Control red to far-red light ratio to limit stretching

FWIW, I just answered a PM a buddy sent me, and I thought it would be worth posting here.

My buddy asked me about something I wrote a few weeks ago and he asked me if he should try to supplement his Sunmaster dual spectrum with additional light to control stretch.

My buddy asked me about this quote of mine:

Some plants like other plants near them, like companion planting. But in general plants don't like to touch other plants because that means they would get shaded by other plants which makes them 'compete' for light. This is a major reason plants stretch, it has to due with the amount of red light intracanopy in relation to far-red light intracaonpy. Far-red light penetrates into the canopy well (passing through upper canopy leafs), but red light does not. The ratio of red to far-red light intracanopy is a major trigger for plants to grow (stretch) because the greater the far-red light and the less the red light intracaonpy makes them think they are being shaded. It's like two people fighting over food...

This topic is one reason plants can stretch more under traditional HPS than traditional MH. Because HPS has more far-red, which means HPS would provide a higher red:far-red ratio intracanopy vs. MH which would provide a lower red:far-red ratio intracanopy (i.e. amount of red and far-red would be closer under MH than under HPS).

Click to expand...

Here is my response:

In terms of red:far-red ratio intraconapy affecting plant stretching I think growers who fit the following descriptions need to be concerned:

• Those who have dense canopies of plants taller than a few inches (ex. > 10")
• Those who have poor lighting in terms of a lamp with or without a reflector providing direct light (esp. traditional HPS) that is not well dispersed over the canopy.
• Those who have light sources with lower intensity (ex. =< 250 watt HPS).
• Those who have a LED array with many of the red diodes in the far-red range of > 700 nm, specifically ~720-740 nm.
• Those who use LED arrays with diodes having narrow irradiation footprint. This has to due with the direct light provided by the diodes and how direct light irradiates intracanopy less well than diffuse light.

The ratio of red (R) to far-red (FR) light in the day under the sun when it reaches plant canopies is usually R:FR of 1:1. The R:FR light ratio below leafs can be around 0.15 [1][2]. The difference is due to how leafs absorb red light very well, but absorb far-red light less well. Much of the far-red light is transmitted through the leaf into the lower canopy. Red light has much lower transmittance rate through leaf. That means more far-red light will reach intracaonpy when the top canopy is dense. In the early am and pm the ratio of R:FR is reduced due to a reduction in red light and increase in far-red light.

Red and far-red light affects the plants' phytochrome responses, red light phytochrome is termed Pr and far-red light phytochrome is termed Pfr

There are a few things that affect plant growth and stretch, the first one has as much of an effect on stretch as does R:FR. We can tweak the following to reduce internodal elongation and plant stretch while keeping plant growth rate high [2][3][4]:I think a dual spectrum lamp should be fine in terms of not providing too much far red. I don't think you need to worry about the red:far-red ratio (i.e. 660-680 nm :720-740 nm), but I have not seen the SPD for the lamp; do you have a link?

You could increase the amount of red light intraconapy or decrease the amount of far-red intractionpy as a means to control the R:FR ratio.

In your case if you want to adjust R:FR using supplemental lighting you can increase the red light intracanopy via. florescent lamps as side lighting. That would provide more red light (with little far-red light) and would effect the red:far-red ratio to our favor (toward 1:1)...and it's cheap to setup and not a lot of heat; you wouldn't be trying to add a lot of extra light.

Making sure you use "diffuse" light and not "direct" light for you HID reflector is also important to keep red:far-red ratio in check. The reason diffuse light is better is the photons travel all kinds of angels to the plant, that means better intracaonpy irradiation (more light incl. red light, reaches the lower canopy) vs. direct light. Diffuse light means less shad spots intracanopy and bigger buds intracanopy. Diffuse light is also better in terms of plant growth because the diffuse light is less intense on the top of the canopy, so the plant grows better vs. under direct light that can hinder plant growth. An example of diffuse light is an HID with a 'pebbled' reflector. An example of direct light is most LED diodes or an HID with a 'mirrored' reflector.

