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

Prawn Connery · Mar 21, 2022

calvin.m16 said:
The degradation is what makes me stick to 1000w DE HPS. I spend $400/yearly to replace all the bulbs and have like new results every year. LED in 3-5 years (once the warranty is up) I might have to buy another $700-1,000 fixture..

Financially doesn't make sense to me. Cool save $100-120/mo on power bill to spend thousands of dollars on lights which get equal or less results depending on light choice of course... Many considerations too because I'm pretty sure the spectrums are useless if your room is cold so unless the room is stuffed with lights I'm doubting the energy savings is going to come into play when your running heaters for proper VPD.

I'll keep LED in the VEG room for now.

Thought I'd posted this earlier, but here goes . . .

So can I ask, why use LED in the veg room?

LEDs have a life of 50,000 hours. HPS efficiency has pretty much hit a wall – it's old tech and is not going to improve that much over the next 4-5 years. Certainly not like LED has and will continue to do. Just look at the advances in LED tech over the past 4-5 years. Prices are also coming down, just like other semi-conductors.

Today's LEDs will still be more efficient than HPS in 4-5 years time. We still have first-gen LEDs running in growrooms that are almost four years old now.

So after 5 years you've spent $2000 on bulbs ($400yr x 5 years). That's $2000 to spend on new LEDs. Plus another $6000-$7200 on power bills ($100-$120 x 12 months x 5 years).

That's almost $10,000 to spend on new LEDs. And "financially it doesn't make sense" to you?

I agree that the advantages of LED are compounded in hot climates. I live in Australia, so it doesn't get that cold here – mostly we battle heat. But LEDs still produce heat and I often suggest to other growers to add a HPS or CMH bulb to a winter grow to increase transpiration. You don't need to add heaters – unless you want to add a gas burner to increase CO2 in the room.

crimsonecho · Mar 21, 2022

Rocket Soul said:
.

Indeed. Its even less for diy: 20-30$ boards, thats less than some bulbs and these will last a lot longer than a few runs. However i doubt 50000-60000 hours in a grow environment and with hard driven diodes. Migros tests showed a fair bit more light loss than datasheets.

These arguments have been had soooo many times and once the bullshit been weeded out will eventually boil down to 2 valid arguments:
- spending more power and some extra $$ on climate control. This is true but theres so many work arounds to grt it to work, recycle some air or a small agro heating mat, not really rocket science. Or even do led+hid: same foot print light so you can just drop in some cmh or so whenever it gets a bit colder.
- No, i just dont wanna change my lights because. Yes, this is also valid as its your own grow and you can do whatever. But then whats the point of arguing that led growers are wrong if its just because.

Led vrs hps arguing is a silly trap, its a bit like a sudoko or something, a thing that lets you lose your time for a bit and catch your attention but its not really worth it in my opinion, eventually growers convince themselves by seeing their buddies grow.

i agree with 50-60K lifespan may be a stretch with diodes driven hard but with proper cooling and low currents i think at least 5 years of continous flowering without noticable difference in light output is not out of the question with the same diodes and by that time i can easily buy a very nice fixture with the money i saved from electricity or get a big fixture off aliexpress or do huge diy fixture and run it at super low current for my 4x4 flower tent.

i just made the calculation by the way and that 400w i mentioned in my post saves me 1.300 dollars in 5 years of continous flowering.

either way i’m not really focused on the spectrum of hps vs leds and which one is “better”. they both grow excellent plants in the hands of good growers. yeah the original study shows increased terpene production under leds etc and i like leds especially indoors because its much safer and less of a fire hazard than hid lights i also get blackouts from time to time and heard thats not good with hid etc etc.

so leds are more expensive to buy but cheaper and safer to run with longer lifespan and increased terpene content.

its just not even a contest for me even if they wouldnt go 60000 but 30000. i can replace them every 5 years easy with the money i saved.

