Far-red light

Discussion in 'Advanced Marijuana Cultivation' started by smokinshogun, Apr 3, 2009.


    wilsoncr17 Well-Known Member

    Ok, so I actually did some spectrum research and a plants reaction to light. What I am about to talk about is from a Sept 2004 issue of Natural History Magazine. The tests were done using LED's to expose various plants to the far-red range of the spectrum.

    Far-Red is actually created naturally as a result of shading (when one plant blocks light from another). The far-red light causes the plant to stretch to try and receive more red to blue light and give itself optimum conditions. If you were to apply an increased amount of far-red your plants would respond as if they needed more light and would stretch to surpass an imaginary competitor. The tests also showed an increase in the number of shoots when exposed to far-red, however as the plant matured the extra shoots died off (this was a result of inadequate nutrient uptake as other plants in the same area competed. This may not be a problem in the controlled environment of a regulated grow-op).

    So what I gathered from this article was that far-red is only naturally occurring when the plant is competing for better light, it could minimize the space between nodes as it causes greater shoot development, but it could also cause stretching as the plant tries to reach for light. If the plant doesn't think it's getting adequate light it could have negative affects. It could however be like an unsatisfied fat kid just getting bigger and bigger and bigger, but I don't know.

    I say try it. If you have the means, and let us know. It appears to have some affect, but to what end, I don't know.

    smokinshogun Active Member

    far red does alot of things though besides stretching... like this

    Light Reflected from Red Mulch to Ripening Strawberries Affects Aroma, Sugar and Organic Acid Concentrations

    Strawberry (Fragaria ananassa) fruit size and flavor are important to both growers and consumers. Plastic mulches are frequently used in raised-bed culture to conserve water, control weeds with less herbicides, keep fruit clean and produce ripe berries earlier in the season. The most commonly used plastic mulch color is black. We hypothesized that changing mulch color to reflect more far-red (FR) and red light (R) and a higher FR/R photon ratio would keep those benefits and improve berry size and flavor by altering phytochrome-mediated regulation of pathways in ripening berries. Size and chemical composition of berries developed in sunlight over a specially formulated red plastic were compared with those that developed over standard black plastic mulch. Berries that ripened over red were about 20% larger, had higher sugar to organic acid ratios and emitted higher concentrations of favorable aroma compounds. We conclude that FR and the FR/R ratio in light reflected from the red mulch on the soil surface acted through the natural phytochrome system within the growing plants to modify gene expression enough to result in increased fruit size and improved concentrations of phytonutrient, flavor and aroma compounds.


    "Cotton leaves that developed over soil covers that reflected a FR/R ratio higher than that of incoming sunlight contained the highest levels of terpenes. It appears, therefore, that increasing the FR/R ratio reflected to developing cotton leaves can increase the amount of volatile terpenoids accumulated in leaves despite their having less weight per unit area"

    but also rooting is affected along with germination, flowering times, and even leaf color (development of certain pigments), among other things....could be useful to adjust R/FR during certain stages of growth

    techhead420 Well-Known Member

    As far as rooting, in a book I have, "Adventious Roots in Cuttings", there is a chapter that discusses the effects of red/far red on getting cuttings to root. The one important point shown is that not all plants benefited from far red light in rooting. I'm actually out of town right now but in a few days I'd be happy to copy a few pages and post them here (under Canadian "fair use" laws, moderators). The book is actually a colection of peer reviewed essays so the credibility is high.

    Far red light, can in some cases, causes inhibitation in seeds:


    If anyone is actually serious about using a pure far red light source, which you will not get with a black body radiation source without band pass filtering (which can be expensive not to mention you'll likely have to use active cooling with the filter), I'd be happy to show anyone how to make the proper constant current power supply needed for high power far red LEDs. It's just a few parts from Radio Shack (lm317 voltage regulator in constant current mode).

    If someone needs a far red light sensor, so they can rely on empricism instead of anecdotes, they can be found here:

    http://www.tecno-el.it/Red Far Red Sensor.pdf

    If one is going to put time and energy into a project, why not do it right?

    born2killspam Well-Known Member

    Apparently bulk 730nm LEDs are available.. I couldn't find a price, but it has to be better than a 2" square of bandpass filter that costs ~$500..:)

    smokinshogun Active Member

    Im just trying to lower the R/FR ratios to something closer to outdoors. I also want to replicate a drop in light levels and a slight increase in FR before and after the main lights go on...

    Fluoros have about a R/FR of about 6-7:1
    HPS is 2.5-3:1, while outdoors is 1.1:1 and it drops down to 0.7:1 during twilight...I'm using incandescents to add FR to the fluoros and to replicate twilight...

    Thanks for those links, eventually I'll fine tune the ratios and want a more effecient source of fr, but for now Im just seeing what responses occur with cannabis...I'd love to see those pages too

    I've found info that by using 33% of the fluoro wattage worth of incandescents you can drop the R/FR ratio to 1.9:1, which is close to outdoors but not exactly right...I'm using more like twice the fluoro wattage worth of incandescents, but since they are wired in series the spectrum is quite different....I'm guessing since they are wired in a pair together, the bulbs go from 3000k to 1500k...At least it looks like they do, since the filament changes from white to red :twisted:

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