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

In terms of yield, HPS still works. But in terms of quality, LED has it all over HPS. When other growers ask me about LED yields vs HPS I will usually tell them that – all else being equal – if you optimise your grow area and lighting, and are a skilled grower, then it is suprisingly difficult to outyield HPS in overall terms. What I do tell them is you can at least equal HPS yields (and often outyield it where conditions are not as favourable due to the extra heat generated) with 2/3 or less power while increasing the quality of your buds in terms of cannabinoids and terpenes.

I believe one of the reasons HPS still yields so well is precisely because it casues plants to stretch more, and so creates a larger area of bud sites that fill in. Lately we've been trying to do the same under LED. One thing I do know is that the best I ever yielded under HPS after growing with it for almost 20 years was around 1.4gpw, whereas I have regularly yielded over 2gpw under LED and most other growers I know have gone from similar yields, up to 1.2gpw under HPS to at least 1.8gpw under LED. That makes sense when you think about it: 1.2gpw to 1.8gpw is exactly 50% more, and LED is on average around 50% more efficient than HPS. The numbers don't lie.

Prawn Connery said:

If you put a HPS in a cool tube then yes you can duct away a fair amount of heat. But if you did the same to an LED, you could do the same.

Click to expand...

That was precisely what I said.

Alfadog#1 said:

Alot of led company's try focusing too much on replicating hps but in a led such as color or spectrum maybe to seem more appealing to old timers or persuade into thinking they are like hps but actually led. Leds can do a much better job at fine tuning spectrum with different diodes not just bright white and far red look into leds with photogenesis spectrum made tailored to grow plants not light up football stadium's

Click to expand...

What LED on the market right now is actually trying to replicate HPS?
It's all White + 660nm and if your real hip you get some 730nm and a UVA diode and then your "Beyond Par"

OneHitDone said:

What LED on the market right now is actually trying to replicate HPS?
It's all White + 660nm and if your real hip you get some 730nm and a UVA diode and then your "Beyond Par"

Click to expand...

I got an updayday with a flower mode advertised as ”HPS” spectrum. While i dont know if its hps spectrum, it is much more yellow than the veg setting.

Milky Weed said:

I got an updayday with a flower mode advertised as ”HPS” spectrum. While i dont know if its hps spectrum, it is much more yellow than the veg setting.
View attachment 5105007View attachment 5105008

Click to expand...

Yes, that light is the anomaly in the market. Unfortunately that is not the spectrum Updayday is putting in their bar lights going forward

OneHitDone said:

Yes, that light is the anomaly in the market. Unfortunately that is not the spectrum Updayday is putting in their bar lights going forward

Click to expand...

Damn thats a shame, glad i got one then. Seemed to really help in the first 4 weeks of flower.

OneHitDone said:

What LED on the market right now is actually trying to replicate HPS?
It's all White + 660nm and if your real hip you get some 730nm and a UVA diode and then your "Beyond Par"

Click to expand...

Ye read my post again cheak into photogenesis spectrum most company's are just bright white and red and far red but what about the other colors in the spectrum the biggest difference is hps do produce a fair amount of IR and leds don't so bring ambient room temp and canopy so the plants metabolic rate can continue and stomata can properly function leds are more superior and can use any issues such as heat issues hps poses and use it as an advantage in your room there is a cost to leds but what you might pay in conditioning your room the trade of all depends in every situation.......but who am I to say what people can afford

25 years and ticking Poot Lichtenergie of Holland.

OneHitDone said:

That was precisely what I said.

Click to expand...

Well, no. What you "precisely" said was . . .

OneHitDone said:

I call BS on this.
A 650W China led contributes more heat to the room than an air cooled 1000W HID if ducted correctly.
I saw this first hand swapping an air cooled thouie in place of a 460W indagro induction. Temp went way down with the higher wattage air cooled setup.
Plus, unless you are in denial you know that in general you could fry an egg on an led driver

Click to expand...

. . . which is not strictly true. If you shift the same amount of air out of the LED room as you do with the HPS cool tube, then the LED will not contribute more heat. The LED does not produce as much heat to begin with so if you have the same amount of airflow, then the LED room will be cooler. There's also a lot more irradiated heat coming off the HPS that increases leaf temperatures as the infrared interacts with the water molecules in the leaves. That's why there is more transpiration at the leaf surface under HPS than LED.

What you're basically saying is, HPS contributes less heat because you cooled it down more – not because it actually produces less heat. There's a difference.

Prawn Connery said:

Well, no. What you "precisely" said was . . .