I am planning on testing far-red light reducing/blocking film (ex. > 700 nm) over the glass in the reflector. That way only reduced levels of far-red light will reach the plants which means less stretch. Replacing the glass of an HID reflector with far-red reducing plastic sheet might also be an option. Either way a reduction in PAR range photons (i.e. irradiance at canopy, PPFD) will be found. Normally about a 5-10% reduction in irradiance is found when light passes through glass; but when using far-red light reducing/blocking film or plastic reductions in irradiance would be around 15-25%. That means using far-red light reducing film or plastic might only be worthwhile for 600w and 1000w HID due to the much higher PPFD value vs. 400w or 250w, etc.

FWIW, I think it's possible to use a 600w or 1,000 watt with far-red blocking film or plastic and still provide ideal (high) level of light (irradiance) per day for cannabis. That is, using the proven ideal PPFD for cannabis (~1,500) adjusted for a natural PPFD diurnal bell-curve over a whole day to find the "Daily Light Integral" (DLI) for a 12 hour day. Thus the ideal (natural environment replicated) PPFD-DLI for cannabis during flowering to reach highest rate of photosynthesis, yield, growth, etc., is 43 to 48 moles/m^2/day. To reach 43 to 48 moles/m^2/day for 12 hours (flowing) we need to provide ~1,000 to 1,100 PPFD [5].

Using peak diurnal PPFD of 1,500 adjusted with an average PPFD diurnal bell-curve from a high irradaince location (ex. Hawaii on relatively cloudless day) to find PPFD-DLI is the best method to measure lighting for a garden. Short of using PPFD weighted with K.McCree's Action Spectra of Photosynthesis once McCree's work is corrected with the new info about high irrdiance white light sourced green light providing as much quantum efficiency as red light (i.e. driving rate of photosynthesis as well as red light).

A bonus to replacing HID glass with far-red reducing plastic would be the UV-b and UV-A light reaching the canopy. Glass for HID blocks UV-B and most of UV-A. The UV-b is beneficial for the blue light sensing system "cryptochrome", it is said to have UV-B range absorption (and blue light too).

Far-red light reducing film or plastic works by a few methods. A common method is far-red light absorbing chemicals in the plastic sheeting, ex. YXE-10 from Mitsui Chemicals. Tests on many species of short-day flowing plants (really they are long-night flowering plants like cannabis) show that the only affect upon flowing vs. not using the plastic sheet is increased time to flower. An additional 1-2 days depending upon the species of plant tested [6].




A few refs:


[1] "Shedding New Light on Greenhouse Production"
http://www.gpnmag.com/Shedding-New-Light-on-Greenhouse-Production-article25


[2] "Non-Chemical Height Control"
http://www.greenhousegrower.com/magazine/?storyid=3893


[3] "Greenhouse Management / Engineering Controlling Plant Height without Chemicals"
http://www.umass.edu/umext/floriculture/fact_sheets/greenhouse_management/altpgr.html


[4] "An Eye On Phosoporus Nutrition"
http://www.greenhousegrower.com/magazine/?storyid=3753


[5] "Feature Article: A Different Look at Lighting: Effects of Prolonged Photoperiod, Spectral Quality, and Light Dosage"
http://www.advancedaquarist.com/2009/5/aafeature


[6] "Plant Growth Regulation by Photoselective Greenhouse Covers: Current Status and Future Prospects"
http://virtual.clemson.edu/groups/hort/sctop/photomor/specfltr.htm


"Spectral Transmittance of Selected Greenhouse Construction and Nursery Shading Material"
M.J. McMahon, J.W. Kelly and D.R. Decoteau
http://www.personal.psu.edu/drd10/Site/Publications_files/SpectralTransGreenhouseMat.pdf


Light meter (check out the Red:Far-Red meter; the PPFD meter is no good)
http://www.specmeters.com/pdf/Light_Brochure.pdf


"Phytochrome Lecture"
...This has good info about phytochrome but info about light color that drives photosynthesis is wrong; green light drives photosynthesis very well under high irradiance HID
http://faculty.caes.uga.edu/pthomas/hort4050.web/Hort4050/Phytochrome lecture.ppt


"The Future of Plant Growth Regulators"
http://www.oardc.ohio-state.edu/floriculture/images/future_of_PGR.pdf


"Update on chemical growth regulators & other production tips"
http://www.hort.uconn.edu/ipm/greenhs/htms/winter update series 2010growthregulators.pdf


"The effects of far red spectral filters and plant density on the growth and development of chrysanthemums"
A. M. Khattak, S. Pearson and C. B. Johnson
Scientia Horticulturae Volume 102, Issue 3, 19 November 2004, Pages 335-341[/quote]

Awesome post! Thank you for taking the time to articulate all of this and put up sources. The community needs more of you.

