Amount of light?

[SHRED]

They appear to be stretching or nearing that point. They look great.

They were starting to go for it and I did two light cycles of ponytail LST


I think it helped.

 

[Death The Cultivator]

@Death The Cultivator @Delps8

I originally wrote this for the owner of my last commercial farm, and it was shared with a scientist from the University of California, Berkeley who also reviewed it, then shared out in multiple cannabis groups I moderate/admin for to get some ideas and feedback on (which the copy-and-paste here is more of an adaptation from where it went to the growers.)

The idea behind this wasn't to say "hey look at the guide I personally wrote," but instead "hey, there is a lot of information generally accepted to be true and here's the science behind the suggestions."

Would you guys be willing to look through this and see if you have anything to add/offer/critique to help make it more clear, or perhaps if some statements are too rigid, ways to properly explain without seeming too biased?

It's missing information about spectrum and individual effects, and I purposely didn't include some of the updated rhetoric from Bugbee (trying to have a better grasp myself.)

---------------------------------------


Good morning growers!

Let's talk LIGHTING!

PAR, PPFD, DLI (oh my!)

I want to talk to you about some of the most important aspects of lighting, whether it's the sun or a grow light, and that is intensity (how many actual photons are hitting the plant over a period of time) and spectrum (the electromagnetic wavelengths of light produced by a light source to promote plant growth.)

In cultivation, this is defined by PAR light.

PAR (which stands for Photosynthetically Active Radiation) is light of wavelengths 400-700 nm and is the portion of the light spectrum utilized by plants for photosynthesis.

View attachment 1480649

We quantify (or to put in a measurable form) PAR light using PPFD (Photosynthetic Photon Flux Density), which is defined as the photon flux density of PAR.

PPFD is measured in micro-mols per second (μmol/s), indicating how many photons in this spectral range fall on the plant each second.

You've likely seen maps of PPFD on descriptions of grow lights. These are generally square diagrams showing PPFD calculations of the light at different fixed heights (like 12" over the canopy, 24" over the canopy, etc) over an area (like 2 foot x 2 foot, 4 foot x 4 foot, etc.) These are very important, because it helps show the area of intensity coverage of your grow light. Many traditional grow lights are very intense in the center and tend to lose intensity towards the edges (much of this is in the design of the individual light.) This helps us plan our canopy space (and to make sure our plants on the edge of our space aren't being under lit.)

DLI (which stands for Daily Light Integral,) is by definition the number of photosynthetically active photons (individual particles of light in the 400-700 nm range) that are delivered to a specific area over a 24-hour period.

Instead of sticking to the old "status quo" of 18/6, 20/4, or 24/0 (traditional lighting schedules for autoflowers, or keeping photos in veg,) DLI can help us make more calculated determinations for how much light to shoot for in a 24 hour period.

There are some generally recommended guidelines for how much light intensity cannabis plants should have for optimal growth in different stages of their life (you will see some variation between these recommendations depending on the source, but they are generally very similar.)

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)

Cannabis in 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. Light saturation normally occurs when some other factor (normally CO2) is limited.

I've included a chart in the attached images that was produced by the engineers from Fluence Bioengineering, a very reputable lighting company in the cannabis industry, from their guide on Photobiology showing the percentage of relative photosynthesis based on average atmospheric CO2 levels in the air (around 400 ppm.) Photosynthesis plateaus in efficiency around 500 PPFD.

View attachment 1480653

So without augmenting the CO2 levels in your grow environment, photosynthesis reaches a plateau at a certain light intensity threshold. 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." There is literally a point where you're just pushing photons against a plant that can withstand them, but not utilize them.

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

OUTDOOR & GREENHOUSE LIGHTING

For outdoor growers, Jim Faust, a professor of Floriculture from Clemson University in South Carolina, developed a well known DLI map of the United States showing average DLI for every month of the year, which greenhouse and outdoor growers use as a guideline.

View attachment 1480650

As an example outdoors (living in Colorado,) in the month of January we averaged around 15-20 DLI from the sun. By comparison, in June we'll see around 50-55 DLI average (which is the most light intense month of the year in the state.) Please note that these are outdoor values for DLI; there is light transmission loss between the the outdoor and indoors from the barriers the greenhouse material creates (which can be calculated.)

So in the winter months here, we're providing only about 1/3 of the actual light intensity the plants would normally receive during the summer months by relying on the sun only (which is why our plants get so much bigger in the summer vs winter months without supplemental lighting.)

