A recent study demonstrated that targeted LEDs could provide efficient lighting for plants grown in space:
Research led by Cary Mitchell, professor of horticulture, and then-master’s student Lucie Poulet found that leaf lettuce thrived under a 95-to-5 ratio of red and blue light-emitting diodes, or LEDs, placed close to the plant canopy. The targeted LED lighting used about 90 percent less electrical power per growing area than traditional lighting and an additional 50 percent less energy than full-coverage LED lighting.
The study suggests that this model could be a valuable component of controlled-environment agriculture and vertical farming systems in space and on Earth, Mitchell said.
I’m reminded of William Gibson‘s aphorism that “the street finds its own uses for things.” LED grow lights have been used here on Earth for not-so-noble purposes for some time, I’d assume.
Green plants reflect most of the sun’s power (in the yellow-green part of the spectrum) and absorb mostly the low energy red end with some high energy blue.
If plants absorbed mostly where the real sun power is, they would be purple. Perfect absorbers would be black. In fact, the first photosynthetic organisms were the purple bacteria. However, they are strict anaerobes, and when blue-green algae evolved (absorbing the left over red-blue regions) they poisoned the purple bacteria with oxygen, and took over.
Andrew Goldsworthy (1987), “Why Trees are Green,” New Scientist, vol. 116, no. 1590, pp. 48-52
Getting this kind of equipment delivered seems like a good way to end up on a law enforcement list. On the other hand the police used to raid homes that consumed suspicious amounts of electricity or showed strange heat signatures; this method wouldn’t be quite as obvious.
Someone is already marketing a stand-alone solution.
Bob:
Am I missing something, or shouldn’t plants have had plenty of time to re-evolve purple pigment?
Steve Johnson, I don’t know anything about the specific chemistry involved, but it might be that it’s simply not tractable for evolution (at least given other constraints, such as the particular elements that are reliably available, and the amino acids that are frozen into the genetic code) to do that in the presence of oxygen. (It’s not nearly practical for human chemists, either, but to the extent that we can conceive of doing it someday, the ability to use arbitrary organic molecules and to choose from something like twice as many potential metal atoms — obscure rare earths, e.g. — would be likely to be helpful.)
Compare nitrogen fixation. For hundreds of millions of years there has been a huge selective pressure for being able to do that in the presence of oxygen, and there’s nothing absolutely fundamental (e.g., violation of laws of thermodynamics) to prevent that happening, but given the constraints above, hundreds of millions of years of evolution have not been enough to get that job done [*], and nitrogen fixation is still done in anaerobic sub-environments like the nodules on the roots of legumes.
[*] But I don’t know what’s going on in the coral reefs mentioned in that article, or indeed in any marine microorganisms that fix nitrogen; possibly it involves some clever biochemistry that I am unfamiliar with, something that doesn’t require physical exclusion of oxygen from the cell, organelle, or whatever.
Why is the job not done? Grasses take advantage of legume nitrogen fixing (and plain old plant decay). They don’t have to deal with doing it themselves.
In a low nitrogen soil environment you get a big percentage of legumes. As the soil N goes up over time the grasses get stronger and become a higher percentage of the sward. In soils with good N there’s no competitive advantage to being able to fix nitrogen.