In regards to this I just have a question: Since lights are off during the 'night' hours and people often run cooling during their 'day' hours, I would assume that the DIF wouldn't be too far from zero ya? And are you saying that you could theoretically have higher temperatures (within reason) during the majority of the day as long as you had a few hours that were cool enough (again, within reason) too bring down this average?

spurr said:

1. (stretch) "DIF" is the difference between averaged day time temp (esp. in early morning hours) and average night time temp. If the DIF is positive then the plant will stretch more. The greater the positive DIF the greater the stretch. A zero DIF means less stretch and a negative DIF means much reduced stretch vs. a positive DIF. The reason DIF affects plant growth is DIF affects levels of GA3 in the plant early in the AM. Less GA3 means less stretch and negative DIF means less GA3.

The most efficient way to control DIF is to keep the first 3-4 hours of 'day' cooler than the rest of the day. This is called early morning "DROP" (aka "DUMP" and "DIP"). Ideally a DROP with a DIF of -5 to -10 (Fahrenheit), or at least zero, for pre-flowering would be employed. Long term negative DIF can hinder plants and biological process; the more negative the greater the effect. Long term zero DIF using DROP for the whole grow will make a very compact plant. I plan to carry out lots of analytical testing on this method with cannabis in the future.

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Hi spurr. A beginner on this stuff so bear with me. You seem to be confusing thigmotropism with what I have learned, lets clear this up and continue please.

Thigmotropism (good touch hehe) results in shorter plants. Shorter plants in limited light environments will increase harvest index. Mechanical stimulation activates a pathway with increased cytosolic Ca++ mediating specific genes which code proteins that affect cell wall properties resulting in physical changes (thigmamorphogenesis). Thigmotropism can be used to advantage to keep plant height down though I have not tested it's usefulness in stretch. Crowding = bad touch. It results in stretch due to phototropic response - shading, not thigmatropic. If the canopy is in the shade (Pfr high) the whole plant will stretch (pre flower example) but once the canopy emerges (Pr elevated) stretch slows and vegetative growth is more normal in ratio to stem growth. Use this to advantage to get fruit and nut trees tall and straight by planting them in shade where they can be in the emergent layer after obtaining height.

This temp differential you speak of - DROP - I think you might pull this off with fans and timers no? Depends on what temps I have to start with but I typically leave the extractor on for the first 6 hours of day and off for the 2nd 6 hours of day (just a circulating fan running inbetween). Halfway through the night the extractor comes back on pulling in cool air. My plants like it when I do this - I was trying to simulate a cool dawn. Did I fluke this drop without knowing why? Never checked temps in there for years since thermometer packed it in.

And - what is SAR?

Hey bro,

I don't' have time to respond right now, but I will soon. You could check out some of the refs. I posted for info on SAR inducer in the from of roughing up the plant.

for now:

SAR = Systemic Acquired Resistance

When a plant has its' SAR induced it grows more, and usually stretches more too, but it can be species dependent in terms of longer internodal lengths/stretching.

best, your friend, spurr

Very interesting. Keep the info and experiments coming.

Read a couple of the references now to get a feel for it.

Thigmotropism is seperated from shading. If anything, I think a crowding thigmotropic response will counteract the phototropic response albeit slightly. Have you checked what the guys are doing with leaf removal to increase yield? This removes some of the crowding effect (but don't do it with finicky plants it'll hermie them).

I drew up a root:shoot life cycle with lots of wee pictures of plants phyllosphere and rhizosphere sizes taking into account pot sizes and events like transplanting, switch to flower, pruning, leaf thinning (senescence too), and resultant change in root:shoot thus hormone ratios... to try and understand what they were doing. Wound up with all sorts of diagrams and arrows and shit - very scientific lol. It helped a bit.

