TLDR: more light = bigger yield
Leaves are slightly translucent, the light will pass through the entire leaf and interact with all chloroplasts; the chloroplasts that allow for photosynthesis are held in the middle of the leaf between the upper and lower epidermis, the underside of leaves can photosynthesize. Just because they do it at a rate far lower because of nature than the top of the leaves is meaningless when it comes to the studies of under canopy lighting. So top lighting 1000 watt HPS = 100% of photosynthesis and the under canopy lighting with weak LEDS can add an additional 5 - 10% yield and growth why knock it? Why the beef? Not to mention as I posted the early 80s studies of blue light under the canopy and stomatal opening... So 85+ degrees + 1600 ppm Co2 + passive blue light under canopy can lead to explosive growth and has been shown in University studies. It's like you're either a bunch of old 1969 dead head Woodstock hippies that are set in your ways or a bunch of young guns that aren't capable of reading a .gov peer reviewed article from a University. I won't bring it up again, do your thing... Have a nice day..
The first part of this statement is true – light does pass through leaves, and there are chloroplasts throughout the leaf structure that can photosynthesise regardless of light direction . . . however, as the stomata are on the underside of the leaf, the top of the leaf allows more light to pass to activate more chloroplasts, so photosynthesis is asymetical.
The next part of the statement is not entirely true, as there is no such thing as "100% photosynthesis". In fact, studies have shown some plants photosynthesise only 4-5% of the light that hits them.
The main problem with the OP's initial post is that the
actual university study that Hawley-David produced explains exactly what is going on.
People shoud read more and argue less. Please read the bit in
bold:
Red-Blue and RGB SCL treatments significantly increased dry bud yield in the second crop cycle, while only RGB SCL significantly increased yield in the first crop cycle (Figure 4.3). This was expected due an overall greater amount of light being delivered to the plants in these treatments relative to the Control treatment (Peat, 1970; Stasiak et al., 1998; Ralph and Gademann, 2005). Further, the additional light energy was being delivered to leaves that would have otherwise been shaded by upper canopy leaves. Regardless, it is notable that Red-Blue and RGB SCL treatments increased yield by 19.8 and 24.5% respectively relative to the control in the second crop cycle, which is a disproportional yield enhancement with the RGB treatment given that the SCL only contributed an additional 19% greater PPFD measured at mid-canopy than the control treatment. By contrast, in the first crop cycle the RGB SCL treatment increased yield by only 18.9% relative to the Control treatment.
As for the increase in cannabinoids, yes blue light has been shown to increase cannabinoids as it is near the UV spectrum and carries more energy than green and red and has the potential to cause DNA damage when exposure is high. The plant produces more cannabinoids to protect itself from DNA damage.
