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Effects of differing wavelengths of light on cana growth.

179 posts in this topic

'allo folks,

So I've been pondering the whole MH/HPs differing effects on canna growth. I've introduced a MH lamp into my HPS flowering room and more recently switched over from fluro tubes to MH in my veg tent.

I've seen a lot of claims, here at UK420, that the reason for plants being smaller/stockier under MH (when compared to HPS) is that the MH lamps are less efficient, the plant is getting less lumens. However from my own observations and listening to others on the effect MH illumination has on their plants, I feel that this may not be the only contributing factor. And may even not be the reason at all, for the altered growth characteristics.

I think it likely that the MH radiation causes a reaction in the plant to make it grow stockier. This seems to happen with a lot of folks here (please don't ask for citations! :D ). It certainly does in my Jedi. With similar wattage MH (switched over from linear fluro), the Jedi is now producing the squat, thickly branched growth I have been seeking for so long. In addition I think HPS illumination makes plants stretch.

Btw I can only get camera phone quality pictures only atm. :rofl:

Granted this may be strain specific. In fact I would be a bit surprised if it wasn't. lol. It would be nice to compare notes and find out what strains do well under what lights. Or has this been done in the strain talk forums? :yes:

I've also been inspired by the diehard LED research crowd here. :yep: They seem attuned to the idea that differing wavelengths of light may produce very specific responses in canna. I've not had any real time to devote to this research so I would be thrilled to hear from other folks on this! :yes:


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Hey Randalizer,

I was about to ask what's the recomended lamp type for Week 1+ of flowering. I have an a pair MH and HPS blubs so far I have only used a MH.

Tried searching the fourm, was getting the impression that HPS should be used for flowering, so I would love to know what one of the two I shoudl be using.


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According to the experts (that I trust :rofl: ) here HPS is good for stretch and MH for stocky growth and increased psyche-activity. I use HPS at the start of flower to get my girls to grow a bit, then switch over to MH for the last 3 weeks of a 9 week flower period.

I've observed the stretch from HPS and also the squat quality from MH. The psyche-active effects I've seen a good research paper write up on. I'll be back with a Jedi smoke report soon, taking into account the MH on my girls. :rofl:

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i grow in tents rands and use mh for the 1st couple of weeks then hps to finish off(helps me loads when running a new strain from seeds, which seem to stretch more than cuts i feel), interesting to hear you do it the other way round, do you have no height restriction or do you flower em short?

be interesting to see the smoke report on the mh, see if its worth using em more for quality of stone etc.

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, do you have no height restriction

None in my flower room, and none to speak of in my veg tent. I also use linear rails on all my HIDs. Check my diaries for pictures and more info.

Edited by Randalizer

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Very interesting.....I would have guessed that the more Watts at the end would have given a heavier bloom, is this method just for quality of smoke?

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The HPS/MH ratio for flowering (60/40) was derived at by OT1 after some research done by him. I can't find the topic (would anyone here like to help me on this please?). In the topic he said he felt that this was the best compromise between potency and yield.

OT1s advice has helped my garden so very much and he is very kind and generous (unless he is grumpy :yes: ). Of all the folks I have read here at UK420 over the past year, I trust him the most. :rofl: :rofl:

BUT I feel more research would be nice. :yes:

Edited by Randalizer
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I might well have to use this method cause ill be using a 600w hps for flowering starting this weekend.

Reckon I will have problems with the stretch and probably would be able to leave the 400w mh closer to them if things are tight, Ill see how things go... How long many weeks can i expect them to stretch for?

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How long many weeks can i expect them to stretch for?


How about if we keep the signal to noise ratio down if we could please? I'm no expert on stretch and there are loads of topics here on that if you search for them. This topic is about wavelengths of light and their effect on canna growth.

Please don't take this personally. I mention it here only in an attempt to keep this topic on track.

Edited by Randalizer

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I took that one to heart, Im off now to cry myself to sleep :rofl:

Yea that was plain laziness :rofl::yes:

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:rofl::yes: :yes:


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As I posted in my first post, I've never grown canna. However, I've done a fair bit of research on it. The sun produces equal amounts of each wavelength of light between certain parameters. HPS bulbs tend to produce more red light than MH bulbs and as a result you can get stretchier plants, larger internodal distances and generally weaker branches which is not what you want to hold your buds! The HPS are also of more benefit to flowering plants because more of the red spectrum is used. MH bulbs produce more of the blue wavelength that is lacking in the HPS and as a result plants develop thicker, stronger stems and don't tend to stretch so much. I can't comment on LEDs, fluorencents or dual spectrum HPSs but I would guess that the dual spectrum HPS bulb is produced in such a way that the missing blue wavelength has been compensated for and that they produce a healthy balance between the two. I know nothing about the radiation they might produce or wavelengths outside the visible spectrum so can't really comment!