This is also in part due to there being less light hours available during the day until winter solstice (the shortest day of the year in December.) In Denver in the month of January, the sunrise occurred around 7:20 am and will set around 4:53 pm. That's a total of 9 hours 33 minutes of lighting. Complicating matters further, during this period of lighting there are only around 4-5 hours of actual intense light (higher PPFD) that support optimal photosynthesis (intensity drops off rapidly in the afternoon until dusk.)

Conversely in the summer time (using June as our example,) the sun rises around 5:30 am and sets around 8:20 pm. That gives 14-15 hours of actual day lighting per day.

In august, the daylight hours drops to about 14, then 13 in September, to 12 hours in October (which helps correlate how photoperiods flower outdoor in our season.)

Photoperiod versus Autoflower

Photoperiods are considered a short-day flowering plant.

Photoperiodism is the physiological reaction of organisms to the length of night or a dark period. Photoperiod cannabis doesn't flower in response to the amount of light receives, but rather the amount of darkness it receives. So the amount of daylight hours versus darkness photoperiods receive, whether artificial or natural, is absolutely critical.

Autoflowers are considered day-neutral flowering plants.

Day-neutral plants do not depend upon the amount of darkness or daylight hours, but instead flower out as a response to aging. As the plant matures, it begins to bloom. While genetics have the most influence on the timing of this, stress and environmental factors can have an impact on this mechanism.

Within these plants, there exists a further division that puts some plants into qualitative and quantitative groups that require specific conditions to perform certain biological tasks, or will still carry out tasks, but sub optimally until conditions are met.

Whether it's a photoperiod or autoflower, the type and quality of light you're giving the plant is very important during different stages of growth. I hope this helps explain things when you're looking at or considering grow lights, or maybe helps understand your own existing setups better!

Appreciated!

Ideally, more information about:

PAR meters and how they work plus why they are the optimal tool for horticultural applications

Spectrum can definitely be talked about as there are advanced lighting strategies in conjunction with crop steering. Special note on far Red, UVA which I've been told works as well as UVB with the damage, and deep red.

I think the DLI numbers are a bit high.

How optics work in lighting and different type of lighting systems available. Most don't know it but LEC/CMH put out improves quality compared to your typical LED because they have an improved spectrum with a higher CRI of 98

CRI is another part as higher CRI has more green/deep red/far Red with 90+ being preferable - overall grow light metrics. Like @BigSm0 had a brilliant product with the Auto Cobs years before everyone else and they still are because of the combined CRI/optics and efficiency.

Why strive for high efficiency lighting? From a commercial or residential standpoint it's a higher Return of Investment.

For example, I pull 32oz in a 4x4 space under a 600w HID at 1.3umols with an 18/6 schedule but that involves a lot of heat and a less than ideal coverage of light versus an LED with 2.4umols efficiency and 500w that gives me 32oz as well on a 18/6. I gain 90% efficiency resulting in more photons reaching the plant rather than becoming heat that I have to manage. That is less impact on HVAC and grow equipment as well as a lower bill. It's improved growth, more overall biomass, and better quality compared to the narrow spectrum of the HID.

How different lighting schemes can be applied to different situations and techniques.

That link I posted further back about photosynthesis is enlightening because most don't know how it works and to what extent it influences the process. I don't think everyone needs to be a horticulturalist but being able to make informed decisions because the information is present leads to better outcomes and consistency.

 

[Death The Cultivator]

They were starting to go for it and I did two light cycles of ponytail LST


I think it helped.

View attachment 1480680

I think it was appropriate to increase the light at this point and around the second to third week, 100% would be the way to go.

 

[Talonxracer]

Hmmm, what is this ponytail LST black magic you talk about.....?

I see them tied up in your pic, but what does it accomplish?

 

[SHRED]

Hmmm, what is this ponytail LST black magic you talk about.....?

I see them tied up in your pic, but what does it accomplish?

It slows the center stalk and encourages side branch growth for a more even canopy.

https://www.autoflower.org/threads/ponytail-lst.88307/

 

[Talonxracer]

Thanks, now that I learned something today, the day isn't wasted!

 

[Hot Joe]

I'm running my autos on full 24 hrs and they seem to be loving it. I live in a small place and I am the form of CO2. Mine will be on day 28 tomorrow if you want to look at them, I posted pictures. Expect a lot to happen over the next few weeks

 

[Butrod]

@Son of Hobbes
Sir, if I may to chime in and correct a minor oversight and maybe give some food for thought...