also i really do think all leds need active cooling doesnt matter if qb, cob, strips etc. the manufacturers are kinda cheaping out in that aspect of led fixtures imho. i know less moving parts makes them more reliable but my diy fixture is about 4 years old now and i havent had a single fan failure during this time and these are the cheapest pc fans i could find. they are so silent and effective i just cant fathom why big name brands dont invest in proper cooling r&d.

i get that people say most lights are not getting that hot but thats really not my experience with it. they get hot. may not get scalding hot but keeping the heatsink temps as cool as you can would really prolong the lifespan but i guess if people could run the same fixture for 13 years those companies would lose a lot of business lol

Norml56 · Mar 21, 2022

The original HLG QB288's came in 2700k. I still have 4 of them going strong. When I originally switched from HPS to LED I only ran the LED a few times before switching back thinking it was the light. It was the environment. I couldn't regulate anything in the current tent situation and everything suffered while using LED. Now that I have almost total control over the environment in a separate building the LEDs are knocking it out of the park.

Prawn Connery · Mar 21, 2022

Kassiopeija said:
Prawn, thanks for your reply. Your interpretation of the green-shifted shadelight is on-point, but let me tell you that this can even happen inside a single leaf.

Yeah their spectrum is available it's somewhat typical 660nm enhanced, and leaf temps was within +-1°C. All things considered, not really precise I'm afraid.
As to the missing data, one can only speculate.

What we know about spectrum quality & photosynthesis rates is sometimes paradoxical, and why? Because there's more than one way to skin a cat. If just a single 2.5mm square is placed in between 2 glasses & fluorescence is measured with pulsating lights or lasers, that may yield a different outcome as if the whole plant is out in a closed chamber with its oxygen production measured.
To make a long story short:
- Green is very strong at high irradiance, or grown-up plants that have much foilage.
- Red n blue is very favourable if the top leaves are still not light-saturated, because these colours are more readily absorbed. But this bonus becomes a drag later, because at high irradiance the tops will be light saturated anyway (regardless from light quality) but what won't be absorbed instantly (green & farred, and some degree yellow & UVA) could be absorbed deeper into the leaf or canopy with the next incidence. Whereas red n blue increasingly will be converted to heat - a process that is called 'non-photochemical quenching'. There are basically 3 ways what can happen with the harvested light-energy:
View attachment 5105298

Chlorophyll fluorescence:
View attachment 5105304
View attachment 5105305
View attachment 5105303
The chlorophyll fluorescence itself consumes a minor fraction of energy. There have been tests done with monochromatic light that have shown that 660nm causes VERY LITTLE fluorescence unlike orange, yellow or green. Blue is powerful enough already to cause a green fluorescene, and UV can cause a few more - but these are mediated from other chromophores.

The fluorescence is extremely important for a lights quality - esp. at high radiant flux - because it presents a method of how the core/antenna supercomplexes deal with excess energy while the trap is still at work (and cannot process additional light) - send out yet another (red-shifted) photon - which, in turn, could be used somewhere else. So this adds transmittance that even fully saturated leaves can support lower leaves, or lower regions in their own tissue.
As opposed to simply converting any excess energy into heat. Which will most likely happen with 660nm.
This is one of the reasons why some light-colors are better photosynthetically than others.

So no far red in the LED spectrum? I see you noted that in one of your comments above. It's something missing in a lot of LED fixtures that HPS has. Especially when you look at area under the curve.

I have started to read the actual test and initially I found it interesting that all the LED cultivars had on average 27% more THCA than HPS – something most LED growers have known all along (LED beast HPS for quality). The one sticking point I had with the test was that it stated:

In this study, all cannabis cultivars grown under LED lights yielded an increase in THCA% with an average increase of 5.39% (mean of 25.06% THCA under LED versus 19.67% under HPS) (Figure 4)

5.39 percentage points is not the same as an increase of 5.39%. It's actually a 27.4% increase. I do wonder when "scientists" don't know the differece between percent and percentage points . . .

