PPFD Guidelines: Mars Hydro Vs. HLG

[tronN00dles]

Hey folks,

I'm curious about PPFD guidelines provided by Mars Hydro and HLG, and was wondering if anyone had some opinions.

Note, the following are for photoperiods and are based on 18/6 veg and 12/12 flower, of course. Values below also assume no CO2 supplementation.

Mars Hydro:

HLG:

Here are the associated DLI conversions for veg and flower:

HLG Veg: 23-32 DLI
MH Veg: 26-39 DLI
HLG Flower: 17-35 DLI
MH Flower: 35-43 DLI

Clearly, HLG's guidelines are much more conservative than Mars Hydro. Does anyone have any thoughts on this?

-tron

 

[Del boy]

Hey folks,

I'm curious about PPFD guidelines provided by Mars Hydro and HLG, and was wondering if anyone had some opinions.

Note, the following are for photoperiods and are based on 18/6 veg and 12/12 flower, of course. Values below also assume no CO2 supplementation.

Mars Hydro: View attachment 1439793

HLG: View attachment 1439794

Here are the associated DLI conversions for veg and flower:




HLG Veg: 23-32 DLI
MH Veg: 26-39 DLI
HLG Flower: 17-35 DLI
MH Flower: 35-43 DLI

Clearly, HLG's guidelines are much more conservative than Mars Hydro. Does anyone have any thoughts on this?

-tron

Hello i run what HLG says roughly
ppfd/umols seedlings 150-300
vegetative 300
Flower 300-600+
It works for me

 

[Son of Hobbes]

Fluence recommends:

In seedling, 100 to 300 PPFD (6 to 19 DLI)
In cuttings (clones,) 75-150 PPFD (5 to 10 DLI)
In vegetative, 300-600 PPFD (19 DLI to 39 DLI)
In flower, 600+ PPFD (26+ DLI minimum)

These are just generally recommended guidelines, I think they are naturally going to vary a bit between the source (I've seen a few variations myself.)

 

[Son of Hobbes]

@tronN00dles

Cannabis is different from typical greenhouse plants in how it thrives under high-intensity light. It's one of the few plants which flourishes growth in full bloom with more than 900 to 1200 PPFD (38 to 52 DLI.)

However, as light intensity (PPFD) increases, photosynthetic rates also increase until a saturation point is reached. Every plant species has a light saturation point where photosynthetic levels plateau and normally occurs when some other factor (normally CO2) is limited.

The chart below was produced by the engineers from Fluence Bioengineering (I really enjoy the research and information this company has done; they have a sterling guide on photobiology,) showing the percentage of relative photosynthesis based on average atmospheric CO2 levels in the air (around 400 ppm.)

So without augmenting the CO2 levels in your grow space, photosynthesis reaches an efficiency plateau at a certain light intensity threshold (which isn't as high as you probably would think.) This gives us a guideline for determining how much light is simply "too much light" based on the environment, as well as "how much is not enough."

It's important to note that if our temperature, humidity, CO2, nutrients, or even the moisture level of the soil are outside the optimum range for cannabis, these attribute to the limitations of photosynthesis.

There gets to be a point where you're simply slamming photons into a plant that can receive them, but not actually utilize them.

 

[tronN00dles]

Thanks @Son of Hobbes for pointing me towards Fluence Bioengineering. I'll check them out for sure!

 

[Delps8]

@tronN00dles

Cannabis is different from typical greenhouse plants in how it thrives under high-intensity light. It's one of the few plants which flourishes growth in full bloom with more than 900 to 1200 PPFD (38 to 52 DLI.)

However, as light intensity (PPFD) increases, photosynthetic rates also increase until a saturation point is reached. Every plant species has a light saturation point where photosynthetic levels plateau and normally occurs when some other factor (normally CO2) is limited.

The chart below was produced by the engineers from Fluence Bioengineering (I really enjoy the research and information this company has done; they have a sterling guide on photobiology,) showing the percentage of relative photosynthesis based on average atmospheric CO2 levels in the air (around 400 ppm.)

View attachment 1439823

So without augmenting the CO2 levels in your grow space, photosynthesis reaches an efficiency plateau at a certain light intensity threshold (which isn't as high as you probably would think.) This gives us a guideline for determining how much light is simply "too much light" based on the environment, as well as "how much is not enough."

It's important to note that if our temperature, humidity, CO2, nutrients, or even the moisture level of the soil are outside the optimum range for cannabis, these attribute to the limitations of photosynthesis.

There gets to be a point where you're simply slamming photons into a plant that can receive them, but not actually utilize them.

For grows that are not using CO2, the practical limit is 700 or 800 µmols. As the Fluence diagram indicates, photosynthesis becomes limited by the lack of CO2 which means is that the law of diminishing returns starts to set in so you're not getting as much of an increase in photosynthesis as you increases your light levels. At 1k µmoles, phototosynthesis is impaired, and cannabis leaves can be damaged. 1k µmoles is the saturation point, lacking CO2.

One source of info is the YouTube video by DeBacca University. He discussed PPFD and switching to 12/12 meaning that he's not talking about autos. His max level PPFD recommended is 900 µmoles which comes out to a DLI of 42 using 12/12.
The DLI chart that's on the Photone site is a good guideline but seems very conservative, which is interesting for a company that sells an app to measure PPFD.

The videos by Dr Bruce Bugbee are really good. He's got one that runs 48 minutes and is chock full of info. One nice feature out his videos is that you can download the transcript. Bugbee started Apogee so he talks about his products, not surprisingly, but he provides tons of valuable information. One of the takeaways from his video is that most commercial growers are not using enough light. To the topic of saturation//diminishing returns, Bugbee does a good job of explaining that…and illustrating that.

The last source off the top of my head is to grab a copy of the "Chandra" paper at this link. Diagram A is the star of the show, indicating that even with CO2 enhancement, photosynthesis diminishes after 1500 µmoles. Bugbee uses a very similar chart but he "fills in the blanks" for non-CO2 environments and, IIRC, you can tell that the max number is about 900 mµoles on his drawing. That's 58 moles at 18/6 which is much higher than a lot of sites recommend.

I've got Gorilla Glue seedlings//early veg and my DLI is 25 moles. I expect to ramp that up to 40 moles quickly and, assuming the plants respond well, could go as high as 750 µmols for 20 hours = 54 moles.