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Far-red light

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


    smokinshogun Active Member

    Has anyone thought about how the "glow" of hps bulbs upon shutdown affect the flowering of our plants?

    The arc tube burns around 700C which is about 1000K, and at those temperatures produce a radiation peak around 3,000nm. This is in the IR range, but there is also some visible light obviously, as it 'glows" for a while upon shutdown. This glow is mostly IR radiation, but theres is also some far-red and just a bit of red. This results in a high FR/R ratio initially and as the bulbs continues to cool the spectrum shifts even farther until no red or far-red is produced.

    The flowering of plants is affected by the LAST 'color' of light the it recieves. Red light interrupts the flowering of short-day plants, and far-red is believed to speed it up. You can flash red/far-red/red/far-red at a plant after hours of darkness, and as long as the last light the plant 'sees' is far-red it will still flower.

    The point is that the end-of-day light will be composed of a high FR/R ratio which increases the rate of flowering in SDP (weed).My advice would be to close your grow box before the HID turns off, so to prevent exposure to other light sources.

    This could also explain why CFLs aren't the greatest for flowering. They stop producing light right when they get shut off, and the R/FR ratios never change. So if Im right, you could theorotically achieve HPS buds with cfls by turning on a hps for only the last few minutes. Just turn off the cfls a little bit before and flip on the HPS until it heats up fully. Then turn it off and let them drift into darkness under the "glow".....

    Any responses appreciated....even if you have nothing more to add than an opinion

    iloveit Well-Known Member

    That last paragraph is that in theory or have you given it a try? If you are right we growers can save a lot of money on electricity bills. That was a great piece of info thank for sharing.

    smokinshogun Active Member

    Its all theory right now, and currently I'm doing a seed grow or I'd probably test it out. Most people dont have both lights, but I just so happen to. You might not even need a HPS though, just something that heats up and produces a deep-red light and slowly cools down....

    I just was trying to figure out why HPS outperforms CFLs even though they have similiar red/far-red ratios, when all of a sudden a little bulb went on in my head (or should I say off in my growbox). The spectrum of HPS isnt always consant and just so happens to change in the right way at the right time.

    So did I figure out the million dollar question of why cfls blow??:o:clap:

    heres some charts too, one shows the R/FR ratios during sunset and the other shows the spectrum given off by objects of certain temperatures

    Attached Files:


    justinbars Well-Known Member

    well it makes sense but there could always be some unknown variable you didn't think about. but if this is true this would be awsome

    lampshade Well-Known Member

    Yes its true that infrared spectrums increase the conversion of phytochrome to flowering type. BUT the amount of infrared from a bulb burning out is very weak and would only be intense for less than 30 secs to a min. You need at least an hour of far red to speed up flowering. Cfls are not as good b/c they dont penetrate very far. Even with the same lumens as a HID it just wont penetrate more than a foot very well. Also studies show plants grow better with one dominant light source. A cfl grow confuses a plant into not nowing which way to grow, so they get bushy and leafy. Lamp

    born2killspam Well-Known Member

    Its funny how theory can be really spot on, yet still doesn't probably explain observation.. I agree with Lampshade, once you kill power, you've got a relative infinitesimal amount of energy in there to release.. You're right about the spectrum being peaked in a nice place for the phytochrome transition, but it peaks knee high to a grasshopper, and dimishes quickly..
    You're trying to work with the actual blackbody nature of the quartz tube which is exactly what HID does not rely on, but that BB energy is always being pumped out when the light is powered up.. Its just dwarfed by the duscharge spectrum.. I know its about ratios, but its more about extended ratios..
    If you want to play around, I'd think about incandescents for a duration near lights out.. Their temperatures are right around 3000K, which correlates to a lambda_max of 966nm.. under that light, 730nm is more intense than 670nm since the peak is above both, outside the visible spectrum..

    smokinshogun Active Member

    I've been thinking of ways to achieve more Far-Red while still maintaining a high ratio of FR/R. I'm thinking I can use a couple CLEAR incandescents wired in series, and this will drop their voltage causing them to run cooler. Instead of 2700K, like most lights, Id achieve about 1000K. Though this will be with less total FR it will contain a greater ratio. It seems this should work...I've tested it and the bulbs go from being white to dark-red.:fire:

    What do you guys think?

    Ive attached another chart, and it appears to me when comparing 3000K to 1000K that the ratios of R/FR are very different.

