Kassiopeija
Well-Known Member
Hello GLA, well green is so ambivalent as there co-exist several reasons of why to use it, one where the lower flux is justified is better CRI for diagnostics.I was under impression that green light was more effective at lower PPFD not higher?
Green has a tendency to become better at higher umol
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but that is a general, non-specific argument here that may be dependant on canopy density, leaf-count, veg time...
The study explains some underlying mechanisms of how it works...
Source:Since red and blue light are absorbed more strongly by photosynthetic pigments than green light, they are predominantly absorbed by the top few cell layers, while green light can penetrate deeper into leaf tissues (Nishio, 2000; Vogelmann and Evans, 2002; Terashima et al., 2009; Brodersen and Vogelmann, 2010), thus giving it the potential to excite photosystems in deeper cell layers. Leaf photosynthesis may benefit from the more uniform light distribution throughout a leaf under green light. Absorption of photons by chloroplasts near the adaxial surface may induce heat dissipation of excess excitation energy in those chloroplasts, while chloroplasts deeper into the leaf receive little excitation energy (Sun et al., 1998; Nishio, 2000). Blue and red photons, therefore, may be used less efficiently and are more likely to be dissipated as heat than green photons.
The misconception that red and blue light are used more efficiently by plants than green light still occasionally appears (Singh et al., 2015), often citing McCree’s action spectrum or the poor absorption of green light by chlorophyll extracts. The limitations of McCree’s action spectrum were explained in his original paper: the quantum yield was measured under low photosynthetic photon flux density (PPFD), using narrow waveband light, and expressed on an incident light basis (McCree, 1971), but these limitations are sometimes ignored. The importance of green light for photosynthesis has been well established in more recent studies (Sun et al., 1998; Nishio, 2000; Terashima et al., 2009; Hogewoning et al., 2012; Smith et al., 2017).
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The interactive effect between light quality and intensity was illustrated in an elegant study that quantified the differential quantum yield, or the increase in leaf CO2 assimilation per unit of additional light (Terashima et al., 2009). The differential quantum yield was measured by adding red or green light to a background illumination of white light of different intensities. At low background white light levels, the differential quantum yield of red light was higher than that of green light, due to the low absorptance of green light. But as the background light level increased, the differential quantum yield of green light decreased more slowly than that of red light, and was eventually higher than that of red light (Terashima et al., 2009). The red light was absorbed efficiently by the chloroplasts in the upper part of leaves. With a high background level of white light, those chloroplasts already received a large amount of excitation energy from white light and up-regulated non-photochemical quenching (NPQ) to dissipate excess excitation energy as heat, causing the additional red light to be used inefficiently. Green light, on the other hand, was able to reach the chloroplasts deeper in the mesophyll and excited those chloroplasts that received relatively little excitation energy from white light. Therefore, with high background white light intensity, additional green light increased leaf photosynthesis more efficiently than red light (Terashima et al., 2009).
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Frontiers | Photosynthetic Physiology of Blue, Green, and Red Light: Light Intensity Effects and Underlying Mechanisms
Red and blue light are traditionally believed to have a higher quantum yield of CO2 assimilation (QY, moles of CO2 assimilated per mole of photons) than gree...
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It's coming from a lettuce-study (like the above diode spectra that Samsung developed for this) but the physical properties of how this color works doesn't change. And that can actually be quite helpful together with a far-red enriched spectrum.
The study states "SPYDR xPLUS"Do you know what spectrum the Fluence was?
I'm not vouching here for HPS either, thread's just about photosynthesis rates. "Just", because it only shows 1 side of the coin anyway... [already seen studies esp. on far-red enrichment that showed lower PS-rate but higher yield (!)].I know I'm expected to defend LED but I would think there would be more to it
Still, electron-transport-rate is an interesting field because a faster ETR may result in less heat-conversion (and ultimately less heat stress) at very high PPFD situations.
How the core & antennas work together as dimers or trimers when various colors mix in due to different time the exciton needs to zip to the trap is still under investigation.... and impossible to predict from a theory how it later will happen because a single color added or missing, a changed ratio, could distort these entanglements.
That's why I'm happy to see good reliable data on PS-rates of different spectrums, esp. when they are taken at various flux strengths. And I hope I can find more...