3 ms·

Close, it's 1/10th of the spectrum not 1/10th of the intensity. The 'fancy mirrors' required would simply be a prism. You'd separate out the red and blue light

Close, it's 1/10th of the spectrum not 1/10th of the intensity. The 'fancy mirrors' required would simply be a prism. You'd separate out the red and blue light and aim it at the plants, and send the green and infrared light to solar cells, to be used for running red and blue LEDs. (Or you could use flourescence if you had something that glowed red or blue when exposed to green or IR light). Check out this spectral plot for chlorophyll-a and -b: http://hyperphysics.phy-astr.gsu.edu/hbase/Biology/ligabs.html http://hyperphysics.phy-astr.gsu.edu/hbase/Biology/ligabs.ht... and compare it to this plot of the solar irradiance at Earth's surface: http://hyperphysics.phy-astr.gsu.edu/hbase/vision/solirrad.html http://hyperphysics.phy-astr.gsu.edu/hbase/vision/solirrad.h... There are peaks in the clorophyl absorption spectrum at 400-500 and 600-700 nm (blue to UV and red), but the sunlight provides energy in an atmosphere-attenuated blackbody curve everywhere from 300-1000nm. In theory, by providing illumination with just 10% the energy of the sunlight's full spectrum in a narrow band from 420-430nm where photosynthesis is most efficient, you could have plants receive the same amount of energy. Unfortunately, solar cells have the exact same problem: Just as the proteins in chlorophyll only use certain spectral energies, so too the semiconductors only make efficient use of certain energies. Multi-bandgap solar cells can help: https://en.wikipedia.org/wiki/Multi-junction_solar_cell#/media/File:StructureMJetspectre.png https://en.wikipedia.org/wiki/Multi-junction_solar_cell#/med... but in both chemical and electrical solar energy extraction, you're working with a particular photon energy and there's going to be waste.

Nition 6y ago
Do the plants actually need the full strength of that red and blue light for optimal growth though? I thought the comment above mine was implying that they don't. So my proposition was that if we started with, say, midday sun, maybe we could divide that up (in brightness, not just by spectrum) to cover a larger area (multiple floors in this case).
frankus 6y ago
Are there materials that fluoresce at a shorter wavelength than what they absorb? I was under the impression that it was a one-way thing (absorb short wavelength and emit longer wavelength).
- Armisael16 6y ago
  Yes. Some materials absorb multiple photons for each one they emit and thus have enough energy to emit at shorter wavelengths. Cesium vapor is one (though probably not a good choice for this application!).

Nition 6y ago

Do the plants actually need the full strength of that red and blue light for optimal growth though? I thought the comment above mine was implying that they don't. So my proposition was that if we started with, say, midday sun, maybe we could divide that up (in brightness, not just by spectrum) to cover a larger area (multiple floors in this case).

frankus 6y ago

Are there materials that fluoresce at a shorter wavelength than what they absorb? I was under the impression that it was a one-way thing (absorb short wavelength and emit longer wavelength).

Armisael16 6y ago
Yes. Some materials absorb multiple photons for each one they emit and thus have enough energy to emit at shorter wavelengths. Cesium vapor is one (though probably not a good choice for this application!).