    Attached Files:


    born2killspam Well-Known Member

    Consider the slope of the blackbody curve at 650-750nm for a given temperature.. If you drop the temperature to 1000k, you're shifting the peak way right to a point where the slope in increasing with lambda, meaning your ratio won't be as high.. Ideally you want a temperature that puts the 650-750nm range right smack-dab on the point of the curve where it changes from concave up to convex up.. Goes back to HS calculus max/min problems if you went through that.. From what I gather from graphs, without actually running the calculus, 2500-3000K is a pretty decent temperature to play with.. Peaks between those will be between 950-1200nm, and their slope maximums (ratio maximums) should lie in the redder part of the visible spectrum or better..

    smokinshogun Active Member

    Around 900K is when objects stop emitting visible light and this chart shows a big increase from 660nm to 730nm when around 1000K. At 3000K there is more Far-Red but the spectrum just does not drop fast enough. There is still a bunch of Red, which Id rather avoid... Also there is barely even a slope, and at 600nm your still close to the maximum. Ill try both ways though on some clones, and keep as many variables the same throughout...

    Its pretty widely accepted with orchid growers to use a combination of fluoro/incandescent when flowering. They think its about the Red (I'm thinking FR), but they seem satisfied with the results? So why does everyone just use CFLs? cause they run cool?

    Attached Files:

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    born2killspam Well-Known Member

    These graphs are arbitrary on the Y-axis (Intensity), so don't worry about the actual slope since its arbitrary as well.. Its the characteristic of the slope that isn't arbitrary.. If you notice the slope characteristic you'll notice that the higher the temperature, the more extreme the slope between 670-730nm.. Any attempt to eliminate red light via temperature dropping when your target area is on the upward slope will eliminate a larger portion of far-red given the same shift.. Only when lambda_max < 730nm will cooling the color have a positive effect on the ratio.. That occurs at an 'actual blackbody' temperature of 3973K.. Confusing because we use correlated color indexes with HID that mimick an actual blackbody of that temperature, as far as the human eye is concerned.. 12pm sun at the equator is ~5800K eqv.. An hour before sunset, that is ~3400K.
    lampshade likes this.

    lampshade Well-Known Member

    KillSpam you really know your shit mang. You guys know they make infrared bulbs right... They also have red in them so ive been trying to find a graph to show how much red vs ir, no luck so far.

    born2killspam Well-Known Member

    Physics background.. Optics was a funny class for me.. I knew too much going in about the aspects related to growing, and ended up getting a few odd looks when I forgot to keep my mouth shut..:(
    Things like solar averages, plant vs human absorbtion, street-light spectrums etc.. All the stuff that a keen PhD would recognize as a tad suspicious..:) Sitting in that class I felt like I was sitting in an interrogation room where they were just waiting for me to incriminate myself..:)
    He was one of those profs that taught with alot of discussion regarding everday things, so it was kind of tough not to blurt out answers so that he'd delve deeper, and even tougher to resist asking questions that should have been well out of the realm of the curriculum.. I purposely asked alot of questions about alot of obscure stuff to make it seem like I was just one of those broad interest absorbers of trivia (like I actually am).. Also made it a real point to always be bright-eyed and bushy tailed whenever I was around him after I stuck my foot in my mouth about the average differences of intensity given various weather conditions.. Played it off like I was interested in solar cells since I grew up in the bush without electricity, but I didn't like the look on his face when he was sizing up that excuse.. Even though he wouldn't hassle ppl for any stupidity they portrayed, I had too much on the line to get a reputation as the obvious pot grower..

    born2killspam Well-Known Member

    Shogun I missed that one comparison graph you posted.. Its a nice chart right in the maximum region, but gets pretty deviant from BB nature at shorter wavelengths..
    'If' you 'want' to check the numbers, you can work out the expected intensity value for any wavelength in terms of its fraction of the intensity at maximum with these equations where k is the Boltzman constant..
    And yes I realize that nobody needs to think about crap like this to grow bomb weed..:)

    Hmm apparently you need to click inside the image box to open it fully in a window to see the image.. Atleast it doesn't show in the applet window on my pc..

    Attached Files:


    techhead420 Well-Known Member

    Unless people are planning on heating up a chunk of iron or something then these black body radiation charts are of little practical help not to mention that black bodies are an incredible waste of energy for any sort of lighting purposes including far red light production. It's simply not how it's done in the engineering world with perhaps the exception of using black body sources for calibration purposes.