I also went looking for the original study that I thought proved green light was more efficient at lower PPFD, but in fact found the opposite :oops:

What I did find was this: https://www.quantamagazine.org/why-are-plants-green-to-reduce-the-noise-in-photosynthesis-20200730/

It is a really interesting article and it's not that scientific that most laymen can't understand. It explains very well why 90% of green light is reflected by plants and also goes some way to explaining why red and blue (and more importantly, violet) are so efficient. Or at least why plants have evolved to particularly absorb certain spectra and not others.

calvin.m16 · Mar 21, 2022

Prawn Connery said:
Thought I'd posted this earlier, but here goes . . .

So can I ask, why use LED in the veg room?

LEDs have a life of 50,000 hours. HPS efficiency has pretty much hit a wall – it's old tech and is not going to improve that much over the next 4-5 years. Certainly not like LED has and will continue to do. Just look at the advances in LED tech over the past 4-5 years. Prices are also coming down, just like other semi-conductors.

Today's LEDs will still be more efficient than HPS in 4-5 years time. We still have first-gen LEDs running in growrooms that are almost four years old now.

So after 5 years you've spent $2000 on bulbs ($400yr x 5 years). That's $2000 to spend on new LEDs. Plus another $6000-$7200 on power bills ($100-$120 x 12 months x 5 years).

That's almost $10,000 to spend on new LEDs. And "financially it doesn't make sense" to you?

I agree that the advantages of LED are compounded in hot climates. I live in Australia, so it doesn't get that cold here – mostly we battle heat. But LEDs still produce heat and I often suggest to other growers to add a HPS or CMH bulb to a winter grow to increase transpiration. You don't need to add heaters – unless you want to add a gas burner to increase CO2 in the room.

I'm not sure how high your power bills are there I'm paying around $0.10/kwh winter $0.15/kwh summer. It gets below freezing here for months at a time. The reason I ran LED in my VEG room is because I did especially notice the price difference when running lights 18 hours vs 12 hours. Also, that room is smaller than the flowering room. VEG is ~26 sq/m or 175 sq/ft and my bloom room is ~500 sq/ft or 46 sq/m. Heat was a big reason I went with LED vs purchasing a mini split for that room. The Flower on the other hand already has a 3-ton Mini SPlit equipped that typically operates at 1 or 2 ton capacity barely costing anything keeping temps below 78 °F with 8 x 1000w DE HPS and a 4-burner LP co2 burner..

To offset the cost of the Double Ended HPS I plan to purchase grid-tie solar system. I can spend around $10,000 and not have to retune everything. I just like how HPS grows flowers. I haven't seen an LED in person that I like yet and I've been in many grows that use LED. I work part time pulling down plants for commercial grows. Maybe they aren't doing it right or I'm stubborn and admittedly bad at math and economics.

I love the constructive feedback and criticism.

Prawn Connery · Mar 21, 2022

calvin.m16 said:
I'm not sure how high your power bills are there I'm paying around $0.10/kwh winter $0.15/kwh summer. It gets below freezing here for months at a time. The reason I ran LED in my VEG room is because I did especially notice the price difference when running lights 18 hours vs 12 hours. Also, that room is smaller than the flowering room. VEG is ~26 sq/m or 175 sq/ft and my bloom room is ~500 sq/ft or 46 sq/m. Heat was a big reason I went with LED vs purchasing a mini split for that room. The Flower on the other hand already has a 3-ton Mini SPlit equipped that typically operates at 1 or 2 ton capacity barely costing anything keeping temps below 78 °F with 8 x 1000w DE HPS and a 4-burner LP co2 burner..

To offset the cost of the Double Ended HPS I plan to purchase grid-tie solar system. I can spend around $10,000 and not have to retune everything. I just like how HPS grows flowers. I haven't seen an LED in person that I like yet and I've been in many grows that use LED. I work part time pulling down plants for commercial grows. Maybe they aren't doing it right or I'm stubborn and admittedly bad at math and economics.

I love the constructive feedback and criticism.

Hey, each to his own. That's what living in a democracy is all about

It's just that if you're using a CO2 burner already maybe there is room for some LED in there after all?