. . . which is not strictly true. If you shift the same amount of air out of the LED room as you do with the HPS cool tube, then the LED will not contribute more heat. The LED does not produce as much heat to begin with so if you have the same amount of airflow, then the LED room will be cooler. There's also a lot more irradiated heat coming off the HPS that increases leaf temperatures as the infrared interacts with the water molecules in the leaves. That's why there is more transpiration at the leaf surface under HPS than LED.

What you're basically saying is, HPS contributes less heat because you cooled it down more – not because it actually produces less heat. There's a difference.

Click to expand...

Your beating a dead horse, I simply stated that the air cooled HPS contributes less space to the grow area than the non air cooled led given the hps was ducted properly

I don't disagree. I've done it with HPS myself. You don't even need cool tubes – you just need a lot of airflow directed at the bulbs. This is 1200W (2x 600W bulbs) BTW. The other bulb is hanging underneath the top one in the middle of the vertical canopy.


And as you can see, there was no burn.


My point is you "called BS" on something that was only half the story. I don't want other growers to get the impression that 1000W of HPS produces less heat than 650w of LED, because it doesn't.

Prawn Connery said:

I don't disagree. I've done it with HPS myself. You don't even need cool tubes – you just need a lot of airflow directed at the bulbs. This is 1200W (2x 600W bulbs) BTW. The other bulb is hanging underneath the top one in the middle of the vertical canopy.
View attachment 5105190

And as you can see, there was no burn.
View attachment 5105193

My point is you "called BS" on something that was only half the story. I don't want other growers to get the impression that 1000W of HPS produces less heat than 650w of LED, because it doesn't.

Click to expand...

Would you agree that @I amTHE...GanjaFarmer 's 650W led is contributing more heat to the grow space than a properly ducted air-cooled 1000W HPS?

No, I would not agree. @I amTHE...GanjaFarmer said he had air-cooled hoods on his HPS – he didn't say where those hoods were vented. It used to be common practice for many HPS growers to air-cool their bulbs to get them closer to the canopy but to vent those air-cooled hoods into the same grow area – where they contributed to heat.

If you are venting into the same space, you are adding more heat. Simple as that.

Now if you wish to interpret his post as saying those air-cooled hoods were vented outside, then the answer could well be the same: if you exchange the same amount of air inside a LED grow as you do a HPS grow, then there will be more heat build-up in the HPS grow for the same amount of light each fixture produces.

Let's say the air-cooled hoods exchange 400cfm. And let's say another 400cfm is exchanged inside the grow area (2x fans = one for the hood, one for the grow area). With the LED grow, all you need to do is exchage 800cfm and you have significantly lowered the temperature in your grow area.

Of course, you don't know exactly what his set-up is or was because you didn't ask: you simply assumed his air-cool hoods vented outside the grow area and that he didn't compensate for this by exchanging more air with the LEDs.

Total exchange is total exchange. It is the amount of air removed from the grow area. How you do that is moot.

And that is my point. You shouldn't criticise someone when you don't know all the facts. That's all I'm syaing.

Prawn Connery said:

View attachment 5104809

Hey mate, someone else pointed this out above, but that graph indicates to me that LED is closing the gap at higher PPFD. @Grow Lights Australia has already shared my views on this, and that is I also believed green was more efficient at lower PPFD than blue and red. It makes sense if you think about it:

* HPS has a very green spectrum which is more photosynthetically active, but mostly at lower levels which is why the LED is able to catch up at higher PPFD levels (it's a shame we don't know which Fluence spectrum was used).

* In a forest or jungle canopy environment, green light penetrates (along with far red) as it is reflected off leaves in the upper canopy into the lower canopy. However, that green light is also being photosynthesised as it is reflected off each leaf. By the time it reaches the lower canopy, there is a lot less green light than at the top (but even less blue and red), so it makes sense that plants have evolved to use green ight at lower PPFD levels than other colours.

I'm sure I have read this somewhere so I'll go off and see if I can find the study, instead of relying on memory.

The bit about cannabis being selectively bred under HPS for 40 years, that's true too. Plants that yielded better under HPS tended to be used for breeding.

I also wonder how much the extra radiated heat from the HPS also speeds up the photosynthetic process? Was there a measure of leaf temperature in that study?

Click to expand...

