Grow Lights Australia
Well-Known Member
Hey Kassiopeija, the green hump is a function of the white phosphor LEDs we use, mainly the Nichia CRI90 2700K which has a dip between 530nm and 560nm, as well as the Seoul Semiconductor CRI95 6500K, pictured below.
We mix this LED in for the near-UV and cyan boost, but it also has a little uptick around 500nm.
Right, easy question out of the way first
As you know I am not a botanist nor even a chemist, so this is just my understanding of the process that may or may not be entirely complete (or even correct). As always I'm happy for anyone to correct me.So my understanding is PSII chlorophyll is made up of 50% A and 50% B, whereas PSI is 100% A, meaning Chlorophyll A has a higher weighting than B across the leaf, which you can see in the McCree Curve.
Finding an accurate graph of photosynthetic absorption isn't as easy as it looks, as there appear to be variations of the same graph. I often wondered about this until I read something the other day which might explain it: chlorophyll absorption peaks change depending on which solution they are in. For scientific purposes you need to dissolve chlorphyll in a solution to measure its absorption, but if you dissolve it in a solvent such as alcohol or some type of ether, then the absorption peaks change slightly because the chlorphyll binds with the solvent (non-free chlorophyll) vs chlorophyll dissolved in an aqueous solution (water) which is free chlorophyll.
Non-free Chlorophyll A has an absorption peak at 430nm. Free Chlorophyll A has an absorption peak at 465nm. The secondary peaks for Chl-A are 660nm in solvent and 730nm in water – right in the Far Red region.
Plants don't grow in solvents, they grow in moist air and are mostly made up of water!
The citation I have for all this is here: http://science.trigunamedia.com/sacred-geometry-not-a-leeway-to-junk-science/
Interestingly if you subscribe to the above theory, then the Chl-A "secondary" peak at 730nm is actually higher than the "primary" peak at 465nm, which may go some way to explaining why Far Red is so important for photosynthesis (in addition to, or perhaps in main part due to the Emerson Effect – but I would need to read more into).
If we ignore the theory that the graphs are wrong and just look at a typical Chlorophyll absoprtion graph such as below, we can see that Chlorophyll A has a secondary absorption peak round 400-405nm that is at least as important as the red peak at 660nm (or 730nm, whichever peak you subscribe to). Although it does depend on the graph you use. Here are two that highlight what I am saying.
I guess it depends on which graph you use, but it appears that Chl-A does absorb significant amounts of 360-400, peaking at 405nm, and that being the most important pigment in PSI and PSII it does drive photosynthesis. It's also interesting to look at the caratenoid profile which also shows absorption throughout the same range and which we know also drives PSI and PSII.
Interestingly, Chl-B peaks right in the cyan region, but very few LEDs have a good amount of cyan.
There is also something else missing fropm this debate,and that is the effect that photomorphogenic response has on photosynthesis. Shade avoidance is a good example. As a plant goes into shade avoidance, leaves increase in overall surface area (but get thinner, as the amount of biomass remains similar) and these larger leaves are able to capture more light. This makes up for the lower amount of light in the shade canopy and enables the plant to grow taller faster to reach the light canopy.
Now if it were possible to kick a plant into shade avoidance in full sun would this also accelerate growth? Or would it simply stress the plant? And if it did stress the plant, would it be possible to get the best of both worlds: faster growth and higher cannabinoid content?
I don't know. I kind of just thought of that then!
