I’m getting ready to start switching over from gavita de to led lights.
Is there a ppfd reading that is max and min for canopy to perform? 1000ppfd? 2000ppfd?
I bought a meter apogee mq500 so I can measure light .
I grow the plants 5 or 6ftish so trying to gather any info or advise I can on led and performance.
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Your environment needs to support your ppfd. Light is the source of energy/metabolism. You need to support the higher quality and density light/energy.
At 2000 ppfd I would be looking to have my feed right around 2.8ec, 1800-2000ppm co2, temps in the mid 80s to low 90’s and humidity around 70%
1500 ppfd is a good target. It will require you to get your fixtures very close.
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Fwiw, purple strains seem to be the first to show bleaching from being too close to the light.
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Excellent that is a good starting point
So is like 1000ppfd the low range?
And is that 1500 in middle of fixture or outer edges as well?
Here’s a chart. Anything over 1,100 umol/s and you really need co2 to get the advantage of more light. You’ll need more feed as well. And make sure everything in your grow is perfect. Extra light and co2 will show you any mistakes very quickly.
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There aren’t specific PPFD targets for LED vs. HID. PPFD targets are irrespective of luminaire type. The reason higher PPFD (>1,250-1,500) is more typically used with LEDs is providing that level of PPFD at high uniformity (>90%) is more costly with HPS. Due to tricker installation (HVAC supply/returns and other ceiling-mounted equipment), and CapEx and OpEx are higher due to lower photosynthetic μmol/joule (PPE) and increased relamping.
But, the main issues with running high PPFD are photobleaching (chlorophyll deactivation), diminishing returns of biomass, and the potency dilution effect (trichome density):
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Dr. Bugbee’s reserach, and reserach by Fluence’s Dr. Hawley is on-going, but so far ≥700 μmol/s/m2 of red photons (600-700 nm) seems to be the photobleaching threshold. Meaning, greater than 700 μmol/s/m2 of red photons typically leads to photobleaching. However, as noted above, some genotypes are more likely to suffer photobleaching than others. Likley due to the concentration of protective secondary metabolites and the leaves’ upper epidermis thickness. Because a thinner upper epidermis is more likely prone to photobleaching at lower μmol/s/m2 red. And some genotypes seem pretty resilient to photobleaching even above 700 μmol/s/m2 red.
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Potency dilution occurs at PPFD greater than 1,250-1,500 (genotype and growing method dependent). It’s caused by a non-linear increase of biomass and trichome density as PPFD increases. Meaning the increase in biomass yield outpaces an increase in trichome density. Cannabis can produce only so many trichomes per mm2 (“trichome density”), just like it can biosynthesize only so much % THC. So, while the flowers are larger and the yield is greater at high PPFD, there is an inflection point where the % THC begins to drop relative to lower PPFD. You get a greater yield but lower % TAC. There are ways to increase the limit a bit, but most growers are unaware of and unable to use those methods.
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As PPFD increases, there is a continual increase in biomass yield up to about 2,000 PPFD. Biomass increase is nearly linear to PPFD increase up to about 1,000-1,250. After which, greater PPFD leads to diminishing returns of biomass yield (even with CO2), and the greater the PPFD, the greater the diminishing returns. Under the highest PPFD, diminishing returns lead to an increase in OpEx (electrical cost) and COGS (reduced g/kWh and THC/g) with a reduction in ROI (lower % THC and g/harvest/kWh).
So, to answer your question, the min/max of PPFD for high yield and AAA flower is 800/1800 if the spectrum is ~40% red because, at 1800 PPFD, the red μmol/s/m2 is 700. You could run PPFD up to 1800 even if the spectrum % red is greater than 40%; just be prepared for the likelihood of photobleaching of the top part of the highest flowers.
Ideally, the max PPFD should be defined based on your spectrum with this equation: PPFD = 700/(% red/100). At least until testing cultivars for photobleaching sensitivity above 600-700 μmol/s/m2 red, or, photobleaching is better understood (e.g., DLI, creation of an action spectrum, etc.) and mitigations identified.
For reference, Gaviat DE HPS spectrum has 48% red. So, using the above equation with its % red as 700/(48/100), you can run 1458 PPFD before hitting the proposed photobleaching threshold of 700 μmol/s/m2 red. Most growers use 1000 PPFD with Gavita, a max of around 1250 PPFD, both of which are well below that threshold.
Note there is a tradeoff between % red in the spectrum and PPE; with lower % red, you can run higher PPFD without fear of photobleaching. But you’ll need more light bars, increased power density per bar, or reduced distance to the canopy to achieve that higher PPFD. Unfortunately, the simplest way to increase PPFD with lower % red (using LEDs) - reducing the distance to the canopy - dramatically decreases the PPFD uniformity over the canopy. So, there will be a greater yield difference between the edges and center of the canopy.
