Study finds HPS spectrum results in higher photosynthesis rate (per light quanta) than LED spectra

Kassiopeija

Kassiopeija

Well-Known Member
Grow Lights Australia said:
I was under impression that green light was more effective at lower PPFD not higher?
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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.
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...
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).

[...]

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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Source:
www.frontiersin.org

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...
www.frontiersin.org www.frontiersin.org

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.

Grow Lights Australia said:
Do you know what spectrum the Fluence was?
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The study states "SPYDR xPLUS"

Grow Lights Australia said:
I know I'm expected to defend LED but I would think there would be more to it
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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 (!)].

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...
 
Horselover fat

Horselover fat

Well-Known Member
Kassiopeija said:
well look at how heterogeneous the data gets in these regions...
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Yes, variance is higher and higher for the led, for some reason. But the avarages seem to get closer. Could it be that as light levels are near saturation the difference gets smaller? This is very interesting. Plain white grows very well, but if a few ir leds (or something) gives me more yield I'm all for it. Same with the uv. I don't see a reason to spend money atm, but probably will at some point if the benefits are proven.
 
grotbags

grotbags

Well-Known Member
i dont think this is that supprising, if all of the following four spectra could be generated at the same efficiency which would you choose for flowering cannabis?...

#1
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#2
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#3
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#4
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Kassiopeija

Kassiopeija

Well-Known Member
Horselover fat said:
But the avarages seem to get closer. Could it be that as light levels are near saturation the difference gets smaller?
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I'm afraid I can only speculate... why those variances do exist at all... locale uneven LED lightspread? did the variances maybe even got worse and they omitted the data??

I re-read that part
(model LI-6800, Li-Cor, Lincoln, NE, USA) with a 2 × 3 cm light source chamber (6400-02B LED, Li-Cor Inc.)
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(response curves for LED could not be measured above 1000 PPFD due to inability to fit the LiCor chamber between canopy and bulb).
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LED "bulb"???
Screenshot_20220318-095732~2.png
tbh they lost me how they couldn't get such a small device under the LED for a higher ppfd measurement...(?)
 
Kassiopeija

Kassiopeija

Well-Known Member
Horselover fat said:
Plain white grows very well, but if a few ir leds (or something) gives me more yield I'm all for it. Same with the uv. I don't see a reason to spend money atm, but probably will at some point if the benefits are proven
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I'm a firm believer in Far-Red enrichment. The evidence is overhelming, for several reasons. I've written much on the Emerson-Effect here, but maybe best you search independantly on studies examinating harvest mass in FR supplemented environments.
 
I amTHE...GanjaFarmer

I amTHE...GanjaFarmer

Member
Grew with HPS bulbs for many years. PAIN IN THE ASS! I remember constant heat problems. I mean I was using 1000watters with air cooled hoods and had to run a mini spit AC just to keep the flower rooms cool. Then regular bulb changes and loss of efficiency if not changed regularly.

No thank you.

I now run 650watt China made LEDS and WOW what a difference. No more heat issues resulting in no mini split and way less need for fans and air movement.

What a headache HPS was compared to the new Tech. AND, well the flowers are bigger, denser, terpier, and more potent.

I don't know anything about all the charts and stuff. Only 35 years of hands on experience with the plant and now both lights. LEDs are way better.

Those that refuse to upgrade are close minded or just cheap. (My electric bill went from $1500 a month to $800 a month with a greater yield.} Easy math man.

Some of you guys are so stuck in your ways you cant see the forest because of the trees...lol Reminds of the old guy who still has a land line cuz cell phones might cause cancer...lol
 
Rocket Soul

Rocket Soul

Well-Known Member
One caveat is that higher photosynthetic yields does not necessarily translate to higher bud yield. I think this is all IR and due to higher temps in the plant leading to higher metabolic rates. But a hot plant also produces buds which are less dense (as in weight per volume at dry, not as in big and hard nugs), the heat seems to make the plant take on more water in its tissue which means the actual dry weight bud yields can be bigger in weight with leds, but often look smaller in volume.
 
grotbags

grotbags

Well-Known Member
Rocket Soul said:
One caveat is that higher photosynthetic yields does not necessarily translate to higher bud yield. I think this is all IR and due to higher temps in the plant leading to higher metabolic rates. But a hot plant also produces buds which are less dense (as in weight per volume at dry, not as in big and hard nugs), the heat seems to make the plant take on more water in its tissue which means the actual dry weight bud yields can be bigger in weight with leds, but often look smaller in volume.
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could well be...
would be good to see the same experiment done a couple more times, one with an ir filter for the sodium, one with matched leaf temperature.
 
Kassiopeija

Kassiopeija

Well-Known Member
grotbags said:
one with an ir filter for the sodium
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But that is an integral part of HPS' spectrum... esp. important given the fact how phononic energy can be used for photosynthesis with photons >700nm

It's a good plus and better than convective heat
 
grotbags

grotbags

Well-Known Member
Kassiopeija said:
But that is an integral part of HPS' spectrum... esp. important given the fact how phononic energy can be used for photosynthesis with photons >700nm

It's a good plus and better than convective heat
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just so you could see the effects of ir leaf heating, it would rule out what rocketsoul was suggesting that the difference in the test results could be from a higher metabolic rate. then do the test again with no ir filter for the sodium but equalised leaf temps for the led plants to see if it equalizes.
 
Rocket Soul

Rocket Soul

Well-Known Member
70's natureboy said:
My results are exactly opposite. My LED crops are about half of my HPS yield. The LED's just make larf about 8" below the canopy. I still play with them but the real yield and quality comes from my HPS crop.
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This seems to depend very much on how one grows and with what led and wattage. The grow i usually consult for we had a 16" deep cannopy with big buds even on small so called sucker branches.
 
Drop That Sound

Drop That Sound

Well-Known Member
I can see the future of lighting.... :sleep:

It will have artificially intelligent projection mapping software.. that identifies only the moving plant\matter (with IR & motion detection), and rapidly scan over only the leaves that photosynthesize with a high powered full spectrum laser at a certain frequency.

It will just look like the plant is a hologram with a projector beaming down on it, glowing a vibrant neon color.

Not a single lumen will be wasted.






 
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blueberrymilkshake

blueberrymilkshake

Well-Known Member
Drop That Sound said:
I can see the future of lighting.... :sleep:

It will have artificially intelligent projection mapping software.. that identifies only the moving plant\matter (with IR & motion detection), and rapidly scan over only the leaves that photosynthesize with a high powered full spectrum laser at a certain frequency.

It will just look like the plant is a hologram with a projector beaming down on it, glowing a vibrant neon color.

Not a single lumen will be wasted.
Click to expand...
We're over here playing checkers and homie is chess boxing before breakfast
 
Drop That Sound

Drop That Sound

Well-Known Member
What if you projected bugs crawling on the surface of the medium, in each of the pots..

Or even an entire artificial environment on the floor.

Would it deter some pests like gnats?

I just scared one off the screen with my mouse courser...
 
Drop That Sound

Drop That Sound

Well-Known Member
It will even train the plants for you, by manipulating the dynamic leaf projection patterns you program in.

Starve the leaves of light in some places and make them move towards more concentrated areas.

Detect height, and know when to back off on some of the tops.

Only shoot light where it needs to be, all automated!...





Ok i'm out haha
 
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