Seriously, though, we have guys mixing LED with HIDs getting great results mostly due to the better spectrum. We used to sell a "High Red" LED panel that had a lot of red, deep red and far red specifically to complement typical CMH spectra. HPS can always do with some extra blue and added UV.

Here's a hybrid LED/CMH grow I helped set up. This one had great yields and excellent quality. Maybe food for thought?

Kassiopeija · Mar 21, 2022

Prawn Connery said:
So no far red in the LED spectrum? I see you noted that in one of your comments above. It's something missing in a lot of LED fixtures that HPS has. Especially when you look at area under the curve.

Actually the Physio-Indoor spec has photosynthetically available FR (700-780nm) in it.
The HPS huge IR spike's photons at 840nm will NOT be captured by chlorophylls

Prawn Connery said:
I have started to read the actual test and initially I found it interesting that all the LED cultivars had on average 27% more THCA than HPS – something most LED growers have known all along (LED beast HPS for quality). The one sticking point I had with the test was that it stated:

Yeah the missing blue in the HPS may be responsible for that mostly as the blue-light-receptors also absorb in the UVA range so it stands to reason much or higher blue causes a somewhat similar response.
Interestingly there have been studies done to supplement HPS with additional blue or green light and they did see an improvement in many ways.... gonna look & see if I can find study again - it's quite fitting to this threads thematic (photosynthesis rates)

Kassiopeija · Mar 21, 2022

Prawn Connery said:
What I did find was this: https://www.quantamagazine.org/why-are-plants-green-to-reduce-the-noise-in-photosynthesis-20200730/

It is a really interesting article and it's not that scientific that most laymen can't understand

New LED lights stretching

Typically a 1000w hps se has about 1700umol at source, 4000 is not right, maybe youre thinking of ppfd and not ppf? sorry typo 2000

www.rollitup.org

That "article" is more esoteric non-sense than anything I've ever read on the subject.
There simply is no such thing as "noise" in photosynthesis

Prawn Connery said:
It explains very well why 90% of green light is reflected by plants

Actually it's still absorbed in like ~~80% of all incidents, red & blue fare a bit better.
That chart you see in that article is grossly misleading... :/

this review explains it well:

Importance of the green color, absorption gradient, and spectral absorption of chloroplasts for the radiative energy balance of leaves - Journal of Plant Research

Terrestrial green plants absorb photosynthetically active radiation (PAR; 400–700 nm) but do not absorb photons evenly across the PAR waveband. The spectral absorbance of photosystems and chloroplasts is lowest for green light, which occurs within the highest irradiance waveband of direct solar...

link.springer.com

Kassiopeija · Mar 21, 2022

Kassiopeija said:
Interestingly there have been studies done to supplement HPS with additional blue or green light and they did see an improvement in many ways.... gonna look & see if I can find study again - it's quite fitting to this threads thematic (photosynthesis rates)

there it is:

(PDF) The impact of supplemental blue and green LED and HPS lamps lighting effects on the photosynthesis parameters of sweet pepper transplants

PDF | The objective of studies was to compare the photosynthesis parameters of sweet pepper transplants under the emission of short-wavelength... | Find, read and cite all the research you need on ResearchGate

www.researchgate.net

Conclusions.
Our investigation revealed that the effect of supplemental 530 nm LED illumination with high pressure sodium lamps increased photosynthetic pigments content, but slowed down photosynthetic rates (Pn), intercellular CO2 concentration (Ci), transpiration rate (Tn) and stomatal conductance (gs) in sweet pepper transplants in winter time. HPS lamps with supplemental cyan 505 nm and blue 470 nm light had great positive effect on the photosynthesis parameters of sweet pepper transplants.

Again, green light is ambivalent. But with greater light-saturation, more plant structure it may have shown better results.
They also didn't monitor harvest mass, which is very important....