For the vast majority of growers, there’s rarely a reason to exceed 1250 PPFD, and less so to exceed 1500 PPFD. So, I would say that unless you’re running a well-funded, optimized commercial operation with automated irrigation and an ideal climate (not exceeding 82-83’F), use 800-1,250 PPFD. You will have outsending yield and flower quality results at 1000-1250 PPFD, with lower CapEx (fewer LED bars or less power density/bar, with reduced power distribution and cooling BTU/h), OpEx (reduced kWh), and cost per gram.
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Most lights have only a few red bulbs per bar. Do those few bulbs really put out 700? It seems like bleached buds would be a much more common occurrence if that were so
It depends upon the % red within the spectrum. To find the μmol/s/m2 of red photons from any given PPFD, multiply the PPFD by the spectrum’s % red and divide by 100. E.g., 1000 PPFD from a spectrum with 60% red (1000*60/100) = 600 μmol/s/m2 of red photons
For example, Fluence indoor spectrum has 40% red. So, a grower could use 700/(40/100) = 1750 PPFD before hitting the proposed photobleaching threshold of 700 μmol/s/m2 red.
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I use co2 currently with 12 gavita de dialed in. So over 1100 ppfd maxing around 1500 with co2 . What do u consider max ppfd?
Thank you for taking the time to provide that information. It will take a couple reads but I think I’m beginning to understand lol
And is adding extra uv to spectrum worth the bang for the buck? I see supplemental uv advertised?
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Everything Ralph is saying right now about reds. Is the entire reason the Emerson effect is so important, and just another reason while people need to be playing with the out of spectrum reds MORE. Kinda crazy just a few nm in color makes a big difference…
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The facility I ran did ~400 for the cloner, 5-650 in veg, 1200 ppfd with Gavita DE’s in flower. They were 4’ on center, turned down to 1000 watts and kept 3’ off of the canopy. Running at 1150 they would get hot spots and bleaching at 4’ canopy clearance.
@vortal is right on about the metabolism and ppfd. It’s only with serious crop steering and constant attention that we were able to push it without automation.
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You’re welcome.
UV-A:
Adding UV-A can be beneficial regarding the cryptochrome action spectra, e.g., cryptochrome’s effects on plants (increased pigmentation, photosynthesis=s, transpiration, etc.). And to a lesser extent, the phototropin action spectra, e.g., increased stomatal conducnce, stalky plants, etc. However, the cryptochrome action spectrum extends into and is strongly affected by blue range photons. So UV-A isn’t critical, which is why few LED mfgs include UV-A. Plus, UV-A LEDs are costly and have a reduced life span. Overall, adding UV-A isn’t worth the hassle. And if you do add it, you only need 10-40 μmol/s/m2.
In one study, during the last two weeks of flowering Larry OG, adding narrow waveband UV-A (~390 nm) at ~66 μmol/s/m2 to ~511 PPFD was found to increase THC by 3.6%. But the UV-A also significantly reduced most terpenes and reduced biomass yield (probably due to growth reduction). In the same study, a similar increase in THC was also found by adding narrow waveband blue (~450 nm) and red (~660 nm) at ~158 μmol/s/m2 to ~511 PPFD white light. Therefore, the THC increase probably wasn’t due to UV-A photochemical response but instead due to increased photosynthetic μmol/s/m2 because 390 nm UV-A is photosynthetic. If the study used a higher PPFD of ~800-1000 without UV-A, the increase in THC would have been much greater than a merger ~2.5-3.6%. See:
UV-B:
It is not needed, and current research has found no increase in THC-A and a trivial and inconsequential increase in THC. The tiny increase in THC is likely not a result of increased biosynthesis but rather from UV-B photooxidative decarboxylation of THC-A into THC. There are no reliable and well-designed peer-reviewed studies that find UV-B increases THC. Dr. Bugbee is studying this topic, but he is doubtful. And until such a finding is realized, if it ever is, it’s simply a myth that UV-B increases THC. A legend based on a poorly designed and conducted 50-year-old paper (Lydon et al., 1987) that cannot be considered reliable. Sadly, a myth is hard to kill once cannabis ‘experts’ proclaim UV-B increases THC.
Because UV-B’s lack of effect on THC and UV-B diodes are even more costly and have an even shorter life span, there are zero reasons to add UV-B at this point. If peer-reviewed studies eventually find UV-B increases THC (or other benefits not already provided by blue photons), it would be worth considering UV-B. But don’t hold your breath.
Many other ways to increase THC exist that are easier, cheaper, safer, and proven effective - so UV-B is not only ineffective but also unnecessary.