1. PPFD is quantum flux expressed over an area over time, so the unit is umol/m^2/s. The umol/s is PPF that is the raw net amount of photons a fixture released as being measured in an Ulbricht-integration sphere.

2. The Light-Saturation-Point given by Fluence is extremely low at ~550ppfd and that's not supported by any study I'm aware of. But what studies did show is that it's different depending on the genotype but generally way higher than that, even before CO2.

3. Outside the sun, even in the mourning or evening hours is already so strong enough to fully light-saturate any leaf that has exposure to direct sunlight. Once you see the sun yellow then it'll be at high ppfd. Then long before midday its fluence will be so high that a photoinhibition sets in that is both the product of too high irradiance and a spectral blueshift. So studies have shown that many plants do better photosynthesis when the sun is not in the zenith.

4. PPFD undervalues the light influx as it only integrates photons ranging from 400-700nm by definition. But plants can use photons from UV to FR/IR, with especially the range of 700-750nm is still plentyful in the SPD and the capture of these wavelength carry great implications that weigh them even far better than any generic weight light.

So what I'm saying is that outside the plants receive way more light than what an incomplete metric as DLI states on paper.

Hope this helps you out a bit

 

[Delps8]

@Son of Hobbes
Sir, if I may to chime in and correct a minor oversight and maybe give some food for thought...

1. PPFD is quantum flux expressed over an area over time, so the unit is umol/m^2/s. The umol/s is PPF that is the raw net amount of photons a fixture released as being measured in an Ulbricht-integration sphere.

2. The Light-Saturation-Point given by Fluence is extremely low at ~550ppfd and that's not supported by any study I'm aware of. But what studies did show is that it's different depending on the genotype but generally way higher than that, even before CO2.

3. Outside the sun, even in the mourning or evening hours is already so strong enough to fully light-saturate any leaf that has exposure to direct sunlight. Once you see the sun yellow then it'll be at high ppfd. Then long before midday its fluence will be so high that a photoinhibition sets in that is both the product of too high irradiance and a spectral blueshift. So studies have shown that many plants do better photosynthesis when the sun is not in the zenith.

4. PPFD undervalues the light influx as it only integrates photons ranging from 400-700nm by definition. But plants can use photons from UV to FR/IR, with especially the range of 700-750nm is still plentyful in the SPD and the capture of these wavelength carry great implications that weigh them even far better than any generic weight light.

So what I'm saying is that outside the plants receive way more light than what an incomplete metric as DLI states on paper.

Hope this helps you out a bit

You raise good points, esp. #3. I never would thought that a plant would not be able to take advantage of the available light.

Re #1 - I use "µmols" as shorthand. It saves HTML.

Re. #4 - "traditional" PAR is 400 to 700 but ePar broadens the range from 400 to 750nm. I was looking at a PPFD map of a Vipar Spectra light and noticed that ePar was being measured. It adds ≈ 50 µmols - not a lot but I believe it's synergistic with red.

 

[Son of Hobbes]

2. The Light-Saturation-Point given by Fluence is extremely low at ~550ppfd and that's not supported by any study I'm aware of. But what studies did show is that it's different depending on the genotype but generally way higher than that, even before CO2.

Do you have links to said studies to support your statement? I mean that in favor of tweaking and altering the guide.

. Outside the sun, even in the mourning or evening hours is already so strong enough to fully light-saturate any leaf that has exposure to direct sunlight. Once you see the sun yellow then it'll be at high ppfd. Then long before midday its fluence will be so high that a photoinhibition sets in that is both the product of too high irradiance and a spectral blueshift. So studies have shown that many plants do better photosynthesis when the sun is not in the zenith.

I actually would disagree to an extent, based on my previous post about how time of year effects light intensity/DLI. At my last my commercial farm, I tested PPFD ranges both insides our greenhouse and outside, and depending on the time of year, light intensity is drastically lower during the morning and late afternoon (during winter months) than it is during spring/summer months. We actually ran into low-lighting conditions in our greenhouse, where there were multiple high-bay LED lighting fixtures (meant for lighting warehouses, not for plants,) and the previous grower had it in his head that just because something provides brightness, it's providing intensity, and because of the low PPFD conditions, we had multiple plants begin to flower regardless of the 24/0 "lighting" conditions provided, in a greenhouse that received full sun in winter.

Again, do you have studies that would support such claims? And again I ask this not to be combative, but simply to support the claim?

Let's build out the "the" lighting guide for cannabis.