Plant Sensitivity Curve

[NorCalFor20]

I saw this plant sensitvity curve, along with an HPS spectrum, i removed the hps spectrum comparison so you could see how the plants optimal light should look on a spectral chart. I will also post HPS and CMH charts, so you can compare. I couldn't find a chart for regular metal halide.

Even though it seems that the CMH does a better job covering the full spectrum than the HPS they both lack the far red spectrum. According to the plant sensitivity curve, plants are affected most by red light so why isn't there a pure red light available for flowering?

 

[FreezerBoy]

It didn't look so bad when the charts were separate. Then I noticed the top chart was a bit stretched out number wise. Overlaid so the numbers match, the gap really shows up.

 

[Daemon]

^^huh....

 

[mdl_aged_crzy]

Sometimes seeming simple questions have very complicated answers.

To sum it up, plant health - at any given stage - requries a balance of spectrum and intensity of light, even stuff you and I cannot see. Light does far more than just bulk photosynthesis. There are hundreds and hundreds of reactions taking place as a result of light hitting a plants leaf.
The plant sensitivity chart is just a reference of weighted averages, not a clear recipe that can be extrapolated into specific bad/good/better.

There is a good page at Sunmaster, click on "Light & Plants" link. There is a nice explanation and it is accurate.

Happy reading,

MAC

 

[Mr Celsius]

These are the peaks for different phytoreceptors. Each one is responsible different components of growth. If you are interested in what makes plants flower, you can check the phytochrome link in my sig.

The only way to possibly match the 'optimal' (this is subjective) spectrums to cannabis is using LED's. The unfortunate reality is that LED's do not have very much intensity and are costly. I'd imagine in 10 years all grow lights will be LED's, but until mass production plants exist, the infrastructure isn't there to support production

 

[yukino_asano]

excellent post, I also wish there was a cost effective way to do it.

 

[knna]

I saw this plant sensitvity curve, along with an HPS spectrum, i removed the hps spectrum comparison so you could see how the plants optimal light should look on a spectral chart. I will also post HPS and CMH charts, so you can compare. I couldn't find a chart for regular metal halide.

Even though it seems that the CMH does a better job covering the full spectrum than the HPS they both lack the far red spectrum. According to the plant sensitivity curve, plants are affected most by red light so why isn't there a pure red light available for flowering?

Thats the Inada's Curve, average of photosynthetic response from 27 herbs plants. Dont think on it as an "ideal" spectrum for flowering, as it dont show that, but the relative photosynthetic response at each nm. Inada's curve only report that, and nothing about the best or optimal shape of the light spectrum for plants grow.

It was obtained by giving same energy (optical watts) at each nm and recording the O2/CO2 evolution. The main problem using this curve is it dont record any sinergy between wavelenghts, as the Emerson effect. Preciselly, Inada's curve are unuseful determining the best working wavelenghts distributions. It only shows the photosynthetic capacity at each individual wavelenght, wich is pretty similar for all superior plants on Earth, while best spectral distribution vary largelly between different plant species.

But, yes, you are right about the lack of red of most lights. Max photosynthetic effect is around 670nm, as you can see in the graph, and best waveband avalaible is the red one, from 610 to 685nm. Most lights emits on the lower end of that range, because its easier tecnically and because it have very far higher photometric value (stronger effect over human eye). As for equal energy, you get twice the lumens using orange or orange red instead of red, and many people buy bulbs by lm, manufacturers choose to do it that way.

 

[Guest]

I need the data sets for these charts... or else they are pretty much useless

 

[knna]

I need the data sets for these charts... or else they are pretty much useless

What do you mean exactly? Do you refer to how many mols of O2/Co2 delivered/uptaked for each mol of photons? The curve shows it, although normalized and averaged for the 27 species.

Desviations for that curve are very small, specially above of 560nm. C4 plants tend to have the fall on far red at longer wavelenghts (700-710nm instead of 685nm). There are two types of plants, one having a peak on the blue, and other with a flat curve between 440 and 550nm. And thats all.

What set of data do you need and why?

 

[asomugha]

Mr Celsius, I see our research led us to same graph, although some precision is needed:
there are indeed 4 kinds of photosynthesis' pigments, but only 3 concern us in our case. The 4th one phycobilins (which are the red phycoerythrin and purple phycocyanin) are exclusively found in algae and cyanobacteries... no interest whatsoever in pot

source:
http://www.snv.jussieu.fr/vie/dossiers/metabo/photosynthese/014pigments.htm
(you'll need to decipher french, the graphs are useful)

That one (if I manage to insert it) is the one you need, my friend:

 

[smokinshogun]

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[smokinshogun]

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[magiccannabus]

Bear in mind that these spectral graphs are relative. The CMH puts out a wider spectrum, but that doesn't mean it emits more photons. HPS kills the CMH in the red department typically, but CMH is still way more of a full spectrum.

 

[smokinshogun]

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[SupraSPL]

and I think R/FR ratios are far more important

If one was to supplement an HPS lamp with 660nm LEDs, would this positively affect the R/FR ratio in terms of yield? If not, would it be worthwhile to supplement with 450nm blue instead?

 

[mrred]

If one was to supplement an HPS lamp with 660nm LEDs, would this positively affect the R/FR ratio in terms of yield? If not, would it be worthwhile to supplement with 450nm blue instead?

search for the led thread..lol

 

[changescome]

led's are not the only way, of t5 there is UVL RED SUN, WAVE POINT ULTRA GROWTH WAVE T8 ZOO MED FLORASUN. Supposedely incandescents are primarily red, i noticed a suggestion for phillips red party bulb. Laser pointers also go by nm wavelength. RED spectrum is essential for photosynthesis