okay all its a great read. long but explains why my 3 watt 3000k led grows my plants so nice.
Whats the best spectrum for cannabis plant growth and flower?
Most indoor gardeners are now aware of the importance of PAR with regards to good vegetative growth and flower, but I'll just run through the basics for people new to the topic.
PAR: = Photosynthetically active radiation and is a measurement of the spectral range of solar radiation. White light is composed of all the different colours combined, and PAR names where these colours are:
e.g. purple / blue starts at 400nm and it runs through green, yellow, orange up to deep red at 700nm.
The band that we are interested in runs from 400nm to 700nm (nanometres), although there are elements outside this range (see below)
We know that plants absorb energy through sunshine, and convert this through the process of photosynthesis into chemical energies that they use for cell growth. Scientific analysis of this process with reference to PAR shows that not all light is equally useful to the plant. The graph below shows higher rates of PAR at different nanometres:
As you can see chlorophyll absorption is twice as much at 460nm as it is at 660nm. The plant uses the blue light during vegetative growth and the red light during flower. It also
hardly absorbs any green light at all, but instead reflects it (which is why plants are green). But because it is twice as efficient at absorbing the blue light as the red, initial pioneers of LED grow lights used a straight 2 spectrum light (usually 460nm and 640nm) with a 2 red: 1 blue ratio.
(and this is the basic spectrum provided by wholesale manufacturers of LED grow lights)
The
two spectrum light works fine for simple crops (salads and herbs for example) but is not sufficient for complex, photophilous plants like marijuana. Second generation LED grow lights added LEDs pinpointed at all 4 spectrum peaks, 439nm, 469nm, 642nm and 667nm. Suddenly LED grow lights began to be taken seriously by indoor cannabis growers worldwide as the combination of minimum heat production and sufficient yields started to work in grow journals posted online.
But there is a type of indoor cannabis grower that is always striving for perfection and maximum yield. For this grower (and they are almost always male!), it is not enough to produce an adequate crop with minimum investment. For him the indoor grow room is a chance to create the absolute optimum conditions for major resin production. These guys follow the scientific journals avidly and have had major impact on the structure of spectrum analysis for LED grow lights and design.
Further analysis of plant PAR reveals peaks of absorption like this:
Chlorophyll A 430, 662
Chlorophyll B 453, 642
Chlorophyll C1 442, 630
Chlorophyll C2 444, 630
Chlorophyll D 401, 455, 696
Chlorophyll F 720
Beta Carotene 450,482
Phycoerthrin 495, 545, 566
Phycocyanin 620
Allophycocaynin 650
Fluorescein 494
Which follows that a LED grow light should contain LEDs at the following nm:
400, 430, 445, 450, 455, 500, 545, 565 (for growth)
620, 630, 640, 660, 700, 720.
And about a year ago many
full spectrum LED grow lights on the market began to appear following these principles. The problem with a full spectrum LED comes down to ratios. In order to configure the number of LEDs at so many distinctive points on the spectrum, the ratio of red elements to blues became reduced. In our opinion these full spectrum lights were great for producing healthy vegetative growth with minimum signs of stress to the cannabis plants, but during flowering bud production was slower.
So what spectrum does Fero recommend?
Last year Fero Canada went into partnership with Area 51 for the development of the AF-600. Atypical of the science guy who wants absolute excellence in his quest for the perfect LED grow light, Area 51 have been researching, testing and developing a
spectrum ratio for maximum cannabis potential that we think is unparalleled. (at least of the ratios we have tested so far!)
The 5:9:1 spectrum used for the original AF-600 followed research done by Kevin Cope for the University of Utah & the International Space Station, into the use of LEDs for growing crops in outer space. Obviously in such an environment, the research is looking at maximising yield of all types of fruits and vegetables with minimum resources.
1:The tough outer skin (the herd) which protects the soft tissue within, and minimizes water loss
2:In the cambium layer, cells divide and diversify to create vascular bundles of transporting tissues and increase stem girth.
3:Vascular bundles of cells carrying water and mineral salts (xylem) or manufactured food (the phloem) from the leaves to all parts of the plant.
4: The pith is a connecting matrix for other tissues.
One premise of the 5:9:1 spectrum is that
enhanced vegetative growth will ultimately lead to increased bud production. A larger dry plant mass that is the result of thicker stems and more foliage inevitably means amplified cellular activity in the cambium layer i.e. more vascular cells transporting water, nutrients and xylem upwards when the cannabis plant is in flower. Just as a city is only as efficient as the transport system enabling its workers to get to work, produce goods and distribute them so a plant is only as efficient as the cellular network distributing nutrients to where they can be used.
What the award winning research done for the ISS found was that whilst both blue and red spectrum light was necessary for photosynthesis, other colours were also important because they penetrated through the canopy (ie were not absorbed by the upper leaves) and were used by the plant lower down. This led to a series of experiments investigating the optimum means of providing plants with the necessary spectra for increased vegetative growth.
