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Ideally what is the BEST* light spectrum for weed plants?

Discussion in 'Advanced Growing Techniques' started by Chapter 4, Sep 5, 2008.

  1. pretending one had unlimited technology for lights....what is the IDEAL wave length for weed plants to grow....both veg and flower.

    many sites i have read about photosynthesis and light absorption are referring to other plants (especially algae and marine plants).

    what is the *best* wavelength(s) for vegetative growth in *marijuana* and for flowering?

    i am well aware of the very very general rule of 6500K 2700K....but that is just whats readily available.

    anyone got any good info on this, or good resources on studies into light efficiency with cannabis?

    thanks for any input :):):):)
  2. I just met the manufacturer of this:
    LED grow light arrays.

    It's worth checking their site for some more in depth information.
  3. thats cool, but doesnt really say much about the wavelengths.

    i am looking for what exactly marijuana needs to absorb light. has there even been any studies with these species?

    i am wanting to make my own LED fixture, i am in contact with a very large LEW manufacturer and we want to make lights for agriculture, and be useful for weed.
  4. I really would like to know this answer also, me and my cousin argued about this the other day.
    I always thought that HPS had the best available light spectrum but I wanna know what the plant actually wants..
    is HPS the best available light?

  5. I like the new "Hortilux EYE" series, they are designed for optimal plant and flower growth, Balanced mixed spectrums with great efficiency.
  6. #6 rigormortis, Sep 6, 2008
    Last edited by a moderator: Sep 6, 2008
    THE Hortilux EYE HUH??!?!
    thats an HPS light? is there anything special about it? can I just go buy that bulb and put it in my current HPS fixture?
    maybe I should go get a couple
    what so special about it?
  7. 450 or so for vegitation and 650 for flowering..........somwhere close to those check out the LED UFO GROW LIGHT
  8. My bad :D I was super blitz when I typed that...It is actually "EYE hortilux " I could explain but instead heres the Link:


  9. thats good to know. i have read similar things in my research, but they were studying other plants. are these wavelengths specific for cannabis?

    for the others, we are looking for what exact wavelengths work good for cannabis (and other plants, but i am here about cannabis). We don't need to know what lights are good, cause we are designing our own. we need to know what exactly cannabis wants to grow best, as far as light. we have lots of research about other plant types and such, but i find marijuana info kind of lacking as to what the leaf wants to absorb light.

    anymore input is GREATLY appreciated, but i am nto looking for other lights that work good (although its good to knwo about them), i am looking more for the biology adn chemistry of the cannabis plant :)

    thanks a ton :)

  10. I'm researching the same thing. I watched a youtube video on 630nm red that beat 650 (660?) by a good margin . . . but it was for tomatoes.

    I'm also thinking that the info might simply not be available -- because cannabis leaves vary in color, which would affect which light spectrum works best for them.

    I hope some studies come to light (pun intended). For LED users light myself, I'd love to know which EXACT red and blue are most efficiently absorbed by cannabis.

    As far as I can tell, the BEST we can do now is combine 630nm and 660nm, since these seem to be the two most popular in the red spectrum.

    I'm trying to find a pure 630nm UFO, because I secretly suspect the 660nm might be the most popular for the wrong reasons (less costly, reliance on anecdotal evidence, looking at the light charts for other plants, etc.)

  11. Well light useage is like most have said in two main spectrums. The first is 420-460nm that's pretty blue and that's the most efficient absorption of energy for vegetative growth. Also worth noting that plants with less blue light than they need get leggy. This is because parts of the blue spectrum allow them to control their internodal length.

    The other part of the spectrum is the red side of things. The red is interesting because not just chlorophyll a and b get activated here this is also the realm of carotenoid(sp?) which are the yellow/auburn pigments. Now in the red range you'll get the most energy absorption somewhere between 640-650. Some why the 620 nm that make healthy plants? Well right around 620nm is a band of light which the plant use to change their metabolism from their night/growing/sleeping mode into an active photosynthetic mode. This takes around 2.5 hours for the plants to get enough of this light to actually start using the higher(640-650) red frequencies. So adding in these 620s won't actually give your plant anymore energy but it will more quickly catalyze your plants metabolism.

  12. Thanks for the input! I'm fairly sure that mj has a different ideal photsynthetic spectrum than other plants, plus I'm quite sure it would vary by strain -- given the wide variance in leaf color.