As auxin is made in the primordia and young leaves, removal of the shade leaves will not alter the levels of production except in it's role in phototropic response to improved red light. Provided nutrient levels in the medium are balanced with a well balanced nute schedule (or in my case well fed and established microherd); leaf removal may result in a decrease in stretch and subsequent increase in production (via resources channeled to cell division not elongation).

I imagine a redistribution of water and ionic solutes as the large shade leaves are removed too.

Sorry if that's too off topic. Increasing harvest index is the vehicle we want to construct yes? - might take a few different tools to make it run fast.

Another aside I thought... you know me... Corn harvest index was increased by getting phenotypes with upright leaves. Denser plantings capturing equivalent light. Some weed strains leaves 'pray' like this. They will catch more light in dense conditions.

Its been awhile since we have talked Spurr, but its good to know you are thinking about the same things as I. Ive got a few links that Ive read over recently that will be of use to others reading this thread. Its nice to see you've taken the far-red blocking film idea and ran with it. I hope to give it a go myself soon. And as usual, I always learn something new when you post. And you have given me too many damned articles to read now..Arrrrg


Measuring Daily Light Integral in a Greenhouse

And here's one I think you'll enjoy although, Its a bit harder to digest for the common man haha, it discusses how DLI affects rooting and growth of cuttings of a couple of flowers.

Photosynthetic Daily Light Integral during Propagation Influences
Rooting and Growth of Cuttings and Subsequent Development of
New Guinea Impatiens and Petunia

And heres an article in Greenhouse Product News discussing PhotoSelective Greenhouse Films. It has plenty of useful info in there. Even discusses how a high perched water table will increase plant stretch. I know you'll love that part of the article.

@ Mr.F,

I don't know if you noticed it, but I responded to your pic message of mine. I will post here today to you, sorry for being slow. I agree with some points you brought up and I want to expand on the a bit. For now, LAI (Leaf Area Index) PPFD-I (PPFD-Intercept) and RUE (Radiation Use Efficiency) are important factors in looking at ideal canopy structure.

The leafs the that pray can be useful if they are a phenotypic expression, but if not they can be a sign of light saturation and photoinhibition, both of which are bad, here is something I wrote in the thread I posted below to Dave:

Watching plants is one way to tell when they are getting too much light at any one time, or over the whole day. If the leafs at the upper canopy angle upward, like they are praying, that usually means the plant is trying to reduce the surface area of the leafs. Plants do this as a means to reduce the photons striking the leafs, which in turn reduces the light-energy for the plant (photon absorption). Kind of like how human squint their eye in bright sun.

Plants also 'canoe' their leafs (curl inward) to reduce surface area to reduce the photons they absorb.

If plants are 'praying' at the top section of canopy, or if the leafs are canoeing, it's a good sign too much light is being provided. If both are happening at the same time then photoinhibition (reduced rate of photosynthesis, etc) is usually soon to follow...

When the plant angles leafs upward or canoes leafs it's the plants' attempt to protect itself from light saturation and photo damage

Click to expand...

@ Dave,

Yup nice to see ya! If you want to read up on my use take on, and use of DLI, and other topics of PPFD and DLI and light hour per day check out this thread: "Why go 24 hours lights on??" https://www.icmag.com/ic/showthread.php?t=194277

Here is my post trying to explain DLI to JapanFreaker and why 24/0 is not good for plants, with lots of links and info about DLI and adjusting DLI for natural diurnal PPFD bell-curve in nature. I have read those links you posted a while ago, the first one is included in my big post I made yesterday: https://www.icmag.com/ic/showpost.php?p=4002179&postcount=132

My calculations to find ideal DLI would be ~46-48 moles/m^2/day using a peak of ~1,500-1,700 PPFD around noon. To reach ~46 moles/m^2/day for 12 hour days (in flowering) we would need to provide 1,000-1,1000 PPFD. Esp. of interest is this link:

"Feature Article: A Different Look at Lighting: Effects of Prolonged Photoperiod, Spectral Quality, and Light Dosage"
http://www.advancedaquarist.com/2009/5/aafeature

AH! Finally with you on the phytochrome mediated crowding response - affects branching and elongation (giberrelin involved?). So many variables! I'm drawing out a big assed plant map with hormone origins, travel, destinations etc to try and understand the antagonism and synergy going on. Plant exam yesterday... damn some of those hormone questions... the professors would be hard pressed to answer them... another A though, I owned most of it. Then I got DRUNK and LAID.