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Nice, I love to see high PPFD for cloning! 
I run 150-200 PPFD for the first few days in domes, then increase to 300 PPFD once rooted. When using domes it’s hard to run high PPFD because it heats up the dome interior too much.
And FWIW, running DE HPS above the lamp’s rated wattage significantly affects the spectrum. It makes the spectrum redder. Running the wattage below its rated wattage makes the spectrum greener. That’s why growers shouldn’t adjust DE HPS wattage.
At 1150 watts, the Gavita lamp goes from ~48% red (other data) to ~54% red! And plugging 54% red into the equations I created for PPFD, using your listed 1200 PPFD, (1200*54/100) gives you ~648 μmol/s/m2 of red photons. That explains why you see photobleaching because many strains will bleach at >650 μmol/s/m2 of red. And, some canopy spots would have gotten greater than 1200 PPFD. So, those spots would have received >700 μmol/s/m2 of red, which is very likely to cause photobleaching.
For comparison, at 1000 watt, ~48% red, and 1200 PPFD, on average your canopy recieved (1200*48/1000) = 576 μmol/s/m2 of red. So, even at spotes with higher PPFD, the red μmol/s/m2 was likely below 650.
One critical environmental factor most growers underrate and don’t measure is air speed voleicy. At high PPFD, it must be at least 1 m/s at the canopy, but 2 m/s is better. And intracanopy must be >0.3 m/s. Otherwise, the leaves will overheat, and bad things will happen, or at least growth and health will suffer.
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All the information provided is awesome. And without getting into all the math of %'s of red and such, I just look at a max ppfd of 1200 to 1500 with co2. Most people don’t have everything dialed in to that point and waist their money on co2.
I’ve used Fulton Lights that had IR on all the time and UV controlled separately. The yields were big, much larger than lights without either. I’ve also used lights that the IR/UV were controlled together, separate from the rest of the light. I must say, the Fulton with the constant IR had better yields, although the other light worked much better during veg and the yields were still better than without IR/UV. With that said…
I think a light with IR and UV, not only controlled separately from the main light, but also separately from each other, is the way to go. Are they necessary for good yields and great flower, no. But used properly, they can sure help.
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I agree a max PPFD of 1200 is a good target for most growers. At that PPFD, 1000-1200 ppm CO2 is ideal. I also agree ~1500 ppm is the max CO2 anyone should use (specifically, 1600 ppm), but only with very high PPFD, and there’s never a reason to exceed 1600 ppm CO2. People forget elevated CO2 brings adverse effects, including reduced transpiration and uptake of mass flow nutrients caused by reduced stomatal conductance.
But, FWIW, science disagrees with you regarding UV and cannabis. Far-red (701-760 nm) does has significant photobiological effects. Still, we only want a limited amount (<5% to total PPFD), and we don’t want any IR beyond 760 nm. For an in-depth discussion on far-red, check out my comments in this thread:
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You call out some great ways we could have improved when I was there. I’m not mad about it!
The Gavita rep told me that their DE fixtures were rated to run at all wattages without significant color change and the lamps break in over 6 months for the ideal color spectrum (for a HPS). This is in contrast with single end lamps like Hortilux that change color temperature and intensity after 4 cycles.
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I wish I could have visited your grow. I’m sure it was terrific 
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But the Gavita rep was ignorant or lying 
. Those data I shared on spectrum shifts with input wattage modulation aren’t from Gavita; they’re from a 3rd party.
It does take 100 hours of operation to reach burn-in. After that point, the lamps and spectrum don’t change without modulating the input wattage (or after its useful life span of ~10,000 hours, or 90% of burn-in PPFD). Those data I shared on spectrum shift were collected after the burn-in period.
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So much evidence I have physically observed is contrary to this study(400umol and you try to supplement 
). Nature itself has 10+% UV… some of the LOUDEST landraces with the BEST genetic traits come from places with a higher than normal UV index. The Kush Mountains, Cape of Africa, Alaskan Bush, etc.
In vitro gene expression is litterally controlled by ultra violet light. It is THE defense response to give you the best results. UV light exposure is a secondary effect. The Harmful raya never even reach the surface of the leaf. The UV is florescent into 400+nm it’s the magic of the cannabinoids… How do you think alot of new chroma works, and fraction finders.
I’m going to go ahead and toot my own horn by saying on average I am testing better and producing more baggable material per square foot utilizing out of spectrum Blues and Reds.
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Thanks for your expertise and resource sharing!
If we were hitting 55-60 grams per square foot (with 8-9 weeks veg) with under-driven (more red spectrum), I wonder how much it would affect quality and yield with properly powered lamps.
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