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:

What is chlorophyll fluorescence? Chlorophyll within a leaf exists as pigment–protein complexes in PSII, PSI, and within the light-harvesting complexes (LHCs) associated with each of these reaction centres. Light energy absorbed by chlorophyll molecules can (i) drive photosynthesis (photochemistry); (ii) be re-emitted as heat; or (iii) be re-emitted as light (fluorescence) (Fig. 1). These three processes do not exist in isolation but rather in competition with each other. Thus the yield of chlorophyll fluorescence emission gives us valuable information about the quantum efficiency of photochemistry and heat dissipation. This is important for plant photosynthesis and ultimately productivity because photochemistry is used to provide energy and reducing power for CO2 assimilation. At room temperature, we assume the variations in the fluorescence signal arise from PSII only and we ignore emission from PSI largely because the signal does not make a significant contribution below 700 nm (Butler, 1978; Pfündel, 1998; Baker, 200 As chlorophyll fluorescence is a measure of re-emitted light (in the red wavebands) from PSII,

Click to expand...

When light sufficient to drive photosynthesis is applied to a leaf after a period of darkness, there is a transient rise (usually for a few seconds) in the level of chlorophyll fluorescence that is usually the result of the reduction of electron carriers in the thylakoid membrane. The special chlorophyll in PSII, P680, ejects an electron derived from water splitting to the electron acceptor QA (a bound quinone) via the initial acceptor pheophytin. However, QA is not able to accept another electron from P680 until it has passed its electron to the next carrier, QB. In this state, the reaction centre is considered to be ‘closed’. Depending on the prevailing conditions such as light intensity or temperature (which affects the metabolic state), a greater or lesser proportion of reaction centres may be closed. Closure will inevitably cause a decline in quantum efficiency of PSII.

Click to expand...

Another factor is the opening of stomata, which increases the availability of CO2 for Rubisco. Stomata tend to open and close an order of magnitude more slowly than photosynthetic events (Lawson et al., 2012). All of these processes provide an increased availability of sinks for the electrons derived from the light-dependent processes in the thylakoid and contribute to the quenching by the process of photosynthesis itself, and this is termed photochemical quenching. Secondly, on illumination, there is a rapid increase in the rate constant for heat dissipation of chlorophyll excitation energy, measured using a parameter termed non-photochemical quenching (NPQ). This is a photoprotective process that removes excess excitation energy within chlorophyll-containing complexes and prevents the likelihood of formation of damaging free radicals. This type of quenching competes with both fluorescence and photochemical quenching, and acts as a ‘safe’ mechanism for dissipating substantial levels of chlorophyll excitation energy, depending on the prevailing conditions and species

Click to expand...

Chlorophyll fluorescence:



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.

Kassiopeija said:

you're right it does and so it did from MH CMH back then...
the diode degradation a huge problem actually shying manufacturers away, yes... though I suspect many LED system have to be replaced due to their innane weakness towards high humidity..
that said pulsed UV may be the thing...

and you could use one of those mexican sombrero hats

Click to expand...

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.

Is this the old timey thread? No more points and condensers for me.

Polly Wog said:

Is this the old timey thread? No more points and condensers for me.

Click to expand...

Old times is when I switched from magnetic to digital ballast

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.

Click to expand...

a typical 60000hrs lifespan for leds is 13 years of continous flowering which would cost about 80bucks a year for leds if its a 1000 bucks fixture and you can easily save 80 bucks via reduced electricity bills yearly. just saying.
even if you change it up every 5 years it comes out to 200 bucks per fixture with half to 3/4 the electric bill makes financial sense because its not very cheap per kwh here so running a 600w led instead of 1000w hps saves around 400w. 400x12=4.8 kwh daily.
in my location that translates into a brand new 450w fixture every 5 years if i buy it from a hydroshop if i diy i can even replace them every 2-3 years and with higher wattage. thats just with the money i save from electricity bills. so for some it really makes sense financially.

I noticed in the first post graphic that the HPS is '4' above the canopy'.

That's a lot of space.

.

crimsonecho said:

a typical 60000hrs lifespan for leds is 13 years of continous flowering which would cost about 80bucks a year for leds if its a 1000 bucks fixture and you can easily save 80 bucks via reduced electricity bills yearly. just saying.
even if you change it up every 5 years it comes out to 200 bucks per fixture with half to 3/4 the electric bill makes financial sense because its not very cheap per kwh here so running a 600w led instead of 1000w hps saves around 400w. 400x12=4.8 kwh daily.
in my location that translates into a brand new 450w fixture every 5 years if i buy it from a hydroshop if i diy i can even replace them every 2-3 years and with higher wattage. thats just with the money i save from electricity bills. so for some it really makes sense financially.

Click to expand...

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.