That's the real student deal right there hehe.

I have some LAI PPFD-I and RUE reading to do then I'll be able to contribute better to this conversation.

I won't bother reading about 24/7 lighting a plant does most it's growing at night so the answer to that is a no brainer. I am certainly interested in your conclusions on optimal photoperiod.

hey spurr, glad you posted this - i was going to ask you if i could post your reply. too much great info not to share

also it means that i can tell you about the t5's that ive ordered. the red (narva) tubes peak at 610-620nm and the overall spectrum is 575-650 - with a small amount of far red ish 710. having them mounted on the walls of my cab just above the canopy should hopefully help the light penetrate...

a bit more orange than i would have liked but it looks like it will still extend the colour spectrum of the hps a bit more into the red and boost red : far red.

unfortunately they will be too late for my blueberry cut which is ludicrously stretchy and needed some severe wrestling to keep withing the bounds of my short-ass cab. its just topped out...

looking forward to seeing where this thread goes.

thanks again

VG

p.s. also while we are talking far red i heard somewhere that far-red increases resin production - any comments on that ??

statusquo said:

In regards to this I just have a question: Since lights are off during the 'night' hours and people often run cooling during their 'day' hours, I would assume that the DIF wouldn't be too far from zero ya?

Click to expand...

It's usually pretty far from zero, say a day temp (average) is 75'F and night temp (average) is 70'F, that is a DIF of +5 (Fahrenheit). And most people don't keep their temps that close, most people have DIF of +5 to +10.

And are you saying that you could theoretically have higher temperatures (within reason) during the majority of the day as long as you had a few hours that were cool enough (again, within reason) too bring down this average?

Click to expand...

Kind of. Using DIF we are most concerned with the early morning temp, not the day temp because it's the early morning temp that effects level of GA3 the most in relation to night temp. So, if a grower uses a DUMP temp of 70'F and a day temp of 75'F and a night temp of 70'F the DUMP DIF will be 0. It's the very early morning temp that matters the most in relation to night temp. If a grower can't lower early morning temp, then the day temp is what they should use to find DIF.

The main reason to use DUMP is to save on electricity and to allow ADT (Average Daily Temp) to stay above 70-70'F, which allows for fastest growth. If a grower can't adjust early more temp (by lowering it) then increasing night temp is the way to go.

MrFista said:

Thigmotropism (good touch hehe) results in shorter plants. Shorter plants in limited light environments will increase harvest index. Mechanical stimulation activates a pathway with increased cytosolic Ca++ mediating specific genes which code proteins that affect cell wall properties resulting in physical changes (thigmamorphogenesis). Thigmotropism can be used to advantage to keep plant height down though I have not tested it's usefulness in stretch.

Click to expand...

Thigmotropism is like phototropism in terms of plant growth direction, and in some cases shorter plants. However, touching (excessive) also can/does induce SAR, which can make plants stretch and grow more, it's a defense mechanism of plants. Mechanical touching of plants is one method to induce SAR, but it is also used for thigmotropism; the difference is the degree/extent of touching.

For example, if I shook a plant, or rubbed the leafs, or cut off a bunch of leafs, that could/does induce SAR.

Crowding = bad touch. It results in stretch due to phototropic response - shading, not thigmatropic.

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Crowding and plant stretch isn't about touching, it's about shading. It think in your latter posts in this thread you make the same point I am making. Crowing increases Red:Far-red ratio intracnoapy and that makes plant stretch more than intracanopy Red:Far-red ratio closer to 1:1.

If the canopy is in the shade (Pfr high) the whole plant will stretch (pre flower example) but once the canopy emerges (Pr elevated) stretch slows and vegetative growth is more normal in ratio to stem growth. Use this to advantage to get fruit and nut trees tall and straight by planting them in shade where they can be in the emergent layer after obtaining height.

Click to expand...

It's more about intracanopy than canopy (ex. top of canopy).

This temp differential you speak of - DROP - I think you might pull this off with fans and timers no?