Kassiopeija · Mar 21, 2022

Kassiopeija said:
there it is:

(PDF) The impact of supplemental blue and green LED and HPS lamps lighting effects on the photosynthesis parameters of sweet pepper transplants

PDF | The objective of studies was to compare the photosynthesis parameters of sweet pepper transplants under the emission of short-wavelength... | Find, read and cite all the research you need on ResearchGate

www.researchgate.net

View attachment 5105734

Again, green light is ambivalent. But with greater light-saturation, more plant structure it may have shown better results.
They also didn't monitor harvest mass, which is very important....

looking over that data I feel like the ranges of 470-505nm did best ... e.g. the highest photosynthsis-rates AND highest cellular CO2 .... but these wavelengths are omitted by many modern LED white chips.

It's called "the cyan gap":

Kassiopeija · Mar 21, 2022

It's like most popular white diode chips are based on a royal blue 450nm pump because the chief engineers think chlorophylls only absorbs blue and red. But that is only true if said chlorophyll is ripped out & torn apart by chemicals in an experiment.
But originally in a working leaf it's vastly different.

Spectra-of-chlorophyll-dissolved-in-diethyl-ether-The-absorption-and-the-emission-spectra~3.png

Forget this, it's a relict of the past, a cave-men approach at genuine science

edit:
I mean if that would be true then HPS would only be able to grow tiny tiny plants, because, as you can see, its emission is right into that middle gap

The-light-spectrum-of-high-pressure-sodium-HPS-and-plasma-lights_Q640 - 2022-03-22T015630.470.jpg

(the doted is plasma lamp)
600nm >> almost NO chlorophyll absorption [sic!]

Fardsnarp · Mar 21, 2022

Kassiopeija said:
It's like most popular white diode chips are based on a royal blue 450nm pump because the chief engineers think chlorophylls only absorbs blue and red. But that is only true if said chlorophyll is ripped out & torn apart by chemicals in an experiment.
But originally in a working leaf it's vastly different.
View attachment 5105757
Forget this, it's a relict of the past, a cave-men approach at genuine science

I think Dr. BB said the problem was that this was based on the best equipment available at the time.

GreenestBasterd · Mar 21, 2022

xtsho said:
I grow with an hps. It works great. I have no plans on changing unless someone wants to buy me a new LED light to replace what I'm currently using.

I still rock cooltubes haha and love them!

Kassiopeija · Mar 21, 2022

Fardsnarp said:
I think Dr. BB said the problem was that this was based on the best equipment available at the time.

But we know, or should know, much better for, at least, the last 30 years or longer.
even in science with its rigorous critical self-claim, an established opinion holds itself over generations. I'm reading discussions between scientists over at science.org where a lot of old farts still adhere to these famous myths like "plants can't absorb green light" even though specialists on the subject are there and present compelling evidence - it's not even looked at!

Bugbee today has the same problem - he's fighting for the inclusion of farred as being officially accepted as photosynthetic lights - but his proposals are rejected based on a faulty interpretation of the data!
Thus, grow light specs will continue to give false numbers out (PPF PPFD = show too small real values)... :/

The attached guide (in german, run it through a translator) is from the university, it explains how the very same chlorophyll-molecule changes its absorbance range - -very bluntly- mostly due to its spatial arrangement in leaf - and that exactly gets destroyed by organic solvents like diethylether or acetone!

Kassiopeija · Mar 21, 2022

This is what organic solvent does to a chlorophyll-molecule:

- It rips 'its tail" apart - that tail is used to create its spatial arrangement within the chloroplast.
- it is suspected it to damage the outer regions of "the disc" which changes the stationairy arrangement of the "free" Pi-electrons, and that is important with the next point (not illustrated here)
- it destroys all dimers or trimers, when 2-4 chlorophyls work together to enable a totally new exciton state. They do this, or can do this, when the discs align in a similar & near spatial arrangement (like 2-3 angström) then the outer electron orbital can connect. Actually this is how exzitons already zip down the antenna - from chlorophyl orbital to orbital but some of these are created by the combination of several molcules.