    With that said, I still can't find anything more than the standard Chlorophyll A and B absorption rate graph . . . which illustrate exactly what you said about which wavelengths to use.

    I'm hoping someone, sometime, does an accurate test of cannabis' specific preferred spectrum/s.

    Fingers crossed,

  13. Comparison of color temperature versus cholorphyll sensitivity graphs indicate that the general Earth plant prefers red light in a narrow band that corresponds closely with the color temperature of 2300K. 2100K bulbs will provide more energy to the plant then most 2700K HPS bulbs, both can be purchased, but if you could dial in the 2300K (the 650 to 660 nm range) that'd be best for inducing flowering hormones.

    The blue range of light offers a wider swath for energy to be absorbed. Basically everything from UV up to about 500 nm (5000K) will be effective. Offering a lot of energy in this range will generally provide the highest values of PAR.

    A combination of 7000K, 6500K, 6000K, 5500K, 5000K, 2700K, 2300K, and 2100K would be a very superior setup. LED offers the possibility for this configuration when you're talking the scale of hundreds of tiny little bulbs. The problem with LED is the casting distance, and you're not going to get the penetration power needed to grow big plants. This is an issue for the grower to come to terms with, but could be fine for the casual home gardener.

  14. I'm probably wrong, but I don't think the Kelvin ratings have much to do with the issue here. Kelvin ratings are an average of the light spectrum produced by a light, and it's not consistent at all from one bulb with the same K-rating as another. That's why you have color spectrum graphs for 1,000's of SPECIFIC lights published all over the web and with some of the lights themselves, when you buy them. Sure, if you wanted a bulb with more small-wavelength blues in it for vegging, you would certainly look toward the higher Kelvin bulbs (4,000k and up). But unless the manufacturer has provided the spectral graph, you have little idea whether the light hits the peak points that you want it to hit.

    Now, let's say you said, "Well, I found a 5,000k CFL that has a GREAT full-spectrum rating (CRI) of 95+ . . . well, that just means that the light being emitted is more broadly distributed across the visible light spectrum. So, it would probably be a poor source for growers, since it doesn't peak specifically in any wavelength, but uses a blend of all of them.

    Colored LED's emit light at a specific wavelength, so that's why you don't often see Kelvin ratings, you see nanometer ratings. And that's why this thread was started. It doesn't appear that much research has been done on which EXACT wavelengths are most absorbed by cannabis. You can consult the GENERIC photosynthetic response graphs, that show the peak areas of light absorption . . . but the graph isn't specific to cannabis.

    So the question still stands: when will we finally have studies specific to cannabis regarding which EXACT light wavelengths are best.

    I suspect eventually we'll find that it varies by strains, depending on factors such as leaf color. And we'll eventually find that certain spectrums (such as 280nm UV light) might have benefits that we are only guessing at now. For example, the 280nm range might spark a "tanning"-type stress response from the plants, causing more resin production for protection from that light.

    We're still in the infancy of testing specific wavelengths on cannabis. Hopefully things will move along quickly . . . and since LED are becoming more efficient (I think they double their efficiency every three years), it'll soon be a no-brainer.

    LED's can target exact light wavelengths. Once we find the optimal wavelengths specific to cannabis, we'll soon be able to get significantly more grams of product per watt of light.

  15. #15 2lsc, Oct 3, 2010
    Last edited by a moderator: Oct 3, 2010
    I used color temperatures because we're talking about indoor lighting. I am well aware of how they, CRI, PAR, and PPFD work and what they represent. I used corresponding nm levels with my color temperatures anyway, it's nothing to be picky about dude. Unfortunately I'm not a botanist with a few hundred thousand dollars laying around to carry out these tests for the good of the community. I think you're barking up the wrong tree.

    If you really want this done communicate it to U Miss or take it upon yourself. It's some serious shit figuring out specifically what wavelengths activate cannabis derived chlorophyll. Especially if you only come to find out that it fits the standard model.

    As this is your field perhaps you should take it upon yourself to learn about how Chlorophyll really works, rather than reading about LED's and charts online. I'm talking about actual school, you know, college. Where they can teach you the knowledge you're after; or at least how to discover it for yourself without using the internet or asking for the answer on a forum. I know that if I was going to buy a horticultural LED I'd want someone who actual understood it to design the system rather than someone who could pick up a catalog and a picture and say to a MFG "build me one of these, I'm going to sell it as the perfect cannabis lamp."