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I wonder if canna wants to see differing wavelengths at differing times. Or by emphasing certain wavelengths at certain times, we get more of what we are looking for.

In any case, a study on UVB radiation and THC production:


Resin glands, and the uv light connection

here's an article i found. A few of us have talked about it on a few threads. An elaboration on the phytochemical process that makes marijuana THC

The resin exuded by the glandular trichome forms a sphere that encases the head cells.

When the resin spheres are separated from the dried plant material by electrostatic attraction and placed on a microscope slide illuminated with a 100W incandescent bulb, they appear very dark when observed through a 300X microscope. Since orange, red, and infrared are the component wavelengths of incandescent light, and since the absorption of light makes an object dark or opaque to the frequency of the incoming wave, one can conclude that these wavelengths are probably not directly involved in energizing the cannabinoid pathway.

However, the resin sphere is transparent to ultraviolet radiation.

The author found through trial and error that only one glandular

trichome exhibits the phytochemical process that will produce the amount of THC associated with pain relief, appetite stimulation and anti-nausea; euphoria and hallucinations are side-effects, however. This trichome is triggered into growth by either of the two ways that the floral bract is turned into fruit.

Of all the ways that optics are involved in the phytochemical production of THC, the most interesting has to be how the head cells and cannabinoid molecules are tremendously magnified by the resin sphere. These and other facts are curiously absent from the literature. The footnotes update the literature to include electrostatic separation of the resin sphere from the dried plant material and marijuana parthenocarpy.

(1) "For all spheres, a ray drawn perpendicular to the sphere's surface will intersect the center of the sphere, no matter what spot on the surface is picked, and the magnifying power(a) of a glass sphere is greater the smaller its size. A sphere of glass can also bring light that is heading to a focus behind it to a point within it, with freedom from two aberrations, spherial aberration and coma, but not from chromatic aberration. Chromatic aberration results when different wavelengths are focused on different planes and is the most difficult of the aberrations to correct. The human eye lens also exhibits chromatic aberration, but a yellow pigment( called the macula lutea in the fovea, an area at the rear of the eyeball, corrects this problem by the way it absorbs blue light."

(a)"The formula to calculate the magnifying power of a sphere is l=333/d, where l is the magnifying power and d is the diameter of the sphere expressed in mm."

(b)Interestingly, the resin exuded by drug-type flowering female marijuana plants has a yellow tint. Could this pigment work to correct chromatic aberration in the resin sphere like the macula lutea does in the fovea for the eyeball?

(2) Quoting from the Mahlberg and Kim study of hemp(a) "THC accumulated in abundance in the secretory cavity where it was associated with the following: cell walls, surface feature of secretory vesicles, fibrillar material released from disc cell wall, and cuticle. It was not associated with the content of the secretory vesicles."

The resin spheres contain the THC. It is not contained in the leaf or floral bract. After the resin spheres are dissolved in solvent or dislodged by electrostatic attraction, and a microscopic examination of the leaf or floral bract has revealed that only the glandular trichomes' stalks remain, no effect will be felt after smoking the dried plant material from which the resin spheres have been removed.

(3) The electrostatic collection of the resin spheres from dried marijuana plants with plenty of ripe seeds has been for hundreds of years the method indigenous people of North Africa and Lebanon have used to make hashish. Obtain a round metal can 8" or so in diameter x 3" or so in depth (the kind that cookies come in) with a smooth lid. Obtain 2 ounces of dried marijuana with plenty of ripe seeds in the tops. To remove the seeds and stems, sift the marijuana tops through a 10-hole-to-the-inch wire kitchen strainer into the can. Close the can with the lid and vigorously shake the closed can three or four times. This gives the resin spheres an excess negative charge. Let the can sit for a moment and then remove the lid. Opposites attract. The negative-charged resin spheres have been attracted to the metal surface of the can and lid which has a positive charge. Take a matchbook cover or credit card and draw the edge across the surface of the lid. Note the collected powder. Observed under 300X magnification, the collected powder from this "shake" is composed of resin spheres with an occasional non-glandular trichome. As the marijuana is shaken again and again, and more of the yellow resin spheres are removed from the plant material, the collected powder gradually becomes green-colored as the number of non-glandular trichomes increases in the collected powder. The greener the powder, the less the effect.

