under the wavelength range of 235-285 nm. While conversion of CBD to THC happens at other wavelengths (and plant age) I think this study shows UV-c and UV-b has an effect on THC. The lamp I use should emit photons in that range considering UV-b starts just below 290 nm and goes to 320 nm.

It should be noted that some sources cite 280 nm as the lowest UV-b wavelength, while other source cite 290 nm as the lowest UV-b wavelength. Considering UV-b has been found to increase THC (Lydons, et al., 1986) and the work of Allwardt, et al., (1971) found CBD converts to THC at the wavelengths of (at least) 235-285 nm I tend to believe UV-b starts closer to 280 nm than 290 nm. I would like to know for sure...