Plants use the FULL PAR spectrum for photosynthesis as well as other biological functions.
I do not disagree with this. I am not debating full spectrum vs. blue red narrowband.
All I have been saying is chlorophyll is more efficient (i.e. absorbs more photons) in the blue and red spectrum. The optimal wavelength being 680nm.
I seem to be having a hard time getting anyone to believe that the primary light‐harvesting pigment in cannabis is chlorophyll. Sure there are some relatively inefficient minor role carotenoid pigments, but even they pass their photon energy to chlorophyll in an accessory role in photosynthsis.
The response here has been I am stupid for saying chlorophyll is the only pigment worth mentioning for light harvesting.
I have never said cannabis does not need green or yellow photons. The bigger question is how many G and Y photons does cannabis need.
I do not believe photosynthesis is the only use of light, but for purposes of photosynthesis chlorophyll is the only pigment worth mentioning.
The main reason white LEDs are popular is they are very inexpensive compared to color LED. That and the lack of published research on photomorphegentics of cannabis.
More important than photosynthesis pigments is light signalling photoreceptor proteins, such as the most well know photoreceptor protein, phytochrome.
I suspect the comments regarding "other" is a confusion on the difference between photosynthesis pigments and photoreceptor proteins.
I am not interested in signaling such as elongation or phytochrome flower initiation. That's very old news.
Far red gets a lot of attention but I believe also yellow and green photoreceptor proteins may be able to mediate THC levels as well.
There is a lot of recent research identifying the terpenoid and cannabinoid compounds like this one which I have attached:
Identification of Terpenoid Chemotypes Among High (-)-trans-delta 9-Tetrahydrocannabinol-Producing Cannabis sativaL. Cultivars
Other research on plants other than cannabis have found Yellow (Y), Green (G), and Far Red (Fr) when combined with photosynthetic spectrum of Blue (B) and Deep Red (R) can modulate the levels of terpenes/terpenoids, sesquiterpenoids, phenylpropanoids,and monoterpenoid volatiles. It was also found that BRY BRFr LED treatments produce these volatiles where the sun does not. It was also found BRG does too, but not as pronounced as the aforementioned.
I do not think there is much to be gained arguing photosynthesis using the 1960's McCree study. While it was a very relevant study that still stands on it's merits today, it used very crude techniques with substantial error rates when compared to today's capabilities. For purposes of photosynthesis and primary metabolite production blue and red are the only significant wavelengths. Green and yellow may be significant in the production of secondary metabolites but not significant for primary metabolites. This is my personal opinion and everyone else can consider it or not.
My next grow will use 3000K strips becasue they are inexpensive and have a good yellow band. While I do have many PC boards with 6 adjustable channels of spectra but they are not affordable to the hobby grower. I am struggling with whether to supplement with deep red.
