Free rate of photosynthesis Essays and Papers - …
The radiometric power of a photon matters not in photosynthesis - a blue photon (with high radiometric power) will drive photosynthesis just as well as a photon of lesser energy (say, a red photon.) So, it would seem that the issue is settled. It is not. The adage 'a photon is a photon' is true when discussing light production by various light sources, but it is not correct when considering how different light wavelengths (or bandwidths) promote photosynthesis.
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The action spectrum of photosynthesis is a graph showing the rate of photosynthesis for each wavelength of light. The rate of photosynthesis will not be the same for every wavelength of light. The rate of photosynthesis is the least with green-yellow light (525 nm-625 nm). Red-orange light (625nm-700nm) shows a good rate of photosynthesis however the best rate of photosynthesis is seen with violet-blue light (400nm-525nm).
This article will examine photosynthetic efficiencies of various LEDs. Specifically, six light sources were tested for photosynthetic responses by zooxanthellae found in the stony coral (most likely of Clade C15.) The light sources include a black light (mostly UV-A produced by a fluorescent lamp), and LEDs radiating energy at peaks of 400nm (UV-A/violet), a 418nm LED (producing mostly violet with a small amount of UV-A), a blue/white LED combination peaking at white light with a peak 443nm and 457nm, a 'white' LED with a blue peak at 443nm, and red LEDs producing maximal light at 631nm and 657nm. All tests were performed when light intensity was at sub-saturating levels. Evidence suggests absorption by carotenoids is responsible for lessened photosynthetic efficiencies at 450 nm and 470 nm.
Pigments for Photosynthesis - HyperPhysics Concepts
Xanthophylls (oxygenated carotenoids) are also found in zooxanthellae. Two xanthophylls (diadinoxanthin and diatoxanthin) play an important role in protecting symbiotic algae and coral hosts from excessive light energy. When light energy is sufficient enough to effect pH changes within the photosynthetic apparatus of zooxanthellae, diadinoxanthin is converted to diatoxanthin. This conversion shunts light energy away from photosynthesis. In darkness, the process reverses, and diatoxanthin becomes diadinoxanthin. Note that these xanthophylls both absorb some violet but most strongly blue wavelengths at ~450 - 490nm. See Figure 28.