(4) "Cannabinoids represent a dimer consisting of a terpene and a phenol component. Cannabigerol (CBG) is the first component of the pathway. It undergoes chemical change to form either cannabichromene (CBC), or cannabidiol (CBD). Delta 9-tetrahydrocannabinol (THC) is derived from CBD."

(5) "Pate (1983) indicated that in areas of high ultraviolet radiation exposure, the UVB (280-320 nm) absorption properties of THC may have conferred an evolutionary advantage to Cannabis capable of greater production of this compound from biogenetic precursor CBD. The extent to which this production is also influenced by environmental UVB has also been experimentally determined by Lydon et al. (1987)."

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

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

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

7am: 12 microwatts/cm2

8am: 74 microwatts/cm2

9am: 142 microwatts/cm2

10am: 192 microwatts/cm2

11am: 233 microwatts/cm2

12pm: 256 microwatts/cm2

1pm: 269 microwatts/cm2

2pm: 262 microwatts/cm2

3pm: 239 microwatts/cm2

4pm: 187 microwatts/cm2

5pm: 131 microwatts/cm2

6pm: 61 microwatts/cm2

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

(6) Capitate-stalked glandular trichome.

(7) #1: The ovum has been fertilized and there is a seed developing: In the areas of the Northern Hemisphere where indigenous people have grown heterozygous drug-type marijuana for hundreds of years, pollination is used to trigger the growth of the capitate-stalked glandular trichome on the floral bract and concomitant leaves of the flowering females before the autumnal equinox(a) so the majority of seeds will be ripe( before November.

(7) #2: The floral bract has become parthenocarpic: Parthenocarpic fruits develop without fertilization and have no seeds. Except for transmutation and turning lead into gold, there has been more nonsense written about seedless marijuana than on any other subject. In marijuana parthenocarpy, the floral bract (the fruit) enlarges in size as though there were a seed growing inside, and the capitate-stalked glandular trichome is triggered into growth on the floral bract and concomitant leaves. "Most popular supermarket tomatoes are parthenocarpic which was induced artificially by the application of dilute hormone sprays (such as auxins) to the flowers." In a trial, marijuana parthenocarpy was not induced by the application of the spray used on tomatoes. Only the photoperiod© will trigger parthenocarpy in flowering female marijuana plants. Marijuana parthenocarpy occurring before the autumnal equinox is considered by the author to be "long-day" and marijuana parthenocarpy occurring after the autumnal equinox to be "short-day".

The longest photoperiod that will trigger parthenocarpy in unfertilized flowering homozygous(d) Indica female marijuana plants is 13:00 hours, give or take 15 minutes. This effect can be obtained in the month of August at N35Lat, and because the capitate-stalked glandular trichomes received plenty of UVB during this month at this latitude, the harvested resin spheres had fully realized THC. Rating: euphoria and hallucinations, major appetite boost and pain relief, deep dreamless sleep. These plants seldom grow taller than four feet but potency makes up for the reduced harvest.

The gene pool is heterozygous if a flowering female marijuana plant is not parthenocarpic by the end of the first week in September in the Northern Hemisphere. If this is the case, pollination is used instead of parthenocarpy to trigger the growth of the capitate-stalked glandular trichome before the autumnal equinox to obtain as much fully realized THC as possible in the harvested resin spheres by the time the majority of the seeds are ripe.

The longest photoperiod that will trigger parthenocarpy in unfertilized flowering heterozygous female marijuana plants is 11:00 hours, give or take 15 minutes: This effect can be obtained in the month of November at N35Lat. Because of the low intensity of UVB radiation at this latitude at sea level during November, the harvested resin spheres evidenced only slightly more THC than precursor compounds. Rating: mild to medium euphoria, appetite boost and pain relief, good snooze.

Thai marijuana falls into this 11:00 hour category, and its parthenocarpy is characterized by an inflorescence in which many floral bracts are attached to an elongated meristem. It is these elongated meristems that are harvested to become a THAI STICK. On the other side of the world, Mexican marijuana grown around the same latitudes (Michoacan, Guerrero, Oaxaca) also falls into this short-day parthenocarpic category and the unfertilized marijuana will become "sensimilla" in the 11:00 hour photoperiod which begins in mid-December in that region. The winter sunshine in those latitudes has enough UVB intensity to produce fully realized THC--unlike the winter sunshine at N35Lat.