But in a glass solution you just have free roaming chl discs that can only absorb on a very narrow range

^^ looks different than a leaf

lusidghost · Mar 21, 2022

Prawn Connery said:
Today's LEDs will still be more efficient than HPS in 4-5 years time. We still have first-gen LEDs running in growrooms that are almost four years old now.

This Spectrum King sk600 was bought on 9/28/2016.

Kassiopeija · Mar 21, 2022

Kassiopeija said:
- it destroys all dimers or trimers,

like these here in PSI:

these are said to absorb farred (only the disc is shown for better view)

Fardsnarp · Mar 21, 2022

Part of the problem with science today is 'publish or perish'. There isn't much incentive to do the replication studies. Science is getting a black eye because of it in my opinion. The electro chemists claiming table top, cold fusion got YEARS of grant money for destroying a battery.

Fact checking the sea of studies being churned out just isn't happening. You really have to be discerning on what sources to trust.

Kassiopeija · Mar 22, 2022

Comprehensive Analysis of Photosynthetic Characteristics and Quality Improvement of Purple Cabbage under Different Combinations of Monochromatic Light

"Light is essential for plant growth. Light intensity, photoperiod, and light quality all affect plant morphology and physiology. Compared to light intensity, photoperiod, little is known about the effects of different monochromatic lights on crop species. To investigate how different lighting conditions influence crops with heterogeneous colors in leaves, we examined photosynthetic characteristics and quality (regarding edibility and nutrition) of purple cabbage under different combinations of lights. Eight different treatments were applied including monochromic red (R), monochromic blue (B), monochromic yellow (Y), monochromic green (G), and the combination of red and blue (3/1, RB), red/blue/yellow (3/1/1, RBY), red/blue/green (3/1/1,RBG), and white light as the control. Our results indicate that RBY (3/1/1) treatment promotes the PSII activity of purple cabbage, resulting in improved light energy utilization. By contrast, both G and Y lights alone have inhibitory effect on the PSII activity of purple cabbage. In addition, RBY (3/1/1) significantly boosts the anthocyanin and flavonoids content compared with other treatments. Although we detected highest soluble protein and vitamin C content under B treatment (increased by 30.0 and 14.3% compared with the control, respectively), RBY (3/1/1) appeared to be the second-best lighting condition (with soluble protein and vitamin C content increased by 8.6 and 4.1%, respectively compared with the control). Thus we prove that the addition of yellow light to the traditional combination of red/blue lighting conditions is beneficial to synthesizing photosynthetic pigments and enables superior outcome of purple cabbage growth. Our results indicate that the growth and nutritional quality of purple cabbage are greatly enhanced under RBY (3/1/1) light, and suggest that strategical management of lighting conditions holds promise in maximizing the economic efficiency of plant production and food quality of vegetables grown in controlled environments."

FIGURE 4. The effects of lighting conditions on photosynthetic PIABS of purple cabbage. White light (CK), Red light (R), Blue light (B), Yellow light (Y), Green light (G).

Frontiers | Comprehensive Analysis of Photosynthetic Characteristics and Quality Improvement of Purple Cabbage under Different Combinations of Monochromatic Light

<p>Light is essential for plant growth. Light intensity, photoperiod, and light quality all affect plant morphology and physiology. Compared to light intensi...

www.frontiersin.org

edit:
in "the forgotten photons" vid by Bugbee he refers to this study when he states that white light doesnt grow better than monochromatic light.

Kassiopeija · Mar 22, 2022

btw I want to add that the core-photosynthetic apparatus PSI & II IS IDENTICAL in all plants, and even in many algae & cyanobacteria, too. There have been phylo-genetical analysis that show a very distant common ancestor (chloroplast have its own genes like mitochondria) that today is explained by endo-symbiont-theory. Which is the reason why scientists studying photosynthesis oftentimes use bacteria or compare results cross-species wide.
The minor differences that exist are mostly due to leaf structure & other physiological or metabolic differences.
Though plant structure as a whole may have a huge influence on that, too (regarding various effects of some light recipes)

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

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