    What you want is an actual far red light source such as found here:


    wilsoncr17 Well-Known Member

    Im pretty sure HID's yield higher because the light is far more intense than CFL's. The plant isn't spectrum bias.

    born2killspam Well-Known Member

    Its both, but some cfls have a decent spectrum for plants..

    techhead420 Well-Known Member

    Plants ARE spectrum biased. The reason that one tends to get a lower yield in using metal halides over HPS in budding is because the blue light in the MH causes a reduction in the amount of auxins (a major plant growth hormone). Auxins are needed for the biosynthesis of ethylene, a female plant growth hormone.

    I'm not trying to be a jerk or be disrespectful but people really need to understand what they're talking about first before posting information that is bogus.


    smokinshogun Active Member

    Of course plants are effected by the spectrum, I can provide countless examples of plants responding positively to red/far red ratios even when the amount of light is lower than the controls... So obviously certain spectrum's cause different reactions in plants.....If thats not bias, I dont know what it is..

    But also you must not have read his whole arguement....He said HPS is SOO INTENSE, I mean all you got to do is look at the light and you can easily tell...There is way more lumens per watt with hps and.........ohh...can't forget about the penetration. All that yellow light, its transmitted through the leaves and then the floor appears to be really bright WITH OUR EYES. It must be cause its intense, I think??? ok enough with the sarcasm

    Its like people think our eyes are perfect and leaves are not very different....And Im NOT not trying to be a jerk, I only ask that you please research a topic before posting something like "its cause its far more intense"

    Back on topic though........There is also a belief that plants seem to respond to the dusk signal, which is a drop in light levels and a change in R/FR ratios.....And even 1 minute of high FR/R has known to cause effects so I personally think the glowing of the bulbs help with flowering...And of course I know blackbody sources are ineffecient but I am using a 400 watt HPS in 4 SQ FT and have temps of around 70-75..I could definetly deal with the extra heat...I was talking about using incandescents also, not heating up a chunk of iron....but the point of the graphs was that when I connect bulbs in series, until there is barely any visible light being emitted, this relates to the filaments temperature. I would rather have only FR, even if its extremely wasteful..I dont want to mess around with LEDs, atm...

    Thanks everyone, I've got a much more detailed topic going on IC if anyone is interested

    techhead420 Well-Known Member

    "I would rather have only FR, even if its extremely wasteful..I dont want to mess around with LEDs, atm..."

    Well, good luck with that. Heck, why use an incandescent? You can just as well use a space heater if you don't care if it's extremely wasteful and don't care about heat.

    Seriously, speaking as an engineer, you're going to make your life a lot easier just by using far red LEDs. That way you're not playing guessing games with the true spectrum, like you will be doing, and can actually use the scientific method. Further more, with far red LEDs you can look up the data sheet and know what the far red optical output is (most light meters intended for plants will not read far red light since most people are only interested in photosynthetic active radiation so why measure far red, most other light meters will give bogus readings for far red light unless it's calibrated for it) so you can get an idea of the photon flux density needed to initiate a far red reaction in the plants.

    You're obviously a scientifically inclined person and a fundamental part of science is not playing guessing games. With far red LEDs you have a known quanitity.

    Either way, I wish you luck in your experiments!

    racer3456 Well-Known Member

    I know some physics, but a lot of this is over my head. However, biology is my subject so I'll approach it from that angle. Plants require many different signaling hormones, one of the more important ones being auxin. So, the light spectrum as well as the light hours will affect these. That is why leaves in the fall turn color and fall off. The daylight hours signal a hormone to tell the tree to start going dormant. What does all this mean? I think that the spectrum only signals the plant to produce the hormone, thus facilitating ripening. Now, is ripening the same as growing and enlarging? No. I have seen plants that have small buds, but are still ripening. The light power, like most of use intuitively know, has much to do with it. So much in fact that the light is the main thing that affects the growth of plants. If you have a bunch of CFL's, it will not stack up to an HPS, watt for watt. Now, if you use your idea and turn the light on for the last few hours, it will not be the same as if it received the intense HPS light all day long. Another way to think about this is someone who uses a MH light. Even though the spectrum is vastly different from an HPS and it doesn't have that spectrum of glow when you turn it off, it still produces massive buds. Some people say they can tell the difference, I usually can't, unless someone tells me. Although, I do use a MH for veg, and HPS for flowering. It's all in the power though. Just my 0.02.

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