    I mean, if you're going to ask for answers that aren't available via a search engine then I hope you'd be willing to find them the real way. Personally, I don't like LED anyway. By the time they are reasonable to purchase Plasma Lighting is going to be available, and that's some real tech. I don't know anyone that swears by LED, and it has been around long enough to be dialed in right, so I don't know if the money into the research is every going to pan out for the LED horticultural business.

    Not enough people will purchase the perfect LED system over time compared to the cost of the research. In the future it's going to be plasma (mini-sun), so maybe think forwards about where the market is going to be in 5 (when you product will be shelf ready) and what technologies have the potential to revolutionize growing. Dedicate yourself to this and you might have a product no one else can match.

    $2000 builds a prototype that can make millions. With the money in this plant there has to be someone around willing to spend a bit to make a bit in this industry. With what they drop into nutrients it really is amazing how little science is behind the lighting. Hell, they'll sell you a street lamp and call it perfect for flowering.
  16. For anyone that is curious why this is: Chlorophyll does not absorb significant amounts of uv light(<400nm). This has to do with how blue light reacts with water. Namely that while blue light carries less energy than red light an individual photon can be split between multiple waters during photolysis. However UV light has so little energy that while it can go through even more waters it's gives even less energy to the plant. Hence the drop in photosynthetic efficieny below 400nm.

    One another note, if someone were to create or find some diagrams which specifically show each accessory pigment's absorption spectrum you could make a more educated guess about your plants depending on leaf color.

  17. I hope no one pays much attention to that post. It's full of misleading info. Saying plasma lights are the answer is silly: they reproduce the sun's photosynthetic curve and their peak wavelength is 520nm. Talk about wasted lumens: the last light I'd be using is one like a plasma light, with a CRI of near 100.

    What use is it to reproduce the sun, when the sun's light spectrum isn't ideal for plants?
  18. 2 x (2200k) for every 1 x (5500K) ... 600 watts are the best! Plain and simple...

  19. I wish we could chuck Kelvin ratings into the Home Decor basket. They don't tell us what growers want to know; they only tell us what home decorators want to know.

    I wish we could sticky one simple fact about lights: unless the spectral graph is given for a particular light, such as with most HID's but NOT with most fluorescents or CFL's, the Kelvin rating is practically useless for growers.

    If it says 5,500K on a light, all you know is the AVERAGE of the color spectrums it produces. In short, a 5,500K light is likely to have a lot of blue in it, but . . . that's not relevant to the thread's question. That answer (in Kelvins) is what we give to newbies who haven't researched lighting, and we don't feel like explaining to them the intricacies of photosynthesis. ;-)

    Since we're more experienced than newbies, we wouldn't take that advice ourselves! -- because we don't want to waste money on a light that we can only GUESS what exact wavelengths it hits heavily. We can let other people waste their money on lights that are like the grab bag you get at parties: maybe you'll get 5,500K that nicely hits the red and blue peaks that you want . . . and maybe you'll get a light that misses the peaks completely.

    Guessing is usually not the way to grow effectively, and choosing a light based on a Kelvin rating, which is just guessing, is not the way to grow effectively. Even if you have the spectral graph, as you would for most HID's, your still sending out quite a lot of light that's not efficiently used by the plants.

    Hence, the thread's question -- which is, to this point, unanswerable. We only have the generic photosynthetic graphs that show the "sweet spots" for generic plants . . . not for cannabis . . . and not for specific strains, which may vary quite a bit based on leaf-color and other factors. (You *can* sometimes find nanometer-specific photosynthesis graphs for plants that have been heavily researched; just an FYI).

    Anyway, I hope we can finally dispense with using Kelvin ratings inappropriately. They aren't the way to check a light's specific wavelengths.

    Sorry to be contradictory!!!! But, honestly Dr. Green, the answer to the thread's question is as far from "plain and simple" as it gets. Plus, an answer to the thread's question is *definitely* not going to be in a generic Kelvin rating.

  20. Wow... First of all you dont even explain anything and second of all the Kelvin's do make a difference. Third all photosynthesis is the same for plants!

    " Anyway, I hope we can finally dispense with using Kelvin ratings inappropriately. They aren't the way to check a light's specific wavelengths. " ....thats what KELVIN are for!!!!

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