Click to expand...

Sure, if you can keep early morning temp close to night temp.

...I was trying to simulate a cool dawn. Did I fluke this drop without knowing why? Never checked temps in there for years since thermometer packed it in.

Click to expand...

Sounds like you did! Cool dawn reduces level of GA3 in tissue and that reduces stretch; the closer to the night temp the less GA3, and if dawn temp is below night temp then GA3 is really reduced. But too much of a good thing can be bad, ex. if the DUMP (aka DROP) DIF is -15 (Fahrenheit) for an extended period of time the plant can suffer.

yrs, spurr

MrFista said:

Read a couple of the references now to get a feel for it.

Click to expand...

Coolio yo!

Thigmotropism is seperated from shading. If anything, I think a crowding thigmotropic response will counteract the phototropic response albeit slightly. Have you checked what the guys are doing with leaf removal to increase yield? This removes some of the crowding effect (but don't do it with finicky plants it'll hermie them).

Click to expand...

Why would thigmotropism counteract phototropism? Do you mean if a light is on the left and thigmotropism is done from the right?

I haven't looked into that thread yet, but I assume the increase in yield is coming from induction of SAR due to removal of leafs; and effects upon Red:Far-red ratio allowing to be closer to 1:1 (but that would more effect stretch than yield).

I think removing leafs isn't the best option, there are many other ways to induce SAR, ex. using methylated jasmoic acid, which also increases trich density and number (separately from inducing SAR).

Removing the solar panels for plants isn't the best option IMO...

I drew up a root:shoot life cycle with lots of wee pictures of plants phyllosphere and rhizosphere sizes taking into account pot sizes and events like transplanting, switch to flower, pruning, leaf thinning (senescence too), and resultant change in root:shoot thus hormone ratios... to try and understand what they were doing. Wound up with all sorts of diagrams and arrows and shit - very scientific lol. It helped a bit.

Click to expand...

Nice, I'd like to see that. Have you seen this paper:

The Effect Of Container Size
D. Scott NeSmith and John R. Duval
http://www.imok.ufl.edu/veghort/docs/cell_size_072602a.pdf

As auxin is made in the primordia and young leaves, removal of the shade leaves will not alter the levels of production except in it's role in phototropic response to improved red light. Provided nutrient levels in the medium are balanced with a well balanced nute schedule (or in my case well fed and established microherd); leaf removal may result in a decrease in stretch and subsequent increase in production (via resources channeled to cell division not elongation).

Click to expand...

True, and also due to SAR inducement via. removal of leafs which the plant consider an 'attack'.

I imagine a redistribution of water and ionic solutes as the large shade leaves are removed too.

Click to expand...

Yup. However, removing large leafs is not the best option IMO. To increase red light intracanopy using a light mover is a good method (ex. for "sunfleck"; which is a short term and not-a-short-term phenomenon). Big leafs not only are the solar panels for plants, but they also allow the plant to fix more Co2, and to carryout respiration at night, etc. The top leafs (ex. apical meristem) is where/how the plant sense temperature, fwiw.

Sorry if that's too off topic. Increasing harvest index is the vehicle we want to construct yes? - might take a few different tools to make it run fast.

Click to expand...

No worries . But yes, increasing harvest index is a good goal.

Another aside I thought... you know me... Corn harvest index was increased by getting phenotypes with upright leaves. Denser plantings capturing equivalent light. Some weed strains leaves 'pray' like this. They will catch more light in dense conditions.

Click to expand...

See what I wrote about photoinhibition and light saturation in terms of plants praying at top of canopy to reduce photon absorption. I agree that praying could be a good thing to look for if it's a phenotype expression, but not if it's a response to light saturation.

Dave Coulier said:

And heres an article in Greenhouse Product News discussing PhotoSelective Greenhouse Films. It has plenty of useful info in there. Even discusses how a high perched water table will increase plant stretch. I know you'll love that part of the article.

Click to expand...

Thanks for the link!

MrFista said:

AH! Finally with you on the phytochrome mediated crowding response - affects branching and elongation (giberrelin involved?).

Click to expand...

Yup, GA3 is a main factor. Same with DIF...

