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spectral absorption by plant chloroplasts
I think it is fairly important that when we discuss the light
absorption of plants for the purposes of photosynthesis we keep in
mind several points:
1) only light energy (photons) of specific frequencies are absorbed by
plant chloroplasts. I don't have information on how wide these
absorption bands are or how efficiently plants use them. Highly
evolved plants (macrophytes) are able to utilize dozens of spectral
bands. My understanding is that there are several pigments which
absorb and chemically assist in converting energy for the
photosynthesis process. I'm very curious to learn how this works.
Perhaps somebody could enlighten us further!?
2) the terms red, green and so forth are too imprecise to be of much
use in technical discussion. These refer to wide bands of frequencies
which correspond to human visual responses. These "colors" of light
are unique to the human perspective and we should try to avoid making
generalizations if we want to be precise.
3) sunlight is a composite of light radiation of a very wide spectral
range. Fluorescent and gas emission type lights emit light radiation
in just a few bands. Incandescent lights, while less efficient at
energy conversion, have a much wider spectrum. This wider spectrum can
be used more effectively by plants than narrow bands which do not
correspond to the absorption bands of plant pigments.
4) points 1 & 3 notwithstanding, plants are able to grow quite
satisfactorily using ordinary cool white fluorescents. There is
sufficient radiation in the important bands. I don't know if specific
types of fluorescent lights are more cost effective for growing plants
than others. We do need a balance of light in several spectra in order
for us humans to perceive the colors of the plants naturally or as we
would under sunlight.
This is a summary of points that have all been made but I'm hoping to
elicit some useful data.
Q: What are the spectral absorption bands for aquatic plants? Do these
bands vary between plant types? Have they been mapped precisely?
Q: How well do scientists understand the mechanics of light energy
conversion with respect to the helper pigments?
Q: How well do the so called "grow lights" match the spectral needs of
aquatic plants? If we value faster growth, are these bulbs a good
investment as opposed to simply more wattage? (hint: show the math)
Steve in Vancouver BC