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this post was submitted on 18 Apr 2024
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Today I Learned (TIL)
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Any plant can grow with "artificial" light. It's just a matter of generating the correct light spectrum for a plant. There's nothing special about the light coming from the sun.
Well, there is one thing special about the light from the Sun... there's a shit ton of it.
Also, it's free.
Well sunlight is full spectrum colour plus ultraviolet and infrared. I'm sure there are benefits to the plant we can't easily measure, since they evolved with full specteum. We found a LED grow bulb with a yellow LED besides RED and BLUE, the plants grow like crazy
That's going to be less efficient per watt though, plant's are green because they don't use the green light, hence red+blue grow lights.
Not all plants reflect the same range of wavelengths though, and different plants will use different wavelengths to grow. This is basically an exercise in finding which wavelengths we can drop without significantly slowing growth for each plant.
This articles says plants only absorb 90% of green photons even though green has moat energy, as a way to mitigate over and under lighting in the chemical process. https://www.quantamagazine.org/why-are-plants-green-to-reduce-the-noise-in-photosynthesis-20200730/
That article just throws out a number. I found a couple papers that give green light absorption numbers between 50% (for lettuce) and 90% (for broadleaf evergreens). Sadly they are paywalled.
The paper that article links talks about pairs of absorption peaks targeting steep portions of the available light spectrum, as a method of reducing power noise in changing conditions. The reason for avoiding green light here would be because the spectrum is too flat around green: there are no pits to help stabilize incoming power. Despite blue light having nearly identical intensity, green plants strongly absorb blue light, supposedly because there's a steep drop off in intensity moving into purple and ultraviolet light. I don't think this explains the decently strong red light absorption though, as the terrestrial spectrum is still rather flat there.
I'd argue this is more a holdover from competition with simpler purple Haloarchaea in ancient oceans, the Purple Earth Hypothesis . Perhaps this avoidance of the otherwise strong green light is what allowed green plants to develop complex structures and those complex structures need much smoother power input, precluding the development of green light photosynthesis. Also possible is that developing new photosynthetic pathways is just too difficult, and green plants are too specialized to try.
Some of those specializations may be the use of green light to direct non-photisynthetic processes, detailed in this paper, which is also more directly relevant to the original point. Some green light increases yields significantly, despite maybe not promoting photosynthesis as efficiently per watt as red & blue light.
Yes, seems highly complex and we may not fully understand it all yet.