So many variables! I'm drawing out a big assed plant map with hormone origins, travel, destinations etc to try and understand the antagonism and synergy going on. Plant exam yesterday... damn some of those hormone questions... the professors would be hard pressed to answer them... another A though, I owned most of it. Then I got DRUNK and LAID.

Click to expand...

Nice, I would like to see that, and good job on the A and the ass!

I have some LAI PPFD-I and RUE reading to do then I'll be able to contribute better to this conversation.

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Here are some good papers about LAI, PPFD-I and RUE, taken from the many other papers at this good resource from the University of Guelph "Plant-BIO-3110 Crop Physiology" (link)

Interception of PPFD by a crop canopy

Leaf net photosynthesis

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

Canopy photosynthesis II (Whole Canopy CO2 Assimilation)

Canopy photosynthesis III (Canopy Photosynthesis Calculations)

I won't bother reading about 24/7 lighting a plant does most it's growing at night so the answer to that is a no brainer. I am certainly interested in your conclusions on optimal photoperiod.

Click to expand...

Don't try to tell some other growers that! I got majorly hated on for stating the same thing as reason to not use 24/7. Also, I read a great study showing plants grow the most during very early morning hours (using a neat tool the measured growth as millimeter per hour), and second most at night. That would make sense considering GA3 increases most in very early morning hours due to DIF.

VerdantGreen said:

hey spurr, glad you posted this - i was going to ask you if i could post your reply. too much great info not to share

Click to expand...

Cool

also it means that i can tell you about the t5's that ive ordered. the red (narva) tubes peak at 610-620nm and the overall spectrum is 575-650 - with a small amount of far red ish 710. having them mounted on the walls of my cab just above the canopy should hopefully help the light penetrate...a bit more orange than i would have liked but it looks like it will still extend the colour spectrum of the hps a bit more into the red and boost red : far red.

Click to expand...

Nice!

p.s. also while we are talking far red i heard somewhere that far-red increases resin production - any comments on that ??

Click to expand...

I haven't read anything about it, I will look into it. I think you got that info from someone who didn't do any testing, just looked at the buds, right? By "increaes reasin production" do you mean density of glandular trichcomes (# of trichs per X area?)?

hi spurr, yes it was a visual report of tric coverage, in a test between 2 led panels. one had had no far red (740nm) whilst the other had a 'standard' amount of far red as part of the 75% or so red in the spectrum. I was told that the panel with far red had more trics and it was 'easily noticeable to the naked eye'. not as scientific as you would like im sure
but it wasnt part of any sales pitch or anything like that - just a conversation between 2 LED enthusiasts.

VG

also where does blue light come into this? most people seem to think that it's more blue light that keeps plants compact. is this because MH lights actually have a better red;far red ratio?

thanks

VG

R:B an' far red free.

R:B an' far red free.

VerdantGreen said:

also where does blue light come into this? most people seem to think that it's more blue light that keeps plants compact. is this because MH lights actually have a better red;far red ratio?

thanks

VG

Click to expand...

Howzit VG.

Dunno 'bout the MH lights.

The only practical, first hand info I have, shows that changing the ratio between 460nm. and 660nm. has a profound effect upon the internode distance.
This experiment was done with just those two wavelengths.
No far red was added or blocked.
I just "dailed back" the deep red and stopped the stretch like throwing a switch.
The girl with the original ratio kept stretchin' for another 8 or 9 days.

Exact time is a difficult call, but the end result was not.
When I set the ratio back on the first light to finish flowering, the first gal was a foot shorter and stayed that way till the chop.

Not claiming this is science, mind you.
But I do call it a clue that is worth looking into.

Aloha, Y'all

Weezard

VerdantGreen said:

also where does blue light come into this? most people seem to think that it's more blue light that keeps plants compact. is this because MH lights actually have a better red;far red ratio?

thanks

VG

Click to expand...

Me and Spurr discussed this awhile back, so I have the answer you're looking for. Metal Halides emit less far-red light than a HPS bulb, so the red/far-red ratio will be more in tune to creating more compact plants.

Ive thought about using MH during the pre-flowering phase to help reduce stretch, but I would be sacrificing some of my DLI by doing so. There are many other ways to control stretch, so its probably not even worth it, but Id like to hear your thoughts on it Spurr.