One conclusion was that the best way to cover all the varied points of blue nm necessary for this enhanced vegetative growth was to study the results of white light (which contains all the spectral range).
"
White LEDs exceed the efficiency of fluorescent lights but have a comparable broad spectrum. As such, they have the potential to replace fluorescent lighting for growth-chamber-based crop production both on Earth and in space"
Experiments were run testing 3 white LED types: cool, neutral and warm, and also more traditional red:blue and red:green:blue combinations:
The study found that:
1. Blue light had a significant effect on both plant growth (dry mass gain) and development (dry mass partitioning)
2. Increasing the absolute amount of blue light (μmol m-2 s-1) led to shorter stems (less stem elongation)
3. Increasing the relative amount (%) of blue light caused a decrease in specific leaf area (leaf area per unit leaf mass) ie leaves were thicker (with increased vascular layers).
4 As the relative amount of blue was increased, chlorophyll concentration per leaf area increased, but remained constant with regard to leaf mass.
ie. The leaves were thicker because they contained more chlorophyll (essential for plant development)
In summary - more blue light avoids stem stretching, whilst at the same time increasing the vascular capabilities of the plant.
BUT what the comparison of the 3 different whites with the RB & RGB showed, was that
"Overall, white LEDs provided a more uniform spectral distribution, reduced stem elongation and leaf area, and maintained or increased dry mass as compared to RB and RGB LEDs. [best of all spectra tested were] Cool white LEDs [which] are more electrically efficient .. and have sufficient blue light for normal plant growth and development at both high and low light intensities"
Put simply: The use of cool whites covers those nanometres NOT covered by the blue LEDs and helps
supercharge the plant's abilities to absorb chlorophyll and photosynthesise. Like supercropping, light emitted by cool whites increases the plants vascular highway.
This is an almost revolutionary development in the theory behind why LEDs can be used to grow better bud.
There is a technical issue with the cool white LEDs: the configuration of them puts more demands on a traditional LED grow light set up than the blues and reds we're becoming used to seeing. Area 51 are taking the grow light back to the drawing board and redesigning every element of its set up in order to use a large ratio of cool white:red (with no blue), and it will be exciting to see how this pans out. But such improvements come with a cost, and for the Bulldog range of LED grow lights, we are sticking with a 5:9:1 ratio that consists of
2 x 6500k (cool white) , 1 x 430nm, 2 x 455nm (blues) : 9 red: (1 x 630nm, 4 x 640nm, 3 x 660nm): 1 infrared (730nm).
Reds for flower
The Cope research admits that whilst cool white LEDs have sufficient blue light for normal plant growth and development at both high and low light intensities, compared to sunlight, they are deficient in red light and may therefore benefit from supplementation with red LEDs. Our red proportion of the spectrum ratio therefore includes elements focused on energysing chlorphyll A, B, C & D as well as Phycocyanin & Allophycocaynin. The "deep red" is particularly useful to heavy resin production.
Why the infrared?
The Emerson Effect was observed using wavelengths of 630, 660, and 730. This is a study that is cited in nearly all modern plant growth studies that relate to the use of specific wavelength of red light and the interaction with far red and infrared.
Emerson ran a series of experiments back in the 60s where he exposed plants to lights at different wavelengths. The conclusion known as the Emerson effect was that there are two different photosystems (PS1 & PS2) involved in photosynthesis, which combine to enhance efficiency:
With PS1 and PS2 in play,
The light excites the chlorophyll molecules at the reaction centre and causes an increase in energy. As the molecule becomes less excited, its energy is transported through a chain of electron carriers to the next photosystem which does much the same thing and produces energy-carrying organic molecules.
The best way to achieve the Emerson effect is by using an infrared (or nearfarred) wavelength of above 700nm in order to accelerate the interaction of molecular energy especially with the reds and deep reds: thus bumping up bud production.
Phew! And congratulations to anyone that's made it this far ..
To sum up:
The Fero spectrum which we use in the Bulldog is the result of close following of scientific research aimed at maximising yield whilst benefiting from LED grow light's other plus points (heat control, low energy consumption etc) . Its actually part of a quest to show that LEDs can grow weed better than HPS (although we're not there .. YET :cough
The 5:9:1 is a compromise of sorts in that it follows the research while maintaining a level of production costs within most LED grow light buyer's budgets. The reason why the AF-600 had to be pulled from production was that simply it cost too much to make to be affordable unless it was priced at the Stealthgrow level: and that's a price too high for many of us.
How does it translate in real life?
The difference is almost intangible and without doing a side by side with a controlled environment, independently tested, impossible to prove. But we have done cannabis grows using this spectrum next door to a traditional LED spectrum set up and the difference was marked.
Stems were thicker, leaves looked more vibrant, the plants were healthier, the bud production bigger. To really sum up: the plants were LUSH.