All unfertilized flowering female marijuana plants will become parthenocarpic in a 9:00 hour photoperiod (15:00 hour dark period): This can be obtained in the month of December at N35Lat. At this latitude in this month there is not even enough UVB in sunlight for precursor vitamin D3 to develop in human skin. The phytochemical process will not produce fully realized THC when UVB falls below a certain level of intensity expressed in µW/cm2. Rating: no effect.

(a)In the Northern Hemisphere above the Tropic of Cancer, the key to all marijuana potency is this: The more days of sunlight the capitate-stalked glandular trichomes' resin spheres accumulate before the autumnal equinox the more fully realized THC.

(b)It is recognized in the indigenous world that drug-type marijuana with a majority of ripe seeds will produce more euphoria, hallucinations, appetite stimulation, pain relief, and sleep aid than with a majority of unripe seeds.

©The photoperiodic response is controlled by phytochrome. "Phytochrome is a blue pigment in the leaves and seeds of plants and is found in 2 forms. One form is a blue form(Pfr), which absorbs red light, and the other is a blue-green form(Pr) that absorbs far-red light. Solar energy has 10X more red (660nm) than far-red (730nm) light causing the accumulation of Pfr." The first and last hour of a day's sunlight is mostly red light because of the scattering effect on blue light. "So at the onset of the dark period much of the phytochrome is in the Pfr form. However, Pfr is unstable and returns to phytochrome Pr in the dark." The red light in sunrise returns the Pr to the Pfr form. "Phytochrome Pfr is the active form and controls flowering and germination. It inhibits flowering of short-day plants (the long night period is required for the conversion of Pfr to Pr) and promotes flowering of long day plants."

(d)In Nepal and nearby areas of India where the capitate-stalked glandular trichome is triggered into growth by parthenocarpy rather than by fertilized ovum, great care is taken to make sure that all male marijuana plants are destroyed as soon as they reveal their sex. This is because unfertilized Indica flowering females can have both stigma and anther protruding from the floral bract. In the Indica gene pool, female-produced pollen carries an allele for long-day parthenocarpy, and seeds resulting from this female-produced pollen will produce another generation of female plants that will also exhibit long-day parthenocarpy during flowering. But if pollen from male plants is introduced into this gene pool, the resulting seeds will produce a generation of females that will exhibit short-day parthenocarpy instead. The allele for long-day parthenocarpy in the female-produced pollen is carried into the gene pool by self-pollination and cross-pollination, and perhaps homozygous is used too loosely here to describe the genetic result.

(8) It appears that the resin sphere acts as an UVB receptor and magnifying lens. The latter apparently lets it gather in a lot more photons than would otherwise be possible; because a lens also acts as a prism, the resin sphere may prevent some wavelengths from being focused where the phytochemical processes are taking place because they could interfere with the phytochemical process that makes THC.

electrostatic collection of resin spheres and non-glandular trichome.

Edited by Randalizer
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so then, lets see what we have then;

1) infra red, red, orange, yellow: Stretchy growth.

2) Green: No effect (afaik) and can be used during dark in flowering without upsetting the plants flowering cycle.

3) Blue: Stocky growth.

4) UVB: More complex and fully realized THC potential. Better taste and high.

From an evolutionary stand point, canna's stretchy growth for 1) may be due to that emf range (infra red to yellow) being able to better penetrated foliage. when a canna plant senses these wavelengths, it knows to stretch so that it can get to the light. And perhaps it get stocky from blue light as that is what it sees when the plants sees blue sky? This telling it not to stretch so much, perhaps because open sky has more wind that may snap branches? ;)

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Excellent thread topic Rand! :headpain: Great discussion!

Nothing to add as of yet... but I am on the side of MH being a great asset to the growing cycle during veg. Bushy, stocky, strong plants which seem to mature faster, and develop better once flipped to 12/12.

I know a good grower who only grows using MH, and has for years.. with very impressive results. I do like the HPS for flowering... buds are just... oh so nice.

Perhaps the best thing is to have a full spectrum of sorts in the flowering room.. or

to really shake things up....

We'd do HPS for the first 2 hours and the last 2 hours... then 8 hours with MH. Or ... some variation of that. In hopes to imitate the morning sun and evening sun when the light is at its most 'red', and MH during the middle of the day to imitate the sun high in the sky surrounded by blue sky? Did I understand part of that Scientific jargon correctly that Rand was so lovingly thoughtful to put up for us all? (very high right now)

Great info, keep it coming!

Thanks Randal!

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